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Sample records for overriding continental plate

  1. Geodynamic models of continental subduction and obduction of overriding plate forearc oceanic lithosphere on top of continental crust

    NASA Astrophysics Data System (ADS)

    Edwards, Sarah J.; Schellart, Wouter P.; Duarte, Joao C.

    2015-07-01

    Continental subduction takes place in the final stage of subduction when all oceanic lithosphere is consumed and continental passive margin is pulled into the mantle. When the overriding plate is oceanic, dense forearc oceanic lithosphere might be obducted onto light continental crust forming an ophiolite (Tethyan-style ophiolite obduction). Four-dimensional dynamic analog subduction models have been constructed to evaluate the mechanical feasibility of continental subduction and forearc oceanic lithosphere obduction on top of continental crust. The roles of continental crust thickness, passive margin length, subducting lithosphere thickness, and overriding plate thickness were investigated to determine the maximum continental subduction depth, maximum forearc obduction distance, and forearc deformation during continental subduction. Our buoyancy-driven experiments indicate that deep continental subduction occurs in most circumstances (down to ~560 km) and that obduction of dense oceanic forearc lithosphere on top of light continental crust is mechanically feasible. Maximum obduction distances are relatively small (~26-37 km) but are sufficient to explain obduction of short ophiolite sheets, such as observed in New Caledonia. When including the thin (5-10 km thick) accretionary wedge of off-scraped deep sea sediments, oceanic crust, and mantle, then maximum obduction distances are much larger, ~60-160 km, sufficient to account for the obducted Northland Allochthon in New Zealand. Results indicate that increasing continental crust thickness decreases continental subduction depth, whereas increasing passive margin length and subducting lithosphere thickness increases continental subduction depth. Notably, during continental subduction, backarc extension continues, while forearc deformation (shortening) increases moderately compared to the preceding phase of normal (oceanic) subduction.

  2. Overriding Plate Controls on Subduction Zone Evolution

    NASA Astrophysics Data System (ADS)

    Sharples, W. K.; Jadamec, M. A.; Moresi, L. N.; Capitanio, F. A.

    2014-12-01

    Seismic data, rock deformation experiments, and geochemical studies indicate variability in the thickness, buoyancy, and strength of the lithosphere at plate boundaries. However, geodynamic models of subduction commonly either omit an overriding plate or do not investigate role of the variation in overriding plate properties on the subduction evolution. We present time-dependent numerical models of subduction that vary the overriding plate thickness, strength, and density and allow for a plate interface that evolves with time via an anisotropic brittle failure rheology. We examine the emergence of (a) asymmetric versus symmetric subduction, (b) trench retreat versus advance, (c) subduction zone geometry, (d) slab stagnation versus penetration into the lower mantle, and (e) flat slab subduction. The majority of the models result in sustained asymmetric subduction. The models demonstrate that trench retreat is correlated with a thin overriding plate, whereas, trench advance is correlated with a thick and/or strong overriding plate. Slab dip, measured at a depth below the plate boundary interface, has a negative correlation with an increase in overriding plate thickness. Overriding plate thickness exerts a first order control over slab penetration into the lower mantle, with penetration most commonly occurring in models with a thick overriding plate. Periods of flat slab subduction occur with thick, strong overriding plates producing strong plate boundary interface coupling. The results provide insight into how the overriding plate plays a role in establishing advancing and retreating subduction, as well as providing an explanation for the variation of slab geometry observed in subduction zones on Earth.

  3. Overriding plate thickness control on subducting plate curvature

    NASA Astrophysics Data System (ADS)

    Holt, Adam F.; Buffett, Bruce A.; Becker, Thorsten W.

    2015-05-01

    Subducting plate (SP) curvature exerts a key control on the amount of bending dissipation associated with subduction, and the magnitude of the subduction-resisting bending force. However, the factors controlling the development of SP curvature are not well understood. We use numerical models to quantify the role of SP rheology on the minimum radius of curvature, Rmin. We find that Rmin depends strongly on the SP thickness when the rheology is viscous. This dependence is substantially reduced when the SP behaves plastically, in line with the lack of correlation between Rmin and SP thickness on Earth. In contrast, plasticity leads to a strong positive correlation between Rmin and the overriding plate (OP) thickness. Using an analysis of Rmin versus OP thickness, we show that such a positive correlation exists on Earth. This suggests that OP structure, in conjunction with SP plasticity, is crucial in generating slab curvature systematics on Earth.

  4. Overriding plate thickness control on subducting slab curvature

    NASA Astrophysics Data System (ADS)

    Holt, A.; Buffett, B. A.; Becker, T. W.

    2014-12-01

    The curvature of subducting lithosphere controls deformation due to bending at the trench, which results in a force that dissipates gravitational potential energy and may affect seismic coupling. We use 2-D, thermo-mechanical subduction models to explore the dependence of the radius of curvature on the thickness of the subducting and overriding plates for models with both viscous and effectively plastic lithospheric rheologies. Such a plastic rheology has been shown to reproduce the bending stresses/moment computed using a kinematic strain rate description and a laboratory derived composite rheology. Laboratory and numerical models show that the bending geometry of subducting slabs with a viscous rheology is strongly dependent on slab thickness; thicker plates have a larger radius of curvature. However, the curvature of subducting plates on Earth, illuminated by the distribution of earthquake hypocenters, shows little to no dependence on the plate thickness or age. Such an observation is instead compatible with plates that have a plastic rheology. Indeed, our numerical models show that the radius of curvature of viscous plates has a stronger dependence on subducting plate thickness than in equivalent plastic models. In viscous plates, the bending moment produces a torque, which balances the torque exerted by buoyancy. However, for the plastic plate case the bending moment saturates at a maximum value and so cannot balance the gravitational torque. The saturation of bending moment means that, (a) the radius of curvature of the bending region is not constrained by this torque balance, and, (b) other forces are required to balance the gravitational torque. We explore the role that the overriding plate could play in controlling the subducting plate curvature in plastic plate models where the bending stresses have saturated. For such plates, we find that increasing the thickness of the overriding plate causes the radius of curvature to increase. The same correlation is found in real subduction zones when the radius of curvature is compared with near-trench overriding lithospheric thickness. We suggest that the thickness of the overriding plate, through controlling the depth extent of the slab suction caused by the strong overriding plate, exerts a primary control on the curvature of subducting lithosphere.

  5. Three-dimensional dynamic models of subducting plate-overriding plate-upper mantle interaction

    NASA Astrophysics Data System (ADS)

    Meyer, C.; Schellart, W. P.

    2013-02-01

    We present fully dynamic generic three-dimensional laboratory models of progressive subduction with an overriding plate and a weak subduction zone interface. Overriding plate thickness (TOP) is varied systematically (in the range 0-2.5 cm scaling to 0-125 km) to investigate its effect on subduction kinematics and overriding plate deformation. The general pattern of subduction is the same for all models with slab draping on the 670 km discontinuity, comparable slab dip angles, trench retreat, trenchward subducting plate motion, and a concave trench curvature. The narrow slab models only show overriding plate extension. Subduction partitioning (vSP? / (vSP? + vT?)) increases with increasing TOP, where trenchward subducting plate motion (vSP?) increases at the expense of trench retreat (vT?). This results from an increase in trench suction force with increasing TOP, which retards trench retreat. An increase in TOP also corresponds to a decrease in overriding plate extension and curvature because a thicker overriding plate provides more resistance to deform. Overriding plate extension is maximum at a scaled distance of ~200-400 km from the trench, not at the trench, suggesting that basal shear tractions resulting from mantle flow below the overriding plate primarily drive extension rather than deviatoric tensional normal stresses at the subduction zone interface. The force that drives overriding plate extension is 5%-11% of the slab negative buoyancy force. The models show a positive correlation between vT? and overriding plate extension rate, in agreement with observations. The results suggest that slab rollback and associated toroidal mantle flow drive overriding plate extension and backarc basin formation.

  6. Trench migration and overriding plate stress in dynamic subduction models

    NASA Astrophysics Data System (ADS)

    Holt, A. F.; Becker, T. W.; Buffett, B. A.

    2015-04-01

    On Earth, oceanic plates subduct beneath a variety of overriding plate (OP) styles, from relatively thin and negatively buoyant oceanic OPs to thick and neutrally/positively buoyant continental OPs. The inclusion of an OP in numerical models of self-consistent subduction has been shown to reduce the rate that subducting slabs roll back relative to the equivalent single plate models. We use dynamic, 2-D subduction models to investigate how the mechanical properties, namely viscosity, thickness, and density, of the OP modify the slab rollback rate and the state of stress of the OP. In addition, we examine the role of the subducting plate (SP) viscosity. Because OP deformation accommodates the difference between the slab rollback rate and the far-field OP velocity, we find that the temporal variations in the rollback rate results in temporal variations in OP stress. The slabs in our models roll back rapidly until they reach the lower mantle viscosity increase, at which point the rollback velocity decreases. Concurrent with this reduction in rollback rate is a switch from an OP dominated by extensional stresses to a compressional OP. As in single plate models, the viscosity of the SP exerts a strong control on subducting slab kinematics; weaker slabs exhibit elevated sinking velocities and rollback rates. The SP viscosity also exerts a strong control on the OP stress regime. Weak slabs, either due to reduced bulk viscosity or stress-dependent weakening, have compressional OPs, while strong slabs have dominantly extensional OPs. While varying the viscosity of the OP alone does not substantially affect the OP stress state, we find that the OP thickness and buoyancy plays a substantial role in dictating the rate of slab rollback and OP stress state. Models with thick and/or negatively buoyant OPs have reduced rollback rates, and increased slab dip angles, relative to slabs with thin and/or positively buoyant OPs. Such elevated trench rollback for models with positively buoyant OPs induces extensional stresses in the OP, while OPs that are strongly negatively buoyant are under compression. While rollback is driven by the negative buoyancy of the subducting slab in such models of free subduction, we conclude that the physical properties of the OP potentially play a significant role in modulating both rollback rates and OP deformation style on Earth.

  7. Tibetan plate overriding the Asian plate in central and northern Tibet

    NASA Astrophysics Data System (ADS)

    Zhao, Wenjin; Kumar, Prakash; Mechie, James; Kind, Rainer; Meissner, Rolf; Wu, Zhenhan; Shi, Danian; Su, Heping; Xue, Guangqi; Karplus, Marianne; Tilmann, Frederik

    2011-12-01

    The southern boundary between India and the Tibetan Plateau represents a classical case of continental subduction, where the Indian continental lithosphere is subducted northwards beneath the Tibetan Plateau. At the northern boundary, southward subduction of Asian lithosphere beneath the Tibetan Plateau has also been proposed, but imaging has been hampered by inadequate data quality. Here we analyse the plate tectonic structure of the northern boundary between Tibet and Asia using the S receiver function technique. Our passive source seismic data build on, and extend further northwards, the existing geophysical data from the International Deep Profiling of Tibet and the Himalaya project. We detect, beneath central and northern Tibet, a relatively thin, but separate, Tibetan lithosphere overriding the flat, southward subducting Asian lithosphere. We suggest that this overriding Tibetan lithosphere helps to accommodate the convergence between India and Asia in central and northern Tibet. We conclude that the Tibetan-Himalayan system is composed of three major parts: the Indian, Asian and Tibetan lithospheres. In the south, the Indian lithosphere underthrusts Tibet. In central and northern Tibet a separate, thin Tibetan lithosphere exists, which is underthrust by the Asian lithosphere from the north.

  8. A thermo-mechanical model of horizontal subduction below an overriding plate

    NASA Astrophysics Data System (ADS)

    van Hunen, Jeroen; van den Berg, Arie P.; Vlaar, Nico J.

    2000-10-01

    Subduction of young oceanic lithosphere cannot be explained by the gravitational driving mechanisms of slab pull and ridge push. This deficiency of driving forces can be overcome by obduction of an actively overriding plate, which forces the young plate either to subduct or to collide. This mechanism leads to shallow flattening of the slab as observed today under parts of the west coast of North and South America. Here this process is examined by means of numerical modeling. The convergence velocity between oceanic and continental lithospheric plates is computed from the modeling results, and the ratio of the subduction velocity over the overriding velocity is used as a diagnostic of the efficiency of the ongoing subduction process. We have investigated several factors influencing the mechanical resistance working against the subduction process. In particular, we have studied the effect of a preexisting lithospheric fault with a depth dependent shear resistance, partly decoupling the oceanic lithosphere from the overriding continent. We also investigated the lubricating effect of a 7 km thick basaltic crustal layer on the efficiency of the subduction process and found a log-linear relation between convergence rate and viscosity prefactor characterizing the strength of the oceanic crust, for a range of parameter values including values for basaltic rocks, derived from empirical data. A strong mantle fixes the subducting slab while being overridden and prevents the slab from further subduction in a Benioff style. Viscous heating lowers the coupling strength of the crustal interface between the converging plates with about half an order of magnitude and therefore contributes significantly to the subduction process. Finally, when varying the overriding velocity from 2.5 to 10 cm yr -1, we found a non-linear increase of the subduction velocity due to the presence of non-linear mantle rheology. These results indicate that active obduction of oceanic lithosphere by an overriding continental lithosphere is a viable mechanism for shallow flat subduction over a wide range of model parameters.

  9. Overriding plate deformation and its energy dissipation in three-dimensional subduction models

    NASA Astrophysics Data System (ADS)

    Chen, Zhihao; Schellart, Wouter; Duarte, Joao

    2015-04-01

    Analogue and numerical models of subduction have been used to investigate overriding plate deformation during subduction. However, most models either exclude an overriding plate or impose an external force/velocity. Here, we present three-dimensional buoyancy-driven laboratory subduction models including an overriding plate to study the progressive deformation of the overriding plate during subduction. Considering there is uncertainty in the effective viscosity ratio between the subducting plate and sub-lithospheric upper mantle (?SP/?UM), a variability in overriding plate thickness (TOP), and complexity of the far-field plate boundary conditions in natural subduction zones, we investigate models in which we vary ?SP/?UMfrom 157 to 560, TOP from 1.0 cm to 2.5 cm (scaling to 50-125 km in nature), and far-field plate boundary conditions of the overriding plate and subducting plate. Our results show that the variability of these three parameters has an influence on the patterns of overriding plate deformation. Furthermore, we have used the subduction models to quantify the force (FOPD) that drives overriding plate deformation and the involved energy dissipation rate (?OPD) during such deformation, and we compare them with the negative buoyancy (FBU) and the total potential energy release rate (?BU) of the subducted slab, respectively. In our models of narrow subduction zones (15 cm in experiment, scaling to 750 km in nature) the overriding plate always experiences overall extension during trench retreat. Overall, FOPD/FBU has average values of 0.5-2.5%, with a maximum of 5.0% and ?OPD/?BUhas average values of 0.10-0.30%, with a maximum of 0.70%, which indicate that only a small portion of the negative buoyancy of the subducted slab is used to deform the overriding plate and an even smaller percentage of the slab's potential energy is consumed during overriding plate deformation. In addition, our results show that 2-30% of the overriding plate energy dissipation is dissipated in the forearc region and 14-42% in the region of maximum backarc extension. Finally, our calculated force to deform overriding plate is of comparable magnitude as the ridge push force in nature.

  10. Quantifying the energy dissipation of overriding plate deformation in three-dimensional subduction models

    NASA Astrophysics Data System (ADS)

    Chen, Zhihao; Schellart, Wouter P.; Duarte, João. C.

    2015-01-01

    In a subduction system the force and the energy required to deform the overriding plate are generally thought to come from the negative buoyancy of the subducted slab and its potential energy, respectively. Such deformation might involve extension and back-arc basin formation or shortening and mountain building. How much of the slab's potential energy is consumed during overriding plate deformation remains unknown. In this work, we present dynamic three-dimensional laboratory experiments of progressive subduction with an overriding plate to quantify the force (FOPD) that drives overriding plate deformation and the associated energy dissipation rate (?OPD), and we compare them with the negative buoyancy (FBU) of the subducted slab and its total potential energy release rate (?BU), respectively. We varied the viscosity ratio between the plates and the sublithospheric upper mantle with ?SP/?UM = 157-560 and the thickness of the overriding plate with TOP = 0.5-2.5 cm (scaling to 25-125 km in nature). The results show that FOPD/FBU has average values of 0.5-2.0%, with a maximum of 5.3%, and ?OPD/?BU has average values of 0.05-0.30%, with a maximum of 0.41%. The results indicate that only a small portion of the negative buoyancy of the slab and its potential energy are used to deform the overriding plate. Our models also suggest that the force required to deform the overriding plate is of comparable magnitude as the ridge push force. Furthermore, we show that in subduction models with an overriding plate bending dissipation at the subduction zone hinge remains low (3-15% during steady state subduction).

  11. A thermo-mechanical model of horizontal subduction below an overriding plate

    E-print Network

    Utrecht, Universiteit

    by the gravitational driving mechanisms of slab pull and ridge push. This deficiency of driving forces can be overcome; viscosity; plates; mantle 1. Introduction Gravitational instability forces such as slab pull and ridge push friction and friction or drag from the overriding plate and mantle below. The dominance of slab pull

  12. Subduction of the Caribbean Plate and Basement Uplifts in the Overriding South American Plate

    NASA Astrophysics Data System (ADS)

    Kellogg, J. N.; Bonini, W. E.

    1982-06-01

    The new tectonic interpretations presented in this paper are based on geologic field mapping and gravity data supplemented by well logs, seismic profiles, and radiometric and earthquake data. The present Caribbean-South American plate boundary is the South Caribbean marginal fault, where subduction is indicated by folding and thrusting in the deformed belt and a seismic zone that dips 30° to the southeast and terminates 200 km below the Maracaibo Basin. The Caribbean-South American convergence rate is estimated as 1.9 ± 0.3 cm/yr on the basis of the 390-km length of the seismic zone and a thermal equilibration time of 10 m.y. The Caribbean-South American convergence has produced a northwest-southeast maximum principal stress direction ?1 in the overriding South American plate. The mean ?1 direction for the Maracaibo-Santa Marta block is 310° ± 10° based on earthquake focal mechanism determinations, and structural and gravity data. On the overriding South American plate, basement blocks have been uplifted 7-12 km in the last 10 m.y. to form the Venezuelan Andes, Sierra de Perija, and the Colombian Santa Marta massif. Crystalline basement of the Venezuelan Andes has been thrust to the northwest over Tertiary sediments on a fault dipping about 25° and extending to the mantle. In the Sierra de Perija, Mesozoic sediments have been thrust 16-26 km to the northwest over Tertiary sandstones along the Cerrejon fault. A thrust fault dipping 15° ± 10° to the southeast is consistent with field mapping, and gravity and density data. The Santa Marta massif has been uplifted 12 km in the last 10 m.y. by northwest thrusting over sediments. The basement block overthrusts of the Perijas, Venezuelan Andes, and the Santa Marta massif are Pliocene-Pleistocene analogs for Laramide orogenic structures in the middle and southern Rocky Mountains of the United States. The nonmagmatic basement block uplifts along low-angle thrust faults reveal horizontal compression in the overriding plate over 500 km from the convergent margin. Present-day east northeast-west southwest (080°) compression is indicated by earthquake focal mechanisms and strike slip motion on the Bocono fault. These earthquakes are intraplate deformation associated with east-west (080°) Nazca-South American convergence.

  13. Sunda-Java trench kinematics, slab window formation and overriding plate deformation since the Cretaceous

    E-print Network

    Müller, Dietmar

    Sunda-Java trench kinematics, slab window formation and overriding plate deformation since along the 3200 km long Sunda-Java trench, one of the largest subduction systems on Earth. Combining window underlying the Java­South Sumatra region, and we propose that decreased mantle wedge viscosities

  14. The Continental Plates are Getting Thicker.

    ERIC Educational Resources Information Center

    Kerr, Richard A.

    1986-01-01

    Reviews seismological studies that provide evidence of the existence of continental roots beneath the continents. Suggests, that through the collisions of plate tectonics, continents stabilized part of the mobile mantle rock beneath them to form deep roots. (ML)

  15. Three-dimensional dynamic laboratory models of subduction with an overriding plate and variable interplate rheology

    NASA Astrophysics Data System (ADS)

    Duarte, João C.; Schellart, Wouter P.; Cruden, Alexander R.

    2013-10-01

    Subduction zones are complex 3-D features in which one tectonic plate sinks underneath another into the deep mantle. During subduction the overriding plate (OP) remains in physical contact with the subducting plate and stresses generated at the subduction zone interface and by mantle flow force the OP to deform. We present results of 3-D dynamic laboratory models of subduction that include an OP. We introduce new interplate materials comprising homogeneous mixtures of petrolatum and paraffin oil to achieve progressive subduction. The rheology of these mixtures is characterized by measurements using a strain rate controlled rheometer. The results show that the strength of the mixture increases with petrolatum content, which can be used as a proxy for the degree of mechanical coupling along the subduction interface. Results of subduction experiments are presented with different degrees of mechanical coupling and the influence this has on the dynamics and kinematics of subduction. The modelling results show that variations in the degree of mechanical coupling between the plates have a major impact on subduction velocities, slab geometry and the rate of OP deformation. In all experiments the OP is displaced following trench migration and experiences overall extension localized in the plate interior. This suggests that OP deformation is driven primarily by the toroidal component of subduction-related mantle return flow. The subduction rate is always very slow in experiments with medium mechanical coupling, and subduction stops prematurely in experiments with very high coupling. This implies that the shear forces along the plate interface in natural subduction zone systems must be relatively low and do not vary significantly. Otherwise a higher variability in natural subduction velocities should be observed for mature, non-perturbed subduction zones. The required low shear force is likely controlled by the rheology of highly hydrated sedimentary and basaltic rocks.

  16. Plate Tectonics and Continental Drift: Classroom Ideas.

    ERIC Educational Resources Information Center

    Stout, Prentice K.

    1983-01-01

    Suggests various classroom studies related to plate tectonics and continental drift, including comments on and sources of resource materials useful in teaching the topics. A complete list of magazine articles on the topics from the Sawyer Marine Resource Collection may be obtained by contacting the author. (JN)

  17. Time-dependent evolution of slab geometry and trench-parallel flow due to non-uniform overriding plates. Results from numerical modeling. (Invited)

    NASA Astrophysics Data System (ADS)

    Rodríguez-González, J.; Billen, M. I.; Negredo, A. M.

    2013-12-01

    The direction of mantle flow, as inferred from observations of seismic anisotropy measurements, shows a poor correlation with plate tectonic motion near subduction zones. Below the slab seismic anisotropy is aligned parallel to the trench in the central region and perpendicular near the edges. Above the slab it has a complex pattern, often showing abrupt transitions between trench-parallel and trench-perpendicular fast directions and sharp changes in intensity. Previous models have shown that overriding plate thermal state influences the slab dip and variations in slab dip can cause trench-parallel flow above the slab. This suggests a causal link between overriding plate structure, slab geometry and mantle flow in subduction zones. We implement generic 3D time dependent thermo mechanical numerical models of buoyancy driven subduction to study the effect of overriding plate structure on the evolution of slab geometry and induced mantle flow. We find that along-strike variation in thermal thickness of the overriding plate causes increased hydrodynamic suction and shallower slab dip beneath the colder portion of the overriding plate; the variation in slab geometry drives strong trench-parallel flow beneath the slab and a complex flow pattern above the slab. The location and strength of trench-parallel flow vary with the time-dependent evolution of the slab, suggesting that the global variability in seismic anisotropy observations in subduction zones is in part due to the non-steady-state behavior of these systems. This new mechanism for driving trench-parallel flow provides a good explanation for seismic anisotropy observations from the Middle and South America subduction zones, where both slab dip and overriding plate thermal state are strongly variable. Slab-induced mantle flow. a. Model A with a uniform overriding plate; b. Model B with a non-uniform overriding plate. Vertical trench-perpendicular cross-sections showing the model predictions after 4.4 Myr of evolution showing the trench-parallel component of the velocity (colors; red and blue indicate north- and south-directed flow respectively) and vertical projection of the velocity field (arrows). The location of the slab is indicated by the 1000°C isotherm (gray line). Due to the variations of the slab dip, Model B shows larger regions of trench-parallel flow both above and below the slab.

  18. Continental tectonics in the aftermath of plate tectonics

    NASA Technical Reports Server (NTRS)

    Molnar, Peter

    1988-01-01

    It is shown that the basic tenet of plate tectonics, rigid-body movements of large plates of lithosphere, fails to apply to continental interiors. There, buoyant continental crust can detach from the underlying mantle to form mountain ranges and broad zones of diffuse tectonic activity. The role of crustal blocks and of the detachment of crustal fragments in this process is discussed. Future areas of investigation are addressed.

  19. Comment on "The potential influence of subduction zone polarity on overriding plate deformation, trench migration and slab dip angle" by W.P. Schellart

    E-print Network

    deformation, trench migration and slab dip angle" by W.P. Schellart Carlo Doglioni Dipartimento di Scienze on overriding plate deformation, trench migration and slab dip angle. Tectonophysics, 445, 363­372.] paper uses of the lithosphere. © 2008 Elsevier B.V. All rights reserved. Keywords: Westward drift Subduction hinge Trench

  20. Author's personal copy Continental lithosphere of the Arabian Plate: A geologic, petrologic, and

    E-print Network

    Stern, Robert J.

    , and a Phanerozoic succession (Arabian Platform) that thickens, and a surface that descends to sea level, eastwardAuthor's personal copy Continental lithosphere of the Arabian Plate: A geologic, petrologic Keywords: Arabian Plate continental crust lithosphere The Arabian Plate originated 25 Ma ago by rifting

  1. Seismic investigation of the transition from continental to oceanic subduction along the western Hellenic Subduction Zone

    E-print Network

    Pearce, Frederick Douglas

    The western Hellenic subduction zone (WHSZ) exhibits well-documented along-strike variations in lithosphere density (i.e., oceanic versus continental), subduction rates, and overriding plate extension. Differences in slab ...

  2. Overriding plate structure of the Nicaragua convergent margin: Constraints on the limits of the seismogenic zone and the 1992 tsunami earthquake

    NASA Astrophysics Data System (ADS)

    Sallarès, V.; Meléndez, A.; Prada, M.; Ranero, C. R.; McIntosh, K.; Grevemeyer, I.

    2012-04-01

    We present 2D P-wave velocity models of the Nicaragua convergent margin along two perpendicular wide-angle seismic profiles acquired in the rupture area of the 1992 tsunami earthquake. The models focus on the structure of the overriding plate and the geometry of the inter-plate boundary. In the trench-perpendicular profile, the basement shows increasing velocity reflecting a progressive decrease in the degree of rock fracturing of the igneous basement. Upper mantle-like velocities are obtained at a depth of ~10 km beneath the fore-arc Sandino basin, indicating that the mantle wedge is shallow and located close to the trench. A mismatch between the inter-plate reflector in the velocity models and along coincident multi-channel seismic profiles is best explained by a ~15% velocity anisotropy, suggesting locally-enhanced rock fracturing which is related with the presence of a prominent subducted seamount. The frontal part of the overriding plate is probably too fractured to store elastic energy, unless the presence of local asperities such as the subducted seamount makes it conditionally stable by locally increasing the normal stress. The downdip limit of the seismogenic zone occurs near the tip of the mantle wedge, indicating that it is probably controlled by the presence of a weak, serpentinized mantle wedge beneath the Sandino basin. The hypocenter of the 1992 main shock is not particularly shallow (20-22 km), but seismological data indicate that it triggered sub-events near the trench, the main of which coincides with the subducted seamount. We show that the slow propagation velocity and long duration of the 1992 earthquake could be explained by rupture propagating within the fractured basement rocks and not into the sediments.

  3. Linking continental drift, plate tectonics and the thermal state of the Earth's mantle

    E-print Network

    Tackley, Paul J.

    tectonics continents thermal insulation mantle convection a b s t r a c t Continents slowly drift at the top regions and are caused by a time- variable efficiency of thermal insulation of the continental convectionLinking continental drift, plate tectonics and the thermal state of the Earth's mantle T. Rolf a

  4. Tectonic features associated with the overriding of an accretionary wedge on top of a rifted continental margin: An example from Taiwan

    E-print Network

    Lin, Andrew Tien-Shun

    obliquely impinged on the northern continental slope of the South China Sea (SCS) margin. We analyzed setting. In the upper SCS slope and adjacent to the accretionary wedge, the rifted continental margin continental margin: An example from Taiwan Andrew T. Lin a, , Char-Shine Liu b , Che-Chuan Lin a , Philippe

  5. INTRODUCTION The collision of two continental plates is initi-

    E-print Network

    Sinclair, Hugh D.

    of the passive margin initiates the foreland basin in a deep-water setting. Third, the emergence of the thrust of the leading edge of one plate on to the outer passive margin of the other. The toe of the deforming thrust transition in peripheral foreland basins has been interpreted as record- ing the passage of the thrust wedge

  6. Large earthquakes in stable continental plate interiors: the need for a new paradigm

    NASA Astrophysics Data System (ADS)

    Calais, Eric; Camelbeeck, Thierry; Stein, Seth

    2014-05-01

    The occurrence of large earthquakes in stable continental plate interiors has so far resisted our understanding. Contrary to plate boundary settings, where a balance is achieved over <1000 years between the rates at which strain accumulates and is released in large events, intraplate earthquakes occur in regions where no discernable strain is building up today. In the absence of current strain accumulation, their triggering mechanism remains elusive, as well as the mechanism by which faults having already ruptured in large events might be reloaded to permit sequences of large events, such as in the New Madrid, Central-Eastern U.S., sequence. Earthquake activity in such settings does not seem to be persistent at the location of past large historical earthquakes, which appear to be episodic, clustered and spatially migrating through time. The relationship between long-term geological structures and earthquakes is poorly understood and the ability of intraplate current producing M3-4 events to rupture in M6 and larger earthquakes is unknown. Finally, the fact that the steady-state plate boundary model -- which forms the basis for seismic hazard estimation -- does not seem to hold in continental interiors makes accurate seismic hazard estimation in such setting particularly challenging. We will review these issues and argue that our understanding of earthquakes in continental plate interiors requires a paradigm shift.

  7. Role of plate kinematics and plate-slip-vector partitioning in continental magmatic arcs: Evidence from the Cordillera Blanca, Peru

    SciTech Connect

    McNulty, B.A.; Farber, D.L.; Wallace, G.S.; Lopez, R.; Palacios, O.

    1998-09-01

    New structural and geochronological data from the Cordillera Blanca batholith in the Peruvian Andes, coupled with Nazca-South American plate-slip-vector data, indicate that oblique convergence and associated strike-slip partitioning strongly influenced continental magmatic arc evolution. Both the strain field and mode of magmatism (plutonism vs. volcanism) in the late Miocene Peruvian Andes were controlled by the degree to which the arc-parallel component of the plate slip vector was partitioned into the arc. Strong strike-slip partitioning at ca. 8 Ma produced arc-parallel sinistral shear, strike-slip intercordilleran basins and east-west-oriented tension fractures that facilitated emplacement of the Cordillera Blanca batholith (ca. 8.2 {+-} 0.2 Ma). Periods during which the strike-slip component was not partitioned into the arc (ca. 10 and ca. 7 Ma) were associated with roughly arc-normal contraction and ignimbrite volcanism. The data thus support the contention that contraction within continental magmatic arcs favors volcanism, whereas transcurrent shear favors plutonism. The tie between oblique convergence and batholith emplacement in late Miocene Peruvian Andes provides a modern analogue for batholiths emplaced as the result of transcurrent shear in ancient arcs.

  8. Asymmetric vs. symmetric deep lithospheric architecture of intra-plate continental orogens

    NASA Astrophysics Data System (ADS)

    Calignano, Elisa; Sokoutis, Dimitrios; Willingshofer, Ernst; Gueydan, Frédéric; Cloetingh, Sierd

    2015-08-01

    The initiation and subsequent evolution of intra-plate orogens, resulting from continental plate interior deformation due to transmission of stresses over large distances from the active plate boundaries, is controlled by lateral and vertical strength contrasts in the lithosphere. We present lithospheric-scale analogue models combining 1) lateral strength variations in the continental lithosphere, and 2) different vertical rheological stratifications. The experimental continental lithosphere has a four-layer brittle-ductile rheological stratification. Lateral heterogeneity is implemented in all models by increased crustal strength in a central narrow block. The main investigated parameters are strain rate and strength of the lithospheric mantle, both playing an important role in crust-mantle coupling. The experiments show that the presence of a strong crustal domain is effective in localizing deformation along its boundaries. After deformation is localized, the evolution of the orogenic system is governed by the mechanical properties of the lithosphere such that the final geometry of the intra-plate mountain depends on the interplay between crust-mantle coupling and folding versus fracturing of the lithospheric mantle. Underthrusting is the main deformation mode in case of high convergence velocity and/or thick brittle mantle with a final asymmetric architecture of the deep lithosphere. In contrast, lithospheric folding is dominant in case of low convergence velocity and low strength brittle mantle, leading to the development of a symmetric lithospheric root. The presented analogue modelling results provide novel insights for 1) strain localization and 2) the development of the asymmetric architecture of the Pyrenees.

  9. Misconceptions and Conceptual Changes Concerning Continental Drift and Plate Tectonics among Portuguese Students Aged 16-17.

    ERIC Educational Resources Information Center

    Marques, Luis; Thompson, David

    1997-01-01

    This study investigates student misconceptions in the areas of continent, ocean, permanence of ocean basins, continental drift, Earth's magnetic field, and plates and plate motions. A teaching-learning model was designed based on a constructivist approach. Results show that students held a substantial number of misconceptions. (Author/DKM)

  10. Role of Plumes and Plates in the Construction and Preservation of Hadean-Archean Continental Nuclei

    NASA Astrophysics Data System (ADS)

    Mueller, P. A.; Mogk, D. W.; Henry, D.; Wooden, J.

    2014-12-01

    Crust and lithosphere formed in modern island arc and plume environments exhibit strong contrasts in both structure and composition compared to present day continents. The limited inventory of Hadean and Eoarchean material available for study, the possibility that the preserved record is biased, and the lack of continental crust on other terrestrial planets, make it difficult to determine the nature of the first continental nuclei. Nonetheless, certain first order similarities in preserved Archean continental crust suggest that these continental nuclei (microcontinents or protocontinents) allow us to establish limits on processes of early crustal genesis Based on geochemical (elemental and isotopic), geochronologic, and petrologic data from Paleo- to Mesoarchean rocks preserved in the northern Wyoming Province, we propose a multi-stage evolution of a continental nucleus that reflects a secular change from plume- to plate-related processes. 1) 4.0-4.1 Ga: mafic and ultramafic magmas formed a section of thickened lithosphere over a zone of upwelling primitive mantle; 2) 3.6-4.0 Ga: continuity of magmatism recorded in detrital zircons does not favor growth by episodic subduction; Hf isotopes in zircon suggest extensive crustal recycling with some juvenile additions; 3) 3.6-3.2 Ga: a major crust-forming interval with infusion of new crust derived from more depleted sources, including a hydrous, garnet-bearing source; 4) intervening granulite facies metamorphism of supracrustal rocks and orthogneisses, clockwise PTt path, coupled with ductile deformation (~ 750-800oC and 6-8 Kbar); 5) ~2.8-2-9 Ga: a second period of major magmatism resulted from subduction and a volcanic arc was built on the older 3.2-3.5 Ga crust. This geochemical record indicates that the earliest crust formed through diapiric upwelling and anhydrous melting of primitive mantle in a plume setting, followed by recycling of this crust with only limited juvenile additions in the Paleoarchean; in the Mesoarchean the tectonic regime changed to a plate environment that produced two major crust-forming events in a volcanic arc setting—the first involved primarily juvenile additions from the mantle (3.5-3.2 Ga interval) and the second (2.8-2.9 Ga) included melting of a deep mafic source and recycling of sediments similar to Phanerozoic arcs.

  11. Peruvian Trench to Andean Thrust Front: Evidence for Coupling of the Peruvian Flat Slab to the Over-Riding South American Plate

    NASA Astrophysics Data System (ADS)

    Bishop, B.; Beck, S. L.; Zandt, G.; Scire, A. C.; Wagner, L. S.; Long, M. D.; Tavera, H.

    2014-12-01

    In central Peru the combination of an unusually shallow Wadati-Benioff zone and lack of arc volcanism are indicators of flat slab subduction and are associated with both the ongoing subduction of the Nazca Ridge and the prior subduction of the Inca Plateau. Data from the PULSE experiment has allowed us to better constrain the geometry of the southern half of the Peruvian flat slab through analysis of teleseismic receiver functions, Pn and Sn phases from regional intermediate (>100 km depth) and deep (>500 km depth) earthquakes at the margins of the flat slab region, and teleseismic tomgraphy. We observe a low velocity anomaly below the subducted portion of the Nazca Ridge in the teleseismic S-wave tomography. Utilizing both Pn and Sn phases from regional intermediate and deep earthquakes at the margins of the flat slab, we have found significant travel time delays for propagation paths passing through this anomaly, confirming the presence of this low velocity anomaly under the flat slab. This anomaly likely contributes to the buoyancy of this segment of the flat slab, increasing the coupling with the upper plate. Both the teleseismic tomographic and our receiver function results indicate that the southern segment of the Peruvian flat slab extends locally more than 100 km further inboard than previous estimates. As the shallow portion of the slab inboard of the subducting Nazca Ridge is largely aseismic, these new results help to better constrain the geometry of the Peruvian flat slab as it re-subducts back into the mantle. Between 10°S and 16°S the subducted oceanic crust along the inboard projection of the Nazca Ridge lies at a depth of 60 km to 70 km while subducted crust immediately north and south of the ridge projection lies at depths of 80 km to 90 km suggesting the slab is sinking north and south of the ridge. The unusually shallow depth of the slab along the ridge's projection may indicate that the subducted Nazca Plate is coupled to the South American Plate far inboard from the trench. This coupling may be causing deformation beyond the active Andean thrust front. The Fitzcarrald Arch, a long-wavelength topographic feature along the ridge's projection and east of the edge of Andean deformation, lies immediately inboard of our shallowest observed subducted oceanic crust and may be an example of this coupling induced deformation.

  12. The Break-up and Drifting of the Continental Plates in 2D Models of Convecting Mantle

    NASA Astrophysics Data System (ADS)

    Dal Zilio, L.; Faccenda, M.; Capitanio, F. A.

    2014-12-01

    Since the early theory of Wegener, the break-up and drift of continents have been controversial and hotly debated topics. To assist the interpretation of the break-up and drift mechanisms and its relation with mantle circulation patterns, we carried out a 2D numerical modelling of the dynamics of these processes. Different regimes of upper plate deformation are studied as consequence of stress coupling with convection patterns. Subduction of the oceanic plate and induced mantle flow propagate basal tractions to the upper plate. This mantle drag forces (FMD) can be subdivided in two types: (1) active mantle drag occurring when the flow drives plate motion (FAD), and (2) passive mantle drag (FPD), when the asthenosphere resists plate motion. The active traction generated by the convective cell is counterbalanced by passive mantle viscous drag away from it and therefore tension is generated within the continental plate. The shear stress profiles indicate that break-up conditions are met where the gradient of the basal shear stress is maximised, however the break-up location varies largely depending on the convection style primarily controlled by slab stagnation on the transition zone, avalanching through or subduction in the lower mantle. We found good correspondence between our models and the evolution of convergent margins on Earth, giving precious insights into the break-up and drifting mechanisms of some continental plates, such as the North and South American plates, Calabria and the Japan Arc.

  13. The Ultimate Fate of Continental Crust is to Melt

    NASA Astrophysics Data System (ADS)

    Whitney, D. L.; Teyssier, C.; Rey, P. F.

    2009-12-01

    Thermal-mechanical models support a link between deep burial of continental crust, melting, and crustal flow in orogens. Deeply buried continental crust may partially melt, adding magma to the overlying continental crust, creating a continental plateau, and accounting for the large melt volumes observed in modern and ancient orogens. In Cordilleran-style orogens, the non-subducting plate is hot, thin and includes a back-arc region favorable for crustal-scale thrusting, high-T metamorphism, and generation of migmatite. Collisional orogens have thicker lithosphere and experience lithosphere-scale thrusting and deeper burial of continental crust, including continental subduction. In either orogenic mode, the ultimate fate of continental crust is partial melting, the depth of which controls the processes and rates of crustal differentiation and exhumation. To explore the relationship between melting and crustal flow associated with deeply buried (subducted) continental crust, we generated 2D thermal-mechanical (Ellipsis) models. In the subducted continental slab, the crust experiences varying amounts of heating relative to decompression depending on subduction depth and position in the slab. Particles at the slab base experience heating during decompression, followed by near-isothermal decompression for particles subducted to >90 km, or near-isobaric heating followed by decompression and cooling. Particles adjacent to the mantle wedge have complex paths, including convection within the partially molten region. Some crust subducted to 110 km remains entrained in the mantle. The shallowest rocks that were tracked in the model (40 km) are heated during extrusion into the lower crust of the overriding continent. Continental rocks exhumed from the coesite stability field exceed typical solidus Ts during decompression. Rocks subducted to <80 km may partially melt depending on maximum depth and position in the slab. These results and a paradigm developed from model and field observations relate continental subduction and crustal melting to lower crustal flow and plateau development in the overriding plate.

  14. Lithosphere continental rifting and necking in 3D analogue experiments: role of plate divergence rate.

    NASA Astrophysics Data System (ADS)

    Nestola, Y.; Storti, F.; Cavozzi, C.

    2014-12-01

    The evolution of lithosphere necking is a fundamental parameter controlling the structural architecture and thermal state of rifted margins. Despite a large number of analogue and numerical modelling studies on lithosphere extension are available in the literature, a quantitative experimental description of lithosphere necking evolution is still lacking. Extensional strain rate and thermal layering of the lithosphere exert a fundamental control on necking shape and evolution. We focused our experimental work on the former parameter and simulated the progression of lithosphere thinning and necking during asymmetric orthogonal rifting at different plate divergence rates. Our models involve a 4-layer mechanical continental lithosphere, which rests on a glucose syrup asthenosphere. Both the topography and the base of the lithosphere were monitored by time-lapse laser scanning. This technical approach allowed us to quantify the evolution in space and time of the thinning factors for the crust, mantle, and lithosphere as a whole. Laser-scanning monitoring provided also a detailed picture of the evolving neck shape, which shows a strong dependency on the strain-rate. At low strain-rates, necking is "boxed" with steep flanks and a flat-lying roof, and few deep basins develop at surface. At high strain-rates, more distributed thinning occurs and isolates portions of less deformed mantle. More distributed deformation affects the model topography. Despite large differences in shape, the aspect ratio (amplitude/wavelength) of the cross-sectional neck shapes converges towards very similar values at the end of the experiments.The significant differences and evolutionary pathways produced by the plate divergence rate on the lithosphere necking profile, suggest that this parameter exert a fundamental control on localization vs. distribution of deformation in the crust as in the whole mechanical lithosphere. Furthermore, it can exert a fundamental control on the time and space distribution of heat flow during rifting. Following up on this we can speculate on the location and timing of synrift magmatism, which is expected to be preferentially produced on one shoulder for slow plate divergence rates, and more widely distributed and delayed at fast divergence rates.

  15. Geodynamic models of terrane accretion: Testing the fate of island arcs, oceanic plateaus, and continental fragments in subduction zones

    NASA Astrophysics Data System (ADS)

    Tetreault, J. L.; Buiter, S. J. H.

    2012-08-01

    Crustal growth at convergent margins can occur by the accretion of future allochthonous terranes (FATs), such as island arcs, oceanic plateaus, submarine ridges, and continental fragments. Using geodynamic numerical experiments, we demonstrate how crustal properties of FATs impact the amount of FAT crust that is accreted or subducted, the type of accretionary process, and the style of deformation on the overriding plate. Our results show that (1) accretion of crustal units occurs when there is a weak detachment layer within the FAT, (2) the depth of detachment controls the amount of crust accreted onto the overriding plate, and (3) lithospheric buoyancy does not prevent FAT subduction during constant convergence. Island arcs, oceanic plateaus, and continental fragments will completely subduct, despite having buoyant lithospheric densities, if they have rheologically strong crusts. Weak basal layers, representing pre-existing weaknesses or detachment layers, will either lead to underplating of faulted blocks of FAT crust to the overriding plate or collision and suturing of an unbroken FAT crust. Our experiments show that the weak, ultramafic layer found at the base of island arcs and oceanic plateaus plays a significant role in terrane accretion. The different types of accretionary processes also affect deformation and uplift patterns in the overriding plate, trench migration and jumping, and the dip of the plate interface. The resulting accreted terranes produced from our numerical experiments resemble observed accreted terranes, such as the Wrangellia Terrane and Klamath Mountain terranes in the North American Cordilleran Belt.

  16. Overriding of the Indian-Antarctic ridge: Origin of emerald basin and migration of late cenozoic volcanism in Southern New zealand and Campbell Plateau

    NASA Astrophysics Data System (ADS)

    Farrar, E.; Dixon, J. M.

    1984-05-01

    Examination of plate reconstructions of the Neogene interactions among the Indian, Antarctic and Pacific plates suggests that the New Zealand and Campbell Plateau portion of the Pacific plate has overridden the site of mantle upwelling formerly associated with the southeastern end of the Indian-Antarctic ridge. The site of mantle upwelling can be projected to have migrated in a fan-shaped pattern from a NNE-SSW trend across South Island, New Zealand and along the western edge of the Campbell Plateau in Oligocene time to its present position along the southeast continental slope of the Campbell Plateau. This migration has been closely followed by the eruption of alkaline basaltic volcanic rocks which display a similar fan-shaped age distribution and which we interpret as evidence of the persistence of the mantle upwelling process for tens of millions of years after its overriding by continental lithosphere. The Emerald Basin and Macquarie Ridge complex, which formed in post-Eocene time at the western margin of the Campbell Plateau, resulted by "secondary spreading" when overriding of the Indian-Antarctic ridge by the Campbell Plateau juxtaposed the Indian and Pacific plates.

  17. Tectonic lineaments in the cenozoic volcanics of southern Guatemala: Evidence for a broad continental plate boundary zone

    NASA Technical Reports Server (NTRS)

    Baltuck, M.; Dixon, T. H.

    1984-01-01

    The northern Caribbean plate boundary has been undergoing left lateral strike slip motion since middle Tertiary time. The western part of the boundary occurs in a complex tectonic zone in the continental crust of Guatemala and southernmost Mexico, along the Chixoy-Polochic, Motogua and possibly Jocotan-Chamelecon faults. Prominent lineaments visible in radar imagery in the Neogene volcanic belt of southern Guatemala and western El Salvador were mapped and interpreted to suggest southwest extensions of this already broad plate boundary zone. Because these extensions can be traced beneath Quaternary volcanic cover, it is thought that this newly mapped fault zone is active and is accommodating some of the strain related to motion between the North American and Caribbean plates. Onshore exposures of the Motoqua-Polochic fault systems are characterized by abundant, tectonically emplaced ultramafic rocks. A similar mode of emplacement for these off shore ultramafics, is suggested.

  18. Dynamics of continental accretion.

    PubMed

    Moresi, L; Betts, P G; Miller, M S; Cayley, R A

    2014-04-10

    Subduction zones become congested when they try to consume buoyant, exotic crust. The accretionary mountain belts (orogens) that form at these convergent plate margins have been the principal sites of lateral continental growth through Earth's history. Modern examples of accretionary margins are the North American Cordilleras and southwest Pacific subduction zones. The geologic record contains abundant accretionary orogens, such as the Tasmanides, along the eastern margin of the supercontinent Gondwana, and the Altaïdes, which formed on the southern margin of Laurasia. In modern and ancient examples of long-lived accretionary orogens, the overriding plate is subjected to episodes of crustal extension and back-arc basin development, often related to subduction rollback and transient episodes of orogenesis and crustal shortening, coincident with accretion of exotic crust. Here we present three-dimensional dynamic models that show how accretionary margins evolve from the initial collision, through a period of plate margin instability, to re-establishment of a stable convergent margin. The models illustrate how significant curvature of the orogenic system develops, as well as the mechanism for tectonic escape of the back-arc region. The complexity of the morphology and the evolution of the system are caused by lateral rollback of a tightly arcuate trench migrating parallel to the plate boundary and orthogonally to the convergence direction. We find geological and geophysical evidence for this process in the Tasmanides of eastern Australia, and infer that this is a recurrent and global phenomenon. PMID:24670638

  19. Rayleigh wave tomography beneath the oceanic and continental margin of the North-America and Pacific plate boundary.

    NASA Astrophysics Data System (ADS)

    Rathnayaka, S.; Escobar, L., Sr.; Weeraratne, D. S.; Kohler, M. D.

    2014-12-01

    The inception of the San Andreas fault, a transform plate boundary system, is the result of subduction of the EPR spreading center, rifting of the Borderland in the Miocene and subsequent plate rotation that is ongoing today. To address the lack of offshore data at this plate boundary, we use Rayleigh waves recorded by a marine seismic array of 34 ocean bottom seismometers (OBS) to tomographically image phase velocities beneath the oceanic and continental margin of the North America-Pacific plate boundary. The OBSs were deployed as part of the ALBACORE project offshore southern California on 18-32 Ma seafloor. The marine seismic array recorded data from August 2010 to 2011 and are combined with 82 land stations from the CISN network. We analyze ~100 teleseismic events at distances ranging from 30° to 120° for Mw ? 5.9, filtered at periods between 16 and 78 s. Strong structural gradients are present across this plate margin; therefore, we perform amplitude corrections for OBS stations that account for velocity variations in water, sediment layer, crustal thickness, marine fossil layers and lithospheric thickness as a function of seafloor age. We use a surface wave inversion that considers a two plane wave method and perform a grid search for inversion parameters. Our results indicate that averaged phase velocities are 1.3% lower than previous studies for the seafloor age bin 20-52 Ma. Phase velocities at lithospheric depths are 5% higher in the oceanic mantle compared to the continental mantle indicating compositional and structural differences due to formation history in the two tectonic environments. Anisotropy in the offshore region of our study is consistent with Pacific plate motion, N 78.5? W, except for periods longer than 40 s in the Borderland where anisotropy demonstrates N-S alignment. The Borderland, a transitional region between the continental and oceanic plate margin where rotation of the transverse ranges involved rifting and extension, shows unique velocity and anisotropic structure compared to the land and deep seafloor regions.

  20. Crustal structure of a transform plate boundary: San Francisco Bay and the central California continental margin

    USGS Publications Warehouse

    Holbrook, W.S.; Brocher, T.M.; ten Brink, U.S.; Hole, J.A.

    1996-01-01

    Wide-angle seismic data collected during the Bay Area Seismic Imaging Experiment provide new glimpses of the deep structure of the San Francisco Bay Area Block and across the offshore continental margin. San Francisco Bay is underlain by a veneer (<300 m) of sediments, beneath which P wave velocities increase rapidly from 5.2 km/s to 6.0 km/s at 7 km depth, consistent with rocks of the Franciscan subduction assemblage. The base of the Franciscan at-15-18 km depth is marked by a strong wide-angle reflector, beneath which lies an 8- to 10-km-thick lower crust with an average velocity of 6.75??0.15 km/s. The lower crust of the Bay Area Block may be oceanic in origin, but its structure and reflectivity indicate that it has been modified by shearing and/or magmatic intrusion. Wide-angle reflections define two layers within the lower crust, with velocities of 6.4-6.6 km/s and 6.9-7.3 km/s. Prominent subhorizontal reflectivity observed at near-vertical incidence resides principally in the lowermost layer, the top of which corresponds to the "6-s reflector" of Brocher et al. [1994]. Rheological modeling suggests that the lower crust beneath the 6-s reflector is the weakest part of the lithosphere; the horizontal shear zone suggested by Furlong et al. [1989] to link the San Andreas and Hayward/Calaveras fault systems may actually be a broad zone of shear deformation occupying the lowermost crust. A transect across the continental margin from the paleotrench to the Hayward fault shows a deep crustal structure that is more complex than previously realized. Strong lateral variability in seismic velocity and wide-angle reflectivity suggests that crustal composition changes across major transcurrent fault systems. Pacific oceanic crust extends 40-50 km landward of the paleotrench but, contrary to prior models, probably does not continue beneath the Salinian Block, a Cretaceous arc complex that lies west of the San Andreas fault in the Bay Area. The thickness (10 km) and high lower-crustal velocity of Pacific oceanic crust suggest that it was underplated by magmatism associated with the nearby Pioneer seamount. The Salinian Block consists of a 15-km-thick layer of velocity 6.0-6.2 km/s overlying a 5-km-thick, high-velocity (7.0 km/s) lower crust that may be oceanic crust, Cretaceous arc-derived lower crust, or a magmatically underplated layer. The strong structural variability across the margin attests to the activity of strike-slip faulting prior to and during development of the transcurrent Pacific/North American plate boundary around 29 Ma. Copyright 1996 by the American Geophysical Union.

  1. Barruol, G., P. G. Silver, and A. Vauchez, 1997. Seismic anisotropy in the Eastern United States; deep structure of a complex continental plate: J. Geophys. Res., v. 102, p. 8329--8348.

    E-print Network

    Menke, William

    margin, Tectonophysics 59, 27-52, 1979. Grow, J, and R Sheridan, US Atlantic Continental Margin: A typical Atlantic-type or passive continental margin, in The Geology of North America I-2, R Sheridan, ed United States; deep structure of a complex continental plate: J. Geophys. Res., v. 102, p. 8329

  2. Influence of continental roots and asthenosphere on plate-mantle Clinton P. Conrad1

    E-print Network

    Conrad, Clint

    ; published 15 March 2006. [1] The shear tractions that mantle flow exerts on the base of Earth's lithosphere contribute to plate-driving forces and lithospheric stresses. We investigate the sensitivity of these tractions to sub-lithospheric viscosity variations by comparing shear tractions computed from a mantle flow

  3. Abbot Ice Shelf, structure of the Amundsen Sea continental margin and the southern boundary of the Bellingshausen Plate seaward of West Antarctica

    PubMed Central

    Cochran, James R; Tinto, Kirsty J; Bell, Robin E

    2015-01-01

    Inversion of NASA Operation IceBridge airborne gravity over the Abbot Ice Shelf in West Antarctica for subice bathymetry defines an extensional terrain made up of east-west trending rift basins formed during the early stages of Antarctica/Zealandia rifting. Extension is minor, as rifting jumped north of Thurston Island early in the rifting process. The Amundsen Sea Embayment continental shelf west of the rifted terrain is underlain by a deeper, more extensive sedimentary basin also formed during rifting between Antarctica and Zealandia. A well-defined boundary zone separates the mildly extended Abbot extensional terrain from the deeper Amundsen Embayment shelf basin. The shelf basin has an extension factor, ?, of 1.5–1.7 with 80–100 km of extension occurring across an area now 250 km wide. Following this extension, rifting centered north of the present shelf edge and proceeded to continental rupture. Since then, the Amundsen Embayment continental shelf appears to have been tectonically quiescent and shaped by subsidence, sedimentation, and the advance and retreat of the West Antarctic Ice Sheet. The Bellingshausen Plate was located seaward of the Amundsen Sea margin prior to incorporation into the Antarctic Plate at about 62 Ma. During the latter part of its independent existence, Bellingshausen plate motion had a clockwise rotational component relative to Antarctica producing convergence across the north-south trending Bellingshausen Gravity Anomaly structure at 94°W and compressive deformation on the continental slope between 94°W and 102°W. Farther west, the relative motion was extensional along an east-west trending zone occupied by the Marie Byrd Seamounts. Key Points: Abbot Ice Shelf is underlain by E-W rift basins created at ?90 Ma Amundsen shelf shaped by subsidence, sedimentation, and passage of the ice sheet Bellingshausen plate boundary is located near the base of continental slope and rise PMID:26709352

  4. Rapid plate motion variations and continental uplift: a window on the history of asthenospheric flow

    NASA Astrophysics Data System (ADS)

    Colli, Lorenzo; Stotz, Ingo; Bunge, Hans-Peter; Smethurst, Mark; Clark, Stuart; Iaffaldano, Giampiero; Tassara, Andres; Guillocheau, Francois

    2015-04-01

    Since the rifting of Gondwana ˜ 150 Myrs ago the South Atlantic Ocean experienced two phases of fast spreading in Late Cretaceous and Oligocene-Miocene, separated by a period of slow spreading around the K-T boundary and concluded by the recent slowdown since the Messinian. At the same time, it is becoming clear that the topographic evolution of Africa is characterized by two main periods of widespread uplift. These periods of uplift are co-eval with the two phases of fast spreading. The present-day situation presents an oceanic basin characterized by a strong topographic gradient with Africa being elevated and South America being depressed by non-isostatic forcing. These observations ' in particular the fast time-scale of plate motion variations ' are difficult to explain via shallow tectonic forces acting in the lithosphere. However, they are completely consistent with the fluid dynamics of a thin and low-viscosity asthenosphere. In particular, they can be easily understood as the result of unsteady pressure-driven flow in such a low-viscosity sublithospheric layer. Moreover, the idea of a thin asthenosphere of low viscosity is corroborated by a number of observations and inferences, ranging from seismic tomography to glacial isostatic adjustment to mineral physics.

  5. Cenozoic analogues support a plate tectonic origin for the Earth’s earliest continental crust

    NASA Astrophysics Data System (ADS)

    Hastie, A. R.; Kerr, A. C.; Mitchell, S. F.; McDonald, I.; Pearce, J. A.; Millar, I. L.; Wolstencroft, M.

    2009-12-01

    Eocene rhyodacite lavas from the Wagwater Basin in eastern Jamaica have adakitic-like major element compositions, low Y and heavy rare Earth element (REE) concentrations and negative Nb and Ta anomalies on a normal mid-ocean ridge basalt normalised multi-element diagram. They also have lower Sr (<400 ppm), MgO (?2.0 wt.%), Ni (mostly ?30 ppm) and Cr (mostly ?40 ppm) concentrations compared to other modern adakites and middle-late Archaean (3.5-2.5 Ga) trondhjemite, tonalite and granodiorite/dacites (TTGs). ?Nd(i) and ?Hf(i) values indicate that the adakites can not been formed by assimilation and fractional crystallisation processes involving any other igneous rock in the area and so the composition of the adakites is the result of the residual mineralogy in the source region. Low Sr and Al2O3 contents indicate a fluid/vapour-absent source with residual plagioclase, and REE systematics point to residual amphibole and garnet in the source region. The plagioclase and garnet residue implies that the Newcastle magmas were derived from partially melting a metabasic protolith at 1.0-1.6 GPa, which would intersect the amphibole dehydration partial melt solidus at ~ 850-900oC. Radiogenic isotopes along with the low MgO, Ni and Cr concentrations in the adakites demonstrate that the garnet amphibolite source region can not be part of (1) the lower Jamaican arc crust, (2) delaminated lower crust or (3) subducted Proto-Caribbean “normal” oceanic crust that may, or may not, have detached. This data, in addition to partial melting models involving a theoretical garnet-amphibolite source region for the Newcastle lavas, shows that the adakites are derived from metamorphosed Caribbean oceanic plateau crust that underthrust Jamaica in the early Tertiary. The underplated oceanic plateau crust partially melted by either (1) influx of basaltic magma during lithospheric extension in the early Tertiary or (2) direct partial melting of the underthrusting (subducting) plateau crust. The Newcastle magmas ascended and erupted without coming into contact with a mantle wedge thus forming the low MgO, Ni and Cr contents. Most Cenozoic adakites have compositions similar to the middle-late Archaean TTG suite of igneous rocks. In contrast, early (>3.5 Ga) Archaean TTG crustal rocks have lower Sr, MgO, Ni and Cr concentrations and prior to this study had no modern adakite analogue. However, the Newcastle adakites have similar compositions to the, early Archaean TTG. The discovery of these rocks has important implications for our understanding of the formation of the Earth’s earliest continental crust and so it is proposed that the Newcastle lavas be classified as a unique sub-group of adakites: Jamaican-type adakite.

  6. Dynamics of upper mantle rocks decompression melting above hot spots under continental plates

    NASA Astrophysics Data System (ADS)

    Perepechko, Yury; Sorokin, Konstantin; Sharapov, Victor

    2014-05-01

    Numeric 2D simulation of the decompression melting above the hot spots (HS) was accomplished under the following conditions: initial temperature within crust mantle section was postulated; thickness of the metasomatized lithospheric mantle is determined by the mantle rheology and position of upper asthenosphere boundary; upper and lower boundaries were postulated to be not permeable and the condition for adhesion and the distribution of temperature (1400-2050°C); lateral boundaries imitated infinity of layer. Sizes and distribution of lateral points, their symmetry, and maximum temperature varied between the thermodynamic condition for existences of perovskite - majorite transition and its excess above transition temperature. Problem was solved numerically a cell-vertex finite volume method for thermo hydrodynamic problems. For increasing convergence of iterative process the method of lower relaxation with different value of relaxation parameter for each equation was used. The method of through calculation was used for the increase in the computing rate for the two-layered upper mantle - lithosphere system. Calculated region was selected as 700 x (2100-4900) km. The time step for the study of the asthenosphere dynamics composed 0.15-0.65 Ma. The following factors controlling the sizes and melting degree of the convective upper mantle, are shown: a) the initial temperature distribution along the section of upper mantleb) sizes and the symmetry of HS, c) temperature excess within the HS above the temperature on the upper and lower mantle border TB=1500-2000oC with 5-15% deviation but not exceed 2350oC. It is found, that appearance of decompression melting with HS presence initiate primitive mantle melting at TB > of 1600oC. Initial upper mantle heating influence on asthenolens dimensions with a constant HS size is controlled mainly by decompression melting degree. Thus, with lateral sizes of HS = 400 km the decompression melting appears at TB > 1600oC and HS temperature (THS) > 1900oC asthenolens size ~700 km. When THS = of 2000oC the maximum melting degree of the primitive mantle is near 40%. An increase in the TB > 1900oC the maximum degree of melting could rich 100% with the same size of decompression melting zone (700 km). We examined decompression melting above the HS having LHS = 100 km - 780 km at a TB 1850- 2100oC with the thickness of lithosphere = 100 km.It is shown that asthenolens size (Lln) does not change substantially: Lln=700 km at LHS = of 100 km; Lln= 800 km at LHS = of 780 km. In presence of asymmetry of large HS the region of advection is developed above the HS maximum with the formation of asymmetrical cell. Influence of lithospheric plate thicknesses on appearance and evolution of asthenolens above the HS were investigated for the model stepped profile for the TB ? of 1750oS with Lhs = 100km and maximum of THS =2350oC. With an increase of TB the Lln difference beneath lithospheric steps is leveled with retention of a certain difference to melting degrees and time of the melting appearance a top of the HS. RFBR grant 12-05-00625.

  7. Geodynamics of continental plate collision during late tertiary foreland basin evolution in the Timor Sea: constraints from foreland sequences, elastic flexure and normal faulting

    NASA Astrophysics Data System (ADS)

    Londoño, John; Lorenzo, Juan M.

    2004-11-01

    Tectonic subsidence of the Australian lithosphere during the Late Tertiary propagates from the southwest to the northeast in the Timor Sea, as a consequence of the oblique collision between the Eurasian and Australian plates. We reconstruct the asynchronous nature of deflection of the Australian plate created during the plate convergence by best-matching the geometry of de-compacted foreland strata against the predictions of simple bending elastic beam models. We infer a maximum subsidence of 3500 m and a maximum width for the basin of ˜470 km. The effective elastic thickness of the Australian lithosphere (˜80 to 100 km) does not change significantly during basin evolution. The low curvature imposed on the plate (˜5.1×10 -8 m -1) during bending is too small to weaken the plate. Yet, abundant but small-slip, normal faulting related to bending implies some degree of inelastic yielding. The polarity of fault propagation supports the oblique nature of the collision. Flexural models indicate that at least 570 km of Australian plate (mostly areas of stretched continental crust) was flexed, primarily by the tectonic loading of the Timor Island and that the total amount of subducted plate was at least 100 km during basin evolution.

  8. Continental Subduction and Subduction Initiation Leading to Extensional Exhumation of Ultra-High Pressure Rocks During Ongoing Plate Convergence in Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Buck, W. R.; Petersen, K. D.

    2014-12-01

    Subduction of continental rocks is necessary to produce ultra-high pressure (UHP) rocks but the mechanism bringing them to the surface is disputed. A major question is whether this involves fairly small diapirs of crust that move up through the mantle or it involves an entire subducted plate that undergoes coherent 'reverse subduction' (sometimes called 'eduction'). Both mechanisms have been invoked to explain the only known region of on-going exhumation of UHP rocks, on the D'Entrecasteaux Islands of Papua New Guinea. Ductile flow fabrics in the island rocks have been used to argue for a diapiric model while constraints on the plate kinematics of the region require relatively large (>100 km) amounts of recent (>6 Myr) extension, supporting eduction as a primary mechanism. A self-consistent thermo-mechanical model of continental subduction shows that eduction can be accompanied by some ductile flow within the crust. Also we show, that subduction and stacking of continental crust can cause a subduction zone to lock up and lead to subduction initiation elsewhere. When this happens the region of earlier continental subduction can reverse direction causing exhumation of rocks from depth of ~100 km followed by localized extension and plate spreading. This can occur even if a region is in overall convergence. Applied to New Guinea our results are consistent with earlier suggestions that extension of the Woodlark Basin was caused by the initiation of the New Britain Trench, as indicated on the attached figure. We suggest that this subduction initiation event triggered eduction that led to exposure of the D'Entrcasteaux Islands and exhumation of the UHP rocks there. Our numerical results are broadly consistent with the recently refined seismic structure of the region around the islands. The model implies that the present-day basement of the ~70 km wide Goodenough Bay, south of the islands, was subducted then exhumed. This can be tested by drilling.

  9. Abbot Ice Shelf, structure of the Amundsen Sea continental margin and the southern boundary of the Bellingshausen Plate seaward of West Antarctica

    NASA Astrophysics Data System (ADS)

    Cochran, James R.; Tinto, Kirsty J.; Bell, Robin E.

    2015-05-01

    Inversion of NASA Operation IceBridge airborne gravity over the Abbot Ice Shelf in West Antarctica for subice bathymetry defines an extensional terrain made up of east-west trending rift basins formed during the early stages of Antarctica/Zealandia rifting. Extension is minor, as rifting jumped north of Thurston Island early in the rifting process. The Amundsen Sea Embayment continental shelf west of the rifted terrain is underlain by a deeper, more extensive sedimentary basin also formed during rifting between Antarctica and Zealandia. A well-defined boundary zone separates the mildly extended Abbot extensional terrain from the deeper Amundsen Embayment shelf basin. The shelf basin has an extension factor, ?, of 1.5-1.7 with 80-100 km of extension occurring across an area now 250 km wide. Following this extension, rifting centered north of the present shelf edge and proceeded to continental rupture. Since then, the Amundsen Embayment continental shelf appears to have been tectonically quiescent and shaped by subsidence, sedimentation, and the advance and retreat of the West Antarctic Ice Sheet. The Bellingshausen Plate was located seaward of the Amundsen Sea margin prior to incorporation into the Antarctic Plate at about 62 Ma. During the latter part of its independent existence, Bellingshausen plate motion had a clockwise rotational component relative to Antarctica producing convergence across the north-south trending Bellingshausen Gravity Anomaly structure at 94°W and compressive deformation on the continental slope between 94°W and 102°W. Farther west, the relative motion was extensional along an east-west trending zone occupied by the Marie Byrd Seamounts. The copyright line for this article was changed on 5 JUN 2015 after original online publication.

  10. Constraints of mapped and unfolded slabs on Oligocene to present-day Western Mediterranean plate reconstructions: potential role of north Iberia continental delamination

    NASA Astrophysics Data System (ADS)

    Lee, Yi-Te; Wu, Jonny; Wu, Yi-Min; Suppe, John; Sibuet, Jean-Claude; Chevrot, Sebastien

    2015-04-01

    Seismic tomographic images of subducted lithospheric remnants under the western Mediterranean have provided new constraints for Oligocene to present-day plate reconstructions. In this study, we mapped slabs under the western Mediterranean and Iberia from regional seismic tomography (Chevrot et al., 2014; Bezada et al., 2013) and from MITP08 global tomography (Li et al., 2008). A newly developed method was used to unfold (ie. structurally restore) the mapped slabs to a model spherical Earth surface, minimizing area and shape distortion. Slab constraints were input into plate tectonic reconstructions using Gplates software. Our mapping confirms the existence of western Mediterranean slabs including the Betic-Alboran, Algerian, and Calabrian slabs that were previously identified by Spakman and Wortel (2004). When unfolded these mapped slabs fit together in an Oligocene plate reconstruction, within tomographic resolution limits. Slab stretching was not required. Slab segmentation supports the existence of a North Balearic transform. Here we emphasize the potential importance for western Mediterranean tectonics of antoher slab under Iberia that we call the 'mid-Iberia slab'. This slab was first identified by Sibuet et al. (2004) and interpreted to be a Neotethyan suture. We have mapped this slab in detail from recent regional tomography (Chevrot et al., 2014). Our mapped slab is sub-vertical and strikes E-W under the southern margins of the Duero and Ebro basins. We newly interpret this slab to be delaminated northern Iberian continental lithosphere. We propose that continental delamination occurred during the Oligocene and produced uplifted Iberian Meseta topography, internally-drained basins, and high mean elevations that still persist today. We show how Oligocene northern Iberian continental delamination could have initiated subduction and rollback of the western Mediterranean

  11. Collapse of the northern Jalisco continental slope:Subduction erosion, forearc slivering, or subduction beneath the Tres Marias escarpment?

    NASA Astrophysics Data System (ADS)

    Bandy, W. L.; Mortera-Gutierrez, C. A.; Ortiz-Zamora, G.; Ortega-Ramirez, J.; Galindo Dominguez, R. E.; Ponce-Núñez, F.; Pérez-Calderón, D.; Rufino-Contreras, I.; Valle-Hernández, S.; Pérez-González, E.

    2010-12-01

    The Jalisco subduction zone exhibits several interesting characteristics. Among these is that convergence between the Rivera and North American plate is highly oblique, especially north of 20N, the obliquity progressively increasing to the NW. By analogy to other better studied subduction zones, this distribution of forces should produce a NW-SE extension in the overriding plate, especially north of 20N. This has led to the proposal that the trench perpendicular Bahia de Banderas is an expression of this extension [Kostoglodov and Bandy, JGR, vol. 100, 1995]. To further investigate this proposal, multibeam bathymetric data and seafloor backscatter images, seismic reflection sub-bottom profiles and marine magnetic data were collected during the MORTIC08 campaign of the B.O. EL PUMA in March 2009. The bathymetric data provides for 100% coverage (20 to 200 meter spacing of the actual measured depth value depending on the water depth) of the continental slope and trench areas north of 20N. These data indicate that a marked change occurs in the morphology of the continental slope at 20N. To the north the slope consists of a broad, fairly flat plain lying between a steep lower inner trench slope to the west and a steep, concave seaward, escarpment to the east. In contrast, to the south the continental slope exhibits a more gradual deepening until the steep lower inner trench slope. A prominent submarine canyon deeply incises the continental slope between these two morphotectonic domains. This canyon appears to represent the boundary between two NW-SE diverging forearc blocks or slivers, consistent with the presence of oblique convergence. In contrast, the broad, fairly flat plain is better explained by subsidence induced by subduction erosion (i.e. erosion of the base of the overriding plate underneath the continental slope area). The shoaling of the trench axis northward towards the Puerto Vallarta Graben and subsequent deepening may be related to subduction of the Rivera Plate beneath the Tres Marias Escarpment.

  12. 43 CFR 3903.53 - Overriding royalties.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 43 Public Lands: Interior 2 2012-10-01 2012-10-01 false Overriding royalties. 3903.53 Section 3903.53 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) OIL SHALE MANAGEMENT-GENERAL Fees, Rentals,...

  13. 43 CFR 3903.53 - Overriding royalties.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 43 Public Lands: Interior 2 2014-10-01 2014-10-01 false Overriding royalties. 3903.53 Section 3903.53 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) OIL SHALE MANAGEMENT-GENERAL Fees, Rentals,...

  14. Linear Electromagnetic Acutator With Manual Override

    NASA Technical Reports Server (NTRS)

    Abel, Stephen G.

    1994-01-01

    Conceptual permanent-magnet-assisted electromagnetic linear actuator used to set axial position of metering component in valve. One notable feature of actuator is external pole-piece subassembly that swivels manually about axis of linear motion (which is also axis of cylindrical symmetry) to vary distribution of magnetic flux in such way as to override electrical position control. Armature and magnets hermetically sealed.

  15. 5 CFR 1320.15 - Independent regulatory agency override authority.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...2010-01-01 false Independent regulatory agency override authority... CONTROLLING PAPERWORK BURDENS ON THE PUBLIC § 1320.15 Independent regulatory agency override authority. (a) An independent regulatory agency which is...

  16. 5 CFR 1320.15 - Independent regulatory agency override authority.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ...2011-01-01 false Independent regulatory agency override authority... CONTROLLING PAPERWORK BURDENS ON THE PUBLIC § 1320.15 Independent regulatory agency override authority. (a) An independent regulatory agency which is...

  17. Continental subduction, surface processes, P-T-t-z conditions and unstable vs. stable plate dynamics: Insights from thermo-mechanical modelling

    NASA Astrophysics Data System (ADS)

    Burov, E.; Yamato, P.

    2007-12-01

    We analyze major mechanisms of shortening of continental lithosphere (simple shear subduction, pure shear collision, folding, Rayleigh-Taylor instabilities). We use a thermo- dynamically coupled thermo-mechanical numerical model that accounts for brittle-elastic-ductile rheology, surface processes and metamorphic phase changes. The model also traces P-T-t-z paths of metamorphic facies that can be compared with petrology data. The experiments suggest that continental subduction occurs in case of relatively strong lithospheres with a competent mantle part (TMoho < 550° C) , at relatively high initial convergence rates (> 1.5-5 cm/yr). Depending on the lower-crustal rheology (strong or weak), either the entire (upper and lower) crust or only the lower crust can be involved in subduction. Pure shear collision is dominant when TMoho > 550° C or convergence rates are lower than 1.5-3 cm/yr (subduction number, S > 0.5). Large-scale folding is favored in case of TMoho=500-650° C and is more effective in case of mechanical coupling between the crust and mantle (e.g., strong diabase lower crust). Gravitational R-T instabilities overcome other mechanisms for very high values of TMoho (>800° C) and lead to the development of subvertical "cold spots." In case of weak metamorphic rheologies, phase changes improve chances for stable subduction. In general, exhumation of UHP-HP rocks to the surface is favored if the crustal rheological profile is characterized by two internal ductile decolement levels (between the upper and lower or intermediate crust and the lower crust and mantle lithosphere). Finally, we investigate the impact of surface processes (erosion/sedimentation) on the amount of continental subduction. The maximal amount of subduction is achieved for intermediate erosion rates when tectonic uplift rates are fine-balanced by denudation rates. In case of India-Asia collision-like scenario (fast convergence > 5 cm/y, stiff lower plate), the optimal balance is achieved for k ~ 3000 m2/yr. The experiments suggest that both extra slow (k < 50-100 m2/yr) and extra rapid erosion (k > 6000-8000 m2/yr) limit, by up to 50%, the total amount of subduction, if not totally prevent it. We suggest that most orogenic belts could have started their formation from continental subduction, yet, in case of slow convergence (< 3 cm/yr) or weak lithosphere the subduction channel locks up after about few Myr, and subduction is then relayed by a different deformation mode such as pure shear collision. In case of India-Asia-like convergence settings, continental subduction may continue for tens of Myr allowing for subduction of 600-800 km continental "slab".

  18. Introducing tectonically and thermo-mechanically realistic lithosphere in the models of plume head -lithosphere interactions (PLI) including intra-continental plate boundaries.

    NASA Astrophysics Data System (ADS)

    Guillou-Frottier, L.; Burov, E.; Cloetingh, S.

    2007-12-01

    Plume-Lithosphere Interactions (PLI) in continets have complex topographic and magmatic signatures and are often identified near boundaries between younger plates (e.g., orogenic) and older stable plates (e.g., cratons), which represent important geometrical, thermal and rheological barriers that interact with the emplacement of the plume head (e.g., Archean West Africa, East Africa, Pannonian - Carpathian system). The observable PLI signatures are conditioned by plume dynamics but also by complex rheology and structure of continental lithosphere. We address this problem by considering a new free-surface thermo-mechanical numerical model of PLI with two stratified elasto-viscous-plastic (EVP) continental plates of contrasting age, thickness and structure. The results show that: (1) surface deformation is poly-harmonic and contains smaller wavelengths (50-500 km) than that associated with the plume head (>1000 km). (2) below intra-plate boundaries, plume head flattening is asymmetric, it is blocked from one side by the cold vertical boundary of the older plate, which leads to mechanical decoupling of crust from mantle lithosphere, and to localized faulting at the cratonic margin; (2) the return flow from the plume head results in sub-vertical down-thrusting (delamination) of the lithosphere at the margin, producing sharp vertical cold boundary down to the 400 km depth; (3) plume head flattening and migration towards the younger plate results in concurrent surface extension above the centre of the plume and in compression (pushing), down-thrusting and magmatic events at the cratonic margin (down-thrusting is also produced at the opposite border of the younger plate); these processes may result in continental growth at the "craton side"; (4) topographic signatures of PLI show basin-scale uplifts and subsidences preferentially located at cratonic margins. Negative Rayleigh-Taylor instabilities in the lithosphere above the plume head provide a mechanism for crustal delamination. In case of several cratonic blocks, the combined effect of subsidence and lithospheric thinning at cratons edges, while plume head material is being stocked in between the cratons, favours major magmatic events at cratonic margins. Numerous field evidence (West Africa, Western Australia) underline the trapping effect of cratonic margins for formation of (e.g.) orogenic gold deposits, which require particular extreme P-T conditions. Location of gemstones deposits is also associated with cratonic margins, as demonstrated by the Tanzanian Ruby belt. Their formation depend on particularly fast isothermal deepening processes, which can be reproduced by slab-like instabilities induced by plume head-cratonic margin interaction. On the other hand, absence of magmatic events should not be interpreted as evidence for the absence of plume: at surface, these events may not necessary have unambiguous deep geochemical signatures, as the hot source plume material stalls below Moho and forms a long-lasting (10 to 100 Myr) sub-Moho reservoir. This should induce strong crustal melting that may overprint deeper signatures since crustal melts are generated at much lower temperatures than mantle, and produce light low-viscous rapidly ascending magmas. Drip-like down- sagging of the lithospheric mantle and metamorphic lower crustal material inside the plume head may contaminate the latter and also alter the geochemical signature of related magmas.

  19. Viscoelastic Postseismic Rebound to Strike-Slip Earthquakes in Regions of Oblique Plate Convergence

    NASA Technical Reports Server (NTRS)

    Cohen, Steven C.

    1999-01-01

    According to the slip partitioning concept, the trench parallel component of relative plate motion in regions of oblique convergence is accommodated by strike-slip faulting in the overriding continental lithosphere. The pattern of postseismic surface deformation due to viscoelastic flow in the lower crust and asthenosphere following a major earthquake on such a fault is modified from that predicted from the conventual elastic layer over viscoelastic halfspace model by the presence of the subducting slab. The predicted effects, such as a partial suppression of the postseismic velocities by 1 cm/yr or more immediately following a moderate to great earthquake, are potentially detectable using contemporary geodetic techniques.

  20. Plate Motion and Crustal Deformation Estimated with Geodetic Data from the Global Positioning System

    NASA Technical Reports Server (NTRS)

    Argus, Donald F.; Heflin, Michael B.

    1995-01-01

    We use geodetic data taken over four years with the Global Positioning System (GPS) to estimate: (1) motion between six major plates and (2) motion relative to these plates of ten sites in plate boundary zones. The degree of consistency between geodetic velocities and rigid plates requires the (one-dimensional) standard errors in horizontal velocities to be approx. 2 mm/yr. Each of the 15 angular velocities describing motion between plate pairs that we estimate with GPS differs insignificantly from the corresponding angular velocity in global plate motion model NUVEL-1A, which averages motion over the past 3 m.y. The motion of the Pacific plate relative to both the Eurasian and North American plates is observed to be faster than predicted by NUVEL-1A, supporting the inference from Very Long B ase- line Interferometry (VLBI) that motion of the Pacific plate has speed up over the past few m.y. The Eurasia-North America pole of rotation is estimated to be north of NUVEL-1A, consistent with the independent hypothesis that the pole has recently migrated northward across northeast Asia to near the Lena River delta. Victoria, which lies above the main thrust at the Cascadia subduction zone, moves relative to the interior of the overriding plate at 30% of the velocity of the subducting plate, reinforcing the conclusion that the thrust there is locked beneath the continental shelf and slope.

  1. Vertical tectonics at a continental crust-oceanic plateau plate boundary zone: Fission track thermochronology of the Sierra Nevada de Santa Marta, Colombia

    NASA Astrophysics Data System (ADS)

    Villagómez, Diego; Spikings, Richard; Mora, AndréS.; GuzmáN, Georgina; Ojeda, GermáN.; CortéS, Elizabeth; van der Lelij, Roelant

    2011-08-01

    The topographically prominent Sierra Nevada de Santa Marta forms part of a faulted block of continental crust located along the northern boundary of the South American Plate, hosts the highest elevation in the world (˜5.75 km) whose local base is at sea level, and juxtaposes oceanic plateau rocks of the Caribbean Plate. Quantification of the amount and timing of exhumation constrains interpretations of the history of the plate boundary, and the driving forces of rock uplift along the active margin. The Sierra Nevada Province of the southernmost Sierra Nevada de Santa Marta exhumed at elevated rates (?0.2 Km/My) during 65-58 Ma in response to the collision of the Caribbean Plateau with northwestern South America. A second pulse of exhumation (?0.32 Km/My) during 50-40 Ma was driven by underthrusting of the Caribbean Plate beneath northern South America. Subsequent exhumation at 40-25 Ma (?0.15 Km/My) is recorded proximal to the Santa Marta-Bucaramanga Fault. More northerly regions of the Sierra Nevada Province exhumed rapidly during 26-29 Ma (˜0.7 Km/My). Further northward, the Santa Marta Province exhumed at elevated rates during 30-25 Ma and 25-16 Ma. The highest exhumation rates within the Sierra Nevada de Santa Marta progressed toward the northwest via the propagation of NW verging thrusts. Exhumation is not recorded after ˜16 Ma, which is unexpected given the high elevation and high erosive power of the climate, implying that rock and surface uplift that gave rise to the current topography was very recent (i.e., ?1 Ma?), and there has been insufficient time to expose the fossil apatite partial annealing zone.

  2. Subduction Drive of Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Hamilton, W. B.

    2003-12-01

    Don Anderson emphasizes that plate tectonics is self-organizing and is driven by subduction, which rights the density inversion generated as oceanic lithosphere forms by cooling of asthenosphere from the top. The following synthesis owes much to many discussions with him. Hinge rollback is the key to kinematics, and, like the rest of actual plate behavior, is incompatible with bottom-up convection drive. Subduction hinges (which are under, not in front of, thin leading parts of arcs and overriding plates) roll back into subducting plates. The Pacific shrinks because bounding hinges roll back into it. Colliding arcs, increasing arc curvatures, back-arc spreading, and advance of small arcs into large plates also require rollback. Forearcs of overriding plates commonly bear basins which preclude shortening of thin plate fronts throughout periods recorded by basin strata (100 Ma for Cretaceous and Paleogene California). This requires subequal rates of advance and rollback, and control of both by subduction. Convergence rate is equal to rates of rollback and advance in many systems but is greater in others. Plate-related circulation probably is closed above 650 km. Despite the popularity of concepts of plumes from, and subduction into, lower mantle, there is no convincing evidence for, and much evidence against, penetration of the 650 in either direction. That barrier not only has a crossing-inhibiting negative Clapeyron slope but also is a compositional boundary between fractionated (not "primitive"), sluggish lower mantle and fertile, mobile upper mantle. Slabs sink more steeply than they dip. Slabs older than about 60 Ma when their subduction began sink to, and lie down on and depress, the 650-km discontinuity, and are overpassed, whereas younger slabs become neutrally buoyant in mid-upper mantle, into which they are mixed as they too are overpassed. Broadside-sinking old slabs push all upper mantle, from base of oceanic lithosphere down to the 650, back under shrinking oceans, forcing rapid Pacific spreading. Slabs suck forward overriding arcs and continental lithosphere, plus most subjacent mantle above the transition zone. Changes in sizes of oceans result primarily from transfer of oceanic lithosphere, so backarcs and expanding oceans spread only slowly. Lithosphere parked in, or displaced from, the transition zone, or mixed into mid-upper mantle, is ultimately recycled, and regional variations in age of that submerged lithosphere may account for some regional contrasts in MORB. Plate motions make no kinematic sense in either the "hotspot" reference frame (HS; the notion of fixed plumes is easily disproved) or the no-net-rotation frame (NNR) In both, for example, many hinges roll forward, impossible with gravity drive. Subduction-drive predictions are fulfilled, and paleomagnetic data are satisfied (as they are not in HS and NNR), in the alternative framework of propulsionless Antarctica fixed relative to sluggish lower mantle. Passive ridges migrate away from Antarctica on all sides, and migration of these and other ridges permits tapping fresh asthenosphere. (HS and NNR tend to fix ridges). Ridge migration and spreading rates accord with subduction drive. All trenches roll back when allowance is made for back-arc spreading and intracontinental deformation. Africa rotates slowly toward subduction systems in the NE, instead of moving rapidly E as in HS and NNR. Stable NW Eurasia is nearly stationary, instead of also moving rapidly, and S and E Eurasian deformation relates to subduction and rollback. The Americas move Pacificward at almost the full spreading rates of passive ridges behind them. Lithosphere has a slow net westward drift. Reference: W.B. Hamilton, An alternative Earth, GSA Today, in press.

  3. Petrology and age of volcanic-arc rocks from the continental margin of the Bering Sea: implications for Early Eocene relocation of plate boundaries

    USGS Publications Warehouse

    Davis, A.S.; Pickthorn, L.-B.G.; Vallier, T.L.; Marlow, M. S.

    1989-01-01

    Eocene volcanic flow and dike rocks from the Beringian margin have arc characteristics, implying a convergent history for this region during the early Tertiary. Chemical and mineralogical compositions are similar to those of modern Aleutian-arc lavas. They also resemble volcanic-arc compositions from western mainland Alaska, although greater chemical diversity and a stronger continental influence are observed in the Alaskan mainland rocks. Early Eocene ages of 54.4-50.2 Ma for the Beringian samples are well constrained by conventional K-Ar ages of nine plagioclase separates and by concordant 40Ar/39Ar incremental heating and total-fusion experiments. A concordant U-Pb zircon age of 53 Ma for the quartz-diorite dike is in good agreement with the K-Ar data. Plate motion studies of the North Pacific Ocean indicate more northerly directed subduction prior to the Tertiary and a continuous belt of arc-type volcanism extending from Siberia, along the Beringian margin, into mainland Alaska. Around 56 Ma (chron 25-24), subduction changed to a more westerly direction and subduction-related volcanism ceased for most of mainland Alaska. The increasingly oblique angle of convergence should have ended subduction along the Beringian margin as well. However, consistent ages of 54-50 Ma indicate a final pulse in arc-type magmatism during this period of plate adjustment. -from Authors

  4. Comparison of deep structure along three transects of the western North American continental margin

    USGS Publications Warehouse

    Fuis, G.S.; Clowes, R.M.

    1993-01-01

    Similarities in geology and potential field data that have in the past been noted among the regions of southern Alaska, southern Vancouver Island, and central California are now seen to be accompanied by similarities in deep crustal structure. A number of tectonic elements have been identified in the deep structure along transects in these three regions, although not all elements are present along each transect. These elements are A) an actively subducting oceanic plate and B) an overriding continental plate that consists of 1) a Cenozoic accretionary prism, 2) a Mesozoic accretionary prism, 3) a backstop to the Mesozoic prism, 4) a tectonically underplated body of oceanic rocks, and 5) a crustal root. -from Authors

  5. Dynamic evolution of continental and oceanic lithosphere in global mantle convection model with plate-like tectonics and one sided subduction.

    NASA Astrophysics Data System (ADS)

    Ulvrova, Martina; Coltice, Nicolas; Tackley, Paul

    2015-04-01

    Drifting of continents, spreading of the seafloor and subduction at convergent boundaries shape the surface of the Earth. On the timescales of several hundreds of millions of years, divergent boundaries at mid-ocean ridges are created and destroyed in within the Wilson cycle. This controls the evolution of the Earth as it determines the heat loss out. Presence of floating continents facilitates the Earth-like mobile lid style of convection as convective stresses are concentrated on the rheological boundary between oceanic and continental lithosphere. Subducting slabs allow for the surface material to be buried down into the mantle and have an important effect on surface tectonics. The main feature of the subduction zones observed on Earth is that it is single-sided forming the deep trenches. Recently, different numerical models were successful in reproducing one-sided subduction by allowing for the vertical deformation of the Earth surface (Crameri and Tackley 2014). In the meantime, advances were made in modelling continental break-up and formation (Rolf et al. 2014). In this study we perform numerical simulations of global mantle convection in spherical annulus geometry with strongly depth and temperature dependent rheology using StagYY code (Tackley 2008). In these models plate tectonics is generated self-consistently and features one-sided subduction on ocean-ocean plate boundary as well as floating continents. We focus on determining (1) the influence of one-sided subduction on the dynamics of the system (2) formation and breakup of continents. Rerefences: Crameri, F. and P. J. Tackley, Spontaneous development of arcuate single-sided subduction in global 3-D mantle convection models with a free surface, J. Geophys. Res., 119(7), 5921-5942, 2014. Rolf, T., N. Coltice and P. J. Tackley (2014), Statistical cyclicity of the supercontinent cycle, Geophys. Res. Lett. 41, 2014. Tackley, P. J., Modellng compressible mantle convection with large viscosity contrasts in a three-dimensional spherical shell using the yin-yang grid, Phys. Earth Planet. Inter, 171 (1-4), 7-18, 2008.

  6. Potential for adaptation overrides cost of resistance

    PubMed Central

    de Sousa, Jorge Moura; Sousa, Ana; Bourgard, Catarina; Gordo, Isabel

    2015-01-01

    Aim To investigate the cost of antibiotic resistance versus the potential for resistant clones to adapt in maintaining polymorphism for resistance. Materials & methods Experimental evolution of Escherichia coli carrying different resistance alleles was performed under an environment devoid of antibiotics and evolutionary parameters estimated from their frequencies along time. Results & conclusion Costly resistance mutations were found to coexist with lower cost resistances for hundreds of generations, contrary to the hypothesis that the cost of a resistance dictates its extinction. Estimated evolutionary parameters for the different resistance backgrounds suggest a higher adaptive potential of clones with costly antibiotic resistance mutations, overriding their initial cost of resistance and allowing their maintenance in the absence of drugs. PMID:26343510

  7. 5 CFR 1320.15 - Independent regulatory agency override authority.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 5 Administrative Personnel 3 2010-01-01 2010-01-01 false Independent regulatory agency override authority. 1320.15 Section 1320.15 Administrative Personnel OFFICE OF MANAGEMENT AND BUDGET OMB DIRECTIVES CONTROLLING PAPERWORK BURDENS ON THE PUBLIC § 1320.15 Independent regulatory agency override authority. (a)...

  8. oZONE Faculty and Staff Course Overrides

    E-print Network

    Oklahoma, University of

    oZONE Faculty and Staff Course Overrides and the Registration Add Errors They Resolve Departments of the overrides within the registration component of oZONE. We have, however, retained a few instances where some. There is also a link to this document on the Student Training and Instructions page in the oZONE info site

  9. How is Silurian-Early Devonian faulting in the North America continental interior related to orogenic processes at plate boundaries? A working hypothesis from the Canadian North

    NASA Astrophysics Data System (ADS)

    Pinet, Nicolas

    2015-04-01

    The Paleozoic Appalachian/Franklinian orogen that rims the North America continent on its eastern and northern sides is comparable in size with Tethyan orogenic belts. However, the far-field effects in the continental interior of the multiple Ordovician to Carboniferous deformation phases that built the orogen were relatively minor if compared with those associated with the Himalayas and Alps, a characteristics related to the high integrated strength of the North American craton. Despite the generally little deformation of the continental interior, two regional-scale tectonic features preserved evidence of significant Paleozoic tectonism: the fault bounded Hudson Bay Central High (HBCH) and the Boothia uplift/Cornwallis fold belt (BUCF) in the Canadian Arctic. In the Hudson Bay intracratonic basin, the lower part of the sedimentary succession (Upper Ordovician to Lower Devonian) is cut by high-angle faults and overlain by a saucer-shape, essentially underformed sedimentary package (Middle to Upper Devonian). The main structural feature is the NNW-trending HBCH that extends for a minimum length of 500 km with normal faults characterized by throws up to 500 m that were mainly active during the Silurian - Early Devonian period. The >700-km long, N-trending BUCF is nearly perpendicular to the deformation front of the Franklinian mobile belt. In its southern segment (Boothia uplift), its western side is characterized by an east-dipping reverse fault zone that puts Precambrian rocks over Paleozoic strata. In its northern segment (Cornwallis fold belt), the Paleozoic succession is involved in open folds and cuts by steeply dipping reverse faults. Syn-tectonic clastic sediments constrain the age of structures to the latest Silurian-Early Devonian. Comparison of the HBCH and BUCF indicates that they are grossly parallel, partly contemporaneous but with different kinematics. This kinematic variability may be explained if they are genetically linked with different segments of the Appalachian/Franklinian orogen. If true, both tectonic features can contribute to the understanding of plate interactions during the Silurian-Early Devonian period. A working hypothesis is proposed in which the HBCH was dynamically linked with the building-up Appalachian orogen located >1400 km to the SE through several grabens where Paleozoic faulting has been inferred. The nearly perpendicular trends of the BUCF and Franklinian mobile belt do not discard a genetic link between both features, as the Franklinian deformation front is much younger (latest Devonian-earliest Carboniferous) than the BUCF. A simple hypothesis, including a major change in strike of the building-up Franklinian orogen north of the Canadian Arctic islands is proposed and successfully accounts for the orientation and kinematic of the BUCF.

  10. Plate detachment, asthenosphere upwelling, and topography across subduction zones

    NASA Astrophysics Data System (ADS)

    Gvirtzman, Zohar; Nur, Amos

    1999-06-01

    This study analyzes the topography across subduction zones, considering the separate contributions of the crust and the mantle lithosphere to the observed surface elevation. We have found a transition from a region where the overriding plate is coupled to the descending slab and pulled down along with it to a region where the overriding plate floats freely on the asthenosphere. When the subducting slab retreats oceanward rapidly this transition is abrupt, and the edge of the overriding plate is uplifted. We propose that at some point during rapid slab rollback the overriding plate detaches and rebounds like a boat released from its keel. This event is associated with suction of asthenospheric material into the gap that is opened between the plates up to the base of the crust. As a result, the forearc uplifts, and magmatism in the arc increases.

  11. 25 CFR 227.26 - Assignments and overriding royalties.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ...227.26 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF CERTAIN LANDS IN WIND RIVER INDIAN RESERVATION, WYOMING, FOR OIL AND GAS MINING Operations § 227.26 Assignments and overriding...

  12. 25 CFR 227.26 - Assignments and overriding royalties.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ...227.26 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF CERTAIN LANDS IN WIND RIVER INDIAN RESERVATION, WYOMING, FOR OIL AND GAS MINING Operations § 227.26 Assignments and overriding...

  13. 25 CFR 227.26 - Assignments and overriding royalties.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ...227.26 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF CERTAIN LANDS IN WIND RIVER INDIAN RESERVATION, WYOMING, FOR OIL AND GAS MINING Operations § 227.26 Assignments and overriding...

  14. 25 CFR 227.26 - Assignments and overriding royalties.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ...227.26 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF CERTAIN LANDS IN WIND RIVER INDIAN RESERVATION, WYOMING, FOR OIL AND GAS MINING Operations § 227.26 Assignments and overriding...

  15. 25 CFR 227.26 - Assignments and overriding royalties.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ...227.26 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF CERTAIN LANDS IN WIND RIVER INDIAN RESERVATION, WYOMING, FOR OIL AND GAS MINING Operations § 227.26 Assignments and overriding...

  16. Drug Interaction Alert Override Rates in the Meaningful Use Era

    PubMed Central

    Bryant, A.D.; Fletcher, G.S.

    2014-01-01

    Summary Background Interruptive drug interaction alerts may reduce adverse drug events and are required for Stage I Meaningful Use attestation. For the last decade override rates have been very high. Despite their widespread use in commercial EHR systems, previously described interventions to improve alert frequency and acceptance have not been well studied. Objectives (1) To measure override rates of inpatient medication alerts within a commercial clinical decision support system, and assess the impact of local customization efforts. (2) To compare override rates between drug-drug interaction and drug-allergy interaction alerts, between attending and resident physicians, and between public and academic hospitals. (3) To measure the correlation between physicians’ individual alert quantities and override rates as an indicator of potential alert fatigue. Methods We retrospectively analyzed physician responses to drug-drug and drug-allergy interaction alerts, as generated by a common decision support product in a large teaching hospital system. Results (1) Over four days, 461 different physicians entered 18,354 medication orders, resulting in 2,455 visible alerts; 2,280 alerts (93%) were overridden. (2) The drug-drug alert override rate was 95.1%, statistically higher than the rate for drug-allergy alerts (90.9%) (p < 0.001). There was no significant difference in override rates between attendings and residents, or between hospitals. (3) Physicians saw a mean of 1.3 alerts per day, and the number of alerts per physician was not significantly correlated with override rate (R2 = 0.03, p = 0.41). Conclusions Despite intensive efforts to improve a commercial drug interaction alert system and to reduce alerting, override rates remain as high as reported over a decade ago. Alert fatigue does not seem to contribute. The results suggest the need to fundamentally question the premises of drug interaction alert systems. PMID:25298818

  17. Incorporating Cutting Edge Scientific Results from the Margins-Geoprisms Program into the Undergraduate Curriculum, Rupturing Continental Lithosphere Part II: Introducing Euler Poles Using Baja-North America Relative Plate Motion Across the Gulf of California

    NASA Astrophysics Data System (ADS)

    Loveless, J. P.; Bennett, S. E. K.; Cashman, S. M.; Dorsey, R. J.; Goodliffe, A. M.; Lamb, M. A.

    2014-12-01

    The NSF-MARGINS Program funded a decade of research on continental margin processes. The NSF-GeoPRISMS Mini-lesson Project, funded by NSF-TUES, is designed to integrate the significant findings from the MARGINS program into open-source college-level curriculum. The Gulf of California (GOC) served as the focus site for the Rupturing Continental Lithosphere (RCL) initiative, which addressed several scientific questions: What forces drive rift initiation, localization, propagation and evolution? How does deformation vary in time and space, and why? How does crust evolve, physically and chemically, as rifting proceeds to sea-floor spreading? What is the role of sedimentation and magmatism in continental extension? We developed two weeks of curriculum, including lectures, labs, and in-class activities that can be used as a whole or individually. This component of the curriculum introduces students to the Euler pole description of relative plate motion (RPM) by examining the tectonic interactions of the Baja California microplate and North American plate. The plate boundary varies in rift obliquity along strike, from highly oblique and strike-slip dominated in the south to slightly less oblique and with a larger extensional component in the north. This Google Earth-based exercise provides students with a visualization of RPM using small circle contours of the local direction and magnitude of Baja-North America movement on a spherical Earth. Students use RPM to calculate the fault slip rates on transform, normal, and oblique-slip faults and examine how the varying faulting styles combine to accommodate RPM. MARGINS results are integrated via comparison of rift obliquity with the structural style of rift-related faults around the GOC. We find this exercise to fit naturally into courses about plate tectonics, geophysics, and especially structural geology, given the similarity between Euler pole rotations and stereonet-based rotations of structural data.

  18. Uplift of continental crustal blocks adjacent to the Rancheria Basin-Guasare area: the effects of Maastrichtian-Paleocene collision along the southern Caribbean plate boundary

    NASA Astrophysics Data System (ADS)

    Bayona, G.; Montes, C.; Jaramillo, C.; Ojeda, G.; Cardona, A.; Pardo, A.; Lamus, F.

    2007-05-01

    In the Rancheria basin (RB) and Guasare area (GA), Maastrichtian-Paleocene synorogenic strata overlie the Aptian-Campanian carbonate platform. Nowadays, RB is bounded to the west by metamorphic-and-igneous cored Santa Marta massif, where Upper Cretaceous strata overlie unconformably pre-Cretaceous rocks. The eastern boundary of the RB is the Perija range that includes volcaniclastic and sedimentary rocks of Jurassic and Cretaceous age in the hanging-wall of a NW-verging, low-angle dipping thrust belt. The GA is on the eastern foothills of the Perija range and corresponds to the western boundary of the Maracaibo basin. Strata architecture, seismic reflectors, gravity, provenance, and paleocurrent analyses carried out in those basins constrain the timing and style of uplift of Santa Marta massif and Perija range, which are linked with tectonism along the southern Caribbean plate. Maastrichtian-Paleocene strata thicken eastward up to 2.2 km in the RB, and this succession includes (in stratigraphic order): foram-rich calcareous mudstone, oyster-pelecypod rich carbonate-siliciclastic strata, coal- bearing mudstones and feldspar-lithic-rich fluvial sandstones. Internal disconformities and truncations of seismic reflectors are identified to the west of the RB, but there are not major thrust faults at this part of the basin to explain such unconformities and truncations. In Early Paleocene, carbonates developed better to the west of the RB, whereas mixed carbonate-siliciclastic deposition continued toward the east of the RB. In early Late Paleocene, influx of terrigenous material (key grains=metamorphic, microcline and garnet fragments) derived from the Santa Marta massif increased to the west, but to the east of the RB and GA carbonate-siliciclastic and carbonate deposition continued, respectively. In mid-Late Paleocene, diachronous eastward advance of paralic/deltaic environments, tropical humid climate, and high subsidence rates favored production and preservation of peat in RB and GA. In the late Late Paleocene, inversion along a buried graben system under the Perija range explain supply toward RB and GA of micritic, volcanic, and sedimentary rock fragments, and the record of a thinner Upper Paleocene strata in the GA than in the RB. Tectonic subsidence in the RB was mainly related to pivoting of the Santa Marta massif as result of collision of the Maracaibo continental sub-plate with the southern margin of the Caribbean oceanic plate. This model explains the generation of accommodation space in the RB without faulting, denudation of upper crustal material of the Santa Marta massif, early capture of terrigenous detritus in the RB that favored carbonate deposition in the GA, the mechanism of initial inversion of the Perija range, and the present positive gravity anomaly under the Santa Marta massif.

  19. H2O-fluid-saturated melting of subducted continental crust facilitates exhumation of ultrahigh-pressure rocks in continental subduction zones

    NASA Astrophysics Data System (ADS)

    Labrousse, L.; Duretz, T.; Gerya, T.

    2015-10-01

    We present two-dimensional numerical models of plate subduction and collision inspired by the Scandinavian Caledonian orogeny to investigate the possible impact of continental crust partial melting on the exhumation of ultra-high pressure metamorphic rocks. Three possible reactions were tested: low temperature solidus representing H2O-fluid-saturated partial melting, and two end-member reaction curves for dehydration melting. Thermo-mechanical effects of partial melting were implemented as (1) a viscosity decrease as a determined rheologically critical melt percentage was reached (here 0.1), (2) a change in effective heat capacity and adiabatic heating/cooling accounting for a latent heat term in the heat equation. Among the 3 tested reactions, only H2O-fluid-saturated partial melting drastically modifies the collision dynamics from the non-melting reference model holding all other parameters constant. A substantially low general viscosity truncation (here 1017 Pa s) is needed to properly resolve the effect of partial melting on deep collision processes. Low temperature melting indeed induces the development of a low viscosity buoyant plume prior to slab detachment, where migmatites exhume from UHP conditions at rates and with pressure-temperature paths similar to the natural values acknowledged for the Norwegian Caledonides. High temperature melting has no drastic influence on early collision dynamics. While positive buoyancy remains the first order driver for the exhumation of buried continental rocks, exhumation initiates in these cases with eduction subsequent to slab detachment. Melting and formation of a migmatite plume can later occur along decompression path while continental crust undergoes thermal reequilibration at temperatures above 900 °C. Some of the partially molten material can also relaminate in the overriding plate rather than exhume within the collision zone. Even if minor in terms of amount of magma produced, H2O-fluid-saturated partial melting at UHP conditions could therefore have a dramatic rheological effect and actually limits continental rocks subduction and facilitates their exhumation.

  20. Ridge torques and continental collision in the Indian-Australian plate Mike Sandiford Department of Geology, University of Adelaide, Adelaide 5005, Australia

    E-print Network

    Sandiford, Mike

    -Australian plate, the net torque due to the asymmetric distribution of mid-ocean ridges and young oceanic litho, such logic ap- plies only to plates where the effective lengths of the mid-ocean ridges and the con- tinental orogen are equivalent; in the Indi- an-Australian plate, the length of the mid- ocean ridge system along

  1. Suggestions for Teaching the Principles of Continental Drift in the Elementary School

    ERIC Educational Resources Information Center

    Glenn, William H.

    1977-01-01

    Provides a brief overview of current geographic ideas regarding continental drift and plate tectonics and suggests techniques for illustrating continental motions to elementary school pupils. (Author/DB)

  2. Self-assembled software and method of overriding software execution

    DOEpatents

    Bouchard, Ann M.; Osbourn, Gordon C.

    2013-01-08

    A computer-implemented software self-assembled system and method for providing an external override and monitoring capability to dynamically self-assembling software containing machines that self-assemble execution sequences and data structures. The method provides an external override machine that can be introduced into a system of self-assembling machines while the machines are executing such that the functionality of the executing software can be changed or paused without stopping the code execution and modifying the existing code. Additionally, a monitoring machine can be introduced without stopping code execution that can monitor specified code execution functions by designated machines and communicate the status to an output device.

  3. First measurement of the displacement rate of the Pacific Plate near the Japan Trench after the 2011 Tohoku-Oki earthquake using GPS/acoustic technique

    NASA Astrophysics Data System (ADS)

    Tomita, Fumiaki; Kido, Motoyuki; Osada, Yukihito; Hino, Ryota; Ohta, Yusaku; Iinuma, Takeshi

    2015-10-01

    The subduction rate of an oceanic plate may accelerate after large earthquakes rupture the interplate coupling between the oceanic and overriding continental plates. To better understand postseismic deformation processes in an incoming oceanic plate, we directly measured the displacement rate of the Pacific Plate near the Japan Trench after the 2011 Tohoku-Oki earthquake using a GPS/acoustic technique over a period of 2 years (September 2012 to September 2014). The displacement rate was measured to be 18.0 ± 4.5 cm yr-1 (N302.0°E) relative to the North American Plate, which is almost twice as fast as the predicted interseismic plate motion. Because the sum of steady plate motion and viscoelastic response to the Tohoku-Oki earthquake roughly accounts for the observed displacement rate, we conclude that viscoelastic relaxation is the primary mechanism responsible for postseismic deformation of the Pacific Plate and that significant subduction acceleration did not occur at least not during the observation period.

  4. 43 CFR 3933.32 - Overriding royalty interests.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 43 Public Lands: Interior 2 2011-10-01 2011-10-01 false Overriding royalty interests. 3933.32 Section 3933.32 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR RANGE MANAGEMENT (4000) MANAGEMENT OF OIL SHALE EXPLORATION AND...

  5. 25 CFR 227.26 - Assignments and overriding royalties.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 25 Indians 1 2010-04-01 2010-04-01 false Assignments and overriding royalties. 227.26 Section 227.26 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF CERTAIN LANDS IN WIND RIVER INDIAN RESERVATION, WYOMING, FOR OIL AND GAS MINING Operations §...

  6. 25 CFR 227.26 - Assignments and overriding royalties.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 25 Indians 1 2011-04-01 2011-04-01 false Assignments and overriding royalties. 227.26 Section 227.26 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF CERTAIN LANDS IN WIND RIVER INDIAN RESERVATION, WYOMING, FOR OIL AND GAS MINING Operations §...

  7. 25 CFR 227.26 - Assignments and overriding royalties.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 25 Indians 1 2012-04-01 2011-04-01 true Assignments and overriding royalties. 227.26 Section 227.26 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF CERTAIN LANDS IN WIND RIVER INDIAN RESERVATION, WYOMING, FOR OIL AND GAS MINING Operations §...

  8. Plate-mantle coupling from post-Pangea plate kinematics

    NASA Astrophysics Data System (ADS)

    Zahirovic, Sabin; Dietmar Müller, R.; Seton, Maria; Flament, Nicolas

    2015-04-01

    Convection in the Earth's mantle that involves plates at the surfaces gives rise to plate velocities that vary through time and depend on the balance of plate boundary forces, with the present-day providing a snapshot of this ongoing process. However, present-day plate velocities do not capture plate behaviour over geologically representative timeframes and thus cannot be used to evaluate factors limiting plate velocities. Previous studies investigated the effects of continental keels on plate speeds by either using the present-day snapshot or a limited number of reconstructed plate configurations, often leading to conflicting results. For example, an early assumption was that continental keels (especially cratons) were unlikely to impede fast plate motions because India's velocity approached ~20 cm/yr in the Eocene prior to the collision with Eurasia. We employ a modern plate reconstruction approach with evolving global topological plate boundaries for the post-Pangea timeframe (since 200 Ma) to evaluate factors controlling plate velocities. Plate boundary configurations and plate velocities are extracted from the open-source and cross-platform plate reconstruction package GPlates (www.gplates.org) at 1 Myr intervals. For each plate, at each timestep, the area of continental and cratonic lithosphere is calculated to evaluate the effect on plate velocities. Our results support that oceanic plates tend to be 2-3 times faster than plates with large portion of continental plate area, consistent with predictions of numerical models of mantle convection. The fastest plates (~8.5 cm/yr RMS) are dominated by oceanic plate area and high subducting portion of plate perimeter, while the slowest plates (~2.6-2.8 cm/yr RMS) are dominated by continental plate area and bounded by transforms and mid-oceanic ridge segments. Importantly, increasing cratonic fractions (both Proterozoic and Archean lithosphere) significantly impede plate velocities, suggesting that deep continental keels impinge on asthenospheric flow to increase shear traction, thus anchoring the plate in the more viscous mantle transition zone. However, plates with significant cratonic fragments exhibit short-lived (~10 Myr) accelerations, such as the rapid motion of the Indian plate that is correlated with plume head arrivals as recorded by large igneous province (LIPs) emplacement, highlighting the necessity to analyse plate velocities over long geological timeframes. By evaluating factors controlling plate velocities in the post-Pangea timeframe, simple principles can be applied to highlight potential plate velocity artefacts for Paleozoic and earlier times for which no hotspot tracks, nor in-situ seafloor spreading histories, are preserved. Based on the post-Pangea timeframe, a principle that can be applied to pre-Pangea times is that plates with less than ~50% continental area can reach RMS velocities of ~20 cm/yr, while plates with more than 50% continental fraction do not exceed RMS velocities of ~10 cm/yr. Similarly, plates with large portions of continental or cratonic area with RMS velocities exceeding ~15 cm/yr for more than ~10 Myr should be flagged as potential artefacts requiring further justification of plate driving forces in such scenarios.

  9. Continental Microplate Tectonics

    NASA Astrophysics Data System (ADS)

    Thatcher, W.

    2007-12-01

    During the past decade, methods of space geodesy have demonstrated that the kinematics of the intra- continental deforming zones that lie between the large global plates can be usefully described as relative motions among small elastic blocks or microplates. At the same time, kinematic models that assume a smoothly varying deformation field have been developed and applied to the same data. Both models generally fit the data comparably well and there is much debate about which approach--blocks or continuum--is 'better'. However, there is really no disagreement about the existence of crustal blocks in deforming zones and only their size and number are contentious. Therefore a perhaps more useful way of framing the debate is to examine the purpose of each modeling approach, its success in meeting that purpose, and its limitations. Continuum modeling approaches are typically a prelude to dynamic modeling of continental deformation, thus far usually using a thin viscous sheet rheology for the lithosphere. The purpose of continuum modeling is then to quantify the forces driving and resisting motions and understand their relation to the observed deformation. This approach has been notably successful in determining the relative importance of plate boundary tractions and internal buoyancy forces (gravitational potential energy) in driving intra-continental deformation, particularly in central Asia and western North America. Continental deformation is block-like because major faults are weak and block interiors are much stronger. The main purpose of simple rigid plate kinematics is to quantify the rate and sense of slip across major faults and mountain belts, with applications to active tectonics and earthquake hazard assessment. Where available, late Quaternary and Holocene fault slip rate estimates, with few (but notable) exceptions, agree with geodetically- estimated rates obtained from the block models. Where block rotations are sufficiently large, late Cenozoic rotation rates can be determined paleomagnetically and these rates commonly agree with the space geodetic estimates. Despite several similarities, continental block kinematics differs in notable ways from global plate tectonics. First, microplates are much smaller, typically ~100-1000 km in size. Departures from block rigidity are small but measurable and represent either heterogeneous internal deformation or a more complex but unresolved block structure. While major oceanic plates may persist for tens or 100s of Ma, continental microplates change and evolve over much shorter timescales, particularly near their often geometrically irregular boundaries. The depth to which discrete block structures extend is uncertain. While some major faults probably extend through the crust into the upper mantle as narrow ductile shear zones, blocks elsewhere may be at least partially decoupled from the mantle lithosphere by pervasive ductile flow of weak lower crust. Continental blocks must ultimately be subject to the same forces that drive and resist global plate motions. However, the role and importance of local forces is often evident from the observed patterns of continental block motion. These local forces include internal buoyancy due to lateral density gradients in continental lithosphere and block boundary forces such as those caused by slab roll-back, trench suction, and resistance to subduction of buoyant lithosphere. The importance of basal tractions that may drive or resist block motions is uncertain and controversial.

  10. Plate Tectonics: A Paradigm under Threat.

    ERIC Educational Resources Information Center

    Pratt, David

    2000-01-01

    Discusses the challenges confronting plate tectonics. Presents evidence that contradicts continental drift, seafloor spreading, and subduction. Reviews problems posed by vertical tectonic movements. (Contains 242 references.) (DDR)

  11. Tectonic plate coupling and elastic thickness derived from the inversion of a steady state viscoelastic model using geodetic data: Application to southern North Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Cohen, Steven C.; Darby, Desmond J.

    2003-03-01

    A steady state viscoelastic model of deformation at an oblique convergence zone is used to analyze crustal velocities deduced from Global Positioning System (GPS) observations in southern North Island, New Zealand. The model is physically more reasonable than elastic dislocation theory because the tectonic plates have finite elastic thicknesses. In an inversion that makes use of Green's functions derived from finite element calculations, we solve for depth-dependent fault backslip rates. The associated chi-squared goodness of fit parameter depends on the values of the elastic thicknesses of the overriding Australian and subducting Pacific Plates. These thicknesses are systematically varied in order to find the chi-squared minimum. We find that: (1) the plates have coupling coefficient between 0.8 and 1.0 to a depth of about 22 km; (2) elastic dislocation theory appears to adequately fit the observations because the effects of viscoelastic flow are small; (3) viscoelastic results depend on the contrast between the elastic moduli of the plates, (4) the trench normal, rather than the trench parallel component of motion is more diagnostic for choosing between models with different parameters; (5) for the favored model (one with a weak continental crust), the estimated value of the Pacific Plate thickness is 40-60 km. Although the estimates of the plate thickness are not tightly constrained, those deduced from geodetic data tend to be larger than those deduced from geologic data, consistent with the idea that thickness estimates depend on the time scale of the loading process.

  12. Whole Earth Structure and Plate Tectonics

    E-print Network

    evolution of Earth: from continental drift (early 1900's) to sea-floor spreading (early 1960's) to plate: summarized in "Our wandering continents, an hypothesis of continental drifting' (1937) 1924-up Jeffrey (continental) flora on S hemisphere (India, Australia, Africa, S America, Antarctica), Permian glaciation

  13. Earthquakes, Plate Boundaries, and Depth Indiana Standard Indicators

    E-print Network

    Polly, David

    , volcanoes, trenches, and mountains. ES.1.24 ­ Understand and discuss continental drift, sea-floor spreading of the ocean and continental crust and the depth of earthquakes, and types of plate boundaries where or continental crust? · What is the explanation behind the earthquakes that do not occur at plate boundaries? #12

  14. GPS constraints on the kinematics of continental deformation

    USGS Publications Warehouse

    Thatcher, W.

    2003-01-01

    Recent GPS observations from the western United States, New Zealand, central Greece, and Japan indicate that present-day continental deformation is typically focused in narrow deforming zones whose extent is much smaller than the intervening largely inactive regions. However, these narrow zones are heterogeneously distributed, reflecting the inherent heterogeneity of continental lithospheric strength and internal buoyancy. Plate driving and resisting forces stress plate boundary zones and plate interiors and drive deformation. These forces change continuously and discontinuously, leading to continental deformation that typically evolves and migrates with time. Magmatic and tectonic processes alter lithospheric rheology and internal buoyancy and also contribute to the time-varying character of continental deformation.

  15. A New Arabia-Africa-Eurasia GPS Velocity Field (1994-2014) and E Mediterranean Block Model: Implications for Continental Deformation in a Zone of Active Plate Interaction

    NASA Astrophysics Data System (ADS)

    Vernant, P.; Floyd, M.; Ozener, H.; Ergintav, S.; Karakhanian, A.; Kadirov, F. A.; Sokhadze, G.; ArRajehi, A.; Nankali, H. R.; Georgiev, I.; Ganas, A.; Paradissis, D.; McClusky, S.; Gomez, F. G.; Reilinger, R. E.

    2014-12-01

    We present new GPS velocities for the Arabia-Africa-Eurasia region determined with GAMIT/GLOBK (>830 velocities) spanning the period 1994-2014. Here we consider the E Mediterranean region of plate interaction. We use DEFNODE software to develop block models and estimate slip rates on major faults and strain of some blocks. The wrms of residual velocities from our new model is 1.3 mm/yr. We identify small E-W extension within the newly defined Anatolian block confined to a 100-200 km wide zone south of the North Anatolian Fault (NAF) reaching 2-3 mm/yr with rates increasing towards the west. Possible causes we consider include, un-modeled postseismic effects of the 1999 Izmit/Duzce earthquake sequence, continuing post-seismic effects of the 20th Century sequence of M>7 earthquakes, and/or toroidal sub-lithospheric flow towards the subducting Hellenic slab. The overall strain rate of the Marmara Sea block is dominantly N-S extension, and the Van block, N-S compression. Present slip rates along the NAF increase from E to W, 22-24 mm/yr along the E to E-central segment and 27-28 mm/yr along the W segment. We quantify extension in the G. of Corinth, central Greece, and G. of Evia; the W, central and E sections of the Hellenic Trench are shortening with extension in the back-arc. The W Hellenic Trench and W Peloponnese have right-lateral strike-slip and the E Hellenic Trench, left-lateral ss. N-S extension (2-4 mm/yr) in N Greece and the N Aegean Sea extends at least to 42°N. Arabia-Sinai left-lateral motion across the Dead Sea Fault is ~5 mm/yr along the S segment; significant residual velocities along the N and S segments indicate lower slip rates in the N and require fault segmentation to account for slip rate variations along strike. We identify E-W contraction of the Arabian (Persian) Gulf (~3-5 mm/yr) that extends into the E part of the Arabian Plate. We will quantify and present these and other observed deformation patterns and discuss their tectonic implications.

  16. A simple continental rift classification

    NASA Astrophysics Data System (ADS)

    Merle, Olivier

    2011-12-01

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

  17. Australian plate motion and topography linked to fossil New Guinea slab below Lake Eyre

    NASA Astrophysics Data System (ADS)

    Schellart, W. P.; Spakman, W.

    2015-07-01

    Unravelling causes for absolute plate velocity change and continental dynamic topography change is challenging because of the interdependence of large-scale geodynamic driving processes. Here, we unravel a clear spatio-temporal relation between latest Cretaceous-Early Cenozoic subduction at the northern edge of the Australian plate, Early Cenozoic Australian plate motion changes and Cenozoic topography evolution of the Australian continent. We present evidence for a ?4000 km wide subduction zone, which culminated in ophiolite obduction and arc-continent collision in the New Guinea-Pocklington Trough region during subduction termination, coinciding with cessation of spreading in the Coral Sea, a ?5 cm/yr decrease in northward Australian plate velocity, and slab detachment. Renewed northward motion caused the Australian plate to override the sinking subduction remnant, which we detect with seismic tomography at 800-1200 km depth in the mantle under central-southeast Australia at a position predicted by our absolute plate reconstructions. With a numerical model of slab sinking and mantle flow we predict a long-wavelength subsidence (negative dynamic topography) migrating southward from ?50 Ma to present, explaining Eocene-Oligocene subsidence of the Queensland Plateau, ?330 m of late Eocene-early Oligocene subsidence in the Gulf of Carpentaria, Oligocene-Miocene subsidence of the Marion Plateau, and providing a first-order fit to the present-day, ?200 m deep, topographic depression of the Lake Eyre Basin and Murray-Darling Basin. We propound that dynamic topography evolution provides an independent means to couple geological processes to a mantle reference frame. This is complementary to, and can be integrated with, other approaches such as hotspot and slab reference frames.

  18. Override the controversy: Analytic thinking predicts endorsement of evolution.

    PubMed

    Gervais, Will M

    2015-09-01

    Despite overwhelming scientific consensus, popular opinions regarding evolution are starkly divided. In the USA, for example, nearly one in three adults espouse a literal and recent divine creation account of human origins. Plausibly, resistance to scientific conclusions regarding the origins of species-like much resistance to other scientific conclusions (Bloom & Weisberg, 2007)-gains support from reliably developing intuitions. Intuitions about essentialism, teleology, agency, and order may combine to make creationism potentially more cognitively attractive than evolutionary concepts. However, dual process approaches to cognition recognize that people can often analytically override their intuitions. Two large studies (total N=1324) found consistent evidence that a tendency to engage analytic thinking predicted endorsement of evolution, even controlling for relevant demographic, attitudinal, and religious variables. Meanwhile, exposure to religion predicted reduced endorsement of evolution. Cognitive style is one factor among many affecting opinions on the origin of species. PMID:26072277

  19. Override of spontaneous respiratory pattern generator reduces cardiovascular parasympathetic influence

    NASA Technical Reports Server (NTRS)

    Patwardhan, A. R.; Vallurupalli, S.; Evans, J. M.; Bruce, E. N.; Knapp, C. F.

    1995-01-01

    We investigated the effects of voluntary control of breathing on autonomic function in cardiovascular regulation. Variability in heart rate was compared between 5 min of spontaneous and controlled breathing. During controlled breathing, for 5 min, subjects voluntarily reproduced their own spontaneous breathing pattern (both rate and volume on a breath-by-breath basis). With the use of this experimental design, we could unmask the effects of voluntary override of the spontaneous respiratory pattern generator on autonomic function in cardiovascular regulation without the confounding effects of altered respiratory pattern. Results from 10 subjects showed that during voluntary control of breathing, mean values of heart rate and blood pressure increased, whereas fractal and spectral powers in heart rate in the respiratory frequency region decreased. End-tidal PCO2 was similar during spontaneous and controlled breathing. These results indicate that the act of voluntary control of breathing decreases the influence of the vagal component, which is the principal parasympathetic influence in cardiovascular regulation.

  20. Petrogenesis of Tertiary continental intra-plate lavas between Siebengebirge and Westerwald, Germany: Constraints from trace element systematics and Nd, Sr and Pb isotopes

    NASA Astrophysics Data System (ADS)

    Schubert, S.; Jung, S.; Pfänder, J. A.; Hauff, F.; Garbe-Schönberg, D.

    2015-10-01

    New 39Ar/40Ar ages and major- and trace-element and radiogenic isotope data are presented for basanites and alkali basalts from the transition area between the Westerwald and Siebengebirge volcanic fields (Germany) that belongs to the Central European Volcanic Province (CEVP). The 39Ar/40Ar ages indicate ages of c. 24 and c. 5 Ma which are fully compatible with previous K/Ar ages indicating that the evolution of this volcanic field belongs to the Westerwald area (28-22 Ma and 5 Ma) rather than to the Siebengebirge area (26-23 Ma). Based on the occurrence of > 30 isolated volcanic plugs with a simple igneous history, this volcanic field can be viewed as a monogenetic volcanic field. Compositions of some basanites are primitive, whereas others and the alkali basalts show decreasing Cr and Ni contents and CaO/Al2O3 ratios. However, increasing TiO2, Al2O3 and incompatible elements (Sr, Zr, Y, Hf, Ta) concentrations with decreasing MgO indicating fractionation of mainly olivine with minor amounts of clinopyroxene and spinel can be noticed. Rare earth element systematics suggest that most of the alkaline rocks are generated by different degrees of melting (5%-10%) of a garnet-bearing peridotite containing some residual amphibole. Negative anomalies of Rb and K in primitive mantle-normalized diagrams and a lack of Ba/Rb fractionation suggest that amphibole was the major OH-bearing mineral phase in the mantle. The alkaline rocks have a restricted range in 87Sr/86Sr and 143Nd/144Nd ratios ranging from 0.7033 to 0.7044 and from 0.51275 to 0.51285, respectively. Lead isotope compositions (206Pb/204Pb: 19.21-19.65; 207Pb/204Pb: 15.62-15.67; 208Pb/204Pb: 39.10-39.46) of the alkaline rocks are within the range of most OIB in which the higher values approach the composition of the European Asthenospheric Reservoir (EAR). The correlation between Sr and Nd isotopes and trace element constraints (Ce/Pb; Nb/U) indicates that for some samples interaction with crustal rocks during fractionation has occurred. Miocene intraplate basaltic volcanism in the area probably occurred as a result of minor "baby plume" activity. Each volcanic plug records evidence of a specific stage of fractionation with or without assimilation; however, in summary the lavas plot on a single fractionation path. This implies that during evolution of the volcanic field initial melting took place in the asthenosphere or at the lithosphere-asthenosphere interface. The melts moved through the lithospheric mantle and stagnated at crustal levels, however the observed fractionation paths suggest that they were fed from a single reservoir. This model, which involves small-scale plume impact followed by asthenosphere-lithosphere interaction together with minor crustal contamination, should also be applicable to other intra-continental rift-related areas.

  1. Crustal growth at active continental margins: Numerical modeling

    NASA Astrophysics Data System (ADS)

    Vogt, Katharina; Gerya, Taras V.; Castro, Antonio

    2012-02-01

    The dynamics and melt sources for crustal growth at active continental margins are analyzed by using a 2D coupled petrological-thermomechanical numerical model of an oceanic-continental subduction zone. This model includes spontaneous slab retreat and bending, dehydration of subducted crust, aqueous fluid transport, partial melting, melt extraction and melt emplacement in form of extrusive volcanics and intrusive plutons. We could identify the following three geodynamic regimes of crustal growth: (i) stable arcs, (ii) compressional arcs with plume development, and (iii) extensional arcs. Crustal growth in a stable subduction setting results in the emplacement of flattened intrusions in the lower crust. At first dacitic melts, extracted from partially molten rocks located atop the slab (gabbros and basalts), intrude into the lower crust followed by mantle-derived (wet peridotite) basaltic melts from the mantle wedge. Thus extending plutons form in the lower crust, characterized by a successively increasing mantle component and low magmatic addition rates (10 km3/km/Myrs). Compressional arcs are accomplished by the formation and emplacement of hybrid plumes. In the course of subduction localization and partial melting of basalts and sediments along the slab induces Rayleigh Taylor instabilities. Hence, buoyant plumes are formed, composed of partially molten sediments and basalts of the oceanic crust. Subsequently, these plumes ascend, crosscutting the lithosphere before they finally crystallize within the upper crust in form of silicic intrusions. Additionally, intrusions are formed in the lower crust derived by partial melting of rocks located atop the slab (basalts, gabbros, wet peridotite) and inside the plume (basalts, sediments). Magmatic addition rates are somewhat higher compared to stable arcs (40-70 km3/km/Myrs). Subduction in an extensional arc setting results in decompression melting of dry peridotite. The backward motion of the subduction zone relative to the motion of the plate leads to thinning of the overriding plate. Thus, hot and dry asthenosphere rises into the neck as the slab retreats, triggering decompression melting of dry peridotite. Consequently large volumes of mafic (oceanic) crust are formed in the backarc region with total magmatic addition rates being as high as 90-170 km3/km/Myrs.

  2. Unintended Consequences: The Impact of Proposition 2½ Overrides on School Segregation in Massachusetts

    ERIC Educational Resources Information Center

    Zabel, Jeffrey

    2014-01-01

    I investigate a possible unintended consequence of Proposition 2½ override behavior--that it led to increased segregation in school districts in Massachusetts. This can occur because richer, low-minority towns tend to have more successful override votes that attract similar households with relatively high demands for public services who can afford…

  3. FUNDAMENTALS OF PLATE TECTONICS Fall Semester 2012-13

    E-print Network

    Polly, David

    of books on plate tectonics and continental drift is also attached. The final section of the list includes. The second portion will focus on the theory's application to fundamental problems of continental and marine

  4. A Video Recall Study of In-session Changes in Sentiment Override.

    PubMed

    Johnson, Lee N; Tambling, Rachel B; Anderson, Shayne R

    2015-09-01

    This study examines in-session changes in sentiment override over the first three sessions of couple therapy. Couples viewed a video recording of therapy sessions immediately after each of the first three sessions and continuously rated their level of sentiment override. Ninety-eight changes were randomly chosen for analysis. Three talk turns prior to each change was coded using the Family Relational Communication Control Coding System. Results show that changes in sentiment override occur frequently. Repeated incidents of communication control were related to negative change in sentiment override for females. Repeated incidents of being left out of the conversation were related to negative changes in sentiment override for females and positive changes for males. PMID:25521172

  5. The Plate Tectonics Project

    ERIC Educational Resources Information Center

    Hein, Annamae J.

    2011-01-01

    The Plate Tectonics Project is a multiday, inquiry-based unit that facilitates students as self-motivated learners. Reliable Web sites are offered to assist with lessons, and a summative rubric is used to facilitate the holistic nature of the project. After each topic (parts of the Earth, continental drift, etc.) is covered, the students will…

  6. Plate motion controls on back-arc spreading. [Cenozoic movement in Western Pacific

    NASA Technical Reports Server (NTRS)

    Fein, J. B.; Jurdy, D. M.

    1986-01-01

    The motions of the subducting and the overriding plates influence the spatial and temporal distribution of back-arc spreading. Cenozoic plate motions in hot spot-fixed and no-net-rotation reference frames were studied with attention to correlations between changes in motion and episodes of back-arc spreading in the western Pacific. The results suggest that major back-arc opening occurs when both the overriding plate retreats from the trench in an absolute sense and the subducting plate undergoes a significant speed-up. Neither phenomenon alone is sufficient to initiate spreading. Three major plate velocity increases can be identified in the Cenozoic: (1) the Pacific plate 5-9 Ma; (2) the Indian plate at 27 Ma; and (3) the Pacific plate at 43 Ma, due to its shift from northerly to more westerly motion. At the present time, the Indian and Philippine are the only overriding plates that are retreating from their Pacific trenches and back-arc spreading occurs only on these two retreating plates. Although the Indian plate has been retreating for at least 25 Ma, back-arc spreading began only following the Pacific plate speed-up 5-9 Ma. Earlier, during the Indian plate speed-up, no overriding plates were retreating strongly and no back-arc spreading epsiodes are preserved from this time. For the earliest Pacific plate shift at 43 Ma, the Eurasian plate was not advancing, thus creating the only favorable plate kinematic conditions in the Cenozoic for back-arc basin formation in this region. It is unclear whether extension in the Japan Sea is a result of these conditions.

  7. Mechanical obstacles to the movement of continent-bearing plates

    NASA Technical Reports Server (NTRS)

    Lowman, P. D., Jr.

    1985-01-01

    Selected geophysical problems associated with the concept of continental drift as an incidental corollary of plate movement are discussed. The problems include the absence of a suitable plate-driving mechanism for plates with continental leading edges, the absence of the low-velocity zone under shields, and continental roots of 400 to 700 km depths. It is shown that if continental drift occurs, it must use mechanisms not now understood, or that it may not occur at all, plate movement being confined to ocean basins.

  8. Cks Overexpression Enhances Chemotherapeutic Efficacy by Overriding DNA Damage Checkpoints

    PubMed Central

    del Rincón, Sonia V.; Widschwendter, Martin; Sun, Dahui; Ekholm-Reed, Susanna; Tat, John; Teixeira, Leonardo K.; Ellederova, Zdenka; Grolieres, Elise; Reed, Steven I.; Spruck, Charles

    2014-01-01

    Cks1 and Cks2 are adaptor-like proteins that bind many cyclin-dependent kinases (Cdks). A wealth of clinical data has shown that Cks proteins are overexpressed in many types of human cancers and this often correlates with increased tumor aggressiveness. Previously, we showed that Cks overexpression abrogates the intra-S phase checkpoint, a major barrier to oncogene-mediated transformation. Interestingly, the intra-S phase checkpoint is crucial for the cellular response to replication stress, a major pathway of apoptosis induction by many chemotherapeutic agents. Here, we demonstrate cancer cells that overexpress Cks1 or Cks2 override the intra-S phase checkpoint in the presence of replication stress-inducing chemotherapies such as 5-Fluorourocil (5-FU) and methotrexate (MTX) leading to enhanced sensitivity in vitro and in vivo. Furthermore, enforced expression of Cks1 in a MTX-resistant breast cancer cell line was found to restore drug sensitivity. Our results suggest that Cks proteins are important determinants of apoptosis induction of replication stress-inducing chemotherapies such as 5-FU. PMID:24858038

  9. Temporal change in plate coupling and long-term slow slip events in southwestern Japan

    NASA Astrophysics Data System (ADS)

    Ochi, Tadafumi

    2015-12-01

    In the southwestern part of Japan, many large earthquakes have been reported and many geodetic or seismic observations have been performed to monitor crustal deformation due to the interaction between the subducting Philippine Sea plate and the overriding continental plate along the Suruga-Nankai trough. These precise observations provide insight into aseismic stress-releasing processes such as slow slip events (SSEs). In this study, I focus on the effect of SSEs on interplate coupling to reveal the overall temporal evolution of interplate states along the trough in southwestern Japan. I focus mainly on the western part of the subduction zone, called the Nankai region. In this part, three SSEs (in 1997, 2003, and 2010) were detected during the period in which observations are available. Interplate coupling recovered quickly after the SSEs terminated. The eastern part of this region shows consistently strong coupling whether SSEs occur or not. Long-term SSEs are distributed between the coupling area and the area where tremors occur. I also examine the balance between stress accumulation and release at four points in the region. Below the eastern part of the strongly coupled area, at a depth of ?15 km, constant coupling of about 7 cm/yr takes place. In the center of the SSE region, at a depth of ?25 km, ?40% of the accumulated stress is released through SSEs, with the rest contributing to the stress accumulation process.

  10. Deformation of the overriding slab during incipient subduction in centrifuge modeling and its tectonic significance

    NASA Astrophysics Data System (ADS)

    Mart, Yossi; Goren, Liran; Koyi, Hemin

    2015-04-01

    Analog models of subduction-related structural deformation emphasize the significance of differences in density and friction between the adjacent plates on the distortion of the overriding slab and its possible effect on the subduction procedure. Centrifuge experiments juxtaposed miniaturized lighter and denser lithospheres, which were floating on denser but less viscous asthenosphere. The lithosphere in the tests comprised brittle and ductile strata, which showed diversified styles of deformation, while factors of equivocal tectonic significance, such as lateral push or negative buoyancy, were not introduced into the experiments. The tests show that the juxtaposition of lighter and denser lithospheres would suffice to drive the denser lithosphere as a wedge between the asthenosphere and the lighter lithosphere, and that the rate of the process would depend on the rate of friction between the slabs, as well as on differential viscosity. It seems that the reduced friction in Nature was derived from the generation of serpentinites, which could be the main agent of lubrication. The underthrusting of the denser lithosphere leads to the uplift and collapse of the edge of the lighter slab, where extension, thinning, normal faulting and rifting took place, and diapiric ascent of parts of the ductile layer of the lighter slab occurred along several rifts. The analog experiments were carried out only to the stage where the denser slab was thrust under the lighter one, but the penetration of the lithosphere into the asthenosphere was not achieved. It seems plausible therefore, that only after eclogitization, and the upward motion of serpentinites, increased the density of the underthrust slab, would it dive and penetrate into the asthenosphere. The experiments indicate the plausibility of the constraints imposed on the subduction process by the deformation of the overthrust slab. The normal faults and rifts in the overthrust block could serve as conduits for the ascent of the lighter mineralogical fraction emanating from the heated and pressurized subducting plate, as well as from the upper mantle material displaced by the subducted slab and their accretion on the lighter plate. The denser fraction of the subducting slab would be eclogitized, and thus pull the underthrust slab into the mantle. The experiments suggest further that ocean-continent juxtaposition is not a prerequisite for subduction, which could also initiate between two lithologic slabs of different densities that were juxtaposed due to transform faulting.

  11. Dynamics of Continental Accretion

    NASA Astrophysics Data System (ADS)

    Moresi, L. N.; Betts, P. G.; Miller, M. S.

    2013-12-01

    Subduction zones become congested when they try to swallow buoyant exotic crust. Accretionary mountain belts (orogens) that form at these convergent plate margins are the principal sites of lateral continental growth through Earth's history. Modern examples of accretionary margins are the North and South American Cordilleras and southwest Pacific. The geologic record is riddled with accretionary orogens, such as the Tasmanides along the eastern margin of the supercontinent Gondwana and the Altaides that formed on the southern margin of Laurasia. Both the modern and ancient examples are characterised by episodic switches between extension and shortening associated with transitions from collision of exotic crust and subduction related rollback. We present three-dimensional dynamic models that show for the first time how accretionary margins evolve from the initial collision, through a period of plate margin instability, to re-establishment of a stable convergent margin. The models illustrate how significant curvature of the orogenic system develops, as well as the mechanism for tectonic escape of the back arc region. The complexity of the morphology and evolution of the system are driven by lateral rollback of a tightly arcuate trench migrating parallel to the plate boundary and orthogonal to the convergence direction. We find geological and geophysical evidence for this process in the Tasmanides of eastern Australia, but infer that this is a global phenomena throughout Earth's evolution.

  12. A Simple Class Exercise on Plate Tectonic Motion.

    ERIC Educational Resources Information Center

    Bates, Denis E. B.

    1990-01-01

    Presented is an activity in which students construct a model of plate divergence with two sheets of paper to show the separation of two continental plates in a system of spreading ridges and faults. Diagrams and procedures are described. (CW)

  13. 43 CFR 3504.26 - May I create overriding royalties on my Federal lease?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ...LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) LEASING OF SOLID MINERALS OTHER THAN COAL AND OIL SHALE Fees, Rental, Royalty and Bonds Royalties § 3504.26 May I create overriding royalties on my Federal lease?...

  14. Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments

    NASA Astrophysics Data System (ADS)

    Tetreault, J. L.; Buiter, S. J. H.

    2014-12-01

    Allochthonous accreted terranes are exotic geologic units that originated from anomalous crustal regions on a subducting oceanic plate and were transferred to the overriding plate by accretionary processes during subduction. The geographical regions that eventually become accreted allochthonous terranes include island arcs, oceanic plateaus, submarine ridges, seamounts, continental fragments, and microcontinents. These future allochthonous terranes (FATs) contribute to continental crustal growth, subduction dynamics, and crustal recycling in the mantle. We present a review of modern FATs and their accreted counterparts based on available geological, seismic, and gravity studies and discuss their crustal structure, geological origin, and bulk crustal density. Island arcs have an average crustal thickness of 26 km, average bulk crustal density of 2.79 g cm-3, and three distinct crustal units overlying a crust-mantle transition zone. Oceanic plateaus and submarine ridges have an average crustal thickness of 21 km and average bulk crustal density of 2.84 g cm-3. Continental fragments presently on the ocean floor have an average crustal thickness of 25 km and bulk crustal density of 2.81 g cm-3. Accreted allochthonous terranes can be compared to these crustal compilations to better understand which units of crust are accreted or subducted. In general, most accreted terranes are thin crustal units sheared off of FATs and added onto the accretionary prism, with thicknesses on the order of hundreds of meters to a few kilometers. However, many island arcs, oceanic plateaus, and submarine ridges were sheared off in the subduction interface and underplated onto the overlying continent. Other times we find evidence of terrane-continent collision leaving behind accreted terranes 25-40 km thick. We posit that rheologically weak crustal layers or shear zones that were formed when the FATs were produced can be activated as detachments during subduction, allowing parts of the FAT crust to accrete and others to subduct. In many modern FATs on the ocean floor, a sub-crustal layer of high seismic velocities, interpreted as ultramafic material, could serve as a detachment or delaminate during subduction.

  15. The Brazilian continental margin

    NASA Astrophysics Data System (ADS)

    Martins, L. R.; Coutinho, P. N.

    1981-04-01

    The Brazilian continental margin, with its interesting morphology, structure and sediments, has become better known only during the last two decades. Six physiographical provinces can be recognized at the continental margin and the adjacent coast: (1) Cabo Orange-Parnaiba delta; (2) Parnaiba delta-Cabo Sa˜o Roque; (3) Cabo Sa˜o Roque-Belmonte; (4) Belmonte-Cabo Frio; (5) Cabo Frio-Cabo Santa Marta; and (6) Cabo Santa Marta-Chui. The shelf is rather wide near the Amazon Mouth, becoming narrower eastwards, continuing very narrow along the northeastern and eastern coast, and becoming wider again in the south towards the Plate River. Prominent morphological features along the margin are the Amazon cone, the marginal plateaus off northeastern Brazil, the Sa˜o Francisco cone and canyon, the Abrolhos Bank, and the deep-sea plateaus of Pernambuco and Sa˜o Paulo. On the shelf proper a number of relief elements exist, such as sand waves east of the Amazon, submarine terraces at various places, and irregularities of structural origin. The shelf break is rather smooth in the far north and south, more abrupt in the remainder. Surface sediments of the Brazilian shelf show five distinct facies types: littoral quartz sands, mud, transition sand-mud, coralline algae, and biodetrital. The terrigenous elastic fractions dominate off the Amazon and in southern Brazil; between these areas they occupy a very narrow strip near the coast. The carbonate facies, predominantly composed of calcareous algae, is abundant between the Parnaiba delta and Cabo Frio; to the south this facies is more biodetrital and restricted to the outer shelf. Economically important on the Brazilian continental margin besides oil, are sands and gravels, carbonate deposits, evaporites and some subsurface coal. Other possible mineral resources could be phosphate, heavy minerals and clays for ceramics.

  16. The buoyancy variation of plate coupling from subduction to collision: an example across the northernmost Manila trench

    NASA Astrophysics Data System (ADS)

    Lo, Chung-Liang; Doo, Wen-Bin; Kuo-Chen, Hao; Hsu, Shu-Kun

    2015-04-01

    The Manila trench is the boundary between the South China Sea (SCS) of Eurasian Plate (EU) and Philippine Sea Plate (PSP). The east subducting of SCS is a ceased rifting oceanic crust. To the north, the subduction is obscured and transits to collision extended to the Taiwan orogenesis. The Taiwan Integrated Geodynamics Research (TAIGER) project has implemented several offshore multichannel seismic (MCS) reflection and wide-angle seismic experiments to model the velocity structure of the incipient arc-continental collision. Amongst, along two trench perpendicular transects (MGL0905_23, 25) are associated with ocean bottom seismometer (OBS) deployed in the northern Manila trench. The transect MCS data and tomographic velocity structure provide well constraint on the recognition between the crust and mantle lithosphere that helps to reconstruct synthetic density structure to fit the observation gravity data. The synthetic gravity result along two transects also show that there exists an anomalous high density (~2.97 g/cm3) mass beneath the accretionary prism in the leading edge of overriding plate; however, unfortunately, the MCS and OBS data have no resolution there. Meanwhile, the buoyancies of crust (Hc) and mantle lithosphere (Hm) can be calculated associated with the residual topography based on the isostatic equilibrium. According to the contribution of Hm, the estimation of the plate coupling effect can be approached. Combining two transects data across the northern Manila trench and one profile across the Hengchun Peninsula in southern Taiwan (T29-33, TAICRUST project), a sequence from subduction to collision of plate coupling effect can therefore be evaluated, and also offers the opportunity to examine the lithospheric structure variation in the zone between Taiwan and northernmost Manila trench.

  17. Differences of Reasons for Alert Overrides on Contraindicated Co-prescriptions by Admitting Department

    PubMed Central

    Ahn, Eun Kyoung; Cho, Soo-Yeon; Shin, Dahye; Jang, Chul

    2014-01-01

    Objectives To reveal differences in drug-drug interaction (DDI) alerts and the reasons for alert overrides between admitting departments. Methods A retrospective observational study was performed using longitudinal Electronic Health Record (EHR) data and information from an alert and logging system. Adult patients hospitalized in the emergency department (ED) and general ward (GW) during a 46-month period were included. For qualitative analyses, we manually reviewed all reasons for alert overrides, which were recorded as free text in the EHRs. Results Among 14,780,519 prescriptions, 51,864 had alerts for DDIs (0.35%; 1.32% in the ED and 0.23% in the GW). The alert override rate was higher in the ED (94.0%) than in the GW (57.0%) (p < 0.001). In an analysis of the study population, including ED and GW patients, 'clinically irrelevant alert' (52.0%) was the most common reason for override, followed by 'benefit assessed to be greater than the risk' (31.1%) and 'others' (17.3%). The frequency of alert overrides was highest for anti-inflammatory and anti-rheumatic drugs (89%). In a sub-analysis of the population, 'clinically irrelevant alert' was the most common reason for alert overrides in the ED (69.3%), and 'benefit assessed to be greater than the risk' was the most common reason in the GW (61.4%). Conclusions We confirmed that the DDI alerts and the reasons for alert overrides differed by admitting department. Different strategies may be efficient for each admitting department. PMID:25405064

  18. Tectonic speed limits from plate kinematic reconstructions

    NASA Astrophysics Data System (ADS)

    Zahirovic, Sabin; Müller, R. Dietmar; Seton, Maria; Flament, Nicolas

    2015-05-01

    The motion of plates and continents on the planet's surface are a manifestation of long-term mantle convection and plate tectonics. Present-day plate velocities provide a snapshot of this ongoing process, and have been used to infer controlling factors on the speeds of plates and continents. However, present-day velocities do not capture plate behaviour over geologically representative periods of time. To address this shortcoming, we use a plate tectonic reconstruction approach to extract time-dependent plate velocities and geometries from which root mean square (RMS) velocities are computed, resulting in a median RMS plate speed of ? 4 cm /yr over 200 Myr. Linking tectonothermal ages of continental lithosphere to the RMS plate velocity analysis, we find that the increasing portions of plate area composed of continental and/or cratonic lithosphere significantly reduces plate speeds. Plates with any cratonic portion have a median RMS velocity of ? 5.8 cm /yr, while plates with more than 25% of cratonic area have a median RMS speed of ? 2.8 cm /yr. The fastest plates (? 8.5 cm /yr RMS speed) have little continental fraction and tend to be bounded by subduction zones, while the slowest plates (? 2.6- 2.8 cm /yr RMS speed) have large continental fractions and usually have little to no subducting part of plate perimeter. More generally, oceanic plates tend to move 2-3 times faster than continental plates, consistent with predictions of numerical models of mantle convection. The slower motion of continental plates is compatible with deep keels impinging on asthenospheric flow and increasing shear traction, thus anchoring the plate in the more viscous mantle transition zone. We also find that short-lived (up to ? 10 Myr) rapid accelerations of Africa (?100 and 65 Ma), North America (?100 and 55 Ma) and India (? 130 , 80 and 65 Ma) appear to be correlated with plume head arrivals as recorded by large igneous province (LIPs) emplacement. By evaluating factors influencing plate speeds over the Mesozoic and Cenozoic, our temporal analysis reveals simple principles that can guide the construction and evaluation of absolute plate motion models for times before the Cretaceous in the absence of hotspot tracks and seafloor spreading histories. Based on the post-Pangea plate motions, one principle that can be applied to pre-Pangea times is that plates with less than ? 50% continental area can reach RMS velocities of ? 20 cm /yr, while plates with more than 50% continental fraction do not exceed RMS velocities of ? 10 cm /yr. Similarly, plates with large portions of continental or cratonic area with RMS velocities exceeding ? 15 cm /yr for more than ? 10 Myr should be considered as potential artefacts requiring further justification of plate driving forces in such scenarios.

  19. 2-D tomographic imaging of continental crust and relic slab beneath Baja California

    NASA Astrophysics Data System (ADS)

    Brothers, D. S.; Harding, A. J.; Kent, G.; Driscoll, N.

    2009-12-01

    Rifting of Baja California from the margin of North America began as, or sometime before, subduction of the Farallon plate ceased (~12 Ma). Many have speculated that increased coupling between the subducted Farallon slab and overriding plate caused the young upper part of the subducted plate to detach from the older, colder, sinking slab. Then as the fragments of the Farallon plate took on Pacific plate motion, traction forces between the relic slab and Baja influenced rift localization in the Gulf of California. To better understand the processes that led to rifting of the Baja peninsula a 350 km seismic refraction/reflection profile was collected in 2002 in an effort to constrain the crustal thickness, the extent of relic slab beneath Baja California and the upper mantle P-wave velocities. The line spans the Baja Peninsula from the paleo-trench to the central Gulf of California, between the Farallon and Pescadero basins. 13 Ocean-Bottom Seismometers and 8 onshore Ref-Tek portable seismometers recorded 35,504 airgun shots from the R/V Ewing. Multichannel seismic (MCS) reflection profiles were collected on either side of the peninsula, providing information on the upper crustal structure and style of post-subduction deformation, particularly along the Tosco-Abreojos and Santa Margarita-San Lazaro fault systems. Here we present the integrated results of the MCS profiles and 2-D travel time tomography. Ray tracing was performed on 13,388 arrival picks, including Pg, Pn and PmP arrivals. Initial tomographic inversions reveal a crustal root beneath Baja California with an average velocity of 6.0 km/s. Continental crust thins to the east into the Gulf of California and has a velocity structure consistent with that of the Alarcon segment of the PESCADOR experiment. Perhaps the most significant observation is an ~6 km thick, 8° east-dipping high velocity zone (mean of 6.7 km/s) that underplates the western Baja margin and extends at least 60 km from the former trench (~40 km west of the shoreline). We interpret this to be relic oceanic crust. We are investigating the extent of the relic slab beneath Baja and its relationship with high-Mg adakitic volcanics exposed on Isla Margarita, ~20 km north of the seismic transect. The existence of a stalled slab beneath the Baja margin suggests frictional and/or viscous coupling along the paleo-subduction interface is an important process in for the geodynamical development of the Gulf of California rift system.

  20. Continental crust beneath southeast Iceland

    PubMed Central

    Torsvik, Trond H.; Amundsen, Hans E. F.; Trønnes, Reidar G.; Doubrovine, Pavel V.; Gaina, Carmen; Kusznir, Nick J.; Steinberger, Bernhard; Corfu, Fernando; Ashwal, Lewis D.; Griffin, William L.; Werner, Stephanie C.; Jamtveit, Bjørn

    2015-01-01

    The magmatic activity (0–16 Ma) in Iceland is linked to a deep mantle plume that has been active for the past 62 My. Icelandic and northeast Atlantic basalts contain variable proportions of two enriched components, interpreted as recycled oceanic crust supplied by the plume, and subcontinental lithospheric mantle derived from the nearby continental margins. A restricted area in southeast Iceland—and especially the Öræfajökull volcano—is characterized by a unique enriched-mantle component (EM2-like) with elevated 87Sr/86Sr and 207Pb/204Pb. Here, we demonstrate through modeling of Sr–Nd–Pb abundances and isotope ratios that the primitive Öræfajökull melts could have assimilated 2–6% of underlying continental crust before differentiating to more evolved melts. From inversion of gravity anomaly data (crustal thickness), analysis of regional magnetic data, and plate reconstructions, we propose that continental crust beneath southeast Iceland is part of ?350-km-long and 70-km-wide extension of the Jan Mayen Microcontinent (JMM). The extended JMM was marginal to East Greenland but detached in the Early Eocene (between 52 and 47 Mya); by the Oligocene (27 Mya), all parts of the JMM permanently became part of the Eurasian plate following a westward ridge jump in the direction of the Iceland plume. PMID:25825769

  1. Continental crust beneath southeast Iceland.

    PubMed

    Torsvik, Trond H; Amundsen, Hans E F; Trønnes, Reidar G; Doubrovine, Pavel V; Gaina, Carmen; Kusznir, Nick J; Steinberger, Bernhard; Corfu, Fernando; Ashwal, Lewis D; Griffin, William L; Werner, Stephanie C; Jamtveit, Bjørn

    2015-04-14

    The magmatic activity (0-16 Ma) in Iceland is linked to a deep mantle plume that has been active for the past 62 My. Icelandic and northeast Atlantic basalts contain variable proportions of two enriched components, interpreted as recycled oceanic crust supplied by the plume, and subcontinental lithospheric mantle derived from the nearby continental margins. A restricted area in southeast Iceland--and especially the Öræfajökull volcano--is characterized by a unique enriched-mantle component (EM2-like) with elevated (87)Sr/(86)Sr and (207)Pb/(204)Pb. Here, we demonstrate through modeling of Sr-Nd-Pb abundances and isotope ratios that the primitive Öræfajökull melts could have assimilated 2-6% of underlying continental crust before differentiating to more evolved melts. From inversion of gravity anomaly data (crustal thickness), analysis of regional magnetic data, and plate reconstructions, we propose that continental crust beneath southeast Iceland is part of ?350-km-long and 70-km-wide extension of the Jan Mayen Microcontinent (JMM). The extended JMM was marginal to East Greenland but detached in the Early Eocene (between 52 and 47 Mya); by the Oligocene (27 Mya), all parts of the JMM permanently became part of the Eurasian plate following a westward ridge jump in the direction of the Iceland plume. PMID:25825769

  2. High Override Rate for Opioid Drug-allergy Interaction Alerts: Current Trends and Recommendations for Future.

    PubMed

    Topaz, Maxim; Seger, Diane L; Lai, Kenneth; Wickner, Paige G; Goss, Foster; Dhopeshwarkar, Neil; Chang, Frank; Bates, David W; Zhou, Li

    2015-01-01

    This study examined trends in drug-allergy interaction (DAI) alert overrides for opioid medications - the most commonly triggered alerts in the computerized provider order entry (CPOE). We conducted an observational analysis of the DAI opioid alerts triggered over the last decade (2004-2013, n=342,338) in two large academic hospitals in Boston (United States). We found an increasing rate of DAI alert overrides culminating in 89.7% in 2013. Allergic reactions included a high proportion (38.2%) of non-immune mediated opioid reactions (e.g. gastrointestinal upset). The DAI alert override rate was high for immune mediated (88.6%) and life threatening reactions (87.8%). Exact allergy-medication matches were overridden less frequently (about 70%) compared to non-exact matches within allergy groups (over 90%). About one-third of the alert override reasons pointed to irrelevant alerts (i.e."Patient has tolerated the medication before") and 44.9% were unknown. Those findings warrant further investigation into providers' reasons for high override rate. User interfaces should evolve to enable less interruptive and more accurate alerts to decrease alert fatigue. PMID:26262047

  3. Continental rifting: a planetary perspective

    SciTech Connect

    Muehlberger, W.R.

    1985-01-01

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

  4. Worldwide distribution of ages of the continental lithosphere derived from a global seismic tomographic model

    E-print Network

    Shapiro, Nikolai

    ). Continental plates do not subduct but oat on the asthenosphere and drift on the surface of the EarthWorldwide distribution of ages of the continental lithosphere derived from a global seismic August 2008 Accepted 27 October 2008 Available online xxxx Keywords: Continental lithosphere Seismic

  5. Dynamic Analysis of Modifications to Simple Plate Tectonic Theory

    NASA Astrophysics Data System (ADS)

    Paczkowski, Karen

    A number of geological and geophysical observations suggest significant departures from simple, first-order plate tectonic theory. In this thesis we address the dynamic implications of some of these observations and propose generalized theories to explain their dynamics and conditions of formation. In Chapter 2, we develop a generalized theory and analytic model to predict the conditions under which large-volume removal of continental lithosphere can occur through the formation of drip instabilities. Using damage physics relevant for Earth, we find a large portion of the lithosphere may be mobilized and entrained into growing drip instabilities. For a critical amount of damage, the growth is accelerated sufficiently that large-volume drip instabilities may form within geologically feasible time frames. Our model suggests large-volume lithospheric drip instabilities may arise independently of tectonic settings through damage-assisted mobilization and entrainment of the highly viscous lithosphere. In Chapter 3, we develop a mechanical model independent of volcanism and thermal weakening to explain the initial formation and length scale of rifting and extension near convergent plate boundaries. We conduct a linear stability analysis of a simple viscous necking model, which includes the lithosphere's negative buoyancy, non-Newtonian rheology, and freely moving top surface, to determine which properties of the lithosphere govern the location of rifting. We find that the negative buoyancy of the lithosphere promotes the formation of rifting structures when simple Newtonian viscosities are present. However, localized weakening, introduced through a power law exponent, is required to generate realistic rifting length scales. Our model suggests that the initial location of rifting in the overriding plate at subduction zones is primarily due to the mechanical extension induced by rollback of the subducting slab. In Chapter 4, we propose a theory to explain the seismic anisotropy directions observed in the subslab mantle of subduction zones globally. We develop a three-dimensional model using COMSOL Multiphysics® to investigate how interactions among the background mantle flow, trench migration, and the geometry of the slab determine the flow direction in the subslab mantle. We find that flow directions are determined primarily by the amount of coupling between the slab and the mantle, and the interaction between the net background flow (including trench migration) and the slab geometry. We present three-dimensional finite strain calculations, which demonstrate that the maximum stretching directions are aligned with the model subslab flow directions, allowing us to compare our flow directions directly to seismic anisotropy splitting directions of subduction zones globally. Our model successfully predicts the flow directions (parallel or perpendicular) suggested by a global dataset of fast splitting directions using only the net background mantle flow, and slab dip and depth.

  6. Plate motion

    SciTech Connect

    Gordon, R.G. )

    1991-01-01

    The motion of tectonic plates on the earth is characterized in a critical review of U.S. research from the period 1987-1990. Topics addressed include the NUVEL-1 global model of current plate motions, diffuse plate boundaries and the oceanic lithosphere, the relation between plate motions and distributed deformations, accelerations and the steadiness of plate motions, the distribution of current Pacific-North America motion across western North America and its margin, plate reconstructions and their uncertainties, hotspots, and plate dynamics. A comprehensive bibliography is provided. 126 refs.

  7. Why does continental convergence stop

    SciTech Connect

    Hynes, A.

    1985-01-01

    Convergence between India and Asia slowed at 45 Ma when they collided, but continues today. This requires that substantial proportions of the Indian and/or Asian lithospheric mantle are still being subducted. The resulting slab-pull is probably comparable with that from complete lithospheric slabs and may promote continued continental convergence even after collision. Since descending lithospheric slabs are present at all collision zones at the time of collision such continued convergence may be general after continental collisions. It may cease only when there is a major (global) plate reorganization which results in new forces on the convergent continents that may counteract the slab-pull. These inferences may be tested on the late Paleozoic collision between Gondwanaland and Laurasia. This is generally considered to have been complete by mid-Permian time (250 Ma). However, this may be only the time of docking of Gondwanaland with North America, not that of the cessation of convergence. Paleomagnetic polar-wander paths for the Gondwanide continents exhibit consistently greater latitudinal shifts from 250 Ma to 200 Ma than those of Laurasia when corrected for post-Triassic drift, suggesting that convergence continued through late Permian well into the Triassic. It may have been accommodated by crustal thickening under what is now the US Coastal Plain, or by strike-slip faulting. Convergence may have ceased only when Pangea began to fragment again, in which case the cause for its cessation may be related to the cause of continental fragmentation.

  8. Subduction-driven recycling of continental margin lithosphere.

    PubMed

    Levander, A; Bezada, M J; Niu, F; Humphreys, E D; Palomeras, I; Thurner, S M; Masy, J; Schmitz, M; Gallart, J; Carbonell, R; Miller, M S

    2014-11-13

    Whereas subduction recycling of oceanic lithosphere is one of the central themes of plate tectonics, the recycling of continental lithosphere appears to be far more complicated and less well understood. Delamination and convective downwelling are two widely recognized processes invoked to explain the removal of lithospheric mantle under or adjacent to orogenic belts. Here we relate oceanic plate subduction to removal of adjacent continental lithosphere in certain plate tectonic settings. We have developed teleseismic body wave images from dense broadband seismic experiments that show higher than expected volumes of anomalously fast mantle associated with the subducted Atlantic slab under northeastern South America and the Alboran slab beneath the Gibraltar arc region; the anomalies are under, and are aligned with, the continental margins at depths greater than 200 kilometres. Rayleigh wave analysis finds that the lithospheric mantle under the continental margins is significantly thinner than expected, and that thin lithosphere extends from the orogens adjacent to the subduction zones inland to the edges of nearby cratonic cores. Taking these data together, here we describe a process that can lead to the loss of continental lithosphere adjacent to a subduction zone. Subducting oceanic plates can viscously entrain and remove the bottom of the continental thermal boundary layer lithosphere from adjacent continental margins. This drives surface tectonics and pre-conditions the margins for further deformation by creating topography along the lithosphere-asthenosphere boundary. This can lead to development of secondary downwellings under the continental interior, probably under both South America and the Gibraltar arc, and to delamination of the entire lithospheric mantle, as around the Gibraltar arc. This process reconciles numerous, sometimes mutually exclusive, geodynamic models proposed to explain the complex oceanic-continental tectonics of these subduction zones. PMID:25391963

  9. Constraints on continental accretion from sedimentation

    NASA Technical Reports Server (NTRS)

    Abbott, Dallas

    1988-01-01

    Heat loss in the ancient Earth was discussed assuming that classical sea floor spreading was the only mechanism. This may be expressed as faster spreading or longer total ridge length. These have important implications as to the size and number of cratonic plates in the distant past, the degree to which they are flooded, the kinds of sediments and volcanics that would be expected, and the amount of recycling of continental material taking place. The higher proportion of marine sedimentary rocks and oceanic volcanics in the Archean, and the relative paucity of evaporites and continental volcanics may in part be due to smaller cratonic blocks. A model was developed of the percentage of continental flooding which utilizes round continents and a constant width of the zone of flooding. This model produces a reasonable good fit to the percentage of flooding on the present day continents.

  10. 77 FR 65169 - Extension of Certain Timber Sale Contracts; Finding of Substantial Overriding Public Interest

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-10-25

    ...The Chief of the Forest Service has determined there is a Substantial Overriding Public Interest (SOPI) in extending for up to 1 year certain National Forest System FS-2400-6/6T and FS-2400-13/13T contracts that terminate on or before December 31, 2013 and meet one or more of the following conditions; (1) Require removal of biomass material, (2) require removal of balsam fir, (3) have been......

  11. Thermal and mechanical structure of the upper mantle: A comparison between continental and oceanic models

    NASA Technical Reports Server (NTRS)

    Froidevaux, C.; Schubert, G.; Yuen, D. A.

    1976-01-01

    Temperature, velocity, and viscosity profiles for coupled thermal and mechanical models of the upper mantle beneath continental shields and old ocean basins show that under the continents, both tectonic plates and the asthenosphere, are thicker than they are beneath the oceans. The minimum value of viscosity in the continental asthenosphere is about an order of magnitude larger than in the shear zone beneath oceans. The shear stress or drag underneath continental plates is also approximately an order of magnitude larger than the drag on oceanic plates. Effects of shear heating may account for flattening of ocean floor topography and heat flux in old ocean basins.

  12. Beyond plate tectonics - Looking at plate deformation with space geodesy

    NASA Technical Reports Server (NTRS)

    Jordan, Thomas H.; Minster, J. Bernard

    1988-01-01

    The requirements that must be met by space-geodetic systems in order to constrain the horizontal secular motions associated with the geological deformation of the earth's surface are explored. It is suggested that in order to improve existing plate-motion models, the tangential components of relative velocities on interplate baselines must be resolved to an accuracy of less than 3 mm/yr. Results indicate that measuring the velocities between crustal blocks to + or - 5 mm/yr on 100-km to 1000-km scales can produce geologically significant constraints on the integrated deformation rates across continental plate-boundary zones such as the western United States.

  13. Earth's continental crustal gold endowment

    NASA Astrophysics Data System (ADS)

    Frimmel, H. E.

    2008-03-01

    The analysis of the temporal distribution of gold deposits, combined with gold production data as well as reserve and resource estimates for different genetic types of gold deposit, revealed that the bulk of the gold known to be concentrated in ore bodies was added to the continental crust during a giant Mesoarchaean gold event at a time (3 Ga) when the mantle temperature reached a maximum and the dominant style of tectonic movement changed from vertical, plume-related to subhorizontal plate tectonic. A magmatic derivation of the first generation of crustal gold from a relatively hot mantle that was characterized by a high degree of partial melting is inferred from the gold chemistry, specifically high Os contents. While a large proportion of that gold is still present in only marginally modified palaeoplacer deposits of the Mesoarchaean Witwatersrand Basin in South Africa, accounting for about 40% of all known gold, the remainder has been recycled repeatedly on a lithospheric scale, predominantly by plate-tectonically induced magmatic and hydrothermal fluid circulation, to produce the current variety of gold deposit types. Post-Archaean juvenile gold addition to the continental crust has been limited, but a mantle contribution to some of the largest orogenic or intrusion-related gold deposits is indicated, notably for the Late Palaeozoic Tien Shan gold province. Magmatic fluids in active plate margins seem to be the most effective transport medium for gold mobilization, giving rise to a large proportion of volcanic-arc related gold deposits. Due to their generally shallow crustal level of formation, they have a low preservation potential. In contrast, those gold deposits that form at greater depth are more widespread also in older rocks. This explains the high proportion of orogenic (including intrusion-related) gold (32%) amongst all known gold deposits. The overall proportion of gold concentrated in known ore bodies is only 7 × 10- 7 of the estimated total amount of gold available in the continental crust. This is less than the solubility of Au in common crustal fluids. A high potential for the existence of voluminous, hitherto undiscovered, gold resources may thus be inferred.

  14. Oceanology of the antarctic continental shelf: Volume 43

    SciTech Connect

    Jacobs, S.S.

    1985-01-01

    This book discusses the seas of the deep continental shelf, which play an important climatic role in sea ice production, deep ocean ventilation and wastage of the Antarctic ice sheet. This volume includes analyses of measurements taken from ships and satellites, and from sea ice and glacial ice. High resolution profiling equipment, long term bottom-moored instruments, continuous remote sensors, geochemical tracers and computer models have provided the basis for new insights into the continental shelf circulation. Color plates and an accompanying GEBCO Circum-Antarctic map effectively portray the continental shelf in relation to the glaciated continent, the sea ice and the surrounding Southern Ocean.

  15. A numerical investigation of continental collision styles

    NASA Astrophysics Data System (ADS)

    Ghazian, Reza Khabbaz; Buiter, Susanne J. H.

    2013-06-01

    Continental collision after closure of an ocean can lead to different deformation styles: subduction of continental crust and lithosphere, lithospheric thickening, folding of the unsubducted continents, Rayleigh-Taylor (RT) instabilities and/or slab break-off. We use 2-D thermomechanical models of oceanic subduction followed by continental collision to investigate the sensitivity of these collision styles to driving velocity, crustal and lithospheric temperature, continental rheology and the initial density difference between the oceanic lithosphere and the asthenosphere. We find that these parameters influence the collision system, but that driving velocity, rheology and lithospheric (rather than Moho and mantle) temperature can be classified as important controls, whereas reasonable variations in the initial density contrast between oceanic lithosphere and asthenosphere are not necessarily important. Stable continental subduction occurs over a relatively large range of values of driving velocity and lithospheric temperature. Fast and cold systems are more likely to show folding, whereas slow and warm systems can experience RT-type dripping. Our results show that a continent with a strong upper crust can experience subduction of the entire crust and is more likely to fold. Accretion of the upper crust at the trench is feasible when the upper crust has a moderate to weak strength, whereas the entire crust can be scraped-off in the case of a weak lower crust. We also illustrate that weakening of the lithospheric mantle promotes RT-type of dripping in a collision system. We use a dynamic collision model, in which collision is driven by slab pull only, to illustrate that adjacent plates can play an important role in continental collision systems. In dynamic collision models, exhumation of subducted continental material and sediments is triggered by slab retreat and opening of a subduction channel, which allows upward flow of buoyant materials. Exhumation continues after slab break-off by reverse motion of the subducting plate (`eduction') caused by the reduced slab pull. We illustrate how a simple force balance of slab pull, slab push, slab bending, viscous resistance and buoyancy can explain the different collision styles caused by variations in velocity, temperature, rheology, density differences and the interaction with adjacent plates.

  16. Kinematics to dynamics in the New Zealand Plate boundary zone: implications for the strength of the lithosphere

    NASA Astrophysics Data System (ADS)

    Lamb, Simon

    2015-05-01

    New Zealand straddles the boundary between the Australian and Pacific Plate. Cenozoic relative plate motion has resulted in a complex pattern of faulting and block rotation in a zone of continental lithosphere up to 250 km wide. I investigate the implications of the short-term kinematics for the strength of the deforming lithosphere. I use a compilation of seismic reflection/refraction studies and high quality receiver function analyses to determine both the regional structure of the crust, which ranges from 20 to 50 km thick, and fields of buoyancy stress (or GPE per unit volume). Deformation over thousands of years is quantified in terms of velocity and strain rate fields, based on an inversion of neotectonic fault slip and palaeomagnetic data, in the context of the short-term relative plate motions. Forces on the subduction megathrust, as well as deviatoric stresses in the behind subduction region, are calculated from simple 2-D force balances across the Hikurangi Margin, given negligible deviatoric stresses at the along-strike transition between backarc extension and compression. Average megathrust shear stresses are in the range 6-15 MPa, and average lithospheric stresses <20 MPa in the overriding plate. The regional lithospheric strength of the plate boundary zone, assuming a viscous rheology (Newtonian or power law), is determined from an inversion of the field of gradients of buoyancy stress (averaged over either the top 25 km of the crust, or 100-km-thick lithosphere) and strain rate, using the thin sheet stress balance equations, calibrated with the subduction force balance analysis. Effective viscosities for the deforming lithosphere and/or crust are in the range 0.1-5 × 1021 Pa s, with marked weakening in zones of high strain rate, and an abrupt transition to viscosities >1022 Pa s at the margins of the rigid plates. If lateral variations in effective viscosity are only due to non-Newtonian behaviour, these data indicate a bulk power law rheology, with exponent n in the range 2-6. Average lithospheric or crustal deviatoric stresses <30 MPa. Such low driving stresses for the deforming crust are likely to be the result of a combination of pore fluid pressures much greater than hydrostatic (?40 per cent lithostatic) and low coefficients of friction (?0.6) on crustal faults.

  17. Deep continental margin reflectors

    USGS Publications Warehouse

    Ewing, J.; Heirtzler, J.; Purdy, M.; Klitgord, Kim D.

    1985-01-01

    In contrast to the rarity of such observations a decade ago, seismic reflecting and refracting horizons are now being observed to Moho depths under continental shelves in a number of places. These observations provide knowledge of the entire crustal thickness from the shoreline to the oceanic crust on passive margins and supplement Consortium for Continental Reflection Profiling (COCORP)-type measurements on land.

  18. Relict basin closure during initial suturing accommodates continental convergence with minimal crustal shortening or reduction in convergence rates

    NASA Astrophysics Data System (ADS)

    Cowgill, E.; Forte, A. M.; Niemi, N. A.; Mumladze, T.; Elashvili, M.; Javakhishvili, Z.; Trexler, C.

    2013-12-01

    In both the Indo-Eurasian and Arabia-Eurasian (Ab-Eu) collisions, documented post-collisional crustal shortening is hundreds to thousands of kilometers less than the amount of plate convergence determined from independent plate reconstructions. We propose that relict-basin closure may help resolve such shortening deficits, based on a synthesis of the late Cenozoic evolution of the Greater Caucasus Mountains in the Ab-Eu collision zone. This range is located ~700 km north of the Bitlis suture and defines the northern margin of the Ab-Eu collision zone between the Black and Caspian seas. The range formed from late Cenozoic tectonic inversion of the Greater Caucasus basin, a relict Mesozoic back-arc basin that originally formed in the Jurassic during north-dipping subduction of Neo-Tethys and rifting of the Lesser Caucasus arc from the southern margin of Eurasia (i.e., Scythia). This basin was originally wide enough to prevent sedimentary exchange of turbidites across it, as shown by provenance studies using U-Pb detrital zircon geochronology. The floor of the relict basin now forms a NE-dipping slab that extends to at least 158 km depth beneath the central and eastern Greater Caucasus, as revealed by a new earthquake compilation. Miocene to Quaternary felsic volcanic and intrusive rocks in the Greater Caucasus have geochemical signatures and eruptive centers similar to those in continental margin arcs. Based on these data we propose the Ab-Eu collision occurred in two stages. The first (soft collision) started when Arabia collided with Eurasia, closed the Bitlis suture, and caused the locus of convergence to jump ~700 km north to the Greater Caucasus basin. Initial exhumation of the Greater Caucasus started at ~25-30 Ma and continued until ~ 5 Ma at rates of a few °C/Ma during north-directed subduction of the back-arc basin, with little structural evidence of this crustal shortening preserved. The second phase (hard collision) started at ~ 5 Ma, when the relict basin finally closed and the Lesser Caucasus collided with Scythia and increased exhumation rates by as much as a factor of ten. Relict basin closure appears to have had a significant impact on the mechanical behavior of the Ab-Eu collision and appears to explain why deceleration of plate convergence was delayed 20-25 Myr after initial collision. Specifically, we suggest that initial collision and formation of the Bitlis suture did not significantly impede Ab-Eu convergence because deformation could jump to a relict basin within the overriding plate, continuing apace until that relict basin closed and triggered a switch from soft to hard collision and an associated structural reorganization of the whole Ab-Eu collision zone. Formation of such relict basins is likely common along continental margins during the protracted subduction and terrane accretion that occurs prior to continental collision at the end of a Wilson cycle. The Ab-Eu collision demonstrates the fundamental role that such basins can play in determining the deformational response of a continent during early collision.

  19. Plate kinematics, slab shape and back-arc stress: A comparison between laboratory models and current subduction zones

    E-print Network

    Demouchy, Sylvie

    5, France b Dip. Scienze Geologiche, Università degli Studi « Roma TRE », Largo S.Leonardo Murialdo­6]. However, a recent global study which considered all present-day oceanic subduction zones has shown of the overriding plate (V Y OP) [8,9]. Trench Earth and Planetary Science Letters 256 (2007) 473­483 www

  20. Initiation and propagation of shear zones in a heterogeneous continental lithosphere

    SciTech Connect

    Tommasi, A.; Vauchez, A.

    1995-11-10

    Numerical methods were used to investigate the deformation of a continental plate in northeastern Brazil. Of particular interest are the perturbations induced by a stiff compressional deformation of a highly heterogeneous continental lithosphere on the development of a shear zone formed at the termination of a stiff block.

  1. Continental rifting - Progress and outlook

    SciTech Connect

    Baker, B.H.; Morgan, P.

    1981-07-21

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

  2. Continental Collisions (Stephan Mueller Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Royden, Leigh

    2013-04-01

    The Mediterranean and Tibetan-Himalayan regions represent two different stages, or types, of continental collision. The former represents an incomplete collisional stage where areas of oceanic and thinned continental crust remain between the two colliding continents. Here, deformation is dominated by the rapid movement of regional scale subduction systems in a direction that is commonly oblique to that of large scale continental convergence. These systems are driven by slab pull and the rate of subduction is exquisitely sensitive to the buoyancy of the subducting lithosphere. Subduction in these systems ends quickly when negatively buoyant foreland lithosphere has been consumed. The geological signature of such subduction systems typically consists of low mountains with little erosion, few high-grade metamorphic rocks, anomalously deep foredeep basins containing deep water sedimentary deposits and regional extension of the upper plate. In contrast, the more advanced Tibetan-Himalayan region has no deep water regions remaining between the colliding plates and a broad zone of convergent deformation has developed greatly thickened crust everywhere. The dominant modes of deformation are crustal shortening and lateral extrustion of material eastward away from the zone of immediate convergence. The mode of eastward extrusion has changed with time, probably responding to changes in the tectonic boundary conditions to the southeast. The geological signature of such subduction systems typically consists of high mountains with significant erosion, common occurrences of high-grade metamorphic rocks, and foredeep basins containing shallow water and non marine sedimentary deposits.

  3. 73 FR 16800 - Proposed Establishment of the Haw River Valley Viticultural Area (2007R-179P)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2008-03-31

    ...igneous activity stemming from island arcs. Island arcs form when a continental plate overrides an oceanic plate, resulting in subduction zones that create volcanoes. In the northeastern part of the proposed viticultural area a caldera formed in an...

  4. 74 FR 14040 - Establishment of the Haw River Valley Viticultural Area (2007R-179P)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2009-03-30

    ...igneous activity stemming from island arcs. Island arcs form when a continental plate overrides an oceanic plate, resulting in subduction zones that create volcanoes. In the northeastern part of the proposed viticultural area a caldera formed in an area of...

  5. Emergence of modern continental crust about 3 billion years ago

    NASA Astrophysics Data System (ADS)

    Dhuime, Bruno; Wuestefeld, Andreas; Hawkesworth, Chris J.

    2015-07-01

    The continental crust is the principal record of conditions on the Earth during the past 4.4 billion years. However, how the continental crust formed and evolved through time remains highly controversial. In particular, the composition and thickness of juvenile continental crust are unknown. Here we show that Rb/Sr ratios can be used as a proxy for both the silica content and the thickness of the continental crust. We calculate Rb/Sr ratios of the juvenile crust for over 13,000 samples, with Nd model ages ranging from the Hadean to Phanerozoic. The ratios were calculated based on the evolution of Sr isotopes in the period between the TDM Nd model age and the crystallization of the samples analysed. We find that the juvenile crust had a low silica content and was largely mafic in composition during the first 1.5 billion years of Earth’s evolution, consistent with magmatism on a pre-plate tectonics planet. About 3 billion years ago, the Rb/Sr ratios of the juvenile continental crust increased, indicating that the newly formed crust became more silica-rich and probably thicker. This transition is in turn linked to the onset of plate tectonics and an increase of continental detritus into the oceans.

  6. Physics of the Earth and Planetary Interiors 163 (2007) 3551 Parallel computing of multi-scale continental deformation

    E-print Network

    Liu, Mian

    2007-01-01

    is one of the best examples of diffuse continental tectonics that deviate from the plate tectonics; Cyberinfrastructure 1. Introduction In the plate tectonics paradigm, the outer shell of the Earth consists of a dozen rheology of continents and (2) driving forces that arise from plate boundaries as well as within

  7. Plate motion and deformation

    SciTech Connect

    Minster, B.; Prescott, W.; Royden, L.

    1991-02-01

    Our goal is to understand the motions of the plates, the deformation along their boundaries and within their interiors, and the processes that control these tectonic phenomena. In the broadest terms, we must strive to understand the relationships of regional and local deformation to flow in the upper mantle and the rheological, thermal and density structure of the lithosphere. The essential data sets which we require to reach our goal consist of maps of current strain rates at the earth's surface and the distribution of integrated deformation through time as recorded in the geologic record. Our success will depend on the effective synthesis of crustal kinematics with a variety of other geological and geophysical data, within a quantitative theoretical framework describing processes in the earth's interior. Only in this way can we relate the snapshot of current motions and earth structure provided by geodetic and geophysical data with long-term processes operating on the time scales relevant to most geological processes. The wide-spread use of space-based techniques, coupled with traditional geological and geophysical data, promises a revolution in our understanding of the kinematics and dynamics of plate motions over a broad range of spatial and temporal scales and in a variety of geologic settings. The space-based techniques that best address problems in plate motion and deformation are precise space-geodetic positioning -- on land and on the seafloor -- and satellite acquisition of detailed altimetric and remote sensing data in oceanic and continental areas. The overall science objectives for the NASA Solid Earth Science plan for the 1990's, are to Understand the motion and deformation of the lithosphere within and across plate boundaries'', and to understand the dynamics of the mantle, the structure and evolution of the lithosphere, and the landforms that result from local and regional deformation. 57 refs., 7 figs., 2 tabs.

  8. Intermittent plate tectonics?

    PubMed

    Silver, Paul G; Behn, Mark D

    2008-01-01

    Although it is commonly assumed that subduction has operated continuously on Earth without interruption, subduction zones are routinely terminated by ocean closure and supercontinent assembly. Under certain circumstances, this could lead to a dramatic loss of subduction, globally. Closure of a Pacific-type basin, for example, would eliminate most subduction, unless this loss were compensated for by comparable subduction initiation elsewhere. Given the evidence for Pacific-type closure in Earth's past, the absence of a direct mechanism for termination/initiation compensation, and recent data supporting a minimum in subduction flux in the Mesoproterozoic, we hypothesize that dramatic reductions or temporary cessations of subduction have occurred in Earth's history. Such deviations in the continuity of plate tectonics have important consequences for Earth's thermal and continental evolution. PMID:18174440

  9. Subduction-Driven Recycling of Continental Margin Lithosphere

    NASA Astrophysics Data System (ADS)

    Levander, Alan; Bezada, Maximiliano; Niu, Fenglin; Palomeras, Imma; Thurner, Sally; Humphreys, Eugene; Carbonell, Ramon; Gallart, Josep; Schmitz, Michael; Miller, Meghan

    2015-04-01

    Subduction recycling of oceanic lithosphere, a central theme of plate tectonics, is relatively well understood, whereas recycling continental lithosphere is more difficult to recognize, and appears far more complicated. Delamination and localized convective downwelling are two widely recognized processes invoked to explain the removal of lithospheric mantle under or adjacent to orogenic belts. Here we describe another process that can lead to the loss of continental lithosphere adjacent to a subduction zone: Subducting oceanic plates can entrain and recycle lithospheric mantle from an adjacent continent and disrupt the continental lithosphere far inland from the subduction zone. Seismic images from recent dense broadband seismograph arrays in northeastern South America (SA) and in the western Mediterranean show higher than expected volumes of positive anomalies identified as the subducted Atlantic slab under northeastern SA, and the Alboran slab beneath the Gibraltar arc region (GA). The positive anomalies lie under and are aligned with the continental margins at depths greater than 200 km. Closer to the surface we find that the continental margin lithospheric mantle is significantly thinner than expected beneath the orogens adjacent to the subduction zones. The thinner than expected lithosphere extends inland as far as the edges of nearby cratonic cores. These observations suggest that subducting oceanic plates viscously entrain and remove continental mantle lithosphere from beneath adjacent continental margins, modulating the surface tectonics and pre-conditioning the margins for further deformation. The latter can include delamination of the entire lithospheric mantle, as around GA, inferred by results from active and passive seismic experiments. Viscous removal of continental margin lithosphere creates lithosphere-asthenosphere boundary (LAB) topography which can give rise to secondary downwellings under the continental interior far inland from the subduction zone: We image one under SA and we infer that one or more have occurred in the past under the western Mediterranean. The process of subduction-driven continental margin lithosphere removal reconciles numerous, sometimes mutually exclusive, geodynamic models proposed to explain the complex oceanic-continental tectonics of these two subduction zones.

  10. How the interior viscosity structure of a terrestrial planet controls plate driving forces and plate tectonics

    NASA Astrophysics Data System (ADS)

    Hoeink, T.; Lenardic, A.; Jellinek, M.; Richards, M. A.

    2011-12-01

    One of the fundamental unresolved problems in Earth and planetary science is the generation of plate tectonics from mantle convection. Important achievements can be made when considering rheological properties in the context of mantle convection dynamics. Among these milestones are (1) a deeper understanding of the balance of forces that drive and resist plate motion and (2) the dynamic generation of narrow plate boundaries (that lead to a piecewise continuous surface velocity distribution). Extending classic plate-tectonic theory we predict a plate driving force due to viscous coupling at the base of the plate from fast flow in the asthenosphere. Flow in the asthenosphere is due to shear-driven contributions from an overriding plate and due to additional pressure-driven contributions. We use scaling analysis to show that the extent to which this additional plate-driving force contributes to plate motions depends on the lateral dimension of plates and on the relative viscosities and thicknesses of lithosphere and asthenosphere. Whereas slab-pull forces always govern the motions of plates with a lateral extent greater than the mantle depth, asthenosphere-drive forces can be relatively more important for smaller (shorter wavelength) plates, large relative asthenosphere viscosities or large asthenosphere thicknesses. Published plate velocities, tomographic images and age-binned mean shear wave velocity anomaly data allow us to estimate the relative contributions of slab-pull and asthenosphere-drive forces driving the motions of the Atlantic and Pacific plates. At the global scale of terrestrial planets, we use 3D spherical shell simulations of mantle convection with temperature-, depth- and stress dependent rheology to demonstrate that a thin low-viscosity layer (asthenosphere) governs convective stresses imparted to the lithosphere. We find, consistent with theoretical predictions, that convective stresses increase for thinner asthenospheres. This result might eliminate the need for special weakening mechanisms to generate plate tectonics from mantle convection. Our results elucidate the role of the asthenosphere for plate tectonics on Earth, and also provide insights into the differences in tectonic styles between Earth and Venus.

  11. Caribbean tectonics and relative plate motions

    NASA Technical Reports Server (NTRS)

    Burke, K.; Dewey, J. F.; Cooper, C.; Mann, P.; Pindell, J. L.

    1984-01-01

    During the last century, three different ways of interpreting the tectonic evolution of the Gulf of Mexico and the Caribbean have been proposed, taking into account the Bailey Willis School of a permanent pre-Jurassic deep sea basin, the Edward Suess School of a subsided continental terrain, and the Alfred Wegener School of continental separation. The present investigation is concerned with an outline of an interpretation which follows that of Pindell and Dewey (1982). An attempt is made to point out ways in which the advanced hypotheses can be tested. The fit of Africa, North America, and South America is considered along with aspects of relative motion between North and South America since the early Jurasic. Attention is given to a framework for reconstructing Caribbean plate evolution, the evolution of the Caribbean, the plate boundary zones of the northern and southern Caribbean, and the active deformation of the Caribbean plate.

  12. The Magnetic Signature of Zones of Continental Collision

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

    Near-surface and satellite maps of the crustal component of the magnetic field can be interpreted in terms of thermal conditions at depth because the magnetic properties of rocks depend on their temperature. Observations related to continental deformation at diffuse plate boundaries are often considered in relation to three length scales: the thickness of the seismogenic upper crust, the entire continental crust, and the mechanical lithosphere. The lower boundary of the magnetic crust coincides with the Moho, or in the presence of an elevated geotherm, with the Curie isotherm. New global perspectives on the magnetic signature of zones of continental collision are afforded by the recently published Magnetic Anomaly Map of the World (Purucker, 2007, EOS, 88, 263), the MF-5 satellite magnetic field (Maus et al., 2007, Gcubed), and NASA's ST-5 constellation mission in 2006. The thickness of the magnetic crust can be estimated by integrating the MF-5 satellite magnetic field into the 3SMAC compositional and thermal model of the lithosphere, and a minimum estimate of the magnetization can be estimated using a Greens function approach. We compare our magnetic maps with the diffuse plate boundary maps of Gordon (1998) and Dumoulin et al. (1998). The diffuse plate boundary zones exhibit intermediate (22-31 km) magnetic thicknessses, significantly less than those of the adjacent stable plate. The diffuse NE Asia plate boundary zone, from the Lena River delta to the Sea of Okhotsk, is especially well- expressed in both satellite and near-surface magnetic maps.

  13. Basins in ARC-continental collisions

    USGS Publications Warehouse

    Draut, Amy E.; Clift, Peter D.

    2012-01-01

    Arc-continent collisions occur commonly in the plate-tectonic cycle and result in rapidly formed and rapidly collapsing orogens, often spanning just 5-15 My. Growth of continental masses through arc-continent collision is widely thought to be a major process governing the structural and geochemical evolution of the continental crust over geologic time. Collisions of intra-oceanic arcs with passive continental margins (a situation in which the arc, on the upper plate, faces the continent) involve a substantially different geometry than collisions of intra-oceanic arcs with active continental margins (a situation requiring more than one convergence zone and in which the arc, on the lower plate, backs into the continent), with variable preservation potential for basins in each case. Substantial differences also occur between trench and forearc evolution in tectonically erosive versus tectonically accreting margins, both before and after collision. We examine the evolution of trenches, trench-slope basins, forearc basins, intra-arc basins, and backarc basins during arc-continent collision. The preservation potential of trench-slope basins is low; in collision they are rapidly uplifted and eroded, and at erosive margins they are progressively destroyed by subduction erosion. Post-collisional preservation of trench sediment and trench-slope basins is biased toward margins that were tectonically accreting for a substantial length of time before collision. Forearc basins in erosive margins are usually floored by strong lithosphere and may survive collision with a passive margin, sometimes continuing sedimentation throughout collision and orogeny. The low flexural rigidity of intra-arc basins makes them deep and, if preserved, potentially long records of arc and collisional tectonism. Backarc basins, in contrast, are typically subducted and their sediment either lost or preserved only as fragments in melange sequences. A substantial proportion of the sediment derived from collisional orogenesis ends up in the foreland basin that forms as a result of collision, and may be preserved largely undeformed. Compared to continent-continent collisional foreland basins, arc-continent collisional foreland basins are short-lived and may undergo partial inversion after collision as a new, active continental margin forms outboard of the collision zone and the orogen whose load forms the basin collapses in extension.

  14. Absolute Plate Velocities from Seismic Anisotropy

    NASA Astrophysics Data System (ADS)

    Kreemer, Corné; Zheng, Lin; Gordon, Richard

    2015-04-01

    The orientation of seismic anisotropy inferred beneath plate interiors may provide a means to estimate the motions of the plate relative to the sub-asthenospheric mantle. Here we analyze two global sets of shear-wave splitting data, that of Kreemer [2009] and an updated and expanded data set, to estimate plate motions and to better understand the dispersion of the data, correlations in the errors, and their relation to plate speed. We also explore the effect of using geologically current plate velocities (i.e., the MORVEL set of angular velocities [DeMets et al. 2010]) compared with geodetically current plate velocities (i.e., the GSRM v1.2 angular velocities [Kreemer et al. 2014]). We demonstrate that the errors in plate motion azimuths inferred from shear-wave splitting beneath any one tectonic plate are correlated with the errors of other azimuths from the same plate. To account for these correlations, we adopt a two-tier analysis: First, find the pole of rotation and confidence limits for each plate individually. Second, solve for the best fit to these poles while constraining relative plate angular velocities to consistency with the MORVEL relative plate angular velocities. The SKS-MORVEL absolute plate angular velocities (based on the Kreemer [2009] data set) are determined from the poles from eight plates weighted proportionally to the root-mean-square velocity of each plate. SKS-MORVEL indicates that eight plates (Amur, Antarctica, Caribbean, Eurasia, Lwandle, Somalia, Sundaland, and Yangtze) have angular velocities that differ insignificantly from zero. The net rotation of the lithosphere is 0.25±0.11° Ma-1 (95% confidence limits) right-handed about 57.1°S, 68.6°E. The within-plate dispersion of seismic anisotropy for oceanic lithosphere (?=19.2° ) differs insignificantly from that for continental lithosphere (?=21.6° ). The between-plate dispersion, however, is significantly smaller for oceanic lithosphere (?=7.4° ) than for continental lithosphere (?=14.7° ). Two of the slowest-moving plates, Antarctica (vRMS=4 mm a-1, ?=29° ) and Eurasia (vRMS=3 mm a-1, ?=33° ), have two of the largest within-plate dispersions, which may indicate that a plate must move faster than ˜5 mm a-1 to result in seismic anisotropy useful for estimating plate motion. We will investigate if these relationships still hold with the new expanded data set and with the alternative set of relative plate angular velocities. We have found systematic differences between the SKS orientations and our predicted plate motion azimuths underneath the Arabia plate, which suggests to us either plate-scale mantle flow process not directly associated with that plate's absolute motion or intrinsic lithospheric anisotropy. We will discuss more of such discrepancies underneath other plates using the enlarged data set.

  15. Characteristics and override rates of order checks in a practitioner order entry system.

    PubMed Central

    Payne, Thomas H.; Nichol, W. Paul; Hoey, Patty; Savarino, James

    2002-01-01

    Order checks are important error prevention tools when used in conjunction with practitioner order entry systems. We studied characteristics of order checks generated in a sample of consecutively entered orders during a 4 week period in an electronic medical record at VA Puget Sound. We found that in the 42,641 orders where an order check could potentially be generated, 11% generated at least one order check and many generated more than one order check. The rates at which the ordering practitioner overrode 'Critical drug interaction' and 'Allergy-drug interaction' alerts in this sample were 88% and 69% respectively. This was in part due to the presence of alerts for interactions between systemic and topical medications and for alerts generated during medication renewals. Refinement in order check logic could lead to lower override rates and increase practitioner acceptance and effectiveness of order checks. PMID:12463894

  16. Is There Really A North American Plate?

    NASA Astrophysics Data System (ADS)

    Krill, A.

    2011-12-01

    Lithospheric plates are typically identified from earthquake epicenters and evidence such as GPS movements. But no evidence indicates a plate boundary between the North American and South American Plates. Some plate maps show them separated by a transform boundary, but it is only a fracture zone. Other maps show an "undefined plate boundary" or put no boundary between these two plates (check Google images). Early plate maps showed a single large American Plate, quite narrow east of the Caribbean Plate (Le Pichon 1968, Morgan 1968). The North and South American Plates became established by the leading textbook Earth (Press & Siever 1974). On their map, from a Scientific American article by John Dewey (1972), these new plates were separated by an "uncertain plate boundary." The reasons for postulating a North American Plate were probably more psychological than geological. Each of the other continents of the world had its own plate, and North American geologists naturally wanted theirs. Similarly, European geographers used to view Europe as its own continent. A single large plate should again be hypothesized. But the term American Plate would now be ambiguous ("Which plate, North or South?") Perhaps future textbook authors could call it the "Two-American Plate." Textbook authors ultimately decide such global-tectonic matters. I became aware of textbook authors' opinions and influence from my research into the history of Alfred Wegener's continental drift (see Fixists vs. Mobilists by Krill 2011). Leading textbook author Charles Schuchert realized that continental drift would abolish his cherished paleogeographic models of large east-west continents (Eria, Gondwana) and small oceans (Poseiden, Nereis). He and his junior coauthors conspired to keep drift evidence out of their textbooks, from the 1934-editions until the 1969-editions (Physical Geology by Longwell et al. 1969, Historical Geology by Dunbar & Waage 1969). Their textbooks ruled in America. Textbooks elsewhere, such as S.J. Shand (1933), E.B. Bailey (1939), and Arthur Holmes (1944), presented continental drift as a working hypothesis that could elegantly solve important geological problems. Americans were preconditioned to dislike continental drift theory, ever since James Dwight Dana taught in his Manual of Geology (1863...1895) that North America was the type continent of the world, and that it had stood alone since earliest time. Such beliefs sometimes trump geologic evidence. As noted by Stephen Jay Gould (1999) Sigmund Freud had much insight into the psychology of scientific revolutions: they involve a scientific development that shows humans to have lesser status than previously perceived. In the Copernican revolution (geocentrism vs. heliocentrism) humans no longer inhabited the center of the universe. In the Darwinian revolution (creationism vs. evolutionism) humans were no longer uniquely created. In the Wegenerian revolution (fixism vs. mobilism) North America was no longer uniquely created; it was just other fragment from Pangaea. North American geologists were pleased when Press & Siever gave them their own lithospheric plate. Being a global-tectonic killjoy, I would like to take away that small consolation as well. Or at least pose the question: Is there really a North American Plate?

  17. Do variations in Arabian plate lithospheric structure control deformation in the Arabian-Eurasian convergence zone?

    E-print Network

    Stern, Robert J.

    to Red Sea rifting and the Afar hotspot. 1. Introduction The Arabian Plate is mostly continental crustDo variations in Arabian plate lithospheric structure control deformation in the Arabian- 4214, USA E-mail: rjstern@utdallas.edu Abstract. The Arabian plate has been converging with Eurasia

  18. Time variability in Cenozoic reconstructions of mantle heat flow: Plate tectonic cycles and implications for

    E-print Network

    Conrad, Clint

    Time variability in Cenozoic reconstructions of mantle heat flow: Plate tectonic cycles character of plate tectonics. We estimate global heat flow from 65 Ma to the present using seafloor age that heat flow experiences short-term fluctuations associated with plate tectonic cyclicity. Continental

  19. An updated digital model of plate boundaries

    NASA Astrophysics Data System (ADS)

    Bird, Peter

    2003-03-01

    A global set of present plate boundaries on the Earth is presented in digital form. Most come from sources in the literature. A few boundaries are newly interpreted from topography, volcanism, and/or seismicity, taking into account relative plate velocities from magnetic anomalies, moment tensor solutions, and/or geodesy. In addition to the 14 large plates whose motion was described by the NUVEL-1A poles (Africa, Antarctica, Arabia, Australia, Caribbean, Cocos, Eurasia, India, Juan de Fuca, Nazca, North America, Pacific, Philippine Sea, South America), model PB2002 includes 38 small plates (Okhotsk, Amur, Yangtze, Okinawa, Sunda, Burma, Molucca Sea, Banda Sea, Timor, Birds Head, Maoke, Caroline, Mariana, North Bismarck, Manus, South Bismarck, Solomon Sea, Woodlark, New Hebrides, Conway Reef, Balmoral Reef, Futuna, Niuafo'ou, Tonga, Kermadec, Rivera, Galapagos, Easter, Juan Fernandez, Panama, North Andes, Altiplano, Shetland, Scotia, Sandwich, Aegean Sea, Anatolia, Somalia), for a total of 52 plates. No attempt is made to divide the Alps-Persia-Tibet mountain belt, the Philippine Islands, the Peruvian Andes, the Sierras Pampeanas, or the California-Nevada zone of dextral transtension into plates; instead, they are designated as "orogens" in which this plate model is not expected to be accurate. The cumulative-number/area distribution for this model follows a power law for plates with areas between 0.002 and 1 steradian. Departure from this scaling at the small-plate end suggests that future work is very likely to define more very small plates within the orogens. The model is presented in four digital files: a set of plate boundary segments; a set of plate outlines; a set of outlines of the orogens; and a table of characteristics of each digitization step along plate boundaries, including estimated relative velocity vector and classification into one of 7 types (continental convergence zone, continental transform fault, continental rift, oceanic spreading ridge, oceanic transform fault, oceanic convergent boundary, subduction zone). Total length, mean velocity, and total rate of area production/destruction are computed for each class; the global rate of area production and destruction is 0.108 m2/s, which is higher than in previous models because of the incorporation of back-arc spreading.

  20. Surface motions and intraplate continental deformation in Alaska driven by mantle flow

    NASA Astrophysics Data System (ADS)

    Finzel, Emily S.; Flesch, Lucy M.; Ridgway, Kenneth D.; Holt, William E.; Ghosh, Attreyee

    2015-06-01

    The degree to which the lithosphere and mantle are coupled and contribute to surface deformation beneath continental regions remains a fundamental question in the field of geodynamics. Here we use a new approach with a surface deformation field constrained by GPS, geologic, and seismicity data, together with a lithospheric geodynamic model, to solve for tractions inferred to be generated by mantle convection that (1) drive extension within interior Alaska generating southward directed surface motions toward the southern convergent plate boundary, (2) result in accommodation of the relative motions between the Pacific and North America in a comparatively small zone near the plate boundary, and (3) generate the observed convergence within the North American plate interior in the Mackenzie mountains in northwestern Canada. The evidence for deeper mantle influence on surface deformation beneath a continental region suggests that this mechanism may be an important contributing driver to continental plate assemblage and breakup.

  1. Continental drift before 1900.

    PubMed

    Rupke, N A

    1970-07-25

    The idea that Francis Bacon and other seventeenth and eighteenth century thinkers first conceived the notion of continental drift does not stand up to close scrutiny. The few authors who expressed the idea viewed the process as a catastrophic event. PMID:16057953

  2. The Continental Crust.

    ERIC Educational Resources Information Center

    Burchfiel, B. Clark

    1983-01-01

    Continental crust underlies the continents, their margins, and also small shallow regions in oceans. The nature of the crust (much older than oceanic crust) and its dynamics are discussed. Research related to and effects of tectonics, volcanism, erosion, and sedimentation on the crust are considered. (JN)

  3. Continental magnetic anomaly constraints on continental reconstruction

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.; Olivier, R.; Bentley, C. R.

    1985-01-01

    Crustal magnetic anomalies mapped by the MAGSAT satellite for North and South America, Europe, Africa, India, Australia and Antarctica and adjacent marine areas were adjusted to a common elevation of 400 km and differentially reduced to the radial pole of intensity 60,000 nT. These radially polarized anomalies are normalized for differential inclination, declination and intensity effects of the geomagnetic field, so that in principle they directly reflected the geometric and magnetic polarization attributes of sources which include regional petrologic variations of the crust and upper mantle, and crustal thickness and thermal perturbations. Continental anomalies demonstrate remarkably detailed correlation of regional magnetic sources across rifted margins when plotted on a reconstruction of Pangea. Accordingly, they suggest further fundamental constraints on the geologic evolution of the continents and their reconstructions.

  4. The Architecture, Chemistry, and Evolution of Continental Magmatic Arcs

    NASA Astrophysics Data System (ADS)

    Ducea, Mihai N.; Saleeby, Jason B.; Bergantz, George

    2015-05-01

    Continental magmatic arcs form above subduction zones where the upper plate is continental lithosphere and/or accreted transitional lithosphere. The best-studied examples are found along the western margin of the Americas. They are Earth's largest sites of intermediate magmatism. They are long lived (tens to hundreds of millions of years) and spatially complex; their location migrates laterally due to a host of tectonic causes. Episodes of crustal and lithospheric thickening alternating with periods of root foundering produce cyclic vertical changes in arcs. The average plutonic and volcanic rocks in these arcs straddle the compositional boundary between an andesite and a dacite, very similar to that of continental crust; about half of that comes from newly added mafic material from the mantle. Arc products of the upper crust differentiated from deep crustal (>40 km) residual materials, which are unstable in the lithosphere. Continental arcs evolve into stable continental masses over time; trace elemental budgets, however, present challenges to the concept that Phanerozoic arcs are the main factories of continental crust.

  5. Plate tectonics beyond plate boundaries: the role of ancient structures in intraplate orogenesis

    NASA Astrophysics Data System (ADS)

    Heron, Philip; Pysklywec, Russell; Stephenson, Randell

    2015-04-01

    The development of orogens that occur at a distance from plate boundaries (i.e., `intraplate' deformation) cannot be adequately explained through conventional plate tectonic theory. Intraplate deformation infers a more complex argument for lithospheric and mantle interaction than plate tectonic theory allows. As a result, the origins of intraplate orogenesis are enigmatic. One hypothesis is the amalgamation of continental material (i.e., micro-plates) leaves inherent scars on the crust and mantle lithosphere. Previous studies into continent-continent collisions identify a number of scenarios from accretionary tectonics that affect the crust and mantle (namely, the development of a Rayleigh-Taylor instability, lithospheric underplating, lithospheric delamination, and lithospheric subduction). Any of these processes may weaken the lithosphere allowing episodic reactivation of faults within continental interiors. Hence, continental convergence (i.e., shortening) at a time after continental collision may cause the already weakened crust and mantle lithosphere to produce intraplate deformation. In order to better understand the processes involved in deformation away from plate boundaries, we present suites of continental shortening models (using the high-resolution thermal-mechanical modelling code SOPALE) to identify the preferred style of deformation. We model ancient structures by applying weak subduction scarring, changing the rheological conditions, and modifying the thermal structure within the lithosphere. To highlight the role of surface processes on plate and lithosphere deformation, the effect of climate-driven erosion and deposition on the tectonic structure of intraplate deformation is also addressed. We explore the relevance of the models to previously studied regions of intraplate orogenesis, including the Pyrenees in Europe, the Laramide orogen in North America, Tien Shan orogen in Central Asia, and Central Australia. The findings of the simulations with regards to past and future North American intraplate deformation are also discussed. Our results indicate that there exists a number of tectonic environments that can be produced relating to continental accretion, and that specific observational constraints to the local area (e.g., geological, geophysical, geodetic) are required to be integrated directly into the analyses for better interpretation. The models shown here find that although rheological changes to the lithosphere can produce a range of deformation during continental convergence (i.e., crustal thickening, thinning, and folding), mantle weak zones from ancient subduction can generate more localized deformation and topography.

  6. INTRODUCTION The continental promontory of the Eurasian plate in SE

    E-print Network

    Royal Holloway, University of London

    , comprising Sumatra, Java, Borneo, the Thai­Malay Peninsula and Indochina, was assembled during the Triassic for a long period. This stability is a myth. The region is today surrounded by subduction and collision zones explains the main- tenance of relief and hence sediment supply over long time periods. #12;which opened

  7. Fuelling decisions in migratory birds: geomagnetic cues override the seasonal effect

    PubMed Central

    Kullberg, Cecilia; Henshaw, Ian; Jakobsson, Sven; Johansson, Patrik; Fransson, Thord

    2007-01-01

    Recent evaluations of both temporal and spatial precision in bird migration have called for external cues in addition to the inherited programme defining the migratory journey in terms of direction, distance and fuelling behaviour along the route. We used juvenile European robins (Erithacus rubecula) to study whether geomagnetic cues affect fuel deposition in a medium-distance migrant by simulating a migratory journey from southeast Sweden to the wintering area in southern Spain. In the late phase of the onset of autumn migration, robins exposed to the magnetic treatment attained a lower fuel load than control birds exposed to the ambient magnetic field of southeast Sweden. In contrast, robins captured in the early phase of the onset of autumn migration all showed low fuel deposition irrespective of experimental treatment. These results are, as expected, the inverse of what we have found in similar studies in a long-distance migrant, the thrush nightingale (Luscinia luscinia), indicating that the reaction in terms of fuelling behaviour to a simulated southward migration varies depending on the relevance for the species. Furthermore, we suggest that information from the geomagnetic field act as an important external cue overriding the seasonal effect on fuelling behaviour in migratory birds. PMID:17609189

  8. Magmatic activity and plate motion during the latent stage of Midcontinent Rift development

    E-print Network

    Swanson-Hysell, N. L.

    The Keweenawan Midcontinent Rift of North America records significant continental rifting between ca. 1110 and 1085 Ma, and preserves the most detailed paleomagnetic record of plate motion of any continent in Precambrian ...

  9. Bulletin of the Seismological Society of America, Vol. 94, No. 6, pp. 23802399, December 2004 Plate-Tectonic Analysis of Shallow Seismicity: Apparent Boundary Width,

    E-print Network

    Bird, Peter

    E Plate-Tectonic Analysis of Shallow Seismicity: Apparent Boundary Width, Beta, Corner Magnitude Abstract A new plate model is used to analyze the mean seismicities of seven types of plate boundary (CRB and continental13.7 ? 3.8 18.02.3 10.8 plate boundaries suggests that here all seismic gaps are dangerous unless

  10. Continental Lower Crust

    NASA Astrophysics Data System (ADS)

    Hacker, Bradley R.; Kelemen, Peter B.; Behn, Mark D.

    2015-05-01

    The composition of much of Earth's lower continental crust is enigmatic. Wavespeeds require that 10-20% of the lower third is mafic, but the available heat-flow and wavespeed constraints can be satisfied if lower continental crust elsewhere contains anywhere from 49 to 62 wt% SiO2. Thus, contrary to common belief, the lower crust in many regions could be relatively felsic, with SiO2 contents similar to andesites and dacites. Most lower crust is less dense than the underlying mantle, but mafic lowermost crust could be unstable and likely delaminates beneath rifts and arcs. During sediment subduction, subduction erosion, arc subduction, and continent subduction, mafic rocks become eclogites and may continue to descend into the mantle, whereas more silica-rich rocks are transformed into felsic gneisses that are less dense than peridotite but more dense than continental upper crust. These more felsic rocks may rise buoyantly, undergo decompression melting and melt extraction, and be relaminated to the base of the crust. As a result of this refining and differentiation process, such relatively felsic rocks could form much of Earth's lower crust.

  11. Time-dependence in mantle convection models featuring dynamically evolving plates

    NASA Astrophysics Data System (ADS)

    Gait, A. D.; Lowman, J. P.

    2007-10-01

    We present the findings from a study of 2-D Cartesian geometry mantle convection simulations carried out to determine how plate velocities and the surface and basal heat flux respond to an evolving plate geometry. We model flow for periods equating to hundreds of millions of years and find that while calculations that feature fixed plate geometries exhibit regular reversals in plate motion, this behaviour is absent in models featuring evolving plate boundaries. However, simulations featuring evolving plate boundaries and plates with either a fixed-thickness or temporally varying thickness are highly time-dependent and their globally averaged mean plate velocities are higher than in simulations featuring static plate geometries. Our models featuring evolving plate geometries assume that (1) young plates override old plates with the velocity of the younger plate and (2) that symmetric seafloor spreading occurs at divergent plate boundaries. Plate velocities are dynamically determined in accord with a force-balance modelling approach and the plate velocities determine the dynamic evolution of the plate boundaries according to criteria (1) and (2), above. Plates in our calculations are highly viscous and are treated as rigid blocks for the purpose of determining whether they will break according to a yield stress criterion. The modelling of plate rifting means that both the number and mean size of the plates in our calculations are time-dependent. We focus on isolating the influence of plate thickness on time-dependent flows and examine the time-dependence of global plate velocities and mantle and core heat flow. In an initial study of unit aspect ratio models we find that there is a transition in the character of time-dependent behaviour as the model plate thickness is increased. Plates that are comparable in thickness to the mean thickness of the thermal boundary layer exhibit periodic reversals. Plates that are much thinner than the thermal boundary layer exhibit no reversals. Intermediate thickness plates reverse intermittently. In aspect ratio 12 calculations, we find that the mean global plate velocity can exhibit variations of more than a factor of two over periods of tens of millions of years. We also find that the mean surface velocity of the plates and the mean global heat flux rise and fall in tandem (although high frequency variations in the global velocity are not reflected in the heat flux time-series). In a simulation spanning almost 3 Gyr we observe several instances of surface heat flux fluctuations of 40-50 per cent occurring within periods of 75-200 Myr.

  12. Circum-arctic plate accretion - Isolating part of a pacific plate to form the nucleus of the Arctic Basin

    USGS Publications Warehouse

    Churkin, M., Jr.; Trexler, J.H., Jr.

    1980-01-01

    A mosaic of large lithospheric plates rims the Arctic Ocean Basin, and foldbelts between these plates contain numerous allochthonous microplates. A new model for continental drift and microplate accretion proposes that prior to the late Mesozoic the Kula plate extended from the Pacific into the Arctic. By a process of circumpolar drift and microplate accretion, fragments of the Pacific basin, including parts of the Kula plate, were cut off and isolated in the Arctic Ocean, the Yukon-Koyukuk basin in Alaska, and the Bering Sea. ?? 1980.

  13. Rotational inertia of continents: A proposed link between polar wandering and plate tectonics

    USGS Publications Warehouse

    Kane, M.F.

    1972-01-01

    A mechanism is proposed whereby displacement between continents and the earth's pole of rotation (polar wandering) gives rise to latitudinal transport of continental plates (continental drift) because of their relatively greater rotational inertia. When extended to short-term polar wobble, the hypothesis predicts an energy change nearly equivalent to the seismic energy rate.

  14. Transform continental margins - part 1: Concepts and models

    NASA Astrophysics Data System (ADS)

    Basile, Christophe

    2015-10-01

    This paper reviews the geodynamic concepts and models related to transform continental margins, and their implications on the structure of these margins. Simple kinematic models of transform faulting associated with continental rifting and oceanic accretion allow to define three successive stages of evolution, including intra-continental transform faulting, active transform margin, and passive transform margin. Each part of the transform margin experiences these three stages, but the evolution is diachronous along the margin. Both the duration of each stage and the cumulated strike-slip deformation increase from one extremity of the margin (inner corner) to the other (outer corner). Initiation of transform faulting is related to the obliquity between the trend of the lithospheric deformed zone and the relative displacement of the lithospheric plates involved in divergence. In this oblique setting, alternating transform and divergent plate boundaries correspond to spatial partitioning of the deformation. Both obliquity and the timing of partitioning influence the shape of transform margins. Oblique margin can be defined when oblique rifting is followed by oblique oceanic accretion. In this case, no transform margin should exist in the prolongation of the oceanic fracture zones. Vertical displacements along transform margins were mainly studied to explain the formation of marginal ridges. Numerous models were proposed, one of the most used is being based on thermal exchanges between the oceanic and the continental lithospheres across the transform fault. But this model is compatible neither with numerical computation including flexural behavior of the lithosphere nor with timing of vertical displacements and the lack of heating related to the passing of the oceanic accretion axis as recorded by the Côte d'Ivoire-Ghana marginal ridge. Enhanced models are still needed. They should better take into account the erosion on the continental slope, and the level of coupling of the transform continental margin with the adjacent oceanic lithosphere.

  15. Mechanisms of continental intraplate earthquakes

    NASA Astrophysics Data System (ADS)

    Gangopadhyay, Abhijit Kumar

    To better understand the mechanisms of continental intraplate earthquakes, a multistep approach was used. The first step involved analysis and synthesis of multidisciplinary data from 39 intraplate earthquakes spanning 20 continental intraplate regions, to identify their characteristic and diagnostic features. This led to the following testable hypothesis: Intraplate earthquakes occur within pre-existing zones of weakness (most commonly failed rifts), in the vicinity of stress concentrators, such as, intersecting faults, buried plutons, and/or rift pillows in the presence of the ambient stress field. The next step involved testing this hypothesis---first with 2-D mechanical models and then with 3-D models. Since two-thirds of the examined intraplate regions had intersecting faults as a stress concentrator, its role was first evaluated. A Distinct Element Method was used wherein the models comprised of the structural framework of the concerned region represented by a set of rock blocks that are assigned elastic properties conforming to the known geology, and subjected to tectonic loading along the direction of maximum regional compression (S Hmax) at a rate similar to the ambient plate velocity. The 2-D modeling was performed for two major intraplate regions in eastern U.S., viz., New Madrid and Middleton Place Summerville seismic zones, using a commercially available code called UDEC. These models adequately explain the spatial distribution of current seismicity in the regions. However, the absence of the third dimension limited the observation of tectonics in the depth dimension. Thus, 3-D models were developed for these two regions using the 3-D version of UDEC, called 3DEC. The preliminary results of these models adequately demonstrate correlation of locations of current seismicity with fault intersections in 3-D space, and also duplicate vertical movements. Although, the mechanical models demonstrated a causal association of seismicity with intersecting faults, their abundance in nature questions their uniqueness in causing seismicity, as many such faults are aseismic. Hence, a 2-D parametric study using UDEC, and a block model consisting of two and three intersecting faults, was performed to investigate whether preferred orientations of intersecting faults were responsible for causing seismicity. In the model, the orientation of the main fault with respect to SHmax was alpha, and the interior angle between the main and intersecting faults was beta. The results of this study showed that the optimum orientation of alpha for causing seismicity was 45° +/- 15°, whereas 65° ? beta ? 125° and 145° ? beta ? 170° were the optimum angles of beta. A similar 2-D parametric study using UDEC was performed of plutons of different shapes, sizes, and density contrasts, to evaluate their role in concentrating stresses to cause seismicity. The results showed that plutons of larger area, ellipticity, and density contrasts concentrated greater shear stresses around their peripheries. Additionally, plutons that are weaker than the surrounding country rocks concentrated larger shear stresses than those that are stronger than them. Cumulatively, the results of this study support the hypothesis of localized stress concentration in response to plate tectonic forces.

  16. Pseudomonas aeruginosa Overrides the Virulence Inducing Effect of Opioids When It Senses an Abundance of Phosphate

    PubMed Central

    Zaborin, Alexander; Gerdes, Svetlana; Holbrook, Christopher; Liu, Donald C.

    2012-01-01

    The gut during critical illness represents a complex ecology dominated by the presence of healthcare associated pathogens, nutrient scarce conditions, and compensatory host stress signals. We have previously identified key environmental cues, opioids and phosphate depletion that independently activate the virulence of Pseudomonas aeruginosa. Opioids induce quinolone signal production (PQS), whereas phosphate depletion leads to a triangulated response between MvfR-PQS, pyoverdin, and phosphosensory/phosphoregulatory systems (PstS-PhoB). Yet how P. aeruginosa manages its response to opioids during nutrient scarce conditions when growth is limited and a quorum is unlikely to be achieved is important in the context of pathogenesis in gut during stress. To mimic this environment, we created nutrient poor conditions and exposed P. aeruginosa PAO1 to the specific k-opioid receptor agonist U-50,488. Bacterial cells exposed to the k-opioid expressed a striking increase in virulence- and multi-drug resistance-related genes that correlated to a lethal phenotype in C. elegans killing assays. Under these conditions, HHQ, a precursor of PQS, rather than PQS itself, became the main inducer for pqsABCDE operon expression. P. aeruginosa virulence expression in response to k-opioids required PqsE since ?PqsE was attenuated in its ability to activate virulence- and efflux pumps-related genes. Extracellular inorganic phosphate completely changed the transcriptional response of PAO1 to the k- opioid preventing pqsABCDE expression, the activation of multiple virulence- and efflux pumps-related genes, and the ability of P. aeruginosa to kill C. elegans. These results indicate that when P. aeruginosa senses resource abundance in the form of phosphate, it overrides its response to compensatory host signals such as opioids to express a virulent and lethal phenotype. These studies confirm a central role for phosphate in P. aeruginosa virulence that might be exploited to design novel anti- virulence strategies. PMID:22514685

  17. Transcriptional override: a regulatory network model of indirect responses to modulations in microRNA expression

    PubMed Central

    2014-01-01

    Background Documented changes in levels of microRNAs (miRNA) in a variety of diseases including cancer are leading to their development as early indicators of disease, and as a potential new class of therapeutic agents. A significant hurdle to the rational application of miRNAs as therapeutics is our current inability to reliably predict the range of molecular and cellular consequences of perturbations in the levels of specific miRNAs on targeted cells. While the direct gene (mRNA) targets of individual miRNAs can be computationally predicted with reasonable degrees of accuracy, reliable predictions of the indirect molecular effects of perturbations in miRNA levels remain a major challenge in molecular systems biology. Results Changes in gene (mRNA) and miRNA expression levels between normal precursor and ovarian cancer cells isolated from patient tissue samples were measured by microarray. Expression of 31 miRNAs was significantly elevated in the cancer samples. Consistent with previous reports, the expected decrease in expression of the mRNA targets of upregulated miRNAs was observed in only 20-30% of the cancer samples. We present and provide experimental support for a network model (The Transcriptional Override Model; TOM) to account for the unexpected regulatory consequences of modulations in the expression of miRNAs on expression levels of their target mRNAs in ovarian cancer. Conclusions The direct and indirect regulatory effects of changes in miRNA expression levels in vivo are interactive and complex but amenable to systems level modeling. Although TOM has been developed and validated within the context of ovarian cancer, it may be applicable in other biological contexts as well, including of potential future use in the rational design of miRNA-based strategies for the treatment of cancers and other diseases. PMID:24666724

  18. Re-purposing clinical kinase inhibitors to enhance chemosensitivity by overriding checkpoints

    PubMed Central

    Beeharry, Neil; Banina, Eugenia; Hittle, James; Skobeleva, Natalia; Khazak, Vladimir; Deacon, Sean; Andrake, Mark; Egleston, Brian L; Peterson, Jeffrey R; Astsaturov, Igor; Yen, Timothy J

    2014-01-01

    Inhibitors of the DNA damage checkpoint kinase, Chk1, are highly effective as chemo- and radio-sensitizers in preclinical studies but are not well-tolerated by patients. We exploited the promiscuous nature of kinase inhibitors to screen 9 clinically relevant kinase inhibitors for their ability to sensitize pancreatic cancer cells to a sub-lethal concentration of gemcitabine. Bosutinib, dovitinib, and BEZ-235 were identified as sensitizers that abrogated the DNA damage checkpoint. We further characterized bosutinib, an FDA-approved Src/Abl inhibitor approved for chronic myelogenous leukemia. Unbeknownst to us, we used an isomer (Bos-I) that was unknowingly synthesized and sold to the research community as “authentic” bosutinib. In vitro and cell-based assays showed that both the authentic bosutinib and Bos-I inhibited DNA damage checkpoint kinases Chk1 and Wee1, with Bos-I showing greater potency. Imaging data showed that Bos-I forced cells to override gemcitabine-induced DNA damage checkpoint arrest and destabilized stalled replication forks. These inhibitors enhanced sensitivity to the DNA damaging agents’ gemcitabine, cisplatin, and doxorubicin in pancreatic cancer cell lines. The in vivo efficacy of Bos-I was validated using cells derived directly from a pancreatic cancer patient’s tumor. Notably, the xenograft studies showed that the combination of gemcitabine and Bos-I was significantly more effective in suppressing tumor growth than either agent alone. Finally, we show that the gatekeeper residue in Wee1 dictates its sensitivity to the 2 compounds. Our strategy to screen clinically relevant kinase inhibitors for off-target effects on cell cycle checkpoints is a promising approach to re-purpose drugs as chemosensitizers. PMID:24955955

  19. Eutrophication effects on greenhouse gas fluxes from shallow-lake mesocosms override those of climate warming.

    PubMed

    Davidson, Thomas A; Audet, Joachim; Svenning, Jens-Christian; Lauridsen, Torben L; Søndergaard, Martin; Landkildehus, Frank; Larsen, Søren E; Jeppesen, Erik

    2015-12-01

    Fresh waters make a disproportionately large contribution to greenhouse gas (GHG) emissions, with shallow lakes being particular hot spots. Given their global prevalence, how GHG fluxes from shallow lakes are altered by climate change may have profound implications for the global carbon cycle. Empirical evidence for the temperature dependence of the processes controlling GHG production in natural systems is largely based on the correlation between seasonal temperature variation and seasonal change in GHG fluxes. However, ecosystem-level GHG fluxes could be influenced by factors, which while varying seasonally with temperature are actually either indirectly related (e.g. primary producer biomass) or largely unrelated to temperature, for instance nutrient loading. Here, we present results from the longest running shallow-lake mesocosm experiment which demonstrate that nutrient concentrations override temperature as a control of both the total and individual GHG flux. Furthermore, testing for temperature treatment effects at low and high nutrient levels separately showed only one, rather weak, positive effect of temperature (CH4 flux at high nutrients). In contrast, at low nutrients, the CO2 efflux was lower in the elevated temperature treatments, with no significant effect on CH4 or N2 O fluxes. Further analysis identified possible indirect effects of temperature treatment. For example, at low nutrient levels, increased macrophyte abundance was associated with significantly reduced fluxes of both CH4 and CO2 for both total annual flux and monthly observation data. As macrophyte abundance was positively related to temperature treatment, this suggests the possibility of indirect temperature effects, via macrophyte abundance, on CH4 and CO2 flux. These findings indicate that fluxes of GHGs from shallow lakes may be controlled more by factors indirectly related to temperature, in this case nutrient concentration and the abundance of primary producers. Thus, at ecosystem scale, response to climate change may not follow predictions based on the temperature dependence of metabolic processes. PMID:26258771

  20. Health research and systems' governance are at risk: should the right to data protection override health?

    PubMed

    Di Iorio, C T; Carinci, F; Oderkirk, J

    2014-07-01

    The European Union (EU) Data Protection Regulation will have profound implications for public health, health services research and statistics in Europe. The EU Commission's Proposal was a breakthrough in balancing privacy rights and rights to health and healthcare. The European Parliament, however, has proposed extensive amendments. This paper reviews the amendments proposed by the European Parliament Committee on Civil Liberties, Justice and Home Affairs and their implications for health research and statistics. The amendments eliminate most innovations brought by the Proposal. Notably, derogation to the general prohibition of processing sensitive data shall be allowed for public interests such as the management of healthcare services,but not health research, monitoring, surveillance and governance. The processing of personal health data for historical, statistical or scientific purposes shall be allowed only with the consent of the data subject or if the processing serves an exceptionally high public interest, cannot be performed otherwise and is legally authorised. Research, be it academic, government,corporate or market research, falls under the same rule.The proposed amendments will make difficult or render impossible research and statistics involving the linkage and analysis of the wealth of data from clinical,administrative, insurance and survey sources, which have contributed to improving health outcomes and health systems performance and governance; and may illegitimise efforts that have been made in some European countries to enable privacy-respectful data use for research and statistical purposes. If the amendments stand as written, the right to privacy is likely to override the right to health and healthcare in Europe. PMID:24310171

  1. Post-rift km-scale uplift of passive continental margins can be caused by compressive stresses within continental crust

    NASA Astrophysics Data System (ADS)

    Chalmers, J. A.

    2012-12-01

    Many passive continental margins are flanked by a mountain range up to more than 2 km high (Elevated Passive Continental Margins; EPCMs), e.g. Norway, east and west Greenland, East Brazil, eastern Australia and other margins elsewhere, that have been uplifted long after continental break-up. Explanations for these uplifted margins have been ad hoc, but there has hitherto been no explanation that accounts for their presence at both volcanic and non-volcanic margins and in both polar and tropical climatic environments. A continent breaks up by extension and thinning of the continental crust. Thinning varies from small amounts in the proximal rift to perhaps a factor of 5 or more adjacent to oceanic crust. Continental crust > ca. 25 km thick contains two weak layers, one between strong upper (quartz-rich) and lower (dioritic) crust and the other between strong lower crust and strong mantle. Continental crust < ca. 20 km thick is too thin for there to be weak layers and the strong layers are effectively annealed to one another and to the underlying strong mantle. Rifting of a passive continental margin must take place under tension. After rifting ceases, however, the margin can come under compression from forces originating elsewhere on or below its plate, e.g. collision between continental plates. The World Stress Map (www.world-stress-mp.org) shows that, where data exists, all EPCMs are currently under compression. Continental crust responds to moderate compression stress in two modes; flow in the weak lower crust and by forming gentle buckle-folds with a wavelength of 200-400 km and an amplitude of ca. 0.5 km. Under moderate compression, material in the crust's weak layers starts to flow towards the rift from under the adjacent continent. The lack of weak layers under the thinned, distal rift basin means, however, that flow cannot continue towards the ocean. Mid- and lower crustal material therefore accumulates under the proximal rift, thickening the crust there and lifting it by isostatic response to the thickening. Material flows into the rift until the crust under it is once more as thick as it was prior to extension, but no thicker. This thickened layer extends gradually further and further below the rift, at speeds of a few km per million years, uplifting it and exposing post-rift sediments. At higher stress, buckling may enhance this uplift, and it may be enhanced even more by the isostatic response to the erosion of deep valleys in the rising mountains. Both the thickening and folding continues until there is a reduction in imposed far-field compressive stress, after which the thickened crust 'freezes' in place.

  2. Composite transform-convergent plate boundaries: description and discussion

    USGS Publications Warehouse

    Ryan, H.F.; Coleman, P.J.

    1992-01-01

    The leading edge of the overriding plate at an obliquely convergent boundary is commonly sliced by a system of strike-slip faults. This fault system is often structurally complex, and may show correspondingly uneven strain effects, with great vertical and translational shifts of the component blocks of the fault system. The stress pattern and strain effects vary along the length of the system and change through time. These margins are considered to be composite transform-convergent (CTC) plate boundaries. Examples are given of structures formed along three CTC boundaries: the Aleutian Ridge, the Solomon Islands, and the Philippines. The dynamism of the fault system along a CTC boundary can enhance vertical tectonism and basin formation. This concept provides a framework for the evaluation of petroleum resources related to basin formation, and mineral exploration related to igneous activity associated with transtensional processes. ?? 1992.

  3. InterContinental Chicago InterContinental Chicago

    E-print Network

    He, Chuan

    InterContinental Chicago InterContinental Chicago 505 N. Michigan Avenue Chicago, IL 60611 by season and are subject to availability. Ask for the University of Chicago rate. Offer is available to all Policy By 4PM CT day of arrival Often regarded as Chicago's answer to the Champs

  4. Steady State Growth of Continental Crust?

    NASA Astrophysics Data System (ADS)

    Bowring, S. A.; Bauer, A.; Dudas, F. O.; Schoene, B.; McLean, N. M.

    2012-12-01

    More than twenty years since the publication of Armstrong's seminal paper, debate still rages about most aspects of the Earth's first billion years. Although orders of magnitude more data have been generated since then, the arguments remain the same. The debate is largely centered on the isotopic systematics of minerals and whole rocks, the major and trace element geochemistry of continental crust, and various geodynamic models for differentiation of the planet. Most agree that earth, like all the terrestrial planets, differentiated into a crust, mantle and core very early in its history. After that, models of crustal evolution diverge significantly, including the suggestions that modern style plate tectonics did not originate until ca. 2.7 Ga or younger and that plumes have played a major role in the generation of continental crust. Many believe that the preserved rock record and the detrital zircon record are consistent with episodic crustal growth, which in turn has led to geodynamic models of episodic mantle convection driving major crust forming events. High-precision and high-throughput geochronology have led to claims of episodicity even more pronounced than that presented in Gastil's 1960 paper. We believe that Earth history has been dominated by plate tectonics and that continental crust is formed largely by amalgamation of island arcs, seamounts, micro continents, and oceanic plateaus. While there are geochemical differences in the average composition of Archean igneous rocks when compared to younger rocks, the processes responsible for their formation may not have changed a great deal. In this view, the so-called crustal growth curves originated by Hurley are in fact crude approximations of crustal preservation. The most highly cited rationales for the view that little silicic crust formed during Earth's first billion years are the lack of known exposed crust older than 3.5 Ga and the paucity of detrital zircons older than 4.0 Ga in sedimentary rocks of any age. If one accepts that the probability of preserving old crust decreases with increasing age, the few exposures of rocks older than 3.5 Ga should not be surprising. The thickness and compositional differences between Archean and younger lithospheric mantle are not fully understood nor is the role of thicker buoyant mantle in preserving continental crust; these lead to the question of whether the preserved rock record is representative of what formed. It is notable that the oldest known rocks, the ca. 4.0 Ga Acasta Gneisses, are tonalities-granodiorites-granites with evidence for the involvement of even older crust and that the oldest detrital zircons from Australia (ca. 4.0-4.4 Ga) are thought to have been derived from granitoid sources. The global Hf and Nd isotope databases are compatible with both depleted and enriched sources being present from at least 4.0 Ga to the present and that the lack of evolution of the MORB source or depleted mantle is due to recycling of continental crust throughout earth history. Using examples from the Slave Province and southern Africa, we argue that Armstrong's concept of steady state crustal growth and recycling via plate tectonics still best explains the modern geological and geochemical data.

  5. Current plate velocities relative to the hotspots incorporating the NUVEL-1 global plate motion model

    SciTech Connect

    Gripp, A.E.; Gordon, R.G. )

    1990-07-01

    NUVEL-1 is a new global model of current relative plate velocities which differ significantly from those of prior models. Here the authors incorporate NUVEL-1 into HS2-NUVEL1, a new global model of plate velocities relative to the hotspots. HS2-NUVEL1 was determined from the hotspot data and errors used by Minster and Jordan (1978) to determine AM1-2, which is their model of plate velocities relative to the hotspots. AM1-2 is consistent with Minster and Jordan's relative plate velocity model RM2. Here the authors compare HS2-NUVEL1 with AM1-2 and examine how their differences relate to differences between NUVEL-1 and RM2. HS2-NUVEL1 plate velocities relative to the hotspots are mainly similar to those of AM1-2. Minor differences between the two models include the following: (1) in HS2-NUVEL1 the speed of the partly continental, apparently non-subducting Indian plate is greater than that of the purely oceanic, subducting Nazca plate; (2) in places the direction of motion of the African, Antarctic, Arabian, Australian, Caribbean, Cocos, Eurasian, North American, and South American plates differs between models by more than 10{degree}; (3) in places the speed of the Australian, Caribbean, Cocos, Indian, and Nazca plates differs between models by more than 8 mm/yr. Although 27 of the 30 RM2 Euler vectors differ with 95% confidence from those of NUVEL-1, only the AM1-2 Arabia-hotspot and India-hotspot Euler vectors differ with 95% confidence from those of HS2-NUVEL1. Thus, substituting NUVEL-1 for RM2 in the inversion for plate velocities relative to the hotspots changes few Euler vectors significantly, presumably because the uncertainty in the velocity of a plate relative to the hotspots is much greater than the uncertainty in its velocity relative to other plates.

  6. Continuum-based 4D Plate Reconstructions: Linking Non-rigid Lithospheric Kinematics to Rigid Plate Motion

    NASA Astrophysics Data System (ADS)

    Kneller, E. A.; Johnson, C. A.; Queffelec, T. A.; Nachtegaele, L.

    2010-12-01

    Non-rigid deformation in regions of continental extension and compression can lead to large lateral strain and changes in the shape and surface area of continental plates. This large lateral strain in turn leads to vertical strain in the lithosphere, which is a fundamental control on mechanical and thermal subsidence. Traditional plate reconstruction approaches only describe 2D changes in the shape of tectonic plates and do not include lateral strain gradients and vertical strain. Incorporating lateral and vertical strain into kinematic plate tectonic models is necessary for quantifying the past configuration of tectonic plates, modeling paleogeography and for linking subsidence and heat flow to lateral plate motion. Furthermore, traditional approaches are limited to describing processes at the surface of the Earth and cannot be used to investigate 3D slab kinematics. We build on previous work and overcome the limitations of traditional methods by developing an inverse non-rigid continuum-based plate reconstruction approach that links lateral plate tectonic motion to large-scale 4D deformation of continental plates and subducting slabs. We also describe how this approach can be implemented in open source 3D animation software that can be used to create extendable and easily maintained interactive tools. These tools allow the modeler to rapidly reconstruct deformation and map data and constrain plate models with 3D information. The methods presented in this work can improve paleogeographic reconstructions, help visualize complicated 4D deformation processes in a reconstructed framework, and constrain subsidence and lithospheric stretching, all of which are important for understanding thermal history and estimating heat flow in sedimentary basins.

  7. Extensional evolution of the central East Greenland Caledonides

    E-print Network

    White, Arthur Percy, 1972-

    2001-01-01

    This thesis addresses the complexity of both syn- and post-orogenic extension in the overriding plate during Caledonian continental collision through field and laboratory investigations in the central East Greenland ...

  8. Magmatism and deformation during continental breakup

    NASA Astrophysics Data System (ADS)

    Keir, Derek

    2013-04-01

    The rifting of continents and the transition to seafloor spreading is characterised by extensional faulting and thinning of the lithosphere, and is sometimes accompanied by voluminous intrusive and extrusive magmatism. In order to understand how these processes develop over time to break continents apart, we have traditionally relied on interpreting the geological record at the numerous fully developed, ancient rifted margins around the world. In these settings, however, it is difficult to discriminate between different mechanisms of extension and magmatism because the continent-ocean transition is typically buried beneath thick layers of volcanic and sedimentary rocks, and the tectonic and volcanic activity that characterised breakup has long-since ceased. Ongoing continental breakup in the African and Arabian rift systems offers a unique opportunity to address these problems because it exposes several sectors of tectonically active rift sector development spanning the transition from embryonic continental rifting in the south to incipient seafloor spreading in the north. Here I synthesise exciting, multidisciplinary observational and modelling studies using geophysical, geodetic, petrological and numerical techniques that uniquely constrain the distribution, time-scales, and interactions between extension and magmatism during the progressive breakup of the African Plate. This new research has identified the previously unrecognised role of rapid and episodic dike emplacement in accommodating a large proportion of extension during continental rifting. We are now beginning to realise that changes in the dominant mechanism for strain over time (faulting, stretching and magma intrusion) impact dramatically on magmatism and rift morphology. The challenge now is to take what we're learned from East Africa and apply it to the rifted margins whose geological record documents breakup during entire Wilson Cycles.

  9. Socioeconomic status overrides age and gender in determining health-seeking behaviour in rural Bangladesh.

    PubMed Central

    Ahmed, Syed Masud; Tomson, Göran; Petzold, Max; Kabir, Zarina Nahar

    2005-01-01

    OBJECTIVE: To study the health-seeking behaviour of elderly members (aged > 60 years) of households in rural Bangladesh, to ascertain how their behaviour differs from that of younger people (aged 20-59 years) living in the same household and to explore the determinants of health-seeking behaviour. METHODS: Structured interviews were conducted to elicit information on the health-seeking behaviour of household members aged > 20 years. Respondents were asked about major illnesses occurring within 15 days prior to the interview. The sample consisted of 966 households that had at least one resident who was aged > 60 (32% of 3031 households). FINDINGS: We found no major differences in health-seeking behaviour between elderly people and younger adults. On average about 35% (405/1169) of those who reported having been ill during the previous 15 days in both age groups chose self-care/self-treatment; for both age groups the most commonly consulted type of provider was a paraprofessional such as a village doctor, a medical assistant or a community health worker. A household's poverty status emerged as a major determinant of health-seeking behaviour. The odds ratio (OR) that individuals from poor households would seek treatment from unqualified allopathic practitioners was 0.6 (95% confidence interval (CI) = 0.40-0.78); the odds ratio that individuals from poor households would seek treatment from qualified allopathic practitioners was 0.7 (95% CI = 0.60-0.95). For self-care or self-treatment it was 1.8 (95% CI = 1.43-2.36). Patients' level of education affected whether they avoided self-care/self-treatment and drugstore salespeople (who are usually unlicensed and untrained but who diagnose illnesses and sell medicine) and instead chose a formal allopathic practitioner (OR = 1.5; 95% CI = 1.15-1.96). When a household's poverty status was controlled for, there were no differences in age or gender in terms of health-care expenditure. CONCLUSION: We found that socioeconomic indicators were the single most pervasive determinant of health-seeking behaviour among the study population, overriding age and sex, and in case of health-care expenditure, types of illness as well. PMID:15744403

  10. On the validity of density overrides for VMAT lung SBRT planning

    SciTech Connect

    Wiant, David Vanderstraeten, Caroline; Maurer, Jacqueline; Pursley, Jan; Terrell, Jonathon; Sintay, Benjamin J.

    2014-08-15

    Purpose: Modeling dose to a moving target in lung is a very difficult task. Current approaches to planning lung stereotactic body radiotherapy (SBRT) generally calculate dose on either free breathing or average computed tomography (CT) scans, which do not always accurately predict dose to parts of the target volume not occupied by tumor on the planning scan. In this work, the authors look at using density overrides of the target volumes to more accurately predict dose for lung SBRT using the analytic anisotropic algorithm (AAA). Methods: Volumetric modulated arc therapy plans were created on free breathing scans (FBP), time average scans (AVGP), free breathing scans with the internal target volume overridden to tumor density (ITVP), free breathing scans with the planning target volume overridden to tumor density (PTVP), and free breathing scan using a hybrid scheme with the internal target volume set to tumor density and the planning target volume minus the internal target volume set to a density intermediate between lung and tumor (HP) for the case of a 4D motion phantom and five patient cases. Radiochromic film measurements were made for the phantom plans, with gamma analysis used to compare the planned to delivered dose. The patient plans were recalculated on each of the phases of a 4DCT to evaluate tumor coverage and conformity index (CI). A modified modulation complexity score (MCSv) and average open area per control point (AA) metrics were used to evaluate multileaf collimator (MLC) modulation for each of the plans. Results: The HP plans showed significantly higher gamma passing rates (p < 0.05) than the FBP, AVGP, and ITVP for criteria of 2 mm/2% and 1 mm/1%. No significant correlation was observed between gamma values and AA or MCSv. The tumor volume was covered by the prescription dose on all phases of the 4DCT for all patient plans. The PTVP and HP yielded lower mean CI than the other plans for all five patients, with three of the cases showing statistically significant differences (p < 0.05). No meaningful correlation was observed between the mean CI and AA or MCSv. Conclusions: These measurements suggest that the HP planning method may provide more accurate dose modeling and decreased normal lung irradiation for lung SBRT compared to the commonly used FBP and AVG planning methods when used with the AAA. The HP method does not appear to have a strong relationship with MLC modulation.

  11. Ras Transformation Overrides a Proliferation Defect Induced by Tpm3.1 Knockout.

    PubMed

    Coombes, Jason D; Schevzov, Galina; Kan, Chin-Yi; Petti, Carlotta; Maritz, Michelle F; Whittaker, Shane; Mackenzie, Karen L; Gunning, Peter W

    2015-12-01

    Extensive re-organisation of the actin cytoskeleton and changes in the expression of its binding proteins is a characteristic feature of cancer cells. Previously we have shown that the tropomyosin isoform Tpm3.1, an integral component of the actin cytoskeleton in tumor cells, is required for tumor cell survival. Our objective was to determine whether cancer cells devoid of Tpm3.1 would evade the tumorgenic effects induced by H-Ras transformation. The tropomyosin isoform (Tpm) expression profile of a range of cancer cell lines (21) demonstrates that Tpm3.1 is one of the most broadly expressed Tpm isoform. Consequently, the contribution of Tpm3.1 to the transformation process was functionally evaluated. Primary embryonic fibroblasts isolated from wild type (WT) and Tpm3.1 knockout (KO) mice were transduced with retroviral vectors expressing SV40 large T antigen and an oncogenic allele of the H-Ras gene, H-RasV12, to generate immortalized and transformed WT and KO MEFs respectively. We show that Tpm3.1 is required for growth factor-independent proliferation in the SV40 large T antigen immortalized MEFs, but this requirement is overcome by H-Ras transformation. Consistent with those findings, we found that Tpm3.1 was not required for anchorage independent growth or growth of H-Ras-driven tumors in a mouse model. Finally, we show that pERK and Importin 7 protein interactions are significantly decreased in the SV40 large T antigen immortalized KO MEFs but not in the H-Ras transformed KO cells, relative to control MEFs. The data demonstrate that H-Ras transformation overrides a requirement for Tpm3.1 in growth factor-independent proliferation of immortalized MEFs. We propose that in the SV40 large T antigen immortalized MEFs, Tpm3.1 is partly responsible for the efficient interaction between pERK and Imp7 resulting in cell proliferation, but this is overidden by Ras transformation. PMID:26274783

  12. Inter-seismic deformation and plate coupling along the Andaman micro-plate margin: geodetic constraints using 1996-2004 GPS data.

    NASA Astrophysics Data System (ADS)

    Earnest, A.; Puchakayala, J.; Rajendran, C. C. P.; Rajendran, K.

    2014-12-01

    Oblique convergence of the Andaman microplate with the Sunda margin results in permanent deformation within the overriding plate and had generated giant plate-boundary ruptures like the 2004 Mw 9.3 Sumatra- Andaman earthquake. Inter-seismic upper plate deformation of this part of the subduction zone remains poorly constrained due to lack of availability of spatially well distributed data. Through this study we are reanalyzing the available GPS geodetic data sets collected by various agencies over different times between 1996-2004 to constrain the pre-earthquake convergence values using a consistent reference frame to determine the crustal deformation in the Andaman Nicobar region, to infer strain rates in the overriding plate, how Andaman microplate was moving relative to Indian plate and what was the extent of plate locking. We will also discuss the details on spatial and temporal variations of convergence rates and variations in plate coupling. To quantify the change in coupling, we calculated the interseismic surface deformation using Okada's formulation, in which locked faults are modelled as dislocations in a halfspace. We defined the subduction zone geometry as three elastically deforming blocks (India, Andaman fore-arc, and Sunda) separated by two faults: the West Andaman Fault and the Sumatra-Andaman megathrust. The bennioff-zone dip and orientation is re-defined using the recently relocated epicentral solutions with higher accuracy and from the slip-distribution models constrained from the various co-seismic geodetic offsets reported from the near-field and far-field GPS sites . The rigid-body motion of each block is specified by a pole of rotation. We modelled the variation in coupling by specifying for each node and integrating the slip deficit over the fault surfaces. The West Andaman Fault is modeled as a vertical strike- lip fault, locked to a depth of ~20 km, with a dextral slip.

  13. Growth Plate Fractures

    MedlinePLUS

    .org Growth Plate Fractures Page ( 1 ) The bones of children and adults share many of the same risks for injury. But because they ... to a unique injury called a growth plate fracture. Growth plates are areas of cartilage located near ...

  14. Lithospheric boundaries and plate motions in the Cyprus area

    NASA Astrophysics Data System (ADS)

    Papazachos, B. C.; Papaioannou, Ch. A.

    1999-07-01

    Accurate location of earthquakes recorded by seismographs and reliable fault plane solutions of strong recent earthquakes are used to define the plate boundaries and the pattern of plate motion in Cyprus and surrounding area. Spatial distribution of shallow ( h<60 km) and intermediate depth (60 km ? h ?130 km) earthquakes define a continuous boundary between the Eurasian and the African lithospheric plates in this area. This boundary is formed of two arcuate structures, the eastern and western, which have their concave side to the north and are connected by a NNE striking transform dextral fault, the Paphos Transform Fault (PTF), just west of Cyprus. The eastern structure consists of the Cyprean arc and its continuation to the Gulf of Adana, which then joins the Eastern Anatolian Fault. The western one is an arc-like structure which strikes in a northwest direction following the Florence rise and joins the Rhodes thrust fault. The African plate is slowly subducted under the Eurasian plate from south to north but in the Cyprean arc the Cyprean microplate overrides also the Levantine lithosphere in a SW direction. Some interesting tectonic similarities between the Cyprean and the Hellenic arcs are pointed out.

  15. Subduction zone plate bending earthquakes and implications for the hydration of the downgoing plate

    NASA Astrophysics Data System (ADS)

    Emry, E. L.; Wiens, D. A.

    2011-12-01

    The greatest uncertainty in the amount of water input into the Earth at subduction zones results from poor constraints on the degree and depth extent of mantle serpentinization in the downgoing slab. The maximum depth of serpentinization is thought to be partly controlled by the maximum depth of tensional earthquakes in the outer rise and trench and is expected to vary from subduction zone to subduction zone or even along-strike for a single subduction zone. We explore the maximum depth of extensional faulting on the incoming plate for various subduction zones in order to gain insight into the possible extent of slab serpentinization. We relocate trench events at island arc subduction zones using hypocentroidal decomposition to determine which earthquakes occurred within the incoming plate. For earthquakes with Mw ~5.5+, we determine accurate depths and refine the CMT focal mechanism by inverting teleseismic P and SH waveforms. Results from the Mariana outer rise indicate that extensional earthquakes occur in the Pacific plate at depths ranging from 10-20 km beneath the top of the crust, with the character of trench seismicity changing significantly between the northern and southern portions of the subduction zone. In comparision, results from the Aleutian subduction zone show extensional trench earthquakes occurring from 5-30 km below the surface of the subducting slab. Compressional incoming plate earthquakes occur only near the Alaskan Peninsula, possibly due to stronger coupling between the slab and overriding plate in this region. Further results from oceanic arc subduction zones will be presented and differences between subduction zones as well as along-strike differences in the character of trench seismicity will be highlighted. If the presence of extensional faulting indicates subducting lithosphere hydration, then we expect that as much as the top 30 km of the slab may be hydrated and that the degree of slab serpentinization may vary significantly between subduction zones, potentially affecting arc geochemistry, intermediate depth seismicity, and the subduction zone water budget.

  16. Dual subduction tectonics and plate dynamics of central Japan shown by three-dimensional P-wave anisotropic structure

    NASA Astrophysics Data System (ADS)

    Ishise, Motoko; Miyake, Hiroe; Koketsu, Kazuki

    2015-07-01

    The central Japanese subduction zone is characterized by a complex tectonic setting affected by the dual subduction of oceanic plates and collisions between the island arcs. To better understand of the subduction system, we performed an anisotropic tomography analysis using P-wave arrival times from local earthquakes to determine the three-dimensional structure of P-wave azimuthal anisotropy in the overriding plate and the Pacific and Philippine Sea (PHS) slabs. The principal characteristics of anisotropy in the subducted and subducting plates are (1) in the overriding plate, the distribution pattern of fast direction of crustal anisotropy coincides with that of the strike of geological structure, (2) in the two oceanic plates, fast propagation directions of P-wave were sub-parallel to the directions of seafloor spreading. Additionally, our tomographic images demonstrate that (1) the bottom of the Median Tectonic Line, the longest fault zone in Japan, reaches to the lower crust, and seems to link to the source region of an inter-plate earthquake along the PHS slab, (2) the segmentation of the PHS slab - the Izu Islands arc, the Nishi-Shichito ridge, and the Shikoku basin - due to the formation history, is reflected in the regional variation of anisotropy. The tomographic study further implies that there might be a fragment of the Pacific slab suggested by a previous study beneath the Tokyo metropolitan area. The overall findings strongly indicate that seismic anisotropy analysis provide potentially useful information to understand a subduction zone.

  17. Foam as an agent to reduce gravity override effect during gas injection in oil reservoirs. Final report

    SciTech Connect

    Chiang, J.C.; Sanyal, S.K.; Castanier, L.M.; Brigham, W.E.; Shah, D.O.

    1980-08-01

    A two-dimensional, vertical, rectangular plexiglas model holding a 45-1/2 in. high by 11-3/8 in. wide by 1/4 in. thick sandpack (1.147 x 0.237 x 0.008 m) was used to investigate gravity override of injected gases in gas drive processes. Saturation of the sandpack by a surfactant solution instead of pure water sharply increased liquid recovery and breakthrough time in a nitrogen flooding process. The improvement in production was shown to be due to a reduction of gravity override caused by in-situ generation of foam at the gas-liquid interface. Solutions of two different surfactants (Suntech IX and IV) of various concentrations with different amounts of alcohol were studied to determine their effectiveness as foamers. Surface tension and rate of drainage of the foamers as functions of surfactant concentration were measured. In-situ foaming in the model increased generally with surfactant concentration until an optimum concentration was reached; above this concentration, additional amounts of surfactant had very little effect on the phenomenon. Alcohols seem to improve the performance of low molecular weight surfactants and exhibitied a negative effect on the others. A similar increase of recovery and delay in the breakthrough time was observed in the oil flooding process. A slug of surfactant solution was injected into the pack which was saturated with a white mineral oil and water at irreducible water saturation, and then nitrogen was injected. Gravity override was much less than in the cases when no surfactant was present.

  18. Transition on the Geometry of the Cocos Plate in Central-Southern Mexico.

    NASA Astrophysics Data System (ADS)

    Rodríguez-Domínguez, M. Á.; Perez-Campos, X.; Valencia-Cabrera, D.; Clayton, R. W.; Cordoba-Montiel, F.; Valdes-Gonzales, C. M.; Brudzinski, M. R.; Cabral-Cano, E.; Arciniega-Ceballos, A.

    2014-12-01

    The tectonic setting, produced by the interaction between the Cocos and North American plates, follows complex geometries along the Pacific coast. Previous studies in central Mexico showed that the slab dips nearly horizontally before steeply subducting into the continental mantle; in contrast, in southern Mexico, the slabs dips under the continental plate at a constant angle. Receiver functions from four seismic networks: GECO (Geometry of Cocos), SSN (Servicio Sismológico Nacional), OxNet (Oaxaca Network) and UV (Universidad Veracruzana) are used to study the crustal structure underneath the stations, and image the subducting Cocos plate in order to define the geometry and the transition angle in central-southern Mexico.

  19. History and Evolution of Precambrian plate tectonics

    NASA Astrophysics Data System (ADS)

    Fischer, Ria; Gerya, Taras

    2014-05-01

    Plate tectonics is a global self-organising process driven by negative buoyancy at thermal boundary layers. Phanerozoic plate tectonics with its typical subduction and orogeny is relatively well understood and can be traced back in the geological records of the continents. Interpretations of geological, petrological and geochemical observations from Proterozoic and Archean orogenic belts however (e.g., Brown, 2006), suggest a different tectonic regime in the Precambrian. Due to higher radioactive heat production the Precambrian lithosphere shows lower internal strength and is strongly weakened by percolating melts. The fundamental difference between Precambrian and Phanerozoic tectonics is therefore the upper-mantle temperature, which determines the strength of the upper mantle (Brun, 2002) and the further tectonic history. 3D petrological-thermomechanical numerical modelling experiments of oceanic subduction at an active plate at different upper-mantle temperatures show these different subduction regimes. For upper-mantle temperatures < 175 K above the present day value a subduction style appears which is close to present day subduction but with more frequent slab break-off. At upper-mantle temperatures 175 - 250 K above present day values steep subduction continues but the plates are weakened enough to allow buckling and also lithospheric delamination and drip-offs. For upper-mantle temperatures > 250 K above the present day value no subduction occurs any more. The whole lithosphere is delaminating and due to strong volcanism and formation of a thicker crust subduction is inhibited. This stage of 200-250 K higher upper mantle temperature which corresponds roughly to the early Archean (Abbott, 1994) is marked by strong volcanism due to sublithospheric decompression melting which leads to an equal thickness for both oceanic and continental plates. As a consequence subduction is inhibited, but a compressional setup instead will lead to orogeny between a continental or felsic terrain and an oceanic or mafic terrain as well as internal crustal convection. Small-scale convection with plume shaped cold downwellings also in the upper mantle is of increased importance compared to the large-scale subduction cycle observed for present temperature conditions. It is also observed that lithospheric downwellings may initiate subduction by pulling at and breaking the plate. References: Abbott, D., Drury, R., Smith, W.H.F., 1994. Flat to steep transition in subduction style. Geology 22, 937-940. Brown, M., 2006. Duality of thermal regimes is the distinctive characteristic of plate tectonics since the neoarchean. Geology 34, 961-964. Brun, J.P., 2002. Deformation of the continental lithosphere: Insights from brittle-ductile models. Geological Society, London, Special Publications 200, 355-370.

  20. Palaeomagnetism and the continental crust

    SciTech Connect

    Piper, J.D.A.

    1987-01-01

    This book is an introduction to palaeomagnetism offering treatment of theory and practice. It analyzes the palaeomagnetic record over the whole of geological time, from the Archaean to the Cenozoic, and goes on to examine the impact of past geometries and movements of the continental crust at each geological stage. Topics covered include theory of rock and mineral magnetism, field and laboratory methods, growth and consolidation of the continental crust in Archaean and Proterozoic times, Palaeozoic palaeomagnetism and the formation of Pangaea, the geomagnetic fields, continental movements, configurations and mantle convection.

  1. Convergent plate margin east of North Island, New Zealand

    SciTech Connect

    Davey, F.J; Hampton, M.; Lewis, K.

    1986-07-01

    The Indian-Pacific plate boundary passes along the eastern margin of North Island, New Zealand, with the Pacific plate being thrust under the Indian plate to the west. The continental slope forming the Indian plate margin is broad with a well-formed series of trench slope basins and intervening ridges along the continental slope and shelf, subparallel to the margin, and continuing onto land. Multichannel seismic reflection data recorded across this margin show a thick (2.5-km) sedimentary section overlying oceanic basement in the deep-water part of the profile, and part of this sedimentary section is apparently being subducted under the accretionary prism. At the toe of the continental slope, nascent thrusts, often showing little apparent offset but a change in reflection amplitude, occur over a broad region. Well-defined trench slope basins show several episodes of basin formation and thrusting and are similar to structural interpretations for adjacent onshore basins. A bottom simulating reflector, which may delineate a gas-hydrate layer, can be traced over the midslope part of the profile. A major reflector, interpreted as the base of the accretionary prism, can be traced discontinuously to the coast where it coincides with the top of a zone of high seismicity, considered to mark the top of the subducted Pacific plate.

  2. Development of transtensional and transpressive plate boundaries due to noncircular (cycloid) relative plate motion

    SciTech Connect

    Cronin, V.S. )

    1990-05-01

    The trace of a transform fault commonly is assumed to be circular and concentric with the finite relative motion of the plates adjacent to the fault. These assumptions have led to controversy as the transform fault label has been applied to the San Andreas fault in California because the San Andreas fault is neither circular nor concentric with the motion of the Pacific plate relative to the North American plate. The assumption of circular relative plate motion over a finite time interval is not generally valid. When finite relative plate motion is not circular, the length and orientation of a transform fault must change through time. The length and orientation of ridge-ridge transform faults in oceanic crust evolve through the migration, propagation, and abandonment of ridge segments. Transform faults that bound continental crust evolve differently than do transform faults along mid-ocean ridges because continental transform faults typically do not have ridges at both ends and because of the rheological differences between oceanic and continental crust. Along continent-continent transform faults in which the initial displacement is entirely strike slip, later displacements will be progressively more divergent or convergent (i.e., transtensive or transpressive). Transtension can result in the development of deep basins with high heat flow. Transpression can result in folding, reverse faulting, and decoupling of the crust from its lower crustal or mantle lithosphere in the region adjacent to the transform fault. Regardless of whether the transform boundary becomes transtensional or transpressional, the boundary evolves from a discrete transform fault to a broader, structurally complex accommodation zone (sensu lato).

  3. Copper Map Plate Detail

    USGS Multimedia Gallery

    A portion of the engraving on the plate used to print points, lines, and text in black ink. Engravings on the plate are left-to-right reversed. This plate was cleaned and treated to improve the visibility of the engraving. The plate was used to print the Washington [D.C.] and vicinity, 1:31,680-sca...

  4. Sputtering and ion plating

    NASA Technical Reports Server (NTRS)

    1972-01-01

    The proceedings of a conference on sputtering and ion plating are presented. Subjects discussed are: (1) concepts and applications of ion plating, (2) sputtering for deposition of solid film lubricants, (3) commercial ion plating equipment, (4) industrial potential for ion plating and sputtering, and (5) fundamentals of RF and DC sputtering.

  5. Coordination: Southeast continental shelf studies

    SciTech Connect

    Menzel, D.W.

    1989-01-26

    The objective of this investigation is to obtain model descriptions of the flow modifications in the Southeast Atlantic continental shelf due to Gulf Stream fluctuations and topographic effects. 2 refs., 4 figs.

  6. Pleistocene tectonic accretion of the continental slope off Washington

    USGS Publications Warehouse

    Silver, E.A.

    1972-01-01

    Interpretation of reflection profiles across the Washington continental margin suggests deformation of Cascadia basin strata against the continental slope. Individual reflecting horizons can be traced across the slope-basin boundary. The sense of offset along faults on the continental slope is predominantly, but not entirely, west side up. Two faults of small displacement are seen to be west-dipping reverse faults. Magnetic anomalies on the Juan de Fuca plate can be traced 40-100 km eastward under the slope, and structural interpretation combined with calculated rates of subduction suggests that approximately 50 km of the outer continental slope may have been formed in Pleistocene time. Rocks of Pleistocene age dredge from a ridge exposing acoustic "basement" on the slope, plus the results of deep-sea drilling off northern Oregon, are consistent with this interpretation. The question of whether or not subduction is occurring at present is unresolved because significant strain has not affected the upper 200 m of section in the Cascadia basin. However, deformation of the outer part of the slope has been episodic and may reflect episodic yield, deposition rate, subduction rate, or some combination of these factors. ?? 1972.

  7. Earth's plate motion evolution and its link to global mantle dynamics

    NASA Astrophysics Data System (ADS)

    Rolf, Tobias; Capitanio, Fabio; Tackley, Paul

    2015-04-01

    Present-day plate motions provide a global dataset that allows us to infer the present convective structure of the Earth's mantle. Moreover, present geological observations combined with the kinematic principles of plate tectonics enables us to reconstruct Earth's tectonic history back until Pangaean times, which improves our understanding of how Earth has evolved to its present state. However, several aspects are not yet sufficiently well understood, for instance, how surface motions are linked to deep mantle processes or how plate motion changes over time, including those timescales of several 100 Myr that are associated with supercontinent formation and dispersal. Here, we use global spherical models of mantle convection to investigate plate motion evolution in a general and dynamically fully consistent manner. These models include tectonic plates self-consistently evolving from mantle flow as well as Earth-like continental drift. We analyze the evolution of plate velocities over long timescales and observe fluctuations of globally averaged plate motions of a factor of 2-3, in agreement with kinematic reconstructions. The fluctuations are mainly driven by the onset of new subduction, highlighting the strong role of slab-related driving forces in the rates of plate motion. Average plate motions are increased with a stronger viscosity contrast between upper and lower mantle, partly due to an increased subduction flux into the lower mantle, which increases the driving forces of plate motion. The motion of individual plates shows much stronger fluctuation. Continental plate motions are modulated by continental assembly and dispersal. Continents usually move slower when strongly clustered and faster during dispersal and before collision. In a further step, we analyze changes in the direction of motion of these individual plates by calculating their Euler pole and its change with time. This allows us to characterize the variety of modeled plate reorganizations and to relate our models to Earth's recent tectonic evolution.

  8. Interrelationships between continental freeboard, tectonics and mantle temperature

    NASA Technical Reports Server (NTRS)

    Galer, S. J. G.

    1991-01-01

    Oceanic hypsometry and isentropic melting models are combined to address the question of freeboard from the middle Archean to the present. In addition to the fraction of continental crust, the factors governing the long-term balance of the continental freeboard include the mantle potential temperature (TP), the oceanic lithosphere thickness, and the plate creation rate (C0). It is shown that variation in TP far outweighs the other factors in importance, with freeboard decreasing by 1 km for every TP increase of about 80 C. The huge ten- to thirtyfold increases in C0 backward in geological time that have been invoked to explain near-constant freeboard are shown to be unnecessary. The low value found for TP is consistent with the preservation of ancient diamonds in the deep South African lithosphere. It is concluded from this that the present cooling rate of the earth of about 46 C/Ga has general applicability over much of geological time.

  9. Plate Tectonics: From Initiation of Subduction to Global Plate Motions (Augustus Love Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Gurnis, Michael

    2013-04-01

    Plates are driven by buoyancy forces distributed in the mantle, within cooling oceanic plates (ridge push) and within subducted slabs. Although the case is often made that subducted slabs provide the principle driving force on plate motion, consensus has not been achieved. This is at least partially due to the great difficulty in realistically capturing the role of slabs in observationally-constrained models as slabs act to drive and resist plate motions through their high effective viscosity. Slab buoyancy acts directly on the edge of the plate (slab pull), while inducing mantle flow that tends to drag both subducting and overriding plates toward the trench. While plates bend during subduction they undergo a form of 'plastic failure' (as evident through faulting, seismicity and reduction of flexural parameters at the outer trench wall). The birth of a new subduction zone, subduction initiation, provides important insight into plate motions and subduction dynamics. About half of all subduction zones initiated over the Cenozoic and the geophysical and geological observations of them provide first order constraints on the mechanics of how these margins evolved from their preexisting tectonic state to self-sustaining subduction. We have examples of subduction initiation at different phases of the initiation process (e.g. early versus late) as well as how margins have responded to different tectonic forcings. The consequences of subduction initiation are variable: intense trench roll back and extensive boninitic volcanism followed initiation of the Izu-Bonin-Mariana arc while both were absent during Aleutian arc initiation. Such differences may be related to the character of the preexisting plates, the size of and forces on the plates, and how the lithosphere was initially bending during initiation. I will address issues associated with the forces driving plate tectonics and initiating new subduction zones from two perspectives. A common thread is the origin and evolution of intense back arc spreading and rapid roll back associated with some ocean-ocean subduction zones. I will look at the dynamics driving global plate motions and the time-dependence of trench rollback regionally. Capitalizing on advances in adaptive mesh refinement algorithms on parallel computers with individual plate margins resolved down to a scale of 1 kilometer, observationally constrained, high-resolution models of global mantle flow now capture the role of slabs and show how plate tectonics is regulated by the rheology of slabs. Back-arc extension and slab rollback are emergent consequences of slab descent in the upper mantle. I will then describe regional, time-dependent models, address the causes and consequences of subduction initiation, and show that most back arc extension follows subduction initiation. Returning to the global models, inverse models using the full adjoint of the variable viscosity, Stokes equation are now possible and allow an even greater link between present-day geophysical observations and the dynamics from local to global scales.

  10. Computer animation of Phanerozoic plate motions

    SciTech Connect

    Scotese, C.R. . Dept. of Geology)

    1992-01-01

    Since 1985, the PALEOMAP Project, in collaboration with research groups both in the US and abroad, has assembled a digital model that describes global plate motions during the last 600 million years. In this paper the authors present a series of computer animations that dynamically illustrates the movement of continents and terranes, and the evolution of the ocean basins since the breakup of the late Precambrian supercontinent. These animations depict the motion of the plates from both equatorial and polar perspectives. Mesozoic and Cenozoic plate tectonic reconstructions are based on a synthesis of linear magnetic anomalies, fracture zone locations, intracontinental rifts, collision and thrust belts, and zones of strike-slip. Paleozoic plate reconstructions, though more speculative, are based on evidence of past subduction, continental collision, and inferred sea floor spreading. The relative longitudinal positions of the continents during the Paleozoic and the width of intervening oceans have been adjusted to best explain changing biogeographic and paleoclimatic patterns. A new paleomagnetic/hot spot reference frame has been constructed that combines paleomagnetic data compiled by Rob Van der Voo (1992) with inferred motion relative to a fixed frame of hot spots. Using probable Early Mesozoic and Paleozoic hot spot tracks on the major continents, the authors have extended plate motions relative to the hot spot reference frame back to 400 million years.

  11. Dynamics of Mid-Palaeocene North Atlantic rifting linked with European intra-plate deformations.

    PubMed

    Nielsen, Søren B; Stephenson, Randell; Thomsen, Erik

    2007-12-13

    The process of continental break-up provides a large-scale experiment that can be used to test causal relations between plate tectonics and the dynamics of the Earth's deep mantle. Detailed diagnostic information on the timing and dynamics of such events, which are not resolved by plate kinematic reconstructions, can be obtained from the response of the interior of adjacent continental plates to stress changes generated by plate boundary processes. Here we demonstrate a causal relationship between North Atlantic continental rifting at approximately 62 Myr ago and an abrupt change of the intra-plate deformation style in the adjacent European continent. The rifting involved a left-lateral displacement between the North American-Greenland plate and Eurasia, which initiated the observed pause in the relative convergence of Europe and Africa. The associated stress change in the European continent was significant and explains the sudden termination of a approximately 20-Myr-long contractional intra-plate deformation within Europe, during the late Cretaceous period to the earliest Palaeocene epoch, which was replaced by low-amplitude intra-plate stress-relaxation features. The pre-rupture tectonic stress was large enough to have been responsible for precipitating continental break-up, so there is no need to invoke a thermal mantle plume as a driving mechanism. The model explains the simultaneous timing of several diverse geological events, and shows how the intra-continental stratigraphic record can reveal the timing and dynamics of stress changes, which cannot be resolved by reconstructions based only on plate kinematics. PMID:18075591

  12. Crustal Recylcing at Ocean Margin and Continental Subduction Zones and the Net Accumulation of Continental Crust

    NASA Astrophysics Data System (ADS)

    Scholl, D. W.; von Huene, R.

    2007-12-01

    CRUSTAL RECYCLING PROCESSES AND VOLUMES: At convergent ocean margins large volumes of rock and sediment are missing from the global length of submerged forearcs. Material is removed by the kindred tectonic process of sediment subduction and subduction erosion, both of which insert sediment and eroded crustal debris into the subduction channel separating the upper and lower plates. The channel transports entrained debris toward the mantle where it is ultimately recycled. Large tracks of exposed high P/T rocks are exposed remnants of subduction channels. Over the past 100-200 my, the average solid-rock volume of recycled crust is estimated to have averaged globally 2.5-3.0 km3/yr--or 2.5 to 3 Armstrong Units (AU). Exposed tracts of UHP rocks at collisional orogens document that crustal material is subducted deep into the mantle at continental subduction zones. Based on missing terranes of extended lower plate, a volume of recycled continental crust detached by slab failure can be estimated at ~5000 km3 for each km of the early Proterozoic Wopmay orogen of the NW Canadian Shield (Hildrenbrand and Bowring, 1999, Geology, v. 27, p.11-14). Averaged over an orogenic episode of ~40 my, the corresponding rate is ~125 km3/my/km of margin. Using the Wopmay- rate as a guide, and assuming that similar to the Cenozoic, collisional orogenic margins averaged 10-12,000 km in global length, then since the early Proterozoic crustal recycling at collisional subduction zones has averaged close to 1.5 AU (i.e., 1.5 km3/yr). Crustal losses from the upper plate have also been recognized for sectors of the Variscan orogen (Oncken, 1998, Geology, v. 26, p. 1975-1078). The missing crust is roughly 40 km3/my for each km of upper plate, thus globally tallying an additional ~0.5 AU. CRUSTAL GROWTH: New information implies that at intra-oceanic subduction zones the long-term (~50 my), global rate of arc magmatic productivity has averaged close to 5 AU, a much higher rate than formerly estimated (~1 AU). It is not clear that this rate, which is based on the growth of the Aleutian and Izu-Bonin-Mariana arc massifs corrected for subduction erosion losses, can be applied to continental or Andean arcs. But allowing that it can, then the combined global rate of additions of juvenile igneous rock to build continents ( 5 AU) is similar to that recycled at ocean margin (2-3 AU) and continental subduction zones (2 AU). Additional losses can arise from delamination of magmatically or tectonically thickened convergent-margin crust. The implication of these estimates and linked assumptions support the Armstrong posit that since the early Archean the yang of magmatic additions to the continents has been matched by the yin of recycling losses.

  13. Switching between alternative responses of the lithosphere to continental collision

    NASA Astrophysics Data System (ADS)

    Baes, Marzieh; Govers, Rob; Wortel, Rinus

    2011-12-01

    We study possible responses to arc-continent or continent-continent collision using numerical models. Our short-term integration models show that the initial stage of deformation following continental collision is governed by the competition between three potential weakness zones: (1) mantle wedge, (2) plate interface and (3) lower continental crust. Depending on which of these is the weakest zone in the system, three different responses can be recognized: (1) subduction polarity reversal, (2) continuation of subduction and (3) delamination and back stepping. Subduction polarity reversal occurs if the mantle wedge is the weakest zone in the system. This happens only if the viscosity of the mantle wedge is at least one order of magnitude lower than the average viscosity of the lithosphere. In continent-continent collision, one additional condition needs to be satisfied for subduction polarity reversal to occur: for the subducting lithosphere the ratio of the viscosity of the lower continental crust to the viscosity of the upper lithospheric mantle must be equal to or higher than 0.006. The time required for polarity reversal depends on several parameters: the convergence rate, the sinking velocity of the detached slab and the relative strength of the mantle wedge, arc and backarc. The response to collision is continued subduction if the plate interface is the weakest zone, and is delamination and back stepping if the lower continental crust is the weakest area in the system. Our finding that a low-viscosity wedge is a prerequisite for a reversal of subduction polarity agrees with inferences about regions for which subduction polarity reversal has been proposed.

  14. A great earthquake rupture across a rapidly evolving three-plate boundary.

    PubMed

    Furlong, Kevin P; Lay, Thorne; Ammon, Charles J

    2009-04-10

    On 1 April 2007 a great, tsunamigenic earthquake (moment magnitude 8.1) ruptured the Solomon Islands subduction zone at the triple junction where the Australia and Solomon Sea-Woodlark Basin plates simultaneously underthrust the Pacific plate with different slip directions. The associated abrupt change in slip direction during the great earthquake drove convergent anelastic deformation of the upper Pacific plate, which generated localized uplift in the forearc above the subducting Simbo fault, potentially amplifying local tsunami amplitude. Elastic deformation during the seismic cycle appears to be primarily accommodated by the overriding Pacific forearc. This earthquake demonstrates the seismogenic potential of extremely young subducting oceanic lithosphere, the ability of ruptures to traverse substantial geologic boundaries, and the consequences of complex coseismic slip for uplift and tsunamigenesis. PMID:19359581

  15. 76 FR 2919 - Outer Continental Shelf Official Protraction Diagram and Supplemental Official Outer Continental...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-01-18

    ... Bureau of Ocean Energy Management, Regulation and Enforcement Outer Continental Shelf Official Protraction Diagram and Supplemental Official Outer Continental Shelf Block Diagrams AGENCY: Bureau of Ocean... American Datum of 1983 (NAD 83) Outer Continental Shelf Official Protraction Diagram and...

  16. The Aravalli sequence of Rajasthan, India: A Precambrian continental margin?

    NASA Technical Reports Server (NTRS)

    Macdougall, J. D.; Willis, R.; Lugmair, G. W.; Roy, A. B.; Gopalan, K.

    1985-01-01

    The extent to which plate tectonics in its present form operated during the Precambrian is unknown, but is a subject of considerable current interest. A remarkable succession of Precambrian rocks in Rajasthan, Northwestern India, which may help to shed more light on this question are discussed. Data indicates that the Aravalli sequence has a number of characteristics generally ascribed to active continental margins. Although much more work is required to bear this out, the evidence suggests that the processes operating in such an environment in the early Proterozoic or late Archean were not vastly different from today.

  17. The northern Egyptian continental margin

    NASA Astrophysics Data System (ADS)

    Badawy, Ahmed; Mohamed, Gad; Omar, Khaled; Farid, Walid

    2015-01-01

    Africa displays a variety of continental margin structures, tectonics and sedimentary records. The northern Egyptian continental margin represents the NE portion of the North African passive continental margin. Economically, this region is of great importance as a very rich and productive hydrocarbon zone in Egypt. Moreover, it is characterized by remarkable tectonic setting accompanied by active tectonic processes from the old Tethys to recent Mediterranean. In this article, seismicity of the northern Egyptian continental margin has been re-evaluated for more than 100-years and the source parameters of three recent earthquakes (October 2012, January 2013 and July 2013) have been estimated. Moment tensor inversions of 19th October 2012 and 17th January 2013 earthquakes reveal normal faulting mechanism with strike-slip component having seismic moment of 3.5E16 N m and 4.3E15 N m respectively. The operation of the Egyptian National Seismic Network (ENSN) since the end of 1997 has significantly enhanced the old picture of earthquake activity across northern Egyptian continental margin whereas; the record-ability (annual rate) has changed from 2-events/year to 54-event/year before and after ENSN respectively. The spatial distribution of earthquakes foci indicated that the activity tends to cluster at three zones: Mediterranean Ridge (MR), Nile Cone (NC) and Eratosthenes Seamount (ERS). However, two seismic gaps are reported along Levant Basin (LEV) and Herodotus Basin (HER).

  18. Earth's Decelerating Tectonic Plates

    SciTech Connect

    Forte, A M; Moucha, R; Rowley, D B; Quere, S; Mitrovica, J X; Simmons, N A; Grand, S P

    2008-08-22

    Space geodetic and oceanic magnetic anomaly constraints on tectonic plate motions are employed to determine a new global map of present-day rates of change of plate velocities. This map shows that Earth's largest plate, the Pacific, is presently decelerating along with several other plates in the Pacific and Indo-Atlantic hemispheres. These plate decelerations contribute to an overall, globally averaged slowdown in tectonic plate speeds. The map of plate decelerations provides new and unique constraints on the dynamics of time-dependent convection in Earth's mantle. We employ a recently developed convection model constrained by seismic, geodynamic and mineral physics data to show that time-dependent changes in mantle buoyancy forces can explain the deceleration of the major plates in the Pacific and Indo-Atlantic hemispheres.

  19. MyPlate

    MedlinePLUS

    ... a Budget Create a Grocery Game Plan Shop Smart to Fill Your Cart Prepare Healthy Meals Sample 2-Week Menus Resources for Professionals 10 Tips ... are here Home / MyPlate MyPlate Error message Notice : Undefined index: title ...

  20. Accelerated plate tectonics.

    PubMed

    Anderson, D L

    1975-03-21

    The concept of a stressed elastic lithospheric plate riding on a viscous asthenosphere is used to calculate the recurrence interval of great earthquakes at convergent plate boundaries, the separation of decoupling and lithospheric earthquakes, and the migration pattern of large earthquakes along an arc. It is proposed that plate motions accelerate after great decoupling earthquakes and that most of the observed plate motions occur during short periods of time, separated by periods of relative quiescence. PMID:17799689

  1. The continental drift convection cell

    NASA Astrophysics Data System (ADS)

    Whitehead, J. A.; Behn, Mark D.

    2015-06-01

    Continents on Earth periodically assemble to form supercontinents and then break up again into smaller continental blocks (the Wilson cycle). Previous highly developed numerical models incorporate fixed continents while others indicate that continent movement modulates flow. Our simplified numerical model suggests that continental drift is fundamental. A thermally insulating continent is anchored at its center to mantle flow on an otherwise stress-free surface for infinite Prandtl number cellular convection with constant material properties. Rayleigh numbers exceed 107, while continent widths and chamber lengths approach Earth's values. The Wilson cycle is reproduced by a unique, rugged monopolar "continental drift convection cell." Subduction occurs at the cell's upstream end with cold slabs dipping at an angle beneath the moving continent (as found in many continent/subduction regions on Earth). Drift enhances vertical heat transport up to 30%, especially at the core-mantle boundary, and greatly decreases lateral mantle temperature differences.

  2. Continental crust: a geophysical approach

    SciTech Connect

    Meissner, R.

    1986-01-01

    This book develops an integrated and balanced picture of present knowledge of the continental crust. Crust and lithosphere are first defined, and the formation of crusts as a general planetary phenomenon is described. The background and methods of geophysical studies of the earth's crust and the collection of related geophysical parameters are examined. Creep and friction experiments and the various methods of radiometric age dating are addressed, and geophysical and geological investigations of the crustal structure in various age provinces of the continents are studied. Specific tectonic structures such as rifts, continental margins, and geothermal areas are discussed. Finally, an attempt is made to give a comprehensive view of the evolution of the continental crust and to collect and develop arguments for crustal accretion and recycling. 647 references.

  3. Planet Earth: Plate Tectonics

    E-print Network

    Watts, A. B. "Tony"

    Planet Earth: Plate Tectonics Recommended Books: An Introduction to Our Dynamic Planet (ODP), 2007, ice and sediment for long periods of geological time (>105 a). · Controlled and passive (e, Problem sets etc Lecture 1: Plate Mechanics and Kinematics The Earth comprises 7 major plates and a number

  4. The flat to normal subduction transition study to obtain the Nazca plate morphology using high resolution seismicity data from the Nazca plate in Central Chile

    NASA Astrophysics Data System (ADS)

    Nacif, Silvina; Triep, Enrique G.; Spagnotto, Silvana L.; Aragon, Eugenio; Furlani, Renzo; Álvarez, Orlando

    2015-08-01

    Data from 45 seismological stations mostly temporary were used to obtain an accurate data set of intraslab seismicity of the Nazca subducted plate between 33°S and 35°S. The interest zone located in the transition section where the Nazca plate changes from flat slab north of ~ 33° to normal slab south of that latitude. In addition, the study region is located where the active volcanic arc appears. From a set of earthquakes which were relocated using a grid-search multiple events algorithm we obtained the plate geometry from latitudes of 33°S to 34.5°S and from 60 km to 120 km in depth. The obtained morphology shows notable similarity in its structure to Maipo Orocline revealing some possible strong connection between the overriding plate and the subducting plate. We suggest that the subducted plate at the trench has been deformed in its shape consistently with the Maipo Orocline pattern and its deformation is observed below the interface zone. Our results are consistent with van Keken et al., 2011 models, and based on this the seismicity located between 70 and 120 km is probably related with dehydration processes rather than mechanical processes. From our precise earthquake locations we observed a complete lack of intraslab seismicity below 120 km depth. This valuable finding can be used to better constrain thermal models for the subduction region of Central Chile.

  5. Bioenergetics of Continental Serpentinites

    NASA Astrophysics Data System (ADS)

    Cardace, D.; Meyer-Dombard, D. R.

    2011-12-01

    Serpentinization is the aqueous alteration of ultramafic (Fe- and Mg-rich) rocks, resulting in secondary mineral assemblages of serpentine, brucite, iron oxyhydroxides and magnetite, talc, and possibly carbonate and silica-rich veins and other minor phases-all depending on the evolving pressure-temperature-composition of the system. The abiotic evolution of hydrogen and possibly organic compounds via serpentinization (McCollom and Bach, 2009) highlights the relevance of this geologic process to carbon and energy sources for the deep biosphere. Serpentinization may fuel life over long stretches of geologic time, throughout the global seabed and in exposed, faulted peridotite blocks (as at Lost City Hydrothermal Field, Kelley et al., 2005), and in obducted oceanic mantle units in ophiolites (e.g., Tiago et al., 2004). Relatively little work has been published on life in continental serpentinite settings, though they likely host a unique resident microbiota. In this work, we systematically model the serpentinizing fluid as an environmental niche. Reported field data for high and moderate pH serpentinizing fluids were modeled from Cyprus, the Philippines, Oman, Northern California, New Caledonia, Yugoslavia, Portugal, Italy, Newfoundland Canada, New Zealand, and Turkey. Values for Gibbs Energy of reaction (?Gr), kJ per mole of electrons transferred for a given metabolism, are calculated for each field site. Cases are considered both for (1) modest assumptions of 1 nanomolar hydrogen and 1 micromolar methane, based on unpublished data for a similar northern California field site (Cardace and Hoehler, in prep.) and (2) an upper estimate of 10 nanomolar hydrogen and 500 micromolar methane. We survey the feasibility of microbial metabolisms for key steps in the nitrogen cycle, oxidation of sulfur in pyrite, iron oxidation or reduction reactions, sulfate reduction coupled to hydrogen or methane oxidation, methane oxidation coupled to the reduction of oxygen, and methanogenesis. We find that there is strong energetic yield from most reactions considered, except for transformation of nitrite to nitrate, ammonia to nitrite, ferrous to ferric iron, and carbon dioxide to methane. Laying out foundational metabolic models for microbiological communities sustained by chemosynthesis in this setting (mining energy from ultramafic rocks and chemical systems, not tied to photosynthesis in any way) has enticing relevance to the search for extraterrestrial life, in that similar rocks have been detected on our sibling planet Mars, with transient atmospheric detection of hydrogen and methane (Schulte et al., 2006, Mumma et al., 2009). To a first order, this work explores the intersection of serpentinite groundwater chemistry and bioenergetics to determine what kinds of life can be sustained in these significant subsurface settings. References cited: Kelley et al. 2005. Science 307:1428-1434. McCollom and Bach. 2009. GCA 73:856-875. Mumma et al., 2009. Science 323:1041-1045. Schulte et al., 2006. Astrobiology 6:364-376.

  6. Feedback cycles in planetary evolution including continental growth and mantle hydration, and the impact of life

    NASA Astrophysics Data System (ADS)

    Höning, Dennis; Spohn, Tilman

    2015-04-01

    The Earth's evolution is significantly affected by several intertwined feedback cycles. One of these feedback loops describes the production and erosion of continental crust. Continents are produced in subduction zones, whose total length in turn is determined by the fraction of continental crust. Furthermore, the fraction of continental crust determines the amount of eroded sediments. These sediments eventually enter subduction zones and affect the water transport into the mantle. As the biosphere enhances weathering and erosion of continental crust, we show how life on Earth can enter this feedback cycle and stabilize the present day state of the Earth. A second feedback loop - coupled to the first one - includes the mantle water cycle. Water in the Earth's mantle reduces its viscosity, and therefore increases the speed of mantle convection and plate subduction. Here, we present a thermal evolution model of the Earth which reproduces the present day observations. We investigate the influence of the biosphere during the Earth's evolution on continental growth and mantle hydration. Finally, we discuss implications on the evolution of plate-tectonics planets beyond our solar system.

  7. An improved plating process

    NASA Technical Reports Server (NTRS)

    Askew, John C.

    1994-01-01

    An alternative to the immersion process for the electrodeposition of chromium from aqueous solutions on the inside diameter (ID) of long tubes is described. The Vessel Plating Process eliminates the need for deep processing tanks, large volumes of solutions, and associated safety and environmental concerns. Vessel Plating allows the process to be monitored and controlled by computer thus increasing reliability, flexibility and quality. Elimination of the trivalent chromium accumulation normally associated with ID plating is intrinsic to the Vessel Plating Process. The construction and operation of a prototype Vessel Plating Facility with emphasis on materials of construction, engineered and operational safety and a unique system for rinse water recovery are described.

  8. Spreading continents kick-started plate tectonics.

    PubMed

    Rey, Patrice F; Coltice, Nicolas; Flament, Nicolas

    2014-09-18

    Stresses acting on cold, thick and negatively buoyant oceanic lithosphere are thought to be crucial to the initiation of subduction and the operation of plate tectonics, which characterizes the present-day geodynamics of the Earth. Because the Earth's interior was hotter in the Archaean eon, the oceanic crust may have been thicker, thereby making the oceanic lithosphere more buoyant than at present, and whether subduction and plate tectonics occurred during this time is ambiguous, both in the geological record and in geodynamic models. Here we show that because the oceanic crust was thick and buoyant, early continents may have produced intra-lithospheric gravitational stresses large enough to drive their gravitational spreading, to initiate subduction at their margins and to trigger episodes of subduction. Our model predicts the co-occurrence of deep to progressively shallower mafic volcanics and arc magmatism within continents in a self-consistent geodynamic framework, explaining the enigmatic multimodal volcanism and tectonic record of Archaean cratons. Moreover, our model predicts a petrological stratification and tectonic structure of the sub-continental lithospheric mantle, two predictions that are consistent with xenolith and seismic studies, respectively, and consistent with the existence of a mid-lithospheric seismic discontinuity. The slow gravitational collapse of early continents could have kick-started transient episodes of plate tectonics until, as the Earth's interior cooled and oceanic lithosphere became heavier, plate tectonics became self-sustaining. PMID:25230662

  9. Estimation of continental precipitation recycling

    NASA Technical Reports Server (NTRS)

    Brubaker, Kaye L.; Entekhabi, Dara; Eagleson, P. S.

    1993-01-01

    The total amount of water that precipitates on large continental regions is supplied by two mechanisms: 1) advection from the surrounding areas external to the region and 2) evaporation and transpiration from the land surface within the region. The latter supply mechanism is tantamount to the recycling of precipitation over the continental area. The degree to which regional precipitation is supplied by recycled moisture is a potentially significant climate feedback mechanism and land surface-atmosphere interaction, which may contribute to the persistence and intensification of droughts. Gridded data on observed wind and humidity in the global atmosphere are used to determine the convergence of atmospheric water vapor over continental regions. A simplified model of the atmospheric moisture over continents and simultaneous estimates of regional precipitation are employed to estimate, for several large continental regions, the fraction of precipitation that is locally derived. The results indicate that the contribution of regional evaporation to regional precipitation varies substantially with location and season. For the regions studied, the ratio of locally contributed to total monthly precipitation generally lies between 0. 10 and 0.30 but is as high as 0.40 in several cases.

  10. Seismological studies of the continental lithosphere

    SciTech Connect

    Not Available

    1984-01-01

    The lithosphere,'' as used here in the generally accepted sense, includes the crust of the earth and that part of its upper mantle that, together with the crust, constitute the moving tectonic plates. These are underlain by the more easily deformed asthenosphere'' at a depth on the order of 100 km. The seismic low-velocity zone (LVZ) in the mantle is usually identified with the asthenosphere. We are convinced that a better understanding of the continental lithosphere is vital to society, much of that understanding can only be gained by the application of modern seismological methods, and to accomplish these objectives the United States needs urgently to upgrade its seismological capability. Our aim in this report is to convey to the reader our convictions with the hope that they will be translated into action. We suggest specific studies that should be undertaken now and some actions that, if taken, should realize the full potential of seismological techniques. 110 refs., 35 figs., 1 tab.

  11. The Dauki Thrust Fault and the Shillong Anticline: An incipient plate boundary in NE India?

    NASA Astrophysics Data System (ADS)

    Ferguson, E. K.; Seeber, L.; Steckler, M. S.; Akhter, S. H.; Mondal, D.; Lenhart, A.

    2012-12-01

    The Shillong Massif is a regional contractional structure developing across the Assam sliver of the Indian plate near the Eastern Syntaxis between the Himalaya and Burma arcs. Faulting associated with the Shillong Massif is a major source of earthquake hazard. The massif is a composite basement-cored asymmetric anticline and is 100km wide, >350km long and 1.8km high. The high relief southern limb preserves a Cretaceous-Paleocene passive margin sequence despite extreme rainfall while the gentler northern limb is devoid of sedimentary cover. This asymmetry suggests southward growth of the structure. The Dauki fault along the south limb builds this relief. From the south-verging structure, we infer a regional deeply-rooted north-dipping blind thrust fault. It strikes E-W and obliquely intersects the NE-SW margin of India, thus displaying three segments: Western, within continental India; Central, along the former passive margin; and Eastern, overridden by the west-verging Burma accretion system. We present findings from recent geologic fieldwork on the western and central segments. The broadly warped erosional surface of the massif defines a single anticline in the central segment, east of the intersection with the hinge zone of the continental margin buried by the Ganges-Brahmaputra Delta. The south limb of the anticline forms a steep topographic front, but is even steeper structurally as defined by the Cretaceous-Eocene cover. Below it, Sylhet Trap Basalts intrude and cover Precambrian basement. Dikes, presumably parallel to the rifted margin, are also parallel to the front, suggesting thrust reactivation of rift-related faults. Less competent Neogene clastics are preserved only near the base of the mountain front. Drag folds in these rocks suggest north-vergence and a roof thrust above a blind thrust wedge floored by the Dauki thrust fault. West of the hinge zone, the contractional structure penetrates the Indian continent and bifurcates. After branching into the Dapsi Fault, the Dauki Fault continues westward as the erosion-deposition boundary combined with a belt of N-S shortening. The Dapsi thrust fault strikes WNW across the Shillong massif and dips NNE. It is mostly blind below a topographically expressed fold involving basement and passive-margin cover. Recent fieldwork has shown that the fault is better exposed in the west, where eventually Archean basement juxtaposes folded and steeply dipping fluvial sediment. Both Dauki and Dapsi faults probably continue beyond the Brahmaputra River, where extreme fluvial processes mask them. The area between the two faults is a gentle southward monocline with little or no shortening. Thus uplift of this area stems from slip on the Dauki thrust fault, not from pervasive shortening. The Burma foldbelt overrides the Shillong Plateau and is warped but continuous across the eastern segment of the Dauki fault. The Haflong-Naga thrust front north of the Dauki merges with the fold-thrust belt in the Sylhet basin to the south, despite >150km of differential advance due to much greater advance of the accretionary prism in the basin. Where the Dauki and Haflong-Naga thrusts cross, the thrust fronts are nearly parallel and opposite vergence. We trace a Dauki-related topographic front eastward across the Burma Range. This and other evidence suggest that the Dauki Fault continues below the foldbelt.

  12. Continental transformrift interaction adjacent to a continental margin: The Levant case study

    E-print Network

    Lyakhovsky, Vladimir

    Continental transform­rift interaction adjacent to a continental margin: The Levant case study Amit between major pre-existing fault systems and adjacent continental margins. We review, compile and evaluate to the Levant continental margin. We demonstrate that the continuous Late Cretaceous Carmel­Fari'a­ASG fault

  13. The role of continental growth on the evolution of seafloor spreading

    NASA Astrophysics Data System (ADS)

    Coltice, Nicolas; Rolf, Tobias; Tackley, Paul J.

    2013-04-01

    The area vs. seafloor age distribution is fundamental information to build plate reconstructions and evaluate sea level changes and heat flow evolution. Recent models of spherical mantle convection with plate-like behavior (Tackley, 2000a, 2000b) and continental drift (Rolf and Tackley, 2011) propose solutions compatible with the area vs. age distribution of present-day seafloor spreading (Coltice et al., 2012). Area vs. age distributions computed in convection models display fluctuations of the rate of seafloor spreading. The shape of the distribution varies from uniformly distributed to strongly dominated by younger ages over the course of a calculation. Two factors influence the computed area vs. age distribution: the time-dependence of the rate of production of new seafloor and the continental area that constrains the geometry of ocean basins. Heat flow or sea level strongly depend on the shape of this distribution; hence it is essential to investigate how continental growth could have modified the area vs. age distribution. We will evaluate the role of increasing continental area on the computed seafloor spreading histories. We will show that the average production rate of new seafloor does not vary with continental area, contrarily to fluctuations that increase with continental area. We will show continental growth tends to favour the consumption of progressively younger seafloor. Consequences on heat flow and sea level will be presented. References Coltice, N., Rolf, T., Tackley P.J., Labrosse, S., Dynamic causes of the relation between area and age of the ocean floor, Science 336, 335-338 (2012). Rolf, T., and P. J. Tackley, Focussing of stress by continents in 3D spherical mantle convection with self-consistent plate tectonics, Geophys. Res. Lett., 38 (2011). Tackley, P.J., Self-consistent generation of tectonic plates in time-dependent, three-dimensional mantle convection simulations, part 1: Pseudoplastic yielding, Geoch. Geophys. Geosys. 1 (2000a). Tackley, P.J., Self-consistent generation of tectonic plates in time-dependent, three-dimensional mantle convection simulations, part 2: Strain weakening and asthenosphere, Geochem. Geophys. Geosys. 1, (2000b).

  14. Role of mantle flow in Nubia-Somalia plate divergence

    NASA Astrophysics Data System (ADS)

    Stamps, D. S.; Iaffaldano, G.; Calais, E.

    2015-01-01

    Present-day continental extension along the East African Rift System (EARS) has often been attributed to diverging sublithospheric mantle flow associated with the African Superplume. This implies a degree of viscous coupling between mantle and lithosphere that remains poorly constrained. Recent advances in estimating present-day opening rates along the EARS from geodesy offer an opportunity to address this issue with geodynamic modeling of the mantle-lithosphere system. Here we use numerical models of the global mantle-plates coupled system to test the role of present-day mantle flow in Nubia-Somalia plate divergence across the EARS. The scenario yielding the best fit to geodetic observations is one where torques associated with gradients of gravitational potential energy stored in the African highlands are resisted by weak continental faults and mantle basal drag. These results suggest that shear tractions from diverging mantle flow play a minor role in present-day Nubia-Somalia divergence.

  15. Comparative biogeochemistryecosystemhuman interactions on dynamic continental margins

    E-print Network

    Meyers, Steven D.

    Comparative biogeochemistry­ecosystem­human interactions on dynamic continental margins Lisa A April 2014 Accepted 24 April 2014 Available online 30 April 2014 Regional terms: Continental margins Europe North Atlantic North Pacific Arctic The oceans' continental margins face strong and rapid change

  16. Earthquakes in Stable Continental Crust.

    ERIC Educational Resources Information Center

    Johnston, Arch C.; Kanter, Lisa R.

    1990-01-01

    Discussed are some of the reasons for earthquakes which occur in stable crust away from familiar zones at the ends of tectonic plates. Crust stability and the reactivation of old faults are described using examples from India and Australia. (CW)

  17. Plates and FEM

    NASA Astrophysics Data System (ADS)

    Blaauwendraad, J.

    The word plate is a collective term for systems in which transfer of forces occurs in two directions; walls, deep beams, floors and bridge slabs are all plates. We distinguish two main categories, plates that are loaded in their plane, and plates loaded perpendicularly to their plane. For both categories we give an approach with differential equations, such that a basic understanding is provided and for certain characteristic cases an exact solution can be determined. We follow the displacement method, working with differential equations. In plates that are loaded in their plane, the plane stress state is called the membrane state. All stress components are parallel to the mid- plane of the plate. In special cases we can simply determine the stresses.

  18. Hypervelocity plate acceleration

    SciTech Connect

    Marsh, S.P.; Tan, T.H.

    1991-01-01

    Shock tubes have been used to accelerate 1.5-mm-thick stainless steel plates to high velocity while retaining their integrity. The fast shock tubes are 5.1-cm-diameter, 15.2-cm-long cylinders of PBX-9501 explosive containing a 1.1-cm-diameter cylindrical core of low-density polystyrene foam. The plates have been placed directly in contact with one face of the explosive system. Plane-wave detonation was initiated on the opposite face. A Mach disk was formed in the imploding styrofoam core, which provided the impulse required to accelerate the metal plate to high velocity. Parametric studies were made on this system to find the effect of varying plate metal, plate thickness, foam properties, and addition of a barrel. A maximum plate velocity of 9.0 km/s has been observed. 6 refs., 17 figs.

  19. Plating methods, a survey

    NASA Technical Reports Server (NTRS)

    Berkowitz, J. B.; Emerson, N. H.

    1972-01-01

    Results are presented of a comprehensive search of the literature available, much of which has been generated by the research centers of NASA and its contractors, on plating and coating methods and techniques. Methods covered included: (1) electroplating from aqueous solutions; (2) electroplating from nonaqueous solutions; (3) electroplating from fused-salt baths; (4) electroforming; (5) electroless plating, immersion plating, and mirroring; (6) electroplating from gaseous plasmas; and (7) anodized films and conversion coatings.

  20. Neotectonism along the Atlantic passive continental margin: A review

    NASA Astrophysics Data System (ADS)

    Gardner, Thomas W.

    1989-09-01

    An extensive body of geologic data including the modern state of stress, historical seismicity, surface and subsurface stratigraphy, numerical models of crustal deformation, surficial geomorphic systems, and historical precise leveling and tidal gauge records constrain the style and rate of neotectonic deformation for the Appalachians and Atlantic passive continental margin. There are two major styles of neotectonism in the eastern United States. The northeastern United States is dominated by isostatic uplift and northward migration of peripheral bulge collapse in response to deglaciation. This locally rapid, but decreasing rate of deformation is superimposed upon slower, long-term deformation along the Atlantic margin. Most of the long-term, continental margin deformation is attributed to lithospheric flexuring in response to sediment loading in sedimentary basins (especially the Baltimore Canyon Trough and Carolina Trough), isostatic deformation in response to continental denudation and water loading of the shelf, and stress from far-field plate tectonic sources. Significant deformational features include an uplift anomaly near Cape Fear, N.C.; northward and southward tilting of the Coastal Plain into the Salisbury and Southeast Georgia Embayments respectively; seaward tilting of the Coastal Plain/Piedmont, and a complex pattern of postglacial uplift and later subsidence in the northeast. Estimates of vertical crustal velocities for similar locations vary over several orders of magnitude. Measurement interval bias and systematic leveling errors may account for some of the discrepancies. Evidence for periodic deformation in the eastern United States in substantial and it is possible that historic data indicate a period of accelerated deformation along the Atlantic continental margin.

  1. Acceleration of metal plates

    SciTech Connect

    Marsh, S.P.; McQueen, R.G.; Tan, T.H.

    1989-01-01

    High-explosive charges have been used to accelerate stainless steel plates to velocities of 6-7 km/s. A two-stage system has been used in which the first stage is a plane-wave detonating system that accelerates the plate down a short barrel. The second stage consists of a hollow cylindrical charge through which the moving plate passes. After an adjustable delay this charge is detonated on the outer circumference of the entry side of the charge. Flash radiographs and witness plates show no breakup in the first stage but bowing and frequent breakup in the second stage. 6 figs.

  2. Dynamics of intraoceanic subduction initiation: 2. Suprasubduction zone ophiolite formation and metamorphic sole exhumation in context of absolute plate motions

    NASA Astrophysics Data System (ADS)

    van Hinsbergen, Douwe J. J.; Peters, Kalijn; Maffione, Marco; Spakman, Wim; Guilmette, Carl; Thieulot, Cedric; Plümper, Oliver; Gürer, Derya; Brouwer, Fraukje M.; Aldanmaz, Ercan; Kaymakc?, Nuretdin

    2015-06-01

    Analyzing subduction initiation is key for understanding the coupling between plate tectonics and the underlying mantle. Here we focus on suprasubduction zone (SSZ) ophiolites and how their formation links to intraoceanic subduction initiation in an absolute plate motion frame. SSZ ophiolites form the majority of exposed oceanic lithosphere fragments and are widely recognized to have formed during intraoceanic subduction initiation. Structural, petrological, geochemical, and plate kinematic constraints on their kinematic evolution show that SSZ crust forms at fore-arc spreading centers at the expense of a mantle wedge, thereby flattening the nascent slab. This leads to the typical inverted pressure gradients found in metamorphic soles that form at the subduction plate contact below and during SSZ crust crystallization. Former spreading centers are preserved in forearcs when subduction initiates along transform faults or off-ridge oceanic detachments. We show how these are reactivated when subduction initiates in the absolute plate motion direction of the inverting weakness zone. Upon inception of slab pull due to, e.g., eclogitization, the sole is separated from the slab, remains welded to the thinned overriding plate lithosphere, and can become intruded by mafic dikes upon asthenospheric influx into the mantle wedge. We propound that most ophiolites thus formed under special geodynamic circumstances and may not be representative of normal oceanic crust. Our study highlights how far-field geodynamic processes and absolute plate motions may force intraoceanic subduction initiation as key toward advancing our understanding of the entire plate tectonic cycle.

  3. Site History and Edaphic Features Override the Influence of Plant Species on Microbial Communities in Restored Tidal Freshwater Wetlands

    PubMed Central

    Prasse, Christine E.; Baldwin, Andrew H.

    2015-01-01

    Restored wetland soils differ significantly in physical and chemical properties from their natural counterparts even when plant community compositions are similar, but effects of restoration on microbial community composition and function are not well understood. Here, we investigate plant-microbe relationships in restored and natural tidal freshwater wetlands from two subestuaries of the Chesapeake Bay. Soil samples were collected from the root zone of Typha latifolia, Phragmites australis, Peltandra virginica, and Lythrum salicaria. Soil microbial composition was assessed using 454 pyrosequencing, and genes representing bacteria, archaea, denitrification, methanogenesis, and methane oxidation were quantified. Our analysis revealed variation in some functional gene copy numbers between plant species within sites, but intersite comparisons did not reveal consistent plant-microbe trends. We observed more microbial variations between plant species in natural wetlands, where plants have been established for a long period of time. In the largest natural wetland site, sequences putatively matching methanogens accounted for ?17% of all sequences, and the same wetland had the highest numbers of genes coding for methane coenzyme A reductase (mcrA). Sequences putatively matching aerobic methanotrophic bacteria and anaerobic methane-oxidizing archaea (ANME) were detected in all sites, suggesting that both aerobic and anaerobic methane oxidation are possible in these systems. Our data suggest that site history and edaphic features override the influence of plant species on microbial communities in restored wetlands. PMID:25769832

  4. Optimal Aggregation of Fc?RI with a Structurally Defined Trivalent Ligand Overrides Negative Regulation Driven by Phosphatases

    PubMed Central

    2015-01-01

    To investigate why responses of mast cells to antigen-induced IgE receptor (Fc?RI) aggregation depend nonlinearly on antigen dose, we characterized a new artificial ligand, DF3, through complementary modeling and experimentation. This ligand is a stable trimer of peptides derived from bacteriophage T4 fibritin, each conjugated to a hapten (DNP). We found low and high doses of DF3 at which degranulation of mast cells sensitized with DNP-specific IgE is minimal, but ligand-induced receptor aggregation is comparable to aggregation at an intermediate dose, optimal for degranulation. This finding makes DF3 an ideal reagent for studying the balance of negative and positive signaling in the Fc?RI pathway. We find that the lipid phosphatase SHIP and the protein tyrosine phosphatase SHP-1 negatively regulate mast cell degranulation over all doses considered. In contrast, SHP-2 promotes degranulation. With high DF3 doses, relatively rapid recruitment of SHIP to the plasma membrane may explain the reduced degranulation response. Our results demonstrate that optimal secretory responses of mast cells depend on the formation of receptor aggregates that promote sufficient positive signaling by Syk to override phosphatase-mediated negative regulatory signals. PMID:24784318

  5. Continental collisions and seismic signature

    NASA Astrophysics Data System (ADS)

    Meissner, R.; Wever, Th.; Sadowiak, P.

    1991-04-01

    Reflection seismics in compressional belts has revealed the structure of crustal shortening and thickening processes, showing complex patterns of indentation and interfingering of colliding crusts and subcrustal lithospheres. Generally, in the upper crust large zones of detachments develop, often showing duplexes and 'crocodile' structures. The lower crust from zones of active collision (e.g. Alps, Pyrenees) is characterized by strongly dipping reflections. The base of the crust with the Moho must be continuously equilibrating after orogenic collapse as areas of former continental collision exhibit flat Mohos and subhorizontal reflections. The depth to the Moho increases during collision and decreases after the onset of post-orogenic extension, until finally the crustal root disappears completely together with the erosion of the mountains. Processes, active during continental collisions and orogenic collapse, create distinct structures which are imaged by reflection seismic profiling. Examples are shown and discussed.

  6. Author's personal copy Plate tectonic reconstructions with continuously closing plates$

    E-print Network

    Bower, Dan J.

    Author's personal copy Plate tectonic reconstructions with continuously closing plates$ Michael May 2011 Keywords: Geodynamics Plate tectonics a b s t r a c t We present a new algorithm for modeling margins and plates, traditional global plate tectonic reconstructions have become inadequate

  7. Neogene rotations and quasicontinuous deformation of the Pacific Northwest continental margin

    SciTech Connect

    England, P. ); Wells, R.E. )

    1991-10-01

    Paleomagnetically determined rotations about vertical axes of 15 to 12 Ma flows of the Miocene Columbia River Basalt Group of Oregon and Washington decrease smoothly with distance from the plate margin, consistent with a simple physical model for continental deformation that assumes the lithosphere behaves as a thin layer of fluid. The average rate of northward translation of the continental margin since 15 Ma calculated from the rotations, using this model, is about 15 mm/year, which suggests that much of the tangential motion between the Juan de Fuca and North American plates since middle Miocene time has been taken up by deformation of North America. The fluid-like character of the large-scale deformation implies that the brittle upper crust follows the motions of the deeper parts of the lithosphere.

  8. Blue Willow Story Plates

    ERIC Educational Resources Information Center

    Fontes, Kris

    2009-01-01

    In the December 1997 issue of "SchoolArts" is a lesson titled "Blue Willow Story Plates" by Susan Striker. In this article, the author shares how she used this lesson with her middle-school students many times over the years. Here, she describes a Blue Willow plate painting project that her students made.

  9. Plate Tectonics Prof. Thomas Herring

    E-print Network

    Herring, Thomas

    1 Plate Tectonics Prof. Thomas Herring MIT 05/14/02 Lexington HS Plate tectonics 2 Contact/14/02 Lexington HS Plate tectonics 3 Overview · Development of the Plate tectonic theory · Geological Data ­ Sea-floor spreading ­ Fault types from earthquakes ­ Transform faults ­ Today's measurements of plate tectonics 05

  10. Plating To Reinforce Welded Joints

    NASA Technical Reports Server (NTRS)

    Otousa, J. E.

    1982-01-01

    Electrodeposition used to strengthen welded joints gouged, nicked, or suffered other mechanical damage. Plating cell, typically of acrylic plastic such as poly (Methylmetacrylate), is assembled around part to be plated. Areas not to be plated are masked with plater's tape. Weld area is plated in standard nickel-plating process.

  11. Biotic vs. abiotic Earth: A model for mantle hydration and continental coverage

    NASA Astrophysics Data System (ADS)

    Höning, Dennis; Hansen-Goos, Hendrik; Airo, Alessandro; Spohn, Tilman

    2014-08-01

    The origin and evolution of life has undoubtedly had a major impact on the evolution of Earth's oceans and atmosphere. Recent studies have suggested that bioactivity may have had an even deeper impact and may have caused a change in the redox-state of the mantle and provided a path for the formation of continents. We here present a numerical model that assumes that bioactivity increases the continental weathering rate and that relates the sedimentation rate to the growth of continents and to the hydration of the mantle using elements of plate tectonics and mantle convection. The link between these factors is provided by assuming that an increase of the thickness of the sedimentary layer of low permeability on top of a subducting oceanic slab will reduce its dewatering upon subduction. This in turn leads to a greater availability of water in the source region of andesitic partial melt, resulting in an enhanced rate of continental crust production, and to an increased regassing rate of the mantle. The mantle in turn responds by reducing the mantle viscosity while increasing the convective circulation rate, degassing rate and plate speed. We use parameters that are observed for the present Earth and gauge uncertain parameters such that the present day continental surface area and mantle water concentration can be obtained. Our steady state results show two stable fixed points in a phase plane defined by the fractional continental surface area and the water concentration in the mantle, one of them pertaining to a wet mantle and the continental surface area of the present day Earth, and the other to a dry mantle and a small continental surface area. When the sedimentation rate is reduced, both fixed points move and the area of attraction of the latter fixed point increases systematically. We conclude that if the presence of life has increased the continental weathering rate, as is widely believed, and led to the observables of a wet mantle and a continental surface coverage of roughly 40%, an abiotic Earth would likely have evolved toward a dry mantle with a small continental surface area instead.

  12. Bile acids override steatosis in farnesoid X receptor deficient mice in a model of non-alcoholic steatohepatitis

    SciTech Connect

    Wu, Weibin; Liu, Xijun; Peng, Xiaomin; Xue, Ruyi; Ji, Lingling; Shen, Xizhong; Chen, She; Gu, Jianxin; Zhang, Si

    2014-05-23

    Highlights: • FXR deficiency enhanced MCD diet-induced hepatic fibrosis. • FXR deficiency attenuated MCD diet-induced hepatic steatosis. • FXR deficiency repressed genes involved in fatty acid uptake and triglyceride accumulation. - Abstract: Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver diseases, and the pathogenesis is still not well known. The farnesoid X receptor (FXR) is a member of the nuclear hormone receptor superfamily and plays an essential role in maintaining bile acid and lipid homeostasis. In this study, we study the role of FXR in the pathogenesis of NFALD. We found that FXR deficient (FXR{sup ?/?}) mice fed methionine- and choline-deficient (MCD) diet had higher serum ALT and AST activities and lower hepatic triglyceride levels than wild-type (WT) mice fed MCD diet. Expression of genes involved in inflammation (VCAM-1) and fibrosis (?-SMA) was increased in FXR{sup ?/?} mice fed MCD diet (FXR{sup ?/?}/MCD) compared to WT mice fed MCD diet (WT/MCD). Although MCD diet significantly induced hepatic fibrosis in terms of liver histology, FXR{sup ?/?}/MCD mice showed less degree of hepatic steatosis than WT/MCD mice. Moreover, FXR deficiency synergistically potentiated the elevation effects of MCD diet on serum and hepatic bile acids levels. The super-physiological concentrations of hepatic bile acids in FXR{sup ?/?}/MCD mice inhibited the expression of genes involved in fatty acid uptake and triglyceride accumulation, which may be an explanation for less steatosis in FXR{sup ?/?}/MCD mice in contrast to WT/MCD mice. These results suggest that hepatic bile acids accumulation could override simple steatosis in hepatic injury during the progression of NAFLD and further emphasize the role of FXR in maintaining hepatic bile acid homeostasis in liver disorders and in hepatic protection.

  13. Mirrored Prominent Deck B Phenomenon: Frequent Small Losses Override Infrequent Large Gains in the Inverted Iowa Gambling Task

    PubMed Central

    Lin, Ching-Hung; Song, Tzu-Jiun; Lin, Yu-Kai; Chiu, Yao-Chu

    2012-01-01

    Since Bechara et al. pioneered its development, the Iowa Gambling Task (IGT) has been widely applied to elucidate decision behavior and medial prefrontal function. Although most decision makers can hunch the final benefits of IGT, ventromedial prefrontal lesions generate a myopic choice pattern. Additionally, the Iowa group developed a revised IGT (inverted IGT, iIGT) to confirm the IGT validity. Each iIGT trial was generated from the trial of IGT by multiplying by a “?” to create an inverted monetary value. Thus, bad decks A and B in the IGT become good decks iA and iB in the iIGT; additionally, good decks C and D in the IGT become bad decks iC and iD in the iIGT. Furthermore, IGT possessed mostly the gain trials, and iIGT possessed mainly the loss trials. Therefore, IGT is a frequent-gain–based task, and iIGT is a frequent-loss–based task. However, a growing number of IGT-related studies have identified confounding factors in IGT (i.e., gain-loss frequency), which are demonstrated by the prominent deck B phenomenon (PDB phenomenon). Nevertheless, the mirrored PDB phenomenon and guiding power of gain-loss frequency in iIGT have seldom been reexamined. This experimental finding supports the prediction based on gain-loss frequency. This study identifies the mirrored PDB phenomenon. Frequent small losses override occasional large gains in deck iB of the iIGT. Learning curve analysis generally supports the phenomenon based on gain-loss frequency rather than final outcome. In terms of iIGT and simple versions of iIGT, results of this study demonstrate that high-frequency loss, rather than a satisfactory final outcome, dominates the preference of normal decision makers under uncertainty. Furthermore, normal subjects prefer “no immediate punishment” rather than “final reward” under uncertainty. PMID:23091612

  14. Bile acids override steatosis in farnesoid X receptor deficient mice in a model of non-alcoholic steatohepatitis.

    PubMed

    Wu, Weibin; Liu, Xijun; Peng, Xiaomin; Xue, Ruyi; Ji, Lingling; Shen, Xizhong; Chen, She; Gu, Jianxin; Zhang, Si

    2014-05-23

    Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver diseases, and the pathogenesis is still not well known. The farnesoid X receptor (FXR) is a member of the nuclear hormone receptor superfamily and plays an essential role in maintaining bile acid and lipid homeostasis. In this study, we study the role of FXR in the pathogenesis of NFALD. We found that FXR deficient (FXR(-/-)) mice fed methionine- and choline-deficient (MCD) diet had higher serum ALT and AST activities and lower hepatic triglyceride levels than wild-type (WT) mice fed MCD diet. Expression of genes involved in inflammation (VCAM-1) and fibrosis (?-SMA) was increased in FXR(-/-) mice fed MCD diet (FXR(-/-)/MCD) compared to WT mice fed MCD diet (WT/MCD). Although MCD diet significantly induced hepatic fibrosis in terms of liver histology, FXR(-/-)/MCD mice showed less degree of hepatic steatosis than WT/MCD mice. Moreover, FXR deficiency synergistically potentiated the elevation effects of MCD diet on serum and hepatic bile acids levels. The super-physiological concentrations of hepatic bile acids in FXR(-/-)/MCD mice inhibited the expression of genes involved in fatty acid uptake and triglyceride accumulation, which may be an explanation for less steatosis in FXR(-/-)/MCD mice in contrast to WT/MCD mice. These results suggest that hepatic bile acids accumulation could override simple steatosis in hepatic injury during the progression of NAFLD and further emphasize the role of FXR in maintaining hepatic bile acid homeostasis in liver disorders and in hepatic protection. PMID:24747563

  15. Earthquakes and plate tectonics.

    USGS Publications Warehouse

    Spall, H.

    1982-01-01

    Earthquakes occur at the following three kinds of plate boundary: ocean ridges where the plates are pulled apart, margins where the plates scrape past one another, and margins where one plate is thrust under the other. Thus, we can predict the general regions on the earth's surface where we can expect large earthquakes in the future. We know that each year about 140 earthquakes of magnitude 6 or greater will occur within this area which is 10% of the earth's surface. But on a worldwide basis we cannot say with much accuracy when these events will occur. The reason is that the processes in plate tectonics have been going on for millions of years. Averaged over this interval, plate motions amount to several mm per year. But at any instant in geologic time, for example the year 1982, we do not know, exactly where we are in the worldwide cycle of strain build-up and strain release. Only by monitoring the stress and strain in small areas, for instance, the San Andreas fault, in great detail can we hope to predict when renewed activity in that part of the plate tectonics arena is likely to take place. -from Author

  16. Thermal models pertaining to continental growth

    NASA Technical Reports Server (NTRS)

    Morgan, Paul; Ashwal, Lew

    1988-01-01

    Thermal models are important to understanding continental growth as the genesis, stabilization, and possible recycling of continental crust are closely related to the tectonic processes of the earth which are driven primarily by heat. The thermal energy budget of the earth was slowly decreasing since core formation, and thus the energy driving the terrestrial tectonic engine was decreasing. This fundamental observation was used to develop a logic tree defining the options for continental growth throughout earth history.

  17. Early breakup of Gondwana: constraints from global plate motion models

    NASA Astrophysics Data System (ADS)

    Seton, Maria; Zahirovic, Sabin; Williams, Simon; Whittaker, Joanne; Gibbons, Ana; Muller, Dietmar; Brune, Sascha; Heine, Christian

    2015-04-01

    Supercontinent break-up and amalgamation is a fundamental Earth cycle, contributing to long-term sea-level fluctuations, species diversity and extinction events, long-term greenhouse-icehouse cycles and changes in the long-wavelength density structure of the mantle. The most recent and best-constrained example involves the fragmentation of Gondwana, starting with rifting between Africa/Madagascar and Antarctica in the Early Jurassic and ending with the separation of the Lord Howe microcontinental blocks east of Australia in the Late Cretaceous. Although the first order configuration of Gondwana within modern reconstructions appears similar to that first proposed by Wegener a century ago, recent studies utilising a wealth of new geophysical and geological data provide a much more detailed picture of relative plate motions both during rifting and subsequent seafloor spreading. We present our latest global plate motion model that includes extensive, new regional analyses. These include: South Atlantic rifting, which started at 150 Ma and propagated into cratonic Africa by 145 Ma (Heine et al., 2013); rifting and early seafloor spreading between Australia, India and Antarctica, which reconciles the fit between Broken Ridge-Kergulean Plateau and the eastern Tasman region (Whittaker et al., 2013); rifting of continental material from northeastern Gondwana and its accretion onto Eurasia and SE Asia including a new model of microcontinent formation and early seafloor spreading in the eastern Indian Ocean (Gibbons et al., 2012; 2013; in review; Williams et al., 2013; Zahirovic et al., 2014); and a new model for the isolation of Zealandia east of Australia, with rifting initiating at 100 Ma until the start of seafloor spreading in the Tasman Sea at ~85 Ma (Williams et al., in prep). Using these reconstructions within the open-source GPlates software, accompanied by a set of evolving plates and plate boundaries, we can explore the factors that govern the behavior of plate motions during supercontinent break-up and subsequent dispersal. For example, a global analysis of absolute plate velocities over the past 200 million years shows that plates dominated by continental material and bounded by transforms and mid-ocean ridge segments, as is characteristic of plates involved in Gondwana break-up, have average speeds of ~2.6-2.8 cm/yr RMS. In contrast, oceanic plates surrounded by subduction have average speeds of ~8.5 cm/yr RMS. An exception, however, is the rapid motion of India (~18 cm/yr RMS) in the Paleocene preceding its collision with Eurasia, which suggests that plates with continental and cratonic keels can exhibit short-lived (~10 Myr) accelerations resulting from a combination of plume head arrival effects and other complementary plate boundary forces (i.e., slab pull and ridge push). In another example, our reconstructions illustrate that a spectrum of rifting styles from orthogonal to oblique is present during rifting, rather than dominantly orthogonal as often assumed. Although our approach has so far been limited to one supercontinent cycle, these types of models can be extended to cover the entire Phanerozoic, capturing continental rifting and plate behavior over several supercontinent cycles.

  18. High loading uranium plate

    SciTech Connect

    Wiencek, T.C.; Domagala, R.F.; Thresh, H.R.

    1990-10-16

    Two embodiments of a high uranium fuel plate are disclosed which contain a meat comprising structured uranium compound confined between a pari of diffusion bonded ductile metal cladding plates uniformly covering the meat, the meat hiving a uniform high fuel loading comprising a content of uranium compound greater than about 45 Vol. % at a porosity not greater than about 10 Vol. %. In a first embodiment, the meat is a plurality of parallel wires of uranium compound. In a second embodiment, the meat is a dispersion compact containing uranium compound. The fuel plates are fabricated by a hot isostatic pressing process.

  19. "Dynamic Kinematics": Towards Linking Earth's Plate Motions to the Evolution of Global Mantle Flow

    NASA Astrophysics Data System (ADS)

    Rolf, T.; Tackley, P. J.

    2014-12-01

    The theory of plate tectonics has been one of the major breakthroughs in solid-Earth science and is capable of explaining many of the tectonic processes on present-day Earth. Moreover, it allows us to reconstruct Earth's tectonic history back until times of the supercontinent Pangaea and thus improves our understanding how Earth developed to its present state. However, plate tectonics remains a kinematic theory that does not sufficiently incorporate the balance of forces in the Earth's mantle and can thus not explain the motion of Earth's tectonic plates in a dynamically consistent manner. Here, we use fully dynamic models of mantle convection in global spherical geometry to overcome this issue. These models include tectonic plates self-consistently evolving from mantle flow (using a viscoplastic rheology) as well as continental drift. We analyze the evolution of plate velocities over time periods considerably longer than those covered by modern plate reconstructions. We observe significant changes in plate velocity magnitude and direction over timescales relevant for the Earth. While some of these plate reorganizations appear to be rather local affecting only very few plates, others seem to have more global consequences. We characterize the variety of different reorganizations based on features of modeled spreading centers and subduction zones, for instance the flux of slab material into the lower mantle. Initial results suggest that global changes in plate configuration correlate with phases of major slab penetration into the lower mantle, while changes on individual plate-scale do not necessarily do so.

  20. Subduction and Plate Edge Tectonics in the Southern Caribbean

    NASA Astrophysics Data System (ADS)

    Levander, A.; Schmitz, M.; Niu, F.; Bezada, M. J.; Miller, M. S.; Masy, J.; Ave Lallemant, H. G.; Pindell, J. L.

    2012-12-01

    The southern Caribbean plate boundary consists of a subduction zone at at either end connected by a strike-slip fault system: In the east at the Lesser Antilles subduction zone, the Atlantic part of the South American plate subducts beneath the Caribbean. In the north and west in the Colombia basin, the Caribbean subducts under South America. In a manner of speaking, the two plates subduct beneath each other. Finite-frequency teleseismic P-wave tomography confirms this, imaging the Atlantic and the Caribbean subducting steeply in opposite directions to transition zone depths under northern South America (Bezada et al, 2010). The two subduction zones are connected by the El Pilar-San Sebastian strike-slip fault system, a San Andreas scale system that has been cut off at the Bocono fault, the southeastern boundary of the Maracaibo block. A variety of seismic probes identify where the two plates tear as they begin to subduct (Niu et al, 2007; Clark et al., 2008; Miller et al. 2009; Growdon et al., 2009; Huang et al., 2010; Masy et al., 2011). The El Pilar system forms at the southeastern corner of the Antilles subduction zone with the Atlantic plate tearing from South America. The deforming plate edges control mountain building and basin formation at the eastern end of the strike-slip system. In northwestern South America the Caribbean plate very likely also tears, as its southernmost element subducts at shallow angles under northernmost Colombia and the northern, nonsubducting part underthrusts the continental edge. The subducting segment rapidly descends to transition zone depths under Lake Maracaibo (Bezada et al., 2010). We believe that the flat slab produces the Merida Andes, the Perija, and the Santa Marta ranges. The nonsubducting part of the Caribbean plate underthrusts northern Venezuela to about the width of the coastal mountains (Miller et al., 2009), where the plate edge supports the coastal mountains, and controls continuing deformation.

  1. Maps of Moho structure under the Arabian plate and margins

    NASA Astrophysics Data System (ADS)

    Mechie, J.; Ben-Avraham, Z.; Weber, M. H.; Goetze, H.; Koulakov, I.; Mohsen, A.; Stiller, M.

    2012-12-01

    In this study two new maps of Moho depths beneath the Arabian plate and margins are presented. The first map is based on the combined gravity model, EIGEN 06C, which includes data from satellite missions and ground-based studies, and thus covers the whole region between 31°E and 60°E and between 12°N and 36°N. The second map is based on seismological and ground-based gravity data and shows gaps due to lack of data coverage especially in the interior of the Arabian plate. Beneath the interior of the Arabian plate the Moho lies between 32 and 45 km depth below sea level (b.s.l.). There is a tendency for higher Pn and Sn velocities beneath the northeastern parts of the plate interior with respect to the southwestern parts of the plate interior. Across the northern, destructive margin with the Eurasian plate, the Moho depths increase to over 50 km beneath the Zagros mountains. Across the conservative western margin, the Dead Sea Transform (DST), Moho depths decrease from almost 40 km beneath the highlands east of the DST to about 22-23 km under the southeastern Mediterranean Sea. This decrease seems to be modulated by a slight depression in the Moho beneath the southern DST. The constructive southwestern and southeastern margins of the Arabian plate also show the Moho shallowing from the plate interior towards the plate boundaries. This shallowing is most abrupt where sea-floor spreading is occurring along the southern Red Sea margin between 17°N and 21°N and across the Gulf of Aden margin at about 54°E. In contrast, along the northern Red Sea margin at 26°N where sea-floor spreading probably has not yet started, the shallowing is smoother, comparable with the smooth transitions in Moho depths beneath the eastern U.S. or Namibian Atlantic continental margins.

  2. 26 CFR 1.638-1 - Continental Shelf areas.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 26 Internal Revenue 7 2014-04-01 2013-04-01 true Continental Shelf areas. 1.638-1 Section 1.638-1...) INCOME TAXES (CONTINUED) Continental Shelf Areas § 1.638-1 Continental Shelf areas. (a) General rule. For.... The terms Continental Shelf of the United States and Continental Shelf of a possession of the...

  3. 26 CFR 1.638-1 - Continental Shelf areas.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 26 Internal Revenue 7 2012-04-01 2012-04-01 false Continental Shelf areas. 1.638-1 Section 1.638-1...) INCOME TAXES (CONTINUED) Continental Shelf Areas § 1.638-1 Continental Shelf areas. (a) General rule. For.... The terms Continental Shelf of the United States and Continental Shelf of a possession of the...

  4. 26 CFR 1.638-1 - Continental Shelf areas.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 26 Internal Revenue 7 2011-04-01 2009-04-01 true Continental Shelf areas. 1.638-1 Section 1.638-1...) INCOME TAXES (CONTINUED) Continental Shelf Areas § 1.638-1 Continental Shelf areas. (a) General rule. For.... The terms Continental Shelf of the United States and Continental Shelf of a possession of the...

  5. 26 CFR 1.638-1 - Continental Shelf areas.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 26 Internal Revenue 7 2010-04-01 2010-04-01 true Continental Shelf areas. 1.638-1 Section 1.638-1...) INCOME TAXES (CONTINUED) Continental Shelf Areas § 1.638-1 Continental Shelf areas. (a) General rule. For.... The terms Continental Shelf of the United States and Continental Shelf of a possession of the...

  6. 26 CFR 1.638-1 - Continental Shelf areas.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 26 Internal Revenue 7 2013-04-01 2013-04-01 false Continental Shelf areas. 1.638-1 Section 1.638-1...) INCOME TAXES (CONTINUED) Continental Shelf Areas § 1.638-1 Continental Shelf areas. (a) General rule. For.... The terms Continental Shelf of the United States and Continental Shelf of a possession of the...

  7. Postcollisional mafic igneous rocks record crust-mantle interaction during continental deep subduction.

    PubMed

    Zhao, Zi-Fu; Dai, Li-Qun; Zheng, Yong-Fei

    2013-01-01

    Findings of coesite and microdiamond in metamorphic rocks of supracrustal protolith led to the recognition of continental subduction to mantle depths. The crust-mantle interaction is expected to take place during subduction of the continental crust beneath the subcontinental lithospheric mantle wedge. This is recorded by postcollisional mafic igneous rocks in the Dabie-Sulu orogenic belt and its adjacent continental margin in the North China Block. These rocks exhibit the geochemical inheritance of whole-rock trace elements and Sr-Nd-Pb isotopes as well as zircon U-Pb ages and Hf-O isotopes from felsic melts derived from the subducted continental crust. Reaction of such melts with the overlying wedge peridotite would transfer the crustal signatures to the mantle sources for postcollisional mafic magmatism. Therefore, postcollisonal mafic igneous rocks above continental subduction zones are an analog to arc volcanics above oceanic subduction zones, providing an additional laboratory for the study of crust-mantle interaction at convergent plate margins. PMID:24301173

  8. Postcollisional mafic igneous rocks record crust-mantle interaction during continental deep subduction

    PubMed Central

    Zhao, Zi-Fu; Dai, Li-Qun; Zheng, Yong-Fei

    2013-01-01

    Findings of coesite and microdiamond in metamorphic rocks of supracrustal protolith led to the recognition of continental subduction to mantle depths. The crust-mantle interaction is expected to take place during subduction of the continental crust beneath the subcontinental lithospheric mantle wedge. This is recorded by postcollisional mafic igneous rocks in the Dabie-Sulu orogenic belt and its adjacent continental margin in the North China Block. These rocks exhibit the geochemical inheritance of whole-rock trace elements and Sr-Nd-Pb isotopes as well as zircon U-Pb ages and Hf-O isotopes from felsic melts derived from the subducted continental crust. Reaction of such melts with the overlying wedge peridotite would transfer the crustal signatures to the mantle sources for postcollisional mafic magmatism. Therefore, postcollisonal mafic igneous rocks above continental subduction zones are an analog to arc volcanics above oceanic subduction zones, providing an additional laboratory for the study of crust-mantle interaction at convergent plate margins. PMID:24301173

  9. Continental Shelf Research 27 (2007) 18011819 Respiration and denitrification in permeable continental shelf

    E-print Network

    Jahnke, Richard A.

    2007-01-01

    Continental Shelf Research 27 (2007) 1801­1819 Respiration and denitrification in permeable continental shelf deposits on the South Atlantic Bight: Rates of carbon and nitrogen cycling from sediment columns packed with southeastern United States continental shelf sands, with high permeability (4.66 Â 10À

  10. Tectonic Plate Movement.

    ERIC Educational Resources Information Center

    Landalf, Helen

    1998-01-01

    Presents an activity that employs movement to enable students to understand concepts related to plate tectonics. Argues that movement brings topics to life in a concrete way and helps children retain knowledge. (DDR)

  11. Reduction of astrometric plates

    NASA Technical Reports Server (NTRS)

    Stock, J.

    1984-01-01

    A rapid and accurate method for the reduction of comet or asteroid plates is described. Projection equations, scale length correction, rotation of coordinates, linearization, the search for additional reference stars, and the final solution are examined.

  12. Assessing Why Plates Move

    NASA Astrophysics Data System (ADS)

    Bowin, C.

    2004-05-01

    Over the past 42 years, since the first realization that the ocean floors are youthful (not ancient relics from early in the history of the Earth), and the concomitant development of the Theory of Plate Tectonics, an understanding of the observed motions has been sought. Speculation and analyses have concentrated upon three principal forces: ridge push, subducted slab pull, and sub-lithosphere traction from Earth's internal convection motions, with forces due to subducted slabs dominating. Some researchers have speculated that the motions of plates are random, however, the author in 1974 noting that a pattern of spreading between Australia and Antarctica progressed in time westward across the Indian Ocean, and then continued opening the Gulf of Aden and on into the Red Sea concluded that plate motions were not random. Recent evidence from the broad exposure of upper mantle rocks (peridotite) on the ocean floor at the ultra slow spreading Gakkel Ridge in the Arctic Ocean, indicate to the author that there is no ridge push force. Thus, seafloor-spreading sites are reactive features, not driving force contributors. A reconstruction of past absolute plate motions shows that sites of subduction have remained near their same arc/trench locations, but spreading centers and transform faults have moved about. Hence, confirming that sites of subduction are an important control for plate motions. The author's analysis of the positive residual geoid anomalies (spherical harmonic degrees 4-10) over arc/trench systems of the world, suggested forces of 2.8x1020-3.2x1021 N are available to drive plate tectonics. Some studies have proposed models for how such forces might couple to plate motions, but none have yet been definitive. New clues are being sought from the unique change in absolute plate motion of the Pacific plate, at about 46-48 Ma ago: from a northward subduction beneath the Aleutian trench/arc during the time when the Emperor seamount chain was formed, to its' present north of west motion subducting beneath the western Pacific trench/arcs, the direction during which the Hawaiian volcanic trend has been formed. Only the Pacific plate shows such a major change in absolute plate motion at that time, and the author takes this change, in but a few million years, to indicate that masses linked to slab subduction are more important than traction from an underlying mantle convection.

  13. The Continental Drift Convection Cell

    NASA Astrophysics Data System (ADS)

    Whitehead, J. A.; Behn, M. D.

    2014-12-01

    Continents on Earth periodically assemble to form supercontinents, and then break up again into smaller continental blocks (the Wilson Cycle). Highly developed but realistic numerical models cannot resolve if continents respond passively to mantle convection or whether they modulate flow. Our simplified numerical model addresses this problem: A thermally insulating continent floats on a stress-free surface for infinite Prandtl number cellular convection with constant material properties in a chamber 8 times longer than its depth. The continent moves back and forth across the chamber driven by a "continental drift convection cell" of a form not previously described. Subduction exists at the upstream end with cold slabs dipping at an angle beneath the moving continent. Fluid moves with the continent in the upper region of this cell with return flow near the bottom. Many continent/subduction regions on Earth have these features. The drifting cell enhances vertical heat transport by approximately 30% compared to a fixed continent, especially at the core-mantle boundary, and significantly decreases lateral mantle temperature differences. However, continent drift or fixity has smaller effects on profiles of horizontally averaged temperature. Although calculations are done at Rayleigh numbers lower than expected for Earth's mantle (2x105 and 106), the drift speed extrapolates to reasonable Wilson Cycle speeds for larger Ra.

  14. Positive battery plate

    NASA Technical Reports Server (NTRS)

    Rowlette, John R. (Inventor)

    1985-01-01

    The power characteristics of a lead acid battery are improved by incorporating a dispersion of 1 to 10% by weight of a thermodynamically stable conductivity additive, such as conductive tin oxide coated glass fibers (34) of filamentary glass wool (42) in the positive active layer (32) carried on the grid (30) of the positive plate (16). Positive plate potential must be kept high enough to prevent reduction of the tin oxide to tin by utilizing an oversized, precharged positive paste.

  15. Fractal multifiber microchannel plates

    NASA Technical Reports Server (NTRS)

    Cook, Lee M.; Feller, W. B.; Kenter, Almus T.; Chappell, Jon H.

    1992-01-01

    The construction and performance of microchannel plates (MCPs) made using fractal tiling mehtods are reviewed. MCPs with 40 mm active areas having near-perfect channel ordering were produced. These plates demonstrated electrical performance characteristics equivalent to conventionally constructed MCPs. These apparently are the first MCPs which have a sufficiently high degree of order to permit single channel addressability. Potential applications for these devices and the prospects for further development are discussed.

  16. Tectonic structure and evolution of the Atlantic continental margin

    SciTech Connect

    Klitgord, K.D.; Schouten, H.; Hutchinson, D.R.

    1985-01-01

    The Atlantic continental margin developed across the boundary between continental and oceanic crust as rifting and then sea-floor spreading broke apart and separated the North American and African plates, forming the Atlantic Ocean Basin. Continental rifting began in Late Triassic with reactivation of Paleozoic thrust faults as normal faults and with extension across a broad zone of subparallel rift basins. Extension became localized in Early to Middle Jurassic along the zone that now underlies the large marginal basins, and other rift zones, such as the Newark, Hartford, and Fundy basins, were abandoned. Rifting and crustal stretching between the two continents gave way to sea-floor spreading Middle Jurassic and the formation of oceanic crust. This tectonic evolution resulted in formation of distinctive structural features. The marginal basins are underlain by a thinner crust and contain a variety of fault-controlled structures, including half-grabens, seaward- and landward-tilted blocks, faults that die out within the crust, and faults that penetrate the entire crust. This variable structure probably resulted from the late Triassic-Early Jurassic pattern of normal, listric, and antithetic faults that evolved from the Paleozoic thrust fault geometry. The boundary between marginal basins and oceanic crust is marked approximately by the East Coast Magnetic Anomaly (ECMA). A major basement fault is located in the Baltimore Canyon trough at the landward edge of the ECMA and a zone of seaward dipping reflectors is found just seaward of the ECMA off Georges Bank. The fracture zone pattern in Mesozoic oceanic crust can be traced landward to the ECMA.

  17. Development of topography in 3-D continental-collision models

    NASA Astrophysics Data System (ADS)

    Pusok, A. E.; Kaus, Boris J. P.

    2015-05-01

    Understanding the formation and evolution of high mountain belts, such as the Himalayas and the adjacent Tibetan Plateau, has been the focus of many tectonic and numerical models. Here we employ 3-D numerical simulations to investigate the role that subduction, collision, and indentation play on lithosphere dynamics at convergent margins, and to analyze the conditions under which large topographic plateaus can form in an integrated lithospheric and upper mantle-scale model. Distinct dynamics are obtained for the oceanic subduction side (trench retreat, slab rollback) and the continental-collision side (trench advance, slab detachment, topographic uplift, lateral extrusion). We show that slab pull alone is insufficient to generate high topography in the upper plate, and that external forcing and the presence of strong blocks such as the Tarim Basin are necessary to create and shape anomalously high topographic fronts and plateaus. Moreover, scaling is used to predict four different modes of surface expression in continental-collision models: (I) low-amplitude homogeneous shortening, (II) high-amplitude homogeneous shortening, (III) Alpine-type topography with topographic front and low plateau, and (IV) Tibet-Himalaya-type topography with topographic front and high plateau. Results of semianalytical models suggest that the Argand number governs the formation of high topographic fronts, while the amplitude of plateaus is controlled by the initial buoyancy ratio of the upper plate. Applying these results to natural examples, we show that the Alps belong to regime (III), the Himalaya-Tibet to regime (IV), whereas the Andes-Altiplano fall at the boundary between regimes (III) and (IV).

  18. Cenozoic evolution of the Antarctic Peninsula continental margin

    SciTech Connect

    Anderson, J.B. )

    1990-05-01

    Cenozoic evolution of the Antarctic Peninsula continental margin has involved a series of ridge (Aluk Ridge)-trench collisions between the Pacific and Antarctic plates. Subduction occurred episodically between segments of the Pacific plate that are bounded by major fracture zones. The age of ridge-trench collisions decreases from south to north along the margin. The very northern part of the margin, between the Hero and Shackleton fracture zones, has the last surviving Aluk-Antarctic spreading ridge segments and the only remaining trench topography. The sedimentary cover on the northern margin is relatively thin generally less than 1.5 km, thus providing a unique setting in which to examine margin evolution using high resolution seismic methods. Over 5,000 km of high resolution (water gun) seismic profiles were acquired from the Antarctic Peninsula margin during four cruises to the region. The margin is divided into discrete fracture-zone-bounded segments; each segment displays different styles of development. Highly tectonized active margin sequences have been buried beneath a seaward-thickening sediment wedge that represents the passive stage of margin development Ice caps, which have existed in the Antarctic Peninsula region since at least the late Oligocene, have advanced onto the continental shelf on numerous occasions, eroding hundreds of meters into the shelf and depositing a thick sequence of deposits characterized by till tongues and glacial troughs. Glacial erosion has been the main factor responsible for overdeepening of the shelf; isostasy is of secondary importance. As the shelf was lowered by glacial erosion, it was able to accommodate thicker and more unstable marine ice sheets. The shelf also became a vast reservoir for cold, saline shelf water, one of the key ingredients of Antarctic bottom water.

  19. How Continental Bank outsourced its "crown jewels.".

    PubMed

    Huber, R L

    1993-01-01

    No industry relies more on information than banking does, yet Continental, one of America's largest banks, outsources its information technology. Why? Because that's the best way to service the customers that form the core of the bank's business, says vice chairman Dick Huber. In the late 1970s and early 1980s, Continental participated heavily with Penn Square Bank in energy investments. When falling energy prices burst Penn Square's bubble in 1982, Continental was stuck with more than $1 billion in bad loans. Eight years later when Dick Huber came on board, Continental was working hard to restore its once solid reputation. Executives had made many tough decisions already, altering the bank's focus from retail to business banking and laying off thousands of employees. Yet management still needed to cut costs and improve services to stay afloat. Regulators, investors, and analysts were watching every step. Continental executives, eager to focus on the bank's core mission of serving business customers, decided to outsource one after another in-house service--from cafeteria services to information technology. While conventional wisdom holds that banks must retain complete internal control of IT, Continental bucked this argument when it entered into a ten-year, multimillion-dollar contract with Integrated Systems Solutions Corporation. Continental is already reaping benefits from outsourcing IT. Most important, Continental staffers today focus on their true core competencies: intimate knowledge of customers' needs and relationships with customers. PMID:10124146

  20. A Facies Model for Temperate Continental Glaciers.

    ERIC Educational Resources Information Center

    Ashley, Gail Mowry

    1987-01-01

    Discusses the presence and dynamics of continental glaciers in the domination of the physical processes of erosion and deposition in the mid-latitudes during the Pleistocene period. Describes the use of a sedimentary facies model as a guide to recognizing ancient temperate continental glacial deposits. (TW)

  1. Continuum calculations of continental deformation in transcurrent environments

    NASA Technical Reports Server (NTRS)

    Sonder, L. J.; England, P. C.; Houseman, G. A.

    1986-01-01

    A thin viscous sheet approximation is used to investigate continental deformation near a strike-slip boundary. The vertically averaged velocity field is calculated for a medium characterized by a power law rheology with stress exponent n. Driving stresses include those applied along boundaries of the sheet and those arising from buoyancy forces related to lateral differences in crustal thickness. Exact and approximate analytic solutions for a region with a sinusoidal strike-slip boundary condition are compared with solutions for more geologically relevant boundary conditions obtained using a finite element technique. The across-strike length scale of the deformation is approximately 1/4pi x sq rt n times the dominant wavelength of the imposed strike-slip boundary condition for both the analytic and the numerical solutions; this result is consistent with length scales observed in continental regions of large-scale transcurrent faulting. An approximate, linear relationship between displacement and rotation is found that depends only on the deformation length scale and the rheology. Calculated displacements, finite rotations, and distribution of crustal thicknesses are consistent with those observed in the region of the Pacific-North America plate boundary in California.

  2. 75 FR 61512 - Outer Continental Shelf Official Protraction Diagrams

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-10-05

    ... Bureau of Ocean Energy Management, Regulation and Enforcement Outer Continental Shelf Official... Outer Continental Shelf Official Protraction Diagrams (OPDs) located within Atlantic Ocean areas, with... informational purposes only. Outer Continental Shelf Official Protraction Diagrams in the North Atlantic,...

  3. 78 FR 6222 - Importation of Avocados From Continental Spain

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-01-30

    ...state that avocados from continental Spain may be imported in...other than Hass variety from continental Spain must be treated for...through the importation or movement of fruits, vegetables...capitata for avocados from continental...

  4. Tectonic implications of post-30 Ma Pacific and North American relative plate motions

    USGS Publications Warehouse

    Bohannon, R.G.; Parsons, T.

    1995-01-01

    The Pacific plate moved northwest relative to North America since 42 Ma. The rapid half rate of Pacific-Farallon spreading allowed the ridge to approach the continent at about 29 Ma. Extinct spreading ridges that occur offshore along 65% of the margin document that fragments of the subducted Farallon slab became captured by the Pacific plate and assumed its motion proper to the actual subduction of the spreading ridge. This plate-capture process can be used to explain much of the post-29 Ma Cordilleran North America extension, strike slip, and the inland jump of oceanic spreading in the Gulf of California. Much of the post-29 Ma continental tectonism is the result of the strong traction imposed on the deep part of the continental crust by the gently inclined slab of subducted oceanic lithosphere as it moved to the northwest relative to the overlying continent. -from Authors

  5. Paleozoic plate-tectonic evolution of the Tarim and western Tianshan regions, western China

    SciTech Connect

    Yangshen, S.; Huafu, L.; Dong, J.

    1994-11-01

    The plate-tectonic evolution of the Tarim basin and nearby western Tianshan region during Paleozoic time is reconstructed in an effort to further constrain the tectonic evolution of Central Asia, providing insights into the formation and distribution of oil and gas resources. The Tarim plate developed from continental rifting that progressed during early Paleozoic time into a passive continental margin. The Yili terrane (central Tianshan) broke away from the present eastern part of Tarim and became a microcontinent located somewhere between the Junggar ocean and the southern Tianshan ocean. The southern Tianshan ocean, between the Tarim craton and the Yili terrane, was subducting beneath the Yili terrane from Silurian to Devonian time. During the Late Devonian-Early Carboniferous, the Tarim plate collided with the Yili terrane by sinistral accretional docking that resulted in a late Paleozoic deformational episode. Intracontinental shortening (A-type subduction) continued through the Permian with the creation of a magmatic belt. 21 refs., 7 figs., 1 tab.

  6. Caribbean plate interactions

    SciTech Connect

    Ball, M. )

    1993-02-01

    Vector analysis of plate motions, derived from studies of Atlantic magnetic lineations and fracture zone trends, indicates the following relative movements between the Caribbean, North American, and South American Plates. (1) During Early Jurassic to Early Cretaceous, the North American Plate moved 1900 km westward and 900 km northward relative to the South American Plate. A broad zone including the Caribbean region, i.e., the zone between the North and South America Plates, was a site of left-lateral shear and north-south extension. (2) During Early Cretaceous to Late Cretaceous, the North American Mate moved an additional 1200 km westward relative to South America across this zone. (3) During Late Cretaceous to the end of the Eocene, the North American Plate moved 200 km westward and 400 km northward relative to the South American Plate. (4) From the end of the Eocene to near the end of the Miocene, North America converged on South America some 200 km and moved 100 km eastward relative to it. Through the Mesozoic and earliest Tertiary history of the Caribbean, the region was a shear zone within which left-lateral displacement exceeded 3000 km and north-south extension exceeded 1300 km. In regard to time, 80% of the history of the Caribbean region is one of north-south extension and left-lateral shear. In terms of space, 97% of the shear is left-lateral and the ratio of divergence versus convergence is 7 to 1. Thus, characterizing the Caribbean region, and the Atlantic to its east, as a zone of north-south extension and left-lateral shear, is a fair generalization.

  7. Deformation in the continental lithosphere

    NASA Astrophysics Data System (ADS)

    The Physical Properties of Earth Materials Committee, a technical committee of AGU's Tectonophysics Section, is organizing a dinner/colloquium as part of the Fall Meeting in San Francisco, Calif. This event will be held Monday, December 3rd, in the Gold Rush Room of the Holiday Inn Golden Gateway Hotel at 1500 Van Ness St. There will be a no-host bar from 6:30 to 7:30 P.M., followed by dinner from 7:30 to 8:30 P.M. Paul Tapponnier will deliver the after-dinner talk, “Large-Scale Deformation Mechanisms in the Continental Lithosphere: Where Do We Stand?” It will start at 8:30 P.M. and a business meeting will follow at 9:30 P.M.

  8. Mapping the evolving strain field during continental breakup from crustal anisotropy in the Afar Depression

    PubMed Central

    Keir, Derek; Belachew, M.; Ebinger, C.J.; Kendall, J.-M.; Hammond, J.O.S.; Stuart, G.W.; Ayele, A.; Rowland, J.V.

    2011-01-01

    Rifting of the continents leading to plate rupture occurs by a combination of mechanical deformation and magma intrusion, yet the spatial and temporal scales over which these alternate mechanisms localize extensional strain remain controversial. Here we quantify anisotropy of the upper crust across the volcanically active Afar Triple Junction using shear-wave splitting from local earthquakes to evaluate the distribution and orientation of strain in a region of continental breakup. The pattern of S-wave splitting in Afar is best explained by anisotropy from deformation-related structures, with the dramatic change in splitting parameters into the rift axis from the increased density of dyke-induced faulting combined with a contribution from oriented melt pockets near volcanic centres. The lack of rift-perpendicular anisotropy in the lithosphere, and corroborating geoscientific evidence of extension dominated by dyking, provide strong evidence that magma intrusion achieves the majority of plate opening in this zone of incipient plate rupture. PMID:21505441

  9. Evolution of Oxidative Continental Weathering

    NASA Astrophysics Data System (ADS)

    Konhauser, Kurt; Lalonde, Stefan

    2014-05-01

    The Great Oxidation Event (GOE) is currently viewed as a protracted process during which atmospheric oxygen levels increased above 10-5 times the present atmospheric level. This value is based on the loss of sulphur isotope mass independent fractionation (S-MIF) from the rock record, beginning at 2.45 Ga and disappearing by 2.32 Ga. However, a number of recent papers have pushed back the timing for oxidative continental weathering, and by extension, the onset of atmospheric oxygenation several hundreds of million years earlier despite the presence of S-MIF (e.g., Crowe et al., 2013). This apparent discrepancy can, in part, be resolved by the suggestion that recycling of older sedimentary sulphur bearing S-MIF might have led to this signal's persistence in the rock record for some time after atmospheric oxygenation (Reinhard et al., 2013). Here we suggest another possibility, that the earliest oxidative weathering reactions occurred in environments at profound redox disequilibrium with the atmosphere, such as biological soil crusts, riverbed and estuarine sediments, and lacustrine microbial mats. We calculate that the rate of O2 production via oxygenic photosynthesis in these terrestrial microbial ecosystems provides largely sufficient oxidizing potential to mobilise sulphate and a number of redox-sensitive trace metals from land to the oceans while the atmosphere itself remained anoxic with its attendant S-MIF signature. These findings reconcile geochemical signatures in the rock record for the earliest oxidative continental weathering with the history of atmospheric sulphur chemistry, and demonstrate the plausible antiquity of a terrestrial biosphere populated by cyanobacteria. Crowe, S.A., Dossing, L.N., Beukes, N.J., Bau, M., Kruger, S.J., Frei, R. & Canfield, D.E. Atmospheric oxygenation three billion years ago. Nature 501, 535-539 (2013). Reinhard, C.T., Planavsky, N.J. & Lyons, T.W. Long-term sedimentary recycling of rare sulphur isotope anomalies. Nature 497, 100-104 (2013).

  10. Quantifying the isotopic ‘continental effect’

    NASA Astrophysics Data System (ADS)

    Winnick, Matthew J.; Chamberlain, C. Page; Caves, Jeremy K.; Welker, Jeffrey M.

    2014-11-01

    Since the establishment of the IAEA-WMO precipitation-monitoring network in 1961, it has been observed that isotope ratios in precipitation (? 2H and ? 18O) generally decrease from coastal to inland locations, an observation described as the 'continental effect.' While discussed frequently in the literature, there have been few attempts to quantify the variables controlling this effect despite the fact that isotopic gradients over continents can vary by orders of magnitude. In a number of studies, traditional Rayleigh fractionation has proven inadequate in describing the global variability of isotopic gradients due to its simplified treatment of moisture transport and its lack of moisture recycling processes. In this study, we use a one-dimensional idealized model of water vapor transport along a storm track to investigate the dominant variables controlling isotopic gradients in precipitation across terrestrial environments. We find that the sensitivity of these gradients to progressive rainout is controlled by a combination of the amount of evapotranspiration and the ratio of transport by advection to transport by eddy diffusion, with these variables becoming increasingly important with decreasing length scales of specific humidity. A comparison of modeled gradients with global precipitation isotope data indicates that these variables can account for the majority of variability in observed isotopic gradients between coastal and inland locations. Furthermore, the dependence of the 'continental effect' on moisture recycling allows for the quantification of evapotranspiration fluxes from measured isotopic gradients, with implications for both paleoclimate reconstructions and large-scale monitoring efforts in the context of global warming and a changing hydrologic cycle.

  11. Role of viscous plate coupling in the late Tertiary Andean tectonics

    NASA Astrophysics Data System (ADS)

    YáñEz, Gonzalo; Cembrano, José

    2004-02-01

    Plate coupling between oceanic and continental plates in convergent margins of Andean type is analyzed from the continuum mechanics approach. We postulate a simple mechanism that accounts for the compressive regime in Andean-type environments. In this mechanism, deformation in the continental lithosphere is split into two distinctive domains: The forearc domain and the arc-foreland domain. The forearc deformation is controlled by the balance between buoyancy forces associated with the trench and continental slope relief and the stress transferred from the convergence velocity through the age- and velocity-dependent slip zone. The arc-foreland deformation is controlled by the absolute plate velocity of the continental plate and the resistance at the slip zone. Strength of the coupling zone is determined by analyzing the dynamic trench topography along the active margin of South America between 0 and 55°S. Using this approach, we found strength values in the range of 20-95 MPa, in strong direct correlation with the age of the subducting plate. The slip layer strength observation has been successfully tested against a thermal- and strain rate-dependent rheological model. From this theoretical result we define an empirical relationship between strength of the slip zone and the age and convergence velocity. Applying this plate coupling model, we reproduce shortening rates in the order of 1-10 km/Myr, in agreement with those reported for the late Tertiary evolution of the Andes. Model results reproduce some first-order features of the geological evolution of the margin, such as the shape of the trench, the overall Andes relief, the Altiplano buildup, and block rotation patterns. In addition, the model provides a mechanism to explain the evolution of the Central Depression, the inversion of Tertiary basins under slow convergence rates during the Miocene, and the segmentation of the margins tectonic erosion.

  12. Cadmium plating replacements

    SciTech Connect

    Nelson, M.J.; Groshart, E.C.

    1995-03-01

    The Boeing Company has been searching for replacements to cadmium plate. Two alloy plating systems seem close to meeting the needs of a cadmium replacement. The two alloys, zinc-nickel and tin-zinc are from alloy plating baths; both baths are neutral pH. The alloys meet the requirements for salt fog corrosion resistance, and both alloys excel as a paint base. Currently, tests are being performed on standard fasteners to compare zinc-nickel and tin-zinc on threaded hardware where cadmium is heavily used. The Hydrogen embrittlement propensity of the zinc-nickel bath has been tested, and just beginning for the tin-zinc bath. Another area of interest is the electrical properties on aluminum for tin-zinc and will be discussed. The zinc-nickel alloy plating bath is in production in Boeing Commercial Airplane Group for non-critical low strength steels. The outlook is promising that these two coatings will help The Boeing Company significantly reduce its dependence on cadmium plating.

  13. Cadmium plating replacements

    NASA Technical Reports Server (NTRS)

    Nelson, Mary J.; Groshart, Earl C.

    1995-01-01

    The Boeing Company has been searching for replacements to cadmium plate. Two alloy plating systems seem close to meeting the needs of a cadmium replacement. The two alloys, zinc-nickel and tin-zinc are from alloy plating baths; both baths are neutral pH. The alloys meet the requirements for salt fog corrosion resistance, and both alloys excel as a paint base. Currently, tests are being performed on standard fasteners to compare zinc-nickel and tin-zinc on threaded hardware where cadmium is heavily used. The Hydrogen embrittlement propensity of the zinc-nickel bath has been tested, and just beginning for the tin-zinc bath. Another area of interest is the electrical properties on aluminum for tin-zinc and will be discussed. The zinc-nickel alloy plating bath is in production in Boeing Commercial Airplane Group for non-critical low strength steels. The outlook is promising that these two coatings will help The Boeing Company significantly reduce its dependence on cadmium plating.

  14. Plate convergence, transcurrent faults and internal deformation adjacent to Southeast Asia and the western Pacific

    NASA Technical Reports Server (NTRS)

    Fitch, T. J.

    1971-01-01

    A model for oblique convergence between plates of lithosphere is proposed in which at least a fraction of slip parallel to the plate margin results in transcurrent movements on a nearly vertical fault which is located on the continental side of a zone of plate consumption. In an extreme case of complete decoupling only the component of slip normal to the plate margin can be inferred from underthrusting. Recent movements in the western Sunda region provide the most convincing evidence for decoupling of slip, which in this region is thought to be oblique to the plate margin. A speculative model for convergence along the margins of the Philippine Sea is constructed from an inferred direction of oblique slip in the Philippine region. This model requires that the triple point formed by the junction of the Japanese and Izu-Bonin trenches and the Nankai trough migrate along the Sagami trough.

  15. Dynamic Linkages Between the Transition Zone & Surface Plate Motion in 2D Models of Subduction

    NASA Astrophysics Data System (ADS)

    Arredondo, K.; Billen, M. I.

    2014-12-01

    Subduction zones exhibit a wide range of behavior, from slab stagnation at 660 km to direct penetration into the lower mantle. Due to uncertainties in the tectonic history of individual subduction zones, such as trench velocities, potential mechanisms for controlling slab behavior in the transition zone are explored using numerical models. Numerical simulations have utilized a range of assumptions to improve computational efficiency, such as ignoring latent heat, ignoring compositional effects or fixing the trench location: the net effect of these assumptions resulting modeled dynamics remains unclear. Additionally the eight major, composition-dependent, phase transitions for pyrolite, harzburgite and eclogite may be an important influence on subducting slab dynamics due to the additional forces that are dependent on depth and compositional layering within the slab (e.g., Ricard et al., 2005). With the goal of developing more complete, self-consistent, and less idealized simulations, we test the importance of various factors on slab behavior: the presence of shear, adiabatic and latent heating, compositional layering, composition-dependent phase transitions and explicit plate speeds versus dynamically evolving plate and trench velocities. Preliminary results indicate that individual components have a relatively minor effect, but produce large changes when combined together. The extent of slab folding and stagnation is overestimated by only modeling the 410 and 660 km phase transitions. Dynamic models with all seven composition-dependent phase transitions are very sensitive to the plate strength and weak zone viscosity, causing large changes in plate speed and slab detachment. Changes to the overriding plate buoyance and strength investigate the origin and influence of trench movement on slab deformation. These feedbacks and parameter-sensitive behavior indicate that the wide range of observed slab behavior may result from subtle differences in plate and plate boundary properties. Ricard, Y., E. Mattern, and J. Matas, Synthetic tomographic images of slabs from mineral physics, in Earth's Deep Mantle: Structure, Composition, and Evolution, Geophysical Monograph Series, vol. 160, American Geophysical Union, 2005.

  16. Bipolar battery plate

    NASA Technical Reports Server (NTRS)

    Rowlette, John J. (Inventor)

    1987-01-01

    A liquid-impermeable plate (10) having through-plate conductivity with essentially zero resistance comprises an insulator sheet (12) having a series of spaced perforations (14) each of which contains a metal element (16) sealingly received into the perforation (14). A low-cost plate can readily be manufactured by punching a thermoplastic sheet (40) such as polypropylene with a punching tool (52), filling the apertures with led spheres (63) having a diameter smaller than the holes (50) but larger than the thickness of the sheet, sweeping excess spheres (62) off the sheet with a doctor blade (60) and then pressing a heated platen (74) onto the sheet to swage the spheres into a cylindrical shape and melt the surrounding resin to form a liquid-impermeable collar (4) sealing the metal into the sheet.

  17. Two opposed subduction modes at the southern Caribbean plate margin of Colombia

    NASA Astrophysics Data System (ADS)

    Kammer, Andreas; Piraquive, Alejandro

    2014-05-01

    Cretaceous to Paleogene convergence at the southern Caribbean plate margin is still little deciphered and a generalized interpretation is hindered by the absence of regionally correlatable tectonic elements, like magmatic arcs, time constraints and an intense crustal fragmentation brought about by Neogene strike-slip tectonics. In order to illustrate the diversity of these subduction settings and discuss possible tectonic controls on their subsequent collisional evolution, we outline the structural evolution along a thickened and a thinned continental segment. The first case is exemplified by the Sierra Nevada de Santa Marta, a triangular block that exposes an imbricated lower crustal section capped by nested plutons and a volcanic sequence of a Jurassic to Early Cretaceous arc. This exceptionally thick crustal section forms the upper plate of a continent-ward dipping main suture that is underlain by strongly sheared platform sediments and transitional basement rocks of a lower plate. Penetrative deformation developed under medium-grade conditions with a uniform top-to-the NE shear attests to a stable subduction interval of a still unknown duration. Onset of a collisional phase is marked by a crustal imbrication further inboard of the main suture, leading to a further crustal thickening, and links in the Paleogene to the emplacement of the dome-like Santa Marta batholith within the lower plate. It is likely that the juxtaposition of thickened continental Southamerican and thinner oceanic Caribbean crust triggered a crustal channel flow that fed the magmatic dome in the transitional part of these crustal realms, leading thus to some gravitational collapse of the continental crust. The opposite case of the juxtaposition of a continental platform, previously thinned by Jurassic to Early Cretaceous rifting and a relatively thick Caribbean crust is documented in the northwestern Guajira Peninsula. Here platform sequences and their corresponding basement were subducted below the Caribbean crust, acquiring a penetrative transpressional deformation under low-grade conditions. An incipient collision is attested by the amplification of the crustal bend of the continental plate and the formation of imbricate slices along backthrusts that involve both basement rocks and platform sediments. Upper plate sediments record structures related to gravity sliding and thus attest to slope-forming processes. These sedimentary sequences further include ultramafic lenses and vestiges of serpentine mud volcanoes. Arc magmatism is recorded solely by a Paleogene stock. The differences in subduction polarity cannot be explained by two events separated in time but reflect two concurrent subduction modes, governed by compositional and physical differences of the continental plate.

  18. Seismic stratigraphic framework of Louisiana Continental Margin: clues to hydrocarbon sourcing

    SciTech Connect

    Dinkelman, M.G.

    1986-09-01

    Interpretation of several thousand miles of multichannel seismic data indicates that large volumes of continental rise and basinal sediments have been continuously entrapped and are overridden by the basinward flow or creep of broad, extensive salt tongues that form the lower slope and Sigsbee Escarpment. Thick accumulations of Lower Cretaceous to upper Miocene sediments are identified beneath the salt at least 60 km landward of the escarpment. Spotty seismic data suggest that the Cretaceous to middle Miocene succession extends up to 120 km landward of the escarpment and beneath the present shelf break. Pleistocene-Holocene sequences of the deep gulf can be traced up to 15 km landward of the escarpment, where they are truncated by the base of the salt. Similar truncation of older deep gulf sequences by salt occurs progressively farther landward of the escarpment. Recently, the case has been made that hydrocarbons found in seeps and reservoirs on the outer shelf and upper slope are generated from Miocene anoxic basins buried at depth. Anoxic slope basins are presently rare, and their total sediment volume is small. It is unlikely that these anoxic basins were significantly more numerous during the Miocene or that their sediment volume was significantly greater. Therefore, the scenario of large allochthonous salt tongues, or flows, overriding flat continental rise and basinal sediments high in organics suggests that: (1) much of the hydrocarbon found in shallow Pliocene-Pleistocene reservoirs along the shelf and upper slope may have been generated from the now deeply buried Cretaceous to early Tertiary marine sedimentary sequences since the late Miocene-early Pliocene, and (2) hydrocarbons migrated vertically upward relatively recently along postsedimentary faults that cut the decollement.

  19. Reduced Plating Ignitron

    NASA Technical Reports Server (NTRS)

    Polzin, Kurt A (Inventor); Pearson, J Boise (Inventor)

    2014-01-01

    An ignitron apparatus has an airtight tubular housing having a first sealed end and a second sealed end. An anode is connected at the first sealed end, projecting into the housing, and a recess at the second sealed and forms a well which contains a quantity of liquid gallium or gallium alloy making up the cathode. An ignitor projects through the liquid metal and into the housing. The inner surface of the housing includes at least one plating-reduction structure to prevent electrical shorting of the apparatus caused by plating of the liquid metal.

  20. Volume 13, Number 10 9 October 2012

    E-print Network

    Tan, Eh

    78758, USA Now at Institute of Earth Sciences, Academia Sinica, Taipei 11529, Taiwan (tan2@earth 78758, USA Arnauld Heuret Dipartimento di Scienze Geologiche, Università degli Studi "Roma Tre", IT00146. Introduction [2] The subduction of an oceanic plate beneath an overriding continental or oceanic plate

  1. Tecronophysics, 160 (1989) 277-291 Elsevier Science Pubhshers B.V., Amsterdam -Printed in The Netheriands

    E-print Network

    Cattin, Rodolphe

    1989-01-01

    the continental margin is eroded by the subducting plate and collapses into the trench. The benthic communities boundaries (the trian- gles are on the side of the overriding plate). Bathymetric contours are given every 2 in The Netheriands 277 Fluid venting along Japanese trenches: tectonic context and thermal modeling P. HENRY I, S

  2. Continental margin tectonics - Forearc processes

    SciTech Connect

    Lundberg, N.; Reed, D.L. )

    1991-01-01

    Recent studies of convergent plate margins and the structural development of forearc terranes are summarized in a critical review of U.S. research from the period 1987-1990. Topics addressed include the geometry of accretionary prisms (Coulomb wedge taper and vertical motion in response to tectonic processes), offscraping vs underplating or subduction, the response to oblique convergence, fluids in forearc settings, the thermal framework and the effects of fluid advection, and serpentinite seamounts. Also included is a comprehensive bibliography for the period.

  3. Linking mantle dynamics, plate tectonics and surface processes in the active plate boundary zones of eastern New Guinea (Invited)

    NASA Astrophysics Data System (ADS)

    Baldwin, S.; Moucha, R.; Fitzgerald, P. G.; Hoke, G. D.; Bermudez, M. A.; Webb, L. E.; Braun, J.; Rowley, D. B.; Insel, N.; Abers, G. A.; Wallace, L. M.; Vervoort, J. D.

    2013-12-01

    Eastern New Guinea lies within the rapidly obliquely converging Australian (AUS)- Pacific (PAC) plate boundary zone and is characterized by transient plate boundaries, rapidly rotating microplates and a globally significant geoid high. As the AUS plate moved northward in the Cenozoic, its leading edge has been a zone of subduction and arc accretion. The variety of tectonic settings in this region permits assessment of the complex interplay among mantle dynamics, plate tectonics, and surface processes. Importantly, the timescale of tectonic events (e.g., subduction, (U)HP exhumation, seafloor spreading) are within the valid bounds of mantle convection models. A record of changes in bathymetry and topography are preserved in high standing mountain belts, exhumed extensional gneiss domes and core complexes, uplifted coral terraces, and marine sedimentary basins. Global seismic tomography models indicate accumulation of subducted slabs beneath eastern New Guinea at the bottom of the upper mantle (i.e., <660km depth). Some of the deeply subducted material may indeed be buoyant subducted AUS continental margin (to depths of ~250-300 km), as well as subducted continental material that has reached the point of no return (i.e., > 250-300 km). Preliminary global-scale backward advected mantle convection models, driven by density inferred from joint seismic-geodynamic tomography models, exhibit large-scale flow associated with these subducted slab remnants and predict the timing and magnitude (up to 1500 m) of dynamic topography change (both subsidence and uplift) since the Oligocene. In this talk we will explore the effects of large-scale background mantle flow and plate tectonics on the evolution of topography and bathymetry in eastern New Guinea, and discuss possible mechanisms to explain basin subsidence and surface uplift in the region.

  4. Negligible effect of hydrogen content on plate strength in East Africa

    NASA Astrophysics Data System (ADS)

    Selway, Kate

    2015-07-01

    Continental rifting requires weak zones to exist within the strong continental plates. This weakening is thought to be induced primarily by high hydrogen contents and temperatures, as well as small grain size. An ideal location to test models of plate strength in situ is the East African Rift--the best exposed continental rift on Earth--which is forming adjacent to the unrifted Tanzanian Craton. Here I use magnetotelluric data to investigate electrical conductivity, and hence hydrogen content, across the East African Rift and Tanzanian Craton. The images show that the Tanzanian Craton is extremely rich in hydrogen, whereas the parts of the continent that are being rifted are anhydrous, suggesting that high hydrogen content does not systematically reduce plate strength. Earlier deformation events may have reduced the grain size of the continental lithosphere in the East African Rift compared to the Tanzanian Craton. I therefore suggest that the localization of rifting and repeated reactivation of deformed regions may not be due to hydrogen content and is instead controlled by small grain size.

  5. Nuclear reactor alignment plate configuration

    DOEpatents

    Altman, David A; Forsyth, David R; Smith, Richard E; Singleton, Norman R

    2014-01-28

    An alignment plate that is attached to a core barrel of a pressurized water reactor and fits within slots within a top plate of a lower core shroud and upper core plate to maintain lateral alignment of the reactor internals. The alignment plate is connected to the core barrel through two vertically-spaced dowel pins that extend from the outside surface of the core barrel through a reinforcement pad and into corresponding holes in the alignment plate. Additionally, threaded fasteners are inserted around the perimeter of the reinforcement pad and into the alignment plate to further secure the alignment plate to the core barrel. A fillet weld also is deposited around the perimeter of the reinforcement pad. To accomodate thermal growth between the alignment plate and the core barrel, a gap is left above, below and at both sides of one of the dowel pins in the alignment plate holes through with the dowel pins pass.

  6. The Cretaceous iron belt of northern Chile: role of oceanic plates, a superplume event, and a major shear zone

    NASA Astrophysics Data System (ADS)

    Oyarzun, Roberto; Oyarzún, Jorge; Ménard, Jean Jacques; Lillo, Javier

    2003-08-01

    The Cretaceous constitutes a turning point in the tectonic, magmatic, and metallogenic history of Chile. The geological evidence indicates that a major change occurred in late Neocomian time when superplume emplacement (Mid-Pacific Superplume) and plate reorganization processes took place in the Pacific. The superplume event resulted in a major ridge-push force resulting in increased coupling between the subducting and overriding plates. This completely changed the tectonic setting of Chile ending the Early Cretaceous extensional period (aborted rifting in the back-arc basin), and increasing stress at a crustal scale. As a consequence, overpressurized dioritic magmas were pushed up mainly along the best possible structural path in northern Chile, i.e., the Atacama Fault Zone, eventually forming a +500-km-long belt of Kiruna-type iron deposits with reserves of ~2,000 Mt (60% Fe), a unique case in Chile's geological history.

  7. The rise and fall of continental arcs: Interplays between magmatism, uplift, weathering, and climate

    NASA Astrophysics Data System (ADS)

    Lee, Cin-Ty A.; Thurner, Sally; Paterson, Scott; Cao, Wenrong

    2015-09-01

    Continental arcs, such as the modern Andes or the Cretaceous Sierra Nevada batholith, are some of the highest topographic features on Earth. Continental arc volcanoes may produce more CO2 than most other types of volcanoes due to the interaction of magmas with sedimentary carbonates stored in the continental upper plate. As such, global flare-ups in continental arc magmatism may amplify atmospheric CO2 concentrations, leading to climatic warming. However, the high elevations of continental arcs may also enhance orographic precipitation and change global atmospheric circulation patterns, possibly increasing the efficiency of chemical weathering and drawdown of atmospheric CO2, which may subdue the climatic warming response to volcanic activity. To better evaluate the climatic response, we develop models that integrate magmatic crustal thickening, topographic uplift, isostasy and erosion. The topographic response is used to predict how soil formation rates, soil residence times, and chemical weathering rates vary during and after a magmatic episode. Although magmatism leads to crustal thickening, which requires topographic uplift, highest elevations peak ?10 My after magmatism ends. Relatively high elevations, which enhance erosion and chemical weathering of the continental arc, persist for tens of million years after magmatism ends, depending on erosion kinetics. It has recently been suggested that the Cretaceous-Paleogene greenhouse (high atmospheric CO2 and warm climate) coincided with a global chain of continental arcs, whereas mid- to late Cenozoic icehouse conditions (low atmospheric CO2 and cold climate) coincided with a lull in continental arc activity after 50 Ma. Application of our models to the Sierra Nevada (California, USA) continental arc, which represents a segment of this global Cretaceous-Paleogene continental arc, reproduces the observed topographic and erosional response. Our models require that the newly formed continental arc crust remained high and continued to erode and weather well after (>50 My) the end of magmatism. Thus, in the aftermath of a global continental arc flare-up, both the total volcanic inputs of CO2 decline and the average weatherability of continents increases, the latter due to the increased proportion of widespread remnant topography available for weathering and erosion. This combination leads to a decrease in the long-term baseline of carbon in the ocean/atmosphere system, leading to cooling. Mid-Cenozoic cooling is often attributed solely to increased weathering rates associated with India-Eurasian collision and the Himalayan orogeny. However, the total area of now-extinct Cretaceous-Paleogene continental arcs is 1.3-2 times larger than that of the Himalayan range front and the Tibetan plateau combined, suggesting that weathering of these remnant volcanic arcs may also play a role in drawing down CO2 through silicate weathering and subsequent carbonate burial. In summary, if global continental arc flare-ups lead to greenhouse conditions, long-lived icehouse conditions should follow in the aftermath due to decreased CO2 inputs and an increase in regional weathering efficiency of remnant arc topography.

  8. Oceanic core complexes in the Philippine Sea: results from Japan's extended continental shelf mapping

    NASA Astrophysics Data System (ADS)

    Ohara, Y.; Yoshida, T.; Nishizawa, A.

    2013-12-01

    The United Nations Commission on the Limits of the Continental Shelf (CLCS) issued its recommendations on Japan's extended continental shelf in April 2012, confirming Japan's rights over the vast areas within the Philippine Sea and Pacific Plates. Japan submitted information on the limits of its continental shelf beyond the EEZ to the CLCS on November 2008, which was the result of 25 years of nation's continental shelf survey project since 1983, involving all of Japan's agency relevant to geosciences. The huge geological and geophysical data obtained through the project give the scientists unprecedented opportunity to study the geology and tectonics of the Philippine Sea and Pacific Plates. In this contribution, we show such an example from the Philippine Sea Plate, relevant to the global mid-ocean ridge problem. Oceanic core complexes (OCC) are dome-shaped bathymetric highs identified in mid-ocean ridges, interpreted as portions of the lower crust and/or upper mantle denuded via low-angle detachment faulting. OCCs are characterized morphologically by axis-normal striations (corrugations, or mullion structure) on the dome, and exposures of mantle peridotite and/or lower crustal gabbro. A strikingly giant OCC (named 'Godzilla Megamullion') was discovered in the Parece Vela Basin by the continental shelf survey project in 2001. Godzilla Megamullion is morphologically the largest OCC in the world, consisting mainly of fertile mantle peridotite along its entire length of over 125 km. Following its discovery in 2001, several academic cruises investigated the structure in detail, providing numerous important findings relevant to mid-ocean ridge tectono-magmatic processes and Philippine Sea evolution, including the slow- to ultraslow-spreading environment for denudation of the detachment fault (< 2.5 cm/y) and associated decreasing degree of partial melting of the peridotites towards the termination of Godzilla Megamullion. In addition to Godzilla Megamullion, several potential OCCs have been discovered in the Philippine Sea Plate by the continental shelf survey project. These are: (1) the ones in the Shikoku Basin spreading axis at around 24 degrees north, (2) the Chaotic Terrain in the Parece Vela Basin, (3) Chaotic Terrain in the West Philippine Basin, near the CBF Rift (formerly known as the Central Basin Fault), (4) Chaotic Terrain in the Kita-Daito Basin, (5) the one in the Shikoku Basin floor to the east of Kyushu-Palau Ridge at 25 degrees north, (6) the Higashi-Ryusei Spur of the Kyushu-Palau Ridge at 26 degrees north, and (7) the one in the Daito Ridge adjoining to the Kida-Daito Basin. OCCs are commonly developed in slow-spreading ridges, providing excellent opportunities as tectonic windows to study the composition and structure of deep oceanic lithosphere. The OCCs in the Philippine Sea Plate in turn provide the opportunities to study the backarc basin lithosphere as well as the continental lithosphere (at the above examples 6 and 7). Although Godzilla Megamullion has been studied very well, the other OCCs are not well documented yet. The next step is to focus on these interesting targets to understand the lithospheric process in the Philippine Sea Plate.

  9. Continental volume and freeboard through geological time

    NASA Technical Reports Server (NTRS)

    Schubert, G.; Reymer, A. P. S.

    1985-01-01

    The consequences of approximately constant freeboard for continental growth are explored using a model that relates the volumes of isostatically compensated continents and oceans to the secular decline in terrestrial heat flow. It is found that a post-Archean increase in freeboard by 200 m requires continental growth of only 10 percent, while a decrease in freeboard by 200 m during this same period necessitates a crustal growth of 40 percent. Shrinkage of the continental crust since the end of the Archean can be ruled out. Changes of more than 10 percent in post-Archean crustal thickness are highly unlikely.

  10. ILLUSTRATIONS. PLATES-PART !.

    E-print Network

    .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 A M~THOD OF LOBSTER CULTURE: Plate VII. (r) General view of houseboat and floats. (2) Inside. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 VIII. (3) Floats from outer corner looking forward. (4) One of the outside floats, car raised. Specimen of rock from sponge beds off Anclote Key, Florida. . . . . . . . . . . . 403 XXIX. (I) Diving boat

  11. INL HIP Plate Fabrication

    SciTech Connect

    B. H. Park; C. R. Clark; J. F. Jue

    2010-02-01

    This document outlines the process used to bond monolithic fuel plates by Hot Isostatic Pressing (HIP). This method was developed at Idaho National Laboratory (INL) for the Reduced Enrichment for Research and Test Reactors (RERTR) program. These foils have been used in a number of irradiation experiments in support of the United States Global Threat Reduction Initiative (GTRI) program.

  12. Unitary plate electrode

    NASA Technical Reports Server (NTRS)

    Rowlette, John J. (Inventor); Clough, Thomas J. (Inventor); Josefowicz, Jack Y. (Inventor); Sibert, John W. (Inventor)

    1985-01-01

    The unitary electrode (10) comprises a porous sheet (12) of fiberglass the strands (14) of which contain a coating (16) of conductive tin oxide. The lower portion of the sheet contains a layer (18) of resin and the upper layer (20) contains lead dioxide forming a positive active electrode on an electrolyte-impervious layer. The strands (14) form a continuous conduction path through both layers (16, 18). Tin oxide is prevented from reduction by coating the surface of the plate facing the negative electrode with a conductive, impervious layer resistant to reduction such as a thin film (130) of lead or graphite filled resin adhered to the plate with a layer (31) of conductive adhesive. The plate (10) can be formed by casting a molten resin from kettle (60) onto a sheet of glass wool (56) overlying a sheet of lead foil and then applying positive active paste from hopper (64) into the upper layer (68). The plate can also be formed by passing an assembly of a sheet ( 80) of resin, a sheet (86) of sintered glass and a sheet (90) of lead between the nip (92) of heated rollers (93, 95) and then filling lead oxide into the pores (116) of the upper layer (118).

  13. Volatile components and continental material of planets

    NASA Technical Reports Server (NTRS)

    Florenskiy, K. P.; Nikolayeva, O. V.

    1986-01-01

    It is shown that the continental material of the terrestrial planets varies in composition from planet to planet according to the abundances and composition of true volatiles (H20, CO2, etc.) in the outer shells of the planets. The formation of these shells occurs very early in a planet's evolution when the role of endogenous processes is indistinct and continental materials are subject to melting and vaporizing in the absence of an atmosphere. As a result, the chemical properties of continental materials are related not only to fractionation processes but also to meltability and volatility. For planets retaining a certain quantity of true volatile components, the chemical transformation of continental material is characterized by a close interaction between impact melting vaporization and endogeneous geological processes.

  14. Modeling the Dynamics of Continental Shelf Carbon

    E-print Network

    Fennel, Katja

    Modeling the Dynamics of Continental Shelf Carbon Eileen E. Hofmann,1 Bronwyn Cahill,2 Katja Fennel, Canada; email: katja.fennel@dal.ca 4 Virginia Institute of Marine Science, College of William & Mary

  15. Continental Lower Crust Bradley R. Hacker,1

    E-print Network

    Hacker, Bradley R.

    Continental Lower Crust Bradley R. Hacker,1 Peter B. Kelemen,2 and Mark D. Behn3 1 Department of Earth Science, University of California, Santa Barbara, California 93106; email: hacker@geol.ucsb.edu 2

  16. Continental transform margins : state of art and future milestones

    NASA Astrophysics Data System (ADS)

    Basile, Christophe

    2010-05-01

    Transform faults were defined 45 years ago as ‘a new class of fault' (Wilson, 1965), and transform margins were consequently individualized as a new class of continental margins. While transform margins represent 20 to 25 % of the total length of continent-ocean transitions, they were poorly studied, especially when compared with the amount of data, interpretations, models and conceptual progress accumulated on divergent or convergent continental margins. The best studied examples of transform margins are located in the northern part of Norway, south of South Africa, in the gulf of California and on both sides of the Equatorial Atlantic. Here is located the Côte d'Ivoire - Ghana margin, where the more complete data set was acquired, based on numerous geological and geophysical cruises, including ODP Leg 159. The first models that encompassed the structure and evolution of transform margins were mainly driven by plate kinematic reconstructions, and evidenced the diachronic end of tectonic activity and the non-cylindrical character of these margins, with a decreasing strike-slip deformation from the convex to the concave divergent-transform intersections. Further thermo-mechanical models were more specifically designed to explain the vertical displacements along transform margins, and especially the occurrence of high-standing marginal ridges. These thermo-mechanical models involved either heat transfer from oceanic to continental lithospheres across the transform faults or tectonically- or gravity-driven mass transfer in the upper crust. These models were far from fully fit observations, and were frequently dedicated to specific example, and not easily generalizable. Future work on transform continental margins may be expected to fill some scientific gaps, and the definition of working directions can benefit from the studies dedicated to other types of margins. At regional scale the structural and sedimentological variability of transform continental margins has to be emphasized. There is not only one type of transform margins, but as for divergent margins huge changes from one margin to another in both structure and evolution. Multiple types have to be evidenced together with the various parameters that should control the variability. As for divergent margins, special attention should be paid to conjugated transform margins as a tool to assess symmetrical / asymmetrical processes in the oceanic opening. Attention should also be focused on the three-dimensional structure of the intersections between transform and divergent margins, such as the one where the giant oil field Jubilee was recently discovered. There is almost no 3D data available in these area, and their structures still have to be described. An other key point to develop is the mechanical behavior of the lithosphere in and in the vicinity of transform margins. The classical behaviors (isostasy, elastic flexure) have be tested extensively. The localization of the deformation by the transform fault, and the coupling of continental and oceanic lithosphere across the transform fault have to be adressed to understand the evolution of these margins. Again as for divergent margins, new concepts are needed to explain the variations in the post-rift and post-transform subsidence, that can not always be explained by classical subsidence models. But the most remarkable advance in our understanding of transform margins may be related to the study of interactions between the lithosphere and adjacent envelops : deep interactions with the mantle, as underplating, tectonic erosion, or possible lateral crustal flow ; surficial interactions between structural evolution, erosion and sedimentation processes in transform margins may affect the topography and bathymetry, thus the oceanic circulation with possible effects on regional and global climate.

  17. A lithospheric seismic profile across northern Taiwan, from arc-continental collision to extension

    NASA Astrophysics Data System (ADS)

    Van Avendonk, H. J.; McIntosh, K. D.; Lavier, L. L.; Wu, F. T.; Okaya, D. A.; Kuochen, H.

    2012-12-01

    Taiwan is one of a few locations where a subduction zone is transitioning to arc-continent collision. The north-south trending Luzon arc, which is built on the Philippine Sea Plate, has been overriding the Eurasian margin here since the Late Miocene. Shortening of the Eurasian margin lead to the formation of the Taiwan mountain belt. The plate boundary is quite complicated in northeastern Taiwan, because the Philippine Sea Plate also subducts beneath the Eurasian plate along the east-west trending Ryukyu trench. Since the Pleistocene, backarc extension behind the Ryukyu arc in the Okinawa Trough has propagated into the Ilan Plain, a region that previously experienced shortening during collision with the Luzon arc. The deep structure of northern Taiwan can therefore give us insight in the evolution of the orogen from compression to post-collisional collapse. During the 2008 and 2009 field seasons of the TAIGER project we acquired active-source and earthquake seismic data in Taiwan and surrounding oceans to better understand the different stages of arc-continent collision. On the island of Taiwan, explosion seismic, onshore-offshore and marine seismic data constrain the crustal structure along three large east-west transects across the plate boundary. In the north, TAIGER transect T6 spans a distance of 360 km from the Taiwan Strait eastward across the Hsuehshan Range and the Central Range, and onto the Ryukyu forearc. Marine seismic data were shot with the R/V Marcus Langseth in the Taiwan Strait and east of Taiwan. Twelve ocean-bottom seismometers from National Taiwan Ocean University (NTOU) recorded seismic refractions offshore, and land-seismic stations from IRIS/PASSCAL recorded airgun shots from the Langseth and 4 large land seismic explosions. These different types of active-source data together provide good spatial coverage for imaging seismic velocity structure across the orogen and the plate boundary. The seismic refraction data include crustal turning waves and wide-angle Moho reflections. To improve our constraints on the crustal root beneath Taiwan and on the upper mantle seismic velocity structure we augment this data set with first-arriving phases from 52 local earthquakes that were recorded on the IRIS/PASSCAL instruments during the active-source seismic experiment. With this combined seismic data set we will develop a detailed seismic velocity model along a profile across northern Taiwan and the Ryukyu forearc.

  18. Seismological constraints on the crustal structures generated by continental rejuvenation in northeastern China

    NASA Astrophysics Data System (ADS)

    Zheng, Tian-Yu; He, Yu-Mei; Yang, Jin-Hui; Zhao, Liang

    2015-10-01

    Crustal rejuvenation is a key process that has shaped the characteristics of current continental structures and components in tectonic active continental regions. Geological and geochemical observations have provided insights into crustal rejuvenation, although the crustal structural fabrics have not been well constrained. Here, we present a seismic image across the North China Craton (NCC) and Central Asian Orogenic Belt (CAOB) using a velocity structure imaging technique for receiver functions from a dense array. The crustal evolution of the eastern NCC was delineated during the Mesozoic by a dominant low seismic wave velocity with velocity inversion, a relatively shallow Moho discontinuity, and a Moho offset beneath the Tanlu Fault Zone. The imaged structures and geochemical evidence, including changes in the components and ages of continental crusts and significant continental crustal growth during the Mesozoic, provide insight into the rejuvenation processes of the evolving crust in the eastern NCC caused by structural, magmatic and metamorphic processes in an extensional setting. The fossil structural fabric of the convergent boundary in the eastern CAOB indicates that the back-arc action of the Paleo-Pacific Plate subduction did not reach the hinterland of Asia.

  19. Seismological constraints on the crustal structures generated by continental rejuvenation in northeastern China

    PubMed Central

    Zheng, Tian-Yu; He, Yu-Mei; Yang, Jin-Hui; Zhao, Liang

    2015-01-01

    Crustal rejuvenation is a key process that has shaped the characteristics of current continental structures and components in tectonic active continental regions. Geological and geochemical observations have provided insights into crustal rejuvenation, although the crustal structural fabrics have not been well constrained. Here, we present a seismic image across the North China Craton (NCC) and Central Asian Orogenic Belt (CAOB) using a velocity structure imaging technique for receiver functions from a dense array. The crustal evolution of the eastern NCC was delineated during the Mesozoic by a dominant low seismic wave velocity with velocity inversion, a relatively shallow Moho discontinuity, and a Moho offset beneath the Tanlu Fault Zone. The imaged structures and geochemical evidence, including changes in the components and ages of continental crusts and significant continental crustal growth during the Mesozoic, provide insight into the rejuvenation processes of the evolving crust in the eastern NCC caused by structural, magmatic and metamorphic processes in an extensional setting. The fossil structural fabric of the convergent boundary in the eastern CAOB indicates that the back-arc action of the Paleo-Pacific Plate subduction did not reach the hinterland of Asia. PMID:26443323

  20. The possible subduction of continental material to depths greater than 200 km.

    PubMed

    Ye, K; Cong, B; Ye, D

    2000-10-12

    Determining the depth to which continental lithosphere can be subducted into the mantle at convergent plate boundaries is of importance for understanding the long-term growth of supercontinents as well as the dynamic processes that shape such margins. Recent discoveries of coesite and diamond in regional ultrahigh-pressure (UHP) metamorphic rocks has demonstrated that continental material can be subducted to depths of at least 120 km (ref. 1), and subduction to depths of 150-300 km has been inferred from garnet peridotites in orogenic UHP belts based on several indirect observations. But continental subduction to such depths is difficult to trace directly in natural UHP metamorphic crustal rocks by conventional mineralogical and petrological methods because of extensive late-stage recrystallization and the lack of a suitable pressure indicator. It has been predicted from experimental work, however, that solid-state dissolution of pyroxene should occur in garnet at depths greater than 150 km (refs 6-8). Here we report the observation of high concentrations of clinopyroxene, rutile and apatite exsolutions in garnet within eclogites from Yangkou in the Sulu UHP metamorphic belt, China. We interpret these data as resulting from the high-pressure formation of pyroxene solid solutions in subducted continental material. Appropriate conditions for the Na2O concentrations and octahedral silicon observed in these samples are met at depths greater than 200 km. PMID:11048717

  1. Seismological constraints on the crustal structures generated by continental rejuvenation in northeastern China.

    PubMed

    Zheng, Tian-Yu; He, Yu-Mei; Yang, Jin-Hui; Zhao, Liang

    2015-01-01

    Crustal rejuvenation is a key process that has shaped the characteristics of current continental structures and components in tectonic active continental regions. Geological and geochemical observations have provided insights into crustal rejuvenation, although the crustal structural fabrics have not been well constrained. Here, we present a seismic image across the North China Craton (NCC) and Central Asian Orogenic Belt (CAOB) using a velocity structure imaging technique for receiver functions from a dense array. The crustal evolution of the eastern NCC was delineated during the Mesozoic by a dominant low seismic wave velocity with velocity inversion, a relatively shallow Moho discontinuity, and a Moho offset beneath the Tanlu Fault Zone. The imaged structures and geochemical evidence, including changes in the components and ages of continental crusts and significant continental crustal growth during the Mesozoic, provide insight into the rejuvenation processes of the evolving crust in the eastern NCC caused by structural, magmatic and metamorphic processes in an extensional setting. The fossil structural fabric of the convergent boundary in the eastern CAOB indicates that the back-arc action of the Paleo-Pacific Plate subduction did not reach the hinterland of Asia. PMID:26443323

  2. Coordination: southeast continental shelf studies. Progress report

    SciTech Connect

    Menzel, D.W.

    1981-02-01

    The objectives are to identify important physical, chemical and biological processes which affect the transfer of materials on the southeast continental shelf, determine important parameters which govern observed temporal and spatial varibility on the continental shelf, determine the extent and modes of coupling between events at the shelf break and nearshore, and determine physical, chemical and biological exchange rates on the inner shelf. Progress in meeting these research objectives is presented. (ACR)

  3. The Continental Margins Program in Georgia

    USGS Publications Warehouse

    Cocker, M.D.; Shapiro, E.A.

    1999-01-01

    From 1984 to 1993, the Georgia Geologic Survey (GGS) participated in the Minerals Management Service-funded Continental Margins Program. Geological and geophysical data acquisition focused on offshore stratigraphic framework studies, phosphate-bearing Miocene-age strata, distribution of heavy minerals, near-surface alternative sources of groundwater, and development of a PC-based Coastal Geographic Information System (GIS). Seven GGS publications document results of those investigations. In addition to those publications, direct benefits of the GGS's participation include an impetus to the GGS's investigations of economic minerals on the Georgia coast, establishment of a GIS that includes computer hardware and software, and seeds for additional investigations through the information and training acquired as a result of the Continental Margins Program. These addtional investigations are quite varied in scope, and many were made possible because of GIS expertise gained as a result of the Continental Margins Program. Future investigations will also reap the benefits of the Continental Margins Program.From 1984 to 1993, the Georgia Geologic Survey (GGS) participated in the Minerals Management Service-funded Continental Margins Program. Geological and geophysical data acquisition focused on offshore stratigraphic framework studies, phosphate-bearing Miocene-age strata, distribution of heavy minerals, near-surface alternative sources of groundwater, and development of a PC-based Coastal Geographic Information System (GIS). Seven GGS publications document results of those investigations. In addition to those publications, direct benefits of the GGS's participation include an impetus to the GGS's investigations of economic minerals on the Georgia coast, establishment of a GIS that includes computer hardware and software, and seeds for additional investigations through the information and training acquired as a result of the Continental Margins Program. These additional investigations are quite varied in scope, and many were made possible because of GIS expertise gained as a result of the Continental Margins Program. Future investigations will also reap the benefits of the Continental Margins Program.

  4. Magnesium isotope fractionation during continental weathering

    NASA Astrophysics Data System (ADS)

    Teng, F. Z.; Huang, K. J.; Li, W.; Liu, X. M.; Ma, L.

    2014-12-01

    Continental weathering links the atmosphere, hydrosphere and continents as it regulates the CO2 content of the atmosphere, shifts the composition of the continental crust from basaltic to andesitic, and ultimately controls the chemical composition of river waters and seawater. Magnesium is a water-soluble major element in the hydrosphere, continental crust and the mantle, and has three stable isotopes (24Mg, 25Mg and 26Mg). Studies of Mg isotopes during continental weathering may help to document the interactions between hydrosphere, crust and mantle. Previous studies have shown that the continental crust has a heterogeneous but on average heavier Mg isotopic composition than the mantle, whereas the hydrosphere is isotopically light. The complementary characteristics of Mg isotopic compositions between continental and hydrosphere have been attributed to continental weathering, with light Mg isotopes partitioned into water, leaving heavy Mg isotopes behind in the crustal residue. Here we summarize our studies of Mg isotope fractionation in four weathering profiles under various climate conditions. We show that large Mg isotope fractionation can occur during continental weathering. Although the weathered residue is usually enriched in heavier Mg isotopes than unaltered parent rocks, some heavily weathered products can be quite light in Mg isotopic composition. The complicated behaviors of Mg isotopes reflect different control factors during weathering such as parent rock lithology, primary mineral dissolution, secondary mineral formation, ion exchange, vegetation uptake etc. Though studies of natural samples can provide direct evidence on isotope fractionation, more well-controlled laboratory experiments on Mg isotope fractionation between fluids and minerals are needed in order to fully understand the behaviors of Mg isotopes during weathering, which ultimately lays the foundation for making Mg isotope geochemistry an important tool for studying different geological problems.

  5. Relamination and the Differentiation of Continental Crust

    NASA Astrophysics Data System (ADS)

    Hacker, Bradley; Kelemen, Peter; Behn, Mark

    2015-04-01

    Most immature crust must be refined to attain the composition of mature continental crust. This refining may take the form of weathering, delamination, or relamination. Although delamination and relamination both call upon gravity-driven separation of felsic rock into the crust and mafic rock into the mantle, delamination involves foundering of rock from the base of active magmatic arcs, whereas relamination involves the (diapiric) underplating of subducted sediment, arc crust, and continent crust to the base of the crust in any convergence zone. Relamination may be more efficient than lower crustal foundering at generating large volumes of material with the major- and trace-element composition of continental crust, and may have operated rapidly enough to have refined the composition of the entire continental crust over the lifetime of Earth. If so, felsic rocks could form much of the lower crust, and the bulk continental crust may be more silica rich than generally considered. Seismic wavespeeds require that only ~10-20% of the lowermost 5-15 km of continental crust must be mafic; combined heat-flow and wavespeed constraints permit continental lower crust to have 49 to 62 wt% SiO2.

  6. Continental crust generated in oceanic arcs

    NASA Astrophysics Data System (ADS)

    Gazel, Esteban; Hayes, Jorden L.; Hoernle, Kaj; Kelemen, Peter; Everson, Erik; Holbrook, W. Steven; Hauff, Folkmar; van den Bogaard, Paul; Vance, Eric A.; Chu, Shuyu; Calvert, Andrew J.; Carr, Michael J.; Yogodzinski, Gene M.

    2015-04-01

    Thin oceanic crust is formed by decompression melting of the upper mantle at mid-ocean ridges, but the origin of the thick and buoyant continental crust is enigmatic. Juvenile continental crust may form from magmas erupted above intra-oceanic subduction zones, where oceanic lithosphere subducts beneath other oceanic lithosphere. However, it is unclear why the subduction of dominantly basaltic oceanic crust would result in the formation of andesitic continental crust at the surface. Here we use geochemical and geophysical data to reconstruct the evolution of the Central American land bridge, which formed above an intra-oceanic subduction system over the past 70 Myr. We find that the geochemical signature of erupted lavas evolved from basaltic to andesitic about 10 Myr ago--coincident with the onset of subduction of more oceanic crust that originally formed above the Galápagos mantle plume. We also find that seismic P-waves travel through the crust at velocities intermediate between those typically observed for oceanic and continental crust. We develop a continentality index to quantitatively correlate geochemical composition with the average P-wave velocity of arc crust globally. We conclude that although the formation and evolution of continents may involve many processes, melting enriched oceanic crust within a subduction zone--a process probably more common in the Archaean--can produce juvenile continental crust.

  7. The Interpretation of Crustal Dynamics Data in Terms of Plate Interactions and Active Tectonics of the Anatolian Plate and Surrounding Regions in the Middle East

    NASA Technical Reports Server (NTRS)

    Toksoz, M. Nafi; Reilinger, Robert E.

    1990-01-01

    During the past 6 months, efforts were concentrated on the following areas: (1) Continued development of realistic, finite element modeling of plate interactions and associated deformation in the Eastern Mediterranean; (2) Neotectonic field investigations of seismic faulting along the active fault systems in Turkey with emphasis on identifying seismic gaps along the North Anatolian fault; and (3) Establishment of a GPS regional monitoring network in the zone of ongoing continental collision in eastern Turkey (supported in part by NSF).

  8. A change in the geodynamics of continental growth 3 billion years ago.

    PubMed

    Dhuime, Bruno; Hawkesworth, Chris J; Cawood, Peter A; Storey, Craig D

    2012-03-16

    Models for the growth of continental crust rely on knowing the balance between the generation of new crust and the reworking of old crust throughout Earth's history. The oxygen isotopic composition of zircons, for which uranium-lead and hafnium isotopic data provide age constraints, is a key archive of crustal reworking. We identified systematic variations in hafnium and oxygen isotopes in zircons of different ages that reveal the relative proportions of reworked crust and of new crust through time. Growth of continental crust appears to have been a continuous process, albeit at variable rates. A marked decrease in the rate of crustal growth at ~3 billion years ago may be linked to the onset of subduction-driven plate tectonics. PMID:22422979

  9. Does strike-slip motion facilitate rifting and continental break-up?

    NASA Astrophysics Data System (ADS)

    Brune, Sascha; Popov, Anton A.; Sobolev, Stephan V.

    2010-05-01

    Initial stages of continental break-up often involve large strike-slip components (e.g. during separation of South America and Africa, ~140 Ma) however there is no clear understanding of how oblique motions effect the break-up development. We use the three-dimensional, thermomechanical FEM code SLIM3D to model rifting of continental lithosphere composed of upper crust, lower crust, and mantle lithosphere. Results show that the force needed to initiate break-up strongly decreases for increased oblique plate motion. Our numerical models allow to quantify the relative importance of the three main weakening mechanisms: (i) friction softening in the brittle domain due to a strain-dependent effective angle of internal friction, as well as (ii) strain rate softening and (iii) shear heating which both reduce viscosity in the ductile domain.

  10. Retrodeforming the Arabia-Eurasia collision zone : Age of collision and magnitude of continental subduction

    NASA Astrophysics Data System (ADS)

    McQuarrie, N.; van Hinsbergen, D. J. J.

    2012-04-01

    When did continents collide, and how is convergence partitioned after collision are first order questions that seem to defy consensus along the Alpine-Himalyan orogen. Estimates on the age of collision for Arabia and Eurasia range from late Cretaceous to Pliocene, based on a wide variety of presumed geologic responses. Both lower Miocene synorgenic strata with growth structures adjacent to the main Zagros fault and upper Oligocene to lower Miocene overlap strata over post-collisional thrusts are derived from Eurasia and require that collision was underway at least by ~25-24 Ma. However, upper plate deformation, exhumation and sedimentation are used to argue for an older, 35 Ma collision age. Africa-North America-Eurasia plate circuit rotations, combined with Red Sea rotations provides precise estimates of the relative positions between the northern Arabian margin and the southern Eurasia margin. Plate circuits indicate, from NW to SE along the collision zone 490-650 km of post-25 Ma Arabia-Eurasia convergence and 810-1070 km since 35 Ma. To assess the consequences of these collision ages for the amount of Arabian continental subduction, we compile all documented shortening within the orogen. The Zagros fold-thrust belt consists of thrusted upper crust that was offscraped from subducted Arabian continental lithosphere. Balanced cross-sections give 105-180 km of Zagros shortening (including estimates from the Zagros proper, 45-90 km, and the Zagros "crush" zone, 60-90 km). Shortening within Eurasia is estimated to be 53-75 km through the Kopet Dagh and Alborz Mountains, plus 38 km across Central Iran. These estimates suggest that the orogen has shortened 200 to 300 km since the early Miocene. Both a 25 and a 35 Ma collision estimate thus requires that a considerable portion of the Arabian plate subducted without recognized accretion of its upper crust. To balance plate circuits and documented shortening requires whole-sale subduction of ~500-800 km of continental crust since 35 Ma; for a 25 Ma collision this would be between 190-450 km. The ophiolitic fragments preserved along the suture zone allow us to test the magnitude of possible continental subduction. The Oman Ophiolite preserves the geometry and distance over which ophiolites obduced over the northern margin of Arabia in the late Cretaceous. The distance from the southwestern edge of the ophiolite to the northeastern edge of the continent is 180 km, suggesting that the Arabian continental margin plus overlying ophiolites may have extended ~200 km beyond the Main Zagros fault. Assuming that 200 km of Arabian continental margin and overlying ophiolites subducted entirely, except the few remnant ophiolite slivers remaining in the suture zone, would reconstruct ~ 400-500 km of post-collisional Arabia-Eurasia convergence, consistent with a ~25 Ma collision age. As much as 500-800 km of continental subduction required by an earlier (~35 Ma) collision age seems unlikely.

  11. North American plate dynamics

    NASA Technical Reports Server (NTRS)

    Richardson, Randall M.; Reding, Lynn M.

    1991-01-01

    Deformation within the North American plate in response to various tectonic processes is modeled using an elastic finite element analysis. The tectonic processes considered in the modeling include ridge forces associated with the normal thermal evolution of oceanic lithosphere, shear and normal stresses transmitted across transforms, normal stresses transmitted across convergent boundaries, stresses due to horizontal density contrasts within the continent, and shear tractions applied along the base of the plate. Model stresses are calculated with respect to a lithostatic reference stress state. Shear stresses transmitted across transform boundaries along the San Andreas and Caribbean are small, of the order of 5-10 MPa. Also, compressive stresses of the order of 5-10 MPa transmitted across the major transforms improve the fit to the data. Compressive stresses across convergent margins along the Aleutians and the Middle America trench are important.

  12. Bipolar battery plate

    NASA Technical Reports Server (NTRS)

    Rowlette, John J. (Inventor)

    1985-01-01

    A liquid-impermeable plate (10) having throughplate conductivity with essentially zero resistance comprises an insulator sheet (12) having a series of spaced perforations (14) each of which contains a metal element (16) sealingly received into the perforation (14). A low-cost plate can readily be manufactured by punching a thermoplastic sheet (40) such as polypropylene with a punching tool (52), filling the apertures with lead spheres (63) having a diameter smaller than the holes (50) but larger than the thickness of the sheet, sweeping excess spheres (62) off the sheet with a doctor blade (60) and then pressing a heated platen (74) onto the sheet to swage the spheres into a cylindrical shape and melt the surrounding resin to form a liquid-impermeable collar (4) sealing the metal into the sheet.

  13. Microchannel plate streak camera

    DOEpatents

    Wang, C.L.

    1984-09-28

    An improved streak camera in which a microchannel plate electron multiplier is used in place of or in combination with the photocathode used in prior streak cameras. The improved streak camera is far more sensitive to photons (uv to gamma-rays) than the conventional x-ray streak camera which uses a photocathode. The improved streak camera offers gamma-ray detection with high temporal resolution. It also offers low-energy x-ray detection without attenuation inside the cathode. Using the microchannel plate in the improved camera has resulted in a time resolution of about 150 ps, and has provided a sensitivity sufficient for 1000 keV x-rays.

  14. Microchannel plate streak camera

    DOEpatents

    Wang, Ching L. (Livermore, CA)

    1989-01-01

    An improved streak camera in which a microchannel plate electron multiplier is used in place of or in combination with the photocathode used in prior streak cameras. The improved streak camera is far more sensitive to photons (UV to gamma-rays) than the conventional x-ray streak camera which uses a photocathode. The improved streak camera offers gamma-ray detection with high temporal resolution. It also offers low-energy x-ray detection without attenuation inside the cathode. Using the microchannel plate in the improved camera has resulted in a time resolution of about 150 ps, and has provided a sensitivity sufficient for 1000 KeV x-rays.

  15. Microchannel plate streak camera

    DOEpatents

    Wang, C.L.

    1989-03-21

    An improved streak camera in which a microchannel plate electron multiplier is used in place of or in combination with the photocathode used in prior streak cameras is disclosed. The improved streak camera is far more sensitive to photons (UV to gamma-rays) than the conventional x-ray streak camera which uses a photocathode. The improved streak camera offers gamma-ray detection with high temporal resolution. It also offers low-energy x-ray detection without attenuation inside the cathode. Using the microchannel plate in the improved camera has resulted in a time resolution of about 150 ps, and has provided a sensitivity sufficient for 1,000 KeV x-rays. 3 figs.

  16. Plated wire memory subsystem

    NASA Technical Reports Server (NTRS)

    Reynolds, L.; Tweed, H.

    1972-01-01

    The work performed entailed the design, development, construction and testing of a 4000 word by 18 bit random access, NDRO plated wire memory for use in conjunction with a spacecraft imput/output unit and central processing unit. The primary design parameters, in order of importance, were high reliability, low power, volume and weight. A single memory unit, referred to as a qualification model, was delivered.

  17. Elastic plate spallation

    NASA Technical Reports Server (NTRS)

    Oline, L.; Medaglia, J.

    1972-01-01

    The dynamic finite element method was used to investigate elastic stress waves in a plate. Strain displacement and stress strain relations are discussed along with the stiffness and mass matrix. The results of studying point load, and distributed load over small, intermediate, and large radii are reported. The derivation of finite element matrices, and the derivation of lumped and consistent matrices for one dimensional problems with Laplace transfer solutions are included. The computer program JMMSPALL is also included.

  18. The Alignment and Spacing of Volcanoes on Earth: Are Oceanic and Continental Settings Really That Different?

    NASA Astrophysics Data System (ADS)

    Naumann, T. R.

    2002-12-01

    The origin of the alignment and spacing of volcanoes has traditionally been treated from two fundamentally different perspectives: continental and oceanic. With the overwhelming evidence from the Hawaiian-Emperor chain, where a robust plume has generated a simple time-transgressive chain of volcanic islands, many oceanic alignments worldwide have been ascribed to plate motion above a fixed source of melting. Conversely, alignments of volcanoes in continental settings are primarily ascribed to some structural or tectonic pathway that serves to guide rising magmas. This fundamental difference of cause and effect, with respect to these two settings, has led to misinterpretations regarding the age and evolution of some island chains. In the Hawaiian Islands attributes like volcano age, elevation, morphology, and lava composition change systematically in the direction of plate motion away from the most recent activity on the island of Hawaii. However, some other plume-related volcanic archipelagoes have more diffuse volcanic activity and the relative ages among some the islands are not so clear. In the Galapagos Islands, although the maximum measured ages of the lava flows increase systematically eastward from Fernandina to San Cristobal, the large western volcanoes are essentially coeval. Similar ages imply that morphological and geochemical differences among these volcanoes are due to differences in melt generation and magma supply imposed by variations in plume strength and lithospheric structure rather than an evolutionary model like that predicted for Hawaiian systems. Comparisons of other volcanic chains and fields less voluminous than Hawaii indicate that although oceanic and continental magmas are chemically quite different, the controls governing their emplacement are not. The emplacement of smaller volume oceanic systems like the Galapagos, Canaries, Reunion, and many seamounts may share more aspects with continental volcanic fields than they do with large volume systems like Hawaii. Magma transport in small volume systems is strongly influenced by lithospheric/crustal thickness, tectonic stresses, and preexisting weaknesses which ultimately provide the dominant control on the location, alignment, geochemical variation, and eruptive volume of volcanoes.

  19. Lower crustal rocks in the Norwegian Caledonides: field analogues for understanding the geodynamics of continental subduction and UHP exhumation

    NASA Astrophysics Data System (ADS)

    Andersen, Torgeir B.

    2010-05-01

    The Scandinavian Caledonides and their counterparts in East-Greenland represent the best ancient example of a Himalayan-type continental collision orogen on the Earth. The mountain- and plateau areas that formed in response to the Scandian continental collision and the extensional tectonics in the Late Silurian to Devonian were comparable in size to the present-day Himalayas and the Tibetan plateau, with a strike length close to 2000 km and a width of more than 500 km. The collision also affected areas within the overriding continent far behind the collision zone, which gave rise to intra-continental mountains in Arctic Canada. The Iapetus ocean intervening Baltica-Avalonia and Laurentia was consumed by rapid subduction (>12 cm/yr) and closed by the Middle Silurian (~430 Ma). The rapid convergence resulted in deep burial of continental lithosphere to (ultra) high-pressure [(U)HP] conditions. Syn-convergent thrust-stacking and upper crust-extension in the late Silurian to early Devonian was succeeded by buoyant eduction of the deeply buried, but still mostly coherent slab of continental rocks and some included lenses of mantle peridotite. These exhumed lower crustal rocks record a pressure-temperature gradient from amphibolite facies immediately below the Caledonian nappes via a wide belt of eclogite facies rocks (600C; 1.8-2 GPa) to coesite eclogites (700-800C; 2.7-2.8 GPa) across the ca 250 km wide Western Gneiss Region. Although the superstructure of the Scandian mountain belt is only rudimentarily preserved restoration of the SE-NW cross-sections can be used to constrain crustal thicknesses during the collision. These restored cross-sections allow explanation of burial and exhumation of coesite eclogite without direct conversion of pressure to burial. The exhumation of the very local and extreme UHP conditions recorded by micro-diamonds, majorite in peridotite garnet and ortho-pyroxene eclogite barometry cannot, however, be adequately explained by the available structures. The global importance of the Caledonides to understand collision geodynamics is primarily related to the structural and metamorphic evolution of the deep parts of orogenic belts, i.e. how UHP rocks are formed and exhumed.

  20. Symmetries in laminated composite plates

    NASA Technical Reports Server (NTRS)

    Noor, A. K.

    1976-01-01

    The different types of symmetry exhibited by laminated anisotropic fibrous composite plates are identified and contrasted with the symmetries of isotropic and homogeneous orthotropic plates. The effects of variations in the fiber orientation and the stacking sequence of the layers on the symmetries exhibited by composite plates are discussed. Both the linear and geometrically nonlinear responses of the plates are considered. A simple procedure is presented for exploiting the symmetries in the finite element analysis. Examples are given of square, skew and polygonal plates where use of symmetry concepts can significantly reduce the scope and cost of analysis.

  1. Lower plate deformation structures along the Costa Rica erosive plate boundary - results from IODP Expedition 344 (CRISP 2)

    NASA Astrophysics Data System (ADS)

    Brandstätter, Jennifer; Kurz, Walter; Micheuz, Peter; Krenn, Kurt

    2015-04-01

    The primary objective of Integrated Ocean Drilling Program (IODP) Expedition 344 offshore the Osa Peninsula in Costa Rica was to sample and quantify the material entering the seismogenic zone of the Costa Rican erosive subduction margin. Fundamental to this objective is an understanding of the nature of both the subducting Cocos plate crust and of the overriding Caribbean plate. The subducting Cocos plate is investigated trying to define its hydrologic system and thermal state. The forearc structures recorded by the sediment deposited on the forearc, instead, document periods of uplift and subsidence and provide important information about the process of tectonic erosion that characterizes the Costa Rica margin. Offshore the western margin of Costa Rica, the oceanic Cocos plate subducts under the Caribbean plate, forming the southern end of the Middle America Trench. Subduction parameters including the age, convergence rate, azimuth, obliquity, morphology, and slab dip all vary along strike. The age of the Cocos plate at the Middle America Trench decreases from 24 Ma offshore the Nicoya Peninsula to 15 Ma offshore the Osa Peninsula. Subduction rates vary from 70 mm/y offshore Guatemala to 90 mm/y offshore southern Costa Rica. Convergence obliquity across the trench varies from offshore Nicaragua, where it is as much as 25° oblique, to nearly orthogonal southeast of the Nicoya Peninsula. Passage of the Cocos plate over the Galapagos hotspot created the aseismic Cocos Ridge, an overthickened welt of oceanic crust. This ridge is ~25 km thick, greater than three times normal oceanic crustal thickness. During IODP Expedition 344, the incoming Cocos plate was drilled at sites U1381 and U1414. Site U1381 is located ~4.5 km seaward of the deformation front offshore the Osa Peninsula and Caño Island. It is located on a local basement high. Basement relief often focuses fluid flow, so data from this site are likely to document the vigor of fluid flow in this area. Site U1414 is located ~1 km seaward of the deformation front offshore the Osa Peninsula and Caño Island. Primary science goals at Site U1414 included characterization of the alteration state of the magmatic basement. Brittle structures within the incoming plate (sites U1380, U1414) are mineralized extensional fractures and shear fractures. The shear fractures mainly show a normal component of shear. Within the sedimentary sequence both types of fractures dip steeply (vertical to subvertical) and strike NNE-SSW. Deformation bands trend roughly ENE-WSW, sub-parallel to the trend of the Cocos ridge. Structures in the Cocos Ridge basalt mainly comprise mineralized veins at various orientations. A preferred orientation of strike directions was not observed. Some veins show straight boundaries, others are characterized by an irregular geometry characterized by brecciated wall rock clasts embedded within vein precipitates. The vein mineralization was analysed in detail by RAMAN spectroscopy. Precipitation conditions and fluid chemistry were analysed by fluid inclusions entrapped within vein minerals. Vein mineralizations mainly consist of carbonate (fibrous aragonite, calcite), chalcedony, and quartz. Vein mineralization is mainly characterized by zoned antitaxial growth of carbonate fibres including a suture along the central vein domains. Quartz is often characterized by fibre growth of crystals perpendicular to the vein boundaries, too. These zoned veins additinally have wall rock alteration seams consisting of clay minerals. The precipitation sequence basically indicates that fluid chemistry evolved from an CO2-rich towards a SiO2- rich fluid.

  2. Tectonic evolution of Brazilian equatorial continental margin basins

    SciTech Connect

    Azevedo, R.P. )

    1993-02-01

    The structural style and stratigraphic relationships of sedimentary basins along the Brazilian Equatorial Atlantic Continental Margin were used to construct an empirical tectonic model for the development of ancient transform margins. The model is constrained by detailed structural and subsidence analyses of several basins along the margin. The structural framework of the basins was defined at shallow and deep levels by the integration of many geophysical and geological data sets. The Barreirinhas and Para-Maranhao Basins were divided in three tectonic domains: the Tutoia, Caete, and Tromai subbasins. The Caete area is characterized by northwest-southeast striking and northeast-dipping normal faults. A pure shear mechanism of basin formation is suggested for its development. The structure of the Tutoia and Tromai subbasins are more complex and indicative of a major strike-slip component with dextral sense of displacement, during early stages of basin evolution. These two later subbasins were developed on a lithosphere characterized by an abrupt transition (<50 km wide) from an unstretched continent to an oceanic lithosphere. The subsidence history of these basins do not comply with the classical models developed for passive margins or continental rifting. The thermo-mechanical model proposed for the Brazilian equatorial margin includes heterogeneous stretching combined with shearing at the plate margin. The tectonic history comprises: (1) Triassic-Jurassic limited extension associated with the Central Atlantic evolution; (2) Neocomian intraplate deformation consisting of strike-slip reactivation of preexisting shear zones; (3) Aptian-Cenomanian two-phase period of dextral shearing; and (4) Late Cretaceous-Cenozoic sea-floor spreading.

  3. On causal links between flood basalts and continental breakup

    NASA Astrophysics Data System (ADS)

    Courtillot, V.; Jaupart, C.; Manighetti, I.; Tapponnier, P.; Besse, J.

    1999-03-01

    Temporal coincidence between continental flood basalts and breakup has been noted for almost three decades. Eight major continental flood basalts have been produced over the last 300 Ma. The most recent, the Ethiopian traps, erupted in about 1 Myr at 30 Ma. Rifting in the Red Sea and Gulf of Aden, and possibly East African rift started at about the same time. A second trap-like episode occurred around 2 Ma and formation of true oceanic crust is due in the next few Myr. We find similar relationships for the 60 Ma Greenland traps and opening of the North Atlantic, 65 Ma Deccan traps and opening of the NW Indian Ocean, 132 Ma Parana traps and South Atlantic, 184 Ma Karoo traps and SW Indian Ocean, and 200 Ma Central Atlantic Margin flood basalts and opening of the Central Atlantic Ocean. The 250 Ma Siberian and 258 Ma Emeishan traps seem to correlate with major, if aborted, phases of rifting. Rifting asymmetry, apparent triple junctions and rift propagation (towards the flood basalt area) are common features that may, together with the relative timings of flood basalt, seaward dipping reflector and oceanic crust production, depend on a number of plume- and lithosphere- related factors. We propose a mixed scenario of `active/passive' rifting to account for these observations. In all cases, an active component (a plume and resulting flood basalt) is a pre-requisite for the breakup of a major oceanic basin. But rifting must be allowed by plate-boundary forces and is influenced by pre-existing heterogeneities in lithospheric structure. The best example is the Atlantic Ocean, whose large-scale geometry with three large basins was imposed by the impact points of three mantle plumes.

  4. Fuel cell end plate structure

    DOEpatents

    Guthrie, Robin J. (East Hartford, CT); Katz, Murray (Newington, CT); Schroll, Craig R. (Glastonbury, CT)

    1991-04-23

    The end plates (16) of a fuel cell stack (12) are formed of a thin membrane. Pressure plates (20) exert compressive load through insulation layers (22, 26) to the membrane. Electrical contact between the end plates (16) and electrodes (50, 58) is maintained without deleterious making and breaking of electrical contacts during thermal transients. The thin end plate (16) under compressive load will not distort with a temperature difference across its thickness. Pressure plate (20) experiences a low thermal transient because it is insulated from the cell. The impact on the end plate of any slight deflection created in the pressure plate by temperature difference is minimized by the resilient pressure pad, in the form of insulation, therebetween.

  5. Global isostatic geoid anomalies for plate and boundary layer models of the lithosphere

    NASA Technical Reports Server (NTRS)

    Hager, B. H.

    1981-01-01

    Commonly used one dimensional geoid models predict that the isostatic geoid anomaly over old ocean basins for the boundary layer thermal model of the lithosphere is a factor of two greater than that for the plate model. Calculations presented, using the spherical analogues of the plate and boundary layer thermal models, show that for the actual global distribution of plate ages, one dimensional models are not accurate and a spherical, fully three dimensional treatment is necessary. The maximum difference in geoid heights predicted for the two models is only about two meters. The thermal structure of old lithosphere is unlikely to be resolvable using global geoid anomalies. Stripping the effects of plate aging and a hypothetical uniform, 35 km, isostatically-compensated continental crust from the observed geoid emphasizes that the largest-amplitude geoid anomaly is the geoid low of almost 120 m over West Antarctica, a factor of two greater than the low of 60 m over Ceylon.

  6. Iberia/Eurasia plate kinematic models as recorded from shortening evolution of the Pyrenees

    NASA Astrophysics Data System (ADS)

    Mouthereau, Frédéric; Filleaudeau, Pierre-Yves; Vacherat, Arnaud

    2014-05-01

    Contrasting reconstructions of Iberia plate motion have been proposed in the Pyrenees, reflecting our difficulties to reconcile interpretations from magnetic anomalies with geological arguments. Here, we confront implications from currently proposed plate kinematic models with the most recent constraints on the thermal history and shortening evolution of the Northern Pyrenees. We particularly focus on the incipient subduction/collision and question the role played by the rifted margin architectures. A good fit with geological constraints is found provided that a significant amount of arc-normal convergence is accommodated at a distal hyper-extended margin, during the earliest stages of collision. After 20 Myrs of plate convergence, the first contact between proximal margins initiated a progressive decrease of plate convergence that was mainly consumed in building the Pyrenean mountain belt. This shortening scenario is shown to be consistent with recent geophysical data on deep crustal processes and finite strain predicted on young continental margins.

  7. Evaluating the effect of rheology on the evolution of continental collision: Application to the Zagros orogen.

    NASA Astrophysics Data System (ADS)

    François, T.; Burov, E.; Agard, P.; Meyer, B.

    2012-04-01

    We explore the impact of thermo-rheological structure of the lithosphere on the transition from oceanic to continental subduction and evolution of the continental collision at moderate convergence rates. We have designed large-scale (3082×590 km), high-resolution fully coupled thermo-mechanical numerical models to (1) study the evolution of continent-continent collision and (2) draw some parallels with the tectonic evolution of the Zagros, where collision between the Arabian craton and the Eurasian lithosphere resulted in the rise of the Iranian plateau. This collision zone is of particular interest due to its disputed resemblance to the faster Himalayan collision between the Indian craton and Eurasia, which gave birth to the vast Tibetan plateau. Our models implement free upper surface boundary, surface erosion, rheological stratification (upper crust, lower crust, lithospheric mantle and asthenosphere), brittle-elastic-ductile rheology, metamorphic phase changes (density and physical properties), and account for the specific crustal and thermal structure of the Arabian and Iranian continental lithospheres. The initial model geometry corresponds to the pre-continental collision phase, with an oceanic, Neotethyan subducting lithosphere still separating the two continents. In the experiments we investigate different thermo-rheological structures for both the lower and upper plate, going from wet to dry olivine (plus Peierls) rheology for the mantle parts and from two-layer to three-layer crustal structures with all possible granite, diorite, granulate and diabase rheologies. As in some previous Himalayan studies, the experiments suggest that, whatever the crustal rheology, the continental subduction occurs only in the case of relatively strong mantle lithospheres with dry olivine rheologies (for the lower plate, temperature at Moho depth, Tm < 550° C) and high initial convergence rates (>1.5-5 cm/yr). Depending on the lower-crustal rheology (strong or weak), either the whole (upper and lower) crust or only the lower crust is involved in subduction. In case of weak metamorphic rheologies, phase changes and progressive densification along the subduction zone improve chances for stable subduction. In general, exhumation of UHP-HP rocks to the surface is favored if the crustal rheological profile is characterized by two internal ductile decollement levels (between the upper and lower or intermediate crust and the lower crust and mantle lithosphere). On the other hand, the formation of the Iranian plateau is compatible with the assumption of rather weak mantle and crustal rheology. Hence, the models show that only a relatively narrow range of rheological parameters is compatible with the evolution of Zagros collision, which in turn allows us to further constrain the long-term rheology of the continental lithosphere.

  8. Earth's earliest continental lithosphere, hydrothermal flux and crustal recycling

    NASA Astrophysics Data System (ADS)

    de Wit, Maarten J.; Hart, Roger A.

    1993-09-01

    The Kaapvaal craton in southern Africa and the Pilbara craton of northwestern Australia are the largest regions on Earth to have retained relatively pristine mid-Archaean rocks (3.0-4.0 Ga). The Kaapvaal craton covers about 1.2×10 6 km 2, and varies in lithospheric thickness between 170 and 350 km. At surface, the craton can be subdivided into a number of Archaean sub-domains; some of the subdomains are also well defined at depth, and local variations in tomography of the lithosphere correspond closely with subdomain boundaries at surface. The Archaean history of the Kaapvaal craton spans about 1 Gyr and can be conveniently subdivided into two periods, each of about the same length as the Phanerozoic. The first period, from circa 3.7-3.1 Ga, records the initial separation of the cratonic lithosphere from the asthenosphere, terminating with a major pulse of accretion tectonics between 3.2 and 3.1 Ga, which includes the formation of "paired metamorphic belts". This period of continental growth can be compared to plate tectonic processes occurring in modern-day oceanic basins. However, the difference is that in the mid-Archaean, these oceanic processes appear to have occurred in shallower water depths than the modern ocean basins. The second period, from circa 3.1-2.6 Ga, records intra-continental and continental-edge processes: continental growth during this period occurred predominantly through a combination of tectonic accretion of crustal fragments and subduction-related igneous processes, in much the same way as has been documented along the margins of the Pacific and Tethys oceans since the Mesozoic. The intra-oceanic processes resulted in small, but deep-rooted continental nucleii; the first separation of this early continental lithosphere could only have occurred when the mean elevation of mid-oceanicridges sank below sea-level. Substantial recycling of continental lithosphere into the mantle must have occurred during this period of Earth history. During the second period, at least two large continental nucleii amalgamated during collisional processes which, together with internal chemical differentiation processes, created the first stable continental landmass. This landmass, which is known to have been substantially bigger than its present outline, may have been part of the Earth's first supercontinent. The oldest known subdomains of the craton include the oceanic-like rocks of the Barberton greenstone belt. The comagmatic mafic-ultramafic rocks (3.48-3.49 Ga) of this belt represent a remnant of very early oceanic-like lithosphere (known as the Jamestown Ophiolite Complex), which was obducted, approximately 45 Ma after its formation, onto a volcanic arc-like terrain by processes similar to those which have emplaced modern ophiolites at convergent margins of Phanerozoic continents. The early metamorphic history, metamorphic mineralogy, oxygen isotope profiles and degree of hydration of the 3.49 Ga Jamestown Ophiolite Complex are similar to present day subseafloor hydrothermal systems. The ratio of ?Mg to ?Si for hydrothermally altered igneous rocks, both present day and Archaean, are remarkably uniform at -5(±0.9) and the same as that of hydrothermal fluids venting on the present-day East Pacific Rise. This observation suggests that the process of Mg exchange for Si in hydrothermal systems was commonplace throughout Earth's history. The chemistry of vent fluids and hydrothermally altered igneous rocks was combined with an inventory of 3He in the mantle to model Earth's total hydrothermal flux. An Archaean flux (at 3.5 Ga) of about 10 times present day was accompanied by a correspondingly greater abundance of Mg(OH), SiO 2, carbonate and Fe?Mn metasomatic rock types as well as massive sulphides. Assuming a constant column of seawater since the Archaean, the average residence time of seawater in the oceanic crust was 1.65-8.90×10 5 years in the Archaean. Assuming that 3He and heat are transported from the mantle in silicate melts in uniform proportions, the model stipulates that accretion of oce

  9. Structural-energetic evolution of the continental crust and some metallogenic consequences

    NASA Astrophysics Data System (ADS)

    Goriainov, P. M.

    Trends in the evolution of the tectonosphere are examined in the light of the theory of endogeneous-energy conversion, and the metallogenic peculiarities of the Precambrian tectonosphere are examined. These issues are discussed from the standpoint of the evolution of the tectonic-energy grid, a characteristic tectonic division of the crust, determined by the dimensions of first-order structures. A comparative analysis of first-order structures of different age on the continents is carried out in an effort to trace irreversible areal changes of sialic masses in consolidated blocks (continental plates and cratons) occurring at the main boundaries of endogenous activity.

  10. Geophysical study of the structure and processes of the continental convergence zones: Alpine-Himalayan Belt

    NASA Technical Reports Server (NTRS)

    Toksoez, M. N.

    1981-01-01

    The seismic wave velocity structure in the crust and upper mantle region beneath the Tibetan plateau was studied in detail. Also, a preliminary study of the uppermost mantle P wave velocity beneath Iran and Turkey was carried out, and the results are compared with those for the Tibetan plateau. These two studies compose the bulk of the efforts on the observational aspects of continental collision zones in addition to satellite derived data. On the theoretical aspects the thermal evolution of converging plate boundaries was explored using a finite difference scheme.

  11. A true polar wander model for Neoproterozoic plate motions

    SciTech Connect

    Ripperdan, R.L. )

    1992-01-01

    Recent paleogeographic reconstructions for the interval 750--500 Ma (Neoproterozoic to Late Cambrian) require rapid rates of plate motion and/or rotation around an equatorial Euler pole to accommodate reconstructions for the Early Paleozoic. Motions of this magnitude appear to be very uncommon during the Phanerozoic. A model for plate motions based on the hypothesis that discrete intervals of rapid true polar wander (RTPW) occurred during the Neoproterozoic can account for the paleogeographic changes with minimum amounts of plate motion. The model uses the paleogeographic reconstructions of Hoffman (1991). The following constraints were applied during derivation of the model: (1) relative motions between major continental units were restricted to be combinations of great circle or small circle translations with Euler poles of rotation = spin axis; (2) maximum rates of relative translational plate motion were 0.2 m/yr. Based on these constraints, two separate sets of synthetic plate motion trajectories were determined. The sequence of events in both can be summarized as: (1) A rapid true polar wander event of ca 90[degree] rafting a supercontinent to the spin axis; (2) breakup of the polar supercontinent into two fragments, one with the Congo, West Africa, Amazonia, and Baltica cratons, the other with the Laurentia, East Gondwana, and Kalahari cratons; (3) great circle motion of the blocks towards the equator; (4) small circle motion leading to amalgamation of Gondwana and separation of Laurentia and Baltica. In alternative 1, rifting initiates between East Antarctica and Laurentia and one episode of RTPW is required. Alternative 2 requires two episodes of RTPW; and that rifting occurred first along the eastern margin and later along the western margin of Laurentia. Synthetic plate motion trajectories are compared to existing paleomagnetic and geological data, and implications of the model for paleoclimatic changes during the Neoproterozoic are discussed.

  12. The basins on the Argentine continental margin

    SciTech Connect

    Urien, C.M.

    1996-08-01

    After the stabilization of the central Gondwana Craton, orogenic belts were accreted, as a result of convergence events and an extensive passive margin developed in southwestern Gondwana. Thermal subsidence in Parana, Karoo-Ventania basins and the Late Paleozoic-Early Mesozoic rifts, were modified by the Gondwana breakup and the South Atlantic opening. Early Paleozoic marine transgressions deposited the Table Mountain Group in Ventania. In southwestern Patagonia foreland clastics were deposited. Magmatic arcs and marine units indicate a tectonic trough was formed, alternating with continental sequences, over Late Paleozoic metamorphics and intrusives, resulting from plastered terrains along the Gondwana margin. In Patagonia, Permo-Carboniferous continental and glacio marine clastics infill the basins, while in Ventania, paralic sequences, grade from neritic to continental to the northeast, extending beneath the continental margin. The Triassic-Jurassic rift basins progressed onto regional widespread acid lavas and were infilled by lagoonal organic-rich sequences. Early drift phase built basins transverse to the margin, with fluvio-lacustrine sequences: Salado, Colorado, Valdes-Rawson, San Julian and North Malvinas intracratonic basins, which underwent transtensional faulting. Post-Oxfordian to Neocomian brackish sequences, onlapped the conjugate basins during the margin`s drift, with petroleum systems, as in Austral and Malvinas. In the Valanginian, basic extrusions commenced to form on the continental border, heralding the oceanic phase. Due to thermal subsidence, offlaping sediments prograded onto the remaining half-grabens. Several petroleum systems, proven and hypothetical, are identified in this region.

  13. Evolving Deformation Style and Rheology During Transpressive Segmentation and Uplift of Continental Lower Crust

    NASA Astrophysics Data System (ADS)

    Dumond, G.; Mahan, K. H.; Williams, M. L.; Goncalves, P.; Jercinovic, M. J.

    2012-12-01

    Understanding mechanisms for strain localization and partitioning in the lower crust beneath major fault systems is critical for constraining exactly how these faults accommodate plate convergence. Lateral and vertical variations in strength and material properties can strongly influence the distribution of strain in continental lithosphere, as observed in the vicinity of continental transform faults and intracontinental strike-slip faults. Numerical models that incorporate rheological heterogeneity highlight the importance of strength contrasts for facilitating strain localization. Questions regarding the importance of diffuse vs. localized strain, reactivation, and the role of lateral variation in rheology can be answered directly by studying exhumed deep crustal shear zones and their wall rocks in rare exposures of continental lower crust. We report on the evolving deformation style and rheology of a large panel of continental lower crust (>20,000 km2) during the interaction of two lithosphere-scale shear zones in the western Canadian Shield. Weak, partially molten rocks were juxtaposed against previously-dehydrated stronger rocks during dextral high-T transcurrent shearing along the >400 km-long Grease River strike-slip shear zone at 1.92-1.90 Ga. The pattern and timing of strain and metamorphism across the shear zone is compatible with development of a deep crustal flower structure coincident with this rheological "dichotomy" at ~30-40 km paleodepths. The Grease River shear zone was cut and uplifted in the hanging wall of the Legs Lake shear zone, a >500 km-long intracontinental thrust-sense structure. Reactivation of the Grease River shear zone occurred during uplift as both structures accommodated dextral transpressive strain during segmentation and uplift of continental lower crust (>1.0 GPa) to middle crustal levels (<0.5 GPa) at 1.85 Ga. The strength and style of deformation evolved from distributed strain across partially molten weak crust to localized strain along discrete shear zones that facilitated translation of strong dehydrated crust during transpressive uplift.

  14. Polyphase Formation and Exhumation of HP-UHP Rocks in Continental Subduction Zone: Numerical Modeling

    NASA Astrophysics Data System (ADS)

    Li, Z.; Gerya, T.

    2008-12-01

    High- to ultrahigh-pressure (HP-UHP) metamorphic rocks commonly form and exhume during the early continental collision, with the protoliths mainly derived from subducted upper and middle continental crust. While the geodynamic significance of HP-UHP complexes is widely recognized and their appearance in the Neoproterozoic is considered as a "hallmark" for establishing modern plate tectonic styles, many questions related to their origin still remain unresolved. Of particular importance is the poly-metamorphic origin of many HP-UHP terranes composed of tectonic units having strongly variable ages, peak metamorphic conditions and P-T paths. In order to address this issue we conducted 2D high-resolution thermomechanical numerical modeling of the continental subduction associated with formation and exhumation of the HP-UHP rocks, with testing different geometrical configurations, rheological properties and varied width of subducting continental margins, convergence velocity, sedimentation and erosion rates. Most of our experiments confirm poly-phase origin of HP-UHP terranes and predict existence of several consequent episodes of (U)HP rocks exhumation related to the inherently cyclic origin of continental crust subduction-detachment-exhumation process. Periodicity of formation of rheologically weak zones (thrusting faults) controlling HP-UHP rocks exhumation processes depends on the competing effects of downward directed subduction drag and upward directed crustal buoyancy forces. The buoyancy forces and related deviatoric stresses accumulate in the subduction channel due to subduction of low-density crustal rocks and are then reset back during rapid exhumation episodes. Numerical modeling suggest that UHP rocks may remain in the sub-lithospheric channel for several million years being heated to 800-900°C by the surrounding hot mantle. At the later stage upward extrusion of such hot partially molten rocks may exhume high-temperature (HT) UHP complexes toward the surface. Therefore, sub-lithospheric channel formation and extrusion processes may provide plausible explanation for occurrence of UHP-HT rocks in nature.

  15. Morphology and geology of the continental shelf and upper slope of southern Central Chile (33°S-43°S)

    NASA Astrophysics Data System (ADS)

    Völker, David; Geersen, Jacob; Contreras-Reyes, Eduardo; Sellanes, Javier; Pantoja, Silvio; Rabbel, Wolfgang; Thorwart, Martin; Reichert, Christian; Block, Martin; Weinrebe, Wilhelm Reimer

    2014-10-01

    The continental shelf and slope of southern Central Chile have been subject to a number of international as well as Chilean research campaigns over the last 30 years. This work summarizes the geologic setting of the southern Central Chilean Continental shelf (33°S-43°S) using recently published geophysical, seismological, sedimentological and bio-geochemical data. Additionally, unpublished data such as reflection seismic profiles, swath bathymetry and observations on biota that allow further insights into the evolution of this continental platform are integrated. The outcome is an overview of the current knowledge about the geology of the southern Central Chilean shelf and upper slope. We observe both patches of reduced as well as high recent sedimentation on the shelf and upper slope, due to local redistribution of fluvial input, mainly governed by bottom currents and submarine canyons and highly productive upwelling zones. Shelf basins show highly variable thickness of Oligocene-Quaternary sedimentary units that are dissected by the marine continuations of upper plate faults known from land. Seismic velocity studies indicate that a paleo-accretionary complex that is sandwiched between the present, relatively small active accretionary prism and the continental crust forms the bulk of the continental margin of southern Central Chile.

  16. A Voyage through Scales - Archives of the Continental Crust

    NASA Astrophysics Data System (ADS)

    Hawkesworth, Chris

    2015-04-01

    Geology and the Earth Sciences have distinctive positions in the sciences. They draw widely on the hard sciences, but for the most part the evidence is already present in the geological records of the history of the Earth. That record is far from complete, and critically it is also biased in what has been preserved and what has been lost. Scale is fundamental as even on outcrop discussions may range from the identification of minerals and fabrics to their implications, to inferred regional conditions of pressure and temperature, and the movement of plates many million years ago. Recent technological developments now make it possible to analyse very small amounts of material. This has highlighted that many rock samples are mixtures of materials of different provenance, and allowed us to be increasingly sure about what is being analysed. U/Pb dating of zircon is the basis for establishing geological time scales, and the combination of imaging techniques and high precision dating of small spots has highlighted the complexity of many grains and the importance of imaging each portion that is dated. Magmatic zircons crystallise from relatively high silica magmas, and so notwithstanding how widely they are used, magmatic zircons only yield ages for certain rock types in the geological record. There are links between the length- and time-scales of natural phenomena. This lecture seeks to explore how material analysed on a wide range of scales influences the models developed and how they may be tested. High-resolution 3-D mapping has illuminated the debate over the oldest preserved fossils. The position-specific isotopic anatomies of organic molecules are now being investigated. The compositions of detrital sediments are widely used as a way to sample the bulk composition of portions of crust. Yet the sedimentary record is biased by preferential sampling of relatively young material in their source terrains. There are now large numbers of radiometric ages, often obtained in regional studies, and globally the continental crust is characterised by distinctive peaks and troughs in the distribution of ages of magmatic activity, metamorphism, continental margins and mineralisation. This is unexpected in the context of steady state plate tectonics, and it is thought to reflect the different preservation potential of rocks generated in different tectonic settings. In contrast there are other signals, such as the Sr isotope ratios of seawater, mantle temperatures, and redox conditions on the Earth, which appear to retain primary records because they are less sensitive to the numbers of samples of different ages that have been analysed. Bias does appear to be significant for signals that rely on distributions of ages.

  17. Geohistory analysis of the Santa Maria basin, California, and its relationship to tectonic evolution of the continental margin

    SciTech Connect

    McCrory, P.A.; Arends, R.G. ); Ingle, J.C. Jr. ); Isaacs, C.M.; Stanley, R.G. ); Thornton, M.L.C. )

    1991-02-01

    The Santa Maria basin of central California is a geologically complex area located along the tectonically active California continental margin. The record of Cenozoic tectonism preserved in Santa Maria strata provides an opportunity to compare the evolution of the region with plate tectonic models for Cenozoic interactions along the margin. Geohistory analysis of Neogene Santa Maria basin strata provides important constraints for hypotheses of the tectonic evolution of the central California margin during its transition from a convergent to a transform plate boundary. Preliminary analyses suggest that the tectonic evolution of the Santa Maria area was dominated by coupling between adjacent oceanic plates and the continental margin. This coupling is reflected in the timing of major hiatuses within the basin sedimentary sequence and margin subsidence and uplift which occurred during periods of tectonic plate adjustment. Stratigraphic evidence indicates that the Santa Maria basin originated on the continental shelf in early Miocene time. A component of margin subsidence is postulated to have been caused by cessation of spreading on adjacent offshore microplates approximately 19-18 ma. A sharp reduction in rate of tectonic subsidence in middle Miocene time, observed in the Santa Maria basin both onshore and offshore, was coeval with rotation of crustal blocks as major shearing shifts shoreward. Tectonic uplift of two eastern sites, offshore Point Arguello and near Point Sal, in the late Miocene may have been related to a change to transpressional motion between the Pacific and North American plates, as well as to rotation of the western Transverse Ranges in a restraining geometry.

  18. Interactions between Eurasian/African and Arabian plates: Eski?ehir Fault, NW Turkey

    NASA Astrophysics Data System (ADS)

    Özden, Süha; Gündo?du, Erdem; Bekler, Tolga

    2015-11-01

    The Eski?ehir Fault is an active right-lateral widespread intra-continental deformation zone which separates central western Anatolia from the Aegean domain. The inversion of fault slip vectors along the Eski?ehir Fault yields a strike-slip stress state with NW-trending ?Hmax (?1) and NE-trending ?Hmin (?3) axes since the Early Pliocene. A change in strike-slip faulting under a compressional stress regime: from old transpression to young transtension, probably occurred in the Quaternary. The inversion of the earthquake source mechanism indicates that the transtensional stress regime continues up to the present. The ?nönü and Eski?ehir Basins developed under the transtensional stress regime producing consistent and local normal faulting with a continuing NE-trending ?Hmin (?3). The stress regime change resulted in a decrease in ?Hmax (?1) and/or an increase in ?Hmin (?3) stress magnitudes due to coeval influence of the superimposed plate forces and the interaction of three plates (Eurasian/African/Arabian): (1) continental collision of Eurasian/Arabian plates with Anatolian block in the east, (2) westward escape of the Anatolian block by anticlockwise rotation at the west-southwest border of the Eurasian and Arabian/African plates and (3) a complex subduction process between African and Eurasian plates along the Aegean (Hellenic) and the Cyprus arcs which favors western extrusion of the Anatolian block in the eastern Mediterranean region.

  19. Dynamics of Tectonic Plates

    E-print Network

    Pechersky, E; Sadowski, G; Yambartsev, A

    2014-01-01

    We suggest a model that describes a mutual dynamic of tectonic plates. The dynamic is a sort of stick-slip one which is modeled by a Markov random process. The process defines a microlevel of the dynamic. A macrolevel is obtained by a scaling limit which leads to a system of integro-differential equations which determines a kind of mean field systems. Conditions when Gutenberg-Richter empirical law are presented on the mean field level. These conditions are rather universal and do not depend on features of resistant forces.

  20. Plated wire memory subsystem

    NASA Technical Reports Server (NTRS)

    Carpenter, K. H.

    1974-01-01

    The design, construction, and test history of a 4096 word by 18 bit random access NDRO Plated Wire Memory for use in conjunction with a spacecraft input/output and central processing unit is reported. A technical and functional description is given along with diagrams illustrating layout and systems operation. Test data is shown on the procedures and results of system level and memory stack testing, and hybrid circuit screening. A comparison of the most significant physical and performance characteristics of the memory unit versus the specified requirements is also included.

  1. Development of three-dimensional basement structure in Taiwan deduced from past plate motion: Consistency with the present seismicity

    NASA Astrophysics Data System (ADS)

    Takada, Youichiro; Fukahata, Yukitoshi; Hashima, Akinori; Terakawa, Toshiko; Fukui, Kenji; Yanagisawa, Takatoshi; Ikeda, Yasutaka; Kimura, Gaku; Matsu'Ura, Mitsuhiro

    2007-06-01

    Using colored clay, we examined geometrical evolution of the three-dimensional basement structure in Taiwan due to relative plate motion under the following assumptions: the motion of the Philippine Sea plate relative to the Eurasian plate has been constant during the last 15 Myr, the Ryukyu and Manila trenches had been connected by a transform fault before the collision between the Luzon arc and Eurasian continental margin, and the collision started at 5 Ma. The basement structure obtained from the clay model was fully consistent with observed deep seismicity, which led us to the following conclusions. There are no oceanic slabs beneath central Taiwan. Instead, the Eurasian continental margin is underthrusting beneath it. The Philippine Sea slab extends northwestward from the Ryukyu trench, while the South China Sea slab extends southeastward from the Manila trench. The downdip length of the South China Sea slab becomes shorter from south to north.

  2. Continental Rifts: Evolution, Structure and Tectonics

    NASA Astrophysics Data System (ADS)

    Bally, A. W.

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

  3. Gas hydrates of outer continental margins

    SciTech Connect

    Kvenvolden, K.A. )

    1990-05-01

    Gas hydrates are crystalline substances in which a rigid framework of water molecules traps molecules of gas, mainly methane. Gas-hydrate deposits are common in continental margin sediment in all major oceans at water depths greater than about 300 m. Thirty-three localities with evidence for gas-hydrate occurrence have been described worldwide. The presence of these gas hydrates has been inferred mainly from anomalous lacoustic reflectors seen on marine seismic records. Naturally occurring marine gas hydrates have been sampled and analyzed at about tensites in several regions including continental slope and rise sediment of the eastern Pacific Ocean and the Gulf of Mexico. Except for some Gulf of Mexico gas hydrate occurrences, the analyzed gas hydrates are composed almost exclusively of microbial methane. Evidence for the microbial origin of methane in gas hydrates includes (1) the inverse relation between methane occurence and sulfate concentration in the sediment, (2) the subparallel depth trends in carbon isotopic compositions of methane and bicarbonate in the interstitial water, and (3) the general range of {sup 13}C depletion ({delta}{sub PDB}{sup 13}C = {minus}90 to {minus}60 {per thousand}) in the methane. Analyses of gas hydrates from the Peruvian outer continental margin in particular illustrate this evidence for microbially generated methane. The total amount of methane in gas hydrates of continental margins is not known, but estimates of about 10{sup 16} m{sup 3} seem reasonable. Although this amount of methane is large, it is not yet clear whether methane hydrates of outer continental margins will ever be a significant energy resource; however, these gas hydrates will probably constitute a drilling hazard when outer continental margins are explored in the future.

  4. MAGSAT anomaly map and continental drift

    NASA Technical Reports Server (NTRS)

    Lemouel, J. L. (principal investigator); Galdeano, A.; Ducruix, J.

    1981-01-01

    Anomaly maps of high quality are needed to display unambiguously the so called long wave length anomalies. The anomalies were analyzed in terms of continental drift and the nature of their sources is discussed. The map presented confirms the thinness of the oceanic magnetized layer. Continental magnetic anomalies are characterized by elongated structures generally of east-west trend. Paleomagnetic reconstruction shows that the anomalies found in India, Australia, and Antarctic exhibit a fair consistency with the African anomalies. It is also shown that anomalies are locked under the continents and have a fixed geometry.

  5. Blocks or Continuous Deformation in Large-Scale Continental Geodynamics: Ptolemy Versus Copernicus, Kepler, and Newton (Invited)

    NASA Astrophysics Data System (ADS)

    Molnar, P. H.

    2010-12-01

    The enhanced precision and resolution of GPS velocity fields within active continental regions have highlighted two views of how best to describe these fields: (1) as relative movements of effectively rigid (or elastic) blocks, essentially plate tectonics with many plates, or (2) as continuous deformation of a (non-Newtonian) viscous fluid in a gravity field. The operative question is not: Are there blocks? Of course, there are. It is: Do blocks help us understand the deformation? Dan McKenzie used to say, 40 years ago, that the reason plate tectonics was accepted so easily was that the kinematics of plate motion could be analyzed separately from the dynamics that underlies that motion. No such separation seems to work for continental tectonics, where crust thickens or thins, and where the dynamics, both stresses and the gravitational body force, and kinematics are intimately connected via a constitutive relation that links strain rate to stress. Treating continental deformation in terms of blocks is like treating planetary orbits in terms of Ptolemaic epicycles; such a treatment provides an accurate description of the kinematics, but obscures dynamics. (Sea captains in the 15th Century would have been wise to use Ptolemy’s epicycles, not yet a Copernican system, to navigate their ships). A description in terms of blocks, however, seems unlikely to reveal insights into the dynamic processes and the viscosity structure of the deforming lithosphere. In Tibet, most hypothesized blocks are cut by obvious faults and must deform, if GPS measurements are not yet accurate enough to resolve such deformation. Presumably as the number of GPS control points and the precision of their velocities increase, so will numbers of blocks needed to describe the velocity field, with numbers of GPS points and numbers of blocks obeying a fractal relationship. The important unanswered question concerns how best to describe the constitutive equation for continental lithosphere? The Tibetan Plateau illustrates this failing of plate tectonics (or crustal blocks) especially well. In particular, because of the large lateral variations in gravitational potential energy, it offers the best region in which to study dynamics of continental deformation.

  6. Tectonics of the Easter plate

    NASA Technical Reports Server (NTRS)

    Engeln, J. F.; Stein, S.

    1984-01-01

    A new model for the Easter plate is presented in which rift propagation has resulted in the formation of a rigid plate between the propagating and dying ridges. The distribution of earthquakes, eleven new focal mechanisms, and existing bathymetric and magnetic data are used to describe the tectonics of this area. Both the Easter-Nazca and Easter-Pacific Euler poles are sufficiently close to the Easter plate to cause rapid changes in rates and directions of motion along the boundaries. The east and west boundaries are propagating and dying ridges; the southwest boundary is a slow-spreading ridge and the northern boundary is a complex zone of convergent and transform motion. The Easter plate may reflect the tectonics of rift propagation on a large scale, where rigid plate tectonics requires boundary reorientation. Simple schematic models to illustrate the general features and processes which occur at plates resulting from large-scale rift propagation are used.

  7. Plastic buckling of ARALL plates

    NASA Astrophysics Data System (ADS)

    Aboudi, J.; Paley, M.

    The plastic bifurcation buckling loads of ARALL (aramid aluminum laminate) plates are predicted. The plastic behavior of the plate is caused by the significant plasticity effects of the aluminum strips. The critical load level at which the ARALL plate loses its stability is determined from the material properties of the elastoplastic aluminum alloy strips and the elastic unidirectional aramid/epoxy composite layers, in conjunction with their geometric characteristics.

  8. Channel plate for DNA sequencing

    DOEpatents

    Douthart, R.J.; Crowell, S.L.

    1998-01-13

    This invention is a channel plate that facilitates data compaction in DNA sequencing. The channel plate has a length, a width and a thickness, and further has a plurality of channels that are parallel. Each channel has a depth partially through the thickness of the channel plate. Additionally an interface edge permits electrical communication across an interface through a buffer to a deposition membrane surface. 15 figs.

  9. Secondary states of vibrating plates

    SciTech Connect

    Matkowsky, R.J.; Putnick, L.J.; Reiss, E.L.

    1981-08-01

    A previously developed perturbation method is used to obtain a new class of periodic motions for the nonlinear vibrations of rectangular, elastic plates. The dynamic von Karman plate theory is used in the analysis. The new solutions arise by secondary bifurcation from the periodic solutions that bifurcate from the natural frequencies of free vibrations of the linearized plate theory. The new motions are a linear combination of two modes of the linearized theory.

  10. Channel plate for DNA sequencing

    DOEpatents

    Douthart, Richard J. (Richland, WA); Crowell, Shannon L. (Eltopia, WA)

    1998-01-01

    This invention is a channel plate that facilitates data compaction in DNA sequencing. The channel plate has a length, a width and a thickness, and further has a plurality of channels that are parallel. Each channel has a depth partially through the thickness of the channel plate. Additionally an interface edge permits electrical communication across an interface through a buffer to a deposition membrane surface.

  11. Ophiolites and Continental Margins of the Mesozoic Western U.S. Cordillera

    NASA Astrophysics Data System (ADS)

    Dilek, Y.

    2001-12-01

    The Mesozoic tectonic history of the western U.S. Cordillera records evidence for multiple episodes of accretionary and collisional orogenic events and orogen-parallel strike-slip faulting. Paleozoic-Jurassic volcanic arc complexes and subduction zone assemblages extending from Mexico to Canada represent an East-Pacific magmatic arc system and an accretionary-type orogen evolved along the North American continental margin. Discontinuous exposures of Paleozoic upper mantle rocks and ophiolitic units structurally beneath this magmatic arc system are remnants of the Panthalassan oceanic lithosphere, which was consumed beneath the North American continent. Pieces of this subducted Panthalassan oceanic lithosphere that underwent high-P metamorphism are locally exposed in the Sierra Nevada foothills (e.g. Feather River Peridotite) indicating that they were subsequently (during the Jurassic) educted in an oblique convergent zone along the continental margin. This west-facing continental margin arc evolved in a broad graben system during much of the Jurassic as a result of extension in the upper plate, keeping pace with slab rollback of the east-dipping subduction zone. Lower to Middle Jurassic volcanoplutonic complexes underlain by an Upper Paleozoic-Lower Mesozoic polygenetic ophiolitic basement currently extend from Baja California-western Mexico through the Sierra-Klamath terranes to Stikinia-Intermontane Superterranes in Canada and represent an archipelago of an east-facing ensimatic arc terrane that developed west and outboard of the North American continental margin arc. The Smartville, Great Valley, and Coast Range ophiolites (S-GV-CR) in northern California are part of this ensimatic terrane and represent the island arc, arc basement, and back-arc tectonic settings, respectively. The oceanic Josephine-Rogue-Chetco-Rattlesnake-Hayfork tectonostratigraphic units in the Klamath Mountains constitute a west-facing island arc system in this ensimatic terrane as a counterpart of the east-facing S-GV-CR system to the south. The Guerrero intra-oceanic island arc system in Mexico was also part of the ensimatic arc terrane. Incorporation of this super arc terrane into the North American continent occurred diachronously along the irregular continental margin in the Middle Jurassic (in the north) through Early Cretaceous (in the south) during an arc-continent collision, marking a collisional orogenic episode in the North American Cordilleran history. Rifting of this accreted arc in the Late Jurassic (155-148 Ma) might have resulted from a sinistral transtensional deformation associated with the rapid NW motion of North America. Magmas generated during this rifting event probably migrated through the accreted arc crust and the continental margin units in the tectonic lower plate. The Franciscan subduction zone dipping eastwards beneath the continent was established in the latest Jurassic, following the collisional event and restoring the North American Cordillera back into an accretionary-type, Andean-style orogen. Different episodes of orogen-parallel intra-continental strike-slip faulting facilitated lateral dispersion of accreted terranes and continental margin units during the Early Cretaceous and transpressional deformation and batholithic magmatism in the Sierra Nevada magmatic arc in the Late Cretaceous. A Jurassic-Cretaceous island arc system (Wrangellia-Insular Superterrane) that had developed west of the Jurassic archipelago collapsed into the edge of North America during Late Cretaceous-Tertiary time and underwent northward lateral translation along the continental margin. These observations and interpretations have strong implications for the tectonic evolution of Central America and the Caribbean region.

  12. Glass-bead peen plating

    NASA Technical Reports Server (NTRS)

    Graves, J. R.

    1974-01-01

    Peen plating of aluminum, copper, and nickel powders was investigated. Only aluminum was plated successfully within the range of peen plating conditions studied. Optimum plating conditions for aluminum were found to be: (1) bead/powder mixture containing 25 to 35% powder by weight, (2) peening intensity of 0.007A as measured by Almen strip, and (3) glass impact bead diameter of at least 297 microns (0.0117 inches) for depositing-100 mesh aluminum powder. No extensive cleaning or substrate preparation is required beyond removing loose dirt or heavy oil.

  13. Carbon-assisted flyer plates

    DOEpatents

    Stahl, David B. (Los Alamos, NM); Paisley, Dennis L. (Santa Fe, NM)

    1994-01-01

    A laser driven flyer plate utilizing an optical fiber connected to a laser. The end of the optical fiber has a layer of carbon and a metal layer deposited onto it. The carbon layer provides the laser induced plasma which is superior to the plasma produced from most metals. The carbon layer plasma is capable of providing a flatter flyer plate, converting more of the laser energy to driving plasma, promoting a higher flyer plate acceleration, and providing a more uniform pulse behind the plate. In another embodiment, the laser is in optical communication with a substrate onto which a layer of carbon and a layer of metal have been deposited.

  14. True Shear Parallel Plate Viscometer

    NASA Technical Reports Server (NTRS)

    Ethridge, Edwin; Kaukler, William

    2010-01-01

    This viscometer (which can also be used as a rheometer) is designed for use with liquids over a large temperature range. The device consists of horizontally disposed, similarly sized, parallel plates with a precisely known gap. The lower plate is driven laterally with a motor to apply shear to the liquid in the gap. The upper plate is freely suspended from a double-arm pendulum with a sufficiently long radius to reduce height variations during the swing to negligible levels. A sensitive load cell measures the shear force applied by the liquid to the upper plate. Viscosity is measured by taking the ratio of shear stress to shear rate.

  15. Geodynamic modeling of passive margin systems from tectonic reconstructions with deforming plate boundaries

    NASA Astrophysics Data System (ADS)

    Williams, S.; Flament, N.; Heine, C.; Hosseinpour Vazifehshenas, M.; Seton, M.; Gurnis, M.; Müller, R. D.

    2012-04-01

    The effect of mantle flow on surface topography has been the subject of considerable interest over the last few years. A common approach to the problem is to link plate tectonic reconstructions and global geodynamic models. An important limitation of this approach is that traditional plate tectonic reconstructions do not take the deformation of the lithosphere into account. We introduce quantitative models of surface plate kinematics that include areas of deforming continental crust. We present a series of global reconstructions including deforming plates in key areas, derived using tools developed within the open source plate modeling software GPlates. In traditional plate reconstructions, the continents are represented as rigid blocks that overlap in full-fit reconstructions. Models that use topological polygons avoid continental overlaps, but plate velocities are still derived on the basis of Euler poles for rigid blocks. To resolve these issues, we use a methodology that requires at minimum two inputs; (1) the relative motions of the rigid blocks within continents; (2) a definition of the regions in which continental crust deformed between these blocks. We use geological and geophysical data to interpret the landward limit of significant extension and crustal thinning along conjugate passive margins. These boundaries are used to construct polygons along both margins that define the extent of the stretched continental crust on either side of the rift. We derive individual motion histories for each point on the conjugate continent/ocean boundaries (COBs). Joined together, these COB points form the topological boundaries of deforming domains in which each vertex moves independently. The deforming domains represented by topological meshes extend forward in time as the major rigid plates drift apart. In our tectonic reconstruction with deforming plates, the timing and the intensity of continental extension is imposed by the progressive, diachronous breakup and initiation of seafloor spreading for each major margin system. The velocity field derived from the plate reconstructions is used as a time-dependent surface boundary condition in mantle convection models that include compositionally distinct crust and continental lithosphere embedded within the thermal lithosphere. In deforming areas, the velocity field is obtained by linearly interpolating velocities from adjacent non-deforming areas within GPlates. We computed forward global mantle flow models using 3D-spherical finite-element code CitcomS to simultaneously quantify the relative contributions of lithospheric stretching, thermal subsidence, and deep mantle flow to the subsidence of passive margins. Applied to the South Atlantic, the method reproduces the first-order asymmetry of the margins. In particular, the large subsidence of the Argentinian margin is due to the dynamic topography induced by ongoing subduction along the narrow southern portion of South America. This result illustrates the importance of dynamic topography to the total subsidence at passive margins.

  16. Calibration of Mean Fault Friction and Mantle Driving Tractions for all Plates on Earth

    NASA Astrophysics Data System (ADS)

    Rucker, W.; Bird, P.

    2006-12-01

    The balanced forces (or torques) on each plate have traditionally been divided into poorly-defined categories such as ridge-push, slab-pull, continental-collision resistance, etc. A more rigorous subdivision is into three categories: (1) Lithostatic pressure tractions integrated over all plate boundaries (even if actual pressure is different due to rock strength); (2) Side-strength tractions (due to deviatoric stresses and pressure anomalies) integrated over plate-bounding fault surfaces; (3) Bottom-strength tractions integrated over the bases of plates, including a horizontal reference surface cutting through any attached subducting slab(s). Since these torques add to zero for each plate, computation of lithostatic-pressure torques and estimation of side-strength torques gives an estimate of bottom-strength torque for each plate. If the plate has no subducting slab attached, this bottom-strength torque must be due to shear tractions reflecting relative plate motion over the subjacent mantle. A complication is that plate-boundary fault strength is not well understood or measured. Thus alternative models are possible in which the bottom-strength torques have different magnitudes and directions. Under plates that have no attached slabs, seismic data showing anisotropy due to shearing fabrics help to constrain the the uncertainty. Furthermore, each alternative model (characterized by a trial mean value of effective fault friction) makes different predictions for intraplate deformation rates, relative velocities, and intraplate stress orientations. We are using thin-shell neotectonic modeling program Shells to perform these computations. An Earth5 grid (52 plates; 13 orogens; 2846 fault elements; 26798 continuum elements; 16008 nodes) describes lithospheric structure incorporating ETOPO5 topography, estimated heat flow, CRUST2 crustal thicknesses, and mantle lithosphere thicknesses based on seismic tomography. For each computation, we initially force correct (PB2002) plate velocities with internal boundary conditions located either (a) where subducting slabs have been omitted from the model; or (b) at strong points of low heat-flow in plate interiors. After determining reaction forces, we remove the artificial singularities around points of class (b) by redistributing the same bottom-strength forces as a smooth field of shear tractions for that plate. Each computed model will be compared to 4 data sets: (I) azimuths of seismic anisotropy under slabless plates; (II) intraplate stress directions; (III) relative geodetic velocities; and (IV) rates of sea-floor spreading. While tests III and IV serve primarily to rule out models with excessive intraplate deformation (due to very high effective friction on plate- bounding faults), tests I and II have the potential to identify the optimum mean value.

  17. OESbathy version 1.0: a method for reconstructing ocean bathymetry with generalized continental shelf-slope-rise structures

    NASA Astrophysics Data System (ADS)

    Goswami, A.; Olson, P. L.; Hinnov, L. A.; Gnanadesikan, A.

    2015-09-01

    We present a method for reconstructing global ocean bathymetry that combines a standard plate cooling model for the oceanic lithosphere based on the age of the oceanic crust, global oceanic sediment thicknesses, plus generalized shelf-slope-rise structures calibrated at modern active and passive continental margins. Our motivation is to develop a methodology for reconstructing ocean bathymetry in the geologic past that includes heterogeneous continental margins in addition to abyssal ocean floor. First, the plate cooling model is applied to maps of ocean crustal age to calculate depth to basement. To the depth to basement we add an isostatically adjusted, multicomponent sediment layer constrained by sediment thickness in the modern oceans and marginal seas. A three-parameter continental shelf-slope-rise structure completes the bathymetry reconstruction, extending from the ocean crust to the coastlines. Parameters of the shelf-slope-rise structures at active and passive margins are determined from modern ocean bathymetry at locations where a complete history of seafloor spreading is preserved. This includes the coastal regions of the North, South, and central Atlantic, the Southern Ocean between Australia and Antarctica, and the Pacific Ocean off the west coast of South America. The final products are global maps at 0.1° × 0.1° resolution of depth to basement, ocean bathymetry with an isostatically adjusted multicomponent sediment layer, and ocean bathymetry with reconstructed continental shelf-slope-rise structures. Our reconstructed bathymetry agrees with the measured ETOPO1 bathymetry at most passive margins, including the east coast of North America, north coast of the Arabian Sea, and northeast and southeast coasts of South America. There is disagreement at margins with anomalous continental shelf-slope-rise structures, such as around the Arctic Ocean, the Falkland Islands, and Indonesia.

  18. The interpretation of crustal dynamics data in terms of plate interactions and active tectonics of the Anatolian plate and surrounding regions in the Middle East

    NASA Technical Reports Server (NTRS)

    Toksoz, M. Nafi; Reilinger, Robert

    1992-01-01

    A detailed study was made of the consequences of the Arabian plate convergence against Eurasia and its effects on the tectonics of Anatolia and surrounding regions of the eastern Mediterranean. A primary source of information is time rates of change of baseline lengths and relative heights determined by repeated SLR measurements. These SLR observations are augmented by a network of GPS stations in Anatolia, Aegea, and Greece, established and twice surveyed since 1988. The existing SLR and GPS networks provide the spatial resolution necessary to reveal the details of ongoing tectonic processes in this area of continental collision. The effort has involved examining the state of stress in the lithosphere and relative plate motions as revealed by these space based geodetic measurements, seismicity, and earthquake mechanisms as well as the aseismic deformations of the plates from conventional geodetic data and geological evidence. These observations are used to constrain theoretical calculations of the relative effects of: (1) the push of the Arabian plate; (2) high topography of Eastern Anatolia; (3) the geometry and properties of African-Eurasian plate boundary; (4) subduction under the Hellenic Arc and southwestern Turkey; and (5) internal deformation and rotation of the Anatolian plate.

  19. Elephant teeth from the atlantic continental shelf

    USGS Publications Warehouse

    Whitmore, F.C., Jr.; Emery, K.O.; Cooke, H.B.S.; Swift, D.J.P.

    1967-01-01

    Teeth of mastodons and mastodons have been recovered by fishermen from at least 40 sites on the continental shelf as deep as 120 meters. Also present are submerged shorelines, peat deposits, lagoonal shells, and relict sands. Evidently elephants and other large mammals ranged this region during the glacial stage of low sea level of the last 25.000 years.

  20. Introduction Fossil age constraints for continental sedimentary

    E-print Network

    Andersen, Torgeir Bjørge

    ) for sedimentary rocks exposed primarily on Hitra and small islands south of Smøla; Early to Mid Devonian agesIntroduction Fossil age constraints for continental sedimentary deposits are invariably more; Osmundsen & Andersen 2001), precise dating of the Devonian sedimentary basins has been particularly

  1. Coordination: Southeast Continental Shelf studies. Progress report

    SciTech Connect

    Menzel, D.W.

    1981-02-01

    An overview of the Oceanograhic Program of Skidaway Institute of Oceanograhy is presented. Included are the current five year plan for studies of the Southeast Continental Shelf, a summary of research accomplishments, proposed research for 1981-1982, current status of the Savannah Navigational Light Tower, and a list of publications. (ACR)

  2. Plate tectonics, damage and inheritance.

    PubMed

    Bercovici, David; Ricard, Yanick

    2014-04-24

    The initiation of plate tectonics on Earth is a critical event in our planet's history. The time lag between the first proto-subduction (about 4?billion years ago) and global tectonics (approximately 3?billion years ago) suggests that plates and plate boundaries became widespread over a period of 1?billion years. The reason for this time lag is unknown but fundamental to understanding the origin of plate tectonics. Here we suggest that when sufficient lithospheric damage (which promotes shear localization and long-lived weak zones) combines with transient mantle flow and migrating proto-subduction, it leads to the accumulation of weak plate boundaries and eventually to fully formed tectonic plates driven by subduction alone. We simulate this process using a grain evolution and damage mechanism with a composite rheology (which is compatible with field and laboratory observations of polycrystalline rocks), coupled to an idealized model of pressure-driven lithospheric flow in which a low-pressure zone is equivalent to the suction of convective downwellings. In the simplest case, for Earth-like conditions, a few successive rotations of the driving pressure field yield relic damaged weak zones that are inherited by the lithospheric flow to form a nearly perfect plate, with passive spreading and strike-slip margins that persist and localize further, even though flow is driven only by subduction. But for hotter surface conditions, such as those on Venus, accumulation and inheritance of damage is negligible; hence only subduction zones survive and plate tectonics does not spread, which corresponds to observations. After plates have developed, continued changes in driving forces, combined with inherited damage and weak zones, promote increased tectonic complexity, such as oblique subduction, strike-slip boundaries that are subparallel to plate motion, and spalling of minor plates. PMID:24717430

  3. Recent Earthquakes in Yellow Sea Region and Amur Plate

    NASA Astrophysics Data System (ADS)

    Kim, W. Y.; Satake, K.

    2014-12-01

    Bird (2003) and others suggested the existence of Amur plate in northeastern Asia with its incipient plate boundary along western Honshu - Sakhalin - Stanovoy Mountains - Lake Baikal - Mongolia - Hebei Province, China - Yellow Sea - East China Sea - Nankai Trough. The seismicity along East China Sea and Yellow Sea sections of the suggested boundary is diffuse and does not delineate such boundary. However, recent earthquakes that have occurred along the Yellow Sea region during 2011-2014 show predominantly strike-slip faulting along near vertical nodal planes. These earthquakes may provide an opportunity to study details of the proposed boundaries of Amur plate. Waveform data from broadband seismographic stations in the region around Yellow Sea are analyzed in an attempt to shed light on the nature of the incipient plate boundary for the proposed Amur plate in Yellow Sea region. Regional waveform modeling and deviatoric moment tensor inversion suggest that a broad scale stress field in Yellow Sea region is ENE-WSW trending subhorizontal compressive stress, ?1, with N-S trending horizontal extensional stress, ?3. In such regional stress regime, earthquake mechanisms are predominantly vertical strike-slip faulting, but it allows some E-W normal faulting due to N-S extension. The most likely mode of deformation in Yellow Sea region appears to be right-lateral strike-slip faulting along N-S trending transform faults, and E-W trending normal faulting that accommodates a broad regional stress regime. This is a typical kinematics of rifting at rifted continental margins such as Gulf of California. We observed a broad regional seismic velocity variation along various wave propagation paths as well as indications of crustal thickness variation. Thinner crust beneath Yellow Sea region is indicated from waveform modeling which can support evolution of rifting process.

  4. A New Absolute Plate Motion Model for Africa

    NASA Astrophysics Data System (ADS)

    Maher, S. M.; Wessel, P.; Müller, D.; Harada, Y.

    2013-12-01

    The India-Eurasia collision, a change in relative plate motion between Australia and Antarctica, and the coeval ages of the Hawaiian Emperor Bend (HEB) and Louisville Bend of ~Chron 22-21 all provide convincing evidence of a global tectonic plate reorganization at ~50 Ma. Yet if it were a truly global event, then there should be a contemporaneous change in Africa absolute plate motion (APM) reflected by physical evidence somewhere on the Africa plate. This evidence might be visible in the Reunion-Mascarene bend, which exhibits many HEB-like features such as a large angular change close to ~50 Ma. Recently, the Reunion hotpot trail has been interpreted as a continental feature with incidental hotspot volcanism. Here we propose the alternative hypothesis that the northern portion of the chain between Saya de Malha and the Seychelles (Mascarene Plateau) formed as the Reunion hotspot was situated on the Carlsberg Ridge, contemporaneously forming the Chagos-Laccadive Ridge on the India plate. We have created a 4-stage model that explores how a simple APM model fitting the Mascarene Plateau can also satisfy the age progressions and geometry of other hotspot trails on the Africa plate. This type of model could explain the apparent bifurcation of the Tristan hotspot chain, the age reversals seen along the Walvis Ridge and the diffuse nature of the St. Helena chain. To test this hypothesis we have made a new African APM model that goes back to ~80 Ma using a modified version of the Hybrid Polygonal Finite Rotation Method. This method uses seamount chains and their associated hotspots as geometric constraints for the model, and seamount age dates to determine its motion through time. The positions of the hotspots can be moved to get the best fit for the model and to explore the possibility that the ~50 Ma bend in the Reunion-Mascarene chain reflects Africa plate motion. We will examine how well this model can predict the key features reflecting Africa plate motion and contrast its predictions with other proposed models.

  5. 49 CFR 195.9 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 3 2012-10-01 2012-10-01 false Outer continental shelf pipelines. 195.9 Section... HAZARDOUS LIQUIDS BY PIPELINE General § 195.9 Outer continental shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf must identify on all their respective pipelines the specific...

  6. 49 CFR 195.9 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 3 2010-10-01 2010-10-01 false Outer continental shelf pipelines. 195.9 Section... HAZARDOUS LIQUIDS BY PIPELINE General § 195.9 Outer continental shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf must identify on all their respective pipelines the specific...

  7. 49 CFR 192.10 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 3 2013-10-01 2013-10-01 false Outer continental shelf pipelines. 192.10 Section... shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf (as defined in the Outer Continental Shelf Lands Act; 43 U.S.C. 1331) must identify on all their respective pipelines...

  8. 49 CFR 192.10 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 3 2010-10-01 2010-10-01 false Outer continental shelf pipelines. 192.10 Section... shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf (as defined in the Outer Continental Shelf Lands Act; 43 U.S.C. 1331) must identify on all their respective pipelines...

  9. 49 CFR 192.10 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 3 2014-10-01 2014-10-01 false Outer continental shelf pipelines. 192.10 Section... shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf (as defined in the Outer Continental Shelf Lands Act; 43 U.S.C. 1331) must identify on all their respective pipelines...

  10. 49 CFR 195.9 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 3 2011-10-01 2011-10-01 false Outer continental shelf pipelines. 195.9 Section... HAZARDOUS LIQUIDS BY PIPELINE General § 195.9 Outer continental shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf must identify on all their respective pipelines the specific...

  11. 49 CFR 195.9 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 3 2014-10-01 2014-10-01 false Outer continental shelf pipelines. 195.9 Section... HAZARDOUS LIQUIDS BY PIPELINE General § 195.9 Outer continental shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf must identify on all their respective pipelines the specific...

  12. CETACEAN HIGHUSE HABITATS OF THE NORTHEAST UNITED STATES CONTINENTAL SHELF

    E-print Network

    CETACEAN HIGH·USE HABITATS OF THE NORTHEAST UNITED STATES CONTINENTAL SHELF 1 RoBERT D. KENNEY at a qualitative level that specific areas of the continental shelf waters off the northeastern U.S. coast-use areas include the continental shelf edge and the region around the eastern end of Georges Bank. High

  13. 49 CFR 195.9 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 3 2013-10-01 2013-10-01 false Outer continental shelf pipelines. 195.9 Section... HAZARDOUS LIQUIDS BY PIPELINE General § 195.9 Outer continental shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf must identify on all their respective pipelines the specific...

  14. 49 CFR 192.10 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 3 2011-10-01 2011-10-01 false Outer continental shelf pipelines. 192.10 Section... shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf (as defined in the Outer Continental Shelf Lands Act; 43 U.S.C. 1331) must identify on all their respective pipelines...

  15. BATHYMETRIC MAPS AND GEOMORPHOLOGY OF THE MIDDLE ATLANTIC CONTINENTAL SHELF

    E-print Network

    BATHYMETRIC MAPS AND GEOMORPHOLOGY OF THE MIDDLE ATLANTIC CONTINENTAL SHELF BY FRANKLIN STEARNS Atlantic Continental Shelf have recently been published. They were compiled at a scale of 1:125,000 from 39963; Livingstone, 1965; and Emery, 1966b). The Middle Atlantic Continental Shelf borders one

  16. 49 CFR 192.10 - Outer continental shelf pipelines.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 3 2012-10-01 2012-10-01 false Outer continental shelf pipelines. 192.10 Section... shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf (as defined in the Outer Continental Shelf Lands Act; 43 U.S.C. 1331) must identify on all their respective pipelines...

  17. 78 FR 32184 - Importation of Fresh Apricots From Continental Spain

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-05-29

    ...RIN 0579-AD62 Importation of Fresh Apricots From Continental Spain AGENCY: Animal...importation into the United States of fresh apricots from continental Spain. This action...vegetables to allow the importation of fresh apricots from continental Spain into the...

  18. Ecological theory and continental margins: where shallow meets deep

    E-print Network

    Levin, Lisa

    Ecological theory and continental margins: where shallow meets deep Lisa A. Levin and Paul K-0218, USA Continental margins, where land becomes ocean and plunges to the deep sea, provide valuable food change. Continental margin ecosystems, with environ- ments, constituents and processes that differ from

  19. Enhanced intraplate seismicity along continental margins: Some causes and consequences

    E-print Network

    Sandiford, Mike

    Enhanced intraplate seismicity along continental margins: Some causes and consequences Mike hundred kilometres wide inboard of continental margins at high angle to the trend in maximum horizontal we explore how the compositional and thermal structuring of continental passive margins may lead

  20. 78 FR 32183 - Importation of Avocados From Continental Spain

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-05-29

    ...APHIS-2012-0002] RIN 0579-AD63 Importation of Avocados From Continental Spain AGENCY: Animal...rule that would allow the importation of avocados from continental Spain (excluding the...regulations to allow the importation of avocados from continental Spain (excluding...

  1. Repeated arc-continent collision as a key mechanism for continental growth

    NASA Astrophysics Data System (ADS)

    Aitchison, J.; Buckman, S.

    2011-12-01

    Prevailing 'consensus' models for the Phanerozoic development of eastern Australia invoke a retreating accretionary orogen model in which slab retreat results in development of offshore island arcs in front of marginal basins. Periodically these basins close and the arcs are retro-thrust back onto the continental margin. Implicit in this model is the notion that all elements develop in an upper plate location upon the accretionary margin and that west-dipping subduction beneath eastern Gondwana was a long-lived phenomenon. We suggest this concept is flawed and instead propose a new testable hypothesis that eastern Australia grew through a series of arc-continent collisions in which east-directed subduction beneath intra-oceanic island arcs led to their collision with eastern Australia. At least four such arc-continent collisions are posited in mid-Cambrian (Mt Stavely arc), Late Ordovician (Macquarie arc), mid-Devonian (Gamilaroi arc) and Late Permian (Gympie arc) times. This process effectively transferred new material to the continental crust resulting in net growth. When collisions were followed by subduction flip episodes of west-directed subduction beneath the continental margin ensued giving rise to the S- and I-type granites for which eastern Australia is famous.

  2. Alps, Carpathians and Dinarides-Hellenides: about plates, micro-plates and delaminated crustal blocks

    NASA Astrophysics Data System (ADS)

    Schmid, Stefan

    2014-05-01

    Before the onset of Europe-Africa continental collision in the Dinarides-Hellenides (around 60Ma) and in the Alps and Western Carpathians (around 35 Ma), and at a large scale, the dynamics of orogenic processes in the Mediterranean Alpine chains were governed by Europe-Africa plate convergence leading to the disappearance of large parts of intervening oceanic lithosphere, i.e. the northern branch of Neotethys along the Sava-Izmir-Ankara suture and Alpine Tethys along the Valais-Magura suture (Schmid et al. 2008). In spite of this, two major problems concerning the pre-collisional stage are still poorly understood: (1) by now we only start to understand geometry, kinematics and dynamics of the along-strike changes in the polarity of subduction between Alps-Carpathians and Dinarides-Hellenides, and (2) it is not clear yet during exactly which episodes and to what extent intervening rifted continental fragments such as, for example, Iberia-Briançonnais, Tisza, Dacia, Adria-Taurides moved independently as micro-plates, and during which episodes they remained firmly attached to Europa or Africa from which they broke away. As Europe-Africa plate convergence slowed down well below 1 cm/yr at around 30 Ma ago these pre-collisional processes driven by plate convergence on a global scale gave way to more local processes of combined roll-back and crustal delamination in the Pannonian basin of the Carpathian embayment and in the Aegean (as well as in the Western Mediterranean, not discussed in this contribution). In the case of the Carpathian embayment E-directed roll back totally unrelated to Europe-Africa N-S-directed convergence, started at around 20 Ma ago, due to the presence relict oceanic lithosphere in the future Pannonian basin that remained un-subducted during collision. Due to total delamination of the crust from the eastward rolling back European mantle lithosphere the anticlockwise rotating ALCAPA crustal block, consisting of Eastern Alps and Western Carpathian thickened crust ripped of the African plate, invaded the northern part of this oceanic embayment, virtually floating on asthenospheric mantle. The presently still surviving semi-detached Vrancea slab in Romania manifests of the combined effect of roll back and delamination of mantle lithosphere. On the other hand Tisza-Dacia, another crustal block formerly ripped off the European plate and forming a single entity since mid-Cretaceous times, also at least partly floating on asthenospheric mantle, invaded the Carpathian embayment from the south. Thereby the Tisza-Dacia crustal block underwent clockwise rotation by as much as 90° due to the corner effect of the Moesian platform firmly attached to Europe since mid-Cretaceous times (Ustaszewski et al. 2008). In the Dinaric-Aegean realm collision occurred much earlier than in the Alps and the Carpathians, i.e. at around the Cretaceous-Cenozoic boundary, provided that one accepts that there is yet no convincing evidence for the existence of a second "Pindos oceanic domain" closing later, i.e. in Eocene times. However, in spite of early collision, the old subduction zone that consumed the northern branch of Neotethys (Meliata-Vardar) since at least mid-Cretaceous times persisted in the eastern Hellenides (but not in the Dinarides) until now, penetrating the transition zone all the way to a depth of some 1500km (Bijwaard et al. 1998). Continued subduction of mantle lithosphere in the Aegean since 60 Ma was concomitant with complete delamination of lithospheric mantle and lower crust from non-subducted or re-exhumed high pressure crustal flakes of largely continental derivation that were piled up to form the subsequently extended Hellenic orogen (Jolivet & Brun 2010). At around 25 Ma when the southern branch of Neotethys (the present-day Eastern Mediterranean ocean) entered this subduction zone, massive extension and core complex formation in the upper plate combined with an acceleration of south-directed hinge retreat of the lower plate did set in (van Hinsbergen & Schmid 2012). Dinarides and northern

  3. A continuum model of continental deformation above subduction zones - Application to the Andes and the Aegean

    NASA Technical Reports Server (NTRS)

    Wdowinski, Shimon; O'Connell, Richard J.; England, Philip

    1989-01-01

    A continuum model of continental deformation above subduction zones was developed that combines the viscous sheet and the corner flow models; the continental lithosphere is described by a two-dimensional sheet model that considers basal drag resulting from the viscous asthenosphere flow underneath, and a corner flow model with a deforming overlying plate and a rigid subducting plate is used to calculate the shear traction that acts on the base of the lithosphere above a subduction zone. The continuum model is applied to the Andes and the Aegean deformations, which represent, respectively, compressional and extensional tectonic environments above subduction zones. The models predict that, in a compressional environment, a broad region of uplifted topography will tend to develop above a more steeply dippping slab, rather than above a shallower slab, in agreement with observations in the various segments of the central Andes. For an extensional environment, the model predicts that a zone of compression can develop near the trench, and that extensional strain rate can increase with distance from the trench, as is observed in the Aegean.

  4. Imaging continental collision and subduction in the Pamir mountain range, Central Asia, by seismic attenuation tomography

    NASA Astrophysics Data System (ADS)

    Schurr, Bernd; Haberland, Christian; Sippl, Christian; Yuan, Xiaohui; Mechie, James; Schneider, Felix; Tipage Team

    2014-05-01

    Subduction of continental crust is the mode of shortening in continental collision that is the least well understood. It is known to occur, as testified e.g., by now exhumed ultra-high-pressure rocks, despite the fact that continental crust is generally too buoyant to submerge into the mantle. Continental crust may, however, subduct in tow of a leading dense oceanic plate at the last stage of the plate tectonic Wilson cycle. Alternatively, if upper and lower crust detach, the latter, together with the underlying cold mantle lithosphere, may become negatively buoyant, enabling their descent. The Pamir mountains in Central Asia have been one of the few places on Earth, where on-going continental subduction has been postulated based on an active Wadati-Benioff zone. The Pamir is situated on an orographic node northwest of Tibet, between the Tarim and Tajik basins, where the Hindu Kush, Karakorum, western Kunlun Shan and Tien Shan ranges coalesce. It formed in the late Paleogene to Neogene, i.e. approximately during the second half of the India-Asia collision, north of the Western Himalayan Syntaxis, on the Asian (retro)continent. We use tomography of seismic attenuation to image the lithospheric-scale structure of the Pamir orogen. Attenuation tomography has been shown to be a powerful tool to study deep process-related structures particularly in oceanic subduction zones. Attenuation at this scale may be seen as a proxy for rheology and hence is very sensitive to e.g., homologous temperature and deformation. We use data from a two-year seismic deployment of the Tien Shan-Pamir Geodynamic Program (TIPAGE). The whole path attenuation parameter t* is determined by inversion of P-wave velocity spectra from 1790 earthquakes and then inverted for a 3D attenuation model (Qp) employing a recently published 3D velocity model. We find a prominent continuous crescent-shaped high-attenuation anomaly (HAA) that penetrates from upper crustal levels to depths of more than 100 km. At mantle depths the HAA follows the seismicity and coincides with low seismic velocities and most probably represents subducted crustal rocks. The HAA appears to be sandwiched between regions of low attenuation. To the north and west this probably represents cold Asian lithospheric mantle. To the south the low attenuation may be an indication of the (Indian?) indenter. The structures we image here are distinctively different from oceanic subduction zones, where HAAs usually occur in the mantle wedge above low attenuation oceanic slabs.

  5. Landscape formation by past continental ice sheets: insights into the subglacial environment

    NASA Astrophysics Data System (ADS)

    Piotrowski, Jan A.

    2014-05-01

    Glaciers and ice sheets are known as most powerful, climatically driven agents of large-scale sediment redistribution and landscape formation in the Earth system. During the Quaternary, repeated waxing and waning of continental ice sheets contributed to profound reshaping of the Earth surface and set the scene for the development of ecosystems in the post-glacial time. Despite the well-established impact of glaciers on the upper lithosphere the specific processes of glacial erosion, transport and deposition and the formation landforms at the ice-bed interface are contentious. In particular, the relative importance of direct ice impact versus the impact of glacial meltwater is highly controversial. Here, we focus on the southern peripheral area of the Scandinavian Ice Sheet hosting thick successions of soft, deformable sediments and examine some spectacular sediment/landform assemblages found nowadays in both terrestrial and marine settings to illustrate the nature of the subglacial processes. In order to decipher the past ice sheet behavior field, experimental and numerical approaches are combined. It is shown that the strength of the coupling between the ice and the bed that controls the response of the substratum to ice overriding and stress propagation depends primarily on the ability of the glacial system to evacuate meltwater from ice-bed interface. Strong coupling, locally enhanced by subglacial permafrost resulted in deeply rooted (100's of meters) glaciotectonic deformation reflected on the surface as ice-shoved hills whereas weak coupling promoted by water accumulating under the ice triggered the formation of deep (100's of meters) tunnel valley networks. Under the arteries of fast-flowing ice known as palaeo-ice streams, remoulding of soft sediments generated mega-scale glacial lineations and drumlins that hold the key to understanding glacier dynamics. The subglacial environment is envisaged as a four-dimensional mosaic of stable and deforming spots transient in time and space whose impact is embedded in the properties of sediment/landform systems.

  6. Generation of Continental Rifts, Basins and Swells by Lithosphere Instabilities

    NASA Astrophysics Data System (ADS)

    Milelli, L.; Fourel, L.; Jaupart, C. P.

    2012-12-01

    Domal uplifts, volcanism, basin formation and rifting have often struck the same continent in different areas at the same time. Their characteristics and orientations are difficult to reconcile with mantle convection or tectonic forces and suggest a driving mechanism that is intrinsic to the continent. The rifts seem to develop preferentially at high angles to the edge of the continent whereas swells and basins seem confined to the interior. Another intriguing geometrical feature is that the rifts often branch out in complicated patterns at their landward end. In Western Africa, for example, magmatic activity currently occurs in a number of uplifted areas including the peculiar Cameroon Volcanic Line that stretches away from the continental margin over about 1000 km. Magmatic and volcanic activity has been sustained along this line for 70 My with no age progression. The mantle upwelling that feeds the volcanoes is not affected by absolute plate motions and hence is attached to the continent. The Cameroon Volcanic Line extends to the Biu swell to the North and the Jos plateau to the West defining a striking Y-shaped pattern. This structure segues into several volcanic domes including the Air, the Hoggar, the Darfur, the Tibesti and the Haruj domes towards the Mediterranean coast. Another example is provided by North America, where the late Proterozoic-early Ordovician saw the formation of four major basins, the Michigan, Illinois, Williston and Hudson Bay, as well as of major rifts in southern Oklahoma and the Mississipi Valley within a short time interval. At the same time, a series of uplifts developed, such as the Ozark and Nashville domes. Motivated by these observations, we have sought an explanation in the continental lithosphere itself. We describe a new type of convective instability at the base of the lithosphere that leads to a remarkable spatial pattern at the scale of an entire continent. We carried out fluid mechanics laboratory experiments on buoyant blocks of finite size that became unstable due to cooling from above and describe the peculiar horizontal planform that developed. Dynamical behaviour depends on three dimensionless numbers, a Rayleigh number for the unstable block, a buoyancy number that scales the intrinsic density contrast to the thermal one and the aspect ratio of the block. Within the block, instability develops in two different ways in an outer annulus and in an inner region. In the outer annulus, upwellings and downwellings take the form of radial rolls spaced regularly. In the interior region, the planform adopts the more familiar form of polygonal cells. Translated to geological conditions, such instabilities should manifest themselves as linear rifts striking at a right angle to the continent-ocean boundary and an array of domal uplifts, volcanic swells and basins in the continental interior. The laboratory data lead to simple scaling laws for the dimensions and spacings of the convective structures. For the sub-continental lithospheric mantle, these dimensions and distances take values in the 500-1000 km range, close to geological examples. The large intrinsic buoyancy of Archean lithospheric roots prevents this type of instability, which explains why the widespread volcanic activity that currently affects Western Africa is confined to post-Archean domains.

  7. Geoid Data and Implications for Plate Tectonic Dynamics

    NASA Astrophysics Data System (ADS)

    Richardson, R. M.; Coblentz, D. D.

    2013-12-01

    It has long been recognized that the motion of the mechanically rigid lithospheric plates of the earth are the surface expression of large-scale convection in the mantle. It is also accepted that the stresses driving plate motion are an amalgam of the basal tractions associated with this convection and long-wavelength density variations within the plates themselves. Parsing the relative contribution from these two sources to the geodynamics of the lithosphere continues to be an important topic of plate dynamics research. Because geoid anomalies are directly related to the local dipole moment of the density-depth distribution, they provide an ideal method for evaluating density variations within the lithosphere and the associated tectonic stresses. The main challenge with this approach is isolating the lithospheric geoid contribution from the full geoid (which is dominated by sources from deeper in the earth, namely the lower mantle). We address this issue by using a high-pass spherical harmonic filtering of the EGM2008-WGS84 geoid (which is complete to spherical harmonic degree and order 2159), with a cosine taper between orders 9 to 13 and 78 to 82 to produce a 'lithospheric' geoid. In the present study we focus on tectonic implications of the lithospheric geoid in three different areas: 1) passive continental margins where we have evaluated over 150 margin-transects spaced roughly every three degrees. The global average geoid anomaly associated with the transition from old oceanic lithosphere to the continent was found to 6-9 meters and appears to be insensitive to a range of geoid filtering degrees and orders; 2) The geoid highs associated with the mid-ocean ridges and the cooling oceanic lithospheric, where we have examined a number of geoid profiles across ridges and find that previous estimates of a geoid anomaly of 10-15 meters associated with ridges to be valid; and 3) continental regions which are characterized by both elevated geoid anomalies (e.g., the Western U.S.) and geoid lows (e.g., the Congo Basin in Africa). All three of these geoid studies have implications for our understanding of the dynamics of plate tectonics. The 10-15 m geoid highs associated globally with ridges are consistent with a net force of ~3x1012 N/m due to 'ridge push.' Converting gradients in the oceanic 'lithospheric' geoid produce net torques on the plates consistent with this magnitude of 'ridge push.' The 6-9 meter geoid step up across passive continental margins is important for two reasons. First, it is consistent with a reduction of the ridge force acting on the continents, as evidenced by increased strike slip and normal deformation on the continents compared to oceanic lithosphere. Second, the very fact that such a small geoid step can affect tectonic style is evidence that even relatively small forces, like the ridge force compared to the negative buoyancy of subducted lithosphere, can be important in plate dynamics. Furthermore, the predicted intraplate stresses computed using a finite-element analysis of a lithospheric shell under traction from the gravitational potential energy forces associated with the lithospheric geoid provide a remarkably good fit between the predicted and observed intraplate stress field at long wavelengths (~1000km) and indicates that tectonic forces associated with the lithospheric density moment play an important role in global geodynamics.

  8. Micro-channel plate detector

    SciTech Connect

    Elam, Jeffrey W.; Lee, Seon W.; Wang, Hsien -Hau; Pellin, Michael J.; Byrum, Karen; Frisch, Henry J.

    2015-09-22

    A method and system for providing a micro-channel plate detector. An anodized aluminum oxide membrane is provided and includes a plurality of nanopores which have an Al coating and a thin layer of an emissive oxide material responsive to incident radiation, thereby providing a plurality of radiation sensitive channels for the micro-channel plate detector.

  9. Metal vapor arc ion plating

    DOEpatents

    Bertram, L.A.; Fisher, R.W.; Mattox, D.M.; Zanner, F.J.

    1986-09-09

    A method and apparatus for ion plating are described. The apparatus uses more negative than a first electrode voltage in a vacuum arc remelt system to attract low energy ions from the anode electrode to the article to be plated. 2 figs.

  10. Earthquake Production by Subduction Zones is Not Linear in Relative Plate Velocity

    NASA Astrophysics Data System (ADS)

    Bird, P.; Kagan, Y. Y.; Jackson, D. D.; Schoenberg, F. P.; Werner, M. J.

    2007-12-01

    The ratio of \\{long-term-average seismic moment production per unit length of plate boundary\\} to \\{relative plate velocity\\} is determined by the "coupled thickness" of seismogenic lithosphere, and also by elastic moduli and geometric factors that are fairly well known. It is generally assumed that coupled thickness is constant within a given class of plate boundary, such as Bird's [2003, G3]: CCB Continental Convergent Boundary, CRB Continental Rift Boundary, CTF Continental Transform Fault, OCB Oceanic Convergent Boundary, OSR Oceanic Spreading Ridge, OTF Oceanic Transform Fault, or SUB Subduction zone. However, Bird et al. [2002, Geodyn. Ser.] and Bird & Kagan [2004, BSSA] found two exceptions: OSR and OTF both have greater coupled thickness at low relative plate velocities. We test for variation of coupled thickness with relative plate velocity in each of the 7 classes of plate boundary. We use shallow (<70 km) earthquakes from the Harvard CMT catalog, 1982.01.01-2007.03.31, above magnitude MW threshold of 5.51 or 5.66. In order to reduce the influence of aftershock swarms, we estimate the probability of independence of each earthquake according to the likelihood stochastic declustering method of Kagan & Jackson [1991; GJI] and use this as a weight. We use the algorithm of Bird & Kagan [2004, BSSA] to assign 95% of shallow earthquakes to plate boundary steps and plate boundary classes, rejecting all earthquakes that fall into one of the 13 orogens of Bird [2003, G3]. We order the plate-boundary steps outside orogens in each class by relative plate velocity according to the PB2002 model of Bird [2003]. Then, we plot cumulative earthquake count as a function of cumulative model tectonic moment (assuming constant coupled thickness and other parameters within each plate boundary class). The null hypothesis is a linear relation; we use 2 measures (Kolmogorov-Smirnov, and Cramer-von Mises) to quantify departures from this line. We use 10,000 simulations of each class with random Poissonian seismicity in each plate boundary step (with expectations based on the tectonic model) to assess the significance of the measures obtained. Subduction zones have velocity-dependent coupled thickness: P < 0.001 for the null hypothesis. Subduction zones with relative plate velocity <67 mm/a (which would comprise 35% of the model tectonic moment rate, in the null hypothesis) actually produce only 20% of the global subduction zone earthquakes (outside orogens), and thus have a coupled thickness about half that of faster subduction zones (if corner magnitude and spectral slope are constant). This result contradicts the uniform coupling of subduction zones inferred by Kreemer et al. [2002, Geodyn. Ser.]; the difference may be due to their exclusion of several slow subduction zones including Aegean, Cascadia, New Zealand, Caribbean, and South Shetland. Continental CCBs show a similarly strong relation (P < 0.001), with an increase in coupled thickness when velocity exceeds 25 mm/a. OSRs show coupled thickness declining with velocity, as in previous studies. OTFs and OCBs give complex results with significant variations (P < 0.01; P < 0.05) that are not easy to interpret. For CRBs and CTFs we do not reject the null hypothesis of constant coupled thickness.

  11. Present-day plate motions

    NASA Technical Reports Server (NTRS)

    Minster, J. B.; Jordan, T. H.

    1977-01-01

    A data set comprising 110 spreading rates, 78 transform fault azimuths and 142 earthquake slip vectors was inverted to yield a new instantaneous plate motion model, designated RM2. The mean averaging interval for the relative motion data was reduced to less than 3 My. A detailed comparison of RM2 with angular velocity vectors which best fit the data along individual plate boundaries indicates that RM2 performs close to optimally in most regions, with several notable exceptions. On the other hand, a previous estimate (RM1) failed to satisfy an extensive set of new data collected in the South Atlantic Ocean. It is shown that RM1 incorrectly predicts the plate kinematics in the South Atlantic because the presently available data are inconsistent with the plate geometry assumed in deriving RM1. It is demonstrated that this inconsistency can be remedied by postulating the existence of internal deformation with the Indian plate, although alternate explanations are possible.

  12. The Moho depth map of the European Plate

    NASA Astrophysics Data System (ADS)

    Grad, Marek; Tiira, Timo

    2009-01-01

    The European Plate has a 4.5 Gy long and complex tectonic history. This is reflected in the present-day large-scale crustal structures. A new digital Moho depth map is compiled from more than 250 data sets of individual seismic profiles, 3-D models obtained by body and surface waves, receiver function results and maps of seismic and/or gravity data compilations. We have compiled the first digital, high-resolution map of the Moho depth for the whole European Plate, extending from the mid-Atlantic ridge in the west to the Ural Mountains in the east, and from the Mediterranean Sea in the south to the Barents Sea and Spitsbergen in the Arctic in the north. In general, three large domains within the European Plate crust are visible. The oldest Archean and Proterozoic crust has a thickness of 40-60 km, the continental Variscan and Alpine crust has a thickness of 20-40 km, and the youngest oceanic Atlantic crust has a thickness of 10-20 km.

  13. Flexural deformation of the continental lithosphere

    NASA Technical Reports Server (NTRS)

    1990-01-01

    Prior work focused primarily on the Adriatic and northern Ionian regions. The results of these studies have been summarized previously, and so are only briefly discussed. More recent work focuses on two different topics: (1) analysis of foredeep basin geometry, sedimentary style, and thrust belt structure in light of the kinematics at the associated plate boundary and subduction zone dynamics; and (2) the evolution and plate strength of early Proterozoic lithosphere.

  14. Utilization of orthotropic graphite plates in plate heat exchangers, analytical modeling

    E-print Network

    Bahrami, Majid

    Utilization of orthotropic graphite plates in plate heat exchangers, analytical modeling Farshid Keywords: Orthotropic media Graphite sheet Plate heat exchanger Effectiveness Critical conductivity a b as promising alternative to conventional metallic plate heat exchangers (PHE). A new analytical model

  15. Polyphase formation and exhumation of high- to ultrahigh-pressure rocks in continental subduction zone: Numerical modeling and application to the Sulu ultrahigh-pressure terrane in eastern China

    NASA Astrophysics Data System (ADS)

    Li, Zhonghai; Gerya, Taras V.

    2009-09-01

    High- to ultrahigh-pressure (HP-UHP) metamorphic rocks commonly form and exhume during the early continental collision, and many questions related to their origin still remain unresolved. We focus our study on explaining the poly metamorphic origins of many HP-UHP terranes composed of tectonic units having strongly variable ages, peak metamorphic conditions, and P-T paths. These features are especially well characterized for the Sulu UHP terrane in eastern China which we have chosen therefore as the reference case. We conducted 2-D thermomechanical numerical modeling of continental subduction associated with formation and exhumation of HP-UHP rocks. Our experiments suggest existence of several consequent episodes of (U)HP rocks exhumation related to the inherently cyclic origin of continental crust subduction-detachment-exhumation processes. Three major phases of these processes are identified in our reference model for the Sulu UHP terrane: (1) first and (2) second exhumation episodes of HP rocks originated in the subduction channel at lithospheric depths and (3) exhumation of UHP rocks originated at asthenospheric depths. Numerical models also suggest that subducted UHP rocks which are positively buoyant compared to the mantle may detach from the slab forming a flattened plume underplating the overriding lithosphere. This sublithospheric plume may exist for several million years being heated to 800-900°C by the surrounding hot mantle. At the later stage, upward extrusion of hot partially molten rocks from the plume may exhume high-temperature (HT) UHP complexes toward the surface.

  16. Strong Lg attenuation in the continental-collision orogenic belt in Middle East

    NASA Astrophysics Data System (ADS)

    Zhao, L.; Xie, X.

    2013-12-01

    The Middle East is a tectonically convergent region involving young continental-collision orogenic belt from Turkish and Iranian plateaus to Pamir plateau and the old Precambrian shields, i.e., Eurasian, Arabian and Indian plates. Crustal Lg attenuation measurement, along with other evidences, such as velocity structures, gravity observations, geochemistry and volcanism, provides insight into the rheology and dynamic processes of the lithosphere beneath this region. We collect 6158 vertical-component seismograms recorded at 144 stations form 318 crustal earthquakes, and calculate the Lg-wave amplitude spectra at several discrete frequencies distributed log-evenly between 0.05 and 10.0 Hz. Based on the single-station, dual-station and dual-event datasets, We use Lg-wave Q tomography to simultaneously obtain a high-resolution broadband Lg-wave attenuation model, 318 source excitation functions, and 144 site responses in Middle East. The maximum spatial resolution is approximately 1.0°×1.0° in the continental-collision orogenic belt from Turkish and Iranian Plateaus to Pamir Plateau for frequencies between 0.05 and 1.5 Hz. The QLg images reveal the relations between attenuations and geological structures. Strong Lg attenuations are observed with a relatively low average Q0 (1 Hz QLg) of 333 (253-438) in the continental-collision orogenic belt. Weaken Lg attenuations are found with higher Q0 values in stable regions: 578 (492-679) for Eurasian Plate, 549 (493-611) for Arabian Plate and 557 (521-595) for Indian plate, respectively. By investigating the frequency dependence of the QLg in different geology formations, we find that the QLg values generally increase with rising frequencies but show complex relationships varying from region to region. The features of the resulting broadband Lg attenuation model suggest that the strong crustal attenuation is mainly caused by the tectonic and thermal activities. On the other hand, the strong attenuation distribution may provide useful constraints to the regions with high temperatures and partial melting.

  17. Kinematics of the western Caribbean: Collision of the Cocos Ridge and upper plate deformation

    NASA Astrophysics Data System (ADS)

    Kobayashi, Daisuke; LaFemina, Peter; Geirsson, Halldór; Chichaco, Eric; Abrego, Antonio A.; Mora, Hector; Camacho, Eduardo

    2014-05-01

    of the Cocos plate and collision of the Cocos Ridge have profound effects on the kinematics of the western Caribbean, including crustal shortening, segmentation of the overriding plate, and tectonic escape of the Central American fore arc (CAFA). Tectonic models of the Panama Region (PR) have ranged from a rigid block to a deforming plate boundary zone. Recent expansion of GPS networks in Panama, Costa Rica, and Colombia makes it possible to constrain the kinematics of the PR. We present an improved kinematic block model for the western Caribbean, using this improved GPS network to test a suite of tectonic models describing the kinematics of this region. The best fit model predicts an Euler vector for the counterclockwise rotation of the CAFA relative to the Caribbean plate at 89.10°W, 7.74°N, 1.193° Ma-1, which is expressed as northwest-directed relative block rates of 11.3 ± 1.0-16.5 ± 1.1 mm a-1 from northern Costa Rica to Guatemala. This model also predicts high coupling along the Nicoya and Osa segments of the Middle American subduction zone. Our models demonstrate that the PR acts as a single tectonic block, the Panama block, with a predicted Euler vector of 107.65°W, 26.50°N, 0.133° Ma-1. This rotation manifests as northeast migration of the Panama block at rates of 6.9 ± 4.0-7.8 ± 4.8 mm a-1 from southern Costa Rica to eastern Panama. We interpret this motion as tectonic escape from Cocos Ridge collision, redirected by collision with the North Andes block, which migrates to the northwest at 12.2 ± 1.2 mm a-1.

  18. Metallogeny of the northeastern Pacific Rim: an example of the distribution of ore deposits along a growing continental margin

    USGS Publications Warehouse

    Goldfarb, R.J.; Hart, C.J.; Mortensen, J.K.

    1999-01-01

    The distribution of mineral deposits within northwestern North America (Alaska, Yukon, and northern British Columbia) allows for an in-depth examination of the metallogenic patterns of a growing continental margin. A more complete understanding of the tectonic evolution of this part of the Pacific Rim, achieved over the last 15 to 20 years, now allows for the placement of ore systems into a well-defined plate tectonic framework. Ore deposits older than about 185 Ma represent hydrothermal systems that were active in the platform/shelf environment of ancestral North America's miogeocline or hydrothermal systems developed in oceanic arcs and continental fragments more distal to the craton. These include important SEDEX, VMS, and pre-accretionary porphyry deposits. In contrast, most mineral deposits younger than about 185 Ma were formed within the growing Cordilleran orogen, as terranes were accreted to the continental margin during interactions between the North America and Pacific/Farallon/Kula plates. Such syn- to post-accretionary mineralised systems include many large lode gold and porphyry/skarn systems.

  19. A harbinger of plate tectonics: a commentary on Bullard, Everett and Smith (1965) ‘The fit of the continents around the Atlantic’

    PubMed Central

    Dewey, John F.

    2015-01-01

    In the 1960s, geology was transformed by the paradigm of plate tectonics. The 1965 paper of Bullard, Everett and Smith was a linking transition between the theories of continental drift and plate tectonics. They showed, conclusively, that the continents around the Atlantic were once contiguous and that the Atlantic Ocean had grown at rates of a few centimetres per year since the Early Jurassic, about 160?Ma. They achieved fits of the continental margins at the 500 fathom line (approx. 900?m), not the shorelines, by minimizing misfits between conjugate margins and finding axes, poles and angles of rotation, using Euler's theorem, that defined the unique single finite difference rotation that carried congruent continents from contiguity to their present positions, recognizing that the real motion may have been more complex around a number of finite motion poles. Critically, they were concerned only with kinematic reality and were not restricted by considerations of the mechanism by which continents split and oceans grow. Many of the defining features of plate tectonics were explicit or implicit in their reconstructions, such as the torsional rigidity of continents, Euler's theorem, closure of the Tethyan ocean(s), major continental margin shear zones, the rapid rotation of small continental blocks (Iberia) around nearby poles, the consequent opening of small wedge-shaped oceans (Bay of Biscay), and misfit overlaps (deltas and volcanic piles) and underlaps (stretched continental edges). This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society. PMID:25750142

  20. A harbinger of plate tectonics: a commentary on Bullard, Everett and Smith (1965) 'The fit of the continents around the Atlantic'.

    PubMed

    Dewey, John F

    2015-04-13

    In the 1960s, geology was transformed by the paradigm of plate tectonics. The 1965 paper of Bullard, Everett and Smith was a linking transition between the theories of continental drift and plate tectonics. They showed, conclusively, that the continents around the Atlantic were once contiguous and that the Atlantic Ocean had grown at rates of a few centimetres per year since the Early Jurassic, about 160?Ma. They achieved fits of the continental margins at the 500 fathom line (approx. 900?m), not the shorelines, by minimizing misfits between conjugate margins and finding axes, poles and angles of rotation, using Euler's theorem, that defined the unique single finite difference rotation that carried congruent continents from contiguity to their present positions, recognizing that the real motion may have been more complex around a number of finite motion poles. Critically, they were concerned only with kinematic reality and were not restricted by considerations of the mechanism by which continents split and oceans grow. Many of the defining features of plate tectonics were explicit or implicit in their reconstructions, such as the torsional rigidity of continents, Euler's theorem, closure of the Tethyan ocean(s), major continental margin shear zones, the rapid rotation of small continental blocks (Iberia) around nearby poles, the consequent opening of small wedge-shaped oceans (Bay of Biscay), and misfit overlaps (deltas and volcanic piles) and underlaps (stretched continental edges). This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society. PMID:25750142

  1. The Golosyiv plate archive digitisation

    NASA Astrophysics Data System (ADS)

    Sergeeva, T. P.; Sergeev, A. V.; Pakuliak, L. K.; Yatsenko, A. I.

    2007-08-01

    The plate archive of the Main Astronomical Observatory of the National Academy of Sciences of Ukraine (Golosyiv, Kyiv) includes about 85 000 plates which have been taken in various observational projects during 1950-2005. Among them are about 25 000 of direct northern sky area plates and more than 600 000 plates containing stellar, planetary and active solar formations spectra. Direct plates have a limiting magnitude of 14.0-16.0 mag. Since 2002 we have been organising the storage, safeguarding, cataloguing and digitization of the plate archive. The very initial task was to create the automated system for detection of astronomical objects and phenomena, search of optical counterparts in the directions of gamma-ray bursts, research of long period, flare and other variable stars, search and rediscovery of asteroids, comets and other Solar System bodies to improve the elements of their orbits, informational support of CCD observations and space projects, etc. To provide higher efficiency of this work we have prepared computer readable catalogues and database for 250 000 direct wide field plates. Now the catalogues have been adapted to Wide Field Plate Database (WFPDB) format and integrated into this world database. The next step will be adaptation of our catalogues, database and images to standards of the IVOA. Some magnitude and positional accuracy estimations for Golosyiv archive plates have been done. The photometric characteristics of the images of NGC 6913 cluster stars on two plates of the Golosyiv's double wide angle astrograph have been determined. Very good conformity of the photometric characteristics obtained with external accuracies of 0.13 and 0.15 mag. has been found. The investigation of positional accuracy have been made with A3± format fixed bed scanner (Microtek ScanMaker 9800XL TMA). It shows that the scanner has non-detectable systematic errors on the X-axis, and errors of ± 15 ?m on the Y-axis. The final positional errors are about ± 2 ?m (± 0 .2). have been obtained after corrections for systematic errors of the scanner and averaging four scans. So we may conclude that astrometric and photometric investigations may be done with precise commercial scanners. It will be necessary to scan plates at a minimum of two positions. We plan to scan the plate archive according to the priority of scientific tasks. Scanning will be done with an optical resolution of 1200 × 1200 dpi (pixel size 20 ?m), and with maximum amplitude resolution. The plate archive of MAO NASU is a unique well equipped instrument for conducting a range of astronomical investigations with a time scale of more than 50 yr.

  2. Designing a license plate.

    PubMed

    Al-Haboubi, M H

    1999-10-01

    The majority of license plates in Saudi Arabia contain a 7-digit code to represent the registration number of vehicles. This information can be difficult to read, memorize, and reproduce in a short period of time, such as in the case of recall of hit-and-run accidents. The study reported proposes a registration code composed of 3 letters and 3 digits. This alphanumeric code can be converted into a numerical value which would give close to 20 million possible permutations, which would cover the projected number of vehicles to the year 2012. The original and proposed designs would give, in addition to two other alphanumeric codes, were tested on 60 participants using computer animations at three exposure times (1, 2, and 3 s). The results of the ANOVA on the errors committed and Sheffe tests reveal a significant difference (alpha = 0.01) between the 7-digit design and the other designs at all time intervals. Validation of the laboratory experiments were conducted on 15 different participants in the field, with similar findings. PMID:10484277

  3. The cretaceous dynamics of the pacific plate and stages of magmatic activity in Northeastern Asia

    NASA Astrophysics Data System (ADS)

    Stepashko, A. A.

    2006-05-01

    The dynamics of the Pacific Plate is recorded in the systematic variation of location and the 40Ar-39Ar age of seamounts in the western Pacific from 120 to 65 Ma ago. The seamounts are grouped into three linear zones as long as 5000 km. The seamounts become younger in the southeastern direction along the strike of these zones. Correlation between age and location of seamounts allows division of the history of their formation into three stages. The rate of seamount growth was relatively low (2-4 cm/yr) during the first and the third stages within the intervals of 120-90 and 85-65 Ma, whereas during the second stage (90-85 Ma), the seamounts were growing very fast (80-100 cm/yr). In the midst of this stage, at ˜87 Ma ago, the magmatic activity increased abruptly. The dynamics of seamount building is in good agreement with (1) pulses in the development of the Ontong Java, Manihiki, and Caribbean-Colombian oceanic plateaus; (2) the age of spreading acceleration in the mid-Cretaceous; and (3) the short period when the Izanagi Plate ceased to exist and the Kula Plate was formed. The variation of the seamounts’ age and location is in consistence with the hypothesis of diffuse extension of the Pacific Plate in the course of its motion with formation of impaired zones of decompression melting. The direction of extension (325°-340° NW) calculated from the strike of seamount zones is consistent with the path of the Pacific Plate (330° NW) in the Late Cretaceous. The immense perioceanic volcanic belts were formed at that time along the margin of the Asian continent. The Okhotsk-Chukchi Peninsula Belt extends at a right angle to the compression vector. Three stages of this belt’s evolution are synchronous with the stages of seamount formation in the Pacific Plate. The delay in the origination of the East Sikhote-Alin Volcanic Belt and its different orientation were caused by counterclockwise rotation of the vector of convergence of oceanic and continental plates in the mid-Cretaceous. At the same time, i.e., 95-85 Ma ago, the volcanic activity embraced the entire continental margin and the tin granites were emplaced everywhere in eastern Asia. This short episode (90 ± 5 Ma) corresponds to the mid-Cretaceous maximum of compression of the continental margin, and its age fits a culmination in extension of the Pacific Plate well.

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

    USGS Publications Warehouse

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

    2005-01-01

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

  5. Cell Cycle Reprogramming for PI3K Inhibition Overrides Relapse-Specific C481S BTK Mutation Revealed by Longitudinal Functional Genomics in Mantle Cell Lymphoma

    PubMed Central

    Chiron, David; Di Liberto, Maurizio; Martin, Peter; Huang, Xiangao; Sharman, Jeff; Blecua, Pedro; Mathew, Susan; Vijay, Priyanka; Eng, Ken; Ali, Siraj; Johnson, Amy; Chang, Betty; Ely, Scott; Elemento, Olivier; Mason, Christopher E.; Leonard, John P.; Chen-Kiang, Selina

    2014-01-01

    Despite the unprecedented clinical activity of the Bruton’s tyrosine kinase inhibitor ibrutinib in MCL, acquired-resistance is common. By longitudinal integrative whole-exome and whole-transcriptome sequencing and targeted sequencing, we identified the first relapse-specific C481S mutation at the ibrutinib-binding site of BTK in MCL cells at progression following a durable response. This mutation enhanced BTK and AKT activation and tissue-specific proliferation of resistant MCL cells driven by CDK4 activation. It was absent, however, in patients with primary-resistance or progression following transient response to ibrutinib, suggesting alternative mechanisms of resistance. Through synergistic induction of PIK3IP1 and inhibition of PI3K-AKT activation, prolonged early G1 arrest induced by PD 0332991 (palbociclib) inhibition of CDK4 sensitized resistant lymphoma cells to ibrutinib killing when BTK was unmutated, and to PI3K inhibitors independent of C481S mutation. These data identify a genomic basis for acquired-ibrutinib resistance in MCL and suggest a strategy to override both primary- and acquired-ibrutinib resistance. PMID:25082755

  6. Evolution of the Earth as an andesite planet: water, plate tectonics, and delamination of anti-continent

    NASA Astrophysics Data System (ADS)

    Tatsumi, Yoshiyuki; Sato, Takeshi; Kodaira, Shuichi

    2015-12-01

    The Earth is unique in our solar system in having a buoyant, highland-forming continental crust with a differentiated, andesitic composition; thus, it can be referred to as an "andesite planet." Andesitic magmatism is associated with convergent plate margins such as subduction zones, leading to a broad consensus that this setting has been the major site of continental crust formation. However, while andesites are dominant in mature continental arcs, they are subordinate in juvenile oceanic arcs, resulting in a great conflict regarding the creation of the continental crust. We focused on the Izu-Bonin-Mariana arc to assess this problem, as it is a juvenile intra-oceanic arc with a mid-crustal layer that has a seismic velocity identical to that of the bulk continental crust. Petrological modeling of the production of andesitic melts by the mixing of mantle-derived basalt with crust-derived, rhyolite magmas successfully reproduced the crust/mantle structure observed in seismic profiles of the Izu-Bonin-Mariana arc. As a result, we presented a challenging hypothesis: the continent was created in the ocean. One key mechanism that differentiates initial basaltic arc crust to evolved, andesitic continental crust may be the delamination of SiO2-depleted residues of crustal melting, termed "anti-continent," from the arc crust.

  7. Continental fragmentation and the strontium isotopic evolution of seawater.

    NASA Astrophysics Data System (ADS)

    Eric, H.; Jean Pascal, C.

    2008-12-01

    The time evolution of the strontium isotopic composition of seawater over the last 600 million years has the form of an asymmetric trough. The values are highest in the Cambrian and recent and lowest in the Jurassic. Superimposed on this trend are a number of smaller oscillations. The mechanisms responsible for these global isotopic fluctuations are subject to much debates. In order to get a quantitative picture of the changing paleogeography, we have characterized land-ocean distributions over Late Proterozoic to Phanerozoic times from measurement of perimeters and areas of continental fragments, based on paleomagnetic reconstructions. These measurements served to calculate geophysically constrainted breakup and scatter indexes of continental land masses from 0 to 1100 Ma (Cogne and Humler, 2008). Both parameters (strontium isotopic ratios of seawater and continental fragmentation indexes) are obviously highly correlated during the last 600 Ma. Low continental dispersion (that is large continental land masses) are associated with low seawater strontium isotopic ratios (that is when the continental inputs to oceans are minimum) and high continental dispersion (that is relatively small and widely distributed continents) with high seawater strontium isotopic ratios (that is when the continental input to ocean is maximum). Importantly, this first order evolution appears to conflict with the common idea of mountains erosion as a source for radiogenic strontium to oceans because high strontium isotopic ratios in seawater correspond to period of maximum dispersion of continents and not with period of general collisions. At first glance, it would seem that continental erosion increases with the degree of continental dispersion. Models showing that continental precipitation increases when continental masses are smaller and more widely dispersed and/or the length of continental margins available for rivers to carry continental material to oceans are thus favoured in order to resolve the paradox.

  8. Regional magnetic anomaly constraints on continental rifting

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.; Olivier, R.; Bentley, C. R.

    1985-01-01

    Radially polarized MAGSAT anomalies of North and South America, Europe, Africa, India, Australia and Antarctica demonstrate remarkably detailed correlation of regional magnetic lithospheric sources across rifted margins when plotted on a reconstruction of Pangea. These major magnetic features apparently preserve their integrity until a superimposed metamorphoric event alters the magnitude and pattern of the anomalies. The longevity of continental scale magnetic anomalies contrasts markedly with that of regional gravity anomalies which tend to reflect predominantly isostatic adjustments associated with neo-tectonism. First observed as a result of NASA's magnetic satellite programs, these anomalies provide new and fundamental constraints on the geologic evolution and dynamics of the continents and oceans. Accordingly, satellite magnetic observations provide a further tool for investigating continental drift to compliment other lines of evidence in paleoclimatology, paleontology, paleomagnetism, and studies of the radiometric ages and geometric fit of the continents.

  9. Lithologic reservoir characterization in continental depressions

    SciTech Connect

    Yun-Ling Yang; Chuan-bo Leng; Xing-cai Liu

    1995-12-31

    An integrated procedure for lithologic reservoir characterization in the continental depressions which were mainly deposited with clastic sediments is proposed in this article. It consists of four main steps: (1) database setting, (2) seismic stratigraphy study, (3) reservoir identification, and (4) comprehensive description; in which the unification of geology and geophysics, the interaction of processing and interpretation, the combination of real data and priori information, and the rolling of exploration and development are strongly emphasized in order to exceed the limitation of geophysical prospecting. An example of eastern China is presented here; and the results of reservoir characterization in the NZ depression shows that the procedure proposed in this article is practical and effective for complicated lithologic reservoir exploration in the continental depressions.

  10. Continental and oceanic crustal magnetization modelling

    NASA Technical Reports Server (NTRS)

    Harrison, C. G. A.; Hayling, K. L.

    1984-01-01

    Inversion of magnetic data from the MAGSAT satellite, to arrive at intensities of magnetization of the Earth's crust, was performed by two different methods. The first method uses a spherical harmonic model of the magnetic field. The coefficients believed to represent sources in the Earth's crust can then be inverted to arrive at vertical dipole moments per unit area at the Earth's surface. The spherical harmonic models contain coefficients of degrees of harmonics up to 23. The dipole moment per unit area for a surface element can then be determined by summing the contribution for each individual degree of harmonic. The magnetic moments were calculated for continental and oceanic areas separately as well as over certain latitudinal segments. Of primary concern was to determine whether there are any differences between continental and oceanic areas. The second analysis with magnetization intensities was made using narrower ranges of degrees of harmonics, assuming that higher degrees are present in the core field signal.

  11. The transition from linear to diuse plate boundary in the Azores^Gibraltar region: results from a thin-sheet model

    E-print Network

    Bird, Peter

    a Institute of Earth Sciences `J. Almera', C.S.I.C., Sole¨ Sabar|¨s s/n, 08028 Barcelona, Spain b Department of Earth and Space Sciences, University of California, Los Angeles, CA 90095-1567, USA Received 27 February of the plate boundary east of the Gorringe Bank is dominated by the transition from oceanic to continental

  12. Precipitation of Continental Origin over South America

    NASA Astrophysics Data System (ADS)

    Martinez-Agudelo, J. A.; Dominguez, F.

    2012-12-01

    The Amazon forest receives high amounts of moisture from the tropical Atlantic. A significant part of this moisture is returned back to the atmosphere by the forest, and further redistributed to the rest of the continent by the meridional flow imposed by the Andes. Thus, the land-atmosphere interaction between the Amazon forest and the large-scale flow affects not only the forest itself but also the downstream regions. We develop a method to quantify the precipitation of continental origin over South America, and identify the contribution that selected source regions make to continental precipitation. The average annual cycle of precipitation of continental origin for the five-year period 2000-2004 shows a band of high values aligned along the northwest-southeast direction, from southern Peru to northeastern Argentina. The lowest values of precipitation of continental origin occur upstream, over the northeastern coast of South America. Precipitation that originates as moisture from the Amazon forest shows maximum values over the western side of the Amazon, east of the Andes, especially over southern Peru. The Amazon forest also contributes to precipitation over La Plata River Basin (LPRB) and the Pacific coast of Colombia. During its dry season, up to 29.3% of the precipitation over LPRB originates as moisture from the Amazon forest. Throughout the year, the contributions to precipitation over LPRB by the Amazon forest and LPRB (recycled precipitation) are in the same range, but out of phase. The average contribution of the rest of the continent to precipitation over LPRB is smaller but of the same order as that of the Amazon and LPRB.

  13. Ocean processes at the Antarctic continental slope.

    PubMed

    Heywood, Karen J; Schmidtko, Sunke; Heuzé, Céline; Kaiser, Jan; Jickells, Timothy D; Queste, Bastien Y; Stevens, David P; Wadley, Martin; Thompson, Andrew F; Fielding, Sophie; Guihen, Damien; Creed, Elizabeth; Ridley, Jeff K; Smith, Walker

    2014-07-13

    The Antarctic continental shelves and slopes occupy relatively small areas, but, nevertheless, are important for global climate, biogeochemical cycling and ecosystem functioning. Processes of water mass transformation through sea ice formation/melting and ocean-atmosphere interaction are key to the formation of deep and bottom waters as well as determining the heat flux beneath ice shelves. Climate models, however, struggle to capture these physical processes and are unable to reproduce water mass properties of the region. Dynamics at the continental slope are key for correctly modelling climate, yet their small spatial scale presents challenges both for ocean modelling and for observational studies. Cross-slope exchange processes are also vital for the flux of nutrients such as iron from the continental shelf into the mixed layer of the Southern Ocean. An iron-cycling model embedded in an eddy-permitting ocean model reveals the importance of sedimentary iron in fertilizing parts of the Southern Ocean. Ocean gliders play a key role in improving our ability to observe and understand these small-scale processes at the continental shelf break. The Gliders: Excellent New Tools for Observing the Ocean (GENTOO) project deployed three Seagliders for up to two months in early 2012 to sample the water to the east of the Antarctic Peninsula in unprecedented temporal and spatial detail. The glider data resolve small-scale exchange processes across the shelf-break front (the Antarctic Slope Front) and the front's biogeochemical signature. GENTOO demonstrated the capability of ocean gliders to play a key role in a future multi-disciplinary Southern Ocean observing system. PMID:24891389

  14. Iceberg scouring on the Norwegian continental shelf

    SciTech Connect

    Lien, R.

    1983-05-01

    This paper is a condensed version of parts of a Dr. ing. thesis to be presented during 1983. The first part of the paper deals with the regional distribution of iceberg scouring on the Norwegian continental shelf, and some general aspects related to it. The second part deals with iceberg scouring as a local phenomenon and its relation to the sea floor topography, sediment distribution, and geological and geotechnical properties of the sediments.

  15. Workshop on the Growth of Continental Crust

    NASA Technical Reports Server (NTRS)

    Ashwal, Lewis D. (editor)

    1988-01-01

    Constraints and observations were discussed on a fundamental unsolved problem of global scale relating to the growth of planetary crusts. All of the terrestrial planets were considered, but emphasis was placed on the Earth's continental crust. The title of each session is: (1) Extraterrestrial crustal growth and destruction; (2) Constraints for observations and measurements of terrestrial rocks; (3) Models of crustal growth and destruction; and (4) Process of crustal growth and destruction.

  16. Ocean processes at the Antarctic continental slope

    PubMed Central

    Heywood, Karen J.; Schmidtko, Sunke; Heuzé, Céline; Kaiser, Jan; Jickells, Timothy D.; Queste, Bastien Y.; Stevens, David P.; Wadley, Martin; Thompson, Andrew F.; Fielding, Sophie; Guihen, Damien; Creed, Elizabeth; Ridley, Jeff K.; Smith, Walker

    2014-01-01

    The Antarctic continental shelves and slopes occupy relatively small areas, but, nevertheless, are important for global climate, biogeochemical cycling and ecosystem functioning. Processes of water mass transformation through sea ice formation/melting and ocean–atmosphere interaction are key to the formation of deep and bottom waters as well as determining the heat flux beneath ice shelves. Climate models, however, struggle to capture these physical processes and are unable to reproduce water mass properties of the region. Dynamics at the continental slope are key for correctly modelling climate, yet their small spatial scale presents challenges both for ocean modelling and for observational studies. Cross-slope exchange processes are also vital for the flux of nutrients such as iron from the continental shelf into the mixed layer of the Southern Ocean. An iron-cycling model embedded in an eddy-permitting ocean model reveals the importance of sedimentary iron in fertilizing parts of the Southern Ocean. Ocean gliders play a key role in improving our ability to observe and understand these small-scale processes at the continental shelf break. The Gliders: Excellent New Tools for Observing the Ocean (GENTOO) project deployed three Seagliders for up to two months in early 2012 to sample the water to the east of the Antarctic Peninsula in unprecedented temporal and spatial detail. The glider data resolve small-scale exchange processes across the shelf-break front (the Antarctic Slope Front) and the front's biogeochemical signature. GENTOO demonstrated the capability of ocean gliders to play a key role in a future multi-disciplinary Southern Ocean observing system. PMID:24891389

  17. Plating on stainless steel alloys

    SciTech Connect

    Dini, J.W.; Johnson, H.R.

    1981-09-11

    Quantitative adhesion data are presented for a variety of electroplated stainless steel type alloys. Results show that excellent adhesion can be obtained by using a Wood's nickel strike or a sulfamate nickel strike prior to final plating. Specimens plated after Wood's nickel striking failed in the deposit rather than at the interface between the substrate and the coating. Flyer plate quantitative tests showed that use of anodic treatment in sulfuric acid prior to Wood's nickel striking even further improved adhesion. In contrast activation of stainless steels by immersion or cathodic treatment in hydrochloric acid resulted in very reduced bond strengths with failure always occurring at the interface between the coating and substrate.

  18. High loading uranium fuel plate

    SciTech Connect

    Wiencek, Thomas C.; Domagala, Robert F.; Thresh, Henry R.

    1990-01-01

    Two embodiments of a high uranium fuel plate are disclosed which contain a meat comprising structured uranium compound confined between a pair of diffusion bonded ductile metal cladding plates uniformly covering the meat, the meat having a uniform high fuel loading comprising a content of uranium compound greater than about 45 Vol. % at a porosity not greater than about 10 Vol. %. In a first embodiment, the meat is a plurality of parallel wires of uranium compound. In a second embodiment, the meat is a dispersion compact containing uranium compound. The fuel plates are fabricated by a hot isostatic pressing process.

  19. Lithospheric controls on magma composition along Earth's longest continental hotspot track.

    PubMed

    Davies, D R; Rawlinson, N; Iaffaldano, G; Campbell, I H

    2015-09-24

    Hotspots are anomalous regions of volcanism at Earth's surface that show no obvious association with tectonic plate boundaries. Classic examples include the Hawaiian-Emperor chain and the Yellowstone-Snake River Plain province. The majority are believed to form as Earth's tectonic plates move over long-lived mantle plumes: buoyant upwellings that bring hot material from Earth's deep mantle to its surface. It has long been recognized that lithospheric thickness limits the rise height of plumes and, thereby, their minimum melting pressure. It should, therefore, have a controlling influence on the geochemistry of plume-related magmas, although unambiguous evidence of this has, so far, been lacking. Here we integrate observational constraints from surface geology, geochronology, plate-motion reconstructions, geochemistry and seismology to ascertain plume melting depths beneath Earth's longest continental hotspot track, a 2,000-kilometre-long track in eastern Australia that displays a record of volcanic activity between 33 and 9 million years ago, which we call the Cosgrove track. Our analyses highlight a strong correlation between lithospheric thickness and magma composition along this track, with: (1) standard basaltic compositions in regions where lithospheric thickness is less than 110 kilometres; (2) volcanic gaps in regions where lithospheric thickness exceeds 150 kilometres; and (3) low-volume, leucitite-bearing volcanism in regions of intermediate lithospheric thickness. Trace-element concentrations from samples along this track support the notion that these compositional variations result from different degrees of partial melting, which is controlled by the thickness of overlying lithosphere. Our results place the first observational constraints on the sub-continental melting depth of mantle plumes and provide direct evidence that lithospheric thickness has a dominant influence on the volume and chemical composition of plume-derived magmas. PMID:26367795

  20. Lithospheric controls on magma composition along Earth's longest continental hotspot track

    NASA Astrophysics Data System (ADS)

    Davies, D. R.; Rawlinson, N.; Iaffaldano, G.; Campbell, I. H.

    2015-09-01

    Hotspots are anomalous regions of volcanism at Earth's surface that show no obvious association with tectonic plate boundaries. Classic examples include the Hawaiian-Emperor chain and the Yellowstone-Snake River Plain province. The majority are believed to form as Earth's tectonic plates move over long-lived mantle plumes: buoyant upwellings that bring hot material from Earth's deep mantle to its surface. It has long been recognized that lithospheric thickness limits the rise height of plumes and, thereby, their minimum melting pressure. It should, therefore, have a controlling influence on the geochemistry of plume-related magmas, although unambiguous evidence of this has, so far, been lacking. Here we integrate observational constraints from surface geology, geochronology, plate-motion reconstructions, geochemistry and seismology to ascertain plume melting depths beneath Earth's longest continental hotspot track, a 2,000-kilometre-long track in eastern Australia that displays a record of volcanic activity between 33 and 9 million years ago, which we call the Cosgrove track. Our analyses highlight a strong correlation between lithospheric thickness and magma composition along this track, with: (1) standard basaltic compositions in regions where lithospheric thickness is less than 110 kilometres; (2) volcanic gaps in regions where lithospheric thickness exceeds 150 kilometres; and (3) low-volume, leucitite-bearing volcanism in regions of intermediate lithospheric thickness. Trace-element concentrations from samples along this track support the notion that these compositional variations result from different degrees of partial melting, which is controlled by the thickness of overlying lithosphere. Our results place the first observational constraints on the sub-continental melting depth of mantle plumes and provide direct evidence that lithospheric thickness has a dominant influence on the volume and chemical composition of plume-derived magmas.

  1. Continental emergence in the Late Archean reconciles early and late continental growth models

    NASA Astrophysics Data System (ADS)

    Flament, Nicolas; Coltice, Nicolas; Rey, Patrice

    2014-05-01

    The analysis of ancient sediments (Rare Earth Element composition of black shales, isotopic strontium composition of marine carbonates, isotopic oxygen composition of zircons) suggests that continental growth culminated around the Archean-Proterozoic transition. In stark contrast, the geochemical analysis of ancient basalts suggests that depletion of the mantle occurred in the Hadean and Eoarchean. This paradox may be solved if continents were extracted from the mantle early in Earth's history, but remained mostly below sea level throughout the Archean. We present a model to estimate the area of emerged land and associated isotopic strontium composition of the mantle and oceans as a function of the coupled evolution of mantle temperature, continental growth and distribution of surface elevations (hypsometry). For constant continental hypsometry and four distinct continental growth models, we show that sea level was between 500 and 2000 m higher in the Archean than at present, resulting in < 12% of emerged land, compared to ~ 28% at present. If in addition the hot Archean lithosphere could not sustain high relief, as little as 2-3% of Earth's surface would have been emerged in the Archean. Using a geochemical box model for the strontium isotopic composition of the mantle and oceans, we show that a reduced area of emerged continental crust can explain why the geochemical fingerprint of continents extracted early in Earth's history was not recorded at the surface of the Earth until the late Archean.

  2. Cretaceous to present kinematics of the Indian, African and Seychelles plates

    NASA Astrophysics Data System (ADS)

    Eagles, Graeme; Hoang, Ha H.

    2014-01-01

    An iterative inverse model of seafloor spreading data from the Mascarene and Madagascar basins and the flanks of the Carlsberg Ridge describes a continuous history of Indian-African Plate divergence since 84 Ma. Visual-fit modelling of conjugate magnetic anomaly data from near the Seychelles platform and Laxmi Ridge documents rapid rotation of a Seychelles Plate about a nearby Euler pole in Palaeocene times. As the Euler pole migrated during this rotation, the Amirante Trench on the western side of the plate accommodated first convergence and later divergence with the African Plate. The unusual present-day morphology of the Amirante Trench and neighbouring Amirante Banks can be related to crustal thickening by thrusting and folding during the convergent phase and the subsequent development of a spreading centre with a median valley during the divergent phase. The model fits FZ trends in the north Arabian and east Somali basins, suggesting that they formed in India-Africa Plate divergence. Seafloor fabric in and between the basins shows that they initially hosted a segmented spreading ridge that accommodated slow plate divergence until 71-69 Ma, and that upon arrival of the Deccan-Réunion plume and an increase to faster plate divergence rates in the period 69-65 Ma, segments of the ridge lengthened and propagated. Ridge propagation into the Indian continental margin led first to the formation of the Laxmi Basin, which accompanied extensive volcanism onshore at the Deccan Traps and offshore at the Saurashtra High and Somnath Ridge. A second propagation episode initiated the ancestral Carlsberg Ridge at which Seychelles-India and India-Africa Plate motions were accommodated. With the completion of this propagation, the plate boundaries in the Mascarene Basin were abandoned. Seafloor spreading between this time and the present has been accommodated solely at the Carlsberg Ridge.

  3. Dynamic Topography and Sea Level Change Inferred from Dipole and Quadrupole Moments of Plate Tectonic Reconstructions

    NASA Astrophysics Data System (ADS)

    Conrad, C. P.; Steinberger, B. M.; Torsvik, T. H.

    2014-12-01

    Although constraints on the history of mantle flow are difficult to obtain, tectonic reconstructions contain information about the longest wavelength patterns of mantle flow that drove plate motions in the past. To examine the influence of this long-wavelength flow on global geodynamics, we computed the dipole and quadrupole moments (harmonic degrees 1 and 2) of the spherical vector fields associated with tectonic reconstructions of plate motions back to 250 Ma. Areas of dipole or quadrupole divergence lie above regions of major mantle upwelling, and convergence regions reside atop major mantle downwellings. To constrain the time-dependence of dynamic topography associated with these upwellings and downwellings, we used a numerical model of present-day mantle flow to relate degree-1 and degree-2 patterns of dynamic topography to the orientations and amplitudes of the dipole and quadrupole moments of present-day plate motions. We then apply this relationship to the dipole and quadrupole moments of past plate motions to compute the long-wavelength components of dynamic topography for the Mesozoic and Cenozoic. Continental motions over this time-evolving dynamic topography predict patterns of continental uplift and subsidence that can be related to geological observations of continental surfaces relative to sea level. Net uplift or subsidence of the global seafloor can also induce eustatic sea level changes. We infer that dispersal of the Pangean supercontinent away from upwelling beneath Africa may have exposed the seafloor to an increasingly larger area of positive dynamic topography since the early Mesozoic that has caused up to 100 m of sea level rise during this time period. This component of sea level change helps to balance observations of Cretaceous and Cenozoic sea level change with an estimated total sea level budget that includes concurrent tectonic and climatic influences that produce sea level drop of up to ~250 m.

  4. Carbon-assisted flyer plates

    DOEpatents

    Stahl, D.B.; Paisley, D.L.

    1994-04-12

    A laser driven flyer plate is described utilizing an optical fiber connected to a laser. The end of the optical fiber has a layer of carbon and a metal layer deposited onto it. The carbon layer provides the laser induced plasma which is superior to the plasma produced from most metals. The carbon layer plasma is capable of providing a flatter flyer plate, converting more of the laser energy to driving plasma, promoting a higher flyer plate acceleration, and providing a more uniform pulse behind the plate. In another embodiment, the laser is in optical communication with a substrate onto which a layer of carbon and a layer of metal have been deposited. 2 figures.

  5. What Are Growth Plate Injuries?

    MedlinePLUS

    ... Academy of Orthopaedic Surgeons. How Are Growth Plate Fractures Diagnosed? First, the doctor will find out how ... x rays to find out what kind of fracture it is. Third, a treatment plan is chosen. ...

  6. The multigap resistive plate chamber

    SciTech Connect

    Zeballos, E. Cerron; Crotty, I.; Hatzifotiadou, D.; Valverde, J. Lamas; Neupane, S.; Williams, M. C. S.; Zichichi, A.

    2015-02-03

    The paper describes the multigap resistive plate chamber (RPC). This is a variant of the wide gap RPC. However it has much improved time resolution, while keeping all the other advantages of the wide gap RPC design.

  7. What Are Growth Plate Injuries?

    MedlinePLUS

    ... of the following: ? Immobilization (a cast or splint) ? Manipulation or surgery (depending on where and how serious ... growth plate injuries. For example, they are: ? Studying gene therapy and finding other ways to help bones ...

  8. The rapid drift of the Indian tectonic plate.

    PubMed

    Kumar, Prakash; Yuan, Xiaohui; Kumar, M Ravi; Kind, Rainer; Li, Xueqing; Chadha, R K

    2007-10-18

    The breakup of the supercontinent Gondwanaland into Africa, Antarctica, Australia and India about 140 million years ago, and consequently the opening of the Indian Ocean, is thought to have been caused by heating of the lithosphere from below by a large plume whose relicts are now the Marion, Kerguelen and Réunion plumes. Plate reconstructions based on palaeomagnetic data suggest that the Indian plate attained a very high speed (18-20 cm yr(-1) during the late Cretaceous period) subsequent to its breakup from Gondwanaland, and then slowed to approximately 5 cm yr(-1) after the continental collision with Asia approximately 50 Myr ago. The Australian and African plates moved comparatively less distance and at much lower speeds of 2-4 cm yr(-1) (refs 3-5). Antarctica remained almost stationary. This mobility makes India unique among the fragments of Gondwanaland. Here we propose that when the fragments of Gondwanaland were separated by the plume, the penetration of their lithospheric roots into the asthenosphere were important in determining their speed. We estimated the thickness of the lithospheric plates of the different fragments of Gondwanaland around the Indian Ocean by using the shear-wave receiver function technique. We found that the fragment of Gondwanaland with clearly the thinnest lithosphere is India. The lithospheric roots in South Africa, Australia and Antarctica are between 180 and 300 km deep, whereas the Indian lithosphere extends only about 100 km deep. We infer that the plume that partitioned Gondwanaland may have also melted the lower half of the Indian lithosphere, thus permitting faster motion due to ridge push or slab pull. PMID:17943128

  9. Formation of plate boundaries: The role of mantle volatilization

    NASA Astrophysics Data System (ADS)

    Seno, Tetsuzo; Kirby, Stephen H.

    2014-02-01

    In the early Earth, convection occurred with the accumulation of thick crust over a weak boundary layer downwelling into the mantle (Davies, G.F., 1992. On the emergence of plate tectonics. Geology 20, 963-966.). This would have transitioned to stagnant-lid convection as the mantle cooled (Solomatov, V.S., Moresi, L.-N., 1997. Three regimes of mantle convection with non-Newtonian viscosity and stagnant lid convection on the terrestrial planets. Geophys. Res. Lett. 24, 1907-1910.) or back to a magma ocean as the mantle heated (Sleep, N., 2000. Evolution of the mode of convection within terrestrial planets. J. Geophys. Res. 105(E7): 17563-17578). Because plate tectonics began operating on the Earth, subduction must have been initiated, thus avoiding these shifts. Based on an analogy with the continental crust subducted beneath Hindu Kush and Burma, we propose that the lithosphere was hydrated and/or carbonated by H2O-CO2 vapors released from magmas generated in upwelling plumes and subsequently volatilized during underthrusting, resulting in lubrication of the thrust above, and subduction of the lithosphere along with the overlying thick crust. Once subduction had been initiated, serpentinized forearc mantle may have formed in a wedge-shaped body above a dehydrating slab. In relict arcs, suture zones, or rifted margins, any agent that warms and dehydrates the wedge would weaken the region surrounding it, and form various types of plate boundaries depending on the operating tectonic stress. Thus, once subduction is initiated, formation of plate boundaries might be facilitated by a major fundamental process: weakening due to the release of pressurized water from the warming serpentinized forearc mantle.

  10. How mantle slabs drive plate tectonics.

    PubMed

    Conrad, Clinton P; Lithgow-Bertelloni, Carolina

    2002-10-01

    The gravitational pull of subducted slabs is thought to drive the motions of Earth's tectonic plates, but the coupling between slabs and plates is not well established. If a slab is mechanically attached to a subducting plate, it can exert a direct pull on the plate. Alternatively, a detached slab may drive a plate by exciting flow in the mantle that exerts a shear traction on the base of the plate. From the geologic history of subduction, we estimated the relative importance of "pull" versus "suction" for the present-day plates. Observed plate motions are best predicted if slabs in the upper mantle are attached to plates and generate slab pull forces that account for about half of the total driving force on plates. Slabs in the lower mantle are supported by viscous mantle forces and drive plates through slab suction. PMID:12364804

  11. A new model of slab tear of the subducting Philippine Sea Plate associated with Kyushu-Palau Ridge subduction

    NASA Astrophysics Data System (ADS)

    Cao, Lingmin; Wang, Zhi; Wu, Shiguo; Gao, Xiang

    2014-12-01

    We suggest that the Kyushu-Palau Ridge (KPR) plays a key role in the subduction process of the Philippine Sea Plate (PSP) and the origin of the Abu volcano in the southwestern Japan. The 3-D P-wave velocity structure was imaged to approximately 300 km beneath the Abu volcano using a large number of P-wave arrivals from local earthquakes and teleseismic events. Our results indicate that a high-velocity anomaly beneath the Abu volcano is associated with the subducting PSP; however, the anomaly is not continuous, being interrupted apparently by a low-velocity anomaly zone extending northwestwards from 80 km to great depth. The PSP appears to be tearing and then forms a 'slab window' corresponding to KPR subduction at ca. 2 Ma. The low-velocity anomaly may indicate hot upper mantle material rising through the slab window and causing partial melting both of the lower crust of the overriding plate and the oceanic crust of the subducted KPR. A new model is presented for slab tearing of the PSP associated with the subduction of the buoyant, wide and thick KPR and directional change in the motion of the plate, contributing to better understanding of the Abu volcanism.

  12. Plate Tectonics on Earth-like Planets: Implications for Habitability

    NASA Astrophysics Data System (ADS)

    Noack, L.; Breuer, D.

    2011-12-01

    Plate tectonics has been suggested to be essential for life (see e.g. [1]) due to the replenishment of nutrients and its role in the stabilization of the atmosphere temperature through the carbon-silicate cycle. Whether plate tectonics can prevail on a planet should depend on several factors, e.g. planetary mass, age of the planet, water content (at the surface and in the interior), surface temperature, mantle rheology, density variations in the mantle due to partial melting, and life itself by promoting erosion processes and perhaps even the production of continental rock [2]. In the present study, we have investigated how planetary mass, internal heating, surface temperature and water content in the mantle would factor for the probability of plate tectonics to occur on a planet. We allow the viscosity to be a function of pressure [3], an effect mostly neglected in previous discussions of plate tectonics on exoplanets [4, 5]. With the pressure-dependence of viscosity allowed for, the lower mantle may become too viscous in massive planets for convection to occur. When varying the planetary mass between 0.1 and 10 Earth masses, we find a maximum for the likelihood of plate tectonics to occur for planetary masses around a few Earth masses. For these masses the convective stresses acting at the base of the lithosphere are strongest and may become larger than the lithosphere yield strength. The optimum planetary mass varies slightly depending on the parameter values used (e.g. wet or dry rheology; initial mantle temperature). However, the peak in likelihood of plate tectonics remains roughly in the range of one to five Earth masses for reasonable parameter choices. Internal heating has a similar effect on the occurrence of plate tectonics as the planetary mass, i.e. there is a peak in the probability of plate tectonics depending on the internal heating rate. This result suggests that a planet may evolve as a consequence of radioactive decay into and out of the plate tectonics regime. References [1] Parnell, J. (2004): Plate tectonics, surface mineralogy, and the early evolution of life. Int. J. Astrobio. 3(2): 131-137. [2] Rosing, M.T.; D.K. Bird, N.H. Sleep, W. Glassley, and F. Albar (2006): The rise of continents - An essay on the geologic consequences of photosynthesis. Palaeogeography, Palaeoclimatology, Palaeoecology 232 (2006) 99-11. [3] Stamenkovic, V.; D. Breuer and T. Spohn (2011): Thermal and transport properties of mantle rock at high pressure: Applications to super-Earths. Submitted to Icarus. [4] Valencia, D., R.J. O'Connell and D.D. Sasselov (2007): Inevitability of plate tectonics on super-Earths. Astrophys. J. Let. 670(1): 45-48. [5] O'Neill, C. and A. Lenardic (2007). Geological consequences of super-sized Earths. GRL 34: 1-41.

  13. Impact on multilayered composite plates

    NASA Technical Reports Server (NTRS)

    Kim, B. S.; Moon, F. C.

    1977-01-01

    Stress wave propagation in a multilayer composite plate due to impact was examined by means of the anisotropic elasticity theory. The plate was modelled as a number of identical anisotropic layers and the approximate plate theory of Mindlin was then applied to each layer to obtain a set of difference-differential equations of motion. Dispersion relations for harmonic waves and correction factors were found. The governing equations were reduced to difference equations via integral transforms. With given impact boundary conditions these equations were solved for an arbitrary number of layers in the plate and the transient propagation of waves was calculated by means of a Fast Fourier Transform algorithm. The multilayered plate problem was extended to examine the effect of damping layers present between two elastic layers. A reduction of the interlaminar normal stress was significant when the thickness of damping layer was increased but the effect was mostly due to the softness of the damping layer. Finally, the problem of a composite plate with a crack on the interlaminar boundary was formulated.

  14. OESbathy version 1.0: a method for reconstructing ocean bathymetry with realistic continental shelf-slope-rise structures

    NASA Astrophysics Data System (ADS)

    Goswami, A.; Olson, P. L.; Hinnov, L. A.; Gnanadesikan, A.

    2015-04-01

    We present a method for reconstructing global ocean bathymetry that uses a plate cooling model for the oceanic lithosphere, the age distribution of the oceanic crust, global oceanic sediment thicknesses, plus shelf-slope-rise structures calibrated at modern active and passive continental margins. Our motivation is to reconstruct realistic ocean bathymetry based on parameterized relationships of present-day variables that can be applied to global oceans in the geologic past, and to isolate locations where anomalous processes such as mantle convection may affect bathymetry. Parameters of the plate cooling model are combined with ocean crustal age to calculate depth-to-basement. To the depth-to-basement we add an isostatically adjusted, multicomponent sediment layer, constrained by sediment thickness in the modern oceans and marginal seas. A continental shelf-slope-rise structure completes the bathymetry reconstruction, extending from the ocean crust to the coastlines. Shelf-slope-rise structures at active and passive margins are parameterized using modern ocean bathymetry at locations where a complete history of seafloor spreading is preserved. This includes the coastal regions of the North, South, and Central Atlantic Ocean, the Southern Ocean between Australia and Antarctica, and the Pacific Ocean off the west coast of South America. The final products are global maps at 0.1° × 0.1° resolution of depth-to-basement, ocean bathymetry with an isostatically adjusted, multicomponent sediment layer, and ocean bathymetry with reconstructed continental shelf-slope-rise structures. Our reconstructed bathymetry agrees with the measured ETOPO1 bathymetry at most passive margins, including the east coast of North America, north coast of the Arabian Sea, and northeast and southeast coasts of South America. There is disagreement at margins with anomalous continental shelf-slope-rise structures, such as around the Arctic Ocean, the Falkland Islands, and Indonesia.

  15. Preparation of Feeder plates for ES cell culture Gelatinize Tissue Culture Plates

    E-print Network

    Preparation of Feeder plates for ES cell culture Gelatinize Tissue Culture Plates Gelatinize plates with 0.1% gelatin at room temperature for two hours. (150 µl/well of 96 well plate; 12 ml/10 cm; 4 ml/6cm. Plate cells in gelatinized plates (150 µl/well of 96 well plate; 12 ml/10 cm; 4 ml/6cm; 2 ml/well of 6

  16. Plate Tectonic Consequences of competing models for the origin and history of the Banda Sea subducted oceanic lithosphere

    E-print Network

    Heine, Christian; McKay, Hamish; Müller, R Dietmar

    2012-01-01

    The Banda Arc, situated west of Irian Jaya and in the easternmost extension of the Sunda subduction zone system, reveals a characteristic bowl-shaped geometry in seismic tomographic images. This indicates that the oceanic lithosphere still remains attached to the surrounding continental margins of northern Australia and the Bird's Head microcontinent. Major controversies exist between authors proposing an allochthonous or autochthonous origin of the Bird's Head block. Either scenario has important implications for plate kinematic models aiming to reconstruct the tectonic evolution of the region and the late Jurassic seaoor spreading geometry of this now subducted Argo-Tanimbar-Seram (ATS) ocean basin. Wider implications affect the tectonic conguration of the Tethyan-Pacic realm, the distribution of plate boundaries as well as the shape and size of continental blocks which have been rifted off the northeastern Gondwana margin during the Late Jurassic and are now accreted to the SE Asia margin. We apply structu...

  17. Dampening prey cycle overrides the impact of climate change on predator population dynamics: a long-term demographic study on tawny owls.

    PubMed

    Millon, Alexandre; Petty, Steve J; Little, Brian; Gimenez, Olivier; Cornulier, Thomas; Lambin, Xavier

    2014-06-01

    Predicting the dynamics of animal populations with different life histories requires careful understanding of demographic responses to multifaceted aspects of global changes, such as climate and trophic interactions. Continent-scale dampening of vole population cycles, keystone herbivores in many ecosystems, has been recently documented across Europe. However, its impact on guilds of vole-eating predators remains unknown. To quantify this impact, we used a 27-year study of an avian predator (tawny owl) and its main prey (field vole) collected in Kielder Forest (UK) where vole dynamics shifted from a high- to a low-amplitude fluctuation regime in the mid-1990s. We measured the functional responses of four demographic rates to changes in prey dynamics and winter climate, characterized by wintertime North Atlantic Oscillation (wNAO). First-year and adult survival were positively affected by vole density in autumn but relatively insensitive to wNAO. The probability of breeding and number of fledglings were higher in years with high spring vole densities and negative wNAO (i.e. colder and drier winters). These functional responses were incorporated into a stochastic population model. The size of the predator population was projected under scenarios combining prey dynamics and winter climate to test whether climate buffers or alternatively magnifies the impact of changes in prey dynamics. We found the observed dampening vole cycles, characterized by low spring densities, drastically reduced the breeding probability of predators. Our results illustrate that (i) change in trophic interactions can override direct climate change effect; and (ii) the demographic resilience entailed by longevity and the occurrence of a floater stage may be insufficient to buffer hypothesized environmental changes. Ultimately, dampened prey cycles would drive our owl local population towards extinction, with winter climate regimes only altering persistence time. These results suggest that other vole-eating predators are likely to be threatened by dampening vole cycles throughout Europe. PMID:24634279

  18. Dampening prey cycle overrides the impact of climate change on predator population dynamics: a long-term demographic study on tawny owls

    PubMed Central

    Millon, Alexandre; Petty, Steve J; Little, Brian; Gimenez, Olivier; Cornulier, Thomas; Lambin, Xavier

    2014-01-01

    Predicting the dynamics of animal populations with different life histories requires careful understanding of demographic responses to multifaceted aspects of global changes, such as climate and trophic interactions. Continent-scale dampening of vole population cycles, keystone herbivores in many ecosystems, has been recently documented across Europe. However, its impact on guilds of vole-eating predators remains unknown. To quantify this impact, we used a 27-year study of an avian predator (tawny owl) and its main prey (field vole) collected in Kielder Forest (UK) where vole dynamics shifted from a high- to a low-amplitude fluctuation regime in the mid-1990s. We measured the functional responses of four demographic rates to changes in prey dynamics and winter climate, characterized by wintertime North Atlantic Oscillation (wNAO). First-year and adult survival were positively affected by vole density in autumn but relatively insensitive to wNAO. The probability of breeding and number of fledglings were higher in years with high spring vole densities and negative wNAO (i.e. colder and drier winters). These functional responses were incorporated into a stochastic population model. The size of the predator population was projected under scenarios combining prey dynamics and winter climate to test whether climate buffers or alternatively magnifies the impact of changes in prey dynamics. We found the observed dampening vole cycles, characterized by low spring densities, drastically reduced the breeding probability of predators. Our results illustrate that (i) change in trophic interactions can override direct climate change effect; and (ii) the demographic resilience entailed by longevity and the occurrence of a floater stage may be insufficient to buffer hypothesized environmental changes. Ultimately, dampened prey cycles would drive our owl local population towards extinction, with winter climate regimes only altering persistence time. These results suggest that other vole-eating predators are likely to be threatened by dampening vole cycles throughout Europe. PMID:24634279

  19. A plate-driven model for enigmatic volcanic history of the Cascades-Yellowstone System

    NASA Astrophysics Data System (ADS)

    Szwaja, S.; Kincaid, C. R.; Druken, K. A.; MacDougall, J.

    2013-12-01

    The Cascades subduction system in the Pacific Northwest (USA) represents a complex tectonic setting, where rollback subduction of the Juan de Fuca plate beneath the North American plate, back-arc extension, and a possible mantle plume have been proposed to explain the complicated volcanic trends observed over the past 20 Ma. Plume and non-plume models have been developed to reconcile the voluminous Columbia River/Steens Flood Basalts (CSFB) (~20 Ma), the age progressive (15 Ma to present) Snake River Plain (SRP) that terminates at Yellowstone and the opposite, or westward trending High Lava Plains (HLP) volcanic track of eastern/central Oregon. We present results from laboratory experiments designed to test a plate-driven model for reproducing gross spatial-temporal characteristics of these three magmatic features. Models use a glucose fluid with temperature dependent viscosity in representing Earth's mantle and continuous rubber belts that kinematically reproduce subduction trends for the Cascades system. Experiments begin at 20 Ma with a volume of mantle residuum in the Cascades wedge that is elongated and restricted in the trench-parallel and trench-normal directions, respectively. The underlying assumption is that residuum was created in the wedge during an earlier plate steepening event that caused the flood basalts. Our models characterize dispersion patterns for the melt residuum material as it deforms within four-dimensional wedge circulation fields driven by rollback subduction (e.g. with a translational component of motion). Results show that residuum viscosity, relative to the ambient fluid, determines whether anomalous fluid can evolve to a morphology that matches the SRP/HLP tracks over ~15-20Ma. A weak residuum (e.g. retained partial melt) deforms over this time scale from the initial north-south oriented feature to an east-west trending morphology that is thin in both depth and north-south extent, material initially beneath CSFB is offset to the south, and is capable of producing opposite age progressions beneath the surface HLP/SRP track locations. The evolution of a high viscosity residuum in rollback-driven flow did not match the observed trends, as the feature deformed into an overly thick and wide morphology in the sub-HLP wedge compared to seismic data. Higher viscosity also produces stress coupling throughout the residuum, causing efficient entrainment from under the SRP towards the trench, leaving only ambient fluid beneath this track. In cases with stronger viscous coupling to the base of the overriding plate, the residuum is not able to deform into a morphology that is consistent with SRP/HLP tracks over the period 15 - 0 Ma. Models show only a limited range of conditions, where a low viscosity residuum is decoupled from the overriding plate, are capable of producing morphologies and offsets that roughly match observed spatial and temporal trends for primary features in the Pacific Northwest. Additional work is needed to understand the vertical heat/mass transfer processes that would enable deforming residuum to continually supply the bimodal magmatic output recorded over ~15Ma along the HLP and SRP tracks.

  20. The dynamics of continental breakup-related magmatism on the Norwegian volcanic margin

    NASA Astrophysics Data System (ADS)

    Breivik, A. J.; Faleide, J. I.; Mjelde, R.

    2004-12-01

    The Vøring margin off mid-Norway was initiated during the earliest Eocene (~54 Ma), and large volumes of magmatic rocks were emplaced during and after continental breakup. In 2003, an ocean bottom seismometer survey was acquired on the Norwegian margin to constrain continental breakup and early seafloor spreading processes. The profile P-wave model described here crosses the northern part of the Vøring Plateau. Maximum igneous crustal thickness was found to be 18 km, decreasing to ~6.5 km over ~6 M.y. after continental breakup. Both the volume and the duration of excess magmatism after breakup is about twice of what is observed off the Møre Margin south of the Jan Mayen Fracture Zone, which offsets the margin segments by ~170 km. A similar reduction in magmatism occurs to the north over an along-margin distance of ~100 km to the Lofoten margin, but without a margin offset. There is a strong correlation between magma productivity and early plate spreading rate, which are highest just after breakup, falling with time. This is seen both at the Møre and the Vøring margin segments, suggesting a common cause. A model for the breakup- related magmatism should be able to (1) explain this correlation, (2) the magma production peak at breakup, and (3) the magmatic segmentation. Proposed end-member hypotheses are elevated upper-mantle temperatures caused by a hot mantle plume, or edge-driven small-scale convection fluxing mantle rocks through the melt zone. Both the average P-wave velocity and the major-element data at the Vøring margin indicate a low degree of melting consistent with convection. However, small scale convection does not easily explain the issues listed above. An elaboration of the mantle plume model by N. Sleep, in which buoyant plume material fills the rift-topography at the base of the lithosphere, can explain these: When the continents break apart, the buoyant plume-material flows up into the rift zone, causing excess magmatism by both elevated temperature and excess flux, and magmatism dies off as this rift-restricted material is spent. The buoyancy of the plume-material also elevates the plate boundaries and enhances plate spreading forces initially. The rapid drop in magma productivity to the north correlates with the northern boundary of the wide and deep Cretaceous Vøring Basin, thus less plume material was accommodated off Lofoten. This model predicts that the magma segmentation will show little variation in the geochemical signature.

  1. The dynamics of continental breakup-related magmatism on the Norwegian volcanic margin

    NASA Astrophysics Data System (ADS)

    Breivik, A. J.; Faleide, J. I.; Mjelde, R.

    2007-12-01

    The Vøring margin off mid-Norway was initiated during the earliest Eocene (~54 Ma), and large volumes of magmatic rocks were emplaced during and after continental breakup. In 2003, an ocean bottom seismometer survey was acquired on the Norwegian margin to constrain continental breakup and early seafloor spreading processes. The profile P-wave model described here crosses the northern part of the Vøring Plateau. Maximum igneous crustal thickness was found to be 18 km, decreasing to ~6.5 km over ~6 M.y. after continental breakup. Both the volume and the duration of excess magmatism after breakup is about twice of what is observed off the Møre Margin south of the Jan Mayen Fracture Zone, which offsets the margin segments by ~170 km. A similar reduction in magmatism occurs to the north over an along-margin distance of ~100 km to the Lofoten margin, but without a margin offset. There is a strong correlation between magma productivity and early plate spreading rate, which are highest just after breakup, falling with time. This is seen both at the Møre and the Vøring margin segments, suggesting a common cause. A model for the breakup- related magmatism should be able to (1) explain this correlation, (2) the magma production peak at breakup, and (3) the magmatic segmentation. Proposed end-member hypotheses are elevated upper-mantle temperatures caused by a hot mantle plume, or edge-driven small-scale convection fluxing mantle rocks through the melt zone. Both the average P-wave velocity and the major-element data at the Vøring margin indicate a low degree of melting consistent with convection. However, small scale convection does not easily explain the issues listed above. An elaboration of the mantle plume model by N. Sleep, in which buoyant plume material fills the rift-topography at the base of the lithosphere, can explain these: When the continents break apart, the buoyant plume-material flows up into the rift zone, causing excess magmatism by both elevated temperature and excess flux, and magmatism dies off as this rift-restricted material is spent. The buoyancy of the plume-material also elevates the plate boundaries and enhances plate spreading forces initially. The rapid drop in magma productivity to the north correlates with the northern boundary of the wide and deep Cretaceous Vøring Basin, thus less plume material was accommodated off Lofoten. This model predicts that the magma segmentation will show little variation in the geochemical signature.

  2. PLATE KINEMATICS (Copyright 2010, David T. Sandwell)

    E-print Network

    Sandwell, David T.

    , Cambridge University Press, 1990, Chapter 2) Plate Motions on a Flat Earth Plate tectonic theory describes-fault-fault (R-F-F), and ridge- trench-trench (R-T-T). Each type of plate boundary has rules about relative1 PLATE KINEMATICS (Copyright 2010, David T. Sandwell) (Reference - The Solid Earth, C.M.R. Fowler

  3. Yellowstone hotspot-continental lithosphere interaction

    NASA Astrophysics Data System (ADS)

    Jean, Marlon M.; Hanan, Barry B.; Shervais, John W.

    2014-03-01

    The Snake River Plain represents 17 m.y. of volcanic activity that took place as the North American continent migrated over a relatively fixed magma source, or hotspot. We present new Pb, Sr, and Nd data for a suite of 25 basalts collected from Western and Central Snake River Plain (SRP). The new isotope data, combined with previously published data from the SRP, provide a traverse of the Wyoming craton margin, from the 87Sr/86Sr = 0.706 line boundary of western SRP with Phanerozoic accreted terranes, east through the central and eastern SRP, to the Yellowstone Plateau. Low-K basalts from the western SRP, overlain by high-K basalts, provide a temporal record of regional source variation from ?16.8 to 0.2 Ma. Principal Component Analysis (PCA) of the new and previously published SRP basalt Pb isotopes reveals that >97% of the total variability is accounted for by mixing between three end-members and is consistent with a sublithospheric Yellowstone hotspot mantle source with a radiogenic isotope composition similar to the mantle source of the early Columbia River Basalt Group (CRBG) and two continental lithosphere end-members, heterogeneous in age and composition. We use the SRP Pb, Sr, and Nd isotope data to model the Yellowstone Hotspot-continental lithosphere interaction by three component mixing between two continental lithospheric components, Archean lithosphere (CL1) that represents older lithosphere underlying the Yellowstone Plateau in the east, and Paleoproterozoic lithosphere (CL2) representing the younger lithosphere underlying the SRP in the west near the craton margin, and a sublithospheric end-member, representing the Yellowstone hotspot (PL). The results suggest a continuous flow of PL material westward as the NA continental lithosphere migrated over the upwelling hotspot along a shoaling gradient in the sub-continental mantle lithosphere. The model shows a decrease in Total Lithosphere end-members (CL1 + CL2) and the Lithosphere Ratio (CL1/CL2), from the craton interior at Yellowstone toward its western margin, consistent with geologic and geophysical evidence that the continental lithosphere beneath the SRP decreases in age and thickness from east to west. The Lithosphere Ratio shows step-like decreases from Yellowstone in the east to the 87Sr/86Sr = 0.706 line in the west, indicating that the SRP cuts across geochemically distinct parcels of lithospheric mantle, consistent with terrane accretion models for the craton margin. In the western SRP, young high-K basalts have a lower mass fraction of Total Lithospheric compared to the underlying low-K tholeiites, but the same Lithosphere Ratio, consistent with a recent (700-900 ka) decrease in lithosphere contribution between eruption of early low- and younger high-K basalts.

  4. Plate Kinematic model of the NW Indian Ocean and derived regional stress history of the East African Margin

    NASA Astrophysics Data System (ADS)

    Tuck-Martin, Amy; Adam, Jürgen; Eagles, Graeme

    2015-04-01

    Starting with the break up of Gondwana, the northwest Indian Ocean and its continental margins in Madagascar, East Africa and western India formed by divergence of the African and Indian plates and were shaped by a complicated sequence of plate boundary relocations, ridge propagation events, and the independent movement of the Seychelles microplate. As a result, attempts to reconcile the different plate-tectonic components and processes into a coherent kinematic model have so far been unsatisfactory. A new high-resolution plate kinematic model has been produced in an attempt to solve these problems, using seafloor spreading data and rotation parameters generated by a mixture of visual fitting of magnetic isochron data and iterative joint inversion of magnetic isochron and fracture zone data. Using plate motion vectors and plate boundary geometries derived from this model, the first-order regional stress pattern was modelled for distinct phases of margin formation. The stress pattern is correlated with the tectono-stratigraphic history of related sedimentary basins. The plate kinematic model identifies three phases of spreading, from the Jurassic to the Paleogene, which resulted in the formation of three main oceanic basins. Prior to these phases, intracontinental 'Karoo' rifting episodes in the late Carboniferous to late Triassic had failed to break up Gondwana, but initiated the formation of sedimentary basins along the East African and West Madagascan margins. At the start of the first phase of spreading (183 to 133 Ma) predominantly NW - SE extension caused continental rifting that separated Madagascar/India/Antarctica from Africa. Maximum horizontal stresses trended perpendicular to the local plate-kinematic vector, and parallel to the rift axes. During and after continental break-up and subsequent spreading, the regional stress regime changed drastically. The extensional stress regime became restricted to the active spreading ridges that in turn adopted trends normal to the plate divergence vector. Away from the active ridges, compressional horizontal stresses caused by ridge-push forces were transmitted through the subsiding oceanic lithosphere, with an SH max orientation parallel to plate divergence vectors. These changes are documented by the lower Bajocian continental breakup unconformity, which can be traced throughout East African basins. At 133 Ma, the plate boundary moved from north to south of Madagascar, incorporating it into the African plate and initiating its separation from Antarctica. The orientation of the plate divergence vector however did not change markedly. The second phase (89 - 61 Ma) led to the separation of India from Madagascar, initiating a new and dramatic change in stress orientation from N-S to ENE-WSW. This led to renewed tectonic activity in the sedimentary basins of western Madagascar. In the third phase (61 Ma to present) asymmetric spreading of the Carlsberg Ridge separated India from the Seychelles and the Mascarene Plateau via the southward propagation of the Carlsberg Ridge to form the Central Indian Ridge. The anti-clockwise rotation of the independent Seychelles microplate between chrons 28n (64.13 Ma) and 26n (58.38 Ma) and the opening of the short-lived Laxmi Basin (67 Ma to abandonment within chron 28n (64.13 - 63.10 Ma)) have been further constrained by the new plate kinematic model. Along the East African margin, SH max remained in a NE - SW orientation and the sedimentary basins experienced continued thick, deep water sediment deposition. Contemporaneously, in the sedimentary basins along East African passive margin, ridge-push related maximum horizontal stresses became progressively outweighed by local gravity-driven NE-SW maximum horizontal stresses trending parallel to the margin. These stress regimes are caused by sediment loading and extensional collapse of thick sediment wedges, predominantly controlled by margin geometry. Our study successfully integrates an interpretation of paleo-stress regimes constrained by the new high resolution plate kinematic and basin his

  5. This Dynamic Planet: World map of volcanoes, earthquakes, impact craters and plate tectonics

    USGS Publications Warehouse

    Simkin, Tom; Tilling, Robert I.; Vogt, Peter R.; Kirby, Stephen H.; Kimberly, Paul; Stewart, David B.

    2006-01-01

    Our Earth is a dynamic planet, as clearly illustrated on the main map by its topography, over 1500 volcanoes, 44,000 earthquakes, and 170 impact craters. These features largely reflect the movements of Earth's major tectonic plates and many smaller plates or fragments of plates (including microplates). Volcanic eruptions and earthquakes are awe-inspiring displays of the powerful forces of nature and can be extraordinarily destructive. On average, about 60 of Earth's 550 historically active volcanoes are in eruption each year. In 2004 alone, over 160 earthquakes were magnitude 6.0 or above, some of which caused casualties and substantial damage. This map shows many of the features that have shaped--and continue to change--our dynamic planet. Most new crust forms at ocean ridge crests, is carried slowly away by plate movement, and is ultimately recycled deep into the earth--causing earthquakes and volcanism along the boundaries between moving tectonic plates. Oceans are continually opening (e.g., Red Sea, Atlantic) or closing (e.g., Mediterranean). Because continental crust is thicker and less dense than thinner, younger oceanic crust, most does not sink deep enough to be recycled, and remains largely preserved on land. Consequently, most continental bedrock is far older than the oldest oceanic bedrock. (see back of map) The earthquakes and volcanoes that mark plate boundaries are clearly shown on this map, as are craters made by impacts of extraterrestrial objects that punctuate Earth's history, some causing catastrophic ecological changes. Over geologic time, continuing plate movements, together with relentless erosion and redeposition of material, mask or obliterate traces of earlier plate-tectonic or impact processes, making the older chapters of Earth's 4,500-million-year history increasingly difficult to read. The recent activity shown on this map provides only a present-day snapshot of Earth's long history, helping to illustrate how its present surface came to be. The map is designed to show the most prominent features when viewed from a distance, and more detailed features upon closer inspection. The back of the map zooms in further, highlighting examples of fundamental features, while providing text, timelines, references, and other resources to enhance understanding of this dynamic planet. Both the front and back of this map illustrate the enormous recent growth in our knowledge of planet Earth. Yet, much remains unknown, particularly about the processes operating below the ever-shifting plates and the detailed geological history during all but the most recent stage of Earth's development.

  6. Transport of particles across continental shelves

    SciTech Connect

    Nittrouer, C.A. ); Wright, L.D. College of William and Mary, Gloucester Point, VA )

    1994-02-01

    Transport of particulate material across continental shelves is well demonstrated by the distributions on the seabed and in the water column of geological, chemical, or biological components, whose sources are found farther landward or farther seaward. This paper addresses passive (incapable of swimming) particles and their transport across (not necessarily off) continental shelves during high stands of sea level. Among the general factors that influence across-shelf transport are shelf geometry, latitudinal constraints, and the timescale of interest. Research studies have investigated the physical mechanisms of transport and have made quantitative estimates of mass flux across continental shelves. Important mechanisms include wind-driven flows, internal wave, wave-orbital flows, infragravity phenomena, buoyant plumes, and surf zone processes. Most particulate transport occurs in the portion of the water column closest to the seabed. Therefore physical processes are effective where and when they influence the bottom boundary layer, causing shear stresses sufficient to erode and transport particulate material. Biological and geological processes at the seabed play important roles within the boundary layer. The coupling of hydrodynamic forces from currents and surface gravity waves has a particularly strong influence on across-shelf transport; during storm events, the combined effect can transport particles tens of kilometers seaward. Several important mechanisms can cause bidirectional (seaward and landward) transport, and estimates of the net flux are difficult to obtain. Also, measurements of across-shelf transport are made difficult by the dominance of along-shelf transport. Geological parameters are often the best indicators of net across-shelf transport integrated over time scales longer than a month. For example, fluvially discharged particles with distinct composition commonly accumulate in the midshelf region. 47 refs., 16 figs.

  7. CSDP: Seismology of continental thermal regime

    SciTech Connect

    Aki, K.

    1989-04-01

    This is a progress report for the past one year of research (year 2 of 5-year project) under the project titled CSDP: Seismology of Continental Thermal Regime'', in which we proposed to develop seismological interpretation theory and methods applicable to complex structures encountered in continental geothermal areas and apply them to several candidate sites for the Continental Scientific Drilling Project. During the past year, two Ph.D. thesis works were completed under the present project. One is a USC thesis on seismic wave propagation in anisotropic media with application to defining fractures in the earth. The other is a MIT thesis on seismic Q and velocity structure for the magma-hydrothermal system of the Valles Caldera, New Mexico. The P.I. co-organized the first International Workshop on Volcanic Seismology at Capri, Italy in October 1988, and presented the keynote paper on the state-of-art of volcanic seismology''. We presented another paper at the workshop on Assorted Seismic Signals from Kilauea Volcano, Hawaii. Another international meeting, namely, the Chapman Conference on seismic anisotropy in the earth's crust at Berkeley, California in May 1988, was co-organized by the co-P.I. (P.C.L), and we presented our work on seismic waves in heterogeneous and anisotropic media. Adding the publications and presentations made in the past year to the list for the preceding year, the following table lists 21 papers published, submitted or presented in the past two years of the present project. 65 refs., 334 figs., 1 tab.

  8. Finite-element models of continental extension

    NASA Technical Reports Server (NTRS)

    Lynch, H. David; Morgan, Paul

    1990-01-01

    Numerical models of the initial deformation of extending continental lithosphere, computed to investigate the control of preexisting thermal and mechanical heterogeneities on the style of deformation, are presented. The finite element method is used to calculate deformation with a viscoelastic-plastic model for the lithosphere. Comparisons of the results of analytic models and finite-element models using this method show that good results may be obtained by the numerical technique, even with elements containing both brittle and viscoelastic sampling points. It is shown that the gross style of initial extensional deformation is controlled by the depth and width of the initial heterogeneity which localizes deformation.

  9. Crew coordination concepts: Continental Airlines CRM training

    NASA Technical Reports Server (NTRS)

    Christian, Darryl; Morgan, Alice

    1987-01-01

    The outline of the crew coordination concepts at Continental airlines is: (1) Present relevant theory: Contained in a pre-work package and in lecture/discussion form during the work course, (2) Discuss case examples: Contained in the pre-work for study and use during the course; and (3) Simulate practice problems: Introduced during the course as the beginning of an ongoing process. These concepts which are designed to address the problem pilots have in understanding the interaction between situations and their own theories of practice are briefly discussed.

  10. ITT Continental Baking tests electric vans

    SciTech Connect

    Not Available

    1983-02-01

    ITT Continental Baking Co., operator of one of the largest truck fleets in the U.S., is studying battery power as an alternative fuel for the future. The company currently has a total of 10 lead battery-powered vans delivering bread and cake products in Sacramento, California, and Spokane, Washington. Through a cost-sharing program with the U.S. Department of Energy (DOE), the company will operate the vehicles through at least June 30, 1985, gathering data on their performance. The joint program began in 1981.

  11. LINKAGE BETWEEN PRODUCTION AND RESPIRATION ON THE LOUISIANA CONTINENTAL SHELF.

    EPA Science Inventory

    Abstract for presentation. Original title, "PRIMARY PRODUCTION, BACTERIOPLANKTON PRODUCTION, AND COMMUNITY RESPIRATION IN STRATIFIED WATERS OF THE NORTHERN GULF OF MEXICO CONTINENTAL SHELF: LINKAGE TO HYPOXIA."

  12. 75 FR 1076 - Outer Continental Shelf Civil Penalties

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-01-08

    ...OF THE INTERIOR Minerals Management Service Outer Continental Shelf Civil Penalties AGENCY: Minerals Management Service (MMS), Interior. ACTION: Notice summarizing review of the maximum daily civil penalty...

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

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

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

  14. Investigating Continental Margins: An Activity to Help Students Better Understand the Continental Margins of North America

    ERIC Educational Resources Information Center

    Poli, Maria-Serena; Capodivacca, Marco

    2011-01-01

    Continental margins are an important part of the ocean floor. They separate the land above sea level from the deep ocean basins below and occupy about 11% of Earth's surface. They are also economically important, as they harbor both mineral resources and some of the most valuable fisheries in the world. In this article students investigate North…

  15. Is a 50 Ma Event Recorded in the Absolute Plate Motion of Africa?

    NASA Astrophysics Data System (ADS)

    Maher, S. M.; Wessel, P.; Müller, R.; Harada, Y.

    2012-12-01

    There is considerable evidence for a global plate tectonic reorganization at ~Chron 21, as suggested by observed changes in global relative plate motion (RPM). The timings of these events appear to coincide with the age of the Hawaiian Emperor Bend (HEB), i.e., ~47-50 Ma. This 120° bend has traditionally been the poster child for the fixed hotspot hypothesis, suggesting the Pacific plate underwent a change in absolute plate motion (APM) as it moved over a more or less stationary Hawaiian hotspot. However, palaeomagnetic evidence favors southward motion of the Hawaii hotspot during the Emperor stage, limiting the amount of APM change required. In the Indo-Atlantic realm, RPMs involving Africa all seem compatible with a change in Africa APM around ~50 Ma. If this global plate reorganization took place there should also be physical evidence on the Africa plate itself due to the change in Africa APM. A candidate for such evidence may be the Réunion-Mascarene bend, which exhibits many HEB-like features. However, the Réunion hotspot also created the Chagos-Laccadive ridge as it encountered (and later crossed) the Carlsberg Ridge, and the oldest Mascarene section closest to the Seychelles may be continental in origin; thus there is some uncertainty in how to interpret the geometry. Furthermore, published APM models have had difficulty modeling this abrupt change in orientation. To reexamine this problem we derived a new Africa APM model that goes back to ~65 Ma using the Hybrid Polygonal Finite Rotation Method. The modeling incorporates the geometry and ages of seamount chains on the Africa plate and their associated hotspots as suitable constraints on an Africa APM model. The present as well as earlier positions of hotspots can be adjusted to get the best fit for the model. We examine how models with or without a ~50 Ma bend satisfy the geometries and age progressions of hotspot chains on the Africa plate and how well the predictions match observed paleolatitudes.

  16. Rapid change in drift of the Australian plate records collision with Ontong Java plateau.

    PubMed

    Knesel, Kurt M; Cohen, Benjamin E; Vasconcelos, Paulo M; Thiede, David S

    2008-08-01

    The subduction of oceanic plateaux, which contain extraordinarily thick basaltic crust and are the marine counterparts of continental flood-basalt provinces, is an important factor in many current models of plate motion and provides a potential mechanism for triggering plate reorganization. To evaluate such models, it is essential to decipher the history of the collision between the largest and thickest of the world's oceanic plateaux, the Ontong Java plateau, and the Australian plate, but this has been hindered by poor constraints for the arrival of the plateau at the Melanesian trench. Here we present (40)Ar-(39)Ar geochronological data on hotspot volcanoes in eastern Australian that reveal a strong link between collision of the Greenland-sized Ontong Java plateau with the Melanesian arc and motion of the Australian plate. The new ages define a short-lived period of reduced northward plate motion between 26 and 23 Myr ago, coincident with an eastward offset in the contemporaneous tracks of seamount chains in the Tasman Sea east of Australia. These features record a brief westward deflection of the Australian plate as the plateau entered and choked the Melanesian trench 26 Myr ago. From 23 Myr ago, Australia returned to a rapid northerly trajectory at roughly the same time that southwest-directed subduction began along the Trobriand trough. The timing and brevity of this collisional event correlate well with offsets in hotspot seamount tracks on the Pacific plate, including the archetypal Hawaiian chain, and thus provide strong evidence that immense oceanic plateaux, like the Ontong Java, can contribute to initiating rapid change in plate boundaries and motions on a global scale. PMID:18685705

  17. Natural vibrations of laminated anisotropic plates

    NASA Technical Reports Server (NTRS)

    Reddy, J. N.; Kuppusamy, T.

    1984-01-01

    This paper contains a description of the three-dimensional elasticity equations and the associated finite element model for natural vibrations of laminated rectangular plates. The numerical results for natural frequencies are compared with those obtained by a shear deformable plate theory. A number of cross-ply and angle-ply rectangular plates are analyzed for natural frequencies. For relatively thick plates, the plate element predicts frequencies higher than those predicted by the 3-D element.

  18. Plates for vacuum thermal fusion

    DOEpatents

    Davidson, James C. (Livermore, CA); Balch, Joseph W. (Livermore, CA)

    2002-01-01

    A process for effectively bonding arbitrary size or shape substrates. The process incorporates vacuum pull down techniques to ensure uniform surface contact during the bonding process. The essence of the process for bonding substrates, such as glass, plastic, or alloys, etc., which have a moderate melting point with a gradual softening point curve, involves the application of an active vacuum source to evacuate interstices between the substrates while at the same time providing a positive force to hold the parts to be bonded in contact. This enables increasing the temperature of the bonding process to ensure that the softening point has been reached and small void areas are filled and come in contact with the opposing substrate. The process is most effective where at least one of the two plates or substrates contain channels or grooves that can be used to apply vacuum between the plates or substrates during the thermal bonding cycle. Also, it is beneficial to provide a vacuum groove or channel near the perimeter of the plates or substrates to ensure bonding of the perimeter of the plates or substrates and reduce the unbonded regions inside the interior region of the plates or substrates.

  19. Continental lithospheric evolution: Constraints from the geochemistry of felsic volcanic rocks in the Dharwar Craton, India

    NASA Astrophysics Data System (ADS)

    Manikyamba, C.; Ganguly, Sohini; Saha, Abhishek; Santosh, M.; Rajanikanta Singh, M.; Subba Rao, D. V.

    2014-12-01

    Felsic magmatism associated with ocean-ocean and ocean-continent subduction processes provide important evidence for distinct episodes of crust-generation and continental lithospheric evolution. Rhyolites constitute an integral component of the tholeiitic to calc-alkaline basalt-andesite-dacite-rhyolite (BADR) association and contribute to crustal growth processes at convergent plate margins. The evolution of the Dharwar Craton of southern peninsular India during Meso- to Neoarchean times was marked by extensive development of greenstone belts. These granite-greenstone terranes have distinct volcano-sedimentary associations consistent with their geodynamic setting. The present study deals with geochemistry of rhyolites from the Chitradurga-Shimoga greenstone belts of western (WDC) and the Gadwal-Kadiri greenstone belts of eastern (EDC) sectors of Dharwar Craton to compare and evaluate their petrogenesis and geodynamic setting and their control on the continental lithospheric evolution of the Dharwar Craton. At a similar range of SiO2, Al2O3, Fe2O3, the rhyolites of WDC are more potassic, whereas the EDC rhyolites are more sodic and less magnesian with slight increase in TiO2. Minor increase in MgO content of WDC rhyolites reflects their ferromagnesian trace elements which are comparatively lower in the rhyolites of EDC. The relative enrichment in LILE (K, Rb) and depletion in HFSE (Nb, Ta, Zr, Hf) marked by negative Nb-Ta, Zr-Hf and Ti anomalies endorse the convergent margin processes for the generation of rhyolites of both the sectors of Dharwar Craton. The high silica potassic rhyolites of Shimoga and Chitradurga greenstone belts of WDC showing prominent negative Eu and Ti anomalies, flat HREE patterns correspond to Type 3 rhyolites and clearly point towards their generation and emplacement in an active continental margin environment. The geochemical characteristics of Gadwal and Kadiri rhyolites from eastern Dharwar Craton marked by aluminous compositions with low and fractionated HREE patterns and minor negative Eu anomalies are in conformity with Type 1 rhyolites and suggest that they were erupted in an intraoceanic island arc system. The overall geochemical systematics of the rhyolites from both the sectors of Dharwar Craton suggest a change in the geodynamic conditions from intraoceanic island arc of eastern Dharwar Craton and an active continental margin of western Dharwar marked by ocean-ocean subduction and migration of oceanic arc towards a continent followed by arc-continent collision that contributed for the evolution of continental lithosphere in the Dharwar Craton.

  20. Plate bending at subduction zones: Consequences for the direction of plate motions

    E-print Network

    between plate bending and various sources of friction at plate boundaries and in the interior toward the trench, especially when the downgoing plate has a distribution of ages [10], and hencePlate bending at subduction zones: Consequences for the direction of plate motions Bruce A. Buffett

  1. overriding-update By julien

    E-print Network

    Vaandrager, Frits

    g) = f by (metis overlap1 swap) lemma (in ax12345 ) eMf : shows e f = e by (metis f ) proof - from distr[where h=f ] have (f B g B h) f = (f B g) f B h f by (metis distr eMf fMe fUe) also from distr[where h=f ] have . .=.f f B g f B h f by (metis distr eMf eUf empty

  2. Vortex dynamics around pitching plates

    NASA Astrophysics Data System (ADS)

    Jantzen, Ryan T.; Taira, Kunihiko; Granlund, Kenneth O.; Ol, Michael V.

    2014-05-01

    Vortex dynamics of wakes generated by rectangular aspect-ratio 2 and 4 and two-dimensional pitching flat plates in free stream are examined with direct numerical simulation and water tunnel experiments. Evolution of wake vortices comprised of tip, leading-edge, and trailing-edge vortices is compared with force history for a range of pitch rates. The plate pivots about its leading edge with reduced frequency from ?/8 to ?/48, which corresponds to pitching over 1 to 6 chord lengths of travel. Computations have reasonable agreement with experiments, despite large differences in Reynolds number. Computations show that the tip effects are confined initially near the wing tips, but begin to strongly affect the leading-edge vortex as the motion of the plate proceeds, with concomitant effects on lift and drag history. Scaling relations based on reduced frequency are shown to collapse aerodynamic force history for the various pitch rates.

  3. Continental water storage variations in Africa

    NASA Astrophysics Data System (ADS)

    Boy, Jean-Paul; Carabajal, Claudia; Luthcke, Scott; Rowlands, David; Lemoine, Frank; Sabaka, Terence

    2010-05-01

    We investigate temporal and spatial variations of continental water storage in Africa as recovered by the GRACE (Gravity Recovery and Climate Experiment) mission. Mass variations are directly inverted from only KBRR (K-band range rate) data using a mascon approach. We compare our solutions to classical spherical harmonic solutions and also to different global hydrology models, and regional models in the African monsoon area (thanks to the ALMIP project). We compare mass estimates of major Africa lakes and reservoirs to volume estimates from laser (ICESat) and radar altimetry. We investigate the improvement of our mass retrievals when hydrology (GLDAS/Noah model) is forward modeled, compared to the more classical approach when continental water storages variations are not taken into when processing GRACE data. We solve the water mass balance equations using different precipitation datasets from remote sensing techniques, as well as ground rain gauge stations, using fresh water fluxes (precipitation minus evaporation) from various atmospheric models (reanalysis and operational). As a result, our runoff are compared to river flux measurements. In addition to the comparison with the ALMIP models, we also pay a special attention to the Lake Chad and Niger river basins, where ground gravity variations are repetitively measured as part of the GHYRAF project in order to investigate seasonal water storage variations at small and larger spatial scales.

  4. Continental water storage variations in Africa

    NASA Astrophysics Data System (ADS)

    Boy, J.; Carabajal, C. C.; Luthcke, S. B.; Rowlands, D. D.; Lemoine, F. G.; Sabaka, T. J.

    2009-12-01

    We investigate the temporal and spatial variations of continental water storage in Africa as recovered by the NASA/DLR Gravity Recovery and Climate Experiment (GRACE) mission. Mass variations are directly inverted from the K-band range rate using the mascon approach. We compare our solution to global different hydrological models. We solve the water mass balance equation, using different precipitation datasets from remote sensing techniques, as well as meteorological stations, using water fluxes (precipitation minus evaporation) from different atmospheric models. As a result, our runoff estimates are compared to river fluxes measurements. We compare mass estimates of major African lakes to volume estimated from space Laser (ICESat) and radar altimetry. As our forward modeling includes the continental water storage variations (using GLDAS/Noah model), leaking effects are significantly reduced. We also pay a special attention to the Lake Chad and Niger river basins, where ground gravity variations are repetitively measured as part of the GHYRAF project in order to investigate seasonal water storage variations at small and larger spatial scales.

  5. Plate motions and deformations from geologic and geodetic data

    NASA Technical Reports Server (NTRS)

    Jordan, Thomas H.

    1989-01-01

    The very long baseline interferometry (VLBI) measurements made in the western U.S. since 1979 provide discrete samples of the temporal and spatial deformation field. The interpretation of the VLBI derived rates of deformation requires an examination of geologic information and more densely sampled ground based geodetic data. Triangulation and trilateration data measured on two regional networks, one in the central Mojave Desert and one in the Coast Ranges east of the San Andreas fault, were processed. At the spatial scales spanned by these local geodetic networks, auxiliary geologic and geophysical data were utilized to examine the relation between measured incremental strain and the accommodation of strain seen in local geologic structures, strain release in earthquakes, and principal stress directions inferred from in situ measurements. VLBI data was also processed from stations distributed across the Pacific-North America plate boundary zone in the western U.S. The VLBI data were used to constrain the integrated rate of deformation across portions of the continental plate boundary in California and to provide a tectonic framework to interpret regional geodetic and geologic studies.

  6. A model for plate tectonic evolution of mantle layers.

    PubMed

    Dickinson, W R; Luth, W C

    1971-10-22

    In plate tectonic theory, lithosphere that descends into the mantle has a largely derivative composition, because it is produced as a refractory residue by partial melting, and cannot be resorbed readily by the parent mantle. We suggest that lithosphere sinks through the asthenosphere, or outer mantle, and accumulates progressively beneath to form an accretionary mesosphere, or inner mantle. According to this model, there is an irreversible physicochemical evolution of the mantle and its layers. We make the key assumption that the rate at which mass has been transferred from the lithosphere to the mesosphere is proportional to the rate of radiogenic heat production. Calculations of mass transfer with time demonstrate that the entire mass of the present mesosphere could have been produced in geologically reasonable times (3 x 10(9) to 4.5 x 10(9) years). The model is consistent with the generation of the continental crust during the last 3 x 1O(9) years and predicts an end to plate tectonic behavior within the next 10(9) years. PMID:17796091

  7. Collision zone magmatism aids continental crustal growth

    NASA Astrophysics Data System (ADS)

    Savov, Ivan; Meliksetian, Khachatur; Ralf, Halama; Gevorg, Navasardian; Chuck, Connor; Massimo, D'Antonio; Samuele, Agostini; Osamu, Ishizuka; Sergei, Karapetian; Arkadi, Karakhanian

    2014-05-01

    The continental crust has a broadly andesitic bulk composition and is predominantly generated at convergent margins. However, estimates of the bulk composition of oceanic arcs indicate a bulk composition closer to basalt than to andesite. Hence, reworking processes that transform basaltic island arc crust into andesitic continental crust are essential[1] and explaining growth of andesitic continental crust via accretion of arc crustal fragments remains problematic. Recent studies of magmatism in the Great Tibetan Plateau[2], as site of multiple and still active continent-continent collisions, have proposed that andesitic CC is generated via amalgamation of large volumes of collision-related felsic magmas generated by melting of hydrated oceanic crust with mantle geochemical signatures. We aim to test this hypothesis by evaluating geochemical data from the volcanically and tectonically active Lesser Caucasus region (Armenia, Azerbaijan, Georgia and E. Turkey), as the only other region where active continent-continent collision takes place. We will benefit from the newly compiled volcano-tectonic database of collision-related volcanic and plutonic rocks of Armenia that is comparable in quality and detail to the one available on Tibet. Our dataset combines several detailed studies from the large Aragats shield volcano[3] and associated monogenetic volcanic fields (near the capital city of Yerevan), as well as > 500 Quaternary to Holocene volcanoes from Gegham, Vardenis and Syunik volcanic highlands (toward Armenia-Nagorno-Karabakh-Azerbaijan-Iran border). The Armenian collision-related magmatism is diverse in volume, composition, eruption style and volatile contents. Interestingly, the majority of exposed volcanics are andesitic in composition. Nearly all collision-related volcanic rocks, even the highly differentiated dacite and rhyolite ignimbrites, have elevated Sr concentrations and 87Sr/86Sr and 143Nd/144Nd ratios varying only little (average ~ 0.7043 and ~ 0.51282, respectively). These isotopic signatures are much more similar to those typical of intra-oceanic subduction zones than those typical of continental crust, likely due to the very young age of the rocks. In contrast, trace element abundances reveal many similarities to average CC, such as Nb-Ta and Ti troughs and Pb peaks. The range of d11B isotope ratios (-8.7 to +2.1 per mil) signifies magmas originating from moderately metasomatised (arc preconditioned) mantle sources. Our combined results reveal that the collision-related mantle melting is capable of generating large volumes of plutons and volcanic rocks that resemble (although not perfectly) the composition of the average CC. We will attempt to use the new combined datasets in order to quantify the importance of the collision zone magmatism for continental crustal growth. [1] Lee et al. (2007) EPSL 263, 370-387; [2] Niu et al. (2013) Earth-Science Reviews 127, 96-110; [3] Connor et al., (2012) J.Applied Volcanology, 1:3, 1-19.

  8. Mesobathic chondrichthyes of the Juan Fernández seamounts: are they different from those of the central Chilean continental slope?

    PubMed

    Andrade, Isabel; Pequeño, Germán

    2008-03-01

    We compared the geographic distribution of groups of chondrychthid fishes of two physically proximal, although geographically different, regions that include the Juan Fernández seamounts and the central Chilean continental slope, both sampl