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1

Overriding plate controls on subduction evolution  

NASA Astrophysics Data System (ADS)

Geologic and geophysical observations indicate that the thickness, density, and strength of the lithosphere vary on the Earth. However, the role of the overriding plate lithosphere properties on the evolution and morphology of subduction is not well understood. This paper presents 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 effect of these parameters on subduction evolution, in particular, 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. Almost all of the models presented result in sustained asymmetric subduction from initiation. Trench advance occurs in models 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 across subduction zones on Earth, where similar patterns of evolution are observed.

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

2014-08-01

2

Evidence for crustal thickening and shortening of the overriding plate during incipient plate/plate subduction  

NASA Astrophysics Data System (ADS)

Evidence from a study of the Macquarie Ridge Complex and comparison with other plate boundaries displaying varying development of intraplate compressional structures, indicate that thickening and shorting of the overriding plate occur during incipient subduction. The Macquarie Ridge Complex has been produced by a tectonic history oblique compression between the Indian/Australian and Pacific plates at their common boundary south of New Zealand. In the central Macquarie Ridge Complex intraplate transpressive forces have resulted in the uplift of oceanic crust of the Indian/Australian plate to form the Macquarie Ridge and incipient subduction of the Pacific oceanic plate at the Macquarie Trench. The uplift has been effected by thickening and shortening of the oceanic crust of the overriding Indian/Australian plate accompanied by shallow seismicity at the ridge, whereas the Pacific plate at the trench has not been thickened. Post-1964 earthquakes of the Macquarie Ridge Complex form a single narrow band some tens of kilometres wide. In the central Macquarie Ridge Complex the band of seismicity is confined to the ridge and not the trench, suggesting that crustal thickening rather than subduction is the preferred style of tectonism for incipient subduction zones. Fault plane solutions indicate dextral motion that is consistent with anticlockwise rotation of the Pacific plate relative to the Australian plate, and with transpression and incipient subduction in the central segment of the Complex.

Williamson, P. E.; Jones, T. D.; McCue, K. F.

1989-04-01

3

Influence of the thermal state of the overriding plate on subduction dynamics and slab geometry  

NASA Astrophysics Data System (ADS)

Significant variability in slab dip can be found between different subduction zones, or along a single subduction zone. The effects on subduction dynamics and slab geometry of a number of factors such as trench motion, the presence of a low viscosity mantle wedge and slab rheology have been previously investigated. In contrast, the influence of the thermal thickness of the overriding plate on slab dip has not been studied before, even though the thermal thickness is expected to significantly influence the suction force acting on the slab due to corner flow in the mantle wedge due to both increased viscosity of a cooler mantle wedge and narrowing of the wedge corner. The main purpose of this study is to perform a systematic analysis of the influence of the thermal state of both the overriding and subducting plates on the balance between gravitational and hydrodynamic torques, and therefore on slab dip. We present the results of non-Newtonian numerical thermo-mechanical modeling of subduction, where we vary the age of both the overriding and subducting plates in order to test its effect on the slab dip at different depth ranges. We find that colder overriding plates result in shallower slab dips, as a result of the increased suction force in the mantle wedge. The influence of the thermal state of the overriding plate on slab dip is shown here to be more important than that of the age of subducting lithosphere. Modeling results are qualitatively compared to the large dip variability of the Cocos slab including a flat-slab segment. We suggest that this variability is likely related to the change of the thermal state of the overriding plates, with flat subduction occurring under cold lithosphere in southwestern Mexico and steep subduction under the warmer lithosphere of the northwestern Caribbean plate.

Rodriguez-Gonzalez, J.; Negredo, A. M.; Billen, M. I.

2010-12-01

4

The role of non-uniform overriding plates on slab dip variability along the trench. Insights from 3D numerical modeling  

NASA Astrophysics Data System (ADS)

Although subduction is the primary force driving plate tectonics, some factors controlling the dynamics and the geometry of subduction processes are still poorly understood. Specifically, the effect of the thermal state of the subducting and overriding plates on the slab dip has been systematically studied in previous works by means of 2D numerical modeling. These 2D models showed that slabs subducting under an old overriding plate are affected by an increased hydrodynamic suction, due to the lower temperature and therefore higher viscosity, of the mantle wedge, which leads to a lower subduction angle, and eventually to the formation of flat slab segments. Two limitations of these previous models are: 1) the 2D approach only accounts for the poloidal component of flow, and 2) subduction is achieved by imposing a kinematic boundary condition (imposed convergence velocity for the subducting plate). Here we present the results of 3D non-Newtonian thermo-mechanical numerical models, considering either kinematically-driven or self-sustained subduction, to test the influence of thermal state of both the overriding and subducting plates on subduction dynamics and slab geometry. The age of both the overriding and subducting plates is systematically varied in order to test its effect on the slab dip at different depth ranges. We have also tested the effect of overriding plates with a non-uniform thermal state in the trench parallel direction to study variations of the slab dip along strike. Modeling results are qualitatively compared to the large dip variability of the Cocos slab and the flat-slab segment of the Pacific plate subducting beneath Northern Chile. We hypothesize that a significant part of this variability is likely related to the change of the thermal state of the overriding plates due to variations in age of the continental crustal blocks. The 3D approach followed in this study accounts for both the poloidal and toroidal components of flow, thus allowing us to compare the results with observations of seismic anisotropy in these regions.

Rodriguez-Gonzalez, J.; Billen, M. I.; Negredo, A. M.

2011-12-01

5

Composition of the continental plates  

USGS Publications Warehouse

The structures of continental plates and of oceanic basins suggested by several seismologists are utilized to estimate the relative volumes of sial and sima in the earth's crust. It seems that sial of the composition of the average igneous rock constitutes fully 26% and perhaps as much as 43% of the total crust. This ratio is far higher than seems likely if the sial had been entirely derived through fractional crystallization of a basaltic magma. The relative paucity of intermediate rocks as compared with granite and gabbro in the crust points in the same direction. The tentative conclusion is reached that the sial owes a large part of its volume to some process other than fractional crystallization of basalt-possibly to the emanation of low-melting constituents such as water, silica, potassa, soda, and alumina directly from the mantle to the crust. ?? 1954 Springer-Verlag.

Gilluly, J.

1954-01-01

6

A regime diagram for subduction dynamics from thermo-mechanical models with a mobile trench and an overriding plate  

NASA Astrophysics Data System (ADS)

The penetration or stagnation of subducted slabs in mantle transition zone and lower mantle influences Earth's thermal, chemical and tectonic evolution. Yet, the mechanisms responsible for the wide range of observed slab morphologies within the transition zone remain debated. Here, we investigate how downgoing and overriding plate ages controls the interaction between subducted slabs and mantle transition zone. We use 2-D thermo-mechanical models of a two-plate subduction system, modeled with the finite-element, adaptative-mesh code Fluidity. We implement a temperature- and stress-dependent rheology, and viscosity increases 30-fold from upper to lower mantle. Trench position evolves freely in response to plate dynamics. Such an approach self-consistently captures feedbacks between temperature, density, flow, strength and deformation. Our results indicate that key controls on subduction dynamics and slab morphology are: (i) the slab's ability to induce trench motion; and (ii) the evolution of slab strength during sinking. We build a regime diagram that distinguishes four subduction styles: (1) a "vertical folding" mode with stationary trench (young subducting plates, comparatively old overriding plates); (2) slabs that are "horizontally deflected" along the 660-km deep viscosity jump (initially young subducting and overriding plates); (3) an inclined slab morphology, resulting from strong trench retreat (old subducting plates, young overriding plates); and (4) a two-stage mode, displaying bent (rolled-over) slabs at the end of upper-mantle descent, that subsequently unbend and achieve inclined morphologies, with late trench retreat (old subducting and overriding plates). We show that all seismically observed slab morphologies can arise from changes in the initial plates ages at the onset of subduction.

Garel, Fanny; Davies, Rhodri; Goes, Saskia; Davies, Huw; Kramer, Stephan; Wilson, Cian

2014-05-01

7

Strain weakening enables continental plate tectonics  

NASA Astrophysics Data System (ADS)

Much debate exists concerning the strength distribution of the continental lithosphere, how it controls lithosphere-scale strain localization and hence enables plate tectonics. No rheological model proposed to date is comprehensive enough to describe both the weakness of plate boundary and rigid-like behaviour of plate interiors. Here we show that the duality of strength of the lithosphere corresponds to different stages of microstructural evolution. Geological constraints on lithospheric strength and large strain numerical experiments reveal that the development of layers containing weak minerals and the onset of grain boundary sliding upon grain size reduction in olivine cause strain localisation and reduce strength in the crust and subcontinental mantle, respectively. The positive feedback between weakening and strain localization leads to the progressive development of weak plate boundaries while plate interiors remain strong.

Gueydan, Frédéric; Précigout, Jacques; Montési, Laurent G. J.

2014-09-01

8

Crustal Structure and Deformation of the Incoming and Overriding Plates of the North Chilean Subduction Zone, 21-23.5ºS  

NASA Astrophysics Data System (ADS)

We present MCS images of the crustal structure of the subduction zone of north Chile. The 50 Ma oceanic Nazca Plate subducts sub-orthogonally below the South American Plate at ~80-90 mm/yr. Here we focus on three reflection lines from Sonne 104 cruise that run perpendicular to the coast for ~450 km, imaging the overriding plate and some ~350 km of the oceanic incoming plate. The ocean plate displays well-defined top of the igneous crust reflections and fairly continuous Moho reflections 2-3 seconds (TWT) deeper. The deepest Moho reflections occur across the Iquique Ridge. The seismic data shows the deformation of the incoming oceanic crust as it approaches the outer rise bulge and bends into the trench. The top of the igneous crust shows clear development of faulting and prominent trenchward dipping reflections appears in the mantle, clearly below the Moho reflection. The bending-related deformation of the incoming plate forming horst-and-graben structures is observed underthursting below the margin. The inter- plate contact is observed about 50 km landward from the deformation front. The trench axis is largely devoid of stratified turbidites. But the three seismic lines show abundant debris from the continental slope accumulates at the slope toe forming a 5-10 km wide sediment prism. The prism is also observable in multibeam bathymetry maps. The landward segment of the frontal prism appears to be partially underthrusting the margin, providing clastic, fluid-rich material to the subduction channel. Thus the amount of fluid-rich sediment in this apparently starved trench seems to be considerable.

Calahorrano, A.; Ranero, C. R.; Barckhausen, U.; Reichert, C.; Grevemeyer, I.

2008-12-01

9

Slab-Dip Variability and Trench-Parallel Flow beneath Non-Uniform Overriding Plates: Insights form 3D Numerical Models  

NASA Astrophysics Data System (ADS)

Forces driving plate tectonics are reasonably well known but some factors controlling the dynamics and the geometry of subduction processes are still poorly understood. The effect of the thermal state of the subducting and overriding plates on the slab dip have been systematically studied in previous works by means of 2D and 3D numerical modeling. These models showed that kinematically-driven slabs subducting under a cold overriding plate are affected by an increased hydrodynamic suction, due to the lower temperature of the mantle wedge, which leads to a lower subduction angle, and eventually to the formation of flat slab segments. In these models the subduction is achieved by imposing a constant velocity at the top of the overriding plate, which may lead to unrealistic results. Here we present the results of 3D non-Newtonian thermo-mechanical numerical models, considering a dynamically-driven self-sustained subduction, to test the influence of a non-uniform overriding plate. Variations of the thermal state of the overriding plate along the trench cause variation in the hydrodynamic suction, which lead to variations of the slab dip along strike (Fig. 1) and a significant trench-parallel flow. When the material can flow around the edges of the slab, through the addition of lateral plates, the trench parallel flow is enhanced (Fig. 2), whereas the variations on the slab dip are diminished.; Effect of a non-uniform overriding plate on slab-dip. 3D view of the 1000 C isosurface. ; Effect of a non-uniform overriding plate on trench-parallel flow. Map view of the slab at different depths and times, showing the viscosity (colormap) and the velocity (arrows).

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

2012-12-01

10

Continental tectonics in the aftermath of plate tectonics  

Microsoft Academic Search

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

Peter Molnar

1988-01-01

11

Overriding plate structure of the Nicaragua convergent margin: Relationship to the seismogenic zone of the 1992 tsunami earthquake  

NASA Astrophysics Data System (ADS)

We present 2-D seismic velocity models and coincident multichannel seismic reflection images of the overriding plate and the inter-plate boundary of the Nicaragua convergent margin along two wide-angle seismic profiles parallel and normal to the trench acquired in the rupture area of the 1992 tsunami earthquake. The trench-perpendicular profile runs over a seamount subducting under the margin slope, at the location where seismological observations predict large coseismic slip. Along this profile, the igneous basement shows increasing velocity both with depth and away from the trench, reflecting a progressive decrease in upper-plate rock degree of fracturing. Upper mantle-like velocities are obtained at ˜10 km depth beneath the fore-arc Sandino basin, indicating a shallow mantle wedge. A mismatch of the inter-plate reflector in the velocity models and along coincident multichannel seismic profiles under the slope is best explained by ˜15% velocity anisotropy, probably caused by subvertical open fractures that may be related to fluid paths feeding known seafloor seepage sites. The presence of a shallow, partially serpentinized mantle wedge, and the fracture-related anisotropy are supported by gravity analysis of velocity-derived density models. The downdip limit of inter-plate seismicity occurs near the tip of the inferred mantle wedge, suggesting that seismicity could be controlled by the presence of serpentinite group minerals at the fault gouge. Near the trench, the inferred local increase of normal stress produced by the subducting seamount in the plate boundary may have made this fault segment unstable during earthquake rupture, which could explain its tsunamigenic character.

Sallarès, Valentí; Meléndez, Adrià; Prada, Manuel; Ranero, César R.; McIntosh, Kirk; Grevemeyer, Ingo

2013-09-01

12

Continental tectonics in the aftermath of plate tectonics  

NASA Technical Reports Server (NTRS)

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.

Molnar, Peter

1988-01-01

13

Interaction of subducted slabs with the mantle transition-zone: A regime diagram from 2-D thermo-mechanical models with a mobile trench and an overriding plate  

NASA Astrophysics Data System (ADS)

zone slab deformation influences Earth's thermal, chemical, and tectonic evolution. However, the mechanisms responsible for the wide range of imaged slab morphologies remain debated. Here we use 2-D thermo-mechanical models with a mobile trench, an overriding plate, a temperature and stress-dependent rheology, and a 10, 30, or 100-fold increase in lower mantle viscosity, to investigate the effect of initial subducting and overriding-plate ages on slab-transition zone interaction. Four subduction styles emerge: (i) a "vertical folding" mode, with a quasi-stationary trench, near-vertical subduction, and buckling/folding at depth (VF); (ii) slabs that induce mild trench retreat, which are flattened/"horizontally deflected" and stagnate at the upper-lower mantle interface (HD); (iii) inclined slabs, which result from rapid sinking and strong trench retreat (ISR); (iv) a two-stage mode, displaying backward-bent and subsequently inclined slabs, with late trench retreat (BIR). Transitions from regime (i) to (iii) occur with increasing subducting plate age (i.e., buoyancy and strength). Regime (iv) develops for old (strong) subducting and overriding plates. We find that the interplay between trench motion and slab deformation at depth dictates the subduction style, both being controlled by slab strength, which is consistent with predictions from previous compositional subduction models. However, due to feedbacks between deformation, sinking rate, temperature, and slab strength, the subducting plate buoyancy, overriding plate strength, and upper-lower mantle viscosity jump are also important controls in thermo-mechanical subduction. For intermediate upper-lower mantle viscosity jumps (×30), our regimes reproduce the diverse range of seismically imaged slab morphologies.

Garel, F.; Goes, S.; Davies, D. R.; Davies, J. H.; Kramer, S. C.; Wilson, C. R.

2014-05-01

14

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)

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 suggests also that this fault system might be still active. The coincident wide-angle seismic data coincident with one MCS profile allow the addition of more information about the deep P-wave velocity structure whereas the streamer tomography (Michaelson-Rotermund et al., this session) around the fault system add more detailed view into the complex structure in the shallow portions (upper 2km) of these structures showing a low velocity zone along one large fault suggesting that this fault is still active. These large-scale structures imaged in the overriding plate within the Shumagin gap are probably sufficiently profound to play a major role in the behavior of the megathrust in this area, segmentation of great earthquake rupture area, tsunami generation and may influence the frictional properties of the seismogenic zone at depth.

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

2013-12-01

15

Resistance of plate motion due to continental deformation (Invited)  

NASA Astrophysics Data System (ADS)

Convergent plate margins that produce high mountains often induce deformation that extends for hundreds to thousands kilometers inboard of the plate boundary. Buoyancy forces that are derived from this thickened, elevated continental crust are commonly thought to resist further convergence and contribute to changes in plate rates as the balance of forces on a plate boundary evolves. For orogens that develop broad plateau-style topography, the strength of the deforming continent and the distance over which it deforms may also contribute to plate forces, although this forcing has rarely been considered. For example, the post-collisional slowing of India with respect to Eurasia challenges the role of topography as the cause of decreasing convergence rates and instead favors the role of deforming a confined mantle lithosphere as the cause of slowing. Here, geologic evidence suggests that compressional deformation began at the distal extent of the orogen when continental collision initiated and that the majority of deformation since has remained localized along what can be considered to be a stationary boundary. As post-collisional convergence continued, convergence rates have declined exponentially as did the distance across the intervening region of deformation. The decline in rate and distance occurred in tandem such that the bulk average strain rate across the orogen remained constant and is equal to the modern strain rate determined by GPS. For both linear and non-linear constitutive relationships, a constant average strain rate implies constant average stress (or constant forcing). A constant force per unit length of the plate boundary might be explained by the viscous resistance of the deforming continental mantle lithosphere, as opposed to a change in forces that would be expected from the buoyancy of the evolving high topography. A viscous resistance of the continental lithosphere has not previously been considered as a type of plate forcing, and the Indo-Asia orogen may offer one extreme example of such. Other examples include the ongoing Arabian-Eurasia continental collision and the ocean-continent subduction beneath South America, where exponentially decreasing convergence rates and mountain building are also observed. Long-lived, far-field deformation in the Arabian example may provide analogous to the Tibet case where decreasing convergence rates follow a decrease over which that convergence is absorbed by continental deformation. Unlike Tibet and Arabia, the outward expansion of deformation away from the plate boundary in the Andean orogen suggests that bulk strain rates must have decreased through time. Possibly, such differences may be related to time-dependent rheologic changes associated with subduction-related magmatism, changes in the frictional resistance along the plate contact, or the diminished role of viscous resistance in subduction settings compared to their continental collision counterpart.

Clark, M. K.

2013-12-01

16

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

E-print Network

Linking continental drift, plate tectonics and the thermal state of the Earth's mantle T. Rolf a, as well as oceanic plate tectonics, are surface expressions of mantle convection and closely linked between continental drift, oceanic plate tectonics and the thermal state of the Earth's mantle, by using

Tackley, Paul J.

17

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

E-print Network

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

Pearce, Frederick Douglas

18

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)

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 from MCS [Bécel et al., this session] we have applied full waveform tomography to the prestack MCS data with the goal to form high-resolution velocity profiles for the shallow sections of the normal fault. The starting velocity model for waveform inversion was formed by traveltime tomography on picked refracted arrivals found at offsets from ~5-8 km. The preliminary, phase-only results along one profile show velocities reducing laterally across the shallow end of the normal fault by 200 m/s (from 2200 to 2000 m/s). We interpret this reduction in velocities to indicate that the fault system is active and that fluid flow may be involved. Some authors suggest that low or zero friction is a required mechanical condition to allow slip on such a normal fault system [McKenzie and Jackson, 2012]. Consequently, the obtained results could prove important to re-assessing both the tsunami risk and the plate interface coupling in the Shumagin Seismic Gap area.

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

2013-12-01

19

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

Microsoft Academic Search

Off southwest Taiwan, a west-advancing orogenic wedge has obliquely impinged on the northern continental slope of the South China Sea (SCS) margin. We analyzed a dense grid of multi-channel seismic profiles to reveal the tectonic features in this oblique collision setting. In the upper SCS slope and adjacent to the accretionary wedge, the rifted continental margin is characterized by a

Andrew T. Lin; Char-Shine Liu; Che-Chuan Lin; Philippe Schnurle; Guan-Yu Chen; Wei-Zhi Liao; Louis S. Teng; Hui-Ju Chuang; Ming-Shyan Wu

2008-01-01

20

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

21

Heterogeneity of frontal structure of overriding plate controls co-seismic megathrust slip distribution in trench axial zone, Japan Trench and other subduction zones  

NASA Astrophysics Data System (ADS)

The 2011 off the Pacific coast of Tohoku earthquake induced a giant tsunami by a dynamic slip with the overshoot of the frontal part of the overriding plate near the Japan Trench axis. The maximum slip during the earthquake was detected beneath the deformed zone in the trench axial region of the Miyagi-oki region. The variation in coseismic slip rate would be controlled by a crustal structural variation in the plate interface, which results in a variation of a frictional nature. We estimated the P-wave velocity (Vp) structure to investigate the structural variation spatially correlating to the coseismic slip distribution during the 2011 earthquake by performing an airgun-ocean bottom seismometer experiment on the along-trench profile on the deformed zone in the Japan Trench axial region. We detected that the high Vp body in the hanging wall of the plate interface corresponding to the Cretaceous layer, which is more rigid than the sediment in the deformed zone, sticks out towards the trench axis in the Miyagi-oki segment. In the Miyagi-oki segment, the distance from the trench axis to the forefront of the rigid Cretaceous layer is shorter by ~40 km than in the Sanriku-oki. This means that the width of the less rigid sedimentary prism layer is smaller in the Miyagi-oki than that in the Sanriku-oki. We suggest that this along-arc variation of the hanging wall side structure would cause the difference in propagation of the dynamic slip toward the trench axis between the Miyagi-oki and the Sanriku-oki; the slip reached the trench axis in the Miyagi-oki but not in the Sanriku-oki during the 2011 earthquake. In addition, we found that the similar relationship between the hanging wall structure and the slip distribution of megathrust earthquake observed in Tohoku can recognized in the rupture zones of several major megathrust events, the 1952 Kamchatka, the 1964 Alaska, 1960 and 2010 Chile earthquakes. For example, the 1960 Chile earthquake exhibits the largest coseismic slip at the segment where the sticks out and sedimentary prism is the smallest. We suggest that surveying distribution of a backstop interface would supply important information to assess the passible location of peak slip during any future megathrust events.

Azuma, R.; Hino, R.; Ito, Y.; Mochizuki, K.; Uehira, K.; Murai, Y.; Sato, T.; Takanami, T.; Shinohara, M.; Kanazawa, T.

2013-12-01

22

Strain weakening enables continental plate tectonics Frdric GUEYDAN (1), Jacques PRCIGOUT (2) and Laurent G.J. MONTESI (3)  

E-print Network

1 Strain weakening enables continental plate tectonics Frédéric GUEYDAN (1), Jacques PR�CIGOUT (2-scale strain localization and hence enables plate tectonics. No rheological model proposed to date is comprehensive enough to describe both the weakness of plate boundary and rigid-like behaviour of plate interiors

Paris-Sud XI, Université de

23

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

E-print Network

Influence of continental roots and asthenosphere on plate-mantle coupling Clinton P. Conrad1, highlighting the geological importance of mantle tractions on the lithosphere. Citation: Conrad, C. P., and C'Connell, 2001; Conrad and Lithgow- Bertelloni, 2002]. These studies assume a lithospheric layer with uniform

Conrad, Clint

24

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

NASA Astrophysics Data System (ADS)

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

Calais, Eric; Camelbeeck, Thierry; Stein, Seth

2014-05-01

25

Overriding Faulty Circuit Breakers  

NASA Technical Reports Server (NTRS)

Retainer keeps power on in emergency. Simple mechanical device attaches to failed aircraft-type push/pull circuit breaker to restore electrical power temporarily until breaker replaced. Device holds push/pull button in closed position; unnecessary for crewmember to hold button in position by continual finger pressure. Sleeve and plug hold button in, overriding mechanical failure in circuit breaker. Windows in sleeve show button position.

Robbins, Richard L.; Pierson, Thomas E.

1987-01-01

26

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

SciTech Connect

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.

McNulty, B.A. [California State Univ., Carson, CA (United States). Dept. of Earth Sciences] [California State Univ., Carson, CA (United States). Dept. of Earth Sciences; Farber, D.L. [Lawrence Livermore National Lab., CA (United States). Inst. of Geophysics and Planetary Physics] [Lawrence Livermore National Lab., CA (United States). Inst. of Geophysics and Planetary Physics; Wallace, G.S.; Lopez, R. [Univ. of California, Santa Cruz, CA (United States). Earth Science Dept.] [Univ. of California, Santa Cruz, CA (United States). Earth Science Dept.; Palacios, O. [Inst. de Geologico Minero y Metalurgico, Lima (Peru)] [Inst. de Geologico Minero y Metalurgico, Lima (Peru)

1998-09-01

27

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

ERIC Educational Resources Information Center

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)

Marques, Luis; Thompson, David

1997-01-01

28

Introduction to TETHYS - an Interdisciplinary GIS Database for Studying Continental Plate Collisions  

NASA Astrophysics Data System (ADS)

The TETHYS GIS database has been developed to integrate, visualize, and analyze geologic, geophysical, geochemical, geochronologic, and remote sensing data sets bearing on Tethyan continental plate collisions. The project is predicated on a need for actualistic model 'templates' for interpreting the Earth's geologic record. The Tethyan belt extends from the western Mediterranean through Asia Minor and Central Eurasia, to east and Southeast Asia and marks successive closure of the Tethyan oceans. Because of their time-transgressive character, Tethyan collisions offer natural laboratories for examining features such as continental `escape', collision-induced upper mantle flow magmatism, and marginal basin opening, associated with modern convergent plate margins. Large integrated geochemical and geophysical databases allow for such models to be tested against the geologic record, leading to a better understanding of continental accretion throughout Earth history. The TETHYS database combines digital topographic and geologic information, remote sensing images, sample-based geochemical, geochronologic, and isotopic data (for pre- and post-collision igneous activity), and data for seismic tomography, shear-wave splitting, space geodesy, and information for plate tectonics reconstructions. For the GIS, Oracle 9i is being used as a database engine. The database system is integrated with ArcGIS and ArcIMS (ARC Internet Map Server) using ArcSDE (ARC Spatial Database Engine). Analysis of data is aided by a suite of interactive custom tools and graphic objects including pixel ID, stretching, profiles, histograms, focal mechanisms, x-y plots, and 3-D visualization tools. The latter is enabling interactive visualization of seismic tomography data for the solid earth. We are currently working on expanding our database and on adding additional tools for data analysis and visualization. Interim partial access to the data and metadata is available at: http://www.esrs.wmich.edu/tethys/ http://geoinfo.geosc.uh.edu/Tethys/

Sultan, M.; Sandvol, E.; Khan, S. D.; Flower, M.; Manocha, N.; Markondiah Jayaprakash, S.; Becker, R.

2005-12-01

29

Continental subduction and a mechanism for exhumation of high-pressure metamorphic rocks: new modelling and field data from Oman  

Microsoft Academic Search

The physical model presented reveals two principal regimes of continental subduction: a highly compressional (HC) regime and a low compressional (LC) regime characterised by high and low pressure between the overriding and subducting plates, respectively. The pressure is inversely proportional to the pull force, which depends on the difference between average density of the subducting lithosphere and density of the

Alexander I. Chemenda; Maurice Mattauer; Alexander N. Bokun

1996-01-01

30

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

NASA Astrophysics Data System (ADS)

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 and West Greenland, close to where continental crust starts to thin towards oceanic crust, illustrates the common association between EPCMs and the edges of cratons. These observations indicate that the elevation of EPCMs may be due to processes operating where there is a rapid change in crustal/lithosphere thickness. Vertical motion of EPCMs may thus be related to lithosphere-scale folding caused by compressive stresses at the edge of a craton (e.g. Cloetingh et al., 2008). The compression may be derived either from orogenies elsewhere on a plate or from differential drag at the base of the lithosphere by horizontal asthenospheric flow (Green et al., 2013). Bonow, Japsen, Nielsen. Global Planet. Change in review. Cloetingh, Beekman, Ziegler, van Wees, Sokoutis, 2008. Geol. Soc. Spec. Publ. (London) 306. Cobbold, Meisling, Mount, 2001. AAPG Bull. 85. Green, Lidmar-Bergström, Japsen, Bonow, Chalmers, 2013. GEUS Bull. 2013/30. Japsen, Chalmers, Green, Bonow 2012a, Global Planet. Change 90-91. Japsen, Bonow, Green, Cobbold, Chiossi, Lilletveit, Magnavita, Pedreira, 2012b. GSA Bull. 124. Japsen, Green, Bonow, Nielsen. Global Planet. Change in review.

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

2014-05-01

31

Dynamics of continental accretion.  

PubMed

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

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

2014-04-10

32

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

USGS Publications Warehouse

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

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

1996-01-01

33

Plate rotation during continental collision and its relationship with the exhumation of UHP metamorphic terranes: application to the Norwegian Caledonides  

NASA Astrophysics Data System (ADS)

Lateral variation and asynchronous onset of collision during the convergence of continents can significantly affect the burial and exhumation of subducting material. We use 3D numerical models for continental collision to discuss how deep burial and exhumation of ultra-high pressure metamorphic rocks are enhanced by oblique convergence and resulting rotation of the colliding plates. Rotation during collision locally favours eduction, the inversion of the subduction process following ocean slab break-off, and may relate to the discontinuous distribution of ultra-high pressure (UHP) terranes along collision zones. For example the terminal (Scandian) collision of Baltica and Laurentia, which formed the Scandinavian Caledonides resulted in the exhumation of only one large high pressure/ultra-high pressure (HP/UHP) terrane, the Western Gneiss Complex (WGC), near the southern end of the collision zone. Rotation of the subducting Baltica plate during collision may provide a likely explanation for this distribution. We explore this hypothesis by comparing orthogonal and oblique collision models and conclude that an oblique collision can transport continental material up to 60km deeper, and heat material up to 300°C hotter, than an orthogonal collision. Our oblique collision model predicts that subducted continental margin material returns to the surface only in the region where collision initiated. The oblique collision model is consistent with petrological and geochonological observations from the Western Gneiss Complex and makes predictions for the general evolution of the Scandinavian Caledonides. We propose the collision between Laurentia and Baltica started at the southern end of the collisional zone, and propagated northward. This asymmetric geometry resulted in the counter clockwise rotation of Baltica and the northwards movement of Baltica's rotational pole with respect to Laurentia, consistent with paleomagnetic data from other studies. Our model has applications to others orogens with regional UHP terranes, such as the Dabie Shan and Papua New Guinea cases, where block rotation during exhumation has also been recorded.

Bottrill, Andrew; van Hunen, Jeroan; Cuthbert, Simon; Allen, Mark; Brueckner, Hannes

2014-05-01

34

Continental island from the Upper Silurian (Ludlow) Sino-Korean plate  

Microsoft Academic Search

Recent field studies on Upper Silurian stratigraphy and paleontology in the Inner Mongolia Autonomous Region (for short Inner\\u000a Mongalia) near Bater Obo (=Bateaobao) resulted in the discovery of a small continental island with fossil invertebrates preserved\\u000a as encrusters (stromatoporoids and corals) attached directly to a rocky shore surface and buried by silty clay mud. The Bater\\u000a island (oamed herein) is

Jiayu Rong; M. E. Johnson; B. G. Baarli; Wenguo Li; Wenbo Su; Jian Wang

2001-01-01

35

Implication of the Central Gulf of California (MX) Earthquake cycle in understanding continental plate boundary rheology  

NASA Astrophysics Data System (ADS)

The Gulf of California is characterized by the development of a highly oblique plate boundary that rifted the Baja California Peninsula from mainland North America through a series of long transform faults and deep basins. Within the central part of Gulf of California 90 % of the relative motion between North America and Pacific plate is localized in a very narrow region between the Baja California peninsula and a chain of islands (in particular Angel de la Guarda and San Lorenzo). In August 2009 and April 2012, two earthquakes (Mw~7) struck the region. The collection of campaign GPS data since 2004 and after the two seismic events, allows an evaluation of the surface deformation during the full earthquake cycle. Here we focus on the surface deformation relative to a rigid Baja California motion (defined by GPS observations along the Peninsula) during the interseismic period before the two seismic events, and the co- and post-seismic period of each earthquake. In particular, we explore the implications of the post-seismic surface deformation in understanding the rheological and mechanical properties underneath the seismogenic layer in a region characterized by a developing plate boundary. a) Interseismic velocity field in a Baja fixed reference frame. b-c) cosesimic displacement fro the 2009 and 2012 seismic events (focal mechanisms from Global CMT web page) Relative position with respect to the first observation of the two stations closest to the coast up to July 1st 2012.

Malservisi, R.; Plattner, C.; Hackl, M.; Suarez Vidal, F.

2012-12-01

36

43 CFR 3903.53 - Overriding royalties.  

...to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) OIL SHALE MANAGEMENT-GENERAL Fees, Rentals, and Royalties § 3903.53 Overriding royalties. The lessee must file...

2014-10-01

37

43 CFR 3903.53 - Overriding royalties.  

Code of Federal Regulations, 2012 CFR

...to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) OIL SHALE MANAGEMENT-GENERAL Fees, Rentals, and Royalties § 3903.53 Overriding royalties. The lessee must file...

2012-10-01

38

43 CFR 3903.53 - Overriding royalties.  

Code of Federal Regulations, 2011 CFR

...Relating to Public Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR RANGE MANAGEMENT (4000) OIL SHALE MANAGEMENT-GENERAL Fees, Rentals, and Royalties § 3903.53 Overriding royalties. The lessee must file...

2011-10-01

39

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

NASA Astrophysics Data System (ADS)

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.

Takeuchi, Christopher S.; Fialko, Yuri

2012-05-01

40

Plate Tectonics  

NSDL National Science Digital Library

Students will go over the main points of plate tectonics, including the theory of continental drift, different types of plate boundaries, seafloor spreading, and convection currents. We have been spending time learning about plate tectonics. We have discussed the theory of continental drift, we have talked about the different types of plate boundaries, we have also learned about seafloor spreading and convection currents. Plate Boundary Diagram Now is your chance ...

Rohlfing, Mrs.

2011-02-03

41

The role that plate tectonics, inferred stress changes and stratigraphic unconformities have on the evolution of the West and Central African Rift System and the Atlantic continental margins  

NASA Astrophysics Data System (ADS)

The Muglad rift basin of Sudan, is a good example of polyphase rifting, with at least three major phases of basin development. Each phase has resulted in the generation of source rock, reservoir and seal geology with structural traps often closely linked to basement highs. In this paper we investigate on a regional scale the tectonic processes that have contributed to rift basin development. On a regional scale, the evolution of the Africa-wide Mesozoic rift system is intimately linked to relative movements of African sub-plates and to global plate tectonic processes and plate interactions. Changes in plate interactions are observed in the oceanic crust as azimuth changes of fracture zone geometries and by inference have caused significant modifications to both the orientation and magnitude of the motions of the African sub-plates. Such plate motion processes have controlled the polyphase development of the West and Central African Rift System. On the basinal scale, changes of sub-plate motions have resulted in changes in the stress field which have had a clear impact on the deformation and fault geometries of rift basins and on the resulting stratigraphy. The construction of the first unified stratigraphic chart for the West and Central African Rift System shows a close correlation in the timing of the major unconformities with the timing of changes in relative plate motion as observed in the changes of the azimuthal geometry of the oceanic fracture zones in the Central Atlantic. Since similarly timed unconformities exist along the continental margins of Africa and South America, we propose that the causative mechanism is change in relative plate motion which leads to an increase or decrease in the tension on the plate and thus controls the strength or effective elastic thickness, Te, of the crust/plate beneath the margins. This results in a focused change in isostatic response of the margin during short-period changes in relative plate motion; i.e. more tension will mean that loads are not compensated locally resulting in local uplift of the margin.

Fairhead, J. D.; Green, C. M.; Masterton, S. M.; Guiraud, R.

2013-05-01

42

Motion of continental slivers and creeping subduction in the northern Andes  

NASA Astrophysics Data System (ADS)

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.

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

43

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

NASA Astrophysics Data System (ADS)

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

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

44

A review of Wilson Cycle plate margins: What is the role of mantle plumes in continental break-up along former sutures?  

NASA Astrophysics Data System (ADS)

It was Tuzo Wilson (1966) who recognised that the different faunal distributions on both sides of the present-day North Atlantic Ocean required the existence of an earlier proto-Atlantic Ocean. The observation that the present-day Atlantic Ocean mainly opened along a former suture was a crucial step in the formulation of the Wilson Cycle theory. The theory implies that collision zones are structures that are able to localize extensional deformation for long times after the collision has waned. We review margin pairs around the Atlantic and Indian Oceans with the aim to evaluate the extent to which oceanic opening used former sutures and to analyse the role of mantle plumes in continental break-up. We aid our analyses with plate tectonic reconstructions using GPlates (www.gplates.org). Already Wilson recognized that Atlantic break-up did not always follow the precise line of previous junction. For example, Atlantic opening did not utilize the Iapetus suture in Great Britain and rather than opening along the younger Rheic suture north of Florida, break-up occurred along the older Pan-African structures south of Florida. As others before us, we find no correlation of suture and break-up age. Often continental break-up occurs some hundreds of Myrs after collision, but it may also take more than a Gyr, as for example for Australia-Antarctica and Congo-São Francisco. This places serious constraints on potential collision zone weakening mechanisms. Several studies have pointed to a link between continental break-up and large-scale mantle upwellings. It is, however, much debated whether plumes use existing rifts as a pathway, or whether plumes play an active role in causing rifting. It is also important to realise that in several cases break-up cannot be related to plume activity. Examples are the Iberia-Newfoundland, Equatorial Atlantic Ocean, and Australia-Antarctica plate margins. For margins that are associated with large igneous provinces (LIPs), we find a positive correlation between break-up age and LIP age. We interpret this to indicate that plumes can aid the factual continental break-up. However, plumes may have been guided towards the rift for margins that experienced a long rift history (e.g., Norway-Greenland), to then trigger the break-up. This could offer a partial reconciliation in the debate of a passive or active role for mantle plumes in continental break-up. (Wilson, J.T., 1966. Did the Atlantic close and then re-open? Nature 211, 676-681)

Buiter, Susanne; Torsvik, Trond

2013-04-01

45

Continental subduction and exhumation of high-pressure rocks: insights from thermo-mechanical laboratory modelling  

NASA Astrophysics Data System (ADS)

Thermo-mechanical physical modelling of continental subduction is performed to investigate the exhumation of deeply subducted continental crust. The model consists of two lithospheric plates made of new temperature sensitive analogue materials. The lithosphere is underlain by liquid asthenosphere. The continental lithosphere contains three layers: the weak sedimentary layer, the crust made of a stronger material, and of a still stronger lithospheric mantle. The whole model is subjected to a constant vertical thermal gradient, causing the strength reduction with depth in each lithospheric layer. Subduction is driven by both push force and pull force. During subduction, the subducting lithosphere is heating and the strength of its layers reduces. The weakening continental crust reaches maximal depth of about 120 km and cannot subduct deeper because its frontal part starts to flow up. The subducted crust undergoes complex deformation, including indicated upward ductile flow of the most deeply subducted portions and localised failure of the subducted upper crust at about 50-km depth. This failure results in the formation of the first crustal slice which rises up between the plates under the buoyancy force. This process is accompanied by the delamination of the crustal and mantle layers of the subducting lithosphere. The delamination front propagates upwards into the interplate zone resulting in the formation of two other crustal slices that also rise up between the plates. Average equivalent exhumation rate of the crustal material during delamination is about 1 cm/year. The crust-asthenosphere boundary near the interplate zone is uplifted. The subducted mantle layer then breaks off, removing the pull force and thereby stopping the delamination and increasing horizontal compression of the lithosphere. The latter produces shortening of the formed orogen and the growth of relief. The modelling reveals an interesting burial/exhumation evolution of the sedimentary cover. During initial stages of continental subduction the sediments of the continental margin are dragged to the overriding plate base and are partially accreted at the deep part of the interplate zone (at 60-70 km-depth). These sediments remain there until the beginning of delamination during which the pressure between the subducted crust and the overriding plate increases. This results in squeezing the underplated sediments out. Part of them is extruded upwards along the interplate zone to about 30-km depth at an equivalent rate of 5-10 cm/year.

Boutelier, David; Chemenda, Alexandre; Jorand, Cedric

2004-05-01

46

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

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

47

oZONE Faculty and Staff Course Overrides  

E-print Network

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

Oklahoma, University of

48

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

NASA Technical Reports Server (NTRS)

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.

Cohen, Steven C.

1999-01-01

49

43 CFR 3933.32 - Overriding royalty interests.  

Code of Federal Regulations, 2012 CFR

...Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR MINERALS MANAGEMENT (3000) MANAGEMENT OF OIL SHALE EXPLORATION AND LEASES Assignments and Subleases § 3933.32 Overriding royalty interests. File at the...

2012-10-01

50

43 CFR 3933.32 - Overriding royalty interests.  

Code of Federal Regulations, 2011 CFR

...Lands (Continued) BUREAU OF LAND MANAGEMENT, DEPARTMENT OF THE INTERIOR RANGE MANAGEMENT (4000) MANAGEMENT OF OIL SHALE EXPLORATION AND LEASES Assignments and Subleases § 3933.32 Overriding royalty interests. File at the...

2011-10-01

51

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

NASA Technical Reports Server (NTRS)

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.

Argus, Donald F.; Heflin, Michael B.

1995-01-01

52

Override problems lead chain to EMS with remote monitor  

SciTech Connect

When R.B. Furniture Co. employees began overriding the Trimax energy management system (EMS) in the company's 61 showrooms, the company shifted to En-Log units for the remaining stores despite the 9- to 22-month payback of the Trimax systems. Remote communications allow monitoring of the En-Log systems and prevent overrides. The case history compares specifications and costs for the two systems. (DCK)

Galvin, C.

1983-09-26

53

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

NASA Astrophysics Data System (ADS)

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.

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

2004-11-01

54

Late-interseismic state of a continental plate-bounding fault: Petrophysical results from DFDP-1 wireline logging and core analysis, Alpine Fault, New Zealand  

NASA Astrophysics Data System (ADS)

We present a geophysical characterization at 0.1-100 m scales of a major plate-bounding continental fault in a late-interseismic state. The Alpine Fault produces MW˜8 earthquakes every 200-400 years and last ruptured in 1717 AD. Wireline geophysical logs and rock cores extending from one side of the Alpine Fault to the other were acquired in two boreholes drilled in 2011 at Gaunt Creek during the first phase of the Deep Fault Drilling Project (DFDP-1). These data document ambient conditions under which the next Alpine Fault earthquake will occur. Principal component analysis of the wireline logging data reveals that >80% of the variance is accounted for by electrical, acoustic, and natural gamma properties, and preliminary multivariate classification enables the lithologies of sections of missing core to be reconstructed from geophysical measurements. The fault zone exhibits systematic variations in properties consistent with common processes of progressive alteration and comminution near the principal slip zone, superimposed on different protolith compositions. Our observations imply that the fault zone has the opposite sense of elastic asymmetry at 0.1-100 m scales to that of the crustal-scale orogen imaged by remote geophysical methods. On the basis of the fault-zone scale asymmetry, the bimaterial interface model of preferred earthquake rupture directions implies a northeastward direction of preferred Alpine Fault rupture. On-going characterization of the structural and hydraulic architecture of the Alpine Fault will improve our understanding of the relationship between in situ conditions, earthquake rupture processes, and the hazards posed by future earthquakes.

Townend, J.; Sutherland, R.; Toy, V. G.; Eccles, J. D.; Boulton, C.; Cox, S. C.; McNamara, D.

2013-09-01

55

Self-assembled software and method of overriding software execution  

DOEpatents

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.

Bouchard, Ann M.; Osbourn, Gordon C.

2013-01-08

56

Plate Tectonics Quiz  

NSDL National Science Digital Library

This quiz for younger students asks them 10 questions about plate motions, rock types in continental and oceanic crust, crustal formation and mountain building, the supercontinent Pangea, and the theory of continental drift. A link to a page on continental drift provides information to answer the questions.

57

Physicians' Decisions to Override Computerized Drug Alerts in Primary Care  

Microsoft Academic Search

Background: Although computerized physician order entry reduces medication errors among inpatients, little is known about the use of this system in primary care. Methods: We calculated the override rate among 3481 consecutivealertsgeneratedat5adultprimarycareprac- tices that use a common computerized physician order entry system for prescription writing. For detailed re- view, we selected a random sample of 67 alerts in which physicians

Saul N. Weingart; Maria Toth; Daniel Z. Sands; Mark D. Aronson; Roger B. Davis; Russell S. Phillips

2003-01-01

58

Overriding of Drug Safety Alerts in Computerized Physician Order Entry  

Microsoft Academic Search

Many computerized physician order entry (CPOE) systems have integrated drug safety alerts. The authors reviewed the literature on physician response to drug safety alerts and interpreted the results using Reason's framework of accident causation. In total, 17 papers met the inclusion criteria. Drug safety alerts are overridden by clinicians in 49% to 96% of cases. Alert overriding may often be

HELEEN VAN DER SIJS; ARNOLD VULTO; MARC BERG

59

Modeling the influence of plate motions on subduction  

NASA Astrophysics Data System (ADS)

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)

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

2014-05-01

60

Plate Tectonics  

NSDL National Science Digital Library

The Plate Tectonics SciPack explores the various materials that make up Earth and the processes they undergo to provide a framework for understanding how continents are created and change over time. The focus is on Standards and Benchmarks related to Earth's layers, oceanic and continental plates and the interactions between plates.In addition to comprehensive inquiry-based learning materials tied to Science Education Standards and Benchmarks, the SciPack includes the following additional components:� Pedagogical Implications section addressing common misconceptions, teaching resources and strand maps linking grade band appropriate content to standards. � Access to one-on-one support via e-mail to content "Wizards".� Final Assessment which can be used to certify mastery of the concepts.Learning Outcomes:Plate Tectonics: Layered Earth� Identify that Earth has layers (not necessarily name them), and that the interior is hotter and more dense than the crust.� Identify the crust as mechanically strong, and the underlying mantle as deformable and convecting.Plate Tectonics: Plates� Identify that the outermost layer of Earth is made up of separate plates.� Choose the correct speed of the motion of plates.� Identify the ocean floor as plate, in addition to the continents (to combat the common idea that only continents are plates, floating around on the oceans).� Recognize that oceans and continents can coexist on the same plate.Plate Tectonics: Plate Interactions� Identify the different interactions between plates.� Discuss what happens as a result of those interactions.Plate Tectonics: Consequences of Plate Interactions� Explain why volcanoes and earthquakes occur along plate boundaries. � Explain how new sea floor is created and destroyed.� Describe features that may be seen on the surface as a result of plate interactions.Plate Tectonics: Lines of Evidence� Use plate tectonics to explain changes in continents and their positions over geologic time.� Provide evidence for the idea of plates, including the location of earthquakes and volcanoes, continental drift, magnetic orientation of rocks in the ocean floor, etc.

National Science Teachers Association (NSTA)

2007-03-21

61

Gender, Threat\\/Control-Override Delusions and Violence  

Microsoft Academic Search

This study brings together the threat\\/control-override perspective and the literature on gender and stress coping to argue that gender moderates the association between threat delusions and violence. We suggest that men are more likely than women to respond to stressors such as threat delusions with violence. We test these ideas using data from the MacArthur Violence Risk Assessment Study, a

Brent Teasdale; Eric Silver; John Monahan

2006-01-01

62

Continental Dynamics  

NSF Publications Database

... structure, composition, and dynamical evolution of the continents and continental building blocks ... geophysical, and geochemical structure and evolution of the continents is still not clearly ...

63

Viscous fingering in the Earth's mantle beneath western North American and the Pacific plate  

NASA Astrophysics Data System (ADS)

The recent advent of high resolution seismic tomography provided by the USArray project in western North American and ocean bottom seismometer deployments on the seafloor have shown a critical link between surface geology, volcanic observations and deep mantle structure. A unique pattern of volcanic lineaments have been observed on the south Pacific seafloor which form a group of parallel linear volcanic chains. Recently, similar features have been proposed on continental plates in western North America as a group of Cenozoic volcanic lineaments consisting of the Yellowstone, St George, Colorado Mineral Belt, and Jimenez volcanic trends. In both the North American continent and Pacific ocean case, an array of seismometers were deployed and seismic tomography images reveal a set of regularly spaced, linear, parallel low velocity anomalies that align in the direction of plate motion and correlate with surface volcanism. Here we consider a fluid dynamic model of viscous fingering in the asthenospheric mantle which links deep mantle flow to surface volcanic observations. We present results from physical fluid experiments scaled to mantle dynamics which indicate that Saffman-Taylor instabilities or viscous fingering may form in the asthenosphere beneath moving tectonic plates. Scaling indicates that the wavelength of fingering (l_f) is strongly dependent on asthenospheric channel thickness (B) as l_f = 4B. The presence of a mobile overriding plate acts to align fingers in the direction of plate motion propagating both upstream and downstream. Tomography images indicate that fingering wavelengths may be significantly larger beneath continental plates compared to oceanic plates. Further scaling between laboratory fluid experiments and mantle seismic tomography including comparison of surface volcanic lineaments, tomographic imaging, and lithosphere-asthenosphere thickness will be presented.

Weeraratne, D. S.; Parmentier, E.; Lekic, V.

2012-12-01

64

Override of spontaneous respiratory pattern generator reduces cardiovascular parasympathetic influence  

NASA Technical Reports Server (NTRS)

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.

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

1995-01-01

65

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

Code of Federal Regulations, 2012 CFR

...Interior 2 2012-10-01 2012-10-01 false May I create overriding royalties on my Federal lease? 3504.26 Section...Rental, Royalty and Bonds Royalties § 3504.26 May I create overriding royalties on my Federal lease? Yes,...

2012-10-01

66

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

Code of Federal Regulations, 2011 CFR

...Interior 2 2011-10-01 2011-10-01 false May I create overriding royalties on my Federal lease? 3504.26 Section...Rental, Royalty and Bonds Royalties § 3504.26 May I create overriding royalties on my Federal lease? Yes,...

2011-10-01

67

Tectonic Settings and Volcanic Activity: Continental volcanic arc & Volcanic-island-arc  

NSDL National Science Digital Library

The representation depicts the formation of volcanic mountains at plate boundaries when an oceanic plate sinks under a continental plate, and when two oceanic plates collide and one sinks under the other. This representation is found under the "Continental volcanic arc" and "Volcanic island arc" tabs.

68

Mountain Maker- Earth Shaker (Convergent Boundary: oceanic-continental)  

NSDL National Science Digital Library

The representation depicts plate boundary interactions. The convergent boundary is one part of a larger interactive diagram (the 2nd slider/ arrow from the left), that focuses on an ocean plate pressing against a continental plate. This review specifically addresses the part of the resource dealing with what happens when plates pull apart. The "show intro" link provides instruction for diagram manipulation.

69

ConcepTest: Plate Tectonic Theory  

NSDL National Science Digital Library

Which of the following statements is not consistent with plate tectonic theory? a. Continental crust is generally older than oceanic crust. b. The number of plates has changed through time. c. Mountain chains are ...

70

Geodynamics: How plumes help to break plates  

NASA Astrophysics Data System (ADS)

Computer models show how hot material that rises from Earth's interior is affected by plate tectonics, producing unexpected irregularities in Earth's topography and assisting in the break-up of continental plates. See Letter p.85

Buiter, Susanne

2014-09-01

71

Continental dynamics and continental earthquakes  

NASA Astrophysics Data System (ADS)

Two key research projects in geoscience field in China since the IUGG meeting in Birmingham in 1999, the project of “East Asian Continental Geodynamics” and the project of “Mechanism and Prediction of Strong Continental Earthquakes” are introduced in this paper. Some details of two projects, such as their sub-projects, some initial research results published are also given here. Because of the large magnitude of the November 14, 2001 Kunlun Mountain Pass M S=8.1 earthquake, in the third part of this paper, some initial research results are reviewed for the after-shock monitoring and the multi-discipline field survey, the impact and disaster of this earthquake on the construction site of Qinghai-Xizang (Tibet) railway and some other infrastructure.

Dong-Ning, Zhang; Guo-Min, Zhang; Pei-Zhen, Zhang

2003-09-01

72

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

Code of Federal Regulations, 2013 CFR

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

2013-10-01

73

Continental Drift  

NSDL National Science Digital Library

This lesson plan is part of the DiscoverySchool.com lesson plan library for grades 6-8. It focuses on Alfred Wegener's theory of Continental Drift and the evidence used to support it. Using fossil types and maps, students view similarities between continents that led Wegener to conclude that they had once been together as a supercontinent, Pangea. Included are objectives, materials, procedures, discussion questions, evaluation ideas, suggested readings, and vocabulary. There are videos available to order which complement this lesson, and links to teaching tools for making custom quizzes, worksheets, puzzles and lesson plans.

74

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

PubMed Central

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

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

2014-01-01

75

Lithospheric deformation during the early stages of continental collision: numerical experiments  

E-print Network

1 Lithospheric deformation during the early stages of continental collision: numerical experiments, Halifax, Nova Scotia, Canada Short title: LITHOSPHERE DEFORMATION DURING COLLISION #12;2 Abstract. The nature of lithospheric deformation during continental plate collision still remains unresolved. While

Beaumont, Christopher

76

The Brazilian continental margin  

NASA Astrophysics Data System (ADS)

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.

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

1981-04-01

77

Plate Borders and Mountain Building  

NSDL National Science Digital Library

This page features animations of four different types of plate boundaries, including one animation of the collision of two pieces of continental crust, forming steep mountain ranges. The animations are all presented in flash, and the plate convergence offers a useful, generic view of orogeny.

Schlumberger Excellence In Educational Development, Inc.

78

Plate Tectonics: Lines of Evidence  

NSDL National Science Digital Library

This Science Object is the fifth of five Science Objects in the Plate Tectonics SciPack. It explores the physical, geographical, and geological evidence for the theory of continental drift and plate tectonics. Plate tectonics provide a unifying framework for understanding Earth processes and history, and is supported by many lines of evidence. Over geologic time, plates move across the globe creating different continents (and positions of continents). Learning Outcomes:� Use plate tectonics to explain changes in continents and their positions over geologic time.� Provide evidence for the idea of plates, including the location of earthquakes and volcanoes, continental drift, magnetic orientation of rocks in the ocean floor, etc.

National Science Teachers Association (NSTA)

2006-11-01

79

A Coupled Thermomechanical Model of Continental Collision in Alpine-Type Mountain Belts  

NASA Astrophysics Data System (ADS)

A fully coupled numerical thermomechanical model that accounts for strain localization, surface processes, phase changes and high viscosity contrasts is used to test different mechanisms of subduction in continental collision zones. The model considers various end member cases including low and high buoyancy of the subducted crustal material after metamorphic reactions. The low buoyancy model predicts steep subduction with early break-off and 3 levels of metamorphic rock exhumation for the same collision context: the "classical" corner flow LP-LT exhumation in the accretionary prism; deeper (70 km) HP-HT exhumation for the thickened subducting crustal-sedimentary wedge, and ultra HP-HT exhumation from the "lower" crustal chamber, forming at the depth of 100-120 km and separated from the upper one by a narrow crustal channel, which width can oscillate in the process of shortening, thus controlling the quantity of the crustal material exchanged between the crustal wedge and the lower crustal chamber. Although both zones of crustal accumulation and the narrow channel between them resemble a vortex-shaped nozzle, this "nozzle" appears to be too soft to produce any significant overpressures. From the upper crustal wedge, the material is exhumed following the ascending shear flow created by the overriding plate assisted by positive buoyancy of the heated crustal material. From the lower crustal chamber, the material is transported upwards to the upper crustal wedge by a flow induced by the asthenospheric traction and a small scale convective instability forming in the lower crustal chamber due to its heating by the overriding asthenosphere. In the case of high buoyancy, underplating may occur and the latter mechanisms become dominant resulting in fast exhumation of the crust to the surface, accelerated or slowed subduction in case of full or partial crustal decoupling, respectively, and upper plate extension. For all scenarios, the experiments demonstrate the primary importance of the pre- and post-metamorphic density contrasts as well as the importance of the lateral shear flow zones systematically created at the boundaries between the upper and lower crust and lower crust and mantle lithosphere (Moho zone). Shear strain localization is also predicted at the lithosphere - asthenosphere boundary.

Burov, E.; Jolivet, L.; Lepourhiet, L.; Toussaint, G.

2001-12-01

80

Geological record of fluid flow and seismogenesis along an erosive subducting plate boundary.  

PubMed

Tectonic erosion of the overriding plate by the downgoing slab is believed to occur at half the Earth's subduction zones. In situ investigation of the geological processes at active erosive margins is extremely difficult owing to the deep marine environment and the net loss of forearc crust to deeper levels in the subduction zone. Until now, a fossil erosive subduction channel-the shear zone marking the plate boundary-has not been recognized in the field, so that seismic observations have provided the only information on plate boundary processes at erosive margins. Here we show that a fossil erosive margin is preserved in the Northern Apennines of Italy. It formed during the Tertiary transition from oceanic subduction to continental collision, and was preserved by the late deactivation and fossilization of the plate boundary. The outcropping erosive subduction channel is approximately 500 m thick. It is representative of the first 5 km of depth, with its deeper portions reaching approximately 150 degrees C. The fossil zone records several surprises. Two décollements were simultaneously active at the top and base of the subduction channel. Both deeper basal erosion and near-surface frontal erosion occurred. At shallow depths extension was a key deformation component within this erosive convergent plate boundary, and slip occurred without an observable fluid pressure cycle. At depths greater than about 3 km a fluid cycle is clearly shown by the development of veins and the alternation of fast (co-seismic) and slow (inter-seismic) slip. In the deepest portions of the outcropping subduction channel, extension is finally overprinted by compressional structures. In modern subduction zones the onset of seismic activity is believed to occur at approximately 150 degrees C, but in the fossil channel the onset occurred at cooler palaeo-temperatures. PMID:18256668

Vannucchi, Paola; Remitti, Francesca; Bettelli, Giuseppe

2008-02-01

81

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

PubMed Central

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 serious patient injuries, even when relatively few false positive alerts are displayed. PMID:24386447

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

2013-01-01

82

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

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

83

Relevance Override: On the Reduced Impact of Cues Under High-Motivation Conditions of Persuasion Studies  

Microsoft Academic Search

This research addressed the reduced impact of cues under high processing motivation of persuasion experiments. The results of 3 studies suggested that such reduced impact is due to a relevance override whereby any more subjectively relevant information swamps the effects of any less subjectively relevant information, given the recipient's sufficient motivation to process both. Because, in much persuasion research, cues

Antonio Pierro; Lucia Mannetti; Arie W. Kruglanski; David Sleeth-Keppler

2004-01-01

84

A global-scale plate reorganization event at 105-100 Ma  

NASA Astrophysics Data System (ADS)

A major plate reorganization is postulated to have occurred at approximately 100 Ma. However, this reorganization has received limited attention, despite being associated with the most prominent suite of fracture zone bends on the planet and many other geological events. We investigate tectonic events from the period ˜110 to 90 Ma and show that the reorganization occurred between 105 and 100 Ma, was global in scale, and affected all major plates. Seafloor evidence for plate motion changes is abundant during this period, with either fracture zone bends or terminations preserved in all ocean basins. Long-lived eastern Gondwanaland subduction ended along a 7000 km long section of the margin, while elsewhere around the proto-Pacific rim subduction continued and there is evidence that compressional stresses increased in the overriding plates. Thrusting in western North America, transpression and basin inversion in eastern Asia, and development of the present-day Andean-style margin along western South America occurred contemporaneous with the development of an extensional regime in eastern Gondwanaland. Basin instability in Africa and western Europe further demonstrates that lithospheric stress regime changes were widespread at this time. Considering the timing of the reorganization and the nature of associated plate boundary changes, we suggest that eastern Gondwanaland subduction cessation is the most likely driving mechanism for the reorganization. Subduction is the dominant driver of plate motion and therefore this event had the potential to strongly modify the balance of driving forces acting on the plates in the southwestern proto-Pacific and neighboring plates, whereby producing widespread changes in plate motion and continental lithospheric stress patterns. We propose that major changes in ridge-trench interaction triggered the cessation of subduction. The progressive subduction of two closely spaced perpendicular mid ocean ridges at the eastern Gondwanaland subduction zone, to the east of Australia and New Zealand, respectively, resulted in very young crust entering the trench and we suggest that by 105-100 Ma there was insufficient negative buoyancy to drive subduction. Finally, we propose that the plume push force of the Bouvet plume, that erupted near the African-Antarctic-South American triple junction, contributed to plate motion changes in the southern Atlantic region.

Matthews, Kara J.; Seton, Maria; Müller, R. Dietmar

2012-11-01

85

GEOPHYSICAL RESEARCH LETTERS, VOL. 27, NO. 19, PAGES 3117-3120, OCTOBER 1, 2000 Rotation and plate locking at the southern  

E-print Network

satellite orbits 1Rensselaer Polytechnic Institute, Troy, New York 2Oregon State University, Corvallis offshore, consistent with earlier studies, and is sufficient to allow occasional great earthquakes inferred- tributed permanent deformation within the overriding plate. Evidence for large thrust earthquakes

Goldfinger, Chris

86

Catastrophic Plate Tectonics: A Global Flood Model of Earth History  

Microsoft Academic Search

In 1859 Antonio Snider proposed that rapid, horizontal divergence of crustal plates occurred during Noah's Flood. Modern plate tectonics theory is now conflated with assumptions of uniformity of rate and ideas of continental \\

Steven A. Austin; John R. Baumgardner; D. Russell Humphreys; Andrew A. Snelling; Larry Vardiman; Kurt P. Wise

87

Impact of Mantle Wind on Subducting Plate Geometry and Interplate Pressure: Insights From Physical Modelling  

Microsoft Academic Search

New physical models of subduction investigate the impact of large-scale mantle flow on the structure of the subducted slab and deformation of the downgoing and overriding plates. The experiments comprise two lithospheric plates made of highly filled silicone polymer resting on a model asthenosphere of low viscosity transparent silicone polymer. Subduction is driven by a piston that pushes the subducting

D. Boutelier; A. R. Cruden

2005-01-01

88

Lateral growth of the continental crust through deep level subduction accretion: a re-evaluation of central Greek Rhodope  

NASA Astrophysics Data System (ADS)

The Rhodope Massif of northern Greece and southern Bulgaria has been variably interpreted as a fragment of pre-Alpine (possibly Hercynian or Precambrian age) continental crust that was actively involved in European margin convergent tectonics during the Mesozoic and Tertiary. Alternatively we propose that, for central Greek Rhodope, the lithological associations and tectonothermal history are consistent with progressive south-directed Mesozoic crustal growth through deep level subduction-accretion, a process which involved the near continuous transferral of material of oceanic and continental margin affinity, from footwall to hanging wall within a north-directed Palaeotethyan subduction system. Central Greek Rhodope comprises a sequence of schists, gneisses and migmatites of wide compositional variation that have undergone intense tectonic intermixing. Extensive occurrences of marble are associated with amphibolites, variably retrogressed eclogites, meta-gabbros and ultramafic rocks. Quartzo-feldspathic gneisses are abundant throughout the area, and are associated with psammitic meta-greywacke sequences, pelites and quartzites. The presence of intercalated marble slivers and thin manganiferous and iron-rich siliceous bands is significant. The various components exposed in the subduction-accretion complex were first underthrust northwards to deep crustal levels, subjected to high pressure, eclogite facies metamorphism and underplated to the base of the overriding Eurasian plate. This latter accretion event was characterised by intense southwest-directed ductile thrusting and pervasive amphibolite facies metamorphic overprinting. It was accompanied by migmatisation and intracrustal melt generation, and followed by subduction related magmatism. Deep level subduction-accretion leads to southward growth of the continental margin, which in turn leads to subduction retreat allowing the encroachment of the magmatic arc from the north. Subsequent extensional tectonic exhumation brought the complex up to its present position within the southern margin of Eurasia. This new interpretation may have implications for other high grade terrains within convergent and collisional systems that have been assumed to represent ancient or pre-existing continental crust. If so, then the importance of deep level subduction-accretion as a mechanism of continental crustal growth has hitherto been underestimated.

Barr, Samantha R.; Temperley, Stephen; Tarney, John

1999-01-01

89

Approach for Analysis of Order Check Overrides in a Computerized Practitioner Order Entry System  

PubMed Central

SUMMARY While it has been established that computer practitioner order entry systems can prevent transcription errors and check orders for severe drug allergies and interactions[1], continuous monitoring of the effectiveness of order checks is important. The goal of this study is to examine the rate at which high severity order checks generated in the computer practitioner order entry system at VA Puget Sound are overridden by clinicians. We compare our results to those of a previous study[2] that found high override rates for Critical Drug Interaction and Allergy-Drug Interaction order check categories. We are interested in determining whether system changes addressing these high rates have been successful in reducing the overall override rate in these categories. Because the method used previously to extract orders is no longer available, the first step in our study was to develop a new procedure to gather order entry data. This procedure is the subject of our report. PMID:16779320

Lin, Ching-Ping; Nichol, W. Paul; Hoey, Patty; Roth, Terry L.; Anderson, Curtis; Gennari, John H.; Payne, Thomas H.

2005-01-01

90

Leading us not unto temptation: momentary allurements elicit overriding goal activation.  

PubMed

The present research explored the nature of automatic associations formed between short-term motives (temptations) and the overriding goals with which they interfere. Five experimental studies, encompassing several self-regulatory domains, found that temptations tend to activate such higher priority goals, whereas the latter tend to inhibit the temptations. These activation patterns occurred outside of participants' conscious awareness and did not appear to tax their mental resources. Moreover, they varied as a function of subjective goal importance and were more pronounced for successful versus unsuccessful self-regulators in a given domain. Finally, priming by temptation stimuli was found not only to influence the activation of overriding goals but also to affect goal-congruent behavioral choices. PMID:12585805

Fishbach, Ayelet; Friedman, Ronald S; Kruglanski, Arie W

2003-02-01

91

AURORA-A amplification overrides the mitotic spindle assembly checkpoint, inducing resistance to Taxol  

Microsoft Academic Search

The serine-threonine kinase gene AURORA-A is commonly amplified in epithelial malignancies. Here we show that elevated Aurora-A expression at levels that reflect cancer-associated gene amplification overrides the checkpoint mechanism that monitors mitotic spindle assembly, inducing resistance to the chemotherapeutic agent paclitaxel (Taxol). Cells overexpressing Aurora-A inappropriately enter anaphase despite defective spindle formation, and the persistence of Mad2 at the kinetochores,

Shubha Anand; Sue Penrhyn-Lowe; Ashok R Venkitaraman

2003-01-01

92

Major Ocean Features: Continental Margin  

E-print Network

of ocean earth sciences. It starts with features of the continental shelf associated with passive margins of continental margins, called the continental shelf. Continental shelves of the world vary greatly in places. The shelf, slope and rise together make up the entire continental margin. Many continental

93

Why does continental convergence stop  

SciTech Connect

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.

Hynes, A.

1985-01-01

94

Crustal architecture and deep structure of the Namibian passive continental margin around Walvis Ridge from wide-angle seismic data  

NASA Astrophysics Data System (ADS)

The opening of the South Atlantic ocean basin was accompanied by voluminous magmatism on the conjugate continental margins of Africa and South America, including the formation of the Parana and Entendeka large igneous provinces (LIP), the build-up of up to 100 km wide volcanic wedges characterized by seaward dipping reflector sequences (SDR), as well as the formation of paired hotspot tracks on the rifted African and South American plates, the Walvis Ridge and the Rio Grande Rise. The area is considered as type example for hotspot or plume-related continental break-up. However, SDR, and LIP-related features on land are concentrated south of the hotspot tracks. The segmentation of the margins offers a prime opportunity to study the magmatic signal in space and time, and investigate the interrelation with rift-related deformation. A globally significant question we address here is whether magmatism drives continental break-up, or whether even rifting accompanied by abundant magmatism is in response to crustal and lithospheric stretching governed by large-scale plate kinematics. In 2010/11, an amphibious set of wide-angle seismic data was acquired around the landfall of Walvis Ridge at the Namibian passive continental margin. The experiments were designed to provide crustal velocity information and to investigate the structure of the upper mantle. In particular, we aimed at identifying deep fault zones and variations in Moho depth, constrain the velocity signature of SDR sequences, as well as the extent of magmatic addition to the lower crust near the continent-ocean transition. Sediment cover down to the igneous basement was additionally constrained by reflection seismic data. Here, we present tomographic analysis of the seismic data of one long NNW oriented profile parallel to the continental margin across Walvis Ridge, and a second amphibious profile from the Angola Basin across Walvis Ridge and into the continental interior, crossing the area of the Etendeka Plateau basalts. The most striking feature is the sharp transition in crustal structure and thickness across the northern boundary of Walvis Ridge. Thin oceanic crust (6.5 km) of the Angola Basin lies next to the up to 35 km thick igneous crustal root founding the highest elevated northern portions of Walvis Ridge. Both structures are separated by a very large transform fault zone. The velocity structure of Walvis Ridge lower crust is indicative of gabbro, and, in the lowest parts, of cumulate sequences. On the southern side of Walvis Ridge there is a smooth gradation into the adjacent 25-30 km thick crust underlying the ocean-continent boundary, with a velocity structure resembling that of Walvis Ridge The second profile shows a sharp transition from oceanic to rifted continental crust. The transition zone may be underlain by hydrated uppermost mantle. Below the Etendeka Plateau, an extensive high-velocity body, likely representing gabbros and their cumulates at the base of the crust, indicates magmatic underplating. We summarize by stating that rift-related lithospheric stretching and associated transform faulting play an overriding role in locating magmatism, dividing the margin in a magmatic-dominated segment to the south, and an amagmatic segment north of Walvis Ridge.

Behrmann, Jan H.; Planert, Lars; Jokat, Wilfried; Ryberg, Trond; Bialas, Jörg; Jegen, Marion

2013-04-01

95

Gravity field and deep structure of the Bengal Fan and its surrounding continental margins, northeast Indian Ocean  

NASA Astrophysics Data System (ADS)

A revised gravity anomaly map for the northeast Indian Ocean shows that the shelf edge underlying the eastern continental margin of India is a rather narrow but extensively linear gravity low (minimum free-air = -149 mGal). The Bengal Fan seaward of the shelf has a depressed gravity field (average free-air = -20 to -30 mGal) in spite of the enormous thickness of sediments of as much as 10-15 km. The two buried ridges below the Bengal Fan—the 85° East and 90° East Ridges—have a large negative (-75 mgal) and a substantial positive (40 mGal) free-air anomaly, respectively. The Andaman and Burmese arcs lying along the east margin of the Bengal Fan are active subduction areas which have typical bipolar gravity signatures with a maximum amplitude of 300 mGal. Gravity interpretation for three regional traverses across the central and northern parts of the Bengal Fan and their surrounding continental margins suggests that a thickened oceanic crustal wedge juxtaposes the transitional crust under the eastern continental slope of India; the 85° East Ridge, that was created when the Indian Ocean lithosphere was very juvenile, appears to underlie a nearly 10 km thick and 120 km wide oceanic crustal block consisting of the ridge material embedded in the upper lithosphere; while the 90° East Ridge submarine topography/buried load below the Bengal Fan is probably isostatically compensated by a low-density mass acting as a cushion at the base of the crust. The Bengal Fan crust, with its thick sediment layer, is carried down the Andaman subduction zone to a depth of about 27 km where, possibly, phase transition takes place under higher pressure. The maximum sediment thickness at the Andaman-Burmese subduction zone is of the order of 10-12 km. The gravity model predicts a low density zone about 60 km wide below the Andaman-Burmese volcanic arc, penetrating from crustal to subcrustal depths in the overriding Burma plate. A more complex density distribution is however, envisaged for the Andaman volcanic arc that is split by the Neogene back arc spreading ridge. The ocean-continent crustal transition possibly occurs farther east of the volcanic arc; below the Shan plateau margin in Burma or below the Mergui terrace at the Malayan continental margin east of the Andaman Sea.

Mukhopadhyay, Manoj; Krishna, M. R.

1991-02-01

96

Overriding Psychiatric Advance Directives: Factors Associated with Psychiatrists' Decisions to Preempt Patients' Advance Refusal of Hospitalization and Medication  

Microsoft Academic Search

Psychiatric advance directives (PADs) are intended to support patients' treatment decisions during a crisis. However, PAD\\u000a statutes give clinicians broad discretion over whether to carry out patients' advance instructions. This study uses data from\\u000a a survey of psychiatrists (N=164) to examine reasons for overriding PADs. In response to a hypothetical vignette, 47% of psychiatrists indicated that\\u000a they would override a

Jeffrey W. Swanson; S. Van McCrary; Marvin S. Swartz; Richard A. Van Dorn; Eric B. Elbogen

2007-01-01

97

Subduction-driven recycling of continental margin lithosphere.  

PubMed

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

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

98

JOURNAL CLUB: Requiring Clinical Justification to Override Repeat Imaging Decision Support: Impact on CT Use.  

PubMed

OBJECTIVE. The purpose of this study was to determine the impact of requiring clinical justification to override decision support alerts on repeat use of CT. SUBJECTS AND METHODS. This before and after intervention study was conducted at a 793-bed tertiary hospital with computerized physician order entry and clinical decision support systems. When a CT order is placed, decision support alerts the orderer if the patient's same body part has undergone CT within the past 90 days. The study cohort included all 28,420 CT orders triggering a repeat alert in 2010. The intervention required clinical justification, selected from a predetermined menu, to override repeat CT decision support alerts to place a CT order; otherwise the order could not be placed and was dropped. The primary outcome, dropped repeat CT orders, was analyzed using three methods: chi-square tests to compare proportions dropped before and after intervention; multiple logistic regression tests to control for orderer, care setting, and patient factors; and statistical process control for temporal trends. RESULTS. The repeat CT order drop rate had an absolute increase of 1.4%; 6.1% (682/11,230) before to 7.5% (1290/17,190) after intervention, which was a 23% relative change (7.5 - 6.1) / 6.1 × 100 = 23%; p < 0.0001). Orders were dropped more often after intervention (odds ratio, 1.3; 95% CI, 1.1-1.4; p < 0.0001). Statistical control analysis supported the association between the increase in the drop rate with intervention rather than underlying trends. CONCLUSION. Adding a requirement for clinical justification to override alerts modestly but significantly improves the impact of repeat CT decision support (23% relative change), with the overall effect of preventing one in 13 repeat CT orders. PMID:25341162

O'Connor, Stacy D; Sodickson, Aaron D; Ip, Ivan K; Raja, Ali S; Healey, Michael J; Schneider, Louise I; Khorasani, Ramin

2014-11-01

99

The Segmented Overriding Plate and Coupling at the South-Central Chilean Margin (36–42°S)  

Microsoft Academic Search

Identifying the parts of subduction zones that are susceptible to great earthquakes is a challenge that warrants considerable\\u000a attention. In south-central Chile, where the 1960 M\\u000a w 9.5 Valdivia earthquake occurred, we have combined surface geology and gravity data into a three-dimensional density model\\u000a that helps to identify trench-parallel changes in fore-arc properties between 36 and 42° S. In light

Ron I. Hackney; Helmut P. Echtler; Gerhard Franz; Hans-Jürgen Götze; Friedrich Lucassen; Dmitriy Marchenko; Daniel Melnick; Uwe Meyer; Sabine Schmidt; Zuzana Tašárová; Andrés Tassara; Susann Wienecke

100

Mantle melting in within-plate continental settings: Sr-Nd-Pb and U-series isotope constraints in alkali basalts from the Sicily Channel (Pantelleria and Linosa Islands, Southern Italy)  

NASA Astrophysics Data System (ADS)

The origin of the mantle sources of the Na-alkaline magmas erupted within the continental rift of the Sicily Channel and their melting behaviour are here investigated through the determination of Sr, Nd and Pb isotope ratios and U-series disequilibria on basaltic volcanic rocks from Linosa and Pantelleria. The isotope data, along with trace element ratios are used to assess the possible role of the interaction with the continental crust and/or the Sub-Continental Lithospheric Mantle (SCLM). The data show little variation in Sr and Nd isotopes and a continuous trend toward more radiogenic Pb isotope composition from Linosa to the oldest mafic activity of Pantelleria (i.e. Paleo-Pantelleria), with intermediate values measured in the youngest Pantelleria lavas (Neo-Pantelleria). Pantelleria basalts have ubiquitous 230Th-excess ranging from 7% to 20%. These data suggest the magmas are originated within the asthenospheric mantle, with little or no interaction with either the continental crust or the SCLM. The increasing FOZO-like character of the studied magmas and the variation of some key trace element ratios (e.g. Rb/La) argue for an increasing role of recycled oceanic material in the form of eclogite/pyroxenite dispersed within the mantle sources of these magmas. A completely distinct isotope composition is recorded in Neo-Pantelleria hawaiites from Khartibucale, which show significantly higher 87Sr/86Sr and lower 143Nd/144Nd, 206Pb/204Pb, (238U/232Th) and (230Th/232Th), but comparable (230Th/238U) with respect to all the other rocks studied. These rocks cannot be considered co-genetic with other Pantelleria basalts and are interpreted either as related to interaction with partial melts of the SCLM or to be originated from a mantle source enriched by recycled crustal material (EM-like). 235U-231Pa disequilibria were also measured in one Neo-Pantelleria hawaiite and one Neo-Pantelleria basalt. The coupled (230Th/238U) = 1.20 and (231Pa/235U) = 1.39 of the latter were used to perform quantitative dynamic melting models in order to constrain physical parameters of mantle melting in the Sicily Channel. The combined modelling yielded positive solutions only for high DU/DTh (? 2.5) and low melting rates (? < 1 × 10- 4 kg/m3/a). These data argue against any important role for amphibole in the genesis of these magmas and are consistent with a peridotite source possibly well mixed with recycled components. The modelled values of ? can also be converted into estimates of the upwelling rate of the mantle that are compatible with slow passive upwelling along the Sicily Channel rift.

Avanzinelli, Riccardo; Braschi, Eleonora; Marchionni, Sara; Bindi, Luca

2014-02-01

101

Dynamic Analysis of Modifications to Simple Plate Tectonic Theory  

NASA Astrophysics Data System (ADS)

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

Paczkowski, Karen

102

Mantle downwelling causes continental depressions  

NASA Astrophysics Data System (ADS)

According to the theory of isostasy, Earth's continents should float in equilibrium upon the denser underlying mantle, much in the same way that icebergs float on the ocean surface. However, this understanding may not accurately portray dynamic continent-mantle interaction. A new study suggests that continents may reside below the level predicted by isostatic theory—nearly 2-3 km below in some areas.In the February issue of Geophysical Research Letters, A. M. Forte, A. M. Dziewonski, and R. L. Woodward of Harvard University and W. R. Peltier of the University of Toronto present evidence that some continents are actively pulled downward by the global-scale flow in the mantle. This flow is also responsible for the so-called “drift” of the Earth's tectonic plates. According to Forte, “our models demonstrate a clear pattern of continental depressions, which are forced by downwelling flow due to colder mantle material extending to great depths. We believe that such forces also operated in the geologic past and were partially responsible for the creation of deep continental basins that are now filled with sediments.”

Blue, Charles

103

Mechanical Models of Coontinental Plate BoundariesL Fault Slip Rates and Interseismic Stress Rotation Rates.  

E-print Network

??We first describe the methodology for a two-dimensional, elastic deformable microplate modeling approach for continental plate boundaries. Deformable microplate models combine discrete slip on microplate… (more)

Langstaff, Meredith Avery

2014-01-01

104

Nature and distribution of the deformation front in the Luzon Arc-Chinese continental margin collision zone at Taiwan  

E-print Network

Nature and distribution of the deformation front in the Luzon Arc-Chinese continental margin, not a surface trace of the plate boundary between the Eurasian and Philippine Sea plates. Introduction The island of Taiwan was formed by oblique col- lision between the Luzon Arc and the Chinese continental

Lin, Andrew Tien-Shun

105

Sediment deformation and plate tectonics in the Gulf of Oman  

Microsoft Academic Search

The continental margin off the Makran coast of Iran and Pakistan is an excellent example of active deformation of sediments at a compressive plate boundary. Seismic reflection profiles across the margin suggest that relatively flat-lying sediments from the Oman abyssal plain are being scraped off the Arabian plate and accreted onto the Eurasian plate in a series of tightly folded

R. S. White; K. Klitgord

1976-01-01

106

Can Preoccupation with Alcohol Override the Protective Properties of Mindful Awareness on Problematic Drinking?  

PubMed Central

Objectives To assess the mediating role of drinking restraint— specifically preoccupation with drinking— on the associations between mindful awareness and alcohol consumption and alcohol-related problems. Methods 390 heavy-drinking, undergraduate, college students (52% male) were assessed on measures of mindfulness, drinking restraint, alcohol consumption (prior 90-days), and alcohol-related problems via self-report surveys. Results Mindfulness was negatively associated with alcohol consumption, problems, and both factors of drinking restraint (emotional preoccupation and behavioral constraint). Emotional preoccupation, but not behavioral constraint, statistically mediated these relationships and demonstrated positive associations with both alcohol consumption and related problems. Conclusions Results replicate previous findings documenting a negative association between mindfulness and alcohol consumption and problems. Statistical mediation models suggest that preoccupation with drinking may be a risk factor that over-rides the health-promoting effects of mindfulness. PMID:23814503

Bramm, Stephanie M.; Cohn, Amy M.; Hagman, Brett T.

2012-01-01

107

When does the good of the group override the advantage of the individual?  

PubMed

In a system of N populations of n reproductive individuals apiece, in which each population has constant variance v(2) and lasts L generations, group selection on a quantitative character has a reasonable chance of overriding selection within populations if (and only if) the populations never exchange migrants, each population is founded by colonists from a single parent population, and the number of populations exceeds the effective number of reproductive individuals per population. If each population derives from a single parent population, then the exchange of a single successful migrant per population per L generations can triple the strength of group selection required to overcome a given selection within populations. If populations exchange no migrants, then the derivation of one in every N populations from two equally represented parents (while the others all derive from a single parent) doubles the strength of group selection required to prevail. Group selection is accordingly likely to be effective only in certain categories of parasites. PMID:16593312

Leigh, E G

1983-05-01

108

Deep vs. shallow expressions of continental cratons: Can cratonic roots be destroyed by subduction?  

NASA Astrophysics Data System (ADS)

Cratons are parts of continents that have remained tectonically quiescent over billion-year timescales. Although cratonic lithosphere has the stabilizing properties of chemical buoyancy and high viscosity, it can still be destroyed. The best known example of a missing cratonic root is beneath the eastern North China Craton (NCC). Despite strong evidence for the past existence of a craton in northern China, high heat flow, Mesozoic basin formation, extensive seismicity, and the lack of a fast seismic root imply that the deep cratonic lithosphere is missing. The mechanism for the lithospheric root loss is a source of much debate. Many mechanisms have been proposed, among them: shearing of the lithospheric root by asthenospheric flow induced by the Indo-Eurasian collision; ponding of the Pacific slab in the transition zone acting as a source of fluids that enable hydrous weakening; and thermal erosion due to the corner-flow upwelling of hot, deep material. It is generally agreed that the influence of subduction is key, both from the temporal coincidence of subduction with increased tectonomagmatic activity on the craton and from the spatial correlation of lithospheric loss adjacent to the Pacific trench. We investigate how cratons extend to depth through comparison between seismic signatures of the cratonic lithosphere in the upper mantle and surficial evidence of cratonic boundaries. We examine global and regional tomography, as well as receiver-function constraints on lithospheric thickness in the NCC. We define craton boundaries at the surface through analyses on crust and lithospheric mantle ages and kimberlite locations. We aim to identify regions where the fast cratonic root has been lost or altered beneath Archean and Proterozoic crust and in particular place constraints on the extent of the remaining cratonic root beneath North China. Given the common emphasis on the role of subduction as a driving force for the root loss beneath the eastern NCC, we focus on subduction-related mechanisms for the destabilization of a continental craton located on the overriding plate. We use the finite-element code CitcomCU to model thermo-mechanical subduction in the presence of a craton. Subduction is dynamically-driven, and the two lithospheric plates are decoupled by a thin weak crust, along which shear is localized. For NCC-type craton geometries, we examine how, and under what rheological parameterizations, the following mechanisms can destabilize a cratonic root: (i) thermal erosion due to the corner flow-driven upwelling of hot asthenosphere; (ii) viscosity reduction due to the hydrolytic weakening of olivine; (iii) collision-induced stress triggered weakening (for non-Newtonian rheologies). Additionally, we examine how various craton geometries and rheological formulations influence the development of a flat slab.

Perry-Houts, J.; Calo, M.; Eddy, C. L.; Guerri, M.; Holt, A.; Hopper, E.; Tesoniero, A.; Romanowicz, B. A.; Becker, T. W.; Wagner, L. S.

2013-12-01

109

Plate Tectonics  

NSDL National Science Digital Library

Create a poster all about Plate Tectonics! Directions: Make a poster about Plate Tectonics. (20 points) Include at least (1) large picture (15 points) on your poster complete with labels of every part (10 points). (15 points) Include at least three (3) facts about Plate Tectonics. (5 points ...

Walls, Mrs.

2011-01-30

110

Plate Tectonics  

NSDL National Science Digital Library

This interactive Flash explores plate tectonics and provides an interactive map where users can identify plate boundaries with name and velocities as well as locations of earthquakes, volcanoes, and hotspots. The site also provides animations and supplementary information about plate movement and subduction. This resource is a helpful overview or review for introductory level high school or undergraduate physical geology or Earth science students.

Smoothstone; Company, Houghton M.

111

Tectonic Growth of a Collisional Continental Margin: Crustal Evolution of Southern Alaska  

E-print Network

Tectonic Growth of a Collisional Continental Margin: Crustal Evolution of Southern Alaska Edited : crustal evolution of southern Alaska / edited by Kenneth D. Ridgway . . . [et al.]. p. cm. -- (Special, Structural--Alaska. 2. Plate tectonics--Alaska. 3. Continental margins--Alaska. 4. Geology, Stratigraphic

112

Initiation and propagation of shear zones in a heterogeneous continental lithosphere  

SciTech Connect

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.

Tommasi, A.; Vauchez, A. [CNRS/Universite de Montpellier II (France)] [CNRS/Universite de Montpellier II (France)

1995-11-10

113

Beyond plate tectonics - Looking at plate deformation with space geodesy  

NASA Technical Reports Server (NTRS)

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.

Jordan, Thomas H.; Minster, J. Bernard

1988-01-01

114

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

PubMed Central

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

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

2007-01-01

115

Continental growth and the crustal record  

NASA Astrophysics Data System (ADS)

The continental crust is the archive of Earth history. The spatial and temporal distribution of the Earth's record of rock units and events is heterogeneous with distinctive peaks and troughs in the distribution of ages of igneous crystallisation, metamorphism, continental margins and mineralisation. This distribution reflects the different preservation potential of rocks generated in different tectonic settings, rather than fundamental pulses of activity, and the peaks of ages are linked to the timing of supercontinent assembly. In contrast there are other signals, such as the Sr isotope ratios of seawater, mantle temperatures, and redox conditions on the Earth, where the records are regarded as primary because they are not sensitive to the numbers of samples of different ages that have been analysed. New models based on the U-Pb, Hf and O isotope ratios of detrital zircons suggest that at least ~ 60-70% of the present volume of the continental crust had been generated by 3 Ga. The growth of continental crust was a continuous rather than an episodic process, but there was a marked decrease in the rate of crustal growth at ~ 3 Ga. This appears to have been linked to significant crustal recycling and the onset plate tectonics. The 60-70% of the present volume of the continental crust estimated to have been present at 3 Ga, contrasts markedly with the < 10% of crust of that age apparently still preserved and it requires ongoing destruction (recycling) of early formed crust and subcontinental mantle lithosphere back into the mantle through processes such as subduction and delamination.

Hawkesworth, Chris; Cawood, Peter; Dhuime, Bruno

2013-12-01

116

Antarctica and Continental Drift.  

National Technical Information Service (NTIS)

Continental drift reconstructions by computerized matching of the 1,000 fm isobaths are presented for Africa/Antarctica, Australia/Antarctica and India/Antarctica. Sufficiently good congruency is obtained for the first two to suggest that they are probabl...

R. S. Dietz, J. C. Holden, W. P. Sproll

1972-01-01

117

Plate Tectonics  

NSDL National Science Digital Library

In this lesson, students are introduced to the theory of plate tectonics and explore how the theory was developed and supported by evidence. Through class discussion, videos, and activities, students seek connections between tectonic activity and geologic features and investigate how the theory of plate tectonics evolved.

2006-01-01

118

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

PubMed Central

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

2014-01-01

119

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

PubMed Central

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

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

2012-01-01

120

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

PubMed

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

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

2014-07-15

121

Shallow subduction, ridge subduction, and the evolution of continental lithosphere  

SciTech Connect

Subduction of oceanic lithosphere beneath continental crust at a shallow angle has occurred throughout the Phanerozoic Eon. Ridge subduction often follows shallow subduction and causes bimodal volcanism and crustal rifting, forming back-arc basins. Recent models for Archean plate tectonics propose very fast rates of spreading (400-800 km/Ma) and convergence, and sinking rates comparable to or slower (<10 km/Ma) than those of today. As faster convergence and slower sinking correspond to subduction at shallower angles, shallow subduction and ridge subduction must have been ubiquitous during the Archean permobile regime. This is compatible with a back-arc-basin origin for Archean greenstone belts. The common coexistence of tholeiitic and calc-alkaline igneous rocks in Archean greenstone belts, also implies ridge subduction. The authors envisage a transition, between 2.4 and 1.8 Ga., from a regime dominated by shallow subduction and repeated ridge subduction to one of normal plate tectonics with steeper subduction. Spreading rates decreased; continental plates became larger and stable shelves could develop at trailing margins. Shallow subduction became the exception, restricted to episodes of abnormally fast convergence; nevertheless, the long span of post-Archean time makes it unlikely that any part of the continental crust has escaped shallow subduction and ridge subduction. These processes recycle much volatile-rich oceanic crust into the sub-continental upper mantle, thereby underplating the crust, effecting upper-mantle metasomatism and affecting intraplate magmatism.

Helmstaedt, H.; Dixon, J.M.; Farrar, E.; Carmichael, D.M.

1985-01-01

122

Subduction Tectonic Erosion, Sediment Accretion and Arc Collisions in maintaining the Continental Crust  

Microsoft Academic Search

Estimates of modern continental crustal recycling in subduction zones can be made from plate convergence velocities, the thicknesses of trench sediments, volumes and ages of accretionary complexes together with rates of trench retreat. Plate convergence rates appear to be the primary control on crustal subduction, with convergence >7.5 cm\\/yr associated with tectonic erosion. Collision of aseismic ridges with trenches drives

P. Clift; P. Vannucchi; H. Schouten

2007-01-01

123

Subduction Tectonic Erosion, Sediment Accretion and Arc Collisions in maintaining the Continental Crust  

Microsoft Academic Search

Estimates of modern continental crustal recycling in subduction zones can be made from plate convergence velocities, the thicknesses of trench sediments, volumes and ages of accretionary complexes together with rates of trench retreat. Plate convergence rates appear to be the primary control on crustal subduction, with convergence >7.5 cm\\/yr associated with tectonic erosion. Collision of aseismic ridges with trenches drives

P. Clift; P. Vannucchi; H. Schouten

2004-01-01

124

Slip partitioning along major convergent plate boundaries  

NASA Astrophysics Data System (ADS)

Along plate boundaries characterized by oblique convergence, earthquake slip vectors are commonly rotated toward the normal of the trench with respect to predicted plate motion vectors. Consequently, relative plate motion along such convergent margins must be partitioned between displacements along the thrust plate interface and deformation within the forearc and back-arc regions. The deformation behind the trench may take the form of strike-slip motion, back-arc extension, or some combination of both. We observe from our analysis of the Harvard Moment Tensor Catalog that convergent arcs characterized by back-arc spreading, specifically the Marianas and New Hebrides, are characterized by a large degree of slip partitioning. However, the observed rates, directions, and location of back-arc spreading are not sufficient to account for degree of partitioning observed along the respective arcs, implying that the oblique component of subduction is also accommodated in part by shearing of the overriding plate. In the case of the Sumatran arc, where partitioning is accommodated by strike-slip faulting in the overriding plate, the degree of partitioning is similar to that observed along the Marianas, but the result is viewed with caution because it is based on a predicted plate motion vector that is based on locally derived earthquake slip vectors. In the case of the Alaskan-Aleutian arc, where back-arc spreading is also absent, the degree of partitioning is less and rotation of slip vectors toward the trench normal appears to increase linearly as a function of the obliquity of convergence. If partitioning in the Alaskan-Aleutian arc is accommodated by strike-slip faulting within the upper plate, the positive relationship between obliquity of convergence and the rotation of earthquake slip vectors to the trench normal may reflect that either (1) the ratio of the depth extent of strike-slip faults behind the trench Z s to the subduction thrust Z t increases westward along the arc, (2) the dip of the subduction thrust increases westward along the arc, or (3) the strength of the subduction thrust decreases westward along the arc.

Yu, Guang; Wesnousky, Steven G.; Ekström, Göran

1993-06-01

125

Varying crustal compositions on the role of continental collision in forming Archean sub-continental lithospheric mantle  

NASA Astrophysics Data System (ADS)

The processes responsible for the formation of thick, strong and cold Archean sub-continental lithospheric mantle remain elusive. One mechanism that has been proposed is a style of imbrication of buoyant oceanic lithosphere during lateral tectonic accretion. Here, we explore a similar mechanism and several alternate styles whereby buoyant sub-continental lithosphere develops into thickened lithosphere during Neoarchean continental collision. The thermo-mechanical evolution of continental lithosphere undergoing orogenesis under Neoarchean-like conditions is studied using forward modeling with an arbitrary Lagrangian-Eulerian finite element technique. The numerical experiments suggest that during the initial stages of continental collision the upper portion of the mantle is characterized by underplating/underthrusting and is “plate-like”, whereas the crust undergoes distributed pure-shear thickening. Depending on the composition/rheology of the crust and the amount of radiogenic heat production in the crust, three dominant modes of mantle lithosphere deformation evolve: (1) a pure-shear thickening style; (2) an imbrication style ; (3) and a style best described as “flat-subduction”. Both the imbrication style and the “flat-subduction” style result in the emplacement of “plate-like” mantle lithosphere at depths between 200 km and 325 km. The imbrication style behavior possibly segues to the “flat-subduction” style behavior after a possible crustal inversion event. We interpret these modeling results in the context of the available geological and geophysical observables for the Superior and Slave provinces.

Gray, R.; Pysklywec, R. N.

2009-12-01

126

Parallel Plate Antenna.  

National Technical Information Service (NTIS)

The invention as disclosed is a parallel plate antenna having a number of stacked horizontal plates and two vertical plates. Alternating ones of the horizontal plates are electrically coupled to one vertical plate such that the horizontal plates coupled t...

D. F. Rivera

2009-01-01

127

Identifying Plate Tectonic Boundaries for a Virtual Ocean Basin  

NSDL National Science Digital Library

Students observe a virtual ocean basin and two adjacent continental margins. From the characteristics of the sea floor and adjacent land, students infer where plate boundaries might be present. They then predict where earthquakes and volcanoes might occur. Finally, they draw their inferred plate boundaries in cross section.

Reynolds, Stephen

128

Evolution of the Mariana Convergent Plate Margin System  

Microsoft Academic Search

The Mariana convergent plate margin system of the western Pacific provides opportunities for studying the tectonic and geochemical processes of intraoceanic plate subduction without the added complexities of continental geology. The system's relative geologic simplicity and the well-exposed sections of lithosphere in each of its tectonic provinces permit in situ examination of processes critical to understanding subduction tectonics. Its general

Patricia Fryer

1996-01-01

129

Evolution of the mariana convergent plate margin system  

Microsoft Academic Search

The Mariana convergent plate margin system of the western Pacific provides opportunities for studying the tectonic and geochemical processes of intraoceanic plate subduction without the added complexities of continental geology. The system's relative geologic simplicity and the well-exposed sections of lithosphere in each of its tectonic provinces permit in situ examination of processes critical to understanding subduction tectonics. Its general

Patricia Fryer

1996-01-01

130

Dynamics of diffuse oceanic plate boundaries: insensitivity to rheology  

Microsoft Academic Search

Diffuse plate boundaries, which are zones of deformation hundreds to thousands of kilometres wide, occur in both continental and oceanic lithosphere. Here, we build on our prior work in which we described analytic approximations to simple dynamical models that assume that the vertically averaged viscous force resisting deformation in diffuse oceanic plate boundaries (DOPBs) is described by either a linear

Stephen Zatman; Richard G. Gordon; Kartik Mutnuri

2005-01-01

131

Intermittent plate tectonics?  

PubMed

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

Silver, Paul G; Behn, Mark D

2008-01-01

132

Plate Motions  

NSDL National Science Digital Library

To prepare for this exercise students read the Chapter on plate tectonics in their text book. In class, they are given a color isochron map of the sea floor. They are given 4 tasks: Answer basic questions about the timing and rate of opening of the N. and S. Atlantic; Determine what has happened to the oceanic crust that is created on the eastern side of the East Pacific Rise; Determine what type of plate boundary existed on the western edge of the N. America plate before the San Andreas Fault and when this transition occurred; and Reconstruct the motion of the plates over the last 40 Ma assuming that the surface area of the Earth has not changed.

Nunn, Jeffrey

133

Plate Tectonics  

NSDL National Science Digital Library

This data tip from Bridge, the Ocean Sciences Education Teacher Resource Center archive, includes a variety of educational sites to visit on plate tectonic theory. Learners can use underwater earthquake data to identify plate boundaries with links to the National Oceanic and Atmospheric Administration's Acoustic Monitoring Program Ocean Seismicity data. Data from the Northeast Pacific, eastern Equatorial Pacific, and North Atlantic are examined in more detail.

2002-09-01

134

Seismic anisotropy, lithospheric deformation, and mantle flow in subduction zones, continental keels, and the core-mantle boundary  

NASA Astrophysics Data System (ADS)

This thesis consists of four chapters that evaluate the location, orientation, and strength of seismic anisotropy in the lithosphere and mantle in several tectonic settings, including two western Pacific subduction zones, the tectonically stable region of eastern North America, and two regions of the core-mantle boundary beneath the Pacific Ocean. The analyses in these chapters not only utilize existing methods, but also develop new, innovative techniques to determine and investigate patterns of shear wave splitting. Beneath northwest Pacific subduction zones, we found evidence for seismic anisotropy to depths as great as 410 km in some regions. In addition, we determined that fast directions are roughly parallel to the direction of absolute Pacific plate motion beneath Izu-Bonin, roughly parallel to the strike of the trench near Japan, and roughly parallel to the direction of transpressional shear in the southern Kurils near Sakhalin Island. In the Marianas subduction zone, we found strong evidence of frequency dependence in fast directions from phases that sample the northwestern portion of the subducting slab, but did not find evidence for frequency dependence in splitting times. All of the data can be explained by models containing anisotropy in the subducting slab and mantle wedge, and possibly anisotropy in the overriding Philippine Sea plate. Beneath eastern North America, we performed measurements of shear wave splitting and combined them with the results of a simple finite-difference model to examine mantle flow around a realistic continental keel. Using this model, we calculated predicted shear wave splitting produced in the mantle resulting from flow around and beneath the keel. We found that splitting produced by modified mantle flow can explain most, but not all, of the shear wave splitting observations in this region. Beneath the central and northern Pacific Oceans, we found evidence for seismic anisotropy within the lowermost mantle (D? ). Beneath the northern Pacific, this anisotropy may be due to lateral flow along the core-mantle boundary induced by lateral spreading of downwelling paleoslab material. Beneath the central Pacific, anisotropy may be due to lateral flow of lower mantle material toward the Hawai'ian plume source.

Fouch, Matthew James

135

Caribbean tectonics and relative plate motions  

NASA Technical Reports Server (NTRS)

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.

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

1984-01-01

136

Plate Tectonics in the Late Paleozoic  

NASA Astrophysics Data System (ADS)

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.

Domeier, Mat; Torsvik, Trond

2014-05-01

137

Reconciling plate-tectonic reconstructions of Alpine Tethys with the geological-geophysical record of spreading and subduction in the Alps  

NASA Astrophysics Data System (ADS)

A new reconstruction of Alpine Tethys combines plate-kinematic modelling with a wealth of geological data and seismic tomography to shed light on its evolution, from sea-floor spreading through subduction to collision in the Alps. Unlike previous models, which relate the fate of Alpine Tethys solely to relative motions of Africa, Iberia and Europe during opening of the Atlantic, our reconstruction additionally invokes independent microplates whose motions are constrained primarily by the geological record. The motions of these microplates (Adria, Iberia, Alcapia, Alkapecia, and Tiszia) relative to both Africa and Europe during Late Cretaceous to Cenozoic time involved the subduction of remnant Tethyan basins during the following three stages that are characterized by contrasting plate motions and driving forces: (1) 131-84 Ma intra-oceanic subduction of the Ligurian part of Alpine Tethys attached to Iberia coincided with Eo-alpine orogenesis in the Alcapia microplate, north of Africa. These events were triggered primarily by foundering of the older (170-131 Ma) Neotethyan subduction slab along the NE margin of the composite African-Adriatic plate; subduction was linked by a sinistral transform system to E-W opening of the Valais part of Alpine Tethys; (2) 84-35 Ma subduction of primarily the Piemont and Valais parts of Alpine Tethys which were then attached to the European plate beneath the overriding African and later Adriatic plates. NW translation of Adria with respect to Africa was accommodated primarily by slow widening of the Ionian Sea; (3) 35 Ma-Recent rollback subduction of the Ligurian part of Alpine Tethys coincided with Western Alpine orogenesis and involved the formation of the Gibraltar and Calabrian arcs. Rapid subduction and arc formation were driven primarily by the pull of the gravitationally unstable, retreating Adriatic and African slabs during slow convergence of Africa and Europe. The upper European-Iberian plate stretched to accommodate this slab retreat in a very mobile fashion, while the continental core of the Adriatic microplate acted as a rigid indenter within the Alpine collisional zone. The subducted lithosphere in this reconstruction can be correlated with slab material imaged by seismic tomography beneath the Alps and Apennines, as well as beneath parts of the Pannonian Basin, the Adriatic Sea, the Ligurian Sea, and the Western Mediterranean. The predicted amount of subducted lithosphere exceeds the estimated volume of slab material residing at depth by some 10-30%, indicating that parts of slabs may be superposed within the mantle transition zone and/or that some of this subducted lithosphere became seismically transparent.

Handy, Mark R.; Schmid, Stefan M.; Bousquet, Romain; Kissling, Eduard; Bernoulli, Daniel

2010-10-01

138

Estimation of continental precipitation recycling  

Microsoft Academic Search

The total amount of water that precipitates on large continental regions is supplied by two mechanisms: (1) advection from the surrounding areas external to the region and (2) evaporation and transpiration from the land surface within the region. The latter supply mechanism is tantamount to the recycling of precipitation over the Continental area. The degree to which regional precipitation is

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

1993-01-01

139

Absolute plate velocities from seismic anisotropy: Importance of correlated errors  

NASA Astrophysics Data System (ADS)

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 (? = 19.2°) differs insignificantly from that for continental lithosphere (? = 21.6°). The between-plate dispersion, however, is significantly smaller for oceanic lithosphere (? = 7.4°) than for continental lithosphere (? = 14.7°). Two of the slowest-moving plates, Antarctica (vRMS = 4 mm a-1, ? = 29°) and Eurasia (vRMS = 3 mm a-1, ? = 33°), have two of the largest within-plate dispersions, which may indicate that a plate must move faster than ? 5 mm a-1 to result in seismic anisotropy useful for estimating plate motion. 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.

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

2014-09-01

140

Geologic evolution of petroliferous basins on continental shelf of China  

SciTech Connect

The coastline of southeastern China is about 18,000 km (11,200 mi) in length, and its aggregate continental shelf area within 200-m (660-ft) water depth is well over 1 million km/sup 2/ (390,000 mi/sup 2/). Recent geophysical exploration and petroleum drilling records aid in understanding the geologic evolution of these petroliferous basins. Two types of tectonic basins are present on the continental shelf areas: (1) Bohai Gulf, South Yellow Sea, and Beibu Gulf are intraplate polyphase rift-depression basins, and (2) East China Sea, mouth of the Pearl River, and the Yingge Sea are epicontinental rift-depressions basins. Both types are believed to be of extensional origin. The severe convergence of the Indian plate with the Eurasia plate produced east-northeast-spreading of the South China Sea basin, which resulted in two triple junctions on its northern margins. The Pacific plate was subducted by downthrust beneath the Eurasia continental crust. The extension mechanism could be the rising of an upper mantle plume to produce two weak north-northeast-trending fracture zones. A series of intraplate and epicontinental riftdepression basins was formed. The depositional models and sea level variations of these basins have been interpreted from drilling records and seismic profiles. They can be explained by the tectonoeustatic changes in sea level and Cenozoic climatic changes in China.

Desheng, L.

1984-08-01

141

Plate TectonicsPlate Tectonics Plate TectonicsPlate Tectonics  

E-print Network

ridge systems #12;Concentration of earthquakes #12;Mid-ocean ridge systems #12;Deep Sea Drilling Project, transform boundaries ­ travel 1 to 11 cm/yr relative to one another #12;14 tectonic plates today #12;Mid-ocean

Siebel, Wolfgang

142

Beyond Plate Tectonics: “Plate ” Dynamics  

E-print Network

Plate tectonics dogma has resulted in a variety of theories that frequently violate first principles. In this article it is suggested that ridges are in compression, not tension from convection cells, triple junctions cause hot spots (not vice versa), mantle plumes do not cause hot spot tracks, chord push creates pressures well in excess of lithostatic load, the arch effect demonstrates that rifts form both in compression and tension, surging (i.e. the sudden and rapid motion of the plates) occurs episodically, the presence of a basal shear zone a few meters thick during surging, the preferred initiation of subduction zones at the ridge, revision of the Wilson Cycle, the conformance of “old ” school geologists and plate tectonicians, earth-based non bolide impact mass extinctions, the loss of the earth’s magnetic field and its subsequent reappearance, additional application of the least work (or maximum

Richard Moody

143

Steady State Growth of Continental Crust?  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

144

Barite-forming environments along a rifted continental margin, Southern California Borderland  

Microsoft Academic Search

The Southern California Continental Borderland (SCCB) is part of the broad San Andreas transform-fault plate boundary that consists of a series of fault-bounded, petroleum-generating basins. The SCCB has high heat flow and geothermal gradients produced by thinned continental crust and Neogene volcanism. Barite deposits in the SCCB occur along faults. Barite samples from two sea-cliff sites and four offshore sites

James R. Hein; Robert A. Zierenberg; J. Barry Maynard; Mark D. Hannington

2007-01-01

145

Barite-forming environments along a rifted continental margin, Southern California Borderland  

Microsoft Academic Search

The Southern California Continental Borderland (SCCB) is part of the broad San Andreas transform-fault plate boundary that consists of a series of fault-bounded, petroleum-generating basins. The SCCB has high heat flow and geothermal gradients produced by thinned continental crust and Neogene volcanism. Barite deposits in the SCCB occur along faults.Barite samples from two sea-cliff sites and four offshore sites in

James R. Hein; Robert A. Zierenberg; J. Barry Maynard; Mark D. Hannington

2007-01-01

146

Palaeomagnetism and the continental crust  

SciTech Connect

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

Piper, J.D.A.

1987-01-01

147

-induced continental warming  

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

148

A Subduction Scissor and Development of the Intervening Plate Collision at South Island, New Zealand  

Microsoft Academic Search

The continental plate collision across South Island, New Zealand is bounded to the north by west-dipping Hikurangi subduction of the Pacific plate and to the south by east-dipping Fiordland-Puysegur subduction of the Australian plate. As such, South Island is in the midst of a type of 'subduction scissor'. The tectonic behaviour of the deep plate portion of South Island (viz.,

R. N. Pysklywec; S. Ellis; A. R. Gorman

2007-01-01

149

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

USGS Publications Warehouse

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.

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

1980-01-01

150

Tectonics of China: Continental scale cataclastic flow  

NASA Astrophysics Data System (ADS)

Stratigraphic, structural, and earthquake evidence indicates that cataclastic flow, that is, flow by brittle mechanisms (e.g., fracture and slip), was dominant in China from late Paleozoic. This process has operated over a range of scales including the continental scale. China is made up of large brittle basement elements immersed in ductile zones which are analogous to porphyroclasts (large, often brittle fragments) surrounded by fluxion (foliation or flow) structures in cataclastic rocks, respectively. This basement fabric for China is seen on Landsat imagery and on tectonic maps and is comparable to cataclastic rock fabrics seen in fault zones, on outcrops, and in thin sections. Brittle basement elements are broken into two or more large rigid blocks, and the dimensions of elements and blocks are within 1 order of magnitude of each other. Ductile zones are made up of fragments which are many orders of magnitude smaller than the ductile zones. Rigid blocks and fragments are identified, and their dimensions are measured through earthquake, fault, and fracture patterns. Rigid basement blocks are surrounded by earthquakes. The sedimentary rocks over the basement faults at the block boundaries seem to be affected by fault movements because they are characterized by facies changes, thickness changes, high-angle faults, and forced folds. Ductile basement zones are earthquake prone, and deformation of the ductile basement affects the overlying sedimentary rocks, as is demonstrated by unconformities and by a wide variety of structures. Thrust faults, buckle folds, and strike slip faults are common in and adjacent to western ductile zones. Structures are most intensely developed where ductile zones abut brittle elements. Both brittle elements and ductile zones are rifted and cut by strike slip faults in eastern China. The mechanical fabric of China and the boundary conditions acting on China are now and always have been determined by its plate tectonic history. This inference is made from recently published plate tectonic interpretations. Geologic maps show that there are six elements and that each element has a Precambrian, crystalline core which is surrounded by upper Paleozoic continental margin suites of rocks, including subduction complexes, among others. Geologic data on ophiolites demonstrate that the brittle elements and their margins were juxtaposed and then welded together along suture zones during Permian and Triassic time to make China. Cenofcoic plate motions affecting China resulted in the collision with India where it converges with southwest China and the extension in eastern China where island arcs move away from the mainland and where grabens are actively forming. The juxtaposition to Siberia, which acts as a buttress against northern China, explains the compression of western China, and the absence of a buttress in the Pacific Ocean explains why eastern China can extend. Furthermore, laboratory data on the mechanical behavior of rock under conditions analogous to the shallow crustal conditions of interest in China show that all rocks are weaker in extension than they are in compression. Basement rock in western China is strong because it is compressed, but this same basement rock is weak in eastern China because it is in extension. The tectonics of China or, in mechanistic terms, the way in which the mechanical framework of China responds to Cenozoic boundary forces was a result of China's previous plate tectonic history. Crystalline cores are the rigid blocks that form brittle elements. Both the continental margin suites and the sutures are the ductile zones. The sutures and sediment patterns seen in the basins and ranges of China can be explained in terms of this tectonic scenario.

Gallagher, John J., Jr.

151

Plate Tectonics II: Plates, plate boundaries, and driving forces  

NSDL National Science Digital Library

The distribution of earthquakes and volcanoes around the world confirmed the theory of plate tectonics first proposed by Wegener. These phenomena also help categorize plate boundaries into three different types: convergent, divergent, and transform.

Egger, Anne

2003-03-18

152

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

Federal Register 2010, 2011, 2012, 2013

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

2011-01-18

153

Edeline et al. Eel continental dispersal Proximate and ultimate control of eel continental  

E-print Network

occurs on the slope of the continental shelf (SchEdeline et al. Eel continental dispersal Chapter 18 Proximate and ultimate control of eel continental dispersal Eric Edeline1* , Sylvie Dufour2 , Pierre Elie3 1 University of Oslo, Department

Paris-Sud XI, Université de

154

Composite transform-convergent plate boundaries: description and discussion  

USGS Publications Warehouse

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.

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

1992-01-01

155

Bioenergetics of Continental Serpentinites  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

156

Caffeine does not cause override of the G2\\/M block induced by UVc or gamma radiation in normal human skin fibroblasts  

Microsoft Academic Search

Caffeine has for many years been known to be involved in the sensitization of DNA to damage. One potential mechanism recently put forward is an override of the G2\\/M block induced by irradiation, which would leave the cells less time for DNA repair prior to mitosis. However, different cell types display a variety of responses and no clear pathway has

G Deplanque; F Vincent; M C M Mah-Becherel; J-P Cazenave; J-P Bergerat; C Klein-Soyer

2000-01-01

157

Mantle Flow in the Rivera-Cocos Subduction Zone  

Microsoft Academic Search

Western Mexico, where the young and small Rivera plate and the adjacent large Cocos plate are subducting beneath the North American plate, is a unique region on Earth where tearing of subducting oceanic plates, as well as fragmentation of the overriding continental plate, is occurring today. Characterizing the mantle flow field that accompanies the subduction of the Rivera and adjacent

G. Leon Soto; J. F. Ni; S. P. Grand; E. A. Sandvol; R. Valenzuela Wong; M. Guzman-Speziale; J. M. Gomez Gonzalez; T. Dominguez Reyes

2009-01-01

158

FAST TRACK PAPER: Mantle flow in the Rivera-Cocos subduction zone  

Microsoft Academic Search

Western Mexico, where the young and small Rivera Plate and the adjacent large Cocos Plate are subducting beneath the North American Plate, is a unique region on Earth where tearing of subducting oceanic plates, as well as fragmentation of the overriding continental plate, is occurring today. Characterizing the mantle flow field that accompanies the subduction of the Rivera and adjacent

Gerardo León Soto; James F. Ni; Stephen P. Grand; Eric Sandvol; Raúl W. Valenzuela; Marco Guzmán Speziale; Juan M. Gómez González; Tonatiuh Domínguez Reyes

2009-01-01

159

Extensional evolution of the central East Greenland Caledonides  

E-print Network

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

White, Arthur Percy, 1972-

2001-01-01

160

Weighing the deep continental biosphere.  

PubMed

There is abundant evidence for widespread microbial activity in deep continental fractures and aquifers, with important implications for biogeochemical cycling on Earth and the habitability of other planetary bodies. Whitman et al. (P Natl Acad Sci USA, 95, 1998, 6578) estimated a continental subsurface biomass on the order of 10(16) -10(17) g C. We reassess this value in the light of more recent data including over 100 microbial population density measurements from groundwater around the world. Making conservative assumptions about cell carbon content and the ratio of attached and free-living microorganisms, we find that the evidence continues to support a deep continental biomass estimate of 10(16) -10(17) g C, or 2-19% of Earth's total biomass. PMID:23991863

McMahon, Sean; Parnell, John

2014-01-01

161

The heat flow through oceanic and continental crust and the heat loss of the earth  

Microsoft Academic Search

Oceans and continents are now considered to be mobile and interconnected. The paper discusses heat flow through the ocean floor, continental heat flow, heat loss of the earth, thermal structure and thickness of the lithosphere, as well as convection in the mantle and the thermal structure of the lithosphere, within the framework of the theory of plate tectonics. It is

J. G. Sclater; C. Jaupart; D. Galson

1980-01-01

162

Strain accommodation by slow slip and dyking in a youthful continental rift, East Africa  

Microsoft Academic Search

Continental rifts begin and develop through repeated episodes of faulting and magmatism, but strain partitioning between faulting and magmatism during discrete rifting episodes remains poorly documented. In highly evolved rifts, tensile stresses from far-field plate motions accumulate over decades before being released during relatively short time intervals by faulting and magmatic intrusions. These rifting crises are rarely observed in thick

Eric Calais; Nicolas D'Oreye; Julie Albaric; Anne Deschamps; Damien Delvaux; Jacques Déverchère; Cynthia Ebinger; Richard W. Ferdinand; François Kervyn; Athanas S. Macheyeki; Anneleen Oyen; Julie Perrot; Elifuraha Saria; Benoît Smets; D. Sarah Stamps; Christelle Wauthier

2008-01-01

163

The Great Continental Drift Mystery  

NSDL National Science Digital Library

This unit introduces students to the development of the theory of continental drift. They will examine the early work of Alfred Wegener and Alexander DuToit, investigate lines of evidence that resulted in the development of the theory, and learn about the final lines of evidence that resulted in the theory's acceptance. There is a set of activities in which the students construct a map of Pangea using Wegener's clues, familiarize themselves with some important geographic locations, and investigate how fossil distribution can be used to enhance the study of continental drift. Study questions and a bibliography are included.

164

Geometrical constraints of rift fissures on the formation of isolated micro continental blocks during transition from continental rifting to oceanic spreading based on analogue modelling  

NASA Astrophysics Data System (ADS)

From global ocean bathymetric data, we can observe many intraplate features such us submerged and non-submerged plateaus below sea level, islands, ridges, banks etc. All these features can be divided in three main groups: (1) blocks with oceanic crust; (2) blocks with continental crust; (3) complex features. There are many hypotheses that try to describe their origin. Hypotheses, which we carried on: (1) features with continental crust formed by ridge jumping into a continental margin; (2) features with igneous composition formed by eruption of huge volumes of volcanic rocks; (3) complex features with jigsaw crust composition. We present preliminary results of our experimental modeling that show geometrical constraints for the formation of isolated blocks in oceanic crust due to the evolution of overlapping spreading centers. These can lead to the formation of an isolated continental block if all following conditions are met: (1) the angle between extension direction and pre-existing fractures are between 45° to 60° ; (2) the length of two pre-existing fractures located on opposite sides of model plate is equal; (3) the offset between two pre-existing fractures located on opposite sides of model plate vary from 1.5 cm to 3 cm. Extension rates in the model vary from V = 1.67 *10-5 m/sec to V = 2.15×10-5 m/sec which correlate with slow spreading rates. The model plate size was 12×25 cm. These experiments provide us with a probable mechanism of isolated continental block formation. In addition, the experiments allow us to distinguish major geometrical parameters of continental break up modelling. These results are preliminary and we will study other experimental settings such us influence of hotspot activity, interaction between propagating ridge and weakened zones and zones with more stable properties. For example, we consider the conditions of formation Elan Bank in Kerguelen Plateau structure.

Makushkina, Anna; Dubinin, Evgeny; Grokholsky, Andrey

2014-05-01

165

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

SciTech Connect

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.

Gripp, A.E.; Gordon, R.G. (Northwestern Univ., Evanston, IL (USA))

1990-07-01

166

Global Cretaceous plate tectonics and paleogeography  

SciTech Connect

The International Geologic Correlation Program (IGCP) Project 191, The Cretaceous Paleoclimatic Atlas Project has compiled 89 Cretaceous paleogeographic maps representing ten regions or continents. The map resolution varies from stage by stage (e.g. North America, Europe, USSR, Australia) to four maps (e.g. China, Southern South America) to a compilation of localities (Antarctica). The paleogeography is plotted here on global plate tectonic reconstructions for each stage. The reconstructions include continental positions and latitude. In addition, the oceanic plates are reconstructed including bathymetry based on a thermal age-depth relationship. The compiled paleogeography and plate tectonic base maps represent the most comprehensive framework for plotting and analyzing sedimentologic, geochemical and paleontologic data with respect to geography and latitude for the Cretaceous time period.

Barron, E.J.; Beeson, D.; Chen, P.; Dingle, R.V.; Frakes, L.A; Funnell, B.M.; Kauffman, E.G.; Petri, S.; Reyment, R.A.; Riccardi, A.C.

1985-01-01

167

Estimation of continental precipitation recycling  

SciTech Connect

The total amount of water that precipitates on large continental regions is supplied by two mechanisms: (1) advection from the surrounding areas external to the region and (2) evaporation and transpiration from the land surface within the region. The latter supply mechanism is tantamount to the recycling of precipitation over the Continental area. The degree to which regional precipitation is supplied by recycled moisture is a potentially significant climate feedback mechanism and land surface-atmosphere interaction, which may contribute to the persistence and intensification of droughts. Gridded data on observed wind and humidity in the global atmosphere are used to determine the convergence of atmospheric water vapor over continental regions. A simplified model of the atmospheric moisture over continents and simultaneous estimates of regional precipitation are employed to estimate, for several large continental regions, the fraction of precipitation that is locally derived. The results indicate that the contribution of regional evaporation to regional precipitation varies substantially with location and season. For the regions studied, the ratio of locally contributed to total monthly precipitation generally lies between 0. 10 and 0.30 but is as high as 0.40 in several cases. 48 refs., 7 figs., 4 tabs.

Brubaker, K.L.; Entekhabi, D.; Eagleson, P.S. (Massachusetts Institute of Technology, Cambridge (United States))

1993-06-01

168

Estimation of continental precipitation recycling  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

169

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

170

Optimal aggregation of Fc?RI with a structurally defined trivalent ligand overrides negative regulation driven by phosphatases.  

PubMed

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

Mahajan, Avanika; Barua, Dipak; Cutler, Patrick; Lidke, Diane S; Espinoza, Flor A; Pehlke, Carolyn; Grattan, Rachel; Kawakami, Yuko; Tung, Chang-Shung; Bradbury, Andrew R M; Hlavacek, William S; Wilson, Bridget S

2014-07-18

171

Spatial distribution of earthquakes and subduction of the Nazca plate beneath South America  

Microsoft Academic Search

A detailed study of the spatial distribution of precisely located hypocenters of South American earthquakes that occurred between lat 0° and 45°S shows that the data can be explained by the simple model of a descending oceanic plate beneath a continental plate and that the following conditions obtain: (1) The hypocenters clearly define five segments of inclined seismic zones, in

Muawia Barazangi; Bryan L. Isacks

1976-01-01

172

Tectonic and deposition model of late Precambrian-Cambrian Arabian and adjoining plates  

Microsoft Academic Search

During the late Precambrian, the terranes of the Arabian and adjoining plates were fused along the northeastern flank of the African plate in Gondwanaland. This phase, which ended approximately 640 to 620 Ma, was followed by continental failure (620 to 580 Ma) and intracontinental extension (600 to approximately 550 Ma). During the Infracambrian extensional phase, a triple junction may have

Husseini

1989-01-01

173

Subduction of the Nazca plate under Peru as evidenced by focal mechanisms and by seismicity  

Microsoft Academic Search

The focal mechanisms of 40 earthquakes in Peru and Ecuador, together with the seismicity of the region, indicate particular features of the subduction of the oceanic plate beneath this portion of South America. At shallow depths near the coast and at foci along the contact between the subduction zone and the continental plate the focal mechanisms indicate an underthrust of

William Stauder

1975-01-01

174

The Continental Distillery: Building Thick Continental Crust in the Central Andes (Invited)  

NASA Astrophysics Data System (ADS)

The formation of stable continental crust and the associated development and destruction of mantle lithospheric roots is central to our understanding of plate tectonics, both at its inception and as an ongoing process today. Subduction zones play an important role in the creation and refinement of continental crust, and also serve as a possible mechanism for the removal of residual mantle material. The central Andes provide an intriguing laboratory for the study of these processes. Up to 400 km wide, 1500 km long, and with an average elevation of 4 km, the Altiplano Plateau is the largest orogen on earth associated with an ocean-continent subduction zone. This is much larger than adjacent 'normal' sections of the Andes, raising the question of why this portion of South American crust became so much more substantial than surrounding areas. Over the past several years, new seismic data have made it possible for us to develop a more complete picture of the lithospheric and asthenospheric processes involved in the development of the Altiplano Plateau and the adjacent narrower orogen further to the north. The 'Central Andean Uplift and the Geodynamics of High Topography' (CAUGHT) comprises in part a broadband deployment of 50 stations across the northern flank of the Altiplano Plateau in southern Peru and northern Bolivia. The adjacent 'PerU Lithosphere and Slab Experiment' (PULSE) includes 40 broadband stations that cover the region directly north of the CAUGHT deployment, encompassing the northern edge of the Altiplano, the transition to 'normal' width orogen, and the transition in slab geometry from normal to flat from south to north across the study area. Uplift of the Altiplano Plateau is likely due to some combination shortening, isostasy due to lithospheric destruction or changes in crustal density, magmatic addition to the crust, and/or flow within the thickened crust. Our studies indicate pervasive low velocities across the Altiplano consistent with a dominantly felsic composition, together with even lower velocities in the mid crust beneath the Western Cordillera and Altiplano that are best explained as the intrusion of a Neogene - to - recent batholith. The lithospheric mantle appears to be highly variable across the study area, with some regions appearing to have lost most of their original roots and others indicating the persistence of a high velocity mantle lithosphere. These studies and others in progress will help us form a better idea of the processes involved in generating thick continental crust from otherwise 'normal' ocean-continent subduction zones, and those responsible for the development and destruction of continental lithospheric roots.

Wagner, L. S.; Beck, S. L.; Zandt, G.; Long, M. D.; Tavera, H.; Minaya, E.; Biryol, C. B.; Bishop, B.; Eakin, C. M.; Franca, G.; Knezevic Antonijevic, S.; Kumar, A.; Ryan, J. C.; Scire, A. C.; Ward, K. M.; Young, B. E.

2013-12-01

175

Capturing Continental Rupture Processes in Afar  

NASA Astrophysics Data System (ADS)

Both continental and oceanic rifting processes are highly 3D, but the stability of the along-axis segmentation from rifting to breakup, and its relationship to seafloor spreading remains debated. Three-dimensional models of the interactions of faults and magmatism in time and space are in development, but modelling and observations suggest that magmatic segments may propagate and/or migrate during periods of magmatism. Our ability to discriminate between the various models in large part depends on the quality of data in the ocean-transition zone, or, observations from zones of incipient plate rupture. Largely 2D crustal-scale seismic data from magmatic passive margins reveal large magmatic additions to the crust, but the timing of this heat and mass transfer is weakly constrained. Thus, the lack of information on the across rift breadth of the deforming zone at rupture, and the relationship between the early rift segmentation and the seafloor spreading segmentation represent fundamental gaps in knowledge. Our study of Earth's youngest magmatic margin, the superbly exposed, tectonically active southern Red Sea, aims to answer the following questions: What are the geometry and kinematics of active fault systems across the 'passive margin' to zone of incipient plate rupture? What is the relationship between the initial border fault segmentation, and the breakup zone segmentation? What is the distribution of active deformation and magmatism, and how does it compare to time-averaged strain patterns? We integrate results of recent experiments that suggest widespread replacement of crust and mantle lithosphere beneath the 'passive' margin, and explain the ongoing seismic deformation as a consequence of bending stresses across the ocean-continent transition, with or without a dynamic component.

Ebinger, Cynthia; Belachew, Manahloh; Tepp, Gabrielle; Keir, Derek; Ayele, Atalay

2014-05-01

176

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

177

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

SciTech Connect

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

Cronin, V.S. (Univ. of Wisconsin, Milwaukee (USA))

1990-05-01

178

Building and Destroying Continental Mantle  

NASA Astrophysics Data System (ADS)

Continents, especially their Archean cores, are underlain by thick thermal boundary layers that have been largely isolated from the convecting mantle over billion-year timescales, far exceeding the life span of oceanic thermal boundary layers. This longevity is promoted by the fact that continents are underlain by highly melt-depleted peridotites, which result in a chemically distinct boundary layer that is intrinsically buoyant and strong (owing to dehydration). This chemical boundary layer counteracts the destabilizing effect of the cold thermal state of continents. The compositions of cratonic peridotites require formation at shallower depths than they currently reside, suggesting that the building blocks of continents formed in oceanic or arc environments and became "continental" after significant thickening or underthrusting. Continents are difficult to destroy, but refertilization and rehydration of continental mantle by the passage of melts can nullify the unique stabilizing composition of continents.

Lee, Cin-Ty A.; Luffi, Peter; Chin, Emily J.

2011-05-01

179

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

PubMed Central

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

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

2012-01-01

180

Dynamic Plate Boundaries and Restored Synthetic Isochrons: The Indispensable Tools To Constrain Plate Tectonic Models  

NASA Astrophysics Data System (ADS)

We developed a plate tectonics model for the Paleozoic and Mesozoic (Ordovician to Cretaceous) integrating dynamic plate boundaries, plate buoyancy, ocean-spreading rates and major tectonic and magmatic events. Plates have been constructed through time by adding/removing oceanic material symbolized by syntethic isochrones, to ma- jor continents and terranes. These oceanic isochrons have been constructed through time in order to define the location of the spreading ridges and to restore subducted ocean basins. To simplify the process we worked with a symmetrical sea floor spread- ing for the main oceans (Paleo- and NeoTethys). Driving forces like slab pull and slab buoyancy were used to constrain the evolution of paleo-oceanic domains. This ap- proach offers a good control on the sea floor spreading and plate kinematics. This new method represents a distinct departure from classical continental drift reconstructions, which are not constrained due to the lack of plate boundaries. This model allows a more comprehensive analysis of the development of the Tethyan realm in space and time. In particular, the relationship between the Variscan and the Cimmerian cycles in the Mediterranean-Alpine realm is clearly illustrated by numerous maps. For the Alpine cycle, the relationship between the Alpides senso stricto and the Tethysides is also explicable in terms of plate tectonic development of the Alpine Tethys-Atlantic domain versus the NeoTethys domain.

Borel, G. D.; Stampfli, G. M.

181

Continental transforms: A view from the Alpine Fault  

NASA Astrophysics Data System (ADS)

Continental transform faults are dominantly highly localized strike-slip shear zones hundreds of kilometers long that accumulate tens to hundreds of kilometers of displacement. From work on the Alpine Fault, we pose the questions: what is the deep structure of a continental transform, and how does the displacement become localized? We review research on the Alpine Fault and propose a model in which the fault partitions at depth into a steep zone extending into the mantle with largely fault-parallel motion and a flat ductile decollement in the lower crust. The fault localizes around two-thirds of the plate motion within a 100 km wide zone of distributed deformation. A review of other active continental fault systems suggests that variation between them may reflect their tectonic origins, the nature of the crust in which they develop, the presence of a significant oblique component of motion, and the displacement rate. All however have evidence for the development of a single principal fault zone that carries ?50% of the total displacement and extends as a localized zone of shear into the upper mantle. We review mechanisms of strain weakening and suggest that localization of a principal fault may be initiated in the seismogenic crust and through a series of positive feedbacks eventually extend through the lower crust into the upper mantle.

Norris, Richard J.; Toy, Virginia G.

2014-07-01

182

Plate Tectonics Animation  

NSDL National Science Digital Library

Plate tectonics describes the behavior of Earth's outer shell, with pieces (plates) bumping and grinding and jostling each other about. Explore these maps and animations to get a jump start on understanding plate tectonic processes, history, and how motion of the plates affects our planet today.

2002-01-01

183

Mapping Plate Tectonic Boundaries  

NSDL National Science Digital Library

To prepare for this activity, students do background reading on Plate Tectonics from the course textbook. Students also participate in a lecture on the discovery and formulation of the unifying theory of plate tectonics, and the relationship between plate boundaries and geologic features such as volcanoes. Lastly, in lecture, students are introduced to a series of geologic hazards caused by certain plate tectonic interactions. The activity gives students practices at identifying plate boundaries and allows them to explore lesser known tectonically active regions.

Kerwin, Michael

184

Anisotropy of the Indian continental lithospheric mantle  

NASA Astrophysics Data System (ADS)

Due to the paucity of seismological data available in the public domain, the structure of the Indian lithosphere is still little known. We investigate the lithospheric structure and potential mechanical coupling between the crust and upper mantle along the Himalayan arc and underneath peninsular India using seismic anisotropy. Shear wave splitting measurements are performed on core-refracted phases. For each event recorded at a given seismological station we measured the orientation of the polarization plane of the fast S wave (phi), assumed to be a proxy for the orientation of the a axis of olivine, and the delay (dt) between the arrival time of the fast and slow S waves. We present a very comprehensive data set recorded at 86 seismological stations, deployed from the Himalayas to the southern tip of the Indian peninsula, in a joint effort by the National Geophysical Research Institute, Hyderabad, India, the University of Cambridge and the Indian Institute of Astrophysics. The unprecedented data set we present sheds light on the mechanisms involved in the India-Eurasia continental collision in a region along the Himalayan arc, south of the Indus-Tsangpo suture zone. At the scale of the Indian plate, the majority of the stations show a NNE-SSW orientation of phi over hundreds of kilometres, from Sri Lanka to the northern part of the Dharwar craton. This direction closely parallels the trend of the Indian plate motion, with respect to a fixed Eurasian plate, as defined through the NUVEL1A plate model. Along the Himalayan arc, from Ladakh in the northwest, to Bhutan and the Shillong plateau in the east, the orientation of phi rotates to become ~EW, perpendicular to the plate motion as defined through NUVEL1A. Unlike previous studies, we do find strong evidence for seismic anisotropy south of the Indus Tsangpo suture zone. A large number of null results have been computed, with consistent orientation of the two fast polarization directions (phi) across the subcontinent. We demonstrate the potential value of the too often neglected null measurements in the interpretation of seismic anisotropy. From these results, we infer the dominance, beneath the Indian lithosphere, of the asthenospheric flow in aligning minerals in the sheared lithosphere-asthenosphere boundary layer, masking any compression induced anisotropy expected to be normal to this direction. Closer to the collision front in northern India, the anisotropy may in part, be due to the foliation planes of the Himalayan fold and thrust belt aligning the a axis of olivine perpendicular to the compression axis, but more likely to the turning of the relative asthenospheric flow along the strike caused by the downthrusting Indian lithosphere acting as a barrier. The continent-wide consistency of results strengthens the understanding that the Indian lithosphere has distinct anisotropic signatures, contrary to the hitherto assumed isotropy and allows one to interpret the results in a coherent framework of Indo-Eurasian convergence.

Heintz, Maggy; Kumar, V. Pavan; Gaur, Vinod K.; Priestley, Keith; Rai, Shyam S.; Prakasam, K. Surya

2009-12-01

185

Observe animations of processes that occur along plate boundaries  

NSDL National Science Digital Library

Here are three animations that reveal how tectonic plates move relative to each other at three types of plate boundaries--transform, convergent, and divergent boundaries. Key features such as the asthenosphere are labeled in the animations. In addition, each animation is equipped with movie control buttons that allow students to play, pause, and move forward and backward through each clip. The animation of a transform boundary shows the North American and Pacific plates sliding past one another, while an oceanic plate subducts under a continental plate producing volcanic activity in the convergent boundary animation. Two coordinated movie clips are used to demonstrate what occurs at a divergent boundary from different viewpoints. Copyright 2005 Eisenhower National Clearinghouse

Education, Terc. C.; Littell, Mcdougal

2003-01-01

186

The role of continental growth on the evolution of seafloor spreading  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

187

Computer animation of Phanerozoic plate motions  

SciTech Connect

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

Scotese, C.R. (Univ. of Texas, Arlington, TX (United States). Dept. of Geology)

1992-01-01

188

Continental Growth and Deformation in Taiwan -Insight from GPS data and Sandbox Experiments  

NASA Astrophysics Data System (ADS)

The Taiwan Mountain Belt is one of the youngest mountain belts on Earth surface. It results from the NW-directed oblique convergence between the Eurasian plate and the Philippine Sea plate. The accretion of the Luzon arc propagates southward and results in the continental growth of Asian continent. In order to figure out the actual accretion of the Luzon Arc to the Asian continent. The former GPS (Global Positioning System) data were recalculated in consideration of Lanyu Island as a fixed point on the Philippine Sea plate. Under this situation the relative movement between Asian continental margin and the Philippine Sea plate can be better clarified. The largest movement vector (102 mm/yr) occurs around the Suao area indicating the recent fast opening rate of Okinawa trough (~25mm/yr). The accretion of the Coastal Range to the Central Range along Western boundary of the Longitudinal Valley is about 79.2mm/yr. On the other hand, the continental deformation is described insight of contours and vectors of the GPS velocity field and sand box modeling. The recent movement and displacement of the Chelungpu fault, back thrust system around the Kuanyin Basement High, the escape tectonics in southwestern Taiwan and the impact of the basement resulting in the occurrence of the out-of-sequence thrust are well documented.

Lu, C.; Yu, S.; Chu, H.; Chiao, L.

2002-12-01

189

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

PubMed

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

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

2007-12-13

190

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

NASA Astrophysics Data System (ADS)

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

Gurnis, Michael

2013-04-01

191

Oceanic sources of continental precipitation  

NASA Astrophysics Data System (ADS)

this special section, the authors have tried to address some of the many unanswered questions related to the transport of moisture from oceanic sources to the continents, including among others that of whether or not the moisture source regions have remained stationary over time, how the many changes in the intensity and position of the sources have affected the distribution of continental precipitation, and also the question of the role of the main modes of climate variability in the variability of the moisture regions.

Gimeno, Luis

2014-05-01

192

Thermal models pertaining to continental growth  

NASA Technical Reports Server (NTRS)

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

Morgan, Paul; Ashwal, Lew

1988-01-01

193

External Resource: Plate Tectonics  

NSDL National Science Digital Library

This Windows to the Universe interactive webpage connects students to the study and understanding of plate tectonics, the main force that shapes our planets surface. Topics: plate tectonics, lithosphere, subduction zones, faults, ridges.

1900-01-01

194

Plate Tectonics: Further Evidence  

NSDL National Science Digital Library

The representation depicts the spreading of the sea floor along the mid-ocean ridges. The resource generally describes the theory of plate tectonics, including the movement of plates with regard to one another.

195

The PLATES Project  

NSDL National Science Digital Library

This is the web page for PLATES, a program of research into plate tectonic and geologic reconstructions at the University of Texas at Austin Institute for Geophysics. The page contains links to a brief overview of plate tectonics and plate reconstructions using the PLATES Project's global plate reconstruction model, in addition to movies in the format of powerpoint animations which can be downloaded for later use. Models are shown on the evolution of the earth's oceans and the movement of the earth's tectonic plates from the Late Precambrian through the present day, reconstructing (i.e. "predicting") geological environments through geologic history. Maps of the following can be accessed: late Neo-Proterozoic, Silurian, early Jurassic, early Cretaceous, Cretaceous-Tertiary Boundary, and Oligocene. Movies are available on the following subjects: global plate motion, Jurassic to present day, opening of the Indian Ocean, and tectonic evolution of the Arctic region.

196

Plate Tectonic Primer  

NSDL National Science Digital Library

This site gives an in-depth look at the theory of plate tectonics and how it works. The structure of the Earth is discussed, with brief rock type descriptions. The structure of the lithosphere, plate boundaries, interplate relationships, and types of plates are all covered in detail.

Fichter, Lynn

197

Optimal truss plates  

Microsoft Academic Search

Sandwich plates comprised of truss cores faced with either planar trusses or solid sheets are optimally designed for minimum weight subject to prescribed combinations of bending and transverse shear loads. Motivated by recent advances in manufacturing possibilities, attention is focussed on plates with truss elements and faces made from a single material. The optimized plates are compared with similarly optimized

Nathan Wicks; John W Hutchinson

2001-01-01

198

Angular shear plate  

Microsoft Academic Search

One or more disc-shaped angular shear plates each include a region thereon having a thickness that varies with a nonlinear function. For the case of two such shear plates, they are positioned in a facing relationship and rotated relative to each other. Light passing through the variable thickness regions in the angular plates is refracted. By properly timing the relative

Mitchell C. Ruda; Alan W. Greynolds; Tilman W. Stuhlinger

2009-01-01

199

Earthquakes and Plate Tectonics  

NSDL National Science Digital Library

This article describes the theory of plate tectonics and its relation to earthquakes and seismic zones. Materials include an overview of plate tectonics, a description of Earth's crustal plates and their motions, and descriptions of the four types of seismic zones.

200

A Simple Linear Age Progression for the Ninetyeast Ridge, Indian Ocean: New Constraints on Indian Plate Tectonics and Hotspot Dynamics  

Microsoft Academic Search

New Ar\\/Ar age constraints on basalt from DSDP and ODP drill sites and new (2007) dredge sites confirm that the Ninetyeast Ridge (NER) is a 5000 km long hotspot track in the Indian Ocean created as the Indian Plate moved rapidly northward from c. 80 to 40 Ma at the fastest known rate of any tectonic plate with significant continental

M. S. Pringle; F. A. Frey; E. E. Mervine

2008-01-01

201

Early Jurassic paleopoles from the Hartford continental rift basin (eastern North America): Was an abrupt change in polar  

E-print Network

Early Jurassic paleopoles from the Hartford continental rift basin (eastern North America biotic turnover at the Triassic/Jurassic boundary, adds impetus for seeking confirmation of possibly to reflect a major plate reorganization or an episode of true polar wander. However, early Jurassic

Olsen, Paul E.

202

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

E-print Network

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

Jahnke, Richard A.

203

Continental Crust Recycling at Collision Zones: Insights From Numerical Modeling and Observations  

NASA Astrophysics Data System (ADS)

In the recent years, an increasing number of geochemical evidences of continental crust (cc) contributions in OIB lavas have been reported worldwide, suggesting that part of the lithospheric continents have sunk and were recycled in the deep mantle. So far, crustal recycling processes have been identified as eclogitization of the lower crust, foundering and subduction of crustal rocks and erosion of continents at ocean-continent and ocean-ocean margins activated by the subducting slab. But what is about continental crust recycling occurring during continental collision? In order to investigate this process, we perform 2D numerical models of subduction under a fix continent of a 1) retreating and 2) advancing oceanic slab attached to a continental passive margin to test this last process. 1) If the slab is retreating, when collision occurs and the continents are poorly coupled, asthenospheric mantle wedges between the continents triggering the retreating and delamination of the converging continental plate. A discrete volume of cc (mainly the lower crust) is then dragged into the deep mantle indicating that this is an efficient process for crustal recycling. Examples of active retreating collisional zone are the Northern Apennines and the Carpatians. 2) If the plates are coupled and convergence does not stop after collision, a large volume of lower cc is transported in the deep mantle. This models is representative of active advancing collisional zone such as the Himalayas where has been calculated that about 2x106 km3 of continental lower crust have been subducted In both cases, the rheologically weak part of the crust (upper crust and sediments, Wet Quartzite flow law) is scraped off and accreted to the accretionary wedge. Results then show that cc recycling occurring after collision is a considerable process that has to be taken into account for both crustal mass balancing and crustal growth models.

Faccenda, M.; Gerya, T. V.; Chakraborty, S.

2008-12-01

204

The Continental Margins of the Norwegian--Greenland Sea: Recent Results and Outstanding Problems: Discussion  

Microsoft Academic Search

Within a framework of plate tectonics the passive continental margins of the Norwegian--Greenland Sea may be classified as composed of rifted and sheared segments. An exception is the margin north of the Greenland-Senja Fracture Zone which appears to be of a combined sheared-rifted type. The margins south of the Greenland-Senja Fracture Zone are in part underlain by basement highs on

G. Wissmann; O. Eldholm

1980-01-01

205

An improved plating process  

NASA Technical Reports Server (NTRS)

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

Askew, John C.

1994-01-01

206

Discovering Plate Boundaries  

NSDL National Science Digital Library

Students are initially assigned to one of four maps of the world: Seismology, Volcanology, Geochronology or Topography. They are also given a map of the world's plate boundaries and are asked to classify the boundaries based upon the data from their assigned map. Students are then assigned to a tectonic plate, such that each plate group contains at least one "expert" on each map. As a group, they must classify their plate's boundaries using data from all four maps. Recent volcanic and seismic events are discussed in the plate tectonic context. Has minimal/no quantitative component Uses geophysics to solve problems in other fields

Henning, Alison

207

An Analysis of Wilson Cycle Plate Margins  

NASA Astrophysics Data System (ADS)

The Wilson Cycle theory that oceans close and open along the same suture is a powerful concept in analyses of ancient plate tectonics. It implies that collision zones are structures that are able to localize extensional deformation for long times after the collision has waned. However, some sutures are seemingly never reactivated and already Tuzo Wilson recognized that Atlantic break-up did not follow the precise line of previous junction. We have reviewed margin pairs around the Atlantic and Indian Oceans with the aim to evaluate the extent to which oceanic opening used former sutures, summarize delay times between collision and break-up, and analyze the role of mantle plumes in continental break-up. We aid our analyses with plate tectonic reconstructions using GPlates (www.gplates.org). Although at first sight opening of the North Atlantic Ocean largely seems to follow the Iapetus and Rheic sutures, a closer look reveals deviations. For example, Atlantic opening did not utilize the Iapetus suture in Great Britain and rather than opening along the younger Rheic suture north of Florida, break-up occurred along the older Pan-African structures south of Florida. We find that today's oceanic Charlie Gibbs Fracture Zone, between Ireland and Newfoundland, is aligned with the Iapetus suture. We speculate therefore that in this region the Iapetus suture was reactivated as a transform fault. As others before us, we find no correlation of suture and break-up age. Often continental break-up occurs some hundreds of Myrs after collision, but it may also take over 1000 Myr, as for example for Australia - Antarctica and Congo - São Francisco. This places serious constraints on potential collision zone weakening mechanisms. Several studies have pointed to a link between continental break-up and large-scale mantle upwellings. It is, however, much debated whether plumes use existing rifts as a pathway, or whether plumes play an active role in causing rifting. We find a positive correlation between break-up age and plume age, which we interpret to indicate that plumes can aid the factual continental break-up. However, plumes may have been guided towards the rift for margins that experienced a long rift history (e.g., Norway-Greenland), to then trigger the break-up. This could offer a partial reconciliation in the debate of a passive or active role for mantle plumes in continental break-up.

Buiter, S.; Torsvik, T. H.

2012-12-01

208

Spreading continents kick-started plate tectonics  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

209

Spreading continents kick-started plate tectonics.  

PubMed

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

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

2014-09-18

210

Stable Continental Region Earthquakes in South China  

Microsoft Academic Search

This paper reviews some remarkable characteristics of earthquakes in a Stable Continental Region (SCR) of the South China Block (SCB). The kernel of the SCB is the Yangtze platform solidified in late Proterozoic time, with continental growth to the southeast by a series of fold belts in Paleozoic time. The facts that the deviatoric stress is low, the orientations of

L. Liu

2001-01-01

211

Anthropogenic impacts on continental surface water fluxes  

Microsoft Academic Search

Impacts of reservoirs and irrigation water withdrawals on continental surface water fluxes are studied within the framework of the Variable Infiltration Capacity (VIC) model for a part of North America, and for Asia. A reservoir model, designed for continental-scale simulations, is developed and implemented in the VIC model. The model successfully simulates irrigation water requirements, and captures the main effects

Ingjerd Haddeland; Thomas Skaugen; Dennis P. Lettenmaier

2006-01-01

212

Paper microzone plates.  

PubMed

This paper describes 96- and 384-microzone plates fabricated in paper as alternatives to conventional multiwell plates fabricated in molded polymers. Paper-based plates are functionally related to plastic well plates, but they offer new capabilities. For example, paper-microzone plates are thin (approximately 180 microm), require small volumes of sample (5 microL per zone), and can be manufactured from inexpensive materials ($0.05 per plate). The paper-based plates are fabricated by patterning sheets of paper, using photolithography, into hydrophilic zones surrounded by hydrophobic polymeric barriers. This photolithography used an inexpensive formulation photoresist that allows rapid (approximately 15 min) prototyping of paper-based plates. These plates are compatible with conventional microplate readers for quantitative absorbance and fluorescence measurements. The limit of detection per zone loaded for fluorescence was 125 fmol for fluorescein isothiocyanate-labeled bovine serum albumin, and this level corresponds to 0.02 the quantity of analyte per well used to achieve comparable signal-to-noise in a 96-well plastic plate (using a solution of 25 nM labeled protein). The limits of detection for absorbance on paper was approximately 50 pmol per zone for both Coomassie Brilliant Blue and Amaranth dyes; these values were 0.4 that required for the plastic plate. Demonstration of quantitative colorimetric correlations using a scanner or camera to image the zones and to measure the intensity of color, makes it possible to conduct assays without a microplate reader. PMID:19572563

Carrilho, Emanuel; Phillips, Scott T; Vella, Sarah J; Martinez, Andres W; Whitesides, George M

2009-08-01

213

Deformation in the continental lithosphere  

NASA Astrophysics Data System (ADS)

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

214

The Theory of Continental Drift  

NSDL National Science Digital Library

This is a brief review of the Theory of Continental Drift and the evidence that led Alfred Wegener to state the theory. It describes evidence of matching but misplaced rocks, uncovered fossils in places they should not have been, and discovered evidence of astounding climatological changes. In addition, fossil remains of a prehistoric reptile known as the Mesosaurus had been uncovered on both sides of the South Atlantic and plant fossils indicated that tropical forests once existed only a few hundred miles from the North Pole. It also cites glacial and stratigraphic evidence. The site discusses objections to the theory and states that at the time of his death in 1930, Wegener's theory seemed well on its way to obscurity.

215

Mantle Convection Moving Plates  

NSDL National Science Digital Library

This demonstration models the manner in which the convection currents in the mantle of the Earth cause movement of the plates. Convection currents in the mantle were thought, for many years, to be solely responsible for plate tectonic movements, with the movement taking rocks down at destructive margins and new rocks forming when plates spread. It is now thought likely that there are three possible driving mechanisms for plate tectonics. In addition to movement of mantle convection currents as shown in this demonstration, scientists also consider the mass of the subducted plate (the sinking slab) at the subduction zone dragging the surface part of the plate across the surface and the new plate material sliding off the higher oceanic ridges at constructive margins.

216

Quantifying the isotopic ‘continental effect’  

NASA Astrophysics Data System (ADS)

Since the establishment of the IAEA-WMO precipitation-monitoring network in 1961, it has been observed that isotope ratios in precipitation (?H2 and ?O18) generally decrease from coastal to inland locations, an observation described as the ‘continental effect.’ While discussed frequently in the literature, there have been few attempts to quantify the variables controlling this effect despite the fact that isotopic gradients over continents can vary by orders of magnitude. In a number of studies, traditional Rayleigh fractionation has proven inadequate in describing the global variability of isotopic gradients due to its simplified treatment of moisture transport and its lack of moisture recycling processes. In this study, we use a one-dimensional idealized model of water vapor transport along a storm track to investigate the dominant variables controlling isotopic gradients in precipitation across terrestrial environments. We find that the sensitivity of these gradients to progressive rainout is controlled by a combination of the amount of evapotranspiration and the ratio of transport by advection to transport by eddy diffusion, with these variables becoming increasingly important with decreasing length scales of specific humidity. A comparison of modeled gradients with global precipitation isotope data indicates that these variables can account for the majority of variability in observed isotopic gradients between coastal and inland locations. Furthermore, the dependence of the ‘continental effect’ on moisture recycling allows for the quantification of evapotranspiration fluxes from measured isotopic gradients, with implications for both paleoclimate reconstructions and large-scale monitoring efforts in the context of global warming and a changing hydrologic cycle.

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

2014-11-01

217

Intrusion of ultramafic magmatic bodies into the continental crust: Numerical simulation  

NASA Astrophysics Data System (ADS)

Intrusions of ultramafic bodies into the lower density continental crust are documented for a large variety of tectonic settings spanning continental shields, rift systems, collision orogens and magmatic arcs. The intriguing point is that these intrusive bodies have a density higher by 300-500 kg m -3 than host rocks. Resolving this paradox requires an understanding of the emplacement mechanism. We have employed finite differences and marker-in-cell techniques to carry out a 2D modeling study of intrusion of partly crystallized ultramafic magma from sublithospheric depth to the crust through a pre-existing magmatic channel. By systematically varying the model parameters we document variations in intrusion dynamics and geometry that range from funnel- and finger-shaped bodies (pipes, dikes) to deep seated balloon-shaped intrusions and flattened shallow magmatic sills. Emplacement of ultramafic bodies in the crust lasts from a few kyr to several hundreds kyr depending mainly on the viscosity of the intruding, partly crystallized magma. The positive buoyancy of the sublithospheric magma compared to the overriding, colder mantle lithosphere drives intrusion while the crustal rheology controls the final location and the shape of the ultramafic body. Relatively cold elasto-plastic crust ( TMoho = 400 °C) promotes a strong upward propagation of magma due to the significant decrease of plastic strength of the crust with decreasing confining pressure. Emplacement in this case is controlled by crustal faulting and subsequent block displacements. Warmer crust ( TMoho = 600 °C) triggers lateral spreading of magma above the Moho, with emplacement being accommodated by coeval viscous deformation of the lower crust and fault tectonics in the upper crust. Strong effects of magma emplacement on surface topography are also documented. Emplacement of high-density, ultramafic magma into low-density rocks is a stable mechanism for a wide range of model parameters that match geological settings in which partially molten mafic-ultramafic rocks are generated below the lithosphere. We expect this process to be particularly active beneath subduction-related magmatic arcs where huge volumes of partially molten rocks produced from hydrous cold plume activity accumulate below the overriding lithosphere.

Gerya, Taras V.; Burg, Jean-Pierre

2007-02-01

218

Metamorphism in Plate Boundary Zones  

NASA Astrophysics Data System (ADS)

Accretionary orogenic systems (AOS) form at sites of subduction of oceanic lithosphere; these systems dominate during supercontinent break-up and dispersal. Collisional orogenic systems (COS) form where ocean basins close and subduction ultimately ceases; these systems dominate during crustal aggregation and assembly of supercontinents. It follows that COS may be superimposed on AOS, although AOS may exist for 100s Ma without terminal collision. AOS are of two types, extensional-contractional AOS in dominantly extensional arc systems, and terrane-dominated AOS in which accretion of allochthonous elements occurs during oblique convergence. On modern Earth, regional metamorphism occurs in plate boundary zones. Blueschists are created in the subduction zone and ultra-high pressure metamorphic (UHPM) rocks are created in collision zones due to deep subduction of continental lithosphere; granulites are created deep under continental and oceanic plateaus and in arcs and collision zones [high-pressure (HP) granulites, ultra-high temperature (UHT) granulites]. In extensional-contractional AOS, basement generally is not exposed, primitive volcanic rocks occur through the history, rift basins step oceanward with time, and a well-defined arc generally is absent. LP-HT metamorphism is dominant, with looping, CW or CCW P-T-t paths and peak metamorphic mineral growth syn-to-late in relation to tectonic fabrics. UHT and HP granulites are absent, and although rare, blueschists may occur early, but UHPM is not recorded. Short-lived contractional phases of orogenesis probably relate to interruptions in the continuity of subduction caused by features on the ocean plate, particularly plateaus. Extensive granite (s.l.) magmatism accompanies metamorphism. Examples include the Lachlan Orogen, Australia, the Acadian Orogen, NE USA and Maritime Canada, and the Proterozoic orogens of the SW USA. At plate boundaries, oblique convergence is partitioned into two components, one directed more orthogonal to the strike of the trench than the convergence vector, and the other directed parallel to the strike of the trench. The orthogonal component is accommodated by subduction, but the margin-parallel component gives rise to block rotations and extension, strike-slip motion, and shortening within the upper plate. In some AOS, it has been argued that `paired' metamorphic belts characterize the metamorphic pattern. Commonly, this is a false construct that results from failure to recognize orogen-parallel terrane migration and the limitations of particular chronological datasets. Whereas a HP-LT (blueschist-eclogite) metamorphic belt may occur outboard, it is generally separated from a LP-HT (And-Sil type) metamorphic belt by a terrane boundary. These are terrane-dominated AOS. In some AOS an additional feature of the orogenic process is ridge subduction, which is reflected in the pattern of LP-HT metamorphism and the magmatism. Granulites may occur at the highest grade of metamorphism in the LP-HT belt, where granite (s.l.) magmatism is common, but UHPM occurs only rarely in the outboard HP-LT belt. Examples include the Mesozoic metamorphic belts of Japan and the North American Cordillera. COS commonly are characterized by syntectonic index minerals that record CW P-T-t paths and Barrovian-type metamorphic field gradients generated by thickening followed by exhumation. However, during the Neoproterozoic, ultra-high temperature granulite facies metamorphism is common in orogens that suture Gondwana, whereas during the Phanerozoic, metamorphism to high-pressure granulite/medium temperature eclogite facies and extreme UHPM conditions commonly occurs and may be more typical of younger COS; examples include the Alpides, the Qinling - Dabie Shan - Sulu orogens, the Variscides and the Caledonides.

Brown, M.

2005-12-01

219

75 FR 1076 - Outer Continental Shelf Civil Penalties  

Federal Register 2010, 2011, 2012, 2013

...Minerals Management Service Outer Continental Shelf Civil Penalties AGENCY: Minerals...SUMMARY: The Outer Continental Shelf Lands Act requires the MMS to...gas operations in the Outer Continental Shelf at least once every 3...

2010-01-08

220

49 CFR 192.10 - Outer continental shelf pipelines.  

Code of Federal Regulations, 2010 CFR

...2010-10-01 false Outer continental shelf pipelines. 192.10 Section...General § 192.10 Outer continental shelf pipelines. Operators of...transportation pipelines on the Outer Continental Shelf (as defined in the Outer...

2010-10-01

221

49 CFR 192.10 - Outer continental shelf pipelines.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 false Outer continental shelf pipelines. 192.10 Section...General § 192.10 Outer continental shelf pipelines. Operators of...transportation pipelines on the Outer Continental Shelf (as defined in the Outer...

2011-10-01

222

49 CFR 195.9 - Outer continental shelf pipelines.  

Code of Federal Regulations, 2010 CFR

...2010-10-01 false Outer continental shelf pipelines. 195.9 Section... General § 195.9 Outer continental shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf must identify...

2010-10-01

223

49 CFR 195.9 - Outer continental shelf pipelines.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 false Outer continental shelf pipelines. 195.9 Section... General § 195.9 Outer continental shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf must identify...

2012-10-01

224

49 CFR 195.9 - Outer continental shelf pipelines.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 false Outer continental shelf pipelines. 195.9 Section... General § 195.9 Outer continental shelf pipelines. Operators of transportation pipelines on the Outer Continental Shelf must identify...

2011-10-01

225

49 CFR 192.10 - Outer continental shelf pipelines.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 false Outer continental shelf pipelines. 192.10 Section...General § 192.10 Outer continental shelf pipelines. Operators of...transportation pipelines on the Outer Continental Shelf (as defined in the Outer...

2012-10-01

226

78 FR 48828 - Airworthiness Directives; Continental Motors, Inc. Reciprocating Engines  

Federal Register 2010, 2011, 2012, 2013

...cylinder. (iii) The presence of oil or a normal dirty appearance...of Teledyne Continental Motors Service Bulletin (SB) No...Aircraft model. (2) Continental Motors, Inc. engine model number...this AD, contact Continental Motors, Inc., PO Box 90,...

2013-08-12

227

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

PubMed

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

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

2013-01-01

228

Irradiation of an elastic plate by a finite-amplitude sound beam with applications to nondestructive evaluation  

NASA Astrophysics Data System (ADS)

This dissertation describes an investigation of nonlinear effects associated with the interaction of ultrasound with plates. The overriding goal is to assess the potential for using immersion techniques to measure the nonlinear acoustical parameters of plates. Three measurement configurations are described, with both theory and experiment reported. Effects of weak nonlinearity are included in the theoretical models. In the first configuration, the goal is to characterize the nonlinear elastic response of an isotropic, homogeneous plate. Plate resonances were used to enhance the nonlinear acoustical response. An experiment was performed with an aluminum plate in water, but nonlinearity due to wave propagation in the plate could not be distinguished from the nonlinear effects associated with propagation of sound through the surrounding fluid. In the second configuration, the interaction of ultrasound with bonded plates is considered. In the theoretical model, nonlinear effects are assumed to occur only at the bond. Particular attention is paid to changes in the reflection and transmission coefficients, as well as the second harmonic radiated from the plate, as a function of bond stiffness. Experiments were performed using bonded aluminum and acrylic plates. Measurements are in qualitative agreement with linear theory, but nonlinear effects at the bond were not observed. In the first two configurations, nonlinearity within the plate is taken into account, but not diffraction of the ultrasound beams. In the third configuration, the interaction of a sound beam with a plate at oblique incidence is examined. Here, beam diffraction is taken into account, but plate nonlinearity is considered to be negligible. The theoretical model is based on an angular spectrum method, and accounts for Lamb wave propagation within the plate. At Lamb excitation angles, nonspecular effects occur in the reflected and transmitted sound beams. Second harmonic generation is assumed to occur only in the fluid. Experiments were performed on an aluminum plate in water, and quantitative agreement is found between theory and measurements.

Younghouse, Steven Joseph

229

Anatomy of a diffuse cryptic suture zone exemplified by European Variscan belt: a new concept of continental tectonics  

NASA Astrophysics Data System (ADS)

The plate tectonics paradigm has offered a link between the horizontal movement of lithospheric plates, closure of intervening oceanic basin and formation of oceanic suture zone preserved even during continental collision. On the example of the Bohemian Massif we document the evolution of Andean type orogen involved in continental collision. Based on combined geological data, geophysical imagery and fully scaled thermomechanical modelling a modified view on the internal architecture of collisional orogens is proposed. The characteristic feature of the model proposed for the Variscan orogen in the Bohemian Massif is the convergence of two contrasting domains of lithosphere, leading to subduction of an attenuated felsic metaigneous crust under the rifted (Gondwana) margin formed by a dense sequence of metasedimentary and metabasic rocks. The relamination of refractory light material rich in radioactive elements underneath the relatively dense upper plate is responsible for the gravitational instabilities that lead to the overturns in the thickened crust. This mechanism results in the formation of a diffuse cryptic suture zone, i.e., a wide zone in which materials from the lower and upper plates are mixed to form a hybrid continental crust. The diffuse cryptic suture zone remains the only evidence of the original plate boundary repeatedly re-appearing within the orogen. We propose that this model may have a general validity and possible link to modern orogens exemplified by comparison of Variscan and Tibetan orogenic systems is proposed based on petrological characteristics and similarities in geophysical signatures.

Lexa, Ondrej; Schulmann, Karel; Janoušek, Vojt?ch; Lardeaux, Jean Marc

2014-05-01

230

Cenozoic evolution of the Antarctic Peninsula continental margin  

SciTech Connect

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

Anderson, J.B. (Rice Univ., Houston, TX (USA))

1990-05-01

231

Continental margin tectonics - Forearc processes  

SciTech Connect

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

Lundberg, N.; Reed, D.L. (USAF, Geophysics Laboratory, Hanscom AFB, MA (United States))

1991-01-01

232

Hypervelocity plate acceleration  

SciTech Connect

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

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

1991-01-01

233

Arctic and Antarctic Crustal Thickness and Continental Lithosphere Thinning from Gravity Inversion  

NASA Astrophysics Data System (ADS)

Mapping crustal thickness, continental lithosphere thinning and oceanic lithosphere distribution represents a substantial challenge for the Polar Regions. The Arctic region formed as a series of small distinct ocean basins leading to a complex distribution of oceanic crust, thinned continental crust and rifted continental margins. Antarctica, both peripherally and internally, experienced poly-phase rifting and continental breakup. We determine Moho depth, crustal basement thickness, continental lithosphere thinning and ocean-continent transition location for the Polar Regions using a gravity inversion method which incorporates a lithosphere thermal gravity anomaly correction. The method is carried out in the 3D spectral domain and predicts Moho depth and incorporates a lithosphere thermal gravity anomaly correction. Ice thickness is included in the gravity inversion, as is the contribution from sediments which assumes a compaction controlled sediment density increase with depth. A correction to the predicted continental lithospheric thinning derived from gravity inversion is made for volcanic material addition produced by decompression melting during continental rifting and seafloor spreading. For the Arctic, gravity data used is from the NGA (U) Arctic Gravity Project, bathymetry is from IBCAO and sediment thickness is from a new regional compilation. For Antarctica and the Southern Oceans, data used are elevation and bathymetry, free-air gravity anomaly, ice and sediment thickness from Smith and Sandwell (2008), Sandwell and Smith (2008) and Laske and Masters (1997) respectively, supplemented by Bedmap2 data south of 60 degrees south. Using gravity anomaly inversion, we have produced the first comprehensive maps of crustal thickness and oceanic lithosphere distribution for the Arctic, Antarctica and the Southern Ocean. Our gravity inversion predicts thin crust and high continental lithosphere thinning factors in the Makarov, Podvodnikov, Nautilus and Canada Basins consistent with these basins being oceanic or highly thinned continental crust. Larger crustal thicknesses, in the range 20 - 30 km, are predicted for the Lomonosov, Alpha and Mendeleev Ridges. Moho depths predicted compare well with seismic estimates. Predicted very thin continental or oceanic crust under the North Chuchki Basin and Laptev Sea has major implications for understanding the plate tectonic history of the Amerasia Basin. Our gravity inversion study predicts thick crust (> 45 km) under interior East Antarctica. Thin crust is predicted under the West Antarctica Rift System and the Ross Sea. Continent scale rifts are also seen within East Antarctica. Intermediate crustal thickness with a pronounced rift fabric is predicted under Coates Land. An extensive region of either thick oceanic crust or highly thinned continental crust is predicted offshore Oates Land and north Victoria Land. Superposition of illuminated satellite gravity data onto crustal thickness maps from gravity inversion provides improved determination of rift orientation, pre-breakup rifted margin conjugacy and continental breakup trajectory (e.g. for the Southern Ocean). Gravity inversion predictions of crustal thickness, OCT location and oceanic lithosphere distribution may be used to test plate tectonic reconstructions. Using gravity anomaly inversion mapping of continental lithosphere thinning we have developed and applied a new technique to predict basement heat-flow, important for the prediction of ice-sheet stability, for the Polar Regions.

Kusznir, Nick J.; Alvey, Andy; Vaughan, Alan P. M.; Ferraccioli, Fausto; Jordan, Tom A. R. M.; Roberts, Alan M.

2013-04-01

234

Understanding Plate Motions  

NSDL National Science Digital Library

This interactive site uses illustrations and photographs along with text to explain the movement of tectonic plates and the result of this movement on the surface of the Earth. There is a detailed discussion of the movement at each of the four types of plate boundaries: divergent, convergent, transform, and plate boundary zones. Both lateral and vertical movements are depicted by maps and diagrams and resulting Earth structures are shown in photographs.

235

Plates on the Move  

NSDL National Science Digital Library

This fun Web article is part of OLogy, where kids can collect virtual trading cards and create projects with them. Here, they learn about the Earth's outer shell and its constant movement. It begins with an overview that explains tectonic plates. There is an animation that shows recent earthquakes and their relationship to plate boundaries. Students can click to explore 12 individual volcanoes, mountains, hotspots, and earthquakes. For each of the geological formations or events, they will see a map that shows how the plates are moving, an animation about plate interaction, stats, and a story about that particular formation or event.

236

Plate Motion Calculator  

NSDL National Science Digital Library

This program calculates tectonic plate motion at any location on Earth using one or more plate motion models. The possible plate motion models are GSRM v1.2 (2004), CGPS (2004), HS3-NUVEL1A, REVEL 2000, APKIM2000.0, HS2-NUVEL1A, NUVEL 1A, NUVEL 1, and two models for ITRF2000. Plates or frames are selected from dropdown lists or can be entered by the user. Position coordinates can be entered in geographic coordinates (decimal degrees, or degrees/minutes/seconds) or in WGS84 cartesian XYZ, as either a single point or multiple points.

Estey, Lou

237

Introduction to Plate Tectonics  

NSDL National Science Digital Library

In this lab students interpret bathymetric, topography, sea floor ages, and earthquake distributions to reinforce concepts about the different types of plate boundaries. Each student must interpret several sets of data to determine the location and type of plate boundary. To develop a set of basic analytical skills, the students draw several diagrams and graphs to reinforce the data presented in figures. Students are also asked to think critically about plate rates and what happens to the crust at the different plate boundaries. This activity uses online and/or real-time data and has minimal/no quantitative component.

Cochran, Elizabeth

238

Regional magnetic anomaly constraints on continental breakup  

SciTech Connect

Continental lithosphere magnetic anomalies mapped by the Magsat satellite are related to tectonic features associated with regional compositional variations of the crust and upper mantle and crustal thickness and thermal perturbations. These continental-scale anomaly patterns when corrected for varying observation elevation and the global change in the direction and intensity of the geomagnetic field show remarkable correlation of regional lithospheric magnetic sources across rifted continental margins when plotted on a reconstruction of Pangea. Accordingly, these anomalies provide new and fundamental constraints on the geologic evolution and dynamics of the continents and oceans.

von Frese, R.R.B.; Hinze, W.J.; Olivier, R.; Bentley, C.R.

1986-01-01

239

Modeling the Dynamics of Continental Shelf Carbon  

NASA Astrophysics Data System (ADS)

Continental margin systems are important contributors to global nutrient and carbon budgets. Effort is needed to quantify this contribution and how it will be modified under changing patterns of climate and land use. Coupled models will be used to provide projections of future states of continental margin systems. Thus, it is appropriate to consider the limitations that impede the development of realistic models. Here, we provide an overview of the current state of modeling carbon cycling on continental margins as well as the processes and issues that provide the next challenges to such models. Our overview is done within the context of a coupled circulation-biogeochemical model developed for the northeastern North American continental shelf region. Particular choices of forcing and initial fields and process parameterizations are used to illustrate the consequences for simulated distributions, as revealed by comparisons to observations using quantitative statistical metrics.

Hofmann, Eileen E.; Cahill, Bronwyn; Fennel, Katja; Friedrichs, Marjorie A. M.; Hyde, Kimberly; Lee, Cindy; Mannino, Antonio; Najjar, Raymond G.; O'Reilly, John E.; Wilkin, John; Xue, Jianhong

2011-01-01

240

Paleogene continental margin truncation in southwestern Mexico: Geochronological evidence  

NASA Astrophysics Data System (ADS)

The reasons for, and mechanisms of, continental margin truncation in SW Mexico where Mesozoic-Cenozoic plutons are situated directly on the Pacific coast, are not yet well understood. Large-scale dextral and/or sinistral displacements of the continental margin terranes, now forming parts of Baja California or the Chortis block, have been proposed. The well-defined along-coast NW-SE decreasing granitoid intrusion age trend (˜1.2 cm/yr in the 100 Ma-40 Ma time interval) between Puerto Vallarta and Zihuatanejo is interpreted by us to be a geometric artifact of oblique continental margin truncation rather than the consequence of a sinistral offset of the Chortis block from those latitudes toward the SE. Changes in the dip and velocity of the NNW-SSE trending Cretaceous-Tertiary subduction zone resulted in a landward migration of the magmatic arc. Taking into account certain stratigraphic affinities of Chortis and the Oaxaca and Mixteca terranes, together with the known displacement rates along the North America-Caribbean Plate boundary, the northwesternmost paleoposition of the Chortis block with respect to SW Mexico was near Zihuatanejo. In contrast, between Zihuatanejo and the Isthmus of Tehuantepec, the cessation of the Tertiary magmatism decreased more rapidly (˜7.7 cm/yr), although the trend is not so obvious. Starting in the late Eocene, Chortis moved about 1100 km to the SE along a transform boundary associated with the opening of the Cayman Trough. Based on our geochronological data and structural relationships between mylonite zones and plutons in the Acapulco-Tehuantepec area, we propose an approximately 650 km SE movement of Chortis from about 40-25 Ma, with a velocity of 6.5-4.3 cm/yr. Since this is considerably slower than the decreasing age trend obtained by us using the geochronological data, we consider batholith formation in this segment to predate and postdate the offshore passage of the North America-Farallon-Caribbean triple junction. Geological observations and paleomagnetic data do not give strong support for large-scale right-lateral displacements of crustal blocks like the Baja California. Given the isotopic data presented, the continental margin truncation in SW Mexico seems to be the consequence of an interaction of mechanisms. Of these, we regard tectonic erosion associated with the subduction process to be the most important in the northwestern segment. On the other hand, the lateral removal of material associated with the displacement of Chortis is more important in the southeastern segment.

Schaaf, Peter; MoráN-Zenteno, Dante; HernáNdez-Bernal, Maria Del Sol; SolíS-Pichardo, Gabriela; Tolson, Gustavo; KöHler, Hermann

1995-12-01

241

Cenozoic tectonic jumping and implications for hydrocarbon accumulation in basins in the East Asia Continental Margin  

NASA Astrophysics Data System (ADS)

Tectonic migration is a common geological process of basin formation and evolution. However, little is known about tectonic migration in the western Pacific margins. This paper focuses on the representative Cenozoic basins of East China and its surrounding seas in the western Pacific domain to discuss the phenomenon of tectonic jumping in Cenozoic basins, based on structural data from the Bohai Bay Basin, the South Yellow Sea Basin, the East China Sea Shelf Basin, and the South China Sea Continental Shelf Basin. The western Pacific active continental margin is the eastern margin of a global convergent system involving the Eurasian Plate, the Pacific Plate, and the Indian Plate. Under the combined effects of the India-Eurasia collision and retrogressive or roll-back subduction of the Pacific Plate, the western Pacific active continental margin had a wide basin-arc-trench system which migrated or ‘jumped’ eastward and further oceanward. This migration and jumping is characterized by progressive eastward younging of faulting, sedimentation, and subsidence within the basins. Owing to the tectonic migration, the geological conditions associated with hydrocarbon and gashydrate accumulation in the Cenozoic basins of East China and its adjacent seas also become progressively younger from west to east, showing eastward younging in the generation time of reservoirs, seals, traps, accumulations and preservation of hydrocarbon and gashydrate. Such a spatio-temporal distribution of Cenozoic hydrocarbon and gashydrate is significant for the oil, gas and gashydrate exploration in the East Asian Continental Margin. Finally, this study discusses the mechanism of Cenozoic intrabasinal and interbasinal tectonic migration in terms of interplate, intraplate and underplating processes. The migration or jumping regimes of three separate or interrelated events: (1) tectonism-magmatism, (2) basin formation, and (3) hydrocarbon-gashydrate accumulation are the combined effects of the Late Mesozoic extrusion tectonics, the Cenozoic NW-directed crustal extension, and the regional far-field eastward flow of the western asthenosphere due to the India-Eurasia plate collision, accompanied by eastward jumping and roll-back of subduction zones of the Pacific Plate.

Suo, Yanhui; Li, Sanzhong; Yu, Shan; Somerville, Ian D.; Liu, Xin; Zhao, Shujuan; Dai, Liming

2014-07-01

242

The Moving Plates  

NSDL National Science Digital Library

This lesson focuses on relative versus absolute velocity. Students can use a program (must be connected to the internet) to calculate the different types of velocities for different points along plate boundaries. A very brief description of the earth's plates is given, with links to additional information and images. Includes discussion questions.

243

Accurate license plate localization  

Microsoft Academic Search

Vehicle license plate identification system is an image- processing technology used to identify vehicles by their license plates. This technology is used in various security and traffic applications. This data is also used for enforcement, data collection, and can be used to keep a time record on the entry or exit of vehicles for automatic payment calculations. The significant advantage

S. Mohamed Mansoor Roomi; M. Anitha; R. Bhargavi

2011-01-01

244

Mapping Plate Boundaries  

NSDL National Science Digital Library

This in-class exercise, profiled on the Starting Point website, is intended to have the students discover plate boundaries based on the uneven geographic occurrence of geologic hazards. The website details the learning goals, teaching notes and materials, and context for this activity. It offers an extensive list of links to additional resources and materials for lecture on geologic hazards and plate tectonics.

Johnson, Rurik

2009-11-12

245

Freshwater peat on the continental shelf  

USGS Publications Warehouse

Freshwater peats from the continental shelf off northeastern United States contain the same general pollen sequence as peats from ponds that are above sea level and that are of comparable radiocarbon ages. These peats indicate that during glacial times of low sea level terrestrial vegetation covered the region that is now the continental shelf in an unbroken extension from the adjacent land areas to the north and west.

Emery, K. O.; Wigley, R. L.; Bartlett, A. S.; Rubin, M.; Barghoorn, E. S.

1967-01-01

246

US Continental Interior Precambrian-Paleozoic  

E-print Network

US Continental Interior Precambrian-Paleozoic #12;© EarthStructure (2nd ed) 2712/5/2010 North America - Time and Terrane #12;© EarthStructure (2nd ed) 2812/5/2010 Geologic Time Scale (GSA, 2009) GSA-DNAG #12;© EarthStructure (2nd ed) 2912/5/2010 US Continental Interior Great Plains (Cr/T) Black Hills (Pc

247

Mg\\/Ca of Continental Ostracode Shells  

Microsoft Academic Search

Marine ionic chemistry is thought to remain constant. This, together with the belief that marine calcifiers partition Mg\\/Ca in a systematic manner as functions of temperature (and Mg\\/Ca) of water forms the basis of the Mg\\/Ca thermometer. In continental settings both of these assumptions are usually not true. Continental waters contain a wide variety of solutes in absolute and relative

E. Ito; R. M. Forester; J. Marco-Barba; F. Mezquita

2007-01-01

248

A plate tectonic model for the Paleozoic and Mesozoic constrained by dynamic plate boundaries and restored synthetic oceanic isochrons  

NASA Astrophysics Data System (ADS)

We developed a plate tectonic model for the Paleozoic and Mesozoic (Ordovician to Cretaceous) integrating dynamic plate boundaries, plate buoyancy, ocean spreading rates and major tectonic and magmatic events. Plates were constructed through time by adding/removing oceanic material, symbolized by synthetic isochrons, to major continents and terranes. Driving forces like slab pull and slab buoyancy were used to constrain the evolution of paleo-oceanic domains. This approach offers good control of sea-floor spreading and plate kinematics. This new method represents a distinct departure from classical continental drift reconstructions, which are not constrained, due to the lack of plate boundaries. This model allows a more comprehensive analysis of the development of the Tethyan realm in space and time. In particular, the relationship between the Variscan and the Cimmerian cycles in the Mediterranean-Alpine realm is clearly illustrated by numerous maps. For the Alpine cycle, the relationship between the Alpides senso stricto and the Tethysides is also explicable in terms of plate tectonic development of the Alpine Tethys-Atlantic domain versus the NeoTethys domain.

Stampfli, G. M.; Borel, G. D.

2002-02-01

249

Visualizing Earthquakes at Convergent Plate Margins  

NSDL National Science Digital Library

This screenshot shows the Fiji subduction zone, one of the featured convergent margins in this visualization. The visualization shows how earthquakes at this margin occur at depth, and define the slope of the subducting plate. This visualization also includes other examples of subduction zones and continental convergent margins (Himalayas). Click the image to enlarge or view the MP4 movie (MP4 Video 30.3MB Dec20 11). The purpose of this activity is to introduce students to the distribution and characteristics of earthquakes associated with convergent plate boundaries. Students will learn about how the magnitude and distribution of earthquakes at convergent boundaries are related to processes that occur at these boundaries and to the geometry and position of the two converging plates. Because the depth of earthquakes can be difficult for students to visualize in 2D representations, this activity allows students to visualize the 3D distribution of earthquakes within Earth's surface, which is essential for understanding how different types of earthquakes occur in different tectonic settings. Locations featured in the visualization include the Chile-Peru Subduction Zone, the Aleutian Islands, the Fiji Subeuction Zone, and the Himalayas. Talking points and questions are included to use this visualization as part of an interactive lecture. In addition to playing back the visualization, instructors can also download the visualization software and data set and explore it themselves.

Harwood, Cara

250

Visualizing Earthquakes at Divergent Plate Margins  

NSDL National Science Digital Library

This screenshot from the visualization shows both continental rift zones, and ocean spreading centers, both types of divergent plate boundaries. The visualization shows how earthquakes at all types of divergent margins are shallow and have a low-magnitude. Click the image to enlarge or view the MP4 movie (MP4 Video 79.3MB Aug22 11).The purpose of this activity is to introduce students to the distribution and characteristics of earthquakes associated with divergent plate boundaries. Students will learn about how the magnitude and distribution of earthquakes at divergent boundaries are related to processes that occur at these boundaries and to the geometry and position of the two diverging plates. Because the depth of earthquakes can be difficult for students to visualize in 2D representations, this activity allows students to visualize the 3D distribution of earthquakes within Earth's surface, which is essential for understanding how different types of earthquakes occur in different tectonic settings. Locations featured in the visualization include the Mid-Atlantic Ridge, the East Pacific Rise, and the East African Rift Zone. Talking points and questions are included to facilitate using this visualization as part of an interactive lecture. In addition to playing back the visualization, instructors can also download the visualization software and data set and explore it themselves.

Harwood, Cara

251

Catastrophic plate tectonics: A global Flood model of earth history  

E-print Network

In 1859 Antonio Snider proposed that rapid, horizontal divergence of crustal plates occurred during Noah’s Flood. Modern plate tectonics theory is now conflated with assumptions of uniformity of rate and ideas of continental “drift. ” Catastrophic plate tectonics theories, such as Snider proposed more than a century ago, appear capable of explaining a wide variety of data—including biblical and geologic data which the slow tectonics theories are incapable of explaining. We would like to propose a catastrophic plate tectonics theory as a framework for Earth history. Geophysically, we begin with a pre-Flood earth differentiated into core, mantle, and crust, with the crust horizontally differentiated into sialic craton and mafic ocean floor. The Flood was initiated as slabs of oceanic floor broke loose and subducted along thousands of kilometers of pre-Flood continental margins. Deformation of the mantle by these slabs raised the temperature and lowered the viscosity of the mantle in the vicinity of the slabs. A resulting thermal runaway of the slabs through the mantle led to meters-per-second mantle convection. Cool oceanic crust which descended to the core/mantle boundary induced rapid reversals of the earth’s magnetic field. Large plumes originating near the core/mantle boundary expressed themselves at the surface as fissure eruptions and flood basalts. Flow

Steven A. Austin; John R. Baumgardner; D. Russell Humphreys; Andrew A. Snelling; Larry Vardiman Phd; Kurt P. Wise

1994-01-01

252

Time-integrated Rb/Sr as a proxy for the composition of the new continental crust through time  

NASA Astrophysics Data System (ADS)

Recent models on continental growth suggest that 65-70% of the present volume of the continental crust was present by 3 Ga, and that the rates of continental growth were significantly higher before 3 Ga than subsequently. This change has been tentatively linked to the onset of subduction-driven plate tectonics and discrete subduction zones. If correct this represents a fundamental change in the evolution of the Earth, with implications for the nature of the magmas generated, the efficiency with which crustal material is returned back into the mantle and the cooling history of the Earth. Geochemical constraints indicate that about 80% of the crust still preserved today was formed in subduction settings, with the rest being mostly related to intraplate magmatism (i.e. oceanic island and continental flood magmas). New continental crust that is currently formed and preserved along destructive plate margins, such as the Andes, has an intermediate/felsic-dominated composition that is similar to the composition of the bulk continental crust. In contrast crust formed in intraplate settings has a more mafic composition. Because of the poor preservation of rocks and minerals after billions of years of crustal evolution, a major uncertainty remains about the composition of new, juvenile continental crust in the Hadean and the Archaean, and hence the conditions and the tectonic setting(s) in which it was generated. One way forward is to evaluate the composition of new continental crust from the time-integrated parent/daughter ratios of isotope systems in magmatic rocks subsequently derived from that new crust. Because of the highly incompatible character of the Rb-Sr system, crustal differentiation processes produce a large range of highly fractionated Rb/Sr ratios. As a consequence mafic crust typically has Rb/Sr at least five times grater than intermediate/felsic bulk crust. We calculated time-integrated Rb/Sr in crustal material with pre- and post-3 Ga Nd model ages. Preliminary data indicate that time-integrated Rb/Sr were, on average, much lower in the Hadean/Mesoarchaean than subsequently. This suggests that new continental crust was principally mafic over the first 1.5 Ga of Earth evolution, that a large volume of pre-3 Ga crust may have been associated with intraplate magmatism, and that ~3 Ga may indeed mark the onset of plate tectonics on Earth.

Dhuime, Bruno; Hawkesworth, Chris; Cawood, Peter

2013-04-01

253

Lack of proportionality. Seven specifications of public interest that override post-approval commercial interests on limited access to clinical data.  

PubMed

For the protection of commercial interests, licensing bodies such as the EMA and health technology assessment institutions such as NICE restrict full access to unpublished evidence. Their respective policies on data transparency, however, lack a systematic account of (1) what kinds of commercial interests remain relevant after market approval has been granted, (2) what the specific types of public interest are that may override these commercial interests post approval, and, most importantly, (3) what criteria guide the trade-off between public interest and legitimate measures for the protection of commercial interest. Comparing potential commercial interests with seven specifications of relevant public interest reveals the lack of proportionality inherent in the current practices of EMA and NICE. PMID:22747684

Strech, Daniel; Littmann, Jasper

2012-01-01

254

Intro to Plate Tectonic Theory  

NSDL National Science Digital Library

This website from PBS provides information about the plate tectonics, the theory that the Earth's outer layer is made up of plates, which have moved throughout time. The four types of plate boundaries are described and illustrated with animations. The first page of plate tectonics also provides a plate tectonics activity and information about related people and discoveries.

2008-05-28

255

Plate Tectonics Prof. Thomas Herring  

E-print Network

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

Herring, Thomas

256

PLATE TECTONICS USING GIS Understanding plate tectonics using real  

E-print Network

PLATE TECTONICS USING GIS Understanding plate tectonics using real global data sets pertaining OF THE UPSTATE, SC An afternoon field trip to observe the evidences for plate tectonic history, and to witness

257

Unroofing history of Late Paleozoic magmatic arcs within the “Turan Plate” (Tuarkyr, Turkmenistan)  

Microsoft Academic Search

Stratigraphic, sedimentologic and petrographic data collected on the Kizilkaya sedimentary succession (Western Turkmenistan) demonstrate that the “Turan Plate” consists in fact of an amalgamation of Late Paleozoic to Triassic continental microblocks separated by ocean sutures. In the Kizilkaya area, an ophiolitic sequence including pyroxenite, gabbro, pillow basalt and chert, interpreted as the oceanic crust of a back-arc or intra-arc basin,

E. Garzanti; M Gaetani

2002-01-01

258

Geometry and seismic properties of the subducting Cocos plate in central Mexico  

Microsoft Academic Search

The geometry and properties of the interface of the Cocos plate beneath central Mexico are determined from the receiver functions (RFs) utilizing data from the Meso America Subduction Experiment (MASE). The RF image shows that the subducting oceanic crust is shallowly dipping to the north at 15° for 80 km from Acapulco and then horizontally underplates the continental crust for

Y. Kim; R. W. Clayton; J. M. Jackson

2010-01-01

259

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

260

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

E-print Network

Author's personal copy Plate tectonic reconstructions with continuously closing plates$ Michael are downwellings controlled by the history of subduction, that these mantle down- wellings push hot mantle

Bower, Dan J.

261

Gondwana breakup and plate kinematics: Business as usual  

NASA Astrophysics Data System (ADS)

A tectonic model of the Weddell Sea is built by composing a simple circuit with optimized rotations describing the growth of the South Atlantic and SW Indian oceans. The model independently and accurately reproduces the consensus elements of the Weddell Sea's spreading record and continental margins, and offers solutions to remaining controversies there. At their present resolutions, plate kinematic data from the South Atlantic and SW Indian oceans and Weddell Sea rule against the proposed, but controversial, independent movements of small plates during Gondwana breakup that have been attributed to the presence or impact of a mantle plume. Hence, although supercontinent breakup here was accompanied by extraordinary excess volcanism, there is no indication from plate kinematics that the causes of that volcanism provided a unique driving mechanism for it.

Eagles, Graeme; Vaughan, Alan P. M.

2009-05-01

262

Crustal and upper mantle structure of stable continental regions in North America and northern Europe  

USGS Publications Warehouse

From an analysis of many seismic profiles across the stable continental regions of North America and northern Europe, the crustal and upper mantle velocity structure is determined. Analysis procedures include ray theory calculations and synthetic seismograms computed using reflectivity techniques. The P wave velocity structure beneath the Canadian Shield is virtually identical to that beneath the Baltic Shield to a depth of at least 800 km. Two major layers with a total thickness of about 42 km characterize the crust of these shield regions. Features of the upper mantle of these region include velocity discontinuities at depths of about 74 km, 330 km, 430 km and 700 km. A 13 km thick P wave low velocity channel beginning at a depth of about 94 km is also present. A number of problems associated with record section interpretation are identified and a generalized approach to seismic profile analysis using many record sections is described. The S wave velocity structure beneath the Canadian Shield is derived from constrained surface wave data. The thickness of the lithosphere beneath the Canadian and Baltic Shields is determined to be 95-100 km. The continental plate thickness may be the same as the lithospheric thickness, although available data do not exclude the possibility of the continental plate being thicker than the lithosphere. ?? 1987 Birkha??user Verlag.

Masse, R.P.

1987-01-01

263

Origin of Indian Ocean Seamount Province by shallow recycling of continental lithosphere  

NASA Astrophysics Data System (ADS)

The origin of the Christmas Island Seamount Province in the northeast Indian Ocean is enigmatic. The seamounts do not form the narrow, linear and continuous trail of volcanoes that would be expected if they had formed above a mantle plume. Volcanism above a fracture in the lithosphere is also unlikely, because the fractures trend orthogonally with respect to the east-west trend of the Christmas Island chain. Here we combine 40Ar/39Ar age, Sr, Nd, Hf and high-precision Pb isotope analyses of volcanic rocks from the province with plate tectonic reconstructions. We find that the seamounts are 47-136 million years old, decrease in age from east to west and are consistently 0-25 million years younger than the underlying oceanic crust, consistent with formation near a mid-ocean ridge. The seamounts also exhibit an enriched geochemical signal, indicating that recycled continental lithosphere was present in their source. Plate tectonic reconstructions show that the seamount province formed at the position where West Burma began separating from Australia and India, forming a new mid-ocean ridge. We propose that the seamounts formed through shallow recycling of delaminated continental lithosphere entrained in mantle that was passively upwelling beneath the mid-ocean ridge. We conclude that shallow recycling of continental lithosphere at mid-ocean ridges could be an important mechanism for the formation of seamount provinces in young ocean basins.

Hoernle, K.; Hauff, F.; Werner, R.; van den Bogaard, P.; Gibbons, A. D.; Conrad, S.; Müller, R. D.

2011-12-01

264

Plate Tectonics Jigsaw  

NSDL National Science Digital Library

This activity is a slight variation on an original activity, Discovering Plate Boundaries, developed by Dale Sawyer at Rice University. I made different maps, including more detail in all of the datasets, and used a different map projection, but otherwise the general progression of the activity is the same. More information about jigsaw activities in general can be found in the Jigsaws module. The activity occurs in several sections, which can be completed in one or multiple classes. In the first section, students are divided into "specialist" groups, and each group is given a global map with a single dataset: global seismicity, volcanoes, topography, age of the seafloor, and free-air gravity. Each student is also given a map of plate boundaries. Their task in the specialist group is to become familiar with their dataset and develop categories of plate boundaries based only on their dataset. Each group then presents their results to the class. In the second section, students reorganize into groups with 1-2 of each type of specialist per group. Each new group is given a plate, and they combine their different datasets on that one plate and look for patterns. Again, each plate group presents to the class. The common patterns and connections between the different datasets quickly become apparent, and the final section of the activity involves a short lecture from the instructor about types of plate boundaries and why the common features are generated at those plate boundaries. A follow-up section or class involves using a problem-solving approach to explain the areas that don't "fit" into the typical boundary types - intra-plate volcanism, earthquakes in the Eastern California Shear Zone, etc.

Egger, Anne

265

The marginal stability of continental margins  

NASA Astrophysics Data System (ADS)

Continental lithosphere is far thicker than its oceanic counterpart. The boundary between continent and ocean marks a transition in lithospheric thermal and chemical properties. This change in lithosphere structure can potentially nucleate downward travelling Rayleigh-Taylor instabilities that have the potential to generate melt, influence margin topography and sedimentary basin development. At the same time there exists a horizontal pressure gradient at this boundary where the continent may spread laterally. This lateral extension if slow may be responsible for large scale continental tilting and the initiation of intra-cratonic basin formation. It may also lead to the eventual initiation of subduction and the transition from a passive to active margin. The question is, does continental lithosphere spread laterally providing prolonged post-rift stretching, or is it destabilised downwards producing dynamic topography that may be transient, or both? We will address this key question by combining numerical and laboratory fluid mechanic experiments. The nature of continental lithosphere destabilisation is a function of its rheology, buoyancy and temperature. Early results indicate that for both Newtonian and non-Newtonian rheologies the style of destabilisation of continental lithosphere is primarily dependent on its buoyancy. For more buoyant continents there is a greater tendency for horizontal extension, while less buoyant lithosphere destabilises through vertical drips. The implication of these results is that margins between cratonic and oceanic lithosphere may tend to extend, producing very broad ramp-like subsidence down to the ocean, as observed in the North American continent. In contrast, the younger continental platform may tend to contain sag like sedimentary basins from a dynamic response to the vertical instabilities, as typified by the basin and swell nature of the African margins. It is also possible that these two modes may operate at different times during the secular evolution of a piece of continental lithosphere.

Armitage, J. J.; Fourel, L.; Allen, P. A.; Jaupart, C. P.

2011-12-01

266

Plate Tectonics at Work  

NSDL National Science Digital Library

This is a brief description of the results of plate movement according to the Theory of Plate Tectonics. It explains how divergence at the mid-ocean ridges accounts for the discoveries of Harry Hess. The site also refers to the invention of the magnetometer and the discovery of the young age of the ocean floor basalt. It concludes that these are the kinds of discoveries and thinking that ultimately led to the development of the theory of plate tectonics and that in just a few decades, have greatly changed our view of and notions about our planet and the sciences that attempt to explain its existence and development.

267

Mountains and Moving Plates  

NSDL National Science Digital Library

These are the lecture notes for a class on plate tectonics and mountain building which is taught at the University of Wisconsin-Madison. The course describes the connections between the earth's tectonic plates, earthquakes, and its many mountain ranges. Topics include basic geography, the structure of the earth's interior, the relationships between the seismic cycle, volcanism, and plate movements, erosion of mountains, and mass wasting. Links are provided to additional resources, including aerial photos of geologic features, an interactive map of geology and topography of the United States, and a glossary.

268

New paradigm for the early Earth: did plate tectonics as we know it not operate until the end of the Archean?  

Microsoft Academic Search

Here, I question the apparent absence of ‘oceanic’ crust from the Archean and whether plate tectonics as we know it, involving ridges, deep oceans, subduction and continent-sized plates, operated during the Archean. The suggestion is advanced that the early seas were formed after the initiation of continental crust at >4 Ga; that this crust was globe enveloping; and that the

G. J. H. McCall

2010-01-01

269

MINING METHODS AND COSTS, CONTINENTAL URANIUM, INC., CONTINENTAL NO. 1 MINE, SAN JUAN COUNTY, UTAH  

Microsoft Academic Search

The Continental No. 1 mine is a~ the south end of the Big Indian mining ; district, San Juan Co., Utah. A 70,000-ton uranium--vanadium ore deposit was ; discovered as a result of an exploratory drilling program completed in 1954. ; Although the Continental No. 1 mine is one of the smaller mines of the Big Indian ; district, it

Dare

1957-01-01

270

Emplacement mechanisms for Continental Flood Basalts and implications for plume activity during incipient continental breakup  

Microsoft Academic Search

We use model experiments to address the dynamics of magma upwelling during incipient break up of the continental lithosphere. In particular we study the emplacement mechanisms responsible for formation of Continental Flood Basalts. The models show that the dynamics of melt upwelling and distribution and the surface topography are all sensitive to the boundary conditions and the rheological stratification. When

Genene Mulugeta; Bekele Abebe; Tesfaye Korme; Dimitrios Sokoutis

2007-01-01

271

Growth Plate Injuries  

MedlinePLUS

... knee or ankle. Prognosis is poor, since premature stunting of growth is almost inevitable. A newer classification, ... and growth. Will the Affected Limb of a Child With a Growth Plate Injury Still Grow? Most ...

272

Half Wave Plate Program  

NSDL National Science Digital Library

The Half Wave Plate program displays the effect of a half wave plate on an incident electromagnetic wave. The default electromagnetic wave is plane polarized but this polarization can be changed by specifying the components of the waveâs Jones vector using the input fields. The slider can be used to rotate the half wave plate to change its orientation. Half Wave Plate is an Open Source Physics program written for the teaching of optics. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the optics_halfwave.jar file will run the program if Java is installed. Other optics programs are also available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Optics.

Simov, Kiril; Christian, Wolfgang

2008-05-20

273

Quarter Wave Plate Program  

NSDL National Science Digital Library

The Quarter Wave Plate program displays the effect of a quarter wave plate on an incident electromagnetic wave. The default electromagnetic wave is plane polarized but this polarization can be changed by specifying the components of the waveâs Jones vector using the input fields. The slider can be used to rotate the quarter wave plate to change its orientation. Quarter Wave Plate is an Open Source Physics program written for the teaching of optics. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the optics_quarterwave.jar file will run the program if Java is installed. Other optics programs are also available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Optics.

Simov, Kiril; Christian, Wolfgang

2008-05-20

274

How Plates Move  

NSDL National Science Digital Library

This information on the two major types of plate interaction and the resulting features discusses the Mid Atlantic Ridge and the mid-ocean ridges in connection with divergence and ocean trenches and connects the Pacific Ring of Fire to the concept of subduction. Volcanic activity as a result of subduction is also covered. The site also features links to goals, objectives, and materials for a hands-on lesson on how plates move.

275

Positive battery plate  

NASA Technical Reports Server (NTRS)

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

Rowlette, John R. (Inventor)

1985-01-01

276

Episodic vs. Continuous Accretion in the Franciscan Accretionary Prism and Direct Plate Motion Controls vs. More Local Tectonic Controls on Prism Evolution  

NASA Astrophysics Data System (ADS)

Subduction at the Franciscan trench began ?170-165 Ma and continues today off Oregon-Washington. Plate motion reconstructions, high-P metamorphic rocks, and the arc magmatic record suggest that convergence and thus subduction were continuous throughout this period, although data for 170 to 120 Ma are less definitive. About 25% of modern subduction zones are actively building an accretionary prism, whereas 75% are nonaccretionary, in which subduction erosion is gradually removing the prism and/or forearc basement. These contrasting behaviors in modern subduction zones suggest that the Franciscan probably fluctuated between accretionary and nonaccretionary modes at various times and places during its 170 million year lifespan. Accumulating geochronologic data are beginning to clarify certain accretionary vs. nonaccretionary intervals. (1) The oldest Franciscan rocks are high-P mafic blocks probably metamorphosed in a subophiolitic sole during initiation of subduction. They yield garnet Lu-Hf and hornblende Ar/Ar ages from ?169 to 147 Ma. Their combined volume is extremely small and much of the Franciscan was probably in an essentially nonaccretionary mode during this period. (2) The South Fork Mountain Schist forms the structural top of the preserved wedge in northern California and thus was apparently the first genuinely large sedimentary body to accrete. This occurred at ?123 Ma (Ar/Ar ages), suggesting major accretion was delayed a full ?45 million years after the initiation of subduction. The underlying Valentine Spring Fm. accreted soon thereafter. This shift into an accretionary mode was nearly synchronous with the end of the Early Cretaceous magmatic lull and the beginning of the prolonged Cretaceous intensification of magmatism in the Sierra Nevada arc. (3) The Yolla Bolly terrane has generally been assigned a latest Jurassic to earliest Cretaceous age. Detrital zircon data confirm that some latest Jurassic sandstones are present, but they may be blocks in olistotromes and the bulk of the terrane may be mid-Cretaceous trench sediments. (4) New data from the Central mélange belt are pending. (5) Detrital zircon ages suggest much of the voluminous Coastal belt was deposited in a short, rapid surge in the Middle Eocene, coincident with major extension, core complex development, volcanism, and erosion in sediment source areas in Idaho-Montana. Rapid Tyee Fm deposition in coastal Oregon occurred at virtually the same time from the same sources. (6) Exposed post-Eocene Franciscan rocks are rare. It is tempting to ascribe subduction zone tectonic events directly to changes in relative motions between the subducting and overriding lithospheric plates. However, in modern subduction zones, varying sediment supply to the trench appears to be a more important control on accretionary prism evolution and this seems to be the case in the Franciscan as well. Franciscan accretion was apparently influenced primarily by complex continental interior tectonics controlling sediment supply from the North American Cordillera (which may in part reflect plate motion changes), rather than directly by changes in the motions of tectonic plates.

Dumitru, T. A.; Ernst, W. G.; Wakabayashi, J.

2011-12-01

277

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

278

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

PubMed

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

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

2012-03-16

279

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

SciTech Connect

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

Yangshen, S.; Huafu, L.; Dong, J. [Nanjing Univ. (China)] [and others

1994-11-01

280

Musical Plates: A Study of Plate Tectonics  

NSDL National Science Digital Library

In this project, students use Real-Time earthquake and volcano data from the Internet to explore the relationship between earthquakes, plate tectonics, and volcanoes. There is a teachers guide that explains how to use real time data, and in the same section, there is a section for curriculum standards, Supplement and enrichment activities, and assessment suggestions. Included on this webpage are four core activities, and three enrichment activities, including an activity where the student writes a letter to the president. There is also a link to reference materials that might also interest you and your students.

2007-01-01

281

Evolution of the oceanic-continental subduction style since the Precambrian  

NASA Astrophysics Data System (ADS)

Plate tectonics is a self-organizing global system driven by the negative buoyancy of the thermal boundary layer resulting in subduction. Although the signature of plate tectonics is recognized with some confidence in the Phanerozoic geological record on continents, evidence for plate tectonics is less certain further back in time. To improve our understanding of plate tectonics on the Earth during the Precambrian, we have to combine knowledge derived from the geological record with results from realistic numerical modeling. In a series of experiments using a 2D petrological-thermomechanical numerical model of oceanic-continental subduction we have systematically investigated the dependence of tectono-metamorphic and magmatic regimes at an active continental margin on upper-mantle temperature, crustal radiogenic heat production, degree of lithospheric weakening as well as other physical parameters. The model includes spontaneous slab bending, dehydration of subducted crust, aqueous fluid transport, mantle wedge melting, and melt extraction from the mantle resulting in crustal growth. We have identified a first-order transition from a "no-subduction" tectonic regime through a "pre-subduction" tectonic regime to the modern style of subduction. The first transition is gradual and occurs at upper-mantle temperatures between 250-200 K above present-day values, whereas the second transition is more abrupt and occurs at 175-160 K. The link between geological observations and model results suggests that the transition to the modern plate tectonics regime might have occurred during the Mesoarchean-Neoarchean time (ca. 3.2-2.5 Ga). In the case of a "pre-subduction" tectonic regime (upper-mantle temperature 175-250 K above present) the plates are weakened by intense percolation of melts derived from the underlying hot melt-bearing sub-lithospheric mantle. In such cases, convergence does not produce self-sustaining one-sided subduction, but rather results in shallow underthrusting of the oceanic plate under the continental plate. A further increase in the upper-mantle temperature (> 250 K above present) induces a transition to a "no-subduction" regime where horizontal movements of small deformable plate fragments are accommodated by internal strain and even under imposed convergence shallow underthrusts do not form. To better understand the underlying physics of these models we performed an additional series of experiments using similar 2D petrological-thermomechanical numerical model but without hydration, melting and extraction procedures. In these models, we have obtained a similarly abrupt transition from the modern style of subduction to the "no-subduction" regime at the upper-mantle temperature 160-180 K above the present-day values. This temperature is approximately the same as determined in the first set of experiments. The "no-subduction" regime is characterized by ‘dripping-off' of the plate tips, most likely because of the small effective viscosity constrast between subducting slab and surrounding mantle. Indeed we do not observe a transitional "pre-subduction" tectonic regime with underthrusting of the oceanic plate in these sets of models. This implies critical role of rheological weakening by sublithospheric melts in defining how transition between ancient "no-subduction" stage and modern plate tectonic regime occurred in the Earth's history.

Sizova, Elena; Gerya, Taras; Kaus, Boris; Brown, Michael; Perchuk, Leonid

2010-05-01

282

Caribbean plate interactions  

SciTech Connect

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

Ball, M. (Geological Survey, Denver, CO (United States))

1993-02-01

283

Active NE-SW Compressional Strain Within the Arabian Plate  

NASA Astrophysics Data System (ADS)

Motion of the Arabian plate with respect to Eurasia has been remarkably steady over more than 25 Myr as revealed by comparison of geodetic and plate tectonic reconstructions (e.g., McQuarrie et al., 2003, GRL; ArRajehi et al., 2010, Tectonics). While internal plate deformation is small in comparison to the rate of Arabia-Eurasia convergence, the improved resolution of GPS observations indicate ~ NE-SW compressional strain that appears to affect much of the plate south of latitude ~ 30°N. Seven ~ NE-SW oriented inter-station baselines all indicated shortening at rates in the range of 0.5-2 mm/yr, for the most part with 1-sigma velocity uncertainties < 0.4 mm/yr. Plate-scale strain rates exceed 2×10-9/yr. The spatial distribution of strain can not be resolved from the sparse available data, but strain appears to extend at least to Riyadh, KSA, ~ 600 km west of the Zagros Fold and Thrust Belt that forms the eastern, collisional boundary of the Arabian plate with Eurasia (Iran). Geodetic velocities in the plate tectonic reference frame for Arabia, derived from magnetic anomalies in the Red Sea (Chu and Gordon, 1998, GJI), show no significant E-W motion for GPS stations located along the Red Sea coast (i.e., geodetic and plate tectonic spreading rates across the Red Sea agree within their resolution), in contrast to sites in the plate interior and along the east side of the plate that indicate east-directed motions. In addition, NE-SW contraction is roughly normal to ~ N-S striking major structural folds in the sedimentary rocks within the Arabian Platform. These relationships suggest that geodetically observed contraction has characterized the plate for at least the past ~ 3 Myr. Broad-scale contraction of the Arabian plate seems intuitively reasonable given that the east and north sides of the plate are dominated by active continental collision (Zagros, E Turkey/Caucasus) while the west and south sides are bordered by mid-ocean ridge spreading (Red Sea and Gulf of Aden). While the dynamic processes responsible for the observed strain remain speculative, we are investigating models involving long-range effects of the Arabia-Eurasia collision, ridge-push along the Red Sea and Gulf of Aden, and gravitational spreading of the higher elevation Arabian Shield towards the lower elevation platform.

Floyd, M. A.; ArRajehi, A.; King, R. W.; McClusky, S.; Reilinger, R. E.; Douad, M.; Sholan, J.; Bou-Rabee, F.

2012-12-01

284

An Introduction to Plate Tectonics  

NSDL National Science Digital Library

This page is a brief introduction to plate tectonics. It starts with a discussion of the evolution of the theory of plate tectonics and the arguments supporting it. It then discusses the processes associated with tectonics and the types of plate boundaries: divergent, convergent and transform boundaries. It concludes with a discussion of the current hypotheses of what causes plates to move.

285

Farallon Plate subduction dynamics and the Laramide orogeny: Numerical models of flat subduction  

NASA Astrophysics Data System (ADS)

The Laramide orogeny (80-50 Ma) resulted in thick-skinned deformation of the western United States, more than 700 km inboard of the plate boundary where the Farallon Plate was subducting below North America. Most studies conclude that this event was the result of low-angle or flat subduction of the Farallon plate, whereby horizontal compressive stress from the shallow slab produced inboard crustal compression and shortening. However, it is still not clear what factors caused the Farallon plate to shallow prior to Laramide time or how stress was transferred from the flat slab to the continental interior. Three hypotheses have been proposed for triggering flat subduction: (1) an increase in the westward velocity of the North American plate; (2) subduction of an buoyant oceanic plateau with abnormally thick crust and possibly a low density harzburgite mantle lithosphere layer; and (3) slab suction produced by subduction-induced mantle wedge flow and enhanced by the presence of thick Colorado Plateau lithosphere in the backarc. In this study, we use numerical models to study the development of low-angle subduction below a continental plate with a structure similar to that of the western US. The two-dimensional, plain strain models use the SOPALE code, in which Arbitrary Lagrangian-Eulerian finite element techniques are used to compute the coupled thermal-mechanical evolution of the lithosphere-upper mantle system. We first assess what factors are needed to dynamically develop low-angle subduction. We find that the main control is the continental velocity, with enhanced slab shallowing as the continental velocity increases. In order to create a section of horizontal (i.e., flat) subduction, a further requirement is the presence of an oceanic plateau with a low-density harzburgite layer. The slab suction force seems to be less capable of creating a flat slab than the other two factors. This may be due to the low viscosity in the mantle wedge in our models (10^19~10^20Pa s), which cannot produce a sufficiently large hydrodynamic force to flatten the oceanic plate. Future work will examine variations in the strength of both the continental plate and the interface between the continent and low-angle oceanic plate, in order to explore the relationship between flat subduction and Rocky Mountain foreland deformation during Laramide time.

Liu, S.; Currie, C. A.

2013-12-01

286

Mapping the descent of Indian and Eurasian plates beneath the Tibetan Plateau from gravity anomalies  

NASA Astrophysics Data System (ADS)

The collision of India with Asia has produced a complicated continental-continental plate boundary involving folding and faulting of variable trends and styles within and along the margins of the Tibetan Plateau. Numerous lines of evidence, including the development of two scales of folding in Tibet, suggest that the lowermost crust is behaving in a ductile fashion. This weak lower crust might then decouple the fundamental plate tectonic motions in the uppermost mantle from the complex pattern of surface faulting. In this study, we use Bouguer gravity anomalies to map out the geometry of Indian and Eurasian plate interactions in the mantle beneath the plateau based on both the inferred geometry of the Moho and lateral variations in lithospheric strength determined from mechanical modeling. In our preferred model, the lithosphere beneath Tibet consists of two distinct units: (1) the underthrust (to the north) Indian plate, which sutures with the Eurasian plate in the upper mantle below the Yarlung-Zangpo Suture or the Gangdese igneous belt, 200-400 km north of the Main Boundary Thrust, and (2) the underthrust (to the south) Eurasian plate. A subducting slab of Indian upper mantle extends about 200 km into the asthenosphere north from the mantle suture and exerts a bending moment of about 3.5 × 1017 N on the Indian plate. Thus the mantle lithosphere appears to be behaving in the simple fashion of converging oceanic plates, while the more buoyant continental crust deforms under high gravitational potential in a complex pattern controlled by its lateral and vertical strength heterogeneity.

Jin, Yu; McNutt, Marcia K.; Zhu, Yong-Sheng

1996-05-01

287

India Plate Motion, Intraplate deformation and Plate Boundary Processes (Invited)  

NASA Astrophysics Data System (ADS)

We use GPS-measured velocities to geodetically constrain India plate motion, intraplate strain, and examine plate boundary deformation and plate interactions around the India plate. Our solution includes 15 GPS velocities from continuously recording stations from within the stable India plate interior that are used to estimate angular velocity of the India plate with respect to its neighbors. We test a two-plate India system divided along the topographically prominent Narmada Son Lineament and find this scenario to be significant only to 89%. Dense station coverage along the Himalayan range front allows us to rigorously test boundary parameterizations and develop a preferred plate boundary model. In our preferred model the Himalayan Range Front accumulates ~50% of the India-Eurasia convergence with as much as 18 mm/yr of slip accumulation along some segments. We compare earthquake slip vector orientations with predicted divergence directions from our preferred model along the India-Somalia plate boundary. We see good agreement between predicted plate directions from our preferred model and the seismological data. Deviations between our model and the slip vectors highlight areas of diffuse oceanic deformation along the plate boundary. We estimate convergence vectors for the relative plate pairs along the Sumatra subduction zone. We test for the transition between Australian plate convergence and India plate convergence along the Sumatra subduction zone and refine the estimated motion of the Burman sliver plate.

Apel, E. V.; Burgmann, R.; Banerjee, P.

2010-12-01

288

Cadmium plating replacements  

SciTech Connect

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

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

1995-03-01

289

Cadmium plating replacements  

NASA Technical Reports Server (NTRS)

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

Nelson, Mary J.; Groshart, Earl C.

1995-01-01

290

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

291

Growth and differentiation of the continental crust  

Microsoft Academic Search

Declining radiogenic heat production since the Archaean has resulted in a secular evolution from a regime of numerous fast-moving small thin torsionally weak plates to the present regime of larger thicker torsionally stronger plates moving at an average rate of less than one-sixth of the Archaean rate; this has been accompanied by episodic changes in geological effects. By 2500 Ma

J. F. Dewey; B. F. Windley

1981-01-01

292

A double seismic zone in the subducting Juan Fernandez Ridge of the Nazca Plate (32°S), central Chile  

NASA Astrophysics Data System (ADS)

The region of central Chile offers a unique opportunity to study the links between the subducting Juan Fernandez Ridge, the flat slab, the double seismic zone (DSZ), and the absence of modern volcanism. Here we report the presence and characteristics of the first observed DSZ within the intermediate-depth Nazca slab using two temporary seismic catalogs (Ovalle 1999 and Chile Argentina Seismological Measurement Experiment). The lower plane of seismicity (LP) is located 20-25 km below the upper plane, begins at 50 km depth, and merges with the lower plane at 120 km depth, where the slab becomes horizontal. Focal mechanism analysis and stress tensor calculations indicate that the slab's state of stress is dominantly controlled by plate convergence and overriding crust thickness: Above 60-70 km depth, the slab is in horizontal compression, and below, it is in horizontal extension, parallel to plate convergence, which can be accounted for by vertical loading of the overriding lithosphere. Focal mechanisms below 60-70 km depth are strongly correlated with offshore outer rise bend faults, suggesting the reactivation of preexisting faults below this depth. The large interplane distances for all Nazca DSZs can be related to the slab's unusually cold thermal structure with respect to its age. Since LPs globally seem to mimic mantle mineral dehydration paths, we suggest that fluid migration and dehydration embrittlement provide the mechanism necessary to weaken the rock and that the stress field determines the direction of rupture.

Marot, M.; Monfret, T.; Pardo, M.; Ranalli, G.; Nolet, G.

2013-07-01

293

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

NASA Astrophysics Data System (ADS)

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

Kammer, Andreas; Piraquive, Alejandro

2014-05-01

294

Bipolar battery plate  

NASA Technical Reports Server (NTRS)

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

Rowlette, John J. (Inventor)

1987-01-01

295

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

NASA Technical Reports Server (NTRS)

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

Fitch, T. J.

1971-01-01

296

Circulation on the newfoundland continental shelf  

Microsoft Academic Search

The circulation on the Newfoundland Continental Shelf derived from a review of different data sources generally agrees with the classical description of the flow in this area given by Smith et al. (1937). Hydrological, surface and bottom drifter, satellite?tracked buoy, ships drift, current meter and sea?level observations are used to estimate mean flows, transports, and fluctuating currents and to define

Brian Petrie; Carl Anderson

1983-01-01

297

Gas hydrate on the continental margin  

Microsoft Academic Search

Because the stability of gas hydrate is constrained mainly by the temperature and pressure condition, gas hydrate on the continental margins had dissociated in response to the global climate changes during the earth's history. Marine gas hydrate hosts isotopically light carbon as gas (mostly methane) and heavy oxygen as water, dissociation of gas hydrate liberates these isotopes into the environment,

Hitoshi Tomaru

298

The nature of the lower continental crust  

SciTech Connect

This book reviews the physical and geochemical properties of the lower continental crust. Reviews cover heat flow, rheology, seismic properties, electrical resistivity, metasomatism, geochemistry and isotope characteristics. The terrains include the western USA, Canada, Labrador, West Greenland, northern Britain, Finland, West Germany, Massif Central, the Alps, the Himalayas, southern India, South Africa and Australia.

Dawson, J.B.; Carswell, D.A. (Dept. of Geology, Univ. of Sheffield, Sheffield (GB)); Hall, J. (Dept. of Geology, Univ. of Glasgoq, Glasgow (GB)); Wedepohl, K.H. (Geochemisches Institut der Universitat, Gottingen (DE))

1986-01-01

299

Continental basaltic volcanoes — Processes and problems  

Microsoft Academic Search

Monogenetic basaltic volcanoes are the most common volcanic landforms on the continents. They encompass a range of morphologies from small pyroclastic constructs to larger shields and reflect a wide range of eruptive processes. This paper reviews physical volcanological aspects of continental basaltic eruptions that are driven primarily by magmatic volatiles. Explosive eruption styles include Hawaiian and Strombolian (sensu stricto) and

G. A. Valentine; T. K. P. Gregg

2008-01-01

300

From a collage of microplates to stable continental crust - an example from Precambrian Europe  

NASA Astrophysics Data System (ADS)

Svecofennian orogen (2.0-1.7 Ga) comprises the oldest undispersed orogenic belt on Baltica and Eurasian plate. Svecofennian orogenic belt evolved from a series of short-lived terrane accretions around Baltica's Archean nucleus during the formation of the Precambrian Nuna supercontinent. Geological and geophysical datasets indicate W-SW growth of Baltica with NE-ward dipping subduction zones. The data suggest a long-lived retreating subduction system in the southwestern parts whereas in the northern and central parts the northeasterly transport of continental fragments or microplates towards the continental nucleus is also documented. The geotectonic environment resembles that of the early stages of the Alpine-Himalayan or Indonesian orogenic system, in which dispersed continental fragments, arcs and microplates have been attached to the Eurasian plate margin. Thus the Svecofennian orogeny can be viewed as proxy for the initial stages of an internal orogenic system. Svecofennian orogeny is a Paleoproterozoic analogue of an evolved orogenic system where terrane accretion is followed by lateral spreading or collapse induced by change in the plate architecture. The exposed parts are composed of granitoid intrusions as well as highly deformed supracrustal units. Supracrustal rocks have been metamorphosed in LP-HT conditions in either paleo-lower-upper crust or paleo-upper-middle crust. Large scale seismic reflection profiles (BABEL and FIRE) across Baltica image the crust as a collage of terranes suggesting that the bedrock has been formed and thickened in sequential accretions. The profiles also image three fold layering of the thickened crust (>55 km) to transect old terrane boundaries, suggesting that the over-thickened bedrock structures have been rearranged in post-collisional spreading and/or collapse processes. The middle crust displays typical large scale flow structures: herringbone and anticlinal ramps, rooted onto large scale listric surfaces also suggestive of spreading. Close to the original ocean-continent plate boundary, in the core of the Svecofennian orogen, the thickened accretionary crust carries pervasive stretching lineations at surface and seismic vp-velocity anisotropy in the crust. The direction of spreading and crustal flow seems to be diverted by shapes of the pre-existing boundaries. It is concluded that lateral spreading and midcrustal flow not only rearrange the bedrock architecture but also stabilize the young accreted continental crust in emerging internal orogenic systems. Pre-existing microplate/terrane boundaries will affect the final architecture of the orogenic belt.

Korja, Annakaisa

2013-04-01

301

Nitrided Metallic Bipolar Plates  

SciTech Connect

The objectives are: (1) Develop and optimize stainless steel alloys amenable to formation of a protective Cr-nitride surface by gas nitridation, at a sufficiently low cost to meet DOE targets and with sufficient ductility to permit manufacture by stamping. (2) Demonstrate capability of nitridation to yield high-quality stainless steel bipolar plates from thin stamped alloy foils (no significant stamped foil warping or embrittlement). (3) Demonstrate single-cell fuel cell performance of stamped and nitrided alloy foils equivalent to that of machined graphite plates of the same flow-field design ({approx}750-1,000 h, cyclic conditions, to include quantification of metal ion contamination of the membrane electrode assembly [MEA] and contact resistance increase attributable to the bipolar plates). (4) Demonstrate potential for adoption in automotive fuel cell stacks. Thin stamped metallic bipolar plates offer the potential for (1) significantly lower cost than currently-used machined graphite bipolar plates, (2) reduced weight/volume, and (3) better performance and amenability to high volume manufacture than developmental polymer/carbon fiber and graphite composite bipolar plates. However, most metals exhibit inadequate corrosion resistance in proton exchange membrane fuel cell (PEMFC) environments. This behavior leads to high electrical resistance due to the formation of surface oxides and/or contamination of the MEA by metallic ions, both of which can significantly degrade fuel cell performance. Metal nitrides offer electrical conductivities up to an order of magnitude greater than that of graphite and are highly corrosion resistant. Unfortunately, most conventional coating methods (for metal nitrides) are too expensive for PEMFC stack commercialization or tend to leave pinhole defects, which result in accelerated local corrosion and unacceptable performance.

Brady, Michael P [ORNL; Tortorelli, Peter F [ORNL; Pihl, Josh A [ORNL; Toops, Todd J [ORNL; More, Karren Leslie [ORNL; Meyer III, Harry M [ORNL; Vitek, John Michael [ORNL; Wang, Heli [National Renewable Energy Laboratory (NREL); Turner, John [National Renewable Energy Laboratory (NREL); Wilson, Mahlon [Los Alamos National Laboratory (LANL); Garzon, Fernando [Los Alamos National Laboratory (LANL); Rockward, Tommy [Los Alamos National Laboratory (LANL); Connors, Dan [GenCell Corp; Rakowski, Jim [Allegheny Ludlum; Gervasio, Don [Arizona State University

2008-01-01

302

Tectonic Plate Motion  

NSDL National Science Digital Library

The representation shows the direction of motion of the Earth's major plates as measured through NASA's satellite laser ranging (SLR) technology. A series of world maps, accompanying text, and the subsequent links explain this technology in great detail. One can click on the Index Map for Satellite Laser Ranging site Velocity and see the vectors (arrows) that indicate the direction and rate of movement of Earth's plates in much more detail. Accompanying text gives a more detailed explanation of what each sub map is showing.

303

Volcanoes, Plates, and Chains  

NSDL National Science Digital Library

In this lesson students will discover how seamounts in the Axial-Cobb-Eikelberg-Patton chain were formed. They will learn about the processes that form seamounts, describe the movement of tectonic plates in the Gulf of Alaska region and explain the types of volcanic activity that might be associated with these movements, and describe how a combination of hotspot activity and tectonic plate movement could produce the arrangement of seamounts observed in this chain. This hands-on activity uses online data resources and includes: focus questions, learning objectives, teaching time, audio/visual materials needed, background information, learning procedures, evaluations, extensions, as well as resources and student handouts.

304

Plate Tectonics and Volcanism  

NSDL National Science Digital Library

This is a lesson where learners explore plate movement and the relationship between plate tectonics and volcanoes. The lesson models scientific inquiry using the 5E instructional model and includes teacher notes, prerequisite concepts, common misconceptions, student journal and reading. This is lesson five in the Astro-Venture Geology Training Unit that was developed to increase students' awareness of and interest in astrobiology and the many career opportunities that utilize science, math and technology skills. The lessons are designed for educators to use with the Astro-Venture multimedia modules.

305

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

306

From Lithospheric Thickening and Divergent Collapse to Active Continental Rifting  

E-print Network

From Lithospheric Thickening and Divergent Collapse to Active Continental Rifting Patrice F. Rey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.5 Lithospheric geometry through time . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5, the Alboran Sea, and the Basin and Range Province suggest that continental lithosphere following gravitational

Rey, Patrice F.

307

Atmospheric residence times of continental aerosols  

SciTech Connect

The global atmospheric distributions of Rn-222 are simulated with a three-dimensional model of atmospheric transport based on the meteorology of the NASA Goddard Institute for Space Studies (GISS) general circulation model. The short-lived radioactive gas Rn-222 (half-life = 3.8d) is emitted almost exclusively from land, at a relatively uniform rate; hence it is an excellent tracer of continental influences. Lead-210 is produced by decay of Rn-222 and immediately condenses to preexisting aerosol surfaces. It provides an excellent measure of aerosol residence times in the atmosphere because its source is accurately defined by the Rn-222 distribution. Results from the three-dimensional model are compared to measurements of Rn-222 and Pb-210 atmospheric concentrations to evaluate model's long-range transport over oceanic regions and to study the deposition mechanisms of atmospheric aerosols. Model results for Rn-222 are used to examine the long-range transport of continental air over two selected oceanic regions, the subantarctic Indian Ocean and the North Pacific. It is shown that the fast transport of air from southern Africa causes substantial continental pollution at southern mid-latitudes, a region usually regarded as pristine. Air over the North Pacific is heavily impacted by continental influences year round, but the altitude at which the transport occurs varies seasonally. Observations of aerosols at island sites, which are commonly used as diagnostics of continental influences, may be misleading because they do not account for influences at high altitude and because aerosols are efficiently scavenged by deposition during transport. The study of Pb-210 focuses on defining the residence times of submicron aerosols in the troposphere. Scavenging in wet convective updrafts is found to provide the dominant sink on a global scale.

Balkanski, Y.J.

1991-01-01

308

Tracing lithosphere amalgamation through time: chemical geodynamics of sub-continental lithospheric mantle  

NASA Astrophysics Data System (ADS)

The theory of plate tectonics is a relatively young concept in the Earth Sciences and describes the surface expression of planetary cooling via magmatism and reconciles mantle convection and plate movement with orogenesis, earthquakes and volcanism. Detailed observation of current tectonic plate movement has purported a relatively clear picture of the planet's geodynamics. Modern oceanic basins are the predominant sites of thermal equilibration of Earth interior resulting from decompressional, convective melting of peridotites. This magmatism generates mid-ocean ridge mafic crust and depleted upper mantle and in this model, oceanic crust becomes associated with buoyant mantle to form oceanic lithosphere. Subduction zones return this material together with sediments into the deeper mantle and presumably aid the formation of continental crust via arc magmatism. The mechanisms of continental crust amalgamation with buoyant mantle are less clear, and distinctly more difficult to trace back in time because metamorphism and metasomatism render the processes associating convecting mantle with continental crust elusive. Paramount in assessing these mechanisms is understanding the timing of crust and mantle formation so that the onset of plate tectonics and potential changes in modi operandi with respect to convection, mantle composition and melting pressure and temperature may be traced from the early Hadean to the present day. Typically the formation age of continental crust is more easily determined from felsic samples that contain accessory and relatively robust phases such as zircon and monazite that render a geochronological approach feasible. The lack of equally robust minerals and pervasive and ubiquitous metasomatism afflicting obducted orogenic peridotites and mantle xenoliths obliterates primary mineralogical and geochemical information. Hence it has proven difficult to acquire mantle depletion ages from continental lithospheric mantle, perhaps with the exception of Re-Os isotope dating of cratonic peridotites. Empiric mineralogical and geochemical data of continental and oceanic lithospheric mantle has been examined extensively and metasomatism has been studied in great detail. I will present a numerical modelling approach generating a comprehensive catalogue of variously depleted plagioclase-, spinel- and garnet-peridotite major and trace element compositions. In addition primary Pb, Sr, Nd, Hf and Os isotope data will approximate refractory mantle generated during Earth's major episodes of depletion and continental crust formation (1.2, 1.8, 2.9, 3.8 Ga). These hypothetical compositions will be compared to natural peridotites from on- and off-cratonic xenoliths, abyssal and orogenic peridotites to identify those rare samples least altered by interaction with silicate, hydrous and carbonatitic melts. Extremely depleted mantle has the potential to harbour Pb, Sr, Nd, Hf and Os isotope compositions that would be easily recognized if silicate melts were generated from this type of pristine mantle and the record of volcanic rocks will be examined to identify potential lithospheric melts.

Wittig, Nadine

2014-05-01

309

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

SciTech Connect

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

McCrory, P.A.; Arends, R.G. (Unocal Corp., Ventura, CA (United States)); Ingle, J.C. Jr. (Stanford Univ., CA (United States)); Isaacs, C.M.; Stanley, R.G. (Geological Survey, Menlo Park, CA (United States)); Thornton, M.L.C. (Unocal Corp., Ventura, CA (United States))

1991-02-01

310

Testing Plate Reconstructions For The High Arctic Using Crustal Thickness Mapping From Gravity Inversion  

NASA Astrophysics Data System (ADS)

The plate tectonic history of the Amerasia Basin (High Arctic) and its distribution of oceanic and continental lithosphere is poorly known. A new method of gravity inversion with an embedded lithosphere thermal gravity anomaly correction has been applied to the NGA (U) Arctic Gravity Project data to predict crustal thickness and to test different plate reconstructions within the Arctic region. Two end member plate reconstruction models have been tested: in one model the Mendeleev Ridge is rifted from the Canadian margin while in the other it is rifted from the Lomonosov Ridge. The inversion of gravity data to map crustal thickness variation within oceanic and rifted continental margin lithosphere requires the incorporation of a lithosphere thermal gravity anomaly correction for both oceanic and continental lithosphere. Oceanic lithosphere and stretched continental margin lithosphere produce a large negative residual thermal gravity anomaly (up to -380 mGal), for which a correction must be made in order to determine realistic Moho depth by gravity anomaly inversion. The lithosphere thermal model used to predict the lithosphere thermal gravity anomaly correction may be conditioned using plate reconstruction models to provide the age and location of oceanic lithosphere. Two end- member plate reconstruction models have been constructed for the opening of the Amerasia Basin and used to determine lithosphere thermal gravity anomaly corrections: in one model the (presumably) continental Mendeleev Ridge is rifted from the Canadian margin in the Jurassic while in the other it is rifted off the Lomonosov Ridge (Eurasia Basin) in the Late-Cretaceous. Crustal thickness predicted by gravity anomaly inversion for the two plate reconstructions is significantly different in the Makarov Basin because of their different lithosphere thermal gravity corrections. The plate reconstruction with younger Makarov Basin ages gives a crustal thickness of the order 6-8 km thinner than the older Makarov Basin model. A crustal thickness of approximately 20 km has been obtained from seismic refraction data (Lebedeva-Ivanova et al., 2006) which would imply a Late Mid-Cretaceous age for the Makarov Basin. In this case plume-related forces may have contributed to the opening of this basin, as regional plate tectonics predict compression and not extension in the Makarov Basin area at this time.

Alvey, A. D.; Gaina, C.; Kusznir, N. J.; Torsvik, T. H.

2006-12-01

311

Glacial morphology and depositional sequences of the Antarctic continental shelf  

E-print Network

Glacial morphology and depositional sequences of the Antarctic continental shelf Uri S. ten Brink model for the unusual depositional sequences and morphology of the Antarctic continental shelf. Our model considers the regional stratal geometry and the reversed morphology of the Antarctic continental

ten Brink, Uri S.

312

BATHYMETRIC MAPS AND GEOMORPHOLOGY OF THE MIDDLE ATLANTIC CONTINENTAL SHELF  

E-print Network

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

313

CETACEAN HIGHUSE HABITATS OF THE NORTHEAST UNITED STATES CONTINENTAL SHELF  

E-print Network

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

314

Estimating denitrification in North Atlantic continental shelf sediments  

Microsoft Academic Search

A model of coupled nitrification\\/denitrification was developed for continental shelf sediments to estimate the spatial distribution of denitrification throughout shelf regions in the North Atlantic basin. Using data from a wide range of continental shelf regions, we found a linear relationship between denitrification and sediment oxygen uptake. This relationship was applied to specific continental shelf regions by combining it with

Sybil P. Seitzinger

1996-01-01

315

Plate Tectonic Movement Visualizations  

NSDL National Science Digital Library

This collection provides a wide array of visual resources and supporting material about plate tectonic movements. Visualizations include simple animations, GIS-based animated maps, paleogeographic maps and globes, and numerous illustrations and photos. This collection is not exhaustive but does represent some of the best sources for teaching. Resources can be incorporated into lectures, labs, or other activities.

2007-04-15

316

Earthquakes and Plates  

NSDL National Science Digital Library

The representation depicts global distribution of earthquakes. A world map shows the location of large earthquakes that occurred from 1975-1995. A slider at the bottom left of the map allows the user to change the map to reveal the location of major plates or to select both views layered on top of one another.

317

elementsair ceramic plate  

E-print Network

and earth to generate electrical power [7, 8]. Temperature differences of about -0.35° to 0.7°C werearth elementsair L ceramic plate Thermoelectric Module Construction for Low Temperature Gradient Power Generation Y. Meydbray, R. Singh, Ali Shakouri University of California at Santa Cruz, Electrical

318

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

NASA Astrophysics Data System (ADS)

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

Dilek, Y.

2001-12-01

319

Growth of early continental crust by partial melting of eclogite.  

PubMed

The tectonic setting in which the first continental crust formed, and the extent to which modern processes of arc magmatism at convergent plate margins were operative on the early Earth, are matters of debate. Geochemical studies have shown that felsic rocks in both Archaean high-grade metamorphic ('grey gneiss') and low-grade granite-greenstone terranes are comprised dominantly of sodium-rich granitoids of the tonalite-trondhjemite-granodiorite (TTG) suite of rocks. Here we present direct experimental evidence showing that partial melting of hydrous basalt in the eclogite facies produces granitoid liquids with major- and trace-element compositions equivalent to Archaean TTG, including the low Nb/Ta and high Zr/Sm ratios of 'average' Archaean TTG, but from a source with initially subchondritic Nb/Ta. In modern environments, basalts with low Nb/Ta form by partial melting of subduction-modified depleted mantle, notably in intraoceanic arc settings in the forearc and back-arc regimes. These observations suggest that TTG magmatism may have taken place beneath granite-greenstone complexes developing along Archaean intraoceanic island arcs by imbricate thrust-stacking and tectonic accretion of a diversity of subduction-related terranes. Partial melting accompanying dehydration of these generally basaltic source materials at the base of thickened, 'arc-like' crust would produce compositionally appropriate TTG granitoids in equilibrium with eclogite residues. PMID:14534583

Rapp, Robert P; Shimizu, Nobumichi; Norman, Marc D

2003-10-01

320

An inverted continental Moho and serpentinization of the forearc mantle.  

PubMed

Volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge, resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere. Asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back-arc region, but the forearc mantle (in the corner of the wedge) is thought to be significantly cooler. Here we explore the structure of the mantle wedge in the southern Cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers. We find very low shear-wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an 'inverted' continental Moho, which reverts to normal polarity seaward of the Cascade arc. This observation provides compelling evidence for a highly hydrated and serpentinized forearc region, consistent with thermal and petrological models of the forearc mantle wedge. This serpentinized material is thought to have low strength and may therefore control the down-dip rupture limit of great thrust earthquakes, as well as the nature of large-scale flow in the mantle wedge. PMID:12037564

Bostock, M G; Hyndman, R D; Rondenay, S; Peacock, S M

2002-05-30

321

Plates with incompatible prestrain  

E-print Network

We study the effective elastic behavior of incompatibly prestrained plates, where the prestrain is independent of thickness as well as uniform through the thickness. We model such plates as three-dimensional elastic bodies with a prescribed pointwise stress-free state characterized by a Riemannian metric $G$ with the above properties, and seek the limiting behavior as the thickness goes to zero. Our results extand the prior analysis in M. Lewicka, M. R. Pakzad ESAIM Control Optim. Calc. Var. 17 (2011), no. 4. We first establish that the $\\Gamma$-limit is a Kirchhoff type bending. Further, we show that the minimum energy configuration contains non-trivial Kirchhoff type bending -- i.e., the scaling of the three-dimensional energy is of the order of the cube of the plate thickness -- if and only if the Riemann curvatures $R^3_{112}, R^3_{221}$ and $ R_{1212}$ of $G$ do not identically vanish. We demonstrate through examples, the existence of a new regime where the three above curvatures of $G$ vanish (while the mid-plane of the plate may or may not be flat), but the limiting configuration still has energy that is of the order of F\\"oppl - von K\\'arm\\'an plates. Finally, we apply these results to a model of nematic glass, including a characterization of the condition when the metric is immersible, for $G=\\mbox{Id}_3 +\\gamma\\vec n\\otimes \\vec n$ given in terms of the inhomogeneous unit director field distribution $\\vec n\\in\\mathbb{R}^3$.

Kaushik Bhattacharya; Marta Lewicka; Mathias Schäffner

2014-01-08

322

Earth: Plates on the Move  

NSDL National Science Digital Library

In this activity, students explore how the movement of tectonic plates forms mountains, volcanoes, oceans, and earthquakes. It first describes the plates and the various types of interaction at plate boundaries. An interactive map of the world shows the relationship between plate boundaries and earthquakes, allowing the student to click on selected place to explore a volcano, mountain, hotspot or earthquake. They then zoom in the see how the plates are moving, play an animation about the plate interaction, and read a story about the event. In addition, a set of links lead to more detailed information.

323

Generation of Continental Rifts, Basins and Swells by Lithosphere Instabilities  

NASA Astrophysics Data System (ADS)

Domal uplifts, volcanism, basin formation and rifting have often struck the same continent in different areas at the same time. Their characteristics and orientations are difficult to reconcile with mantle convection or tectonic forces and suggest a driving mechanism that is intrinsic to the continent. The rifts seem to develop preferentially at high angles to the edge of the continent whereas swells and basins seem confined to the interior. Another intriguing geometrical feature is that the rifts often branch out in complicated patterns at their landward end. In Western Africa, for example, magmatic activity currently occurs in a number of uplifted areas including the peculiar Cameroon Volcanic Line that stretches away from the continental margin over about 1000 km. Magmatic and volcanic activity has been sustained along this line for 70 My with no age progression. The mantle upwelling that feeds the volcanoes is not affected by absolute plate motions and hence is attached to the continent. The Cameroon Volcanic Line extends to the Biu swell to the North and the Jos plateau to the West defining a striking Y-shaped pattern. This structure segues into several volcanic domes including the Air, the Hoggar, the Darfur, the Tibesti and the Haruj domes towards the Mediterranean coast. Another example is provided by North America, where the late Proterozoic-early Ordovician saw the formation of four major basins, the Michigan, Illinois, Williston and Hudson Bay, as well as of major rifts in southern Oklahoma and the Mississipi Valley within a short time interval. At the same time, a series of uplifts developed, such as the Ozark and Nashville domes. Motivated by these observations, we have sought an explanation in the continental lithosphere itself. We describe a new type of convective instability at the base of the lithosphere that leads to a remarkable spatial pattern at the scale of an entire continent. We carried out fluid mechanics laboratory experiments on buoyant blocks of finite size that became unstable due to cooling from above and describe the peculiar horizontal planform that developed. Dynamical behaviour depends on three dimensionless numbers, a Rayleigh number for the unstable block, a buoyancy number that scales the intrinsic density contrast to the thermal one and the aspect ratio of the block. Within the block, instability develops in two different ways in an outer annulus and in an inner region. In the outer annulus, upwellings and downwellings take the form of radial rolls spaced regularly. In the interior region, the planform adopts the more familiar form of polygonal cells. Translated to geological conditions, such instabilities should manifest themselves as linear rifts striking at a right angle to the continent-ocean boundary and an array of domal uplifts, volcanic swells and basins in the continental interior. The laboratory data lead to simple scaling laws for the dimensions and spacings of the convective structures. For the sub-continental lithospheric mantle, these dimensions and distances take values in the 500-1000 km range, close to geological examples. The large intrinsic buoyancy of Archean lithospheric roots prevents this type of instability, which explains why the widespread volcanic activity that currently affects Western Africa is confined to post-Archean domains.

Milelli, L.; Fourel, L.; Jaupart, C. P.

2012-12-01

324

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

NASA Technical Reports Server (NTRS)

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

Toksoz, M. Nafi; Reilinger, Robert E.

1990-01-01

325

Plate Puzzle Page 1 of 20 Plate Puzzle 1  

E-print Network

plotting activities. Good follow-up activities are: plate tectonics flip book, epicenter plotting using tectonics. The map is an attractive display of plate tectonic features such earthquake epicenters boundaries so that one can examine the relationship of the tectonic features to the plate boundaries. The map

Benitez-Nelson, Claudia

326

Regional magnetic anomaly constraints on continental rifting  

NASA Technical Reports Server (NTRS)

Radially polarized MAGSAT anomalies of North and South America, Europe, Africa, India, Australia and Antarctica demonstrate remarkably detailed correlation of regional magnetic lithospheric sources across rifted margins when plotted on a reconstruction of Pangea. These major magnetic features apparently preserve their integrity until a superimposed metamorphoric event alters the magnitude and pattern of the anomalies. The longevity of continental scale magnetic anomalies contrasts markedly with that of regional gravity anomalies which tend to reflect predominantly isostatic adjustments associated with neo-tectonism. First observed as a result of NASA's magnetic satellite programs, these anomalies provide new and fundamental constraints on the geologic evolution and dynamics of the continents and oceans. Accordingly, satellite magnetic observations provide a further tool for investigating continental drift to compliment other lines of evidence in paleoclimatology, paleontology, paleomagnetism, and studies of the radiometric ages and geometric fit of the continents.

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

1985-01-01

327

A budget for continental growth and denudation  

USGS Publications Warehouse

Oceanic crustal material on a global scale is re-created every 110 million years. From the data presented it is inferred that potential sialic material is formed at a rate of about 1.35 cubic kilometers per year, including hemipelagic volcanic sediments that accumulate at a rate of about 0.05 cubic kilometer per year. It is estimated that the influx of 1.65 cubic kilometers per year of terrigenous and biogenic sediment is deposited on the deep ocean, and this represents continental denudation. Because all this material is brought into a subduction zone, continental accretion rates, which could include all this material, may be as high as 3.0 cubic kilometers per year with a potential net growth for continents of 1.35 cubic kilometers per year.

Howell, D. G.; Murray, R. W.

1986-01-01

328

Landscape formation by past continental ice sheets: insights into the subglacial environment  

NASA Astrophysics Data System (ADS)

Glaciers and ice sheets are known as most powerful, climatically driven agents of large-scale sediment redistribution and landscape formation in the Earth system. During the Quaternary, repeated waxing and waning of continental ice sheets contributed to profound reshaping of the Earth surface and set the scene for the development of ecosystems in the post-glacial time. Despite the well-established impact of glaciers on the upper lithosphere the specific processes of glacial erosion, transport and deposition and the formation landforms at the ice-bed interface are contentious. In particular, the relative importance of direct ice impact versus the impact of glacial meltwater is highly controversial. Here, we focus on the southern peripheral area of the Scandinavian Ice Sheet hosting thick successions of soft, deformable sediments and examine some spectacular sediment/landform assemblages found nowadays in both terrestrial and marine settings to illustrate the nature of the subglacial processes. In order to decipher the past ice sheet behavior field, experimental and numerical approaches are combined. It is shown that the strength of the coupling between the ice and the bed that controls the response of the substratum to ice overriding and stress propagation depends primarily on the ability of the glacial system to evacuate meltwater from ice-bed interface. Strong coupling, locally enhanced by subglacial permafrost resulted in deeply rooted (100's of meters) glaciotectonic deformation reflected on the surface as ice-shoved hills whereas weak coupling promoted by water accumulating under the ice triggered the formation of deep (100's of meters) tunnel valley networks. Under the arteries of fast-flowing ice known as palaeo-ice streams, remoulding of soft sediments generated mega-scale glacial lineations and drumlins that hold the key to understanding glacier dynamics. The subglacial environment is envisaged as a four-dimensional mosaic of stable and deforming spots transient in time and space whose impact is embedded in the properties of sediment/landform systems.

Piotrowski, Jan A.

2014-05-01

329

Suggestion overrides automatic audiovisual integration.  

PubMed

Cognitive scientists routinely distinguish between controlled and automatic mental processes. Through learning, practice, and exposure, controlled processes can become automatic; however, whether automatic processes can become deautomatized - recuperated under the purview of control - remains unclear. Here we show that a suggestion derails a deeply ingrained process involving involuntary audiovisual integration. We compared the performance of highly versus less hypnotically suggestible individuals (HSIs versus LSIs) in a classic McGurk paradigm - a perceptual illusion task demonstrating the influence of visual facial movements on auditory speech percepts. Following a posthypnotic suggestion to prioritize auditory input, HSIs but not LSIs manifested fewer illusory auditory perceptions and correctly identified more auditory percepts. Our findings demonstrate that a suggestion deautomatized a ballistic audiovisual process in HSIs. In addition to guiding our knowledge regarding theories and mechanisms of automaticity, the present findings pave the road to a more scientific understanding of top-down effects and multisensory integration. PMID:24398260

Déry, Catherine; Campbell, Natasha K J; Lifshitz, Michael; Raz, Amir

2014-02-01

330

Ocean processes at the Antarctic continental slope.  

PubMed

The Antarctic continental shelves and slopes occupy relatively small areas, but, nevertheless, are important for global climate, biogeochemical cycling and ecosystem functioning. Processes of water mass transformation through sea ice formation/melting and ocean-atmosphere interaction are key to the formation of deep and bottom waters as well as determining the heat flux beneath ice shelves. Climate models, however, struggle to capture these physical processes and are unable to reproduce water mass properties of the region. Dynamics at the continental slope are key for correctly modelling climate, yet their small spatial scale presents challenges both for ocean modelling and for observational studies. Cross-slope exchange processes are also vital for the flux of nutrients such as iron from the continental shelf into the mixed layer of the Southern Ocean. An iron-cycling model embedded in an eddy-permitting ocean model reveals the importance of sedimentary iron in fertilizing parts of the Southern Ocean. Ocean gliders play a key role in improving our ability to observe and understand these small-scale processes at the continental shelf break. The Gliders: Excellent New Tools for Observing the Ocean (GENTOO) project deployed three Seagliders for up to two months in early 2012 to sample the water to the east of the Antarctic Peninsula in unprecedented temporal and spatial detail. The glider data resolve small-scale exchange processes across the shelf-break front (the Antarctic Slope Front) and the front's biogeochemical signature. GENTOO demonstrated the capability of ocean gliders to play a key role in a future multi-disciplinary Southern Ocean observing system. PMID:24891389

Heywood, Karen J; Schmidtko, Sunke; Heuzé, Céline; Kaiser, Jan; Jickells, Timothy D; Queste, Bastien Y; Stevens, David P; Wadley, Martin; Thompson, Andrew F; Fielding, Sophie; Guihen, Damien; Creed, Elizabeth; Ridley, Jeff K; Smith, Walker

2014-07-13

331

Meeting the Challenges of Continental Pollutant Pathways  

NSDL National Science Digital Library

The Ecological Monitoring and Assessment Network (discussed in the February 4, 1998 Scout Report for Science & Engineering) has released this interesting case study on mercury entitled "Meeting the Challenges of Continental Pollutant Pathways." The eight sections of the report cover human health, ecosystem science, product pathways for mercury, policy and science issues, and recommendations, in addition to introductory and reference materials. The report includes text, numerous figures, tables, and several recommended links.

332

Iceberg scouring on the Norwegian continental shelf  

SciTech Connect

This paper is a condensed version of parts of a Dr. ing. thesis to be presented during 1983. The first part of the paper deals with the regional distribution of iceberg scouring on the Norwegian continental shelf, and some general aspects related to it. The second part deals with iceberg scouring as a local phenomenon and its relation to the sea floor topography, sediment distribution, and geological and geotechnical properties of the sediments.

Lien, R.

1983-05-01

333

Workshop on the Growth of Continental Crust  

NASA Technical Reports Server (NTRS)

Constraints and observations were discussed on a fundamental unsolved problem of global scale relating to the growth of planetary crusts. All of the terrestrial planets were considered, but emphasis was placed on the Earth's continental crust. The title of each session is: (1) Extraterrestrial crustal growth and destruction; (2) Constraints for observations and measurements of terrestrial rocks; (3) Models of crustal growth and destruction; and (4) Process of crustal growth and destruction.

Ashwal, Lewis D. (editor)

1988-01-01

334

Complex Faulting in the Pacific-North America Transform Offshore Southern California And Implications on Plate Boundary Tectonics and Tsunamigenesis  

Microsoft Academic Search

Complexity in the tectonic model for Pacific-North America transform motion in the offshore southern California region is demonstrated by earthquakes near San Clemente Island and Fortymile Bank. Observed focal mechanisms show movements opposite to those predicted by the plate tectonic theory for right-slip on NW- trending transform faults and observed in other parts of the California Continental Borderland. Also, there

M. R. Legg; A. Barberopoulou

2007-01-01

335

Senonian basin inversion and rejuvenation of rifting in Africa and Arabia: synthesis and implications to plate-scale tectonics  

Microsoft Academic Search

The late Paleozoic to Tertiary stratigraphic record of much of the African plate reflects the effects of continental rifting and passive margin development. Several short-lived, but widespread and tectonically important, compressional or wrench-dominated events occurred, however, during the Permian to Recent evolution of Africa. We focus here on the best documented of these events, which occurred during the late Santonian.

René Guiraud; William Bosworth

1997-01-01

336

Conditions for lower lithosphere exhumation from continental collision: South Island, New Zealand  

NASA Astrophysics Data System (ADS)

The South Island of New Zealand provides a unique opportunity for the investigation of active deep crustal dynamics and the effects of surface processes during collision, as a fairly young and relatively well-constrained convergent plate boundary. One of the uncertainties of the orogenesis is the fate of the lower crust during the continental collision: portions of the crust are exhumed along the Alpine Fault, but the lowermost crust does not seem to follow. This work focuses on the fate of the mid- and lower-crust during the collision, investigating several of the primary controls - rheology, boundary conditions, temperature - that regulate the behaviour of the crust during an idealized continental collision event. We use forward thermo-mechanical numerical modelling of the mantle and lithosphere, with variable surface boundary conditions of erosion and deposition, to explore the deformation of the crust and mantle lithosphere via the collision; the 2D models are configured for a South Island-type system using available observational constraints. The models show several end member modes of behaviour of the lower crust from complete exhumation, to 'ponding'/ accumulation at the base of the orogen, to subduction and deep entrainment. The rheology of the lower crust is the dominant factor controlling these behaviours, although there is also modification of the dynamics depending on the rates of continental convergence, the presence of active and varying degrees of erosion, and the effects of differing ratios of deposition.

Cunje, A.; Pysklywec, R. N.

2013-12-01

337

Selective Akt Inhibitors Synergize with Tyrosine Kinase Inhibitors and Effectively Override Stroma-Associated Cytoprotection of Mutant FLT3-Positive AML Cells  

PubMed Central

Objectives Tyrosine kinase inhibitor (TKI)-treated acute myeloid leukemia (AML) patients commonly show rapid and significant peripheral blood blast cell reduction, however a marginal decrease in bone marrow blasts. This suggests a protective environment and highlights the demand for a better understanding of stromal:leukemia cell communication. As a strategy to improve clinical efficacy, we searched for novel agents capable of potentiating the stroma-diminished effects of TKI treatment of mutant FLT3-expressing cells. Methods We designed a combinatorial high throughput drug screen using well-characterized kinase inhibitor-focused libraries to identify novel kinase inhibitors capable of overriding stromal-mediated resistance to TKIs, such as PKC412 and AC220. Standard liquid culture proliferation assays, cell cycle and apoptosis analysis, and immunoblotting were carried out with cell lines or primary AML to validate putative candidates from the screen and characterize the mechanism(s) underlying observed synergy. Results and Conclusions Our study led to the observation of synergy between selective Akt inhibitors and FLT3 inhibitors against mutant FLT3-positive AML in either the absence or presence of stroma. Our findings are consistent with evidence that Akt activation is characteristic of mutant FLT3-transformed cells, as well as observed residual Akt activity following FLT3 inhibitor treatment. In conclusion, our study highlights the potential importance of Akt as a signaling factor in leukemia survival, and supports the use of the co-culture chemical screen to identify agents able to potentiate TKI anti-leukemia activity in a cytoprotective microenvironment. PMID:23437141

Zhang, Xin; Nelson, Erik; Sattler, Martin; Liu, Feiyang; Nicolais, Maria; Zhang, Jianming; Mitsiades, Constantine; Smith, Robert W.; Stone, Richard; Galinsky, Ilene; Nonami, Atsushi; Griffin, James D.; Gray, Nathanael

2013-01-01

338

Dampening prey cycle overrides the impact of climate change on predator population dynamics: a long-term demographic study on tawny owls.  

PubMed

Predicting the dynamics of animal populations with different life histories requires careful understanding of demographic responses to multifaceted aspects of global changes, such as climate and trophic interactions. Continent-scale dampening of vole population cycles, keystone herbivores in many ecosystems, has been recently documented across Europe. However, its impact on guilds of vole-eating predators remains unknown. To quantify this impact, we used a 27-year study of an avian predator (tawny owl) and its main prey (field vole) collected in Kielder Forest (UK) where vole dynamics shifted from a high- to a low-amplitude fluctuation regime in the mid-1990s. We measured the functional responses of four demographic rates to changes in prey dynamics and winter climate, characterized by wintertime North Atlantic Oscillation (wNAO). First-year and adult survival were positively affected by vole density in autumn but relatively insensitive to wNAO. The probability of breeding and number of fledglings were higher in years with high spring vole densities and negative wNAO (i.e. colder and drier winters). These functional responses were incorporated into a stochastic population model. The size of the predator population was projected under scenarios combining prey dynamics and winter climate to test whether climate buffers or alternatively magnifies the impact of changes in prey dynamics. We found the observed dampening vole cycles, characterized by low spring densities, drastically reduced the breeding probability of predators. Our results illustrate that (i) change in trophic interactions can override direct climate change effect; and (ii) the demographic resilience entailed by longevity and the occurrence of a floater stage may be insufficient to buffer hypothesized environmental changes. Ultimately, dampened prey cycles would drive our owl local population towards extinction, with winter climate regimes only altering persistence time. These results suggest that other vole-eating predators are likely to be threatened by dampening vole cycles throughout Europe. PMID:24634279

Millon, Alexandre; Petty, Steve J; Little, Brian; Gimenez, Olivier; Cornulier, Thomas; Lambin, Xavier

2014-06-01

339

European Society of Biomechanics S.M. Perren Award 2012: the external mechanical environment can override the influence of local substrate in determining stem cell fate.  

PubMed

The aim of this study was to explore how cell-matrix interactions and extrinsic mechanical signals interact to determine stem cell fate in response to transforming growth factor-?3 (TGF-?3). Bone marrow derived mesenchymal stem cells (MSCs) were seeded in agarose and fibrin hydrogels and subjected to dynamic compression in the presence of different concentrations of TGF-?3. Markers of chondrogenic, myogenic and endochondral differentiation were assessed. MSCs embedded within agarose hydrogels adopted a spherical cell morphology, while cells directly adhered to the fibrin matrix and took on a spread morphology. Free-swelling agarose constructs stained positively for chondrogenic markers, with MSCs appearing to progress towards terminal differentiation as indicated by mineral staining. MSC seeded fibrin constructs progressed along an alternative myogenic pathway in long-term free-swelling culture. Dynamic compression suppressed differentiation towards any investigated lineage in both fibrin and agarose hydrogels in the short-term. Given that fibrin clots have been shown to support a chondrogenic phenotype in vivo within mechanically loaded joint defect environments, we next explored the influence of long term (42 days) dynamic compression on MSC differentiation. Mechanical signals generated by this extrinsic loading ultimately governed MSC fate, directing MSCs along a chondrogenic pathway as opposed to the default myogenic phenotype supported within unloaded fibrin clots. In conclusion, this study demonstrates that external cues such as the mechanical environment can override the influence specific substrates, scaffolds or hydrogels have on determining mesenchymal stem cell fate. The temporal data presented in this study highlights the importance of considering how MSCs respond to extrinsic mechanical signals in the long term. PMID:22925995

Thorpe, Stephen D; Buckley, Conor T; Steward, Andrew J; Kelly, Daniel J

2012-10-11

340

Embryonic stage of plate subduction in the Huatung Basin, off eastern Taiwan  

NASA Astrophysics Data System (ADS)

The Philippine Sea Plate is convergent northwestward with respect to the Eurasian Plate. Since ca. 9 Ma, the Luzon arc (belong to the Philippine Sea Plate) has collided the margin of the Eurasian Plate and formed the current Taiwan orogen. The Taiwan orogeny is still active as demonstrated by the 1999 Chi-Chi thrusting earthquake in western Taiwan. The uplift rate of the Central Range in Taiwan could be still as high as 35 mm/yr (Liu, 1995). However, several strike-slip earthquakes trending NE-SW are distributed along a belt roughly parallel to the Taitung Canyon in the Huatung Basin, off eastern Taiwan. We have processed two multi-channel reflection seismic profiles across the Taitung Canyon and found that the whole crust was ruptured along a surface dipping northwestward. The overriding plate is slightly uplifted near the top of the rupture surface. This is also demonstrated by a relatively uplifted bathymetry. The arched bathymetry is also revealed by relatively high free-air and Bouguer gravity anomalies. The 'new' subduction zone is almost perpendicular to the northwestward convergent direction. This subduction nucleation does not follow a fracture zone or a transform fault; instead, the future trench has cut obliquely to the fracture zones. However, currently most of the earthquakes observed along this zone are either strike-slip faulting or normal faulting. Almost no thrusting earthquakes are observed along this zone. Thus, we consider this zone as a very embryonic stage of the trench where the Philippine Sea Plate will subduct.

Hsu, S.; Yeh, Y.; Lo, C.; Doo, W.; Tsai, C.; Sibuet, J.

2013-12-01

341

Mantle convection with continental drift and heat source around the mantle transition zone  

NASA Astrophysics Data System (ADS)

Geological studies have suggested that significant amount of granitic crustal materials have been lost from the surface by the delamination (~1.1 km^3/yr) [1], continental collision (~0.4-0.7 km^3/yr) [1, 2], and subduction at ocean-margin (~2.5-3 km^3/yr) [1, 2]. At ocean-margin subduction zones, most of the granitic materials subducted from the surface are expected to be conveyed through subduction channels by viscous drag to 270km depth [Ichikawa el al., in revision]. If so, then the subducted crustal materials might be expected to be trapped in the mid-mantle owing to the density difference from peridotitic materials induced by the phase transition from coesite to stishovite at 270km depth. In other words, strong heat source materials are most likely to be accumulated around the mantle transition zone, at least, near the plate subduction zones. In this study, we conducted two-dimensional numerical experiments of mantle convection with continental drift and a heat source placed around the mantle transition zone, in order to study the effect of the subducted granitic materials drifting around the mantle transition zone. The simulations deal with a time-dependent convection of fluid under the extended Boussinesq approximation in a model of a two-dimensional rectangular box of 2900km height and 11600km width, where a continent and heat source is imposed. We found that the addition of the heat source considerably reduces the time scale of continental drift. In the absence of the heat source, the resulting time scale is too long compared with that of the so-called supercontinent cycle, where the breakup is induced from a plume generated by an insulating effect of the continent. The heat source also causes massive mechanical mixing especially on the upper mantle. The result suggests that the heat source drifting around mantle transition zone can be a possible candidate inducing the supercontinent cycle in an appropriate time scale. [1] Clift, P. D., P. Vannucchi, and J. P. Morgan (2009), Crustal redistribution, crust-mantle recycling and Phanerozoic evolution of the continental crust, Earth-Science Reviews. [2] Stern, R. J., and D. W. Scholl (2010), Yin and yang of continental crust creation and destruction by plate tectonic processes, International Geology Review, 52(1), 1-31.

Ichikawa, H.; Kameyama, M.; Kawai, K.

2012-12-01

342

Imaging continental collision and subduction in the Pamir mountain range, Central Asia, by seismic attenuation tomography  

NASA Astrophysics Data System (ADS)

Subduction of continental crust is the mode of shortening in continental collision that is the least well understood. It is known to occur, as testified e.g., by now exhumed ultra-high-pressure rocks, despite the fact that continental crust is generally too buoyant to submerge into the mantle. Continental crust may, however, subduct in tow of a leading dense oceanic plate at the last stage of the plate tectonic Wilson cycle. Alternatively, if upper and lower crust detach, the latter, together with the underlying cold mantle lithosphere, may become negatively buoyant, enabling their descent. The Pamir mountains in Central Asia have been one of the few places on Earth, where on-going continental subduction has been postulated based on an active Wadati-Benioff zone. The Pamir is situated on an orographic node northwest of Tibet, between the Tarim and Tajik basins, where the Hindu Kush, Karakorum, western Kunlun Shan and Tien Shan ranges coalesce. It formed in the late Paleogene to Neogene, i.e. approximately during the second half of the India-Asia collision, north of the Western Himalayan Syntaxis, on the Asian (retro)continent. We use tomography of seismic attenuation to image the lithospheric-scale structure of the Pamir orogen. Attenuation tomography has been shown to be a powerful tool to study deep process-related structures particularly in oceanic subduction zones. Attenuation at this scale may be seen as a proxy for rheology and hence is very sensitive to e.g., homologous temperature and deformation. We use data from a two-year seismic deployment of the Tien Shan-Pamir Geodynamic Program (TIPAGE). The whole path attenuation parameter t* is determined by inversion of P-wave velocity spectra from 1790 earthquakes and then inverted for a 3D attenuation model (Qp) employing a recently published 3D velocity model. We find a prominent continuous crescent-shaped high-attenuation anomaly (HAA) that penetrates from upper crustal levels to depths of more than 100 km. At mantle depths the HAA follows the seismicity and coincides with low seismic velocities and most probably represents subducted crustal rocks. The HAA appears to be sandwiched between regions of low attenuation. To the north and west this probably represents cold Asian lithospheric mantle. To the south the low attenuation may be an indication of the (Indian?) indenter. The structures we image here are distinctively different from oceanic subduction zones, where HAAs usually occur in the mantle wedge above low attenuation oceanic slabs.

Schurr, Bernd; Haberland, Christian; Sippl, Christian; Yuan, Xiaohui; Mechie, James; Schneider, Felix; Tipage Team

2014-05-01

343

North American plate dynamics  

NASA Technical Reports Server (NTRS)

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

Richardson, Randall M.; Reding, Lynn M.

1991-01-01

344

Microchannel plate streak camera  

DOEpatents

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

Wang, C.L.

1984-09-28

345

Microchannel plate streak camera  

DOEpatents

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

Wang, Ching L. (Livermore, CA)

1989-01-01

346

Microchannel plate streak camera  

DOEpatents

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

Wang, C.L.

1989-03-21

347

Bipolar battery plate  

NASA Technical Reports Server (NTRS)

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

Rowlette, John J. (Inventor)

1985-01-01

348

Geological evolution history of petroliferous basins on continental shelf of China  

SciTech Connect

Coastlines of China are about 18,000 km (11,118 mi) in length, and their aggregate continental shelf area within 200 m (656 ft) seawater depth is more than one million km/sup 2/ (386,102 mi/sup 2/). Recent geophysical exploration work and numerous petroleum drilling records are available and give a general understanding of the geological evolution history of these petroliferous basins. There are two tectonic types of basins distributed on the continental shelf areas: the tectonic types of Bohai Gulf, South Yellow Sea, and Beibu Gulf basins are the intraplate polyphase rifting-depression basins; the East China Sea, Pearl River mouth, and Yingge Sea basin are the epicontinental rifting-depression basins. They are believed to be extensional in origin. Because of the severe convergence of Indian plate with Eurasia plate, there has been produced NNE-spreading movement of the South China Sea basin, which permits two triple junctions on its northern margins. The extension mechanism could be derived from the rising of an upper mantle plume to produce two NNE weak fracturing zones, resulting in a series of intraplate and epicontinental rifting-depression basins. The depositional models and sea-level variations of these basins are interpreted from the drilling records and seismic profiles. They can be explained by the tectono-eustatic changes in sea level and Cenozoic climate changes of China.

Lidesheng

1983-03-01

349

Continental emergence in the Late Archean reconciles early and late continental growth models  

NASA Astrophysics Data System (ADS)

The analysis of ancient sediments (Rare Earth Element composition of black shales, isotopic strontium composition of marine carbonates, isotopic oxygen composition of zircons) suggests that continental growth culminated around the Archean-Proterozoic transition. In stark contrast, the geochemical analysis of ancient basalts suggests that depletion of the mantle occurred in the Hadean and Eoarchean. This paradox may be solved if continents were extracted from the mantle early in Earth's history, but remained mostly below sea level throughout the Archean. We present a model to estimate the area of emerged land and associated isotopic strontium composition of the mantle and oceans as a function of the coupled evolution of mantle temperature, continental growth and distribution of surface elevations (hypsometry). For constant continental hypsometry and four distinct continental growth models, we show that sea level was between 500 and 2000 m higher in the Archean than at present, resulting in < 12% of emerged land, compared to ~ 28% at present. If in addition the hot Archean lithosphere could not sustain high relief, as little as 2-3% of Earth's surface would have been emerged in the Archean. Using a geochemical box model for the strontium isotopic composition of the mantle and oceans, we show that a reduced area of emerged continental crust can explain why the geochemical fingerprint of continents extracted early in Earth's history was not recorded at the surface of the Earth until the late Archean.

Flament, Nicolas; Coltice, Nicolas; Rey, Patrice

2014-05-01

350

Flutter of a rectangular plate?  

Microsoft Academic Search

We address theoretically the linear stability of a variable aspect ratio, rectangular plate in an uniform and incompressible axial flow. The flutter modes are assumed to be two-dimensional but the potential flow is calculated in three dimensions. For dierent values of aspect ratio, two boundary conditions are studied: a clamped- free plate and a pinned-free plate. We assume that the

Christophe Eloy; Claire Souilliez; Lionel Schouveiler

2006-01-01

351

Warm Working of Armor Plate.  

National Technical Information Service (NTIS)

Taking advantage of warm working to improve the toughness of armor plate requires that the plates be able to be rolled on present day mills. Calculations indicated that a 50 inch wide steel plate with hardnesses in excess of 400 BHN could not be rolled th...

E. J. Ripling, N. N. Breyer, R. P. O'Shea

1967-01-01

352

Vibration analysis of folded plates  

Microsoft Academic Search

The finite element-transfer matrix method (FETMM) is used to study the natural frequencies of folded plate structures. The FETMM used is based on combining the stiffness and mass matrices of each flat plate element in one strip to establish the transfer matrix relation between the left side and right side of a folded strip. The cantilever folded plate or supported

W. H. Liu; C. C. Huang

1992-01-01

353

Lesson 3. Plate Tectonics Overview  

E-print Network

Lesson 3. Plate Tectonics #12;Overview · Prior to the 1970s that with the development of the theory of plate tectonics. · Knowledge of the ocean floors of the Earth #12;Overview · Plate tectonics explains the formaBon of the Earth's two

Chen, Po

354

Characterizing Plate Boundaries  

NSDL National Science Digital Library

To prepare for this exercise students read about the processes that operate at plate boundaries and how they are related to the distinct patterns of seismicity, volcanism, surface elevations (e.g., ridges versus trenches), and seafloor ages characteristic of different boundary types. During the week the assignment is available online, students have access to: (1) an index map that locates three boundaries they are to study; and (2) four maps from Sawyer's Discovering Plate Boundaries website that provide the data mentioned above. Student tasks are to: (1) document patterns in each type of data along the three targeted boundaries; and (2) use these observations in conjunction with their understandings of the processes that operate along different types of boundaries to decide whether each of the targeted sites is most likely to be a divergent, convergent, or shear boundary. This activity gives students practice in map reading, interpreting the likely tectonic setting of a boundary by pulling together constraints from several types of data, and collaborating with their classmates in an online environment. The activity also provides a foundation for understanding a wide range of phenomena that are discussed later in the semester in the context of plate tectonic processes. Teaching Tips Adaptations that allow this activity to be successful in an online environment Sawyer's Discovering Plate Boundaries is a jigsaw exercise in which students collaboratively develop an empirical classification of plate boundaries by first studying an individual data set (e.g., seismicity) and then working as part of a multidisciplinary team to develop a composite classification for the boundaries of a single plate using several types of data. In order for the classification to be truly empirical, students are not introduced to the "traditional" classification of plate boundaries till the end of the exercise. In adapting this assignment to the online environment I have: (1) asked students to prepare by becoming familiar with the standard classification of plate boundaries and the processes that operate at them; (2) limited their work to three targeted boundaries of different types; and (3) provided guidance about which features to look for in the each data set. I have found that these modifications help online students, who often work alone "on their own schedules", to avoid getting "lost" and frustrated with the assignment and to compensate for the lack of collaborative input they would receive in a classroom setting. Elements of this activity that are most effective The success of this exercise is really seems to depend on how well a student follows the directions. If a student learns about the geologic differences among plate boundaries, makes careful observations, and thoughtfully compares his or her observations to the expected patterns he or she typically does quite well based on answers to the follow-up questions. If, on the other hand, a student simply looks up the types of the targeted boundaries on a map and then attempts to "back out" the observations that he or she thinks should fit, the result is often inconsistency and a poor score on the questions. (I can often tell which approach a student is taking based on the queries they post to the discussion board, but rarely seem to be able to get those who are trying to work backwards through the assignment to change direction.) Recommendations for other faculty adapting this activity to their own course: To date my experience developing an engaging online exercise to help students learn the principles of plate tectonics has only been partly successful. I think that having such an exercise is critical, however, because this topic provides the framework for so much of what we learn in the geosciences. Based on my efforts to adapt elements of Discovering Plate Boundaries to an online environment I would offer three recommendations. (1) Provide examples. Confronted with an unfamiliar map students are sometimes confused when asked to decide if seafloor age, for example, is uniform or variable along the length of a boundary. Showing them what you mean using snapshots from a map can often clear questions like this up quickly. Similarly, for written work a single example that gives them a clear sense of "what you're looking for" and can often head off a lot of questions. (2) Choose the boundaries you ask students to study carefully. The scarcity of documented volcanism along a mid-ocean ridge or the burial of seafloor age belts by sediment along a trench can result in student observations that are correct, but problematic for correctly assessing the nature of a boundary. (3) Stay on top of student questions and comments, and be prepared to make well-publicized "mid-course corrections" if something you thought was clear turns out to be misunderstood. These minor corrections happen naturally in face-to-face classes but can require real diligence to catch and correct in the online environment.

Hirt, Bill

355

The Theory of Plate Tectonics  

NSDL National Science Digital Library

This is a brief overview of the Theory of Plate Tectonics. According to the theory, the Earth's surface layer, or lithosphere, consists of seven large and 18 smaller plates that move and interact in various ways. Along their boundaries, they converge, diverge, and slip past one another, creating the Earth's seismic and volcanic activities. These plates lie atop a layer of partly molten rock called the asthenosphere. The plates can carry both continents and oceans, or exclusively one or the other. The site also explains interaction at the plate boundaries, which causes earthquakes, volcanoes and other forms of mountain building.

356

Paleomap PC: Plate tectonic reconstructions on IBM compatible computers  

SciTech Connect

PALEOMAP-PC (PMAPPC) allows users to interactively view Phanerozoic plate reconstructions on IBM compatible personal computers. This software compliments Macintosh and Unix software developed to conjunction with the PALEOMAP Project at the University of Texas at Arlington. The past positions of the continents can be viewed on the PC monitor in a variety of map projections including the spherical projection which gives a 3-D perspective of the Earth. Once a reconstruction time has been entered, the total finite rotations for over 150 independently moving plates are calculated and the plates are rotated back through time and drawn in reconstructed coordinates. The user can zoom in and out focusing on particular areas of interest. Hard copy output is available to a variety of output devices, both as a screen dump utility and as a selected option within the program. Although visualizing continental configurations through time is the core of the program, its primary strength is that user-defined data, such as stratigraphic or structural data, can be incorporated and plotted on reconstructed basemaps. This allows the time aspect of all geological data to be united with other user-supplied data within the plate tectonic framework.

Walsh, D.B.; Scotese, C.R. (Univ. of Texas, Arlington, TX (United States). Dept. Geology)

1993-02-01

357

Anomalous Subsidence at the Ocean Continent Transition of the Gulf of Aden Rifted Continental Margin  

NASA Astrophysics Data System (ADS)

It has been proposed that some rifted continental margins have anomalous subsidence and that at break-up they were elevated at shallower bathymetries than the isostatic response predicted by classical rift models (McKenzie, 1978). The existence of anomalous syn- or early-post break-up subsidence of this form would have important implications for our understanding of the geodynamics of continental break-up and sea-floor spreading initiation. We have investigated subsidence of the young rifted continental margin of the eastern Gulf of Aden, focussing on the western Oman margin (break-up age 17.6 Ma). Lucazeau et al. (2008) have found that the observed bathymetry here is approximately 1 km shallower than the predicted bathymetry. In order to examine the proposition of an anomalous early post break-up subsidence history of the Omani Gulf of Aden rifted continental margin, we have determined the subsidence of the oldest oceanic crust adjacent to the continent-ocean boundary (COB) using residual depth anomaly (RDA) analysis corrected for sediment loading and oceanic crustal thickness variation. RDAs corrected for sediment loading using flexural backstripping and decompaction have been calculated by comparing observed and age predicted oceanic bathymetries in order to identify anomalous subsidence of the Gulf of Aden rifted continental margin. Age predicted bathymetric anomalies have been calculated using the thermal plate model predictions of Crosby and McKenzie (2009). Non-zero RDAs at the Omani Gulf of Aden rifted continental margin can be the result of non standard oceanic crustal thickness or the effect of mantle dynamic topography or a non-classical rift and break-up model. Oceanic crustal basement thicknesses from gravity inversion together with Airy isostasy have been used to predict a "synthetic" gravity RDA, in order to determine the RDA contribution from non-standard oceanic crustal thickness. Gravity inversion, used to determine crustal basement thickness, incorporates a lithosphere thermal gravity anomaly correction and uses sediment thicknesses from 2D seismic data. Reference Moho depths used in the gravity inversion have been calibrated against seismic refraction Moho depths. The difference between the sediment corrected RDA and the "synthetic" gravity derived RDA gives the component of the RDA which is not due to variations in oceanic crustal thickness. This RDA corrected for sediment loading and crustal thickness variation has a magnitude between +600m and +1000m (corresponding to anomalous uplift) and is comparable to that reported (+1km) by Lucazeau et al. (2008). We are unable to distinguish whether this anomalous uplift is due to mantle dynamic topography or anomalous subsidence with respect to classical rift model predictions.

Cowie, Leanne; Kusznir, Nick; Leroy, Sylvie

2013-04-01

358

An updated global earthquake catalogue for stable continental regions: Reassessing the correlation with ancient rifts  

USGS Publications Warehouse

We present an updated global earthquake catalogue for stable continental regions (SCRs; i.e. intraplate earthquakes) that is available on the Internet. Our database contains information on location, magnitude, seismic moment and focal mechanisms for over 1300 M (moment magnitude) ??? 4.5 historic and instrumentally recorded crustal events. Using this updated earthquake database in combination with a recently published global catalogue of rifts, we assess the correlation of intraplate seismicity with ancient rifts on a global scale. Each tectonic event is put into one of five categories based on location: (i) interior rifts/taphrogens, (ii) rifted continental margins, (iii) non-rifted crust, (iv) possible interior rifts and (v) possible rifted margins. We find that approximately 27 per cent of all events are classified as interior rifts (i), 25 per cent are rifted continental margins (ii), 36 per cent are within non-rifted crust (iii) and 12 per cent (iv and v) remain uncertain. Thus, over half (52 per cent) of all events are associated with rifted crust, although within the continental interiors (i.e. away from continental margins), non-rifted crust has experienced more earthquakes than interior rifts. No major change in distribution is found if only large (M ??? 6.0) earthquakes are considered. The largest events (M ??? 7.0) however, have occurred predominantly within rifts (50 per cent) and continental margins (43 per cent). Intraplate seismicity is not distributed evenly. Instead several zones of concentrated seismicity seem to exist. This is especially true for interior rifts/taphrogens, where a total of only 12 regions are responsible for 74 per cent of all events and as much as 98 per cent of all seismic moment released in that category. Of the four rifts/taphrogens that have experienced the largest earthquakes, seismicity within the Kutch rift, India, and the East China rift system, may be controlled by diffuse plate boundary deformation more than by the presence of the ancient rifts themselves. The St. Lawrence depression, Canada, besides being an ancient rift, is also the site of a major collisional suture. Thus only at the Reelfoot rift (New Madrid seismic zone, NMSZ, USA), is the presence of features associated with rifting itself the sole candidate for causing seismicity. Our results suggest that on a global scale, the correlation of seismicity within SCRs and ancient rifts has been overestimated in the past. Because the majority of models used to explain intraplate seismicity have focused on seismicity within rifts, we conclude that a shift in attention more towards non-rifted as well as rifted crust is in order. ?? 2005 RAS.

Schulte, S.M.; Mooney, W.D.

2005-01-01

359

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

360

A true polar wander model for Neoproterozoic plate motions  

SciTech Connect

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

Ripperdan, R.L. (Weizmann Inst. of Science, Rehovot (Israel))

1992-01-01

361

Metallogeny of the northeastern Pacific Rim: an example of the distribution of ore deposits along a growing continental margin  

USGS Publications Warehouse

The distribution of mineral deposits within northwestern North America (Alaska, Yukon, and northern British Columbia) allows for an in-depth examination of the metallogenic patterns of a growing continental margin. A more complete understanding of the tectonic evolution of this part of the Pacific Rim, achieved over the last 15 to 20 years, now allows for the placement of ore systems into a well-defined plate tectonic framework. Ore deposits older than about 185 Ma represent hydrothermal systems that were active in the platform/shelf environment of ancestral North America's miogeocline or hydrothermal systems developed in oceanic arcs and continental fragments more distal to the craton. These include important SEDEX, VMS, and pre-accretionary porphyry deposits. In contrast, most mineral deposits younger than about 185 Ma were formed within the growing Cordilleran orogen, as terranes were accreted to the continental margin during interactions between the North America and Pacific/Farallon/Kula plates. Such syn- to post-accretionary mineralised systems include many large lode gold and porphyry/skarn systems.

Goldfarb, R. J.; Hart, C. J.; Mortensen, J. K.

1999-01-01

362

Dynamics of Tectonic Plates  

E-print Network

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

Pechersky, E; Sadowski, G; Yambartsev, A

2014-01-01

363

Ultrafast microchannel plate photomultipliers.  

PubMed

Performance characteristics of several new types of photomultiplier tubes (PMT) with microchannel plates (MCP) are presented in this paper. They are the MCP-PMT with 6-microm diam channels, MCP-PMT with an S-l photocathode, and MCP-PMT with multi (discrete) anode and gatable MCP-PMT. Important requirements of an optical detector for picosecond lasers, fluorescence measurements, and material analysis are low light detectability, ultrafast time response, and versatile operation including modulation. The basic configuration, characteristics, and practical results of these detectors are described. PMID:20531532

Kume, H; Koyama, K; Nakatsugawa, K; Suzuki, S; Fatlowitz, D

1988-03-15

364

Earthquakes and Plate Tectonics  

NSDL National Science Digital Library

This activity, from the Real World Learning Objects Resource Library, allows students to use first-hand data analysis to "determine if there is any pattern to earthquake events and speculate on the causes of earthquakes." Intended to be an introductory activity for a unit of study on earthquakes, this 60-minute activity is complete with learning goals, step-by-step classroom procedures, materials, assessment activities, and resources for further information. The "Content Materials" section contains directions for students and graphics to help students understand earthquakes and plate tectonics. This is an excellent resource for geology and earth science instructors that is ready to use for the classroom.

2007-10-04

365

Plated wire memory subsystem  

NASA Technical Reports Server (NTRS)

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

Carpenter, K. H.

1974-01-01

366

Shuttle plate braiding machine  

NASA Technical Reports Server (NTRS)

A method and apparatus for moving yarn in a selected pattern to form a braided article. The apparatus includes a segmented grid of stationary support elements and a plurality of shuttles configured to carry yarn. The shuttles are supported for movement on the grid assembly and each shuttle includes a retractable plunger for engaging a reciprocating shuttle plate that moves below the grid assembly. Such engagement at selected times causes the shuttles to move about the grid assembly in a selected pattern to form a braided article of a particular geometry.

Huey, Jr., Cecil O. (Inventor)

1994-01-01

367

Plates on the Move  

NSDL National Science Digital Library

In this activity, students create a model of sea floor spreading using two sheets of white paper and a metric ruler. The paper strips are pulled through a slit representing a mid-ocean ridge and divergent plate boundary. The model mimics how molten material rises to the surface and then spreads out in both directions. The resource is part of the teacher's guide accompanying the video, NASA SCI Files: The Case of the Shaky Quake. Lesson objectives supported by the video, additional resources, teaching tips and an answer sheet are included in the teacher's guide.

368

CSDP: Seismology of continental thermal regime  

SciTech Connect

This is a progress report for the past one year of research (year 2 of 5-year project) under the project titled CSDP: Seismology of Continental Thermal Regime'', in which we proposed to develop seismological interpretation theory and methods applicable to complex structures encountered in continental geothermal areas and apply them to several candidate sites for the Continental Scientific Drilling Project. During the past year, two Ph.D. thesis works were completed under the present project. One is a USC thesis on seismic wave propagation in anisotropic media with application to defining fractures in the earth. The other is a MIT thesis on seismic Q and velocity structure for the magma-hydrothermal system of the Valles Caldera, New Mexico. The P.I. co-organized the first International Workshop on Volcanic Seismology at Capri, Italy in October 1988, and presented the keynote paper on the state-of-art of volcanic seismology''. We presented another paper at the workshop on Assorted Seismic Signals from Kilauea Volcano, Hawaii. Another international meeting, namely, the Chapman Conference on seismic anisotropy in the earth's crust at Berkeley, California in May 1988, was co-organized by the co-P.I. (P.C.L), and we presented our work on seismic waves in heterogeneous and anisotropic media. Adding the publications and presentations made in the past year to the list for the preceding year, the following table lists 21 papers published, submitted or presented in the past two years of the present project. 65 refs., 334 figs., 1 tab.

Aki, K.

1989-04-01

369

Crew coordination concepts: Continental Airlines CRM training  

NASA Technical Reports Server (NTRS)

The outline of the crew coordination concepts at Continental airlines is: (1) Present relevant theory: Contained in a pre-work package and in lecture/discussion form during the work course, (2) Discuss case examples: Contained in the pre-work for study and use during the course; and (3) Simulate practice problems: Introduced during the course as the beginning of an ongoing process. These concepts which are designed to address the problem pilots have in understanding the interaction between situations and their own theories of practice are briefly discussed.

Christian, Darryl; Morgan, Alice

1987-01-01

370

Finite-element models of continental extension  

NASA Technical Reports Server (NTRS)

Numerical models of the initial deformation of extending continental lithosphere, computed to investigate the control of preexisting thermal and mechanical heterogeneities on the style of deformation, are presented. The finite element method is used to calculate deformation with a viscoelastic-plastic model for the lithosphere. Comparisons of the results of analytic models and finite-element models using this method show that good results may be obtained by the numerical technique, even with elements containing both brittle and viscoelastic sampling points. It is shown that the gross style of initial extensional deformation is controlled by the depth and width of the initial heterogeneity which localizes deformation.

Lynch, H. David; Morgan, Paul

1990-01-01

371

Evolution of the continental crust as recorded in accessory minerals  

NASA Astrophysics Data System (ADS)

Recent developments in precise in situ isotopic analysis by LA-ICPMS and SIMS allow correlating multiple isotopic systems within single grains of accessory minerals such as zircon and monazite. The combined isotope systematics have provided valuable insights into the evolution of the continental crust. Zircon, a common accessory phase in granitoids, can be precisely dated by the U-Pb system. Zircon Lu-Hf isotopic composition is a function of crustal residence time of the magmatic protolith, whereas the O isotopic composition is a sensitive record of reworking of mature sediments such as pelite. An integration of U-Pb, Lu-Hf and O isotopic data for detrital zircons from modern large rivers indicates that: (1) the preserved continental crust dominantly formed between 3.6 and 1.0 Ga, (2) the major mode of crustal development would change during the supercontinent cycle, i.e., the generation of juvenile crust during supercontinent fragmentation versus the stabilization of the generated crust via crustal remelting during supercontinent fragmentation, and (3) reworking of mature sediments increased abruptly at ca. 2.1 Ga. No granitoids are known to have survived since 4.03 Ga. Yet evidence of an even older evolved crust is provided by detrital zircons with ages up to 4.4 Ga from Mt. Narryer and Jack Hills metasedimentary rocks in the Yilgarn Craton, Western Australia. Recently, such Hadean zircons have been found from outside the Yilgarn Craton, indicating that the young Earth had widespread granitoid crust. In addition, another accessory phase, monazite, in the Mt. Narryer and Jack Hills metasedimentary rocks offers an unique opportunity to advance our knowledge of early crustal evolution. Monazite, a light rare earth element phosphate mineral, occurs as an igneous accessory phase particularly in low-Ca granitoids, in contrast to the occurrence of igneous zircon in a wide range of granitoids. U-Pb and Sm-Nd isotope systematic of monazite are analogous to U-Pb and Lu-Hf isotope systematics of zircon in that they define the timing of the crystallization and magmatic protolith formation (model age), respectively. The lack of monazites having >3.6 Ga crystallization ages as well as >4.0 Ga Nd model ages in the Mt. Narryer and Jack Hills metasedimentary rocks suggests that the source rocks of the Hadean detrital zircons are not low-Ca granitoids and therefore contained few monazites. Given that low-Ca granitoid magmas generated mainly by melting of pre-existing mid-lower crust, this finding may indicate minor intra-crustal melting and, by extension, crustal stabilization until ca. 3.6 Ga. This is consistent with the picture portrayed by the detrital zircons from modern rivers. Presumably, the hotter and rheologically weaker lithospheric mantle fostered many small plates and island arcs early in Earth's history, and the young arc crust was efficiently returned to the mantle via subduction. Accordingly, net growth of continental crust was essentially minor in early Earth's history despite high rates of crust generation.

Iizuka, Tsuyoshi

2013-04-01

372

Automatic number plate detection for Korean vehicles  

Microsoft Academic Search

We consider the task of detection of Korean vehicle number plates (also named license plates or registration plates in other countries). A system for number plate detection must cope with wide variations in the appearance of the plates. Few yeas ago, Korea government permits the new types of license plates with wide width as same as foreign country. It occurred

Ho-Sub Yoon; Hong-Chang Lee; Jae-Yeon Lee

2009-01-01

373

Dynamic Linkages Between the Transition Zone & Surface Plate Motions in 2D Models of Subduction  

NASA Astrophysics Data System (ADS)

While slab pull is considered the dominant force controlling plate motion and speed, its magnitude is controlled by slab behavior in the mantle, where tomographic studies show a wide range of possibilities from direct penetration to folding, or stagnation directly above the lower mantle (e.g. Fukao et al., 2009). Geodynamic studies have investigated various parameters, such as plate age and two phase transitions, to recreate observed behavior (e.g. B?hounková and Cízková, 2008). However, past geodynamic models have left out known slab characteristics that may have a large impact on slab behavior and our understanding of subduction processes. Mineral experiments and seismic observations have indicated the existence of additional phase transitions in the mantle transition zone that may produce buoyancy forces large enough to affect the descent of a subducting slab (e.g. Ricard et al., 2005). The current study systematically tests different common assumptions used in geodynamic models: kinematic versus free-slip boundary conditions, the effects of adiabatic heating, viscous dissipation and latent heat, compositional layering and a more complete suite of phase transitions. Final models have a complete energy equation, with eclogite, harzburgite and pyrolite lithosphere compositional layers, and seven composition-dependent phase transitions within the olivine, pyroxene and garnet polymorph minerals. Results show important feedback loops between different assumptions and new behavior from the most complete models. Kinematic models show slab weakening or breaking above the 660 km boundary and between compositional layers. The behavior in dynamic models with a free-moving trench and overriding plate is compared to the more commonly found kinematic models. The new behavior may have important implications for the depth distribution of deep earthquakes within the slab. Though the thermodynamic parameters of certain phase transitions may be uncertain, their presence and feedback to other added processes remain important, which could encourage mineralogical research into multiphase systems. Feedback from the compositionally complex slab to the dynamic trench may improve understanding on the mechanics of slab behavior in the upper and lower mantle and surface behavior of the subducting and overriding plates. B?hounková, M., and H. Cízková, Long-wavelength character of subducted slabs in the lower mantle, Earth and Planetary Science Letters, 275, 43-53, 2008. Fukao, Y., M. Obayashi, T. Nakakuki, and the Deep Slab Project Group, Stagnant slab: A review, Annual Reviews of Earth and Planetary Science, 37, 19-46, 2009. Ricard, Y., E. Mattern, and J. Matas, Synthetic tomographic images of slabs from mineral physics, in Earth's Deep Mantle: Structure, Composition, and Evolution, Geophysical Monograph Series, vol. 160, American Geophysical Union, 2005.

Arredondo, K.; Billen, M. I.

2013-12-01

374

Plate boundary forces at subduction zones and trench-arc compression  

NASA Astrophysics Data System (ADS)

Viscoelastic finite element modelling has been used to study the state of stress in the overriding and subducting plates meeting at a subduction zone. The subduction fault is included using the dual node technique. It is demonstrated that substantial horizontal deviatoric compressive stress occurs in the trench-arc region as a result of the downpull of the dense slab and the associated surface depression including the trench and other downflexing of the plates. This may be masked at the trench by bending stress. It is the lack of significant shearing stress along an unlocked subduction fault in the presence of this compressive stress that gives rise to the slab pull and trench suction plate boundary forces. Slab pull and trench suction were found to be of comparable magnitude within the range 1.0 to 4.0 × 10 12 N/m in models studied with vertical subduction, and there are indications that this may also apply when the slab dips at 45° as a result of viscous flow induced by rollback. When the slab dips beneath the arc-backarc region, it is shown that horizontal deviatoric compression can occur in this region contemporaneous with plate interior tension produced by trench suction. This suggests that backarc tension associated with Marianas type trench-arch systems may be related to the nearly vertical slab whereas backarc compression in the Chilean type may result from the low dip and small downpull of the slab. It is also shown that successive locking and unlocking of the subduction fault may give rise to large variations of stress in plate interiors.

Bott, M. H. P.; Waghorn, G. D.; Whittaker, A.

1989-12-01

375

Strength, strain, and structure of the Australian continental lithosphere  

NASA Astrophysics Data System (ADS)

The diverse geologic makeup of Australia makes the continent an ideal candidate to investigate the relation of lithospheric strength to the age of the overlying crust. Australia is made up from Archean cratons, Proterozoic orogens and Phanerozoic formations in a west-to-east age decrease. Surrounded by active earthquake belts, Australia is ideally suited for regional seismic tomographic studies. High-quality seismic data sets from portable SKIPPY instruments have been inverted to yield detailed models of the three-dimensional wave speed structure, including its anisotropy. Australia's topography is subdued, which makes strength measurements using traditional admittance/coherence techniques between gravity and topography rather difficult. However, the development of advanced spectral techniques has made measurements of the relative strength of the lithosphere possible. In particular, the application of multitaper techniques for cross-spectral analysis has enabled us to study elastic thickness variations with location (and thus age) as well as azimuth (measuring strength anisotropy). Using our seismic wave speed model we have estimated the thickness of the high-velocity lid underlying the Australian continent and compared it to coherence estimates of its elastic thickness. The variations in seismic thickness within broad age divisions of the Australian continent are larger than the differences between the means over the age groups. This is especially surprising for the Australian Archean, whose high-velocity lid is far less pronounced than traditional evolution models would have suggested. Following a similar pattern, the mechanical strength of the lithosphere increases with age to first order only, and substantial strength differences exist within domains of equal crustal age. Seismically thicker continental keels are not necessarily mechanically stronger, and shallow mechanical strength does not appear to control the preservation of such keels. The seismic data set and the two-dimensional coherence measurements can respectively be analyzed for anisotropy in the wave speed deviations or mechanical strength variations. Surface-wave tomography and gravity-topography analysis can thus provide independent measures of elastic anisotropy (one instantaneous, the second long-term) and, by implication, strain in the lithospheric upper mantle. The depth variation of their relation resolves a change both in the character of seismic anisotropy and in its relation to strain near ˜200 km depth in the Australian subcontinental lithospheric mantle. In our interpretation, the top 200 km of the Australian lithosphere primarily records the coherent signature of past deformation episodes, whereas below 200 km, active processes related to current plate motion provide the dominant explanation for the observed seismic anisotropy. The alignment of the fast axes in the flow direction is consistent with the deformation of a dry olivine mantle by simple shear. The correspondence between seismic fast axes and plate motion of Australia is best when the latter is expressed in a hot-spot reference frame. Thus, seismic anisotropy can add information on plate motion with respect to the underlying mantle that is independent from geodetic and plate-circuit constraints. Finally, the comparison of our results with mantle convection simulations suggests how seismic and mechanical models of the lithosphere are approaching resolutions at which they can be treated as ``data'' to refine forward models, thereby strengthening the crucial links between seismology, tectonics, and geodynamics.

van der Hilst, R. D.; Simons, F. J.

2003-12-01

376

Investigating Continental Margins: An Activity to Help Students Better Understand the Continental Margins of North America  

ERIC Educational Resources Information Center

Continental margins are an important part of the ocean floor. They separate the land above sea level from the deep ocean basins below and occupy about 11% of Earth's surface. They are also economically important, as they harbor both mineral resources and some of the most valuable fisheries in the world. In this article students investigate North…

Poli, Maria-Serena; Capodivacca, Marco

2011-01-01

377

Movement of sediment on the Gulf of Mexico, continental slope and upper continental shelf  

Microsoft Academic Search

Grain size, coarse fraction analyses, and depositional environment as interpreted from microfauna are related to the character of sparker reflections at the location of core holes drilled by Exxon, Chevron, Gulf, and Mobil on the continental slope of the northern Gulf of Mexico. Continuous sparker reflections are correlated with slowly deposited, evenly bedded sediments containing bathyal faunas. The coarse fraction

H. O. Woodbury

1977-01-01

378

Plating on difficult-to-plate metals: what's new  

SciTech Connect

Some of the changes since 1970 in procedures for plating on such materials as titanium, molybdenum, silicon, aluminum, and gallium arsenide are summarized. While basic procedures for plating some of these materials were developed as many as 30 to 40 years ago, changes in the end uses of the plated products have necessitated new plating processes. In some cases, vacuum techniques - such as ion bombardment, ion implantation, and vacuum metallization - have been introduced to improve the adhesion of electrodeposits. In other cases, these techniques have been used to deposit materials upon which electrodeposits are required.

Wiesner, H.J.

1980-07-30

379

LINKAGE BETWEEN PRODUCTION AND RESPIRATION ON THE LOUISIANA CONTINENTAL SHELF.  

EPA Science Inventory

Abstract for presentation. Original title, "PRIMARY PRODUCTION, BACTERIOPLANKTON PRODUCTION, AND COMMUNITY RESPIRATION IN STRATIFIED WATERS OF THE NORTHERN GULF OF MEXICO CONTINENTAL SHELF: LINKAGE TO HYPOXIA."...

380

Estimating Continental and Terrestrial Precipitation Averages from Raingauge Networks  

E-print Network

Influences of varying rain-gauge networks on continental and terrestrial precipitation averages (derived from data observed on those networks) are evaluated. Unsystematically and systematically designed station networks ...

Willmott, Cort J.; Robeson, Scott M.; Feddema, Johannes J.

1994-01-01

381

Continental water storage variations in Africa  

NASA Astrophysics Data System (ADS)

We investigate the temporal and spatial variations of continental water storage in Africa as recovered by the NASA/DLR Gravity Recovery and Climate Experiment (GRACE) mission. Mass variations are directly inverted from the K-band range rate using the mascon approach. We compare our solution to global different hydrological models. We solve the water mass balance equation, using different precipitation datasets from remote sensing techniques, as well as meteorological stations, using water fluxes (precipitation minus evaporation) from different atmospheric models. As a result, our runoff estimates are compared to river fluxes measurements. We compare mass estimates of major African lakes to volume estimated from space Laser (ICESat) and radar altimetry. As our forward modeling includes the continental water storage variations (using GLDAS/Noah model), leaking effects are significantly reduced. We also pay a special attention to the Lake Chad and Niger river basins, where ground gravity variations are repetitively measured as part of the GHYRAF project in order to investigate seasonal water storage variations at small and larger spatial scales.

Boy, J.; Carabajal, C. C.; Luthcke, S. B.; Rowlands, D. D.; Lemoine, F. G.; Sabaka, T. J.

2009-12-01

382

When and How Did Continental Crust Form?  

NSDL National Science Digital Library

Given the extensive literature on the composition and evolution of continental crust there are a number of teaching strategies that can be employed to encourage active learning by students. A critical reading of this collection of articles will provide students with a good opportunity to evaluate the chemical isotopic and physical evidence that has led to the development of these models of continental crustal growth. These instructional approaches build on recommendations from Project 2061, Science for all Americans: 1) Start with questions about nature. 2) Engage students actively. 3) Concentrate onthe collection and use of evidence. 4) Provide historical perspectives. 5) Use a team approach. 6) Do not separate knowing from finding out. A compilation from the primary literature has been provided (see the reference list at the end of this web page: http://serc.carleton.edu/NAGTWorkshops/earlyearth/questions/crust.html), along with guiding questions for deeper exploration and discovery. Recommended instructional methods include: jigsaw method, role playing or debates (have each student play the role of Richard Armstrong, Ross Taylor, William Fyfe...), reading the primary literature, or problem-based learning (which is purposefully ambiguous and addresses questions that require independent discovery).

Mogk, Dave

383

Anthropogenic impacts on continental surface water fluxes  

NASA Astrophysics Data System (ADS)

Impacts of reservoirs and irrigation water withdrawals on continental surface water fluxes are studied within the framework of the Variable Infiltration Capacity (VIC) model for a part of North America, and for Asia. A reservoir model, designed for continental-scale simulations, is developed and implemented in the VIC model. The model successfully simulates irrigation water requirements, and captures the main effects of reservoir operations and irrigation water withdrawals on surface water fluxes, although consumptive irrigation water use is somewhat underestimated. For the North American region, simulated irrigation water requirements and consumptive irrigation water uses are 191 and 98 km3year-1, while the corresponding numbers for the Asian region are 810 and 509 km3year-1, respectively. The consumptive uses represent a decrease in river discharge of 4.2 percent for the North American region, and 2.8 percent for the Asian region. The largest monthly decrease is about 30 percent, for the area draining the Western USA in June. The maximum monthly increase in streamflow (28 percent) is in March for the Asian Arctic region.

Haddeland, Ingjerd; Skaugen, Thomas; Lettenmaier, Dennis P.

2006-04-01

384

The science behind Plate Tectonics  

NSDL National Science Digital Library

Plate tectonics is a quantitative, robust and testable, geologic model describing the surface motions of Earth's outer skin. It is based on real data and assumptions, and built using the scientific method. New space geodesy data provide important quantitative (and independent) tests of this model. In general, these new data show a close match to model predictions, and suggest that plate motion is steady and uniform over millions of years. Active research continues to refine the model and to better our understanding of plate motion and tectonics. The exercise presented here aims to help students experience the process of doing science and to understand the science underlying the plate tectonic theory. Key words: plate tectonics, global plate motion models, assumptions, geologic data (spreading rates, transform fault azimuths, earthquake slip vectors), space geodesy tests.

Weber, John

385

Tectonics of the Easter plate  

NASA Technical Reports Server (NTRS)

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

Engeln, J. F.; Stein, S.

1984-01-01

386

Collision zone magmatism aids continental crustal growth  

NASA Astrophysics Data System (ADS)

The continental crust has a broadly andesitic bulk composition and is predominantly generated at convergent margins. However, estimates of the bulk composition of oceanic arcs indicate a bulk composition closer to basalt than to andesite. Hence, reworking processes that transform basaltic island arc crust into andesitic continental crust are essential[1] and explaining growth of andesitic continental crust via accretion of arc crustal fragments remains problematic. Recent studies of magmatism in the Great Tibetan Plateau[2], as site of multiple and still active continent-continent collisions, have proposed that andesitic CC is generated via amalgamation of large volumes of collision-related felsic magmas generated by melting of hydrated oceanic crust with mantle geochemical signatures. We aim to test this hypothesis by evaluating geochemical data from the volcanically and tectonically active Lesser Caucasus region (Armenia, Azerbaijan, Georgia and E. Turkey), as the only other region where active continent-continent collision takes place. We will benefit from the newly compiled volcano-tectonic database of collision-related volcanic and plutonic rocks of Armenia that is comparable in quality and detail to the one available on Tibet. Our dataset combines several detailed studies from the large Aragats shield volcano[3] and associated monogenetic volcanic fields (near the capital city of Yerevan), as well as > 500 Quaternary to Holocene volcanoes from Gegham, Vardenis and Syunik volcanic highlands (toward Armenia-Nagorno-Karabakh-Azerbaijan-Iran border). The Armenian collision-related magmatism is diverse in volume, composition, eruption style and volatile contents. Interestingly, the majority of exposed volcanics are andesitic in composition. Nearly all collision-related volcanic rocks, even the highly differentiated dacite and rhyolite ignimbrites, have elevated Sr concentrations and 87Sr/86Sr and 143Nd/144Nd ratios varying only little (average ~ 0.7043 and ~ 0.51282, respectively). These isotopic signatures are much more similar to those typical of intra-oceanic subduction zones than those typical of continental crust, likely due to the very young age of the rocks. In contrast, trace element abundances reveal many similarities to average CC, such as Nb-Ta and Ti troughs and Pb peaks. The range of d11B isotope ratios (-8.7 to +2.1 per mil) signifies magmas originating from moderately metasomatised (arc preconditioned) mantle sources. Our combined results reveal that the collision-related mantle melting is capable of generating large volumes of plutons and volcanic rocks that resemble (although not perfectly) the composition of the average CC. We will attempt to use the new combined datasets in order to quantify the importance of the collision zone magmatism for continental crustal growth. [1] Lee et al. (2007) EPSL 263, 370-387; [2] Niu et al. (2013) Earth-Science Reviews 127, 96-110; [3] Connor et al., (2012) J.Applied Volcanology, 1:3, 1-19.

Savov, Ivan; Meliksetian, Khachatur; Ralf, Halama; Gevorg, Navasardian; Chuck, Connor; Massimo, D'Antonio; Samuele, Agostini; Osamu, Ishizuka; Sergei, Karapetian; Arkadi, Karakhanian

2014-05-01

387

A relatively reduced Hadean continental crust  

NASA Astrophysics Data System (ADS)

Among the physical and chemical parameters used to characterize the Earth, oxidation state, as reflected by its prevailing oxygen fugacity (fO2), is a particularly important one. It controls many physicochemical properties and geological processes of the Earth's different reservoirs, and affects the partitioning of elements between coexisting phases and the speciation of degassed volatiles in melts. In the past decades, numerous studies have been conducted to document the evolution of mantle and atmospheric oxidation state with time and in particular the possible transition from an early reduced state to the present oxidized conditions. So far, it has been established that the oxidation state of the uppermost mantle is within ±2 log units of the quartz-fayalite-magnetite (QFM) buffer, probably back to ~4.4 billion years ago (Ga) based on trace-elements studies of mantle-derived komatiites, kimberlites, basalts, volcanics and zircons, and that the O2 levels of atmosphere were initially low and rose markedly ~2.3 Ga known as the Great Oxidation Event (GOE), progressively reaching its present oxidation state of ~10 log units above QFM. In contrast, the secular evolution of oxidation state of the continental crust, an important boundary separating the underlying upper mantle from the surrounding atmosphere and buffering the exchanges and interactions between the Earth's interior and exterior, has rarely been addressed, although the presence of evolved crustal materials on the Earth can be traced back to ~4.4 Ga, e.g. by detrital zircons. Zircon is a common accessory mineral in nature, occurring in a wide variety of igneous, sedimentary and metamorphic rocks, and is almost ubiquitous in crustal rocks. The physical and chemical durability of zircons makes them widely used in geochemical studies in terms of trace-elements, isotopes, ages and melt/mineral inclusions; in particular, zircons are persistent under most crustal conditions and can survive many secondary processes such as metamorphism, weathering and erosion. Thus, zircons in granites of shallow crust may record the chemical/isotopic composition of the deep crust that is otherwise inaccessible, and offer robust records of the magmatic and crust-forming events preserved in the continental crust. In fact, due to the absence of suitable rock records (in particular for periods older than ~4.0 Ga), studies in recent years concerning the nature, composition, growth and evolution of the continental crust, and especially the Hadean crust, have heavily relied on inherited/detrital zircons. Natural igneous zircons incorporate rare-earth elements (REE) and other trace elements in their structure at concentrations controlled by the temperature, pressure, fO2 and composition of their crystallization environment. Petrological observations and recent experiments have shown that the concentration of Ce relative to other REE in igneous zircons can be used to constrain the fO2 during their growth. By combining available trace-elements data of igneous zircons of crustal origin, we show that the Hadean continental crust was significantly more reduced than its modern counterpart and experienced progressive oxidation till ~3.6 billions years ago. We suggest that the increase in the oxidation state of the Hadean continental crust is related to the progressive decline in the intensity of meteorite impacts during the late veneer. Impacts of carbon- and hydrogen-rich materials during the formation of Hadean granitic crust must have favoured strongly reduced magmatism. The conjunction of cold, wet and reduced granitic magmatism during the Hadean implies the degassing of methane and water. When impacts ended, magma produced by normal decompression melting of the mantle imparted more oxidizing conditions to erupted lavas and the related crust.

Yang, Xiaozhi; Gaillard, Fabrice; Scaillet, Bruno

2014-05-01

388

Channel plate for DNA sequencing  

DOEpatents

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

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

1998-01-01

389

Channel plate for DNA sequencing  

DOEpatents

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

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

1998-01-13

390

Tectonic Plate Movements and Hotspots  

NSDL National Science Digital Library

This lesson introduces the idea that rates and directions of plate movements can be measured. The discussion centers on the use of mantle 'hotspots' to determine plate motions. Examples include the Hawaiian Islands, the Galapagos Islands, and the Yellowstone hotspot. The lesson includes an activity in which students use online resources to answer questions about the Galapagos Islands and measure plate movement rates using online data for the Hawaiian Islands hotspot.

Rhinehart, Ken

391

Carbon-assisted flyer plates  

DOEpatents

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

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

1994-01-01

392

The Nature of Tectonic Plates  

NSDL National Science Digital Library

This lesson provides an overview of the various types of interactions between tectonic plates. The discussion uses the analogy of a cracked egg to describe the tectonic plates composing Earth's crust. Other topics include the concentrated earthquake and volcanic activity associated with plate boundaries, types of interactions at the boundaries, and how plate motions are affecting the Atlantic and Pacific Oceans. The lesson includes an activity in which students will use online references to locate a hypothetical nuclear power plant in a geologically safe area, investigate the history of large earthquakes in South Carolina, provide a likely location for a hypothetical geothermal power plant, and others.

Rhinehart, Ken

393

License Plates of the World  

NSDL National Science Digital Library

Whether you're interested in collecting license plates, or are just moving to Andorra and wonder what your car will be wearing when it gets there, this site provided by collector Michael Kustermann can be a handy reference. A winner in the "labor of love" website category, this frames-based directory contains pictures of and descriptive information about a dizzying range of automobile license plates, arranged geographically. Special issue and commemorative plates are also covered, as well as links to collector's clubs and a bibliography about the art and science of license plate hunting and gathering. You'll never look at bumpers quite the same way.

394

Plate Tectonics: Earthquake Epicenter  

NSDL National Science Digital Library

This lesson provides an overview of destructive earthquakes and their connection to tectonic movements of the Earth's crust. It includes a discussion of some especially destructive historic earthquakes, and a brief introduction to contintental drift and the theory of plate tectonics. There is also discussion of basic seismology (types of waves) and measures of the magnitude of an earthquake (the Richter Scale). The lesson inlcudes an activity in which students use an online simulator to locate the epicenter of an earthquake using readings from three different seismograph stations. After they have completed the simulation, they attempt to locate the epicenter of a real earthquake using data from the United States Geological Survey (USGS) earthquake website.

Pratte, John

395

Continental boundaries of the Jalisco block and their influence in the Pliocene-Quaternary kinematics of western Mexico  

NASA Astrophysics Data System (ADS)

Extensional faulting observed in southwestern Mexico has been related to the incipient rifting of the Jalisco block from the Mexican mainland since the Pliocene. On the basis of new structural and geophysical data, we propose that (1) the continental boundaries of the Jalisco block are ancient structures reactivated since the Pliocene at a low (<1 mm/yr) rate of deformation, and (2) Pliocene-Quaternary extensional faulting at the edges of Jalisco block is a basement-controlled intraplate deformation related to plate boundary forces rather than to active continental rifting. The Jalisco block boundaries first developed in response to the uplift of the Puerto Vallarta batholith in pre-Neogene time and underwent a complex contractile deformation before the Pliocene. During Pliocene-Quaternary times north-northeast extension reactivated the northern boundary, forming the Tepic-Zacoalco rift, whereas east-southeast extension formed the northern Colima rift. South of the Colima volcano, active extension is found only west of the so-called southern Colima rift and partly reactivates old northeast-trending basement faults. The parallelism between the subducted Rivera-Cocos plate boundary zone and the eastern neotectonic boundary of the Jalisco block supports east-southeastward motion of the southern Mexican blocks induced by the differential motion and oblique subduction of the Cocos and Rivera plates. On the other hand, we envisage Pliocene-Quaternary extension along the northern boundary as an upper-plate response to the low convergence rate and the steep subduction angle of the Rivera plate.

Rosas-Elguera, José; Ferrari, Luca; Garduño-Monroy, Victor Hugo; Urrutia-Fucugauchi, Jaime

1996-10-01

396

Modeling RERTR experimental fuel plates using the plate code  

Microsoft Academic Search

Modeling results using the PLATE dispersion fuel performance code are presented for the U-Mo\\/Al experimental fuel plates from the RERTR-1, ?2, -3 and -5 irradiation tests. Agreement of the calculations with experimental data obtained in postirradiation examinations of these fuels, where available, is shown to be good. Use of the code to perform a series of parametric evaluations highlights the

S. L. Hayes; M. K. Meyer; G. L. Hofman; J. L. Snelgrove

2007-01-01

397

Writing a Rosetta stone: insights into continental-margin sedimentary processes and strata  

E-print Network

and strata in time and space. Keywords Continental margin, continental shelf, continental slopeWriting a Rosetta stone: insights into continental-margin sedimentary processes and strata CHARLES, Charlottesville, VA 22904, USA ABSTRACT Continental margins are valuable for many reasons, including the rich

Lin, Andrew Tien-Shun

398

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

NASA Astrophysics Data System (ADS)

Before the onset of Europe-Africa continental collision in the Dinarides-Hellenides (around 60Ma) and in the Alps and Western Carpathians (around 35 Ma), and at a large scale, the dynamics of orogenic processes in the Mediterranean Alpine chains were governed by Europe-Africa plate convergence leading to the disappearance of large parts of intervening oceanic lithosphere, i.e. the northern branch of Neotethys along the Sava-Izmir-Ankara suture and Alpine Tethys along the Valais-Magura suture (Schmid et al. 2008). In spite of this, two major problems concerning the pre-collisional stage are still poorly understood: (1) by now we only start to understand geometry, kinematics and dynamics of the along-strike changes in the polarity of subduction between Alps-Carpathians and Dinarides-Hellenides, and (2) it is not clear yet during exactly which episodes and to what extent intervening rifted continental fragments such as, for example, Iberia-Briançonnais, Tisza, Dacia, Adria-Taurides moved independently as micro-plates, and during which episodes they remained firmly attached to Europa or Africa from which they broke away. As Europe-Africa plate convergence slowed down well below 1 cm/yr at around 30 Ma ago these pre-collisional processes driven by plate convergence on a global scale gave way to more local processes of combined roll-back and crustal delamination in the Pannonian basin of the Carpathian embayment and in the Aegean (as well as in the Western Mediterranean, not discussed in this contribution). In the case of the Carpathian embayment E-directed roll back totally unrelated to Europe-Africa N-S-directed convergence, started at around 20 Ma ago, due to the presence relict oceanic lithosphere in the future Pannonian basin that remained un-subducted during collision. Due to total delamination of the crust from the eastward rolling back European mantle lithosphere the anticlockwise rotating ALCAPA crustal block, consisting of Eastern Alps and Western Carpathian thickened crust ripped of the African plate, invaded the northern part of this oceanic embayment, virtually floating on asthenospheric mantle. The presently still surviving semi-detached Vrancea slab in Romania manifests of the combined effect of roll back and delamination of mantle lithosphere. On the other hand Tisza-Dacia, another crustal block formerly ripped off the European plate and forming a single entity since mid-Cretaceous times, also at least partly floating on asthenospheric mantle, invaded the Carpathian embayment from the south. Thereby the Tisza-Dacia crustal block underwent clockwise rotation by as much as 90° due to the corner effect of the Moesian platform firmly attached to Europe since mid-Cretaceous times (Ustaszewski et al. 2008). In the Dinaric-Aegean realm collision occurred much earlier than in the Alps and the Carpathians, i.e. at around the Cretaceous-Cenozoic boundary, provided that one accepts that there is yet no convincing evidence for the existence of a second "Pindos oceanic domain" closing later, i.e. in Eocene times. However, in spite of early collision, the old subduction zone that consumed the northern branch of Neotethys (Meliata-Vardar) since at least mid-Cretaceous times persisted in the eastern Hellenides (but not in the Dinarides) until now, penetrating the transition zone all the way to a depth of some 1500km (Bijwaard et al. 1998). Continued subduction of mantle lithosphere in the Aegean since 60 Ma was concomitant with complete delamination of lithospheric mantle and lower crust from non-subducted or re-exhumed high pressure crustal flakes of largely continental derivation that were piled up to form the subsequently extended Hellenic orogen (Jolivet & Brun 2010). At around 25 Ma when the southern branch of Neotethys (the present-day Eastern Mediterranean ocean) entered this subduction zone, massive extension and core complex formation in the upper plate combined with an acceleration of south-directed hinge retreat of the lower plate did set in (van Hinsbergen & Schmid 2012). Dinarides and northern

Schmid, Stefan

2014-05-01

399

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

NASA Technical Reports Server (NTRS)

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