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1

The East African rift system  

NASA Astrophysics Data System (ADS)

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.

Chorowicz, Jean

2005-10-01

2

Geophysical studies of the West Antarctic Rift System  

Microsoft Academic Search

The West Antarctic rift system extends over a 3000 × 750 km, largely ice covered area from the Ross Sea to the base of the Antarctic Peninsula, comparable in area to the Basin and Range and the East African rift system. A spectacular rift shoulder scarp along which peaks reach 4–5 km maximum elevation marks one flank and extends from

J. C. Behrendt; W. E. LeMasurier; A. K. Cooper; F. Tessensohn; A. Tréhu; D. Damaske

1991-01-01

3

Heat flow in the Keweenawan rift system  

NASA Astrophysics Data System (ADS)

The emplacement of large volumes of mafic volcanic rocks during the Keweenawan rifting has modified the average crustal composition and affects the present steady state heat flux in the region. We have combined new heat flux measurements in the Superior Province of the Canadian Shield and previously published data to characterize the heat flux field around the Keweenawan rift system. For the Nipigon embayment, North of lake Superior in Ontario, mafic intrusions associated with the Keweenawan rifting have resulted in an increase in the volume of mafic rocks in the crust and caused a very small <3mW m-2 decrease in the mean heat flux. There is a very marked decrease in the heat flux (? Q ? 20mW m-2) beneath the western half of Lake Superior and to the west. The very low values of the surface heat flux (? 22mW m-2 correlate with the maximum Bouguer gravity anomaly. The heat flux at the base of the crust in the Canadian Shield has been determined from surface heat flux, heat production, and crustal stucture to be ? 15 mW m-2. In the Keweenawan rift, the surface heat flux is only a few mW m-2 higher than the mantle heat flux, which implies that the contribution of the entire crustal column to the surface heat flux is small and that the crust is exclusively made up of depleted mafic volcanic rocks. In the eastern part and northeast of Lake Superior, there is a marked increase in heat flux that correlates with a lower Bouguer anomaly. Local high heat flux anomalies due to intrusions by felsic rocks are superposed with a long wavelength trend of higher heat flow suggesting a more felsic crustal composition in the eastern part of the Keweenawan rift. Simple models suggest that such a thick dense volcanic pile as accumulated in the Keweenawan rift is almost invariably unstable and that very particular conditions were required for it to stabilize in the crust.

Perry, C.; Mareschal, J.; Jaupart, C. P.

2012-12-01

4

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

NASA Astrophysics Data System (ADS)

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

Klyuchevskii, Anatoly V.

2014-07-01

5

Continental rift systems and anorogenic magmatism  

Microsoft Academic Search

Precambrian Laurentia and Mesozoic Gondwana both rifted along geometric patterns that closely approximate truncated-icosahedral tessellations of the lithosphere. These large-scale, quasi-hexagonal rift patterns manifest a least-work configuration. For both Laurentia and Gondwana, continental rifting coincided with drift stagnation, and may have been driven by lithospheric extension above an insulated and thermally expanded mantle. Anorogenic magmatism, including flood basalts, dike swarms,

James W. Sears; Gregory M. St. George; J. Chris Winne

2005-01-01

6

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

7

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

8

Neotectonic activity along the Shanxi rift system, China  

NASA Astrophysics Data System (ADS)

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

Xu, Xiwei; Ma, Xingyuan; Deng, Qidong

1993-03-01

9

Fault system at the southeastern boundary of the Okavango Rift, Botswana  

Microsoft Academic Search

The seismically active Okavango Rift in northwestern Botswana is probably the southern extension of the East Africa Rift System. Relief is low and many of the geomorphic features of the incipient rift are subtle. The northeast-southwest trending Kunyere and Thamalakane Faults form the southeastern boundary of the rift. Proterozoic structural fabrics of similar trend, belonging to the Ghanzi-Chobe Belt, control

M. P. Modisi

2000-01-01

10

Venus: Geology of beta Regio Rift System.  

National Technical Information Service (NTIS)

Beta Regio is characterized by the existence of rift structures. We compiled new geologic maps of Beta Regio according to Magellan data. There are many large uplifted tesserae on beta upland. These tesserae are partly buried by younger volcanic cover. We ...

A. M. Nikishin V. K. Borozdin N. N. Bobina

1992-01-01

11

Magmatic lithospheric heating and weakening during continental rifting: A simple scaling law, a 2-D thermomechanical rifting model and the East African Rift System  

NASA Astrophysics Data System (ADS)

Continental rifting is accompanied by lithospheric thinning and decompressional melting. After extraction, melt is intruded at shallower depth thereby heating and weakening the lithosphere. In a feedback mechanism this weakening may assist rifting and melt production. A one-dimensional kinematic lithospheric thinning model is developed including decompressional melting and intrusional magma deposition. The intrusional heating effect is determined as a function of thinning rate and amount, melting parameters, potential temperature, and the depth range of emplacement. The temperature increases approximately proportionally to the square root of the thinning rate and to the square of the supersolidus potential temperature. Simple scaling laws are derived allowing predicting these effects and the surface heat flux for arbitrary scenarios. Two-dimensional thermomechanical extension models are carried out for a multicomponent (crust-mantle) two-phase (melt-matrix) system with a rheology based on laboratory data including magmatic weakening. In good agreement with the 1-D kinematic models it is found that the lithosphere may heat up by several 100 K. This heating enhances viscous weakening by one order of magnitude or more. In a feedback mechanism rifting is dynamically enforced, leading to a significant increase of rift induced melt generation. Including the effect of lateral focusing of magma toward the rift axis the laws are applied to different segments of the East African Rift System. The amount of intrusional heating increases with maturity of the rift from O(10 K) to up to 200 K or 400 K at the Afar Rift depending on the depth range of the magmatic emplacement.

Schmeling, Harro; Wallner, Herbert

2012-08-01

12

Petroleum system of the Shelf Rift Basin, East China Sea  

SciTech Connect

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.

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

1996-01-01

13

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

14

Geophysical studies of the West Antarctic Rift System  

NASA Astrophysics Data System (ADS)

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

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

1991-12-01

15

Seismicity of the Baikal rift system from regional network observations  

NASA Astrophysics Data System (ADS)

In the paper we report the state-of-the-art of seismicity study in the Baikal rift system and the general results obtained. At present, the regional earthquake catalog for fifty years of the permanent instrumental observations consists of over 185,000 events. The spatial distribution of the epicenters, which either gather along well-delineated belts or in discrete swarms is considered in detail for different areas of the rift system. At the same time, the hypocenters are poorly constrained making it difficult to identify the fault geometry. Clustered events like aftershock sequences or earthquake swarms are typical patterns in the region; moreover, aftershocks of M ? 4.7 earthquakes make up a quarter of the whole catalog. The maximum magnitude of earthquakes recorded instrumentally is MLH7.6 for a strike-slip event in the NE part of the Baikal rift system and MLH6.8 for a normal fault earthquake in the central part of the rift system (Lake Baikal basin). Predominant movement type is normal faulting on NE striking faults with a left lateral strike-slip component on W-E planes. In conclusion, some shortcomings of the seismic network and data processing are pointed out.

Radziminovich, N. A.; Gileva, N. A.; Melnikova, V. I.; Ochkovskaya, M. G.

2013-01-01

16

Thermal and Mechanical Development of the East African Rift System.  

National Technical Information Service (NTIS)

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

C. E. Ebinger

1988-01-01

17

Hydrothermal vents in Lake Tanganyika, East African, Rift system  

Microsoft Academic Search

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

Jean-Jacques Tiercelin; Catherine Pflumio; Maryse Castrec; Jacques Boulégue; Pascal Gente; Joël Rolet; Christophe Coussement; Karl O. Stetter; Robert Huber; Sony Buku; Wafula Mifundu

1993-01-01

18

Isotopic and geochemical evidence for a heterogeneous mantle plume origin of the Virunga volcanics, Western rift, East African Rift system  

Microsoft Academic Search

Virunga volcanics in the western rift of the East African Rift system (EARS) show silica-undersaturated, ultra-alkaline, alkalic-mafic compositions. The two active Virunga volcanoes, Nyiragongo and Nyamuragira, are 15 km apart. Nyiragongo shows unusual compositions not seen globally and has the lowest recorded viscosity among terrestrial magmas while Nyamuragira is unusually effusive. These volcanoes occur along the fringes of a topographic uplift

Ramananda Chakrabarti; Asish R. Basu; Alba P. Santo; Dario Tedesco; Orlando Vaselli

2009-01-01

19

Hydrothermal vents in Lake Tanganyika, East African, Rift system  

NASA Astrophysics Data System (ADS)

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 °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 NaHCO3-enriched fluid similar to the NaHCO3 thermal fluids from lakes Magadi and Bogoria in the eastern branch off 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 off 219 and 179 °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 °N normal-dextral faults that intersect the north- south major rift trend. The source 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.

Tiercelin, Jean-Jacques; Pflumio, Catherine; Castrec, Maryse; Boulégue, Jacques; Gente, Pascal; Rolet, Joël; Coussement, Christophe; Stetter, Karl O.; Huber, Robert; Buku, Sony; Mifundu, Wafula

1993-06-01

20

Clastic rocks associated with the Midcontinent rift system in Iowa  

USGS Publications Warehouse

The Middle Proterozoic Midcontinent Rift System (MRS) of North America is a failed rift that formed in response to region-wide stresses about 1,100 Ma. In Iowa, the MRS is buried beneath 2,200?3,500 ft of Paleozoic and Mesozoic sedimentary rocks and Quaternary glaciogenic deposits. An extremely large volume of sediments was deposited within basins associated with the rift at several stages during its development. Although the uplift of a rift-axial horst resulted in the erosional removal of most of these clastic rocks from the central region of the MRS in Iowa, thick sequences are preserved in a series of horst-bounding basins. Recent studies incorporating petrographic analysis, geophysical modeling, and other analytical procedures have led to the establishment of a preliminary stratigraphy for these clastic rocks and interpretations of basin geometries. This information has allowed the refinement of existing theories and history of MRS formation in Iowa. Additionally, drill samples previously interpreted as indicating the existence of early Paleozoic basins overlying the Proterozoic MRS basins were re-examined. Samples previously interpreted as deep-lying Paleozoic rocks are now known to have caved from upper levels of the drillhole and were out of stratigraphic position. No deep Paleozoic basins exist in this area. These investigations led to the development of petrographic parameters useful in differentiating the Proterozoic MRS Red clastics from Paleozoic clastic rocks having similar lithologies.

Anderson, Raymond R.; McKay, Robert M.

1997-01-01

21

Volcanism, tectonism, sedimentation, and the paleoanthropological record in the Ethiopian Rift System  

Microsoft Academic Search

The Ethiopian Rift System consists of basins that are in different stages of evolu- tion. Some of the rift-related basins in southwestern Ethiopia are half-grabens that have not evolved to symmetrical rifts since the initiation of rifting here in the middle Miocene. These basins contain fossiliferous Pliocene-Pleistocene volcaniclastic sedi- ments and volcanic rocks and have been occupied by early hominid

Giday WoldeGabriel; Grant Heiken; Tim D. White; Berhane Asfaw; William K. Hart; Paul R. Renne

2000-01-01

22

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

23

Eocene to Miocene geometry of the West Antarctic Rift System  

Microsoft Academic Search

Tectonic models for the Late Cretaceous\\/Tertiary evolution of the West Antarctic Rift System range from hundreds of kilometres of extension to negligible strike-slip displacement and are based on a variety of observations, as well as kinematic and geodynamic models. Most data constraining these models originate from the Ross Sea\\/Adare Trough area and the Transantarctic Mountains. We use a new Antarctic

R. D. Müller; K. Gohl; S. C. Cande; A. Goncharov; A. V. Golynsky

2007-01-01

24

Geochemical Overview of the East African Rift System  

NASA Astrophysics Data System (ADS)

Mafic volcanics of the East African Rift System (EARS) record a protracted history of continental extension that is linked to mantle plume activity. The modern EARS traverses two post-Miocene topographic domes separated by a region of polyphase extension in northern Kenya and southern Ethiopia. Basaltic magmatism commenced ˜45 Ma in this highly extended region, while the onset of plume-related activity took place ˜30 Ma with eruption of flood basalts in central Ethiopia. A spatial and temporal synthesis of EARS volcanic geochemistry shows progressive lithospheric removal (by erosion and melting) as the degree of rifting increases, with basalts in the most highly extended areas recording melting of depleted asthenosphere. Plume contributions are indicated locally in the northern half of the EARS, but are absent from the southern half. The geochemical signatures are compatible with a physical model in which the entire EARS is fed by a discontinuous plume emanating from the core-mantle boundary as the South African Superswell. Quaternary basaltic lavas erupted in the Afar triangle, Red Sea and Gulf of Aden define the geochemical signature attributed to the Afar plume (87Sr/86Sr 0.7034-0.7037, 143Nd/144Nd 0.5129-0.5130; La/Nb 0.6-0.9; Nb/U 40-50). These suites commonly record mixing with ambient upper mantle having less radiogenic isotopes but generally overlapping incompatible trace element abundances. Within the Ethiopian dome both lithospheric and sub-lithoshperic contributions can be documented clearly; lithospheric contributions are manifest in more radiogenic isotope values (87Sr/86Sr up to 0.7050) and distinctive trace element abundances (e.g., La/Nb <2.0, Nb/U > 10). The degree of lithospheric contribution is lowest within the active Main Ethiopian Rift and increases towards the southern margin of the dome. The estimated depth of melting (65-75 km) is consistent with geophysical observations of lithospheric thickness. In regions of prolonged volcanism the lithospheric contributions and estimated melting depths decrease through time, corresponding to a higher degree of rifting. In the Kenyan dome, including the western rift, the degree of extension is low and lithospheric melting is the dominant source for basaltic magmatism. Mafic lavas from these regions have generally lower MgO but higher contents of alkalis, P2O5 and many incompatible trace elements than are observed in the Ethiopian Rift. High values of 87Sr/86Sr, 207Pb/204Pb and Zr/Hf relative to other parts of the EARS indicate melting of metasomatized lithosphere. Melting in this area occurs at depths up to 100+ km, consistent with the thick crustal section observed seismically. Between the topographic domes, basalts from the Turkana region record melting at shallow levels ( ˜35 km) consistent with seismic evidence for nearly complete rifting of the crustal section. The geochemistry of these lavas is dominated by asthenospheric source materials, with only minor lithospheric involvement. Temporal evolution of EARS geochemistry reflects progressive rifting of the thick craton. This change is manifest within lavas that are interpreted as plume-derived, as Tb/Yb values decrease from 30 Ma through the present. The modern thermal anomaly associated with Afar volcanism does not appear to extend below the shallow mantle, but may reflect a large blob of deep mantle material that became stuck to Africa 30 Ma and has contributed to regional volcanism ever since. Relative contributions from this deep mantle source, shallow asthenosphere and lithosphere are controlled by the extent of rifting and cannot be predicted solely on the basis of surface topography.

Furman, T.

2003-12-01

25

Earthquakes along the East African Rift System: A multiscale, system-wide perspective  

Microsoft Academic Search

On the basis of a comprehensive data set of precisely determined depths of 121 large to moderate-sized earthquakes along and near the entire East African Rift System (EARS), there are three distinct patterns in focal depths which seem to correlate with progressive stages in the development of the largest active rift in the world. First, away from both ends of

Zhaohui Yang; Wang-Ping Chen

2010-01-01

26

The Afro-Arabian rift system—an overview  

NASA Astrophysics Data System (ADS)

The Afro-Arabian rift system is reviewed beginning with the Dead Sea transform and Gulf of Suez in the north, followed by the Gulf of Aden and Red Sea and ending with a brief mention of rifting through eastern and southern Africa. A consistent interpretation is obtained for geophysical data from the Gulf of Aden and Red Sea and geological data for the Dead Sea transform, Suez graben and Red Sea and Gulf of Aden margins. Geophysical data are used to estimate the locations of the ocean-continent boundaries in the northern Red Sea; these are found to coincide when the total 107 km shear along the Dead Sea is restored. The Red Sea is therefore reconstructed in stages beginning with the 45 km post-Miocene shear and 62 km early-Miocene shear along the Dead Sea transform followed by estimates for extension in the early Red Sea-Suez graben. When this is done, there is a remarkable alignment of various features revealed on Landsat TM imagery for both sides of the northern Red Sea. North-south differences in the Red Sea and west-east differences hi the Gulf of Aden are discussed and found to be best explained by a propagating rift model.

Girdler, R. W.

1991-10-01

27

Hydrothermal vents is Lake Tanganyika, East African Rift system  

SciTech Connect

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.

Tiercelin, J.J. [Universite de Bretagne Occidentale, Brest (France)] [Universite de Bretagne Occidentale, Brest (France); Pflumio, C.; Castrec, M. [Universite Paris VI, Paris (France)] [and others] [Universite Paris VI, Paris (France); and others

1993-06-01

28

Rift System Architecture on Venus and Implications for Lithospheric Structure  

NASA Astrophysics Data System (ADS)

Terrestrial continental rifts are half graben, with a master boundary fault on only 1 side of the rift basin. Devana Chasma on Venus has long segments with full graben morphologies (2 boundary faults), indicating differences in lithosphere structure.

Kiefer, W. S.

2014-05-01

29

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

NASA Astrophysics Data System (ADS)

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.

Rilling, Sarah E.

30

The East African rift system in the light of KRISP 90  

USGS Publications Warehouse

On the basis of a test experiment in 1985 (KRISP 85) an integrated seismic-refraction/teleseismic survey (KRISP 90) was undertaken to study the deep structure beneath the Kenya rift down to depths of 100-150 km. This paper summarizes the highlights of KRISP 90 as reported in this volume and discusses their broad implications as well as the structure of the Kenya rift in the general framework of other continental rifts. Major scientific goals of this phase of KRISP were to reveal the detailed crustal and upper mantle structure under the Kenya rift, to study the relationship between mantle updoming and the development of sedimentary basins and other shallow structures within the rift, to understand the role of the Kenya rift within the Afro-Arabian rift system and within a global perspective and to elucidate fundamental questions such as the mode and mechanism of continental rifting. The KRISP results clearly demonstrate that the Kenya rift is associated with sharply defined lithospheric thinning and very low upper mantle velocities down to depths of over 150 km. In the south-central portion of the rift, the lithospheric mantle has been thinned much more than the crust. To the north, high-velocity layers detected in the upper mantle appear to require the presence of anistropy in the form of the alignment of olivine crystals. Major axial variations in structure were also discovered, which correlate very well with variations in the amount of extension, the physiographic width of the rift valley, the regional topography and the regional gravity anomalies. Similar relationships are particularly well documented in the Rio Grande rift. To the extent that truly comparable data sets are available, the Kenya rift shares many features with other rift zones. For example, crustal structure under the Kenya, Rio Grande and Baikal rifts and the Rhine Graben is generally symmetrically centered on the rift valleys. However, the Kenya rift is distinctive, but not unique, in terms of the amount of volcanism. This volcanic activity would suggest large-scale modification of the crust by magmatism. Although there is evidence of underplating in the form of a relatively high-velocity lower crustal layer, there are no major seismic velocity anomalies in the middle and upper crust which would suggest pervasive magmatism. This apparent lack of major modification is an enigma which requires further study. ?? 1994.

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

1994-01-01

31

From Post-Orogenic Collapse to Continental Breakup: Evolution and Fate of the Alpine Tethys and Atlantic Rift Systems in Western Europe  

NASA Astrophysics Data System (ADS)

The Alpine Tethys-Atlantic rift systems in Western Europe document a complete extensional cycle ranging from post-orogenic collapse to continental breakup. The collapse of the Variscan orogen in Permian time was followed by the development of 3 major rift systems, the Late Triassic Meliata-Vardar system in Eastern Europe, the Early to Middle Jurassic Alpine Tethys system in Central Europe, and the Late Jurassic to Early Cretaceous system in the Iberia-Bay of Biscay domain in Western Europe. While the former two rift systems are dominated by hyper-extended crust, exhumed subcontinental mantle and embryonic oceanic domains, the latter went to breakup and formation of steady state oceanic crust. Remnants of these rift systems are preserved in the Alps, Pyrenees and drilled offshore Iberia. The study of these remnants enables to access rocks derived from different crustal and mantle levels and to link their evolution with the stratigraphic record documented in the overlying pre-, syn- and post-rift sedimentary sequences. The results of our study show that each of these rift systems was affected by a sequence of extensional events that include: 1) post-orogenic collapse related to the loss of the Variscan orogenic roots associated with major magmatic activity and thinning of the crust to 30 km, 2) diffuse decoupled rifting, 3) localized hyper-extension leading to thin brittle crust, less than 10km thick, and 4) mantle exhumation and formation of embryonic oceanic crust. The transition from orogenic collapse to onset of rifting to final breakup is recorded by: 1) the evolution from continental to shallow marine to final deep marine deposits, 2) the development from magma-rich extension during collapse, to magma-poor rifting and onset of a MOR system during breakup, and 3) the occurrence of extensional detachment systems that thin the crust and exhume deeper crustal and subcontinental mantle rocks. In our study we show that the strain and magmatic evolution of the Alpine Tethys - Atlantic rift systems in Western Europe are initially controlled by structural, thermal and compositional inheritances while final rifting seems to be controlled by the thermal erosion, hydration and magmatic activity of the mantle and crustal rocks during hyper-extension.

Manatschal, G.; Mohn, G.; Masini, E.; Beltrando, M.; Stanton, N.; Tugend, J.; Petri, B.; Haupert, I.; Pinto, V. H.

2012-12-01

32

Lithospheric cross sections of the European Cenozoic rift system  

NASA Astrophysics Data System (ADS)

The lithospheric structure of the European Cenozoic rift system ( ECRIS) is presented in transects through the southern Rhine Graben and the Rhenish Massif/Hessen depression, emphasizing the geophysical structure of the lithosphere based on seismic refraction/reflection investigations, teleseismic tomography, electromagnetic depth-sounding models, and gravity, aeromagnetic, earthquake, uplift/subsidence and heat flow data. The rift is clearly expressed in the Rhine Graben, but is not evident at the surface in the area of the Rhenish Massif where its existence is indicated by seismicity. It is characterized by abnormal crustal and upper-mantle structures which vary considerably in horizontal direction. For example, under the Rhine Graben the crust is thinned to 25 km, but at 40 km depth anomalously high velocities are observed. In contrast, beneath the Rhenish Massif the crust is thickened to 35-37 km and under its eastern part a high-velocity thin upper-mantle slice is seen at 30 km depth within the lower crust which, towards the Hessen depression, is gradually replaced by normal Variscan mantle with the Moho near 30 km depth. Under the western part of the Rhenish Massif P- and S-wave velocities are reduced below 50 km depth which is not seen east of the Rhine river. Under the Rhine Graben the existence of a low-velocity upper mantle above 100 km cannot be generalized, but is restricted to confined regions.

Prodehl, C.; Mueller, St.; Glahn, A.; Gutscher, M.; Haak, V.

1992-07-01

33

Initial process of rifting  

Microsoft Academic Search

The generally accepted model of rifting (the McKenzie model) has certain geometric and spatial constraints that seem to preclude its operation in the earliest stage of rifting. It may be a more advanced stage of the rifting process, if it is correctly described. An aborted rift system can be studied in the subsurface of the Permian basin. The Delaware, Val

Elam

1985-01-01

34

Earthquakes along the East African Rift System: A multi-scale, continent-wide perspective  

Microsoft Academic Search

Based on a comprehensive dataset of precisely determined depths of 121 large to moderate-sized earthquakes along and near the entire East African Rift system (EARS), there are three distinct patterns in focal depths which seem to reflect progressive stages in the development of the largest active rift in the world. First, away from both ends of the western, younger branch

Z. Yang; W. Chen

2009-01-01

35

Beta Regio rift system on Venus: Geologic interpretation of Magellan images  

NASA Technical Reports Server (NTRS)

Magellan SAR images and altimetric data were used to produce a new geologic map of the Northern part of Beta Regio within the frames of C1-30N279 mapsheet. It was part of our contributions into C1-formate geologic mapping efforts. The original map is at 1:8,000,000 scale. The rift structures are typical for Beta Regio on Venus. There are many large uplifted tessera areas on Beta upland. They occupy areas of higher topography. These tessera are partly burried by younger volcanic cover of plain material. These observations show that Beta upland was formed mainly due to lithospheric tectonical uplifting, and only partly was constructed by volcanic activity. A number of rift valleis traverse Beta upland and spread to the surrounding lowlands. The largest rift crosses Beta N to S. Typical width of rifts is 40 to 160 km. Rift valleis in this region are structurally represented by crustal grabens and half-grabens. There are symmetrical and asymmetrical rifts. A lot of them have shoulder uplifts with the relative high up to 0.5-1 km and width 40 to 60 km. Preliminary analysis of the largest rift valley structural cross-sections leads to the conclusion that it originated due to a 5-10 percent crustal extension. The prominent shield volcano - Theia Mons - is located at the center of Beta rift system. It could be considered as the surface manifestation of the upper mantle hot spot. Most of the rift belts are located radially to Theia Mons. The set of these data leads to conclusion that Beta rift system has an 'active-passive' origin. It was formed due to the regional tectonic lithospheric extension. Rifting was accelerated by the upper mantle hot spot located under the center of passive extension (under Beta Regio).

Nikishin, A. M.; Bobina, N. N.; Borozdin, V. K.; Burba, G. A.

1993-01-01

36

Oligocene Miocene formation of the Haifa basin: Qishon Sirhan rifting coeval with the Red Sea Suez rift system  

NASA Astrophysics Data System (ADS)

During mid-Oligocene to early-Miocene times the northeastern Afro-Arabian plate underwent changes, from continental breakup along the Red Sea in the south, to continental collision with Eurasia in the north and formation of the N-S trending Dead Sea fault plate boundary. Concurrent uplift and erosion of the entire Levant area led to an incomplete sedimentary record, obscuring reconstructions of the transition between the two tectonic regimes. New well data, obtained on the continental shelf of the central Levant margin (Qishon Yam 1), revealed a uniquely undisturbed sedimentary sequence which covers this time period. Evaporitic facies found in this well have only one comparable location in the entire eastern Mediterranean area (onland and offshore) over the same time frame — the Red Sea-Suez rift system. Analysis of 4150 km of multi and single-channel seismic profiles, offshore central Levant, shows that the sequence was deposited in a narrow basin, restricted to the continental shelf. This basin (the Haifa Basin) evolved as a half graben along the NW trending Carmel fault, which at present is one of the main branches of the Dead Sea fault. Re-evaluation of geological data onland, in view of the new findings offshore, indicates that the Haifa basin is the northwestern-most of a larger series of basins, comprising a failed rift along the Qishon-Sirhan NW-SE trend. This failed rift evolved spatially parallel to the Red Sea-Suez rift system, and at the same time frame. The Carmel fault would therefore seem to be related to processes occurring several million years earlier than previously thought, before the formation of the Dead Sea fault. The development of a series of basins in conjunction with a young spreading center is a known phenomenon in other regions worldwide; however this is the only known example from across the Arabian plate.

Schattner, U.; Ben-Avraham, Z.; Reshef, M.; Bar-Am, G.; Lazar, M.

2006-06-01

37

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

Microsoft Academic Search

The Proterozoic Midcontinent Rift System of North America is remarkably similar to Phanerozoic rifted continental margins and flood basalt provinces. Like the younger analogues, the volcanism within this older rift can be explained by decompression melting and rapid extrusion of igneous material during lithospheric extension above a broad, asthenospheric, thermal anomaly which the authors call the Keweenaw hot spot. Great

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

1990-01-01

38

West Antarctic Rift System: Extension and Collapse of a West Antarctic Plateau  

NASA Astrophysics Data System (ADS)

Recent thermochronologic data along the Byrd Glacier Outlet of the Transantarctic Mountains are consistent with the hypothesis that the West Antarctic Rift System developed during the extension and collapse of a West Antarctic Plateau. Apatite fission track ages of samples collected along the length of the outlet vary from Early Cretaceous (~112 Ma) to Oligocene (~32 Ma). The ages vary in a systematic fashion: older ages are found at higher elevations and/or towards the East Antarctic Craton, while younger samples are located at lower elevations and/or towards the Ross Sea end of the outlet. This systematic variation in ages is consistent with a Cretaceous stage of incision by rivers flowing from West Antarctica towards the craton, followed by Tertiary incision by rivers flowing in the reverse direction, with a final, Oligocene, stage of incision by glacial erosion. This cooling evolution and proposed switch in drainage direction is consistent with other evidence suggesting the presence and collapse of a West Antarctic Plateau including: 1) geodynamic models of extension and thinning of the West Antarctic Rift System, and 2) geomorphic evidence of major paleo-drainage systems flowing through the TAM from West Antarctic into East Antarctica. Although no one piece of evidence is conclusive in and of itself, taken in toto, the evidence is best explained by the presence and subsequent collapse of a West Antarctic Plateau.

Huerta, A. D.; Blythe, A. E.

2010-12-01

39

ALVIN investigation of an active propagating rift system, Galapagos 95.5?? W  

USGS Publications Warehouse

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. ?? 1992 Kluwer Academic Publishers.

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. P.; Neal, C. A.

1992-01-01

40

Mapping of the Major Structures of the African Rift System.  

National Technical Information Service (NTIS)

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 s...

P. Mohr

1973-01-01

41

Magmatism in rifting and basin formation  

NASA Astrophysics Data System (ADS)

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.

Thybo, H.

2008-12-01

42

Influence of heterogeneities within the lithosphere on the deformation pattern of continental rift systems.  

NASA Astrophysics Data System (ADS)

Understanding how heterogeneities within the lithosphere influence the deformation pattern in continental rifts still remains a challenge and is of real importance to constrain continental break-up. We have selected the Main Ethiopian Rift in East Africa and the Rio Grande Rift in the south-western U.S. These two rifts are perfect natural laboratories to investigate the effect of inherited as they share similar structural characteristics but develop above different kinds of lithosphere-scale heterogeneities. From a structural point of view both rifts show similar length (1000km), width (50 to 70 km) and asymmetry. The Main Ethiopian rift is the NE-SW trending plate boundary between the Nubian and Somalian plates that has been developing for the past 11 Ma above a palaeo-Proterozoic lithospheric-scale weak zone re-heated by the Afar hotspot, whereas the Rio Grande Rift is the eastern "boundary" of the Basin & Range system which has been developing for the past 30 Ma in the frame of a westward-retreating Farallon subduction zone. However, the Rio Grande Rift shows evidence of low angle normal faulting whereas the Main Ethiopian Rift shows steeply dipping (with a mean close to 70°) normal faults. The Main Ethiopian Rift shows larger volume of erupted lavas than the Rio Grande Rift. Combined with a structural analyses of both rifts, we present here a series of 2D cross sections numerical models that allow better understanding of the influence of initial heterogeneities such as 1) the rheological state of the crust; 2) the presence of a crustal-scale to lithospheric-scale discrete weak or strong zone, 3) the effects of the presence of magma. We illustrate that rheological boundaries are not reactivated if the rheological contrast it too high, which is the case of the Rio Grande Rift that developed to the east of the North American Craton within thinned lithosphere. We also illustrate that the width of the weak zone do no have any influence on the exhumation of the asthenospheric mantle. The temperature at the base of the lithosphere is the parameter controlling the asthenosphere rising.

Philippon, Melody; Thieulot, Cedric; van Wijk, Jolante; Sokoutis, Dimitrios; Willingshofer, Ernst; Cloetingh, Sierd

2013-04-01

43

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

44

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

45

Comparisons between the rift systems of East Africa, Earth and Beta Regio, Venus  

NASA Astrophysics Data System (ADS)

The rift systems of southern East Africa and Beta Regio, Venus are similar in a number of ways. The rifted East African and Venusian lithospheres have effective elastic thicknesses of ˜ 30 km, suggesting that both lithospheres maintain significant flexural strength during rifting. Both rift systems have maximum fault segment lengths of ˜ 100 km. The effective elastic thickness and maximum fault segment length of both rifts are greater than those seen in many other active extensional regions on Earth, despite the high surface temperatures on Venus. We suggest that the southern East African and Venusian elastic thicknesses and maximum fault segment lengths are due to stronger lithosphere. The rift systems differ in the maximum width of their half graben. East African half grabens are up to ˜ 50 km wide, whilst those on Venus are up to ˜ 150 km wide. To support the topography associated with such half grabens requires shear stresses to act on the bounding faults. In East Africa the greater elastic thickness (compared to most other terrestrial extensional regions) means that wide half grabens can form without requiring the shear stresses acting on the bounding faults to be greater than the ˜ 1-10 MPa (10-100 bars) stress drop typically seen in earthquakes. However, on Venus the absence of sediment infill, greater widths and larger effective topographic steps of the half grabens require shear stresses of up to ˜ 80 MPa (800 bars) to act on the bounding faults. This difference is significant; Venusian faults must be stronger than those on Earth.

Foster, Adrian; Nimmo, Francis

1996-09-01

46

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

NASA Technical Reports Server (NTRS)

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.

Mohr, P. A.

1974-01-01

47

Failure was not an option- the Mid-Continent Rift system succeeded  

NASA Astrophysics Data System (ADS)

The 1.1 Ga Mid-Continent Rift (MCR) in North America is often viewed as a failed rift formed by isolated midplate volcanism and extension within the ~1.3-~0.98 Ga Grenville orogeny. An alternative view is suggested by analogy with younger and morphologically similar rift systems, whose plate tectonic settings are more easily understood because their surroundings - including seafloor with magnetic anomalies - have not been deformed or destroyed by subsequent collisions and rifting events. In this view, the MCR was part of a larger plate boundary rifting event that resulted in a successful episode of seafloor spreading. This view is motivated by various pieces of evidence. The MCR rifting looks much like rigid plate block motion, such as associated with the West Central African Rift systems formed during the Mesozoic breakup of Africa and South America and the ongoing rifting in the East African Rift region with seafloor spreading in the Gulf of Aden and the Red Sea. This view explains the affinities of the Grenville-age rocks in the central and southern Appalachians to Amazonia rather than Canadian Grenville-age Appalachian rocks. The MCR extends farther to the south than traditionally assumed along the East Continental Gravity High (a buried feature from Ohio to Alabama). This failed portion of the rift system connected to the rift successfully separating Laurentia and Amazonia. The seafloor spreading separating Amazonia from Laurentia may explain the former's relative motion toward Greenland and Baltica. This model is consistent with some of the ~1.1 Ga geological events in Amazonia. A change in the apparent polar wander path for Laurentia during the period of volcanism of the MCR could be attributed to this plate reconfiguration. The extensional phase on the MCR may have ended because motion was taken up by seafloor spreading between Laurentia and Amazonia rather ending due to another continental collision. Later reverse faulting on the MCR normal faults due to compression, perhaps from collisions around Rodinia's margins, would not be unexpected because the MCR would be a relatively weak intraplate zone due to higher crustal temperatures and faults.

Merino, M.; Stein, C. A.; Stein, S. A.; Keller, G. R.; Flesch, L. M.; Jurdy, D. M.

2013-12-01

48

Variation in magma volume along the two arms of the Midcontinent Rift System  

NASA Astrophysics Data System (ADS)

The 2000km-long Midcontinent Rift System (MCRS) has two major arms meeting in the Lake Superior region. One extends southwestward at least as far as central Kansas, and the other extends southeastward through Michigan. Gravity and magnetic anomalies delimit the rift zone because the highly magnetic and dense mafic igneous rocks filling the central grabens of the rift system have strong susceptibility and density contrasts with adjacent rock formations. Because the rift lies hidden beneath gently dipping Phanerozoic sedimentary rocks except in the Lake Superior region, most models of rift structure have been extrapolated from the few areas that have seismic reflection data. A fundamental question is how the two arms differ. The west arm is more pronounced than the east arm in the gravity data. Whether this difference is due to the east arm being buried by the Michigan Basin or reflects magma volume has implications for the formation of the MCRS. Existing gravity models are not standardized across the rift and therefore cannot be used to directly compare the arms. We have thus conducted gravity modeling with a uniform approach and find that the west arm has significantly more magma and that the magma volume along the west arm increases toward Lake Superior. These results imply that there was more spreading along the western arm and that the spreading on this arm decreased southward, consistent with the arms being boundaries of a microplate rotating with respect to the Superior province with its rotation pole to the southwest.

Merino, M.; Keller, G. R.; Stein, S. A.

2012-12-01

49

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

NASA Astrophysics Data System (ADS)

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.

Bottenberg, Helen Carrie

50

Fault system at the southeastern boundary of the Okavango Rift, Botswana  

NASA Astrophysics Data System (ADS)

The seismically active Okavango Rift in northwestern Botswana is probably the southern extension of the East Africa Rift System. Relief is low and many of the geomorphic features of the incipient rift are subtle. The northeast-southwest trending Kunyere and Thamalakane Faults form the southeastern boundary of the rift. Proterozoic structural fabrics of similar trend, belonging to the Ghanzi-Chobe Belt, control the regional trend of the primary Cenozoic fault set of the rift. Geophysical evidence indicates that these are dominantly normal faults forming boundaries to northeast-southwest trending strips of horsts, grabens and half grabens. Two other major sets trend northwest-southeast and north-south. The northwest-southeast set occurs within the interfault strips of the major northeast-southwest trending faults. The latter act as local transfer faults forming boundaries to stress domains within which the secondary northwest-southeast trending faults are produced. Remote sensing imagery shows a weakly developed north-south set that is spatially associated with, and truncated by the northwest-southeast set. The whole fault system probably produces predominantly dip-slip displacements on multiple fault sets responding to a subcontinental east- west extension.

Modisi, M. P.

2000-04-01

51

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

52

A regional gravity study of the West African rift system in Nigeria and Cameroon and its tectonic interpretation  

NASA Astrophysics Data System (ADS)

This study brings together existing and new gravity data to investigate the nature and cause of the Bouguer gravity field associated with the Cretaceous West African rift system in Nigeria and Cameroon. The new gravity measurements include data collected over the basement area between the Benue Trough and the Cameroon border and fill an important gap in the gravity coverage. After removal of the long wavelength negative anomaly from the observed gravity field the remaining positive gravity anomaly, associated with the rift system, is interpreted in terms of two and three dimensional crustal models. These models are constrained by crustal thicknesses derived from a seismic refraction study carried out across and to the south of the Yola rift. The results of simple three dimensional gravity modelling indicate the crust beneath the lower and middle Benue is approximately 20 km thick while beneath the Gongola rift the crust is approximately 25 km thick relative to a normal crustal thickness of 34 km away from the rift. Assuming the thinned crust associated with the rift system is the result of simple lithospheric stretching, then the maximum possible crustal extensions of 95, 65 and 55 km have taken place perpendicular to the Benue, Gongola and Yola rifts respectively. These crustal extensions do not necessarily reflect the total crustal movement affecting these rifts since the Benue and Yola rifts have been subjected to varying amounts of shear displacement during the Cretaceous and early Tertiary times. Crustal extension estimates across the West African rift system could be as much as four times greater than the published extension estimates across the East African rift system. These rift systems have the same plate tectonic setting being the failed third arms of successful triple junctions and are the result of extensional and shear tectonics. The differences in crustal extension and the resulting isostatic response of the lithosphere beneath these rifts can explain why the West African rift system has been associated with subsidence processes throughout its development whereas the East African rift system in Northeast Africa has been strongly affected by uplift.

Fairhead, J. D.; Okereke, C. S.

1987-11-01

53

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

54

Stratigraphy, Structure, and Ore Deposits of the Southern Limb of the Midcontinent Rift System  

NSDL National Science Digital Library

This site features an overview of the Midcontinent Rift system of North America, an area that extends for more than 2000 km northeasterly from Kansas, through the Lake Superior region, and then southeasterly through lower Michigan. This summary of the stratigraphy, structure, and mineralization of rift rocks provides an overview of the geologic history in northern Wisconsin and upper Michigan. Separate sections describe the tectonic history and structural features of the area, the stratigraphy of volcanic and sedimentary deposits, and the mineralization that produced rich copper and silver deposits. Information is supported by numerous citations while maps and diagrams help illustrate the concepts.

Bornhorst, T.; Woodruff, L.; Nicholson, S.; University, Michigan T.

55

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

Microsoft Academic Search

The Afar triangle in northeastern Ethiopia is where the Red Sea rift, the Carlsberg Ridge of the Indian Ocean, and the Rift Valley system of east Africa meet. In 1979, J. Welhan and H. Craig reported that hydrothermal vents at 21°N, on the East Pacific Rise, are discharging turbid waters. Mixtures of the plumes with ambient seawater contain significant amounts

Osamu Fukuta

1984-01-01

56

The Midcontinent rift system and the Precambrian basement in southern Michigan  

SciTech Connect

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.

Smith, W.A. (Western Michigan Univ., Kalamazoo, MI (United States). Dept. of Geology)

1994-04-01

57

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

Microsoft Academic Search

East African Rift System magmatism began over 40 my ago and has continued through the present. Numerical models have determined two plumes are necessary to create the spatial and temporal distribution of volcanism. Geochemical data support the presence of two chemically distinct plumes initially located beneath the Afar Depression (NE Ethiopia) and the Turkana Depression (SW Ethiopia\\/N Kenya). The timing

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

2007-01-01

58

The transition from diffuse to focused extension: Modeled evolution of the West Antarctic Rift system  

Microsoft Academic Search

Two distinct stages of extension are recognized in the West Antarctic Rift system (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

Audrey D. Huerta; Dennis L. Harry

2007-01-01

59

Revised Eocene-Oligocene kinematics for the West Antarctic rift system  

NASA Astrophysics Data System (ADS)

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> <div class="credits"> <p class="dwt_author">Granot, R.; Cande, S. C.; Stock, J. M.; Damaske, D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">60</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19730011665&hterms=african+cities&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dafrican%2Bcities"> <span id="translatedtitle">Mapping of the major structures of the African <span class="hlt">rift</span> <span class="hlt">system</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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 <span class="hlt">rift</span> valley.</p> <div class="credits"> <p class="dwt_author">Mohr, P. A. (principal investigator)</p> <p class="dwt_publisher"></p> <p class="publishDate">1973-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_2");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a style="font-weight: bold;">3</a> <a onClick='return showDiv("page_4");' 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id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_3");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a style="font-weight: bold;">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_5");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">61</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Nelson, C. H.; Karabanov, E. B.; Colman, S. M.; Escutia, C.</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">62</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40848188"> <span id="translatedtitle">Two mantle plumes beneath the East African <span class="hlt">rift</span> <span class="hlt">system</span>: Sr, Nd and Pb isotope evidence from Kenya <span class="hlt">Rift</span> basalts</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Major and trace element and radiogenic isotope ratios (Sr, Nd and Pb) are presented for a suite of Neogene to Recent basalts (MgO>4 wt%) from the axial regions of the Kenya <span class="hlt">Rift</span>. Samples have compositions ranging from hypersthene-normative basalt through alkali basalt to basanite and are a subset of a larger database in which compositions extend to nephelinite. A broadly</p> <div class="credits"> <p class="dwt_author">Nick Rogers; Ray Macdonald; J. Godfrey Fitton; Rhiannon George; Martin Smith; Barbara Barreiro</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">63</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Delvaux, Damien; Kervyn, François; Mulumba, Jean-Luc; Kipata, Louis; Sebagenzi, Stanislas; Mavonga, Georges; Macheyeki, Athanas; Temu, Elly Bryan</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">64</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://dx.doi.org/10.1016/S0040-1951(98)00155-3"> <span id="translatedtitle">Transect across the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> in the Ross Sea, Antarctica</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">In 1994, the ACRUP (Antarctic Crustal Profile) project recorded a 670-km-long geophysical transect across the southern Ross Sea to study the velocity and density structure of the crust and uppermost mantle of the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>. Ray-trace modeling of P- and S-waves recorded on 47 ocean bottom seismograph (OBS) records, with strong seismic arrivals from airgun shots to distances of up to 120 km, show that crustal velocities and geometries vary significantly along the transect. The three major sedimentary basins (early-<span class="hlt">rift</span> grabens), the Victoria Land Basin, the Central Trough and the Eastern Basin are underlain by highly extended crust and shallow mantle (minimum depth of about 16 km). Beneath the adjacent basement highs, Coulman High and Central High, Moho deepens, and lies at a depth of 21 and 24 km, respectively. Crustal layers have P-wave velocities that range from 5.8 to 7.0 km/s and S-wave velocities from 3.6 to 4.2 km/s. A distinct reflection (PiP) is observed on numerous OBS from an intra-crustal boundary between the upper and lower crust at a depth of about 10 to 12 km. Local zones of high velocities and inferred high densities are observed and modeled in the crust under the axes of the three major sedimentary basins. These zones, which are also marked by positive gravity anomalies, may be places where mafic dikes and sills pervade the crust. We postulate that there has been differential crustal extension across the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>, with greatest extension beneath the early-<span class="hlt">rift</span> grabens. The large amount of crustal stretching below the major <span class="hlt">rift</span> basins may reflect the existence of deep crustal suture zones which initiated in an early stage of the <span class="hlt">rifting</span>, defined areas of crustal weakness and thereby enhanced stress focussing followed by intense crustal thinning in these areas. The ACRUP data are consistent with the prior concept that most extension and basin down-faulting occurred in the Ross Sea during late Mesozoic time, with relatively small extension, concentrated in the western half of the Ross Sea, during Cenozoic time.</p> <div class="credits"> <p class="dwt_author">Trey, H.; Cooper, A. K.; Pellis, G.; Della, Vedova, B.; Cochrane, G.; Brancolini, G.; Makris, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">65</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/55988923"> <span id="translatedtitle">Feedback between magmatic, tectonic and glacial processes in the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> (Invited)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The western Ross Sea coast of the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> (WARS) is littered with mid-Eocene to Present alkaline plutons, dike swarms and volcanoes. The mafic igneous products have OIB-HIMU signature, similar to basalts associated with long-lived hotspot tracks, pointing to the possible occurrence of one or more mantle plumes active during the Cenozoic or the Mesozoic. However, He and</p> <div class="credits"> <p class="dwt_author">S. Rocchi</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">66</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1990JGR....9510869H"> <span id="translatedtitle">Keweenaw hot spot: Geophysical evidence for a 1.1 Ga mantle plume beneath the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Proterozoic Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> of North America is remarkably similar to Phanerozoic <span class="hlt">rifted</span> continental margins and flood basalt provinces. Like the younger analogues, the volcanism within this older <span class="hlt">rift</span> can be explained by decompression melting and rapid extrusion of igneous material during lithospheric extension above a broad, asthenospheric, thermal anomaly which we call the Keweenaw hot spot. Great Lakes International Multidisciplinary Program on Crustal Evolution seismic reflection profiles constrain end-member models of melt thickness and stretching factors, which yield an inferred mantle potential temperature of 1500°-1570°C during <span class="hlt">rifting</span>. Combined gravity modeling and subsidence calculations are consistent with stretching factors that reached 3 or 4 before <span class="hlt">rifting</span> ceased, and much of the lower crust beneath the <span class="hlt">rift</span> consists of relatively high density intruded or underplated synrift igneous material. The isotopic signature of Keweenawan volcanic rocks, presented in a companion paper by Nicholson and Shirey (this issue), is consistent with our model of passive <span class="hlt">rifting</span> above an asthenospheric mantle plume.</p> <div class="credits"> <p class="dwt_author">Hutchinson, D. R.; White, R. S.; Cannon, W. F.; Schulz, K. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1990-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">67</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5456203"> <span id="translatedtitle">Keweenaw hot spot: Geophysical evidence for a 1. 1 Ga mantle plume beneath the Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The Proterozoic Midcontinent <span class="hlt">Rift</span> <span class="hlt">System</span> of North America is remarkably similar to Phanerozoic <span class="hlt">rifted</span> continental margins and flood basalt provinces. Like the younger analogues, the volcanism within this older <span class="hlt">rift</span> can be explained by decompression melting and rapid extrusion of igneous material during lithospheric extension above a broad, asthenospheric, thermal anomaly which the authors call the Keweenaw hot spot. Great Lakes International Multidisciplinary Program on Crustal evolution seismic reflection profiles constrain end-member models of melt thickness and stretching factors, which yield an inferred mantle potential temperature of 1,500-1,570C during <span class="hlt">rifting</span>. Combined gravity modeling and subsidence calculations are consistent with stretching factors that reached 3 or 4 before <span class="hlt">rifting</span> ceased, and much of the lower crust beneath the <span class="hlt">rift</span> consists of relatively high density intruded or underplated synrift igneous material. The isotopic signature of Keweenawan volcanic rocks, presented in a companion paper by Nicholson and Shirey (this issue), is consistent with the model of passive <span class="hlt">rifting</span> above an asthenospheric mantle plume.</p> <div class="credits"> <p class="dwt_author">Hutchinson, D.R. (Geological Survey, Woods Hole, MA (USA)); White, R.S. (Cambridge Univ. (England)); Cannon, W.F.; Schulz, K.J. (Geological Survey, Reston, VA (USA))</p> <p class="dwt_publisher"></p> <p class="publishDate">1990-07-10</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">68</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Mukasa, S. B.; Rilling-Hall, S.; Marcano, M. C.; Wilson, T. J.; Lawver, L. A.; LeMasurier, W. E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">69</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/42051412"> <span id="translatedtitle">Patterns of late Cenozoic volcanic and tectonic activity in the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> revealed by aeromagnetic surveys</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Aeromagnetic surveys, spaced <=5 km, over widely separated areas of the largely ice- and sea-covered West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>, reveal similar patterns of 100- to 1700-nT, shallow-source magnetic anomalies interpreted as evidence of extensive late Cenozoic volcanism. We use the aeromagnetic data to extend the volcanic <span class="hlt">rift</span> interpretation over West Antarctica starting with anomalies over (1) exposures of highly magnetic,</p> <div class="credits"> <p class="dwt_author">John C. Behrendt; Richard Saltus; Detlef Damaske; Anne McCafferty; Carol A. Finn; Donald Blankenship; Robin E. Bell</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">70</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/48944115"> <span id="translatedtitle">Patterns of late Cenozoic volcanic and tectonic activity in the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> revealed by aeromagnetic surveys</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Aeromagnetic surveys, spaced ?5 km, over widely separated areas of the largely ice- and sea-covered West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>, reveal similar patterns of 100- to 1700-nT, shallow-source magnetic anomalies interpreted as evidence of extensive late Cenozoic volcanism. We use the aeromagnetic data to extend the volcanic <span class="hlt">rift</span> interpretation over West Antarctica starting with anomalies over (1) exposures of highly magnetic,</p> <div class="credits"> <p class="dwt_author">John C. Behrendt; Richard Saltus; Detlef Damaske; Anne McCafferty; Carol A. Finn; Donald Blankenship; Robin E. Bell</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">71</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1999GPC....23...61W"> <span id="translatedtitle">Lithospheric dynamics and mantle sources of alkaline magmatism of the Cenozoic West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Lithospheric extension in the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> and the Ross Sea embayment is related to Cenozoic alkaline volcanism. Basanites and alkali basalts define the two endmembers of primary magmas with distinct petrographic, chemical and isotopic compositions. Basanites are generally more primitive and significantly more enriched in incompatible trace elements than alkali basalts. Parallel incompatible trace-element distribution patterns in both rock types but slightly different isotopic compositions suggest a derivation by different degrees of partial melting from different mantle sources. Sr-, Nd- and Pb-isotopes allow the identification of distinct magma sources: asthenospheric mantle, enriched lithospheric mantle and a HIMU plume component which is widespread beneath the entire area. Spatial and temporal variations in isotopic compositions suggest a relationship between the dynamics of lithospheric extension and changing mantle sources of related magmas. Geothermobarometry on mantle xenoliths documents a pressure-temperature-time evolution of the mantle lithosphere which is related to <span class="hlt">rifting</span>, uplift and cooling of mantle below the Ross Sea <span class="hlt">Rift</span>-Transantarctic Mountain transition. This paper reviews existing data and ideas but is biased towards the author's own working area, the Western Ross Sea.</p> <div class="credits"> <p class="dwt_author">Wörner, G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">72</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Stab, Martin; Bellahsen, Nicolas; Pik, Raphaël; Leroy, Sylvie; Ayalew, Dereje</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">73</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Homuth, Benjamin; Löbl, Ulrike; Batte, Arthur; Link, Klemens; Kasereka, Celestine; Rümpker, Georg</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">74</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1991Tectp.191...55C"> <span id="translatedtitle">Post-Pan-African tectonic evolution of South Malawi in relation to the Karroo and recent East African <span class="hlt">rift</span> <span class="hlt">systems</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Structural studies conducted in the Lengwe and Mwabvi Karroo basins and in the basement in South Malawi, using regional maps and published data extended to cover Southeast Africa, serve to propose a series of geodynamic reconstructions which reveal the persistence of an extensional tectonic regime, the minimum stress ?3 of which has varied through time. The period of Karroo <span class="hlt">rifting</span> and the tholeiitic and alkaline magmatism which terminated it, were controlled by NW-SE extension, which resulted in the creation of roughly NE-SW troughs articulated by the Tanganyika-Malawi and Zambesi pre-transform <span class="hlt">systems</span>. These were NW-SE sinistral-slip <span class="hlt">systems</span> with directions of movement dipping slightly to the Southeast, which enabled the Mwanza fault to play an important role in the evolution of the Karroo basins of the Shire Valley. The Cretaceous was a transition period between the Karroo <span class="hlt">rifting</span> and the formation of the Recent East African <span class="hlt">Rift</span> <span class="hlt">System</span>. Extension was NE-SW, with some evidence for a local compressional episode in the Lengwe basin. Beginning in the Cenozoic, the extension once more became NW-SE and controlled the evolution in transtension of the Recent East African <span class="hlt">Rift</span> <span class="hlt">System</span>. This history highlights the major role of transverse faults <span class="hlt">systems</span> dominated by strike-slip motion in the evolution and perpetuation of the continental <span class="hlt">rift</span> <span class="hlt">systems</span>. These faults are of a greater geological persistence than the normal faults bounding the grabens, especially when they are located on major basement anisotropies.</p> <div class="credits"> <p class="dwt_author">Castaing, C.</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">75</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AGUFM.T13C2202M"> <span id="translatedtitle">The Alpine Tethys <span class="hlt">Rift</span> <span class="hlt">System</span> in Western Europe: From Variscan Inheritance to Alpine Inversion</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Carboniferous to present evolution of Western Europe represents one of the best-documented Wilson cycles. However, despite more than one century of geological investigations, the detailed temporal and spatial evolution of the orogenic cycle remains a subject of numerous debates. Its tectonic evolution is controlled by the collapse of the Variscan orogen, the closure of the Paleo-and Neo-Tethys and the relative movement of Africa relative to Europe that changed from left-lateral to north directed in Santonian/Campanian time resulting in its reactivation and the formation of the present-Alpine chain. Slab-pull forces derived from the subduction of slabs along the northwestern margin of the Palaeo-Tethys may account for distributed extensional strain within the Alpine domain during Triassic time and the subsequent localization and extension within domains that underwent extreme crustal thinning and mantle exhumation before being reactivated and subducted during Alpine convergence. This process can account for the diachronous evolution of <span class="hlt">rift</span> domains ranging from Late Triassic (Meliata-Vardar), to Middle Jurassic (Alpine Tethys) to Early Cretaceous (Iberia-Atlantic) and the younging of the subsequent syn-collisional facies (flysch/molasse) from Upper Jurassic (Meliata) to Eocene/Oligocene (Pyrenees/Alps) to present (eastern Mediterranean) across the Alpine <span class="hlt">system</span>. Thus, the Alpine <span class="hlt">system</span> in Western Europe results from a complex paleogeographic evolution and represents an orogenic collage in which coeval lateral domains evolved at different times. The strain localization is likely to be controlled by structural, thermal and compositional inheritances in the continental lithosphere that resulted from repeated tectonic events. Based on the example of the Alpine Tethys <span class="hlt">rift</span> <span class="hlt">system</span>, I will discuss the importance of lithospheric inheritance resulting from the Variscan orogeny and how it may have controlled the evolution of the Tethys <span class="hlt">rift</span> <span class="hlt">system</span> and in turn the onset of subduction and the architecture of the Alpine <span class="hlt">system</span> in western Europe. I will show that: 1) hyper-extended <span class="hlt">rift</span> <span class="hlt">systems</span> formed as v-shaped basins floored either by exhumed crust or subcontinental mantle and localized at the edges of stronger lithospheric domains or were guided by inherited structures; 2) the “oceanic” domains behaved rigid during onset of convergence; and 3) the strong segmentation of the Alpine domain is largely controlled by inherited structures.</p> <div class="credits"> <p class="dwt_author">Manatschal, G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">76</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009EGUGA..11.2637M"> <span id="translatedtitle">The Alpine Tethys <span class="hlt">Rift</span> <span class="hlt">System</span> in Western Europe: From Variscan Inheritance to Alpine Inversion</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Permian to Cenozoic evolution of the Tethys <span class="hlt">system</span> in Western Europe remains a subject of numerous debates. Its tectonic evolution is controlled by the collapse of the Variscan orogen, the closure of the Paleo-Tethys and the relative movement of Africa relative to Europe that changed from left-lateral to north directed in Santonian/Campanian time. Slab-pull forces derived from the subduction of slabs along the north-western margin of the Palaeo-Tethys may account for distributed extensional strain within the Alpine domain during Triassic time and the subsequent localization and extension within domains that underwent extreme crustal thinning and mantle exhumation before being reactivated and subducted during Alpine convergence. This process can account for the diachronous evolution of <span class="hlt">rift</span> domains ranging from Late Triassic (Meliata-Vardar), to Middle Jurassic (Alpine Tethys) to Early Cretaceous (Iberia-Atlantic) and the younging of the subsequent syn-collisional facies (flysch/molasse) from Upper Jurassic (Meliata) to Eocene/Oligocene (Pyrenees/Alps) to present (eastern Mediterranean) across the Alpine <span class="hlt">system</span>. Thus, the Alpine <span class="hlt">system</span> in Western Europe results from a complex paleogeographic evolution and represents an orogenic collage in which coeval lateral domains evolved at different times. The strain localization is likely to be controlled by structural, thermal and compositional inheritances in the continental lithosphere that resulted from repeated tectonic events. Based on the example of the Alpine Tethys <span class="hlt">rift</span> <span class="hlt">system</span>, I will discuss the importance of lithospheric inheritance and how it may control the evolution of a <span class="hlt">rift</span> <span class="hlt">system</span> and subsequent mantle exhumation and in turn the onset of subduction and the architecture of the resulting collisional orogen. I will show that: 1) <span class="hlt">rift</span> <span class="hlt">systems</span> localized at the edges of stronger lithospheric domains, were guided by inherited structures and formed as v-shaped basins floored either by exhumed crust or subcontinental mantle; 2) during onset of convergence the "oceanic" domains behaved rigid and the plate kinematic response was instantaneous and distributed across conjugate margins; and 3) the Alpine domain is strongly segmented and largely controlled by inherited structures.</p> <div class="credits"> <p class="dwt_author">Manatschal, G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">77</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014GeoJI.198..414A"> <span id="translatedtitle">Upper mantle seismic anisotropy beneath the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> and surrounding region from shear wave splitting analysis</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We constrain azimuthal anisotropy in the West Antarctic upper mantle using shear wave splitting parameters obtained from teleseismic SKS, SKKS and PKS phases recorded at 37 broad-band seismometres deployed by the POLENET/ANET project. We use an eigenvalue technique to linearize the rotated and shifted shear wave horizontal particle motions and determine the fast direction and delay time for each arrival. High-quality measurements are stacked to determine the best fitting splitting parameters for each station. Overall, fast anisotropic directions are oriented at large angles to the direction of Antarctic absolute plate motion in both hotspot and no-net-rotation frameworks, showing that the anisotropy does not result from shear due to plate motion over the mantle. Further, the West Antarctic directions are substantially different from those of East Antarctica, indicating that anisotropy across the continent reflects multiple mantle regimes. We suggest that the observed anisotropy along the central Transantarctic Mountains (TAM) and adjacent West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> (WARS), one of the largest zones of extended continental crust on Earth, results from asthenospheric mantle strain associated with the <span class="hlt">final</span> pulse of western WARS extension in the late Miocene. Strong and consistent anisotropy throughout the WARS indicate fast axes subparallel to the inferred extension direction, a result unlike reports from the East African <span class="hlt">rift</span> <span class="hlt">system</span> and <span class="hlt">rifts</span> within the Basin and Range, which show much greater variation. We contend that ductile shearing rather than magmatic intrusion may have been the controlling mechanism for accumulation and retention of such coherent, widespread anisotropic fabric. Splitting beneath the Marie Byrd Land Dome (MBL) is weaker than that observed elsewhere within the WARS, but shows a consistent fast direction, possibly representative of anisotropy that has been `frozen-in' to remnant thicker lithosphere. Fast directions observed inland from the Amundsen Sea appear to be radial to the dome and may indicate radial horizontal mantle flow associated with an MBL plume head and low upper mantle velocities in this region, or alternatively to lithospheric features associated with the complex Cenozoic tectonics at the far-eastern end of the WARS.</p> <div class="credits"> <p class="dwt_author">Accardo, Natalie J.; Wiens, Douglas A.; Hernandez, Stephen; Aster, Richard C.; Nyblade, Andrew; Huerta, Audrey; Anandakrishnan, Sridhar; Wilson, Terry; Heeszel, David S.; Dalziel, Ian W. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">78</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014GeoJI.tmp..183A"> <span id="translatedtitle">Upper mantle seismic anisotropy beneath the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> and surrounding region from shear wave splitting analysis</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We constrain azimuthal anisotropy in the West Antarctic upper mantle using shear wave splitting parameters obtained from teleseismic SKS, SKKS and PKS phases recorded at 37 broad-band seismometres deployed by the POLENET/ANET project. We use an eigenvalue technique to linearize the rotated and shifted shear wave horizontal particle motions and determine the fast direction and delay time for each arrival. High-quality measurements are stacked to determine the best fitting splitting parameters for each station. Overall, fast anisotropic directions are oriented at large angles to the direction of Antarctic absolute plate motion in both hotspot and no-net-rotation frameworks, showing that the anisotropy does not result from shear due to plate motion over the mantle. Further, the West Antarctic directions are substantially different from those of East Antarctica, indicating that anisotropy across the continent reflects multiple mantle regimes. We suggest that the observed anisotropy along the central Transantarctic Mountains (TAM) and adjacent West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> (WARS), one of the largest zones of extended continental crust on Earth, results from asthenospheric mantle strain associated with the <span class="hlt">final</span> pulse of western WARS extension in the late Miocene. Strong and consistent anisotropy throughout the WARS indicate fast axes subparallel to the inferred extension direction, a result unlike reports from the East African <span class="hlt">rift</span> <span class="hlt">system</span> and <span class="hlt">rifts</span> within the Basin and Range, which show much greater variation. We contend that ductile shearing rather than magmatic intrusion may have been the controlling mechanism for accumulation and retention of such coherent, widespread anisotropic fabric. Splitting beneath the Marie Byrd Land Dome (MBL) is weaker than that observed elsewhere within the WARS, but shows a consistent fast direction, possibly representative of anisotropy that has been `frozen-in' to remnant thicker lithosphere. Fast directions observed inland from the Amundsen Sea appear to be radial to the dome and may indicate radial horizontal mantle flow associated with an MBL plume head and low upper mantle velocities in this region, or alternatively to lithospheric features associated with the complex Cenozoic tectonics at the far-eastern end of the WARS.</p> <div class="credits"> <p class="dwt_author">Accardo, Natalie J.; Wiens, Douglas A.; Hernandez, Stephen; Aster, Richard C.; Nyblade, Andrew; Huerta, Audrey; Anandakrishnan, Sridhar; Wilson, Terry; Heeszel, David S.; Dalziel, Ian W. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">79</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Zal, H. J.; Ebinger, C. J.; Wood, D. J.; Scholz, C. A.; d'Oreye, N.; Carn, S. A.; Rutagarama, U.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">80</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUFMPP41D..04H"> <span id="translatedtitle">Geodynamic Constraints on the Tectonic Evolution of the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Finite element models show that the key aspects of the tectonic evolution of the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> were controlled primarily by the pre-<span class="hlt">rift</span> thermal structure of the lithosphere. The parameters found to exert primary control on the structural behavior of the models are the initial crustal thickness of West Antarctica, the mantle potential temperature (or mantle heat flux), and the distribution of heat producing elements in the West Antarctic crust. Models that best reproduce the basic aspects of the tectonic evolution of the West Antarctic <span class="hlt">Rift</span> <span class="hlt">system</span> (initial diffuse extension in the Late Cretaceous followed by focused Cenozoic extension near the East Antarctica-West Antarctica boundary) require a pre-<span class="hlt">rift</span> crustal thickness greater than 40 km in West Antarctica, a mantle heat flux of less than 25 mW m-2 (corresponding to a mantle potential temperature ? 1325 °C), and a greater abundance of heat producing elements in the West Antarctic lower crust in comparison to East Antarctica. Under these conditions, extension is initially distributed across the relatively warm (and hence weak) Ross Sea region of West Antarctica. The portion of West Antarctica immediately adjacent to East Antarctica is refrigerated by the cool East Antarctic craton, and remains relatively strong and undergoes no extension. As extension in West Antarctica progresses the heat producing crust thins. This leads to cooling and strengthening of the lithosphere in this region. As a consequence, the unthinned part of West Antarctica immediately adjacent to East Antarctica becomes the weakest region, resulting in cessation of extension in the central Ross Sea and focusing of extension in the Victoria Land Basin region. The models predict decompression melting of the asthenosphere beginning at approximately 50 Ma, ultimately producing ca. 7 x 105 km3 of magmatic rocks beneath the West Antarctic Ice Sheet. The models also predict a modern surface heat flux of 112 mW m-2, in good agreement with the 115 mW m-2 measured in the AND-1B borehole beneath the McMurdo Ice Shelf by the ANDRILL Science Team.</p> <div class="credits"> <p class="dwt_author">Harry, D. L.; Anoka, J. L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_3");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a style="font-weight: bold;">4</a> <a 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src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_4");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a style="font-weight: bold;">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_6");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">81</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014EGUGA..1614255D"> <span id="translatedtitle">Ambient Noise Tomography of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> in Mozambique</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Project MOZART - MOZAmbique <span class="hlt">Rift</span> Tomography (funded by FCT, Lisbon) deployed a total of 30 temporary broadband seismic stations from the SEIS-UK Pool in central and south Mozambique and in NE South Africa. The purpose of this project is the study of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) in Mozambique. We estimated preliminary locations with the data recorded from April 2011 to July 2012. A total of 307 earthquakes were located, with ML magnitudes ranging from 0.9 to 3.9. We observe a linear northeast-southwest distribution of the seismicity that seems associated to the Inhaminga fault. The seismicity in the northeast sector correlates well with the topography, tracing the Urema <span class="hlt">rift</span> valley. The seismicity extends to ~300km, reaching the M7 2006 Machaze earthquake area. In order to obtain an initial velocity model of the region, we applied the ambient noise method to the MOZART data and two additional stations from AfricaARRAY. Cross-correlations were computed between all pairs of stations, and we obtained Rayleigh wave group velocity dispersion curves for all interstation paths, in the period range from 3 to 50 seconds. The geographical distribution of the group velocity anomalies is in good agreement with the geology map of Mozambique, having lower group velocities in sedimentary basins areas and higher velocities in cratonic regions. We also observe two main regions with different velocities that may indicate a structure not proposed in previous studies. We perform a three-dimensional inversion to obtain the S-wave velocity of the crust and upper mantle, and in order to extend the investigation to longer periods we apply a recent implementation of the surface-wave two-station method (teleseismic interferometry), while augmenting our dataset with Rayleigh wave phase velocities curves in broad period ranges. In this way we expect to be able to look into the lithosphere-asthenosphere depth range.</p> <div class="credits"> <p class="dwt_author">Domingues, Ana; Custódio, Susana; Chamussa, José; Silveira, Graça; Chang, Sung-Joon; Lebedev, Sergei; Ferreira, Ana; Fonseca, João</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">82</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/52271265"> <span id="translatedtitle">Structural Evolution of the Incipient Okavango <span class="hlt">Rift</span> Zone, NW Botswana</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Studies of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) and other continental <span class="hlt">rifts</span> have significantly improved our understanding of <span class="hlt">rifting</span> processes; however, we particularly lack studies of the embryonic stages of <span class="hlt">rift</span> creation. The Okavango <span class="hlt">Rift</span> Zone (ORZ), NW Botswana is one of few places worldwide where one can study the early stages of continental extension prior to the accumulation of</p> <div class="credits"> <p class="dwt_author">E. A. Atekwana; B. D. Kinabo; M. P. Modisi; J. P. Hogan; D. D. Wheaton</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">83</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/14849936"> <span id="translatedtitle">Relationships between pre-<span class="hlt">rift</span> structure and <span class="hlt">rift</span> architecture in Lakes Tanganyika and Malawi, East Africa</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Continental <span class="hlt">rift</span> <span class="hlt">systems</span> are rips in plates caused by focusing of extensional stresses along some zone. In the same way that tensile cracks in the side of a brick building generally follow the mortar between bricks, <span class="hlt">rifts</span> initially follow the weakest pathways in the pre-<span class="hlt">rift</span> materials. There has even been a suggestion that the occurrence of <span class="hlt">rifts</span> is controlled by</p> <div class="credits"> <p class="dwt_author">J. Versfelt; B. R. Rosendahl</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">84</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5930257"> <span id="translatedtitle">Continental <span class="hlt">rifts</span> and mineral resources</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Continental <span class="hlt">rifts</span> are widespread and range in age from the present to 3 b.y. Individual <span class="hlt">rifts</span> may form parts of complex <span class="hlt">systems</span> as in E. Africa and the Basin and Range. <span class="hlt">Rifts</span> have originated in diverse environments such as arc-crests, sites of continental collision, collapsing mountain belts and on continents at rest over the mantle circulation pattern. Continental <span class="hlt">rift</span> resources can be classified by depth of origin: For example, in the Great Dike, Norilsk and Mwadui magma from the mantle is the host. At shallower depths continental crust partly melted above mafic magma hosts ore (Climax, Henderson). <span class="hlt">Rift</span> volcanics are linked to local hydrothermal <span class="hlt">systems</span> and to extensive zeolite deposits (Basin and Range, East Africa). Copper (Zambia, Belt), zinc (Red Dog) and lead ores (Benue) are related to hydrothermal <span class="hlt">systems</span> which involve hot rock and water flow through both pre-<span class="hlt">rift</span> basement and sedimentary and volcanic <span class="hlt">rift</span> fill. Economically significant sediments in <span class="hlt">rifts</span> include coals (the Gondwana of Inida), marine evaporites (Lou Ann of the Gulf of Mexico) and non-marine evaporites (East Africa). Oil and gas in <span class="hlt">rifts</span> relate to a variety of source, reservoir and trap relations (North Sea, Libya), but <span class="hlt">rift</span>-lake sediment sources are important (Sung Liao, Bo Hai, Mina, Cabinda). Some ancient iron ores (Hammersley) may have formed in <span class="hlt">rift</span> lakes but Algoman ores and greenstone belt mineral deposits in general are linked to oceanic and island arc environments. To the extent that continental environments are represented in such areas as the Archean of the Superior and Slave they are Andean Arc environments which today have locally <span class="hlt">rifted</span> crests (Ecuador, N. Peru). The Pongola, on Kaapvaal craton may, on the other hand represent the world's oldest preserved, little deformed, continental <span class="hlt">rift</span>.</p> <div class="credits"> <p class="dwt_author">Burke, K. (Univ. of Houston, TX (United States). Geosciences Dept.)</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">85</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1993Geo....21..511C"> <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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Age estimates for ancient lakes are important for determining their histories and their rates off 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 off these, herein called the reflection seismic-radiocarbon method (RSRM), combines estimates off 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 from 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 off estimates for different segments of the lake. is equivocal, and may be due to erosional loss off 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>.</p> <div class="credits"> <p class="dwt_author">Cohen, Andrew S.; Soreghan, Michael J.; Scholz, Christopher A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">86</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Cohen, A.; Soreghan, M.J. [Univ. of Arizona, Tucson, AZ (United States)] [Univ. of Arizona, Tucson, AZ (United States); Scholz, C.A. [Duke Univ. Marine Lab., Beaufort, NC (United States)] [Duke Univ. Marine Lab., Beaufort, NC (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">87</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19850053973&hterms=China+today&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DChina%2Btoday"> <span id="translatedtitle"><span class="hlt">Rift</span> basins - Origin, history, and distribution</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary"><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> <div class="credits"> <p class="dwt_author">Burke, K. C.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">88</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">LePera, Alan; Atekwana, Estella; Abdelsalam, Mohamed</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">89</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/52572606"> <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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">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</p> <div class="credits"> <p class="dwt_author">M. Studinger</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">90</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=STS032-94-040&hterms=tea&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3D%2522tea%2522"> <span id="translatedtitle">East African <span class="hlt">Rift</span> Valley, Kenya</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">1990-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">91</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AGUFM.T21B2542Y"> <span id="translatedtitle">Crustal and mantle structure and anisotropy beneath the incipient segments of the East African <span class="hlt">Rift</span> <span class="hlt">System</span>: Preliminary results from the ongoing SAFARI</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Despite the vast wealth of research conducted toward understanding processes associated with continental <span class="hlt">rifting</span>, the extent of our knowledge is derived primarily from studies focused on mature <span class="hlt">rift</span> <span class="hlt">systems</span>, such as the well-developed portions of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) north of Lake Malawi. To explore the dynamics of early <span class="hlt">rift</span> evolution, the SAFARI (Seismic Arrays for African <span class="hlt">Rift</span> Initiation) team deployed 50 PASSCAL broadband seismic stations across the Malawi, Luangwa, and Okavango <span class="hlt">rifts</span> of the EARS during the summer of 2012. The cumulative length of the profiles is about 2500 km and the planned recording duration is 2 years. Here we present the preliminary results of systematic analyses of data obtained from the first year of acquisition for all 50 stations. A total of 446 high-quality shear-wave splitting measurements using PKS, SKKS, and SKS phases from 84 teleseismic events were used to constrain fast polarization directions and splitting times throughout the region. The Malawi and Okavango <span class="hlt">rifts</span> are characterized by mostly NE trending fast directions with a mean splitting time of about 1 s. The fast directions on the west side of the Luangwa <span class="hlt">Rift</span> Zone are parallel to the <span class="hlt">rift</span> valley, and those on the east side are more N-S oriented. Stacking of approximately 1900 radial receiver functions reveals significant spatial variations of both crustal thickness and the ratio of crustal P and S wave velocities, as well as the thickness of the mantle transition zone. Stations situated within the Malawi <span class="hlt">rift</span> demonstrate a southward increase in observed crustal thickness, which is consistent with the hypothesis that the Malawi <span class="hlt">rift</span> originated at the northern end of the <span class="hlt">rift</span> <span class="hlt">system</span> and propagated southward. Both the Okavango and Luangwa <span class="hlt">rifts</span> are associated with thinned crust and increased Vp/Vs, although additional data is required at some stations to enhance the reliability of the observations. Teleseismic P-wave travel-time residuals show a delay of about 1 s at stations in the Okavango <span class="hlt">rift</span> relative to the Limpopo belt. The study region is characterized by a relatively average mantle transition zone thickness of 250 km except for stations located within and to the immediate NW of the Okavango <span class="hlt">rift</span>, where it is probably abnormally thin. Additional seismological techniques will be applied to the data set, and the preliminary results from the above initial analyses will be confirmed or modified by data from the SAFARI stations in the second year.</p> <div class="credits"> <p class="dwt_author">Yu, Y.; Reed, C. A.; Gao, S. S.; Liu, K. H.; Massinque, B.; Mdala, H. S.; moidaki, M.; Mutamina, D. M.; Atekwana, E. A.; Ingate, S. F.; Reusch, A.; Barstow, N.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">92</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014EGUGA..16.3022C"> <span id="translatedtitle">Unravelling the influence of orogenic inheritance on the architecture and tectonic evolution of hyper-extended <span class="hlt">rift</span> <span class="hlt">systems</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The aim of this starting PhD thesis is to determine under what conditions inheritance produced by former orogens influences subsequent <span class="hlt">rifting</span>, and to unravel the influence of inherited structures and heterogeneities on the architecture and tectonic evolution of hyper-extended <span class="hlt">rift</span> <span class="hlt">systems</span>. To complete this task, we map along the Central and North Atlantic margin 1) <span class="hlt">rift</span> domains; 2) age of the major <span class="hlt">rift</span> events; and 3) key structure and heterogeneities inherited from the Caledonian and Variscan orogens. We will then study these data in the light of minimal numerical modelling experiments and use them as a basis for designing more comprehensive numerical models for the North Atlantic <span class="hlt">rifting</span>. In order to map the Atlantic margins, we use gravity, magnetic data, seismic reflection and refraction to identify the necking zone and the continentward limit of the oceanic domain. This allows us to define the proximal domain where continental crust is not or barely thinned on one side, the unequivocal oceanic domain on the other side, and the hyper-extended domain between them. Within the hyper-extended domain, we rely on seismic data (refraction and reflection) to distinguish the area where the crust and the mantle are decoupled from the area where they are coupled, and to identify potential zones with mantle exhumation and/or magmatic additions. Previous studies mapped these domains along Iberia-Newfoundland and Bay of Biscay. The objective of this PhD is to extend this mapping further to the North, along the Irish, UK and Norwegian margins, into domains with polyphase <span class="hlt">rifting</span> and magmatic additions. One of the goals of this work is to highlight potential correlations between first-order changes in the architecture and/or magmatic evolution of the Atlantic margin and first-order structures and heterogeneities inherited from the Caledonian and/or Variscan orogens. We also aim to assess the importance of inheritance in structuring and controlling the evolution of hyper-extended magma-rich versus magma-poor <span class="hlt">rift</span> <span class="hlt">systems</span>. We present our three preliminary maps, displaying 1) <span class="hlt">rifts</span> structural domains; 2) the age of necking; and 3) the major Caledonian and Variscan inherited features in Western Europe. We also give insight into the numerical experiments we intend to run.</p> <div class="credits"> <p class="dwt_author">Chenin, Pauline; Manatschal, Gianreto; Lavier, Luc</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">93</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/42032671"> <span id="translatedtitle">Usually deep earthquakes in East Africa: Constraints on the thermo-mechanical structure of a continental <span class="hlt">rift</span> <span class="hlt">system</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Shudofsky [1985] has established that earthquakes associated with the East African <span class="hlt">rift</span> <span class="hlt">system</span> have well-constrained focal depths as great as 25-30 km. Using published heat flow measurements as a guide to the local geotherm, we find through simple stress envelope calculations that the deepest earthquakes probably occur in the lower crust in a region where the lithosphere is strong. These</p> <div class="credits"> <p class="dwt_author">Gordon N. Shudofsky; Sierd Cloetingh; Rinus Wortel; Seth Stein</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">94</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40451116"> <span id="translatedtitle">On the use of global potential field models for regional interpretation of the West and Central African <span class="hlt">Rift</span> <span class="hlt">System</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The use in regional interpretations of the Earth Gravity Model (EGM08) and Earth magnetic model (EMAG2) is evaluated by comparison to ground gravity and aeromagnetic data in the central sector of the West and Central African <span class="hlt">Rift</span> <span class="hlt">System</span> (WCARS). The comparison includes upward continuation, spectral analysis and pseudogravity calculation and statistical evaluation. A correlation between EMAG2 (which contains roughly 25km</p> <div class="credits"> <p class="dwt_author">Albert Eyike; Stephanie C. Werner; Jörg Ebbing; E. Manguelle Dicoum</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">95</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/41998288"> <span id="translatedtitle">Active deformation of the Corinth <span class="hlt">rift</span>, Greece: Results from repeated Global Positioning <span class="hlt">System</span> surveys between 1990 and 1995</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Between 1990 and 1995, we carried out seven Global Positioning <span class="hlt">System</span> (GPS) campaigns in the Corinth <span class="hlt">rift</span> area in order to constrain the spatial and temporal crustal deformation of this active zone. The network, 193 points over ~10,000 km2, samples most of the active faults. In order to estimate the deformation over a longer period, 159 of those points are</p> <div class="credits"> <p class="dwt_author">P. Briole; A. Rigo; H. Lyon-Caen; J. C. Ruegg; K. Papazissi; C. Mitsakaki; A. Balodimou; G. Veis; D. Hatzfeld; A. Deschamps</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">96</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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 ?Hf- ?Nd values of the ADDB suite fall in a tight cluster substantially above the mantle array. The isotopic characteristics of the ADDB suite cannot be explained by melting of existing inferred asthenospheric or lithospheric reservoirs. Alternatively, we suggest the ADDB suite is the result of melting at shallow levels in the lithospheric mantle. Advanced lithospheric thinning within the Afar depression has exposed this shallow reservoir to melt generation. In less extended regions, such as in the Ethiopian <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> <div class="credits"> <p class="dwt_author">Rooney, T. O.; Yirgu, G.; Dosso, L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">97</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://earth.unh.edu/bryce/quatturkanajpetmay2004.pdf"> <span id="translatedtitle">East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) Plume Structure: Insights from Quaternary Mafic Lavas of Turkana, Kenya</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Quaternary mafic lavas from Lake Turkana (northern Kenya) provide information on processes operating beneath the East African <span class="hlt">Rift</span> in an area of anomalous lithospheric and crustal thinning. Inferred depths of melting beneath Turkana (15---20km) are shal- lower than those recorded elsewhere along the <span class="hlt">rift</span>, consistent with the anomalously thin crustal section. The mafic lavas have elevated incompatible trace element contents</p> <div class="credits"> <p class="dwt_author">TANYA FURMAN; JULIA G. BRYCE; JEFFREY KARSON; ANNAMARIA IOTTI</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">98</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Ivanov, Alexei V; Demonterova, Elena I</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">99</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Sankov, Vladimir; Parfeevets, Anna; Lukhnev, Andrey; Miroshnitchenko, Andrey; Ashurkov, Sergey; Sankov, Alexey; Usynin, Leonid; Eskin, Alexander; Bryzhak, Evgeny</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">100</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://pubs.er.usgs.gov/publication/70014173"> <span id="translatedtitle">The Goodman swell: a lithospheric flexure caused by crustal loading along the Midcontinent <span class="hlt">rift</span> <span class="hlt">system</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">Rb-Sr biotite ages of Archean and Early to Middle Proterozoic crystalline rocks in northern Wisconsin and adjacent Upper Peninsula of Michigan describe a regionally systematic pattern related to differential uplift. An "age low' occurs in northern Wisconsin where values range from 1070-1172 Ma for rocks with crystallization ages of 1760 to 1865 Ma. These values overlap with the main episode of mafic igneous activity (1090 to 1120 Ma) along the Midcontinent <span class="hlt">rift</span> <span class="hlt">system</span> (MRS). We interpret these low biotite ages as registering closure due to cooling below the 300??C isotherm as a consequence of uplift and rapid erosion of an area that we are informally naming the Goodman swell. We interpret the swell to be a forebulge imposed on an elastic crust by loading of mafic igneous rocks along and within the axis of the MRS. -from Authors</p> <div class="credits"> <p class="dwt_author">Peterman, Z. E.; Sims, P. K.</p> <p class="dwt_publisher"></p> <p class="publishDate">1988-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_4");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_5");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a style="font-weight: bold;">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' 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onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">101</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007AGUFM.T31F..05H"> <span id="translatedtitle">Melt distribution in the Ethiopian <span class="hlt">rift</span> <span class="hlt">system</span>: Constraints from seismic observations and modelling</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Seismic observations from the EAGLE experiment in the Main Ethiopian <span class="hlt">Rift</span> have been interpreted in terms of melt-induced anisotropy and support ideas of magma-assisted <span class="hlt">rifting</span> in continental regions. Following the 2005 Dabbahu <span class="hlt">rifting</span> event in Afar a further 9 broadband seismometers were installed around the newly active <span class="hlt">rift</span> segment. These recorded more than one year of continuous data and shear-wave splitting observed in core phases (SKS/SKKS) shows considerable variability across the array. Three stations centred above the Dabbahu <span class="hlt">rift</span> segment show markedly different splitting characteristics from the other stations. The fast direction is oriented roughly north/south and parallel to the Dabbahu magmatic segment, compared to NNE/SSW orientations at nearby stations. Also the magnitude of splitting is slightly larger at the <span class="hlt">rift</span> stations compared to those nearby (~1s compared to 0.7-0.9s). These observations supports previous work in the Main Ethiopian <span class="hlt">Rift</span> (MER), where fast directions change abruptly from being <span class="hlt">rift</span> parallel on the <span class="hlt">rift</span> flanks to magmatic-segment parallel in the <span class="hlt">rift</span> valley. Furthermore, observations of frequency-dependent splitting in the data further suggest that the underlying cause of the anisotropy is related to aligned melt inclusions. Poroelastic modelling support mechanisms for melt-induced anisotropy due to vertically-aligned melt pockets that are on the order of centimetres in length scale. The abrupt change in splitting parameters over small lateral distances (~ 30 ° over ~30~km) suggests that the source of anisotropy is shallow. To further constrain the location of the anisotropy and study the influence of the <span class="hlt">rift</span> transition on shear-wave splitting results, we model finite-frequency waveforms for a suite of model representations of the <span class="hlt">rift</span> zone. In each model, the orientation of the anisotropic fabric varies laterally (i.e., the symmetry axis of the HTI symmetry rotates between 0° and 30°), but the strength of anisotropy and depth of transition differs. Waveforms are modeled using a narrow-angle one-way elastic vector wave equation to simulate finite-frequency waveform effects for an incident near-planar S-wave. The modelling is used to examine the influence of changing anisotropic symmetry across the <span class="hlt">rift</span> as a function of wavefront curvature, and strength and depth of transition as well as lateral width of transition zone. The results show how a simple model with two regimes of anisotropy can explain the variability across the <span class="hlt">rift</span>, in both delay time and shear-wave polarization, over short length scales.</p> <div class="credits"> <p class="dwt_author">Hammond, J.; Kendall, J.; Angus, D.; Wookey, J.; Keir, D.; Ebinger, C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">102</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004AGUFM.T31F..05H"> <span id="translatedtitle">Melt distribution in the Ethiopian <span class="hlt">rift</span> <span class="hlt">system</span>: Constraints from seismic observations and modelling</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Seismic observations from the EAGLE experiment in the Main Ethiopian <span class="hlt">Rift</span> have been interpreted in terms of melt-induced anisotropy and support ideas of magma-assisted <span class="hlt">rifting</span> in continental regions. Following the 2005 Dabbahu <span class="hlt">rifting</span> event in Afar a further 9 broadband seismometers were installed around the newly active <span class="hlt">rift</span> segment. These recorded more than one year of continuous data and shear-wave splitting observed in core phases (SKS/SKKS) shows considerable variability across the array. Three stations centred above the Dabbahu <span class="hlt">rift</span> segment show markedly different splitting characteristics from the other stations. The fast direction is oriented roughly north/south and parallel to the Dabbahu magmatic segment, compared to NNE/SSW orientations at nearby stations. Also the magnitude of splitting is slightly larger at the <span class="hlt">rift</span> stations compared to those nearby (~1s compared to 0.7-0.9s). These observations supports previous work in the Main Ethiopian <span class="hlt">Rift</span> (MER), where fast directions change abruptly from being <span class="hlt">rift</span> parallel on the <span class="hlt">rift</span> flanks to magmatic-segment parallel in the <span class="hlt">rift</span> valley. Furthermore, observations of frequency-dependent splitting in the data further suggest that the underlying cause of the anisotropy is related to aligned melt inclusions. Poroelastic modelling support mechanisms for melt-induced anisotropy due to vertically-aligned melt pockets that are on the order of centimetres in length scale. The abrupt change in splitting parameters over small lateral distances (~ 30 ° over ~30~km) suggests that the source of anisotropy is shallow. To further constrain the location of the anisotropy and study the influence of the <span class="hlt">rift</span> transition on shear-wave splitting results, we model finite-frequency waveforms for a suite of model representations of the <span class="hlt">rift</span> zone. In each model, the orientation of the anisotropic fabric varies laterally (i.e., the symmetry axis of the HTI symmetry rotates between 0° and 30°), but the strength of anisotropy and depth of transition differs. Waveforms are modeled using a narrow-angle one-way elastic vector wave equation to simulate finite-frequency waveform effects for an incident near-planar S-wave. The modelling is used to examine the influence of changing anisotropic symmetry across the <span class="hlt">rift</span> as a function of wavefront curvature, and strength and depth of transition as well as lateral width of transition zone. The results show how a simple model with two regimes of anisotropy can explain the variability across the <span class="hlt">rift</span>, in both delay time and shear-wave polarization, over short length scales.</p> <div class="credits"> <p class="dwt_author">Hammond, J.; Kendall, J.; Angus, D.; Wookey, J.; Keir, D.; Ebinger, C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">103</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013SolED...5...41H"> <span id="translatedtitle">Kinematics of the South Atlantic <span class="hlt">rift</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The South Atlantic <span class="hlt">rift</span> basin evolved as branch of a large Jurassic-Cretaceous intraplate <span class="hlt">rift</span> zone between the African and South American plates during the <span class="hlt">final</span> breakup of western Gondwana. While the relative motions between South America and Africa for post-breakup times are well resolved, many issues pertaining to the fit reconstruction and particular the relation between kinematics and lithosphere dynamics during pre-breakup remain unclear in currently published plate models. We have compiled and assimilated data from these intraplated <span class="hlt">rifts</span> and constructed a revised plate kinematic model for the pre-breakup evolution of the South Atlantic. Based on structural restoration of the conjugate South Atlantic margins and intracontinental <span class="hlt">rift</span> basins in Africa and South America, we achieve a tight fit reconstruction which eliminates the need for previously inferred large intracontinental shear zones, in particular in Patagonian South America. By quantitatively accounting for crustal deformation in the Central and West African <span class="hlt">rift</span> zone, we have been able to indirectly construct the kinematic history of the pre-breakup evolution of the conjugate West African-Brazilian margins. Our model suggests a causal link between changes in extension direction and velocity during continental extension and the generation of marginal structures such as the enigmatic Pre-salt sag basin and the São Paulo High. We model an initial E-W directed extension between South America and Africa (fixed in present-day position) at very low extensional velocities until Upper Hauterivian times (?126 Ma) when <span class="hlt">rift</span> activity along in the equatorial Atlantic domain started to increase significantly. During this initial ?17 Myr-long stretching episode the Pre-salt basin width on the conjugate Brazilian and West African margins is generated. An intermediate stage between 126.57 Ma and Base Aptian is characterised by strain localisation, rapid lithospheric weakening in the equatorial Atlantic domain, resulting in both progressively increasing extensional velocities as well as a significant rotation of the extension direction to NE-SW. From Base Aptian onwards diachronous lithospheric breakup occurred along the central South Atlantic <span class="hlt">rift</span>, first in the Sergipe-Alagoas/Rio Muni margin segment in the northernmost South Atlantic. <span class="hlt">Final</span> breakup between South America and Africa occurred in the conjugate Santos-Benguela margin segment at around 113 Ma and in the Equatorial Atlantic domain between the Ghanaian Ridge and the Piauí-Ceará margin at 103 Ma. We conclude that such a multi-velocity, multi-directional <span class="hlt">rift</span> history exerts primary control on the evolution of this conjugate passive margins <span class="hlt">systems</span> and can explain the first order tectonic structures along the South Atlantic and possibly other passive margins.</p> <div class="credits"> <p class="dwt_author">Heine, C.; Zoethout, J.; Müller, R. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">104</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014GeoRL..41.2304H"> <span id="translatedtitle">A common mantle plume source beneath the entire East African <span class="hlt">Rift</span> <span class="hlt">System</span> revealed by coupled helium-neon systematics</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">report combined He-Ne-Ar isotope data of mantle-derived xenoliths and/or lavas from all segments of the East Africa <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS). Plume-like helium isotope (3He/4He) ratios (i.e., greater than the depleted MORB mantle (DMM) range of 8 ± 1RA) are restricted to the Ethiopia <span class="hlt">Rift</span> and Rungwe, the southernmost volcanic province of the Western <span class="hlt">Rift</span>. In contrast, neon isotope trends reveal the presence of an ubiquitous solar (plume-like) Ne component throughout the EARS, with (21Ne/22Ne)EX values (where (21Ne/22Ne)EX is the air-corrected 21Ne/22Ne ratio extrapolated to Ne-B) as low as 0.034, close to that of solar Ne-B (0.031). Coupling (21Ne/22Ne)EX with 4He/3He ratios indicates that all samples can be explained by admixture between a single mantle plume source, common to the entire <span class="hlt">rift</span>, and either a DMM or subcontinental lithospheric mantle source. Additionally, we show that the entire sample suite is characterized by low 3He/22NeS ratios (mostly < 0.2)—a feature characteristic of oceanic hot spots such as Iceland. We propose that the origin of these unique noble gas signatures is the deeply rooted African Superplume which influences magmatism throughout eastern Africa. We argue that the Ethiopia and Kenya domes represent two different heads of this common mantle plume source.</p> <div class="credits"> <p class="dwt_author">Halldórsson, Sæmundur A.; Hilton, David R.; Scarsi, Paolo; Abebe, Tsegaye; Hopp, Jens</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">105</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AGUFM.S51C2382M"> <span id="translatedtitle">Tectonics of the Nafir-Skjálfandadjúp volcanic <span class="hlt">system</span>, Tjörnes Fracture Zone, offshore North Iceland: A case of transtensional <span class="hlt">rifting</span> along a divergent plate boundary</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Multibeam bathymetric and high resolution seismic reflection data (Chirp) have been used to illuminate the structural framework of the Nafir-Skjálfandadjúp volcanic <span class="hlt">system</span>, located within the offshore Grímsey Oblique <span class="hlt">Rift</span>, Tjörnes Fracture Zone. Tectonic movements within the Tjörnes Fracture Zone are distributed within three NW-trending <span class="hlt">rift</span> and/or transform zones in the form of seismic lineaments; Grímsey Oblique <span class="hlt">Rift</span>, Húsavík-Flatey Faults and Dalvík Lineament, which are superimposed on NS trending sediment filled <span class="hlt">rift</span> basins. The Grímsey Oblique <span class="hlt">Rift</span> was formed ~2 myrs ago and currently takes up most part of the tectonic movements within the Tjörnes Fracture Zone. The Grímsey Oblique <span class="hlt">Rift</span> is 140 km long, composed of four NS to NNW-SSE trending, left-stepping, en echelon volcanic <span class="hlt">systems</span>; Mánáreyjar, Nafir-Skjálfandadjúp (NaS), Hóllinn and Stóragrunn, which all exhibit Holocene volcanism. South of the Grímsey Oblique <span class="hlt">Rift</span> is the Húsavík-Flatey Fault <span class="hlt">System</span>, a <span class="hlt">system</span> of right-lateral strike-slip faults which take up a part of the tectonic movements within the Tjörnes Fracture Zone. The Nafir-Skjálfandadjúp volcanic <span class="hlt">system</span> is oriented approximately NS on the Grímsey Oblique <span class="hlt">Rift</span>. It is composed of the Nafir seamounts which form the volcanic center of the NaS, and the Skjálfandadjúp <span class="hlt">rift</span> basin which is the foci of maximum extension and sediment accumulation. The Skjálfandadjúp <span class="hlt">rift</span> basin is made up of normal faults with up to 50-60 m vertical displacement along its rim, and 5-15 m within the center of the basin. Comparison of the structure of the NaS with models and natural occurrences of oblique <span class="hlt">rifting</span> indicate that it is at an early stage of deformation, with tectonic activity moving from the border faults towards the internal faults of the basin. Correlation of Chirp data with tephrochronology from the sediment core MD99-2275 provided constraints on tectonic movements along individual faults from Early Postglacial time throughout Holocene. Post-glacial tectonic activity commenced as early as 14-15 kyrs BP, followed by four major <span class="hlt">rifting</span> episodes at 12 kyrs, 11 kyrs, 10 kyrs and 3 kyrs. The 10-12 kyr period of enhanced tectonic activity was accompanied by numerous local eruptions within the TFZ, followed by more moderate activity throughout Holocene. This increase in eruption rates within Grímsey Oblique <span class="hlt">Rift</span> corresponds with enhanced eruption rates on land, observed within the Northern and Western Volcanic Zones of Iceland at 10-12 kyrs.</p> <div class="credits"> <p class="dwt_author">Magnusdottir, S.; Brandsdottir, B.; Driscoll, N. W.; Detrick, R. S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">106</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19950015372&hterms=Weise&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3D%2522Weise%2522"> <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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">(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> <div class="credits"> <p class="dwt_author">Griesshaber, E.; Weise, S.; Darling, G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">107</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1987JAfES...6..103K"> <span id="translatedtitle">East African <span class="hlt">rift</span> and northeast lineaments: continental spreading—transform <span class="hlt">system</span>?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Seafloor spreading and transform faulting processes are also likely to be operative during continental <span class="hlt">rifting</span> events. Continental lines of old weakness oriented at high angles to the direction of continental <span class="hlt">rifting</span> may be reactivated by transform faulting. These older continental transform faults, which predate and accomodate the <span class="hlt">rifting</span>, will continue to propagate as younger oceanic transform faults as the <span class="hlt">rift</span> develops into seas and oceans. This model is applied to the East African <span class="hlt">Rift</span> which is postulated to be a continental spreading <span class="hlt">rift</span> that is accommodated by east-northeast continental transform lineaments that are reactivated older crustal defects of appropriate orientation. At least five continental transform lineaments can be tentatively identified by empirical best fits to oceanic transform directions of the South Atlantic Ocean and to various continental African northeast-trending structures: (1) Cape Town-Maputo (CT-LM); (2) Orange River-Beira (OR-B); (3) Luderitz-Lindi (L-Li); (4) Walvis Bay-Mombasa-Mogadishu (WB-M-Mo); and (5) Luanda-Afar (Lu-Af). As these postulated lineaments are perennial deep seated crustal defects they may also control the development of mineral deposits.</p> <div class="credits"> <p class="dwt_author">Katz, M. B.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">108</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20110023310&hterms=Public+Health&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3D%2522Public%2BHealth%2522"> <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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Anyamba, Assaf; Tucker, Compton J.; Linthicum, Kenneth J.; Witt, Clara J.; Gaydos, Joel C.; Russell, Kevin L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">109</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AGUFM.V23E..01H"> <span id="translatedtitle">He-Ne-Ar isotope studies of mafic volcanic rocks and mantle xenoliths from the East African <span class="hlt">Rift</span> <span class="hlt">System</span> - contrasting isotope signals in different <span class="hlt">rift</span> branches</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Helium isotope studies of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) suggest the involvement of a deep mantle plume(s) beneath the northern (Ethiopian) segment [1-3]. The highest 3He/4He (RA) signatures found to date show a close association with the greatest magma volumes erupted since the Early Cenozoic in the region. While the helium isotope characteristics are well established in the Ethiopia-Afar region, Ne and Ar systematics remain poorly constrained. Using a combined He-Ne-Ar isotope approach, our aim is to determine the regional extent of the influence of the Afar plume and to distinguish between subcontinental lithospheric mantle (SCLM) and/or a possible second mantle plume sources located to the south of the Turkana Depression. Xenoliths and mafic lavas from N-Tanzania display a limited range in He isotopes (5-7 RA) with exceptions at Arusha (7.8RA) and Labait (8.7RA), through 7.1-8.7 RA in N-Kenya and S-Ethiopia, to 14.3 RA in the Main Ethiopian <span class="hlt">Rift</span> and Afar, spanning nearly the entire range of previously reported values. The mean 3He/4He ratio from of lavas and xenoliths from N-Tanzania is remarkably close to the global average of 6.1±0.9 (RA) for continental xenoliths and basalts, thought to represent the SCLM [4]. Thus far, only MORB-like values of 7.3-8.3 RA have been found in volcanics of the Western <span class="hlt">rift</span>. Initial Ne isotope data reveal the presence of a solar-like Ne component in xenoliths from the Ethiopia-Afar region, with extrapolated 21Ne/22Neex ratios of 0.0365 (assuming Ne-B = 12.5). This trend overlaps that of the Loihi-Kilauea line (L-K). Interestingly, a xenolith from N-Tanzania has a 21Ne/22Neex ratio of 0.0415, falling on a trajectory intermediate between MORB and L-K. The highest 40Ar/36Ar ratio obtained on phenocrysts/xenoliths to date is 1510. The generally low 3He/4He ratios of N-Tanzania likely result from different mixing proportions of asthenospheric sources with lithospheric material, the latter having developed lower 3He/4He ratios over time, presumably via lithospheric enrichment/aging events. The finding of a possible solar neon component in N-Tanzanina suggests a mantle plume underlies the area, but with isotopic characteristics distinct from the Afar plume [5]. This finding is consistent with seismic evidence [6], geodynamic modeling [7] and Os isotope results [8]. [1] Marty, B., et al. (1996). Earth Planet. Sci. Lett. 144, 223-237, [2] Pik, R., et al. (2006). Chem. Geol. 226, 100-114, [3] Scarsi, P., Craig, H., (1996). Earth Planet. Sci. Lett. 144, 505-516, [4] Gautheron and Moreira, Planet. Sci. Lett. 2002, [5] George et al. (1998) Geology 26, 923-926, [6] Nyblade et al. (2000) Geology 28, 7, 599-602, [7] Lin et al. (2005) Earth Planet. Sci. Lett. 237, 175-192, [8] Chesley et al., 1999, Geochim. Cosmochim. Acta</p> <div class="credits"> <p class="dwt_author">Halldorsson, S. A.; Hilton, D. R.; Scarsi, P.; Abebe, T.; Massi, K. M.; Barry, P. H.; Fischer, T. P.; de Moor, J.; Rudnick, R. L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">110</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Located in the tectonically active Main Ethiopian <span class="hlt">Rift</span> <span class="hlt">system</span>, the Gidabo River Basin in Ethiopia has a complex hydrogeological setting. The strong physiographic variation from highland to <span class="hlt">rift</span> floor, variability in volcanic structures and disruption of lithologies by cross-cutting faults contribute for their complex nature of hydrogeology in the area. Until now, the groundwater dynamics and the impact of the tectonic setting on groundwater flow in this region are not well understood, though the local population heavily depends on groundwater as the major water supply. A combined approach based on hydrochemical and isotopic data was applied to investigate the regional flow dynamics of the groundwater and the impact of tectonic setting. Groundwater evolves from slightly mineralized Ca-Mg-HCO3 on the highland to highly mineralized Na-HCO3 dominating type in the deep <span class="hlt">rift</span> floor aquifers. ?18O and ?D composition of groundwater show a general progressive enrichment from the highland to the <span class="hlt">rift</span> floor, except in thermal and deep <span class="hlt">rift</span> floor aquifers. Relatively the thermal and deep <span class="hlt">rift</span> floor aquifers are depleted and show similar signature to the groundwaters of highland, indicating groundwater inflow from the highland. Correspondingly, rising HCO3 and increasingly enriched signatures of ? 13C points to hydrochemical evolution of DIC and diffuse influx of mantle CO2 into the groundwater <span class="hlt">system</span>. Thermal springs gushing out along some of the fault zones, specifically in the vicinity of Dilla town, display clear influence of mantle CO2 and are an indication of the role of the faults acting as a conduit for deep circulating thermal water to the surface. By considering the known geological structures of the <span class="hlt">rift</span>, hydrochemical and isotopic data we propose a conceptual groundwater flow model by characterizing flow paths to the main <span class="hlt">rift</span> axis. The connection between groundwater flow and the impact of faults make this model applicable to other active <span class="hlt">rift</span> <span class="hlt">systems</span> with similar tectonic settings.</p> <div class="credits"> <p class="dwt_author">Degu, Abraham; Birk, Steffen; Dietzel, Martin; Winkler, Gerfried; Moggessie, Aberra</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">111</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008AGUFMDI22A..02A"> <span id="translatedtitle">Melt Distribution in the Ethiopian <span class="hlt">Rift</span> <span class="hlt">System</span>: Constraints From Seismic Observations and Finite-Frequency Modelling</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">As part of the Ethiopian Afar Geoscientific Lithospheric Experiment (EAGLE) 79 seismic stations were deployed, for up to 18 months, in the Main Ethiopian <span class="hlt">Rift</span> (MER). Many indicators of melt were observed leading to the idea that magma was driving the <span class="hlt">rifting</span> process in this region. Some of the best evidence for melt came from observations of anisotropy in studies of surface waves and shear-wave splitting. The shear- wave splitting shows fast directions which change abruptly from being <span class="hlt">rift</span> parallel on the <span class="hlt">rift</span> flanks to magmatic-segment parallel in the <span class="hlt">rift</span> valley. This was interpreted in terms of melt-induced anisotropy. The abrupt change in splitting parameters over small lateral distances suggests that the source of anisotropy is shallow. To further constrain the location of the anisotropy and study the ability of shear-wave splitting to identify sharp lateral changes in anisotropy, we model finite-frequency waveforms for a suite of model representations of the <span class="hlt">rift</span> zone. This allows us to determine the lateral and vertical extent of the melt-induced anisotropy. The results show how a simple model with two regimes of anisotropy can explain the variability across the <span class="hlt">rift</span>, in both delay time and shear-wave polarization, over short length scales of the order 20- 40 km. Our models have enabled us to constrain the anisotropic characteristics beneath the MER. Our best model has a 9% anisotropy on the western <span class="hlt">rift</span> margin, with fast directions of 30°, a 100 km wide <span class="hlt">rift</span> zone with fast direction of 20° inside the <span class="hlt">rift</span> zone and with 9% anisotropy close to the western margin, 7% elsewhere, and 7% anisotropy on the eastern margin with fast directions of 30°. In all regions of the model we constrain anisotropy to begin at a depth of 90 km. The depth of anisotropy co-incides with the proposed depth of melt initiation beneath the region, based on geochemistry. Also the elevated splitting beneath the western margin supports evidence of low velocities and highly conductive bodies from seismic tomography and magneto-tellurics, suggesting melt is more focused along the western margin. This study shows that SKS-wave splitting is a powerful technique that can map sharp lateral changes, and has the potential to constrain the depth of the anisotropy.</p> <div class="credits"> <p class="dwt_author">Angus, D.; Hammond, J. O.; Kendall, J.; Wookey, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">112</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://jvi.asm.org/cgi/reprint/79/9/5606.pdf"> <span id="translatedtitle"><span class="hlt">Rift</span> Valley Fever Virus Nonstructural Protein NSs Promotes Viral RNA Replication and Transcription in a Minigenome <span class="hlt">System</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary"><span class="hlt">Rift</span> Valley fever virus (RVFV), which belongs to the genus Phlebovirus, family Bunyaviridae, has a tripartite negative-strand genome (S, M, and L segments) and is an important mosquito-borne pathogen for domestic animals and humans. We established an RVFV T7 RNA polymerase-driven minigenome <span class="hlt">system</span> in which T7 RNA polymerase from an expression plasmid drove expression of RNA transcripts for viral proteins</p> <div class="credits"> <p class="dwt_author">Tetsuro Ikegami; C. J. Peters; Shinji Makino</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">113</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/61369052"> <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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">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</p> <div class="credits"> <p class="dwt_author">Dickas</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">114</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004AGUSM.T32B..01K"> <span id="translatedtitle">Structural And Depositional Style Of The Syn-<span class="hlt">Rift</span> <span class="hlt">Systems</span> Of The West African And Brazilian Continental Margins: Regional Subsidence Independent Of Brittle Deformation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The West African and Brazilian passive continental margins are characterized by the regional distribution of syn-<span class="hlt">rift</span> and post-<span class="hlt">rift</span> sediment assemblages that are inconsistent with the minor amounts of brittle deformation interpreted from seismic sections across the margin or from field mapping of exposed <span class="hlt">rift</span> <span class="hlt">systems</span>. Fundamentally, the <span class="hlt">rift</span> phase of West Africa and Brazil consists of a series of stacked sag basins. Ostracod data from the West African margin indicate that the distal syn-<span class="hlt">rift</span> sag basins, where dated, are Neocomian to Aptian in age and are contemporaneous with proximal syn-<span class="hlt">rift</span> deposits developed inboard of a major hinge zone, the Atlantic Hinge zone. Despite being syn-<span class="hlt">rift</span> deposits (by virtue of their age), the sag basins exhibit none of the diagnostic characteristics of brittle deformation, such as the existence of normal faults, the rotation of crustal blocks, the existence of prominent <span class="hlt">rift</span> onset unconformities (onlap surfaces), and the generation of sediment wedges. Seismic sections across the Camamu-Almada margin of Brazil indicate that the regional generation of space is essentially independent of faulting, as indicated by an absence of stratigraphic growth across normal faults and a regional seaward dip of the entire syn-<span class="hlt">rift</span> stratigraphic package. The late syn-<span class="hlt">rift</span> history of the West African and Brazilian margins is dominated by the creation of regional but shallow depositional environments that allowed the accumulation of the Loeme and Ezanga evaporites of West Africa and the Ibura, Taipus Mirim, and Mariricu evaporites of Brazil. Following break-up, the margins underwent significant post-<span class="hlt">rift</span> subsidence allowing the deposition of the late Cretaceous, Paleogene and Neogene sedimentary packages. The development of significant post-<span class="hlt">rift</span> accommodation in the same region characterized by minor syn-<span class="hlt">rift</span> faulting and shallow depositional environments is the crucial observation requiring an explanation in terms of extensional strain partitioning through the lithosphere, lower crustal flow, major dyking of the lower crust during the extension process, and the thermal effects of mantle plumes. This presentation will show seismic and drilling data for the West African and Brazilian margins that clearly demonstrates the structural and depositional style of syn-<span class="hlt">rift</span> <span class="hlt">systems</span>: the stacking of syn-<span class="hlt">rift</span> sag sequences showing subtle stratal relationships rather than the more familiar (and expected) characteristics of brittle deformation. Driscoll and Karner (1998) have suggested that the formation of syn-<span class="hlt">rift</span> sag basins requires partitioning of extension across a mid-crustal decoupling zone separating upper crust (the upper plate) from a ductile-deforming lower crust and lithospheric mantle (the lower plate). The obvious problem with this hypothesis is that extension within the upper and lower plate needs to be laterally balance. The exact form and location of the counterbalancing upper plate extension presumably exists in the vicinity of the ocean-continent transition zone where the extensional balance through the upper crust probably occurs by a combination of thinned and "rafted" crustal blocks and exposed continental mantle. Nevertheless, it remains to be shown that this strain balance actually exists in addition to exploring alternative mechanisms that can augment syn-<span class="hlt">rift</span> and post-<span class="hlt">rift</span> subsidence without upper crustal brittle deformation.</p> <div class="credits"> <p class="dwt_author">Karner, G. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">115</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1990EOSTr..71..995M"> <span id="translatedtitle">Lake Superior <span class="hlt">Rift</span> basins</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Sedimentary basins of late Precambrian age have been identified beneath Lake Superior using seismic reflection profiles leased by Argonne National Laboratory, Argonne, Ill., from Grant Norpac, Inc. [McGinnis et al., 1989]. These data, along with 650 km of Great Lakes International Multidisciplinary Program for Crustal Evolution (GLIMPCE) profiles [Behrendt et al., 1988], are being used to develop an understanding of failed <span class="hlt">rift</span> processes, from initial plate separation, through basin evolution, to <span class="hlt">final</span> quiescence.</p> <div class="credits"> <p class="dwt_author">McGinnis, L. D.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">116</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Thompson, M.D.; McGinnis, L.D. [Argonne National Lab., IL (United States); Ervin, C.P. [Northern Illinois Univ., DeKalb, IL (United States); Mudrey, M.G. [Wisconsin Geologic and Natural History Survey, Madison, WI (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">117</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5904409"> <span id="translatedtitle">Controls on contrasting sandbody architectures in resedimented oolitic units from <span class="hlt">rift</span> <span class="hlt">systems</span> of the Mediterranean Jurassic</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Localized development of a small, prograding, sand-rich oolitic fan occurs in the deep-water Brenha Formation (Toarcian-Bajocian) of western Portugal. Controlled by prefan tectonism and a limited source area, its fan characteristics are contrasted with two radically different contemporary oolitic aprons. The Cutri Formation (Bathonian), a minor apron <span class="hlt">system</span> from Mallorca, is characterized by infrequently initiated, high-density oolitic turbidites related to phases of tectonic activity on platform bounding faults. Affected by minor tectonism and subsidence, this apron was short lived because the source platform was drowned. This contrasts with the Vajont oolite formation (Bajocian-lower Oxfordian), northern Italy, a major resedimented oolitic sandbody interpreted as a tectonically aggraded faulted-slope apron. Predominantly sheet-like oolitic turbidites were fed via a line source from a gullied margin into a deep, narrow <span class="hlt">rift</span> basin. The resulting wedge-shape sandbody formed from overlapping turbidites stacked into poorly developed, mainly fining-upward cycles aggraded by major fault-related subsidence.</p> <div class="credits"> <p class="dwt_author">Abbots, F.V.</p> <p class="dwt_publisher"></p> <p class="publishDate">1988-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">118</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5694691"> <span id="translatedtitle">Oil source rocks in lacustrine sequences from Tertiary grabens, western Mediterranean <span class="hlt">rift</span> <span class="hlt">system</span>, northeast Spain</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Lacustrine sequences, 100-250 m thick, containing oil-prone, organic-rich mudstones (ORM) are exposed in five Tertiary basins in northeastern Spain. They were deposited in small lacustrine basins (up to 50 km/sup 2/) that developed in grabens of the western Mediterranean <span class="hlt">rift</span> <span class="hlt">system</span>. ORMs from the Rubielos basin comprise laminated gray mudstones with interbedded rhythmite intervals (up to 2.5 m thick) formed by couplets of organic- and carbonate-rich laminae (< 1 mm thick). In marginal zones, ORMs (up to 10 m thick) alternate with lean, bioturbated green marls (up to 5 m thick). ORMs (Rock-Eval yields /approximately/ 40 kg/MT, HI /approximately/ 850 mg HC/g TOC) had a dominant waxy terrestrial plant input, with significant and variable algal/bacterial input. ORMs in these basins are immature for petroleum generation. Larger lacustrine basins similar to those described above, in more appropriate burial/thermal situations, can be envisioned as zones of potential interest for lacustrine oil exploration in the western Mediterranean.</p> <div class="credits"> <p class="dwt_author">Anadon, P.; Cawley, S.J.; Julia, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">1988-08-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">119</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AGUSM.V41B..06R"> <span id="translatedtitle">Tectonic localization of multi-plume hydrothermal fluid flow in a segmented <span class="hlt">rift</span> <span class="hlt">system</span>, Taupo Volcanic Zone, New Zealand</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">High-temperature (>250°C) multi-plume hydrothermal <span class="hlt">systems</span> occur in a range of tectonic settings, though most are extensional or transtensional. A key feature of such settings is their tendency to partition into discrete structural elements that scale with the thickness of the seismogenic zone. The late Miocene to present record of arc magmatism and <span class="hlt">rifting</span> in the North Island of New Zealand illustrates the importance of structural segmentation and reactivation of inherited basement fabrics on the localisation of hydrothermal upflow. The <2 My-old Taupo Volcanic Zone (TVZ) represents the most recent NE-SW-trending locus of heat and mass transfer in a >15 My record of similarly-oriented magmatism, <span class="hlt">rifting</span> and hydrothermal activity associated with subduction of the Pacific Plate beneath the North Island of New Zealand. Lateral migration of the locus of arc magmatism, concomitant with roll-back of the subducting slab, is supported by the SE-directed younging of: 1) volcanism; 2) fault-controlled <span class="hlt">rift</span> basins; and 3) hydrothermal activity, represented by the distribution of epithermal mineralisation within the ~15-3 Ma Coromandel Volcanic Zone (CVZ), and geothermal activity within the TVZ. Currently the TVZ is extending in a NW-SE direction at a rate that varies from ~3 mm/yr to ~15 mm/yr from SW to NE, respectively. The TVZ is partitioned into discrete <span class="hlt">rift</span> segments, comprising arrays of NE-striking normal faults of ~20 km in length, as expected on mechanical grounds for the 6-8 km-thick seismogenic zone. Transfer zones between <span class="hlt">rift</span> segments coincide with N-to-NW-trending alignments of geothermal fields, <61 ka volcanic vents, and margins of rhombic shaped caldera boundaries, which supports the notion that such tectonic features are important sites for heat and mass transfer. Although masked at the surface, upward continued aeromagnetic data reveals deep lineations that align with transfer zones and major faults in exposed Mesozoic metasedimentary basement rocks proximal to the TVZ. Transfer zones are thus inferred to be hard-linked at depth via reactivated basement faults, some of which appear to extend into the CVZ. Two similarly oriented features spaced ~ 30 km apart can be recognized elsewhere within the CVZ. The most productive epithermal deposits to date are localised where these inferred transfer zones intersect arc-parallel fault arrays. A similar tectonic configuration occurs in the Deseado Massif, Argentinian Patagonia, where interplay between transfer and <span class="hlt">rift</span> faults is inferred to have localized hydrothermal fluids in small pull-apart basins and arrays of extension veins for durations >30 My.</p> <div class="credits"> <p class="dwt_author">Rowland, J. V.; Downs, D. T.; Scholz, C.; de P. S. Zuquim, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">120</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AGUFM.T11F..01S"> <span id="translatedtitle">Kinematics of <span class="hlt">Rift</span>-Parallel Deformation Along the Rukwa <span class="hlt">Rift</span>, Western Branch, and Main Ethiopian <span class="hlt">Rift</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The East African <span class="hlt">Rift</span> <span class="hlt">System</span> spans N-S ~5000 km and currently experiences E-W extension. Previous kinematic studies of the EARS delineated 3 relatively rigid sub-plates (Victoria, Rovuma, and Lwandle) between the Nubian and Somalian plates. GPS observations of these block interiors confirm the rigid plate model, but we also detect a systematic along-<span class="hlt">rift</span> deformation pattern at GPS stations located within <span class="hlt">rift</span> zones bounding the western Victoria block and continuing north between the Nubian and Somalian plates. Here we present a kinematic model of present-day <span class="hlt">rift</span>-parallel deformation along the Western branch, Rukwa <span class="hlt">Rift</span>, and Main Ethiopian <span class="hlt">Rift</span> constrained by a new GPS solution, earthquake slip vectors, and mapped active fault structures. We test the roles of block rotation, elastic deformation, and anelastic deformation by varying block geometry, fault slip distribution parameters, estimating permanent strain rate, and scoring each model with GPS observations. We also explore how the present-day deformation patterns relate to longer-term paleostress indicators. Observations of slickensides and offsets in seismic reflection profiles in the northern Western branch (Albertine <span class="hlt">rift</span>) indicate a change from ~NNE trending normal faulting to include strike-slip motion within the past 7 My that may be related to previously studied stress changes in the Turkana <span class="hlt">rift</span>. Preliminary results from the kinematic modeling demonstrate simple elastic strain accumulation on major border faults cannot explain an observed systematic northward component in GPS velocities relative to the Victoria block and the Nubian plate.</p> <div class="credits"> <p class="dwt_author">Stamps, D.; Koehn, D.; Burke, K. C.; d'Oreye, N.; Saria, E.; Xu, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_5");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return 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id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_6");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a style="font-weight: bold;">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_8");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">121</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1987Tectp.143..119O"> <span id="translatedtitle">Rio Grande <span class="hlt">rift</span>: An overview</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Olsen, Kenneth H.; Scott Baldridge, W.; Callender, Jonathan F.</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">122</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Swenson, J. B.; Person, M.; Raffensperger, J. P.; Cannon, W. F.; Woodruff, L. G.; Berndt, M. E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">123</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2002Geomo..45..147B"> <span id="translatedtitle">Fluvial <span class="hlt">systems</span> response to <span class="hlt">rift</span> margin tectonics: Makhtesh Ramon area, southern Israel</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The geomorphic evolution of Makhtesh Ramon, a feather-shaped erosional valley, and the Nahal Neqarot drainage <span class="hlt">system</span> to the south occurred largely in response to tectonic activity along the Dead Sea <span class="hlt">Rift</span> and its western shoulder. Remnants of Miocene clastic sediments (Hazeva Formation) deposited on an erosional peneplain that formed over this area during the Oligocene epoch provide a datum plane for reconstructing subsequent fluvial evolution. These clastic remnants are presently located on the shoulders of Makhtesh Ramon at various elevations. The peneplain truncating the Makhtesh Ramon block has been tilted 0.7% northeastward since the Pliocene epoch (post-Hazeva Formation), whereas that of the Neqarot syncline, south of the Ramon, has been tilted 1.2%. The elliptical exposure of friable Lower Cretaceous sandstone, exposed in the core of the truncated Ramon structure, governed the development of a new ENE directed (riftward) drainage <span class="hlt">system</span> through capture of streams that previously drained toward the Mediterranean Sea to the northwest. Incised fluvial gaps in the southern rim of Makhtesh Ramon and alluvial fan relicts within Makhtesh Ramon attest to original drainage into the Makhtesh from the south. Remnants of the Plio-Pleistocene Arava Conglomerate on the eastern end of the Neqarot syncline contain clasts from rocks exposed within Makhtesh Ramon, also indicating that streams flowed into the Makhtesh from the southern Neqarot block through the western gaps, then turning eastward and exiting the Makhtesh via the next (Sha'ar-Ramon) gap to the east. Further down-faulting of the Neqarot block during Mid-Late Pleistocene time led to westward retreat of the Neqarot valley and capture of the last stream flowing northward into the Ramon, leaving the modern Makhtesh Ramon isolated from the southern drainage <span class="hlt">system</span>.</p> <div class="credits"> <p class="dwt_author">Ben-David, Ram; Eyal, Yehuda; Zilberman, Ezra; Bowman, Dan</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">124</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008AGUFM.T43A2002G"> <span id="translatedtitle">Magmatism in a Cambrian Laurentian Plate <span class="hlt">Rift</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Evidences of the Cambrian Southern Oklahoma Aulacogen extend over 1000km from about Dallas out to the Uncompahgre Plateau in SW Colorado. The signature of this originally extensional feature can be traced geophysically, and in some places at the present surface, petrologically and temporally, by the presence of mafic rock. It appears to have been the intracontinental third arm of a plume-generated? triple junction which helped to dismember the southern part of Laurentia on the <span class="hlt">final</span> break-up of a Neoproterozoic supercontinent. Other parts of Laurentia <span class="hlt">rifted</span> away and are now found in the Precordillera of Argentina. <span class="hlt">Rift</span> magmatism appears to have been concentrated nearer the plate edge during the breakup. Perhaps as much as 40,000 km3 of mostly subaerial silicic volcanics and shallow-seated granites overlay and filled the top of the <span class="hlt">rift</span> in the area of SW Oklahoma. The <span class="hlt">rift</span> fill below the silicic rocks is large, layered mafic complexes and smaller, layered, hydrous gabbros, the whole set appearing as a shallow AMCG complex. Unusually, direct <span class="hlt">rift</span> sediments are not obvious. Furthermore, silicic and mafic rocks have identical Nd signatures. <span class="hlt">Finally</span>, about 20 Ma after <span class="hlt">rifting</span> ceased and later into the Paleozoic during sea incursion, overlying sediments are thickened 4X compared to equivalent units 100's of kms to the <span class="hlt">rift</span> sides. This <span class="hlt">rift</span> appears distinct from most modern <span class="hlt">rifts</span>. Conclusions are 1) This was a hot, narrow <span class="hlt">rift</span>; 2) Basaltic magmatism , not sedimentation, filled the <span class="hlt">rift</span>; 3) Magmatic intensity varied along the <span class="hlt">rift</span> strike; 4) Silicic rocks were generated mostly directly from new mantle-derived basalt liquids through fractionation, not melting of older crustal rocks; 5) Laurentian lithosphere was weak allowing centering of the Early/Middle Paleozoic large "Oklahoma" basin (pre-Anadarko) over the <span class="hlt">rift</span>.</p> <div class="credits"> <p class="dwt_author">Gilbert, M. C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">125</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Fukuta, O.</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">126</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Behrendt, J. C.; Hutchinson, D. R.; Lee, M.; Thornber, C. R.; Trehu, A.; Cannon, W.; Green, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1990-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">127</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40451771"> <span id="translatedtitle">Kinematic modelling of the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span>, Ross Sea, Antarctica</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">In this study, we investigate the thermo-mechanical controls on the formation of the Ross Sea basin (Antarctica) and the uplift of the adjacent Transantarctic Mountains (TAM) <span class="hlt">rift</span> shoulder, which started in the Late Cretaceous and continued until the present time. Quantitative forward modelling has been performed along three 700 to 800 km long East–West offshore profiles, extended inland to the</p> <div class="credits"> <p class="dwt_author">Martina Busetti; Giacomo Spadini; Frederik M. Van der Wateren; Sierd Cloetingh; Claudio Zanolla</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">128</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AGUFM.T11F..03D"> <span id="translatedtitle">Ambient Noise Tomography of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> in Mozambique</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A wide range of studies has shown that the cross-correlation of ambient noise can provide an estimate of the Greens functions between pairs of stations. Project MOZART (funded by FCT, Lisbon, PI J. Fonseca) deployed 30 broadband (120s) seismic stations from the SEIS-UK Pool in Central Mozambique and NE South Africa, with the purpose of studying the East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) in Mozambique. We applied the Ambient Noise Tomography (ANT) method to broadband seismic data recorded from March 2011 until July 2012. Cross-correlations were computed between all pairs of stations, and from these we obtained Rayleigh wave group velocity dispersion curves for all interstation paths, in the period range from 3 to 50 seconds. We tested various approaches for pre-processing the ambient noise data regarding time-domain and spectral normalisation, as well as the use of phase cross-correlations. Moreover, we examined the robustness of our dispersion maps by splitting our dataset into various sub-sets of Green's functions with similar paths and by quantifying the differences between the dispersion maps obtained from the various sub-sets of data. We find that while the geographical distribution of the group velocity anomalies is well constrained, the amplitudes of the anomalies are slightly less robust. We performed a three-dimensional inversion to obtain the S-wave velocity of the crust and upper mantle. In addition, our preliminary results show a good correlation between the Rayleigh wave group velocity and the geology of Mozambique. In order to extend the investigation to longer periods and, thus, to be able to look into the lithosphere-asthenosphere depth range in the upper mantle, we apply a recent implementation of the surface-wave two-station method (teleseismic interferometry) and augment our dataset with Rayleigh wave phase velocities curves in broad period ranges.</p> <div class="credits"> <p class="dwt_author">Domingues, A.; Chamussa, J.; Silveira, G. M.; Custodio, S.; Lebedev, S.; Chang, S.; Ferreira, A. M.; Fonseca, J. F.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">129</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/41099825"> <span id="translatedtitle">Geochemical evidence of lithospheric thinning in the southern Main Ethiopian <span class="hlt">Rift</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Lithospheric thinning is a fundamental process associated with the transition from continental to oceanic regimes during continental <span class="hlt">rifting</span>. Precisely how and when this lithospheric thinning proceeds are first order controls on <span class="hlt">rift</span> basin evolution. The Main Ethiopian <span class="hlt">Rift</span>, part of the ?2000km long East African <span class="hlt">Rift</span> <span class="hlt">System</span>, is the archetypical modern example of continental <span class="hlt">rifting</span>, and a key location in</p> <div class="credits"> <p class="dwt_author">Tyrone O. Rooney</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">130</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Bartok, P. (EGEP Consultores, Caracus (Venezuela))</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">131</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011JAfES..59..168A"> <span id="translatedtitle">Influence of pre-existing fabrics on fault kinematics and <span class="hlt">rift</span> geometry of interacting segments: Analogue models based on the Albertine <span class="hlt">Rift</span> (Uganda), Western Branch-East African <span class="hlt">Rift</span> <span class="hlt">System</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">This study aims at showing how far pre-existing crustal weaknesses left behind by Proterozoic mobile belts, that pass around cratonic Archean shields (Tanzania Craton to the southeast and Congo Craton to the northwest), control the geometry of the Albertine <span class="hlt">Rift</span>. Focus is laid on the development of the Lake Albert and Lake Edward/George sub-segments and between them the greatly uplifted Rwenzori Mountains, a horst block located within the <span class="hlt">rift</span> and whose highest peak rises to >5000 m above mean sea level. In particular we study how the southward propagating Lake Albert sub-segment to the north interacts with the northward propagating Lake Edward/George sub-segment south of it, and how this interaction produces the structures and geometry observed in this section of the western branch of the East African <span class="hlt">Rift</span>, especially within and around the Rwenzori horst. We simulate behaviour of the upper crust by conducting sandbox analogue experiments in which pre-cut rubber strips of varying overstep/overlap connected to a basal sheet and oriented oblique and/or orthogonal to the extension vector, are placed below the sand-pack. The points of connection present velocity discontinuities to localise deformation, while the rubber strips represent ductile domain affected by older mobile belts. From fault geometry of developing <span class="hlt">rift</span> segments in plan view and section cuts, we study kinematics resulting from a given set of boundary conditions, and results are compared with the natural scenario. Three different basal model-configurations are used to simulate two parallel <span class="hlt">rifts</span> that propagate towards each other and interact. Wider overstep (model SbR3) produces an oblique transfer zone with deep grabens (max. 7.0 km) in the adjoining segments. Smaller overlap (model SbR4) ends in offset <span class="hlt">rift</span> segments without oblique transfer faults to join the two, and produces moderately deep grabens (max. 4.6 km). When overlap doubles the overstep (model SbR5), <span class="hlt">rifts</span> propagate sub-orthogonal to the extension direction and form shallow valleys (max. 2.9 km). Relative ratios of overlap/overstep between <span class="hlt">rift</span> segments dictate the kind of transition zone that develops and whether or not a block (like the Rwenzoris) is captured and rotates; hence determining the end-member geometry. Rotation direction is controlled by pre-existing fabrics. Fault orientation, fault kinematics, and block rotation (once in play) reinforce each other; and depending on the local kinematics, different parts of a captured block may rotate with variable velocities but in the same general direction. Mechanical strength anisotropy of pre-structured crust only initially centres fault nucleation and propagation parallel to the grain of weakness of the basement, but at later stages of a protracted period of crustal extension, such boundaries are locally defied.</p> <div class="credits"> <p class="dwt_author">Aanyu, K.; Koehn, D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">132</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20050176001&hterms=venus&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dvenus"> <span id="translatedtitle">Parga Chasma: Coronae and <span class="hlt">Rifting</span> on Venus</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Smrekar, S. E.; Stofan, E. R.; Buck, W. R.; Martin, P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">133</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Myers, Tanya L.; Broocks, Bryan T.; Phillips, Mark C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">134</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Siddoway, C.S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">135</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19850066340&hterms=Southern+Africa&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3D%2522Southern%2BAfrica%2522"> <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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Burke, K.; Kidd, W. S. F.; Kusky, T.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">136</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1996EOSTr..77..255B"> <span id="translatedtitle">Continental <span class="hlt">Rifts</span>: Evolution, Structure and Tectonics</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Twenty one “friends of continental <span class="hlt">rifts</span>” 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> <div class="credits"> <p class="dwt_author">Bally, A. W.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">137</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2003Tectp.369..231T"> <span id="translatedtitle">Supracrustal faults of the St. Lawrence <span class="hlt">rift</span> <span class="hlt">system</span>, Québec: kinematics and geometry as revealed by field mapping and marine seismic reflection data</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The St. Lawrence <span class="hlt">rift</span> <span class="hlt">system</span> from the Laurentian craton core to the offshore St. Lawrence River <span class="hlt">system</span> is a seismically active zone in which fault reactivation is believed to occur along late Proterozoic to early Paleozoic normal faults related to the opening of the Iapetus ocean. The <span class="hlt">rift</span>-related faults fringe the contact between the Grenvillian basement to the NW and Cambrian-Ordovician rocks of the St. Lawrence Lowlands to the SE and occur also within the Grenvillian basement. The St. Lawrence <span class="hlt">rift</span> <span class="hlt">system</span> trends NE-SW and represents a SE-dipping half-graben that links the NW-SE-trending Ottawa-Bonnechère and Saguenay River grabens, both interpreted as Iapetan failed arms. Coastal sections of the St. Lawrence River that expose fault rocks related to the St. Lawrence <span class="hlt">rift</span> <span class="hlt">system</span> have been studied between Québec city and the Saguenay River. Brittle faults marking the St. Lawrence <span class="hlt">rift</span> <span class="hlt">system</span> consist of NE- and NW-trending structures that show mutual crosscutting relationships. Fault rocks consist of fault breccias, cataclasites and pseudotachylytes. Field relationships suggest that the various types of fault rocks are associated with the same tectonic event. High-resolution marine seismic reflection data acquired in the St. Lawrence River estuary, between Rimouski, the Saguenay River and Forestville, identify submarine topographic relief attributed to the St. Lawrence <span class="hlt">rift</span> <span class="hlt">system</span>. Northeast-trending seismic reflection profiles show a basement geometry that agrees with onshore structural features. Northwest-trending seismic profiles suggest that normal faults fringing the St. Lawrence River are associated with a major topographic depression in the estuary, the Laurentian Channel trough, with up to 700 m of basement relief. A two-way travel-time to bedrock map, based on seismic data from the St. Lawrence estuary, and comparison with the onshore <span class="hlt">rift</span> segment suggest that the Laurentian Channel trough varies from a half-graben to a graben structure from SW to NE. It is speculated that natural gas occurrences within both the onshore and offshore sequences of unconsolidated Quaternary deposits are possibly related to degassing processes of basement rocks, and that hydrocarbons were drained upward by the <span class="hlt">rift</span> faults.</p> <div class="credits"> <p class="dwt_author">Tremblay, Alain; Long, Bernard; Massé, Manon</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">138</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Masini, E.; Manatschal, G.; Tugend, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">139</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013SolE....4..215H"> <span id="translatedtitle">Kinematics of the South Atlantic <span class="hlt">rift</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The South Atlantic <span class="hlt">rift</span> basin evolved as a branch of a large Jurassic-Cretaceous intraplate <span class="hlt">rift</span> zone between the African and South American plates during the <span class="hlt">final</span> break-up of western Gondwana. While the relative motions between South America and Africa for post-break-up times are well resolved, many issues pertaining to the fit reconstruction and particularly the relation between kinematics and lithosphere dynamics during pre-break-up remain unclear in currently published plate models. We have compiled and assimilated data from these intraplated <span class="hlt">rifts</span> and constructed a revised plate kinematic model for the pre-break-up evolution of the South Atlantic. Based on structural restoration of the conjugate South Atlantic margins and intracontinental <span class="hlt">rift</span> basins in Africa and South America, we achieve a tight-fit reconstruction which eliminates the need for previously inferred large intracontinental shear zones, in particular in Patagonian South America. By quantitatively accounting for crustal deformation in the Central and West African <span class="hlt">Rift</span> Zones, we have been able to indirectly construct the kinematic history of the pre-break-up evolution of the conjugate west African-Brazilian margins. Our model suggests a causal link between changes in extension direction and velocity during continental extension and the generation of marginal structures such as the enigmatic pre-salt sag basin and the São Paulo High. We model an initial E-W-directed extension between South America and Africa (fixed in present-day position) at very low extensional velocities from 140 Ma until late Hauterivian times (?126 Ma) when <span class="hlt">rift</span> activity along in the equatorial Atlantic domain started to increase significantly. During this initial ?14 Myr-long stretching episode the pre-salt basin width on the conjugate Brazilian and west African margins is generated. An intermediate stage between ?126 Ma and base Aptian is characterised by strain localisation, rapid lithospheric weakening in the equatorial Atlantic domain, resulting in both progressively increasing extensional velocities as well as a significant rotation of the extension direction to NE-SW. From base Aptian onwards diachronous lithospheric break-up occurred along the central South Atlantic <span class="hlt">rift</span>, first in the Sergipe-Alagoas/Rio Muni margin segment in the northernmost South Atlantic. <span class="hlt">Final</span> break-up between South America and Africa occurred in the conjugate Santos-Benguela margin segment at around 113 Ma and in the equatorial Atlantic domain between the Ghanaian Ridge and the Piauí-Ceará margin at 103 Ma. We conclude that such a multi-velocity, multi-directional <span class="hlt">rift</span> history exerts primary control on the evolution of these conjugate passive-margin <span class="hlt">systems</span> and can explain the first-order tectonic structures along the South Atlantic and possibly other passive margins.</p> <div class="credits"> <p class="dwt_author">Heine, C.; Zoethout, J.; Müller, R. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">140</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012BVol...74.2415G"> <span id="translatedtitle">A common feeding <span class="hlt">system</span> of the NE and S <span class="hlt">rifts</span> as revealed by the bilateral 2002/2003 eruptive event at Mt. Etna (Sicily, Italy)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Mount Etna volcano is often characterized by bilateral eruptive events, involving both the south (S) and the north east (NE) <span class="hlt">rifts</span>. The last event occurred in 2002-2003 from October 27 to January 28. A detailed, stratigraphically time-controlled sampling of lavas and tephra of the southern eruptive fissure was performed in order to (1) track the petrological features of products during the eruption and (2) integrate the results with those previously obtained on the NE <span class="hlt">rift</span>. Whole-rock composition and textural observations were implemented by major and minor element analyses of plagioclases in lavas and tephra from both sides of the volcano. Fractionation models constrained by mass balance (major and trace elements) and Rayleigh calculations suggest that magmas are linked by the same liquid line of descent by fractionating 9.11 % of a mineral assemblage of Cpx (52.69 %), Plg (21.41), and Ol (7.46 %). These new data allowed us to identify at least two feeding episodes through the southern fissure and infer that high-K2O porphyritic magmas, emitted on both the S and NE <span class="hlt">rifts</span>, derives by fractionation from the same parent magma. However, lavas and tephra from the southern flank were slightly more primitive. Textural and petrological study of plagioclase moreover indicates that chemical-physical conditions in the deep feeding <span class="hlt">system</span> were similar for magmas erupting from both <span class="hlt">rifts</span> as suggested by the presence of dissolved rounded cores in both lavas. Magmas evolved differently on the S and the NE <span class="hlt">rifts</span> only at shallow levels. Comparison with published seismotectonic data supports the idea that the main magma feeding the eruption on October 27 ascended along the same pathway at depth and was intercepted by the fracture <span class="hlt">system</span> of the S and NE <span class="hlt">rifts</span> at shallow depth, between 6 and 3 km b.s.l.</p> <div class="credits"> <p class="dwt_author">Giacomoni, P. P.; Ferlito, C.; Alesci, G.; Coltorti, M.; Monaco, C.; Viccaro, M.; Cristofolini, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_6");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return 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showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_9");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">141</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1996Tecto..15..660B"> <span id="translatedtitle">Patterns of late Cenozoic volcanic and tectonic activity in the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> revealed by aeromagnetic surveys</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Aeromagnetic surveys, spaced ?5 km, over widely separated areas of the largely ice- and sea-covered West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span>, reveal similar patterns of 100- to 1700-nT, shallow-source magnetic anomalies interpreted as evidence of extensive late Cenozoic volcanism. We use the aeromagnetic data to extend the volcanic <span class="hlt">rift</span> interpretation over West Antarctica starting with anomalies over (1) exposures of highly magnetic, late Cenozoic volcanic rocks several kilometers thick in the McMurdo-Ross Island area and elsewhere; continuing through (2) volcanoes and subvolcanic intrusions directly beneath the Ross Sea continental shelf defined by marine magnetic and seismic reflection data and aeromagnetic data and (3) volcanic structures interpreted beneath the Ross Ice Shelf partly controlled by seismic reflection determinations of seafloor depth to (4) an area of similar magnetic pattern over the West Antarctic Ice Sheet (400 km from the nearest exposed volcanic rock), where interpretations of late Cenozoic volcanic rocks at the base of the ice are controlled in part by radar ice sounding. North trending magnetic <span class="hlt">rift</span> fabric in the Ross Sea-Ross Ice Shelf and Corridor Aerogeophysics of the Southeast Ross Transect Zone (CASERTZ) areas, revealed by the aeromagnetic surveys, is probably a reactivation of older <span class="hlt">rift</span> trends (late Mesozoic?) and is superimposed on still older crosscutting structural trends revealed by magnetic terrace maps calculated from horizontal gradient of pseudogravity. Long-wavelength (˜ 100-km wide) magnetic terraces from sources within the subvolcanic basement cross the detailed survey areas. One of these extends across the Ross Sea survey from the front of the Transantarctic Mountains with an east-southeast trend crossing the north trending <span class="hlt">rift</span> fabric. The Ross Sea-Ross Ice Shelf survey area is characterized by highly magnetic northern and southern zones which are separated by magnetically defined faults from a more moderately magnetic central zone. Aeromagnetic data in the south delineate the Ross fault of unknown age. The extension of the southern Central Basin south of the Ross fault is associated with an 825-nT magnetic anomaly over the Ross Ice Shelf requiring inferred late Cenozoic volcanic rock essentially at the seafloor at its south end, as shown by magnetic models. Models show that the thickness of magnetic volcanic rocks beneath Hut Point Peninsula at McMurdo Station is probably <2 km. The detailed surveys, combined with data from > 100,000 km of widely spaced aeromagnetic profiles, led to the interpretation of the mostly subglacial West Antarctic flood basalts(?) or their subglacially erupted and intruded equivalent. The volume of the exposed volcanos is small in contrast to the much greater volume (> 106 km³) of late Cenozoic magmatic rock remaining at volcanic centers beneath the continental shelf, Ross Ice Shelf and West Antarctic Ice Sheet. We suggest as an alternative or supplemental explanation to the previously proposed mantle plume hypothesis for the late Cenozoic volcanism significantly greater lower lithosphere (mantle) stretching resulting in greater decompression melting than the limited Cenozoic crustal extension allows. However, this implies a space problem that is not obviously resolved, because the Antarctic Plate is essentially surrounded by spreading centers.</p> <div class="credits"> <p class="dwt_author">Behrendt, John C.; Saltus, Richard; Damaske, Detlef; McCafferty, Anne; Finn, Carol A.; Blankenship, Donald; Bell, Robin E.</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">142</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012AGUFM.G23B0912T"> <span id="translatedtitle">Inter-<span class="hlt">Rifting</span> and Inter-Seismic Strain Accumulation in a Propagating Ridge <span class="hlt">System</span>: A Geodetic Study from South Iceland</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Mid-Atlantic Ridge, a slow spreading (~19 mm/yr) mid-ocean ridge boundary between the North American and Eurasian plates, is exposed subaerially in Iceland as the result of ridge-hotspot interaction. Plate spreading in Iceland is accommodated along neovolcanic zones comprised of central volcanoes and their fissure swarms. In south Iceland plate motion is partitioned between the Western Volcanic Zone (WVZ) and Eastern Volcanic Zone (EVZ). The EVZ is propagating to the southwest, while the WVZ is dying out from the northeast. Plate motion across both <span class="hlt">systems</span> has been accommodated by repeated <span class="hlt">rifting</span> events and fissure eruptions. In this study we investigate whether the WVZ is active and accumulating strain, and how strain is partitioned between the WVZ and EVZ. We also test how strain is accumulating along fissure swarms within the EVZ (i.e. is strain accumulation localized to one fissure swarm, or are multiple <span class="hlt">systems</span> active?). We use GPS data and elastic block models run using the program DEFNODE to investigate these issues. GPS data are processed using the GIPSY-OASIS II software, and have been truncated to the 2000.5-2011 time period to avoid co-seismic displacement from the two June 2000 South Iceland Seismic Zone earthquakes. We also truncate the time series for sites within 20 km of Eyjafjallajökull to the beginning of 2010 to eliminate deformation associated with the March 2010 eruption of that volcano. We correct for co-seismic displacement from the two May 2008 SISZ earthquakes, inflation at Hekla volcano and the horizontal component of glacial isostatic rebound (GIA). Our best-fit model for inter-<span class="hlt">rifting</span> and inter-seismic elastic strain accumulation suggests 80-90% of spreading is accommodated in the EVZ with the other 10-20% accommodated by the WVZ. The best-fit location of the EVZ is between Veidivotn and Lakigigar in an area of no Holocene volcanic activity. We suggest the WVZ is only active at Hengill and its associated fissure swarm. Geologic and geophysical evidence in the form of historical seismic swarms, inflation and <span class="hlt">rifting</span> events has been documented in the Hengill <span class="hlt">system</span>, along with ongoing geothermal activity. Our velocity field reveals a small velocity gradient at Thingvellir and no discernable gradient in the northern WVZ, suggesting 0-2 mm/yr of spreading accommodated across the southern WVZ and no spreading in the northern WVZ. This would indicate 17-19 mm/yr accommodated across the EVZ.</p> <div class="credits"> <p class="dwt_author">Travis, M. E.; La Femina, P. C.; Geirsson, H.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">143</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/48903182"> <span id="translatedtitle">The Aigion–Neos Erineos coastal normal fault <span class="hlt">system</span> (western Corinth Gulf <span class="hlt">Rift</span>, Greece): Geomorphological signature, recent earthquake history, and evolution</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">At the westernmost part of the Corinth <span class="hlt">Rift</span> (Greece), an area of rapid extension and active normal faulting, geomorphological observations reveal the existence and geometry of an active NW-SE trending coastal fault <span class="hlt">system</span>, which includes the Aigion fault. We recognize a similar fault pattern on both the coastal range front to the NW of Aigion town and the Holocene fan</p> <div class="credits"> <p class="dwt_author">N. Palyvos; D. Pantosti; P. M. De Martini; F. Lemeille; D. Sorel; K. Pavlopoulos</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">144</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/41998302"> <span id="translatedtitle">An elastic wedge model for the development of coeval normal and thrust faulting in the Mauna Loa-Kilauea <span class="hlt">rift</span> <span class="hlt">system</span> in Hawaii</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A long-standing enigma of the Mauna Loa-Kilauea <span class="hlt">rift</span> <span class="hlt">system</span> in Hawaii is the coeval development of normal and thrust faults that are vertically partitioned. To address this question, we developed a simple elastic wedge model that explores plausible boundary conditions in terms of tractions for generating such a fault pattern. Analytical solutions that best simulate the observed faulting style and</p> <div class="credits"> <p class="dwt_author">An Yin; T. K. Kelty</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">145</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/24589100"> <span id="translatedtitle">Analysis of surveillance <span class="hlt">systems</span> in place in European Mediterranean countries for West Nile virus (WNV) and <span class="hlt">Rift</span> Valley fever (RVF).</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">West Nile virus (WNV) and <span class="hlt">Rift</span> Valley fever virus (RVFV) represent an important group of viral agents responsible for vector-borne zoonotic diseases constituting an emerging sanitary threat for the Mediterranean Basin and the neighbouring countries. WNV infection is present in several Mediterranean countries, whereas RVF has never been introduced into Europe, but it is considered a major threat for North African countries. Being vector-borne diseases, they cannot be prevented only through an animal trade control policy. Several approaches are used for the surveillance of WNV and RVFV. With the aim of assessing the surveillance <span class="hlt">systems</span> in place in Mediterranean countries, two disease-specific questionnaires (WNV, RVFV) have been prepared and submitted to Public Health and Veterinary Authorities of six EU countries. This study presents the information gathered through the questionnaires and describes some critical points in the prevention and surveillance of these diseases as emerged by the answers received. PMID:24589100</p> <div class="credits"> <p class="dwt_author">Cito, F; Narcisi, V; Danzetta, M L; Iannetti, S; Sabatino, D D; Bruno, R; Carvelli, A; Atzeni, M; Sauro, F; Calistri, P</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">146</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://dx.doi.org/10.1016/j.epsl.2008.12.032"> <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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">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 ?202Hg from - 1.02‰ to 0.58‰ (± 0.11‰, 2SD) and solid precipitate samples from Guaymas Basin range in ?202Hg from - 0.37‰ to - 0.01‰ (± 0.14‰, 2SD). Fluid samples from Ojo Caliente display mass-dependent fractionation (MDF) of Hg from the vent (?202Hg = 0.10‰ ± 0.11‰, 2SD) to the end of the outflow channel (&delta202Hg = 0.58‰ ± 0.11‰, 2SD) in conjunction with a decrease in Hg concentration from 46.6pg/g to 20.0pg/g. Although a small amount of Hg is lost from the fluids due to co-precipitation with siliceous sinter, we infer that the majority of the observed MDF and Hg loss from waters in Ojo Caliente is due to volatilization of Hg0(aq) to Hg0(g) and the preferential loss of Hg with a lower ?202Hg value to the atmosphere. A small amount of mass-independent fractionation (MIF) was observed in all samples from Ojo Caliente (?199Hg = 0.13‰ ±1 0.06‰, 2SD) but no significant MIF was measured in the sea-floor <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> <div class="credits"> <p class="dwt_author">Sherman, L. S.; Blum, J. D.; Nordstrom, D. K.; McCleskey, R. B.; Barkay, T.; Vetriani, C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">147</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Olsen, P. E.; Kent, D. V.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">148</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Kelson, K.I. (Wm. Lettis Associates, Oakland, CA (United States)); Hemphill-Haley, M.A.; Wong, I.G. (Woodward-Clyde Federal Services, Oakland, CA (United States)); Gardner, J.N.; Reneau, S.L. (Los Alamos National Lab., NM (United States))</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">149</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013Tectp.594..118F"> <span id="translatedtitle">The role that plate tectonics, inferred stress changes and stratigraphic unconformities have on the evolution of the West and Central African <span class="hlt">Rift</span> <span class="hlt">System</span> and the Atlantic continental margins</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Muglad <span class="hlt">rift</span> basin of Sudan, is a good example of polyphase <span class="hlt">rifting</span>, with at least three major phases of basin development. Each phase has resulted in the generation of source rock, reservoir and seal geology with structural traps often closely linked to basement highs. In this paper we investigate on a regional scale the tectonic processes that have contributed to <span class="hlt">rift</span> basin development. On a regional scale, the evolution of the Africa-wide Mesozoic <span class="hlt">rift</span> <span class="hlt">system</span> is intimately linked to relative movements of African sub-plates and to global plate tectonic processes and plate interactions. Changes in plate interactions are observed in the oceanic crust as azimuth changes of fracture zone geometries and by inference have caused significant modifications to both the orientation and magnitude of the motions of the African sub-plates. Such plate motion processes have controlled the polyphase development of the West and Central African <span class="hlt">Rift</span> <span class="hlt">System</span>. On the basinal scale, changes of sub-plate motions have resulted in changes in the stress field which have had a clear impact on the deformation and fault geometries of <span class="hlt">rift</span> basins and on the resulting stratigraphy. The construction of the first unified stratigraphic chart for the West and Central African <span class="hlt">Rift</span> <span class="hlt">System</span> shows a close correlation in the timing of the major unconformities with the timing of changes in relative plate motion as observed in the changes of the azimuthal geometry of the oceanic fracture zones in the Central Atlantic. Since similarly timed unconformities exist along the continental margins of Africa and South America, we propose that the causative mechanism is change in relative plate motion which leads to an increase or decrease in the tension on the plate and thus controls the strength or effective elastic thickness, Te, of the crust/plate beneath the margins. This results in a focused change in isostatic response of the margin during short-period changes in relative plate motion; i.e. more tension will mean that loads are not compensated locally resulting in local uplift of the margin.</p> <div class="credits"> <p class="dwt_author">Fairhead, J. D.; Green, C. M.; Masterton, S. M.; Guiraud, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">150</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007JAfES..48..125K"> <span id="translatedtitle">Early structural development of the Okavango <span class="hlt">rift</span> zone, NW Botswana</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Aeromagnetic and gravity data collected across the Okavango <span class="hlt">rift</span> zone, northwest Botswana are used to map the distribution of faults, provide insights into the two-dimensional shallow subsurface geometry of the <span class="hlt">rift</span>, and evaluate models for basin formation as well as the role of pre-existing basement fabric on the development of this nascent continental <span class="hlt">rift</span>. The structural fabric (fold axes and foliation) of the Proterozoic basement terrane is clearly imaged on both gravity and magnetic maps. The strike of <span class="hlt">rift</span>-related faults (030-050° in the north and 060-070° in the south) parallels fold axes and the prominent foliation directions of the basement rocks. These pre-existing fabrics and structures represent a significant strength anisotropy that controlled the orientation of younger brittle faults within the stress regime present during initiation of this <span class="hlt">rift</span>. Northwest dipping faults consistently exhibit greater displacements than southeast dipping faults, suggesting a developing half-graben geometry for this <span class="hlt">rift</span> zone. However, the absence of fully developed half-grabens along this <span class="hlt">rift</span> zone suggests that the border fault <span class="hlt">system</span> is not fully developed consistent with the infancy of <span class="hlt">rifting</span>. Three en-echelon northeast trending depocenters coincide with structural grabens that define the Okavango <span class="hlt">rift</span> zone. Along the southeastern boundary of the <span class="hlt">rift</span>, developing border faults define a 50 km wide zone of subsidence within a larger 150 km wide zone of extension forming a <span class="hlt">rift-in-rift</span> structure. We infer from this observation that the localization of strain resulting from extension is occurring mostly along the southeastern boundary where the border fault <span class="hlt">system</span> is being initiated, underscoring the important role of border faults in accommodating strain even during this early stage of <span class="hlt">rift</span> development. We conclude that incipient <span class="hlt">rift</span> zones may provide critical insights into the development of <span class="hlt">rift</span> basins during the earliest stages of continental <span class="hlt">rifting</span>.</p> <div class="credits"> <p class="dwt_author">Kinabo, B. D.; Atekwana, E. A.; Hogan, J. P.; Modisi, M. P.; Wheaton, D. D.; Kampunzu, A. B.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">151</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">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 class="dwt_publisher"></p> <p class="publishDate">1986-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">152</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19730006633&hterms=Gumbi&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3D%2522Gumbi%2522"> <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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Mohr, P. A. (principal investigator)</p> <p class="dwt_publisher"></p> <p class="publishDate">1973-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">153</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Behrendt, J.C. (Geological Survey, Denver, CO (USA)); Cooper, A. (Geological Survey, Menlo Park, CA (USA))</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">154</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014EGUGA..1615547R"> <span id="translatedtitle">Elliptical caldera formation throughout the Kenyan <span class="hlt">Rift</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Many of the world's calderas are elliptical in shape, and their orientation is often used as a proxy for the local stress regime. However, in some <span class="hlt">rift</span> settings, pre-existing structural trends have been shown to control caldera orientation. We test these competing hypotheses in the Kenyan <span class="hlt">Rift</span>, which consists of two distinct <span class="hlt">rift</span> segments, with different tectonic and magmatic characteristics. Of the fourteen Quaternary volcanoes lying along the central <span class="hlt">rift</span> axis, seven have undergone caldera collapse and six are highly elliptical. We present a remote-sensing study that investigates the structural and tectonic control on caldera ellipticity and orientation within the Kenyan <span class="hlt">Rift</span>. Satellite-based mapping using ArcGIS on imagery derived from ASTER and GDEM data to identify the orientations of the main East African <span class="hlt">Rift</span> border faults, intra-<span class="hlt">rift</span> faults and the geometry of Kenyan calderas to determine the extensional setting, horizontal compressive stress orientations and the pre-existing <span class="hlt">rift</span> fabric direction. Other data sources included the GPS-derived plate-kinematic model of East Africa and information from the literature. We find that deformation in the Kenyan <span class="hlt">Rift</span> is characterised by orthogonal extension in the north and oblique opening in the south, suggesting that both tectonic stresses and magmatic pressures drive intra-<span class="hlt">rift</span> fault formation. The long axis elongation of calderas are orientated NW-SE in the north, aligned with pre-existing structures and perpendicular to recent <span class="hlt">rift</span>-faults. In contrast, the long axes are aligned NE-SW in the southern group of volcanoes, at an angle which is highly oblique to the recent <span class="hlt">rift</span> faults, but aligned with pre-existing structures. Thus we conclude that in oblique continental <span class="hlt">rifts</span>, pre-existing structures play a dominant role in the rise of magma through the crust. Understanding the geometry of caldera <span class="hlt">systems</span> gives us important information as to the structural controls on magmatic and tectonic behaviour in extensional settings and the mechanisms by which continental <span class="hlt">rifts</span> evolve from fault-controlled basins into mid-ocean ridges.</p> <div class="credits"> <p class="dwt_author">Robertson, Elspeth; Biggs, Juliet; Cashman, Katharine; Floyd, Michael; Vye-Brown, Charlotte</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">155</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4003290"> <span id="translatedtitle">Evidence of <span class="hlt">rift</span> valley fever seroprevalence in the Sahrawi semi-nomadic pastoralist <span class="hlt">system</span>, Western Sahara</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">Background The increasing global importance of <span class="hlt">Rift</span> Valley fever (RVF) is clearly demonstrated by its geographical expansion. The presence of a wide range of host and vector species, and the epidemiological characteristics of RVF, have led to concerns that epidemics will continue to occur in previously unaffected regions of Africa. The proximity of the Sahrawi territories of Western Sahara to endemic countries, such as Mauritania, Senegal, and Mali with periodic isolation of virus and serological evidence of RVF, and the intensive livestock trade in the region results in a serious risk of RVF spread in the Sahrawi territories, and potentially from there to the Maghreb and beyond. A sero-epidemiological survey was conducted in the Saharawi territories between March and April 2008 to investigate the possible presence of the RVF virus (RVFV) and associated risk factors. A two-stage cluster sampling design was used, incorporating 23 sampling sites. Results A total of 982 serum samples was collected from 461 sheep, 463 goats and 58 camels. Eleven samples (0.97%) tested positive for IgG against the RVFV. There were clusters of high seroprevalence located mostly in the Tifariti (7.69%) and Mehaires (7.14%) regions, with the Tifariti event having been found in one single flock (4/26 positive animals). Goats and older animals were at a significantly increased risk being seropositive (p?=?0.007 and p?=?0.007, respectively). Conclusion The results suggest potential RVF activity in the study area, where intense livestock movement and trade with neighbouring countries might be considered as a primary determinant in the spread of the disease. The importance of a continuous field investigation is reinforced, in light of the risk of RVF expansion to historically unaffected regions of Africa.</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">2014-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">156</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19930069932&hterms=bouguer+anomaly+gravity&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dbouguer%2Banomaly%2Bgravity"> <span id="translatedtitle">Implications of new gravity data for Baikal <span class="hlt">Rift</span> zone structure</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Ruppel, C.; Kogan, M. G.; Mcnutt, M. K.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">157</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Gummert, Michael; Lindenfeld, Michael; Wölbern, Ingo; Rümpker, Georg; Kasereka, Celestin; Batte, Arthur</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">158</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFM.H51C1222M"> <span id="translatedtitle">Exploring for geothermal resource in a dormant volcanic <span class="hlt">system</span>: The Haleakala Southwest <span class="hlt">Rift</span> Zone, Maui, Hawai'i</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Suites of new geophysical and geochemical surveys provide compelling evidence for geothermal resource at the Haleakala Southwest <span class="hlt">Rift</span> Zone (HSWRZ) on Maui Island, Hawai'i. Ground-based gravity (~400 stations) coupled with heli-borne magnetics (~1500 line kilometers) define both deep and shallow fractures/faults while also delineating potentially widespread subsurface hydrothermal alteration on the lower flanks (below approximately 1800 feet a.s.l.). Multi-level, upward continuation calculations and 2-D gravity and magnetic modeling provide information on source depths, but lack of lithologic information leaves ambiguity in the estimates. Lithology and physical property data from future drilling will improve these interpretations. Additionally, several well-defined gravity lows (possibly vent zones) lie coincident with magnetic highs suggesting the presence of dike intrusions at depth; a potentially young source of heat for a modern geothermal <span class="hlt">system</span>. Soil CO2 fluxes were measured along transects across geophysically-defined faults and fractures as well as young cinder cones along the HSWRZ; a weak anomalous flux signal was observed at one young cinder cone location. Dissolved inorganic carbon concentrations and ?13C compositions and 3He/4He values measured in several shallow groundwater samples indicate addition of magmatic CO2 and He to the groundwater <span class="hlt">system</span>. The general lack of observed magmatic surface CO2 signals on the HSWRZ is therefore likely due to a combination of groundwater 'scrubbing' of CO2 and relatively high biogenic surface CO2 fluxes that mask magmatic CO2. Similar surveys at the Puna geothermal field on the Kilauea Lower East <span class="hlt">Rift</span> Zone (KLERZ) also showed a lack of surface CO2 flux signals attributed to a magmatic source, while aqueous geochemistry indicated contribution of magmatic CO2 and He to shallow groundwaters at both Maui and Puna. As magma has been intercepted in geothermal drilling at the Puna field, the lack of measured surface CO2 flux associated with upflow of magmatic fluids here is likely due to the aforementioned 'scrubbing' from extensive groundwater flow, as well as high background biogenic CO2 flux. Deep, temperature gradient core holes have been sited based on these geophysical and geochemical datasets.</p> <div class="credits"> <p class="dwt_author">Martini, B. A.; Lewicki, J. L.; Kennedy, B. M.; Lide, C.; Oppliger, G.; Drakos, P. S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">159</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Bouvier, L.; Pinti, D. L.; Tremblay, A.; Minarik, W. G.; Roden-Tice, M. K.; Pik, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">160</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012AGUFM.T43F2745S"> <span id="translatedtitle">Minimal Role of Basal Shear Tractions in Driving Nubia-Somalia Divergence Across the East African <span class="hlt">Rift</span> <span class="hlt">System</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Nubian and Somalian plates actively diverge along the topographically high, ~5000 km long East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS). As no major subduction zones bound Africa, one can assume that the forces driving the Nubia-Somalia plate <span class="hlt">system</span> result primarily from mantle buoyancies and lateral variation in lithospheric gravitational potential energy. Images from seismic tomography and convection models suggest active mantle flow beneath Africa. However, the contribution from large-scale convection to the force balance driving plate divergence across the EARS remains in question. In this work we investigate the impact of mantle shear tractions on the dynamics of Nubia-Somalia divergence across the EARS. We compare surface motions inferred from GPS observations with strain rates and velocities predicted from dynamic models where basal shear stresses are (1) derived from forward mantle circulation models and (2) inferred from stress field boundary conditions that balance buoyancy forces in the African lithosphere. Upper mantle anisotropy derived from seismic observations beneath Africa provide independent constraints for the latter. Preliminary results suggest that basal shear tractions play a minor role in the dynamics of Nubia-Somalia divergence along the EARS. This result implies mantle-lithosphere decoupling, possibly promoted by a low viscosity asthenosphere. We corroborate the robustness of our results with estimates of upper mantle viscosity based on local upper mantle temperature estimates and rheological parameters obtained from laboratory experiments.</p> <div class="credits"> <p class="dwt_author">Stamps, D. S.; Calais, E.; Iaffaldano, G.; Flesch, L. M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_7");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_10");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">161</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Bosworth, W.</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">162</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007PhDT.......218K"> <span id="translatedtitle">Incipient continental <span class="hlt">rifting</span>: Insights from the Okavango <span class="hlt">Rift</span> Zone, northwestern Botswana</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In this dissertation aeromagnetic, gravity, and Shuttle Radar Topography Mission Digital Elevation Model (SRTM DEM) data from the Okavango <span class="hlt">Rift</span> Zone in northwest Botswana are used to map the distribution of <span class="hlt">rift</span> and basement structures. The distribution of these structures provide useful insights into the early stages of continental <span class="hlt">rifting</span>. The objectives of this study are (1) assessing the role of pre-existing structures on <span class="hlt">rift</span> basin development, (2) characterizing the geometry of the nascent <span class="hlt">rift</span> basins, (3) documenting fault growth and propagation patterns, and (4) investigating the border fault development. Potential field data especially aeromagnetic data are used to map out structures in the sediment covered basement, whereas SRTM DEM data express the surface morphology of the structures. The azimuth of <span class="hlt">rift</span> faults parallel the orientation of the fold axes and the prominent foliation directions of the basement rocks. This indicates that pre-existing structures in the basement influenced the development of the <span class="hlt">rift</span> structures. NE dipping faults consistently exhibit greater displacements than SE dipping faults, suggesting a developing half-graben geometry. Individual faults grow by along axis linkage of small segments that develop from soft linkage (under lapping to overlapping segments) to hard linkage (hooking, fused segments). Major <span class="hlt">rifts</span> faults are also linking through transfer zones by the process of "fault piracy" to establish an immature border fault <span class="hlt">system</span>. The relationships between scam heights and vertical throws reveal that the young and active faults are located outside the <span class="hlt">rift</span> while the faults with no recent activities are in the middle suggesting that the <span class="hlt">rift</span> is also growing in width. This study demonstrates the utility of potential field data and SRTM DEM to provide a 3-D view of incipient continental <span class="hlt">rifting</span> processes such as fault growth and propagation.</p> <div class="credits"> <p class="dwt_author">Kinabo, Baraka Damas</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">163</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFM.T43G2469N"> <span id="translatedtitle">Upper Mantle Structure Beneath the Whitmore Mountains, West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span>, and Marie Byrd Land from Body-Wave Tomography</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">As part of the International Polar Year in Antarctica, 37 seismic stations have been installed across West Antarctica as part of the Polar Earth Observing Network (POLENET). 23 stations form a sparse backbone network of which 21 are co-located on rock sites with a network of continuously recording GPS stations. The remaining 14 stations, in conjunction with 2 backbone stations, form a seismic transect extending from the Ellsworth Mountains across the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> (WARS) and into Marie Byrd Land. Here we present preliminary P and S wave velocity models of the upper mantle from regional body wave tomography using P and S travel times from teleseismic events recorded by the seismic transect during the first year (2009-2010) of deployment. Preliminary P wave velocity models consisting of ~3,000 ray paths from 266 events indicate that the upper mantle beneath the Whitmore Mountains is seismically faster than the upper mantle beneath Marie Byrd Land and the WARS. Furthermore, we observe two substantial upper mantle low velocity zones located beneath Marie Byrd Land and near the southern boundary of the WARS.</p> <div class="credits"> <p class="dwt_author">Nyblade, A.; Lloyd, A. J.; Anandakrishnan, S.; Wiens, D. A.; Aster, R. C.; Huerta, A. D.; Wilson, T. J.; Shore, P.; Zhao, D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">164</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010Tectp.492...25E"> <span id="translatedtitle">On the use of global potential field models for regional interpretation of the West and Central African <span class="hlt">Rift</span> <span class="hlt">System</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The use in regional interpretations of the Earth Gravity Model (EGM08) and Earth magnetic model (EMAG2) is evaluated by comparison to ground gravity and aeromagnetic data in the central sector of the West and Central African <span class="hlt">Rift</span> <span class="hlt">System</span> (WCARS). The comparison includes upward continuation, spectral analysis and pseudogravity calculation and statistical evaluation. A correlation between EMAG2 (which contains roughly 25 km resolution aeromagnetic data in the region) and near-surface aeromagnetic data over WCARS is only true for the very low wavelength part but a strong similarity between EGM08 and ground gravity data can be confirmed. Interpretation of the EGM08 data allows identifying and confirming the position of major structural trends, and provides new information on the crustal architecture. The lineaments limiting different grabens forming the Logone Birni basin and in the southern Chad basin are identified. The results presented here show the use of EGM08 data for regional interpretations over Cameroon and adjacent countries, which can overcome the absence and sparseness of data in developing countries and remote areas.</p> <div class="credits"> <p class="dwt_author">Eyike, Albert; Werner, Stephanie C.; Ebbing, Jörg; Dicoum, E. Manguelle</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">165</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5840034"> <span id="translatedtitle">Cenozoic <span class="hlt">rift</span> tectonics of the Japan Sea</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Kimura, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">1988-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">166</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AGUFM.T13A2514Q"> <span id="translatedtitle">Understanding the thermal and tectonic evolution of Marie Byrd Land from a reanalysis of airborne geophysical data in the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span> (WARS) is a region characterized by a significant topographic range, a complex tectonic history, and active subglacial volcanism. Those elements exert a large influence on the stability of the West Antarctic Ice Sheet, which flows within the cradle-shaped <span class="hlt">rift</span> <span class="hlt">system</span> and is currently grounded well below sea level. This potentially unstable configuration is the motivation for gaining a better understanding of the ice sheet boundary conditions dictated by <span class="hlt">rift</span> evolution and how they impact the ice flow. In this study we focus on characterizing the distribution of and transition between sedimentary basins and inferred geothermal heat flux from the flanks to the floor of the <span class="hlt">rift</span> <span class="hlt">system</span>. We do so through analysis of gravity data both for sources within the deep lithosphere and near surface targets in the crust. A compilation of gravity datasets over West and Central Antarctica and the analysis thereof is presented. In particular we use gravity data collected during several airborne geophysical surveys: CASERTZ (1994-1997), SOAR/WMB (1997-1998), AGASEA (2004-2005), ICEBRIDGE (2008-2011), and GIMBLE (2012-2013). New processing and data reduction methodologies are applied to the older gravity surveys to improve the high frequency signal content and to make these surveys compatible with modern works (i.e. AGASEA, ICEBRIDGE, GIMBLE). The high frequency signal provides better resolution of small-scale features within survey blocks but long-wavelength integrity is retained by registering the airborne free-air disturbance within those blocks to the gravity disturbance derived from the GOCE global satellite gravity field. This allows for consistent long wavelength interpretation across the merged surveys and provides improved gravity analysis of the deep lithosphere while retaining the capacity to study smaller scale features. A crustal model for the area is produced using the Bouguer anomaly and spectral analyses of the Bouguer anomaly and free-air disturbance. Airy isostatic corrections are applied to the Bouguer anomaly where permissible to set the foundation for the identification and discrimination of sedimentary basins and intrusive/extrusive complexes beneath the West Antarctic Ice Sheet. This analysis also provides a framework for interpreting POLENET seismic studies in the region. Successful integration of the gravity and seismic results will ultimately be necessary for understanding the thermal evolution of Marie Byrd Land and its context within the West Antarctic <span class="hlt">Rift</span> <span class="hlt">System</span>.</p> <div class="credits"> <p class="dwt_author">Quartini, E.; Powell, E. M.; Richter, T.; Damiani, T.; Burris, S. G.; Young, D. A.; Blankenship, D. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">167</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Kinabo, B. D.; Hogan, J. P.; Atekwana, E. A.; Abdelsalam, M. G.; Modisi, M. P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">168</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013JGRB..118..302L"> <span id="translatedtitle">Trench-parallel flow in the southern Ryukyu subduction <span class="hlt">system</span>: Effects of progressive <span class="hlt">rifting</span> of the overriding plate</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><title type="main">AbstractThe Okinawa trough in the Ryukyu subduction <span class="hlt">system</span> is one of a few actively extending back arc basins within the continental lithosphere. Recent shear-wave splitting measurements show variable fast directions along the trough suggesting a complex three-dimensional mantle flow field. In this study we use numerical subduction models to demonstrate that the thickness variations of the continental lithosphere bounding the edge of a subduction zone can result in complicated mantle circulation and regional dynamics. The model results for the southern Ryukyu show a combination of two effects: Along the Okinawa trough, the increasing thickness of the overriding Eurasian plate toward Taiwan due to a gradually diminishing <span class="hlt">rifting</span> induces pressure gradients that drive trench-parallel flow to the edge in the shallow portion of the mantle wedge, and the thick Eurasian lithosphere to the west effectively blocks and diverts this along-arc flow and limits the toroidal flow around the slab edge below it. The toroidal flow thus enters the mantle wedge at depths of more than about 100 km, opposite in direction with and largely below the along-arc flow. These combined geometry effects of the Eurasian lithosphere create an intricate three-dimensional flow structure at the southern edge of the Ryukyu subduction zone. Model predictions for lattice preferred orientations of olivine aggregates show rotation patterns that agree with the observed shear-wave splitting patterns. This three-dimensional scenario echoes the geochemical and seismological evidence worldwide that indicates complex, depth-varying mantle circulations in subduction <span class="hlt">systems</span>.</p> <div class="credits"> <p class="dwt_author">Lin, Shu-Chuan; Kuo, Ban-Yuan</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">169</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/42039788"> <span id="translatedtitle">Crustal deformation in the Baikal <span class="hlt">rift</span> from GPS measurements</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Three years and four campaigns of Global Positioning <span class="hlt">System</span> (GPS) measurements (1994-1997) in the Baikal <span class="hlt">rift</span> zone, largest active continental <span class="hlt">rift</span> <span class="hlt">system</span> in Eurasia, show crustal extension at a rate of 4.5+\\/-1.2mm\\/yr in a WNW-ESE direction. A comparison with moment release of large historical earthquakes suggests that elastic strain is currently accumulating in the Baikal <span class="hlt">rift</span> zone along active faults</p> <div class="credits"> <p class="dwt_author">Eric Calais; Olivia Lesne; Jacques Déverchère; Vladimir San'kov; Andrei Lukhnev; Andrei Miroshnichenko; Vladimir Buddo; Kirill Levi; Vjacheslav Zalutzky; Yuri Bashkuev</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">170</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://marine.usgs.gov/fact-sheets/baikal/index.html"> <span id="translatedtitle">Lake Baikal - A Touchstone for Global Change and <span class="hlt">Rift</span> Studies</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">This is a United States Geological Survey (USGS) fact sheet about the Lake Baikal <span class="hlt">rift</span> <span class="hlt">system</span>. This site provides a good general overview of this <span class="hlt">rift</span> <span class="hlt">system</span>, illustrating its importance to the overall study of plate tectonics. The Lake Baikal <span class="hlt">rift</span> <span class="hlt">system</span> is a modern analogue for formation of ancient Atlantic-type continental margins. It tells us the first chapter in the story of how continents separate and ultimately develop into ocean basins like the Atlantic Ocean. Continental <span class="hlt">rifting</span> is an important component of plate tectonics theory.</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">171</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Hayes, J.M.; Pratt, L.M. [Indiana Univ., Bloomington, IN (United States); Knoll, A.H. [Harvard Univ., Cambridge, MA (United States). Dept. of Organismal and Evolutionary Biology</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-12-31</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">172</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Sankov, Vladimir; Sankov, Aleksei; Lebedeva, Marina; Ashurkov, Sergey; Parfeevets, Anna</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">173</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014GeoJI.197...33H"> <span id="translatedtitle">InSAR observations of post-<span class="hlt">rifting</span> deformation around the Dabbahu <span class="hlt">rift</span> segment, Afar, Ethiopia</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Increased displacement rates have been observed following manylarge earthquakes and magmatic events. Although an order of magnitude smaller than the displacements associated with the main event, the post-seismic or post-<span class="hlt">rifting</span> deformation may continue for years to decades after the initial earthquake or dyke intrusion. Due to the rare occurrence of subaerial <span class="hlt">rifting</span> events, there are very few observations to constrain models of post-<span class="hlt">rifting</span> deformation. In 2005 September, a 60-km-long dyke was intruded along the Dabbahu segment of the Nubia-Arabia Plate boundary (Afar, Ethiopia), marking the beginning of an ongoing <span class="hlt">rifting</span> episode. Continued activity has been monitored using satellite radar interferometry and data from global positioning <span class="hlt">system</span> instruments deployed around the <span class="hlt">rift</span> in response to the initial intrusion. Using multiple satellite passes, we are able to separate the <span class="hlt">rift</span> perpendicular and vertical displacement fields around the Dabbahu segment. <span class="hlt">Rift</span> perpendicular and vertical rates of up to 180 and 240 mm yr-1, respectively. Here, we show that models of viscoelastic relaxation alone are insufficient to reproduce the observed deformation field and that a large portion of the observed signal is related to the movement of magma within the <span class="hlt">rift</span> segment. Our models suggest upper mantle viscosities of 1018-19 Pa s overlain by an elastic crust of between 15 and 30 km. To fit the observations, inflation and deflation of magma chambers in the centre of the <span class="hlt">rift</span> and to the south east of the <span class="hlt">rift</span> axis is required at rates of ˜0.13 and -0.08 km3 yr-1.</p> <div class="credits"> <p class="dwt_author">Hamling, Ian J.; Wright, Tim J.; Calais, Eric; Lewi, Elias; Fukahata, Yukitoshi</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">174</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6747539"> <span id="translatedtitle">Volcanism at <span class="hlt">rifts</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">White, R.S.; McKenzie, D.P.</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">175</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014EGUGA..1614214H"> <span id="translatedtitle">Controls on (anomalous) topography in <span class="hlt">rifted</span> margin settings</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Contrasting end members of volcanic and non-volcanic passive margin formation show a large variability in basin shape and structure, subsidence history, and associated topographic evolution of the onshore <span class="hlt">rifted</span> margins. The large range of structural style and associated topography of these <span class="hlt">systems</span> imply a strong variability in the underlying thermo-mechanical conditions at the time of <span class="hlt">rifting</span>. <span class="hlt">Rift</span> - passive margin styles ranging from narrow to ultra wide are explained using forward numerical models with varying rheological structure, with strong crust lithosphere leading to narrow <span class="hlt">rift</span> formation associated with highly elevated <span class="hlt">rift</span> shoulders and conversely weak crust lithosphere resulting in highly stretched wide <span class="hlt">rifted</span> conjugate margins and little flank morphology. In some cases <span class="hlt">rifted</span> margins appear to indicate the formation of anomalous post <span class="hlt">rift</span> topography. A number of mechanisms including small-scale convective removal of the lower lithosphere, lithosphere counter-flow, and dynamic topography, have been invoked to explain the anomalous topography. Forward numerical models are used to predict the magnitude and characteristic topography associated with each of these mechanisms and to evaluate their potential for explaining these apparent anomalous characteristics of <span class="hlt">rifts</span> and <span class="hlt">rifted</span> margins.</p> <div class="credits"> <p class="dwt_author">Huismans, Ritske S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">176</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010Tecto..29.6016A"> <span id="translatedtitle">Analog models of oblique <span class="hlt">rifting</span> in a cold lithosphere</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">New lithospheric analog models of oblique <span class="hlt">rifting</span> presented here capture the main characteristics of natural oblique <span class="hlt">rifts</span> and provide insights into the fault evolution, basin segmentation, and mantle exhumation occurring during <span class="hlt">rift</span> localization. We present two models: one with a preexisting oblique lithospheric weakness (model B) and another with no weakness zone (model A). Both oblique <span class="hlt">rifts</span> have an obliquity of about 40°. The main results are as follows. (1) The fault populations, especially during the early stages of deformation, are composed of faults that in strike are largely intermediate between <span class="hlt">rift</span>-parallel and perpendicular to displacement. This fault population is characteristic of oblique <span class="hlt">rifts</span> observed in previous studies. (2) In later stages, faults parallel to the <span class="hlt">rift</span> become numerous in both models. Buoyancy forces related to thickness variations in the lithosphere during <span class="hlt">rift</span> localization play a significant role and control the initiation of <span class="hlt">rift</span>-parallel faults. (3) During the <span class="hlt">final</span> stages of extension, in model B the crust is deformed by <span class="hlt">rift</span>-parallel faults, while in the basins the small-scale deformation pattern is composed of displacement-normal faults. However, in model A, displacement-normal faults tend to accommodate most of the extension, controlling its <span class="hlt">final</span> stages. They probably also control the formation of the ocean-continent transition, any possible mantle exhumation, as well as the geometry of oceanic accretion centers. These results provide an insight into the possible evolution of the Gulf of Aden conjugate margins, which developed in an oblique context and most probably without any preexisting <span class="hlt">rift</span>-parallel localizing heterogeneity in the lithosphere.</p> <div class="credits"> <p class="dwt_author">Autin, Julia; Bellahsen, Nicolas; Husson, Laurent; Beslier, Marie-Odile; Leroy, Sylvie; D'Acremont, Elia</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">177</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://dx.doi.org/10.1111/j.1365-246X.2005.02554.x"> <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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Schulte, S. M.; Mooney, W. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">178</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Daoud, Mohamed A.; Le Gall, Bernard; Maury, René C.; Rolet, JoëL.; Huchon, Philippe; Guillou, Hervé</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">179</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://perso-sdt.univ-brest.fr/~jacdev/pdf/deverch01.pdf"> <span id="translatedtitle">Depth distribution of earthquakes in the Baikal <span class="hlt">rift</span> <span class="hlt">system</span> and its implications for the rheology of the lithosphere</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The correspondence between the predicted brittle-plastic transition within the crust and the maximum depth of earthquakes is examined in the case of the Baikal <span class="hlt">rift</span>, Siberia. Although little accurate information on depths is available through large- and moderate-size earthquakes, there are frequent indications of foci at 20km depth and more. We have relocated 632 events recorded at nearby stations that</p> <div class="credits"> <p class="dwt_author">Jacques Déverchère; Carole Petit; Nadejda Gileva; Natalia Radziminovitch; Valentina Melnikova; Vladimir San'Kov</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">180</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6132104"> <span id="translatedtitle">Structure of Mid-Continent <span class="hlt">rift</span> beneath Lake Superior</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The 1.1 Ga Mid-Continent <span class="hlt">rift</span> <span class="hlt">system</span> extends from Kansas through the Lake Superior region and into southern Michigan. The <span class="hlt">rift</span> is filled with thick sequences of basalt and clastic sedimentary rocks, which are now mostly buried beneath Paleozoic rocks. Rocks of the <span class="hlt">rift</span> <span class="hlt">system</span> are exposed only in the Lake Superior region and comprise the Keweenawan supergroup. Seismic reflection surveys by GLIMPCE in 1986 imaged much of the deep structure of the <span class="hlt">rift</span> beneath the lake in detail. Reflection profiles reveal a deep asymmetrical central graben whose existence and magnitude was not previously documented. Volcanic and sedimentary rocks, in places greater than 30 km thick, fill the central graben, which is bounded by normal growth faults. Thinner volcanic and sedimentary units lie on broad flanks of the <span class="hlt">rift</span> outside of the graben. Near the <span class="hlt">rift</span> axis, the pre-<span class="hlt">rift</span> crust is thinned to about one-fourth of its original thickness, apparently by low-angle extensional faulting and ductile stretching or distributed shear. The sense of asymmetry of the central graben changes along the trend of the <span class="hlt">rift</span>, documenting the segmented nature of the structure and suggesting the existence of accommodation zones between the segments. The location of the accommodation zones is inferred from abrupt disruptions in the Bouguer gravity anomaly associated with the <span class="hlt">rift</span>. Late uplift of the central graben transposed graben-bounding normal faults into high-angle reverse faults with throws of 5 km or more.</p> <div class="credits"> <p class="dwt_author">Cannon, W.F.</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-03-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_8");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return 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showDiv("page_11");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">181</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Guo, L.; Keller, G. R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">182</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Masini, E.; Manatschal, G.; Tugend, J.; Kusznir, N. J.; Flament, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">183</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.mna.it/MER/utilities.htm"> <span id="translatedtitle">Evolution of Oblique <span class="hlt">Rifting</span> on the Main Ethiopian <span class="hlt">Rift</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">Movie showing the evolution of oblique <span class="hlt">rifting</span> in analogue models (from Corti, 2008, Nature Geosc). Obliquity in this model is 30° (angle between the normal to the <span class="hlt">rift</span> axis and the direction of extension). Note the two-phase <span class="hlt">rift</span> evolution with a first phase of boundary fault activity and basin subsidence, followed by activation of en-echelon arranged internal faults obliquely cutting the <span class="hlt">rift</span> floor.</p> <div class="credits"> <p class="dwt_author">Corti, Giacomo</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">184</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=DE94009848"> <span id="translatedtitle">Data acquisition <span class="hlt">systems</span>. <span class="hlt">Final</span> report.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">The program has included continued extension and maintenance of the specifications for data acquisition <span class="hlt">systems</span> for high energy physics applications. Work continued on the study, development and specification of the FASTBUS <span class="hlt">system</span> and of other <span class="hlt">systems</span> to ...</p> <div class="credits"> <p class="dwt_author">L. Costrell</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">185</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Philip Holmes</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-12-31</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">186</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.agu.org/journals/jb/v076/i008/JB076i008p01967/JB076i008p01967.pdf"> <span id="translatedtitle">Ethiopian <span class="hlt">Rift</span> and Plateaus: Some Volcanic Petrochemical Differences</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Volcanism on the Arabo-Ethiopian swell has accompanied the development of the three traversing spreading zones conjoining at Afar: the Red Sea, Gulf of Aden, and African <span class="hlt">rift</span> <span class="hlt">systems</span>. The Red Sea and Gulf of Aden floors are formed by oceanic tholerites, but Afar and the main Ethiopian <span class="hlt">rift</span> show a wider range of more alkaline volcanics, related to slower crustal</p> <div class="credits"> <p class="dwt_author">P. A. Mohr</p> <p class="dwt_publisher"></p> <p class="publishDate">1971-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">187</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Kolowith, R.; Berg, J.D.; Miller, W.C.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">188</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Central Main Ethiopian <span class="hlt">Rift</span> basin is a continental <span class="hlt">rift</span> <span class="hlt">system</span> characterized by volcano-tectonic depression endowed with huge geothermal resource and associated natural geochemical changes on groundwater quality. Chemical composition of groundwater in the study area showed a well defined trend along flow from the highland and escarpment to the <span class="hlt">rift</span> floor aquifer. The low TDS (< 500mg/l) Ca-Mg-HCO3 dominated water at recharge area in the highlands and escarpments evolve progressively into Ca-Na-HCO3 and Na-Ca-HCO3 type waters along the <span class="hlt">rift</span> ward groundwater flow paths. These waters <span class="hlt">finally</span> appear as moderate TDS (mean 960mg/l) Na-HCO3 type and as high TDS (> 1000 mg/l) Na-HCO3-Cl type in volcano-lacustrine aquifers of the <span class="hlt">rift</span> floor. High concentrations of fluoride (up to 97.2 mg/l) and arsenic (up to 98?g/l) are recognized feature of groundwaters which occur mostly in the vicinity of the geothermal fields and the <span class="hlt">rift</span> lakes in the basin. Fluoride and arsenic content of dry volcaniclastic sediments close to these areas are in the range 666-2586mg/kg and 10-13mg/kg respectively. The relationship between fluoride and calcium concentrations in groundwaters showed negative correlation. Near-equilibrium state attained between the mineral fluorite (CaF2) and the majority of fluoride-rich (>30mg/l) thermal groundwater and shallow cold groundwater. This indicated that the equilibrium condition control the high concentration of fluoride in the groundwaters. Whereas undersaturation state of fluorite in some relatively low-fluoride (<30mg/l) thermal waters indicated a dilution by cold waters. Laboratory batch leaching experiments showed that fast dissolution of fluoride from the sediment samples suddenly leached into the interacting water at the first one hour and then remain stable throughout the experiment. The concentrations of leached fluoride from the hot spring deposits, the lacustrine sediments, and the pyroclastic rock are usually low (1% of the total or less than the content in the sediment or rock) but strongly correlated with the concentrations in groundwaters in the local vicinity. The readily leachable hot spring deposits and local lacustrine sediments, which were leached easily as high as three fold of other sediments leachability, are considered as the reservoir for the potential fluoride contamination of the <span class="hlt">rift</span> groundwater. Leaching of fluoride in the sub-surface <span class="hlt">system</span> is simulated with sediment-packed column leached by flowing water and applying temporary interruption of flow during the experiment. The result indicated that a sharp increase of fluoride concentration (up to 58mg/kg) observed in leachates before one pore-volume of water eluted from the column. The concentration of leached fluoride consequently declined with the increased flowing pore-volume of water and <span class="hlt">finally</span> the lowest concentrations of leached fluoride occurred in the end of the experiment. Flow interruption during column leaching experiment causes a noticeable fluoride concentration perturbation due to the heterogeneity of the sediment.</p> <div class="credits"> <p class="dwt_author">Weldesenbet, S. F.; Wohnlich, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">189</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Central Main Ethiopian <span class="hlt">Rift</span> basin is a continental <span class="hlt">rift</span> <span class="hlt">system</span> characterized by volcano-tectonic depression endowed with huge geothermal resource and associated natural geochemical changes on groundwater quality. Chemical composition of groundwater in the study area showed a well defined trend along flow from the highland and escarpment to the <span class="hlt">rift</span> floor aquifer. The low TDS (< 500mg/l) Ca-Mg-HCO3 dominated water at recharge area in the highlands and escarpments evolve progressively into Ca-Na-HCO3 and Na-Ca-HCO3 type waters along the <span class="hlt">rift</span> ward groundwater flow paths. These waters <span class="hlt">finally</span> appear as moderate TDS (mean 960mg/l) Na-HCO3 type and as high TDS (> 1000 mg/l) Na-HCO3-Cl type in volcano-lacustrine aquifers of the <span class="hlt">rift</span> floor. High concentrations of fluoride (up to 97.2 mg/l) and arsenic (up to 98?g/l) are recognized feature of groundwaters which occur mostly in the vicinity of the geothermal fields and the <span class="hlt">rift</span> lakes in the basin. Fluoride and arsenic content of dry volcaniclastic sediments close to these areas are in the range 666-2586mg/kg and 10-13mg/kg respectively. The relationship between fluoride and calcium concentrations in groundwaters showed negative correlation. Near-equilibrium state attained between the mineral fluorite (CaF2) and the majority of fluoride-rich (>30mg/l) thermal groundwater and shallow cold groundwater. This indicated that the equilibrium condition control the high concentration of fluoride in the groundwaters. Whereas undersaturation state of fluorite in some relatively low-fluoride (<30mg/l) thermal waters indicated a dilution by cold waters. Laboratory batch leaching experiments showed that fast dissolution of fluoride from the sediment samples suddenly leached into the interacting water at the first one hour and then remain stable throughout the experiment. The concentrations of leached fluoride from the hot spring deposits, the lacustrine sediments, and the pyroclastic rock are usually low (1% of the total or less than the content in the sediment or rock) but strongly correlated with the concentrations in groundwaters in the local vicinity. The readily leachable hot spring deposits and local lacustrine sediments, which were leached easily as high as three fold of other sediments leachability, are considered as the reservoir for the potential fluoride contamination of the <span class="hlt">rift</span> groundwater. Leaching of fluoride in the sub-surface <span class="hlt">system</span> is simulated with sediment-packed column leached by flowing water and applying temporary interruption of flow during the experiment. The result indicated that a sharp increase of fluoride concentration (up to 58mg/kg) observed in leachates before one pore-volume of water eluted from the column. The concentration of leached fluoride consequently declined with the increased flowing pore-volume of water and <span class="hlt">finally</span> the lowest concentrations of leached fluoride occurred in the end of the experiment. Flow interruption during column leaching experiment causes a noticeable fluoride concentration perturbation due to the heterogeneity of the sediment.</p> <div class="credits"> <p class="dwt_author">Weldesenbet, S. F.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">190</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://files.eric.ed.gov/fulltext/ED026849.pdf"> <span id="translatedtitle">Inventory <span class="hlt">Systems</span> Laboratory. <span class="hlt">Final</span> Report.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p class="result-summary">Four computer programs to aid students in understanding inventory <span class="hlt">systems</span>, constructing mathematical inventory models, and developing optimal decision rules are presented. The program series allows a user to set input levels, simulates the behavior of major variables in inventory <span class="hlt">systems</span>, and provides performance measures as output. Inventory…</p> <div class="credits"> <p class="dwt_author">Naddor, Eliezer</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">191</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/5426478"> <span id="translatedtitle">Laboratory test <span class="hlt">system</span>. <span class="hlt">Final</span> report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">This project was initiated to develop a laboratory test capability for evaluating new and existing digital product designs. In recent years, Bendix Kansas City has become more active in syppling early development hardware to the design laboratories for evaluation. Because of the more complex electronic designs being used in new components, more highly automated test <span class="hlt">systems</span> are needed to evaluate development hardware. To meet this requirement, a universal test <span class="hlt">system</span> was developed to provide both basic test capabilities and flexibility to adapt easily to specific product applications. This laboratory evaluation <span class="hlt">system</span> will reduce the need to develop complex dedicated test <span class="hlt">systems</span> for each new product design, while still providing the benefits of an automated <span class="hlt">system</span>. A special purpose interface chassis was designed and fabricated to permit a standardized interface between the test <span class="hlt">system</span> and the product application. Connector assignments by <span class="hlt">system</span> functions provide convenience and function isolation. Standard cables were used to reduce the need for special purpose hardware. Electrical testing of a developmental electronics assembly demonstrated the adaptability of this <span class="hlt">system</span> for a typical product application. Both the interface hardware and the software were developed for this application.</p> <div class="credits"> <p class="dwt_author">Asher, G.L.</p> <p class="dwt_publisher"></p> <p class="publishDate">1980-03-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">192</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Erickson, R.A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-11-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">193</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.agu.org/journals/gc/gc1006/2010GC003036/2010GC003036.pdf"> <span id="translatedtitle">Melt-induced seismic anisotropy and magma assisted <span class="hlt">rifting</span> in Ethiopia: Evidence from surface waves</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The East African <span class="hlt">rift</span> in Ethiopia is unique worldwide because it captures the <span class="hlt">final</span> stages of transition from continental <span class="hlt">rifting</span> to seafloor spreading. A recent study there has shown that magma intrusion plays an important role during the <span class="hlt">final</span> stages of continental breakup, but the mechanism by which it is incorporated into the extending plate remains ambiguous: wide-angle seismic data</p> <div class="credits"> <p class="dwt_author">I. D. Bastow; S. Pilidou; J.-M. Kendall; G. W. Stuart</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">194</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://eric.ed.gov/?q=growth+AND+plate&pg=2&id=EJ394260"> <span id="translatedtitle">Volcanism at <span class="hlt">Rifts</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">White, Robert S.; McKenzie, Dan P.</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">195</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012AGUFM.T43C2694V"> <span id="translatedtitle">Rapid onset of narrowing and along-strike propagation of an intra-arc <span class="hlt">rift</span>: The Taupo <span class="hlt">Rift</span>, New Zealand</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Intra-arc active continental <span class="hlt">rifting</span> occurs within the Taupo <span class="hlt">Rift</span> in the North Island, New Zealand. Based on geological and geophysical evidence, we show that the Taupo <span class="hlt">rift</span> has narrowed via inward and eastward migration of faulting (asymmetric narrowing) and propagated southwards along its axis. This evolution has occurred at relatively high rates of ~25 km/Ma (narrowing), ~ 7 to 15 km/Ma (eastward migration), and ~ < 200 to 275 km/Ma (southward propagation; rates only for the last ~ 340 kyr). The initial onshore narrow <span class="hlt">rift</span> width is likely to be an effect of a narrow propagating <span class="hlt">rift</span> from offshore. While several process are likely to influence rapid evolution, we propose that the main control on further rapid narrowing appears to be the presence of large heterogeneities in the crust that enable concentration of deformation, such as large magma bodies of the volcanic arc of Hikurangi subduction margin. The presence of these magma bodies localises faulting. Once faulting is localised it propagates along strike from the heterogeneity into non volcanic segments of the <span class="hlt">rift</span>, which causes generalised narrowing. Temporal and spatial correlation between voluminous volcanic eruptions and major active faulting migration supports this model. Eastward migration of faulting also follows the eastward migration of the volcanic arc and is likely related to slab rollback. <span class="hlt">Finally</span>, we show that southward propagation of <span class="hlt">rifting</span> is linked to southward migration of the Hikurangi plateau and occurs episodically aided by voluminous local volcanism. The detailed recent spatial and temporal evolution of continental <span class="hlt">rifting</span> in the Taupo <span class="hlt">Rift</span> reveals the early stages of continental break-up and demonstrates fast evolution of <span class="hlt">rifting</span> when aided by large scale volcanic processes such as rhyolitic supereruptions.</p> <div class="credits"> <p class="dwt_author">Villamor, P.; Berryman, K. R.; Ellis, S. M.; Schreurs, G.; Wallace, L. M.; Leonard, G.; Langridge, R. M.; Nairn, I. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">196</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://oaspub.epa.gov/eims/eimsapi.dispdetail?deid=241528"> <span id="translatedtitle"><span class="hlt">Final</span> Barrier: Small <span class="hlt">System</span> Compliance</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://oaspub.epa.gov/eims/query.page">EPA Science Inventory</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">197</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Callender, J.F.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">198</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Lyakhovsky, Vladimir; Segev, Amit; Weinberger, Ram; Schattner, Uri</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">199</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012EGUGA..1414477E"> <span id="translatedtitle">Deformation rates and localization of an active fault <span class="hlt">system</span> in relation with rheological and frictional slip properties: The Corinth <span class="hlt">Rift</span> case</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Gulf of Corinth in Greece has attracted increasing attention because of its seismically active complex fault <span class="hlt">system</span> and considerable seismic hazard. It is one of the most active extensional regions in the Mediterranean area. However, there are still open questions concerning the role and the geometry of the numerous active faults bordering the basin, as well as the mechanisms governing the seismicity. The Corinth <span class="hlt">Rift</span> Laboratory (CRL http://crlab.eu) project is based on the cooperation of various European institutions that merge their efforts to study fault mechanics and related hazards in this natural laboratory with 10 destructive earthquakes per century (Magnitude > 6), among which 4 in the selected region of CRL. This active <span class="hlt">rift</span> continues to open over 10-12 Km of width at a rate of 1:5 cm=yr. Most of the faults of the investigated area are in their latest part of cycle, so that the probability of at least one moderate to large earthquake (Magnitude = 6 to 6:7) is very high within a few decades. In the first part of this work, two-dimensional finite element models of a fault <span class="hlt">system</span> is considered to estimate the effects of the crust rheological parameters on the stress distribution, the horizontal and vertical deformation in the vicinity of the faults, and the plastic deformation localization. We consider elasto-visco-plastic rheology with a power law viscosity for dislocation creep modelling and the Drucker-Prager yield criterion for plasticity. We investigate the rheological properties of the crust and examine their compatibility with both horizontal and vertical GPS observations recorded during campaigns conducted in the last twenty years. The second part is devoted to simulations involving rate and slip history friction laws for earthquake occurence prediction and seismogenic depth approximation. The case of a single fault is examined first, then two active faults are considered to highlight the effect of their interactions on the seismic cycle characteristics and improve our ability to predict earthquakes.</p> <div class="credits"> <p class="dwt_author">El Arem, S.; Lyon-Caen, H.; Bernard, P.; Garaud, J. D.; Rolandone, F.; Briole, P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">200</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010JGRB..115.1205T"> <span id="translatedtitle">Gas isotopic signatures (He, C, and Ar) in the Lake Kivu region (western branch of the East African <span class="hlt">rift</span> <span class="hlt">system</span>): Geodynamic and volcanological implications</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">On 17 January 2002, the city of Goma was partly destroyed by two of the several lava flows erupted from a roughly N-S oriented fracture <span class="hlt">system</span> opened along the southern flank of Mount Nyiragongo (Democratic Republic of Congo), in the western branch of the East African <span class="hlt">rift</span> <span class="hlt">system</span>. A humanitarian and scientific response was promptly organized by international, governmental, and nongovernmental agencies coordinated by the United Nations and the European Union. Among the different scientific projects undertaken to study the mechanisms triggering this and possible future eruptions, we focused on the isotopic (He, C, and Ar) analysis of the magmatic-hydrothermal and cold gas discharges related to the Nyiragongo volcanic <span class="hlt">system</span>, the Kivu and Virunga region. The studied area includes the Nyiragongo volcano, its surroundings, and peripheral areas inside and outside the <span class="hlt">rift</span>. They have been subdivided into seven regions characterized by distinct 3He/4He (expressed as R/Rair) ratios and/or ?13C-CO2 values. The Nyiragongo summit crater fumaroles, whose R/Rair and ?13C-CO2 values are up to 8.73 and from -3.5‰ to -4.0‰ VPDB, respectively, show a clear mantle, mid-ocean ridge basalt (MORB)-like contribution. Similar mantle-like He isotopic values (6.5-8.3 R/Rair) are also found in CO2-rich gas emanations (mazukus) along the northern shoreline of Lake Kivu main basin, whereas the 13?C-CO2 values range from -5.3‰ to -6.8‰ VPDB. The mantle influence progressively decreases in (1) dissolved gases of Lake Kivu (2.6-5.5 R/Rair) and (2) the distal gas discharges within and outside the two sides of the <span class="hlt">rift</span> (from 0.1 to 1.7 R/Rair). Similarly, ?13C-CO2 ratios of the peripheral gas emissions are lighter (from -5.9‰ to -11.6‰ VPDB) than those of the crater fumaroles. Therefore, the spatial distribution of He and C signatures in the Lake Kivu region is mainly produced by mixing of mantle-related (e.g., Nyiragongo crater fumaroles and/or mazukus gases) and crustal-related (e.g., gas discharges in the Archean craton) fluids. The CO2/3He ratio (up to 10 × 1010) is 1 order of magnitude higher than those found in MORB, and it is due to the increasing solubility of CO2 in the foiditic magma feeding the Nyiragongo volcano. However, the exceptionally high 40Ar*/4He ratio (up to 8.7) of the Nyiragongo crater fumaroles may be related to the difference between He and Ar solubility in the magmatic source. The results of the present investigation suggest that in this area the uprising of mantle-originated f luids seems strongly controlled by regional tectonics in relation to the geodynamic assessment of the <span class="hlt">rift</span>. These fluids are mainly localized in a relatively small zone between Lake Kivu and Nyiragongo volcano, with important implications in terms of volcanic activity.</p> <div class="credits"> <p class="dwt_author">Tedesco, D.; Tassi, F.; Vaselli, O.; Poreda, R. J.; Darrah, T.; Cuoco, E.; Yalire, M. M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_9");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">201</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010JSAES..29..306N"> <span id="translatedtitle">Detrital zircon analysis from the Neoproterozoic-Cambrian sedimentary cover (Cuyania terrane), Sierra de Pie de Palo, Argentina: Evidence of a <span class="hlt">rift</span> and passive margin <span class="hlt">system</span>?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Metamorphic basement and its Neoproterozoic to Cambrian cover exposed in the Sierra de Pie de Palo, a basement block of the Sierras Pampeanas in Argentina, lie within the Cuyania terrane. Detrital zircon analysis of the cover sequence which includes, in ascending order, the El Quemado, La Paz, El Desecho, and Angacos Formations of the Caucete Group indicate a Laurentian origin for the Cuyania terrane. The lower section represented by the El Quemado and La Paz Formations is interpreted as having an igneous source related to a <span class="hlt">rift</span> setting similar to that envisioned for the southern and eastern margins of Laurentia at approximately 550 Ma. The younger strata of the El Desecho Formation are correlative with the Cerro Totora Formation of the Precordillera, and both are products of <span class="hlt">rift</span> sedimentation. <span class="hlt">Finally</span>, the Angacos Formation and the correlative La Laja Formation of the Precordillera were deposited on the passive margin developed on the Cuyania terrane. The maximum depositional ages for the Caucete Group include ca. 550 Ma for the El Quemado Formation and ca. 531 Ma for the El Desecho Formation. Four different sediment sources areas were interpreted in the provenance analysis. The main source is crystalline basement dominated by early Mesoproterozoic igneous rocks related to the Granite-Rhyolite province of central and eastern Laurentia. Possible source areas for 1600 Ma metamorphic detrital zircons of the Caucete Group include the Yavapai-Mazatzal province ( ca. 1800-1600 Ma) of south-central to southwestern Laurentia. Younger Mesoproterozoic zircon is likely derived from Grenville-age medium- to high-grade metamorphic rocks and subordinate igneous rocks that form the basement of Cuyania as well as the southern Grenville province of Laurentia itself. <span class="hlt">Finally</span>, Neoproterozoic igneous zircon in the Caucete Group records different magmatic pulses along the southern Laurentian margin during opening of Iapetus and break-up of Rodinia. Northwestern Cuyania terrane includes a small basement component derived from the Granite-Rhyolite province of Laurentia, which was the source for detrital zircons found in the middle Cambrian passive margin sediments of Cuyania.</p> <div class="credits"> <p class="dwt_author">Naipauer, M.; Vujovich, G. I.; Cingolani, C. A.; McClelland, W. C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-03-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">202</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://pubs.er.usgs.gov/publication/70017177"> <span id="translatedtitle">Depositional and tectonic framework of the <span class="hlt">rift</span> basins of Lake Baikal from multichannel seismic data</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">Recent multichannel seismic reflection data from Lake Baikal, located in a large, active, continental <span class="hlt">rift</span> in central Asia, image three major stratigraphic units totalling 3.5 to 7.5 km thick in four subbasins. A major change in <span class="hlt">rift</span> deposition and faulting between the oldest and middle-<span class="hlt">rift</span> units probably corresponds to the change from slow to fast <span class="hlt">rifting</span>. A brief comparison of the basins of Lake Baikal with those of the East African <span class="hlt">rift</span> <span class="hlt">system</span> highlights differences in structural style that can be explained by differences in age and evolution of the surrounding basement rocks. -from Authors</p> <div class="credits"> <p class="dwt_author">Hutchinson, D. R.; Golmshtok, A. J.; Zonenshain, L. P.; Moore, T. C.; Scholz, C. A.; Klitgord, K. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">203</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1984SedG...40...51J"> <span id="translatedtitle">Formation of foreland <span class="hlt">rifts</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Lower Permian Rotliegendes troughs in Central Europe are directly comparable to the Upper Cenozoic Basin and Range province in the western United States in most tectonostratigraphic aspects. These intracratonic <span class="hlt">rifts</span> were formed by extensional tectonics in the foreland area of major Cordilleran-type orogenies beginning 20-25 Ma after mountain building. The main characteristics of the basins include: crustal thinning from 40-45 to 30 km, change from calc-alkaline magmatic arc suites to basaltic or bimodal (basalt-rhyolite) igneous suites, normal to listric block faulting, high heat flow and hydrothermal activity, regional uplift, and immature clastic and evaporite sediments rapidly deposited within the subsiding <span class="hlt">rifts</span> in a semi-desert environment. The genetic model proposed for these "foreland <span class="hlt">rifts</span>" assumes that an extensional force under the continental foreland results from mantle material being drawn back towards the subducting plate by viscous drag. This force is counteracted by a compressional force produced at the trench by subducting a young, relatively buoyant plate until subduction is ended, at which time the plate breaks off and continues to sink. Tension in the foreland, possibly produced by the sinking slab, continues for some time later, causing stretching and thinning of the continental crust, extensional tectonics and higher regional heat flow and uplift. The decrease in overburden pressure and higher heat flow induces partial melting in the lower lithosphere and bimodal volcanism. Hotter asthenosphere rising up behind the trailing edge of the sinking plate causes thermal expansion and further uplift. The heat flow anomaly rapidly decays by hydrothermal activity within 15-20 Ma after last volcanism. Block faulting and <span class="hlt">rift</span> basin infilling follow the main period of volcanism and continue until the sinking slab is decoupled from the overriding plate and no longer influences the continental foreland.</p> <div class="credits"> <p class="dwt_author">Jowett, E. Craig; Jarvis, Gary T.</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">204</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.oie.int/boutique/extrait/613-624gerdes.pdf?PHPSESSID=a43083ef616217ee1fa2c72fe2d5ae24"> <span id="translatedtitle"><span class="hlt">Rift</span> Valley fever</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Summary <span class="hlt">Rift</span> Valley fever (RVF) is an arthropod-borne viral disease of ruminants, camels and humans. It is also a significant zoonosis which may be encountered as an uncomplicated influenza-like illness, but may also present as a haemorrhagic disease with liver involvement; there may also be ocular or neurological lesions. In animals, RVF may be inapparent in non-pregnant adults, but outbreaks</p> <div class="credits"> <p class="dwt_author">G. H. Gerdes</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">205</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005AGUFM.S32B..04L"> <span id="translatedtitle">Fault-Segment Linkage during <span class="hlt">Rifting</span> in the Initial Phase of Basin Evolution: A North German Case Study</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In general, <span class="hlt">rift</span> <span class="hlt">systems</span> are characterized structurally by grabens and half-grabens. During the <span class="hlt">rifting</span> period extensional fault <span class="hlt">systems</span> commonly develop from individual segments with isolated sub-basins to zones of interacting fault <span class="hlt">systems</span>. This leads to segment linkage, accommodation zones or relay ramps, which can result in polarity changes of fault <span class="hlt">systems</span> along the <span class="hlt">rift</span> axis. We show examples from a 3-D seismic survey located in the NW German Basin, a sedimentary basin where oblique <span class="hlt">rifting</span> during the Permian produced a fracture <span class="hlt">system</span> of nearly N-S striking normal faults. We interpret these syn-sedimentary graben faults in 3-D and analyze them in terms of morphology, segment linkage and relay ramps using seismic interpretation and modelling tools. Analysis of the fault morphology indicates fault segments coalesced through breached relay structures. A prominent, helicoidally-shaped fault points to segment linkage between oppositely-dipping faults, in which a polarity change occurred along a length of only 2 to 3 km. Clarifying the spatial and temporal development of the graben faults observed in the study area in terms of lithology and reactivation of older structures will yield the input for modelling studies, and <span class="hlt">finally</span> allow the comparison with natural data sets at different scales.</p> <div class="credits"> <p class="dwt_author">Lohr, T.; Krawczyk, C. M.; Tanner, D. C.; Oncken, O.; Endres, H.; Samiee, R.; Trappe, H.; Kukla, P. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">206</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19780016081&hterms=geology+kings+canyon+national+park&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dgeology%2Bkings%2Bcanyon%2Bnational%2Bpark"> <span id="translatedtitle">Martian canyons and African <span class="hlt">rifts</span>: Structural comparisons and implications</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Frey, H. V.</p> <p class="dwt_publisher"></p> <p class="publishDate">1978-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">207</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19790043898&hterms=East+Africa&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3D%2522East%2BAfrica%2522"> <span id="translatedtitle">Martian canyons and African <span class="hlt">rifts</span> - Structural comparisons and implications</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Frey, H.</p> <p class="dwt_publisher"></p> <p class="publishDate">1979-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">208</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary"><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> <div class="credits"> <p class="dwt_author">Tran, A; Ippoliti, C; Balenghien, T; Conte, A; Gely, M; Calistri, P; Goffredo, M; Baldet, T; Chevalier, V</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-11-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">209</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005AGUSM.T43B..07A"> <span id="translatedtitle">Structural Evolution of the Incipient Okavango <span class="hlt">Rift</span> Zone, NW Botswana</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Studies of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS) and other continental <span class="hlt">rifts</span> have significantly improved our understanding of <span class="hlt">rifting</span> processes; however, we particularly lack studies of the embryonic stages of <span class="hlt">rift</span> creation. The Okavango <span class="hlt">Rift</span> Zone (ORZ), NW Botswana is one of few places worldwide where one can study the early stages of continental extension prior to the accumulation of significant amounts of sediments, volcanism, and multiphase deformation that obscure the investigation of these early time processes in more evolved continental <span class="hlt">rift</span> zones. In this study, gravity and aeromagnetic data have been used to examine the initiation and development of the nascent ORZ. The Okavango basin in NW Botswana is located at the southern tip of the southwestern branch of the EARS. The <span class="hlt">rift</span> is hosted within the Proterozoic fold and thrust belt of the Ghanzi-Chobe formation. Our objectives include (1) assessing the role of pre-existing structures on the development of <span class="hlt">rift</span> faults and basin architecture, (2) Examining fault linkage patterns and boarder fault development, and (3) determining the shallow subsurface basin geometry. Aeromagnetic data from the ORZ suggest two main structural trends: 1) northeast-southwest (030- 070o) and 2) northwest - southeast (290 - 320o). The 030- 070o structures occur within the <span class="hlt">rift</span> zone and throughout the surrounding basement. They form the main bounding fault <span class="hlt">system</span> of this incipient <span class="hlt">rift</span>. The NE - SW orientations of <span class="hlt">rift</span> faults mirror the fold axes and foliation of the basement rocks, suggesting that the basement fabric played an important role in localizing the development of faults within the stress regime present during the initiation of this <span class="hlt">rift</span>. Additionally, the greatest throw (~400- ~700 m) occurs along the Kunyere (NW dipping) and Tsau faults (SE dipping), defining a full graben as observed on gravity models. This differs from the half-graben model typical of most continental <span class="hlt">rift</span> zones. Thus, it appears the basin geometry was strongly influenced by the position of these pre-existing faults. Evidence of fault linkage is seen along some of the faults. Linked segments of faults are well defined and some are > 200 km long. We suggest from this result that fault linkage and propagation occurred very early and prior to significant basin development. We conclude that basement fabric seems to be a controlling factor at least in the early stages of basin architecture and structural evolution of ORZ.</p> <div class="credits"> <p class="dwt_author">Atekwana, E. A.; Kinabo, B. D.; Modisi, M. P.; Hogan, J. P.; Wheaton, D. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">210</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=N20050176001"> <span id="translatedtitle">Parga Chasma: Coronae and <span class="hlt">Rifting</span> on Venus.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">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. However, the relationship between coronae and <span class="hlt">rifts</span> remains unclear. There is evidence that coronae can form...</p> <div class="credits"> <p class="dwt_author">S. E. Smrekar E. R. Stofan W. R. Buck P. Martin</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">211</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008AGUFM.T32B..04G"> <span id="translatedtitle">The Main Ethiopian <span class="hlt">Rift</span>: a Narrow <span class="hlt">Rift</span> in a Hot Craton?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Main Ethiopian <span class="hlt">Rift</span> (MER) is a classic example of a narrow <span class="hlt">rift</span>, but a synthesis of our results from the EAGLE (Ethiopia-Afar Geoscientific Lithospheric Experiment Phase I broadband experiment) and from the EBSE experiment (Ethiopia Broadband Seismic Experiment) suggests the MER formed in thin, hot, weak continental lithosphere, in strong contrast with predictions of the Buck model of modes of continental lithospheric extension. Our joint inversion of receiver functions and Rayleigh-wave group velocities yields shear-wave velocities of the lowermost crust and uppermost mantle across the MER and the Ethiopian Plateau that are significantly lower than the equivalent velocities in the Eastern and Western branches of the East African <span class="hlt">Rift</span> <span class="hlt">System</span>. The very low shear-wave velocities, high electrical conductivity in the lower-crust, and high shear-wave splitting delay times beneath a very broad region of the MER and the Ethiopian Plateau indicate that the lower-crust is hot and likely contains partial melt. Our S-receiver function data demonstrate shallowing of the lithosphere-asthenosphere boundary from 90 km beneath the northwestern Ethiopian Plateau to 60 km beneath the MER. Although we lack good spatial resolution on the lithosphere-asthenosphere boundary, the region of thinned lithosphere may be intermediate in width between the narrow surface <span class="hlt">rift</span> (< 100 km) and the broader zone of strain in the lower crust (~ 300 km). The MER developed as a narrow <span class="hlt">rift</span> at the surface, localized along the Neoproterozoic suture that joined East and West Gondwana. However, a far broader of lower crust and uppermost mantle remains thermally weakened since the Oligocene formation of the flood basalts by the Afar plume head. If the lithosphere- asthenosphere boundary is indeed a strain marker then lithospheric mantle deformation is localized beneath the surface <span class="hlt">rift</span>. The development of both the Eastern/Western branches of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> to the south and of the MER in the north as narrow <span class="hlt">rifts</span>, despite vastly different lithospheric strength profiles, indicates that inherited structure, rather than rheological stratification, is the primary control on the mode of extension in these continental <span class="hlt">rifts</span>.</p> <div class="credits"> <p class="dwt_author">Gashawbeza, E.; Keranen, K.; Klemperer, S.; Lawrence, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">212</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014Tecto..33..485P"> <span id="translatedtitle">Evolution, distribution, and characteristics of <span class="hlt">rifting</span> in southern Ethiopia</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Ethiopia is a key region to understand the evolution of the East African <span class="hlt">rift</span> <span class="hlt">system</span>, since it is the area of interaction between the main Ethiopian <span class="hlt">rift</span> (MER) and the Kenyan <span class="hlt">rift</span>. However, geological data constraining <span class="hlt">rift</span> evolution in this remote area are still relatively sparse. In this study the timing, distribution, and style of <span class="hlt">rifting</span> in southern Ethiopia are constrained by new structural, geochronological, and geomorphological data. The border faults in the area are roughly parallel to preexisting basement fabrics and are progressively more oblique with respect to the regional Nubia-Somalia motion proceeding southward. Kinematic indicators along these faults are mainly dip slip, pointing to a progressive rotation of the computed direction of extension toward the south. Radiocarbon data indicate post 30 ka faulting at both western and eastern margins of the MER with limited axial deformation. Similarly, geomorphological data suggest recent fault activity along the western margins of the basins composing the Gofa Province and in the Chew Bahir basin. This supports that interaction between the MER and the Kenyan <span class="hlt">rift</span> in southern Ethiopia occurs in a 200 km wide zone of ongoing deformation. Fault-related exhumation at ~10-12 Ma in the Gofa Province, as constrained by new apatite fission track data, occurred later than the ~20 Ma basement exhumation of the Chew Bahir basin, thus pointing to a northward propagation of the Kenyan <span class="hlt">rift</span>-related extension in the area.</p> <div class="credits"> <p class="dwt_author">Philippon, Melody; Corti, Giacomo; Sani, Federico; Bonini, Marco; Balestrieri, Maria-Laura; Molin, Paola; Willingshofer, Ernst; Sokoutis, Dimitrios; Cloetingh, Sierd</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">213</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=ADA225496"> <span id="translatedtitle">Studies of Infection and Dissemination of <span class="hlt">Rift</span> Valley Fever Virus in Mosquitoes (<span class="hlt">Final</span> Report 14 May 86-14 May 89, Annual Report 15 May 88-14 May 89).</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">We have been engaged in a multimethod study of <span class="hlt">Rift</span> Valley fever (RVF) virus in mosquitoes. During this year, we have carried out: (1) immunocytochemical and ultrastructural studies of the proventriculus of adult, female Culex pipiens infected with RVF vi...</p> <div class="credits"> <p class="dwt_author">W. S. Romoser</p> <p class="dwt_publisher"></p> <p class="publishDate">1990-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">214</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/41975402"> <span id="translatedtitle"><span class="hlt">Rifting</span> of old oceanic lithosphere</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Geophysical data from five regions in the Pacific and Indian oceans reveal that long distance (>400 km) spreading center jumps have occurred in the past. The present-day seafloor morphology is used to develop a scenario for a spreading center jump. The major events are (1) thinning and weakening of the lithosphere at the future <span class="hlt">rifting</span> site, (2) <span class="hlt">rifting</span> of the</p> <div class="credits"> <p class="dwt_author">J. Mammerickx; D. Sandwell</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">215</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Masterton, S.; Fairhead, J. D.; Green, C. M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">216</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Lyakhovsky, V.; Segev, A.; Schattner, U.; Weinberger, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">217</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Walter, Bastien; Géraud, Yves; Diraison, Marc</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">218</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://dx.doi.org/10.1029/2008GC002293"> <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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">[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> <div class="credits"> <p class="dwt_author">Keranen, K. M.; Klemperer, S. L.; Julia, J.; Lawrence, J. F.; Nyblade, A. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">219</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009GGG....10.AB01K"> <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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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.</p> <div class="credits"> <p class="dwt_author">Keranen, Katie M.; Klemperer, Simon L.; Julia, Jordi; Lawrence, Jesse F.; Nyblade, Andy A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">220</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=STS006-40-723&hterms=East+Africa&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3D%2522East%2BAfrica%2522"> <span id="translatedtitle">TDRS satellite over African <span class="hlt">Rift</span> Valley, Kenya, Africa</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">1983-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_10");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return 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class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_11");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return 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title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">221</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2003AGUFM.S51F..07K"> <span id="translatedtitle">Melt migration and mantle anisotropy beneath the Ethiopian <span class="hlt">rift</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The EAGLE broadband experiment aims to study the crust and upper-mantle structure in the northern Ethiopian <span class="hlt">rift</span>, a region of transition from continental to oceanic <span class="hlt">rifting</span>. 30 broadband seismometers have been deployed for a period of 16 months over an area of 250 km2, centered on the Nazret volcanic zone. These stations are complimented by data from a 3-month deployment of 50 instruments concentrated in the <span class="hlt">rift</span> valley. We present analysis of upper-mantle anisotropy from measurements of shear-wave splitting in SKS, SKKS and PKS phases. The concentrated station coverage and nearly 500 splitting measurements provide a detailed picture of mantle anisotropy in a <span class="hlt">rifting</span> environment. In general the results are of high quality with low error estimates. The highest splitting (> 2 secs) occurs on the <span class="hlt">rift</span> flanks, where the strain partitioning is expected to be highest. There is an asymmetry in results from either side of the <span class="hlt">rift</span> (i.e., the Ethiopia plateau vs. the Somalian plate). Within the <span class="hlt">Rift</span> there is a consistent increase in delay times towards the north and Afar, from 1.0 secs in the south to 1.6 secs in the north. Outside the <span class="hlt">Rift</span>, the polarisations of the fast shear-wave lie in a NE--SW <span class="hlt">rift</span>--parallel trend and do not align with the direction of absolute plate motion. Within the <span class="hlt">Rift</span> the orientations swing to more northerly azimuths, following magmatic segments and faulting patterns. The increase in <span class="hlt">rift</span> splitting times northwards correlates with the amount of magma within the <span class="hlt">system</span>. Large variations in magnitude of splitting or orientation of the shear-wave over short distances suggests that the source of the anisotropy is quite shallow (<100 km). Cumulatively, these results suggest that the anisotropy is associated with melt migration beneath the <span class="hlt">rift</span>. To explain these results we appeal to recent deformation experiments of Holtzman et al. (2003) which show anisotropy in partially molten rocks being due to a combination of preferred melt inclusion alignment, layering and olivine crystal alignment.</p> <div class="credits"> <p class="dwt_author">Kendall, J.; Stuart, G.; Bastow, I.; Ebinger, C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">222</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1995JSG....17.1559C"> <span id="translatedtitle">Interference pattern of extensional fault <span class="hlt">systems</span>: a case study of the Miocene <span class="hlt">rifting</span> of the Alboran basement (North of Sierra Nevada, Betic Chain)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In the Betic-Rif orogenic belt, in the westernmost part of the Mediterranean, early and middle Miocene crustal thinning of the upper part of the Alboran basement is well established by previous studies. In the Alboran domain of the central Betics, the present distribution of the Alpujarride units results from the extensional dismembering of a pre-Miocene nappe stack under brittle conditions. The interference of two subperpendicular and successive extensional fault <span class="hlt">systems</span> can explain the current geometric pattern of the Alpujarride units: upper-Burdigalian-Langhian north-south extension was followed by west- to southwestward extension of Serravallian age. Northeast of Sierra Nevada, these two extensional <span class="hlt">systems</span> have resulted in a spectacular chocolate tablet megastructure and the cropping out, at any one vertical sequence, of a varying number of extensional units belonging to the Alpujarride complex. This pattern can be considered representative of the middle Miocene tectonics of the entire Alboran domain in the Betics, and illustrates the development of <span class="hlt">rifting</span> processes in the upper crust.</p> <div class="credits"> <p class="dwt_author">Crespo-Blanc, Ana</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-11-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">223</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19900012177&hterms=age+range&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dage%2Brange"> <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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Larsen, Shawn; Reilinger, Robert</p> <p class="dwt_publisher"></p> <p class="publishDate">1990-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">224</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010Tecto..29.5010G"> <span id="translatedtitle">Neoproterozoic <span class="hlt">rifting</span> in the southern Georgina Basin, central Australia: Implications for reconstructing Australia in Rodinia</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A <span class="hlt">system</span> of northwest striking Neoproterozoic <span class="hlt">rift</span> basins underlies Paleozoic strata in the southern Georgina Basin of central Australia. Normal faults bounding these <span class="hlt">rift</span> basins were selectively reactivated during the mid-Paleozoic Alice Springs Orogeny and are now expressed as high-angle reverse faults that invert the preexisting <span class="hlt">rift</span> basins. Exhumed and eroded <span class="hlt">rift</span> basin remnants are present in the hanging wall of the Oomoolmilla, Lucy Creek, Tarlton, and Toomba reverse faults, and <span class="hlt">rift</span> basins may be preserved in the subsurface beneath the Toko Syncline and Burke River Structural Belt. <span class="hlt">Rift</span> basin fill indicates two periods of extension: a major <span class="hlt">rift</span>-forming episode between approximately 700 and 650 Ma (coeval with Sturtian glacial deposits) and a second episode of extension at approximately 600 Ma (coeval with Marinoan glacial deposits). This northwest striking <span class="hlt">rift</span> <span class="hlt">system</span> in central Australia supports results from other regions, indicating that the Neoproterozoic continental margin of Australia consisted of northwest striking <span class="hlt">rift</span> segments offset by northeast striking transform faults. Such a configuration is geometrically incompatible with a Laurentian continental margin consisting of northeast striking <span class="hlt">rift</span> segments and conflicts with reconstructions such as SWEAT and AUSWUS that match Australia with western Laurentia in the Rodinia supercontinent.</p> <div class="credits"> <p class="dwt_author">Greene, David C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">225</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The isotope geochemistry of pedogenic carbonate and fossil herbivore enamel is a powerful tool to reconstruct paleoenvironmental conditions in particular when climate change plays a key role in the evolution of ecosystems. Here, we present the first Plio-Pleistocene long-term carbon (?13C), oxygen (?18O) and clumped isotope (?47) records from pedogenic carbonate and herbivore teeth in the Malawi <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 ?13C data from fossil enamel of different suid, bovid, and equid species and contrast these with ?13C and ?18O values of pedogenic carbonate. We complement the latter with clumped isotope soil temperature data. Results of almost 800 pedogenic carbonate samples from over 20 sections consistently average ?13C = -8.5 ‰ over the past 5 Ma with no significant short-term ?13C excursions or long-term trends. The data from molar tooth enamel of nine individual suids of the genera Metridiochoerus, Notochoerus and Nyanzachoerus support these findings with average ?13C = -10.0 ‰. The absence of long-term trends towards more positive ?13C values contrasts the increasing role of C4-grasslands in the southern EARS which is well documented for sites in Ethiopia, Kenya and Tanzania. Our data hence point to regional differences in climate and vegetation dynamics during the Plio-Pleistocene in the EARS and documents persistence of paleoenvironmental conditions in the southern branch of the EARS at times of early hominid evolution.</p> <div class="credits"> <p class="dwt_author">Lüdecke, Tina; Thiemeyer, Heinrich; Schrenk, Friedemann; Mulch, Andreas</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">226</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40492940"> <span id="translatedtitle">Molten core model for Hawaiian <span class="hlt">rift</span> zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Kilauea volcano's East <span class="hlt">Rift</span> Zone (ERZ) is extraordinary in that abundant lateral dike intrusions and <span class="hlt">rift</span> zone widening associated with seaward slip of the south flank over a basal fault may have allowed an extensive molten core to develop. The <span class="hlt">rift</span> zones of Mauna Loa and the Southwest <span class="hlt">Rift</span> Zone (SWRZ) of Kilauea do not appear to have such extensive</p> <div class="credits"> <p class="dwt_author">Daniel J. Johnson</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">227</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://pubs.er.usgs.gov/publication/70024528"> <span id="translatedtitle">Crustal structure of central Lake Baikal: Insights into intracontinental <span class="hlt">rifting</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">The Cenozoic <span class="hlt">rift</span> <span class="hlt">system</span> of Baikal, located in the interior of the largest continental mass on Earth, is thought to represent a potential analog of the early stage of breakup of supercontinents. We present a detailed P wave velocity structure of the crust and sediments beneath the Central Basin, the deepest basin in the Baikal <span class="hlt">rift</span> <span class="hlt">system</span>. The structure is characterized by a Moho depth of 39-42.5 km; an 8-km-thick, laterally continuous high-velocity (7.05-7.4 km/s) lower crust, normal upper mantle velocity (8 km/s), a sedimentary section reaching maximum depths of 9 km, and a gradual increase of sediment velocity with depth. We interpret the high-velocity lower crust to be part of the Siberian Platform that was not thinned or altered significantly during <span class="hlt">rifting</span>. In comparison to published results from the Siberian Platform, Moho under the basin is elevated by <3 km. On the basis of these results we propose that the basin was formed by upper crustal extension, possibly reactivating structures in an ancient fold-and-thrust belt. The extent and location of upper mantle extension are not revealed by our data, and it may be offset from the <span class="hlt">rift</span>. We believe that the Baikal <span class="hlt">rift</span> structure is similar in many respects to the Mesozoic Atlantic <span class="hlt">rift</span> <span class="hlt">system</span>, the precursor to the formation of the North Atlantic Ocean. We also propose that the Central Baikal <span class="hlt">rift</span> evolved by episodic fault propagation and basin enlargement, rather than by two-stage <span class="hlt">rift</span> evolution as is commonly assumed.</p> <div class="credits"> <p class="dwt_author">ten, Brink, U. S.; Taylor, M. H.</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">228</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary"><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> <div class="credits"> <p class="dwt_author">Tchouassi, David P; Sang, Rosemary; Sole, Catherine L; Bastos, Armanda D S; Teal, Peter E A; Borgemeister, Christian; Torto, Baldwyn</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">229</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary"><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.</p> <div class="credits"> <p class="dwt_author">Tchouassi, David P.; Sang, Rosemary; Sole, Catherine L.; Bastos, Armanda D. S.; Teal, Peter E. A.; Borgemeister, Christian; Torto, Baldwyn</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">230</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Cameselle, Alejandra L.; Ranero, César R.; Franke, Dieter; Barckhausen, Udo</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">231</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Krassilnikov, A. S.; Kostama, V.-P.; Aittola, M.; Guseva, E. N.; Cherkashina, O. S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">232</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AGUFM.T12B..02K"> <span id="translatedtitle">Contribution of Transverse Structures, Magma, and Crustal Fluids to Continental <span class="hlt">Rift</span> Evolution: The East African <span class="hlt">Rift</span> in Southern Kenya</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Magadi <span class="hlt">rift</span> in southern Kenya formed at ~7 Ma within Proterozoic rocks of the Mozambique orogenic belt, parallel to its contact with the Archean Tanzania craton. The <span class="hlt">rift</span> is bounded to the west by the ~1600-m-high Nguruman border fault. The <span class="hlt">rift</span> center is intensely dissected by normal faults, most of which offset ~1.4-0.8 Ma lavas. Current E-W extensional velocities are ~2-4 mm/yr. Published crustal tomography models from the <span class="hlt">rift</span> center show narrow high velocity zones in the upper crust, interpreted as cooled magma intrusions. Local, surface-wave, and SKS-splitting measurements show a <span class="hlt">rift</span>-parallel anisotropy interpreted to be the result of aligned melt zones in the lithosphere. Our field observations suggest that recent fault activity is concentrated at the <span class="hlt">rift</span> center, consistent with the location of the 1998 seismic swarm that was associated with an inferred diking event. Fault zones are pervasively mineralized by calcite, likely from CO2-rich fluids. A <span class="hlt">system</span> of fault-fed springs provides the sole fluid input for Lake Magadi in the deepest part of the basin. Many of these springs emanate from the Kordjya fault, a 50-km-long, NW-SE striking, transverse structure connecting a portion of the border fault <span class="hlt">system</span> (the NW-oriented Lengitoto fault) to the current locus of strain and magmatism at the <span class="hlt">rift</span> center. Sampled springs are warm (44.4°C) and alkaline (pH=10). Dissolved gas data (mainly N2-Ar-He) suggests two-component mixing (mantle and air), possibly indicating that fluids are delivered into the fault zone from deep sources, consistent with a dominant role of magmatism to the focusing of strain at the <span class="hlt">rift</span> center. The Kordjya fault has developed prominent fault scarps (~150 m high) despite being oblique to the dominant ~N-S fault fabric, and has utilized an en echelon alignment of N-S faults to accommodate its motion. These N-S faults show evidence of sinistral-oblique motion and imply a bookshelf style of faulting to accommodate dextral-oblique motion along the Kordjya fault. Fault relationships imply that the NW-SE transverse structures represent recent activity in the <span class="hlt">rift</span>, and have locally tilted Late Pleistocene sediments. Given the abundance of N-S striking faults in the <span class="hlt">rift</span>, the tendency for fault activity along transverse features suggests a change in the <span class="hlt">rifting</span> driving forces that are likely the result of an interplay between strain localization at the <span class="hlt">rift</span> center, inherited crustal fabric (NW structures in the Mozambique belt), a possible counterclockwise rotation of stress related to interacting <span class="hlt">rift</span> segments in southern Kenya, and an active hydrothermal fluid regime that facilitates faulting. By connecting the Lengitoto fault to the <span class="hlt">rift</span> center, the Kordjya fault has effectively caused the Magadi <span class="hlt">rift</span> to bypass the Nguruman border fault, which has been rendered inactive and thus no longer a contributor to the <span class="hlt">rifting</span> process.</p> <div class="credits"> <p class="dwt_author">Kattenhorn, S. A.; Muirhead, J.; Dindi, E.; Fischer, T. P.; Lee, H.; Ebinger, C. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">233</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007JAfES..48..147F"> <span id="translatedtitle">Geochemistry of East African <span class="hlt">Rift</span> basalts: An overview</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Mafic lavas erupted along the East African <span class="hlt">Rift</span> <span class="hlt">System</span> from the Afar triangle in northern Ethiopia to the Rungwe province in southern Tanzania display a wide range of geochemical and isotopic compositions that reflect heterogeneity in both source and process. In areas with the lowest degree of crustal extension (the Western and Southern Kenya <span class="hlt">Rifts</span>) primitive lavas record the greatest extent of lithospheric melting, manifest in elevated abundances of incompatible elements and highly radiogenic Sr-Nd-Pb isotopic compositions. Where prolonged extension has removed most or all of the mantle lithosphere (the Turkana and Northern Kenya <span class="hlt">Rifts</span>), a larger role for sub-lithospheric processes is indicated. At intermediate degrees of extension (the Main Ethiopian <span class="hlt">Rift</span>) both lithospheric and sub-lithospheric contributions are observed, and crustal assimilation occurs in some cases. Despite the wide compositional range of African <span class="hlt">Rift</span> basalts, a restricted number of source domains contribute to magmatism throughout the area. These individual domains are: (1) the subcontinental mantle lithosphere; (2) a plume source with high-? Sr-Nd-Pb-He isotopic affinities, present in all areas within and south of the Turkana Depression; and (3) a plume source with isotopic signatures analogous to those observed in some ocean islands, including high 3He/ 4He values, present throughout the Ethiopian <span class="hlt">Rift</span> and the Afar region. The two plume sources may both be derived from the South African Superplume, which is likely to be a compositionally heterogeneous feature of the lower mantle.</p> <div class="credits"> <p class="dwt_author">Furman, Tanya</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">234</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://globalchange.umich.edu/ben/publications/06_ijes_schleicher.pdf"> <span id="translatedtitle">Fluid focusing and back-reactions in the uplifted shoulder of the Rhine <span class="hlt">rift</span> <span class="hlt">system</span>: a clay mineral study along the Schauenburg Fault zone (Heidelberg, Germany)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A retrograde sequence of fluid-controlled, low-temperature mineral reactions has been preserved along an east-west striking,\\u000a dextral-oblique-slip fault in the uplifted Rhine Graben shoulder. This fault (the Schauenburg Fault, near Heidelberg), juxtaposes\\u000a Permian rhyolite against Carboniferous (Variscan) granite and shows syn- or post-<span class="hlt">rift</span> displacement of the north–south trending,\\u000a eastern boundary fault of the <span class="hlt">rift</span> basin. Both mineral texture and rock fabric</p> <div class="credits"> <p class="dwt_author">A. M. Schleicher; L. N. Warr; B. A. van der Pluijm</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">235</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/24066364"> <span id="translatedtitle">Unique device identification <span class="hlt">system</span>. <span class="hlt">Final</span> rule.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">The Food and Drug Administration (FDA) is issuing a <span class="hlt">final</span> rule to establish a <span class="hlt">system</span> to adequately identify devices through distribution and use. This rule requires the label of medical devices to include a unique device identifier (UDI), except where the rule provides for an exception or alternative placement. The labeler must submit product information concerning devices to FDA's Global Unique Device Identification Database (GUDID), unless subject to an exception or alternative. The <span class="hlt">system</span> established by this rule requires the label and device package of each medical device to include a UDI and requires that each UDI be provided in a plain-text version and in a form that uses automatic identification and data capture (AIDC) technology. The UDI will be required to be directly marked on the device itself if the device is intended to be used more than once and intended to be reprocessed before each use. PMID:24066364</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">2013-09-24</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">236</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6637448"> <span id="translatedtitle">Cooperating knowledge-based <span class="hlt">systems</span>. <span class="hlt">Final</span> report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">This <span class="hlt">final</span> report covers work performed under Contract NCC2-220 between NASA Ames Research Center and the Knowledge <span class="hlt">Systems</span> Laboratory, Stanford University. The period of research was from March 1, 1987 to February 29, 1988. Topics covered were as follows: (1) concurrent architectures for knowledge-based <span class="hlt">systems</span>; (2) methods for the solution of geometric constraint satisfaction problems, and (3) reasoning under uncertainty. The research in concurrent architectures was co-funded by DARPA, as part of that agency's Strategic Computing Program. The research has been in progress since 1985, under DARPA and NASA sponsorship. The research in geometric constraint satisfaction has been done in the context of a particular application, that of determining the 3-D structure of complex protein molecules, using the constraints inferred from NMR measurements.</p> <div class="credits"> <p class="dwt_author">Feigenbaum, E.A.; Buchanan, B.G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1988-08-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">237</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2006AGUFM.T53A1574T"> <span id="translatedtitle">Crustal Structure of the Ethiopian <span class="hlt">Rift</span> and Adjacent Plateaus: Results of new integrated interpretation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Ethiopian <span class="hlt">rift</span> is the large part of the East African <span class="hlt">Rift</span> <span class="hlt">system</span>, which represents an incipient divergent plate boundary. This important structure provides excellent opportunities to study the transition from continental to oceanic. As a result, geophysical data are becoming increasingly available but some results are contradictory. We used a newly enhanced gravity database and seismic information to produce an integrated interpretation of the crustal structure beneath the Ethiopian <span class="hlt">rift</span> and the adjacent plateaus. Wide regions have been covered to assess the regional structures including the Kenyan and Ethiopian <span class="hlt">rifts</span> and the area covered by the Ethiopian flood basalt. Broad negative Bouguer gravity anomalies are delineated over the Ethiopian Plateaus and the Kenyan dome. Residual gravity anomalies, which parallel the major border faults clearly highlight the segregation between the plateaus and the <span class="hlt">rift</span> valleys. Results of other filtering techniques have clearly revealed individual volcanic centers within the <span class="hlt">rift</span> valleys. Positive gravity anomalies outside the <span class="hlt">rift</span> valleys may be associated with older structures, shield volcanoes, or structures that are related to the initiation and propagation of <span class="hlt">rifting</span>. A long axial profile from the central part of Kenya to the Afar triple junction has been modeled to investigate along-axis crustal variation of the East African <span class="hlt">rift</span> <span class="hlt">system</span>, with emphasis on the Ethiopian <span class="hlt">rift</span>. This modeling has been constrained using seismic refraction data from the Ethiopian Afar Geoscientific Lithospheric Experiment (EAGLE) and Kenya <span class="hlt">Rift</span> International Seismic Project (KRISP) results. We are able to see a thin crust (~26 km) in the Afar triangle with a gradual thickening (~40 km) southwards towards the Main Central Ethiopian <span class="hlt">rift</span> (MER). The crust thickness decreases towards Turkana <span class="hlt">rift</span> (~22 km), and increases again towards the central eastern <span class="hlt">rift</span> section in Kenya. Our profile model across the MER has revealed that the eastern <span class="hlt">rift</span> flank has thicker crust than the western <span class="hlt">rift</span> flank near the MER. The cross profile modeled across the southern part of the Afar triple junction shows a shallow Moho. This may be the result of the <span class="hlt">rift</span> being initiated by a plume as suggested elsewhere in many studies.</p> <div class="credits"> <p class="dwt_author">Tadesse, K.; Keller, G. R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">238</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><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> <div class="credits"> <p class="dwt_author">Mohn, Geoffroy; Karner, Garry; Manatschal, Gianreto; Johnson, Christopher</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">239</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Dalati, Moutaz</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">240</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/39726129"> <span id="translatedtitle">Toarcian–Kimmeridgian depositional cycles of the south-western Morondava Basin along the <span class="hlt">rifted</span> continental margin of Madagascar</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">After <span class="hlt">rifting</span> and <span class="hlt">final</span> breakup of Gondwana along the former East-African-Antarctic Orogen during the Toarcian–Aalenian, passive\\u000a margins formed around the Proto-Indian Ocean. Sedimentological and stratigraphic studies in the southern Morondava Basin contribute\\u000a to an improved reconstruction of palaeoenvironmental changes during the syn-<span class="hlt">rift</span> and post-<span class="hlt">rift</span> margin formation. Depositional\\u000a models based on outcrop and literature data in combination with subsurface data sets</p> <div class="credits"> <p class="dwt_author">Markus Geiger; Günter Schweigert</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_11");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return 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showDiv("page_14");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">241</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20140000469&hterms=final&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dfinal"> <span id="translatedtitle"><span class="hlt">Final</span> Report - Regulatory Considerations for Adaptive <span class="hlt">Systems</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Wilkinson, Chris; Lynch, Jonathan; Bharadwaj, Raj</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">242</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012JGRB..117.8402B"> <span id="translatedtitle">Modeling suggests that oblique extension facilitates <span class="hlt">rifting</span> and continental break-up</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In many cases the initial stage of continental break-up was and is associated with oblique <span class="hlt">rifting</span>. That includes break-up in the Southern and Equatorial Atlantic, separation from eastern and western Gondwana as well as many recent <span class="hlt">rift</span> <span class="hlt">systems</span>, like Gulf of California, Ethiopia <span class="hlt">Rift</span> and Dead Sea fault. Using a simple analytic mechanical model and advanced numerical, thermomechanical modeling techniques we investigate the influence of oblique extension on the required tectonic force in a three-dimensional setting. While magmatic processes have been already suggested to affect <span class="hlt">rift</span> evolution, we show that additional mechanisms emerge due to the three-dimensionality of an extensional <span class="hlt">system</span>. Focusing on non-magmatic <span class="hlt">rift</span> settings, we find that oblique extension significantly facilitates the <span class="hlt">rift</span> process. This is due to the fact that oblique deformation requires less force in order to reach the plastic yield limit than <span class="hlt">rift</span>-perpendicular extension. The model shows that in the case of two competing non-magmatic <span class="hlt">rifts</span>, with one perpendicular and one oblique to the direction of extension but otherwise having identical properties, the oblique <span class="hlt">rift</span> zone is mechanically preferred and thus attracts more strain.</p> <div class="credits"> <p class="dwt_author">Brune, Sascha; Popov, Anton A.; Sobolev, Stephan V.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">243</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary"><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> <div class="credits"> <p class="dwt_author">Kakani, Sravan; LaBeaud, A Desirée; King, Charles H</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">244</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/21295425"> <span id="translatedtitle">[<span class="hlt">Rift</span> Valley fever].</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary"><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> <div class="credits"> <p class="dwt_author">Pépin, M</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">245</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20140006387&hterms=NASA&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DNASA"> <span id="translatedtitle">Multi-Point Combustion <span class="hlt">System</span>: <span class="hlt">Final</span> Report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Goeke, Jerry; Pack, Spencer; Zink, Gregory; Ryon, Jason</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">246</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5168137"> <span id="translatedtitle"><span class="hlt">Rift</span> basins of ocean-continent convergent margins</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Modern and ancient circum-Pacific convergent margins contain many examples of forearc basins where subsidence, occurring simultaneously with subduction of oceanic lithosphere, is controlled by <span class="hlt">rifting</span> transverse to the margin. The elongate axes of these deep and narrow basins jut obliquely from the plate margin into the interior of the forearc. Similar to aulacogens, faulting and related subsidence appear greatest at their seaward limits and decreases inland. Examples from eastern Pacific forearcs suggest that localized <span class="hlt">rifting</span> accommodates margin-parallel extension of forearc blocks that are kinetically linked to motions along major margin-parallel strike-slip fault <span class="hlt">systems</span>. The most prominent examples of modern forearc <span class="hlt">rift</span> basins are the Sanak and East Sanak basins of the western Alaska Peninsula subduction zone. In this region, the continental shelf is being <span class="hlt">rifted</span> apart by a series of northwest- and northeast-trending faults. Basement-activated normal faults bounding the basins have listric geometries. Seismostratigraphic relationships within the basins indicate the protracted, synsedimentary, and active nature of faulting and basin subsidence. Along the Peru-Chile trench, two prominent <span class="hlt">rifted</span> basins also occur: the Gulf of Guayaquil and the Gulf of Penas-Taitao basin of southern Chile. There, margin-parallel <span class="hlt">rifting</span> controls subsidence in localized basins at the southern terminus to margin-parallel dextral fault <span class="hlt">systems</span>. These and other examples suggest that strike-slip motion and transverse <span class="hlt">rifting</span> of forearcs is a common phenomenon inadequately described by existing two-dimensional models of forearcs. Margin-parallel motions of forearc blocks can be related not only to oblique plate convergence, but also to the geometric and compositional nature of the overriding and subducted plates.</p> <div class="credits"> <p class="dwt_author">Forsythe, R.D.; Newcomb, K.R.</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">247</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5349259"> <span id="translatedtitle"><span class="hlt">Final</span> design development of silicone southwall glazing <span class="hlt">system</span>. <span class="hlt">Final</span> report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">This cooperative solar project was undertaken to design, fabricate and test a southwall glazing <span class="hlt">system</span> based on a flexible silicone glazing. In addition, preliminary cost, performance and market development guidelines were established. A specific silicone glazing was selected and was shown to have a solar transmission of 88%, tensile strength of greater than 50 Newtons/cm, estimated durability greater than 20 years, and to meet an industry standard flame test. A unique and simple film tensioning device was developed by the Architects Taos under contract to maintain the flexible glazing in a taunt condition over its long life without wind flutter and resulting potential damage. The selected silicone glazing was evaluated by using two southwall glazing <span class="hlt">systems</span>: on passive test chambers and on a concrete block wall of a Dow Corning warehouse building. The evaluation was conducted at Dow Corning Midland, Michigan facilities (43.4/sup 0/N latitude) from April 1981 to March 1982. The data obtained showed that the silicone southwall glazing <span class="hlt">system</span> using a selective adsorber on a vented concrete block wall provided over 750 MJ/m/sup 2/ of thermal energy during a winter heating <span class="hlt">system</span>. One experiment demonstrated the performance and ease of installation of the tensioning device developed by this project. Preliminary cost estimates indicate the southwall glazing <span class="hlt">system</span> with a selective adsorber could be installed for about $55/m/sup 2/ ($5/ft/sup 2/); with a flat black (non-selective adsorber) the installed cost is estimated to be about $40//m/sup 2/ ($4/ft/sup 2/). Prorated over a minimum ten year life, with a capital recovery factor of 0.20, this <span class="hlt">system</span> would be cost competitive for fuel displacement with $8.00/GJ ($8.44/M Btu) heating energy when vertical wall insolation exceeds 2.5 GJ/m/sup 2/ (0.22 x 10/sup 6/ Btu/ft/sup 2/) for a heating season.</p> <div class="credits"> <p class="dwt_author">Vanwert, B.; Currin, C.; Mingenbach, W.</p> <p class="dwt_publisher"></p> <p class="publishDate">1983-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">248</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1986E%26PSL..77..176M"> <span id="translatedtitle">The geometry of propagating <span class="hlt">rifts</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">McKenzie, Dan</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">249</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Florendo, Federico F.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">250</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012AGUFM.T51H..06F"> <span id="translatedtitle">The MOZART Project - MOZAmbique <span class="hlt">Rift</span> Tomography</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">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 class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">251</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUFM.T23F..05M"> <span id="translatedtitle">How Magmatic are Magma-Poor <span class="hlt">Rifted</span> Margins?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The results of the Ocean Drilling Program (ODP) together with seismic reflection and refraction surveys from the West Iberia and East Greenland <span class="hlt">rifted</span> margins show a divergent style of margin architecture and evolution in which quantity and distribution of syn-<span class="hlt">rift</span> magmatism and fault structures are the most variable features. These observations led to an oversimplified classification of <span class="hlt">rifted</span> margins as either volcanic or non-volcanic. Although this simple concept may lead to the idea that margins evolve either under the presence or absence of magma, the available results show that so called “non-volcanic” margins are not necessarily amagmatic. This leads to the question about nature and timing of magmatic processes in “non”-volcanic or magma-poor <span class="hlt">rifted</span> margins and their role in controlling the rheology, thermal structure and isostatic evolution of these margins during <span class="hlt">final</span> <span class="hlt">rifting</span> and continental breakup. In our presentation, we review results from the Iberia/Newfoundland and Alpine Tethys <span class="hlt">rifted</span> margins with the aim to discuss their magmatic evolution during <span class="hlt">final</span> <span class="hlt">rifting</span> and onset of seafloor spreading. Along these margins the volume of magma increases oceanwards and the emplacement processes are either controlled by infiltration via porous flow, dyking or extrusion at the seafloor. Based on field relationships, direct dating of magmatic rocks or related sediments it can be shown that: 1) infiltration predates mantle exhumation at the seafloor, 2) the emplacement of intrusive and extrusive magmatic rocks of MOR composition post date first mantle exhumation and marks the onset of seafloor spreading, and 3) alkaline magmas are occasionally emplaced in the Ocean Continent Transition even after onset of seafloor spreading. Thus, the magmatic processes observed on these margins are complex and polyphase. The observations suggest that entirely non-magmatic margins do not exist. However, it remains unclear whether decompression melting is the driving force or rather the consequence of extension. In our presentation we will discuss to what extent magma may control the rheology, thermal structure and isostatic evolution of magma-poor <span class="hlt">rifted</span> margins during continental breakup.</p> <div class="credits"> <p class="dwt_author">Manatschal, G.; Muntener, O.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">252</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://dx.doi.org/10.1016/S0031-0182(98)00022-4"> <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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Scholz, C. A.; Moore, Jr. , T. C.; Hutchinson, D. R.; Golmshtok, A. Ja.; Klitgord, K. D.; Kurotchkin, A. G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">253</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/54491350"> <span id="translatedtitle">He and Ne isotopic ratios along the Terceira <span class="hlt">Rift</span>: implications for the Azores mantle source</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Noble gas data (He and Ne) on olivine phenocrysts obtained from Azores' lavas sampled along the Terceira <span class="hlt">Rift</span> will be presented in this work. The Terceira <span class="hlt">Rift</span> is considered as one of the slowest spreading <span class="hlt">system</span> in the world (Vogt & Jung, 2004). Lava samples were collected inland at S. Miguel, Terceira, Graciosa, Pico and Faial Islands as well at</p> <div class="credits"> <p class="dwt_author">P. Madureira; M. A. Moreira; J. Nunes; N. Lourenco; M. Carvalho; J. Mata; M. Pinto de Abreu</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">254</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Holzförster, F.; Schmidt, U.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">255</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/14810490"> <span id="translatedtitle">Current <span class="hlt">rifting</span> episode in north Iceland</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A major <span class="hlt">rifting</span> episode is now occurring in north Iceland. This started on 20 December 1975, with a basaltic eruption, an exceptionally intense earthquake swarm and movement on an 80-km segment of the plate boundary. Inflation and deflation of the Krafla caldera indicate upwelling of magma and injection into the <span class="hlt">rift</span> zone. Historical records show that similar episodic <span class="hlt">rifting</span> occurs</p> <div class="credits"> <p class="dwt_author">Axel Björnsson; Kristján Saemundsson; Páll Einarsson; Eysteinn Tryggvason; Karl Grönvold</p> <p class="dwt_publisher"></p> <p class="publishDate">1977-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">256</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012DPS....4450508A"> <span id="translatedtitle"><span class="hlt">Final</span> Origin of the Saturn <span class="hlt">System</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Saturn’s middle-sized moons (MSMs) are of diverse geology and composition, totaling 4.4% of the <span class="hlt">system</span> mass. The rest is Titan, with more mass per planet than Jupiter’s satellites combined. Jupiter has four large satellites with 99.998% of the <span class="hlt">system</span> mass, and no MSMs. Models to explain the discrepancy exist (e.g. Canup 2010; Mosqueira et al. 2010; Charnoz et al. 2011) but have important challenges. We introduce a new hypothesis, in which Saturn starts with a comparable family of major satellites (Ogihara and Ida 2012). These satellites underwent a <span class="hlt">final</span> sequence of mergers, each occurring at a certain distance from Saturn. Hydrocode simulations show that galilean satellite mergers can liberate ice-rich spiral arms, mostly from the outer layers of the smaller of the accreting pair. These arms gravitate into clumps 100-1000 km diameter that resemble Saturn’s MSMs in diverse composition and other major aspects. Accordingly, a sequence of mergers (ultimately forming Titan) could leave behind populations of MSMs at a couple of formative distances, explaining their wide distribution in semimajor axis. However, MSMs on orbits that cross that of the merged body are rapidly accumulated unless scattered by resonant interactions, or circularized by mutual collisions, or both. Scattering is likely for the first mergers that take place in the presence of other resonant major satellites. Lastly, we consider that the remarkable geophysical and dynamical vigor of Titan and the MSMs might be explained if the proposed sequence of mergers happened late, triggered by impulsive giant planet migration (Morbidelli et al. 2009). The dynamical scenario requires detailed study, and we focus on analysis of the binary collisions. By analysis of the hydrocode models, we relate the provenance of the MSMs to their geophysical aspects (Thomas et al. 2010), and consider the geophysical, thermal and dynamical implications of this hypothesis for Titan’s origin.</p> <div class="credits"> <p class="dwt_author">Asphaug, Erik; Reufer, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">257</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://dx.doi.org/10.1038/nature10566"> <span id="translatedtitle">East Antarctic <span class="hlt">rifting</span> triggers uplift of the Gamburtsev Mountains</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Ferraccioli, F.; Finn, Carol A.; Jordan, Tom A.; Bell, Robin E.; Anderson, Lester M.; Damaske, Detlef</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">258</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Ferraccioli, Fausto; Finn, Carol A; Jordan, Tom A; Bell, Robin E; Anderson, Lester M; Damaske, Detlef</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-11-17</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">259</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2003AGUFM.V22A0574P"> <span id="translatedtitle">Rapid opening of the Asal <span class="hlt">rift</span> in Afar observed with radar interferometry</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Located at the western end of the Aden ridge, the Asal <span class="hlt">rift</span> is the first emerged section of the ridge propagating into Afar and the locus of intense volcanic and seismic activity. We use radar interferometry data acquired by the Canadian satellite Radarsat between 1997 and 2003 from both ascending and descending passes to measure the surface deformation in a 100 km wide region centered on the <span class="hlt">rift</span>. The turbulent atmosphere in this sub-tropical region produces a phase delay error in the data exceeding the tectonic signal we seek. To estimate the deformation rates from the series of interferograms, we solve a least-square problem and derive the vertical and <span class="hlt">rift</span>-perpendicular, horizontal components of the surface velocity from the series of ascending and descending line of sight observations by the radar. The resulting 2-component surface velocity map of the <span class="hlt">rift</span> area shows the following features: A ~40 km wide zone centered on the <span class="hlt">rift</span> is inflating at a rate of ~7 mm/yr. The ~8 km-wide central <span class="hlt">rift</span> subsides at a rate of ~2mm/yr with respect to the shoulders of the <span class="hlt">rifts</span>. The horizontal velocity indicates extension across the central <span class="hlt">rift</span> at a rate of up to 20 mm/yr, gradually decreasing in the far field, the maxima of the horizontal velocity being located on both side of the <span class="hlt">rift</span>, ~12 km from its axis. This local opening rate exceeds the 13 mm/yr far-field plate motion between the Arabia and Nubia plates, suggesting that magmatic activity is currently controlling the opening of the Asal <span class="hlt">rift</span>. Preliminary models shows that a 4 km deep dyke <span class="hlt">system</span> expanding both laterally and upward accounts for the observed velocity field across the Asal <span class="hlt">rift</span>.</p> <div class="credits"> <p class="dwt_author">Peltzer, G.; Mignan, A.; King, G.; Manighetti, I.</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">260</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010Litho.117...33R"> <span id="translatedtitle">Geochemical evidence of lithospheric thinning in the southern Main Ethiopian <span class="hlt">Rift</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Lithospheric thinning is a fundamental process associated with the transition from continental to oceanic regimes during continental <span class="hlt">rifting</span>. Precisely how and when this lithospheric thinning proceeds are first order controls on <span class="hlt">rift</span> basin evolution. The Main Ethiopian <span class="hlt">Rift</span>, part of the ˜ 2000 km long East African <span class="hlt">Rift</span> <span class="hlt">System</span>, is the archetypical modern example of continental <span class="hlt">rifting</span>, and a key location in which to study the evolution of the lithosphere during extension. This study explores lithospheric modification in the interface region between the Main Ethiopian <span class="hlt">rift</span> and northward propagating <span class="hlt">rifting</span> from Kenya through a major and trace element study of <span class="hlt">rift</span> initiation and maturation using the 19 myr magmatic record preserved in this region. Initial <span class="hlt">rifting</span> in southern Ethiopia is coincident with the eruption of basalts along the <span class="hlt">rift</span> shoulders that are characterized by deep fractionation trends (0.5 GPa) and poorly developed magmatic pathways. The earliest of these basalts are derived from melting columns where the aluminum phase is garnet-dominated (Tb N/Yb N ˜ 1.8-2) and has geochemical characteristics interpreted as melting of the lithospheric mantle. The transition from initial <span class="hlt">rift</span> shoulder magmatism to Quaternary magmatic-tectonic fault belts on the modern <span class="hlt">rift</span> floor at Arba Minch (6°N) is coincident with a shallowing of the melting column (Tb N/Yb N ˜ 1.3-1.7), less significant contributions from the lithospheric mantle, and the establishment of a shallow fractionation regime (0.1 GPa). At Chencha (˜ 6.3°N) newly dated (12.32 ± 0.17 Ma) magmatism on the <span class="hlt">rift</span> shoulder has similar fractionation paths to contemporaneous magmatism to the south (0.5 GPa), but is derived from a different, shallower mantle source (Tb N/Yb N ˜ 1.3-1.5) that we interpret results from lithospheric thinning associated with the now-inactive Chow Bahir <span class="hlt">rift</span>. Between 6.5 and 8°N, significant surface faulting and shallow magmatic fractionation paths (0.1 GPa) in the dominant Quaternary structure of the Main Ethiopian <span class="hlt">Rift</span> (the Wonji Fault Belt and Silti-Debre Zeyit Fault Zone), highlights the strong connection between magmatism and extensional tectonics in these structures. Along the eastern <span class="hlt">rift</span> margin, Wonji Fault Belt magmas are derived from a dominantly shallow melting column (Tb N/Yb N ˜ 1.4-1.7) that is similar in composition to the older <span class="hlt">rift</span> shoulder lavas at Chencha. Adjacent to the western <span class="hlt">rift</span> margin, magmas erupted in the Silti-Debre Zeyit Fault Zone are interpreted to have erupted through a thicker lithosphere as these magmas are derived from a deeper melting column (Tb N/Yb N ˜ 1.7-2.1) that contains some minor apatite. The inferred variations in lithospheric thickness in southern Ethiopia outlined in this study illustrate the interaction between northward and southward <span class="hlt">rift</span> propagation in addition to lateral variations across the <span class="hlt">rift</span> floor as extension migrates into zones of focused magmatic intrusion. The results of this investigation show that geochemical techniques can be applied to probe the history of lithospheric modification during <span class="hlt">rifting</span> and provide new constraints for models of <span class="hlt">rift</span> development.</p> <div class="credits"> <p class="dwt_author">Rooney, Tyrone O.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-06-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_12");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" 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showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_15");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">261</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=DE2001763210"> <span id="translatedtitle"><span class="hlt">Final</span> Report: Sensor <span class="hlt">System</span> to Monitor Ammonia.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">This <span class="hlt">final</span> technical report summarizes the results of a project to develop a prototype integrated optic ammonia NHJ sensor for agricultural and industrial applications. The majority of the support for this project was provided by the Department of Energy ...</p> <div class="credits"> <p class="dwt_author">J. G. Edwards</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">262</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012EGUGA..1413065R"> <span id="translatedtitle"><span class="hlt">Rifting</span> of the Tyrrhenian Basin, a complex interaction among faulting , magmatism and mantle exhumation.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Tyrrhenian basin has been created during the extension of continental lithosphere driven by the retreat of a Ionian slab across the mantle. The basin does not seem to be actively extending, but its preserved crustal structure provides information of the time evolution of the processes involved in <span class="hlt">rifting</span>. The basin <span class="hlt">rifted</span> from north to south, with <span class="hlt">rifting</span> stopping after progressively larger stretching factor towards the south. The northern region stopped opening after a relatively low extension factor. Towards the south extension increased up to full crustal separation that produced mantle exhumation. The <span class="hlt">final</span> structure displays two conjugate margins with asymmetric structures. Thus, the basin provides a natural laboratory to investigate a full <span class="hlt">rift</span> <span class="hlt">system</span>, that displays variable amounts of extension. We present observations from a two-ship seismic experiment that took place in spring 2010. The cruise took place on two legs. In the first leg, the Spanish R/V Sarmiento de Gamboa and the Italian R/V Urania collected five E-W trending wide-angle seismic (WAS) profiles across the entire basin using 17 Ocean Bottom Seismometers and 25 Ocean Bottom Hydrophones and a 4800 c.i. G-II gun array. The profiles were extended with land stations that recorded the marine shots. During a second leg the R/V Sarmiento de Gamboa collected 16 Multichannel Seismic Reflection (MCS) profiles using a 3.75 km-long streamer and a 3000 c.i. G-II gun array. MCS profiles were acquired coincident with the WAS profiles, and a number of additional lines concentrated in the central region of the basin where mantle exhumation took place. The seismic profiles were located to cover regions of the basin that displays different amount of extension, and the coincident wide-angle and MCS transects cross the entire basin to image the two conjugate margins. In this presentation we compare observations from different transects mapping the structures produced at different extension factors. A comparison of the different transects permits to trade space (different transects mapping different extension factors) for time (different transects provide an evolutionary snapshot of the extension process). Each transect provides the tectonic structure, the geometry of sedimentary deposits, and P-wave seismic velocity distribution. This information allows to interpret the mechanisms of deformation, infer the importance and potential role of magmatism in the <span class="hlt">rifting</span> process, and estimate the region of mantle exhumation, currently inferred from one drill site. The analysis of the data provides insight in the process of formation of asymmetry structure conjugated margins.</p> <div class="credits"> <p class="dwt_author">Ranero, C. R.; Sallarés, V.; Grevemeyer, I.; Zitellini, N.; Guzman, M.; Prada, M.; Moeller, S.; de Franco, R.; Medoc Cruise Party</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">263</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19830060639&hterms=heat+process&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dheat%252Bprocess"> <span id="translatedtitle">Constraints on <span class="hlt">rift</span> thermal processes from heat flow and uplift</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Morgan, P.</p> <p class="dwt_publisher"></p> <p class="publishDate">1983-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">264</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009EGUGA..1111346H"> <span id="translatedtitle">Anatomy and crustal evolution of the central Lhasa terrane (S-Tibet) revealed by investigations in the Xainza <span class="hlt">rift</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The present-day appearance of the Himalayan-Tibetan orogen is the result of ongoing northward translation of the Indian subcontinent. Terrane amalgation, subduction of oceanic lithosphere during closure of the Neo-Tethys, and the <span class="hlt">final</span> hard-collision of India with Asia resulted in crustal shortening, extensive magmatism, and late-stage <span class="hlt">rifting</span> across the uplifted Tibetan plateau. This study presents zircon LA-MC-ICPMS U-Pb and zircon and apatite (U-Th)/He data from the central Lhasa terrane (Xainza <span class="hlt">rift</span>) providing new insights into the evolution of the central Lhasa terrane from subduction and collision related crustal thickening to initiation of E-W extension. The Xainza <span class="hlt">rift</span>, terminated by the right-lateral Gyaring-Co fault in the north and the Indus Yalu Suture Zone (IYSZ) in the south, comprises the following main tectono-stratigraphic units. (1) WNW-trending thrust sheets composed of Paleozoic limestone and low-grade slate that preserve ductile fabrics pre-dating extensive Gangdese magmatism. (2) Voluminous granitic to granodioritic plutonic rocks and associated rhyolitic to andesitic volcanic rocks dominate the central Lhasa terrane crustal section exposed along <span class="hlt">rift</span>-bounding normal faults within the Xainza <span class="hlt">rift</span>. Zircon LA-MC-ICPMS U-Pb data define two distinct episodes of plutonism and coeval volcanism dated at 129-132 Ma in the northern and central part of the Xainza <span class="hlt">rift</span> and 50-60 Ma in both the northern and southern portions of the <span class="hlt">rift</span>. (3) A Miocene granite, exposed as a ~30 km long exhumed extensional fault block within the massive southern portion of the Gangdese Batholith, yielded a zircon U-Pb age of ~14 Ma. The structural development of the central Lhasa terrane is characterized by the following major tectonic events. (1) N-S directed shortening related to the early Cretaceous Lhasa-Qiangtang collision that resulted in large-scale folding, thrusting, and low-grade metamorphism of Paleozoic sediments. Following a long period of crustal growth by extensive magmatism, (2) initiation of <span class="hlt">rift</span> <span class="hlt">systems</span> perpendicular to the older structural grain reshaped the central Lhasa terrane. Detailed low-temperature zircon and apatite (U-Th)/He thermochronological studies elucidate the initiation and timing of exhumation of the <span class="hlt">rift</span> flanks. Zircon (U-Th)/He data from the northern portion of the <span class="hlt">rift</span> yielded middle Miocene ages indicating an early phase of <span class="hlt">rifting</span>, while apatite (U-Th)/He ages from samples collected along normal faults throughout the <span class="hlt">rift</span> reveal a regional episode of accelerated exhumation in the late Miocene (6-10 Ma), as do zircon (U-Th)/He ages from the southern portion of the Xainza <span class="hlt">rift</span> that has experienced large-magnitude extension. Based on integrated structural and thermochronometric constraints, we propose that N-S directed crustal shortening in the central Lhasa terrane resulted in early Cretaceous Lhasa-Qiangtang thin-skinned thrust tectonics accompanied by low-grade metamorphism. Post-kinematic granite emplacement and volcanic activities mark the end of this shortening event. After a period of magmatic quiescence, late Cretaceous to early Cenozoic arc magmatism and crustal growth dominated the Lhasa terrane driven by northward subduction of the Neo-Tethys oceanic crust. Slab rollback and influx of hot asthenosphere beneath the Lhasa terrane is thought to have triggered extensive arc magmatism and volcanism throughout the southern and central Lhasa terrane. Neo-Tethyan convergence culminated in hard-collision of India and Asia followed by underplating of Indian lithosphere beneath the Lhasa terrane. There is no evidence of Neogene N-S shortening within the Xainza <span class="hlt">rift</span> suggesting that ongoing northward translation of India was predominately accommodated by thrusting at the margins of the plateau and within the Himalayas. Consistent with other investigations, we propose that E-W extension in the Lhasa terrane started as early as the middle Miocene. This middle Micoene <span class="hlt">rift</span> pulse is likely responsible for the latest magmatic event at ~14 Ma within the Gangdese Batholith. The modern <span class="hlt">rift</span> morphology </p> <div class="credits"> <p class="dwt_author">Hager, C.; Stockli, D. F.; Dewane, T. J.; Gehrels, G.; Ding, L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">265</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..15.5441M"> <span id="translatedtitle">Earthquake clusters in Corinth <span class="hlt">Rift</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Mesimeri, Maria; Papadimitriou, Eleftheria; Karakostas, Vasilios; Tsaklidis, George</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">266</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014NatGe...7..297M"> <span id="translatedtitle">Off-<span class="hlt">rift</span> volcanism in <span class="hlt">rift</span> zones determined by crustal unloading</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">When continents are stretched over a long period of time, deep elongated <span class="hlt">rift</span> valleys form at Earth's surface and zones of ponded magma, centred beneath the <span class="hlt">rift</span>, form at the crust-mantle boundary. Ascending magma sometimes erupts within the <span class="hlt">rift</span> valley or, counterintuitively, at volcanic fields away from the <span class="hlt">rift</span> valley that are offset by tens of kilometres from the source of magma at depth. The controls on the distribution of this off-<span class="hlt">rift</span> volcanism are unclear. Here we use a numerical model of magmatic dyke propagation during <span class="hlt">rifting</span> to investigate why some dykes reach the surface outside the <span class="hlt">rift</span> valley, whereas others are confined to the valley. We find that the location of magmatism is governed by the competition between tectonic stretching and gravitational unloading pressure, caused by crustal thinning and faulting along the <span class="hlt">rift</span> borders. When gravitational unloading dominates over tectonic stretching forces, dykes ascending from the ponded magma are steered towards the <span class="hlt">rift</span> sides, eventually causing off-<span class="hlt">rift</span> eruptions. Our model also predicts the formation of stacked magma sills in the lower crust above the magma-ponding zone, as well as the along-<span class="hlt">rift</span> propagation of shallow dykes during <span class="hlt">rifting</span> events, consistent with observations of magmatism and volcanism in <span class="hlt">rift</span> zones globally. We conclude that <span class="hlt">rift</span> topography-induced stress changes provide a fundamental control on the transfer of magma from depth to the surface.</p> <div class="credits"> <p class="dwt_author">Maccaferri, Francesco; Rivalta, Eleonora; Keir, Derek; Acocella, Valerio</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">267</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010Tectp.486..101K"> <span id="translatedtitle">Reactivations of boundary faults within a buried ancient <span class="hlt">rift</span> <span class="hlt">system</span> by ductile creeping of weak shear zones in the overpressured lower crust: The 2004 mid-Niigata Prefecture Earthquake</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We elucidated fine-scale heterogeneities of the seismogenic structure associated with the 2004 mid-Niigata Prefecture Earthquake (thrust fault), Japan, by deploying a dense portable seismic array in the southwestern edge of the source region to observe the aftershocks. A velocity model inverted from double-difference tomographic analysis with first arrival times shows that most aftershocks were aligned between sedimentary strata in the hanging wall and the basement in the footwall. The basement is characterized by clear step-like and tilted block structures that gradually deepen toward the west. The domino-tilted block structures of the basement reveal evidence of a Miocene <span class="hlt">rift</span> <span class="hlt">system</span> buried beneath the thick sedimentary sequence. The aftershocks appear to be aligned roughly along pre-existing boundaries of the step-like array of tilted blocks. In addition, we used the Natural Earthquake Reflection Profile (NERP) method to image reflective zones in the lower crust, defining a set of relatively strong reflectors. Low seismic velocity anomalies combined with high electrical conductivity in the lower crust suggest that a plausible explanation for the reflective zones is the presence of reservoirs of overpressured crustal fluids. Given these considerations, we propose that pre-existing boundary faults within the buried ancient <span class="hlt">rift</span> <span class="hlt">system</span> were reactivated through ductile creeping of weak shear zones in the overpressured lower crust.</p> <div class="credits"> <p class="dwt_author">Kato, Aitaro; Iidaka, Takashi; Iwasaki, Takaya; Hirata, Naoshi; Nakagawa, Shigeki</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">268</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">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 class="dwt_publisher"></p> <p class="publishDate">2013-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">269</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004EOSTr..85..273W"> <span id="translatedtitle">Geoscience Methods Lead to Paleo-anthropological Discoveries in Afar <span class="hlt">Rift</span>, Ethiopia</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">With few exceptions, most of the hominid evolutionary record in Africa is closely associated with the East African <span class="hlt">Rift</span> <span class="hlt">System</span>. The exceptions are the South African and Chadian hominids collected from the southern and west-central parts of the continent, respectively. The Middle Awash region stands alone as the most prolific paleoanthropological area ever discovered (Figure 1). Its paleontological record has yielded over 13,000 vertebrate fossils, including several hominid taxa, ranging in age from 5.8 Ma to the present. The uniqueness of the Middle Awash hominid sites lies in their occurrence within long, > 6 Ma volcanic and sedimentary stratigraphic records. The Middle Awash region has yielded the longest hominid record yet available. The region is characterized by distinct geologic features related to a volcanic and tectonic transition zone between the continental Main Ethiopian and the proto-oceanic Afar <span class="hlt">Rifts</span>. The <span class="hlt">rift</span> floor is wider-200 km-than other parts of the East African <span class="hlt">Rift</span> (Figure 1). Moreover, its Quaternary axial <span class="hlt">rift</span> zone is wide and asymetrically located close to the western margin. The fossil assemblages and the lithostratigraphic records suggest that volcanic and tectonic activities within the broad <span class="hlt">rift</span> floor and the adjacent <span class="hlt">rift</span> margins were intense and episodic during the late Neogene <span class="hlt">rift</span> evolution.</p> <div class="credits"> <p class="dwt_author">WoldeGabriel, Giday; Renne, Paul R.; Hart, William K.; Ambrose, Stanley; Asfaw, Berhane; White, Tim D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">270</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Ghergut, I.; Meixner, J.; Rettenmaier, D.; Maier, F.; Nottebohm, M.; Ptak, T.; Sauter, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">271</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009EGUGA..11.8390M"> <span id="translatedtitle">Unraveling the crustal structure of hyper-extended <span class="hlt">rifted</span> margins: the example of the Bernina domain in the Alpine Tethys (SE Switzerland)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A long-standing problem in Earth Sciences is to understand how continents break apart to form new oceanic basins. The discovery of exhumed continental mantle and hyper-extended crust devoid of significant normal faulting directly overlain by shallow marine sediments, as observed in many <span class="hlt">rifted</span> margins, is proving fundamental in defining the controls and processes that thin the continental lithosphere. This leads to the questions of what structures/processes can explain major crustal thinning and when and where they were active? A more direct access to the sedimentary record of deep <span class="hlt">rifted</span> margins and the underlying crust/mantle lithosphere is exposed in the Alps in Western Europe. Remnants of the ancient Alpine Tethys <span class="hlt">rifted</span> margins are well exposed and the palaeo-geographic position of these units can be reconstructed satisfactorily. We initiated a research project in the Bernina domain in SE Switzerland, where remnants of the transition between the proximal and the distal/deep Adriatic margin, comparable with the necking zone in present-day magma-poor <span class="hlt">rifted</span> margins are exposed. The Bernina domain preserves a pre-<span class="hlt">rift</span> crustal section formed by (1) lower and middle crust comprising Permian gabbros and granulites, (2) upper crust formed by a poly-metamorphic basement intruded by post Variscan granitoids, and (3) remnants of a sedimentary cover, which comprises a Permo-Triassic pre-<span class="hlt">rift</span> sequence and Lower to Middle Jurassic syn-<span class="hlt">rift</span> sequence that are overlain by Upper Jurassic to Lower Cretaceous deep water post-<span class="hlt">rift</span> sediments. The thinning of the continental crust is characterized by a <span class="hlt">system</span> of conjugate crustal scale detachment <span class="hlt">systems</span> along which the middle crust (e.g. Campo/Grosina units) is omitted (necking zone). As a result, upper crustal rocks are juxtaposed against lower crustal and mantle rocks (e.g. Margna shear zone). Locally, these faults reach the surface (e.g. Val dal Fain) and form top-basement detachment faults, which are overlain by extensional allochthons or syn-<span class="hlt">rift</span> sediments that were onlapped by post-<span class="hlt">rift</span>. How detachment <span class="hlt">systems</span> are organized and evolve on a crustal scale in space and time and how they can thin and <span class="hlt">finally</span> omit the middle crust within the necking zone remains, however, a major question. Field mapping of the relations between mid-crustal rocks and detachment/décollement structures, coupled with new data on the thermo-chronological evolution of the Campo and Grosina units will enable the unraveling of the deformation history of the mid-crustal level during the extreme crustal thinning. The results of this study will lead to better constraints of the thinning processes of the crust and give access to the deformation of the middle crust during the <span class="hlt">rifting</span>. These results have major implications for the thermal evolution and consequently for the rheology and isostasy of the extending lithosphere.</p> <div class="credits"> <p class="dwt_author">Mohn, G.; Masini, E.; Manatschal, G.; Beltrando, M.; Müntener, O.; Kusznir, N.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">272</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=ADA191677"> <span id="translatedtitle">Surveillance for <span class="hlt">Rift</span> Valley Fever in Egypt During 1983.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">In 1977, Egypt experienced its first recorded outbreak of <span class="hlt">Rift</span> Valley Fever (RVF). Since the last isolation of RVF virus in 1981, continued transmission of RVF in Egypt has been disputed. A surveillance <span class="hlt">system</span> was established by NAMRU-3 in 1982 using acce...</p> <div class="credits"> <p class="dwt_author">B. A. Botros P. W. Mellick A. W. Salib A. K. Soliman M. T. Dalam</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">273</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.agu.org/journals/gc/gc1008/2010GC003105/2010GC003105.pdf"> <span id="translatedtitle">Postspreading <span class="hlt">rifting</span> in the Adare Basin, Antarctica: Regional tectonic consequences</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Extension during the middle Cenozoic (43–26 Ma) in the north end of the West Antarctic <span class="hlt">rift</span> <span class="hlt">system</span> (WARS) is well constrained by seafloor magnetic anomalies formed at the extinct Adare spreading axis. Kinematic solutions for this time interval suggest a southward decrease in relative motion between East and West Antarctica. Here we present multichannel seismic reflection and seafloor mapping data</p> <div class="credits"> <p class="dwt_author">R. Granot; S. C. Cande; J. M. Stock; F. J. Davey; R. W. Clayton</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">274</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Keir, Derek; Bastow, Ian D.; Pagli, Carolina; Chambers, Emma L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-11-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">275</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/60406722"> <span id="translatedtitle">Hydrogen supplementation <span class="hlt">system</span> evaluation study. <span class="hlt">Final</span> report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">An economic assessment was made of producing and utilizing electrolytic Hâ based on applications by typical electric\\/gas utility <span class="hlt">systems</span>. The four <span class="hlt">systems</span> selected for evaluation are Mid-Atlantic (combination electric\\/gas <span class="hlt">system</span>, summer electric peak), Midwest region (separate electric and gas <span class="hlt">systems</span> with overlapping service territories, summer electric peak), Northeast region (combination electric\\/gas <span class="hlt">system</span>, winter electric peak), and Pacific Coast region (combination</p> <div class="credits"> <p class="dwt_author">W. S. Ku; D. C. Nielsen; J. Zemkoski; D. L. Leich; P. Yatcko; G. P. Gaebe</p> <p class="dwt_publisher"></p> <p class="publishDate">1977-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">276</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/754794"> <span id="translatedtitle">Liquid waste treatment <span class="hlt">system</span>. <span class="hlt">Final</span> report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Pretreatment of high-level liquid radioactive waste (HLW) at the West Valley Demonstration Project (WVDP) involved three distinct processing operations: decontamination of liquid HLW in the Supernatant Treatment <span class="hlt">System</span> (STS); volume reduction of decontaminated liquid in the Liquid Waste Treatment <span class="hlt">System</span> (LWTS); and encapsulation of resulting concentrates into an approved cement waste form in the Cement Solidification <span class="hlt">System</span> (CSS). Together, these <span class="hlt">systems</span> and operations made up the Integrated Radwaste Treatment <span class="hlt">System</span> (IRTS).</p> <div class="credits"> <p class="dwt_author">Baker, M.N.; Houston, H.M.</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">277</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1992Tectp.213..235R"> <span id="translatedtitle">Comparison of the Tanganyika, Malawi, Rukwa and Turkana <span class="hlt">Rift</span> zones from analyses of seismic reflection data</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Northwest-southeast extension has opened the East African <span class="hlt">Rift</span> <span class="hlt">System</span> along two main branches, the Western and Eastern Branches. <span class="hlt">Rift</span> zones along the Western Branch are marked by narrow lakes floored by thick piles of fluvial clastic and 'pelagic' sediment. Magmatism is restricted to a few small areas in the 'arches' between the lakes. In contrast, <span class="hlt">rift</span> zones along the Eastern Branch are largely filled with volcanic and volcaniclastic materials and magmatism is generally perceived to be an integral part of the <span class="hlt">rifting</span> process. In an attempt to sort out the significance and meaning of these and other differences, we have compared multifold seismic data from three Western Branch <span class="hlt">rift</span> zones (Tanganyika, Rukwa and Malawi) and one Eastern Branch zone (Turkana). The Tanganyika and Malawi <span class="hlt">Rift</span> Zones are composed of half-graben basins linked in complex ways by accommodation zones which generally trend oblique to the <span class="hlt">rift</span> axes, and sometimes oblique to the extension direction. Half-grabens alternate basinal polarities where the <span class="hlt">rift</span> crosses Proterozoic dislocation zones. Complex fault geometries are associated with some accommodation zones; elsewhere faults are almost exclusively planar. Sedimentary fill reaches at least 4-5 km and the section is mostly Cenozoic in age. Patches of Permo-Triassic sedimentary rocks are believed to occur within both <span class="hlt">rift</span> zones. The Rukwa <span class="hlt">Rift</span> is a pull-apart zone that connects the northern (Livingstone) basin of Lake Malawi to the Kalemie Basin in central Lake Tanganyika. The entire pull-apart <span class="hlt">system</span> may be a series of down-to-the-east half-grabens. An accommodation zone develops along a short stretch of the Rukwa <span class="hlt">Rift</span>, but no full polarity reversal occurs. The break-away faults of the Livingstone, Rukwa and Kalemie basins are essentially coincident with the Proterozoic Rukwa dislocation zone, which sub-parallels the inferred extension direction. Fault geometries in the Rukwa <span class="hlt">Rift</span> are markedly listric, especially in the pre-Cenozoic section. Sedimentary fill ranges in age from pre-Karroo through Cenozoic and locally exceeds 10 km in thickness. The Turkana <span class="hlt">Rift</span> is composed of short, linear, NNE-trending normal fault segments that are offset in a left-lateral sense by numerous, NW-SE trending transfer faults, linking facing border fault segments together. The overall trend of the <span class="hlt">rift</span> zone is oblique to the opening direction, like the Tanganyika and Malawi cases, but the border fault segments are sub-perpendicular. Fault geometries are highly variable, but flower structures associated with transfer faults predominate. Igneous activity is ubiquitous and appears to be localized along the transfer faults. Basin fill reaches 4-5 km in thickness and is dominated by fluvial clastic, volcaniclastic and volcanic materials. The structural differences within the Tanganyika-Rukwa-Malawi <span class="hlt">system</span> stem mainly from the modifying effects of pre-<span class="hlt">rift</span> anistropies on strain expressions. Fundamentally, this <span class="hlt">system</span> is a NW-SE trending series of single-polarity pull-apart basins. At the two ends of the pull-apart zone, the <span class="hlt">rift</span> is deflected into more N-S trending basins which have a high tendency to alternate polarities along strike. This explanation does not account for the differences in fault forms between the Tanganyika-Malawi (planar) and Rukwa (listric) <span class="hlt">Rifts</span>. For the time being, we presume these differences arise from systematic differences between Tanganyika-Malawi and Rukwa in the age ranges of the fill and/or the maximum depths of seismic imaging. <span class="hlt">Rifting</span> in Turkana is profoundly different than in the Tanganyika-Rukwa-Malawi sub-branch and seems to involve a softer, more ductile, more organized style of extension which may be closer to the ideal case. In a thermal sense, <span class="hlt">rifting</span> has progressed further in Turkana than along the Western Branch zones. This does not preclude original, fundamental difference in the thermal states of two branches.</p> <div class="credits"> <p class="dwt_author">Rosendahl, Bruce R.; Kilembe, Elias; Kaczmarick, Kurt</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">278</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2002AGUFM.T11D1289S"> <span id="translatedtitle">The EAGLE Broadband Seismic Experiment - A Study of Continental <span class="hlt">Rifting</span> in the Ethiopia</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The EAGLE broadband experiment aims to study the crust and upper-mantle structure in a region of transition from continental to oceanic <span class="hlt">rifting</span> - the northern Ethiopian <span class="hlt">Rift</span>. 30 broadband seismometers have been deployed for a period of 16 months over an area of 250 km2, centred on the Nazret volcanic zone of the Ethiopian <span class="hlt">Rift</span>. Preliminary SKS splitting results show delay times varying from 1.5 -- 1.8 secs on the Ethiopian Plateau in the west, to 1.6 -- 2.1 secs in the east towards the Somalia Plate. Within the <span class="hlt">Rift</span> there is a consistent increase in delay times towards the north and Afar from 1.0 secs in the south to 2.1 secs in the north. Outside the <span class="hlt">Rift</span>, the polarisations of the fast shear-wave lie on a NE--SW <span class="hlt">rift</span>-parallel trend; within the <span class="hlt">Rift</span> the orientations swing to more northerly azimuths. The increased delay times in the east on the Somalia plate was unexpected and initially interpreted in terms of stretched/fractured lithosphere or alternatively represents different tectonic domain. The increase in <span class="hlt">Rift</span> splitting times northwards correlates with the amount of magma within the <span class="hlt">system</span> and may be related to the presence of magma-filled cracks. Teleseismic traveltime residuals are used to further investigate mantle velocity structure. Average residuals show a regional trend (c. 0.5 secs per 100km), upon which the <span class="hlt">Rift</span> signature is perched; on average there are faster ray paths to the east and slower ones to the west on the uplifted Ethiopian Plateau. The regional trend may represent a plume signature or a change in tectonic domain either side of the <span class="hlt">Rift</span>. This clear asymmetry in the cross-axis direction is consistent with the SKS patterns. Traveltime tomography will be used to further investigate the detailed velocity structure.</p> <div class="credits"> <p class="dwt_author">Stuart, G.; Kendall, M.; Bastow, I.; Ayele, A.; Ebinger, C.; Maguire, P.; Fowler, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">279</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007AGUFMNS11A0156B"> <span id="translatedtitle">Radar, electromagnetic, and active seismic investigation of a propagating ice shelf <span class="hlt">rift</span> tip</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A <span class="hlt">rift</span> <span class="hlt">system</span> has been growing inward from the seaward edge of the Amery Ice Shelf in East Antarctica for over twenty years. Currently active, the 'Loose Tooth' <span class="hlt">rift</span> <span class="hlt">system</span> is in the process of calving off an iceberg that will be at least 30 x 30 km in size. Over the past five field seasons passive seismic and geodetic measurements have been made at one of the propagating tips of the <span class="hlt">rift</span> <span class="hlt">system</span>. During the 2006-07 field season pilot Ground Penetrating Radar and Transient Electromagnetic (TEM) data were collected over and near that propagating <span class="hlt">rift</span> tip, to provide complimentary constraints regarding the internal structure of the ice shelf and to look for evidence of penetration of electrically conductive seawater into the <span class="hlt">rift</span> from below. In another auxiliary experiment, small charges were set off near the <span class="hlt">rift</span> tip to provide calibration and velocity structure information for the primary passive seismic data set. Preliminary results are presented in comparison with the passive seismic and geodetic results, as well as a discussion of practical constraints and challenges in collecting these types of data at an ice shelf <span class="hlt">rift</span>.</p> <div class="credits"> <p class="dwt_author">Behrens, J.; Bassis, J.; Fricker, H.; Coleman, R.; Darnell, D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">280</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=PB2005103001"> <span id="translatedtitle">Ferret Workflow Anomaly Detection <span class="hlt">System</span>, <span class="hlt">Final</span> Report.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">The Ferret workflow anomaly detection <span class="hlt">system</span> project (203-2044) has provided validation and anomaly detection in accredited workflows in secure knowledge management <span class="hlt">systems</span> through the use of continuous automated audits. A workflow, process, or procedure ...</p> <div class="credits"> <p class="dwt_author">T. J. Smith S. Bryant</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_13");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">281</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=AD663568"> <span id="translatedtitle">Warning <span class="hlt">Systems</span> Research Support: <span class="hlt">Final</span> Report.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">The report describes the current warning environment, accordingly updates the requirements for an integrated national warning <span class="hlt">system</span>, and then specifies a <span class="hlt">system</span> design that will meet these requirements. Additionally, it discusses in detail various aspect...</p> <div class="credits"> <p class="dwt_author">A. E. Bornstein N. M. Bosak L. J. Hoddy B. D. Miller M. I. Rosenthal</p> <p class="dwt_publisher"></p> <p class="publishDate">1966-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">282</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=BNL24099"> <span id="translatedtitle">Hydrogen Supplementation <span class="hlt">System</span> Evaluation Study. <span class="hlt">Final</span> Report.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">An economic assessment was made of producing and utilizing electrolytic H sub 2 based on applications by typical electric/gas utility <span class="hlt">systems</span>. The four <span class="hlt">systems</span> selected for evaluation are Mid-Atlantic (combination electric/gas <span class="hlt">system</span>, summer electric peak...</p> <div class="credits"> <p class="dwt_author">W. S. Ku D. C. Nielsen J. Zemkoski D. L. Leich P. Yatcko</p> <p class="dwt_publisher"></p> <p class="publishDate">1977-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">283</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Jacobson, Eric</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">284</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://eric.ed.gov/?q=%22moi%22&pg=3&id=ED194687"> <span id="translatedtitle">Michigan Occupational Information <span class="hlt">System</span> <span class="hlt">Final</span> Evaluation Report.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p class="result-summary">An evaluation of the Michigan Occupational Information <span class="hlt">System</span> (MOIS) was conducted. (The MOIS is a <span class="hlt">system</span> designed to provide reliable and current career information organized in a readily accessible <span class="hlt">system</span> for individuals involved in career exploration and decision making.) Three types of survey instruments (site, staff, and client surveys) were…</p> <div class="credits"> <p class="dwt_author">Gordon, Eric M.; And Others</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">285</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/10178298"> <span id="translatedtitle">Statistical mechanics of polymer <span class="hlt">systems</span>. <span class="hlt">Final</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Work on computer simulation of polymer dynamics and the statistical mechanics of quenched <span class="hlt">systems</span> carried out over seven years with the support of this grant is reviewed. The computer simulation work has focused on elucidation the roles of the excluded volume and the nearest-neighbor attractive interactions in the dynamics of polymers. To study quenched <span class="hlt">systems</span> we have applied the formalism suggested long ago by Mazo to two model <span class="hlt">systems</span> and found qualitative agreement with the properties of real glasses.</p> <div class="credits"> <p class="dwt_author">Kovac, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">286</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009EGUGA..11.9120A"> <span id="translatedtitle">Evolution and segmentation of oblique <span class="hlt">rift</span> in a cold lithosphere: Insights from analogue modeling</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">New lithospheric analogue models of oblique <span class="hlt">rifting</span> provide insights into the fault evolution, basin segmentation, and mantle exhumation during <span class="hlt">rift</span> localization and capture main characteristics of natural oblique <span class="hlt">rifts</span>. We present two models of oblique <span class="hlt">rifting</span>: an oblique <span class="hlt">rift</span> (obliquity about 50°) with a pre-existing lithospheric weakness (heterogeneous model) and one homogeneous. The following evolution is observed: (i) The fault populations, especially in early stages of deformation, are composed of faults that are, in strike, intermediate between the <span class="hlt">rift</span>-parallel trend and the perpendicular to the opening direction. This fault population is characteristic of oblique <span class="hlt">rifts</span> as in previous studies. (ii) In later stages, faults parallel to the <span class="hlt">rift</span> become numerous in both models. In the homogeneous model, displacement-normal faults also play a major role. The <span class="hlt">rift</span> localization in an oblique direction involves a thinning in an oblique direction and variations of crustal thickness. The induced local (extensional) stresses seems to control the formation of <span class="hlt">rift</span>-parallel faults. (iii) During <span class="hlt">final</span> stages of extension, in the heterogeneous model, the crust is deformed by <span class="hlt">rift</span>-parallel faults, and in the basins, displacement-normal faults compose the small-scale deformation pattern. Other main result is the complete different pattern of deformation of the entire lithosphere with or without pre-existing lithospheric weakness. Indeed, the heterogeneous model shows the start of mantle exhumation in an oblique direction whereas in the homogeneous model the extension is accommodated in en-echelon displacement-normal graben. The probable direction of ocean-continent transition, mantle exhumation if any, and the geometry of oceanic accretion centres would thus be very different according to the presence of a pre-existing lithospheric oblique weakness. Moreover, counterclockwise rotations of horsts are observed mainly in the homogeneous models. They result in the initiation of transfer zones. Such structures are parallel to the extension direction, particularly observed in the brittle mantle layer. We propose that they could represent proto-transfer/transform fracture zones observed in oblique <span class="hlt">rifts</span> and oceanic basins. Those results may provide insights into the possible evolution of the Gulf of Aden conjugate margins.</p> <div class="credits"> <p class="dwt_author">Autin, J.; Bellahsen, N.; Husson, L.; Beslier, M.-O.; Leroy, S.; D'Acremont, E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">287</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://files.eric.ed.gov/fulltext/ED109375.pdf"> <span id="translatedtitle">Developing a Career Information <span class="hlt">System</span>: <span class="hlt">Final</span> Report.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p class="result-summary">The report reviews three years of progress toward implementing the Career Information <span class="hlt">System</span> (CIS), a statewide interagency consortium that provides current labor market and educational information in usable forms to students and clients and assists in the integration of such information into schools and social agencies in Oregon. The <span class="hlt">system</span>'s…</p> <div class="credits"> <p class="dwt_author">McKinlay, Bruce</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">288</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">McDonnell Douglas Astronautics Co. - East, St. Louis, MO.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">289</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=DE2008932225"> <span id="translatedtitle">Downhole Vibration Monitoring and Control <span class="hlt">System</span>, (<span class="hlt">Final</span>).</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">The objective of this program is to develop a <span class="hlt">system</span> to both monitor the vibration of a bottomhole assembly, and to adjust the properties of an active damper in response to these measured vibrations. The key feature of this <span class="hlt">system</span> is its use of a magnetor...</p> <div class="credits"> <p class="dwt_author">M. Cobern</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">290</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008LPI....39.2107C"> <span id="translatedtitle">Simulated ChemCam Laboratory Investigations of East African <span class="hlt">Rift</span> Sedimentary Samples</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The East African <span class="hlt">Rift</span> (EAR) <span class="hlt">system</span> may be a good Earth analogue for martian surface sediments. Seventeen EAR samples were probed with a remote LIBS instrument designed to replicate the ChemCam instrument at a 9 m standoff distance.</p> <div class="credits"> <p class="dwt_author">Clegg, S. M.; Wiens, R. C.; Barefield, J. E.; Dyar, M. D.; Delaney, J. S.; Ashley, G. M.; Driese, S. G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">291</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1988JGR....93.4759B"> <span id="translatedtitle">Deformational models of <span class="hlt">rifting</span> and folding on Venus</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Features of presumed tectonic origin on Venus are reviewed, and lithospheric strength envelopes are derived based on laboratory measurements of the deformational properties of crustal and subcrustal rocks, extrapolated to conditions appropriate to Venus. Models for <span class="hlt">rifting</span> and folding are developed that use this lithospheric structure and take into account both brittle and ductile yielding as well as finite elastic strength. For both <span class="hlt">rifting</span> and folding, structures with characteristic widths and spacings are predicted whose size depends on the thickness of the lithosphere, density contrast, and elastic properties of the layer. <span class="hlt">Finally</span>, the model predictions are compared with the widths and spacings of observed tectonic features, and it is concluded that they are consistent with a relatively strong mantle layer separated from a thin brittle surface layer by a ductile lower crust. These results allow constraints to be placed on the crustal thickness and thermal gradient on Venus.</p> <div class="credits"> <p class="dwt_author">Banerdt, W. B.; Golombek, M. P.</p> <p class="dwt_publisher"></p> <p class="publishDate">1988-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">292</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012AGUFM.T43E2717F"> <span id="translatedtitle">Low-temperature thermochronologic constraints on cooling and exhumation trends along conjugate margins, within core complexes and eclogite-bearing gneiss domes of the Woodlark <span class="hlt">rift</span> <span class="hlt">system</span> of eastern Papua New Guinea</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In eastern Papua New Guinea, active sea-floor spreading within the Woodlark Basin has been propagating westward since at least 6 Ma into heterogeneous crust of the Woodlark <span class="hlt">Rift</span>. The seafloor spreading <span class="hlt">system</span> divides the northern conjugate margin (Woodlark Rise) from the southern margin (Pocklington Rise). West of the seafloor spreading <span class="hlt">rift</span>-tip are high-standing extensional gneiss domes and core complexes of the D'Entrecasteaux Islands (DEI). Domes comprise amphibolite and eclogite-facies gneisses, and Pleistocene granitoid intrusions. Flanked by mylonitic shear zone carapaces and normal faults, the domes are juxtaposed against an upper plate that includes ultramafic rocks and gabbro, correlated with the Papuan ultramafic belt. Petrologic and structural evidence from the DEI has been interpreted as evidence for diapiric ascent of the largely felsic domes, with thermo-mechanical modeling proposing (U)HP exhumation in terms of diapiric flow aided by propagating extension, with feedback between the two. Core complexes lacking evidence for diapiric-aided exhumation include the Prevost Range (eastern Normanby Island), Dayman Dome (Papuan Peninsula), and Misima Island (southern conjugate margin). Thermochronology is being applied to understand the thermal and exhumation history, and hence help constrain mechanisms of (U)HP exhumation. AFT and AHe ages from samples near sea-level along conjugate margins and DEI range from ca. 12 Ma to <1 Ma, generally decreasing from east to west, although with some localized variation. Confined track length distributions (CTLD), obtained using 252Cf implantation, generally indicate rapid cooling (means ?~14 ?m), except on Goodenough Island, the western-most and highest-standing dome. On Goodenough Island, samples from the core zone have AFT ages from ~3 - <1 Ma with age decreasing with decreasing elevation. Core zone samples have mean track lengths (7-13 ?m) and are positively skewed, whereas samples from shear zones are younger (<1 Ma) and have mean lengths that are typically longer (11-13 ?m). The CTLD's indicate cooling, then residence in an apatite partial annealing zone (PAZ) and significant partial annealing followed by rapid cooling. Inverse thermal models do not constrain well the timing of initial cooling into the PAZ, but core zone samples from higher elevations cooled earlier. Later thermal annealing was initiated ca 2-4 Ma (core earlier than shear zone) coincident with granodiorite intrusion, with subsequent very rapid cooling initiated ~0.5 Ma. This thermochronologic dataset indicates a complex thermal history and is being used to constrain thermokinematic models (PeCube) in order to test the relative roles of buoyancy and normal faulting during exhumation of eclogite-bearing domes within the Woodlark <span class="hlt">rift</span> <span class="hlt">system</span>.</p> <div class="credits"> <p class="dwt_author">Fitzgerald, P. G.; Baldwin, S.; Bermudez, M. A.; Miller, S. R.; Webb, L. E.; Little, T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">293</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Both continental and marine <span class="hlt">rift</span> settings are characterized by hydrothermal vents (smokers) that include important components of mantle-derived "endogenic" fluids. These fluids ascend along extensional faults and provide unique biologic settings. We hypothesize that deep crustal processes support near-surface metabolic strategies by delivering chemically reduced constituents to partially oxidized surface environments. Lost City hydrothermal field, a marine vent <span class="hlt">system</span> located 15 km west of the Mid-Atlantic ridge, exhibits a range of temperatures (40 to 75°C), pH (9-9.8), and mineral compositions (carbonate rather than sulfide-dominated) that were originally thought to be non-existent in marine vent <span class="hlt">systems</span>. Travertine depositing CO2 springs within the Rio Grande <span class="hlt">rift</span>, NM exhibit striking similarities in many respects to vents in Lost City. Previous research has already determined the importance of methanogenic and sulfur metabolizing microorganisms in carbonate structures at Lost City. Phylogenetic analysis of 16S rRNA genes from a terrestrial CO2 spring was performed. In addition, cells from bacteria and fungi were also cultured with oligotrophic media. Both archaeal phylotypes from the terrestrial spring grouped within Marine Group I of the Crenarchaeota, a clade dominated by sequences from hydrothermal marine vents, including some from Lost City. We will report comparative analyses of sequences from Lost City and both cultured and environmental clone libraries from the terrestrial spring using UniFrac. Geochemical modeling of data (water and gas chemistry from both locations) is used to rank the energy available for dozens of metabolic reactions. SEM and microprobe data are presented to compare mineral compositions. Our results will be discussed in respect to the tectonic setting, microbial community distributions, and the geochemical composition and textural properties of the carbonates that are precipitated in each of these <span class="hlt">systems</span>.</p> <div class="credits"> <p class="dwt_author">Cron, B. R.; Crossey, L.; Hall, J.; Takacs-Vesbach, C.; Dahm, K.; Northup, D.; Karlstrom, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">294</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Hemker, P.</p> <p class="dwt_publisher"></p> <p class="publishDate">1981-12-24</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">295</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=DE84007745"> <span id="translatedtitle">District Energy <span class="hlt">System</span> Project. <span class="hlt">Final</span> Report.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">A planned total energy <span class="hlt">system</span> for an urban low-income community is described. The problems which plagued the project and its eventual collapse are detailed. The project plan is included. (ERA citation 09:018688)</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">1984-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">296</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=DE87013406"> <span id="translatedtitle">Adaptive Distribution <span class="hlt">System</span> Protection: <span class="hlt">Final</span> Report.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">This report presents concepts, functions, and organizations of adaptive distribution <span class="hlt">system</span> protection (ADSP) schemes. ADSP constantly monitors real time data, update relay characteristics and upper and lower bounds of control functions when required, and...</p> <div class="credits"> <p class="dwt_author">K. R. Shan</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">297</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=DE83902305"> <span id="translatedtitle">Railroad Electrification on Utility <span class="hlt">Systems</span>. <span class="hlt">Final</span> Report.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">A nine-month project was undertaken on the subject of the impact of railroad electrification on utility <span class="hlt">systems</span>. The objectives of this study were achieved by a review of the literature, discussions with railroads and electric utilities with electrificati...</p> <div class="credits"> <p class="dwt_author">J. J. Burke J. W. Feltes</p> <p class="dwt_publisher"></p> <p class="publishDate">1983-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">298</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Beauchamp, W.H. [Cornell Univ., Ithaca, NY (United States); Ries, A.C. [Ries-Coward Associates Ltd., Caversham (United Kingdom); Coward, M.P. [Imperial College, London (United Kingdom)] [and others</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">299</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Schiffries, C.M.; Milling, M.E.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-03-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">300</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">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 class="dwt_publisher"></p> <p class="publishDate">2004-04-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" 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onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_17");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">301</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/670070"> <span id="translatedtitle">[Develop mine communications <span class="hlt">system</span>]. <span class="hlt">Final</span> technical report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The objective of this project was to develop, design, and build a <span class="hlt">system</span> prototype to demonstrate the practicality of two-way, wireless through-the-earth communications between the interior of a mine and the surface. The <span class="hlt">system</span> was to communicate data for process and environment monitoring and control, and provide real-time voice communication for emergency situations and for daily operations use. Transmitters and receivers were designed, built, and tested in actual mines. A wireless in-mine communications <span class="hlt">system</span> was also developed. The feasibility of the concept and the marketability of the product were successfully demonstrated. Additional work must be done to make the product suitable for, and marketable to, the coal mining industry.</p> <div class="credits"> <p class="dwt_author">Meiksin, Z.H.</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-09-15</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">302</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5907572"> <span id="translatedtitle">Lightning protection of distribution <span class="hlt">systems</span>. <span class="hlt">Final</span> report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Analyses are presented of experimental data obtained in the Tampa Bay area during 1978 and 1979 concerning the physical and phenomenological properties of lightning and the interaction of that lightning with the local distribution power <span class="hlt">systems</span>. Specific results are given regarding: (1) the physical and phenomenology properties of lightning in the Tampa Bay area and its relation to lightning elsewhere; (2) measurement and theory concerning lightning-induced voltages on distribution lines; (3) distribution <span class="hlt">system</span> operation in the presence of lightning and analytical modeling and prediction of that operation.</p> <div class="credits"> <p class="dwt_author">Uman, M.A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">303</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005DPS....37.3219G"> <span id="translatedtitle">Elastic Lithosphere Thickness and Heat Flux Estimates from <span class="hlt">Rift</span> Valley Topography: Coracis Fossae, Mars</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Coracis Fossae in the Thaumasia region on Mars are two several hundred kilometer long and ˜50 km wide extensional structures. Their complex morphology, fractured graben floors and segmented border faults, which are arranged in en echelon pattern, suggest that they are Martian analogues to terrestrial <span class="hlt">rift</span> <span class="hlt">systems</span>. At Coracis Fossae's NE segment <span class="hlt">rift</span> flank uplift is most pronounced, the <span class="hlt">rift</span> shoulders having heights of more than 1000 m with respect to the surrounding planes. We model the uplift by fitting a flexed broken plate to the topography data obtained by the Mars Orbiter Laser Altimeter. Thus, the elastic thickness at the time of <span class="hlt">rifting</span> is constrained to 10.3 - 12.5 km. Assuming a diabase composition of the crust, this corresponds to a thermal gradient of 27 - 33 K km-1. Investigating the key surface units associated with the <span class="hlt">rifting</span>, the time of <span class="hlt">rift</span> formation is determined by measuring their crater size-frequency distribution and comparing the results to an impact cratering chronology model. The time of <span class="hlt">rifting</span> is thus constrained to 3.5 - 3.9 Gyr b.p. Given the fault block topography and elastic thickness, the stresses acting on the bounding faults which support the topography may be calculated. We estimate that at the Coracis Fossae the faults need not withstand stresses in excess of 5 MPa, a value comparable to terrestrial faults. We take this weakness as an indication that the faults are or have been in contact with liquid water below the surface.</p> <div class="credits"> <p class="dwt_author">Grott, M.; Hauber, E.; Werner, S. C.; Kronberg, P.; Neukum, G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">304</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://eric.ed.gov/?q=Financial+AND+Accounting+AND+Integrated+AND+Approach&id=ED160888"> <span id="translatedtitle">Alabama Vocational Management Information <span class="hlt">System</span>. <span class="hlt">Final</span> Report.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Patterson, Douglas; And Others</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">305</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/27009220"> <span id="translatedtitle">Modular reconfigurable flexible <span class="hlt">final</span> assembly <span class="hlt">systems</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Market turbulence forces assembly plants to constantly adjust their production volume of products, variants and quantities. At the same time, assembly plant managers must protect long-term investments in the flexible assembly <span class="hlt">system</span>. For reconfigurability and agility the best solution is the modular semi-automatic approach by combining flexible automation and human skills. It gives managers possibility to adjust volume by adding</p> <div class="credits"> <p class="dwt_author">Juhani Heilala; Paavo Voho</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">306</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=DE20111023141"> <span id="translatedtitle">DCE Bio Detection <span class="hlt">System</span>. <span class="hlt">Final</span> Report.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">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. Th...</p> <div class="credits"> <p class="dwt_author">C. Batishko G. Dunham G. Morgen J. Willett M. Lind M. Warner S. Owsley</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">307</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=DE84000795"> <span id="translatedtitle">Dual-Fuel Carburetion <span class="hlt">Systems</span>. <span class="hlt">Final</span> Report.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">A carburetor and fuel delivery <span class="hlt">system</span> with a method of remotely changing fuel delivery and metering so that an engine could operate solely and correctly on either of two fuels is described. The remote actuator is in the form of an electric switch on the d...</p> <div class="credits"> <p class="dwt_author">J. Elledge</p> <p class="dwt_publisher"></p> <p class="publishDate">1981-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">308</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/60356224"> <span id="translatedtitle">Stationary flywheel energy storage <span class="hlt">systems</span>. <span class="hlt">Final</span> report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The aim of this <span class="hlt">system</span> study is to find out industrial applications of Stationary Flywheel Energy Accumulators. The economic value for the consumer and the effects on the power supply grid should be investigated. As to overall economy, compensation of short time maximum power out-put seems to be more favorable at the power stations. An additional possibility for energy storage</p> <div class="credits"> <p class="dwt_author">A. Gilhaus; E. Hau; G. Gassner; G. Huss; H. Schauberger</p> <p class="dwt_publisher"></p> <p class="publishDate">1982-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">309</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=DE20111025215"> <span id="translatedtitle">Advanced Microturbine <span class="hlt">System</span> Program Technical <span class="hlt">Final</span> Report.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">Dept. of Energy (DOE) Cooperative Agreement DE-FC02-00-CH11061 was originally awarded to Honeywell International, Inc.-Honeywell Power <span class="hlt">Systems</span> Inc. (HPSI) division located in Albuquerque, NM in October 2000 to conduct a program titled Advanced Microturbin...</p> <div class="credits"> <p class="dwt_author">L. Lindberg</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">310</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6651208"> <span id="translatedtitle">Stationary flywheel energy storage <span class="hlt">systems</span>. <span class="hlt">Final</span> report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The aim of this <span class="hlt">system</span> study is to find out industrial applications of Stationary Flywheel Energy Accumulators. The economic value for the consumer and the effects on the power supply grid should be investigated. As to overall economy, compensation of short time maximum power out-put seems to be more favorable at the power stations. An additional possibility for energy storage by flywheels is given where otherwise lost energy can be used effectively, according to the successful brake energy storage in vehicles. Under this aspect the future use of flywheels in wind-power-plants seems to be promising. Attractive savings of energy can be obtained by introducing modern flywheel technology for emergency power supply units which are employed for instance in telecommunication <span class="hlt">systems</span>. Especially the application for emergency power supply, in power stations and in combination with wind energy converters needs further investigation.</p> <div class="credits"> <p class="dwt_author">Gilhaus, A.; Hau, E.; Gassner, G.; Huss, G.; Schauberger, H.</p> <p class="dwt_publisher"></p> <p class="publishDate">1982-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">311</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/650134"> <span id="translatedtitle">Integrated radwaste treatment <span class="hlt">system</span>. <span class="hlt">Final</span> report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">In May 1988, the West Valley Demonstration Project (WVDP) began pretreating liquid high-level radioactive waste (HLW). This HLW was produced during spent nuclear fuel reprocessing operations that took place at the Western New York Nuclear Service Center from 1966 to 1972. Original reprocessing operations used plutonium/uranium extraction (PUREX) and thorium extraction (THOREX) processes to recover usable isotopes from spent nuclear fuel. The PUREX process produced a nitric acid-based waste stream, which was neutralized by adding sodium hydroxide to it. About two million liters of alkaline liquid HLW produced from PUREX neutralization were stored in an underground carbon steel tank identified as Tank 8D-2. The THOREX process, which was used to reprocess one core of mixed uranium-thorium fuel, resulted in about 31,000 liters of acidic waste. This acidic HLW was stored in an underground stainless steel tank identified as Tank 8D-4. Pretreatment of the HLW was carried out using the Integrated Radwaste Treatment <span class="hlt">System</span> (IRTS), from May 1988 until May 1995. This <span class="hlt">system</span> was designed to decontaminate the liquid HLW, remove salts from it, and encapsulate the resulting waste into a cement waste form that achieved US Nuclear Regulatory Commission (NRC) criteria for low-level waste (LLW) storage and disposal. A thorough discussion of IRTS operations, including all <span class="hlt">systems</span>, subsystems, and components, is presented in US Department of Energy (DOE) Topical Report (DOE/NE/44139-68), Integrated Radwaste Treatment <span class="hlt">System</span> Lessons Learned from 2 1/2 Years of Operation. This document also presents a detailed discussion of lessons learned during the first 2 1/2 years of IRTS operation. This report provides a general discussion of all phases of IRTS operation, and presents additional lessons learned during seven years of IRTS operation.</p> <div class="credits"> <p class="dwt_author">Baker, M.N.; Houston, H.M.</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">312</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">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 class="dwt_publisher"></p> <p class="publishDate">2014-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">313</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/24274469"> <span id="translatedtitle"><span class="hlt">Rift</span> Valley fever in Namibia, 2010.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">During May-July 2010 in Namibia, outbreaks of <span class="hlt">Rift</span> Valley fever were reported to the National Veterinary Service. Analysis of animal specimens confirmed virus circulation on 7 farms. Molecular characterization showed that all outbreaks were caused by a strain of <span class="hlt">Rift</span> Valley fever virus closely related to virus strains responsible for outbreaks in South Africa during 2009-2010. PMID:24274469</p> <div class="credits"> <p class="dwt_author">Monaco, Federica; Pinoni, Chiara; Cosseddu, Gian Mario; Khaiseb, Siegfried; Calistri, Paolo; Molini, Umberto; Bishi, Alec; Conte, Annamaria; Scacchia, Massimo; Lelli, Rossella</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">314</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/41974082"> <span id="translatedtitle">Dynamics of crustal <span class="hlt">rifting</span> in NE Iceland</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Magnetotelluric measurements have revealed a crustal thickness of 8-10 km in the axial <span class="hlt">rift</span> zone of NE Iceland and above the proposed hot spot in central east and north Iceland. The crust thickens with age and is 20-30 km thick in the older Tertiary areas to the east and west of the axial <span class="hlt">rift</span> zone. It also thickens toward north</p> <div class="credits"> <p class="dwt_author">Axel Björnsson</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">315</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/17738437"> <span id="translatedtitle"><span class="hlt">Rifting</span> in iceland: new geodetic data.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Small but measurable lengthening of several survey lines within the eastern <span class="hlt">rift</span> zone of Iceland occurred between 1967 and 1970. The changes can be interpreted as a widening of the <span class="hlt">rift</span> by 6 to 7 centimeters, possibly during the 1970 eruption of Hekla volcano. PMID:17738437</p> <div class="credits"> <p class="dwt_author">Decker, R W; Einarsson, P; Mohr, P A</p> <p class="dwt_publisher"></p> <p class="publishDate">1971-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">316</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3840870"> <span id="translatedtitle"><span class="hlt">Rift</span> Valley Fever in Namibia, 2010</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">During May–July 2010 in Namibia, outbreaks of <span class="hlt">Rift</span> Valley fever were reported to the National Veterinary Service. Analysis of animal specimens confirmed virus circulation on 7 farms. Molecular characterization showed that all outbreaks were caused by a strain of <span class="hlt">Rift</span> Valley fever virus closely related to virus strains responsible for outbreaks in South Africa during 2009–2010.</p> <div class="credits"> <p class="dwt_author">Monaco, Federica; Pinoni, Chiara; Khaiseb, Siegfried; Calistri, Paolo; Molini, Umberto; Bishi, Alec; Conte, Annamaria; Scacchia, Massimo; Lelli, Rossella</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">317</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Myers, Tanya L.; Broocks, Bryan T.; Cannon, Bret D.; Ho, Nicolas</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">318</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2003EAEJA....11729L"> <span id="translatedtitle">Thermo-tectonic evolution of the Upper Rhine Graben <span class="hlt">rift</span> shoulders</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Upper Rhine Graben (URG) is the central segment of the European Cenozoic <span class="hlt">rift</span> <span class="hlt">system</span>, extending from the Mediterranean to the North Sea (Ziegler, 1992). The URG extends over a distance of 300 km from Basel (Switzerland) to Frankfurt (Germany) with an average width of 30--40 km. An initial <span class="hlt">rifting</span> phase is recognised by Middle Eocene (Lutetian) lake deposits. The main <span class="hlt">rifting</span> phase started at the end of the Eocene (Priabonian) and was followed by prominent uplift in the southern URG area in the Miocene (Schumacher, 2002). Apatite fission track (FT) dating is used to constrain the thermo-tectonic evolution of the <span class="hlt">rift</span> shoulders. By FT data modelling varying cooling histories are derived for different tectonic blocks of the <span class="hlt">rift</span> shoulders. In some areas tectonic uplift started in the Upper Cretaceous, a long time before the initial <span class="hlt">rifting</span> of the URG. In the modelled data no increase in cooling, which might represent <span class="hlt">rift</span> shoulder uplift and denudation related to the main <span class="hlt">rifting</span> phase, can be observed. In contrast, in the southern part, the cooling rate increased in Miocene times due to greater uplift and denudation, although the climate changed to cooler and dryer conditions. Contemporaneous with this phase is enormous sediment erosion in the southern graben segment. As a consequence, the driving forces leading to the observed thermo-tectonic evolution of the <span class="hlt">rift</span> shoulders cannot be explained by URG formation and/or climate changes alone, but must be seen in the context of a European intraplate stress regime. References: Schumacher, M.E. (2002): Tectonics, 21: 1--17. Ziegler, P.A. (1992): Tectonophysics, 208: 91--111.</p> <div class="credits"> <p class="dwt_author">Link, K.; Rahn, M.; Keller, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">319</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19950045496&hterms=b10&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3D%2522b10%2522"> <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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Ebinger, C. J.; Deino, A. L.; Tesha, A. L.; Becker, T.; Ring, U.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">320</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/192410"> <span id="translatedtitle">Imaging <span class="hlt">systems</span> for biomedical applications. <span class="hlt">Final</span> report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Many of the activities of the human body manifest themselves by the presence of a very weak magnetic field outside the body, a field that is so weak that an ultra-sensitive magnetic sensor is needed for specific biomagnetic measurements. Superconducting QUantum Interference Devices (SQUIDs) are extremely sensitive detectors of magnetic flux and have been used extensively to detect the human magnetocardiogram, and magnetoencephalogram. and other biomagnetic signals. In order to utilize a SQUID as a magnetometer, its transfer characteristics should be linearized. This linearization requires extensive peripheral electronics, thus limiting the number of SQUID magnetometer channels in a practical <span class="hlt">system</span>. The proposed digital SQUID integrates the processing circuitry on the same cryogenic chip as the SQUID magnetometer and eliminates the sophisticated peripheral electronics. Such a <span class="hlt">system</span> is compact and cost effective, and requires minimal support electronics. Under a DOE-sponsored SBIR program, we designed, simulated, laid out, fabricated, evaluated, and demonstrated a digital SQUID magnetometer. This report summarizes the accomplishments under this program and clearly demonstrates that all of the tasks proposed in the phase II application were successfully completed with confirmed experimental results.</p> <div class="credits"> <p class="dwt_author">Radparvar, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-06-06</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_15");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous 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class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_16");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return 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showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_18");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">321</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6673298"> <span id="translatedtitle"><span class="hlt">Final</span> solar-<span class="hlt">systems</span> monitoring report, 1985</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The Active Solar Monitoring Project was conducted by the Ministry of Energy of the Province of Ontario, Canada, between November, 1982, and October, 1985. The objective of the project was to instrument, monitor, assess, and report on the energy performance and reliability of the solar energy demonstration projects sponsored by the Ministry. The monitoring project was an essential part of Ontario's Solar Energy Program, which included over 190 solar-heating demonstration projects, and 2 photovoltaic demonstration projects. These were located on government buildings, and on commercial, industrial, municipal, institutional, and religious buildings. The solar energy <span class="hlt">systems</span> on some of these buildings, and their monitoring activities, were sponsored jointly by the Ministry of Energy, and Energy Mines, and Resources Canada.</p> <div class="credits"> <p class="dwt_author">Not Available</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">322</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6254586"> <span id="translatedtitle">Improved windpower generating <span class="hlt">system</span>. <span class="hlt">Final</span> report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The following report describes a research and development program to investigate an improved windpower generating <span class="hlt">system</span>. The improved rotor design combines the high starting torque of multi-blade horizontal-axis rotors with the high efficiency of ''propeller'' type rotors. The resulting ''compound'' rotor is believed to have significant advantages over more conventional rotors, particularly for pumping operations. The R and D program involved both analysis and testing. Computer-based rotor analysis programs were modified to accommodate the aerodynamic characteristics of the compounds rotor. The performance of single-surface airfoil sections were investigated in a series of wind tunnel tests. Based on the analytic and airfoil test results, a compound rotor with a diameter of 20.5 ft was designed and tested. The test data verified the calculated performance of the compound rotor and provided the basis for application studies. 10 refs., 50 figs.</p> <div class="credits"> <p class="dwt_author">Bergey, K.; Frazier, J.; Craig, K.; Veragen, P.</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">323</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/578546"> <span id="translatedtitle">Buried waste containment <span class="hlt">system</span> materials. <span class="hlt">Final</span> Report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">This report describes the results of a test program to validate the application of a latex-modified cement formulation for use with the Buried Waste Containment <span class="hlt">System</span> (BWCS) process during a proof of principle (POP) demonstration. The test program included three objectives. One objective was to validate the barrier material mix formulation to be used with the BWCS equipment. A basic mix formula for initial trials was supplied by the cement and latex vendors. The suitability of the material for BWCS application was verified by laboratory testing at the Idaho National Engineering and Environmental Laboratory (INEEL). A second objective was to determine if the POP BWCS material emplacement process adversely affected the barrier material properties. This objective was met by measuring and comparing properties of material prepared in the INEEL Materials Testing Laboratory (MTL) with identical properties of material produced by the BWCS field tests. These measurements included hydraulic conductivity to determine if the material met the US Environmental Protection Agency (EPA) requirements for barriers used for hazardous waste sites, petrographic analysis to allow an assessment of barrier material separation and segregation during emplacement, and a set of mechanical property tests typical of concrete characterization. The third objective was to measure the hydraulic properties of barrier material containing a stop-start joint to determine if such a feature would meet the EPA requirements for hazardous waste site barriers.</p> <div class="credits"> <p class="dwt_author">Weidner, J.R.; Shaw, P.G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">324</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6758597"> <span id="translatedtitle">Condenser inleakage monitoring <span class="hlt">system</span> development. <span class="hlt">Final</span> report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">An instrument/hardware package for air and condenser cooling water inleakage location employing the helium and freon techniques was designed and fabricated. The package consists of design details for tracer gas distribution hardware, injection plenums, and a sample preconditioner and instrument module. Design of the package was based on an evaluation of helium and freon leak detectors and a survey of utility user's experience with the helium and freon techniques. The applicability of the instrument/hardware package to air and cooling water inleakage location was demonstrated at Pacific Gas and Electric Company's Moss Landing Station. The use of calibrated leaks indicated that cooling water leaks down to 1.5 x 10/sup -4/ gpm (0.56 ml/min) and air leaks down to 0.05 cfm were readily detectable with the helium technique, whereas a 4 x 10/sup -4/ gpm (1.5 ml/min) liquid leak was the readily detectable minimum via the freon technique. The field demonstration and in-house detector testing showed the helium technique to be preferable to the freon technique for inleakage location at PWRs, BWRs, and fossil-fueled <span class="hlt">systems</span>.</p> <div class="credits"> <p class="dwt_author">Kassen, W.R.; Putkey, T.A.; Sawochka, S.G.; Pearl, W.L.; Clouse, M.E.</p> <p class="dwt_publisher"></p> <p class="publishDate">1982-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">325</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/52809628"> <span id="translatedtitle">Local Moho Updoming Beneath The Western Eger <span class="hlt">Rift</span>, Central Europe ? Results From Teleseismic Receiver Functions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The Eger <span class="hlt">rift</span> is part of the European Cainozoic <span class="hlt">rift</span> <span class="hlt">system</span>. The tectono-magmatic activity in this area started in the uppermost Cretaceous. The Quaternary to active period is associated with CO2-emanations at the surface, alkaline volcanic activity, neotectonic uplift in the Slavskovsky Les area, active basin formation of the Cheb basin and earthquake swarm activity in the German\\/Czech boundary region</p> <div class="credits"> <p class="dwt_author">W. H. Geissler; R. Kind; H. Kaempf; K. Klinge; T. Plenefisch; J. Zednik; J. Horalek</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">326</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.see.leeds.ac.uk/afar/afar_text/Hamling_DabbahuDykes_GJI2009early.pdf"> <span id="translatedtitle">Geodetic observations of the ongoing Dabbahu <span class="hlt">rifting</span> episode: new dyke intrusions in 2006 and 2007</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A 60-km-long dyke intruded the Dabbahu segment of the Nubia-Arabia Plate boundary (Afar, Ethiopia) in 2005 September, marking the beginning of an ongoing <span class="hlt">rifting</span> episode. We have monitored the continuing activity using Satellite Radar Interferometry (InSAR) and with data from Global Positioning <span class="hlt">System</span> (GPS) instruments and seismometers deployed around the <span class="hlt">rift</span> in response to the initial intrusion. These data show</p> <div class="credits"> <p class="dwt_author">Ian J. Hamling; Atalay Ayele; Laura Bennati; Eric Calais; Cynthia J. Ebinger; Derek Keir; Elias Lewi; Tim J. Wright; Gezahegn Yirgu</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">327</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19770028469&hterms=marathon&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dmarathon"> <span id="translatedtitle">The Sagatu Ridge dike swarm, Ethiopian <span class="hlt">rift</span> margin. [tectonic evolution</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Mohr, P. A.; Potter, E. C.</p> <p class="dwt_publisher"></p> <p class="publishDate">1976-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">328</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Ola, O. B.; Frederiksen, A. W.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">329</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/902726"> <span id="translatedtitle">Next-Generation Linear Collider <span class="hlt">Final</span> Focus <span class="hlt">System</span> Stability Tolerances</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The design of <span class="hlt">final</span> focus <span class="hlt">systems</span> for the next generation of linear colliders has evolved largely from the experience gained with the design and operation of the Stanford Linear Collider (SLC) and with the design of the <span class="hlt">Final</span> Focus Test Beam (FFTB). We will compare the tolerances for two typical designs for a next-generation linear collider <span class="hlt">final</span> focus <span class="hlt">system</span>. The chromaticity generated by strong focusing <span class="hlt">systems</span>, like the <span class="hlt">final</span> quadrupole doublet before the interaction point of a linear collider, can be canceled by the introduction of sextupoles in a dispersive region. These sextupoles must be inserted in pairs separated by a -I transformation (Chromatic Correction Section) in order to cancel the strong geometric aberrations generated by sextupoles. Designs proposed for both the JLC or NLC <span class="hlt">final</span> focus <span class="hlt">systems</span> have two separate chromatic correction sections, one for each transverse plane separated by a ''{beta}-exchanger'' to manipulate the {beta}-function between the two CCS. The introduction of sextupoles and bending magnets gives rise to higher order aberrations (long sextupole and chrome-geometries) and radiation induced aberrations (chromaticity unbalance and ''Oide effect'') and one must optimize the lattice accordingly.</p> <div class="credits"> <p class="dwt_author">Roy, G.; Irwin, J.; /SLAC</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-04-25</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">330</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005AGUFM.T53E..06D"> <span id="translatedtitle">Along-axis Segmentation of the Main Ethiopian <span class="hlt">Rift</span> from Tomographic Inversion of Local Earthquakes</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Geophysical, structural, and geochemical data indicate that the East African <span class="hlt">rift</span> <span class="hlt">system</span> in Ethiopia is in a stage of development transitional between continental and oceanic spreading. In the northern Main Ethiopian <span class="hlt">rift</span> (MER) the archetypal continental <span class="hlt">rift</span> stage border fault <span class="hlt">systems</span> bounding the asymmetric <span class="hlt">rift</span> basins formed at ~11 Ma. After 3.5 Ma, strain localised to fault <span class="hlt">systems</span> within the central basin. By 1.8 Ma, faulting and magmatism localised to an en echelon series of 20 km-wide zone, 50-60 km-long 'magmatic segments' comprising felsic shield volcanoes and basaltic fissural flows and dikes. As part of the international EAGLE project, 50 broadband Guralp 6TD seismometers were deployed across 3 magmatic segments, and a sector of the <span class="hlt">rift</span> without magmatic segments. These instruments nested within the Leeds University broadband array, and the combined net of 80 instruments was used to locate local and regional events. P wave inversion for velocity with a series of synthetic tests will be presented at the meeting along with the best 1d velocity model for locating local earthquakes within the Main Ethiopian <span class="hlt">rift</span>. Results indicate a series of high velocity zones beneath the magnetic segments at a depth of 10km.</p> <div class="credits"> <p class="dwt_author">Daly, E.; Ebinger, C.; Stuart, G.; Keir, D.; Ayele, A.; Waltham, D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">331</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008AGUFM.T43A1984W"> <span id="translatedtitle">Tectonic-Volcanic Interplay in the Dabbahu Segment of the Afar <span class="hlt">Rift</span> from Cosmogenic 3He Constraints</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Afar <span class="hlt">Rift</span> in Ethiopia is one of the only subaerial locations in the world where the transition from continental break-up to oceanic-spreading can be observed. Extension and volcanism in the Afar is concentrated in tectono-magmatic segments (TMS), similar in size and morphology to those that characterise spreading ridges. The Dabbahu TMS is the southernmost of the western Afar and has recently been the site of significant activity. A massive seismic event in late 2005, triggered by the injection of an 8-m wide dyke, heralded the onset of a new <span class="hlt">rifting</span> period in the Dabbahu TMS. Volcanic activity associated with the periods of magma-driven extension, which have recurred at 4-8 mth intervals, has been both silicic (explosive) and basaltic (fissural). The most recent activity in the Afar thus testifies to the close interplay of tectonics and magmatism in <span class="hlt">rifting</span> environments. In an effort to decipher the long-term structural and volcanic evolution of Dabbahu TMS we have employed the cosmogenic nuclide dating technique to provide chronological data for the segment. This method has advantages over other geochronological tools in that we can target both volcanic and tectonic surfaces of a few Kyr to several Myr age. Baddi Volcano, located off-axis on the western margin of the TMS, is a bimodal central stratovolcano typical of the Afar TMS. Late-stage basaltic lava flows cap an acidic base, which has been dated at 290 ± 4 ka using the K-Ar technique (Lahitte et al., 2003). Following preliminary sampling in 2007, we have determined a cosmogenic 3He age of 53.4 ± 3.7 ka from multiple samples from one of the basaltic flows on the NW flank of Baddi. These data show a significant time gap (240 Kyr) between the <span class="hlt">final</span> phase of acidic volcanism and the onset of basaltic activity at the central volcanoes, presumably related to the rate of magma chamber replenishment. To test whether the spectacular shift to basaltic activity at 53 ka represents replenishment of the entire sub-<span class="hlt">rift</span> plumbing <span class="hlt">system</span>, work is underway to measure cosmogenic 3He ages of further structural and volcanic features in the TMS, including the flows that form the extensive basaltic floor of the segment and large fault scarps formed during the initiation of <span class="hlt">rifting</span>. Reference: Lahitte et al., 2003. EPSL 207, 103-116</p> <div class="credits"> <p class="dwt_author">Williams, A.; Pik, R.; Burnard, P.; Lahitte, P.; Yirgu, G.; Adem, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">332</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014EGUGA..16.8467S"> <span id="translatedtitle">Three-Dimensional (3D) Structure of the Malawi <span class="hlt">Rift</span> from Remote Sensing and Geophysics Data</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Malawi <span class="hlt">rift</span> is a Cenozoic aged <span class="hlt">rift</span> representing the southernmost segment of the Western Branch of the East African <span class="hlt">Rift</span> <span class="hlt">System</span> (EARS). This <span class="hlt">rift</span> extends over 900 km from the Rungwe volcanic province (Tanzania) in the north to the Urema graben (Mozambique) to the south, with an average width of 50km. It traverses a complex array of Proterozoic orogenic belts of different ages and Permo-Triassic (Karoo) and cretaceous graben <span class="hlt">systems</span>. The <span class="hlt">rift</span>'s depth is between 3 to 5km partitioned between the topographic escarpment and the sediments fill. The basin's subsidence reflects accumulation of sediments and <span class="hlt">rift</span> flank uplift. Regardless of its importance in understanding <span class="hlt">rift</span> tectonics, especially in Africa, the three-dimensional (3D) geometry of the <span class="hlt">rift</span> is not fully understood. This research presents results from detailed analysis of Digital Elevation Model (DEM) extracted from the Shuttle Radar Topography Mission (SRTM) data to map surface morphological expressions of the entire basin. These results are compared with available seismic data to provide along-strike and at depth variation of the geometry of the border fault <span class="hlt">systems</span>, nature of <span class="hlt">rift</span> segmentation and alternation of the polarity of half-grabens, and the partitioning of displacement between exposed and sub-surface border faults. Our results show the following: (1) Surface expression of border faults show that, unlike the typical half-graben en-echelon <span class="hlt">rift</span> model, where half-graben segments with opposite polarity are linked together through accommodation zones indicative of soft linkage, the Malawi <span class="hlt">rift</span> shows along-strike segmentation by changing geometry from half-graben to full graben geometry. A half-graben with specific polarity passes through a full-graben geometry before giving place to a half-graben with the opposite polarity. The length of half-gaben and graben segments becomes shorter as the <span class="hlt">rift</span> progresses from north to south, and this is accompanied by a decrease in displacement within border faults. This geometry is indicative of the propagation of border faults through hard linkage. (2) The continuation of border faults at the subsurface show patterns consistent with those observed at the surface. At the sub-surface, the general trend of <span class="hlt">rift</span> segmentation, formation of full grabens at the end of each segment, and the decreases in the length of the segments from north to south is consistent with observations at the surface. This suggests the homogeneity of strain accommodation throughout the depth of border faults. (3) Zones of segmentation of the Malawi <span class="hlt">rift</span> coincide with regions where the pre-existing structures (both the Proterozoic basement and the Karoo grabens) are at high angle to the trend of the <span class="hlt">rift</span> whereas well-developed border faults of the basin coincides with N-trending pre-existing structures sub-parallel to the <span class="hlt">rift</span>.</p> <div class="credits"> <p class="dwt_author">Salmi, Haifa S. Al; Abdelsalam, Mohamed G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">333</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/52792810"> <span id="translatedtitle">The Corinth <span class="hlt">Rift</span> Laboratory (CRL) strainmeters: calibration and data analysis</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The Gulf of Corinth (Greece) is one of the most seismic regions in Europe, producing some strong earthquakes in the decades, 1 to 1.5 cm\\/yr of north-south extension, and frequent seismic swarms. This structure is a 110 km long, N110E oriented graben bounded by <span class="hlt">systems</span> of very recent normal faults. The Corinth <span class="hlt">Rift</span> Laboratory (CRL) project is concentrated in the</p> <div class="credits"> <p class="dwt_author">A. Canitano; P. Bernard; A. T. Linde; S. I. Sacks; F. Boudin</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">334</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.springerlink.com/index/c37351p5g81wp848.pdf"> <span id="translatedtitle">A Mathematical Model of <span class="hlt">Rift</span> Valley Fever with Human Host</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary"><span class="hlt">Rift</span> Valley Fever is a vector-borne disease mainly transmitted by mosquito. To gain some quantitative insights into its dynamics,\\u000a a deterministic model with mosquito, livestock, and human host is formulated as a <span class="hlt">system</span> of nonlinear ordinary differential\\u000a equations and analyzed. The disease threshold $$\\\\mathcal{R}_0$$ is computed and used to investigate the local stability of the equilibria. A sensitivity analysis is</p> <div class="credits"> <p class="dwt_author">Saul C. MpesheHeikki; Heikki Haario; Jean M. Tchuenche</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">335</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/14819896"> <span id="translatedtitle">Age of volcanism and <span class="hlt">rifting</span> in southwestern Ethiopia</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">It has been suggested that volcanism in the Ethiopian region of the Afro-Arabian <span class="hlt">Rift</span> <span class="hlt">System</span> has migrated with time, both laterally towards the present axial zone1-3 and longitudinally southwards from the Red Sea4,5. Field data and K-Ar isotopic ages from southwestern Ethiopia, summarised below, indicate that volcanism in this area began earlier than previously suspected, and that Quaternary volcanism was</p> <div class="credits"> <p class="dwt_author">A. Davidson; D. C. Rex</p> <p class="dwt_publisher"></p> <p class="publishDate">1980-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">336</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Sanford, A.; Balch, R. [New Mexico Inst. of Mining and Technology, Socorro, NM (United States); House, L.; Hartse, H. [Los Alamos National Lab., NM (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">337</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4055548"> <span id="translatedtitle"><span class="hlt">Rift</span> Valley Fever Virus Encephalitis Is Associated with an Ineffective <span class="hlt">Systemic</span> Immune Response and Activated T Cell Infiltration into the CNS in an Immunocompetent Mouse Model</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">Background <span class="hlt">Rift</span> Valley fever virus (RVFV) causes outbreaks of severe disease in livestock and humans throughout Africa and the Arabian Peninsula. In people, RVFV generally causes a self-limiting febrile illness but in a subset of individuals, it progresses to more serious disease. One manifestation is a delayed-onset encephalitis that can be fatal or leave the afflicted with long-term neurologic sequelae. In order to design targeted interventions, the basic pathogenesis of RVFV encephalitis must be better understood. Methodology/Principal Findings To characterize the host immune responses and viral kinetics associated with fatal and nonfatal infections, mice were infected with an attenuated RVFV lacking NSs (?NSs) that causes lethal disease only when administered intranasally (IN). Following IN infection, C57BL/6 mice developed severe neurologic disease and succumbed 7–9 days post-infection. In contrast, inoculation of ?NSs virus subcutaneously in the footpad (FP) resulted in a subclinical infection characterized by a robust immune response with rapid antibody production and strong T cell responses. IN-inoculated mice had delayed antibody responses and failed to clear virus from the periphery. Severe neurological signs and obtundation characterized end stage-disease in IN-inoculated mice, and within the CNS, the development of peak virus RNA loads coincided with strong proinflammatory responses and infiltration of activated T cells. Interestingly, depletion of T cells did not significantly alter survival, suggesting that neurologic disease is not a by-product of an aberrant immune response. Conclusions/Significance Comparison of fatal (IN-inoculated) and nonfatal (FP-inoculated) ?NSs RVFV infections in the mouse model highlighted the role of the host immune response in controlling viral replication and therefore determining clinical outcome. There was no evidence to suggest that neurologic disease is immune-mediated in RVFV infection. These results provide important insights for the future design of vaccines and therapeutic options.</p> <div class="credits"> <p class="dwt_author">Dodd, Kimberly A.; McElroy, Anita K.; Jones, Tara L.; Zaki, Sherif R.; Nichol, Stuart T.; Spiropoulou, Christina F.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">338</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007GGG.....810002H"> <span id="translatedtitle">Faults and damage zones in fast-spread crust exposed on the north wall of the Hess Deep <span class="hlt">Rift</span>: Conduits and seals in seafloor hydrothermal <span class="hlt">systems</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The northern escarpments of the Hess Deep <span class="hlt">Rift</span> provide cross-sectional views of in situ, ˜1-Ma-old, upper oceanic crust that underwent extensive, spreading-related brittle deformation. Most of the deformation and associated alteration occurred within the locus of magmatic construction of the East Pacific Rise, in the presence of high-temperature hydrothermal fluids. Passing laterally from undeformed host rocks, brittle deformation zones are classified as (1) damage zones where densely spaced fractures overprint the primary structure of dikes and lavas, (2) cataclastic zones where interconnected fractures, comminuted grains, and matrix minerals define deformational fabrics, and (3) very fine-grained, gouge-filled fault cores. Relative to the host rock, damage and cataclastic zones are rich in veins of chlorite and/or actinolite, and lesser amounts of titanite, epidote, and quartz. These phases mark relict hydrothermal fluid pathways. Trace and major element compositions of representative samples also indicate fault-localized hydrothermal alteration, including an increase in MgO by several weight percent within cataclastic and damage zones. In contrast, the fault cores are composed of very finely comminuted basaltic material and have MgO concentrations similar to the damage zones. Integrated compositional, textural, and outcrop-scale structural data inform an evolutionary model for fault growth from the early, widespread dilational phases of damage-zone development to more restricted noncoaxial strain in the cataclastic zones. With continued fault development, gouge develops and seals the fault cores. While the fault cores are sealed by gouge, surrounding zones remain conduits to hydrothermal fluid flow, except where sealed by secondary minerals. Sealed faults can later be reactivated as conduits with additional increments of fault slip. The dual behavior of faults as conduits and seals inevitably leads to compartmentalization of the flow regime in subaxial and ridge-flank areas.</p> <div class="credits"> <p class="dwt_author">Hayman, Nicholas W.; Karson, Jeffrey A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">339</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/411873"> <span id="translatedtitle">Intracontinental <span class="hlt">rifting</span> and inversion: Missour basin and Atlas Mountains, Morocco</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The intracontinental High and Middle Atlas mountain belts in Morocco intersect to form the southern and western margins of the Missour basin, an intermontane basin formed as a result of the uplift and inversion of the Mesozoic Atlas paleorifts. These <span class="hlt">rifts</span> were areas where the crust was greatly attenuated and more subject to deformation in response to nearby plate boundary tectonics. Data from observations based on seismic reflection profiles and wells over the Missour basin for hydrocarbon exploration and field mapping were used to understand the basin evolution, structural styles, and inversion timing of the nearby Atlas Mountains. Hercynian and Mesozoic normal faults were reactivated into high-angle reverse and thrust faults in the Mesozoic during the Jurassic, Early Cretaceous (early Alpine phase), and the Paleogene (late Alpine phase). The reactivation of synrift normal faults of the paleo-Atlas <span class="hlt">rifts</span> inverted previous half grabens into anticlinal structures, with the axis of the half graben centered below the axis of the inverted anticline. The resulting inverted fold geometries are controlled by the geometries of the extensional planar or listric faults. The Atlas paleorift <span class="hlt">system</span> is one of the largest <span class="hlt">rift</span> <span class="hlt">systems</span> in Africa. Little hydrocarbon exploration has occurred within the Atlas Mountains and the margins of the paleo-Atlas <span class="hlt">rift</span> <span class="hlt">system</span>. Inversion of synrift structures can lead to both the destruction and preservation of synrift traps and the creation of new hydrocarbon traps. The study of the effects of inversion in the Missour basin may lead to the discovery of footwall subthrust hydrocarbon traps in the Mesozoic sedimentary sequence of the Atlas Mountains.</p> <div class="credits"> <p class="dwt_author">Beauchamp, W.; Barazangi, M. [Cornell Univ., Ithaca, NY (United States); Demnati, A.; Alji, M.E. [Office National de Recherches et d`Exploitations Petrolieres, Rabat (Morocco)</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">340</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2003AGUFM.C12B..07B"> <span id="translatedtitle">An Investigation Into the Causes and Limiting Factors of an Active <span class="hlt">Rift</span> on the Amery Ice Shelf: Fieldwork and Modeling Results</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Amery Ice Shelf <span class="hlt">rift</span> <span class="hlt">system</span>, colloquially known as the "Loose Tooth", consists of two longitudinal (parallel-to-flow) <span class="hlt">rifts</span> that formed about 15 years ago, and two transverse <span class="hlt">rifts</span> that together with the western longitudinal <span class="hlt">rift</span>, form a triple junction. A variety of satellite imagery spanning more than one decade has shown that the transverse <span class="hlt">rifts</span> have both been actively propagating over the past decade, and have been, on average, speeding up (Young et al, this session). This past Antarctic field season (2002-2003), we instrumented the main transverse <span class="hlt">rift</span> with 6 GPS and 8 vertical component seismometers. Results indicate that there are several periods of high seismic activity during which the <span class="hlt">rift</span> widens rapidly. Comparison of experimental values of the critical stress intensity factor (a measure of the strength of the ice) with the stress acting at the tip of the <span class="hlt">rift</span> calculated for an elastic ice shelf, suggest that the <span class="hlt">rift</span> should propagate unstably. In an attempt to resolve this paradox we consider two possible explanations. First we examine the effect of a viscoelastic rheology of ice on dissipation of the stress at the tip of the <span class="hlt">rift</span>; the associated time scale competes with the time scales attached to the loading mechanisms which control the rate of stress accumulation. In contrast the effect of an array of longitudinal crevasses on the stress field concentrated ahead of the <span class="hlt">rift</span> is largely geometrical. <span class="hlt">Rift</span> propagation is hindered because the crevasses create areas that are effectively weaker than the surrounding ice. We use a boundary element model to evaluate the effect of an array of crevasses on the stress concentrated at the tip of the <span class="hlt">rift</span>.</p> <div class="credits"> <p class="dwt_author">Bassis, J. N.; Fricker, H.; Coleman, R.; Minster, B.</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-12-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_16");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a 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href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a style="font-weight: bold;">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_19");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">341</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=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> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p class="result-summary">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> <div class="credits"> <p class="dwt_author">Campbell, J. Olin; And Others</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">342</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..15.8882D"> <span id="translatedtitle">Faulting Mode Characterization using fault attributes : Example of a nascent oceanic <span class="hlt">rift</span> the Manda-Hararo <span class="hlt">rift</span> in Afar (Ethiopia)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Manda-Hararo <span class="hlt">rift</span> segment, located in the Afar depression, underwent a major dyke injection of 65 km long in September 2005, that initiated a <span class="hlt">rifting</span> episode. From June 2006 to May 2010, 13 other successive dykes were intruded and monitored using InSAR and seismic surveys. Aside from its recent activity, the Manda-Hararo <span class="hlt">rift</span> architecture shows some particularities which distinguish the segment North of the central magma chamber from the rest of the <span class="hlt">rift</span>. This Northern segment shows a change of strike of the <span class="hlt">rift</span> axis and of the overlying faults, as well as a marked asymmetry featured by high no-conjugated west-dipping scarps. These observations led to wonder how the Northern part of this <span class="hlt">rift</span> has been integrated into the long-term evolution of the whole <span class="hlt">rift</span>, and whether its deformation mode and fault growth processes might be influenced by the Dabbahu volcano. To address such questions, we focus our analysis on the scaling laws applied to the fault attributes such as fault length, fault scarps or spacing between adjacent faults. This study is based on a fault mapping which was done using optical images (SPOT and, QUICKBIRD images) together with SAR interferograms and coherence images. This map is divided into three regions to isolate the different sources of deformation : the Northern segment close to the Dabbahu volcano, the central one where the main magma reservoir is located and dyke intrusions occurred, and <span class="hlt">finally</span> the southernmost one coinciding with the segment end. A first stage in determining the scaling law, and consequently the growth mode, consists in characterizing the displacement (Dmax) versus length (L) relationship. With our whole dataset and the different groups of segments defined previously, we observe a scattering suggesting no clear evidence for a linear trend associated with self-similar processes. A possible explanation for such observation in addition to the sampling issue would be a distributed mode of deformation (Soliva et al. 2008). Next, for each of these three regions, we determine the distribution law and discuss them in terms of fault growth pro