Science.gov

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 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

  4. Seismic evidence for deep fluid circulation in the overriding plate of subduction zones

    NASA Astrophysics Data System (ADS)

    Tauzin, B.; Reynard, B.; Bodin, T.; Perrillat, J. P.; Debayle, E.

    2015-12-01

    In subduction zones, non-volcanic tremors are associated with fluid circulations (Obara, 2002). Their sources are often located on the interplate boundary (Rogers and Dragert, 2003; Shelly et al, 2006; La Rocca, 2009), consistent with fluids released by the dehydration of subducted plates (Hacker et al., 2003). Reports of tremors in the overriding continental crust of several subduction zones in the world (Kao et al., 2005; Payero et al., 2008; Ide, 2012) suggest fluid circulation at shallower depths but potential fluid paths are poorly documented. Here we obtained seismic observations from receiver functions that evidence the close association between the shallow tremor zone, electrical conductivity, and tectonic features of the Cascadia overriding plate. A seismic discontinuity near 15 km depth in the crust of the overriding North American plate is attributed to the Conrad discontinuity. This interface is segmented, and its interruption is spatially correlated with conductive regions and shallow swarms of seismicity and non-volcanic tremors. These observations suggest that shallow fluid circulation, tremors and seismicity are controlled by fault zones limiting blocks of accreted terranes in the overriding plate (Brudzinski and Allen, 2007). These zones constitute fluid "escape" routes that may contribute unloading fluid pressure on the megathrust. Obara, K. (2002). Science, 296, 1679-1681. Rogers, G., & Dragert, H. (2003). Science, 300, 1942-1943. Shelly, D. R., et al. (2006). Nature, 442, 188-191. La Rocca, M., et al. (2009). Science, 323, 620-623. Kao, H., et al. (2005). Nature, 436, 841-844. Payero, J. S., et al. (2008). Geophysical Research Letters, 35. Ide, S. (2012). Journal of Geophysical Research: Solid Earth, 117. Brudzinski, M. R., & Allen, R. M. (2007). Geology, 35, 907-910.

  5. Influence of overriding plate velocity changes on slab dip and deformation: insights from laboratory models

    NASA Astrophysics Data System (ADS)

    Guillaume, Benjamin; Hertgen, Solenn; Martinod, Joseph

    2016-04-01

    Over geological times, plate reorganization associated with mantle convection led to changes in absolute plate velocities, which may in turn have impacted the geometry of the subducting plate as well as the overriding plate regime of deformation. Indeed, previous studies have shown a very good correlation between the absolute motion of the overriding plate on one hand and slab dip and overriding plate deformation on the other hand: extension and steep slab are associated with an overriding plate moving away from the trench while shortening and shallow slab occur if the upper plate goes the other way. However, these correlations are established when subduction has reached a steady-state regime and for a constant motion of the overriding plate over the subducting plate, which may not always be the case on Earth. The response of the subduction system to changes in absolute overriding plate velocity still remain an open question. In this study, we conducted a set of 3-D mantle-scale laboratory models of subduction in which we incrementally changed the velocity of the overriding plate to reproduce changes of velocities that may arise from variations of far-field boundary conditions in Nature. We first show that strain rates in the overriding plate are correlated with overriding plate absolute velocity but also that the regime of deformation adjusts rapidly to changes of velocity. This may explain for instance why despite the subduction has been continuous beneath South America since at least the middle Jurassic, shortening along its active margin is only recorded episodically, the main phases of Andean orogeny roughly corresponding to periods of South American plate westward acceleration. We also show that slab dip adjusts to changes of overriding plate velocity but it requires several Myr before it stabilizes. It may explain why the correlation between absolute overriding plate motion and slab dip from the analysis of present-day subduction zones is only moderate, part

  6. 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 (ΦOPD), and we compare them with the negative buoyancy (FBU) of the subducted slab and its total potential energy release rate (ΦBU), respectively. We varied the viscosity ratio between the plates and the sublithospheric upper mantle with ηSP/ηUM = 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 ΦOPD/ΦBU 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).

  7. A numerical study of the interaction between the mantle wedge, subducting slab, and overriding plate

    NASA Astrophysics Data System (ADS)

    Eberle, Michael A.; Grasset, Olivier; Sotin, Christophe

    2002-12-01

    We have formulated a numerical model with strongly temperature-dependent viscosity to calculate thermal structure and flow-field in subduction zones. One important particularity of the model is that the overriding plate is not fixed over its whole thickness in order to allow material exchange between the wedge and the upper lithosphere. Numerical problems due to very high-viscosity contrasts are avoided by coupling a finite difference method and a finite element method for solving the energy conservation equation and the Stockes equation, respectively. In this model, a temperature decrease from 1400 to 1300 °C increases the viscosity by an order of magnitude. We study the temperature structure and the velocity field of the subducting slab and mantle wedge. Surface heat flow, velocity anomalies, and geometry of the partial melting zone are also calculated. To study the effect that boundary conditions play on the interaction between the mantle wedge, overriding plate and subducting plate, we examine models with both fixed and free-slip conditions applied to the overriding plate. When the overriding plate is allowed to move laterally (free-slip), the subducting slab is thick, and both the temperature field and the convective motions in the mantle wedge are similar to those observed when using constant viscosity numerical models or analytical corner flow models. If the surface of the overriding plate is fixed, the subducting slab is thin and the mantle wedge impinges upon the overriding plate forming a high-temperature nose between the overriding plate and subducting lithosphere. Furthermore, viscous decoupling occurs implicitly at shallow depth between the slab and the wedge because hot material from the wedge is entrained close to the trench. In that case, the subducting slab tectonically erodes the lower lithosphere of the overriding plate leading to high-temperatures, low seismic velocities, high attenuation and high heat flow beneath volcanic arc, in agreement

  8. Stress fields of the overriding plate at convergent margins and beneath active volcanic arcs.

    PubMed

    Apperson, K D

    1991-11-01

    Tectonic stress fields in the overriding plate at convergent plate margins are complex and vary on local to regional scales. Volcanic arcs are a common element of overriding plates. Stress fields in the volcanic arc region are related to deformation generated by subduction and to magma generation and ascent processes. Analysis of moment tensors of shallow and intermediate depth earthquakes in volcanic arcs indicates that the seismic strain field in the arc region of many convergent margins is subhorizontal extension oriented nearly perpendicular to the arc. A process capable of generating such a globally consistent strain field is induced asthenospheric corner flow below the arc region. PMID:17774792

  9. 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)

  10. 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.

  11. Abrupt plate accelerations shape rifted continental margins.

    PubMed

    Brune, Sascha; Williams, Simon E; Butterworth, Nathaniel P; Müller, R Dietmar

    2016-08-11

    Rifted margins are formed by persistent stretching of continental lithosphere until breakup is achieved. It is well known that strain-rate-dependent processes control rift evolution, yet quantified extension histories of Earth's major passive margins have become available only recently. Here we investigate rift kinematics globally by applying a new geotectonic analysis technique to revised global plate reconstructions. We find that rifted margins feature an initial, slow rift phase (less than ten millimetres per year, full rate) and that an abrupt increase of plate divergence introduces a fast rift phase. Plate acceleration takes place before continental rupture and considerable margin area is created during each phase. We reproduce the rapid transition from slow to fast extension using analytical and numerical modelling with constant force boundary conditions. The extension models suggest that the two-phase velocity behaviour is caused by a rift-intrinsic strength--velocity feedback, which can be robustly inferred for diverse lithosphere configurations and rheologies. Our results explain differences between proximal and distal margin areas and demonstrate that abrupt plate acceleration during continental rifting is controlled by the nonlinear decay of the resistive rift strength force. This mechanism provides an explanation for several previously unexplained rapid absolute plate motion changes, offering new insights into the balance of plate driving forces through time. PMID:27437571

  12. 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)

  13. Causes for the Onset and Stability of Flat Slabs and Associated Overriding Plate Deformation Inferred from Numerical Thermo-Mechanical Models

    NASA Astrophysics Data System (ADS)

    Kanda, R. V. S.; Lowry, A. R.; Buiter, S. J.; Ellis, S. M.

    2015-12-01

    Flat slab subduction comprises only ~10% of the present-day subduction systems. We systematically explore flat-slab subduction and over-riding plate deformation due to previously recognized factors (including a weak mantle wedge, a buoyant oceanic plateau/ridge, slab-age, presence of thick cratonic upper plate), as well as additional factors not considered before (transient plate-velocity variations, and the presence of stagnant slabs at the mantle transition zone). We use a visco-elasto-plastic code, SULEC (Buiter & Ellis, 2012), restrict ourselves to 2D models, and ignore phase transformations. We model a 6000 km by 1500 km domain with 1-10 km variable grid spacing using up-to-date laboratory-derived constitutive laws, and explore the effects of: (a) lateral/vertical structure of the crust and lithosphere (e.g., continental lithosphere with/without a craton; oceanic lithosphere with thickness governed by plate cooling, and a harzburgite layer); (b) a true free upper-surface to predict surface topography; and (c) only far-field (boundary) velocities driving plates, with trench-velocity depending on over-riding plate deformation and slab pull. As in previous studies, we find that positive trench-retreat velocity and weak integrated slab-strength (as measured by differential stress) are necessary, but not sufficient, conditions for flat-slab subduction. While mantle-wedge suction associated with the presence of a craton does promote flat slab subduction, models without a craton also produce flat-slabs when (a) trench-retreat velocities are large and (b) either the slab is positively (structurally or thermally) buoyant or there is an underlying slab at the mantle transition zone. In our models, the duration of flat slab subduction depends on overall slab buoyancy. Younger oceanic lithosphere, esp. if it contains a plateau/ridge, provides a longer-lasting flat-slab (~ 10 Myr or longer, e.g., central Mexico), while older slabs with oceanic ridge/plateau (e.g., Peru

  14. Overriding plate deformation and variability of fore-arc deformation during subduction: Insight from geodynamic models and application to the Calabria subduction zone

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    In nature, subducting slabs and overriding plate segments bordering subduction zones are generally embedded within larger plates. Such large plates can impose far-field boundary conditions that influence the style of subduction and overriding plate deformation. Here we present dynamic laboratory models of progressive subduction in three-dimensional space, in which the far-field boundary conditions at the trailing edges of the subducting plate (SP) and overriding plate (OP) are varied. Four configurations are presented: Free (both plates free), SP-Fixed, OP-Fixed, and SP-OP-Fixed. We investigate their impact on the kinematics and dynamics of subduction, particularly focusing on overriding plate deformation. The results indicate that the variation in far-field boundary conditions has an influence on the slab geometry, subduction partitioning, and trench migration partitioning. Our models also indicate that in natural (narrow) subduction zones, assuming a homogeneous overriding plate, the formation of back-arc basins (e.g., Tyrrhenian Sea, Aegean Sea, and Scotia Sea) is generally expected to occur at a comparable location (250-700 km from the trench), irrespective of the boundary condition. In addition, our models indicate that the style of fore-arc deformation (shortening or extension) is influenced by the mobility of the overriding plate through controlling the force normal to the subduction zone interface (trench suction). Our geodynamic model that uses the SP-OP-Fixed setup is comparable to the Calabria subduction zone with respect to subduction kinematics, slab geometry, trench curvature, and accretionary configuration. Furthermore, the model can explain back-arc and fore-arc extension at the Calabria subduction zone since the latest middle Miocene as a consequence of subduction of the narrow Calabrian slab and the immobility of the subducting African plate and overriding Eurasian plate. This setting induced strong trench suction, driving fore-arc extension, and

  15. Current plate motions. [continental groupings and global modelling

    NASA Technical Reports Server (NTRS)

    Demets, C.; Gordon, R. G.; Argus, D. F.; Stein, S.

    1990-01-01

    A global plate motion model, named NUVEL-1, which describes current plate motions between 12 rigid plates is described, with special attention given to the method, data, and assumptions used. Tectonic implications of the patterns that emerged from the results are discussed. It is shown that wide plate boundary zones can form not only within the continental lithosphere but also within the oceanic lithosphere; e.g., between the Indian and Australian plates and between the North American and South American plates. Results of the model also suggest small but significant diffuse deformation of the oceanic lithosphere, which may be confined to small awkwardly shaped salients of major plates.

  16. 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.

  17. Dynamics of continental collision: influence of the plate contact

    NASA Astrophysics Data System (ADS)

    De Franco, Roberta; Govers, Rob; Wortel, Rinus

    2008-09-01

    Observations shows that continental collision may evolve in different ways, resulting in a wide range of tectonic responses. In search of the controlling conditions and parameters, we start from the results of our previous work, which demonstrated that the properties of the plate contact are important for the overall dynamics of convergent plate margins. Two fundamental types of subduction plate contact can be distinguished: one based on a fault and the other based on a weak subduction channel. In this study, we investigate how the plate contact affects the initial stage of continental collision. We use a finite element method to solve the heat and the time-dependent momentum equations for elastic, (power-law) viscous and plastic rheologies. For the same rheological properties and driving forces, varying the nature of the plate contact leads to three types of responses. The presence of a subduction channel promotes coherent and, when the boundary conditions allow it, plate-like subduction of the continental margin. In models with a subduction fault, coherent subduction of the incoming continental lithosphere occurs when the colliding passive margin has a gentle slope. The approaching continental sliver starts to subduct and the subduction is characterized by a non-plate like behaviour-slower subduction velocity than in channel models and strong slab deformation. If the continental margin is steep and the strength of the incoming continental crust is high, fault models result in locking of the trench, eventually leading to slab break-off. If the crustal strength is relatively low, shear delamination of part of the crust is expected. In the channel model, this type of delamination never occurs. The tectonic settings used in our experiments (prescribed plate velocity of the subducting plate versus fixed subducting plate corresponding to a landlocked basin setting) do not significantly influence the nature of the model response. We conclude that initial stages of

  18. Plate boundary and major fault system in the overriding plate within the Shumagin gap at the Alaska-Aleutian subduction zone

    NASA Astrophysics Data System (ADS)

    Becel, A.; Shillington, D. J.; Nedimovic, M. R.; Keranen, K. M.; Li, J.; Webb, S. C.; Kuehn, H.

    2013-12-01

    Structure in the overriding plate is one of the parameters that may increase the tsunamigenic potential of a subduction zone but also influence the seismogenic behavior and segmentation of great earthquake rupture. The Alaska-Aleutian margin is characterized by along-strike changes in plate interface coupling over relatively small distances. Here, we present trench normal multichannel seismic (MCS) profiles acquired across the Shumagin gap that has not broken in many decades and appears to be weakly coupled. The high fold, deep penetration (636 channel, 8-km long streamer, 6600 cu.in airgun source) MCS data were acquired as part of the ALEUT project. This dataset gives us critical new constraints on the interplate boundary that can be traced over ~100 km distance beneath the forearc with high variation in its reflection response with depth. These profiles also reveal the detailed upper plate fault structure and forearc morphology. Clear reflections in the overriding plate appear to delineate one or more large faults that cross the shelf and the upper slope. These faults are observed 75 km back from the trench and seem to branch at depth and connect to the plate interface within this gap at ~11 s twtt. We compare the reflective structure of these faults to that of the plate boundary and examine where it intersects the megathrust with respect of the expected downdip limit of coupling. We also compare this major structure with the seismicity recorded in this sector. The imaged fault system is associated with a large deep basin (~6s twt) that is an inherited structure formed during the pre-Aleutian period. Basins faults appear to have accommodated primarily normal motion, although folding of sediments near the fault and complicated fault geometries in the shallow section may indicate that this fault has accommodated other types of motion during its history that may reflect the stress-state at the megathrust over time. The deformation within the youngest sediment also

  19. Modelling continental deformation within global plate tectonic reconstructions

    NASA Astrophysics Data System (ADS)

    Williams, S.; Whittaker, J.; Heine, C.; Müller, P.

    2010-12-01

    A limitation of regional and global plate tectonic models is the way continental deformation is represented. Continental blocks are typically represented as rigid polygons - overlaps or gaps between adjacent continental blocks represent extension or compression respectively. Full-fit reconstructions of major ocean basins result in large overlaps between the conjugate continental plates, on the basis that the continental margins are highly extended compared to their pre-rift state. A fundamental challenge in generating more robust global-scale plate reconstructions is the incorporation of a more quantitative description of the kinematics within extended passive margins, based on observations. We have used the conjugate Southern Australia and Wilkes Land, Antarctica margins as a case study, and as part of this work have generated revised sediment thickness maps for these margins. These datasets are used to test different approaches for generating full-fit reconstructions in order to create a framework of methodologies that is globally applicable. One approach is to restore two conjugate continent-ocean boundaries (COBs) to their pre-rift configuration and then use the geometric fitting method of Hellinger (1981) and Royer and Chang (1991), used to generate fits of seafloor isochrons, to generate a “full-fit” Euler pole. To quantitatively restore the COBs to their palinspastic pre-rift configuration we integrate estimates of crustal thickness along small circle paths, defined by an initial estimate of the Euler stage pole describing plate motions during continental rifting. We then use the conjugate sets of restored COB’s as inputs to the geometric fitting method, treating them as isochrons, and so generate poles of rotation for the plate configuration prior to rifting. Two potential shortcomings of this methodology are that (1) the conjugate margins are treated independently, whereas in reality they were actually one continuous continental basin during rifting

  20. 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.

  1. Deciphering the mechanics of an imaged fault system in the over-riding plate at the Shumagin Seismic Gap, Alaska subduction zone using MCS waveform tomography

    NASA Astrophysics Data System (ADS)

    Michaelson, C. A.; Delescluse, M.; Becel, A.; Nedimovic, M. R.; Shillington, D. J.; Louden, K. E.; Webb, S. C.

    2013-12-01

    The 2011 ALEUT program acquired 3500 km of multichannel seismic (MCS) data along a part of the western Alaska subduction zone, from the freely slipping Shumagin Seismic Gap to the locked regions in the Semidi segment and the western Kodiak asperity. The MCS profiles were acquired on the R/V Langseth using two 8-km-long streamers and span the entire locked zone on the megathrust, including the updip and downdip transitions to stable sliding. The primary goal was to characterize variations in the geometry and properties of the megathrust and the downgoing plate and relate them to downdip and along-strike changes in slip behavior and seismogenesis. The images capture the targeted megathrust reflectivity and its spatial variation. Notably, the two westernmost profiles show reflections arising from a major fault in the overriding plate within the Shumagin Seismic Gap located 75 km from the trench, which can be followed from the seafloor to the megathrust. The imaged normal fault bounds the seaward end of the Sanak forearc Cenozoic basin, formed after the Early Eocene reorganization of the Alaska subduction zone. The new reflection images also show that the seaward pair of the previously interpreted growth faults, thought to indicate deposition contemporaneous with basin subsidence, is a part of the imaged fault system. The unexpected imaging of this major fault system in the over-riding plate raises important questions: Has this fault been active during the most recent nearby megathrust earthquakes, such as the 1946 and 1948 earthquakes? Was the Sanak basin formed as a result of slip on the imaged normal fault system or is it a result of growth faulting that predates the formation of this fault? The timing and style of deformation on this fault has significant implications for both coupling on the megathrust seaward and landward of where the normal fault roots and tsunamigenesis. To complement constraints on the geometry and reflection characteristics of this structure

  2. Convective Removal of Continental Margin Lithosphere at the Edges of Subducting Oceanic Plates

    NASA Astrophysics Data System (ADS)

    Levander, A.; Bezada, M. J.; Palomeras, I.; Masy, J.; Humphreys, E.; Niu, F.

    2013-12-01

    Although oceanic lithosphere is continuously recycled to the deeper mantle by subduction, the rates and manner in which different types of continental lithospheric mantle are recycled is unclear. Cratonic mantle can be chemically reworked and essentially decratonized, although the frequency of decratonization is unclear. Lithospheric mantle under or adjacent to orogenic belts can be lost to the deeper mantle by convective downwellings and delamination phenomena. Here we describe how subduction related processes at the edges of oceanic plates adjacent to passive continental margins removes the mantle lithosphere from beneath the margin and from the continental interior. This appears to be a widespread means of recycling non-cratonic continental mantle. Lithospheric removal requires the edge of a subducting oceanic plate to be at a relatively high angle to an adjacent passive continental margin. From Rayleigh wave and body wave tomography, and receiver function images from the BOLIVAR and PICASSO experiments, we infer large-scale removal of continental margin lithospheric mantle from beneath 1) the northern South American plate margin due to Atlantic subduction, and 2) the Iberian and North African margins due to Alboran plate subduction. In both cases lithospheric mantle appears to have been removed several hundred kilometers inland from the subduction zones. This type of ';plate-edge' tectonics either accompanies or pre-conditions continental margins for orogenic activity by thinning and weakening the lithosphere. These processes show the importance of relatively small convective structures, i.e. small subducting plates, in formation of orogenic belts.

  3. From Oceanic Lithosphere Subduction To Continental Collision: Influence Of The Plate Contact

    NASA Astrophysics Data System (ADS)

    de Franco, R.; Govers, R.; Wortel, R.

    2004-12-01

    We showed recently that the overall dynamics of oceanic subduction differ depending on whether the plate contact is a fault or a channel (De Franco & al., 2007. GJI, doi: 10.1111/j.1365-246X.2006.03498.x). Here we investigate how the plate contact affects the transition from oceanic lithosphere subduction to continental collision. We use a finite element method to solve the heat and the time dependent momentum equations for elastic, (power law) viscous and plastic rheologies. For the same rheological properties and driving forces , varying the nature of the plate contact leads to three types of responses: subduction of the entire continental lithosphere, shear delamination of the continental crust or slab break-off. We make the following observations from our numerical experiments. The presence of a subduction channel promotes coherent and, when the boundary conditions allow it, plate-like subduction of the continental margin. In models with a subduction fault, coherent subduction of the incoming continental lithosphere occurs when the colliding passive margin has a gentle ocean-continent transition. The approaching continental sliver starts to subduct and the subduction is characterized by a non-plate-like behavior, slower subduction velocity than in channel models and strong slab deformation. If the continental margin is steep and the strength of the incoming continental crust is high, fault models result in locking of the trench, eventually leading to slab break-off. If the crustal strength is relatively low, shear delamination of the upper crust is expected. In the channel model this type of delamination never occurs. The tectonic setting does not significantly affect the nature of the model response. We conclude that the plate contact type, together with the geometrical and rheological properties of the incoming continental fragment, is a crucial subduction characteristic controlling the response of continental collision during the transition from oceanic

  4. From Oceanic Lithosphere Subduction To Continental Collision: Influence Of The Plate Contact

    NASA Astrophysics Data System (ADS)

    de Franco, R.; Govers, R.; Wortel, R.

    2007-12-01

    We showed recently that the overall dynamics of oceanic subduction differ depending on whether the plate contact is a fault or a channel (De Franco & al., 2007. GJI, doi: 10.1111/j.1365-246X.2006.03498.x). Here we investigate how the plate contact affects the transition from oceanic lithosphere subduction to continental collision. We use a finite element method to solve the heat and the time dependent momentum equations for elastic, (power law) viscous and plastic rheologies. For the same rheological properties and driving forces , varying the nature of the plate contact leads to three types of responses: subduction of the entire continental lithosphere, shear delamination of the continental crust or slab break-off. We make the following observations from our numerical experiments. The presence of a subduction channel promotes coherent and, when the boundary conditions allow it, plate-like subduction of the continental margin. In models with a subduction fault, coherent subduction of the incoming continental lithosphere occurs when the colliding passive margin has a gentle ocean-continent transition. The approaching continental sliver starts to subduct and the subduction is characterized by a non-plate-like behavior, slower subduction velocity than in channel models and strong slab deformation. If the continental margin is steep and the strength of the incoming continental crust is high, fault models result in locking of the trench, eventually leading to slab break-off. If the crustal strength is relatively low, shear delamination of the upper crust is expected. In the channel model this type of delamination never occurs. The tectonic setting does not significantly affect the nature of the model response. We conclude that the plate contact type, together with the geometrical and rheological properties of the incoming continental fragment, is a crucial subduction characteristic controlling the response of continental collision during the transition from oceanic

  5. 30 CFR 281.31 - Overriding royalties.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 2 2010-07-01 2010-07-01 false Overriding royalties. 281.31 Section 281.31 Mineral Resources MINERALS MANAGEMENT SERVICE, DEPARTMENT OF THE INTERIOR OFFSHORE LEASING OF MINERALS OTHER THAN OIL, GAS, AND SULPHUR IN THE OUTER CONTINENTAL SHELF Financial Considerations §...

  6. Lateral variations in the structure of the overriding and down-going plates in response to subduction of the Louisville Ridge seamount chain at the Tonga-Kermadec Trench

    NASA Astrophysics Data System (ADS)

    Stratford, W. R.; Peirce, C.; Watts, A. B.; Grevemeyer, I.; Paulatto, M.; Bassett, D.; Hunter, J.; Kalnins, L. M.

    2011-12-01

    Seamount subduction at the Tonga-Kermadec trench is investigated using ~1800 km of new geophysical data collected along four profiles acquired during April-June, 2011 aboard the R/V Sonne. This NERC funded multidisciplinary, multi-institutional project obtained wide-angle and normal incidence seismic, gravity, magnetic and swath bathymetry data in the region of the Louisville Ridge subduction. Subduction of seamounts can be associated with changes in subduction zone seismogenesis, crustal structure, and trench strike and depth. Subduction of the Louisville ridge seamounts has already occurred at the trench and is postulated to have caused accelerated tectonic erosion of the overlying plate, collapse of the overriding plate into the trench and a gap in seismicity. The Tonga-Kermadec subduction system is of particular interest as it has some of the highest convergence rates seen globally, and has produced fatal earthquakes and Tsunami in recent years. Due to the oblique collision of the seamount chain at the trench, there is southward migration of the collision zone of ~200 km/Ma. Thus to the north of the Louisville Ridge, the forearc has already undergone seamount subduction, whereas to the south, it is yet to be perturbed by this process. We investigate collision at the trench with three new trench perpendicular profiles, one along axis of the seamount chain, one to the north and one to the south. The profiles were designed to cross the main tectonic features of the subduction zone explicitly to elucidate differences in crustal structure in the overlying plate. In addition, magmatic alteration of the crust of the down-going plate by the Louisville hot spot is investigated for flexural loading studies of the seamount chain and its intersection with the trench outer rise. New models for the crustal velocity structure from wide-angle data are presented and results are discussed in the context of changes in structure of the overriding plate associated with varying

  7. Analysis of Stress Field in Caribean Continental Plate - Southern Costa Rica zone - from CMT Solutions

    NASA Astrophysics Data System (ADS)

    Zevallos, I.; Quintero, R.; Jimenez, W.

    2007-12-01

    During the of period 1984 2007, 51 earthquakes were registered with magnitudes above 5.1 mb in southern Costa Rica. Depth distribution of hypocenters shows shallow (0 20 km) earthquakes located in continental area; intermediate depth hypocenters (20 60 km) corresponding to subduction of the Coco plate under the Caribean plate; and just one earthquake have focus under 60 km depth. We choose hypocenters shallower than 100 km because our goal is to study intraplate stresses. Centroid Moment Tensor solutions for subduction zone earthquakes have inverse fault mechanism. But, in continental area there are evidences of strike slip and normal fault mechanisms. Direction of main stress (σ3) at the southern continental zone is NE-SW; in the Pacific ocean border region, the main stresses are oriented parallel to the coast line; inside the valley region, mechanisms are predominantly strike slip with σ1 in the near N-S direction. This is a complex stress field, with rotation of main stresses in a short space. σ1 is vertical in some continental areas due to influence of elevated terrain. Stress axis paralell to coast line maybe also due to gravitational body force.

  8. 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.

  9. 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.

  10. EAG Eminent Speaker: Two types of Archean continental crust: plume and plate tectonics on early Earth

    NASA Astrophysics Data System (ADS)

    Van Kranendonk, M. J.

    2012-04-01

    Over 4.5 billion years, Earth has evolved from a molten ball to a cooler planet with large continental plates, but how and when continents grew and plate tectonics started remain poorly understood. In this paper, I review the evidence that 3.5-3.2 Ga continental nuclei of the Pilbara (Australia) and Kaapvaal (southern Africa) cratons formed as thick volcanic plateaux over hot, upwelling mantle and survived due to contemporaneous development of highly depleted, buoyant, unsubductable mantle roots. This type of crust is distinct from, but complimentary to, high-grade gneiss terranes, as exemplified by the North Atlantic Craton of West Greenland, which formed through subduction-accretion tectonics on what is envisaged as a vigorously convecting early Earth with small plates. Thus, it is proposed that two types of crust formed on early Earth, in much the same way as in modern Earth, but with distinct differences resulting from a hotter Archean mantle. Volcanic plateaux provided a variety of stable habitats for early life, including chemical nutrient rich, shallow-water hydrothermal systems and shallow marine carbonate platforms.

  11. 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)

  12. 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

  13. 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

  14. Deep crust and mantle structure linked to subduction of the Pacific plate at a continental margin from an active seismic source study

    NASA Astrophysics Data System (ADS)

    Stern, T. A.; Okaya, D. A.; Henrys, S. A.; Savage, M. K.; Sato, H.; Iwasaki, T.

    2013-12-01

    We present new results that bear on mantle structure in a subduction zone of both the down going and over-riding plates. Wellington region, New Zealand, sits on the Australian plate a mere ~ 15-25 km above the subducted Pacific plate. This is rare: most active continental margins have at least 30-50 km of free board above subduction zones (cf, Pacific NW, Honshu). Such a shallow setting offers unusually good conditions for making terrestrial observations of the subduction process. In 2010-11 an active source seismic experiment (SAHKE) was carried out across the Wellington region. Both active and passive seismic methods were used to establish a model of the crustal structure and upper mantle structure beneath SAHKE (Henrys et al , 2013). We recorded 12 x 500 kg dynamite shots on ~ 1000 recorders place at 100 m spacing from coast to coast. These data contain excellent returns from the subduction zone at two-way travel times of 7-15 s, but we also recorded coherent reflection energy down to 30 s two-way-travel-time on vertical recorders and 47 s on horizontal recorders. We performed a low-fold stack of these deep reflections and see two zones. The deepest reflections define a westward 17 degree-dipping zone at ~ 100 km deep that is possibly the base of the subducted Pacific plate. The westward dip on this 100 km deep reflector matches that for the top of the plate. Moreover, the total plate thickness implied is ~ 80 km, which matches that predicted for 100 my old oceanic lithosphere. The other deep reflection zone dips eastward across the shot gathers and is typically seen at two-way travel times of 18-25 s on the vertical phones. We also see the same event as a Vs arrival on horizontal phones at two-way travel times of 34-47s. When migrated these reflections define an east dipping reflector that is within the mantle of the overriding Australian plate, and the surface projection of the reflector is ~ 80 km west of SAHKE line. This finding raises the question of what

  15. Is Present Day Continental Deformation Nearly Plate-Like? If so, Why?

    NASA Astrophysics Data System (ADS)

    Thatcher, W.

    2001-12-01

    Some indicators of deformation (seismicity, late Cenozoic faulting, regional topographic relief) suggest broad deformation zones. However, space geodetic mappings of current movements and Holocene fault distributions often show straining focussed in very narrow zones. Conventional wisdom has it that continental deformation is spread over broad regions while straining of oceanic lithosphere occurs in narrow zones. Here I present evidence, largely from recent GPS surveys, suggesting present day continental deformation is actually occurring in a largely plate-like manner through the relative motions of a small number of micro-plates within each deforming zone, sometimes perturbed by isolated zones of deformation driven by local lithospheric density gradients. How can this be so? I speculate that this behavior is caused by the inherent lateral heterogeneity of continental lithosphere and by frictional and ductile weakening and strengthening mechanisms that promote focussed deformation that migrates with time. Qualitative indications of active deformation can sometimes be misleading. In many active regions erosion and tectonism are in balance and very low rates of slip on inclined faults can generate significant steady-state topography. However, in currently inactive regions, erosion rates are very low, much less than rates of vertical movement in even moderately active deforming zones. Therefore landscape relief provides evidence for current activity but preserves it over long periods, millions to tens of millions of years (Ma) (e.g. Alps, Rocky Mountains). Secondly, background seismicity is a qualitative measure of tectonic activity and only the largest earthquakes contribute significantly to representative long term deformation rates, so the spatial distribution of all smaller events can be misleading. Finally, many mappings of `active' faults encompass features up to several Ma old that are not necessarily representative of current activity. In contrast, late

  16. Changes in plate motion and vertical movements along passive continental margins

    NASA Astrophysics Data System (ADS)

    Japsen, P.; Cobbold, P. R.; Chalmers, J. A.; Green, P. F.; Bonow, J. M.

    2012-04-01

    The origin of the forces that produce elevated, passive continental margins (EPCMs) has been a hot topic in geoscience for many years. Studies of individual margins have led to models, which explain high elevations by invoking specific conditions for each margin in question. We have studied the uplift history of several margins and have found some striking coincidences between episodes of uplift and changes in plate motion. In the Campanian, Eocene and Miocene, pronounced events of uplift and erosion affected not only SE Brazil (Cobbold et al., 2001), but also NE Brazil and SW Africa (Japsen et al., 2012a). The uplift phases in Brazil also coincided with three main phases of Andean orogeny (Cobbold et al., 2001, 2007). These phases, Peruvian (90-75 Ma), Incaic (50-40 Ma), and Quechuan (25-0 Ma), were also periods of relatively rapid convergence at the Andean margin of South America (Pardo-Casas and Molnar, 1987). Because Campanian uplift in Brazil coincides, not only with rapid convergence at the Andean margin of South America, but also with a decline in Atlantic spreading rate, we suggest that all these uplift events have a common cause, which is lateral resistance to plate motion (Japsen et al., 2012a). Because the uplift phases in South America and Africa are common to the margins of two diverging plates, we also suggest that the driving forces can transmit across the spreading axis, probably at great depth, e.g. in the asthenosphere (Japsen et al., 2012a). Similarly, a phase of uplift and erosion at the Eocene-Oligocene transition (c. 35 Ma), which affected margins around the North Atlantic, correlates with a major plate reorganization there (Japsen et al., 2012b). Passive continental margins clearly formed as a result of extension. Despite this, the World Stress Map shows that, where data exist, all EPCMs are today under compression. We maintain that folds, reverse faults, reactivated normal faults and strike-slip faults that are typical of EPCMs are a result

  17. Continental lithosphere of the Arabian Plate: A geologic, petrologic, and geophysical synthesis

    NASA Astrophysics Data System (ADS)

    Stern, Robert J.; Johnson, Peter

    2010-07-01

    The Arabian Plate originated ˜ 25 Ma ago by rifting of NE Africa to form the Gulf of Aden and Red Sea. It is one of the smaller and younger of the Earth's lithospheric plates. The upper part of its crust consists of crystalline Precambrian basement, Phanerozoic sedimentary cover as much as 10 km thick, and Cenozoic flood basalt (harrat). The distribution of these rocks and variations in elevation across the Plate cause a pronounced geologic and topographic asymmetry, with extensive basement exposures (the Arabian Shield) and elevations of as much as 3000 m in the west, and a Phanerozoic succession (Arabian Platform) that thickens, and a surface that descends to sea level, eastward between the Shield and the northeastern margin of the Plate. This tilt in the Plate is partly the result of marginal uplift during rifting in the south and west, and loading during collision with, and subduction beneath, the Eurasian Plate in the northeast. But a variety of evidence suggests that the asymmetry also reflects a fundamental crustal and mantle heterogeneity in the Plate that dates from Neoproterozoic time when the crust formed. The bulk of the Plate's upper crystalline crust is Neoproterozoic in age (1000-540 Ma) reflecting, in the west, a 300-million year process of continental crustal growth between ˜ 850 and 550 Ma represented by amalgamated juvenile magmatic arcs, post-amalgamation sedimentary and volcanic basins, and granitoid intrusions that make up as much as 50% of the Shield's surface. Locally, Archean and Paleoproterozoic rocks are structurally intercalated with the juvenile Neoproterozoic rocks in the southern and eastern parts of the Shield. The geologic dataset for the age, composition, and origin of the upper crust of the Plate in the east is smaller than the database for the Shield, and conclusions made about the crust in the east are correspondingly less definitive. In the absence of exposures, furthermore, nothing is known by direct observation about the

  18. 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.

  19. Continental Collision and the STEP-wise Evolution of Convergent Plate Boundaries: The Mediterranean Region

    NASA Astrophysics Data System (ADS)

    Wortel, M. J.; Govers, R.; Spakman, W.

    2008-12-01

    This contribution focusses on terminal stage subduction, often triggered by continent-continent or arc- continent collision. The landlocked basin setting of the Mediterranean region provides unique opportunities to study terminal stage subduction and its consequences. We use seismic tomography results on lithosphere and upper mantle structure as a source of information on plate boundary structure, and concentrate on the lithospheric scale aspects. Combining this structural information with process-oriented numerical modelling studies and regional observations, we present a 3D model for convergent plate boundary evolution after collision, in which slab detachment and the formation of tear or STEP (Subduction-Transform-Edge-Propagator; see R. Govers and M.J.R. Wortel, EPSL, 236, 505- 523, 2005) faults are key elements. A STEP fault laterally decouples subducting lithosphere from non- subducting lithosphere in a scissor type of fashion. It enhances the ability of a slab to retreat through the mantle flow around the edge of the subducted slab. In this way collision and back-arc extension may occur in close proximity. In our study area this specifically pertains to collision along the north African margin, STEP formation in easterly direction, CCW rotation of the southern Apennines slab and the opening of the Tyrrhenian Sea. Vertical tearing of subducted lithosphere may play an important role as well, but is probably not crucial. Similar processes are likely to have occurred in the eastern Mediterranean. On the basis of the good agreement between the Mediterranean-based model and the evolution of the Tonga-Fiji region we expect that the model may shed light on other complex convergent plate boundary regions, as well. In summary: Upon continental (or arc-continent) collision, along-trench variations in lithospheric properties of the subducting lithosphere may lead to disruption and segmentation of the subduction system. Following slab detachment along limited segments of

  20. Uplift along passive continental margins, changes in plate motion and mantle convection

    NASA Astrophysics Data System (ADS)

    Japsen, Peter; Green, Paul F.; Chalmers, James A.; Bonow, Johan M.

    2014-05-01

    The origin of the forces that produce elevated, passive continental margins (EPCMs) is a hot topic in geoscience. It is, however, a new aspect in the debate that episodes of uplift coincide with changes in plate motion. This has been revealed, primarily, by studies of the burial, uplift and exhumation history of EPCMs based on integration on stratigraphic landscape analysis, low-temperature thermochronology and evidence from the geological record (Green et al., 2013). In the Campanian, Eocene and Miocene, uplift and erosion affected the margins of Brazil and Africa (Japsen et al., 2012b). The uplift phases in Brazil coincided with main phases of Andean orogeny which were periods of relatively rapid convergence at the Andean margin of South America (Cobbold et al., 2001). Because Campanian uplift in Brazil coincides, not only with rapid convergence at the Andean margin of South America, but also with a decline in Atlantic spreading rate, Japsen et al. (2012b) suggested that all these uplift events have a common cause, which is lateral resistance to plate motion. Because the uplift phases are common to margins of diverging plates, it was also suggested that the driving forces can transmit across the spreading axis; probably at great depth, e.g. in the asthenosphere. Late Eocene, Late Miocene and Pliocene uplift and erosion shaped the elevated margin of southern East Greenland (Bonow et al., in review; Japsen et al., in review). These regional uplift phases are synchronous with phases in West Greenland, overlap in time with similar events in North America and Europe and also correlate with changes in plate motion. The much higher elevation of East Greenland compared to West Greenland suggests dynamic support in the east from the Iceland plume. Japsen et al. (2012a) pointed out that EPCMs are typically located above thick crust/lithosphere that is closely juxtaposed to thinner crust/lithosphere. The presence of mountains along the Atlantic margin of Brazil and in East

  1. 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

  2. Development of the New Zealand and San Andreas Continental Transforms: From Plate Kinematics to Lithospheric Geodynamics (Invited)

    NASA Astrophysics Data System (ADS)

    Furlong, K. P.

    2009-12-01

    Although oftentimes compared as being two similar continental transforms, the development of the San Andreas and Alpine Fault plate boundary systems reflect two distinctly different geodynamic paths to formation, localization, and evolution. Characteristics that lead to fundamental differences in their present-day tectonic behavior. The San Andreas system has formed in response to the migration of two triple junctions, and it lengthens over time at these transitions from subduction to translation. The San Andreas system forms within the region of thin lithosphere left in the wake of slab removal or subduction cessation, and therefore thermal processes dominate in the development of a localized plate boundary. There are associated short-lived deformational events including significant crustal thickening and subsequent crustal thinning that serve to substantially modify the overlying North American crust during this 3-5 million year transition time. In contrast the development of the Alpine Fault plate boundary system through New Zealand follows a different geodynamic path, and this transform boundary reflects an intermediate point in the overall transition of that Australia-Pacific plate boundary through New Zealand from an extensional to convergent boundary. Since approximately 25 Ma, with rapid changes in Australia-Pacific plate interactions, the plate boundary structure through continental New Zealand rapidly changed from extensional to translation/transpression. This transpression was accommodated by the initiation of two subduction regimes, whose positions were controlled by continent-ocean transitions linked by the translational/transpressional (proto) Alpine Fault system. This trench-transform-trench plate boundary system has migrated southward, maintaining essentially a constant length, but not constant localization, and along the way, ephemerally incorporating segments of the Australia and Pacific plates into the boundary - modifying, exhuming, and removing

  3. Plate motions at the transition from the Lomonosov Ridge to Eurasian Continental Shelf

    NASA Astrophysics Data System (ADS)

    Artyushkov, Eugene; Chekhovich, Peter; Petrov, Eugene

    2016-04-01

    Distribution of the Cenozoic plate motions in the Amerasian Basin is a serious problem. Cenozoic opening of the Gakkel Ridge has resulted in the eastward drift of the Lomonosov Ridge and Podvodnikov Basin. According to a popular point of view these two structures are separated from the Eurasian continent by the Khatanga-Lomonosov Transform Fault. It is supposed that this fault with a right-lateral displacement of about 300 km begins at the southern end of the Gakkel Ridge, passes between the southern end of the Lomonosov Ridge and the Asian Shelf probably continuing further to the east into the Podvodnikov Basin. During the last decade the area was covered by a number of seismic profiles. In 2007 reference profile A-7 was shot (Kazanin, Ivanov, UNCLOS Symposium, St.-Petersburg, May 26, 27 2014). This longitudinal profile 832 km long includes both seismic reflection and deep seismic profiling. It follows the eastern slope of the Lomonosov Ridge in the north and crosses the Asian Continental Rise and shelf of the Laptev Sea terminating near the Novosibirsk Islands in the south. The quality of the data is very high because at that time the area was completely free of ice. Transform faults with large strike-slip displacement are crossing many sedimentary basins (Liemiszki, Brown, GSA Bull., 1988, v. 100, p. 665-676 and others). In such basins the structure of the sedimentary cover changes completely across the fault. Not only sedimentary beds become disrupted but the thicknesses of synchronous sedimentary units on the fault walls commonly appear to be quite different. This indicates that during their movement the units were far one from another. The Khatanga-Lomonosov Transform Fault, if it exists, should cross profile A-7 in its middle part. The profile includes some normal faults slightly disrupting the sedimentary sequences. However, on both fault walls the thickness of the main units of the sedimentary cover separated by regional unconformities remains the same

  4. 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.

  5. 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.

  6. 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

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

    NASA Astrophysics Data System (ADS)

    Holbrook, W. Steven; Brocher, Thomas M.; ten Brink, Uri S.; Hole, John A.

    1996-10-01

    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

  8. 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

  9. Deformation of plate boundaries associated with subduction of continental margins: insights from 3D thermo-mechanical laboratory experiments (Invited)

    NASA Astrophysics Data System (ADS)

    Boutelier, D. A.; Cruden, A. R.

    2013-12-01

    The general sequence of tectonic events leading to the formation of collisional mountain belts includes closure of an ocean basin through oceanic subduction, subduction of a continental margin and deformation of the lithosphere. Laboratory experiments reproducing this fundamental chain of events investigate the three-dimensional and thermo-mechanical mechanics of the associated processes. Experiments reveal that this basic scenario can be considerably modified at the beginning of continental subduction. The buoyancy of the subducted passive margin causes a strong horizontal compression in the plates, which can lead to the formation of new thrusts in the magmatic arc or back-arc spreading center if the collision was preceded by oceanic subduction in the tensile regime. Several complex scenarios can develop, depending on the polarity of the new thrusts. If the new thrust in the arc or back-arc has the same polarity as the main subduction zone, the entire area located between the trench and the new thrust can be subducted, leaving little evidence of its former existence in the geological record. This process also modifies the thermal and mechanical regime of the subducted lithosphere, resulting in lower temperatures in the subducted crust thereby allowing deeper subduction. If the polarity of the new thrust is opposite to that of the existing subduction zone, the two slabs collide at depth, with the new slab generally cutting through the pre-existing slab. The distribution of convergence across several thrusts necessarily leads to a reduction of the convergence rate on the pre-existing subduction thrust. This leads to a reduction of the viscous coupling supporting the subducted lithosphere, causing an increase in downdip tension in the slab, and a rapid decrease of the slab strength due to temperature increase, eventually leading to slab break-off. Finally, the deformation caused by the subduction of the buoyant continental crust is fundamentally three

  10. Processes of subduction and exhumation of continental blocks in collisional orogeny

    NASA Astrophysics Data System (ADS)

    Tirel, C.; Brun, J.; Burov, E. B.; Wortel, M. J.; Lebedev, S.

    2009-12-01

    Understanding the mechanism of accretion, subduction and exhumation of rocks during orogeny is a fundamental issue for plate tectonics. Numerous models have been proposed in order to explain the tectonic events that accompany continental subduction. Here, in order to examine the different processes in a simple, self-consistent manner, the fully coupled thermo-mechanical numerical code PARAFLAM is used to perform a parametric study on the subduction mode and, particularly, on the continental subduction processes. A wide range of parameters including slab-pull magnitude, temperature and viscosity distribution, initial geometry of the subduction zone and rheology, is explored to understand the dynamics of accretion, the different processes of exhumation, the deformation of the slab and the deformation of the overriding plate. The first results of this study show the evolution of one or two small continental blocks (terranes) reaching the subduction-zone continental margin. A set of experiments demonstrates that the progressive incorporation of a continental block into the over-riding plate is governed by the dynamics of subduction. Initially, the continental block is partly or entirely subducted, which increases its buoyancy and induces its detachment from the subducting slab. By the time the emplacement of the block into the continental margin is completed, exhumation is likely to have occurred, depending mainly on the slab pull magnitude and the rheology of the continental block itself. As an example, some experiments show the continuous subduction of a continental block followed by an UHP-HP exhumation and a metamorphic-core-complex type of exhumation. These cases can be compared with the pattern of deformation observed in the Aegean-Sea domain or in the Tyrrhenian one.

  11. Processes accompanying of mantle plume emplacement into continental lithosphere: Evidence from NW Arabian plate, Western Syria

    NASA Astrophysics Data System (ADS)

    Sharkov, E. V.

    2015-12-01

    Lower crustal xenoliths occurred in the Middle Cretaceous lamprophyre diatremes in Jabel Ansaria (Western Syria) (Sharkov et al., 1992). They are represented mainly garnet granulites and eclogite-like rocks, which underwent by deformations and retrograde metamorphism, and younger fresh pegmatoid garnet-kaersutite-clinopyroxene (Al-Ti augite) rocks; mantle peridotites are absent in these populations. According to mineralogical geothermobarometers, forming of garnet-granulite suite rocks occurred under pressure 13.5-15.4 kbar (depths 45-54 kn) and temperature 965-1115oC. At the same time, among populations of mantle xenoliths in the Late Cenozoic platobasalts of the region, quite the contrary, lower crustal xenoliths are absent, however, predominated spinel lherzolites (fragments of upper cooled rim of a plume head), derived from the close depths (30-40 km: Sharkov, Bogatikov, 2015). From this follows that ancient continental crust was existed here even in the Middle Cretaceous, but in the Late Cenozoic was removed by extended mantle plume head; at that upper sialic crust was not involved in geomechanic processes, because Precambrian metamorphic rocks survived as a basement for Cambrian to Cenozoic sedimentary cover of Arabian platform. In other words, though cardinal rebuilding of deep-seated structure of the region occurred in the Late Cenozoic but it did not affect on the upper shell of the ancient lithosphere. Because composition of mantle xenolithis in basalts is practically similar worldwide, we suggest that deep-seated processes are analogous also. As emplacement of the mantle plume heads accompanied by powerful basaltic magmatism, very likely that range of lower (mafic) continental crust existence is very convenient for extension of plume heads and their adiabatic melting. If such level, because of whatever reasons, was not reached, melting was limited but appeared excess of volatile matters which led to forming of lamprophyre or even kimberlite.

  12. The fluid budget of a continental plate boundary fault: Quantification from the Alpine Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    Menzies, Catriona D.; Teagle, Damon A. H.; Niedermann, Samuel; Cox, Simon C.; Craw, Dave; Zimmer, Martin; Cooper, Matthew J.; Erzinger, Jörg

    2016-07-01

    Fluids play a key role in modifying the chemical and physical properties of fault zones, which may prime them for repeated rupture by the generation of high pore fluid pressures and precipitation of commonly weak, secondary minerals. Fluid flow paths, sources and fluxes, and the permeability evolution of fault zones throughout their seismic cycles remain poorly constrained, despite their importance to understanding fault zone behaviour. Here we use geochemical tracers of fluid-rock exchange to determine budgets for meteoric, metamorphic and mantle fluids on a major compressional tectonic plate boundary. The Alpine Fault marks the transpressional Pacific-Australian plate boundary through South Island, New Zealand and appears to fail in regular (329 ± 68 yrs) large earthquakes (Mw ∼ 8) with the most recent event in 1717 AD. Significant convergent motion has formed the Southern Alps and elevated geothermal gradients in the hangingwall, which drive crustal fluid flow. Along the Alpine Fault the Alpine Schist of the Pacific Plate is thrust over radiogenic metasedimentary rocks on the Australian plate. The absence of highly radiogenic (87Sr/86Sr > 0.7200) strontium isotope ratios of hangingwall hot springs and hydrothermal minerals formed at a range of depths in the Alpine Fault damage zone indicates that the fluid flow is restricted to the hangingwall by a cross-fault fluid flow barrier throughout the seismogenic crust. Helium isotope ratios measured in hot springs near to the Alpine Fault (0.15-0.81 RA) indicate the fault is a crustal-scale feature that acts as a conduit for fluids from the mantle. Rock-exchanged oxygen, but meteoric water-like hydrogen isotope signatures of hydrothermal veins indicate that partially rock-exchanged meteoric fluids dominate down to the top of the brittle to ductile transition zone at ∼6 km. Geochemical tracer transport modelling suggests only ∼0.02 to 0.05% of total rainfall west of the Main Divide penetrates to depth, yet this

  13. Dynamic models of interseismic deformation and stress transfer from plate motion to continental transform faults

    NASA Astrophysics Data System (ADS)

    Takeuchi, Christopher S.; Fialko, Yuri

    2012-05-01

    We present numerical models of earthquake cycles on a strike-slip fault that incorporate laboratory-derived power law rheologies with Arrhenius temperature dependence, viscous dissipation, conductive heat transfer, and far-field loading due to relative plate motion. We use these models to explore the evolution of stress, strain, and thermal regime on "geologic" timescales (˜106-107 years), as well as on timescales of the order of the earthquake recurrence (˜102 years). Strain localization in the viscoelastic medium results from thermomechanical coupling and power law dependence of strain rate on stress. For conditions corresponding to the San Andreas fault (SAF), the predicted width of the shear zone in the lower crust is ˜3-5 km; this shear zone accommodates more than 50% of the far-field plate motion. Coupled thermomechanical models predict a single-layer lithosphere in case of "dry" composition of the lower crust and upper mantle, and a "jelly sandwich" lithosphere in case of "wet" composition. Deviatoric stress in the lithosphere in our models is relatively insensitive to the water content, the far-field loading rate, and the fault strength and is of the order of 102 MPa. Thermomechanical coupling gives rise to an inverse correlation between the fault slip rate and the ductile strength of the lithosphere. We show that our models are broadly consistent with geodetic and heat flow constrains from the SAF in Northern California. Models suggest that the regionally elevated heat flow around the SAF may be at least in part due to viscous dissipation in the ductile part of the lithosphere.

  14. 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, β, 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

  15. Craton stability and continental lithosphere dynamics during plume-plate interaction

    NASA Astrophysics Data System (ADS)

    Wang, H.; Van Hunen, J.; Pearson, D.

    2013-12-01

    Survival of thick cratonic roots in a vigorously convecting mantle system for billions of years has long been studied by the geodynamical community. A high cratonic root strength is generally considered to be the most important factor. We first perform and discuss new numerical models to investigate craton stability in both Newtonian and non-Newtonian rheology in the stagnant lid regime. The results show that only a modest compositional rheological factor of Δη=10 with non-Newtonian rheology is required for the survival of cratonic roots in a stagnant lid regime. A larger rheological factor (100 or more) is needed to maintain similar craton longevity in a Newtonian rheology environment. Furthermore, chemical buoyancy plays an important role on craton stability and its evolution, but could only work with suitable compositional rheology. During their long lifespan, cratons experienced a suite of dynamic, tectonothermal events, such as nearby subduction and mantle plume activity. Cratonic nuclei are embedded in shorter-lived, more vulnerable continental areas of different thickness, composition and rheology, which would influence the lithosphere dynamic when tectonothermal events happen nearby. South Africa provides a very good example to investigate such dynamic processes as it hosts several cratons and there are many episodic thermal events since the Mesozoic as indicated by a spectrum of magmatic activity. We numerically investigate such an integrated system using the topographic evolution of cratons and surrounding lithosphere as a diagnostic observable. The post-70Ma thinning of pericratonic lithosphere by ~50km around Kaapvaal craton (Mather et al., 2011) is also investigated through our numerical models. The results show that the pericratonic lithosphere cools and grows faster than cratons do, but is also more likely to be effected by episodic thermal events. This leads to surface topography change that is significantly larger around the craton than within

  16. 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.

  17. Formation of Australian continental margin highlands driven by plate-mantle interaction

    NASA Astrophysics Data System (ADS)

    Müller, R. Dietmar; Flament, Nicolas; Matthews, Kara J.; Williams, Simon E.; Gurnis, Michael

    2016-05-01

    Passive margin highlands occur on most continents on Earth and play a critical role in the cycle of weathering, erosion, and atmospheric circulation. Yet, in contrast to the well-developed understanding of collisional mountain belts, such as the Alps and Himalayas, the origin of less elevated (1-2 km) passive margin highlands is still unknown. The eastern Australian highlands are a prime example of these plateaus, but compared to others they have a well-documented episodic uplift history spanning 120 million years. We use a series of mantle convection models to show that the time-dependent interaction of plate motion with mantle downwellings and upwellings accounts for the broad pattern of margin uplift phases. Initial dynamic uplift of 400-600 m from 120-80 Ma was driven by the eastward motion of eastern Australia's margin away from the sinking eastern Gondwana slab, followed by tectonic quiescence to about 60 Ma in the south (Snowy Mountains). Renewed uplift of ∼700 m in the Snowy Mountains is propelled by the gradual motion of the margin over the edge of the large Pacific mantle upwelling. In contrast the northernmost portion of the highlands records continuous uplift from 120 Ma to present-day totalling about 800 m. The northern highlands experienced a continuous history of dynamic uplift, first due to the end of subduction to the east of Australia, then due to moving over a large passive mantle upwelling. In contrast, the southern highlands started interacting with the edge of the large Pacific mantle upwelling ∼ 40- 50 million years later, resulting in a two-phase uplift history. Our results are in agreement with published uplift models derived from river profiles and the Cretaceous sediment influx into the Ceduna sub-basin offshore southeast Australia, reflecting the fundamental link between dynamic uplift, fluvial erosion and depositional pulses in basins distal to passive margin highlands.

  18. 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

    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.

  19. What do Great Subduction Earthquakes tell us About Continental Deformation of the Upper Plate in the Central Andes Forearc? Insights From Seismotectonics, Continental Deformation and Coulomb Modelisation Along Southern Peru Margin

    NASA Astrophysics Data System (ADS)

    Audin, L.; Perfettini, H.; Tavera, H.

    2007-05-01

    Subduction of the Nazca plate beneath the Peruvian margin has produced numerous megathrust earthquakes during the last century and still constitutes mature seismic gaps in some places such as in between Ilo (Peru) and Arica (Chile). The rupture zones of the 1604, 1784 and 1868 southern Peru events were partially reactivated by the Arequipa 2001 (Mw = 8.5) seismic event, whose rupture zone was about 350km-long and stopped its propagation towards the south on Ilo Peninsula. Just after the occurrence of 2001 event, some reactivation of continental fault systems are identified and monitored thanks to the Peruvian seismic network and describe continental deformation processes occurring perpendicularly to the trench or parallel to the trench, traducing the continental plate response to major subduction earthquakes and some partitioning of the deformation. The Chololo and associated ( perpendicular to the trench) fault systems define some 80-km-long margin crustal blocks and the major one coincides with the 2001 earthquake southern limit of the rupture zone as it propagated to the south. These blocks are made from Late Jurassic and Cretaceous plutonic rocks from the Coastal Batholith; these are outcropping in some places and are evidenced by the aeromagnetic mapping elsewhere around the area. Northward along the subduction zone, another boundary between two rupture zones of major subduction earthquake was reactivated recently, perpendicularly to the trench, by the seismic crisis of October 2006, M=6.4, near Lima, right at the southern end of the rupture zone of the 1974 event (Mw=8.1).Those boundaries corresponding to discontinuities (lithospheric fault systems) in the upper plate, trending nearly perpendicular to the trench, act as earthquake barriers during rupture of large seismic events. Additionally occurred on 20 of November 2006 another seismic event (Mw=5.6 Neic, Ml=5.3) in Tacna region, showing a reverse focal mechanism compatible with the trend of the Sama

  20. 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.

  1. 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, β, 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.

  2. 30 CFR 581.31 - Overriding royalties.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 2 2012-07-01 2012-07-01 false Overriding royalties. 581.31 Section 581.31 Mineral Resources BUREAU OF OCEAN ENERGY MANAGEMENT, DEPARTMENT OF THE INTERIOR OFFSHORE LEASING OF... interest of conservation, necessary to prevent premature abandonment of a producing mine, or to...

  3. 30 CFR 281.31 - Overriding royalties.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 2 2011-07-01 2011-07-01 false Overriding royalties. 281.31 Section 281.31 Mineral Resources BUREAU OF OCEAN ENERGY MANAGEMENT, REGULATION, AND ENFORCEMENT, DEPARTMENT OF THE... denial is determined to be in the interest of conservation, necessary to prevent premature abandonment...

  4. 30 CFR 581.31 - Overriding royalties.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 2 2013-07-01 2013-07-01 false Overriding royalties. 581.31 Section 581.31 Mineral Resources BUREAU OF OCEAN ENERGY MANAGEMENT, DEPARTMENT OF THE INTERIOR OFFSHORE LEASING OF... interest of conservation, necessary to prevent premature abandonment of a producing mine, or to...

  5. 30 CFR 581.31 - Overriding royalties.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 2 2014-07-01 2014-07-01 false Overriding royalties. 581.31 Section 581.31 Mineral Resources BUREAU OF OCEAN ENERGY MANAGEMENT, DEPARTMENT OF THE INTERIOR OFFSHORE LEASING OF... interest of conservation, necessary to prevent premature abandonment of a producing mine, or to...

  6. Ancient plate kinematics derived from the deformation pattern of continental crust: Paleo- and Neo-Tethys opening coeval with prolonged Gondwana-Laurussia convergence

    NASA Astrophysics Data System (ADS)

    Kroner, Uwe; Roscher, Marco; Romer, Rolf L.

    2016-06-01

    The formation and destruction of supercontinents requires prolonged convergent tectonics between particular plates, followed by intra-continental extension during subsequent breakup stages. A specific feature of the Late Paleozoic supercontinent Pangea is the prolonged and diachronous formation of the collisional belts of the Rheic suture zone coeval with recurrent continental breakup and subsequent formation of the mid-ocean ridge systems of the Paleo- and Neo-Tethys oceans at the Devonian and Permian margins of the Gondwana plate, respectively. To decide whether these processes are causally related or not, it is necessary to accurately reconstruct the plate motion of Gondwana relative to Laurussia. Here we propose that the strain pattern preserved in the continental crust can be used for the reconstruction of ancient plate kinematics. We present Euler pole locations for the three fundamental stages of the Late Paleozoic assembly of Pangea and closure of the Rheic Ocean: (I) Early Devonian (ca. 400 Ma) collisional tectonics affected Gondwana at the Armorican Spur north of western Africa and at the promontory of the South China block/Australia of eastern Gondwana, resulting in the Variscan and the Qinling orogenies, respectively. The Euler pole of the rotational axis between Gondwana and Laurussia is positioned east of Gondwana close to Australia. (II) Continued subduction of the western Rheic Ocean initiates the clockwise rotation of Gondwana that is responsible for the separation of the South China block from Gondwana and the opening of Paleo-Tethys during the Late Devonian. The position of the rotational axis north of Africa reveals a shift of the Euler pole to the west. (III) The terminal closure of the Rheic Ocean resulted in the final tectonics of the Alleghanides, the Mauritanides and the Ouachita-Sonora-Marathon belt, occurred after the cessation of the Variscan orogeny in Central Europe, and is coeval with the formation of the Central European Extensional

  7. 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

  8. Collision of continental corner from 3-D numerical modeling

    NASA Astrophysics Data System (ADS)

    Li, Zhong-Hai; Xu, Zhiqin; Gerya, Taras; Burg, Jean-Pierre

    2013-10-01

    Continental collision has been extensively investigated with 2-D numerical models assuming infinitely wide plates or insignificant along-strike deformation in the third dimension. However, the corners of natural collision zones normally have structural characteristics that differ from linear parts of mountain belt. We conducted 3-D high-resolution numerical simulations to study the dynamics of a continental corner (lateral continental/oceanic transition zone) during subduction/collision. The results demonstrate different modes between the oceanic subduction side (continuous subduction and retreating trench) and the continental collision side (slab break-off and topography uplift). Slab break-off occurs at a depth (⩽100 km to ˜300 km) that depends on the convergence velocity. The numerical models produce lateral extrusion of the overriding crust from the collisional side to the subduction side, which is also a phenomenon recognized around natural collision of continental corners, for instance around the western corner of the Arabia-Asia collision zone and around the eastern corner of the India-Asia collision zone. Modeling results also indicate that extrusion tectonics may be driven both from above by the topography and gravitational potentials and from below by the trench retreat and asthenospheric mantle return flow, which supports the link between deep mantle dynamics and shallower crustal deformation.

  9. Motion of continental slivers and creeping subduction in the northern Andes

    NASA Astrophysics Data System (ADS)

    Nocquet, J.-M.; Villegas-Lanza, J. C.; Chlieh, M.; Mothes, P. A.; Rolandone, F.; Jarrin, P.; Cisneros, D.; Alvarado, A.; Audin, L.; Bondoux, F.; Martin, X.; Font, Y.; Régnier, M.; Vallée, M.; Tran, T.; Beauval, C.; Maguiña Mendoza, J. M.; Martinez, W.; Tavera, H.; Yepes, H.

    2014-04-01

    Along the western margin of South America, plate convergence is accommodated by slip on the subduction interface and deformation of the overriding continent. In Chile, Bolivia, Ecuador and Colombia, continental deformation occurs mostly through the motion of discrete domains, hundreds to thousands of kilometres in scale. These continental slivers are wedged between the Nazca and stable South American plates. Here we use geodetic data to identify another large continental sliver in Peru that is about 300-400 km wide and 1,500 km long, which we call the Inca Sliver. We show that movement of the slivers parallel to the subduction trench is controlled by the obliquity of plate convergence and is linked to prominent features of the Andes Mountains. For example, the Altiplano is located at the boundary of converging slivers at the concave bend of the central Andes, and the extending Gulf of Guayaquil is located at the boundary of diverging slivers at the convex bend of the northern Andes. Motion of a few large continental slivers therefore controls the present-day deformation of nearly the entire Andes mountain range. We also show that a 1,000-km-long section of the plate interface in northern Peru and southern Ecuador slips predominantly aseismically, a behaviour that contrasts with the highly seismic neighbouring segments. The primary characteristics of this low-coupled segment are shared by ~20% of the subduction zones in the eastern Pacific Rim.

  10. 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

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

    NASA Astrophysics Data System (ADS)

    Heuret, A.; Funiciello, F.; Faccenna, C.; Lallemand, S.

    2007-04-01

    A combination of statistical studies on present-day subduction zones and three-dimensional (3D) laboratory models is performed with the aim to clarify the way that plate kinematics control the geometry of the slab and the overriding plate deformation in subduction zones. In 3D laboratory models, the analogue of a two layer linearly viscous lithosphere-upper mantle system is achieved by means of silicon putty glucose syrup tank experiment. The subducting and overriding plate velocities are systematically changed by exploring the variability field of natural plate kinematics. Both statistical and modelling approaches recognize the importance of overriding plate motion on subduction process behavior: (1) trenches migrate at a rate close to the overriding plate motion, but always move slower than the overriding plates. The mechanism at work is a direct consequence of "slab anchoring" opposed by both lithosphere and mantle viscous resistance and is responsible for overriding plate deformation and slab geometry variability. (2) An overriding plate shortens when the overriding plate moves toward the trench and conditions that are favourable for overriding plate extension are created when the overriding plate moves away from the trench. (3) Shallow and steep dips are found if the overriding plate moves toward and away from the trench, respectively.

  12. 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

  13. Focusing of relative plate motion at a continental transform fault: Cenozoic dextral displacement >700 km on New Zealand's Alpine Fault, reversing >225 km of Late Cretaceous sinistral motion

    NASA Astrophysics Data System (ADS)

    Lamb, Simon; Mortimer, Nick; Smith, Euan; Turner, Gillian

    2016-03-01

    The widely accepted ˜450 km Cenozoic dextral strike-slip displacement on New Zealand's Alpine Fault is large for continental strike-slip faults, but it is still less than 60% of the Cenozoic relative plate motion between the Australian and Pacific plates through Zealandia, with the remaining motion assumed to be taken up by rotation and displacement on other faults in a zone up to 300 km wide. We show here that the 450 km total displacement across the Alpine Fault is an artifact of assumptions about the geometry of New Zealand's basement terranes in the Eocene, and the actual Cenozoic dextral displacement across the active trace is greater than 665 km, with more than 700 km (and <785 km since 25 Ma) occurring in a narrow zone less than 10 km wide. This way, the Alpine Fault has accommodated almost all (>94%) of the relative plate motion in the last 25 Ma at an average rate in excess of 28 mm/yr. It reverses more than 225 km (and <300 km) of sinistral shear through Zealandia in the Late Cretaceous, when Zealandia lay on the margin of Gondwana, providing a direct constraint on the kinematics of extension between East and West Antarctica at this time.

  14. 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

  15. Numerical modeling of outer rise deformation in the Tonga subduction system: Coupling between outer rise deformation, slab weakening and plate velocities

    NASA Astrophysics Data System (ADS)

    Naliboff, J. B.; Billen, M. I.; Gerya, T.; Saunders, J. K.

    2012-12-01

    During subduction, bending and flexure of oceanic lithosphere generates a topographic bulge seaward of the trench known as the outer rise, which commonly exhibits extensional deformation attributed to slab pull forces and bending stresses. The resulting brittle and viscous deformation may play a significant role in long-term geodynamic processes by limiting the ability of subducted oceanic lithosphere to act as a stress guide driving surface plate motions through slab pull. Recent numerical studies provide varying estimates of slab pull's contribution to surface plate motions [e.g., van Summeren et al. 2012, Ghosh & Holt 2012], while observational constraints suggest old oceanic lithosphere may weaken by 3-4 orders of magnitude as it bends and descends beneath the overriding plate [Arredondo & Billen, 2012]. Preliminary numerical models of outer rise deformation during oceanic-continental convergence (40 Myr oceanic lithosphere) exhibit 10x-150x viscous weakening in the upper plate near the trench, with time-dependent variations related to both changes in slab depth and downgoing-overriding plate coupling (Naliboff et al., in prep). In order to more closely examine the relationship between outer rise deformation, geophysical observations and plate velocities, we consider 2D subduction models of the Tonga subduction system where flow will be strictly driven by upper mantle slab buoyancy as defined by the Slab1.0 model [Hayes et al. 2012]. The resulting subducting plate deformation patterns are compared to observations of outer rise faulting, elastic thickness measurements and outer rise seismicity. While keeping buoyancy forces fixed, we will examine the role of brittle rheology, hydration and downgoing-overriding plate coupling in patterns of subducting plate deformation. These results will provide improved physical understanding of the relationship between slab pull, plate velocities and downgoing plate weakening, and a basis for future work examining the role of

  16. 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.

  17. 19 CFR 102.19 - NAFTA preference override.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 19 Customs Duties 1 2011-04-01 2011-04-01 false NAFTA preference override. 102.19 Section 102.19... TREASURY RULES OF ORIGIN Rules of Origin § 102.19 NAFTA preference override. (a) Except in the case of... single NAFTA country, the country of origin of such good is the last NAFTA country in which that...

  18. 19 CFR 102.19 - NAFTA preference override.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 19 Customs Duties 1 2010-04-01 2010-04-01 false NAFTA preference override. 102.19 Section 102.19... TREASURY RULES OF ORIGIN Rules of Origin § 102.19 NAFTA preference override. (a) Except in the case of... single NAFTA country, the country of origin of such good is the last NAFTA country in which that...

  19. 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)...

  20. 5 CFR 1320.15 - Independent regulatory agency override authority.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 5 Administrative Personnel 3 2014-01-01 2014-01-01 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)...

  1. 5 CFR 1320.15 - Independent regulatory agency override authority.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 5 Administrative Personnel 3 2012-01-01 2012-01-01 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)...

  2. 5 CFR 1320.15 - Independent regulatory agency override authority.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 5 Administrative Personnel 3 2011-01-01 2011-01-01 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)...

  3. 5 CFR 1320.15 - Independent regulatory agency override authority.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 5 Administrative Personnel 3 2013-01-01 2013-01-01 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)...

  4. Late Cenozoic tectonics of the Middle Atlas Mountains, Morocco: Continental deformation in the diffuse western Mediterranean plate boundary

    NASA Astrophysics Data System (ADS)

    Gomez, Francisco Gustavo

    -Eurasian plate convergence since the Early Miocene. The diffuse plate boundary comprises large, relatively rigid crustal blocks (Moroccan Meseta, High Plateau, and Saharan Platform) bounded by narrow deformable zones (the Atlas). In this context, the Middle Atlas can be interpreted as an accommodation zone resulting from differential movements between two large crustal blocks impinging on stable Africa. The Atlas Mountains exemplify the possible structural influence of inherited crustal weaknesses in a diffuse plate boundary such as the western Mediterranean region.

  5. 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.

  6. Formation and metasomatism of continental lithospheric mantle in intra-plate and subduction-related tectonic settings

    NASA Astrophysics Data System (ADS)

    Ionov, Dmitri

    2010-05-01

    Our knowledge of the origin and evolution of the continental lithospheric mantle (CLM) remains fragmentary and partly controversial in spite of recent advances in petrologic, geochemical and geophysical studies of the deep Earth and experimental work. Debate continues on a number of essential topics, like relative contributions of partial melting, metasomatism and ‘re-fertilisation' as well as the timing, conditions and tectonic settings of those processes. These topics can be addressed by studies of ultramafic xenoliths in volcanic rocks which arguably provide the least altered samples of modern and ancient CLM. The subcontinental lithosphere is thought to be a mantle region from which melts have been extracted, thus making the lithosphere more refractory. Melting degrees can be estimated from Al contents while the depth of melt extraction can be assessed from Al-Fe (Mg#) relations in unmetasomatized melting residues in comparison with experimental data, e.g. [1]. High silica and opx in the residues may indicate melting in water-rich conditions. High-precision Mg# and Mn for olivine may constrain degrees and conditions of partial melting and/or metasomatism, tectonic settings, modal compositions (e.g. presence of garnet) and equilibration conditions of mantle peridotites [2]. These estimates require both adequate sampling and high-quality major element and modal data; sampling and analytical uncertainties in published work may contribute substantially to chemical heterogeneities (and different origins) inferred for CLM domains [3]. Very fertile peridotite xenolith suites are rare worldwide [3]. They were initially viewed as representing mantle domains that experienced only very small degrees of melt extraction but are attributed by some workers to ‘refertilization' of refractory mantle by percolating asthenospheric melts. Such alternative mechanisms might be valid for some rare hybrid and Fe-enriched peridotites but they fail to comprehensively explain modal

  7. 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

  8. 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

  9. 4-D Subduction Models Incorporating an Upper Plate

    NASA Astrophysics Data System (ADS)

    Stegman, D.; Capitanio, F. A.; Moresi, L.; Mueller, D.; Clark, S.

    2007-12-01

    Thus far, relatively simplistic models of free subduction have been employed in which the trench and plate kinematics are emergent features completely driven by the negative buoyancy of the slab. This has allowed us to build a fundamental understanding of subduction processes such as the kinematics of subduction zones, the strength of slabs, and mantle flow-plate coupling. Additionaly, these efforts have helped to develop appreciable insight into subduction processes when considering the energetics of subduction, in particular how energy is dissipated in various parts of the system such as generating mantle flow and bending the plate. We are now in a position to build upon this knowledge and shift our focus towards the dynamic controls of deformation in the upper plate (vertical motions, extension, shortening, and dynamic topography). Here, the state of stress in the overriding plate is the product of the delicate balance of large tectonic forces in a highly-coupled system, and must therefore include all components of the system: the subducting plate, the overriding plate, and the underlying mantle flow which couples everything together. We will present some initial results of the fully dynamic 3-D models of free subduction which incorporate an overriding plate and systematically investigate how variations in the style and strength of subduction are expressed by the tectonics of the overriding plate. Deformation is driven in the overriding plate by the forces generated from the subducting plate and the type of boundary condition on the non-subducting side of the overriding plate (either fixed or free). Ultimately, these new models will help to address a range of issues: how the overriding plate influences the plate and trench kinematics; the formation and evolution of back-arc basins; the variation of tractions on the base of the overriding plate; the nature of forces which drive plates; and the dynamics controls on seismic coupling at the plate boundary.

  10. Nature of the plate contact and subduction zones diversity

    NASA Astrophysics Data System (ADS)

    De Franco, Roberta; Govers, Rob; Wortel, Rinus

    2008-07-01

    In recent studies we showed that the nature of the plate contact in subduction zones is an important physical feature in both oceanic lithospheric subduction and continental collision. We investigated two fundamental states of the plate contact: one based on a fault and the other based on a subduction channel. Using geodynamic modeling, we determined the specific signatures of both states of the subduction contact. We established that the nature of the plate contact influences the dynamic response of the overriding and subducting plate, and is one of the controlling factors whether back-arc extension develops or not. In the present study, we combine results of our previous numerical experiments with a re-analysis of published observations. Overall, our synthesis connects seismic moment release with back-arc deformation and tectonic processes at the margin. It leads us to identify four classes of subduction zones. The first two classes result directly from our numerical experiments. In class 1, subduction zones are characterized by a plate contact that is largely fault-like with an accretionary margin. In class 2, the plate contacts are largely channel-type and have an erosive margin. Class 3, where the plate contact is entirely channel-like, consists of accretionary margins with a high sediment supply. Subduction zones of class 4, mostly characterized by an erosive convergent margin (northern Chile, Peru, Honshu and Kuril), are more complicated. They can be explained by incorporating regional observations.

  11. Crustal structure of the Peruvian continental margin from wide-angle seismic studies

    NASA Astrophysics Data System (ADS)

    Krabbenhöft, A.; Bialas, J.; Kopp, H.; Kukowski, N.; Hübscher, C.

    2004-11-01

    Active seismic investigations along the Pacific margin off Peru were carried out using ocean bottom hydrophones and seismometers. The structure and the P-wave velocities of the obliquely subducting oceanic Nazca Plate and overriding South American Plate from 8°S to 15°S were determined by modelling the wide-angle seismic data combined with the analysis of reflection seismic data. Three detailed cross-sections of the subduction zone of the Peruvian margin and one strike-line across the Lima Basin are presented here. The oceanic crust of the Nazca Plate, with a thin pelagic sediment cover, ranging from 0-200 m, has an average thickness of 6.4 km. At 8°S it thins to 4 km in the area of Trujillo Trough, a graben-like structure. Across the margin, the plate boundary can be traced to 25 km depth. As inferred from the velocity models, a frontal prism exists adjacent to the trench axis and is associated with the steep lower slope. Terrigeneous sediments are proposed to be transported downslope due to gravitational forces and comprise the frontal prism, characterized by low seismic P-wave velocities. The lower slope material accretes against a backstop structure, which is defined by higher seismic P-wave velocities, 3.5-6.0 km s-1. The large variations in surface slope along one transect may reflect basal removal of upper plate material, thus steepening the slope surface. Subduction processes along the Peruvian margin are dominated by tectonic erosion indicated by the large margin taper, the shape and bending of the subducting slab, laterally varying slope angles and the material properties of the overriding continental plate. The erosional mechanisms, frontal and basal erosion, result in the steepening of the slope and consequent slope failure.

  12. 14. INTERIOR, OPERATOR'S HOUSE, FOOTOPERATED LIMITED OVERRIDE SWITCHES New ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    14. INTERIOR, OPERATOR'S HOUSE, FOOT-OPERATED LIMITED OVERRIDE SWITCHES - New York, New Haven & Hartford Railroad, Mystic River Bridge, Spanning Mystic River between Groton & Stonington, Groton, New London County, CT

  13. 30 CFR 1202.250 - Overriding royalty interest.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 1202.250 Mineral Resources OFFICE OF NATURAL RESOURCES REVENUE, DEPARTMENT OF THE INTERIOR NATURAL RESOURCES REVENUE ROYALTIES Coal § 1202.250 Overriding royalty interest. The regulations governing... in 43 CFR group 3400....

  14. 30 CFR 1202.250 - Overriding royalty interest.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 1202.250 Mineral Resources OFFICE OF NATURAL RESOURCES REVENUE, DEPARTMENT OF THE INTERIOR NATURAL RESOURCES REVENUE ROYALTIES Coal § 1202.250 Overriding royalty interest. The regulations governing... in 43 CFR group 3400....

  15. 30 CFR 1202.250 - Overriding royalty interest.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 1202.250 Mineral Resources OFFICE OF NATURAL RESOURCES REVENUE, DEPARTMENT OF THE INTERIOR NATURAL RESOURCES REVENUE ROYALTIES Coal § 1202.250 Overriding royalty interest. The regulations governing... in 43 CFR group 3400....

  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. 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

  18. Two-dimensional numerical modeling of tectonic and metamorphic histories at active continental margins

    NASA Astrophysics Data System (ADS)

    Gerya, Taras; Stöckhert, Bernhard

    2006-04-01

    The evolution of an active continental margin is simulated in two dimensions, using a finite difference thermomechanical code with half-staggered grid and marker-in-cell technique. The effect of mechanical properties, changing as a function of P and T, assigned to different crustal layers and mantle materials in the simple starting structure is discussed for a set of numerical models. For each model, representative P T paths are displayed for selected markers. Both the intensity of subduction erosion and the size of the frontal accretionary wedge are strongly dependent on the rheology chosen for the overriding continental crust. Tectonically eroded upper and lower continental crust is carried down to form a broad orogenic wedge, intermingling with detached oceanic crust and sediments from the subducted plate and hydrated mantle material from the overriding plate. A small portion of the continental crust and trench sediments is carried further down into a narrow subduction channel, intermingling with oceanic crust and hydrated mantle material, and to some extent extruded to the rear of the orogenic wedge underplating the overriding continental crust. The exhumation rates for (ultra)high pressure rocks can exceed subduction and burial rates by a factor of 1.5 3, when forced return flow in the hanging wall portion of the self-organizing subduction channel is focused. The simulations suggest that a minimum rate of subduction is required for the formation of a subduction channel, because buoyancy forces may outweigh drag forces for slow subduction. For a weak upper continental crust, simulated by a high pore pressure coefficient in the brittle regime, the orogenic wedge and megascale melange reach a mid- to upper-crustal position within 10 20 Myr (after 400 600 km of subduction). For a strong upper crust, a continental lid persists over the entire time span covered by the simulation. The structural pattern is similar in all cases, with four zones from trench toward arc

  19. Modeling the influence of plate motions on subduction

    NASA Astrophysics Data System (ADS)

    Hillebrand, Bram; Thieulot, Cedric; van den Berg, Arie; Spakman, Wim

    2014-05-01

    Subduction zones are widely studied complex geodynamical systems. Their evolution is influenced by a broad range of parameters such as the age of the plates (both subducting and overriding) as well as their rheology, their nature (oceanic or continental), the presence of a crust and the involved plate motions to name a few. To investigate the importance of these different parameters on the evolution of subduction we have created a series of 2D numerical thermomechanical subduction models. These subduction models are multi-material flow models containing continental and oceanic crusts, a lithosphere and a mantle. We use the sticky air approach to allow for topography build up in the model. In order to model multi-material flow in our Eulerian finite element code of SEPRAN (Segal and Praagman, 2000) we use the well benchmarked level set method (Osher and Sethian, 1988) to track the different materials and their mode of deformation through the model domain. To our knowledge the presented results are the first subduction model results with the level set method. We will present preliminary results of our parametric study focusing mainly on the influence of plate motions on the evolution of subduction. S. Osher and J.A. Sethian. Fronts propagating with curvature-dependent speed: Algorithms based on hamilton-jacobi formulations. JCP 1988 A. Segal and N.P. Praagman. The SEPRAN package. Technical report, 2000 This research is funded by The Netherlands Research Centre for Integrated Solid Earth Science (ISES)

  20. 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.

  1. 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.

  2. 25 CFR 227.26 - Assignments and overriding royalties.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 25 Indians 1 2013-04-01 2013-04-01 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 §...

  3. 25 CFR 227.26 - Assignments and overriding royalties.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 25 Indians 1 2014-04-01 2014-04-01 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 §...

  4. 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 §...

  5. 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 §...

  6. 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 §...

  7. 25 CFR 213.38 - Assignments and overriding royalties.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 25 Indians 1 2014-04-01 2014-04-01 false Assignments and overriding royalties. 213.38 Section 213.38 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF RESTRICTED LANDS OF MEMBERS OF FIVE CIVILIZED TRIBES, OKLAHOMA, FOR MINING Operations § 213.38...

  8. 25 CFR 213.38 - 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. 213.38 Section 213.38 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF RESTRICTED LANDS OF MEMBERS OF FIVE CIVILIZED TRIBES, OKLAHOMA, FOR MINING Operations § 213.38...

  9. 25 CFR 213.38 - Assignments and overriding royalties.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 25 Indians 1 2013-04-01 2013-04-01 false Assignments and overriding royalties. 213.38 Section 213.38 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF RESTRICTED LANDS OF MEMBERS OF FIVE CIVILIZED TRIBES, OKLAHOMA, FOR MINING Operations § 213.38...

  10. 25 CFR 213.38 - 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. 213.38 Section 213.38 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF RESTRICTED LANDS OF MEMBERS OF FIVE CIVILIZED TRIBES, OKLAHOMA, FOR MINING Operations § 213.38...

  11. 25 CFR 213.38 - 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. 213.38 Section 213.38 Indians BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF RESTRICTED LANDS OF MEMBERS OF FIVE CIVILIZED TRIBES, OKLAHOMA, FOR MINING Operations § 213.38...

  12. 30 CFR 202.250 - Overriding royalty interest.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... interests, production payments, or similar interests created under Federal coal leases are in 43 CFR group... 30 Mineral Resources 2 2010-07-01 2010-07-01 false Overriding royalty interest. 202.250 Section 202.250 Mineral Resources MINERALS MANAGEMENT SERVICE, DEPARTMENT OF THE INTERIOR MINERALS...

  13. 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

  14. The Peruvian Continental Margin: Results from wide angle seismic Data

    NASA Astrophysics Data System (ADS)

    Krabbenhoeft, A.; Bialas, J.; Kopp, H.; Kukowski, N.; Huebscher, C.

    2003-04-01

    Within the scope of the GEOPECO (Geophysical Experiments at the Peruvian Continental Margin) project, seismic investigations along the Pacific margin of Peru were carried out using ocean bottom hydrophones (OBH) and seismometers (OBS) recording marine airgun shots. The structure and the P- wave velocity of the oblique subducting Nazca and overriding South-American Plates from 8°S to 15°S were determined by forward modeling and tomographic inversion of the wide-angle seismic data combined with the analysis of reflection seismic data. The region south of 12°S has been influenced by the southward migration of the aseismic Nazca Ridge the past 11 Ma. The oceanic Nazca Plate is divided by Mendana Fracture Zone (MFZ) which marks a transition zone of a different crustal age of approximately 28 Ma in the north to 38 Ma in the south at the Peruvian trench. North of MFZ the oceanic crust is influenced by Trujillo Trough trending N15E and the surrounding extensional stresses leading to a crustal thinning as can be seen in the northernmost refraction seismic model. The oceanic crust south of MFZ is overall homogeneous with a thin pelagic sedimentary layer and normal oceanic crustal layers. The P-wave velocity of the mantle is overall 7.9-8.1km/s. The Peruvian Continental Margin is characterized by the continental slope and several basins, Trujillo and Yaquina basin, Lima basin and Pisco basin, which are partly affected by the southward migration of the subducting Nazca Ridge. This caused uplift and subsidence along the margin leading to erosional tectonic features. The basins and continental basement could be mapped with forward modeling and tomographic inversion as well as the continental backstop on each profile. An accretionary prism is set up with a width of 20 to 30 km and 4 to 5 km thickness which does not further increase in size as revealed by the profiles recorded further north of Nazca Ridge. This and a taper of 14- 17 degrees at the collision zone indicates that

  15. 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)

  16. Controls on continental strain partitioning above an oblique subduction zone, Northern Andes

    NASA Astrophysics Data System (ADS)

    Schütt, Jorina M.; Whipp, David M., Jr.

    2016-04-01

    Strain partitioning is a common process at obliquely convergent plate margins dividing oblique convergence into margin-normal slip on the plate-bounding fault and horizontal shearing on a strike-slip system parallel to the subduction margin. In subduction zones, strain partitioning in the upper continental plate is mainly controlled by the shear forces acting on the plate interface and the strength of the continental crust. The plate interface forces are influenced by the subducting plate dip angle and the obliquity angle between the normal to the plate margin and the convergence velocity vector, and the crustal strength of the continent is strongly affected by the presence or absence of a volcanic arc, with the presence of the volcanic arcs being common at steep subduction zones. Along the ˜7000 km western margin of South America the convergence obliquity, subduction dip angles and presence of a volcanic arc all vary, but strain partitioning is only observed along parts of it. This raises the questions, to what extent do subduction zone characteristics control strain partitioning in the overriding continental plate, and which factors have the largest influence? We address these questions using lithospheric-scale 3D numerical geodynamic experiments to investigate the influence of subduction dip angle, convergence obliquity, and weaknesses in the crust owing to the volcanic arc on strain partitioning behavior. We base the model design on the Northern Volcanic Zone of the Andes (5° N - 2° S), characterized by steep subduction (˜ 35°), a convergence obliquity between 31° -45° and extensive arc volcanism, and where strain partitioning is observed. The numerical modelling software (DOUAR) solves the Stokes flow and heat transfer equations for a viscous-plastic creeping flow to calculate velocity fields, thermal evolution, rock uplift and strain rates in a 1600 km x 1600 km box with depth 160 km. Subduction geometry and material properties are based on a

  17. Interplate coupling at oblique subduction zones: influence on upper plate erosion.

    NASA Astrophysics Data System (ADS)

    Malatesta, Cristina; Gerya, Taras; Crispini, Laura; Federico, Laura; Scambelluri, Marco; Capponi, Giovanni

    2014-05-01

    In active subduction zones, when the converging plates cannot slip freely past each other, "plate coupling" occurs. The moving subducting slab and therefore the coupling/decoupling relationship between plates control both short- and long-term deformation of the upper plate. Short-term deformation is dominantly elastic, occurs at human timescales and can be directly associated with earthquakes. Long-term deformation is cumulative, permanent and prevails at the geological timescale (Hoffman-Rothe et al., 2006, Springer Berlin Heidelberg). Here we used 3D numerical simulations to test oblique subduction zones and to investigate: 1) how long-term deformation and coupling relationship vary along the trench-axis; 2) how this relationship influences erosion and down-drag of upper plate material. Our models are based on thermo-mechanical equations solved with finite differences method and marker-in-cell techniques combined with a multigrid approach (Gerya, 2010, Cambridge Univ. Press). The reference model simulates an intraoceanic subduction close to the continental margin (Malatesta et al., 2013, Nature Communications, 4:2456 DOI:10.1038/ncomms3456). The oceanic crust is layered with a 5-km-thick layer of gabbro overlain by a 3-km-thick layer of basalt. The ocean floor is covered by 1-km-thick sediments. Plates move with a total velocity of 3.15 cm/yr; the oblique convergence is obtained using velocity vectors that form an angle of 45° with the initial starting point of subduction (weak zone in the lithosphere). After initiation of plate convergence, part of sediments on top of the incoming plate enters the subduction zone and is buried; another part is suddenly transferred along strike at shallow depths and along the subducting slab according to the direction of the along-trench velocity component of subduction. The lateral migration of sediment causes the evolution of the trench along its strike from sediment-poor to sediment-rich. As soon as subduction starts, where

  18. Stereotypes override grammar: Social knowledge in sentence comprehension.

    PubMed

    Molinaro, Nicola; Su, Jui-Ju; Carreiras, Manuel

    2016-01-01

    Many studies have provided evidence for the automaticity and immediacy with which stereotypical knowledge affects our behavior. However, less is known about how such social knowledge interacts with linguistic cues during comprehension. In this ERP sentence processing study we took advantage of the rich grammatical gender morphology of Spanish to explore the processing of role nouns in which stereotype and grammatical cues were simultaneously manipulated, in a factorial design. We show that stereotypical knowledge overrides syntactic cues, highlighting the immediacy with which stereotype knowledge is activated during language comprehension and supporting proposals claiming that social knowledge impacts on language processing differently from other forms of semantics. PMID:27108245

  19. Cognition overrides orientation dependence in tactile viewpoint selection.

    PubMed

    Hartcher-O'Brien, Jessica; Auvray, Malika

    2016-07-01

    Humans are capable of extracting spatial information through their sense of touch: when someone strokes their hand, they can easily determine stroke direction without visual information. However, when it comes to the coordinate system used to assign the spatial relations to the stimulation, it remains poorly understood how the brain selects the appropriate system for passive touch. In the study reported here, we investigated whether hand orientation can determine coordinate assignment to ambiguous tactile patterns, whether observers can cognitively override any orientation-driven perspectives on touch, and whether the adaptation transfers across body surfaces. Our results demonstrated that the orientation of the hand in the vertical plane determines the perspective taken: an external perspective is adopted when the hand faces the observer and a gaze-centred perspective is selected when the hand faces away. Participants were then adapted to a mirror-reversed perspective through training, and the results revealed that this adapted perspective holds for the adapted surface and generalises to non-adapted surfaces, including across the body midline. These results reveal plasticity in perspective taking which relies on low-level postural cues (hand orientation) but also on higher-order somatosensory processing that can override the low-level cues. PMID:26894892

  20. Linking plate reconstructions with deforming lithosphere to geodynamic models

    NASA Astrophysics Data System (ADS)

    Müller, R. D.; Gurnis, M.; Flament, N.; Seton, M.; Spasojevic, S.; Williams, S.; Zahirovic, S.

    2011-12-01

    While global computational models are rapidly advancing in terms of their capabilities, there is an increasing need for assimilating observations into these models and/or ground-truthing model outputs. The open-source and platform independent GPlates software fills this gap. It was originally conceived as a tool to interactively visualize and manipulate classical rigid plate reconstructions and represent them as time-dependent topological networks of editable plate boundaries. The user can export time-dependent plate velocity meshes that can be used either to define initial surface boundary conditions for geodynamic models or alternatively impose plate motions throughout a geodynamic model run. However, tectonic plates are not rigid, and neglecting plate deformation, especially that of the edges of overriding plates, can result in significant misplacing of plate boundaries through time. A new, substantially re-engineered version of GPlates is now being developed that allows an embedding of deforming plates into topological plate boundary networks. We use geophysical and geological data to define the limit between rigid and deforming areas, and the deformation history of non-rigid blocks. The velocity field predicted by these reconstructions can then be used as a time-dependent surface boundary condition in regional or global 3-D geodynamic models, or alternatively as an initial boundary condition for a particular plate configuration at a given time. For time-dependent models with imposed plate motions (e.g. using CitcomS) we incorporate the continental lithosphere by embedding compositionally distinct crust and continental lithosphere within the thermal lithosphere. We define three isostatic columns of different thickness and buoyancy based on the tectonothermal age of the continents: Archean, Proterozoic and Phanerozoic. In the fourth isostatic column, the oceans, the thickness of the thermal lithosphere is assimilated using a half-space cooling model. We also

  1. Earthquakes and plate tectonics

    USGS Publications Warehouse

    Spall, H.

    1977-01-01

    An explanation is to be found in plate tectonics, a concept which has revolutionized thinking in the Earth sciences in the last 10 years. The theory of plate tectonics combines many of the ideas about continental drift (originally proposed in 1912 by Alfred Wegener in Germany) and sea-floor spreading (suggested originally by Harry Hess of Princeton University). 

  2. Deformation and topography above the lateral transition from continental to oceanic subduction in three-dimensional laboratory models: what can we learn on the Hellenic subduction?

    NASA Astrophysics Data System (ADS)

    Guillaume, B.; Funiciello, F.; Faccenna, C.; Husson, L.; Royden, L. H.

    2012-04-01

    We use three-dimensional dynamically self-consistent laboratory models to analyze relationships between surface evolution and deep dynamics at convergent margins. Our models are setup with a viscous plate of silicone (lithosphere) subducting under negative buoyancy in a viscous layer of glucose syrup (upper mantle). We focus on the subduction of a laterally heterogeneous lithosphere characterized by an abrupt transition of density using negatively and positively buoyant silicone to reproduce oceanic and continental subduction, respectively. We quantify and establish relationships between the subduction dynamics and resulting slab geometry, trench kinematics and pattern of horizontal/vertical deformation for both the overriding plate and the upper mantle. Assuming that our modeling results can be representative of the natural behavior of subduction zones, we compare them to the Neogene to Quaternary evolution of the Hellenic subduction zone. We more particularly focus on the deformation and topography of the Hellenic upper plate, which may have been influenced by the difference in subduction dynamics north and south of the Kephalonia Transform Zone, with a slowly subducting Adriatic continental lithosphere in the north and a rapidly subducting Ionian oceanic lithosphere in the south.

  3. 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

  4. Effects of rheological weakening by fluids and melts for defining geodynamic regimes of oceanic-continental subduction

    NASA Astrophysics Data System (ADS)

    Gerya, Taras; Meilick, Irena

    2010-05-01

    The dynamics of subduction under an active margin is analyzed by using a 2D coupled petrological-thermomechanical numerical model of an oceanic-continental subduction process. This model includes spontaneous slab bending, dehydration of the subducted crust, aqueous fluid transport, partial melting of both crustal and mantle rocks and melt extraction processes resulting in magmatic arc crust growth. Based on our models we identify the following five geodynamic regimes of subduction which may potentially from at active margins: (1) stable subduction with no backarc spreading center and without plumes in the mantle wedge, (2) retreating subduction with the focused backarc spreading center and without plumes, (3) retreating subduction with distributed intra-arc extension and trans-lithospheric sedimentary plumes, (4) advancing subduction with underplating (laterally extending) sub-lithospheric plumes, (5) stable to advancing subduction with stationary (laterally limited) sub-lithospheric plumes. Transitions between these different regimes are mainly caused by the concurrence of rheological weakening effects of (1) aqueous fluids percolating from the subducting slab into the mantle wedge and (2) melts propagating from the partially molten areas formed in the mantle wedge toward the surface. The aqueous fluids mainly affect the forearc region. Strong fluid-related weakening promotes plates decoupling and reduces subduction drag causing stacking of sediments in the accretion prism. In contrast, reduced weakening by fluids results in strong coupling of the plates and leads to advancing collision-like subduction with enhanced subduction erosion. Thickening of the overriding plate and large sedimentary plumes in the mantle wedge are the consequences. On the other hand, melts are extracted from the hot regions above the slab and rheologically weaken mainly the lithosphere below the arc controlling overriding plate extension/shortening processes. Strong rheological weakening

  5. 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

  6. 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.

  7. Implications of a comprehensive, spreading-aligned plate motion reference frame in light of seismic anisotropy and global trench migration

    NASA Astrophysics Data System (ADS)

    Becker, T. W.; Schaeffer, A. J.; Lebedev, S.; Conrad, C. P.

    2015-12-01

    An absolute plate motion model is required to address issues such as the thermo-chemical evolution of Earth's mantle, yet all such models have to rely on indirect inferences. Given that azimuthal seismic anisotropy in the uppermost mantle appears to show fast axes parallel to seafloor spreading, we explore a new, spreading-aligned reference frame. We show that this reference frame indeed fits azimuthal seismic anisotropy from surface waves and SKS splitting very well. The corresponding Euler pole (at 64∘E, 61∘S, with rotation of ~0.25∘/Myr) is close to those of hot spot reference frames, as expected if hot spots were due to relatively stationary mantle plumes. The new Euler pole is also close to that of ridge motion minimizing models, and its amplitude broadly consistent with estimates of net rotation generation by mantle convection with strong continental keels and a weak asthenosphere. The finding that relative spreading aligns with absolute plate motions implies that ridges are passive and that transform faults weak, allowing for easy realignment of spreading centers during slab-driven plate reorganizations. We also explore the implications of our new reference frame for slabs where we find that all of the major eastern Pacific subduction zone trenches are rolling back (away from the overriding plate). Fast trench advance is only predicted in regions with strong corner flow and pivoting (Tonga), continental plate interactions (Sumatra and Caribbean), and most clearly in an ocean-ocean setting for the Philippine Sea Plate where double subduction, slab-slab interactions may explain the fast advance of the Marianas. We conclude that a net rotation pole guided by the spreading-aligned model could indeed represent a comprehensive reference frame for present-day plate motions with respect to the deep mantle.

  8. 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)

  9. 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.

  10. 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…

  11. 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

  12. 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

    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.

  13. 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.

  14. Western Hellenic subduction and Cephalonia Transform: local earthquakes and plate transport and strain

    NASA Astrophysics Data System (ADS)

    Sachpazi, M.; Hirn, A.; Clément, C.; Haslinger, F.; Laigle, M.; Kissling, E.; Charvis, P.; Hello, Y.; Lépine, J.-C.; Sapin, M.; Ansorge, J.

    2000-04-01

    Focal parameters of local earthquakes in the region of the Ionian Islands of western Greece are constrained with a temporary dense array of three-component seismographs operated jointly offshore and onshore. Seismic deformation is documented to be confined to the east of the N20°E-striking steep continental slope west of Cephalonia island, the right-lateral Cephalonia Transform Fault, CTF, inferred from large earthquakes. The pre-Apulian continental material appears to be only deforming east of the transform fault, where it is in upper plate position to the Hellenic subduction. East of the transform fault, the transmission velocity tomography from local earthquakes, compared in depth-section with a previous marine reflection profile, provides evidence in support of a shallow landward dipping boundary around 12 km deep under the Ionian Islands along which they may override the lower plate. On either side of this interface local earthquakes occur with different focal mechanisms, in support with its interpretation as the interplate. Under Cephalonia island, reverse-faulting deforms the upper plate along NW-SE structures, which may also be affected by left-lateral bookshelf-faulting. Small earthquakes show normal faulting along the western coast of Cephalonia and its extension 20 km SSW, the trace of the CTF as inferred from the occurrence of the large strike-slip earthquakes. Another group of normal-fault earthquakes locates in the lower plate from under Cephalonia to Zante, just outboard of a possible change of interplate dip suggested from reflection seismics landward under the islands. These normal-fault earthquakes appear to coincide in position with that of the load imposed by the upper plate transported over them, rather than occurring in an outer rise, outboard the plate boundary and trench, as observed in other subductions and attributed to the control by the flexural bending of the lower plate under the pull of the sinking slab. Interpretation has to

  15. Continental aggregation, subduction initiation, and plume generation

    NASA Astrophysics Data System (ADS)

    Heron, P. J.; Lowman, J. P.

    2013-12-01

    Several processes unfold during the supercontinent cycle, more than one of which might result in an elevation in subcontinental mantle temperatures through the generation of mantle plumes. Paleogeographic plate reconstructions have indicated that sub-continental mantle upwellings appear below large continents that are extensively ringed by subduction zones. Moreover, several numerical simulations of supercontinent formation and dispersal attribute the genesis of sub-continental plumes to the generation of subduction zones on the edges of the supercontinent, rather than resulting from continental insulation. However, the role of the location of downwellings in producing a return-flow upwelling, and on increasing sub-continental mantle temperatures, is not fully understood. In this mantle convection study, we examine the evolution of mantle dynamics after supercontinent accretion over a subduction zone (analogous to the formation of Pangea) for a range of continental coverage. We present 2D and 3D Cartesian geometry mantle convection simulations, featuring geotherm- and pressure-dependent viscosity with thermally and mechanically distinct oceanic and continental plates. Through changing the size of the continent we are able to analyze the factors involved in the generation of mantle plumes in purely thermal convection. Furthermore, we change the upper and lower mantle viscosity to determine their relation to plume formation in vigorous mantle convection simulations. Elevated sub-continental temperatures are analyzed in relation to continental coverage to further understand the influence of continental tectonics on the thermal evolution of the mantle.

  16. Active Arc-Continent Accretion in Timor-Leste: New Structural Mapping and Quantification of Continental Subduction

    NASA Astrophysics Data System (ADS)

    Tate, G. W.; McQuarrie, N.; Bakker, R.; van Hinsbergen, D. J.; Harris, R. A.

    2010-12-01

    The island of Timor represents the active accretion of the Banda volcanic arc to the Australian continental margin. Arc accretion marks the final closure of an ocean basin in the canonic Wilson tectonic cycle, yet the incipient stages as visible now on Timor are still poorly understood. In particular, ocean closure brings continental material into the subduction zone as part of the down-going plate. The positive buoyancy of this subducting continental crust presents a complex problem in crustal dynamics, with possible effects on overall plate motions, migration and/or reversal of the active subduction zone, and the modes of faulting within the upper crust. New mapping in Timor-Leste has provided a detailed view of the structural repetition of Australian continental sedimentary units structurally below overriding Banda Arc material. The central Dili-Same transect begins in the north with the low-grade metamorphic Aileu Formation of Australian affinity, thrust over the time-equivalent more proximal Maubisse Formation to the south. These in turn are thrust over the Australian intra-continental strata, the Triassic Aitutu and the Permian Cribas Formations. The Aitutu and Cribas Formations are deformed in a series of faulted ENE-striking anticlines exposed along the central axis of Timor. The southern end of the transect reveals a 15-km wide piggyback basin of synorogenic marine clays north of another faulted anticline of Aututu and Cribas on the south coast. The eastern Laclo-Barique transect exposes a deeper erosional level, showing three regional NNE-striking thrust faults with approximately 3 km spacing and 50-75 km along-strike extent, each one repeating the Aitutu and Cribas stratigraphy. The strike of Australian-affinity units in the eastern transect is rotated 50-60 degrees to the north compared to the units in the central transect. The Jurassic Wailuli shales and the Bobonaro tectonic mélange act as the upper décollement between this duplex and the Lolotoi

  17. 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

  18. 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.

  19. 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.

  20. 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…

  1. Continental Rifts

    NASA Astrophysics Data System (ADS)

    Rosendahl, B. R.

    Continental Rifts, edited by A. M. Quennell, is a new member of the Benchmark Papers in Geology Series, edited in toto by R. W. Fairbridge. In this series the individual volume editors peruse the literature on a given topic, select a few dozen papers of ostensibly benchmark quality, and then reorder them in some sensible fashion. Some of the original papers are republished intact, but many are chopped into “McNuggets™” of information. Depending upon the volume editor, the chopping process can range from a butchering job to careful and prudent pruning. The collecting, sifting, and reorganizing tasks are, of course, equally editor-sensitive. The end product of this series is something akin to a set of Reader's Digest of Geology.

  2. 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.

  3. Characteristics and Consequences of Drug Allergy Alert Overrides in a Computerized Physician Order Entry System

    PubMed Central

    Hsieh, Tyken C.; Kuperman, Gilad J.; Jaggi, Tonushree; Hojnowski-Diaz, Patricia; Fiskio, Julie; Williams, Deborah H.; Bates, David W.; Gandhi, Tejal K.

    2004-01-01

    Objective: The aim of this study was to determine characteristics of drug allergy alert overrides, assess how often they lead to preventable adverse drug events (ADEs), and suggest methods for improving the allergy-alerting system. Design: Chart review was performed on a stratified random subset of all allergy alerts occurring during a 3-month period (August through October 2002) at a large academic hospital. Measurements: Factors that were measured were drug/allergy combinations that triggered alerts, frequency of specific override reasons, characteristics of ADEs, and completeness of allergy documentation. Results: A total of 6,182 (80%) of 7,761 alerts were overridden in 1,150 patients. In this sample, only 10% of alerts were triggered by an exact match between the drug ordered and allergy listed. Physicians' most common reasons for overriding alerts were “Aware/Will monitor” (55%), “Patient does not have this allergy/tolerates” (33%), and “Patient taking already” (10%). In a stratified random subset of 320 patients (28% of 1,150) on chart review, 19 (6%) experienced ADEs attributed to the overridden drug; of these, 9 (47%) were serious. None of the ADEs was considered preventable, because the overrides were deemed clinically justifiable. The degree of completeness of patients' allergy lists was highly variable and generally low in both paper charts and the CPOE system. Conclusion: Overrides of drug-allergy alerts were common and about 1 in 20 resulted in ADEs, but all of the overrides resulting in ADEs appeared clinically justifiable. The high rate of alert overrides was attributable to frequent nonexact match alerts and infrequent updating of allergy lists. Based on these findings, we have made specific recommendations for increasing the specificity of alerting and thereby improving the clinical utility of the drug allergy alerting system. PMID:15298998

  4. 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.

  5. 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.

  6. 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

  7. Magmatic processes that generate chemically distinct silicic magmas in NW Costa Rica and the evolution of juvenile continental crust in oceanic arcs

    NASA Astrophysics Data System (ADS)

    Vogel, T. A.; Deering, C. D.; Patino, L. C.; Alvarado, G. E.; Szymanski, D. W.

    2010-12-01

    Northwestern Costa Rica is built upon an oceanic plateau that has developed chemical and geophysical characteristics of the upper continental crust. A major factor in converting the oceanic plateau to continental crust is the production, evolution and emplacement of silicic magmas. In Costa Rica, the Caribbean Large Igneous Province (CLIP) forms the overriding plate in the subduction of the Cocos Plate - a process that has occurred for at least the last 25 my. Igneous rocks in Costa Rica older than about 10 Ma have chemical compositions typical of oceanic basalts and intra-oceanic arcs. In contrast, younger igneous deposits (<10 Ma) contain abundant silicic rocks with geochemical signatures similar to the average continental crust, which are significantly enriched in SiO2, alkalis and light rare-earth elements. The silicic deposits of NW Costa Rica occur in two major compositional groups: a high-Ti and a low-Ti group with no overlap between the two. The major and trace element characteristics of these groups are consistent with these magmas being derived from liquids that were extracted from crystal mushes. In relative terms, the high-Ti silicic liquids were extracted from a hot, dry crystal mush with low-oxygen fugacity where plagioclase and pyroxene were the dominant phases crystallizing, along with lesser amounts of hornblende. In contrast, the low-Ti silicic liquids were extracted from a cool, wet crystal mush with high oxygen fugacity where plagioclase and amphibole were the dominant phases crystallizing. The hot-dry-reducing magmas dominate the older sequence, but the youngest sequence contains only magmas from the cold-wet-oxidized group. Silicic volcanic deposits from other oceanic arcs (e.g. Izu-Bonin, Marianas) have chemical characteristics distinctly different from continental crust, whereas the NW Costa Rican silicic deposits have chemical characteristics nearly identical to the upper continental crust. The transition in NW Costa Rica from mafic oceanic

  8. 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.

  9. 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

  10. 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

  11. 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)

  12. Mesozoic Plate Tectonic Evolution of the Northern Margin of Pangea

    NASA Astrophysics Data System (ADS)

    Miller, E. L.

    2011-12-01

    Canadian margin and the Arctic-Siberian margin) might be explained by along-strike differences in the nature of motion of the overriding (continental) plate with respect to paleo-Pacific subduction zones (towards vs. away).

  13. BOLIVAR & GEODINOS: Investigations of the Southern Caribbean Plate Boundary

    NASA Astrophysics Data System (ADS)

    Levander, A.; Schmitz, M.; Working Groups, B.

    2006-12-01

    , and is associated with broad uplift of the coastal regions. This is likely a site of continental growth. 2) The accretionary wedge terranes of the Southern Caribbean Deformed Belt formed in the Neogene, and extend as far east as the Aves Ridge. They result from SA overriding the CAR LIP, which for a number of reasons, we do not regard as normal subduction. 3) Igneous rocks on the islands of the Leeward Antilles arc, Aruba to Los Testigos, show a steady decrease in age from west to east (94.7-37.4 Ma), suggesting that the islands have been progressively captured from the Antilles arc by the plate boundary during the prolonged island arc-continent collision. Terrane capture models thus far cannot completely explain the data. 4) High (> 6.5 km/s) P-velocity bodies are found in the shallow crust along the main strike-slip faults along much of the plate boundary. We interpret these as elements of the HP/LT metamorphic terranes found in the adjacent thrust belts of central Venezuela. This suggests to us that displacement partitioning in the trench and subsequent strike-slip both play important roles in exhumation of the HP/LT terranes. 5) Crustal thickness variations in the plate boundary region are large (> 10 km), of short spatial wavelength (< 100 km), and indicate that the highest elevations of the coastal mountain belts are not supported isostatically.

  14. 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.

  15. Revenue/Expenditure Limits and Override Elections: The Experience of California School Districts.

    ERIC Educational Resources Information Center

    Osman, Jack W.; Gemello, John M.

    The revenue and expenditure limit contained in California's SB-90 legislation was the legislature's response to the Supreme Court's mandate to equalize spending among the state's public schools. An escape valve written into SB-90 granted districts the power to override the revenue limit by a simple majority vote. This paper examines the strategies…

  16. Family override of valid donor consent to postmortem donation: issues in law and practice.

    PubMed

    Downie, J; Shea, A; Rajotte, C

    2008-06-01

    In 2005, 3974 Canadians were on waiting lists for organ transplants and 275 patients died while waiting. Canada's organ shortage has led to calls for changes to Canada's organ donation system and its legal framework. Herein we examine an issue in which law reform could both increase the number of available organs and better align practice with respect for autonomy, a core value underpinning the Canadian legal system: the issue of family overrides of a valid donor consent to postmortem donation. That is, we examine what should happen when an individual consented to postmortem donation but the family would like to override that consent. First, we examine the requirements for valid donor consent. Second, we consider the legal status of family overrides of valid donor consent in relation to postmortem donation. Third, we describe the available data with regard to the practice of permitting families to override valid donor consent and discuss the possible reasons for this practice. Finally, we describe and defend the desired results with respect to law reform and describe the actions needed to realize these results. PMID:18589083

  17. Continental Growth and the Sedimentary Record

    NASA Astrophysics Data System (ADS)

    Dhuime, B.; Hawkesworth, C. J.; Robinson, R. A. J.; Cawood, P. A.

    2014-12-01

    Detrital sedimentary rocks provide average samples of the continental crust formed at different times and in different places. Some materials are more susceptible to erosion and/or to preservation bias than others, and one issue is to understand how the compositions of a range of source rocks are then recorded in the sediments. Here we considered two different approaches to model the growth of the continental crust: (i) The variation of Nd isotopes in continental shales with different deposition ages, which requires a correction of the bias induced by preferential erosion of younger rocks through an erosion parameter usually referred to as 'K'. The determination of K, and the extent to which it varies in different erosion systems, thus have fundamental implications for the models of continental growth based on radiogenic isotopes in continental sediments. (ii) The variations in U-Pb, Hf and O isotopes in detrital zircons, from 'modern' sediments sampled worldwide. In this approach, O isotopes are used to screen 'hybrid' Hf model ages (i.e. ages resulting from mixing processes of crustal material from different ages) from Hf model ages that represent actual crust formation ages. These two approaches independently suggest that the continental crust has been generated continuously, but with a marked decrease in the continental growth rate at ~3 Ga. The >4 Ga to ~3 Ga period is characterised by relatively high net rates of continental growth (~3.0 km3.a-1), which are similar to the rates at which new crust is generated, and destroyed, at the present time. Net growth rates are much lower since 3 Ga (~0.8 km3.a-1), which may be attributed to higher rates of destruction of continental crust. The inflexion in the continental growth curve at ~3 Ga indicates a change in the way the crust was generated and preserved. This change may be linked to onset of subduction-driven plate tectonics and discrete subduction zones.

  18. 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.

  19. 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

  20. Aeromagnetic data and geological structure of continental China: A review

    NASA Astrophysics Data System (ADS)

    Xiong, Sheng-Qing; Tong, Jing; Ding, Yan-Yun; Li, Zhan-Kui

    2016-06-01

    We review the latest aeromagnetic geological data of continental China. We discuss the latest achievements in geological mapping and the newly detected features based on aeromagnetic data. Using aeromagnetic data collected for more than 50 years, a series of 1:5000000 and 1:1000000 aeromagnetic maps of continental China were compiled using state-of-the-art digital technology, and data processing and transformation. Guided by plate tectonics and continental dynamics, rock physical properties, and magnetic anomalies, we compiled maps of the depth of the magnetic basement of continental China and the major geotectonic units, and presented newly detected geological structures based on the aeromagnetic data.

  1. Upper Plate Tectonics and Fluid Flow Along the Middle America Convergent Margin

    NASA Astrophysics Data System (ADS)

    Huguen, C.; Ranero, C. R.; Weinrebe, W.; Sahling, H.; Borhmann, G.; Klaucke, I.

    2002-12-01

    We present new multibeam bathymetry, side scan sonar, sub-bottom profiling, deep towed video camera images and sampling from active structures related to tectonics and fluid flow at the overriding plate of the Middle America subduction zone. Data were collected during SONNE 163-1 cruise at key locations based on full bathymetric coverage of the margin with a ~ 100 m grid. We surveyed normal faults along the middle-upper continental slope and associated mounds. Also, the locus of seamount subduction was investigated. The new bathymetry has been gridded at ~ 25 m. Deep towed side scan sonar data have a resolution of ~ 1 m. Subbottom high resolution profiling images the upper ~ 100 m of slope sediment. Deep towed camera observations and sampling were used to ground truth the geophysical data. The canyon system present in the upper slope terminates abruptly at the ~ mid slope where normal faulting develops. Roughly coincident with the faulting development, groups of small mounds (few 100s m to 1 km long and < 100 m to 150 m high) occur along the upper-middle slope. These mounds, previously interpreted as mud volcanoes, do not show evidence of mud flows in the side scan data. Deep towed camera and dredging at numerous locations indicate that the surface of the mounds is made of chemoherm carbonates that yield a characteristic high reflectivity in back scatter images. The mounds seem to be areas of fluid discharge and chemosynthetic fauna was observed locally in all of the structures investigated. The mounds are spatially coincident and may be associated to the development of the faults. Their fate may also be related to the faulting: mounds disappear downslope as the fault throw increases. Data from the areas of active seamount subduction show clear evidence for recent/ongoing tectonism at the uplifted overriding plate. The largest deformation occurs at the summit of the uplift and at the trail of the seamount where sliding and slumping are active. Areas of the summit

  2. Magmatic processes that generate chemically distinct silicic magmas in NW Costa Rica and the evolution of juvenile continental crust in oceanic arcs

    NASA Astrophysics Data System (ADS)

    Deering, Chad D.; Vogel, Thomas A.; Patino, Lina C.; Szymanski, David W.; Alvarado, Guillermo E.

    2012-02-01

    Northwestern Costa Rica is built upon an oceanic plateau that has developed chemical and geophysical characteristics of the upper continental crust. A major factor in converting the oceanic plateau to continental crust is the production, evolution, and emplacement of silicic magmas. In Costa Rica, the Caribbean Large Igneous Province (CLIP) forms the overriding plate in the subduction of the Cocos Plate—a process that has occurred for at least the last 25 my. Igneous rocks in Costa Rica older than about 8 Ma have chemical compositions typical of ocean island basalts and intra-oceanic arcs. In contrast, younger igneous deposits contain abundant silicic rocks, which are significantly enriched in SiO2, alkalis, and light rare-earth elements and are geochemically similar to the average upper continental crust. Geophysical evidence (high Vp seismic velocities) also indicates a relatively thick (~40 km), addition of evolved igneous rocks to the CLIP. The silicic deposits of NW Costa Rica occur in two major compositional groups: a high-Ti and a low-Ti group with no overlap between the two. The major and trace element characteristics of these groups are consistent with these magmas being derived from liquids that were extracted from crystal mushes—either produced by crystallization or by partial melting of plutons near their solidi. In relative terms, the high-Ti silicic liquids were extracted from a hot, dry crystal mush with low oxygen fugacity, where plagioclase and pyroxene were the dominant phases crystallizing, along with lesser amounts of hornblende. In contrast, the low-Ti silicic liquids were extracted from a cool, wet crystal mush with high oxygen fugacity, where plagioclase and amphibole were the dominant phases crystallizing. The hot-dry-reducing magmas dominate the older sequence, but the youngest sequence contains only magmas from the cold-wet-oxidized group. Silicic volcanic deposits from other oceanic arcs (e.g., Izu-Bonin, Marianas) have chemical

  3. 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.

  4. SU-E-T-599: Patient Safety Enhancements Through a Study of R&V System Override Data

    SciTech Connect

    Hendrickson, K; Vimolchalao, S

    2015-06-15

    Purpose: Record and verify (R&V) software systems include safety checks that compare actual machine parameters with prescribed values for a patient’s treatment, such as treatment couch position, linac, energy, and MUs. The therapist is warned of a mismatch with a pop-up and prompted to approve an override in order to continue without changes. Override approval is often legitimate, but the pop-up can also genuinely indicate a problem that would Result in the wrong treatment. When there are numerous pop-up warnings, human nature leads us to approve any override without careful reading, undermining the effectiveness of the safety mechanism. Methods: Override data was collected from our R&V system for all patients treated between October 8 and 29, 2012, on four linacs and entered into a spreadsheet. Additional data collected included treatment technique, disease site, immobilization, time, linac, and whether localization images were obtained. Data were analyzed using spreadsheet tools to reveal trends, patterns and associations that might suggest appropriate process changes that could decrease the total number of overrides. Results: 76 out of 113 patients had overrides. Out of the 944 treatments, 599 override items were generated. The majority were due to couch positions. 74 of the 84 overrides on a linac equipped with a 6D couch were due to the use of the rotational corrections and the fact that the 6D couch control does not communicate with the R&V system; translations required to rotate the couch appear to the R&V system as translations outside the tolerance range. Conclusion: Many findings were interesting but did not suggest a process change. Proposed process changes include creating site-specific instead of just technique-specific tolerance tables for couch shifts. Proposed improvements to the vendor are to facilitate direct communication between the 6D couch and the R&V system to eliminate those override warnings related to lack of communication.

  5. 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

  6. Subduction-Driven Recycling of Continental Margin Lithosphere

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    While subduction recycling of oceanic lithosphere is one of the central themes of plate tectonics, recycling continental lithosphere appears far more complicated and is 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 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 arrays on opposite sides of the Atlantic show higher than expected volumes of positive anomalies identified as the subducted Atlantic (ATL) slab under northeastern South America (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. 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. Secondary downwellings develop under the continental interior inland from the subduction zone: We image one under SA and one or more in the past were likely under GA. The process of subduction-driven continental margin lithosphere removal reconciles numerous, sometimes mutually

  7. 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.

  8. Are We Heeding the Warning Signs? Examining Providers’ Overrides of Computerized Drug-Drug Interaction Alerts in Primary Care

    PubMed Central

    Slight, Sarah P.; Seger, Diane L.; Nanji, Karen C.; Cho, Insook; Maniam, Nivethietha; Dykes, Patricia C.; Bates, David W.

    2013-01-01

    Background Health IT can play a major role in improving patient safety. Computerized physician order entry with decision support can alert providers to potential prescribing errors. However, too many alerts can result in providers ignoring and overriding clinically important ones. Objective To evaluate the appropriateness of providers’ drug-drug interaction (DDI) alert overrides, the reasons why they chose to override these alerts, and what actions they took as a consequence of the alert. Design A cross-sectional, observational study of DDI alerts generated over a three-year period between January 1st, 2009, and December 31st, 2011. Setting Primary care practices affiliated with two Harvard teaching hospitals. The DDI alerts were screened to minimize the number of clinically unimportant warnings. Participants A total of 24,849 DDI alerts were generated in the study period, with 40% accepted. The top 62 providers with the highest override rate were identified and eight overrides randomly selected for each (a total of 496 alert overrides for 438 patients, 3.3% of the sample). Results Overall, 68.2% (338/496) of the DDI alert overrides were considered appropriate. Among inappropriate overrides, the therapeutic combinations put patients at increased risk of several specific conditions including: serotonin syndrome (21.5%, n=34), cardiotoxicity (16.5%, n=26), or sharp falls in blood pressure or significant hypotension (28.5%, n=45). A small number of drugs and DDIs accounted for a disproportionate share of alert overrides. Of the 121 appropriate alert overrides where the provider indicated they would “monitor as recommended”, a detailed chart review revealed that only 35.5% (n=43) actually did. Providers sometimes reported that patients had already taken interacting medications together (15.7%, n=78), despite no evidence to confirm this. Conclusions and Relevance We found that providers continue to override important and useful alerts that are likely to cause

  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. Characteristics and effects of nurse dosing over-rides on computer-based intensive insulin therapy protocol performance

    PubMed Central

    May, Addison K; Waitman, Lemuel R; Ozdas, Asli; Lorenzi, Nancy M; Gadd, Cynthia S

    2011-01-01

    Objective To determine characteristics and effects of nurse dosing over-rides of a clinical decision support system (CDSS) for intensive insulin therapy (IIT) in critical care units. Design Retrospective analysis of patient database records and ethnographic study of nurses using IIT CDSS. Measurements The authors determined the frequency, direction—greater than recommended (GTR) and less than recommended (LTR)— and magnitude of over-rides, and then compared recommended and over-ride doses' blood glucose (BG) variability and insulin resistance, two measures of IIT CDSS associated with mortality. The authors hypothesized that rates of hypoglycemia and hyperglycemia would be greater for recommended than over-ride doses. Finally, the authors observed and interviewed nurse users. Results 5.1% (9075) of 179 452 IIT CDSS doses were over-rides. 83.4% of over-ride doses were LTR, and 45.5% of these were ≥50% lower than recommended. In contrast, 78.9% of GTR doses were ≤25% higher than recommended. When recommended doses were administered, the rate of hypoglycemia was higher than the rate for GTR (p=0.257) and LTR (p=0.033) doses. When recommended doses were administered, the rate of hyperglycemia was lower than the rate for GTR (p=0.003) and LTR (p<0.001) doses. Estimates of patients' insulin requirements were higher for LTR doses than recommended and GTR doses. Nurses reported trusting IIT CDSS overall but appeared concerned about recommendations when administering LTR doses. Conclusion When over-riding IIT CDSS recommendations, nurses overwhelmingly administered LTR doses, which emphasized prevention of hypoglycemia but interfered with hyperglycemia control, especially when BG was >150 mg/dl. Nurses appeared to consider the amount of a recommended insulin dose, not a patient's trend of insulin resistance, when administering LTR doses overall. Over-rides affected IIT CDSS protocol performance. PMID:21402737

  11. Seismic slip on an upper-plate normal fault during a large subduction megathrust rupture

    NASA Astrophysics Data System (ADS)

    Hicks, Stephen P.; Rietbrock, Andreas

    2016-04-01

    Quantification of stress accumulation and release during subduction zone seismic cycles requires an understanding of the distribution of fault slip during earthquakes. Reconstructions of slip are typically constrained to a single, known fault plane. Yet, slip has been shown to occur on multiple faults within the subducting plate owing to stress triggering, resulting in phenomena such as earthquake doublets. However, rapid stress triggering from the plate interface to faults in the overriding plate has not been documented before. We have analysed seismic data from the magnitude 7.1 Araucania earthquake that occurred in the Chilean subduction zone in January 2011. We find that the earthquake, which was reported as a single event in global moment tensor solutions, was instead composed of two ruptures on two separate faults. We use 3-D full waveform simulations to better constrain the centroid of the second rupture. Within 12 s, a thrust earthquake (Mw 6.8) on the plate interface triggered a second large rupture on a normal fault 30 km away in the overriding plate (Mw 6.7). We define this set of events as a 'closely spaced doublet' (CSD). This configuration of partitioned rupture is consistent with normal-faulting mechanisms in the ensuing aftershock sequence. We conclude that plate interface rupture can trigger almost instantaneous slip in the overriding plate of a subduction zone. This shallow upper-plate rupture may be masked from teleseismic data, posing a challenge for real-time tsunami warning systems.

  12. 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

  13. 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.

  14. Freshly brewed continental crust

    NASA Astrophysics Data System (ADS)

    Gazel, E.; Hayes, J. L.; Caddick, M. J.; Madrigal, P.

    2015-12-01

    Earth's crust is the life-sustaining interface between our planet's deep interior and surface. Basaltic crusts similar to Earth's oceanic crust characterize terrestrial planets in the solar system while the continental masses, areas of buoyant, thick silicic crust, are a unique characteristic of Earth. Therefore, understanding the processes responsible for the formation of continents is fundamental to reconstructing the evolution of our planet. We use geochemical and geophysical data to reconstruct the evolution of the Central American Land Bridge (Costa Rica and Panama) over the last 70 Ma. We also include new preliminary data from a key turning point (~12-6 Ma) from the evolution from an oceanic arc depleted in incompatible elements to a juvenile continental mass in order to evaluate current models of continental crust formation. We also discovered that seismic P-waves (body waves) travel through the crust at velocities closer to the ones observed in continental crust worldwide. Based on global statistical analyses of all magmas produced today in oceanic arcs compared to the global average composition of continental crust we developed a continental index. Our goal was to quantitatively correlate geochemical composition with the average P-wave velocity of arc crust. We suggest 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 Achaean where most continental landmasses formed, can produce the starting material necessary for juvenile continental crust formation.

  15. Overriding "doing wrong" and "not doing right": validation of the Dispositional Self-Control Scale (DSC).

    PubMed

    Ein-Gar, Danit; Sagiv, Lilach

    2014-01-01

    We present the Dispositional Self-Control (DSC) Scale, which reflects individuals' tendency to override 2 types of temptations, termed doing wrong and not doing right. We report a series of 5 studies designed to test the reliability and validity of the scale. As hypothesized, high DSC predicts distant future orientation and low DSC predicts deviant behaviors such as aggression, alcohol misuse, and aberrant driving. DSC also predicts task performance among resource-depleted participants. Taken together, these findings suggest that the DSC Scale could be a useful tool toward further understanding the role of personality in overcoming self-control challenges. PMID:24611844

  16. Dual fuel gradients in uranium silicide plates

    SciTech Connect

    Pace, B.W.

    1997-08-01

    Babcock & Wilcox has been able to achieve dual gradient plates with good repeatability in small lots of U{sub 3}Si{sub 2} plates. Improvements in homogeneity and other processing parameters and techniques have allowed the development of contoured fuel within the cladding. The most difficult obstacles to overcome have been the ability to evaluate the bidirectional fuel loadings in comparison to the perfect loading model and the different methods of instilling the gradients in the early compact stage. The overriding conclusion is that to control the contour of the fuel, a known relationship between the compact, the frames and final core gradient must exist. Therefore, further development in the creation and control of dual gradients in fuel plates will involve arriving at a plausible gradient requirement and building the correct model between the compact configuration and the final contoured loading requirements.

  17. Numerical comparison of different convergent plate contacts: subduction channel and subduction fault

    NASA Astrophysics Data System (ADS)

    De Franco, Roberta; Govers, Rob; Wortel, Rinus

    2007-10-01

    At convergent plate boundaries, the properties of the actual plate contact are important for the overall dynamics. Convergent plate boundaries both mechanically decouple and link tectonic plates and accommodate large amounts of strain. We investigate two fundamental physical states of the subduction contact: one based on a fault and the other based on a subduction channel. Using a finite element method, we determine the specific signatures of both states of the subduction contact. We pay particular attention to the overriding plate. In a tectonic setting of converging plates, where the subducting plate is freely moving, the subduction channel reduces compression relative to the fault model. In a land-locked basin setting, where the relative motion between the far field of the plates is zero, the subduction channel model produces tensile stress regime in the overriding plate, even though the amount of slab roll-back is small. The fault model shows a stronger development of slab roll-back and a compressive stress regime in the upper plate. Based on a consistent comparison of fault and channel numerical models, we find that the nature of the plate contact is one of the controlling factors in developing or not of backarc extension. We conclude that, the type of plate contact plays a decisive role in controlling the backarc state of stress. To obtain backarc extension, roll-back is required as an underling geodynamic process, but it is not always a sufficient condition.

  18. 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

  19. Plate tectonics conserves angular momentum

    NASA Astrophysics Data System (ADS)

    Bowin, C.

    2009-03-01

    of seafloor spreading) are adjustment zones that accommodate strains in the lithosphere. Further, the interlocked pattern of the Australian and Pacific plates the past 42 Million years (with their absolute plate motions near 90° to each other) is taken as strong evidence that large thermally driven "roller" convection cells previously inferred as the driving mechanism in earlier interpretations of continental drift and plate tectonics, have not been active in the Earth's mantle the past 42 Million years, if ever. This report also presents estimates of the changes in location and magnitude of the Earth's axis of total plate tectonic angular momentum for the past 62 million years.

  20. 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.

  1. 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.

  2. Continental rifting - Progress and outlook

    NASA Technical Reports Server (NTRS)

    Baker, B. H.; Morgan, P.

    1981-01-01

    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.

  3. 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.

  4. Petrogenesis of Cretaceous mafic intrusive rocks in the Fosdick Mountains, Marie Byrd Land, West Antarctica: melting of metasomatized sub-continental arc mantle along the active plate margin of Gondwana

    NASA Astrophysics Data System (ADS)

    Saito, S.; Brown, M.; Korhonen, F. J.; Mcfadden, R. R.; Siddoway, C. S.

    2013-12-01

    A diorite pluton and widely distributed mafic dykes occur in the Fosdick migmatite-granite complex, which is interpreted to represent middle-to-lower crustal rocks of the paleo-Pacific active continental margin of Gondwana. The mafic dykes exhibit a variety of relationships with host rocks in the field ranging from undeformed dykes with sharp contacts with host gneisses to dismembered dykes with comingled textures and numerous back-veins of leucosome intruded from host migmatitic gneisses suggestive of significant interaction with crustal rocks. U-Pb ages for magmatic zircon in these rocks yields Cretaceous crystallization ages ranging from ca. 113 Ma to ca. 98 Ma for the mafic dykes and ca. 100 Ma for the diorite pluton. These mafic intrusive rocks, which contain abundant hydrous minerals, are medium- to high-K-series calc-alkaline rocks with basic-intermediate compositions (47-59 wt % SiO2 for mafic dykes and 52-56 wt % SiO2 for the diorite pluton). They have trace element patterns characterized by LILE enrichments and negative Nb anomalies indicating an origin from a hydrous mantle source metasomatized by slab-derived components. The samples without evidence of interaction with crustal rocks, which are likely to better reflect the mantle source composition, have positive ɛSr(100Ma) values (+8.1 to +14.5) and negative to slightly positive ɛNd(100Ma) values (-1.6 to +2.5) consistent with derivation from an enriched mantle source. These samples may be divided into two groups either characterized by higher LILE/HFSE ratios, less radiogenic ɛSr(100Ma) values and more radiogenic ɛNd(100Ma) values, or characterized by relatively lower LILE/ HFSE ratios, more radiogenic ɛSr(100Ma) values and less radiogenic ɛNd(100Ma) values suggesting differences in the mantle source. The results of this study are consistent with melting of a variably metasomatized sub-arc mantle source during a transition from a wrench to a transtensional tectonic setting, but are inconsistent

  5. Subduction evolution and mantle dynamics at a continental margin: Central North Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Stern, T. A.; Stratford, W. R.; Salmon, M. L.

    2006-12-01

    Central North Island, New Zealand, provides an unusually complete geological and geophysical record of the onset and evolution of subduction at a continental margin. Whereas most subduction zones are innately two-dimensional, North Island of New Zealand displays a distinct three-dimensional character in the back-arc regions. Specifically, we observe "Mariana-type" subduction in the back-arc areas of central North Island in the sense of back-arc extension, high heat flow, prolific volcanism, geothermal activity, and active doming and exhumation of the solid surface. Evidence for emplacement of a significant percent of new lithosphere beneath the central North Island comes from heat flux of 25 MW/km of strike (of volcanic zone) and thinned crust underlain by rocks with a seismic wave speed consistent with underplated new crust. Seismic attenuation (Qp-1) is high (˜240), and rhyolitic and andesitic volcanism are widespread. Almost complete removal of mantle lithosphere is inferred here in Pliocene times on the basis of the rock uplift history and upper mantle seismic velocities as low as 7.4 ± 0.1 km/s. In contrast, southwestern North Island exhibits "Chilean-type" back-arc activity in the sense of compressive tectonics, reverse faulting, low-heat-flow, thickened lithosphere, and strong coupling between the subducted and overriding plates. This rapid switch from Mariana-type to Chilean-type subduction occurs despite the age of the subducted plate being constant under North Island. Moreover, stratigraphic evidence shows that processes that define the extensional back-arc area (the Central Volcanic Region) are advancing southward into the compressional system (Wanganui Basin) at about 10 mm/yr. We link the progression from one system to another to a gradual and viscous removal of thickened mantle lithosphere in the back-arc regions. Thickening occurred during the Miocene within the Taranaki Fault Zone. The process of thickening and convective removal is time- and

  6. Relationship between plume and plate tectonics

    NASA Astrophysics Data System (ADS)

    Puchkov, V. N.

    2016-07-01

    The relationship between plate- and plume-tectonics is considered in view of the growth and breakdown of supercontinents, active rifting, the formation of passive volcanic-type continental margins, and the origin of time-progressive volcanic chains on oceanic and continental plates. The mantle wind phenomenon is described, as well as its effect on plume morphology and anisotropy of the ambient mantle. The interaction of plumes and mid-ocean ridges is discussed. The principles and problems of plume activity analysis in subduction- and collision-related foldbelts are considered and illustrated with examples.

  7. Overriding parents' medical decisions for their children: a systematic review of normative literature.

    PubMed

    McDougall, Rosalind J; Notini, Lauren

    2014-07-01

    This paper reviews the ethical literature on conflicts between health professionals and parents about medical decision-making for children. We present the results of a systematic review which addressed the question 'when health professionals and parents disagree about the appropriate course of medical treatment for a child,under what circumstances is the health professional ethically justified in overriding the parents' wishes?’ We identified nine different ethical frameworks that were put forward by their authors as applicable across various ages and clinical scenarios. Each of these frameworks centred on a different key moral concept including harm,constrained parental autonomy, best interests, medically reasonable alternatives, responsible thinking and rationality. PMID:23824967

  8. 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

  9. The adenovirus E1A protein overrides the requirement for cellular ras in initiating DNA synthesis.

    PubMed Central

    Stacey, D W; Dobrowolski, S F; Piotrkowski, A; Harter, M L

    1994-01-01

    The adenovirus E1A protein can induce cellular DNA synthesis in growth-arrested cells by interacting with the cellular protein p300 or pRb. In addition, serum- and growth factor-dependent cells require ras activity to initiate DNA synthesis and recently we have shown that Balb/c 3T3 cells can be blocked in either early or late G1 following microinjection of an anti-ras antibody. In this study, the E1A 243 amino acid protein is shown through microinjection not only to shorten the G0 to S phase interval but, what is more important, to override the inhibitory effects exerted by the anti-ras antibody in either early or late G1. Specifically, whether E1A is co-injected with anti-ras into quiescent cells or injected 18 h following a separate injection of anti-ras after serum stimulation, it efficiently induces cellular DNA synthesis in cells that would otherwise be blocked in G0/G1. Moreover, injection of a mutant form of E1A that can no longer associate with p300 is just as efficient as wild-type E1A in stimulating DNA synthesis in cells whose ras activity has been neutralized by anti-ras. The results presented here show that E1A is capable of overriding the requirement of cellular ras activity in promoting the entry of cells into S phase. Moreover, the results suggest the possibility that pRb and/or pRb-related proteins may function in a ras-dependent pathway that enables E1A to achieve this activity. Images PMID:7813447

  10. Effects of successive relearning on recall: Does relearning override the effects of initial learning criterion?

    PubMed

    Vaughn, Kalif E; Dunlosky, John; Rawson, Katherine A

    2016-08-01

    Retrieval practice improves memory for many kinds of materials, and numerous factors moderate the benefits of retrieval practice, including the amount of successful retrieval practice (referred to as the learning criterion). In general, the benefits of retrieval practice are greater with more than with less successful retrieval practice; however, learning items to a higher (vs. lower) criterion requires more time and effort. If students plan on relearning material in a subsequent study session, does the benefit of learning to a higher criterion during an initial session persist? In Session 1, participants studied and successfully recalled Swahili-English word pairs one, two, three, four, five, six, or seven times. In subsequent sessions, all of the pairs were relearned to a criterion of one correct recall at one-week intervals across four or five successive relearning sessions. Experiments 1 and 2 revealed that the substantial benefits of learning to a higher initial criterion during the first session do not persist across relearning sessions. This relearning-override effect was also demonstrated in Experiment 2 after a one-month retention interval. The implications of relearning-override effects are important for theory and for education. For theories of test-enhanced learning, they support the predictions of one theory and appear inconsistent with the predictions of another. For education, if relearning is to occur, using extra time to learn to a higher initial learning criterion is not efficient. Instead, students should devote their time to subsequent spaced relearning sessions, which produce substantial gains in recall performance. PMID:27027887

  11. 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.

  12. 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

  13. Continental rift jumps

    NASA Astrophysics Data System (ADS)

    Wood, Charles A.

    1983-05-01

    Continental rift jumps, analogous to jumps of oceanic spreading ridges, are here proposed to be common. Good examples exist in Iceland and Afar (both transitional from ridge to rift jumps), West Africa (Benue Trough and Cameroon Volcanic Line), and Kenya. Indeed, the Kenya rift appears to have jumped c. 100 km eastward c. 10 m.y. ago and is currently jumping further to the east. Possible jumps exist in the Baikal rift, the Limagne-Bresse rift pair, and parallel to ancient continental margins (e.g., the Triassic basins of the eastern U.S. to Baltimore Canyon and Georges Bank). Continental rifts jump distances that are approximately equal to local lithosphere thickness, suggesting that jumped rifts are controlled by lithosphere fracturing, but there appears to be no reason for the fracturing except migration of hot spots.

  14. 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

  15. 43 CFR 3512.19 - Must I notify BLM if I intend to transfer an overriding royalty to another party?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 43 Public Lands: Interior 2 2012-10-01 2012-10-01 false Must I notify BLM if I intend to transfer an overriding royalty to another party? 3512.19 Section 3512.19 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR...

  16. 43 CFR 3512.19 - Must I notify BLM if I intend to transfer an overriding royalty to another party?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 43 Public Lands: Interior 2 2014-10-01 2014-10-01 false Must I notify BLM if I intend to transfer an overriding royalty to another party? 3512.19 Section 3512.19 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR...

  17. 43 CFR 3512.19 - Must I notify BLM if I intend to transfer an overriding royalty to another party?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 43 Public Lands: Interior 2 2013-10-01 2013-10-01 false Must I notify BLM if I intend to transfer an overriding royalty to another party? 3512.19 Section 3512.19 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR...

  18. 43 CFR 3512.19 - Must I notify BLM if I intend to transfer an overriding royalty to another party?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 43 Public Lands: Interior 2 2011-10-01 2011-10-01 false Must I notify BLM if I intend to transfer an overriding royalty to another party? 3512.19 Section 3512.19 Public Lands: Interior Regulations Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR...

  19. Tectonic and sedimentary evolution of a Cretaceous continental arc-backarc system in the Korean peninsula: New view

    NASA Astrophysics Data System (ADS)

    Chough, S. K.; Sohn, Y. K.

    2010-08-01

    This paper focuses on the tectonic and sedimentary evolution of the Cretaceous volcanic rocks and nonmarine successions in the southeastern part of the Korean peninsula, which constitute an ancient continental arc system. The arc system (Gyeongsang Arc System), comprising an arc platform (Gyeongsang Volcanic Arc) and a backarc basin (Gyeongsang Backarc Basin), was a southwestward extension of the Japanese Arc formed by oblique northward subduction of the proto-Pacific (Izanagi) plate under the Asian continent. The backarc basin was initiated in the southeastern part of the Korean peninsula in the Early Cretaceous as a narrow NS-trending trough. The basin was bounded by a major fault in the northern part of the basin from which sediments largely emanated. Sediments were deposited in streamflow-dominated alluvial fans adjacent to the fault-bounded basin margin in the north and low-gradient fluvial systems of braided channels that extended southward and southeastward for tens of kilometers. Sediments were also derived from the western highland margin, draining Precambrian to Jurassic basement rocks. The initially narrow trough progressively expanded toward the east, resulting in eastward migration of depocenters that eventually generated a broad fluvio-lacustrine plain fringing the volcanic arc platform. The arc platform played an important role for the derivation of volcanogenic materials and accreted sediments into the backarc basin via extensive fluvial network. Pyroclastic density currents and landslides, which originated from the arc platform, also entered the basin. In addition, extrusion of basaltic volcanic rocks was continual within the basin during basin expansion. The resultant succession of mixed sedimentary and volcanogenic rocks is generally indicative of a temporal increase in volcanic activity in the arc platform and in subsidence rate of the basin. In the Late Cretaceous, andesitic to rhyolitic volcanism became climactic in the arc platform, producing

  20. 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

  1. Lasting mantle scars lead to perennial plate tectonics

    PubMed Central

    Heron, Philip J.; Pysklywec, Russell N.; Stephenson, Randell

    2016-01-01

    Mid-ocean ridges, transform faults, subduction and continental collisions form the conventional theory of plate tectonics to explain non-rigid behaviour at plate boundaries. However, the theory does not explain directly the processes involved in intraplate deformation and seismicity. Recently, damage structures in the lithosphere have been linked to the origin of plate tectonics. Despite seismological imaging suggesting that inherited mantle lithosphere heterogeneities are ubiquitous, their plate tectonic role is rarely considered. Here we show that deep lithospheric anomalies can dominate shallow geological features in activating tectonics in plate interiors. In numerical experiments, we found that structures frozen into the mantle lithosphere through plate tectonic processes can behave as quasi-plate boundaries reactivated under far-field compressional forcing. Intraplate locations where proto-lithospheric plates have been scarred by earlier suturing could be regions where latent plate boundaries remain, and where plate tectonics processes are expressed as a ‘perennial' phenomenon. PMID:27282541

  2. Lasting mantle scars lead to perennial plate tectonics.

    PubMed

    Heron, Philip J; Pysklywec, Russell N; Stephenson, Randell

    2016-01-01

    Mid-ocean ridges, transform faults, subduction and continental collisions form the conventional theory of plate tectonics to explain non-rigid behaviour at plate boundaries. However, the theory does not explain directly the processes involved in intraplate deformation and seismicity. Recently, damage structures in the lithosphere have been linked to the origin of plate tectonics. Despite seismological imaging suggesting that inherited mantle lithosphere heterogeneities are ubiquitous, their plate tectonic role is rarely considered. Here we show that deep lithospheric anomalies can dominate shallow geological features in activating tectonics in plate interiors. In numerical experiments, we found that structures frozen into the mantle lithosphere through plate tectonic processes can behave as quasi-plate boundaries reactivated under far-field compressional forcing. Intraplate locations where proto-lithospheric plates have been scarred by earlier suturing could be regions where latent plate boundaries remain, and where plate tectonics processes are expressed as a 'perennial' phenomenon. PMID:27282541

  3. Lasting mantle scars lead to perennial plate tectonics

    NASA Astrophysics Data System (ADS)

    Heron, Philip J.; Pysklywec, Russell N.; Stephenson, Randell

    2016-06-01

    Mid-ocean ridges, transform faults, subduction and continental collisions form the conventional theory of plate tectonics to explain non-rigid behaviour at plate boundaries. However, the theory does not explain directly the processes involved in intraplate deformation and seismicity. Recently, damage structures in the lithosphere have been linked to the origin of plate tectonics. Despite seismological imaging suggesting that inherited mantle lithosphere heterogeneities are ubiquitous, their plate tectonic role is rarely considered. Here we show that deep lithospheric anomalies can dominate shallow geological features in activating tectonics in plate interiors. In numerical experiments, we found that structures frozen into the mantle lithosphere through plate tectonic processes can behave as quasi-plate boundaries reactivated under far-field compressional forcing. Intraplate locations where proto-lithospheric plates have been scarred by earlier suturing could be regions where latent plate boundaries remain, and where plate tectonics processes are expressed as a `perennial' phenomenon.

  4. 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.

  5. 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.

  6. 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)

  7. Continental Flood Basalts

    NASA Astrophysics Data System (ADS)

    Continental flood basalts have been receiving considerable scientific attention lately. Recent publications have focused on several particular flood-basalt provinces (Brito-Arctic, Karoo, Parana', Deccan, and Columbia Plateau), and much attention has been given to the proposed connection between flood-basalt volcanism, bolide impacts, and mass extinctions. The editor of Continental Flood Basalts, J. D. Macdougall, conceived the book to assemble in a single volume, from a vast and scattered literature, an overview of each major post-Cambrian flood-basalt province.Continental Flood Basalts has 10 chapters; nine treat individual flood-basalt provinces, and a summary chapter compares and contrasts continental flood-basalts and mid-oceanic ridge basalts. Specifically, the chapters address the Columbia River basalt, the northwest United States including the Columbia River basalt, the Ethiopian Province, the North Atlantic Tertiary Province, the Deccan Traps, the Parana' Basin, the Karoo Province, the Siberian Platform, and Cenozoic basaltic rocks in eastern China. Each chapter is written by one or more individuals with an extensive background in the province.

  8. 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

  9. Continental subduction induced tremor activity?

    NASA Astrophysics Data System (ADS)

    Tai, H. J.; Chen, K. H.; Ide, S.; Mouyen, M.; Byrne, T. B.

    2015-12-01

    Southern Central Range of Taiwan, a place where deep-seated tectonic tremors (a proxy of slow slip) and earthquake swarms are closely located in space and highly correlated in time, provides rare opportunity towards the understanding of physical mechanisms governing different style of slip. To identify tremor events, we used the identification scheme similar to Ide et al. (2015) but applied slightly different techniques: (1) Higher waveform cross-correlation coefficient (>0.6) (2) careful visual inspection for excluding local earthquakes and short-lasted event (duration < 60 s) (3) Signal to noise ratio higher than 1.2 and lower than 30 (4) No spatio-temporal clustering technique used. During the study period of 2007-2012, we identified 2320 tremor events with duration ranging from 60 s to 1550 s. They are located underneath southern Central Range, forming a NS-striking and SE-dipping pipe-like structure at a depth of 20-40 km. The up-dip extension of this tremor structure reaches an aseismic zone under the western flank of Central Range at shallow depths, where is an area characterized by high heat flow, low Vp and Vs anomaly. Such seismic gap was explained by the buoyancy induced crust detachment during continental subduction of Eurasian Plate. This detachment may open a new channel for hot and ductile material ascending to shallow depth, producing high temperatures along the way. This provides a common mechanism for down-dip tremor and up-dip shallow seismic gap along the same eastern dipping channel. In addition, the tremor events are found to be mostly occurred in high tides and exhibit higher correlation with tide data from west coast of Taiwan. This may again imply the association between tremor activity and subduction of Eurasian Plate.

  10. Interseismic Plate coupling and strain partitioning in the Northeastern Caribbean

    NASA Astrophysics Data System (ADS)

    Manaker, D. M.; Calais, E.; Freed, A. M.; Ali, S. T.; Przybylski, P.; Mattioli, G.; Jansma, P.; Prépetit, C.; de Chabalier, J. B.

    2008-09-01

    The northeastern Caribbean provides a natural laboratory to investigate strain partitioning, its causes and its consequences on the stress regime and tectonic evolution of a subduction plate boundary. Here, we use GPS and earthquake slip vector data to produce a present-day kinematic model that accounts for secular block rotation and elastic strain accumulation, with variable interplate coupling, on active faults. We confirm that the oblique convergence between Caribbean and North America in Hispaniola is partitioned between plate boundary parallel motion on the Septentrional and Enriquillo faults in the overriding plate and plate-boundary normal motion at the plate interface on the Northern Hispaniola Fault. To the east, the Caribbean/North America plate motion is accommodated by oblique slip on the faults bounding the Puerto Rico block to the north (Puerto Rico subduction) and to the south (Muertos thrust), with no evidence for partitioning. The spatial correlation between interplate coupling, strain partitioning and the subduction of buoyant oceanic asperities suggests that the latter enhance the transfer of interplate shear stresses to the overriding plate, facilitating strike-slip faulting in the overriding plate. The model slip rate deficit, together with the dates of large historical earthquakes, indicates the potential for a large (Mw7.5 or greater) earthquake on the Septentrional fault in the Dominican Republic. Similarly, the Enriquillo fault in Haiti is currently capable of a Mw7.2 earthquake if the entire elastic strain accumulated since the last major earthquake was released in a single event today. The model results show that the Puerto Rico/Lesser Antilles subduction thrust is only partially coupled, meaning that the plate interface is accumulating elastic strain at rates slower than the total plate motion. This does not preclude the existence of isolated locked patches accumulating elastic strain to be released in future earthquakes, but whose

  11. Peen plating

    NASA Technical Reports Server (NTRS)

    Babecki, A. J. (Inventor); Haehner, C. L.

    1973-01-01

    A process for metal plating which comprises spraying a mixture of metallic powder and small peening particles at high velocity against a surface is described. The velocity must be sufficient to impact and bond metallic powder onto the surface. In the case of metal surfaces, the process has as one of its advantages providing mechanical working (hardening) of the surface simultaneously with the metal plating.

  12. More than Motility: Salmonella Flagella Contribute to Overriding Friction and Facilitating Colony Hydration during Swarming

    PubMed Central

    Partridge, Jonathan D.

    2013-01-01

    We show in this study that Salmonella cells, which do not upregulate flagellar gene expression during swarming, also do not increase flagellar numbers per μm of cell length as determined by systematic counting of both flagellar filaments and hooks. Instead, doubling of the average length of a swarmer cell by suppression of cell division effectively doubles the number of flagella per cell. The highest agar concentration at which Salmonella cells swarmed increased from the normal 0.5% to 1%, either when flagella were overproduced or when expression of the FliL protein was enhanced in conjunction with stator proteins MotAB. We surmise that bacteria use the resulting increase in motor power to overcome the higher friction associated with harder agar. Higher flagellar numbers also suppress the swarming defect of mutants with changes in the chemotaxis pathway that were previously shown to be defective in hydrating their colonies. Here we show that the swarming defect of these mutants can also be suppressed by application of osmolytes to the surface of swarm agar. The “dry” colony morphology displayed by che mutants was also observed with other mutants that do not actively rotate their flagella. The flagellum/motor thus participates in two functions critical for swarming, enabling hydration and overriding surface friction. We consider some ideas for how the flagellum might help attract water to the agar surface, where there is no free water. PMID:23264575

  13. 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.

  14. Plate tectonics conserves angular momentum

    NASA Astrophysics Data System (ADS)

    Bowin, C.

    2010-03-01

    velocity on the crests of convection cells driven by rising heat. The magnitude of these sinking mass anomalies is inferred also to be sufficient to overcome basal plate and transform fault frictions. These results imply that spreading centers are primarily passive reactive features, and fracture zones (and wedge-shaped sites of seafloor spreading) are adjustment zones that accommodate strains in the lithosphere. Further, the interlocked pattern of the Australian and Pacific plates the past 42 Million years (with their absolute plate motions near 90° to each other) is taken as strong evidence that large thermally driven "roller" convection cells previously inferred as the driving mechanism in earlier interpretations of continental drift and plate tectonics, have not been active in the Earth's mantle the past 42 Million years, if ever. This report also presents estimates of the changes in location and magnitude of the Earth's axis of total plate tectonic angular momentum for the past 62 million years.

  15. 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.

  16. 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.

  17. Plate Tectonics in the Late Paleozoic

    NASA Astrophysics Data System (ADS)

    Domeier, Mat; Torsvik, Trond

    2014-05-01

    As the chronicle of plate motions through time, paleogeography is fundamental to our understanding of plate tectonics and its role in shaping the geology of the present-day. To properly appreciate the history of tectonics—and its influence on the deep Earth and climate—it is imperative to seek an accurate and global model of paleogeography. However, owing to the incessant loss of oceanic lithosphere through subduction, the paleogeographic reconstruction of 'full-plates' (including oceanic lithosphere) becomes increasingly challenging with age. Prior to 150 Ma ~60% of the lithosphere is missing and reconstructions are developed without explicit regard for oceanic lithosphere or plate tectonic principles; in effect, reflecting the earlier mobilistic paradigm of continental drift. Although these 'continental' reconstructions have been immensely useful, the next-generation of mantle models requires global plate kinematic descriptions with full-plate reconstructions. Moreover, in disregarding (or only loosely applying) plate tectonic rules, continental reconstructions fail to take advantage of a wealth of additional information in the form of practical constraints. Following a series of new developments, both in geodynamic theory and analytical tools, it is now feasible to construct full-plate models that lend themselves to testing by the wider Earth-science community. Such a model is presented here for the late Paleozoic (410-250 Ma). Although we expect this model to be particularly useful for numerical mantle modeling, we hope that it can also serve as a general framework for understanding late Paleozoic tectonics, one on which future improvements can be built and further tested.

  18. Geometric figure–ground cues override standard depth from accretion-deletion

    PubMed Central

    Tanrıkulu, Ömer Dağlar; Froyen, Vicky; Feldman, Jacob; Singh, Manish

    2016-01-01

    Accretion-deletion is widely considered a decisive cue to surface depth ordering, with the accreting or deleting surface interpreted as behind an adjoining surface. However, Froyen, Feldman, and Singh (2013) have shown that when accretion-deletion occurs on both sides of a contour, accreting-deleting regions can also be perceived as in front and as self-occluding due to rotation in three dimensions. In this study we ask whether geometric figure–ground cues can override the traditional “depth from accretion-deletion” interpretation even when accretion-deletion takes place only on one side of a contour. We used two tasks: a relative-depth task (front/back), and a motion-classification task (translation/rotation). We conducted two experiments, in which texture in only one set of alternating regions was moving; the other set was static. Contrary to the traditional interpretation of accretion-deletion, the moving convex and symmetric regions were perceived as figural and rotating in three dimensions in roughly half of the trials. In the second experiment, giving different motion directions to the moving regions (thereby weakening motion-based grouping) further weakened the traditional accretion-deletion interpretation. Our results show that the standard “depth from accretion-deletion” interpretation is overridden by static geometric cues to figure–ground. Overall, the results demonstrate a rich interaction between accretion-deletion, figure–ground, and structure from motion that is not captured by existing models of depth from motion. PMID:26982528

  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

  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. 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.

  2. The nature and location of the plate boundary between the Anatolian and African plates

    NASA Astrophysics Data System (ADS)

    deǧer Özbakır, Ali; Wortel, Rinus; Govers, Rob

    2010-05-01

    Overall convergence of the African, Arabian and Eurasian plates, and the westward escape of Anatolia has resulted in an evolving plate boundary zone since the Miocene. In the Eastern Mediterranean, the current location and nature of the plate boundary between the Anatolian and the African plates is difficult to trace due to the scattered crustal earthquakes, and the absence of deeper earthquakes. In this study we aim to better constrain the nature and the location of the plate boundary. GPS-derived velocity field and stresses from earthquake mechanism solutions comprise the datasets which short time scale (elastic) models can be compared to. We model the stresses and deformation on the overriding plate by incorporating convergence of Africa and Arabia towards stable Eurasia, and rollback of the Hellenic trench. Investigation of the plate boundary consists of constraining the directions of motions over the segments which make up the boundary. We assume various types and locations for the plate boundary within the observational limits. We use a spherical plane stress finite element model to test these possibilities. We find that stresses and displacements are sensitive to both the location and the nature of the plate boundary. We obtain the minimum misfit with the data in a model where we assume the following: (1) the segment between Hellenic and the Cyprus arcs have both down-dip and fault parallel motions, (2) the connection between the Cyprus arc and Arabia--Eurasia collision zone is pure strike-slip. In all our models, an extra pull force on Anatolia is required to explain the high velocities in southwest Anatolia. This force may be related to return flow around the lateral edge of the Aegean slab.

  3. 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

  4. Caribbean plate tectonics from seismic tomography

    NASA Astrophysics Data System (ADS)

    Ten Brink, U. S.; Villasenor, A.

    2012-12-01

    New seismic tomography in the Caribbean shows close links between the geometry and dynamics of subducting slabs and the geology of the overriding plate. Unlike most oceanic plates, the Caribbean plate lacks identifiable seafloor magnetic anomalies and fracture zones. The plate's history has therefore been inferred primarily from land geology along the plate boundary, which is complicated by large-scale shear deformation, and from finite rotations of surrounding plates.We used more than 14 million arrival times from 300,000 earthquakes to identify P-wave velocity anomalies. We relate the anomalies to the geometry and dynamics of subducting slabs and to patterns of earthquake activity, volcanism, topographic relief, and tectonic deformation. For example, we detect two separate slabs belonging to the North and South American plates, respectively, which appear to be responsible for morphologic and tectonic differences between the arcs of the Northern (from Guadeloupe northward) and Southern (from Dominica southward) Lesser Antilles. Variations in earthquake activity between Haiti and the Dominican Republic can be explained by a change in slab geometry from an underplated slab beneath Haiti to a subducting slab under the Dominican Republic. A shallow tear in the slab may explain the anomalously deep Puerto Rico Trench and the frequent earthquake swarms there. The westward shift in volcanic activity in the Northern Lesser Antilles from the Miocene Limestone Caribbees to the present arc can be attributed to the limit on convective flow imposed by the 3-D geometry of the slab at depth. A thinned South America slab under the southern Lesser Antilles may result from traction imposed on the slab by a wide forearc wedge. Variations in tectonic deformation of northern South America could be related to the location of the Caribbean Large Igneous Province north of the Maracaibo Block.

  5. Generation of continental crust in intra-oceanic arcs

    NASA Astrophysics Data System (ADS)

    Gazel, E.; Hayes, J. L.; Kelemen, P. B.; Everson, E. D.; Holbrook, W. S.; Vance, E.

    2014-12-01

    The origin of continental crust is still an unsolved mystery in the evolution of our planet. Although the best candidates to produce juvenile continental crust are intra-oceanic arcs these systems are dominated by basaltic lavas, and when silicic magmas are produced, the incompatible-element compositions are generally too depleted to be a good match for continental crust estimates. Others, such as the W. Aleutians, are dominated by andesitic melts with trace element compositions similar to average continental crust. In order to evaluate which intra-oceanic arcs produced modern continental crust, we developed a geochemical continental index (CI) through a statistical analysis that compared all available data from modern intra-oceanic arcs with global estimates of continental crust. Our results suggest that magmas from Costa Rica (<10 Ma) have a CI <50, closer to the CI (~20) computed from available average continental crust estimates. Transitional CI values of 50-100 were found in the Aleutians, the Iwo-Jima segment of Izu-Bonin, the L. Antilles, Panama, Nicaragua, and Vanuatu. The geochemical signature of the Costa Rican lavas is controlled by melts from the subducting Galapagos tracks. Iwo-Jima and Vanuatu are in a similar tectonic scenario with subducting intraplate seamounts. Melts from the subducting oceanic crust are thought to significantly control the geochemical signature in the W. Aleutians and Panama. In the L. Antilles and E. Aleutians the continental signature may reflect recycling of a component derived from subducting continental sediments. Most of Izu-Bonin, Marianas, S. Scotia and Tonga arcs with a CI >100 have the least continent-like geochemical signatures. In these arcs the subducting plate is old (>100 Ma), not overprinted by enriched intraplate volcanism and the geochemistry may be dominated by slab-derived, aqueous fluids. We also found a strong correlation between the CI and average crustal P-wave velocity, validating the geochemical index

  6. Absolute plate velocities from seismic anisotropy: Importance of correlated errors

    NASA Astrophysics Data System (ADS)

    Zheng, Lin; Gordon, Richard G.; Kreemer, Corné

    2014-09-01

    The errors in plate motion azimuths inferred from shear wave splitting beneath any one tectonic plate are shown to be 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. Our preferred set of angular velocities, SKS-MORVEL, is 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 (σ = 19.2°) differs insignificantly from that for continental lithosphere (σ = 21.6°). The between-plate dispersion, however, is significantly smaller for oceanic lithosphere (σ = 7.4°) than for continental lithosphere (σ = 14.7°). Two of the slowest-moving plates, Antarctica (vRMS = 4 mm a-1, σ = 29°) and Eurasia (vRMS = 3 mm a-1, σ = 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. The tendency of observed azimuths on the Arabia plate to be counterclockwise of plate motion may provide information about the direction and amplitude of superposed asthenospheric flow or about anisotropy in the lithospheric mantle.

  7. Converting your Continental

    SciTech Connect

    Wirz, B.M.

    1981-07-01

    Inflation and higher fuel and environmental costs make conventional-generated power as unaffordable (as a Lincoln Continental in the automobile market) for retail and industrial customers, many of whom are looking for alternatives to purchase electric power. The loss of revenue from competing energy sources eliminates the monopoly status that utilities have enjoyed and is forcing utilities to provide what customers want and do it better than the competition. Utilities have only research and development or fuel switching to improve efficiency unless they rethink their approach and come up with new alternatives. 1 table. (DCK)

  8. On the Evolution of Glaciated Continental Margins

    NASA Astrophysics Data System (ADS)

    Sverre Laberg, Jan; Rydningen, Tom Arne; Safronova, Polina A.; Forwick, Matthias

    2016-04-01

    Glaciated continental margins, continental margins where a grounded ice sheet repeatedly has been at or near the shelf break, are found at both northern and southern high-latitudes. Their evolution are in several aspects different from their low-latitude counterparts where eustatic sea-level variations possess a fundamental control on their evolution and where fluvial systems provide the main sediment input. From studies of the Norwegian - Barents Sea - Svalbard and NE Greenland continental margins we propose the following factors as the main control on the evolution of glaciated continental margins: 1) Pre-glacial relief controlling the accommodation space, 2) Ice sheet glaciology including the location of fast-flowing ice streams where source area morphology exerts a fundamental control, 3) Composition of the glacigenic sediments where the clay content in previous studies have been found to be important, and 4) Sea-level controlled both by eustacy and isostacy. From three case studies, 1) the western Barents Sea, 2) part of the North Norwegian (Troms), and 3) the Mid-Norwegian margin, the influence on these factors for the sea-floor morphology, sedimentary processes of the continental slope - deep sea and continental margin architecture are discussed. The pre-glacial relief of the mid-Norwegian and Troms margins relates to the onset of rifting and plate break-up from the early Cenozoic while for the SW Barents Sea, plate shear was followed by rifting. A wide zone of extended continental crust occurs offshore mid-Norway while this zone is much narrower offshore Troms leading to a more pronounced pre-glacial relief. Regarding sediment delivery and ice sheet glaciology the western Barents Sea exemplifies very high sediment input corresponding to an estimated average erosion of the source area of ~0.4 mm/yr (SW Barents Sea), much of which is related to subglacial erosion of Mesozoic - Cenozoic sedimentary rocks from large paleo-ice streams. The mid-Norwegian margin

  9. 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

  10. 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

  11. 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

    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

  12. 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

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. Continental collision slowing due to viscous mantle lithosphere rather than topography.

    PubMed

    Clark, Marin Kristen

    2012-03-01

    Because the inertia of tectonic plates is negligible, plate velocities result from the balance of forces acting at plate margins and along their base. Observations of past plate motion derived from marine magnetic anomalies provide evidence of how continental deformation may contribute to plate driving forces. A decrease in convergence rate at the inception of continental collision is expected because of the greater buoyancy of continental than oceanic lithosphere, but post-collisional rates are less well understood. Slowing of convergence has generally been attributed to the development of high topography that further resists convergent motion; however, the role of deforming continental mantle lithosphere on plate motions has not previously been considered. Here I show that the rate of India's penetration into Eurasia has decreased exponentially since their collision. The exponential decrease in convergence rate suggests that contractional strain across Tibet has been constant throughout the collision at a rate of 7.03 × 10(-16) s(-1), which matches the current rate. A constant bulk strain rate of the orogen suggests that convergent motion is resisted by constant average stress (constant force) applied to a relatively uniform layer or interface at depth. This finding follows new evidence that the mantle lithosphere beneath Tibet is intact, which supports the interpretation that the long-term strain history of Tibet reflects deformation of the mantle lithosphere. Under conditions of constant stress and strength, the deforming continental lithosphere creates a type of viscous resistance that affects plate motion irrespective of how topography evolved. PMID:22382982

  18. 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.

  19. MACMA: a Virtual Lab for Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Grigne, C.; Combes, M.; Tisseau, C.

    2013-12-01

    boundaries is a feature that clearly seems interesting to students. They are used to see dynamic representations of continental drift, but this does not include the dynamics of the oceanic lithosphere and the corresponding fluctuations in seafloor age distribution. The 2-D geometry of the simulator is a simplification that actually brings a clearer view of plate boundary creations, migrations, and collisions, together with global plate tectonics reorganization events.

  20. 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.

  1. A high-resolution local network study of the Nazca plate Wadati-Benioff zone under western Argentina

    NASA Technical Reports Server (NTRS)

    Smalley, Robert F., Jr.; Isacks, Bryan L.

    1987-01-01

    Seismic data, recorded by INPRES telemetered network located above one of the subhorizontal segments of the subducted Nazca plate Wadati-Benioff zone beneath western Argentina, were analyzed to determine the zone's fine structure. The depth of the center and the thickness of the subhorizontal Wadati-Benioff zone beneath the network were calculated to be about 107 km and about 20 km, respectively, with most of the seismogenic zone concentrated in a region about 12 km thick. The Nazca plate is interpreted to be in a state of down-dip tension and to be decoupled from the overriding South American plate by a weak zone of asthenospheric or shear-heated material. The South American plate is estimated to be 80 km thick, based on the location of the subducted Nazca plate and an inferred decoupling zone between the plates.

  2. -induced continental warming

    NASA Astrophysics Data System (ADS)

    Kamae, Youichi; Watanabe, Masahiro; Kimoto, Masahide; Shiogama, Hideo

    2014-11-01

    In this the second of a two-part study, we examine the physical mechanisms responsible for the increasing contrast of the land-sea surface air temperature (SAT) in summertime over the Far East, as observed in recent decades and revealed in future climate projections obtained from a series of transient warming and sensitivity experiments conducted under the umbrella of the Coupled Model Intercomparison Project phase 5. On a global perspective, a strengthening of land-sea SAT contrast in the transient warming simulations of coupled atmosphere-ocean general circulation models is attributed to an increase in sea surface temperature (SST). However, in boreal summer, the strengthened contrast over the Far East is reproduced only by increasing atmospheric CO2 concentration. In response to SST increase alone, the tropospheric warming over the interior of the mid- to high-latitude continents including Eurasia are weaker than those over the surrounding oceans, leading to a weakening of the land-sea SAT contrast over the Far East. Thus, the increasing contrast and associated change in atmospheric circulation over East Asia is explained by CO2-induced continental warming. The degree of strengthening of the land-sea SAT contrast varies in different transient warming scenarios, but is reproduced through a combination of the CO2-induced positive and SST-induced negative contributions to the land-sea contrast. These results imply that changes of climate patterns over the land-ocean boundary regions are sensitive to future scenarios of CO2 concentration pathways including extreme cases.

  3. Dynamics of continental deformation in Asia

    NASA Astrophysics Data System (ADS)

    Vergnolle, M.; Calais, E.; Dong, L.

    2007-11-01

    The relevance of plate tectonics concepts to the description of deformation of large continental areas like Asia is subject to much debate. For some, the deformation of continents is better described by rigid motion of lithospheric blocks with strain concentrated along narrow fault zones. For others, it is better described by viscous flow of a continuously deforming solid in which faults play a minor role. Discriminating these end-member hypotheses requires spatially dense measurements of surface strain rates covering the whole deforming area. Here we revisit the issue of the forces and rheological structure that control present-day deformation in Asia. We use the "thin sheet" theory, with deformation driven by the balance of boundary and buoyancy stresses acting on a faulted lithosphere with laterally varying strength. Models are validated against a recent, homogeneous, GPS velocity field that covers most of Asia. In the models, deformation in compressional areas (Himalayas, Tien Shan, Altay) is well reproduced with strong coupling at the India/Eurasia plate contact, which allows for boundary forces to transfer into Asia. Southeastward motions observed in north and south China, however, require tensional, oceanward directed stresses, possibly generated by gravitational potential energy gradients across the Indonesian and Pacific subductions. Model and observed strain rates show that a large part of Asia undergoes no resolvable strain, with a kinematics apparently consistent with block- or plate-like motions. Internal strain, possibly continuous, is limited to high-elevation, mechanically weaker areas. Lateral variations of lithospheric strength appear to control the style of deformation in Asia, with a dynamics consistent with the thin sheet physical framework.

  4. New Alert Override Codes for the Drug Utilization Review System Derived from Outpatient Prescription Data from a Tertiary Teaching Hospital in Korea

    PubMed Central

    Yoo, Ki-Bong; Kim, Woojae; Park, Man Young; Ahn, Eun Kyoung; Park, Rae Woong

    2016-01-01

    Objectives This paper proposes new alert override reason codes that are improvements on existing Drug Utilization Review (DUR) codes based on an analysis of DUR alert override cases in a tertiary medical institution. Methods Data were obtained from a tertiary teaching hospital covering the period from April 1, 2012 to January 15, 2013. We analyzed cases in which doctors had used the 11 overlapping prescription codes provided by the Health Insurance Review and Assessment Service (HIRA) or had provided free-text reasons. Results We identified 27,955 alert override cases. Among these, 7,772 (27.8%) utilized the HIRA codes, and 20,183 (72.2%) utilized free-text reasons. According to the free-text content analysis, 8,646 cases (42.8%) could be classified using the 11 HIRA codes, and 11,537 (57.2%) could not. In the unclassifiable cases, we identified the need for codes for "prescription relating to operation" and "emergency situations." Two overlapping prescription codes required removal because they were not used. Codes A, C, F, H, I, and J (for drug non-administration cases) explained surrounding situations in too much detail, making differentiation between them difficult. These 6 codes were merged into code J4: "patient was not taking/will not take the medications involved in the DDI." Of the 11 HIRA codes, 6 were merged into a single code, 2 were removed, and 2 were added, yielding 6 alert override codes. We could codify 23,550 (84.2%) alert override cases using these codes. Conclusions These new codes will facilitate the use of the drug–drug interactions alert override in the current DUR system. For further study, an appropriate evaluation should be conducted with prescribing clinicians. PMID:26893949

  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. Geodynamic settings of microcontinents, non-volcanic islands and submerged continental marginal plateau formation

    NASA Astrophysics Data System (ADS)

    Dubinin, Evgeny; Grokholsky, Andrey; Makushkina, Anna

    2016-04-01

    Complex process of continental lithosphere breakup is often accompanied by full or semi isolation of small continental blocks from the parent continent such as microcontinents or submerged marginal plateaus. We present different types of continental blocks formed in various geodynamic settings. The process depends on thermo-mechanical properties of rifting. 1) The continental blocks fully isolated from the parent continent. This kind of blocks exist in submerged form (Elan Bank, the Jan-Mayen Ridge, Zenith Plateau, Gulden Draak Knoll, Batavia Knoll) and in non-submerged form in case of large block size. Most of listed submerged blocks are formed in proximity of hot-spot or plume. 2) The continental blocks semi-isolated from the parent continent. Exmouth Plateau, Vøring, Agulhas, Naturaliste are submerged continental plateaus of the indicated category; Sri Lanka, Tasmania, Socotra are islands adjacent to continent here. Nowadays illustration of this setting is the Sinai block located between the two continental rifts. 3) The submerged linear continental blocks formed by the continental rifting along margin (the Lomonosov Ridge). Suggested evolution of this paragraph is the rift propagation along existing transtensional (or another type) transform fault. Future example of this type might be the California Peninsula block, detached from the North American plate by the rifting within San-Andreas fault. 4) The submerged continental blocks formed by extensional processes as the result of asthenosphere flow and shear deformations. Examples are submerged blocks in the central and southern Scotia Sea (Terror Bank, Protector Basin, Discovery Bank, Bruce Bank etc.). 5) The continental blocks formed in the transform fault systems originated in setting of contradict rifts propagation in presence of structure barriers, rifts are shifted by several hundreds kilometers from each other. Examples of this geodynamic setting are Equatorial Atlantic at the initial development stage

  7. Mantle flow geometry from ridge to trench beneath the Gorda-Juan de Fuca plate system

    NASA Astrophysics Data System (ADS)

    Martin-Short, Robert; Allen, Richard M.; Bastow, Ian D.; Totten, Eoghan; Richards, Mark A.

    2015-12-01

    Tectonic plates are underlain by a low-viscosity mantle layer, the asthenosphere. Asthenospheric flow may be induced by the overriding plate or by deeper mantle convection. Shear strain due to this flow can be inferred using the directional dependence of seismic wave speeds--seismic anisotropy. However, isolation of asthenospheric signals is challenging; most seismometers are located on continents, whose complex structure influences the seismic waves en route to the surface. The Cascadia Initiative, an offshore seismometer deployment in the US Pacific Northwest, offers the opportunity to analyse seismic data recorded on simpler oceanic lithosphere. Here we use measurements of seismic anisotropy across the Juan de Fuca and Gorda plates to reconstruct patterns of asthenospheric mantle shear flow from the Juan de Fuca mid-ocean ridge to the Cascadia subduction zone trench. We find that the direction of fastest seismic wave motion rotates with increasing distance from the mid-ocean ridge to become aligned with the direction of motion of the Juan de Fuca Plate, implying that this plate influences mantle flow. In contrast, asthenospheric mantle flow beneath the Gorda Plate does not align with Gorda Plate motion and instead aligns with the neighbouring Pacific Plate motion. These results show that asthenospheric flow beneath the small, slow-moving Gorda Plate is controlled largely by advection due to the much larger, faster-moving Pacific Plate.

  8. Tillering in the sugary1 sweet corn is maintained by overriding the teosinte branched1 repressive signal

    PubMed Central

    Kebrom, Tesfamichael H; Brutnell, Thomas P

    2015-01-01

    The evolution of apical dominance in maize during domestication from teosinte is associated with higher expression from the teosinte branched1 (tb1) gene that inhibits tiller bud outgrowth. Unlike many standard maize varieties, the sweet corn inbred P39 that carries a mutation in a starch biosynthesis gene sugary1 produces multiple tillers and providing an opportunity to explore the diversification of the tb1 signal in maize. Through gene expression analysis, we show that tiller buds in P39 continue to grow by overriding the high expression level of tb1 that arrests bud outgrowth in maize inbred B73. In addition, we demonstrate that while B73 is largely non-responsive to shade, both P39 and teosinte respond through tb1-independent and tb1-dependent molecular mechanisms, respectively, leading to inhibition of tiller bud outgrowth. PMID:26399727

  9. Tillering in the sugary1 sweet corn is maintained by overriding the teosinte branched1 repressive signal.

    PubMed

    Kebrom, Tesfamichael H; Brutnell, Thomas P

    2015-01-01

    The evolution of apical dominance in maize during domestication from teosinte is associated with higher expression from the teosinte branched1 (tb1) gene that inhibits tiller bud outgrowth. Unlike many standard maize varieties, the sweet corn inbred P39 that carries a mutation in a starch biosynthesis gene sugary1 produces multiple tillers and providing an opportunity to explore the diversification of the tb1 signal in maize. Through gene expression analysis, we show that tiller buds in P39 continue to grow by overriding the high expression level of tb1 that arrests bud outgrowth in maize inbred B73. In addition, we demonstrate that while B73 is largely non-responsive to shade, both P39 and teosinte respond through tb1-independent and tb1-dependent molecular mechanisms, respectively, leading to inhibition of tiller bud outgrowth. PMID:26399727

  10. Reaction-induced rheological weakening enables oceanic plate subduction.

    PubMed

    Hirauchi, Ken-Ichi; Fukushima, Kumi; Kido, Masanori; Muto, Jun; Okamoto, Atsushi

    2016-01-01

    Earth is the only terrestrial planet in our solar system where an oceanic plate subducts beneath an overriding plate. Although the initiation of plate subduction requires extremely weak boundaries between strong plates, the way in which oceanic mantle rheologically weakens remains unknown. Here we show that shear-enhanced hydration reactions contribute to the generation and maintenance of weak mantle shear zones at mid-lithospheric depths. High-pressure friction experiments on peridotite gouge reveal that in the presence of hydrothermal water, increasing strain and reactions lead to an order-of-magnitude reduction in strength. The rate of deformation is controlled by pressure-solution-accommodated frictional sliding on weak hydrous phyllosilicate (talc), providing a mechanism for the 'cutoff' of the high peak strength at the brittle-plastic transition. Our findings suggest that infiltration of seawater into transform faults with long lengths and low slip rates is an important controlling factor on the initiation of plate tectonics on terrestrial planets. PMID:27562366