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1

Downgoing plate controls on overriding plate deformation in subduction zones  

NASA Astrophysics Data System (ADS)

Although subduction zones are convergent margins, deformation in the upper plate can be extensional or compressional and tends to change through time, sometimes in repeated episodes of strong deformation, e.g, phases of back-arc extension. It is not well understood what factors control this upper plate deformation. We use the code Fluidity, which uses an adaptive mesh and a free-surface formulation, to model a two-plate subduction system in 2-D. The model includes a composite temperature- and stress-dependent rheology, and plates are decoupled by a weak layer, which allows for free trench motion. We investigate the evolution of the state of stress and topography of the overriding plate during the different phases of the subduction process: onset of subduction, free-fall sinking in the upper mantle and interaction of the slab with the transition zone, here represented by a viscosity contrast between upper and lower mantle. We focus on (i) how overriding plate deformation varies with subducting plate age; (ii) how spontaneous and episodic back-arc spreading develops for some subduction settings; (iii) the correlation between overriding plate deformation and slab interaction with the transition zone; (iv) whether these trends resemble observations on Earth.

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

2014-05-01

2

Role of the overriding plate in the subduction process: Insights from numerical models  

NASA Astrophysics Data System (ADS)

Active convergent margins are primarily shaped by the interplay among the subducting plate, overriding plate, and mantle. The effect of important forces, like far-field mantle flow, overriding plate motion, and inter-plate coupling, however, remains partially ambiguous. In a preliminary attempt to clarify their role, a self-consistent, viscoelastic, plane-strain, mechanical finite element model, in which subducting plate, overriding plate and mantle interact dynamically, is developed. In this quasi-static framework with a freely moving slab, trench, and inter-plate fault, the role of a compressive overriding plate on subduction zone kinematics, morphology and stress-state is characterized. A slab interacting solely with a semi-analytical three-dimensional mantle flow formulation shows that local non-induced mantle flow influences slab geometry and kinematics, adding an important dynamic term to the system. The impact of an overriding plate on this system is determined completely by overriding plate trench-ward motions and is only pertinent if the overriding plate actively advances the trench. A trench-ward moving overriding plate indents the slab and thereby enforces trench retreat and decreases slab dip. It also stimulates over-thrusting of the overriding plate onto the slab, and thereby permits mountain building within the overriding plate. Frictional resistance is observed to have a dominant local effect within the overriding plate as it is increasingly dragged down, thereby inhibiting the growth of overriding plate topography. A distinguishable effect on large-scale trench motions and deep slab dip is, however, absent for re-normalized friction coefficients ranging up to about 0.2. Minor additional effects include a decrease in plate motions of about 15% and slab bending stresses of about 10%.

van Dinther, Ylona; Morra, Gabriele; Funiciello, Francesca; Faccenna, Claudio

2010-03-01

3

Role of the Overriding Plate in the Subduction Process: Insights from Numerical Models  

NASA Astrophysics Data System (ADS)

Active convergent margins are primarily shaped by the interplay among the subducting plate, overriding plate, and mantle. The effect of important forces, like far-field mantle flow, overriding plate motion, and inter-plate coupling, however, remains partially ambiguous. In a preliminary attempt to clarify their role, a self-consistent, visco-elastic, plane-strain, mechanical finite element model, in which subducting plate, overriding plate and mantle interact dynamically, is developed. In this quasi-static framework with a freely moving slab, trench, and inter-plate fault, the role of a compressive overriding plate on subduction zone kinematics, morphology and stress-state is characterized. A slab interacting solely with a semi-analytical three-dimensional mantle flow formulation shows that local non-induced mantle flow influences slab geometry and kinematics, adding an important dynamic term to the system. The impact of an overriding plate on this system is determined completely by overriding plate trench-ward motions and is only pertinent if the overriding plate actively advances the trench. A trench-ward moving overriding plate indents the slab and thereby enforces trench retreat and decreases slab dip. It also stimulates over-thrusting of the overriding plate onto the slab, and thereby permits mountain building within the overriding plate. Frictional resistance is observed to have a dominant local effect within the overriding plate as it is increasingly dragged down, thereby inhibiting the growth of overriding plate topography. A distinguishable effect on large-scale trench motions and deep slab dip is, however, absent for renormalized friction coefficients ranging up to about 0.2. Minor additional effects include a decrease in plate motions of about 15% and slab bending stresses of about 10%.

Funiciello, F.; Dinther, Y. V.; Morra, G.; Faccenna, C.

2009-12-01

4

Dynamics of 3-D thermo-mechanical subduction with an overriding plate  

NASA Astrophysics Data System (ADS)

Characterizing the role of the upper plate in dynamic subduction models is of paramount importance in understanding the subduction system as a whole. We investigate the effect of the overriding plate on subduction dynamics in a 3D, purely dynamic thermo-mechanical setup of the finite element code, CitcomCU (Moresi & Gurnis, 1996; Zhong, 2006). The reference models are purely Newtonian with a temperature dependent viscosity. Subduction is initiated by an asymmetric notch in the down going plate, and the two plates are decoupled by a weak, 15 km thick crustal layer, along shear is localized. As observed in previous 2D modeling studies the presence of an overriding plate decreases the vertical extent of the poloidal flow, resulting in reduced vertical subduction velocity, reduced trench retreat and a larger dip angle. This increased dip angle results in preferential slab folding, as opposed to flattening, at the 660-km discontinuity when the overriding plate is included. It has recently been suggested that toroidal flow, due to slab rollback, creates trench-perpendicular gradients in basal traction below the overriding lithosphere which can cause back-arc extension (Schellart & Moresi, 2013; Duarte et al., 2013). In our models, we also observe long wavelength back-arc extensional stresses, and more localized forearc compressive stresses. As in Piromallo et al. (2010), we decompose the velocity field into toroidal and poloidal components, in order to attempt to quantify the relationship between toroidal flow and overriding plate stress state for various model set-ups. We focus on how the presence of an overriding plate, and variable upper plate widths and strengths, modifies the partition between toroidal and poloidal flow, as well as overriding plate stress state and subducting plate dynamics (i.e. trench plate and penetration velocities). The presence of an overriding plate reduces the toroidal flow component of the velocity field and so significantly reduces the rate at which trench curvature, previously shown to occur in due to toroidal flow in 3D single plate models (e.g. Stegman et al., 2006), develops. Thus, dynamic modeling studies that neglect the presence of the overriding plate may be significantly overestimating the effect of toroidal flow on trench curvature. Finally, we examine how the presence of a piece of compositionally buoyant lithosphere, both in the subducting and overriding plates, modifies the dynamics of the subducting slab and the stress state of the overriding plate.

Holt, A.; Becker, T. W.

2013-12-01

5

Tibetan plate overriding the Asian plate in central and northern Tibet  

NASA Astrophysics Data System (ADS)

Seismological imaging has identified the Indian lithosphere penetrating underneath Tibet up to 500km to the north and to a depth of at least 200km along a front that is more than 1000km long. This is a classical case of continental subduction. In contrast, the collision of Tibet with the stable Tarim Basin in the north-west caused thickening of the Tibetan lithosphere to about 200km, whereas collision with the Sichuan Basin in the east caused thinning of the Tibetan lithosphere to about 70km. No sufficient seismic data on the mantle lithosphere have been available up to now at the boundary of Tibet to the Qaidam Basin, where subduction of the Asian lithosphere beneath Tibet was suggested. We report on results from a recent seismic passive source experiment in this region, which continued the series of INDEPTH experiments to the Qaidam Basin in the north-east. We used the S receiver function technique for data analysis, which is especially sensitive for observations of the lithosphere-asthenosphere boundary (LAB). As a surprising result, we found evidence that a newly identified relatively thin Tibetan lithosphere is overriding the flat subducting Asian lithosphere.

Kind, R.; Zhao, W.; Kumar, P.; Mechie, J.; Karplus, M.; Tilmann, F. J.

2011-12-01

6

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

7

The Continental Plates are Getting Thicker.  

ERIC Educational Resources Information Center

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

Kerr, Richard A.

1986-01-01

8

Seismicity and state of stress within the overriding plate of the Tonga-Kermadec subduction zone  

NASA Astrophysics Data System (ADS)

To reassess the main tectonic units and to quantify the slip partitioning within the overriding plate of the Tonga-Kermadec subduction zone, a seismotectonic study was performed using global seismicity and focal mechanisms catalogs. (1) New tectonic features were identified within the Lau Basin and the volcanic arc by remarkable shallow hypocenters alignments. (2) The Centroid Moment Tensor solutions catalog was processed in order to map the stress tensor variation in the upper plate. We found the tectonic features characterized by a diffuse seismicity are subjected to a composite stress regime and they are interpreted as diffuse immature plate boundaries controlled by the high thermal anomaly lying beneath the Lau Basin. (3) We quantified the margin-parallel rates of motion using the azimuth of the maximum compressive stress component computed within the interplate zone. The results highlight a major tectono-kinematic segmentation related to the subduction of the Louisville Seamount Chain.

Bonnardot, M.-A.; RéGnier, M.; Ruellan, E.; Christova, C.; Tric, E.

2007-10-01

9

Plate Tectonics and Continental Drift: Classroom Ideas.  

ERIC Educational Resources Information Center

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

Stout, Prentice K.

1983-01-01

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

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

12

Effect of aseismic ridge subduction on slab geometry and overriding plate deformation: Insights from analogue modeling  

E-print Network

Tectonics, Dipartamento di Scienze Geologiche, Università degli studi Roma TRE, Roma, Italy Abstract: We since the beginnings of plate tectonics theory (e.g., Vogt, 1973; Vogt et al., 1976; Cross and Pilger,version1-16Mar2013 Author manuscript, published in "Tectonophysics 588 (2013) 39-55" DOI : 10.1016/j

Paris-Sud XI, Université de

13

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

14

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

15

Fault reactivation within Avalonia: plate margin to continental interior deformation  

NASA Astrophysics Data System (ADS)

Lithotectonic terranes commonly have faults with movement histories that reflect their original tectonic setting and their subsequent re-activation during terrane accretion and post-accretionary dispersal. Since later movements tend to overprint evidence of earlier motions, documenting fault reactivation can be a difficult task. Avalonia, the largest terrane within the Canadian Appalachians preserves evidence for repeated episodes of movement along NE-trending fault zones in a variety of tectonic settings between the late Neoproterozoic and late Paleozoic. Evidence of Neoproterozoic motion is preserved in pre-final crystallization deformation fabrics in arc-related igneous complexes which intrude shear zones. These record strike-slip motion related to oblique subduction along the continental margin of Gondwana. In the Paleozoic, Avalonia migrated from its original peri-Gondwanan setting. Mid-Ordovician to earliest Silurian deformation and magmatism is attributed to the sinistral accretion of Avalonia to Laurentia. This reactivated Neoproterozoic shear zones and resulted in basin inversion in mainland Nova Scotia and the formation of mylonites and injection of dikes into brittle fractures in southern New Brunswick. Sinistral motion was accompanied by terrane dispersal and was followed in the Late Silurian and Early Devonian by further reactivation in the form of dextral strike-slip that reflects convergence between Laurentia and Gondwana. Following the accretion and dispersal of Avalonia, the fault zones became stranded within the continental interior. Subsequently, the fault zones accommodated local stresses which were far-field responses to collisional tectonics associated with the mid-Late Devonian Acadian and the Late Carboniferous Alleghanian orogenies. Hence, the generation of these fault systems along plate margins in the late Neoproterozoic and early Paleozoic profoundly influenced the tectonic evolution of late Paleozoic intra-continental deformation. Late Carboniferous deformation is recorded in (a) the mylonitic and cataclastic fabrics of the shear zones themselves, (b) the orientations of spatially related fold structures, (c) local controls on basin formation and sedimentary facies and (d) offsets in stratigraphy. This motion was predominantly dextral and records continued convergence between Laurentia and Gondwana during the amalgamation of Pangea.

Murphy, J. Brendan; Keppie, J. Duncan; Nance, R. Damian

1999-05-01

16

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

17

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

18

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

19

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

20

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

21

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

22

Continental Margin Tectonics Along the Convergent Plate Boundary of Central Chile  

NASA Astrophysics Data System (ADS)

Multibeam bathymetry along central Chile provides a detailed map of recent tectonic deformation of the margin and incoming oceanic plate from about 28? S to 36? S. The data were collected during R/V SONNE cruises 101, 102, 104 and 161 and a cruise with R/V Vidal Gormaz. Individual pings were edited and cleaned and the different surveys have been merged after depth calculations using a different measured velocity function for each of them. The oceanic Nazca plate is covered by about 100 m of pelagic sediment and the morphology of the igneous basement is displayed well in the bathymetric maps. The oceanic plate topography changes markedly along the subduction zone and exerts a first order control in the distribution of trench sediment infill and in the tectonic style of deformation of the margin. A major boundary occurs at latitude 32?-33? S where the hotspot volcanic chain of Juan Fernadez is currently subducting. The chain subducts oblique to the margin strike and thus the tectonic boundary has been migrating along the subduction zone through time. South of the area of ridge subduction the trench is filled with turbidites and a 20-40 km wide accretionary prism occurs at the front of the continental slope. The upper slope has a smooth morphology indicative of a quiet tectonic domain. At the current area of ridge subduction and north of it (28?-33?S) the trench has a reduced turbiditic infill. The trench infill seems to be at minimum at 31-32S and slightly larger to the north as the trench axis becomes deeper. Here, a small ridge at the slope toe may indicate that reduced accretion is active. The continental slope is deeper and more rugged that to the south displaying a series of small midslope basins. Here, the continental slope morphotectonic structure is the product of tectonic erosion due to the passage of the volcanic ridge.

Weinrebe, W.; Ranero, C. R.; Diaz, J.; Reichert, C.; Vera, E. E.

2003-12-01

23

Dike-induced contraction along oceanic and continental divergent plate boundaries  

NASA Astrophysics Data System (ADS)

axis of divergent plate boundaries shows extension fractures and normal faults at the surface. Here we present evidence of contraction along the axis of the oceanic ridge of Iceland and the continental Main Ethiopian Rift. Contraction is found at the base of the tilted hanging wall of dilational normal faults, balancing part of their extension. Our experiments suggest that these structures result from dike emplacement. Multiple dike injection induces subsidence above and uplift to the sides of the dikes; the transition in between is accommodated by reverse faults and subsequent peripheral inward dipping normal faults. Our results suggest that contraction is a direct product of magma emplacement along divergent plate boundaries, at various scales, marking a precise evolutionary stage and initiating part of the extensional structures (extension fractures and normal faults).

Trippanera, D.; Acocella, V.; Ruch, J.

2014-10-01

24

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

25

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

26

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

27

Eocene to Quaternary mafic-intermediate volcanism in San Luis Potosí, central Mexico: The transition from Farallon plate subduction to intra-plate continental magmatism  

NASA Astrophysics Data System (ADS)

The San Luis Potosí Volcanic Field (SLPVF) of central Mexico includes volcanic sequences of felsic, intermediate and basic compositions that were erupted as discrete episodes from the Eocene to the Pleistocene. Volcanism was dominated by widespread and voluminous rhyolitic ignimbrites of the mid-Tertiary Ignimbrite Flare-up. However, the complete volcanic history must consider basaltic and andesitic Eocene-Pleistocene volcanic successions that provide key evidence for understanding the geochemical evolution of the volcanism in the SLPVF during this time span. Five sequences are recognized according to their geochemical characteristics, each comprising a volcano-tectonic episode. The first episode comprises basaltic andesites and andesites erupted during three intervals, 45-42 Ma, 36-31 Ma, and 31-30 Ma. The oldest was derived from subduction magmatism, whereas the youngest has an intra-plate magmatic signature and this represents the transition from the end of a long lasting subduction regime of the Farallon plate to the initiation of intra-plate continental extension in the North American plate. The second episode, at 29.5-28 Ma, comprises a bimodal succession of high-silica rhyolites and alkaline basalts (hawaiites) that are interpreted as magmatism generated in an intra-plate continental extension regime during the Basin and Range faulting. The third episode, at 21 Ma, is characterized by trachybasalts and trachyandesites that represent mantle basaltic melts that were contaminated through assimilation of the lower crust during advanced stage of intra-plate extension that started at Oligocene. The fourth episode includes 12 Ma alkaline basalts and andesites that were erupted from fissures. These mantle derived magmas evolved to andesites by crustal anatexis and crystal fractionation within a continued, extensional, intra-plate regime. Lastly, the fifth episode comprises 5.0 to 0.6 Ma alkaline basalts (basanites) containing mantle xenoliths, that were erupted from maars and tuff cones, which are the youngest manifestations of mantle-derived intra-plate extensional events. Based upon this volcanic record, the last subduction manifestations of the extinct Farallon plate occurred at about 42 Ma, this was followed by a transition to intra-plate magmatism between 42 and 31 Ma, and an extensional, intra-plate tectonic setting from 31 Ma to almost Present.

Aguillón-Robles, Alfredo; Tristán-González, Margarito; de Jesús Aguirre-Díaz, Gerardo; López-Doncel, Rubén A.; Bellon, Hervé; Martínez-Esparza, Gilberto

2014-04-01

28

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

NASA Technical Reports Server (NTRS)

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

Baltuck, M.; Dixon, T. H.

1984-01-01

29

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

30

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)

variation and asynchronous onset of collision during the convergence of continents can significantly affect the burial and exhumation of subducted continental crust. Here we use 3-D numerical models for continental collision to discuss how deep burial and exhumation of high and ultrahigh pressure metamorphic (HP/UHP) rocks are enhanced by diachronous collision and the resulting rotation of the colliding plates. Rotation during collision locally favors eduction, the inversion of the subduction, and may explain 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 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 an explanation for this distribution. We explore this hypothesis by comparing orthogonal and diachronous collision models and conclude that a diachronous collision can transport continental material up to 60 km deeper, and heat material up to 300°C hotter, than an orthogonal collision. Our diachronous collision model predicts that subducted continental margin material returns to the surface only in the region where collision initiated. The diachronous collision model is consistent with petrological and geochonological observations from the WGC 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 with respect to Laurentia, consistent with paleomagnetic data from other studies. Our model may have applications to other 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, A. D.; van Hunen, J.; Cuthbert, S. J.; Brueckner, H. K.; Allen, M. B.

2014-05-01

31

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

32

Estimates of Continental Plate Motions Derived From Continuous GPS Measurements of Station Coordinates and Velocities, 1996-2004  

NASA Astrophysics Data System (ADS)

Analysis Centres of the International GPS Service (IGS) currently compute daily Earth Rotation Parameters (ERPs) and weekly precise coordinates for over 200 globally distributed tracking stations. These estimates are made available to the scientific community in the Solution Independent Exchange (SINEX) format, developed for exchange and analysis of position estimates from techniques such as SLR, LLR, VLBI, DORIS and GPS. On behalf of the IGS, National Resources Canada (NRCan) has been combining, officially since 1999, all weekly SINEX files from the ACs to form weekly and cumulative solutions. The weekly solution (named igsyyPwwww, yy = 2-digit year, wwww = 4-digit GPS week) contains estimates of station coordinates, ERPs and geocentre pertaining to the GPS week, and the cumulative solution (named IGSyyPWW, WW = 2-digit week number, 01 to 52, within the year) comprises station coordinates and velocities in a common reference epoch, Jan. 1, 1998. For example, two solutions produced for week 1253 (2nd week of year 2004) were igs04P1253 (weekly) and IGS04P02 (cumulative). Since week 1253, all IGS solutions have been aligned to IGb00, a realization of IGS's most recent International Terrestrial Reference Frame, ITRF2000. IGb00 was obtained from coordinates and velocities of 99 globally distributed reference stations by alignment to ITRF2000 at GPS week 1231 of cumulative solution IGS03P33. Before week 1143, a realization of IGS's previous reference frame, ITRF97, was used instead. Using the cumulative solution from any given week, the rotation components of any continental plate with at least two stations are estimated and compared with published results. These include three known plate models: NNR NUVEL 1, NNR NUVEL 1A and the most recent REVEL 2000 aligned to ITRF97. The findings can be summarized as follows: Continental rotations derived from IGS04P02 are shown to be significantly different at 99% confidence level from NNR NUVEL 1A's estimates for North American, Eurasian, Australian, Pacific, Antarctic, Indian, Nazca and Nubian (the latter compared to NNR NUVEL 1A African) plates. In addition, certain plates previously regarded as belonging to an adjacent, larger continent in NNR NUVEL 1 or 1A are now seen to move significantly differently; e.g., Amurian distinct from Eurasian, Adriatic and Sinai distinct from NNR NUVEL 1A African. North American, Eurasian, Australian and Pacific plates show significantly different rotations in IGS04P02 than predicted by REVEL 2000, yet not from the alignment of REVEL 2000 to IGb00. Certain pairs of adjacent plates show relative Euler poles near their plate boundaries; e.g., Eurasian and North American, Amurian and Eurasian, Amurian and South-China, Adriatic and Eurasian, Arabian and Nubian, Sinai and Nubian, Sinai and Arabian, Nubian and Somali. This phenomenon can be expected when bordering plates show no subduction or obduction. RMS difference between velocities of stations used in Euler pole calculation in IGS04P02 and those expected from NNR NUVEL 1A rise to 4.3 mm/yr in the horizontal component and 8.7 mm/yr in the vertical. The horizontal RMS velocity difference decreases significantly to 2.4 mm/yr when IGS04P02 is compared with REVEL 2000.

Hutchison, D. A.

2004-05-01

33

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

34

The ancient continental margins of the North American and South American plates and regularities in the occurrence of oil and gas accumulations in them  

NASA Astrophysics Data System (ADS)

Various stages of the development of sedimentary basins along the ancient margins of the North American and South American plates are considered. It is shown that the potential of the oil-and-gas bearing is related to a certain stage of evolution of the basins. For the margins of the North American plate, it is the first stage of development in the structure of the ancient Paleozoic continental margins that developed under passive tectonic conditions. For the basins along the ancient margins of the South American plate, it is the second stage, which is the stage of the formation and development of foredeeps overlaid on the earlier structures. An interesting regularity is displayed: than younger the folding-mountain structures that originated in the distal parts of the continental margins, than greater the age range of source rocks in the sedimentary basins preserved there.

Zabanbark, A.; Lobkovskii, L. I.

2012-02-01

35

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

36

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

37

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

38

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

39

GPS constraints on continental deformation in the Africa-Arabia-Eurasia continental collision zone and implications for the dynamics of plate interactions  

Microsoft Academic Search

The GPS-derived velocity field (1988-2005) for the zone of interaction of the Arabian, African (Nubian, Somalian), and Eurasian plates indicates counterclockwise rotation of a broad area of the Earth's surface including the Arabian plate, adjacent parts of the Zagros and central Iran, Turkey, and the Aegean\\/Peloponnesus relative to Eurasia at rates in the range of 20-30 mm\\/yr. This relatively rapid

Robert Reilinger; Simon McClusky; Philippe Vernant; Shawn Lawrence; Semih Ergintav; Rahsan Cakmak; Haluk Ozener; Fakhraddin Kadirov; Ibrahim Guliev; Ruben Stepanyan; Merab Nadariya; Galaktion Hahubia; Salah Mahmoud; K. Sakr; Abdullah ArRajehi; Demitris Paradissis; A. Al-Aydrus; Mikhail Prilepin; Tamara Guseva; Emre Evren; Andriy Dmitrotsa; S. V. Filikov; Francisco Gomez; Riad Al-Ghazzi; Gebran Karam

2006-01-01

40

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

41

Tectonic isolation of the Levant basin offshore Galilee-Lebanon effects of the Dead Sea fault plate boundary on the Levant continental margin, eastern Mediterranean  

NASA Astrophysics Data System (ADS)

The continental margin of the central Levant, offshore northern Israel and southern Lebanon is characterized by a sharp continental-oceanic crustal transition, exhibited on the bathymetry as a steep continental slope. At the base of the slope a narrow zone of faulting deforms the upper Messinian-recent sedimentary sequence. Further into the basin no major deformations are observed. However, onland a restraining bend along the Dead Sea fault plate boundary results in the formation of the Lebanon and anti-Lebanon mountain ranges, which exhibit a large positive isostatic anomaly not compensated at depth. All these geologic features follow a NNE-SSW trend. A dense network of multi-channel and single-channel seismic profiles, covering 5000 km of ship-track offshore northern Israel and southern Lebanon, was analyzed for the purpose of characterizing the continental margin. Additional seismic surveys covering the area between the Levant margin and the Cyprean arc were examined. Data were then incorporated with magnetic, gravity and earthquake measurements to reveal the deep crustal structure of the area and integrated with bathymetry data to describe the behavior of the young sedimentary basin fill. Results indicate that the Levant basin, offshore northern Israel and southern Lebanon (up to Beirut) is more-or-less unaffected by the intense tectonic deformation occurring onland. The transition between the deformed area onland and the undeformed Levant basin occurs along the base of the continental slope. Along the base, the upper Messinian-recent sedimentary sequence is cut by two sets of faults: shallow growth faults resulting from salt tectonics and high angle faults, marking the surface expression of a deeper crustal discontinuity - the marine extension of the Carmel fault zone. The central Levant continental margin is being reactivated by transpressional faulting of the marine continuation of the Carmel fault, at the base of the continental slope. This fault system coincides with the sharp continental-oceanic crustal transition, and acts as an isolator between the Levant basin and its land counterpart. To the north, this feature may initiate the formation of a new triple junction, with the Latakia ridge (part of the eastern Cyprean arc) and the East Anatolian fault.

Schattner, U.; Ben-Avraham, Z.; Lazar, M.; Hüebscher, C.

2006-11-01

42

16 Years, 16 Cruises, 1.6 Billion Soundings: a Compilation of High-Resolution Multibeam Bathymetry of the Active Plate Boundary Along the Chilean Continental Margin  

NASA Astrophysics Data System (ADS)

Chile, a country stranding the active plate boundary between the South-American and the Nazca Plate is afflicted by recurrent earthquakes and hazardous volcanic eruptions. The strongest earthquake ever recorded occurred here, and volcanic hazards are frequent. Consequently, this area has been studied by geoscientists for many years to improve the understanding of subduction zone processes. Swath bathymetry mapping of the ocean floor has proven to bear a large potential for the interpretation of subduction-related processes, such as tectonic deformation of the marine forearc, release and migration of fluids as well as earthquake-triggered mass wasting. Multibeam bathymetry data of 16 major cruises of German, British, and Chilean research vessels recorded between 1995 and December 2010, in total more than 10,000 data files comprising about 1.6 billion soundings, have now been carefully reprocessed, compiled and merged into a unifying set of high-resolution bathymetric maps of the Chilean continental margin from latitude 40°S to 20°S. The imprint of subsurface processes on the surface morphology is well displayed in the case of the Chilean continental margin. The 3,500 km long Chilean convergent margin is not uniform, as various segments with different tectonic characteristics can be distinguished. Major factors that control margin morphology and thus the style of subduction are (1) relief and structure of the incoming oceanic plate, (2) supply of trench sediment, (3) turbidite transport within the trench, and (4) the input of terrigeneous sediments down the continental slope. A major segment boundary occurs at latitude 32°-33° S where the hotspot-related volcanic chain of Juan Fernandez is presently subducting. South of the area of ridge subduction the trench is filled with turbidites, and accretionary ridges develop across the base of the slope along most of the segment, whereas north of this boundary the turbiditic infill is reduced and subduction erosion is prevailing.

Weinrebe, W.; Flueh, E. R.; Hasert, M.; Behrmann, J. H.; Voelker, D.; Geersen, J.; Ranero, C. R.; Diaz-Naveas, J. L.

2011-12-01

43

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

44

Fluid seepage at the continental margin offshore Costa Rica and southern Nicaragua  

NASA Astrophysics Data System (ADS)

A systematic search for methane-rich fluid seeps at the seafloor was conducted at the Pacific continental margin offshore southern Nicaragua and northern central Costa Rica, a convergent margin characterized by subduction erosion. More than 100 fluid seeps were discovered using a combination of multibeam bathymetry, side-scan sonar imagery, TV-sled observations, and sampling. This corresponds, on average, to a seep site every 4 km along the continental slope. In the northwestern part of the study area, subduction of oceanic crust formed at the East Pacific Rise is characterized by pervasive bending-induced faulting of the oceanic plate and a relatively uniform morphology of the overriding continental margin. Seepage at this part of the margin typically occurs at approximately cone-shaped mounds 50 - 100 m high and up to 1 km wide at the base. Over 60 such mounds were identified on the 240 km long margin segment. Some normal faults also host localized seepage. In contrast, in the southeast, the 220 km long margin segment overriding the oceanic crust formed at the Cocos-Nazca Spreading Centre has a comparatively more irregular morphology caused mainly by the subduction of ridges and seamounts sitting on the oceanic plate. Over 40 seeps were located on this part of the margin. This margin segment with irregular morphology exhibits diverse seep structures. Seeps are related to landslide scars, seamount-subduction related fractures, mounds, and faults. Several backscatter anomalies in side-scan images are without apparent relief and are probably related to carbonate precipitation. Detected fluid seeps are not evenly distributed across the margin but occur in a roughly margin parallel band centered 28 ± 7 km landward of the trench. This distribution suggests that seeps are possibly fed to fluids rising from the plate boundary along deep-penetrating faults through the upper plate.

Sahling, Heiko; Masson, Douglas G.; Ranero, CéSar R.; Hühnerbach, Veit; Weinrebe, Wilhelm; Klaucke, Ingo; Bürk, Dietmar; Brückmann, Warner; Suess, Erwin

2008-05-01

45

An elastic plate model for interseismic deformation in subduction Ravi V. S. Kanda1  

E-print Network

the subducting and overriding plates, as well as zero net steady state vertical offset between the two plates, 1983]. The BSM accomplishes this zero net strain in the overriding plate by parameterizing interseismic case of zero plate thickness, thereby providing an alternative motivation for the BSM. The ESPM also

46

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

47

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

USGS Publications Warehouse

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

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

1993-01-01

48

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

49

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

NASA Astrophysics Data System (ADS)

Our knowledge of the origin and evolution of the continental lithospheric mantle (CLM) remains fragmentary and partly controversial in spite of recent advances in petrologic, geochemical and geophysical studies of the deep Earth and experimental work. Debate continues on a number of essential topics, like relative contributions of partial melting, metasomatism and ‘re-fertilisation' as well as the timing, conditions and tectonic settings of those processes. These topics can be addressed by studies of ultramafic xenoliths in volcanic rocks which arguably provide the least altered samples of modern and ancient CLM. The subcontinental lithosphere is thought to be a mantle region from which melts have been extracted, thus making the lithosphere more refractory. Melting degrees can be estimated from Al contents while the depth of melt extraction can be assessed from Al-Fe (Mg#) relations in unmetasomatized melting residues in comparison with experimental data, e.g. [1]. High silica and opx in the residues may indicate melting in water-rich conditions. High-precision Mg# and Mn for olivine may constrain degrees and conditions of partial melting and/or metasomatism, tectonic settings, modal compositions (e.g. presence of garnet) and equilibration conditions of mantle peridotites [2]. These estimates require both adequate sampling and high-quality major element and modal data; sampling and analytical uncertainties in published work may contribute substantially to chemical heterogeneities (and different origins) inferred for CLM domains [3]. Very fertile peridotite xenolith suites are rare worldwide [3]. They were initially viewed as representing mantle domains that experienced only very small degrees of melt extraction but are attributed by some workers to ‘refertilization' of refractory mantle by percolating asthenospheric melts. Such alternative mechanisms might be valid for some rare hybrid and Fe-enriched peridotites but they fail to comprehensively explain modal, major and trace element and isotope compositions of fertile lherzolites and thus cannot provide viable alternatives to the concept of melt extraction from pristine mantle as the major mechanism of CLM formation. Published data on xenoliths from andesitic volcanoes and on supra-subduction oceanic peridotites [4] show that the most common rocks in mantle wedge lithosphere are highly refractory harzburgites characterized by a combination of variable but generally high modal opx (18-30%) with very low modal cpx (1.5-3%). At a given olivine (or MgO) content, they have higher opx and silica, and lower cpx, Al and Ca contents than normal refractory peridotite xenoliths in continental basalts; the Mg-Si and Al-Si trends in those rocks resemble those in cratonic peridotites. These features may indicate either fluid fluxing during melting in the mantle wedge or selective post-melting metasomatic enrichments in silica to transform some olivine to opx. High oxygen fugacities and radiogenic Os-isotope compositions in those rocks may be related to enrichments by slab-derived fluids, but these features are not always coupled with trace element enrichments or patterns commonly attributed to "subduction zone metasomatism" deduced from studies of arc volcanic rocks and experiments. The valuable insights provided by experimental work and xenolith case studies are difficult to apply to many natural peridotite series because late-stage processes commonly overlap the evidence for initial melting. References: [1] Herzberg C., J. Petrol. 45: 2507 (2004). [2] Ionov D. & Sobolev A., GCA 72 (S1): A410 (2008). [3] Ionov D., Contrib. Miner. Petrol. (2007) [4] Ionov D., J. Petrol. doi: 10.1093/petrology/egp090 (2010)

Ionov, Dmitri

2010-05-01

50

Tectonic isolation of the Levant basin offshore Galilee-Lebanon – effects of the Dead Sea fault plate boundary on the Levant continental margin, eastern Mediterranean  

Microsoft Academic Search

The continental margin of the central Levant, offshore northern Israel and southern Lebanon is characterized by a sharp continental-oceanic crustal transition, exhibited on the bathymetry as a steep continental slope. At the base of the slope a narrow zone of faulting deforms the upper Messinian-recent sedimentary sequence. Further into the basin no major deformations are observed. However, onland a restraining

U. Schattner; Z. Ben-Avraham; M. Lazar; C. Hüebscher

2006-01-01

51

25 CFR 213.38 - Assignments and overriding royalties.  

...BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF RESTRICTED LANDS OF MEMBERS OF FIVE CIVILIZED TRIBES, OKLAHOMA, FOR MINING Operations § 213.38 Assignments and overriding royalties. (a)...

2014-04-01

52

25 CFR 213.38 - Assignments and overriding royalties.  

Code of Federal Regulations, 2013 CFR

...BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF RESTRICTED LANDS OF MEMBERS OF FIVE CIVILIZED TRIBES, OKLAHOMA, FOR MINING Operations § 213.38 Assignments and overriding royalties. (a)...

2013-04-01

53

25 CFR 213.38 - Assignments and overriding royalties.  

Code of Federal Regulations, 2012 CFR

...BUREAU OF INDIAN AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF RESTRICTED LANDS OF MEMBERS OF FIVE CIVILIZED TRIBES, OKLAHOMA, FOR MINING Operations § 213.38 Assignments and overriding royalties. (a)...

2012-04-01

54

25 CFR 227.26 - Assignments and overriding royalties.  

Code of Federal Regulations, 2013 CFR

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

2013-04-01

55

25 CFR 227.26 - Assignments and overriding royalties.  

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

2014-04-01

56

25 CFR 227.26 - Assignments and overriding royalties.  

Code of Federal Regulations, 2012 CFR

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

2012-04-01

57

25 CFR 227.26 - Assignments and overriding royalties.  

Code of Federal Regulations, 2011 CFR

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

2011-04-01

58

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

59

25 CFR 213.38 - Assignments and overriding royalties.  

Code of Federal Regulations, 2011 CFR

...AFFAIRS, DEPARTMENT OF THE INTERIOR ENERGY AND MINERALS LEASING OF RESTRICTED LANDS OF MEMBERS OF FIVE CIVILIZED TRIBES, OKLAHOMA, FOR MINING Operations § 213.38 Assignments and overriding royalties. (a) Leases or any interest...

2011-04-01

60

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.

61

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

ERIC Educational Resources Information Center

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

Glenn, William H.

1977-01-01

62

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

63

Primordial Ooze and Continental Drift  

NSDL National Science Digital Library

In this lesson, students will learn that continental plates drift and this affects the layers of the earth. Following a directed reading and discussion, they will perform an experiment in which they use chocolate frosting and graham crackers to simulate tectonic plates sliding about on the mantle.

64

Major Ocean Features: Continental Margin  

E-print Network

.noaa.gov 42 Continental margins may be geologically active or passive. Active margins occur along tectonic plate boundaries where earthquakes and/or volcanoes are common. Passive margins are not associated with plate boundaries, experiencing little volcanism and relatively fewer earthquakes. The Atlantic Ocean

65

oZONE Faculty and Staff Course Overrides  

E-print Network

Classes page, click the Back button on your browser to go back to the Look Up Classes page, and then click, click the Back button on your browser to go back to the Look Up Classes page, and then click on the CRN with a College Restriction override. Registration Add Errors display one at a time as the student resolve

Oklahoma, University of

66

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

NASA Astrophysics Data System (ADS)

In active subduction zones, when the converging plates cannot slip freely past each other, "plate coupling" occurs. The moving subducting slab and therefore the coupling/decoupling relationship between plates control both short- and long-term deformation of the upper plate. Short-term deformation is dominantly elastic, occurs at human timescales and can be directly associated with earthquakes. Long-term deformation is cumulative, permanent and prevails at the geological timescale (Hoffman-Rothe et al., 2006, Springer Berlin Heidelberg). Here we used 3D numerical simulations to test oblique subduction zones and to investigate: 1) how long-term deformation and coupling relationship vary along the trench-axis; 2) how this relationship influences erosion and down-drag of upper plate material. Our models are based on thermo-mechanical equations solved with finite differences method and marker-in-cell techniques combined with a multigrid approach (Gerya, 2010, Cambridge Univ. Press). The reference model simulates an intraoceanic subduction close to the continental margin (Malatesta et al., 2013, Nature Communications, 4:2456 DOI:10.1038/ncomms3456). The oceanic crust is layered with a 5-km-thick layer of gabbro overlain by a 3-km-thick layer of basalt. The ocean floor is covered by 1-km-thick sediments. Plates move with a total velocity of 3.15 cm/yr; the oblique convergence is obtained using velocity vectors that form an angle of 45° with the initial starting point of subduction (weak zone in the lithosphere). After initiation of plate convergence, part of sediments on top of the incoming plate enters the subduction zone and is buried; another part is suddenly transferred along strike at shallow depths and along the subducting slab according to the direction of the along-trench velocity component of subduction. The lateral migration of sediment causes the evolution of the trench along its strike from sediment-poor to sediment-rich. As soon as subduction starts, where the sedimentary infill of the trench is almost nonexistent, short-term shallow coupling occurs and friction between the frontal sector of the overriding plate and the downgoing plate triggers upper-plate bending. In this sector, after the early short-term coupling, the overriding plate is hereafter decoupled from the subducting slab. Moving along trench-strike, where sediments amount increases, the upper plate couples with the subducting plate and is dragged coherently downwards. If a large amount of sediments is stored in the trench the overriding plate is scraped off and incorporated as fragments along the plate interface. Our results suggest that a) one main parameter controlling coupling at convergent plate margins is the occurrence and the amount of sediment at the trench; b) the upper plate margin is dragged to depth or destroyed only where sediments thickness at the trench is large enough to promote interplate coupling, suggesting that a variation of sediment amount along the trench-axis influences the amount and style of transport of upper-plate material in the mantle.

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

2014-05-01

67

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

68

Oceanic-ridge subduction vs. slab break off: Plate tectonic evolution along the Baja California Sur continental margin since 15 Ma  

Microsoft Academic Search

The interaction of the Pacific-Farallon spreading centers with the North American convergent margin off Baja California, Mexico, supposedly ceased at 12 Ma, when plate convergence and seafloor spreading stopped. We propose a new geodynamic evolution based on full bathymetry coverage and magnetic profiles from 23°N to 27°N (Famex cruise of the R\\/V L'Atalante, April 2002). The data unveil a major

F. Michaud; J. Y. Royer; J. Bourgois; J. Dyment; T. Calmus; W. Bandy; M. Sosson; C. Mortera-Gutiérrez; B. Sichler; M. Rebolledo-Viera; B. Pontoise

2006-01-01

69

Internet Geography: Plate Tectonics  

NSDL National Science Digital Library

This site is part of GeoNet Internet Geography, a resource for pre-collegiate British geography students and their instructors. This page focuses on the structure of the Earth and the theory of plate tectonics, including continental drift, plate boundaries, the Ring of Fire, and mountains.

70

2-Aminopurine overrides multiple cell cycle checkpoints in BHK cells.  

PubMed Central

BHK cells blocked at any of several points in the cell cycle override their drug-induced arrest and proceed in the cycle when exposed concurrently to the protein kinase inhibitor 2-aminopurine (2-AP). For cells arrested at various points in interphase, 2-AP-induced cell cycle progression is made evident by arrival of the drug-treated cell population in mitosis. Cells that have escaped from mimosine G1 arrest, from hydroxyurea or aphidicolin S-phase arrest, or from VM-26-induced G2 arrest subsequently have all the hallmarks of mitosis--such as a mitotic microtubule array, nuclear envelope breakdown, and chromatin condensation. In a synchronous population, the time course of arrival in mitosis and its duration in 2-AP-treated cells that have escaped drug-induced cell cycle blocks is indistinguishable from control cells. Cells arrested in mitosis by nocodazole or taxol quickly escape mitotic arrest and enter interphase when exposed to 2-AP. 2-AP by itself does not influence the timing of cell cycle progression. We conclude that 2-AP acts to override checkpoints in every phase of the cell cycle, perhaps by inhibiting a protein kinase responsible for control of multiple cell cycle checkpoints. Images PMID:1549593

Andreassen, P R; Margolis, R L

1992-01-01

71

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.

72

Plate Tectonics: A Paradigm under Threat.  

ERIC Educational Resources Information Center

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

Pratt, David

2000-01-01

73

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.

74

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

75

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

76

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 ...

77

Earthquakes, Plate Boundaries, and Depth Indiana Standard Indicators  

E-print Network

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

Polly, David

78

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

79

Tectono-stratigraphic evolution of the continental Miocene basins in southern Anatolia  

NASA Astrophysics Data System (ADS)

The exposed portion of the Tauride fold-thrust belt in southern Turkey is flanked and overlain by Neogene sedimentary basins. To the south and on top of the high ranges, these basins are mainly marine, whereas previously poorly studied intra-montane basins dominated by continental deposits are exposed to the north. We have studied the stratigraphy and structure of these continental basins - the Alt?napa, Yalvaç and Ilg?n Basins. Their stratigraphy displays overall fining upward sequences of fluvio-lacustrine sediments, deposition of which interrupted by basin-wide unconformities; similar hiatuses seems to exist in each basin. The most prominent unconformity surface occurred during the Middle Miocene and corresponds to the timing of volcanic activity in the region. 40Ar/39Ar dating of the volcaniclastic samples from the Alt?napa and Ilg?n basins yielded 11.8-11.6 Ma ages. The main basin forming regional deformation phase was extensional and occurred during the Middle Miocene. The extension directions obtained from paleostress inversion techniques indicate multidirectional extension under vertical uniaxial stress which are compatible with the recent seismic activity and available focal mechanism solutions. The main basin-bounding faults, however, are constrained mainly N-S to NW-SE implying that they are reactivated structures. The Middle Miocene and onwards extensional history of these basins occurs behind and atop a thrust front along the Cyprus arc, extending towards the Antalya nappes and Aksu thrust in the heart of the Isparta angle. The synchrounous, curved pairs of thrust fronts associated with subduction and overriding plate extension suggests that the Cyprus subduction zone has been retreating relative to central Anatolia since, at least, the Middle Miocene time. In addition to extensional history of the region, these continental basins contain evidence for the post-Late Miocene differential uplift of the Taurides in southern Anatolia. All of these continental basins were above sea level during the Middle and Late Miocene and are now found at an elevation of 1 km. On the other hand, the upper Miocene marine deposits just south of the study area currently are at an elevation of ~2 km, and have therefore been uplifted at least 1 km more than the continental basins to the north. We conclude that the current high elevation of the Taurides is synchronous with, and at least in part related to late Neogene extension and vertical differential uplift, likely related to the dynamics of the Cyprian subduction zone.

Koç, Ayten; Kaymakci, Nuretdin; van Hinsbergen, Douwe J. J.; Kuiper, Klaudia F.; Vissers, Reinoud L. M.

2014-05-01

80

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.

81

Dynamics of Continental Accretion  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

82

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

83

Centromere fragmentation is a common mitotic defect of S and G2 checkpoint override  

PubMed Central

DNA damaging agents, including those used in the clinic, activate cell cycle checkpoints, which blocks entry into mitosis. Given that checkpoint override results in cell death via mitotic catastrophe, inhibitors of the DNA damage checkpoint are actively being pursued as chemosensitization agents. Here we explored the effects of gemcitabine in combination with Chk1 inhibitors in a panel of pancreatic cancer cell lines and found variable abilities to override the S phase checkpoint. In cells that were able to enter mitosis, the chromatin was extensively fragmented, as assessed by metaphase spreads and Comet assay. Notably, electron microscopy and high-resolution light microscopy showed that the kinetochores and centromeres appeared to be detached from the chromatin mass, in a manner reminiscent of mitosis with unreplicated genomes (MUGs). Cell lines that were unable to override the S phase checkpoint were able to override a G2 arrest induced by the alkylator MMS or the topoisomerase II inhibitors doxorubicin or etoposide. Interestingly, checkpoint override from the topoisomerase II inhibitors generated fragmented kinetochores (MUGs) due to unreplicated centromeres. Our studies show that kinetochore and centromere fragmentation is a defining feature of checkpoint override and suggests that loss of cell viability is due in part to acentric genomes. Furthermore, given the greater efficacy of forcing cells into premature mitosis from topoisomerase II-mediated arrest as compared with gemcitabine-mediated arrest, topoisomerase II inhibitors maybe more suitable when used in combination with checkpoint inhibitors. PMID:23624842

Beeharry, Neil; Rattner, Jerome B.; Caviston, Juliane P.; Yen, Tim

2013-01-01

84

The Arctic plate boundary  

Microsoft Academic Search

Earthquakes provide information on the regional segmentation and seismotectonics of the poorly known boundary between the Eurasian and the North American plates from the Knipovich Ridge to the Laptev Sea continental margin. To this end, we have sorted earthquake epicenter locations and focal mechanism solutions from global and regional catalogs, assessed location errors and network detectabilities, and compiled a well-constrained

Øyvind Engen; Olav Eldholm; Hilmar Bungum

2003-01-01

85

The Plate Tectonics Project  

Microsoft Academic Search

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

Annamae J. Hein

2011-01-01

86

The Plate Tectonics Project  

ERIC Educational Resources Information Center

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

Hein, Annamae J.

2011-01-01

87

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

88

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.

89

Continental Subduction Settings: Reduced Volatile Transport of Cl and S to the Surface?  

NASA Astrophysics Data System (ADS)

A research focus of the Collaborative Research Center SFB 574 is the magmatic output of chlorine and sulfur as determined by melt inclusion analyses of primitive and evolved tephra deposits from the Central American (CAVA) and Southern Chilean (SVZ) arcs. Here we integrate our comprehensive geochemical data sets from the CAVA, consisting of 1200 melt inclusion and 300 whole-rock analyses from 71 volcanic centers, with our preliminary data from the SVZ and literature data from the Izu-Bonin-Marianas system (IBM). The highest chlorine contents in melt inclusions are reported from the IBM, an oceanic subduction zone endmember, whereas lower overall concentrations occur at the transitional CAVA. Melt-inclusion Cl-contents of both mafic and felsic CAVA rocks reach highest values in Nicaragua, where slab fluids dominate and the crust is thinnest, and gradually decrease towards the more continental Guatemalan segment of the arc. An exception to this trend are the high Cl contents in central Costa Rican tephras where the influence of the subducted, compositionally OIB-like Cocos Ridge is high. Preliminary analyses from the SVZ continental endmember reveal low melt Cl concentrations. Cl contents inversely correlate with Nd isotope ratios along the SVZ, with very low Cl and the highest Nd isotope ratios occurring at Llaima Volcano. Possible causes of this inverse relation are Cl-increase by crustal contamination reflected in lower Nd isotope ratios as well as lower degrees of partial melting of more enriched (pyroxenitic/eclogitic) material beneath thicker crust. The overall correlation, however, is modulated by local tectonic and compositional controls. Sulfur concentrations are also significantly lower in SVZ eruptives than at the CAVA, possibly reflecting absence of a S-rich source component at the SVZ. S-contents in mafic melt inclusions gradually decrease from ca. 2500 ppm in the southern SVZ to 500 ppm further north where the crust is thicker. This may reflect northward increasing S degassing during the melt's prolonged passage through the continually thickening continental crust. Although the total magma fluxes and magma production rates of the SVZ are still being determined, these first constraints on eruptive volatile output as recorded by melt inclusion geochemistry, integrated with comprehensive findings from the CAVA and IBM, may point to a broad picture of more limited volatile turnover in the subduction segments characterized by thick continental crust and thus a control on volatile contents based on the nature and thickness of the overriding plate.

Wehrmann, H.; Kutterolf, S.; Hoernle, K.; Freundt, A.; Portnyagin, M.; Heydolph, K.

2008-12-01

90

Mechanical obstacles to the movement of continent-bearing plates  

NASA Technical Reports Server (NTRS)

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

Lowman, P. D., Jr.

1985-01-01

91

Iranian Geology and Continental Drift in the Middle East  

Microsoft Academic Search

This article summarizes Iranian geology and continental drift in the Middle East. The relation of the two suggests that plate tectonics satisfactorily explain the geological development of the Middle East.

Manoochehr Takin

1972-01-01

92

GPS Constraints on the Kinematics of Continental Deformation  

Microsoft Academic Search

Recent GPS observations from the western United States, New Zealand, central Greece, and Japan indicate that present-day continental deformation is typically focused in narrow deforming zones whose extent is much smaller than the intervening largely inactive regions. However, these narrow zones are heterogeneously distributed, reflecting the inherent heterogeneity of continental lithospheric strength and internal buoyancy. Plate driving and resisting forces

Wayne Thatcher

2003-01-01

93

Plate T-11: Appalachian Mountains  

NSDL National Science Digital Library

Appalachian Mountain landforms clearly demonstrate the relation of plate tectonics and structure to geomorphology. The folded rocks record the convergence of two continental plates in Pennsylvanian/Permian time. This page uses text, maps, and remotely sensed imagery to explain the relationship between plate tectonics, geologic structures, and the resulting landforms. It is part of an out-of-print NASA publication entitled 'Geomorphology from Space'. Links to the rest of the book are provided.

94

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. PMID:25405064

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

2014-01-01

95

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

96

Continental rifting: a planetary perspective  

SciTech Connect

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

Muehlberger, W.R.

1985-01-01

97

Plate Tectonics: Plate Interactions  

NSDL National Science Digital Library

This Science Object is the fourth of five Science Objects in the Plate Tectonic SciPack. It identifies the events that may occur and landscapes that form as a result of different plate interactions. The areas along plate margins are active. Plates pushing against one another can cause earthquakes, volcanoes, mountain formation, and very deep ocean trenches. Plates pulling apart from one another can cause smaller earthquakes, magma rising to the surface, volcanoes, and oceanic valleys and mountains from sea-floor spreading. Plates sliding past one another can cause earthquakes and rock deformation. Learning Outcomes:? 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.

National Science Teachers Association (NSTA)

2006-11-01

98

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

E-print Network

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

Shapiro, Nikolai

99

BOLIVAR & GEODINOS: Investigations of the Southern Caribbean Plate Boundary  

NASA Astrophysics Data System (ADS)

The southern Caribbean-South American plate boundary has many similarities to California's San Andreas system: 1) The CAR-SA system consists of a series of strands of active right lateral strike-slip faults extending >1000 km from the Antilles subduction zone. This system has several names and includes the El Pilar, Coche, San Sebastian, Moron, and Oca faults. 2) The CAR-SA relative velocity has been about 20 mm/yr of mostly right lateral motion since about 55 Ma, giving a total displacement on the CAR-SA plate boundary similar to that of the San Andreas system. 3) The plate boundary has about 10% convergence in western SA, with less as one moves eastward due to relative convergence between North and South America. 4) The CAR-SA system has fold and thrust belts best developed continentward of the strike-slip faults, similar to the San Andreas. 5) There is a big bend in the CAR plate boundary at approximately the same distance from the Antilles trench as the big bend in Southern California is from the Cascadia subduction zone. The tectonic origins of the CAR-SA plate boundary and the San Andreas are very different, however, despite the similarities between the systems. Rather than impingement of a ridge on a trench, the CAR-SA system is thought to have resulted from a continuous oblique collision of the southern end of a Cretaceous island arc system with the northern edge of South America. During this process the CAR island arc and the modern CAR plate overrode a proto-Caribbean plate and destroyed a Mesozoic passive margin on the northern edge of SA. BOLIVAR and GEODINOS are multi-disciplinary investigations of the lithosphere and deeper structures associated with the diffuse CAR-SA plate boundary zone. We review a number of observations regarding the plate boundary obtained or confirmed from these studies: 1) The Caribbean Large Igneous Province, being overridden by the Maracaibo block in western Venezuela, can be identified beneath Aruba and coastal Venezuela, and is associated with broad uplift of the coastal regions. This is likely a site of continental growth. 2) The accretionary wedge terranes of the Southern Caribbean Deformed Belt formed in the Neogene, and extend as far east as the Aves Ridge. They result from SA overriding the CAR LIP, which for a number of reasons, we do not regard as normal subduction. 3) Igneous rocks on the islands of the Leeward Antilles arc, Aruba to Los Testigos, show a steady decrease in age from west to east (94.7-37.4 Ma), suggesting that the islands have been progressively captured from the Antilles arc by the plate boundary during the prolonged island arc-continent collision. Terrane capture models thus far cannot completely explain the data. 4) High (> 6.5 km/s) P-velocity bodies are found in the shallow crust along the main strike-slip faults along much of the plate boundary. We interpret these as elements of the HP/LT metamorphic terranes found in the adjacent thrust belts of central Venezuela. This suggests to us that displacement partitioning in the trench and subsequent strike-slip both play important roles in exhumation of the HP/LT terranes. 5) Crustal thickness variations in the plate boundary region are large (> 10 km), of short spatial wavelength (< 100 km), and indicate that the highest elevations of the coastal mountain belts are not supported isostatically.

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

2006-12-01

100

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

101

Continental lids and mantle convective stirring efficiency  

NASA Astrophysics Data System (ADS)

Interpreting surface geochemical data requires understanding the dynamic mechanisms that preserve or erase heterogeneities over geological times. Among these, the presence of continental lids is known to have a first order impact on mantle convective dynamics and heat transfer. On Earth, oceanic plates are recycled into the mantle and are characterized by a relatively strong heat flux, while continents are more insulating, lighter and therefore not subductable. Numerical and laboratory experiments have demonstrated that this dichotomy between continents and oceans can have a first order influence on mantle motion. One should therefore expect that this also influences the efficiency of convective stirring over billions of years. However, this effect has not been considered in previous studies that investigated mantle convective stirring efficiency. We have therefore investigated the influence of continental lids on convective stirring efficiency using numerical experiments at infinite Prandtl number in a rectangular domain. Differences between oceanic and continental plates are accounted for by imposing heterogeneous surface boundary conditions for temperature and velocities: oceanic plates are described by Dirichlet boundary conditions while continents are modeled as highly viscous, floating lids of variable extent, with locally imposed prescribed surface heat fluxes. We quantify the convective stirring efficiency using various diagnostics such as mixing time and Lyapunov exponent distribution. This numerical set up allows us to quantify systematically the influence of several governing parameters on the convective stirring efficiency: the Rayleigh number Ra, the horizontal extent of continental lids, as well as viscous rheological parameters.

Deo, B.; Aleksandrov, V.; Samuel, H.

2010-12-01

102

Plate Tectonics Learning Module  

NSDL National Science Digital Library

This plate tectonics unit was designed to be used with a college course in physical geography. Subject matter covered includes: the development of the theory including Wegener's Continental Drift Hypothesis and the existence of Pangaea, Harry Hess and his work on sea-floor spreading, and the final theory. It points out that global features such as deep oceanic trenches, mid-ocean ridges, volcanic activity, and the location of earthquake epicenters can now be related to the story of plate tectonics, since most geological activity occurs along plate boundaries. Divergent, convergent and transform plate boundaries are discussed in detail. This module contains a study guide and outline notes, study questions, and practice quizzes. One feature of the module is a web exploration section with links to twelve outside sites that augment the instruction.

Haberlin, Rita

103

Caffeine stabilizes Cdc25 independently of Rad3 in S chizosaccharomyces pombe contributing to checkpoint override  

PubMed Central

Cdc25 is required for Cdc2 dephosphorylation and is thus essential for cell cycle progression. Checkpoint activation requires dual inhibition of Cdc25 and Cdc2 in a Rad3-dependent manner. Caffeine is believed to override activation of the replication and DNA damage checkpoints by inhibiting Rad3-related proteins in both S chizosaccharomyces pombe and mammalian cells. In this study, we have investigated the impact of caffeine on Cdc25 stability, cell cycle progression and checkpoint override. Caffeine induced Cdc25 accumulation in S . pombe independently of Rad3. Caffeine delayed cell cycle progression under normal conditions but advanced mitosis in cells treated with replication inhibitors and DNA-damaging agents. In the absence of Cdc25, caffeine inhibited cell cycle progression even in the presence of hydroxyurea or phleomycin. Caffeine induces Cdc25 accumulation in S . pombe by suppressing its degradation independently of Rad3. The induction of Cdc25 accumulation was not associated with accelerated progression through mitosis, but rather with delayed progression through cytokinesis. Caffeine-induced Cdc25 accumulation appears to underlie its ability to override cell cycle checkpoints. The impact of Cdc25 accumulation on cell cycle progression is attenuated by Srk1 and Mad2. Together our findings suggest that caffeine overrides checkpoint enforcement by inducing the inappropriate nuclear localization of Cdc25. PMID:24666325

Alao, John P; Sjölander, Johanna J; Baar, Juliane; Özbaki-Yagan, Nejla; Kakoschky, Bianca; Sunnerhagen, Per

2014-01-01

104

An Introduction to the ABCs of Plate Tectonics  

NSDL National Science Digital Library

This introduction to plate tectonics covers plates and boundaries, subduction zones, colliding continents, plumes, and earthquakes. There is also more advanced material on buoyancy, floating continents, and rates of isostasy; sedimentation, continental growth, rifts and creation of continental margins, passive and active margins, and island arcs and back-arc basins; continental collision, folding of sedimentary layers, and collision of cratons; and the mechanism of plate tectonics including convective mantles, convection models, distribution of plumes, plume driven convection, plate rifting models, and triple junctions.

Blanchard, Donald

105

Plate TectonicsPlate Tectonics Plate TectonicsPlate Tectonics  

E-print Network

Plate TectonicsPlate Tectonics #12;Plate TectonicsPlate Tectonics · Lithosphere ­ strong, rigid, transform boundaries ­ travel 1 to 11 cm/yr relative to one another #12;14 tectonic plates today #12;Mid asthenosphere that flows · 8 large lithospheric plates and 6 smaller ones ­ separated by divergent, convergent

Siebel, Wolfgang

106

Constraints on continental accretion from sedimentation  

NASA Technical Reports Server (NTRS)

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

Abbott, Dallas

1988-01-01

107

Whole Earth Structure and Plate Tectonics  

E-print Network

Whole Earth Structure and Plate Tectonics Earth Structure (2nd Edition), 2004 W.W. Norton & Co, New York Slide show by Ben van der Pluijm © WW Norton; unless noted otherwise #12;© EarthStructure (2nd ed evolution of Earth: from continental drift (early 1900's) to sea-floor spreading (early 1960's) to plate

108

The Plate Tectonic Story: A Scientific Jigsaw  

NSDL National Science Digital Library

This activity has students read and answer questions based upon the article 'The plate tectonic story: a scientific jigsaw.' The article starts with the continental drift theory of Alfred Wegener and adds the evidence from the seafloor to arrive at plate tectonics. It concludes with remarks about mantle dynamics and the future ability to predict earthquakes.

109

Earth's continental crustal gold endowment  

NASA Astrophysics Data System (ADS)

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

Frimmel, H. E.

2008-03-01

110

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

111

Deep continental margin reflectors  

USGS Publications Warehouse

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

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

1985-01-01

112

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

113

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

114

What on Earth is Plate Tectonics?  

NSDL National Science Digital Library

This abbreviated explanation of the subject of plate tectonics is divided into several parts. The first section, entitled Into the Earth, describes the crust, mantle and core of the Earth, while the next section shows a world map with the plates delineated. The section called Action at the Edges uses text and diagrams to explain what is occurring at the plate boundaries. Links lead to a detailed discussion of converging boundaries including ocean-ocean, ocean-continental, and continental-continental. A wide range illustration shows both surface and cross-section views of plate interaction and a link leads to a similar diagram with labels. In the Moving through Time section, a series of color-coded maps is shown, illustrating the relative position of the continents over the past 650 million years. The last section shows a paleogeographic reconstruction of the Earth and explains how paleomagnetism, magnetic anomalies, paleobiogeography, paleoclimatology, and geologic history are used to create it.

115

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

NASA Technical Reports Server (NTRS)

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

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

1976-01-01

116

Oceanology of the antarctic continental shelf: Volume 43  

SciTech Connect

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

Jacobs, S.S.

1985-01-01

117

Earthquakes in stable continental crust  

SciTech Connect

Earthquakes can strike even in stable crust, well away from the familiar earthquake zones at the edges of tectonic plates, but their mere occurrence is both a source of concern in planning critical facilities such as nuclear power plants. The authors sought answers to two major questions: Just how much seismic activity does take place within the stable parts of continents And are there specific geologic features that make some areas of stable crust particularly susceptible to earthquakes They began by studying North America alone, but it soon became clear that the fairly short record of these rare events on a single continent would not provide enough data for reliable analysis. Hence, they decided to substitute space for time--to survey earthquake frequency and distribution in stable continental areas worldwide. This paper discusses their findings.

Johnson, A.C.; Kanter, L.R. (Memphis State Univ., TN (USA))

1990-03-01

118

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

119

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

120

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

121

Plate motion  

SciTech Connect

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

Gordon, R.G. (USAF, Geophysics Laboratory, Hanscom AFB, MA (United States))

1991-01-01

122

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

123

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

PubMed

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

McDougall, Rosalind J; Notini, Lauren

2014-07-01

124

Seismic investigation of the continental margin off- and onshore Valparaiso, Chile  

Microsoft Academic Search

At the latitude of Valparaiso, Chile, a fundamental change in the configuration of the Benioff zone, volcanic activity, and the structure of the continental margin occurs opposite the subducting Juan Fernandez Ridge. Three legs of the German RVSonne (cruises SO101, SO103 and SO104) surveyed the continental margin and oceanic plate offshore Valparaiso, aiming at studying the crustal structure and investigating

E. R. Flueh; N. Vidal; C. R. Ranero; A. Hojka; R. von Huene; J. Bialas; K. Hinz; D. Cordoba; J. J. Dañobeitia; C. Zelt

1998-01-01

125

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

126

Plate Boundaries  

NSDL National Science Digital Library

This site provides information on plate boundaries, which are found at the edge of the lithospheric plates and are of three types: convergent, divergent and conservative. Wide zones of deformation are usually characteristic of plate boundaries because of the interaction between two plates. The three boundaries are characterized by their distinct motions which are described in the text and depicted with block diagram illustrations, all of which are animated. There are also two maps that show the direction of motion of the plates. Active links lead to more information on plate tectonics.

127

The extent of continental crust beneath the Seychelles  

NASA Astrophysics Data System (ADS)

The granitic islands of the Seychelles Plateau have long been recognised to overlie continental crust, isolated from Madagascar and India during the formation of the Indian Ocean. However, to date the extent of continental crust beneath the Seychelles region remains unknown. This is particularly true beneath the Mascarene Basin between the Seychelles Plateau and Madagascar and beneath the Amirante Arc. Constraining the size and shape of the Seychelles continental fragment is needed for accurate plate reconstructions of the breakup of Gondwana and has implications for the processes of continental breakup in general. Here we present new estimates of crustal thickness and VP/VS from H-? stacking of receiver functions from a year long deployment of seismic stations across the Seychelles covering the topographic plateau, the Amirante Ridge and the northern Mascarene Basin. These results, combined with gravity modelling of historical ship track data, confirm that continental crust is present beneath the Seychelles Plateau. This is ˜30-33 km thick, but with a relatively high velocity lower crustal layer. This layer thins southwards from ˜10 km to ˜1 km over a distance of ˜50 km, which is consistent with the Seychelles being at the edge of the Deccan plume prior to its separation from India. In contrast, the majority of the Seychelles Islands away from the topographic plateau show no direct evidence for continental crust. The exception to this is the island of Desroche on the northern Amirante Ridge, where thicker low density crust, consistent with a block of continental material is present. We suggest that the northern Amirantes are likely continental in nature and that small fragments of continental material are a common feature of plume affected continental breakup.

Hammond, J. O. S.; Kendall, J.-M.; Collier, J. S.; Rümpker, G.

2013-11-01

128

Upper mantle structure beneath the Caribbean-South American plate boundary from surface wave tomography  

E-print Network

-slip fault system along the northern coast of Venezuela, illustrating the differences between the South beneath the South American plate. In eastern Venezuela, linear crustal low velocities are associated the buoyant continental South American plate offshore of northeastern Venezuela. The continental lithosphere

Niu, Fenglin

129

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

130

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

PubMed

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

Clark, Marin Kristen

2012-03-01

131

What Does a Late-Interseismic Continental Plate-Bounding Fault Look Like Up Close? 0.1-100 m-Scale Structure of the Alpine Fault Revealed by DFDP-1 Wireline Logging Data and Core Samples (Invited)  

NASA Astrophysics Data System (ADS)

Understanding the physical conditions prevailing in a fault zone immediately prior to a large earthquake would provide primary observational constraints on processes operating at different times and on different scales during the seismic cycle. The almost 300 years that have elapsed since the last Alpine Fault earthquake (MW~7.9 in 1717 AD) constitute a large fraction of the fault's 200-400 year average recurrence interval. In other words, the Alpine Fault appears to be late in the cycle of stress accumulation that will ultimately result in another large earthquake. The first phase of the Deep Fault Drilling Project (DFDP-1) was completed in early 2011 with the drilling at Gaunt Creek of two boreholes intersecting the shallow Alpine Fault. Core samples, wireline logging data, and hydraulic measurements document ambient conditions and fault zone structures at 0.1-100 m scales and enable us to describe the conditions under which the next Alpine Fault earthquake will occur. In this presentation, we discuss key characteristics of the individual DFDP-1 data sets, and their combined implications for fault zone evolution and deep structure. At Gaunt Creek, the Alpine Fault exhibits asymmetry at 0.1-100 m scales, or larger, in at least four senses: geometric asymmetry imposed by its non-vertical dip; hydraulic asymmetry governed by the low-permeability of a >30 m-thick hydrologically and geochemically distinct alteration zone; elastic asymmetry associated with the bulk properties of the wallrocks and superimposed fracturing; and topographic asymmetry reflecting its transpressive kinematics. The combined effects of these asymmetries on rupture propagation have yet to be fully considered, but our observations from DFDP-1 provide an opportunity to inform numerical models of earthquake rupture with direct field observations of a late-interseismic crustal-scale continental fault. On the basis of the elastic asymmetry documented in DFDP-1, the bimaterial interface model of preferred rupture propagation implies a northeastward direction of preferred Alpine Fault rupture. Further characterizing the structural and hydraulic architecture of the Alpine Fault will improve our understanding of the relationship between ambient conditions, quasi-periodic earthquake rupture, and the hazards posed by future large earthquakes.

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

2013-12-01

132

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.

133

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

134

The Magnetic Signature of Zones of Continental Collision  

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

135

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

E-print Network

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

Liu, Mian

136

Tectonic Plates and Plate Boundaries  

NSDL National Science Digital Library

This interactive activity adapted from NASA features world maps that identify different sections of the Earth's crust called tectonic plates. The locations of different types of plate boundaries are also identified, including convergent, divergent, and transform boundaries.

2005-12-17

137

Continental Thermal Isostasy  

Microsoft Academic Search

The sources of continental elevations are partitioned into a combination of compositional, thermal, and geodynamic buoyancy. Because the potential elevation due to crustal compositional variations are large, an isostatic correction normalizing the effect of crustal composition on elevation is applied to reveal the effects of thermal buoyancy. Particular attention is paid to the uncertainties related to removing compositional effects. The

D. Hasterok; D. S. Chapman

2005-01-01

138

The Continental Crust.  

ERIC Educational Resources Information Center

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

Burchfiel, B. Clark

1983-01-01

139

Continental magnetic anomaly constraints on continental reconstruction  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

140

Genetic control of plant development by overriding a geometric division rule.  

PubMed

Formative cell divisions are critical for multicellular patterning. In the early plant embryo, such divisions follow from orienting the division plane. A major unanswered question is how division plane orientation is genetically controlled, and in particular whether this relates to cell geometry. We have generated a complete 4D map of early Arabidopsis embryogenesis and used computational analysis to demonstrate that several divisions follow a rule that uses the smallest wall area going through the center of the cell. In other cases, however, cell division clearly deviates from this rule, which invariably leads to asymmetric cell division. By analyzing mutant embryos and through targeted genetic perturbation, we show that response to the hormone auxin triggers a deviation from the "shortest wall" rule. Our work demonstrates that a simple default rule couples division orientation to cell geometry in the embryo and that genetic regulation can create patterns by overriding the default rule. PMID:24684831

Yoshida, Saiko; Barbier de Reuille, Pierre; Lane, Brendan; Bassel, George W; Prusinkiewicz, Przemyslaw; Smith, Richard S; Weijers, Dolf

2014-04-14

141

Tumor suppression by miR-26 overrides potential oncogenic activity in intestinal tumorigenesis.  

PubMed

Down-regulation of miR-26 family members has been implicated in the pathogenesis of multiple malignancies. In some settings, including glioma, however, miR-26-mediated repression of PTEN promotes tumorigenesis. To investigate the contexts in which the tumor suppressor versus oncogenic activity of miR-26 predominates in vivo, we generated miR-26a transgenic mice. Despite measureable repression of Pten, elevated miR-26a levels were not associated with malignancy in transgenic animals. We documented reduced miR-26 expression in human colorectal cancer and, accordingly, showed that miR-26a expression potently suppressed intestinal adenoma formation in Apc(min/+) mice, a model known to be sensitive to Pten dosage. These studies reveal a tumor suppressor role for miR-26 in intestinal cancer that overrides putative oncogenic activity, highlighting the therapeutic potential of miR-26 delivery to this tumor type. PMID:25395662

Zeitels, Lauren R; Acharya, Asha; Shi, Guanglu; Chivukula, Divya; Chivukula, Raghu R; Anandam, Joselin L; Abdelnaby, Abier A; Balch, Glen C; Mansour, John C; Yopp, Adam C; Richardson, James A; Mendell, Joshua T

2014-12-01

142

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

PubMed Central

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

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

1994-01-01

143

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

PubMed

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

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

1994-12-15

144

Interseismic Plate coupling and strain partitioning in the Northeastern Caribbean  

NASA Astrophysics Data System (ADS)

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

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

2008-09-01

145

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

146

ELSEVIER Earth-Science Reviews 40 (1996) 229-258 Continental break-up and collision in the Neoproterozoic and  

E-print Network

ELSEVIER Earth-Science Reviews 40 (1996) 229-258 Continental break-up and collision geodynamic models which limited the speeds at which large continental plates could move to an arbitrarily low value. Baltica and Laurentia probably shared a common drift history for the time interval 750-600 Ma

Torsvik, Trond Helge

147

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

148

Metamorphism and Continental Collision  

NSDL National Science Digital Library

Physical Geology students are required to understand the processes involved in plate tectonics. They are expected to know the geologic differences between continents and ocean basins and should be able to recall and use simple geologic terms to describe geologic processes and events. This activity is designed to improve student comprehension of the varied Earth materials and complex processes involved in plate collisions. The activity synthesizes material covered during the first eight weeks of Physical Geology on plate tectonics, rock types, volcanoes, and Earth's composition. The instructor introduces the exercise to the students as a component of the college's Critical Thinking Initiative. The "hook" for the students is that the exercise represents a chance for self-appraisal of course content and understanding prior to the next semester test. The grading rubric for the lab is discussed with the students in terms of the Bloom Pyramid so that they can assess their level of progress in the course.

Howard, Kenneth

149

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

150

It's under control: top-down search strategies can override attentional capture.  

PubMed

Bacon and Egeth (1994) proposed that observed instances of attentional capture by feature singletons (e.g., color) were the result of a salience-based strategy adopted by subjects (singleton detection mode) and, thus, were not automatic. They showed that subjects could override capture by adopting strategies based on searching for specific target features (feature search mode). However, Theeuwes (2004) has recently argued that Bacon and Egeth's results arose from experimental confounds. He elaborated a model in which attentional capture must be expected when salient distractors fall within a spatial window of attention. According to Theeuwes's (2004) model, there exist two essential criteria for examining stimulus-driven capture. First, search latencies cannot increase with display size, since the search must be parallel; second, the salience of the irrelevant distractor must not be compromised by characteristics of the search display. Contrary to the predictions of Theeuwes's (2004) model, we provide evidence that involuntary capture can be overridden when both of these criteria are met. Our results are consistent with Bacon and Egeth's proposal. PMID:16724780

Leber, Andrew B; Egeth, Howard E

2006-02-01

151

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

152

Plate motion and deformation  

SciTech Connect

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

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

1991-02-01

153

Slab eduction following continental subduction and slab detachment  

NASA Astrophysics Data System (ADS)

The geodynamic process of slab eduction characterizes the normal-sense extraction of previously subducted continental plate. Eduction leads to a coherent motion of the continental lithosphere and can partly accommodate the exhumation of high pressure domains. This motion is driven by the buoyancy of subducted crust, it may take place after slab detachment and the loss of slab pull. In order to test the eduction model, we employ two-dimensional thermo-mechanical modeling. Our results indicate that eduction triggers adiabatic decompression of the subducted crust (~2 GPa) in a narrow timespan (~5 Ma). As the slab is educted, large strain takes place in the former subduction channel and topography builds up with ongoing extension. To further quantify the parameters involved into eduction, we compare parametric tests to analytic plate velocity estimations. We could show that eduction is a viable mechanism under a reasonable range of mantle viscosity, subduction channel viscosity and orogenic root buoyancy.

Duretz, Thibault; Gerya, Taras V.; Andersen, Torgeir B.

2013-04-01

154

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

155

Peen plating  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

156

Is There Really A North American Plate?  

NASA Astrophysics Data System (ADS)

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

Krill, A.

2011-12-01

157

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

158

GEO-Logic: Continental Drift and Plate Tectonics  

NSDL National Science Digital Library

Students are asked to match up lecturers with what day and time they teach, and how many students they have based on clues given from several different perspectives. In the second part of the activity, students are asked to learn more about the historic figures mentioned in the activity by doing reading and web research.

Guertin, Laura

159

INTRODUCTION The continental promontory of the Eurasian plate in SE  

E-print Network

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

Royal Holloway, University of London

160

An updated digital model of plate boundaries  

NASA Astrophysics Data System (ADS)

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

Bird, Peter

2003-03-01

161

Caribbean plate tectonics from seismic tomography  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

162

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

163

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

164

E2F-1:DP-1 induces p53 and overrides survival factors to trigger apoptosis.  

PubMed Central

The E2F DNA binding activity consists of a heterodimer between E2F and DP family proteins, and these interactions are required for association of E2F proteins with pRb and the pRb-related proteins p107 and p130, which modulate E2F transcriptional activities. E2F-1 expression is sufficient to release fibroblasts from G0 and induce entry into S phase, yet it also initiates apoptosis. To investigate the mechanisms of E2F-induced apoptosis, we utilized interleukin-3 (IL-3)-dependent 32D.3 myeloid cells, a model of hematopoietic progenitor programmed cell death. In the absence of IL-3, E2F-1 alone was sufficient to induce apoptosis, and p53 levels were diminished. DP-1 alone was not sufficient to induce cell cycle progression or alter rates of death following IL-3 withdrawal. However, overexpression of both E2F-1 and DP-1 led to the rapid death of cells even in the presence of survival factors. In the presence of IL-3, levels of endogenous wild-type p53 increased in response to E2F-1, and coexpression of DP-1 further augmented p53 levels. These results provide evidence that E2F is a functional link between the tumor suppressors p53 and pRb. However, induction of p53 alone was not sufficient to trigger apoptosis, suggesting that the ability of E2F to override survival factors involves additional effectors. PMID:8524253

Hiebert, S W; Packham, G; Strom, D K; Haffner, R; Oren, M; Zambetti, G; Cleveland, J L

1995-01-01

165

Magmatism and deformation during continental breakup  

NASA Astrophysics Data System (ADS)

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

Keir, Derek

2013-04-01

166

Growth Plate Injuries  

MedlinePLUS

Growth Plate Injuries May 2014 Questions and Answers about Growth Plate Injuries This publication contains general information about ... Classification of Growth Plate Injuries What Is the Growth Plate? The growth plate, also known as the ...

167

Musical Plates  

NSDL National Science Digital Library

This on-line project is part of the Center for Improved Engineering and Science Education (CIESE) program. As they complete this series of lessons, students will use real-time data to solve a problem, study the correlation between earthquakes and tectonic plates, and determine whether or not there is a relationship between volcanoes and plate boundaries. Musical Plates has four Core Activities that will teach students how to access and interpret real-time earthquake and volcano data and to how use the information to solve a real-world problem. Each of the core activities is designed to be used in a 45-minute class period. This unit also has three enrichment lessons and a final project lesson that can also be used for assessment.

2007-12-12

168

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

Microsoft Academic Search

The enhanced precision and resolution of GPS velocity fields within active continental regions have highlighted two views of how best to describe these fields: (1) as relative movements of effectively rigid (or elastic) blocks, essentially plate tectonics with many plates, or (2) as continuous deformation of a (non-Newtonian) viscous fluid in a gravity field. The operative question is not: Are

P. H. Molnar

2010-01-01

169

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

170

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

USGS Publications Warehouse

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

Kane, M.F.

1972-01-01

171

Estimating the global volume of deeply recycled continental crust at continental collision zones  

NASA Astrophysics Data System (ADS)

CRUSTAL RECYCLING AT OCEAN MARGINS: Large volumes of rock and sediment are missing from the submerged forearcs of ocean margin subduction zones--OMSZs. This observation means that (1) oceanic sediment is transported beneath the margin to either crustally underplate the coastal region or reach mantle depths, and that (2) the crust of the forearc is vertically thinned and horizontally truncated and the removed material transported toward the mantle. Transport of rock and sediment debris occurs in the subduction channel that separates the upper and lower plates. At OMSZs the solid-volume flux of recycling crustal material is estimated to be globally ~2.5 km3/yr (i.e., 2.5 Armstrong units or AU). The corresponding rate of forearc truncation (migration of the trench axis toward a fix reference on the continent) is a sluggish 2-3 km/Myr (about 1/50th the orthogonal convergence rate). Nonetheless during the past 2.5 Gyr (i.e., since the beginning of the Proterozoic) a volume of continental material roughly equal to the existing volume (~7 billion cubic km) has been recycled to the mantle at OMSZs. The amount of crust that has been destroyed is so large that recycling must have been a major factor creating the mapped rock pattern and age-fabric of continental crust. RECYCLING AT CONTINENT/ARC COLLISIONS: The rate at which arc magmatism globally adds juvenile crust to OMSZs has been commonly globally estimated at ~1 AU. But new geophysical and dating information from the Aleutian and IBM arcs imply that the addition rate is at least ~5 AU (equivalent to ~125 km3/Myr/km of arc). If the Armstrong posit is correct that since the early Archean a balance has existed between additions and losses of crust, then a recycling sink for an additional 2-3 AU of continental material must exist. As the exposure of exhumed masses of high P/T blueschist bodies documents that subcrustal streaming of continental material occurs at OMSZs, so does the occurrence of exhumed masses of UHP metamorphic rock imply recycling also takes place at CCSZs. We thus target CCSZs as the setting for long-term crustal losses summing worldwide to 2-3 AU. An example is the ~10,000-km-long and 50-Myr duration of the Alpine- Himalaya CCSZ. Recycling is presumably effected by subduction (tectonic) erosion of the upper plate, injection of lower plate material into mantle circulation, and crustal delamination at collision-thickened orogenic welts. ALTERNATIVE MODEL: If the Armstrong assumption is incorrect and no long-term balance exist between the addition and losses of continental crust, then significant crustal recycling at CCSZs may not occur and the global volume of arc-magmatically generated continental crust has been growing with time.

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

2006-12-01

172

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

173

Tectonic Plates and Plate Boundaries  

NSDL National Science Digital Library

Continents were once thought to be static, locked tight in their positions in Earth's crust. Similarities between distant coastlines, such as those on opposite sides of the Atlantic, were thought to be the work of a scientist's overactive imagination, or, if real, the result of erosion on a massive scale. This interactive feature shows 11 tectonic plates and their names, the continents that occupy them, and the types of boundaries between them.

174

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

175

Plate motions: fundamentals  

E-print Network

lithospheric plates" · Plate tectonics = a kinematic theory ­ Rigid plates (no intraplate deformation") · Convergent = subductions ("trenches") · Strike-slip = transform faults · Plate tectonics describesPlate motions: fundamentals · Assume a pie-shaped wedge plate B, rotating around E (=rotation pole

Déverchère, Jacques

176

The northern Egyptian continental margin  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

177

Plate Tectonics  

NSDL National Science Digital Library

In this activity, presented by the Lane Community College MAPS GIS Program, students will learn the concept of a digital data viewer, and how this resource can help them learn more about plate tectonics. Students will learn terminology associated with both geology and computer aided GIS. The activity is presented as a PDF, and helps the student learn by presenting a series of easy to follow questions. This allows students to learn at their own pace, as it tests their knowledge every step of the way. Visitors will find links to the instructor and student versions of the lesson and links to the web-based GIS utility used in the activity.

2008-12-11

178

Anatomy and formation of oblique continental collision: South Falkland basin  

NASA Astrophysics Data System (ADS)

The South Falkland basin is a partially filled Cenozoic foreland basin located south of the Falkland Plateau. It was formed by flexure of this southern edge of the South American plate when the load represented by Burdwood Bank collided. This continental fragment belongs to the predominantly oceanic Scotia plate. Flexure probably started in early Cenozoic times and has continued to the present day. The whole region is submarine and so the detailed stratigraphy and structure of the basin has been well imaged by seismic reflection profiling. The clarity of this imagery has made analysis of structures within the collision zone possible. The plate boundary itself is an active oblique thrust fault which has controlled the growth of a frontal fold. There is evidence for older phases of thrusting and folding further south. Within and beneath the sediments which blanket the flexed South American plate, normal faulting occurs on a variety of scales. Episodes of stratigraphic growth associated with the largest of these faults demonstrates that they were active during flexural bending. We have modeled the development of the South Falkland basin using two different approaches, both of which are based upon the simplest elastic model. Inverse modeling of free-air gravity and bathymetric profiles suggest that the elastic thickness of the loaded crust is 5-20 km. A complementary approach based upon the spectral analysis of free-air gravity and bathymetry shows that the elastic thickness is 15 ± 5 km. Both techniques indicate that the flexed continental lithosphere is weak, a conclusion supported by the presence of normal faults within the flexed plate. A small increase in elastic thickness from west to east appears consistent with a change in the density and penetration of normal faulting.

Bry, Madeleine; White, Nicky; Singh, Satish; England, Richard; Trowell, Carl

2004-08-01

179

MACMA: a Virtual Lab for Plate Tectonics  

NASA Astrophysics Data System (ADS)

MACMA (Multi-Agent Convective MAntle) is a tool developed to simulate evolutive plate tectonics and mantle convection in a 2-D cylindrical geometry (Combes et al., 2012). The model relies mainly on a force balance to compute the velocity of each plate, and on empirical rules to determine how plate boundaries move and evolve. It includes first-order features of plate tectonics: (a) all plates on Earth do not have the same size, (b) subduction zones are asymmetric, (c) plates driven by subducting slabs and upper plates do not exhibit the same velocities, and (d) plate boundaries are mobile, can collide, merge and disappear, and new plate boundaries can be created. The MACMA interface was designed to be user-friendly and a simple use of the simulator can be achieved without any prerequisite knowledge in fluid dynamics, mantle rheology, nor in numerical methods. As a preliminary study, the simulator was used by a few students from bachelor's degree to master's degree levels. An initial configuration for plate tectonics has to be created before starting a simulation: the number and types of plate boundaries (ridge, subduction, passive margins) has to be defined and seafloor ages must be given. A simple but interesting exercise consists in letting students build such an initial configuration: they must analyze a map of tectonic plates, choose a 2-D section and examine carefully a map of seafloor ages. Students mentioned that the exercise made them realize that the 3-D spherical structure of plate tectonics does not translate directly in a simple 2-D section, as opposed to what is usually shown in books. Physical parameters: e.g. mantle viscosity, number of layers to consider in the mantle (upper and lower mantle, possible asthenosphere), initial time and mantle temperature, have to be chosen, and students can use this virtual lab to see how different scenarios emerge when parameters are varied. Very importantly, the direct visualization of the mobility of plate boundaries is a feature that clearly seems interesting to students. They are used to see dynamic representations of continental drift, but this does not include the dynamics of the oceanic lithosphere and the corresponding fluctuations in seafloor age distribution. The 2-D geometry of the simulator is a simplification that actually brings a clearer view of plate boundary creations, migrations, and collisions, together with global plate tectonics reorganization events.

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

2013-12-01

180

Plate mouse  

PubMed Central

Fracture shaft humerus when surgically fixed is known to go into non-union and one of the main reasons of this is implant failure. The causes of implant failure may lie in the fracture personality, faulty implant material or choice, dubious surgical technique & faulty mechanics of fixation. Implants may break and cut-through but a unique type of implant migration from one surgical compartment to the other or one anatomical part of body to the other has not been hitherto reported. A 45-year-old male, farmer by occupation, was operated for fracture shaft of humerus 15 years back. He presented to us because of pain due to subcutaneous presence of plate in forearm. X-ray of the elbow with forearm showed that the plate used for fixation of humerus had migrated from one body part to another that is from arm to forearm. The patient on deliberation regarding the pros and cons of surgical treatment options, chose not to get his humerus non-union resolved surgically. This was because he could do his activities related to farming reasonably well.

Lal, Hitesh; Sharma, Deepak Kumar; Mittal, Deepak

2012-01-01

181

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

182

Continental rifts and mineral resources  

SciTech Connect

Continental rifts are widespread and range in age from the present to 3 b.y. Individual rifts may form parts of complex systems as in E. Africa and the Basin and Range. Rifts have originated in diverse environments such as arc-crests, sites of continental collision, collapsing mountain belts and on continents at rest over the mantle circulation pattern. Continental rift resources can be classified by depth of origin: For example, in the Great Dike, Norilsk and Mwadui magma from the mantle is the host. At shallower depths continental crust partly melted above mafic magma hosts ore (Climax, Henderson). Rift volcanics are linked to local hydrothermal systems and to extensive zeolite deposits (Basin and Range, East Africa). Copper (Zambia, Belt), zinc (Red Dog) and lead ores (Benue) are related to hydrothermal systems which involve hot rock and water flow through both pre-rift basement and sedimentary and volcanic rift fill. Economically significant sediments in rifts include coals (the Gondwana of Inida), marine evaporites (Lou Ann of the Gulf of Mexico) and non-marine evaporites (East Africa). Oil and gas in rifts relate to a variety of source, reservoir and trap relations (North Sea, Libya), but rift-lake sediment sources are important (Sung Liao, Bo Hai, Mina, Cabinda). Some ancient iron ores (Hammersley) may have formed in rift lakes but Algoman ores and greenstone belt mineral deposits in general are linked to oceanic and island arc environments. To the extent that continental environments are represented in such areas as the Archean of the Superior and Slave they are Andean Arc environments which today have locally rifted crests (Ecuador, N. Peru). The Pongola, on Kaapvaal craton may, on the other hand represent the world's oldest preserved, little deformed, continental rift.

Burke, K. (Univ. of Houston, TX (United States). Geosciences Dept.)

1992-01-01

183

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.

184

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

185

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

186

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

187

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

188

Constraints on the Character of Plate Tectonics From the Study of Diffuse Plate Boundaries  

NASA Astrophysics Data System (ADS)

While the main global expression of tectonics at Earth's surface is that of plate tectonics, i.e., narrow boundaries between rigid plates, a significant fraction of the lithosphere (perhaps 15% of both ocean basins and continents) is undergoing diffuse deformation. The existence of these zones of deformation (often termed ``diffuse plate boundaries'') raises the question of why the majority of deformation occurs at narrow boundaries, and how narrow boundaries may form. Study of the best characterized diffuse zone of oceanic deformation, which occurs in the equatorial Indian Ocean and may also be the best candidate for an incipient convergent plate margin, may help to elucidate these questions. The Indo-Australian composite plate comprises 3 component plates (i.e., the nondeforming portions of the composite plate) and multiple diffuse plate boundaries. We determine the general relation between the relative angular velocity between two component plates and the torque that the two component plates exert on one another across their mutual diffuse boundary. We show that the torque between the Indian and Capricorn component plates (respectively north and south of the equatorial diffuse plate boundary) is oriented far from the relative angular velocity vector between the two plates, and is subparallel to the torque exerted on India by the Tibetan plateau. With earlier work showing that onset of the current episode of deformation in the Indian Ocean coincided with the attainment of maximum elevation of the Tibetan plateau, this indicates that the lithospheric deformation in the equatorial Indian Ocean is being driven by the outward push of the Tibetan plateau. To achieve a torque balance, we find that the force per unit length exerted by the Tibetan plateau on the Indian component plate must be nearly identical to the strength of the oceanic lithosphere, which we infer to be 9 (+/- 2) x 1012 N m-1. Given that the effect of plateau formation by horizontal shortening of continental crust strongly influences the compressive stress available to deform oceanic lithosphere, this coincidence may be necessary for plate tectonics to continue and evolve on geologically long time scales while restricting these zones of diffuse deformation to relatively minor proportions of the oceanic plate, if narrow plate boundaries such as subduction zones evolve from diffuse plate boundaries.

Gordon, R. G.; Zatman, S.

2001-12-01

189

Continental Paleobiogeography as Phylogenetic Evidence  

Microsoft Academic Search

Morphological convergence between members of clades isolated on different landmasses can mislead phylogenetic analyses, and can imply intercontinental dispersals that are unlikely given reconstructed paleogeography. It is argued here that paleobiogeographic data, like chronostratigraphic data, are relevant to the process of inferring phylogenetic relationships. In order to allow the dynamic history of continental paleogeography to influence phylogenetic analysis, a ?chronobiogeographic

James B. Rossie; Erik R. Seiffert

190

Some remarks on continental drift  

Microsoft Academic Search

Summary The continental drift may be explained by an expanding Earth only. In fact, there is a differences in the rate of heat flow between continents and oceans. Principially, there is a possibility of deriving the value of ancient radii by palaeomagnetic and age measurements.

L. Egyed

1960-01-01

191

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

192

Earth's Decelerating Tectonic Plates  

Microsoft Academic Search

Space geodetic and oceanic magnetic anomaly constraints on tectonic plate motions are employed to determine a new global map of present-day rates of change of plate velocities. This map shows that Earth's largest plate, the Pacific, is presently decelerating along with several other plates in the Pacific and Indo-Atlantic hemispheres. These plate decelerations contribute to an overall, globally averaged slowdown

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

2008-01-01

193

Continental Factors in International Real Estate Returns  

Microsoft Academic Search

This paper examines the extent to which real estate returns are driven by continental factors. This subject is relevant for determining the country allocation of international real estate portfolios. If returns are driven by a continental factor, investors should look for diversification opportunities outside their own continent. This paper finds strong continental factors in North America and especially in the

Piet Eichholtz; Ronald Huisman; Kees Koedijk; Lisa Schuin

1998-01-01

194

Convergent plate margin east of North Island, New Zealand  

SciTech Connect

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

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

1986-07-01

195

Plate Tectonics: Consequences of Plate Interactions  

NSDL National Science Digital Library

This Science Object is the fourth of five Science Objects in the Plate Tectonic SciPack. It identifies the events that may occur and landscapes that form as a result of different plate interactions. The areas along plate margins are active. Plates pushing against one another can cause earthquakes, volcanoes, mountain formation, and very deep ocean trenches. Plates pulling apart from one another can cause smaller earthquakes, magma rising to the surface, volcanoes, and oceanic valleys and mountains from sea-floor spreading. Plates sliding past one another can cause earthquakes and rock deformation. Learning Outcomes:? 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.

National Science Teachers Association (NSTA)

2006-11-01

196

Growth Plate Fractures  

MedlinePLUS

... 2013 by the American Academy of Orthopaedic Surgeons. Growth Plate Fractures Description The bones of children and ... also subject to a unique injury called a growth plate fracture. Growth plates are areas of developing ...

197

Caribbean plate tectonics  

NSDL National Science Digital Library

This illustration available at Wikimedia Commons shows the plate tectonic setting in the Caribbean. Plate boundaries are color-coded by margin type and plate motions are noted with direction and magnitude in mm/yr.

Sting; Commons, Wikimedia

198

Continental collisions and seismic signature  

NASA Astrophysics Data System (ADS)

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

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

1991-04-01

199

Earthquakes in Stable Continental Crust.  

ERIC Educational Resources Information Center

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

Johnston, Arch C.; Kanter, Lisa R.

1990-01-01

200

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

201

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

202

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

203

Strain rate and strength of the continental lithosphere  

NASA Astrophysics Data System (ADS)

Under the Wilson Cycle and Plate Tectonics paradigms, continents are divided between stable continental regions (SCR), which tend to remain un-deformed, and plate boundary zones (PBZ) that repeatedly accommodate deformation associated with opening and closing of tectonic plates. This long-term (> 1 Ma) perspective is reflected in short-term (< 100 a) deformation markers such as seismicity and GPS measurements, which highlight the first-order contrast in strain rates between SCR and PBZ. However, poor data resolution at low strain rates provides only rough upper limits on actual long- and short-term strain and seismicity rates in SCR regions, including in intraplate weak zones (paleo-PBZ) where debate is ongoing regarding short- and long-term deformation rates (e.g., New Madrid seismic zone). We propose to constrain first-order continental strain (and seismicity) rates using lithosphere rheological models, including new strain-weakening rheologies, driven by tectonic forces. We estimate average strain rates that satisfy near-failure equilibrium between net driving forces and lithosphere strength for cases that typify PBZ, cratons, and intraplate weak zones. Our model yields a range of strain rates that vary by up to six orders of magnitude between PBZ and cratons. In intraplate weak zones, structural and tectonic heritage results in significant weakening and yields strain rates compatible with GPS, seismicity, and geological markers. These results provide first-order constraints on long-term lithosphere strength and deformation rates. In particular, we explore upper and lower bounds of possible strain rates in intraplate weak zones of North America, using a range of geotherm, rheology, and local stress conditions. These can be used to derived limits on seismicity rates in these regions.

Mazzotti, S.; Gueydan, F.

2013-12-01

204

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

205

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

206

A record of stable continental region earthquakes from Western Australia spanning the late Pleistocene: Insights for contemporary seismicity  

Microsoft Academic Search

In plate boundary regions moderate to large earthquakes are often sufficiently frequent that fundamental seismic parameters such as the recurrence intervals of large earthquakes and maximum credible earthquake (Mmax) can be estimated with some degree of confidence. The same is not true for the Stable Continental Regions (SCRs) of the world. Large earthquakes are so infrequent that the data distributions

Mark Leonard; Dan Clark

2011-01-01

207

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

208

Thermal and isostatic consequences of simple shear extension of the continental lithosphere  

NASA Astrophysics Data System (ADS)

Quantitative results are presented for a model involving large-scale simple shear of continental lithosphere. The locally compensated, finite element model includes the effects of sedimentation, radiogenic heat production in the crust and sediments, and finite rates of extension. Flexural effects during firting are examined using a simple shear model with a uniform initial elastic thickness. The locally compensated model predicts that a breakup unconformity develops on the upper plate when extension occurs at typical plate tectonic velocities. Subsidence occurs as the upper and lower lithospheric plates separate. Extension creates the potential for large accumulations of sediment ( ˜ 20 km), most of which is syn-rift if sedimentation keeps pace with subsidence. The effect of flexure is to modify the shape of the detachment surface and the uplift patterns on the flanks of the upper and lower plate sedimentary basins. A model which incorporates flexure predicts significant uplift of the lower plate as it is unloaded by the upper plate during extension. The Wernicke simple shear model can be distinguished from its opposite end member, the McKenzie pure shear model, by the predicted asymmetry in thermal evolution (higher predicted heat flux within the upper plate), uplift/subsidence histories and stratigraphic development of the upper and lower plates.

Issler, Dale; McQueen, Herbert; Beaumont, Christopher

1989-01-01

209

Research Paper: Evaluating Clinical Decision Support Systems: Monitoring CPOE Order Check Override Rates in the Department of Veterans Affairs' Computerized Patient Record System  

Microsoft Academic Search

ObjectiveTo measure critical order check override rates in VA Puget Sound Health Care System's computerized practitioner order entry (CPOE) system and to compare 2006 results to a similar 2001 study.DesignAnalysis of ordering and order check data gathered by a post-hoc logging program. Use of Pearson's chi-square contingency table test comparing results from this study and the earlier study.MeasurementsFactors measured were

Ching-Ping Lin; Thomas H. Payne; W. Paul Nichol; Patricia J. Hoey; Curtis L. Anderson; John H. Gennari

2008-01-01

210

Thermal regime of continental subduction: the record from exhumed HP-LT terranes (New Caledonia, Oman, Corsica)  

NASA Astrophysics Data System (ADS)

Unlike the thermal regimes of present-day subduction or collision zones, the variety of possible thermal evolutions accompanying the transient stage of continental subduction (i.e., the shift from oceanic subduction to continental collision) remains poorly known. We herein show that the thermal regime of continental subduction can be confidently retrieved from three well-documented fossil settings (i.e., from high-pressure low temperature continental material from Oman, New Caledonia, Corsica) that were not modified by later collision or a later metamorphic imprint. We primarily focus on their thermal structures (derived from estimates of maximum temperatures, P-T data and age constraints) and overall tectonic organization. For the sake of comparison, new petrological investigations were performed on the metamorphic architecture of northern New Caledonia (Pam Peninsula) and are presented here. We show that the overall structure and metamorphic patterns of these three HP belts derived from continental subduction evidence striking similarities. In particular, the inferred thermal regime of continental subduction appears largely independent from the initial geodynamic setting (i.e., from the initial thermal regime of oceanic subduction, the nature of the incoming plate or of the upper plate). This suggests that continental cover units subducted over a short time period represent cold underplated material that buffers the subduction thermal regime, whatever the exact structure, nature, or thermal state of incoming material. Similarities in the type, size and P-T conditions of the various tectonic units and in the overall tectonic organization point to specific accretionary-type subduction dynamics, yet to differences in mechanical coupling between the three case studies. Our study thereby provides constraints on exhumation dynamics and models of continental subduction

Agard, Philippe; Vitale-Brovarone, Alberto

2013-04-01

211

Thermal regime of continental subduction: The record from exhumed HP-LT terranes (New Caledonia, Oman, Corsica)  

NASA Astrophysics Data System (ADS)

Unlike the thermal structures of present-day subduction or collision zones, the variety of possible thermal evolutions (or "thermal regimes") accompanying the transient stage of continental subduction (i.e., the shift from oceanic subduction to continental collision) remains poorly known. We herein show that the thermal regime of continental subduction can be confidently retrieved from three well-documented fossil settings (i.e., from high-pressure low temperature continental material from Oman, New Caledonia, Corsica) that were not modified by later collision or a later metamorphic imprint. Based on recently published data, we show the striking similarity of the overall thermal and tectonic patterns of these three HP belts derived from the subduction of a continental margin. These natural examples suggest that the thermal regime of continental subduction is largely invariant through time (hence suggesting a steady-state thermal structure) and independent from the initial geodynamic setting (i.e., from the initial thermal structure of oceanic subduction, the nature of the incoming plate or of the upper plate). We propose that continental cover units subducted over a short time period (i.e., ~ 10 My) represent cold underplated material that buffers the subduction thermal regime, whatever the exact structure, nature, or thermal structure of incoming material. Similarities in the type, size and P-T conditions of the various tectonic units and in the overall tectonic organization point to specific accretionary-type subduction dynamics, yet to differences in long-term mechanical coupling between the three case studies. Our study thereby provides constraints on exhumation dynamics and models of continental subduction.

Agard, Philippe; Vitale-Brovarone, Alberto

2013-08-01

212

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

213

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

PubMed Central

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

214

Canyon incision model for prograding continental slopes  

Microsoft Academic Search

Continental slopes have a number of features in common with subaerial landscapes, which suggest that some concepts and methodologies for representing landscape form and process developed in subaerial quantitative geomorphology could be adapted for studying them. As part of that general effort, we have developed a model for deep canyons on the USA East coast continental slope, which are believed

N. C. Mitchell; W. B. Dade

2003-01-01

215

A Facies Model for Temperate Continental Glaciers.  

ERIC Educational Resources Information Center

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

Ashley, Gail Mowry

1987-01-01

216

Continental insulation, mantle cooling, and the surface area of oceans and continents [rapid communication  

NASA Astrophysics Data System (ADS)

It is generally assumed that continents, acting as thermal insulation above the convecting mantle, inhibit the Earth's internal heat loss. We present theory, numerical simulations, and laboratory experiments to test the validity of this intuitive and commonly used assumption. A scaling theory is developed to predict heat flow from a convecting mantle partially covered by stable continental lithosphere. The theory predicts that parameter regimes exist for which increased continental insulation has no effect on mantle heat flow and can even enhance it. Partial insulation leads to increased internal mantle temperature and decreased viscosity. This, in turn, allows for the more rapid overturn of oceanic lithosphere and increased oceanic heat flux. Depending on the ratio of continental to oceanic surface area, global mantle heat flow can remain constant or even increase as a result. Theoretical scaling analyses are consistent with results from numerical simulations and laboratory experiments. Applying our results to the Earth we find, in contrast to conventional understanding, that continental insulation does not generally reduce global heat flow. Such insulation can have a negligible effect or even enhance mantle cooling, depending on the magnitude of the temperature dependence of mantle viscosity. The theory also suggests a potential constraint on continental surface area. Increased surface area enhances the subduction rate of oceanic lithosphere. If continents are produced in subduction settings this could enhance continental growth up to a critical point where increased insulation causes convective stress levels to drop to values approaching the lithospheric yield stress. This condition makes weak plate margins difficult to maintain which, in turn, lowers subduction rates and limits the further growth of continents. The theory is used to predict the critical point as a function of mantle heat flow. For the Earth's rate of mantle heat loss, the predicted continental surface area is in accord with the observed value.

Lenardic, A.; Moresi, L.-N.; Jellinek, A. M.; Manga, M.

2005-06-01

217

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.

218

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

219

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.

220

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

221

78 FR 32183 - Importation of Avocados From Continental Spain  

Federal Register 2010, 2011, 2012, 2013

...Importation of Avocados From Continental Spain AGENCY: Animal and Plant Health Inspection...importation of avocados from continental Spain (excluding the Balearic Islands and Canary...importation of avocados from continental Spain (excluding the Balearic Islands and...

2013-05-29

222

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

223

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.

2007-07-13

224

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.

225

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

226

Rotatable shear plate interferometer  

DOEpatents

A rotatable shear plate interferometer comprises a transparent shear plate mounted obliquely in a tubular supporting member at 45.degree. with respect to its horizontal center axis. This tubular supporting member is supported rotatably around its center axis and a collimated laser beam is made incident on the shear plate along this center axis such that defocus in different directions can be easily measured.

Duffus, Richard C. (Livermore, CA)

1988-01-01

227

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.

228

Subduction of continental margins and the uplift of high-pressure metamorphic rocks  

NASA Astrophysics Data System (ADS)

The mechanism by which high-pressure metamorphosed continental material is emplaced at high structural levels is a major unsolved problem of collisional orogenesis. We suggest that the emplacement results from partial subduction of the continental margin which, because of its high flexural rigidity, produces a rapid change in the trajectory of the descending slab. We assume a two-fold increase in effective elastic thickness of the lithosphere as the continental margin approaches the subduction zone, and calculate the flexural profile of a thin plate for progressive downward migration of the zone of increased rigidity. We assess the effect of changes in the flexural profile on the overlying accretionary prism and mantle wedge as the continent approaches by estimating the extra stresses that are imposed on the wedge due to the bending moment exerted by the continental part of the plate. The wedges overlying the subduction zones, and the subducting slab itself, experience substantial extra compressional stress at depths of around 100 km, and extensional stress at shallower depths, as the continental margin passes through the zone of maximum curvature. The magnitudes of such extra stresses are probably adequate to effect significant deformation of the wedge and/or the descending plate, and are experienced in a time interval of less than 5 m.y. for typical subduction rates. The spatial variation of yield stresses in the region of the wedge and descending slab indicates that much of this deformation may be taken up in the crustal part of the descending slab, which is the weakest region in the deeper parts of the subduction zone. This may result in rapid upward migration of the crust of the partially subducted continental margin, against the flow of subduction. High-pressure metamorphosed terranes emplaced by the mechanism envisaged in this paper would be bounded by thrust faults below and normal faults above. Movement on the faults would have been coeval, and would have resulted in rapid unroofing of the high-pressure terranes, synchronous with arrival of the continental margin at the subduction zone and, therefore, relatively early in the history of a collisional orogen.

Hynes, Andrew; Arkani-Hamed, Jafar; Greiling, Reinhard

1996-05-01

229

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

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

2014-11-01

230

Evolution of Oxidative Continental Weathering  

NASA Astrophysics Data System (ADS)

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

Konhauser, Kurt; Lalonde, Stefan

2014-05-01

231

The Arctic Plate Boundary: Seismotectonics at Ultra-slow Spreading  

Microsoft Academic Search

Earthquakes reveal the dynamics of the Arctic midocean ridge (MOR) system between the Knipovich Ridge and the Laptev Sea continental margin, where the Eurasian and North American plates separate by 1.5-0.5 cm\\/a. By assessing location errors and network detectabilities we have evaluated and quality sorted earthquake reports north of 72°N from 1955-99. Sorting the earthquakes by number of recording stations

O. Eldholm; H. Bungum

2002-01-01

232

Continuum calculations of continental deformation in transcurrent environments  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

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

Adjustable orifice plate seal  

SciTech Connect

This patent describes an orifice fitting of the type having a body with a flow passage for connecting into a pipeline, an orifice plate seal seat located in a slot in the flow passage, a plate carrier which carries an orifice plate having a orifice for the passage of fluid, and gear means in the body for moving the plate carrier from an inactive position out of the flow passage to an active position in the slot in engagement with the seat and with the orifice plate in the flow passage, an improved mans for sealing the orifice plate against the seat. It comprises the plate carrier having a mounting hole therethrough which has an axis, the orifice plate locating in the mounting hole with the orifice concentric with the axis; an annular seal member located on a downstream side of the plate carrier and encircling the mounting hole, the seal member having a downstream face for engaging the seat; a retaining ring located in the mounting hole, sandwiching the orifice plate between the retaining ring and the seal member; mounting means for mounting the retaining ring to the plate carrier so that the retaining ring may protrude in an upstream direction from the plate carrier by an amount that may be adjusted to fit the axial width of the slot; and wherein the mounting means comprises: a set of threads on the perimeter of the retaining ring which engages the threads in the mounting hole, so that rotating the retaining ring relative to the plate carrier will provide a selected protrusion of the retaining ring from the plate carrier; and set screws located in threaded apertures spaced around the retaining ring and extending through the retaining ring into engagement with the orifice plate, so that rotating the set screws in one direction in the threaded.

Foster, J.H.; Beson, J.

1992-03-10

235

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

236

Angular shear plate  

SciTech Connect

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 rotation of the plates and by the use of an appropriate polynomial function for the thickness of the shear plate, light passing therethrough can be focused at variable positions.

Ruda, Mitchell C. (Tucson, AZ); Greynolds, Alan W. (Tucson, AZ); Stuhlinger, Tilman W. (Tucson, AZ)

2009-07-14

237

Flexural characteristics of pre- and post-subduction lithosphere - the influence of large-scale plate loads  

NASA Astrophysics Data System (ADS)

Global studies show an association between seamount subduction and rapid changes in subduction zone characteristics. Observations of seismic and volcanic quiescence, uplift and deformation of the overriding plate, and variations in back-arc extension rate have all been documented near subducting seamounts. Modelling of plate interactions suggests that it is the rate and angle of convergence that determines the style and extent of deformation observed. However, these studies do not include along-strike variations in the structure of the overriding plate or density variations in the subducting plate. Nor do they address the question of whether deformation is a flexural response to bending of a loaded plate or a plastic response due to crustal thickening during convergence. The collision zone between the Louisville Ridge seamount chain and the Tonga-Kermadec trench at 26°S is associated with changes in subduction zone seismogenesis, crustal structure, and trench strike and depth. This makes it an ideal locality to determine not only the mechanical properties of both the down-going and overriding plates, but also the effect of large-scale plate topography on subduction zone processes. Approximately 1800 km of coincident multi-channel and wide-angle seismic data, coupled with gravity, magnetic and swath bathymetry data were acquired throughout the Tonga-Kermadec-Louisville Ridge region between April-June 2011 during a cruise aboard the R/V Sonne (SO215), the second leg of the TOTAL (Tonga Thrust earthquake asperity at Louisville Ridge) project. Profiles follow a trend both parallel and perpendicular to the trench, and oblique to and along the Louisville Ridge. The along and across ridge profiles were designed to determine the background structure of the down-going plate, the response to magmatic and topographic loading and the volume and extent of any crustal underplate. The across trench profiles were designed to determine the structure of both the pre- and post-collisional crust proximal to the trench, to the south and north of the collision zone respectively. Variations in seismic velocity structure from the pre-to-post collision zones elucidate the degree of crustal deformation due to faulting, and alteration due to fluid ingress and serpentinisation. The resulting crustal models, coupled with those for profiles from the first leg of the TOTAL project (cruise SO195), are used to provide the crustal structure reference for flexural modelling of the system, to determine how the seamounts are deformed on subduction, and what role they play in the region's seismogenesis, in effect testing the Kelleher and McCann hypothesis that bathymetric features control aspects of arc seismicity.

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

2012-12-01

238

Multicolor printing plate joining  

NASA Technical Reports Server (NTRS)

An upper plate having ink flow channels and a lower plate having a multicolored pattern are joined. The joining is accomplished without clogging any ink flow paths. A pattern having different colored parts and apertures is formed in a lower plate. Ink flow channels each having respective ink input ports are formed in an upper plate. The ink flow channels are coated with solder mask and the bottom of the upper plate is then coated with solder. The upper and lower plates are pressed together at from 2 to 5 psi and heated to a temperature of from 295 F to 750 F or enough to melt the solder. After the plates have cooled and the pressure is released, the solder mask is removed from the interior passageways by means of a liquid solvent.

Waters, W. J. (inventor)

1984-01-01

239

Continental volume and freeboard through geological time  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

240

The effect of continental lids on the long-term efficiency of mantle convective stirring  

NASA Astrophysics Data System (ADS)

Interpreting surface geochemical data requires the understanding of the dynamic mechanisms that can preserve or erase chemical heterogeneities over geological times. Among these, the presence of continental lids is known to have a first order impact on mantle convective dynamics and heat transfer. On Earth oceanic plates are recycled into the mantle and are characterized by a relatively strong heat flux, while continents are more insulating, lighter and therefore not subductable. Numerical and laboratory experiments have demonstrated that the dichotomy between continents and oceans can have a first order influence on mantle motions. One should therefore expect that this influence also reflects on the efficiency of convective stirring over billions of years. However, this effect has not been considered in previous studies that investigated mantle convective stirring efficiency. We have therefore investigated the influence of continental lids on convective stirring efficiency using numerical experiments at infinite Prandtl number, in rectangular domain. Differences between oceanic and continental plates are accounted for by imposing heterogeneous surface boundary conditions for temperature and velocities: oceanic plates are described by Dirichlet boundary conditions while continents are modeled as highly viscous, floating lids of variable extent, locally imposing a prescribed surface heat flux. We use passively advected tracers to quantify the stirring efficiency with various diagnostics such as mixing time and Lyapunov exponent distribution. This numerical set up allows us to quantify systematically the influence of several governing parameters on the convective stirring efficiency: the Rayleigh number Ra, the horizontal extent of continental lids, as well as the magnitude of their insulating character.

Samuel, Henri; Deo, Bhaskar

2010-05-01

241

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

242

Pyrenean orogeny and plate kinematics  

NASA Astrophysics Data System (ADS)

The evolution of the Pyrenees, a mountain range between Iberia and Eurasia, has remained the subject of many debates between geologists and geophysicists for a long time. By combining the identification of seafloor spreading anomalies A33o to M0 in the Bay of Biscay with those in the North Atlantic, we have derived a position of a mean pole of rotation for the entire opening of the Bay of Biscay. Four hundred kilometers of shortening took place between the Iberian and Eurasian plates in the Pyrenean domain during the opening of the Bay of Biscay, from chrons M0 to A33o time (118 to 80 Ma). The deep seismic Etude Continentale et Océanique par Réflexion et réfraction Sismique (ECORS) profile shot across the Pyrenees and teleseismic data show the presence of two distinct slabs, which dip to the north. The southern slab is linked to the subduction of the neo-Tethys Ocean, which was created from late Jurassic to early Aptian. Simultaneously, elongated back arc basins formed along the future Pyrenean domain. This slab was active from at least 118 Ma (early Aptian) to 100 Ma (late Albian). The northern slab, active since 85 Ma, is linked to the subduction of the lower continental crust located south of the Pyrenean domain. In the upper crust, normal faults as well as the north Pyrenean fault became reverse faults, and former back arc basins were inverted, giving rise to the uplift of the Pyrenees as a double asymmetrical wedge.

Sibuet, Jean-Claude; Srivastava, Shiri P.; Spakman, Wim

2004-08-01

243

78 FR 56622 - Airworthiness Directives; Continental Motors, Inc. Reciprocating Engines With Superior Air Parts...  

Federal Register 2010, 2011, 2012, 2013

...38896, August 5, 2009), for certain Teledyne Continental Motors reciprocating engines...Continental Motors, Inc. (formerly Teledyne Continental Motors, Continental...cylinder compression tests can be found in Teledyne Continental Aircraft Engine Service...

2013-09-13

244

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

245

Deep Continental Studies in India  

NASA Astrophysics Data System (ADS)

The Department of Science and Technology, Government of India, under Earth System Science deals with Research and Development programs related to Earth and Atmospheric Sciences. One of the major ongoing programs includes the Deep Continental Studies (DCS) wherein projects undertaking studies of deep structural configuration of the Indian Lithosphere are supported. Challenging and critical areas of research are first identified and transect corridors are selected for integrated multidisciplinary research to be carried out on a National scale by involving Universities, National Institutions, Survey organizations amongst others. Although results from individual projects are published independently, efforts are made to publish a special issue of a National journal containing papers with the main results. Some of the successfully completed multi-disciplinary transects include Himprobe (NW Himalaya), Nagaur-Jhalawar (NW India), Mungwani-Kalimati (Central India), Kuppam-Palani (South India). The efforts during the recent years have resulted in multi-institutional, multi- disciplinary collaboration and synthesis of data across disciplinary boundaries, augmentation of high cost instrumentation facilities as well as in building up of expertise in some of the advanced techniques. Significant achievements s made under DCS including highlights of the projects, future strategy for research in the area etc. will be presented.

Rajaram, M.; Gupta, K. R.

2003-12-01

246

Volatile components and continental material of planets  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

247

Modeling the dynamics of continental shelf carbon.  

PubMed

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. PMID:21329200

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

248

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

249

Plates and FEM  

NASA Astrophysics Data System (ADS)

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

Blaauwendraad, J.

250

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.

2007-12-12

251

Plating methods, a survey  

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

252

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

253

Continental transform margins : state of art and future milestones  

NASA Astrophysics Data System (ADS)

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

Basile, Christophe

2010-05-01

254

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.

Cara Harwood

255

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 May 2011 Keywords: Geodynamics Plate tectonics a b s t r a c t We present a new algorithm for modeling margins and plates, traditional global plate tectonic reconstructions have become inadequate

Bower, Dan J.

256

Images may show start of European-African plate collision  

NASA Astrophysics Data System (ADS)

Aspects of the initial stages of a collision between European and African plates may have been documented in a geophysical survey of the central Mediterranean Ridge (MR) conducted last year. The idea of an incipient collision was first suggested by Finetti [1976],and details of the seafloor and tectonic deformation along the MR, revealed for the first time in the survey, seem to point in that direction.A unique opportunity may therefore exist for studying the beginnings of such a collision—between the passive margin of a major plate (Africa) acting as a continental indenter against the active margin of another plate (Europe). More wide angle data, deep penetrating multichannel seismic data, and drilling data are crucial to better assess the nature and the architecture of the underlying lithosphere, the styles of sedimentary deformation, and the consequences on fluid releases. Such data will make it possible to establish, or reject, a geodynamic collision model.

Mascle, J.; Huguen, C.; Benkhelil, J.; Chamot-Rooke, N.; Chaumillon, E.; Foucher, J. P.; Griboulard, R.; Kopf, A.; Lamarche, G.; Volkonskaia, A.; Woodside, J.; Zitter, T.

257

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.

258

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

259

How Do Plates Move?  

NSDL National Science Digital Library

The representation shows the circulation of convection cells in the mantle related to plate movement. A static cross-sectional diagram and accompanying text illustrates the how material heated by the core rises and then sinks when it eventually cools down and attributes this cycle of heating and cooling to tectonic plate movement.

260

Plating To Reinforce Welded Joints  

NASA Technical Reports Server (NTRS)

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

Otousa, J. E.

1982-01-01

261

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

262

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

263

Fashion Plate Collection  

NSDL National Science Digital Library

There are fashion plates, and then there are the exquisite fashion plates that constitute the University of Washington Libraries digitized collection. The plates were first collected by long-time home economics professor Blanche Payne, who taught at the University from 1927 to 1966. The plates come from leading French, American, and British fashion journals of the 19th and early 20th century and they document many stylistic periods, such as the Empire, Romantic, Victorian, and Edwardian. Visitors will want to start by reading an essay on the collection, and then they should feel welcome to browse the collection of over 400 plates at their leisure, or to browse the collection by subject. One fascinating aspect of the site is an extended excerpt from the 1913 book "Dame fashion" which comments on the history and transformation of various fashions during the 19th century.

264

Thermophoresis of Graphene Plates  

NASA Astrophysics Data System (ADS)

Thermophoresis of graphene plates in an air medium is discussed within the framework of a molecular-kinetic approach. Its rate is found to be independent of the plate area and the aspect ratio of a rectangular graphene. It does depend on the plate orientation in space, which is controlled by the principle of least resistance. The dependence is expressed via a geometrical parameter ?, whose limiting values within the variation interval are found to be 0.46 and 0.65. A solution of the Euler problem on the Brownian rotation of a plate around its center of mass as a result of collisions of molecules in the temperature gradient field allowed us to obtain for the graphene plates a statistical average of ? =0.5. This value turned out to be the same as the one for spherical nanoparticles, for which rotations are irrelevant.

Bubenchikov, A. M.; Bubenchikov, M. A.; Potekaev, A. I.; Maslov, A. S.; Ovcharenko, V. V.; Usenko, O. V.

2014-11-01

265

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

266

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

PubMed

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 lithosphere during the initial stages of rifting. Here we show that most of the strain during the July-August 2007 seismic crisis in the weakly extended Natron rift, Tanzania, was released aseismically. Deformation was achieved by slow slip on a normal fault that promoted subsequent dyke intrusion by stress unclamping. This event provides compelling evidence for strain accommodation by magma intrusion, in addition to slip along normal faults, during the initial stages of continental rifting and before significant crustal thinning. PMID:19079058

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

2008-12-11

267

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

268

An explanation for the age independence of oceanic elastic thickness estimates from flexural profiles at subduction zones, and implications for continental rheology  

NASA Astrophysics Data System (ADS)

Most properties of oceanic lithosphere are widely observed to be dependent on the age of the plate, such as water depth, heat flow, and seismogenic thickness. However, estimates of the ‘effective elastic thickness' of oceanic lithosphere based on the deflection of the plate as it enters a subduction zone show little correlation with the age of the incoming lithosphere. This paradox requires reconciliation if we are to gain a full understanding of the structure, rheology, and behaviour of oceanic lithosphere. Here, we show that the permanent deformation of the plate due to outer-rise faulting, combined with uncertainties in the yield stress of the lithosphere, the in-plane forces transmitted through subduction zones, and the levels of noise in bathymetric and gravity data, prevents simple elastic plate modelling from accurately capturing the underlying rheological structure of the incoming plate. The age-independent estimates of effective elastic thickness obtained by purely elastic plate modelling are therefore not likely to represent the true rheology of the plate, and hence are not expected to correspond to the plate age. Similar effects may apply to estimates of elastic thickness from continental forelands, with implications for our understanding of continental rheology.

Craig, Timothy J.; Copley, Alex

2014-04-01

269

The basins on the Argentine continental margin  

SciTech Connect

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

Urien, C.M. [Buenos Aires Technological Institute Petroleum School, Buenos Aires (Argentina)

1996-08-01

270

Subduction and Plate Edge Tectonics in the Southern Caribbean  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

271

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

USGS Publications Warehouse

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

Bohannon, R.G.; Parsons, T.

1995-01-01

272

Earthquakes and plate tectonics.  

USGS Publications Warehouse

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

Spall, H.

1982-01-01

273

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

NASA Astrophysics Data System (ADS)

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

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

1993-09-01

274

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

275

New magnetic anomaly map of the East Antarctic continental margin  

NASA Astrophysics Data System (ADS)

Marine magnetic survey coverage of the southern part of Indian Ocean is to a certain extent limited for defining the magnetic pattern of the continental margin of East Antarctica. The USA research vessels collected the bulk of the marine magnetic data in the beginning of 1960's. During the succeeding years Australian, German, Japanese, Russian and other international scientific programs made major contributions to the network of marine magnetic data. Since the beginning of new century only two nations (Russian and Australian) have acquired the marine magnetic data in the southern part of Indian Ocean. The marine surveys in the Cosmonaut Sea, the western part of the Cooperation Sea in the Davis and Mawson Seas were accomplished by the PMGRE in 2000-2009 field seasons. The marine magnetic data collected during two seasons (2001-2002) within the AASOPP Project which was established in early 2000 to define the outer limits of the continental shelf offshore of the Australian Antarctic Territory (AAT) covered the full length of the AAT from 40OE to 160OE. The new magnetic anomaly map of the East Antarctic continental margin incorporates all available data acquired by the international community since the IGY 1957-58 through to 2009. Results of the compilation do not radically alter recent models describing first-order motions between the Antarctic, Australian and Indian plates, but they help to resolve uncertainties in early break-up history of opening between these plates. The timing and direction of early seafloor spreading in the area off the Antarctic margin, once conjugate to part of the Southern Greater Indian margin and to Australian margin, along the largely unknown region of the Enderby Basin, Davis Sea and Mawson Sea has been analyzed by many authors using different data sets. It is highly likely that spreading in the Enderby Basin occurred around the same time as the well documented M-sequence (anomalies M10 to M0) off the Perth Basin, Western Australia (Powell et al. 1988). The history of the early spreading is complicated further by the likelihood of one or several ridge jumps in which most early seafloor crust was transferred to the Antarctic plate and the Elan Bank micro-continent was isolated from the Indian continent (Muller et al. 2001). Additionally, a large amount of the seafloor crust is now probably overprinted by igneous activity associated with the Kerguelen Plume, which began forming the Kerguelen LIP from about 120-110 Ma. However all available results of interpretations do not match to the magnetic anomaly pattern which can be distinguished by the newly compiled map. Our observations suggest that this is especially correct to the Enderby Basin and to lesser degree for the region that was conjugate to Australia. The prominent magnetic anomaly boundary signal and sharp basement step correlated with the MacRobertson Coast Anomaly or the Enderby Basin Anomaly (Golynsky et al., 2007) is not observed elsewhere in the Enderby Basin, Princess Elizabeth Trough or Davis Sea. In the central Enderby Basin there some evidences for an abandoned ‘fossil' spreading centre that might continue to the west of the Kerguelen Plateau, east of Gunnerus Ridge. The estimated timing of its extinction corresponding to the early surface expression of the Kerguelen Plume at the Southern Kerguelen Plateau around 120 Ma and the subsequent formation of the Elan Bank microcontinent. Alternatively, the ridge jump occurred only in the central Enderby basin, due to the proximity of the Kerguelen plateau, whereas seafloor spreading continued in the western Enderby basin and conjugate south of Sri Lanka basin.

Golynsky, Alexander; Ivanov, Sergey; Kazankov, Andrey

2010-05-01

276

Farallon Plate remnants  

NSDL National Science Digital Library

The Rockies are fifteen hundred kilometers, or one thousand miles, to the east. The cause must be the tectonic plate that built these mountains. Its name is Farallon. Farallon started off normally enough. It plunged beneath the North American Plate at a forty-five degree angle. This process sprouted volcanoes to form the Sierra Nevada in what is now California. Next, mantle motions pulled North America westward over Farallon, and the plate scraped along the bottom of the continent - for fifteen hundred kilometers. As North America continued its westward trek, Farallon settled to the bottom of the mantle.

Stuart Snodgrass

2002-03-14

277

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.

278

MAGSAT anomaly map and continental drift  

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

279

Do the pyramids show continental drift?  

PubMed

The mystery of the orientation of the Great Pyramids of Giza has remained unexplained for many decades. The general alignment is 4 minutes west of north. It is argued that this is not a builders' error but is caused by movement over the centuries. Modern theories of continental drift do not predict quite such large movements, but other causes of polar wandering give even smaller shifts. Thus, continental drift is the most likely explanation, although somewhat implausible, especially as relevant measurements have been made over a 50-year period, whereas geophysical measurements of sea-floor spreading relate to million-year time scales. PMID:17832769

Pawley, G S; Abrahamsen, N

1973-03-01

280

Ions in oceanic and continental air masses  

NASA Astrophysics Data System (ADS)

Results are presented of measurements of tropospheric ions and several trace atmospheric neutral species, performed at a continental location (the Cheeka Peak Research Station, located at the very northwest corner of the conitnental U.S.) and at a mid-oceanic location (Mauna Loa Observatory). In contrast to previous reports, NH4(+) and protonated pyridine were often encountered as terminal positive ion speices at the Mauna Loa location. Two new positive ion species were identifiled: protonated caprolactam and a saturated six-carbon primary amine. The differences between ions observed in continental and mid-oceanic air masses are discussed.

Tanner, D. J.; Eisele, F. L.

1991-01-01

281

A geodynamic constraint on Archean continental geotherms  

NASA Astrophysics Data System (ADS)

Dewey (1988) observed that gravitational collapse appears to currently limit the altitudes of large plateaus on Earth to about 3 to 5 km above sea level. Arndt (1999) summarized the evidence for the failure of large parts of the continental crust to reach even sea-level during the Archean. If this property of Archean continental elevations was also enforced by gravitational collapse, it permits an estimation of the geothermal gradient in Archean continental crust. If extensional (collapse) tectonics is primarily a balance between gravitational power and the power consumed by extensional (normal) faulting in the upper brittle crust, as analysed by Bailey (1999), then it occurs when continental elevations above ocean bottoms exceed about 0.4 times the thickness of the brittle crust (Bailey, 2000). Assuming an Archean oceanic depth of about 5 km, it follows that that the typical thickness of Archean continental brittle crustal must have been less than about 12 km. Assuming the brittle-ductile transition to occur at about 350 degrees Celsius, this suggests a steep geothermal gradient of at least 30 degrees Celsius per kilometer for Archean continents, during that part of the Archean when continents were primarily submarine. This result does not help resolve the Archean thermal paradox (England and Bickle, 1984) whereby the high global heat flow of the Archean conflicts with the rather shallow crustal Archean geotherms inferred from geobarometry. In fact, the low elevation of Archean continental platforms raises another paradox, a barometric one: that continents were significantly below sea-level implies, by isostasy, that continental crustal thicknesses were significantly less than 30 km, yet the geobarometric data utilized by England and Bickle indicated burial pressures of Archean continental material of up to 10 kb. One resolution of both paradoxes (as discussed by England and Bickle) would be to interpret such deep burials as transient crustal thickening events of duration less than the crustal thermal equilibriation time (about 10 to 30 Ma). Temporary entrainment in the wake of basal eclogite ``sinkers'' might provide such transient burial. Vlaar's (1994) modelling of this eclogite delamination process (tectonically elaborated by Zegers and van Keken (2001)) indicates such sinker events would be significantly shorter than 10 Ma. The topographic re-equilibriation of a hot moho above such a process would be similarly short (Kaufmann and Royden, 1994).

Bailey, R. C.

2003-04-01

282

The nature of the plate interface and driving force of interseismic deformation in the New Zealand plate-boundary zone, revealed by the continuous GPS velocity field  

NASA Astrophysics Data System (ADS)

New Zealand straddles the boundary between the Australian and Pacific plates. Cenozoic relative plate motion has resulted in a complex pattern of faulting and block rotation, with displacements on individual faults up to hundreds of kilometers. However, over periods of several years, GPS measurements show a remarkably smooth pattern of velocities. We show here using a new method of back slip analysis, that almost the entire plate-boundary continuous GPS velocity field can be predicted within measurement error from a simple model of elastic distortion due to deep slip on a single plate interface (megathrust in the Hikurangi and Putsegur subduction zones or fault through continental lithosphere beneath the Southern Alps) at the relative plate motion rates. This suggests that the main driving force of plate-boundary deformation is slip on the deeper moving part of the plate interface, without buried creep in localized shear zones beneath individual surface faults. The depth at which this deep slip terminates (locking point line) determines the width of deformation. Along the Hikurangi margin, there is also clockwise rotation of ~150 km long segment of the fore arc (Wairoa domain) at 4.5° ± 1 Ma, relative to the Australian Plate, about a pole in western North Island; model residuals in the velocity field are mainly a result of incomplete averaging of the cycle of slow slip events on the plate interface, downdip of the locking point.

Lamb, Simon; Smith, Euan

2013-06-01

283

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

284

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

285

Violin plate modes.  

PubMed

As the first step toward developing a generic model for the acoustically radiating vibrational modes of the violin and related instruments, the modes of both freely supported and edge-constrained top and back plates have been investigated as functions of shape, arching height, elastic anisotropy, the f-holes and associated island area, thickness graduations, and the additional boundary constraints of the ribs, soundpost, and bass-bar present in the assembled instrument. Comsol shell structure finite element software has been used as a quasi-experimental tool, with physical and geometric properties varied smoothly, often over several orders of magnitude, allowing the development of the plate modes to be followed continuously from those of an initially square plate to those of doubly-arched, guitar-shaped, orthotropic plates and their dependence on all the above factors. PMID:25618046

Gough, Colin

2015-01-01

286

Feynman's wobbling plate  

NASA Astrophysics Data System (ADS)

In the book Surely You Are Joking, Mr. Feynman! Richard Feynman tells a story of a Cornell cafeteria plate being tossed into the air. As the plate spun, it wobbled. Feynman noticed a relation between the two motions. He solved the motion of the plate by using the Lagrangian approach. This solution didn't satisfy him. He wanted to understand the motion of the plate by analyzing the motion of its individual particles and the forces acting on them. He was successful, but he didn't tell us how he did it. We provide an elementary explanation for the two-to-one ratio of wobble to spin frequencies, based on an analysis of the motion of the particles and the forces acting on them. We also demonstrate the power of numerical simulation and computer animation to provide insight into a physical phenomenon and guidance on how to do the analysis.

Tuleja, Slavomir; Gazovic, Boris; Tomori, Alexander; Hanc, Jozef

2007-03-01

287

Tectonic Plate Movement.  

ERIC Educational Resources Information Center

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

Landalf, Helen

1998-01-01

288

Flat plate solar oven  

SciTech Connect

The construction of an Indian Rs. 186 (US $20.33) flat-plate solar oven is described. Detailed drawings are provided and relevant information on cooking times and temperature for different foods is given.

Parikh, M.

1981-01-01

289

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

290

From plume head to continental lithosphere in the Arabian-Nubian shield  

NASA Astrophysics Data System (ADS)

The lithosphere of the Arabian-Nubian shield was mainly formed during an interval of about 150 million years near the end of the Proterozoic aeon. The events recorded in the rocks of the shield indicate that an oceanic plateau, formed by the head of an upwelling mantle plume, was later overprinted with continent-like characteristics by plate convergence and its associated magmatism. Similar sequences of events are seen in the geological record from Archaean to recent times, suggesting that the transformation from plume head to continental lithosphere has been an important component of continent generation throughout Earth history.

Stein, Mordechai; Goldstein, Steven L.

1996-08-01

291

Plate Tectonics: An Introduction  

NSDL National Science Digital Library

In the early 1900s, most geologists thought that Earth's appearance, including the arrangement of the continents, had changed little since its formation. This video segment describes the impact the theory of plate tectonics has had on our understanding of Earth's geological history, and provides a brief overview of what is currently known about the Earth's tectonic plates and their motions. The segment is two minutes twenty-one seconds in length. A background essay and list of discussion questions are also provided.

292

Fractal multifiber microchannel plates  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

293

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.

294

Thin Viscous Sheet Models for Distributed Deformation of Oceanic Lithosphere Accommodating Motion Between the India, Capricorn, and Australia Plates  

NASA Astrophysics Data System (ADS)

While it has been long recognized that plate boundaries through continents were typically diffuse, it has taken longer to recognize the extent of diffuse plate boundaries in the oceans. The strain rates in diffuse oceanic plate boundaries are typically lower than in diffuse continental boundaries, but about the same fraction of oceanic lithosphere is diffuse boundary as is found in continental lithosphere. Many fundamental questions remain unanswered or poorly constrained. E.g., What controls the length-scale of this deformation? What is the rheology of deforming oceanic lithosphere? What controls the sense and style of deformation? Displacement rates range up to ?15 mm a^{-1} and strain rates up to 10^{-16} s^{-1}. Diffuse oceanic plate boundaries are much wider than traditionally defined narrow plate boundaries such as mid-ocean ridges for which the main boundary zone is 1 to 2 km wide. In contrast the diffuse boundary between the India and Australia plates seaward of the Java-Sumatra trench is thousands of km wide. The inferred strain rates are one to three orders of magnitude greater than the average oceanic intraplate strain rate inferred from seismic moment release or thermal contraction in old oceanic lithosphere, but many orders of magnitude lower than in traditional narrow plate boundaries. In this presentation, we review some key observations of diffuse oceanic plate boundaries and present an investigation of the rheology and dynamics of the India-Capricorn-Australia plate boundaries mainly through the application and analysis of thin viscous sheet models.

Gordon, R. G.; Houseman, G. A.

2011-12-01

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

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

297

Elephant teeth from the atlantic continental shelf.  

PubMed

Teeth of mastodons and mammoths have been recovered by fishermen from at least 40 sites on the continental shelf as deep as 120 meters. Also present are submerged shorelines, peat deposits, lagoonal shells, anz relict sands. Evidently elephants and other large mammals ranged this region during the glacial stage of low sea level of the last 25,000 years. PMID:17741070

Whitmore, F C; Emery, K O; Cooke, H B; Swift, D J

1967-06-16

298

Seismotectonics of the Norwegian continental margin  

Microsoft Academic Search

The Norwegian continental margin and surrounding areas are seismically less active than some other passive margins worldwide, indicating a potential earthquake deficit. The adjacent oceanic crust is mostly aseismic except for parts of the Lofoten and Norway Basins which have experienced rapid deposition of glacial sediments. The excess load has enhanced the local stress field and, in turn, the seismic

Unni Byrkjeland; Hilmar Bungum; Olav Eldholm

2000-01-01

299

Continental thermal isostasy: 1. Methods and sensitivity  

Microsoft Academic Search

Continental elevations result from a combination of compositional and thermal buoyancy and geodynamic forces. Thermal effects are often masked by compositional variations to crustal density and thickness that produce equal or greater relief. We have developed a method by which compositional variations in the crust may be removed, thereby isolating the thermal contribution to elevation. This isostatic correction normalizes the

Derrick Hasterok; David S. Chapman

2007-01-01

300

Moroccan Crustal Response to Continental Drift  

Microsoft Academic Search

The formation and development of a zone of spreading beneath the continental crust resulted in the breakup of Pangea and formation of the Atlantic Ocean. The crust of Morocco bears an extremely complete record of the crustal response to this episode of mantle dynamics. Structural and related depositional patterns indicate that the African margin had stabilized by the Middle Jurassic

W. H. Kanes; M. Saadi; E. Ehrlich; A. Alem

1973-01-01

301

Introduction Fossil age constraints for continental sedimentary  

E-print Network

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

Andersen, Torgeir Bjørge

302

Do the Pyramids Show Continental Drift?  

Microsoft Academic Search

The mystery of the orientation of the Great Pyramids of Giza has remained unexplained for many decades. The general alignment is 4 minutes west of north. It is argued that this is not a builders' error but is caused by movement over the centuries. Modern theories of continental drift do not predict quite such large movements, but other causes of

G. S. Pawley; N. Abrahamsen

1973-01-01

303

Elephant teeth from the atlantic continental shelf  

USGS Publications Warehouse

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

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

1967-01-01

304

Rates of continental erosion and mountain building  

Microsoft Academic Search

The first objective of this work was to obtain values for the rates at which continental erosion can smooth out or remove the topographic expression produced by orogeny. The dominant part is played by mechanical erosion, which acts most strongly in regions of large topographic expression. Chemical erosion depends strongly on precipitation or runoff in individual river drainage basins, but

C. G. A. Harrison

1994-01-01

305

Submarine landslide geomorphology, US continental slope  

Microsoft Academic Search

The morphometric analysis of submarine landslides in four distinctly different tectonic environments on the continental slopes of Oregon, central California, Texas, and New Jersey provides useful insight into submarine process, including sediment transport mechanisms and slope stability. Using Geographic Information System (GIS) software, we identify landslides from multibeam bathymetric and GLORIA sidescan surveys based solely on surficial morphology and reflectivity.

B. g. Mcadoo; L. f. Pratson; D. l. Orange

2000-01-01

306

Present-day velocity and stress fields of the Amurian Plate from thin-shell finite-element modelling  

Microsoft Academic Search

SUMMARY Most numerical models of Asian deformation focus on rapidly deforming zones close to the Indian indenter, and seldom extend to its northern 'deformation front'. In this study, we examine the present-day deformation of the Amurian continental plate (northeast Asia) which faces stable Eurasia along the Baikal-Stanovoy boundary. The present-day velocity and stress fields of the Amurian Plate are reproduced

Carole Petit; Marc Fournier

2004-01-01

307

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

E-print Network

;Edeline et al. Eel continental dispersal INTRODUCTION Eels Anguilla spp. are fishes belonging) habitats. Such a ubiquity is exceptional among teleost fishes. However, the mechanisms controlling eel of morphological, physiological and behavioural adaptive changes. In the eel, metamorphosis of translucent

Paris-Sud XI, Université de

308

Scintillating plate calorimeter mechanical design  

Microsoft Academic Search

Progress on designs for compensating scintillator plate calorimeters will be presented. One design includes a lead composite absorber, fiber readout, and radiation hardened scintillator plates, and the second design has depleted uranium absorbers, wave length shifter plate readout, and scintillator plates. The lead absorber is cast with slots to accept the scintillator in the first design, while the depleted uranium

A. Buehring; N. Hill; T. Kirk; J. Nasiatka; E. Petereit; L. Price; J. Proudfoot; H. Spinka; D. Underwood; M. Burke; D. Hackworth; T. Hordubay; D. Marshik; D. Scherbarth; R. Swensrud

1990-01-01

309

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.

310

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

311

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

312

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

313

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

314

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

315

78 FR 32184 - Importation of Fresh Apricots From Continental Spain  

Federal Register 2010, 2011, 2012, 2013

...Importation of Fresh Apricots From Continental Spain AGENCY: Animal and Plant Health Inspection...States of fresh apricots from continental Spain. This action will allow interested persons...importation of fresh apricots from continental Spain into the United States subject to a...

2013-05-29

316

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

NASA Astrophysics Data System (ADS)

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

Molnar, P. H.

2010-12-01

317

Diffuse Oceanic Plate Boundaries, Thin Viscous Sheets of Oceanic Lithosphere, and Late Miocene Changes in Plate Motion and Tectonic Regime  

NASA Astrophysics Data System (ADS)

Diffuse plate boundaries are often viewed as a characteristic only of continental lithosphere and as a consequence of its rheology, while narrow boundaries and plate rigidity are viewed as characteristic of oceanic lithosphere. Here we review some of the evidence that shows that deformation in the ocean basins is in many places just as diffuse as deformation in the continents. Moreover, we argue that the best description of these oceanic deforming zones is the un-plate tectonic-like representation as a fluid. Diffuse oceanic plate boundaries are deforming zones that are typically thousands of kilometers long (along strike) and hundreds to thousands of kilometers wide (across strike). These plate boundaries also appear to have deformation that is broadly distributed with no single fault or system of faults taking up most of the relative plate motion. Consequently the spatially averaged strain rates across diffuse oceanic plate boundaries are orders of magnitude lower than in narrow plate boundaries. One of Earth's best examples of a diffuse oceanic plate boundary is located in the equatorial Indian Ocean. A fluid-like representation of deformation in this diffuse boundary explains many observations, including the steadiness of the deformation process, the characteristic across-strike width of deformation relative to the along-strike length of the deforming zone, and the change of style in deformation across the 86°E fracture zone. In addition, poles of relative rotation between adjacent component plates tend to lie within the diffuse plate boundary that separates them; this is also predicted by models of diffuse plate boundaries that assume a power-law fluid approximation, irrespective of rheology (for power-law rheologies between Newtonian and plastic end-members). A change in behavior of the lithosphere from elastic or visco-elastic to that of a fluid may be interpreted as a phase change, not in microscopic but in megascopic properties, above a certain threshold of force per unit length applied to the lithosphere. There remain many outstanding fundamental kinematic, dynamical, and rheological questions, the answers to which would enhance our understanding of diffuse oceanic plate boundaries. These questions include the timing of initiation and acceleration of motion across various diffuse oceanic plate boundaries, the relative and absolute strengths of the upper and lower oceanic lithosphere, changes in torques across diffuse oceanic plate boundaries and their role in causing rapid changes in plate motion. Of particular interest is the role of diffuse oceanic plate boundaries in the widespread re-organization of plate motion and tectonic regime that occurred at ~8 Ma in the Tibetan Plateau, Indian Ocean, Pacific Ocean, and western North America. Diffuse plate boundaries, especially in the oceans, are excellent natural laboratories, not only as windows on the mechanical and rheological properties of the lithosphere, but also--at least in the oceans--for investigating a variety of styles of widely distributed deformation that is ignored by traditional plate tectonics.

Gordon, R. G.; Royer, J.

2005-12-01

318

Tectonic Plates, Earthquakes, and Volcanoes  

NSDL National Science Digital Library

According to theory of plate tectonics, Earth is an active planet -- its surface is composed of many individual plates that move and interact, constantly changing and reshaping Earth's outer layer. Volcanoes and earthquakes both result from the movement of tectonic plates. This interactive feature shows the relationship between earthquakes and volcanoes and the boundaries of tectonic plates. By clicking on a map, viewers can superimpose the locations of plate boundaries, volcanoes and earthquakes.

319

Towards 3D numerical modelling of Alpine-like continental collision  

NASA Astrophysics Data System (ADS)

The driving forces and the main deformation processes leading to the development and the evolution of a mountain belt have been matter of debate since the acceptance of plate tectonics. Most of the kinematic reconstructions of the 3D evolution of collision zones based on geological and geophysical data are generally not mechanically consistent. Since 20 years, reliable numerical models propose key parameters to rely the physical causes to the deformation observed, but, for technological reasons, they have been limited for long to two dimensions, inducing important limitations to understand the collision zones processes. For example, in 2D, it is impossible to take into account both the crustal thickening and micro-plate rotation and translation, which are two processes having a major role during collision, but which relative importance is debated. The European Alps are an excellent example of a well accessible small-scale mountain belt, which has been thoroughly examined from a geological point of view. During the past decades, the geological information has been complemented with geophysical data on the deep crustal structure of the Alps. Much of this information highlights the three-dimensional structure of the region, in which an Adriatic micro-plate is wedged between the Adriatic and European crust. Recently, a change in subduction polarity has been found between the Western and Eastern Alps, which is thought to be related to the anticlockwise rotation of the Adriatic micro-plate during collision. We recently developed a massively parallel 3D thermomechanical deformation code that is ideally suited to solve coupled mantle, lithosphere and surface processes and can model large deformations. Here, we employ this code to study several scenarios that might have resulted in the formation of the European Alps. The computations have been performed on Juqueen, FZ Jülich. Our model setup consists of an oceanic plate bearing a small rigid continent (Adria micro-plate) that moves northwards with an anticlockwise rotation component and subducts beneath a more viscous continental plate (Europe). We present initial results in which we vary the rheology of the continental and oceanic lithosphere.

Boutonnet, Emmanuelle; Kaus, Boris; Popov, Anton

2013-04-01

320

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

321

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

322

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

323

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

324

Lithium in the deep continental crust  

NASA Astrophysics Data System (ADS)

Samples from Archean high-grade metamorphic terranes in East China and granulite xenoliths from China and eastern Australia have been measured to constrain the average Li concentration and isotopic composition of the middle and lower continental crust. Thirty samples from eight metamorphic terranes show limited variability in ?7Li (from +1.7 to +7.5) with an average value of +4 ± 1.4 (1?). These results suggest that the middle continental crust is relatively homogenous in Li isotopic composition and indistinguishable from the upper mantle. In contrast to metamorphic terrane samples, all three suites of granulite xenoliths, including both whole rocks and mineral separates, have lower Li concentrations and exhibit a much larger range in ?7Li values, from ~ -18 to ~ +17, with pyroxene equal to or lighter than coexisting plagioclase by up to -16. This large Li isotopic variation between minerals and in whole-rock granulites likely reflects diffusion-driven kinetic isotopic fractionation during interactions of xenoliths with host magma. Only those xenoliths that lack inter-mineral isotopic fractionation may still preserve their lower crustal Li isotopic signatures. Eight of such samples have been used to estimate the average Li isotopic composition of the lower continental crust, which has ?7Li from -14 to +14.3, with a concentration weighted average of +2.5. The isotopically heterogeneous lower continental crust likely reflects the combined effects of isotopic fractionation during prograde metamorphism, arrested kinetic Li isotopic fractionation associated with basaltic intrusions and variable protolith compositions. Based on available data for granulite xenoliths, the average Li concentration of the lower crust is estimated to be ~ 8 ppm. Together with previous estimates of Li concentration of the upper and middle crust, the average Li concentration of the bulk continental crust is estimated to be 18 ppm, similar to previous estimates. Collectively, the average Li isotopic composition of the continental crust is estimated to be +1, which is isotopically lighter than upper mantle and may reflect the loss of isotopically heavy Li from the continents during weathering and metamorphic dehydration.

Teng, F.; Rudnick, R. L.; McDonough, W. F.; Gao, S.; Liu, Y.; Tomascak, P. B.

2008-12-01

325

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

326

Discovering Plate Boundaries  

NSDL National Science Digital Library

???d?ersity's Earth Science Department offers the Discovering Plate Boundaries educational activity. The exercise is described as a data rich exercise to help students discover the processes that occur at plate tectonic boundaries and has been used successfully with 5th graders to undergraduates. The site provides the necessary downloads of maps; earthquake, volcanic, seafloor, topographic, and bathymetric data; and teacher guides and complete instructions. Because the activity can be geared towards such a large range of students, is well designed, and is easily accessible, educators will definitely appreciate the site.

2007-12-12

327

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.

328

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

329

Nuclear reactor alignment plate configuration  

DOEpatents

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

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

2014-01-28

330

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

331

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

332

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

333

Continental and oceanic crustal magnetization modelling  

NASA Technical Reports Server (NTRS)

Inversion of magnetic data from the MAGSAT satellite, to arrive at intensities of magnetization of the Earth's crust, was performed by two different methods. The first method uses a spherical harmonic model of the magnetic field. The coefficients believed to represent sources in the Earth's crust can then be inverted to arrive at vertical dipole moments per unit area at the Earth's surface. The spherical harmonic models contain coefficients of degrees of harmonics up to 23. The dipole moment per unit area for a surface element can then be determined by summing the contribution for each individual degree of harmonic. The magnetic moments were calculated for continental and oceanic areas separately as well as over certain latitudinal segments. Of primary concern was to determine whether there are any differences between continental and oceanic areas. The second analysis with magnetization intensities was made using narrower ranges of degrees of harmonics, assuming that higher degrees are present in the core field signal.

Harrison, C. G. A.; Hayling, K. L.

1984-01-01

334

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

335

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

336

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.

337

Continental sources of halocarbons and nitrous oxide  

NASA Technical Reports Server (NTRS)

Estimates of continental sources of CFC-11, CFC-12, CCl4, CH3CCl3 and N2O are derived from the atmospheric lifetime experiment in Adrigole, Ireland, and anthropogenic emissions of CCl4 and N2O from Europe have been identified. Relative source strengths are consistent with global budgets for the halocarbons and N2O. Different industrial release patterns for halocarbons are observed for Europe, the western United States and Australia.

Prather, M. J.

1985-01-01

338

Madagascar basalts: tracking oceanic and continental sources  

Microsoft Academic Search

Extensive Upper Cretaceous volcanism in southern Madagascar was fed in part by mantle sources resembling those expressed today in the Indian Ocean at Marion and Prince Edward islands and on the central Southwest Indian Ridge. In addition, very low ?Nd(T) (to -17.4), high (87Sr\\/86Sr)T (to 0.72126) tholeiites in southwestern Madagascar were variably but highly contaminated by ancient continental material broadly

J. Mahoney; C. Nicollet; C. Dupuy

1991-01-01

339

Precipitation of Continental Origin over South America  

NASA Astrophysics Data System (ADS)

The Amazon forest receives high amounts of moisture from the tropical Atlantic. A significant part of this moisture is returned back to the atmosphere by the forest, and further redistributed to the rest of the continent by the meridional flow imposed by the Andes. Thus, the land-atmosphere interaction between the Amazon forest and the large-scale flow affects not only the forest itself but also the downstream regions. We develop a method to quantify the precipitation of continental origin over South America, and identify the contribution that selected source regions make to continental precipitation. The average annual cycle of precipitation of continental origin for the five-year period 2000-2004 shows a band of high values aligned along the northwest-southeast direction, from southern Peru to northeastern Argentina. The lowest values of precipitation of continental origin occur upstream, over the northeastern coast of South America. Precipitation that originates as moisture from the Amazon forest shows maximum values over the western side of the Amazon, east of the Andes, especially over southern Peru. The Amazon forest also contributes to precipitation over La Plata River Basin (LPRB) and the Pacific coast of Colombia. During its dry season, up to 29.3% of the precipitation over LPRB originates as moisture from the Amazon forest. Throughout the year, the contributions to precipitation over LPRB by the Amazon forest and LPRB (recycled precipitation) are in the same range, but out of phase. The average contribution of the rest of the continent to precipitation over LPRB is smaller but of the same order as that of the Amazon and LPRB.

Martinez-Agudelo, J. A.; Dominguez, F.

2012-12-01

340

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

341

Evolution of gravity anomalies across collisional mountain belts: Clues to the amount of continental convergence and underthrusting  

NASA Astrophysics Data System (ADS)

A series of density models illustrates the gross form of free air and Bouguer gravity anomalies anticipated during ocean basin closure and consequent development of collisional orogens. When compared to gravity anomalies observed across some mountain belts, the hypothetical anomalies provide a clue to the degree of under thrusting of crust associated with one lithospheric plate beneath crust of the opposing plate margin. The results of the study suggest very early stage collision in the Ouachita Mountains of Arkansas and the Sulaiman Range of Pakistan, with thin transitional or oceanic crust still intact on the lower plate. In contrast, the Himalaya of Pakistan represent a much more advanced stage of collision, where continental crust may have underthrust the mountains for 600 km.

Lillie, Robert J.

1991-08-01

342

Flexural deformation of the continental lithosphere  

NASA Technical Reports Server (NTRS)

Prior work focused primarily on the Adriatic and northern Ionian regions. The results of these studies have been summarized previously, and so are only briefly discussed. More recent work focuses on two different topics: (1) analysis of foredeep basin geometry, sedimentary style, and thrust belt structure in light of the kinematics at the associated plate boundary and subduction zone dynamics; and (2) the evolution and plate strength of early Proterozoic lithosphere.

1990-01-01

343

Stainless steel bipolar plates  

Microsoft Academic Search

In this research, a specific surface modification technology was developed for stainless steel bipolar plates to obtain a corrosion-resistant oxide film. The surface roughness was measured, and an electron spectroscopy analysis (ESCA) was conducted to verify the chemical composition of the surface layer. From the binding energy of the ESCA spectrum, the amounts of chemical shift were used to identify

Shuo-Jen Lee; Jian-Jang Lai; Ching-Han Huang

2005-01-01

344

Bipolar battery plate  

SciTech Connect

A method is described of forming a bipolar plate for a battery comprising the steps of: disposing metal pellets in each aperture of a perforated thermoplastic sheet to form an assembly; heating and pressing the assembly to seal the pellets into the apertures with first and second surfaces exposed in the opposite faces of the sheet.

Rowlette, J.J.

1987-04-21

345

INL HIP Plate Fabrication  

SciTech Connect

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

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

2010-02-01

346

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.

347

Stainless steel bipolar plates  

NASA Astrophysics Data System (ADS)

In this research, a specific surface modification technology was developed for stainless steel bipolar plates to obtain a corrosion-resistant oxide film. The surface roughness was measured, and an electron spectroscopy analysis (ESCA) was conducted to verify the chemical composition of the surface layer. From the binding energy of the ESCA spectrum, the amounts of chemical shift were used to identify the major chemical compositions. The thickness of the oxide film was analyzed by auger electron spectroscopy (AES). From the results of the ESCA and AES analyses, the effects of the surface modification on the integrity of the surface were evaluated. Uniform corrosion and localized corrosion tests were also conducted to investigate any improvement on the corrosion characteristics. A single cell was assembled for cell performance tests. The surface of the treated plates was bright and smooth. The ESCA and AES analyses showed that the treated plates had a much higher chrome content. The metallurgical structure was dense with substantially less defects. The chemical and electrochemical properties were more stable. The corrosion rates of the treated plates were also much improved, resulting in better electric conductivity, stable cell performance as well as longer cell life.

Lee, Shuo-Jen; Lai, Jian-Jang; Huang, Ching-Han

348

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.

349

Anisotropy beneath a highly extended continental rift  

NASA Astrophysics Data System (ADS)

have employed shear wave splitting techniques to image anisotropy beneath the D'Entrecasteaux Islands, in southeastern Papua New Guinea. Our results provide a detailed picture of the extending continent that lies immediately ahead of a propagating mid-ocean ridge tip; we image the transition from continental to oceanic extension. A dense shear wave splitting data set from a 2010 to 2011 passive-source seismic deployment is analyzed using single and multichannel methods. Splitting delay times of 1-1.5 s are observed and fast axes of anisotropy trending N-S, parallel to rifting direction, predominate the results. This trend is linked to lattice-preferred orientation of olivine, primarily in the shallow convecting mantle, driven by up to 200 km of N-S continental extension ahead of the westward-propagating Woodlark Rift. This pattern differs from several other continental rifts that evince rift-strike-parallel fast axes and is evident despite the complex recent tectonic history. We contend that across most of this rift, the unusually high rate and magnitude of extension has been sufficient to produce a regime change to a mid-ocean-ridge-like mantle fabric. Stations in the south of our array show more complex splitting that might be related to melt or to complex inherited structure at the edge of the extended region.

Eilon, Zachary; Abers, Geoffrey A.; Jin, Ge; Gaherty, James B.

2014-03-01

350

Moho and magmatic underplating in continental lithosphere  

NASA Astrophysics Data System (ADS)

Underplating was originally proposed as the process of magma ponding at the base of the crust and was inferred from petrologic considerations. This process not only may add high density material to the deep crust, but also may contribute low density material to the upper parts of the crust by magma fractionation during cooling and solidification in the lower crust. Separation of the low density material from the high-density residue may be a main process of formation of continental crust with its characteristic low average density, also during the early evolution of the Earth. Despite the assumed importance of underplating processes and associated fractionation, the available geophysical images of underplated material remain relatively sparse and confined to specific tectonic environments. Direct ponding of magma at the Moho is only observed in very few locations, probably because magma usually interacts with the surrounding crustal rocks which leads to smearing of geophysical signals from the underplated material. In terms of processes, there is no direct discriminator between the traditional concept of underplated material and lower crustal magmatic intrusions in the form of batholiths and sill-like features, and in the current review we consider both these phenomena as underplating. In this broad sense, underplating is observed in a variety of tectonic settings, including island arcs, wide extensional continental areas, rift zones, continental margins and palaeo-suture zones in Precambrian crust. We review the structural styles of magma underplating as observed by seismic imaging and discuss these first order observations in relation to the Moho.

Thybo, H.; Artemieva, I. M.

2013-12-01

351

Subduction-related metamorphism beneath ophiolites (Oman) and during early stages of continental collision (Himalaya)  

NASA Astrophysics Data System (ADS)

Subduction-related metamorphism occurs beneath ophiolites (Oman), beneath island arcs (Kohistan) and during the early stages of continental collision (Kaghan, Tso Morari; Himalaya). Ophiolite obduction necessarily involves subduction of first oceanic, then continental crust to mantle depths beneath the ophiolite. In Oman an inverted pressure and temperature profile is exposed beneath the Semail ophiolite from garnet+clinopyroxene-bearing granulite to hornblende+plagioclase amphibolite down through epidote amphibolite and a variety of greenschist facies meta-sediments, dominantly cherts, marbles and quartzites. Thermobarometry on Grt+Cpx-bearing amphibolites immediately beneath the contact with mantle sequence harzburgites shows that the upper sole rocks formed at PT conditions of 770-900°C and 11-13 kbar, equivalent to depths of 30-40 km in oceanic lithosphere. Heat for metamorphism can only have been derived from the overlying mantle peridotites. Pressures are higher than can be accounted for by the thickness of the preserved ophiolite (15-20 km). Timing of peak metamorphism was synchronous with formation of the ophiolite gabbroic - trondhjemite crustal sequence and eruption of the pillow lavas (Cenomanian; 96-95 Ma). During the later stages of obduction the continental margin was dragged down to depths of nearly 100 km and basaltic sills within calc-schists were converted to eclogites (20-25 kbar; 500-560oC; 79.1 Ma), then exhumed back up the same subduction channel. Apparent 'extensional' fabrics throughout the HP units are related to upward flow of deeply buried rocks in a wholly compressional environment. Eclogites in a similar structural position occur along the Himalaya in the northernmost exposures of Indian plate rocks. These eclogites formed either during the latest stage of ophiolite obduction or the earliest stage of continental collision.

Searle, Mike; Waters, David; Cowan, Robert; Cherry, Alan; Cooper, Charles

2014-05-01

352

Arctic Crustal Thickness and Oceanic Lithosphere Distribution from Gravity Inversion: Constraining Plate Reconstructions  

NASA Astrophysics Data System (ADS)

Mapping crustal thickness, continental lithosphere thinning and oceanic lithosphere distribution represents a substantial challenge for the Polar Regions. Using gravity anomaly inversion, we have produced the first comprehensive maps of crustal thickness and oceanic lithosphere distribution for the Arctic. The Arctic region formed as a series of small distinct ocean basins leading to a complex distribution of oceanic crust, thinned continental crust, possible micro-continents and rifted continental margins. Mapping of continental lithosphere thinning factor and crustal thickness from gravity inversion provide predictions of ocean-continent transition structure and magmatic type and continent ocean boundary location independent of magnetic isochrons. Restoration of crustal thickness and continent-ocean boundary location from gravity inversion may be used to test plate tectonic reconstructions. Using crustal thickness and continental lithosphere thinning factor maps with superimposed shaded-relief free-air gravity anomaly, we improve the determination of pre-breakup rifted margin conjugacy and sea-floor spreading trajectory within the Arctic basins. By restoring crustal thickness & continental lithosphere thinning maps of the Eurasia Basin & NE Atlantic to their initial post-breakup configuration we show the geometry and segmentation of the rifted continental margins at their time of breakup, together with the location of highly-stretched failed breakup basins and rifted micro-continents. 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 underlain by 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 has major implications for understanding the plate tectonic history of the Amerasia Basin. Thinned continental crust rather than oceanic crust is predicted under the Laptev Sea. We interpret gravity inversion crustal thicknesses underneath Morris Jessop Rise & Yermak Plateau as continental crust which provided a barrier to the tectonic and palaeo-oceanic linkage between the Arctic & North Atlantic until the Oligocene. Before this time, we link the seafloor spreading within the Eurasia Basin to that in Baffin Bay. We determine Moho depth, crustal basement thickness, continental lithosphere thinning and ocean-continent transition location using a 3D spectral domain gravity inversion method which incorporates a lithosphere thermal gravity anomaly correction. The gravity anomaly contribution from sediments is included in the gravity inversion and 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. Gravity anomaly and bathymetry data used in the gravity inversion are from the NGA (U) Arctic Gravity Project and IBCAO respectively; sediment thickness is from a new regional compilation.

Kusznir, N. J.; Alvey, A.; Roberts, A. M.

2013-12-01

353

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

354

The Organization of Lawyers' Work: Hemispheres, Tectonic Plate Movements, and Continental Drift  

Microsoft Academic Search

This paper compares findings from two surveys of Chicago lawyers, the first conducted in 1975 and the second in 1995. The earlier study indicated that the Chicago bar was then divided into two broad sectors or \\

John P. Heinz; Robert L. Nelson; Edward O. Laumann; Ethan Michelson

355

Obduction at plate boundaries : thermo-mechanical modelling  

NASA Astrophysics Data System (ADS)

Obduction involves the emplacement of fragments of oceanic lithosphere (ophiolites) over a continental one. Ophiolitic sequences, composed of mafic to ultramafic lithologies, are characterized by a much higher density than continental material. For this reason the processes that control obduction are not straightforward and remain enigmatic in the framework of plate tectonics. The occurrence of large ophiolitic complexes in Oman (the Semail ophiolite) or New Caledonia nevertheless suggests that obduction can take place over large, regional-scale areas. Such obducted ophiolites are generally underlain by a thin, high temperature metamorphic sole and thrust onto high-pressure continental metamorphic units, both of which formed as a result of short-lived, almost coeval processes (~10 Ma offset between these main metamorphic events). In this study we present two-dimensional thermo-mechanical models of obduction. These models involve several different geodynamic settings (based on margin geometry, presence of a ridge, boundary conditions,...) that may lead or not to obduction. Major, first-order geological features (petrological, geochronological, structural data) are critically used to discriminate between these different models. An important result is that few situations actually enable to reproduce obduction in our numerical simulations, which indicates that only a narrow range of parameters can lead to realistic obduction. After assessing the respective influence of the key parameters, we finally propose a geodynamic model for the formation of the Semail ophiolite which is consistent with available data.

Duretz, Thibault; Agard, Philippe; Yamato, Philippe; Burov, Evgueni

2013-04-01

356

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

357

Tectonic Plates, Earthquakes, and Volcanoes  

NSDL National Science Digital Library

The representation shows earthquake and volcanic activity corresponds to plate boundaries. This interactive topographical map with the ocean water removed shows the boundaries of major plates and the locations of major volcanic eruptions and earthquakes worldwide.

358

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

NASA Technical Reports Server (NTRS)

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

Hager, B. H.

1981-01-01

359

Glacial isostasy and plate motion  

Microsoft Academic Search

The influence of glacial-isostatic adjustment (GIA) on the motion of tectonic plates is usually neglected. Employing a recently developed numerical approach, we examine the effect of glacial loading on the motion of the Earth’s tectonic plates where we consider an elastic lithosphere of laterally variable strength and the plates losely connected by low viscous zones. The aim of this paper

Volker Klemann; Zdenek Martinec; Erik R. Ivins

2008-01-01

360

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

361

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

362

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

363

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

364

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

365

A planetary perspective on Earth evolution: Lid Tectonics before Plate Tectonics  

NASA Astrophysics Data System (ADS)

Plate Tectonics requires a specific range of thermal, fluid and compositional conditions before it will operate to mobilise planetary lithospheres. The response to interior heat dispersion ranges from mobile lids in constant motion able to generate zones of subduction and spreading (Plate Tectonics), through styles of Lid Tectonics expressed by stagnant lids punctured by volcanism, to lids alternating between static and mobile. The palaeomagnetic record through Earth history provides a test for tectonic style because a mobile Earth of multiple continents is recorded by diverse apparent polar wander paths, whilst Lid Tectonics is recorded by conformity to a single position. The former is difficult to isolate without extreme selection whereas the latter is a demanding requirement and easily recognised. In the event, the Precambrian palaeomagnetic database closely conforms to this latter property over very long periods of time (~ 2.7-2.2 Ga, 1.5-1.3 Ga and 0.75-0.6 Ga); intervening intervals are characterised by focussed loops compatible with episodes of true polar wander stimulated by disturbances to the planetary figure. Because of this singular property, the Precambrian palaeomagnetic record is highly effective in showing that a dominant Lid Tectonics operated throughout most of Earth history. A continental lid comprising at least 60% of the present continental area and volume had achieved quasi-integrity by 2.7 Ga. Reconfiguration of mantle and continental lid at ~ 2.2 Ga correlates with isotopic signatures and the Great Oxygenation Event and is the closest analogy in Earth history to the resurfacing of Venus. Change from Lid Tectonics to Plate Tectonics is transitional and the geological record identifies incipient development of Plate Tectonics on an orogenic scale especially after 1.1 Ga, but only following break-up of the continental lid (Palaeopangaea) in Ediacaran times beginning at ~ 0.6 Ga has it become comprehensive in the style evident during the Phanerozoic Eon (< 0.54 Ga).

Piper, John D. A.

2013-03-01

366

Multiagent simulation of evolutive plate tectonics applied to the thermal evolution of the Earth  

NASA Astrophysics Data System (ADS)

The feedback between plate tectonics and mantle convection controls the Earth's thermal evolution via the seafloor age distribution. We therefore designed the MACMA model to simulate time-dependent plate tectonics in a 2D cylindrical geometry with evolutive plate boundaries, based on multiagent systems that express thermal and mechanical interactions. We compute plate velocities using a local force balance and use explicit parameterizations to treat tectonic processes such as trench migration, subduction initiation, continental breakup and plate suturing. These implementations allow the model to update its geometry and thermal state at all times. Our approach has two goals: (1) to test how empirically- and analytically-determined rules for surface processes affect mantle and plate dynamics, and (2) to investigate how plate tectonics impact the thermal regime. Our predictions for driving forces, plate velocities and heat flux are in agreement with independent observations. Two time scales arise for the evolution of the heat flux: a linear long-term decrease and high-amplitude short-term fluctuations due to surface tectonics. We also obtain a plausible thermal history, with mantle temperature decreasing by less than 200 K over the last 3 Gyr. In addition, we show that on the long term, mantle viscosity is less thermally influential than tectonic processes such as continental breakup or subduction initiation, because Earth's cooling rate depends mainly on its ability to replace old insulating seafloor by young thin oceanic lithosphere. We infer that simple convective considerations alone cannot account for the nature of mantle heat loss and that tectonic processes dictate the thermal evolution of the Earth.

Combes, M.; Grigné, C.; Husson, L.; Conrad, C. P.; Le Yaouanq, S.; ParenthoëN, M.; Tisseau, C.; Tisseau, J.

2012-05-01

367

Plated wire memory subsystem  

NASA Technical Reports Server (NTRS)

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

Reynolds, L.; Tweed, H.

1972-01-01

368

Plate Tectonics: The Mechanism  

NSDL National Science Digital Library

This text explains how detailed mapping of the ocean floor led scientists like Howard Hess and R. Deitz to revive the Holmes convection theory. Hess and Deitz modified the theory considerably and called their new theory Sea-floor Spreading. Among the seafloor features that supported the sea-floor spreading hypothesis were: mid-oceanic ridges, deep sea trenches, island arcs, geomagnetic patterns, and fault patterns. These features are treated in detail and related to the current Theory of Plate Tectonics.

369

Martian plate tectonics  

NASA Astrophysics Data System (ADS)

The northern lowlands of Mars have been produced by plate tectonics. Preexisting old thick highland crust was subducted, while seafloor spreading produced thin lowland crust during late Noachian and Early Hesperian time. In the preferred reconstruction, a breakup margin extended north of Cimmeria Terra between Daedalia Planum and Isidis Planitia where the highland-lowland transition is relatively simple. South dipping subduction occured beneath Arabia Terra and east dipping subduction beneath Tharsis Montes and Tempe Terra. Lineations associated with Gordii Dorsum are attributed to ridge-parallel structures, while Phelegra Montes and Scandia Colles are interpreted as transfer-parallel structures or ridge-fault-fault triple junction tracks. Other than for these few features, there is little topographic roughness in the lowlands. Seafloor spreading, if it occurred, must have been relatively rapid. Quantitative estimates of spreading rate are obtained by considering the physics of seafloor spreading in the lower (approx. 0.4 g) gravity of Mars, the absence of vertical scarps from age differences across fracture zones, and the smooth axial topography. Crustal thickness at a given potential temperature in the mantle source region scales inversely with gravity. Thus, the velocity of the rough-smooth transition for axial topography also scales inversely with gravity. Plate reorganizations where young crust becomes difficult to subduct are another constraint on spreading age. Plate tectonics, if it occurred, dominated the thermal and stress history of the planet. A geochemical implication is that the lower gravity of Mars allows deeper hydrothermal circulation through cracks and hence more hydration of oceanic crust so that more water is easily subducted than on the Earth. Age and structural relationships from photogeology as well as median wavelength gravity anomalies across the now dead breakup and subduction margins are the data most likely to test and modify hypotheses about Mars plate tectonics.

Sleep, N. H.

1994-03-01

370

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

371

Has 7% of Continental Crust been Lost since Pangea Broke Up?  

NASA Astrophysics Data System (ADS)

After modern plate tectonics began, the net growth or loss of continental crust predominantly involved the mass balance at subduction zones (SZs) between the yin of adding mantle-sourced arc igneous rocks and the subtracting yang of recycling existing crust back into the mantle. Field observations suggest that during Mesozoic and Cenozoic time, a rough long-term balance existed at ocean-margin SZs (e.g., W. N. America, Andes). But a different picture, one of net loss, emerges when additions and losses at collisional or crust-suturing SZs (e.g., India-Tibet) are considered. GAINS AND LOSSES SINCE ~200 Ma Because Mesozoic and Cenozoic convergent margins can be field inspected, the net growth of continental crust after the breakup of Pangea at ~200 Ma can be estimated. Pangea breakup also marked the beginning of the present supercontinent cycle. Newly established (Eocene) ocean-margin SZs (e.g., IBM, Tonga-Kermadec) added juvenile arc crust for at least 10-15 Myr at rates ~10-15 times higher than later and elsewhere at long-established SZs (~30 km3/Myr/km). During the Cenozoic, at colliding SZs (e.g., Alps, India-Tibet, Arabia-Eurasia) tomographic and geological data document losses of subducted continental crust sustained for 15-50 Myr at rates ~15 times that typical from the upper plate at ocean-margin SZs (~70 km3/Myr/km). For additions, we considered that as the Atlantic opened in early Jurassic time, new, prodigiously productive SZs were initiated along the western margin of North and Middle America but not along western South America and the eastern margin of Eurasia. In the Cretaceous, new SZs formed along much of the northern margin of the Tethys, along western Sumatra and southern Java, and at the great arc of the Caribbean. In the early Eocene, in the offshore, a lengthy (~20,000 km) curtain of new, voluminously productive intra-oceanic SZs formed from the Aleutian Islands southward to the Kermadec Islands. For subtractions, we applied subduction losses (~70 km3/Myr/km) previously estimated for Cenozoic ocean-margin SZs. During the past 50 Myr, at Tethyan SZs from Gibraltar to western Australia, we estimate an average rate of lower plate continental crust recycling at ~900 km3/Myr/km. NEGATIVE CRUSTAL GROWTH AND IMPLICATIONS After the breakup of Pangea, the volume of continental crust recycled into the mantle is estimated to be ~500 x 10^6 km3 greater than that created (~400 x 10^6 km3). The net loss is ~7% of Earth's continental crust existing volume (7 x 10^9 km3), an estimate that does not include delamination losses. A large part of SZ losses (~40%) occurred during the past 50 Myr as a consequence of closing the Tethys, a process still underway. It seems likely that a long supercontinent cycle of breakup and dispersal of fragments favors positive crustal growth effected by elevated rates of magmatism at new SZs, whereas a shorter cycle involving rapid reassembly favors negative crustal growth effected by elevated rates of losses at crustal collision zones. Fragmentation of Pangea and the partial reassembly of its parts within 150 Myrs may be representative of a short, crustal destructive supercontinent cycle.

Scholl, D. W.; Stern, R. J.

2012-12-01

372

Discovering Plate Boundaries  

NSDL National Science Digital Library

Discovering Plate Boundaries is based on 5 world maps containing earthquake, volcano, topography, satellite gravity, and seafloor age data. The novel aspect of the exercise is the "jigsaw" manner in which student groups access the maps and use them to discover, classify, and describe plate boundary types. The exercise is based only on observation and description, which makes it useful at a wide variety of levels; it has been used successfully in 5th grade classes, as well as in non-major earth science classes. The exercise is based on a set of wall maps that are not consumed during the exercise. Other inexpensive materials required include two 11x17 black and white copies per student and colored pencils. Because the exercise is not based on student access to the web, it is not dependent on classroom technology equipment. The exercise takes three 50-minute class periods to complete, and involves the students in making presentations to one another in small groups as well as to the whole class. The students come away from the exercise with knowledge of the key features of each type of plate boundary and a sense of why each looks and acts the way it does.

Dale Sawyer

1997-09-15

373

Effects of continental configuration on mantle heat loss  

NASA Astrophysics Data System (ADS)

(2D) and three-dimensional (3D) simulations are used to explore the effects of continental distribution on mantle convection. In both 2D and 3D, at total surface areas < 50%, internal temperature is weakly sensitive to continental configuration. Mantle heat flux values show mild variations with changing configuration. In 3D, at total continental area > 50%, the dependence of mantle heat loss on continental configuration becomes stronger. Mantle temperature continues to increase with total continental area but now varies by 5%-7% with changing configurations. When distributed, continents can cause flow patterns to become locked. This leads to significant variations in mantle temperature below continental and oceanic regions. This differs from the expectation that supercontinents would preferentially lead to large lateral variations in mantle temperatures and suggests that insulation-induced thermal anomalies could exist below continents today if they have remained fixed relative to mantle flow (e.g., Africa).

Cooper, C. M.; Moresi, L.-N.; Lenardic, A.

2013-06-01

374

Yellowstone hotspot-continental lithosphere interaction  

NASA Astrophysics Data System (ADS)

The Snake River Plain represents 17 m.y. of volcanic activity that took place as the North American continent migrated over a relatively fixed magma source, or hotspot. We present new Pb, Sr, and Nd data for a suite of 25 basalts collected from Western and Central Snake River Plain (SRP). The new isotope data, combined with previously published data from the SRP, provide a traverse of the Wyoming craton margin, from the 87Sr/86Sr = 0.706 line boundary of western SRP with Phanerozoic accreted terranes, east through the central and eastern SRP, to the Yellowstone Plateau. Low-K basalts from the western SRP, overlain by high-K basalts, provide a temporal record of regional source variation from ?16.8 to 0.2 Ma. Principal Component Analysis (PCA) of the new and previously published SRP basalt Pb isotopes reveals that >97% of the total variability is accounted for by mixing between three end-members and is consistent with a sublithospheric Yellowstone hotspot mantle source with a radiogenic isotope composition similar to the mantle source of the early Columbia River Basalt Group (CRBG) and two continental lithosphere end-members, heterogeneous in age and composition. We use the SRP Pb, Sr, and Nd isotope data to model the Yellowstone Hotspot-continental lithosphere interaction by three component mixing between two continental lithospheric components, Archean lithosphere (CL1) that represents older lithosphere underlying the Yellowstone Plateau in the east, and Paleoproterozoic lithosphere (CL2) representing the younger lithosphere underlying the SRP in the west near the craton margin, and a sublithospheric end-member, representing the Yellowstone hotspot (PL). The results suggest a continuous flow of PL material westward as the NA continental lithosphere migrated over the upwelling hotspot along a shoaling gradient in the sub-continental mantle lithosphere. The model shows a decrease in Total Lithosphere end-members (CL1 + CL2) and the Lithosphere Ratio (CL1/CL2), from the craton interior at Yellowstone toward its western margin, consistent with geologic and geophysical evidence that the continental lithosphere beneath the SRP decreases in age and thickness from east to west. The Lithosphere Ratio shows step-like decreases from Yellowstone in the east to the 87Sr/86Sr = 0.706 line in the west, indicating that the SRP cuts across geochemically distinct parcels of lithospheric mantle, consistent with terrane accretion models for the craton margin. In the western SRP, young high-K basalts have a lower mass fraction of Total Lithospheric compared to the underlying low-K tholeiites, but the same Lithosphere Ratio, consistent with a recent (700-900 ka) decrease in lithosphere contribution between eruption of early low- and younger high-K basalts.

Jean, Marlon M.; Hanan, Barry B.; Shervais, John W.

2014-03-01

375

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

376

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

377

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

378

Symmetries in laminated composite plates  

NASA Technical Reports Server (NTRS)

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

Noor, A. K.

1976-01-01

379

Daly Lecture: Geochemical insights into continental dynamics  

NASA Astrophysics Data System (ADS)

Its been known for over a century that the continental crust has an average composition that is intermediate ("andesitic"). Because primary melts of mantle peridotite are basaltic or even more magnesian (e.g., picritic), the average andesitic composition of the continental crust requires the return of mafic to ultramafic material from the crust into the convective mantle. This may be accomplished in several ways, the most popular of which are 1) slab melting and return of mafic/ultramafic residue via subduction and 2) transformation of mafic/ultramafic rock to eclogite at the base of a thickened crust and its subsequent sinking (foundering) or delamination (peeling away). Petrological and geochemical studies of deep-seated xenoliths and continental magmatism offer insights that allow these hypotheses to be tested. As an example, I highlight on-going studies from the North China craton (NCC), where a stable, Archean craton was transformed into tectonically and magmatically active continental lithosphere during the Mesozoic. The NCC consists of two ancient blocks (the western, or Ordos, block and the eastern block) that collided to form the central zone during the late Archean (2.5) or Paleoproterozoic (1.9). Based on Os isotopic studies of peridotitic xenoliths, Archean lithosphere was removed below the central zone in the Paleoproterozoic, consistent with replacement of deep lithosphere during collisional orogeny. This newly formed Paleoproterozoic lithosphere persists beneath the central zone today. In contrast, Archean lithosphere persisted beneath the eastern block throughout much of the Phanerozoic, as refractory Archean peridotites are found in Ordovician diamondiferous kimberlites from the eastern block. However, Cenozoic basalts from the eastern block carry peridotites that have Os isotopic compositions indistinguishable from modern convecting mantle, requiring removal of the cratonic mantle lithosphere sometime between the Ordovician and Cenozoic. Mesozoic high Mg andesites, adakites and dacites have geochemical characteristics consistent with their derivation from mafic lower crust that foundered from the base of the NCC. Moreover, eclogite xenoliths in early Mesozoic magmas document the presence of an eclogitic root formed by Mesozoic high P metamorphism of Archean lower crust during the Mesozoic. Collectively, these observations point to a fundamental transformation of the NCC lithosphere, including density foundering of mafic/ultramafic lower crust, which accompanied Mesozoic collisional orogenies. The NCC may be a unique example of lower crustal foundering within an Archean craton. However, other regions of Archean- aged crust that are no longer cratonic (e.g., Mozambique fold belt of Tanzania) may also have experienced lithospheric thinning. The degree to which lower crustal foundering is responsible for the non-basaltic crust of Archean cratons is yet to be established.

Rudnick, R. L.

2006-05-01

380

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."...

381

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 Available online 14 March 2007 Abstract Nitrogen (N) cycling and respiration rates were measured in sediment was uniform in nearly all columns, with minimal dead zones and channeling. Significant respiration (O2

Jahnke, Richard A.

382

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

383

Fuel cell end plate structure  

DOEpatents

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

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

1991-04-23

384

Microseismicity evidence for subduction of the Caribbean plate beneath the South American Plate in northwestern Venezuela  

NASA Astrophysics Data System (ADS)

Over 1100 microearthquakes with body wave magnitude mb<4 have been located in western Venezuela and the southwestern Caribbean region since the installation in 1980 of the Venezuelan Seismological Array, together with 120 events of mb?4, one of them with surface wave magnitude Ms˜6. This tectonically complex region is part of the boundary between the Caribbean and the South American plates. The main seismically active feature inland in western Venezuela is the northeast striking, 600-km long, 100-km wide, right-lateral strike-slip Boconó fault zone along the Venezuelan Andes. About 80% of the earthquakes located in the entire region in the period 1980-mid-1995 have occurred on this fault zone, at focal depths <20 km. Microearthquake activity at lower rates also occurs northwest of the Venezuelan Andes, both in the continental and Caribbean sea regions. Part of this activity takes place at depths down to ˜150 km. Northwest oriented seismicity depth profiles show the existence of a Benioff zone dipping to the southeast beneath northwestern Venezuela and northern Colombia. This indicates the presence of a northeast striking, southeast dipping subducted slab of the Caribbean plate beneath the South American plate. Hypocentral locations show that the northeastern end of this subduction occurs northwest of the Curaçao-Aruba region, in the vicinity of a northwest trending, right-lateral strike-slip fault zone that joins up with the northeastern end of the Boconó fault zone. This latter place turns out to be the western end of the east-west striking San Sebastián fault along the Venezuelan coast.

PéRez, Omar J.; Jaimes, Martha A.; Garciacaro, Emilio

1997-08-01

385

Dynamics of diffuse oceanic plate boundaries: insensitivity to rheology  

NASA Astrophysics Data System (ADS)

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 Newtonian viscous rheology or a yield-stress (high-exponent power-law) rheology. An important observation is that the poles of relative rotation of adjacent component plates tend to lie in the diffuse plate boundary that separates them. A key cause of this tendency is that a faster spin is needed to balance a component of torque through the middle of a diffuse plate boundary than to balance an equal component of torque lying 90° from the middle of the diffuse boundary. The strength of that tendency depends on rheology, however, with the tendency being stronger for a yield-stress rheology than for a Newtonian viscous rheology. For the special case of the pole of rotation lying outside of and along the strike of the boundary, these large differences can be simply explained in terms of the distribution of boundary-perpendicular normal forces acting across the boundary. In the Newtonian case, the distribution of forces has an along-strike gradient that can balance a component of torque about the middle of the boundary, while in the yield-stress case, the distribution of forces has zero along-strike gradient and cannot balance a component of torque about the middle of the diffuse plate boundary. To expand our analysis to intermediate power laws of geophysical interest (i.e. power-law exponents of 3 to 30), as well as to investigate more thoroughly the behaviour for a high-exponent power law, we numerically integrate the force distribution to obtain the torques. Results for intermediate power laws resemble the yield-stress rheology much more than they resemble the Newtonian rheology and depend only weakly on the width of the deforming zone. To quantify the probability that a pole of rotation lies in a diffuse plate boundary, we numerically integrate the expectation assuming that all orientations of torque are equally probable. For a power-law exponent of n= 10: 49 per cent of possible torque orientations produce angular velocities outside the diffuse plate boundary if the boundary is 55° long (similar in length to the boundary between the Nubian and Somalian component plates); 21 per cent of possible torque orientations produce angular velocities outside the diffuse plate boundary if the boundary is 30° long (similar in length to the boundary between the Indian and Capricorn component plates and to that between the Capricorn and Australian component plates); and 6 per cent of possible torque orientations produce angular velocities outside the diffuse plate boundary if the boundary is 15° long (similar in length to the boundary between the North American and South American component plates and to that between the Macquarie and Australian component plates). These results reinforce the prior conclusion that the pole is more strongly locked into the boundary if a DOPB is short than if it is long. For all boundary lengths, but even more so for short boundaries, the relationship between angular velocity and torque depends only weakly on the power-law exponent of the rheology as long as n>= 3. From this, we conclude that orientation of the relative torque across a DOPB can be inferred from the location of the pole of rotation without precise knowledge of the appropriate power-law exponent.

Zatman, Stephen; Gordon, Richard G.; Mutnuri, Kartik

2005-07-01

386

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

387

Continental water storage variations in Africa  

NASA Astrophysics Data System (ADS)

We investigate temporal and spatial variations of continental water storage in Africa as recovered by the GRACE (Gravity Recovery and Climate Experiment) mission. Mass variations are directly inverted from only KBRR (K-band range rate) data using a mascon approach. We compare our solutions to classical spherical harmonic solutions and also to different global hydrology models, and regional models in the African monsoon area (thanks to the ALMIP project). We compare mass estimates of major Africa lakes and reservoirs to volume estimates from laser (ICESat) and radar altimetry. We investigate the improvement of our mass retrievals when hydrology (GLDAS/Noah model) is forward modeled, compared to the more classical approach when continental water storages variations are not taken into when processing GRACE data. We solve the water mass balance equations using different precipitation datasets from remote sensing techniques, as well as ground rain gauge stations, using fresh water fluxes (precipitation minus evaporation) from various atmospheric models (reanalysis and operational). As a result, our runoff are compared to river flux measurements. In addition to the comparison with the ALMIP models, we also pay a special attention to the Lake Chad and Niger river basins, where ground gravity variations are repetitively measured as part of the GHYRAF project in order to investigate seasonal water storage variations at small and larger spatial scales.

Boy, Jean-Paul; Carabajal, Claudia; Luthcke, Scott; Rowlands, David; Lemoine, Frank; Sabaka, Terence

2010-05-01

388

Role of inherited structures on the strength and strain rate of continental lithosphere  

NASA Astrophysics Data System (ADS)

Under the Wilson Cycle and Plate Tectonics paradigms, continents are divided between stable continental regions (SCR), which tend to remain un-deformed, and plate boundary zones (PBZ) that repeatedly accommodate deformation associated with opening and closing of tectonic plates. This long-term (> 1 Ma) perspective is reflected in short-term (< 100 a) deformation markers such as seismicity and GPS measurements, which highlight the first-order contrast in strain rates between SCR and PBZ. Despite this clear first-order view, significant debate remains regarding short- and long-term strength and deformation rates in intraplate weak zones (e.g., Rhine Graben, New Madrid seismic zone). We propose to constrain first-order strength and strain rates using lithosphere rheological models, including new strain-weakening rheologies, driven by tectonic forces. We estimate average strain rates that satisfy near-failure equilibrium between net driving forces and lithosphere strength for cases that typify PBZ, cratons, and intraplate weak zones. Our model yields a range of strain rates that vary by up to six orders of magnitude between PBZ and cratons. In intraplate weak zones, structural and tectonic heritage results in significant weakening and yields strain rates compatible with GPS, seismicity, and geological markers. These results provide first-order constraints on long-term lithosphere strength and deformation rates. In particular, we explore upper and lower bounds of possible strain rates in intraplate weak zones, using a range of geotherm, rheology, and local stress conditions.

Mazzotti, Stephane; Gueydan, Frédéric

2014-05-01

389

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

390

Tectonic Models For Deep Subduction and Exhumation At Both Sides of The Highly Assymetric North Atlantic Caledonides  

Microsoft Academic Search

The Caledonian orogeny in East Greenland and Scandinavia is typically portrayed as Ordovician to Silurian destruction of the Iapetus Ocean ending by continental collision of Baltica and Laurentia. The orogen is highly asymmetric, and typically modelled as subduction of Baltica, below the overriding Laurentian plate. The Scandinavian Caledonides are characterized by a deeply subducted rifted margin, metamorphosed to Ultra High

E. H. Hartz; F. Corfu; A. Andresen; T. B. Andersen

2002-01-01

391

Tethered Triangular Plate  

NSDL National Science Digital Library

Simulation Software: Glotzer Group Code Simulation Method: Brownian Dynamics BD simulation of polymer tethered triangular plates. A system of building blocks of composition P10bT18b at a concentration of 0.20, was run starting at an effectively infinite temperature then instantaneously quenched to a temperature of 0.83. The system was then run for 12,000,000 time steps forming a hexagonally packing twisted columnar phase.The solve was favorable for the tethers. Simulation Model: United Atom Bead Spring with Lennard-Jones and FENE

Zhang, Zhenli

2005-01-31

392

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.

393

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

394

Plate Tectonics: Further Evidence  

NSDL National Science Digital Library

Early evidence showing striking similarities between regions on opposite sides of vast oceans suggested that in Earth's distant past what are now separate continents may once have been connected. However, this evidence said nothing about how the continents could have moved to their present positions. This video shows how seafloor spreading creates new oceanic crust and how the crust is destroyed by subduction into Earth's mantle, providing the mechanism and forces that propel tectonic plates across Earth's surface. The segment is two minutes nine seconds in length.

395

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

396

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

397

Continental lithospheric evolution: Constraints from the geochemistry of felsic volcanic rocks in the Dharwar Craton, India  

NASA Astrophysics Data System (ADS)

Felsic magmatism associated with ocean-ocean and ocean-continent subduction processes provide important evidence for distinct episodes of crust-generation and continental lithospheric evolution. Rhyolites constitute an integral component of the tholeiitic to calc-alkaline basalt-andesite-dacite-rhyolite (BADR) association and contribute to crustal growth processes at convergent plate margins. The evolution of the Dharwar Craton of southern peninsular India during Meso- to Neoarchean times was marked by extensive development of greenstone belts. These granite-greenstone terranes have distinct volcano-sedimentary associations consistent with their geodynamic setting. The present study deals with geochemistry of rhyolites from the Chitradurga-Shimoga greenstone belts of western (WDC) and the Gadwal-Kadiri greenstone belts of eastern (EDC) sectors of Dharwar Craton to compare and evaluate their petrogenesis and geodynamic setting and their control on the continental lithospheric evolution of the Dharwar Craton. At a similar range of SiO2, Al2O3, Fe2O3, the rhyolites of WDC are more potassic, whereas the EDC rhyolites are more sodic and less magnesian with slight increase in TiO2. Minor increase in MgO content of WDC rhyolites reflects their ferromagnesian trace elements which are comparatively lower in the rhyolites of EDC. The relative enrichment in LILE (K, Rb) and depletion in HFSE (Nb, Ta, Zr, Hf) marked by negative Nb-Ta, Zr-Hf and Ti anomalies endorse the convergent margin processes for the generation of rhyolites of both the sectors of Dharwar Craton. The high silica potassic rhyolites of Shimoga and Chitradurga greenstone belts of WDC showing prominent negative Eu and Ti anomalies, flat HREE patterns correspond to Type 3 rhyolites and clearly point towards their generation and emplacement in an active continental margin environment. The geochemical characteristics of Gadwal and Kadiri rhyolites from eastern Dharwar Craton marked by aluminous compositions with low and fractionated HREE patterns and minor negative Eu anomalies are in conformity with Type 1 rhyolites and suggest that they were erupted in an intraoceanic island arc system. The overall geochemical systematics of the rhyolites from both the sectors of Dharwar Craton suggest a change in the geodynamic conditions from intraoceanic island arc of eastern Dharwar Craton and an active continental margin of western Dharwar marked by ocean-ocean subduction and migration of oceanic arc towards a continent followed by arc-continent collision that contributed for the evolution of continental lithosphere in the Dharwar Craton.

Manikyamba, C.; Ganguly, Sohini; Saha, Abhishek; Santosh, M.; Rajanikanta Singh, M.; Subba Rao, D. V.

2014-12-01

398

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

399

Anthrax toxin receptor 1/tumor endothelial marker 8: mutation of conserved inserted domain residues overrides cytosolic control of protective antigen binding.  

PubMed

Anthrax toxin receptor 1 (ANTXR1)/tumor endothelial marker 8 (TEM8) is one of two known proteinaceous cell surface anthrax toxin receptors. A metal ion dependent adhesion site (MIDAS) present in the integrin-like inserted (I) domain of ANTXR1 mediates the binding of the anthrax toxin subunit, protective antigen (PA). Here we provide evidence that single point mutations in the I domain can override regulation of ANTXR1 ligand-binding activity mediated by intracellular signals. A previously reported MIDAS mutant of ANTXR1 (T118A) was found to retain normal metal ion binding and secondary structure but failed to bind PA, consistent with a locked inactive state. Conversely, mutation of a conserved I domain phenylalanine residue to a tryptophan (F205W) increased the proportion of cell-surface ANTXR1 that bound PA, consistent with a locked active state. Interestingly, the K(D) and total amount of PA bound by the isolated ANTXR1 I domain were not affected by the F205W mutation, indicating that ANTXR1 is preferentially found in the active state in the absence of inside-out signaling. Circular dichroism (CD) spectroscopy and (1)H-(15)N heteronuclear single-quantum coherence (HSQC) nuclear magnetic resonance (NMR) revealed that structural changes between T118A, F205W, and WT I domains were minor despite a greater than 10(3)-fold difference in their abilities to bind toxin. Regulation of toxin binding has important implications for the design of toxin inhibitors and for the targeting of ANTXR1 for antitumor therapies. PMID:20690680

Ramey, Jordan D; Villareal, Valerie A; Ng, Charles; Ward, Sabrina C; Xiong, Jian-Ping; Clubb, Robert T; Bradley, Kenneth A

2010-08-31

400

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

PubMed Central

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

2014-01-01

401

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

402

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

403

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

404

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 under the Hellenic Arc and southwestern Turkey; and (5) internal deformation and rotation of the Anatolian plate.

Toksoz, M. Nafi; Reilinger, Robert

1992-01-01

405

Gravity models of two-level collision of lithospheric plates in northeastern Asia  

NASA Astrophysics Data System (ADS)

Structural forms of emplacement of crustal and mantle rigid sheets in collision zones of lithospheric plates in northeastern Asia are analyzed using formalized gravity models reflecting the rheological properties of geological media. Splitting of the lithosphere of moving plates into crustal and mantle constituents is the main feature of collision zones, which is repeated in the structural units irrespective of their location, rank, and age. Formal signs of crustal sheet thrusting over convergent plate boundaries and subduction of the lithospheric mantle beneath these boundaries have been revealed. The deep boundaries and thickness of lithospheric plates and asthenospheric lenses have been traced. A similarity in the deep structure of collision zones of second-order marginal-sea buffer plates differing in age is displayed at the boundaries with the Eurasian, North American, and Pacific plates of the first order. Collision of oceanic crustal segments with the Mesozoic continental margin in the Sikhote-Alin is characterized, as well as collision of the oceanic lithosphere with the Kamchatka composite island arc. A spatiotemporal series of deep-seated Middle Mesozoic, Late Mesosoic, and Cenozoic collision tectonic units having similar structure is displayed in the transitional zone from the Asian continent to the Pacific plate.

Petrishchevsky, A. M.

2013-11-01

406

Late Neogene continental stages in NW Europe revisited  

Microsoft Academic Search

Pollen records from fluvial deposits in The Netherlands have traditionally been used to establish continental stages for the Neogene in NW Europe. These stages are still widely used across Europe for stratigraphic correlations and palaeoclimatic studies. Despite their extensive use, the validity of this continental correlation scheme for the Plio- and Pleistocene has never been tested in the area where

Timme H. Donders; Marloes L. Kloosterboer-van Hoeve; Wim Westerhoff; Roel M. C. H. Verreussel; André F. Lotter

2007-01-01

407

On causal links between flood basalts and continental breakup  

Microsoft Academic Search

Temporal coincidence between continental flood basalts and breakup has been noted for almost three decades. Eight major continental flood basalts have been produced over the last 300 Ma. The most recent, the Ethiopian traps, erupted in about 1 Myr at 30 Ma. Rifting in the Red Sea and Gulf of Aden, and possibly East African rift started at about the

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

1999-01-01

408

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

409

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

410

75 FR 30290 - Airworthiness Directives; Teledyne Continental Motors (TCM) 240, 346, 360, 470, 520, and 550...  

Federal Register 2010, 2011, 2012, 2013

...2120-AA64 Airworthiness Directives; Teledyne Continental Motors (TCM) 240, 346... Fax: (202) 493-2251. Contact Teledyne Continental Motors, Inc., P...airworthiness directive: 2010-11-04 Teledyne Continental Motors (Formerly...

2010-06-01

411

Global Topography and Tectonic Plates  

NSDL National Science Digital Library

The goal of this activity is to investigate global topographic and tectonic features, especially the tectonic plates and their boundaries. Using a double-page size digital topographic map of the Earth that includes both land and sea floor topography, students are asked to draw plate boundaries, deduce plate motions and interactions, and explore the connections between topography and tectonic processes at the global scale.

David Greene

412

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

413

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

414

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

415

Ion plating for the future  

NASA Technical Reports Server (NTRS)

The ion plating techniques are classified relative to the instrumental set up, evaporation media, and mode of transport. A distinction is drawn between the low vacuum (plasma) and high vacuum (ion beam) techniques. Ion plating technology is discussed at the fundamental and industrial level. At the fundamental level, the capabilities and limitations of the plasma (evaporant flux) and film characteristics are evaluated. And on the industrial level, the performance and potential uses of ion plated films are discussed.

Spalvins, T.

1981-01-01

416

Geoid Data and Implications for Plate Tectonic Dynamics  

NASA Astrophysics Data System (ADS)

It has long been recognized that the motion of the mechanically rigid lithospheric plates of the earth are the surface expression of large-scale convection in the mantle. It is also accepted that the stresses driving plate motion are an amalgam of the basal tractions associated with this convection and long-wavelength density variations within the plates themselves. Parsing the relative contribution from these two sources to the geodynamics of the lithosphere continues to be an important topic of plate dynamics research. Because geoid anomalies are directly related to the local dipole moment of the density-depth distribution, they provide an ideal method for evaluating density variations within the lithosphere and the associated tectonic stresses. The main challenge with this approach is isolating the lithospheric geoid contribution from the full geoid (which is dominated by sources from deeper in the earth, namely the lower mantle). We address this issue by using a high-pass spherical harmonic filtering of the EGM2008-WGS84 geoid (which is complete to spherical harmonic degree and order 2159), with a cosine taper between orders 9 to 13 and 78 to 82 to produce a 'lithospheric' geoid. In the present study we focus on tectonic implications of the lithospheric geoid in three different areas: 1) passive continental margins where we have evaluated over 150 margin-transects spaced roughly every three degrees. The global average geoid anomaly associated with the transition from old oceanic lithosphere to the continent was found to 6-9 meters and appears to be insensitive to a range of geoid filtering degrees and orders; 2) The g