WorldWideScience

Sample records for model lithosphere behaves

  1. Do you BEHAVE? - Application of the BehavePlus fire modeling system

    Science.gov (United States)

    Pat Andrews

    2010-01-01

    The BehavePlus fire modeling system is the successor to BEHAVE, which was first used in the field in 1984. It is public domain software, available for free use on personal computers. Information on user communities and fire management applications can be useful in designing next generation systems. Several sources of information about BehavePlus are summarized to...

  2. Fuel model selection for BEHAVE in midwestern oak savannas

    Science.gov (United States)

    Grabner, K.W.; Dwyer, J.P.; Cutter, B.E.

    2001-01-01

    BEHAVE, a fire behavior prediction system, can be a useful tool for managing areas with prescribed fire. However, the proper choice of fuel models can be critical in developing management scenarios. BEHAVE predictions were evaluated using four standardized fuel models that partially described oak savanna fuel conditions: Fuel Model 1 (Short Grass), 2 (Timber and Grass), 3 (Tall Grass), and 9 (Hardwood Litter). Although all four models yielded regressions with R2 in excess of 0.8, Fuel Model 2 produced the most reliable fire behavior predictions.

  3. Analog Modeling of Continental Lithosphere Subduction

    Science.gov (United States)

    Willingshofer, E.; Sokoutis, D.; Luth, S.; Beekman, F.; Cloetingh, S.

    2012-12-01

    Lithospheric-scale analog modeling sheds light on the consequences of decoupling within the continental lithosphere and along plate interfaces during continental collision. The model results provide valuable information in terms of strain localization, deformation of the subducting slab and the evolution and architecture of the overlying mountain belt and its topography. A weak layer has been implemented in three-layer models to simulate decoupling along the plate interface and at different levels of the lithosphere (brittle-ductile transition, entire lower crust, crust-mantle boundary). Additionally, varying the strength of the mantle lithosphere of both the upper as well as the lower plate regulated the degree of plate coupling. Plate boundaries were orthogonal to the convergence direction. All models emphasize that strong decoupling at the plate interface is a pre-requisite for the subduction of continental lithosphere. In addition, deformation of the subducting slab was found to be sensitive to the strength contrast between the subduction zone and the mantle lithosphere of the downgoing as well as the upper plate. As such, a low strength contrast between the plate interface and the lower plate leads to deformation of the subducting slab by thickening and the development of a shallow slab. Conversely, when the strength contrast is high, deep slabs evolve which undergo relatively less deformation. Furthermore, the level of decoupling in the downgoing plate governs how much continental crust is subducted together with the mantle lithosphere. Shallow decoupling, at the brittle-ductile transition, results in subduction of the lower crust whereas small amounts of lower crust are subducted when decoupling occurs at the level of the Moho. Weak plate coupling and a weak lower crust of the lower plate steer the evolution of mountain belts such that deformation propagates outward, in the direction of the incoming plate, by successive imbrication of upper crustal thrust

  4. Lithospheric Thickness Modeled from Long Period Surface Wave Dispersion

    Energy Technology Data Exchange (ETDEWEB)

    Pasyanos, M E

    2008-05-15

    The behavior of surface waves at long periods is indicative of subcrustal velocity structure. Using recently published dispersion models, we invert surface wave group velocities for lithospheric structure, including lithospheric thickness, over much of the Eastern Hemisphere, encompassing Eurasia, Africa, and the Indian Ocean. Thicker lithosphere under Precambrian shields and platforms are clearly observed, not only under the large cratons (West Africa, Congo, Baltic, Russia, Siberia, India), but also under smaller blocks like the Tarim Basin and Yangtze craton. In contrast, it is found that remobilized Precambrian structures like the Saharan Shield and Sino-Korean Paraplatform do not have well-established lithospheric keels. The thinnest lithospheric thickness is found under oceanic and continental rifts, as well as along convergence zones. We compare our results to thermal models of continental lithosphere, lithospheric cooling models of oceanic lithosphere, lithosphere-asthenosphere boundary (LAB) estimates from S-wave receiver functions, and velocity variations of global tomography models. In addition to comparing results for the broad region, we examine in detail the regions of Central Africa, Siberia, and Tibet. While there are clear differences in the various estimates, overall the results are generally consistent. Inconsistencies between the estimates may be due to a variety of reasons including lateral and depth resolution differences and the comparison of what may be different lithospheric features.

  5. Well behaved anisotropic compact star models in general relativity

    Science.gov (United States)

    Jasim, M. K.; Maurya, S. K.; Gupta, Y. K.; Dayanandan, B.

    2016-11-01

    Anisotropic compact star models have been constructed by assuming a particular form of a metric function e^{λ}. We solved the Einstein field equations for determining the metric function e^{ν}. For this purpose we have assumed a physically valid expression of radial pressure (pr). The obtained anisotropic compact star model is representing the realistic compact objects such as PSR 1937 +21. We have done an extensive study about physical parameters for anisotropic models and found that these parameters are well behaved throughout inside the star. Along with these we have also determined the equation of state for compact star which gives the radial pressure is purely the function of density i.e. pr=f(ρ).

  6. Recovering lateral variations in lithospheric strength from bedrock motion data using a coupled ice sheet-lithosphere model

    NARCIS (Netherlands)

    Berg, J. van den; Wal, R.S.W. van de; Oerlemans, J.

    2006-01-01

    A vertically integrated two-dimensional ice flow model was coupled to an elastic lithosphere-Earth model to study the effects of lateral variations in lithospheric strength on local bedrock adjustment. We used a synthetic bedrock profile and a synthetic climate to model a characteristic ice sheet

  7. Recovering lateral variationin lithospheric strength from bedrock motion data using a coupled ice sheet-lithosphere model

    NARCIS (Netherlands)

    van de Berg, W.J.; van de Wal, R.S.W.; Oerlemans, J.

    2006-01-01

    A vertically integrated two-dimensional ice flow model was coupled to an elastic lithosphere-Earth model to study the effects of lateral variations in lithospheric strength on local bedrock adjustment. We used a synthetic bedrock profile and a synthetic climate to model a characteristic ice sheet

  8. Post-processing scheme for modelling the lithospheric magnetic field

    Directory of Open Access Journals (Sweden)

    V. Lesur

    2013-03-01

    Full Text Available We investigated how the noise in satellite magnetic data affects magnetic lithospheric field models derived from these data in the special case where this noise is correlated along satellite orbit tracks. For this we describe the satellite data noise as a perturbation magnetic field scaled independently for each orbit, where the scaling factor is a random variable, normally distributed with zero mean. Under this assumption, we have been able to derive a model for errors in lithospheric models generated by the correlated satellite data noise. Unless the perturbation field is known, estimating the noise in the lithospheric field model is a non-linear inverse problem. We therefore proposed an iterative post-processing technique to estimate both the lithospheric field model and its associated noise model. The technique has been successfully applied to derive a lithospheric field model from CHAMP satellite data up to spherical harmonic degree 120. The model is in agreement with other existing models. The technique can, in principle, be extended to all sorts of potential field data with "along-track" correlated errors.

  9. Current status and future needs of the BehavePlus Fire Modeling System

    Science.gov (United States)

    Patricia L. Andrews

    2014-01-01

    The BehavePlus Fire Modeling System is among the most widely used systems for wildland fire prediction. It is designed for use in a range of tasks including wildfire behaviour prediction, prescribed fire planning, fire investigation, fuel hazard assessment, fire model understanding, communication and research. BehavePlus is based on mathematical models for fire...

  10. Lithospheric structure models applied for locating the Romanian seismic events

    Directory of Open Access Journals (Sweden)

    V. Oancea

    1994-06-01

    Full Text Available The paper presents our attempts made for improving the locations obtained for local seismic events, using refined lithospheric structure models. The location program (based on Geiger method supposes a known model. The program is run for some seismic sequences which occurred in different regions, on the Romanian territory, using for each of the sequences three velocity models: 1 7 layers of constant velocity of seismic waves, as an average structure of the lithosphere for the whole territory; 2 site dependent structure (below each station, based on geophysical and geological information on the crust; 3 curves deseribing the dependence of propagation velocities with depth in the lithosphere, characterizing the 7 structural units delineated on the Romanian territory. The results obtained using the different velocity models are compared. Station corrections are computed for each data set. Finally, the locations determined for some quarry blasts are compared with the real ones.

  11. Effect Of Oceanic Lithosphere Age Errors On Model Discrimination

    Science.gov (United States)

    DeLaughter, J. E.

    2016-12-01

    The thermal structure of the oceanic lithosphere is the subject of a long-standing controversy. Because the thermal structure varies with age, it governs properties such as heat flow, density, and bathymetry with important implications for plate tectonics. Though bathymetry, geoid, and heat flow for young (geoid, and heat flow data to an inverse model to determine lithospheric structure details. Though inverse models usually include the effect of errors in bathymetry, heat flow, and geoid, they rarely examine the effects of errors in age. This may have the effect of introducing subtle biases into inverse models of the oceanic lithosphere. Because the inverse problem for thermal structure is both ill-posed and ill-conditioned, these overlooked errors may have a greater effect than expected. The problem is further complicated by the non-uniform distribution of age and errors in age estimates; for example, only 30% of the oceanic lithosphere is older than 80 MY and less than 3% is older than 150 MY. To determine the potential strength of such biases, I have used the age and error maps of Mueller et al (2008) to forward model the bathymetry for half space and GDH1 plate models. For ages less than 20 MY, both models give similar results. The errors induced by uncertainty in age are relatively large and suggest that when possible young lithosphere should be excluded when examining the lithospheric thermal model. As expected, GDH1 bathymetry converges asymptotically on the theoretical result for error-free data for older data. The resulting uncertainty is nearly as large as that introduced by errors in the other parameters; in the absence of other errors, the models can only be distinguished for ages greater than 80 MY. These results suggest that the problem should be approached with the minimum possible number of variables. For example, examining the direct relationship of geoid to bathymetry or heat flow instead of their relationship to age should reduce uncertainties

  12. Understanding lithospheric stresses in Arctic: constraints and models

    Science.gov (United States)

    Medvedev, Sergei; Minakov, Alexander; Lebedeva-Ivanova, Nina; Gaina, Carmen

    2016-04-01

    This pilot project aims to model stress patterns and analyze factors controlling lithospheric stresses in Arctic. The project aims to understand the modern stresses in Arctic as well as to define the ways to test recent hypotheses about Cenozoic evolution of the region. The regions around Lomonosov Ridge and Barents Sea are of particular interest driven by recent acquisition of high-resolution potential field and seismic data. Naturally, the major contributor to the lithospheric stress distribution is the gravitational potential energy (GPE). The study tries to incorporate available geological and geophysical data to build reliable GPE. In particular, we use the recently developed integrated gravity inversion for crustal thickness which incorporates up-to-date compilations of gravity anomalies, bathymetry, and sedimentary thickness. The modelled lithosphere thermal structure assumes a pure shear extension and the ocean age model constrained by global plate kinematics for the last ca. 120 Ma. The results of this approach are juxtaposed with estimates of the density variation inferred from the upper mantle S-wave velocity models based on previous surface wave tomography studies. Although new data and interpretations of the Arctic lithosphere structure become available now, there are areas of low accuracy or even lack of data. To compensate for this, we compare two approaches to constrain GPE: (1) one that directly integrates density of modelled lithosphere and (2) one that uses geoid anomalies which are filtered to account for density variations down to the base of the lithosphere only. The two versions of GPE compared to each other and the stresses calculated numerically are compared with observations. That allows us to optimize GPE and understand density structure, stress pattern, and factors controlling the stresses in Arctic.

  13. Fifth generation lithospheric magnetic field model from CHAMP satellite measurements

    OpenAIRE

    Maus, S.; Hermann Lühr; Martin Rother; Hemant, K.; Balasis, G.; Patricia Ritter; Claudia Stolle

    2007-01-01

    Six years of low-orbit CHAMP satellite magnetic measurements have provided an exceptionally high-quality data resource for lithospheric magnetic field modeling and interpretation. Here we describe the fifth-generation satellite-only magnetic field model MF5. The model extends to spherical harmonic degree 100. As a result of careful data selection, extensive corrections, filtering, and line leveling, the model has low noise levels, even if evaluated at the Earth's surface. The model is particu...

  14. Lithospheric Architecture, Heterogenities, Instabilities, Melting - insight form numerical modelling

    Science.gov (United States)

    Gorczyk, Weronika; Hobbs, Bruce; Ord, Alison; Gessner, Klaus; Gerya, Taras V.

    2010-05-01

    The seismological structure of the Earth's lithosphere is identified to be strongly heterogeneous in terms of thermal and rheological structures. Lithospheric discontinuities (sharp changes in the thermal and/or compositional structure) are thought to be long lived and are mostly correlated with major tectonic boundaries that commonly have been reactivated and which subsequently are the foci of magma intrusion and major mineralization. Resent studies have shown that mantle metasomatism is also controlled by such boundaries. This paper explores the control that lithospheric heterogeneity exerts on the thermal and chemical evolution during deformation subsequent to the development of the heterogeneity. We explore the behaviour of the rheological heterogeneous lithosphere in a compressional regime. The occurrence of such variations may be caused for instance by amalgamation of micro-continents such as is thought to be characteristic of the Yilgarn, Western Australia or South Africa. Theses micro-continents, due to diverse histories may be characterised by various thermal and rheological structures. The models are simplistic but illustrate the basic principles. The code used in this study is based on a conservative finite-difference, multi-grid, marker in cell method. Devolatilisation reactions and melting can affect the physical properties of rocks and are incorporated in a self-consistent manner. We use a petrological-thermomechanical modelling approach with all rock properties including mechanical properties calculated in the Lagrangian scheme for rock markers at every time step based on Gibbs free energy minimization as a function of the local pressure, temperature and rock composition. The results illustrate that initial structural complexity is necessary for and has a dramatic effect on fault and development, the growth of deep basins, core complex formation, melting and devolatilisation within the lithosphere. The horizontal and vertical variation in plastic

  15. New isostatic model of the lithosphere and gravity field

    Science.gov (United States)

    Kaban, M. K.; Schwintzer, P.; Reigber, Ch.

    2003-04-01

    A new global model of the isostatic gravity field based on the up-to-date data sets is computed in terms of gravity and geoid. The initial gravity field model is improved using the new CHAMP data. For a construction of the isostatic model of the lithosphere we use the latest compilation of crustal data. Globally this is the CRUST2.0 model, which is supplemented by detailed original data for large parts of North America and North Eurasia. The long-wavelengths of the computed isostatic anomalies up to spherical harmonic degree 20 reflect deep density heterogeneities and the influence of mantle convection through the dynamic topography. The signal contribution of the isostatically balanced lithosphere to the observed gravity or geoid is still significant also for the long-wavelengths: -30- +60 mGal and -15- +40 m peak-to-peak, respectively. Generally the long-wavelength isostaticaly reduced gravity field has much less correlation with the lithosphere patterns than the observed field. This demonstrates that the long-wavelength isostatic gravity field is more appropriate for a modelling of mantle convection than the observed one. The smaller scale isostatic anomalies (wavelengths less than 2000 km) on the other hand are highly sensitive to the quality of the input data used for their computation. To a large extent they reflect internal crustal density inhomogeneities, not included in the isostatic compensation scheme, and uncertainties in the initial crustal data. Thus, small-scale isostatic anomalies may not be always interpreted as a measure of the disturbances of isostatic balance of the lithosphere. Instead we suggest to compute for the smaller scale spectral part the non-isostatic residual topography. The initial crust - upper mantle density model is corrected by gravity inversion in a least squares adjustment. Then, the residual (unbalanced) topography computed with the corrected density distribution represents the isostatic state of the lithosphere. The maximum

  16. Swarm magnetic and GOCE gravity gradient grids for lithospheric modelling

    DEFF Research Database (Denmark)

    Bouman, Johannes; Ebbing, Jörg; Kotsiaros, Stavros

    We explore how Swarm magnetic gradient and GOCE gravity gradient data can improve modelling of the Earth’s lithosphere and thereby contribute to a better understanding of Earth’s dynamic processes. We study the use of gradient grids to provide improved information about the lithosphere and upper...... mantle in the well-surveyed North-East Atlantic Margin. In particular, we present the computation of magnetic and gravity gradient grids at satellite altitude (roughly 450 km and 250 km above the Earth for Swarm and GOCE respectively). It is shown that regional solutions based on a tesseroid approach may...... contain more signal content than global models do. The patchwork of regional grids is presented as well as the subsequent error reduction through iterative downward and upward continuation using the Poisson integral equation. The promises and pitfalls are discussed of using grids at mean satellite...

  17. BEHAVE: fire behavior prediction and fuel modeling system--FUEL subsystem

    Science.gov (United States)

    Robert E. Burgan; Richard C. Rothermel

    1984-01-01

    This manual documents the fuel modeling procedures of BEHAVE--a state-of-the-art wildland fire behavior prediction system. Described are procedures for collecting fuel data, using the data with the program, and testing and adjusting the fuel model.

  18. BEHAVE: fire behavior prediction and fuel modeling system-BURN Subsystem, part 1

    Science.gov (United States)

    Patricia L. Andrews

    1986-01-01

    Describes BURN Subsystem, Part 1, the operational fire behavior prediction subsystem of the BEHAVE fire behavior prediction and fuel modeling system. The manual covers operation of the computer program, assumptions of the mathematical models used in the calculations, and application of the predictions.

  19. Structure of the Lithosphere in Central Europe: Integrated Density Modelling

    Science.gov (United States)

    Bielik, M.; Grinč, M.; Zeyen, H. J.; Plašienka, D.; Pasteka, R.; Krajňák, M.; Bošanský, M.; Mikuška, J.

    2014-12-01

    Firstly, we present new results related to the lithospheric structure and tectonics of the Central Europe and the Western Carpathians. For geophysical study of the lithosphere in Central Europe we calculated four original 2D lithosphere-scales transects crossing this area from the West European Platform in the North to the Aegean Sea in the South and from the Adriatic Sea in the West to the East European Platform in the East. Modelling is based on the joint interpretation of gravity, geoid, topography and surface heat flow data with temperature-dependent density. Wherever possible, crustal structure is constrained by seismic data. The thickness of the lithosphere decreases from the older and colder platforms to the younger and hotter Pannonian Basin with a maximum thickness under the Eastern and Southern Carpathians. The thickness of the Carpathian arc lithosphere varies between 150 km in the North (the Western Carpathians) and about 300 km in the Vrancea zone (the Eastern and Southern Carpathian junction). In the Platform areas it is between 120 and 150 km and in the Pannonian Basin it is about 70 km. The models show that the Moesian Platform is overthrust from the North by the Southern Carpathians and from the South by the Balkanides and characterized by bending of this platform. In all transects, the thickest crust is found underneath the Carpathian Mountains or, as in the case of the Vrancea area, under their immediate foreland. The thickest crust outside the orogens is modelled for the Moesian Platform with Moho depths of up to 45 km. The thinnest crust is located under the Pannonian Basin with about 26-27 km. Secondly, our presentation deals with construction of the stripped gravity map in the Turiec Basin, which represents typical intramontane Neogene depression of the Western Carpathians. Based on this new and original gravity map corrected by regional gravity effect we were able to interpret the geological structure and tectonics of this sedimentary basin

  20. Lithospheric scale model of Merida Andes, Venezuela (GIAME Project)

    Science.gov (United States)

    Schmitz, M.; Orihuela, N. D.; Klarica, S.; Gil, E.; Levander, A.; Audemard, F. A.; Mazuera, F.; Avila, J.

    2013-05-01

    Merida Andes (MA) is one of the most important orogenic belt in Venezuela and represents the northern culmination of South America Andes. During the last 60 years, several models have been proposed to explain the shallow and deep structure, using different geological, geophysical, seismological, geochemical and petrologic concepts; nevertheless, most of them have applied local observation windows, and do not represent the major structure of MA. Therefore, a multidisciplinary research group, coordinated by FUNVISIS, in close cooperation with UCV, ULA and PDVSA, is proposed in order to get the outlined goals in the project entitled GIAME ("Geociencia Integral de los Andes de MErida") was established, which aims to generate a lithospheric scale model and the development of a temporal dynamic model for the MA. As a base for lithospheric investigations of the Merida Andes, we are proposing three wide angle seismic profiles across the orogen on three representative sites, in order to determine the inner structure and its relation with the orogen's gravimetric root. To the date, there are no seismic studies at lithospheric scale which cross MA. The wide angle seismic will be complemented with the re-processing and re-interpretation of existing reflection seismic data, which will allow to establish a relationship between MA and its associated flexural basins (Maracaibo and Barinas-Apure basins). Depending on the results of the VENCORP Project (VENezuelan COntinental Reflection Profiling), which might show some reliable results about crustal features and Moho reflectors along three long seismic profiles at Caribbean Moutain system, a reflection seismic profile across the central portion of MA is proposed. Additional tasks, consisting in MA quaternary deformation studies, using research methods like neotectonics and paleoseismology, georadar, numerical modeling, cinematic GPS, SAR interferometry, thermocronology, detailed studies on regional geology, flexural modeling

  1. Thermal structure of the lithosphere: a petrologic model.

    Science.gov (United States)

    Macgregor, I D; Basu, A R

    1974-09-20

    A preliminary evaluation of the thermal history of the upper mantle as determined by petrologic techniques indicates a general correspondence with theoretically derived models. The petrologic data supply direct information which may be used as an independent calibration of calculated models, serve as a base for evaluating the assumptions of the theoretical approach, and allow more careful selection of the variables describing mantle thermal properties and processes. Like the theoretical counterpart, the petrological approach indicates that the lithosphere is dominated by two thermal regimes: first, there is a continental regime which cools at rates of the order of 10(9) years and represents the longterm cooling of the earth. Secondly, superimposed on the continental evolution is the thermal event associated with the formation of an oceanic basin, and which may be thought of as a 10(8) year convective perturbation on the continental cycle. Of special interest is petrologic evidence for a sudden steepening of the thermal gradients across the lithosphere-asthenosphere boundary not seen in the theoretical models. The unexpected change of slope points to the need for a critical reevaluation of the thermal processes and properties extant in the asthenosphere. The potential of the petrologic contribution has yet to be fully realized. For a start, this article points to an important body of independent evidence critical to our understanding of the earth's thermal history.

  2. Combinatorial Clustering Algorithm of Quantum-Behaved Particle Swarm Optimization and Cloud Model

    Directory of Open Access Journals (Sweden)

    Mi-Yuan Shan

    2013-01-01

    Full Text Available We propose a combinatorial clustering algorithm of cloud model and quantum-behaved particle swarm optimization (COCQPSO to solve the stochastic problem. The algorithm employs a novel probability model as well as a permutation-based local search method. We are setting the parameters of COCQPSO based on the design of experiment. In the comprehensive computational study, we scrutinize the performance of COCQPSO on a set of widely used benchmark instances. By benchmarking combinatorial clustering algorithm with state-of-the-art algorithms, we can show that its performance compares very favorably. The fuzzy combinatorial optimization algorithm of cloud model and quantum-behaved particle swarm optimization (FCOCQPSO in vague sets (IVSs is more expressive than the other fuzzy sets. Finally, numerical examples show the clustering effectiveness of COCQPSO and FCOCQPSO clustering algorithms which are extremely remarkable.

  3. The Cascadia Subduction Zone: two contrasting models of lithospheric structure

    Science.gov (United States)

    Romanyuk, T.V.; Blakely, R.; Mooney, W.D.

    1998-01-01

    The Pacific margin of North America is one of the most complicated regions in the world in terms of its structure and present day geodynamic regime. The aim of this work is to develop a better understanding of lithospheric structure of the Pacific Northwest, in particular the Cascadia subduction zone of Southwest Canada and Northwest USA. The goal is to compare and contrast the lithospheric density structure along two profiles across the subduction zone and to interpet the differences in terms of active processes. The subduction of the Juan de Fuca plate beneath North America changes markedly along the length of the subduction zone, notably in the angle of subduction, distribution of earthquakes and volcanism, goelogic and seismic structure of the upper plate, and regional horizontal stress. To investigate these characteristics, we conducted detailed density modeling of the crust and mantle along two transects across the Cascadia subduction zone. One crosses Vancouver Island and the Canadian margin, the other crosses the margin of central Oregon.

  4. An Equivalent Source Method for Modelling the Global Lithospheric Magnetic Field

    DEFF Research Database (Denmark)

    Kother, Livia Kathleen; Hammer, Magnus Danel; Finlay, Chris;

    We produce a new model of the global lithospheric magnetic field based on 3-component vector field observations at all latitudes from the CHAMP satellite using an equivalent source technique.......We produce a new model of the global lithospheric magnetic field based on 3-component vector field observations at all latitudes from the CHAMP satellite using an equivalent source technique....

  5. Dynamic Network Traffic Flow Prediction Model based on Modified Quantum-Behaved Particle Swarm Optimization

    Directory of Open Access Journals (Sweden)

    Hongying Jin

    2013-10-01

    Full Text Available This paper aims at effectively predicting the dynamic network traffic flow based on quantum-behaved particle swarm optimization algorithm. Firstly, the dynamic network traffic flow prediction problem is analyzed through formal description. Secondly, the structure of the network traffic flow prediction model is given. In this structure, Users can used a computer to start the traffic flow prediction process, and data collecting module can collect and return the data through the destination device. Thirdly, the dynamic network traffic flow prediction model is implemented based on BP Neural Network. Particularly, in this paper, the BP Neural Network is trained by a modified quantum-behaved particle swarm optimization(QPSO. We modified the QPSO by utilizing chaos signals to implement typical logistic mapping and pursuing the fitness function of a particle by a set of optimal parameters. Afterwards, based on the above process, dynamic network traffic flow prediction model is illustrated. Finally, a series of experiments are conduct to make performance evaluation, and related analyses for experimental results are also given

  6. The effects of strain heating in lithospheric stretching models

    Science.gov (United States)

    Stanton, M.; Hodge, D.; Cozzarelli, F.

    1985-01-01

    The deformation by stretching of a continental type lithosphere has been formulated so that the problem can be solved by a continuum mechanical approach. The deformation, stress state, and temperature distribution are constrained to satisfy the physical laws of conservation of mass, energy, momentum, and an experimentally defined rheological response. The conservation of energy equation including a term of strain energy dissipation is given. The continental lithosphere is assumed to have the rheology of an isotropic, incompressible, nonlinear viscous, two layered solid.

  7. Constitutive models of faults in the viscoelastic lithosphere

    Science.gov (United States)

    Moresi, Louis; Muhlhaus, Hans; Mansour, John; Miller, Meghan

    2013-04-01

    Moresi and Muhlhaus (2006) presented an algorithm for describing shear band formation and evolution as a coallescence of small, planar, fricition-failure surfaces. This algorithm assumed that sliding initially occurs at the angle to the maximum compressive stress dictated by Anderson faulting theory and demonstrated that shear bands form with the same angle as the microscopic angle of initial failure. Here we utilize the same microscopic model to generate frictional slip on prescribed surfaces which represent faults of arbitrary geometry in the viscoelastic lithosphere. The faults are actually represented by anisotropic weak zones of finite width, but they are instantiated from a 2D manifold represented by a cloud of points with associated normals and mechanical/history properties. Within the hybrid particle / finite-element code, Underworld, this approach gives a very flexible mechanism for describing complex 3D geometrical patterns of faults with no need to mirror this complexity in the thermal/mechanical solver. We explore a number of examples to demonstrate the strengths and weaknesses of this particular approach including a 3D model of the deformation of Southern California which accounts for the major fault systems. L. Moresi and H.-B. Mühlhaus, Anisotropic viscous models of large-deformation Mohr-Coulomb failure. Philosophical Magazine, 86:3287-3305, 2006.

  8. A Magma Accretion Model for the Formation of Oceanic Lithosphere: Implications for Global Heat Loss

    Directory of Open Access Journals (Sweden)

    Valiya M. Hamza

    2010-01-01

    Full Text Available A magma accretion model of oceanic lithosphere is proposed and its implications for understanding its thermal field examined. The new model (designated Variable Basal Accretion—VBA assumes existence of lateral variations in magma accretion rates and temperatures at the boundary zone between the lithosphere and the asthenosphere. However, unlike the previous thermal models of the lithosphere, the ratio of advection to conduction heat transfer is considered a space dependent variable. The results of VBA model simulations reveal that the thickness of the young lithosphere increases with distance from the ridge axis, at rates faster than those predicted by Half-Space Cooling models. Another noteworthy feature of the new model is its ability to account for the main features in the thermal behavior of oceanic lithosphere. The improved fits to bathymetry have been achieved for the entire age range and without the need to invoke the ad-hoc hypothesis of large-scale hydrothermal circulation. Also, use of VBA model does not lead to artificial discontinuities in the temperature field of the lithosphere, as is the case with GDH (Global Depth Heat Flow reference models. The results suggest that estimates of global heat loss need to be downsized by at least 25%.

  9. Elysium Region, Mars: Tests of Lithospheric Loading Models for the Formation of Tectonic Features

    Science.gov (United States)

    Hall, J. L.; Solomon, S. C.; Head, J. W.

    1985-01-01

    In an effort to constrain the tectonic history and mechanical properties of the lithosphere in the Elysium province, the stress fields predicted by different models are compared to the observed tectonic features of the region. The models are all products of volcanic loading of the Martian lithosphere, but at three different scales: global (Tharsis), regional (Elysium Planitia), and local (individual shields). Conclusions: The concentric graben surrounding Elysium Mons can be ascribed to the flexural response of an approximately 50-km-thick elastic lithosphere to loading by the volcano. No tectonic evidence for the support of larger-scale Elysium Planitia volcanic units by lithospheric flexure. The quasi-global loading of the Tharsis rise appears to have produced identifiable tectonic effects in the Elysium region.

  10. Possible link between numerical modeling of the lithospheric deformation and MT research fields

    OpenAIRE

    Stephan V. Sobolev; [Child, Sir Josiah, bart.] 

    2004-01-01

    There is almost no connection established yet between two rapidly developing fields of the lithospheric research, namely between numerical simulation of the thermo-mechanical processes and MT studies. To compensate for this gap I focus here on the numerical modeling of the strain localization processes at the lithosphere-scale continental transform faults and on prediction of the possible electrical conductivity structures associated with these processes. First, I use a finite-element thermo-...

  11. Elysium region, Mars - Tests of lithospheric loading models for the formation of tectonic features

    Science.gov (United States)

    Hall, J. Lynn; Solomon, Sean C.; Head, James W.

    1986-01-01

    The hypothesis that the tectonic features in the Elysium region are the product of stress produced by loading of the Martian lithosphere is tested. The lithospheric loading models for the formation of tectonic features in the Elysium region are evaluated under local loading, regional loading of the lithosphere from above and below, and quasi-global loading by Tharsis. The physiographic features in the Elysium region are described. The stress fields predicted by volcanic loading and uplift of the Martian lithosphere are compared with the tectonic features in the Elysium region. It is noted that the comparison suggests the succession of stress fields operating at different times in the region and supports the hypothesis.

  12. Inelastic models of lithospheric stress - I. Theory and application to outer-rise plate deformation

    Science.gov (United States)

    Mueller, S.; Choy, G.L.; Spence, W.

    1996-01-01

    Outer-rise stress distributions determined in the manner that mechanical engineers evaluate inelastic stress distributions within conventional materials are contrasted with those predicted using simple elastic-plate models that are frequently encountered in studies of outer-rise seismicity. This comparison indicates that the latter are inherently inappropriate for studies of intraplate earthquakes, which are a direct manifestation of lithospheric inelasticity. We demonstrate that the common practice of truncating elastically superimposed stress profiles so that they are not permitted to exceed laboratory-based estimates of lithospheric yield strength will result in an accurate characterization of lithospheric stress only under relatively restrictive circumstances. In contrast to elastic-plate models, which predict that lithospheric stress distributions depend exclusively upon the current load, inelastic plate models predict that stress distributions are also significantly influenced by the plate-loading history, and, in many cases, this influence is the dominant factor in determining the style of potential seismicity (e.g. thrust versus normal faulting). Numerous 'intuitive' interpretations of outer-rise earthquakes have been founded upon the implicit assumption that a unique relationship exists between a specified combination of plate curvature and in-plane force, and the resulting lithospheric stress distribution. We demonstrate that the profound influence of deformation history often invalidates such interpretations. Finally, we examine the reliability of 'yield envelope' representations of lithospheric strength that are constructed on the basis of empirically determined frictional sliding relationships and silicate plastic-flow laws. Although representations of this nature underestimate the strength of some major interplate faults, such as the San Andreas, they appear to represent a reliable characterization of the strength of intraplate oceanic lithosphere.

  13. 3D Integrated geophysical-petrological modelling of the Iranian lithosphere

    Science.gov (United States)

    Mousavi, Naeim; Ardestani, Vahid E.; Ebbing, Jörg; Fullea, Javier

    2016-04-01

    The present-day Iranian Plateau is the result of complex tectonic processes associated with the Arabia-Eurasia Plate convergence at a lithospheric scale. In spite of previous mostly 2D geophysical studies, fundamental questions regarding the deep lithospheric and sub-lithospheric structure beneath Iran remain open. A robust 3D model of the thermochemical lithospheric structure in Iran is an important step toward a better understanding of the geological history and tectonic events in the area. Here, we apply a combined geophysical-petrological methodology (LitMod3D) to investigate the present-day thermal and compositional structure in the crust and upper mantle beneath the Arabia-Eurasia collision zone using a comprehensive variety of constraining data: elevation, surface heat flow, gravity potential fields, satellite gravity gradients, xenoliths and seismic tomography. Different mantle compositions were tested in our model based on local xenolith samples and global data base averages for different tectonothermal ages. A uniform mantle composition fails to explain the observed gravity field, gravity gradients and surface topography. A tectonically regionalized lithospheric mantle compositional model is able to explain all data sets including seismic tomography models. Our preliminary thermochemical lithospheric study constrains the depth to Moho discontinuity and intra crustal geometries including depth to sediments. We also determine the depth to Curie isotherm which is known as the base of magnetized crustal/uppermost mantle bodies. Discrepancies with respect to previous studies include mantle composition and the geometry of Moho and Lithosphere-Asthenosphere Boundary (LAB). Synthetic seismic Vs and Vp velocities match existing seismic tomography models in the area. In this study, depleted mantle compositions are modelled beneath cold and thick lithosphere in Arabian and Turan platforms. A more fertile mantle composition is found in collision zones. Based on our 3

  14. Comparison of plate and asthenospheric flow models for the thermal evolution of oceanic lithosphere

    Science.gov (United States)

    Stein, Carol A.; Stein, Seth

    1994-04-01

    Although seafloor depth and heat flow for young oceanic lithosphere can be descibed by modeling the lithosphere as the boundary layer of a cooling halfspace, a long standing question has been why data at older ages deviate from those expected for a halfspace. Two classes of models have been proposed for these deviations. In one, heat added from below 'flattens' depth and heat flow. In the other, asthenospheric flow beneath the lithosphere perturbs the depths. We compare recent versions of the model classes: the GDH1 thin-lithosphere plate model (Stein and Stein, 1992) and an asthenospehric flow model (Phipps Morgan and Smith, 1992). The plate model fits heat flow data better than the flow model for all cases considered, and topographic data in all but one case. The flow model significantly overpredicts depths for the North Atlantic, because the assumed asthenospheric flow in the plate motion direction would yield deepening for old ages rather than the observed flattening. Overall, the GDH1 global average model does better than this flow model, whose parameters were fit to specific plates. Moreover, the plate models fit to specific plates do better than the flow model. Plate models thus appear more useful than this flow model, suggesting that deviations from a cooling halfspace are largely thermal in origin.

  15. Numerical models of mantle lithosphere weakening, erosion and delamination induced by melt extraction and emplacement

    Science.gov (United States)

    Wallner, Herbert; Schmeling, Harro

    2016-09-01

    Continental rifting caused by extension and heating from below affects the lithosphere or cratons in various ways. Volcanism and melt intrusions often occur along with thinning, weakening and even breaking lithosphere. Although mechanical necking models of the lithosphere are often applied, the aspects of melting and the implications due to melt transport and emplacement at shallower depths are not well understood. A two-phase flow approach employing melt extraction and shallow emplacement associated with thermal weakening is developed and compared with observations. The results of this comparison indicate the importance of partial melts and an asthenospheric magma source for increasing the rising rate of the lithosphere-asthenosphere boundary during extension. Thermo-mechanical physics of visco-plastic flow is approximated using the Finite Difference method with Eulerian formulation in 2D. The conservation of mass, momentum and energy equations are solved for a multi-component (crust-mantle) and two-phase (melt-matrix) system. Rheology is temperature- and stress-dependent. In consideration of depletion and enrichment melting and solidification are controlled by a simplified linear binary solid solution model. Melt is extracted and emplaced in predefined depth regions (emplacement zones) in the lithospheric mantle and crust. The Compaction Boussinesq Approximation was applied; its validity was tested against the Full Compaction formulation and found fully satisfactory for the case of sublithospheric melting models. A simple model guided by the geodynamic situation of the Rwenzori region typically results in updoming asthenosphere with melt-assisted erosion of the lithosphere's base. Even with a conservative approach for a temperature anomaly melting alone doubles the lithospheric erosion rate in comparison with a model without melting. With melt extraction and intrusion lithospheric erosion and upwelling of the lithosphere-asthenosphere boundary speeds up by a

  16. Samovar: a thermomechanical code for modeling of geodynamic processes in the lithosphere-application to basin evolution

    OpenAIRE

    Elesin, Y; Gerya, T.; Artemieva, Irina; Thybo, Hans

    2010-01-01

    We present a new 2D finite difference code, Samovar, for high-resolution numerical modeling of complex geodynamic processes. Examples are collision of lithospheric plates (including mountain building and subduction) and lithosphere extension (including formation of sedimentary basins, regions of extended crust, and rift zones). The code models deformation of the lithosphere with viscoelastoplastic rheology, including erosion/sedimentation processes and formation of shear zones in areas of hig...

  17. An Equivalent Source Method for Modelling the Global Lithospheric Magnetic Field

    DEFF Research Database (Denmark)

    Kother, Livia Kathleen; Hammer, Magnus Danel; Finlay, Chris

    2015-01-01

    are also employed to minimize the influence of the ionospheric field. The model for the remaining lithospheric magnetic field consists of magnetic equivalent potential field sources (monopoles) arranged in an icosahedron grid at a depth of 100 km belowthe surface. The corresponding model parameters......We present a new technique for modelling the global lithospheric magnetic field at Earth’s surface based on the estimation of equivalent potential field sources. As a demonstration we show an application to magnetic field measurements made by the CHAMP satellite during the period 2009–2010 when...

  18. Using open sidewalls for modelling self-consistent lithosphere subduction dynamics

    NARCIS (Netherlands)

    Chertova, M.V.; Geenen, T.; van den Berg, A.; Spakman, W.

    2012-01-01

    Subduction modelling in regional model domains, in 2-D or 3-D, is commonly performed using closed (impermeable) vertical boundaries. Here we investigate the merits of using open boundaries for 2-D modelling of lithosphere subduction. Our experiments are focused on using open and closed (free

  19. A Magma Accretion Model for the Formation of Oceanic Lithosphere: Implications for Global Heat Loss

    CERN Document Server

    Hamza, V M; Alexandrino, C H

    2010-01-01

    A simple magma accretion model of the oceanic lithosphere is proposed and its implications for understanding the thermal field of oceanic lithosphere examined. The new model (designated VBA) assumes existence of lateral variations in magma accretion rates and temperatures at the boundary zone between the lithosphere and the asthenosphere. Heat flow and bathymetry variations calculated on the basis of the VBA model provide vastly improved fits to respective observational datasets. The improved fits have been achieved for the entire age range and without the need to invoke the ad-hoc hypothesis of large-scale hydrothermal circulation in stable ocean crust. The results suggest that estimates of global heat loss need to be downsized by at least 25%.

  20. BEHAVE: fire behavior prediction and fuel modeling system - BURN subsystem, Part 2

    Science.gov (United States)

    Patricia L. Andrews; Carolyn H. Chase

    1989-01-01

    This is the third publication describing the BEHAVE system of computer programs for predicting behavior of wildland fires. This publication adds the following predictive capabilities: distance firebrands are lofted ahead of a wind-driven surface fire, probabilities of firebrands igniting spot fires, scorch height of trees, and percentage of tree mortality. The system...

  1. An Equivalent Source Method for Modelling the Global Lithospheric Magnetic Field

    DEFF Research Database (Denmark)

    Kother, Livia Kathleen; Hammer, Magnus Danel; Finlay, Chris

    2014-01-01

    are also employed to minimize the influence of the ionospheric field. The model for the remaining lithospheric magnetic field consists of magnetic point sources (monopoles) arranged in an icosahedron grid. The corresponding source values are estimated using an iteratively reweighted least squares algorithm......We present a new technique for modelling the global lithospheric magnetic field at Earth's surface based on the estimation of equivalent potential field sources. As a demonstration we show an application to magnetic field measurements made by the CHAMP satellite during the period 2009-2010 when...

  2. An Equivalent Source Method for Modelling the Lithospheric Magnetic Field Using Satellite and Airborne Magnetic Data

    DEFF Research Database (Denmark)

    Kother, Livia Kathleen; Hammer, Magnus Danel; Finlay, Chris

    for the remaining lithospheric magnetic field consists of magnetic point sources (monopoles) arranged in an icosahedron grid with an increasing grid resolution towards the airborne survey area. The corresponding source values are estimated using an iteratively reweighted least squares algorithm that includes model......We present a technique for modelling the lithospheric magnetic field based on estimation of equivalent potential field sources. As a first demonstration we present an application to magnetic field measurements made by the CHAMP satellite during the period 2009-2010. Three component vector field....... Advantages of the equivalent source method include its local nature and the ease of transforming to spherical harmonics when needed. The method can also be applied in local, high resolution, investigations of the lithospheric magnetic field, for example where suitable aeromagnetic data is available...

  3. Cenozoic lithospheric evolution of the Bohai Bay Basin, eastern North China Craton: Constraint from tectono-thermal modeling

    Science.gov (United States)

    Liu, Qiongying; He, Lijuan; Huang, Fang; Zhang, Linyou

    2016-01-01

    It is well established that the lithosphere beneath the eastern North China Craton (NCC) had been thinned before the Cenozoic. A 2D multi-phase extension model, in which the initial crustal and lithospheric thicknesses are variable, is presented to reconstruct the initial thicknesses of the crust and lithosphere in the early Cenozoic and to further investigate the lithospheric evolution beneath the eastern NCC through the Cenozoic. We conduct thermal modeling along three profiles from east to west in the Bohai Bay Basin, which is the center of the lithospheric destruction and thinning of the NCC. Using multiple constraints, such as tectonic subsidence, the present-day heat flow and the Moho depth, we determine the initial crustal and lithospheric thicknesses of the Bohai Bay Basin before the Cenozoic rift to be 33-36 km and 80-105 km, respectively. The model results show that the most rapid lithospheric thinning during the Cenozoic occurred in the middle Eocene for most depressions, and the thinning activity ceased at the end of the Oligocene, reaching a minimum lithospheric thickness of 53-74 km, followed by a thermal relaxation phase. Combined with previous studies, we infer that the lithosphere beneath the eastern NCC experienced two stages of alternating thinning and thickening: notable thinning in the Early Cretaceous and Paleogene, and thickening in the Late Cretaceous and late Cenozoic. We believe that thermo-chemical erosion, together with extension, was probably the major mechanism of the significant lithospheric removal during the Mesozoic, whereas the Cenozoic lithospheric thinning was mainly dominated by tectonic extension in the eastern NCC; lithospheric thickening was generally a result of thermal cooling.

  4. Evolving Models of Pavlovian Conditioning: Cerebellar Cortical Dynamics in Awake Behaving Mice

    Directory of Open Access Journals (Sweden)

    Michiel M. ten Brinke

    2015-12-01

    Full Text Available Three decades of electrophysiological research on cerebellar cortical activity underlying Pavlovian conditioning have expanded our understanding of motor learning in the brain. Purkinje cell simple spike suppression is considered to be crucial in the expression of conditional blink responses (CRs. However, trial-by-trial quantification of this link in awake behaving animals is lacking, and current hypotheses regarding the underlying plasticity mechanisms have diverged from the classical parallel fiber one to the Purkinje cell synapse LTD hypothesis. Here, we establish that acquired simple spike suppression, acquired conditioned stimulus (CS-related complex spike responses, and molecular layer interneuron (MLI activity predict the expression of CRs on a trial-by-trial basis using awake behaving mice. Additionally, we show that two independent transgenic mouse mutants with impaired MLI function exhibit motor learning deficits. Our findings suggest multiple cerebellar cortical plasticity mechanisms underlying simple spike suppression, and they implicate the broader involvement of the olivocerebellar module within the interstimulus interval.

  5. Use of along-track magnetic field differences in lithospheric field modelling

    DEFF Research Database (Denmark)

    Kotsiaros, Stavros; Finlay, Chris; Olsen, Nils

    2015-01-01

    , using 2 yr of low altitude data from the CHAMP satellite, we show that use of along-track differences of vector field data results in an enhanced recovery of the small scale lithospheric field, compared to the use of the vector field data themselves. We show that the along-track technique performs....... Experiments in modelling the Earth's lithospheric magnetic field with along-track differences are presented here as a proof of concept. We anticipate that use of such along-track differences in combination with east–west field differences, as are now provided by the Swarm satellite constellation...

  6. Joint modeling of lithosphere and mantle dynamics: Evaluation of constraints from global tomography models

    Science.gov (United States)

    Wang, Xinguo; Holt, William E.; Ghosh, Attreyee

    2015-12-01

    With the advances in technology, seismological theory, and data acquisition, a number of high-resolution seismic tomography models have been published. However, discrepancies between tomography models often arise from different theoretical treatments of seismic wave propagation, different inversion strategies, and different data sets. Using a fixed velocity-to-density scaling and a fixed radial viscosity profile, we compute global mantle flow models associated with the different tomography models and test the impact of these for explaining surface geophysical observations (geoid, dynamic topography, stress, and strain rates). We use the joint modeling of lithosphere and mantle dynamics approach of Ghosh and Holt (2012) to compute the full lithosphere stresses, except that we use HC for the mantle circulation model, which accounts for the primary flow-coupling features associated with density-driven mantle flow. Our results show that the seismic tomography models of S40RTS and SAW642AN provide a better match with surface observables on a global scale than other models tested. Both of these tomography models have important similarities, including upwellings located in Pacific, Eastern Africa, Iceland, and mid-ocean ridges in the Atlantic and Indian Ocean and downwelling flows mainly located beneath the Andes, the Middle East, and central and Southeast Asia.

  7. Constraining the rheology of the lithosphere and upper mantle with geodynamic inverse modelling

    Science.gov (United States)

    Kaus, Boris; Baumann, Tobias

    2016-04-01

    The rheology of the lithosphere is of key importance for the physics of the lithosphere. Yet, it is probably the most uncertain parameter in geodynamics as experimental rock rheologies have to be extrapolated to geological conditions and as existing geophysical methods such as EET estimations make simplifying assumptions about the structure of the lithosphere. In many geologically interesting regions, such as the Alps, Andes or Himalaya, we actually have a significant amount of data already and as a result the geometry of the lithosphere is quite well constrained. Yet, knowing the geometry is only one part of the story, as we also need to have an accurate knowledge on the rheology and temperature structure of the lithosphere. Here, we discuss a relatively new method that we developed over the last few years, which is called geodynamic inversion. The basic principle of the method is simple: we compile available geophysical data into a realistic geometric model of the lithosphere and incorporate that into a thermo-mechanical numerical model of lithospheric deformation. In order to do so, we have to know the temperature structure, the density and the (nonlinear) rheological parameters for various parts of the lithosphere (upper crust, upper mantle, etc.). Rather than fixing these parameters we assume that they are all uncertain. This is used as a priori information to formulate a Bayesian inverse problem that employs topography, gravity, horizontal and vertical surface velocities to invert for the unknown material parameters and temperature structure. In order to test the general methodology, we first perform a geodynamic inversion of a synthetic forward model of intra-oceanic subduction with known parameters. This requires solving an inverse problem with 14-16 parameters, depending on whether temperature is assumed to be known or not. With the help of a massively parallel direct-search combined with a Markov Chain Monte Carlo method, solving the inverse problem

  8. Lithospheric processes

    Energy Technology Data Exchange (ETDEWEB)

    Baldridge, W. [and others

    2000-12-01

    The authors used geophysical, geochemical, and numerical modeling to study selected problems related to Earth's lithosphere. We interpreted seismic waves to better characterize the thickness and properties of the crust and lithosphere. In the southwestern US and Tien Shari, crust of high elevation is dynamically supported above buoyant mantle. In California, mineral fabric in the mantle correlate with regional strain history. Although plumes of buoyant mantle may explain surface deformation and magmatism, our geochemical work does not support this mechanism for Iberia. Generation and ascent of magmas remains puzzling. Our work in Hawaii constrains the residence of magma beneath Hualalai to be a few hundred to about 1000 years. In the crust, heat drives fluid and mass transport. Numerical modeling yielded robust and accurate predictions of these processes. This work is important fundamental science, and applies to mitigation of volcanic and earthquake hazards, Test Ban Treaties, nuclear waste storage, environmental remediation, and hydrothermal energy.

  9. Samovar: a thermomechanical code for modeling of geodynamic processes in the lithosphere-application to basin evolution

    DEFF Research Database (Denmark)

    Elesin, Y; Gerya, T; Artemieva, Irina;

    2010-01-01

    We present a new 2D finite difference code, Samovar, for high-resolution numerical modeling of complex geodynamic processes. Examples are collision of lithospheric plates (including mountain building and subduction) and lithosphere extension (including formation of sedimentary basins, regions...... of extended crust, and rift zones). The code models deformation of the lithosphere with viscoelastoplastic rheology, including erosion/sedimentation processes and formation of shear zones in areas of high stresses. It also models steady-state and transient conductive and advective thermal processes including...... partial melting and magma transport in the lithosphere. The thermal and mechanical parts of the code are tested for a series of physical problems with analytical solutions. We apply the code to geodynamic modeling by examining numerically the processes of lithosphere extension and basin formation...

  10. Lithospheric architecture of the Levant Basin (Eastern Mediterranean region): A 2D modeling approach

    Science.gov (United States)

    Inati, Lama; Zeyen, Hermann; Nader, Fadi Henri; Adelinet, Mathilde; Sursock, Alexandre; Rahhal, Muhsin Elie; Roure, François

    2016-12-01

    This paper discusses the deep structure of the lithosphere underlying the easternmost Mediterranean region, in particular the Levant Basin and its margins, where the nature of the crust, continental versus oceanic, remains debated. Crustal thickness and the depth of the lithosphere-asthenosphere boundary (LAB) as well as the crustal density distribution were calculated by integrating surface heat flow data, free-air gravity anomaly, geoid and topography. Accordingly, two-dimensional, lithospheric models of the study area are discussed, demonstrating the presence of a progressively attenuated crystalline crust from E to W (average thickness from 35 to 8 km). The crystalline crust is best interpreted as a strongly thinned continental crust under the Levant Basin, represented by two distinct components, an upper and a lower crust. Further to the west, the Herodotus Basin is believed to be underlain by an oceanic crust, with a thickness between 6 and 10 km. The Moho under the Arabian Plate is 35-40 km deep and becomes shallower towards the Mediterranean coast. It appears to be situated at depths ranging between 20 and 23 km below the Levant Basin and 26 km beneath the Herodotus Basin, based on our proposed models. At the Levantine margin, the thinning of the crust in the transitional domain between the onshore and the offshore is gradual, indicating successive extensional regimes that did not reach the beak up stage. In addition, the depth to LAB is around 120 km under the Arabian and the Eurasian Plates, 150 km under the Levant Basin, and it plunges to 180 km under the Herodotus Basin. This study shows that detailed 2D lithosphere modeling using integrated geophysical data can help understand the mechanisms responsible for the modelled lithospheric architecture when constrained with geological findings.

  11. Numerical models on thermal and rheological sensitivity of deformation pattern at the lithosphere-asthenosphere boundary

    Science.gov (United States)

    Fuchs, Lukas; Schmeling, Harro; Koyi, Hemin

    2014-05-01

    Understanding the interaction between the oceanic lithosphere and the upper mantle is a crucial part in understanding plate tectonics/kinematic, especially along the lithosphere-asthenosphere boundary (LAB). In this study, we analyzed finite deformation (f = log(a b) , where a and b are the major and minor axis of the strain ellipse, respectively) integrated over time, within the upper 400 km of the mantle. The velocity field was numerically calculated within a two-dimensional channel of certain depth and length with a constant plate velocity on top (Couette flow), with no slip bottom boundary and open side boundaries. The viscosity is described by a composite rheology (dislocation and diffusion creep) which is given by a temperature field based on a half-space cooling model for an oceanic lithospheric plate using variable thermal parameters. A constant pressure was applied at the left boundary of the channel to obtain a faster flowing asthenosphere (additional Poiseuille flow). The depth of the LAB is assumed to be mechanically defined and corresponds to the depth at which no additional strain is accumulated on the downstream side, separating the high-viscous non-deforming lithosphere from the low-viscous asthenosphere. Model results show that the lower part of the lithosphere defined in this way is characterized by large inherited strains (f ~ 2). Due to the applied kinematic boundary conditions for a Couette-flow model and the lateral viscosity variations within the channel a minor induced Poiseuille-flow component is obtained within the model. Thus, the stresses vary significantly in comparison to the 1D solution of a Couette-flow. Preliminary results show that deformation along the LAB is strongly governed by the temperature and the plate velocity. The maximum depth of the lithosphere defined in the above way is 120 km, and correlates with the 1230 °C temperature contour line. Moreover, assuming steady state, the finite deformation will always increase with

  12. What can we learn from lithosphere-scale models of passive margins?

    Science.gov (United States)

    Scheck-Wenderoth, Magdalena; Maystrenko, Yuriy; Hirsch, Katja K.

    2010-05-01

    To understand the present day structure and the mechanisms of subsidence at passive margins we assess first-order heterogeneities in the sediments, crust and upper mantle. Thus, we explore how far a good knowledge of the sedimentary and upper crustal configuration can provide constraints for the deeper parts of the system and how far the preserved record of deposits holds the key to unravel margin history. The present-day geometry and distribution of physical properties within the upper and middle crust is integrated into data-based, 3D structural models, which, in turn, provide the base for the analysis of the deep crust and the lithospheric mantle. Different configurations of the deep lithosphere can be tested against two independent observables: gravity and temperature, using isostatic, 3D gravity and 3D thermal modelling. Results from the 55 mio year old Norwegian passive volcanic margin indicate that there, the oceanic lithospheric mantle is less dense than the continental lithospheric mantle (Maystrenko and Scheck-Wenderoth, 2009), that this is mainly due to thermal effects (Scheck-Wenderoth and Maystrenko, 2008) and that the transition between continental and oceanic lithosphere thickness is sharp (Maystrenko and Scheck-Wenderoth, 2009). Furthermore, the thickness of the young oceanic lithosphere in the North Atlantic is smaller than predicted by plate cooling models but consistent with seismologically derived estimates. We also find that the oceanic lithosphere-asthenosphere boundary strongly influences the shallow thermal field of the margin and that surface heat flow increases from the continent to the ocean. In contrast, at the South Atlantic margin offshore South Africa, a thicker and older (~130 mio years) oceanic lithosphere is present. Based on previous studies of the crustal configuration (Hirsch et al., 2009), first lithosphere configurations have been tested. There the transition between continent and ocean appears equilibrated and surface heat

  13. Impact of the rheological layering of the lithosphere on the topography generated by sublithospheric density anomalies: Insights from analog modeling

    Science.gov (United States)

    Sembroni, A.; Globig, J.; Rozel, A.; Faccenna, C.; Funiciello, F.; Fernandez, M.

    2013-12-01

    Density anomalies located beneath the lithosphere are thought to generate dynamic topography at the surface of the Earth. Tomographic models are often used to infer the later variations of the density field in the mantle. Surface topography can then be computed using analytical solutions or numerical simulations of mantle convection. It has been shown that the viscosity profile of the upper mantle has a strong influence on the magnitude and spectral signature of surface topography and uplift rate. Here we present results from analogue modeling of the interaction between a rising ball-shaped density anomaly and the lithosphere in an isoviscous, isothermal Newtonian mantle system. Preliminary data show that surface topography is strongly influenced not only by mantle viscosity but also by density and viscosity profiles of the lithosphere. Our apparatus consists of a plexiglass square box (40x40x50 cm3) filled with glucose syrup. From the bottom a silicon ball was free to rise up until impinging a silicon plate floating on top of the syrup, mimicking the lithosphere. In order to investigate the role of lithospheric thickness and layered continental crust on stress partitioning, maximum dynamic topography, uplift rate and signal wavelength, two different configurations were tested: homogeneous lithosphere and stratified lithosphere including a low-viscosity lower crust. The topographic evolution of the surface was tracked using a laser scanning the top of the apparatus. The rise of the density anomaly was recorded by a side camera. We observe that a thick and then more resistant lithosphere makes up to 2 times lower and laterally wider topographic signatures. Layered lithospheres including a decoupling lower crust decrease the equilibrium topography and its lateral extend by ~30% to 40%. Most importantly, the uplift rate is strongly affected by the choice of lithosphere model. Both lithosphere width and the presence of a decoupling lower crust may modify the uplift

  14. Postcollisional lithospheric evolution of the Southeast Carpathians: Comparison of geodynamical models and observations

    Science.gov (United States)

    Göǧüş, Oǧuz H.; Pysklywec, Russell N.; Faccenna, Claudio

    2016-05-01

    Seismic evidence and thermal and topographic transients have led to the interpretation of lithospheric removal beneath the Southeast Carpathians region. A series of numerical geodynamic experiments in the context of the tectonic evolution of the region are conducted to test the surface-crustal response to lithosphere delamination and slab break-off. The results show that a delamination-type removal ("plate-like" migrating instability) causes a characteristic pattern of surface uplift/subsidence and crustal extension/shortening to occur due to the lithospheric deformation and dynamic/thermal forcing of the sublithospheric mantle. These features migrate with the progressive removal of the underlying lithosphere. Model results for delamination are comparable with observables related to the geodynamic evolution of the Southeast Carpathians since 10 Ma: the mantle structure inferred by seismic tomography, migrating patterns of uplift (>1.5 km) and subsidence (>2 km) in the region, crustal thinning in the Carpathian hinterland and thickening at the Focsani depression, and regional extension in the Carpathian corner (e.g., opening of Brasov basin) correlating with volcanism (e.g., Harghita and Persani volcanics) in the last 3 Myr.

  15. An Equivalent Source Method for Modelling the Lithospheric Magnetic Field Using Satellite and Airborne Magnetic Data

    Science.gov (United States)

    Kother, L. K.; Hammer, M. D.; Finlay, C. C.; Olsen, N.

    2014-12-01

    We present a technique for modelling the lithospheric magnetic field based on estimation of equivalent potential field sources. As a first demonstration we present an application to magnetic field measurements made by the CHAMP satellite during the period 2009-2010. Three component vector field data are utilized at all latitudes. Estimates of core and large-scale magnetospheric sources are removed from the satellite measurements using the CHAOS-4 model. Quiet-time and night-side data selection criteria are also employed to minimize the influence of the ionospheric field. The model for the remaining lithospheric magnetic field consists of magnetic point sources (monopoles) arranged in an icosahedron grid with an increasing grid resolution towards the airborne survey area. The corresponding source values are estimated using an iteratively reweighted least squares algorithm that includes model regularization (either quadratic or maximum entropy) and Huber weighting. Data error covariance matrices are implemented, accounting for the dependence of data error variances on quasi-dipole latitudes. Results show good consistency with the CM5 and MF7 models for spherical harmonic degrees up to n = 95. Advantages of the equivalent source method include its local nature and the ease of transforming to spherical harmonics when needed. The method can also be applied in local, high resolution, investigations of the lithospheric magnetic field, for example where suitable aeromagnetic data is available. To illustrate this possibility, we present preliminary results from a case study combining satellite measurements and local airborne scalar magnetic measurements of the Norwegian coastline.

  16. Inherited structure and coupled crust-mantle lithosphere evolution: Numerical models of Central Australia

    Science.gov (United States)

    Heron, Philip J.; Pysklywec, Russell N.

    2016-05-01

    Continents have a rich tectonic history that have left lasting crustal impressions. In analyzing Central Australian intraplate orogenesis, complex continental features make it difficult to identify the controls of inherited structure. Here the tectonics of two types of inherited structures (e.g., a thermally enhanced or a rheologically strengthened region) are compared in numerical simulations of continental compression with and without "glacial buzzsaw" erosion. We find that although both inherited structures produce deformation in the upper crust that is confined to areas where material contrasts, patterns of deformation in the deep lithosphere differ significantly. Furthermore, our models infer that glacial buzzsaw erosion has little impact at depth. This tectonic isolation of the mantle lithosphere from glacial processes may further assist in the identification of a controlling inherited structure in intraplate orogenesis. Our models are interpreted in the context of Central Australian tectonics (specifically the Petermann and Alice Springs orogenies).

  17. Automatic 1D integrated geophysical modelling of lithospheric discontinuities: a case study from Carpathian-Pannonian Basin region

    Science.gov (United States)

    Grinč, Michal; Zeyen, Hermann; Bielik, Miroslav

    2014-06-01

    Using a very fast 1D method of integrated geophysical modelling, we calculated models of the Moho discontinuity and the lithosphere-asthenosphere boundary in the Carpathian-Pannonian Basin region and its surrounding tectonic units. This method is capable to constrain complicated lithospheric structures by using joint interpretation of different geophysical data sets (geoid and topography) at the same time. The Moho depth map shows significant crustal thickness variations. The thickest crust is found underneath the Carpathian arc and its immediate Foredeep. High values are found in the Eastern Carpathians and Vrancea area (44 km). The thickest crust modelled in the Southern Carpathians is 42 km. The Dinarides crust is characterized by thicknesses more than 40 km. In the East European Platform, crust has a thickness of about 34 km. In the Apuseni Mountains, the depth of the Moho is about 36 km. The Pannonian Basin and the Moesian Platform have thinner crust than the surrounding areas. Here the crustal thicknesses are less than 30 km on average. The thinnest crust can be found in the SE part of the Pannonian Basin near the contact with the Southern Carpathians where it is only 26 km. The thickest lithosphere is placed in the East European Platform, Eastern Carpathians and Southern Carpathians. The East European Platform lithosphere thickness is on average more than 120 km. A strip of thicker lithosphere follows the Eastern Carpathians and its Foredeep, where the values reach in average 160 km. A lithosphere thickness minimum can be observed at the southern border of the Southern Carpathians and in the SE part of the Pannonian Basin. Here, it is only 60 km. The extremely low values of lithospheric thickness in this area were not shown before. The Moesian Platform is characterized by an E-W trend of lithospheric thickness decrease. In the East, the thickness is about 110 km and in the west it is only 80 km. The Pannonian Basin lithospheric thickness ranges from 80 to

  18. Constraints on the lithospheric structure of Venus from mechanical models and tectonic surface features

    Science.gov (United States)

    Zuber, Maria T.

    1987-01-01

    The evidence for the extensional or compressional origins of some prominent Venusian surface features disclosed by radar images is discussed. Using simple models, the hypothesis that the observed length scales (10-20 km and 100-300 km) of deformations are controlled by dominant wavelengths arising from unstable compression or extension of the Venus lithosphere is tested. The results show that the existence of tectonic features that exhibit both length scales can be explained if, at the time of deformation, the lithosphere consisted of a crust that was relatively strong near the surface and weak at its base, and an upper mantle that was stronger than or nearly comparable in strength to the upper crust.

  19. Global Lithospheric Apparent Susceptibility Distribution Converted from Geomagnetic Models by CHAMP and Swarm Satellite Magnetic Measurements

    Science.gov (United States)

    Du, Jinsong; Chen, Chao; Xiong, Xiong; Li, Yongdong; Liang, Qing

    2016-04-01

    Recently, because of continually accumulated magnetic measurements by CHAMP satellite and Swarm constellation of three satellites and well developed methodologies and techniques of data processing and geomagnetic field modeling etc., global lithospheric magnetic anomaly field models become more and more reliable. This makes the quantitative interpretation of lithospheric magnetic anomaly field possible for having an insight into large-scale magnetic structures in the crust and uppermost mantle. Many different approaches have been utilized to understand the magnetized sources, such as forward, inversion, statistics, correlation analysis, Euler deconvolution, signal transformations etc. Among all quantitative interpretation methods, the directly converting a magnetic anomaly map into a magnetic susceptibility anomaly map proposed by Arkani-Hamed & Strangway (1985) is, we think, the most fast quantitative interpretation tool for global studies. We just call this method AS85 hereinafter for short. Although Gubbins et al. (2011) provided a formula to directly calculate the apparent magnetic vector distribution, the AS85 method introduced constraints of magnetized direction and thus corresponding results are expected to be more robust especially in world-wide continents. Therefore, in this study, we first improved the AS85 method further considering non-axial dipolar inducing field using formulae by Nolte & Siebert (1987), initial model or priori information for starting coefficients in the apparent susceptibility conversion, hidden longest-wavelength components of lithospheric magnetic field and field contaminations from global oceanic remanent magnetization. Then, we used the vertically integrated susceptibility model by Hemant & Maus (2005) and vertically integrated remanent magnetization model by Masterton et al. (2013) to test the validity of our improved method. Subsequently, we applied the conversion method to geomagnetic field models by CHAMP and Swarm satellite

  20. Geodynamic evolution of the lithosphere beneath the Eastern Anatolia region: Constraints from geodynamic modeling

    Science.gov (United States)

    Memis, Caner; Hakan Gogus, Oguz; Pysklywec, Russell; Keskin, Mehmet; Celal Sengor, A. M.; Topuz, Gultekin

    2016-04-01

    The east Anatolian orogenic plateau is characterized by an average elevation of 2 km, and is delimited by the Bitlis-Zagros collision zone to the south and the Pontide arc to the north. Stratigraphic evidence suggests that the high plateau attained its current elevation since the Serravallian (about 12 million years ago), but probably did not reach its present height until at least the latest Pliocene. While the crustal shortening following the Arabia-Eurasia collision in the south enabled its relatively rapid rise and regional tectonic evolution, the presumed removal of the downgoing slab beneath east Anatolia has potentially played a significant role in this geodynamic configuration. According to the proposed scenario, the northward subducting slab of Neo-Tethys peels away from the overlying crust similar to the lithospheric delamination model. In this work, we performed a series of lithospheric removal models by varying rheological, physical and mechanical properties by using 2D numerical geodynamic experiments, (e.g. plate convergence rate, crustal thickness, mantle lithosphere yield-stress). Our model results show that the average amount of delamination hinge motion is maximum (18 km/my) when the lower crustal rheology is felsic granulite. The slab break-off only occurs at lower convergence rates (≤ 2 cm/yr), and is imposed on the margin of delaminating mantle lithosphere. The surface uplift takes place above the asthenospheric column (or plateau gap) through isostatic and thermal support of asthenospheric upwelling, and varies dependent on the width of the asthenospheric column. However; with higher plate convergence rates (≥3 cm/yr), the asthenospheric column does not widen enough and the continental collision occurs rather than delamination/peeling away. In this case, the average uplift appears in the central section of the crust, and this exceeds a surface elevation of 3 km. All model results are consistent with the observations from the Eastern

  1. The lithosphere-asthenosphere system beneath Ireland from integrated geophysical-petrological modeling II: 3D thermal and compositional structure

    Science.gov (United States)

    Fullea, J.; Muller, M. R.; Jones, A. G.; Afonso, J. C.

    2014-02-01

    The lithosphere-asthenosphere boundary (LAB) depth represents a fundamental parameter in any quantitative lithospheric model, controlling to a large extent the temperature distribution within the crust and the uppermost mantle. The tectonic history of Ireland includes early Paleozoic closure of the Iapetus Ocean across the Iapetus Suture Zone (ISZ), and in northeastern Ireland late Paleozoic to early Mesozoic crustal extension, during which thick Permo-Triassic sedimentary successions were deposited, followed by early Cenozoic extrusion of large scale flood basalts. Although the crustal structure in Ireland and neighboring offshore areas is fairly well constrained, with the notable exception of the crust beneath Northern Ireland, the Irish uppermost mantle remains to date relatively unknown. In particular, the nature and extent of a hypothetical interaction between a putative proto Icelandic mantle plume and the Irish and Scottish lithosphere during the Tertiary opening of the North Atlantic has long been discussed in the literature with diverging conclusions. In this work, the present-day thermal and compositional structure of the lithosphere in Ireland is modeled based on a geophysical-petrological approach (LitMod3D) that combines comprehensively a large variety of data (namely elevation, surface heat flow, potential fields, xenoliths and seismic tomography models), reducing the inherent uncertainties and trade-offs associated with classical modeling of those individual data sets. The preferred 3D lithospheric models show moderate lateral density variations in Ireland characterized by a slightly thickened lithosphere along the SW-NE trending ISZ, and a progressive lithospheric thinning from southern Ireland towards the north. The mantle composition in the southern half of Ireland (East Avalonia) is relatively and uniformly fertile (i.e., typical Phanerozoic mantle), whereas the lithospheric composition in the northern half of Ireland (Laurentia) seems to vary

  2. Investigating Lithosphere Strength With Thin-Shell Tectonic Modeling

    Science.gov (United States)

    Moder, C.; Carena, S.

    2007-12-01

    The behavior of many major faults on Earth can only be explained if they are assumed to be much weaker than expected from Byerlee's Law alone. However, there is no agreement over what is a realistic range of friction parameters for faults, or its possible dependency on fault network geometry. Both can be studied with numerical forward modeling, but this requires knowledge of the detailed 3-D geometry of the faults. The latter is now available for most of California, thanks to the SCEC Community Fault Model (southern California) and to the USGS program "3-D Geologic Maps and Visualization" (San Francisco Bay and surrounding region). We model the behavior of the California fault network with the finite-element code SHELLS. We use as input a coarse global grid, with local high-resolution representation of actual faults based on the existing 3-D fault maps. By comparing the simulation results with data on fault-slip rates, we can determine how the faults in this network interact, the role of small faults, and we can quantify the typical fault strength in a continental transform plate boundary setting.

  3. An equivalent source method for modelling the global lithospheric magnetic field

    Science.gov (United States)

    Kother, Livia; Hammer, Magnus D.; Finlay, Christopher C.; Olsen, Nils

    2015-10-01

    We present a new technique for modelling the global lithospheric magnetic field at Earth's surface based on the estimation of equivalent potential field sources. As a demonstration we show an application to magnetic field measurements made by the CHAMP satellite during the period 2009-2010 when it was at its lowest altitude and solar activity was quiet. All three components of the vector field data are utilized at all available latitudes. Estimates of core and large-scale magnetospheric sources are removed from the measurements using the CHAOS-4 model. Quiet-time and night-side data selection criteria are also employed to minimize the influence of the ionospheric field. The model for the remaining lithospheric magnetic field consists of magnetic equivalent potential field sources (monopoles) arranged in an icosahedron grid at a depth of 100 km below the surface. The corresponding model parameters are estimated using an iteratively reweighted least-squares algorithm that includes model regularization (either quadratic or maximum entropy) and Huber weighting. Data error covariance matrices are implemented, accounting for the dependence of data variances on quasi-dipole latitude. The resulting equivalent source lithospheric field models show a degree correlation to MF7 greater than 0.7 out to spherical harmonic degree 100. Compared to the quadratic regularization approach, the entropy regularized model possesses notably lower power above degree 70 and a lower number of degrees of freedom despite fitting the observations to a very similar level. Advantages of our equivalent source method include its local nature, the possibility for regional grid refinement and the production of local power spectra, the ability to implement constraints and regularization depending on geographical position, and the ease of transforming the equivalent source values into spherical harmonics.

  4. Lithosphere temperature model and resource assessment for deep geothermal exploration in Hungary

    Science.gov (United States)

    Bekesi, Eszter; van Wees, Jan-Diederik; Vrijlandt, Mark; Lenkey, Laszlo; Horvath, Ferenc

    2017-04-01

    The demand for deep geothermal energy has increased considerably over the past years. To reveal potential areas for geothermal exploration, it is crucial to have an insight into the subsurface temperature distribution. Hungary is one of the most suitable countries in Europe for geothermal development, as a result of Early and Middle Miocene extension and subsequent thinning of the lithosphere. Hereby we present the results of a new thermal model of Hungary extending from the surface down to the lithosphere-astenosphere boundary (LAB). Subsurface temperatures were calculated through a regular 3D grid with a horizontal resolution of 2.5 km, a vertical resolution of 200 m for the uppermost 7 km, and 3 km down to the depth of the LAB The model solves the heat equation in steady-state, assuming conduction as the main heat transfer mechanism. At the base, it adopts a constant basal temperature or heat flow condition. For the calibration of the model, more than 5000 temperature measurements were collected from the Geothermal Database of Hungary. The model is built up by five sedimentary layers, upper crust, lower crust, and lithospheric mantle, where each layer has its own thermal properties. The prior thermal properties and basal condition of the model is updated through the ensemble smoother with multiple data assimilation technique. The conductive model shows misfits with the observed temperatures, which cannot be explained by neglected transient effects related to lithosphere extension. These anomalies are explained mostly by groundwater flow in Mesozoic carbonates and other porous sedimentary rocks. To account for the effect of heat convection, we use a pseudo-conductive approach by adjusting the thermal conductivity of the layers where fluid flow may occur. After constructing the subsurface temperature model of Hungary, the resource base for EGS (Enhanced Geothermal Systems) is quantified. To this end, we applied a cash-flow model to translate the geological

  5. Mathematical modeling suggests that periodontitis behaves as a non-linear chaotic dynamical process

    NARCIS (Netherlands)

    Papantonopoulos, G.H.; Takahashi, K.; Bountis, T.; Loos, B.G.

    2013-01-01

    Background: This study aims to expand on a previously presented cellular automata model and further explore the non-linear dynamics of periodontitis. Additionally the authors investigated whether their mathematical model could predict the two known types of periodontitis, aggressive (AgP) and

  6. Mathematical modeling suggests that periodontitis behaves as a non-linear chaotic dynamical process

    NARCIS (Netherlands)

    Papantonopoulos, G.H.; Takahashi, K.; Bountis, T.; Loos, B.G.

    2013-01-01

    Background: This study aims to expand on a previously presented cellular automata model and further explore the non-linear dynamics of periodontitis. Additionally the authors investigated whether their mathematical model could predict the two known types of periodontitis, aggressive (AgP) and chroni

  7. Lithosphere tectonics and thermo-mechanical properties: An integrated modelling approach for Enhanced Geothermal Systems exploration in Europe

    Science.gov (United States)

    Cloetingh, S.; van Wees, J. D.; Ziegler, P. A.; Lenkey, L.; Beekman, F.; Tesauro, M.; Förster, A.; Norden, B.; Kaban, M.; Hardebol, N.; Bonté, D.; Genter, A.; Guillou-Frottier, L.; Ter Voorde, M.; Sokoutis, D.; Willingshofer, E.; Cornu, T.; Worum, G.

    2010-10-01

    Knowledge of temperature at drillable depth is a prerequisite in site selection for geothermal exploration and development of enhanced geothermal systems (EGS). Equally important, the thermo-mechanical signature of the lithosphere and crust provides critical constraints for the crustal stress field and basement temperatures where borehole observations are rare. The stress and temperature field in Europe is subject to strong spatial variations often linked to polyphase extensional and compressional reactivation of the lithosphere, in different modes of deformation. The development of innovative combinations of numerical and analogue modelling techniques is key to thoroughly understand the spatial and temporal variations in crustal stress and temperature. In this paper we present an overview of advances in developing and applying analogue and numerical thermo-mechanical models to quantitatively assess the interplay of lithosphere dynamics and basin (de)formation. Field studies of kinematic indicators and numerical modelling of present-day and paleo-stress fields in selected areas yield new constraints on the causes and the expression of intraplate stress fields in the lithosphere, driving basin (de)formation. The actual basin response to intraplate stress is strongly affected by the rheological structure of the underlying lithosphere, the basin geometry, fault dynamics and interplay with surface processes. Integrated basin studies show that the rheological structure of the lithosphere plays an important role in the spatial and temporal distribution of stress-induced vertical motions, varying from subtle faulting to basin reactivation and large wavelength patterns of lithospheric folding. These findings demonstrate that sedimentary basins are sensitive recorders of the intraplate stress field. The long lasting memory of the lithosphere, in terms of lithospheric scale weak zones, plays a far more important role in basin formation and reactivation than hitherto assumed

  8. Lithospheric flexure and sedimentary basin evolution: depositional cycles in the steer's head model

    Science.gov (United States)

    Moore, James; Watts, Tony

    2016-04-01

    Backstripping studies of biostratigraphic data from deep wells show that sediment loading is one of the main factors controlling the subsidence and uplift history of sedimentary basins. Previous studies based on single layer models of elastic and viscoelastic plates overlying an inviscid fluid have shown that sediment loading, together with a tectonic subsidence that decreases exponentially with time, can explain the large-scale 'architecture' of rift-type basins and, in some cases, details of their internal stratigraphy such as onlap and offlap patterns. One problem with these so-called 'steer's head' models is that they were based on a simple rheological model in which the long-term strength of the lithosphere increased with thermal age. Recent oceanic flexure studies, however, reveal that the long-term strength of the lithosphere depends not only on thermal age, but also load age. We have used the thermal structure based on plate cooling models, together with recent experimentally-derived flow laws, to compute the viscosity structure of the lithosphere and a new analytical model to compute the flexure of a multilayer viscoelastic plate by a trapezoid-shaped sediment load at different times since basin initiation. The combination of basin subsidence and viscoelastic flexural response results in the fluctuation of the depositional surface with time. If we define the nondimensional number Dw= τm/τt, where τm is the Maxwell time constant and τt is the thermal time constant, we find that for Dw>1 the flexure approximates that of a viscoelastic plate and is dominated by "offlapping" stratigraphy, with the basin edges evolving through shallow marine facies; though erosion late in the basin formation prevents much of this from being recorded in the stratigraphy. Interestingly Dw~1 produces a basin in which onlap dominates its early evolution while offlap dominates its later evolution with an unconformity separating the two different stratal patterns. This case lends

  9. Global Models of Ridge-Push Force, Geoid, and Lithospheric Strength of Oceanic plates

    Science.gov (United States)

    Mahatsente, Rezene

    2017-08-01

    An understanding of the transmission of ridge-push related stresses in the interior of oceanic plates is important because ridge-push force is one of the principal forces driving plate motion. Here, I assess the transmission of ridge-push related stresses in oceanic plates by comparing the magnitude of the ridge-push force to the integrated strength of oceanic plates. The strength is determined based on plate cooling and rheological models. The strength analysis includes low-temperature plasticity (LTP) in the upper mantle and assumes a range of possible tectonic conditions and rheology in the plates. The ridge-push force has been derived from the thermal state of oceanic lithosphere, seafloor depth and crustal age data. The results of modeling show that the transmission of ridge-push related stresses in oceanic plates mainly depends on rheology and predominant tectonic conditions. If a lithosphere has dry rheology, the estimated strength is higher than the ridge-push force at all ages for compressional tectonics and at old ages (>75 Ma) for extension. Therefore, under such conditions, oceanic plates may not respond to ridge-push force by intraplate deformation. Instead, the plates may transmit the ridge-push related stress in their interior. For a wet rheology, however, the strength of young lithosphere (tectonics. In this case, the ridge-push related stress may dissipate in the interior of oceanic plates and diffuses by intraplate deformation. The state of stress within a plate depends on the balance of far-field and intraplate forces.

  10. Topography caused by mantle density variations: observation-based estimates and models derived from tomography and lithosphere thickness

    Science.gov (United States)

    Steinberger, Bernhard

    2016-04-01

    Large-scale topography may be due to several causes, including (1) variations in crustal thickness and density structure, (2) oceanic lithosphere age differences, (3) subcrustal density variations in the continental lithosphere and (4) convective flow in the mantle beneath the lithosphere. The last contribution in particular may change with time and be responsible for continental inundations; distinguishing between these contributions is therefore important for linking Earth's history to its observed geological record. As a step towards this goal, this paper aims at such distinction for the present-day topography: the approach taken is deriving a `model' topography due to contributions (3) and (4), along with a model geoid, using a geodynamic mantle flow model. Both lithosphere thickness and density anomalies beneath the lithosphere are inferred from seismic tomography. Density anomalies within the continental lithosphere are uncertain, because they are probably due to variations in composition and temperature, making a simple scaling from seismic to density anomalies inappropriate. Therefore, we test a number of different assumptions regarding these. As a reality check, model topography is compared, in terms of both correlation and amplitude ratio, to `residual' topography, which follows from observed topography after subtracting contributions (1) and (2). The model geoid is compared to observations as well. Comparatively good agreement is found if there is either an excess density of ≈0.2 per cent in the lithosphere above ≈150 km depth, with anomalies below as inferred from tomography, or if the excess density is ≈0.4 per cent in the entire lithosphere. Further, a good fit is found for viscosity ≈1020 Pa s in the asthenosphere, increasing to ≈1023 Pa s in the lower mantle above D'. Results are quite dependent on which tomography models they are based on; for some recent ones, topography correlation is ≈0.6, many smaller scale features are matched

  11. Prosthetic Avian Vocal Organ Controlled by a Freely Behaving Bird Based on a Low Dimensional Model of the Biomechanical Periphery

    Science.gov (United States)

    Arneodo, Ezequiel M.; Perl, Yonatan Sanz; Goller, Franz; Mindlin, Gabriel B.

    2012-01-01

    Because of the parallels found with human language production and acquisition, birdsong is an ideal animal model to study general mechanisms underlying complex, learned motor behavior. The rich and diverse vocalizations of songbirds emerge as a result of the interaction between a pattern generator in the brain and a highly nontrivial nonlinear periphery. Much of the complexity of this vocal behavior has been understood by studying the physics of the avian vocal organ, particularly the syrinx. A mathematical model describing the complex periphery as a nonlinear dynamical system leads to the conclusion that nontrivial behavior emerges even when the organ is commanded by simple motor instructions: smooth paths in a low dimensional parameter space. An analysis of the model provides insight into which parameters are responsible for generating a rich variety of diverse vocalizations, and what the physiological meaning of these parameters is. By recording the physiological motor instructions elicited by a spontaneously singing muted bird and computing the model on a Digital Signal Processor in real-time, we produce realistic synthetic vocalizations that replace the bird's own auditory feedback. In this way, we build a bio-prosthetic avian vocal organ driven by a freely behaving bird via its physiologically coded motor commands. Since it is based on a low-dimensional nonlinear mathematical model of the peripheral effector, the emulation of the motor behavior requires light computation, in such a way that our bio-prosthetic device can be implemented on a portable platform. PMID:22761555

  12. Prosthetic avian vocal organ controlled by a freely behaving bird based on a low dimensional model of the biomechanical periphery.

    Directory of Open Access Journals (Sweden)

    Ezequiel M Arneodo

    Full Text Available Because of the parallels found with human language production and acquisition, birdsong is an ideal animal model to study general mechanisms underlying complex, learned motor behavior. The rich and diverse vocalizations of songbirds emerge as a result of the interaction between a pattern generator in the brain and a highly nontrivial nonlinear periphery. Much of the complexity of this vocal behavior has been understood by studying the physics of the avian vocal organ, particularly the syrinx. A mathematical model describing the complex periphery as a nonlinear dynamical system leads to the conclusion that nontrivial behavior emerges even when the organ is commanded by simple motor instructions: smooth paths in a low dimensional parameter space. An analysis of the model provides insight into which parameters are responsible for generating a rich variety of diverse vocalizations, and what the physiological meaning of these parameters is. By recording the physiological motor instructions elicited by a spontaneously singing muted bird and computing the model on a Digital Signal Processor in real-time, we produce realistic synthetic vocalizations that replace the bird's own auditory feedback. In this way, we build a bio-prosthetic avian vocal organ driven by a freely behaving bird via its physiologically coded motor commands. Since it is based on a low-dimensional nonlinear mathematical model of the peripheral effector, the emulation of the motor behavior requires light computation, in such a way that our bio-prosthetic device can be implemented on a portable platform.

  13. Geodynamical evolution of the Southern Carpathians: inferences from computational models of lithospheric gravitational instability

    Science.gov (United States)

    Lorinczi, Piroska; Houseman, Gregory

    2010-05-01

    The Carpathians are a geologically young mountain chain which, together with the Alps and the Dinarides, surround the extensional Pannonian and Transylvanian basins of Central Europe. The tectonic evolution of the Alpine-Carpathian-Pannonian system was controlled by convergence between the Adriatic and European plates, by the extensional collapse of thickened Alpine crust and by the retreat of the Eastern Carpathians driven by either a brief episode of subduction or by gravitational instability of the continental lithospheric mantle. The Southeast corner of the Carpathians has been widely studied due to its strong seismic activity. The distribution and rate of moment release of this seismic activity provides convincing evidence of a mantle drip produced by gravitational instability of the lithospheric mantle developing beneath the Vrancea region now. The question of why gravitational instability is strongly evident beneath Vrancea and not elsewhere beneath the Southern Carpathians is unresolved. Geological and geophysical interpretations of the Southern Carpathians emphasise the transcurrent deformation that has dominated recent tectonic evolution of this mountain belt. We use computational models of gravitational instability in order to address the question of why the instability appears to have developed strongly only at the eastern end of this mountain chain. We use a parallelised 3D Lagrangean-frame finite deformation algorithm, which solves the equations of momentum and mass conservation in an incompressible viscous fluid, assuming a non-linear power-law that relates deviatoric stress and strain-rate. We consider a gravitationally unstable system, with a dense mantle lithosphere overlying a less dense asthenosphere, subject to boundary conditions which simulate the combination of shear and convergence that are thought to have governed the evolution of the South Carpathians. This program (OREGANO) allows 3D viscous flow fields to be computed for spatially

  14. Samovar: a thermomechanical code for modeling of geodynamic processes in the lithosphere-application to basin evolution

    DEFF Research Database (Denmark)

    Elesin, Y; Gerya, T; Artemieva, Irina

    2010-01-01

    . The results are directly applicable to the Basin and Range province, western USA, and demonstrate the roles of crust–mantle coupling, preexisting weakness zones, and erosion rate on the evolutionary trends of extending continental regions. Modeling of basin evolution indicates a critical role of syn......We present a new 2D finite difference code, Samovar, for high-resolution numerical modeling of complex geodynamic processes. Examples are collision of lithospheric plates (including mountain building and subduction) and lithosphere extension (including formation of sedimentary basins, regions...... of extended crust, and rift zones). The code models deformation of the lithosphere with viscoelastoplastic rheology, including erosion/sedimentation processes and formation of shear zones in areas of high stresses. It also models steady-state and transient conductive and advective thermal processes including...

  15. Thermal models, lithosphere thickness and heat flow in South Portugal. Some comments about the subject

    Science.gov (United States)

    Rosa Duque, Maria

    2016-04-01

    Reinterpretation of old heat flow data or use of new data and new techniques of detection of the temperature under the surface have conducted to new heat flow density values in some regions of the globe. The problem of ice melting in Greenland and Antarctica caught the public's attention to the importance of knowledge on heat flow values and thermal structure of the globe. In the last years, several models were presented trying to obtain lithosphere and Moho thickness of the Iberia Peninsula. The work we intend to present is related with the SW part of the Iberia Peninsula ( south of the Ossa Morena zone, South Portuguese Zone and Algarve). The results obtained show a decrease in the thickness of the crust and the lithosphere in this region. Density anomalies in the crust are also referred. I intend to make the connection between the results of these models and the heat flow thermal conductivity, heat production and geological data available for the region, trying to explain the results of heat flow density data obtained.

  16. Understanding plate-motion changes over the past 100 Myr with quantitative models of the coupled lithosphere/mantle system

    Science.gov (United States)

    Stotz, Ingo; Iaffaldano, Giampiero; Rhodri Davies, D.

    2015-04-01

    The volume of geophysical datasets has grown substantially over recent decades. Our knowledge of continental evolution has increased due to advances in interpreting the records of orogeny and sedimentation. Ocean-floor observations now allow one to resolve past plate motions (e.g. in the North Atlantic and Indian Ocean over the past 20 Myr) at temporal resolutions of about 1 Myr. Altogether, these ever-growing datasets allow us to reconstruct the past evolution of Earth's lithospheric plates in greater detail. This is key to unravelling the dynamics of geological processes, because plate motions and their temporal changes are powerful probe into the evolving force balance between shallow- and deep-rooted processes. However, such progress is not yet matched by the ability to quantitatively model past plate-motion changes and, therefore, to test hypotheses on the dominant controls. The main technical challenge is simulating the rheological behaviour of the lithosphere/mantle system, which varies significantly from viscous to brittle. Traditionally computer models for viscous mantle flow on the one hand, and for the motions of the brittle lithosphere on the other hand, have been developed separately. Coupling of these two independent classes of models has been accomplished only for neo-tectonic scenarios, without accounting for the impact of time-evolving mantle-flow (e.g. Iaffaldano and Bunge 2009). However, we have built a coupled model to simulate the lithosphere/mantle system (using SHELLS and TERRA, respectively) through geological time, and to exploit the growing body of geophysical data as a primary constraint on these quantitative models. TERRA is a global spherical finite-element code for mantle convection (e.g. Baumgardner 1985, Bunge et al. 1996, Davies et al. 2013), whilst SHELLS is a thin-sheet finite-element code for lithosphere dynamics (e.g. Bird 1998). Our efforts are focused, in particular, on achieving the technical ability to: (i) simulate the

  17. Links between long-term and short-term rheology of the lithosphere: insights from strike-slip fault modelling

    Science.gov (United States)

    Le Pourhiet, Laetitia

    2014-05-01

    The study of geodetic data across strike-slip fault zones is believed to play a key role in our understanding of the lithosphere mechanical behaviour. InSAR and GPS measurements permits to determine more and more accurately both large and rapid co-seismic displacements and the slower deformation associated with the inter-seismic and post-seismic phases of the earthquake cycle on continents. However, no modern geodetic observation spans a complete earthquake cycle for any single fault in the world. Understanding this time variability through modelling is therefore crucial to reconstruct a global pattern. It is non trivial to compare the effective parameters retrieved from the different simple models are used to extract effective parameters from the geodetic data. Using the popular visco-elastic relaxation model reaches two paradoxes: - the lower crust must be very strong in order to fit the data long after the earthquake and very weak to fit the data during the early post-seismic period. - the retrieved a mantle lithosphere viscosity is as weak as 10^17 - 10^20 Pa.s and differ significantly from those deduced from post glacial rebound models and long term geodynamic models requirements in order to generate self consistent plate tectonics. Rather than assuming that the rheology of the lithosphere changes with time scale, it would be preferable to go on quest for an Earth's lithosphere rheological model based on some simple physics, which would be equally valid at all time scale from inter-seismic to orogeny. 3D models of long term strain localisation in wrenching context show that localisation of strain across strike slip faults modifies locally the rheological architecture of the lithosphere and lead to some sort of structural weakening. That weakening occurs because as strain localises the "jelly sandwich" type lithosphere evolves self-consistently into a "banana split" type rheological structure. This strain localisation process is very efficient when the lower

  18. Sixth generation lithospheric magnetic field model, MF6, from CHAMP satellite magnetic measurements

    Science.gov (United States)

    Maus, S.; Fan, Y.; Manoj, C.; Rother, M.; Rauberg, J.; Stolle, C.; Luhr, H.

    2007-12-01

    The CHAMP satellite continues to provide highly accurate magnetic field measurements with decreasing orbital altitudes (<350km) at solar minimum conditions. A promising new CHAMP data product has become available, which provides the total field with one order of magnitude smaller noise amplitudes. The product is inferred from suitably merged Fluxgate and Overhauser magnetometer data. While the low-noise Fluxgate measurements are used in the short-period range (<900sec, or <6000km wavelength), we take advantage of the high stability provided by the Overhauser for the longer periods. The new data set is used for generating an improved lithospheric magnetic field model (MF6). Although MF6 is still in production at the time of writing this abstract, we anticipate significant benefits in terms of resolving small- scale low-amplitude crustal features from the new data. Further improvements include a new correction for steady ocean circulation and an expansion to higher spherical harmonic degrees of the model.

  19. An improved coupling model for the lithosphere-atmosphere-ionosphere system (Invited)

    Science.gov (United States)

    Lee, L.; Kuo, C.; Huba, J. D.

    2013-12-01

    In order to explain the observed ionospheric TEC variations before strong earthquakes, we have developed a comprehensive model for the lithosphere-atmosphere-ionosphere (LAI) coupling [Kuo et al., 2011]. In our previous model, the dynamo current flows from the lithosphere, through the atmosphere, and into the ionosphere. The TEC variations in the ionosphere are numerically calculated based on NRL SAMI3 code. Nighttime plasma bubbles are generated for large earthquakes. However, the current in the atmosphere is obtained by first solving the electric field Ε from ▽(σΕ), where the conductivity tensor σ consists of Pedersen and Hall conductivity. The background magnetic field is assumed to be perpendicular to the horizontal plane. In the present paper, we improve the calculation of currents in the atmosphere by solving the current density J directly from the current continuity equation ▽J = 0. The currents in the atmosphere can be solved for any arbitrary angle of magnetic field, i.e., any magnetic latitude. The effects of atmospheric currents and electric fields on the ionosphere with lithosphere current source located at low magnetic altitude 15° and middle magnetic altitude 30° are obtained. For upward (downward) atmospheric currents flowing into the ionosphere, the simulation results show that the westward (eastward) electric fields dominate. At magnetic latitude 15°, the upward (downward) current causes the increase (decrease) of TEC, while the upward (downward) current causes the decrease (increase) of TEC at higher magnetic latitude 30°. The dynamo current density required to generate the same amount of TEC variation in the improved model is found to be smaller by a factor of 30 as compared to that obtained in our earlier paper. We also calculate the ionosphere dynamics with imposed zonal westward and eastward electric field based on SAMI3 code. In the nighttime ionosphere, it is found that the westward electric field may trigger two plasma bubbles

  20. A New Model of Lithosphere Deformation Beneath the Okinawa Trough Based on Gravity Data

    Institute of Scientific and Technical Information of China (English)

    ZHAO Lihong; JIANG Xiaodian; ZHANG Weigang

    2002-01-01

    The Ryukyu trench-arc system can be divided into two types according to its subduction model. The normal sub-duction in the northern part of the Philippine Sea plate creates a hinge sedimentary wedge with large deformation at the col-lision front, while the oblique subduction in the southern part gives rise to a smaller accretion with small deformation thanthat in the northern part. The mechanisms that cause the distinction between these two types have been analysed and calcu-lated by using gravity data based on the lithosphere rheology and the stress state of the lithosphere in the subduction bound-ary. The two types of subduction model are associated with the internal extension in the southern Okinawa Trough and thesmall extension in the northern part. The difference of the stress state between the two types of subduction model is alsomanifested in other tectonic features, such as topography, volcanic activity and crust movement. Modeling bathymetric andgravity data from this area suggests that the oblique subduction of low angle, together with smooth geometry of the overlyingplate crust, results in small stress released on the south of the trench by the subduction plate. The intraplate faults in thesouthern Okinawa Trough behind the trench stand in surplus intensive stress. On the other hand, the normal subduction ofhigh angle, together with strong undulation geometry of the overlying crust, results in more intensive stress released in thenorthern Ryukyu Trench than that in the south. The intraplate faults in the northern Okinawa Trough behind the northernRyukyu Trench stand in small stress.

  1. Inverse modeling of Central American lavas: old lithospheric and young asthenospheric heterogeneities

    Science.gov (United States)

    Feigenson, M.; Gazel, E.; Carr, M. J.

    2009-12-01

    In recent years, there have been a number of models proposed to account for the OIB-like geochemical characteristics of lavas from central Costa Rica. The source for most basalts of the Central American volcanic front (ranging from Guatemala to northern Costa Rica) is dominantly DM (depleted MORB-source mantle) fluxed by subduction-derived fluids. In contrast, central Costa Rican basalts display striking isotopic similarities to the Galapagos hotspot. How the Galapagos signature is introduced into the Central American source is at the heart of the conflicting theories. Several models incorporate asthenospheric flow of this enriched mantle, either around the Central American arc via South America, or through a slab window, which may have opened about 5 my ago beneath central Costa Rica. Alternatively, passage of the Caribbean plate over the Galapagos hotspot may have left veins of unerupted melt within the sub-Caribbean lithosphere. These veins may be preferentially tapped during later superimposed arc volcanism. Although these models yield identical isotopic systematics, it may be possible to distinguish between them by a geochemical technique that can indicate the presence of garnet in the source region. This method, developed by Hofmann and coworkers in the 1980s, is termed inverse modeling, and uses the variation of REEs in lavas to assess the relative importance of garnet vs. clinopyroxene during partial melting. We have applied this method to new REE data from back arc lavas throughout Central America, and preliminary results indicate that garnet is not present in their sources. In contrast, direct slab melts (adakites) from Central America, as well as volcanic front lavas and alkaline basalt (with minimal slab signature) from central Costa Rica and Panama, require a source with garnet. Therefore, enriched mantle in the back arc is likely stored in the shallow lithosphere rather than introduced through asthenospheric flow. Enriched material in the volcanic

  2. Experimental and modeling constraints on the seismic structure of oceanic lithosphere

    Science.gov (United States)

    Faul, Ulrich; Jackson, Ian; Hall, Paul

    2014-05-01

    Seismological techniques provide different views of the structure of the oceanic upper mantle. Surface waves can not resolve sharp changes in velocities with depth, but provide absolute velocities. Receiver functions are sensitive to sharp changes, but these steps in velocities have to be reconciled with absolute velocities. Experimental measurements of seismic properties can be used to translate velocities into a physical state and to explore possible mechanisms for sharp changes. Current experiments at elevated pressures and temperatures are designed to resolve the onset of the deviation from elastic behavior at temperatures above 600ºC. Initial experiments with copper jackets, which avoid the interference from phase transitions in mild steel, confirm the existence of a plateau in dissipation in olivine that is due to the grain-scale process of elastically accommodated grain boundary sliding. As this mechanism is solely due to temperature it occurs everywhere in the thermal boundary layer, although the sharpness will depend on the temperature gradient. Forward modeling of seismic velocities with the experimentally determined properties predict velocity gradients in the thermal boundary layer that are not sharp enough to generate receiver functions. However, particularly for younger oceanic lithosphere these gradients only need to be enhanced by a relatively small amount by other factors. Possible mechanisms include the presence of melt and/or volatiles. For older oceanic lithosphere small scale convection may steepen the temperature gradient beneath the lid. We are currently conducting numerical models with experimentally derived rheological parameters with the aim to determine the thermal structure and calculate seismic velocities from it. If operative, small scale convection may also lead to cooling of the whole upper mantle as a function of age. In the upper part of the lithosphere seismologic observations imply a constant, high velocity lid. This contrasts

  3. An improved coupling model for the lithosphere-atmosphere-ionosphere system

    Science.gov (United States)

    Kuo, C. L.; Lee, L. C.; Huba, J. D.

    2014-04-01

    In our previous model for the lithosphere-atmosphere-ionosphere coupling, the background magnetic field was assumed to be perpendicular to the horizontal plane. In the present paper, we improve the calculation of currents in the atmosphere by solving the current density J directly from the current continuity equation ∇ • J = 0. The currents in the atmosphere can be solved for any arbitrary angle of magnetic field, i.e., any magnetic latitude. In addition, a large ratio (~10) of Hall to Pedersen conductivities is used to generate a large Hall electric field. The effects of atmospheric currents and electric fields on the ionosphere with lithosphere current source located at magnetic latitudes of 7.5°, 15°, 22.5°, and 30° are obtained. For upward (downward) atmospheric currents flowing into the ionosphere, the simulation results show that the westward (eastward) electric fields dominate. At magnetic latitude of 7.5° or 15°, the upward (downward) current causes the increase (decrease) of total electron content (TEC) near the source region, while the upward (downward) current causes the decrease (increase) of TEC at magnetic latitude of 22.5°or 30°. The dynamo current density required to generate the same amount of TEC variation in the improved model is found to be smaller by a factor of 30 as compared to that obtained in our earlier paper. We also calculate the ionosphere dynamics with imposed zonal westward and eastward electric field based on SAMI3 code. It is found that the eastward (westward) electric field may trigger one (two) plasma bubble(s) in the nighttime ionosphere.

  4. Head and cervical spine posture in behaving rats: implications for modeling human conditions involving the head and cervical spine.

    Science.gov (United States)

    Griffin, C; Choong, W Y; Teh, W; Buxton, A J; Bolton, P S

    2015-02-01

    The aim of this study was to define the temporal and spatial (postural) characteristics of the head and cervical vertebral column (spine) of behaving rats in order to better understand their suitability as a model to study human conditions involving the head and neck. Time spent in each of four behavioral postures was determined from video tape recordings of rats (n = 10) in the absence and presence of an intruder rat. Plain film radiographic examination of a subset of these rats (n = 5) in each of these postures allowed measurement of head and cervical vertebral column positions adopted by the rats. When single they were quadruped or crouched most (∼80%) of the time and bipedal either supported or free standing for only ∼10% of the time. The introduction of an intruder significantly (P cervical spine was orientated (median, 25-75 percentile) near vertical (18.8°, 4.2°-30.9°) when quadruped, crouched (15.4°, 7.6°-69.3°) and bipedal supported (10.5°, 4.8°-22.6°) but tended to be less vertical oriented when bipedal free standing (25.9°, 7.7°-39.3°). The range of head positions relative to the cervical spine was largest when crouched (73.4°) and smallest when erect free standing (17.7°). This study indicates that, like humans, rats have near vertical orientated cervical vertebral columns but, in contrast to humans, they displace their head in space by movements at both the cervico-thoracic junction and the cranio-cervical regions. © 2014 Wiley Periodicals, Inc.

  5. Formation and stability of ridge-ridge-ridge triple junctions in rheologically realistic lithosphere model

    Science.gov (United States)

    Gerya, Taras; Burov, Evgueni

    2015-04-01

    -branch junction formation and evolution by using high-resolution 3D numerical mechanical experiments that take into account realistic thermo-rheological structure and rheology of the lithosphere. We find that two major types of quadruple and triple junctions are formed under bi-directional or multidirectional far-field stress field: (i) plate rifting junctions are formed by the initial plate fragmentation and can be subsequently re-arranged into (ii) oceanic spreading junctions controlled by the new oceanic crust accretion. In particular, we document initial formation and destabilization of quadruple R-R-R-R junctions as initial plate rifting structures under bi-directional extension. In most cases, quadruple plate rifting junctions rapidly (typically within 1-2 Myr) evolve towards formation of two diverging triple oceanic spreading junctions connected by a linear spreading center lengthening with time. This configuration remains stable over long time scales. However, under certain conditions, quadruple junctions may also remain relatively stable. Asymmetric stretching results in various configurations, for example formation of "T-junctions" with trans-extensional components and combination of fast and slow spreading ridges. Combined with plume impingement, this scenario evolves in realistic patterns closely resembling observed plate dynamics. In particular, opening of the Red Sea and of the Afar rift system find a logical explanation within a single model. Numerical experiments also suggest that several existing oceanic spreading junctions form as the result of plate motions rearrangements after which only one of two plates spreading along the ridge become subjected to bi-directional spreading.

  6. Intra-cratonic melting as a result of delamination of mantle lithosphere - insight from numerical modelling

    Science.gov (United States)

    Gorczyk, W.; Vogt, K.; Gerya, T.; Hobbs, B. E.

    2012-12-01

    It is becoming increasingly apparent that intense deformation, metamorphism and metasomatism occur within continental cratonic blocks far removed form subducting margins Such changes may occur intra-cratonically arising from lithospheric thickening and the development of gravitational instabilities, but mostly occur at the boundary of cratonic blocks. The contact of two cratons is characterized by rheological lateral variations within mantle-lithosphere and overlying crust. Tectonic stresses acting on craton/craton boundaries may lead to thinning or thickening due to delamination of the mantle lithosphere. This is reflected in tectonic deformation, topography evolution, melting and crustal metamorphism. To understand the controls on these processes a number of 2D, coupled petrological thermo-mechanical numerical experiments has been performed to test the response of a laterally weakened zone to a compressional regime. The results indicate that the presence of water-bearing minerals in the lithosphere and lower crust is essential to initiate melting, which in the later stages may expand to dry melting of crust and mantle. In the case of anhydrous crust and lithosphere, no melting occurs. Thus a variety of instabilities, melting behaviour and topographic responses occurs at the base of the lithosphere as well as intensive faulting and buckling in the crust dependent on the strength and "water" content of the lithosphere.

  7. Lithospheric-scale effects of a subduction-driven Alboran plate: improved neotectonic modeling

    Science.gov (United States)

    Neres, Marta; Carafa, Michele; Terrinha, Pedro; Fernandes, Rui; Matias, Luis; Duarte, João; Barba, Salvatore

    2016-04-01

    The presence of a subducted slab under the Gibraltar arc is now widely accepted. However, discussion still remains on whether subduction is active and what is its influence in the lithospheric processes, in particular in the observed geodesy, deformation rates and seismicity. Aiming at bringing new insights into the discussion, we have performed a neotectonic numerical study of a segment of the Africa-Eurasia plate boundary, from the Gloria fault to the Northern Algerian margin. Specifically, we have tested the effect of including or excluding an independently driven Alboran plate, i.e. testing active subduction versus inactive subduction (2plates versus 3plates scenarios). We used the dynamic code SHELLS (Bird et al., 2008) to model the surface velocity field and the ongoing deformation, using a new up-to-date simplified tectonic map of the region, new available lithospheric data and boundary conditions determined from two alternative Africa-Eurasia angular velocities, respectively: SEGAL2013, a new pole based on stable Africa and stable Eurasia gps data (last decades); and MORVEL, a geological-scale pole (3.16 Ma). We also extensively studied the variation within the parametric space of fault friction coefficient, subduction resistance and surface velocities imposed to the Alboran plate. The final run comprised a total of 5240 experiments, and each generated model was scored against geodetic velocities, stress direction data and seismic strain rates. The preferred model corresponds to the 3plates scenario, SEGAL2013 pole and fault friction of 0.225, with scoring results: gps misfit of 0.78 mm/yr; SHmax misfit of 13.6° and correlation with seismic strain rate of 0.62, significantly better than previous models. We present predicted fault slip rates for the recognized active structures and off-faults permanent strain rates, which can be used for seismic and tsunami hazard calculations (the initial motivation for this work was contributing for calculation of

  8. INVESTIGATION OF LITHOSPHERIC STRUCTURE IN MONGOLIA: INSIGHTS FROM INSAR OBSERVATIONS AND MODELLING

    Directory of Open Access Journals (Sweden)

    Z. Jing

    2017-09-01

    Full Text Available The western Mongolia is a seismically active intracontinental region, with ongoing tectonic deformation and widespread seismicity related to the far-field effects of India-Eurasia collision. During the 20th century, four earthquakes with the magnitude larger than 8 occurred in the western Mongolia and its surrounding regions, providing a unique opportunity to study the geodynamics of intracontinental tectonic deformations. The 1957 magnitude 8.3 Gobi-Altai earthquake is one of the largest seismic events. The deformation pattern of rupture zone associated with this earthquake is complex, involving left-lateral strike-slip and reverse dip-slip faulting on several distinct geological structures in a 264 × 40 km wide zone. To understand the relationship between the observed postseismic surface deformation and the rheological structure of the upper lithosphere, Interferometric Synthetic Aperture Radar (InSAR data are used to study the 1957 earthquake. Then we developed a postseismic model in a spherical, radially layered elastic-viscoelastic Earth based on InSAR results, and further analysed the dominant contribution to the surface deformation. This work is important for understanding not only the regional tectonics, but also the structure and dynamics of the lithosphere. SAR data were acquired from the ERS1/2 and Envisat from 1996 to 2010. Using the Repeat Orbit Interferometry Package (ROI_PAC, 124 postseismic interferograms are produced on four adjacent tracks. By stacking these interferograms, the maximum InSAR line-of-sight deformation rate along the Gobi-Altai fault zone is obtained. The main results are as follows: (1 The maximum InSAR line-of-sight deformation velocity along this large fault zone is about 6 mm/yr; (2 The modelled surface deformation suggests that the viscoelastic relaxation is the most reasonable mechanism to explain the observed surface motion; (3 The optimal model cover the Gobi-Altai seismogenic thickness is 10

  9. Investigation of Lithospheric Structure in Mongolia: Insights from Insar Observations and Modelling

    Science.gov (United States)

    Jing, Z.; Bihong, F.; Pilong, S.; Qiang, G.

    2017-09-01

    The western Mongolia is a seismically active intracontinental region, with ongoing tectonic deformation and widespread seismicity related to the far-field effects of India-Eurasia collision. During the 20th century, four earthquakes with the magnitude larger than 8 occurred in the western Mongolia and its surrounding regions, providing a unique opportunity to study the geodynamics of intracontinental tectonic deformations. The 1957 magnitude 8.3 Gobi-Altai earthquake is one of the largest seismic events. The deformation pattern of rupture zone associated with this earthquake is complex, involving left-lateral strike-slip and reverse dip-slip faulting on several distinct geological structures in a 264 × 40 km wide zone. To understand the relationship between the observed postseismic surface deformation and the rheological structure of the upper lithosphere, Interferometric Synthetic Aperture Radar (InSAR) data are used to study the 1957 earthquake. Then we developed a postseismic model in a spherical, radially layered elastic-viscoelastic Earth based on InSAR results, and further analysed the dominant contribution to the surface deformation. This work is important for understanding not only the regional tectonics, but also the structure and dynamics of the lithosphere. SAR data were acquired from the ERS1/2 and Envisat from 1996 to 2010. Using the Repeat Orbit Interferometry Package (ROI_PAC), 124 postseismic interferograms are produced on four adjacent tracks. By stacking these interferograms, the maximum InSAR line-of-sight deformation rate along the Gobi-Altai fault zone is obtained. The main results are as follows: (1) The maximum InSAR line-of-sight deformation velocity along this large fault zone is about 6 mm/yr; (2) The modelled surface deformation suggests that the viscoelastic relaxation is the most reasonable mechanism to explain the observed surface motion; (3) The optimal model cover the Gobi-Altai seismogenic thickness is 10 km; (4) The

  10. The Kenya rift revisited: insights into lithospheric strength through data-driven 3-D gravity and thermal modelling

    Science.gov (United States)

    Sippel, Judith; Meeßen, Christian; Cacace, Mauro; Mechie, James; Fishwick, Stewart; Heine, Christian; Scheck-Wenderoth, Magdalena; Strecker, Manfred R.

    2017-01-01

    We present three-dimensional (3-D) models that describe the present-day thermal and rheological state of the lithosphere of the greater Kenya rift region aiming at a better understanding of the rift evolution, with a particular focus on plume-lithosphere interactions. The key methodology applied is the 3-D integration of diverse geological and geophysical observations using gravity modelling. Accordingly, the resulting lithospheric-scale 3-D density model is consistent with (i) reviewed descriptions of lithological variations in the sedimentary and volcanic cover, (ii) known trends in crust and mantle seismic velocities as revealed by seismic and seismological data and (iii) the observed gravity field. This data-based model is the first to image a 3-D density configuration of the crystalline crust for the entire region of Kenya and northern Tanzania. An upper and a basal crustal layer are differentiated, each composed of several domains of different average densities. We interpret these domains to trace back to the Precambrian terrane amalgamation associated with the East African Orogeny and to magmatic processes during Mesozoic and Cenozoic rifting phases. In combination with seismic velocities, the densities of these crustal domains indicate compositional differences. The derived lithological trends have been used to parameterise steady-state thermal and rheological models. These models indicate that crustal and mantle temperatures decrease from the Kenya rift in the west to eastern Kenya, while the integrated strength of the lithosphere increases. Thereby, the detailed strength configuration appears strongly controlled by the complex inherited crustal structure, which may have been decisive for the onset, localisation and propagation of rifting.

  11. Lithospheric architecture of the Levant Basin (Eastern Mediterranean region): A 2D modeling approach

    Science.gov (United States)

    Inati, Lama; Zeyen, Hermann; Nader, Fadi-Henri; Adelinet, Mathilde; Sursock, Alexandre; Rahhal, Muhsin Elie; Roure, Francois

    2016-04-01

    One of the major uncertainties regarding the Levant Basin, known to be the site of rifting in the Late Paleozoic and Early Mesozoic, concerns its deep crustal configuration despite numerous old and recent geophysical studies in this region. The aim of this study is to deduce the deep structure of the lithosphere underlying the easternmost Mediterranean region, in particular the Levant Basin and its margins, where the nature of the crust, continental versus oceanic, remains debated and has major implications on understanding the regional tectonic and thermal evolution, and on constraining potential petroleum systems. The algorithm used is a trial and error method that delivers the crustal thickness and the depth of the lithosphere-asthenosphere boundary (LAB) as well as the crustal density distribution by integrating surface heat flow data, free-air gravity anomaly, Geoid and topography data. Moho depth and crustal thickness were locally constrained by refraction data where available. The models representing two EW sections show a progressively attenuated crystalline crust in an EW direction (35 to 8 km). The SN section represents a 12 km thick crust to the south, thins to 9-7 km towards the Lebanese coast and reaches 20 km in the north. The crystalline crust is best interpreted as a strongly thinned continental crust under the Levant Basin, represented by two distinct components, an upper and a lower crust. Nevertheless, the Herodotus Basin shows a thin crust, likely oceanic, with a thickness between 6 and 10 kms. West of the Eratosthenes Seamount, a local crustal anomaly is interpreted to be the result of an underlying continental crust with a thickness of 13 kms. The Moho under the Arabian plate is 35-40 km deep and becomes shallower towards the Mediterranean coast. Within the Levant Basin, the Moho appears to be situated between 20 and 23 km, reaching 26 km in the Herodotus Basin. While depth to LAB is around 110 km under the Arabian and the Eurasian plates, it

  12. The mechanisms of driving lithospheric deformation in India-Asia collision zone: a perspective from 3-D numerical modeling

    Science.gov (United States)

    Yang, Jianfeng; Kaus, Boris

    2016-04-01

    The mechanism of intraplate deformation remains incompletely understood by plate tectonics theory. The India-Asia collision zone is the largest present-day example of continental collision, which makes it an ideal location to study the processes of continental deformation. Existing models of lithospheric deformation are typically quasi two-dimensional and often assume that the lithosphere is a thin viscous sheet, which deforms homogeneously as a result of the collision, or flows above a partially molten lower crust, which explains the exhumation of Himalayan units and lateral spreading of Tibetan plateau. An opposing view is that most deformation localize in shear zones separating less deformed blocks, requiring the lithosphere to have an elasto-plastic rather than a viscous rheology. In order to distinguish which model best fits the observations we develop a 3-D visco-elasto-plastic model, which can model both distributed and highly localized deformation. In our preliminary result, most of the large-scale strike-slips faults including Altyn-Tagh fault, Xianshuihe fault, Red-River fault, Sagaing fault and Jiali fault can be simulated. The topography is consistent with observations that flat plateau in central Tibet and steep, abrupt margins adjacent to Sichuan basin, and gradual topography in southeast Tibet. These models suggest that the localized large-scale strike-slip faults accommodate the continental deformation. These results show the importance of a weak lower crust and topographic effects, as well as the effect of rheology and temperature structure of the lithosphere on the deformation patterns.

  13. Thrust fault modeling and Late-Noachian lithospheric structure of the circum-Hellas region, Mars

    Science.gov (United States)

    Egea-Gonzalez, Isabel; Jiménez-Díaz, Alberto; Parro, Laura M.; López, Valle; Williams, Jean-Pierre; Ruiz, Javier

    2017-05-01

    The circum-Hellas area of Mars borders Hellas Planitia, a giant impact ∼4.0-4.2 Ga old making the deepest and broadest depression on Mars, and is characterized by a complex pattern of fracture sets, lobate scarps, grabens, and volcanic plains. The numerous lobate scarps in the circum-Hellas region mainly formed in the Late Noachian and, except Amenthes Rupes, have been scarcely studied. In this work, we study the mechanical behavior and thermal structure of the crust in the circum-Hellas region at the time of lobate scarp formation, through the modeling of the depth of faulting beneath several prominent lobate scarps. We obtain faulting depths between ∼13 and 38 km, depending on the lobate scarp and accounting for uncertainty. These results indicate low surface and mantle heat flows in Noachian to Early Hesperian times, in agreement with heat flow estimates derived from lithospheric strength for several regions of similar age on Mars. Also, faulting depth and associate heat flows are not dependent of the local crustal thickness, which supports a stratified crust in the circum-Hellas region, with heat-producing elements concentrated in an upper layer that is thinner than the whole crust.

  14. Support for a Uniformitarian Model of Continental Mantle Lithosphere Formation from the "Near-Cratonic" Composition of Proterozoic Southern African Mantle Lithosphere

    Science.gov (United States)

    Janney, P. E.

    2014-12-01

    The transition at the end of the Archean between the generation of cratonic and mobile belt continental lithosphere is regarded as a first-order change in the mode of generation of continental lithosphere. It is widely debated whether this transition represented a fundamental change in the process by which the lithospheric mantle was generated (i.e., as melting residues of deep-seated mantle upwellings to residues of relatively shallow mantle melting at subduction zones), or whether it primarily reflected a more gradual change in the conditions (i.e., temperatures, depths and degrees of melting) of lithosphere generation in a suprasubduction zone setting. The marked contrast, in many cases, between the major element compositions of peridotite xenoliths from Archean cratons and those from adjacent post-Archean mobile belts has accentuated the significance of this transition. Peridotite xenoliths from the post-Archean mobile belt terranes surrounding the Kaapvaal craton in southern Africa are clearly Proterozoic in age from Re-Os isotope constraints, but they are unusual in that they share several key similarities in composition and mineralogy with Archean Kaapvaal peridotites (e.g., low bulk-rock Al2O3, relatively low modal olivine and high modal orthopyroxene). Although they lack the low FeO and high olivine Mg# values of the most extreme Kaapvaal samples, they show a very large degree of overlap (extending to olivine Mg# values of greater than 93 for example). These similarities support a common mode of origin for cratonic and post-cratonic lithosphere in southern Africa (although varying somewhat in the degrees and depths of melt extraction) and a similar history of post-formation modification. A comparison of the conditions of melt extraction for cratonic and post-cratonic lithosphere inferred from compatible and mildly incompatible trace elements will be presented.

  15. Upper mantle viscosity and lithospheric thickness under Iceland determined from a microphysical modelling approach of mantle rheology

    Science.gov (United States)

    Barnhoorn, A.; van der Wal, W.; Drury, M. R.

    2012-04-01

    The Vatnajökull glacier, located in the south-east of Iceland is the largest ice cap of Iceland having a mean radius of ~50 km covering an area of ˜8100 km2. The Vatnajökull glacier is situated directly on top of the spreading axis in the eastern volcanic zone (EVZ) of the Icelandic mid-ocean ridge and near the inferred center of the Icelandic hotspot. Due to the vicinity of the glacier to the active tectonic area, the response of the solid earth to melting of the ice cap is strongly controlled by the properties of the hot newly formed upper mantle underneath the mid-ocean ridge. The relatively high temperatures in the mantle during rifting result in relatively low upper mantle viscosities and fast relaxation times in comparison with tectonically inactive glaciated areas such as in. In this study, estimates for lithospheric thickness and upper mantle viscosity under Iceland are produced by a microphysical modelling approach using the theoretical temperature distribution under mid-ocean ridges combined with olivine diffusion and dislocation creep flow laws. Large lateral variations in upper mantle viscosity and especially lithospheric thickness are expected for Iceland perpendicular to the ridge axis due to the large changes in temperatures away from the ridge axis. The lithospheric thickness (27-40 km) and upper mantle viscosity (2 × 1018-1019 Pa s) outcomes for the recent glaciation are consistent with previous reports of viscosity and lithospheric thickness from glacial isostatic adjustment studies. A combination of a 40 km thick elastic lithosphere and an average upper mantle viscosity of 5 × 1018 Pa s would suggest that the upper mantle under Iceland is most likely dry. Also, the results indicate that the presence of a plume under Iceland cannot explain the recent low viscosity values reported for Iceland. Using a larger extent and larger thickness of the Icelandic icecap during the Weichselian glaciation event (˜10,000 BP) this study predicts that during

  16. The continental lithosphere

    DEFF Research Database (Denmark)

    Artemieva, Irina

    2009-01-01

    The goal of the present study is to extract non-thermal signal from seismic tomography models in order to distinguish compositional variations in the continental lithosphere and to examine if geochemical and petrologic constraints on global-scale compositional variations in the mantle are consist......The goal of the present study is to extract non-thermal signal from seismic tomography models in order to distinguish compositional variations in the continental lithosphere and to examine if geochemical and petrologic constraints on global-scale compositional variations in the mantle...... are consistent with modern geophysical data. In the lithospheric mantle of the continents, seismic velocity variations of a non-thermal origin (calculated from global Vs seismic tomography data [Grand S.P., 2002. Mantle shear-wave tomography and the fate of subducted slabs. Philosophical Transactions...... of the Royal Society of London. Series A, 360, 2475–2491.; Shapiro N.M., Ritzwoller M.H. 2002. Monte-Carlo inversion for a global shear velocity model of the crust and upper mantle. Geophysical Journal International 151, 1–18.] and lithospheric temperatures [Artemieva I.M., Mooney W.D., 2001. Thermal structure...

  17. Shallow and buoyant lithospheric subduction : causes and implications from thermo-chemical numerical modeling

    NARCIS (Netherlands)

    Hunen, Jeroen van

    2001-01-01

    Where two lithospheric plates converge on the Earth, one of them disappears into the mantle. The dominant driving mechanism for plate motion is regarded to be `slab pull': the subducted plate, the slab, exerts a pulling force on the attached plate at the surface. However, what has been puzzling geod

  18. Shallow and buoyant lithospheric subduction : causes and implications from thermo-chemical numerical modeling

    NARCIS (Netherlands)

    Hunen, Jeroen van

    2001-01-01

    Where two lithospheric plates converge on the Earth, one of them disappears into the mantle. The dominant driving mechanism for plate motion is regarded to be `slab pull': the subducted plate, the slab, exerts a pulling force on the attached plate at the surface. However, what has been puzzling

  19. Shallow and buoyant lithospheric subduction : causes and implications from thermo-chemical numerical modeling

    NARCIS (Netherlands)

    Hunen, Jeroen van

    2002-01-01

    Where two lithospheric plates converge on the Earth, one of them disappears into the mantle. The dominant driving mechanism for plate motion is regarded to be `slab pull': the subducted plate, the slab, exerts a pulling force on the attached plate at the surface. However, what has been puzzling geod

  20. Modeling the interaction between lithospheric and surface processes in foreland basins

    NARCIS (Netherlands)

    Garcia-Castellanos, D.; Cloetingh, S.

    2012-01-01

    This chapter reviews a number of key advances in quantitative understanding of foreland basins since the early 1990s, with a focus on the interplay between lithospheric flexure, erosion, and river transport. Flexure can be the result of topographic loading and slab-pull forces, though can also refle

  1. Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) Model - An Unified Concept for Earthquake Precursors Validation

    Science.gov (United States)

    Pulinets, S.; Ouzounov, D.

    2010-01-01

    The paper presents a conception of complex multidisciplinary approach to the problem of clarification the nature of short-term earthquake precursors observed in atmosphere, atmospheric electricity and in ionosphere and magnetosphere. Our approach is based on the most fundamental principles of tectonics giving understanding that earthquake is an ultimate result of relative movement of tectonic plates and blocks of different sizes. Different kind of gases: methane, helium, hydrogen, and carbon dioxide leaking from the crust can serve as carrier gases for radon including underwater seismically active faults. Radon action on atmospheric gases is similar to the cosmic rays effects in upper layers of atmosphere: it is the air ionization and formation by ions the nucleus of water condensation. Condensation of water vapor is accompanied by the latent heat exhalation is the main cause for observing atmospheric thermal anomalies. Formation of large ion clusters changes the conductivity of boundary layer of atmosphere and parameters of the global electric circuit over the active tectonic faults. Variations of atmospheric electricity are the main source of ionospheric anomalies over seismically active areas. Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) model can explain most of these events as a synergy between different ground surface, atmosphere and ionosphere processes and anomalous variations which are usually named as short-term earthquake precursors. A newly developed approach of Interdisciplinary Space-Terrestrial Framework (ISTF) can provide also a verification of these precursory processes in seismically active regions. The main outcome of this paper is the unified concept for systematic validation of different types of earthquake precursors united by physical basis in one common theory.

  2. Modeling the 2012 Wharton Basin Earthquakes off-Sumatra; Complete Lithospheric Failure (Invited)

    Science.gov (United States)

    Wei, S.; Helmberger, D. V.; Avouac, J.

    2013-12-01

    A sequence of large strike-slip earthquakes occurred west of Sunda Trench beneath the Wharton Basin. First reports indicate that the mainshock was extremely complex, involving three to four subevents (Mw>8) with a maze of aftershocks. We investigate slip models of the two largest earthquakes by joint inversion of regional and teleseismic waveform data. Using the Mw7.2 foreshock, we developed hybrid Green's Functions for the regional stations to approximate the mixture of oceanic and continental paths. The mainshock fault geometry is defined based on the back-projection results, point-source mechanisms, aftershock distribution and fine tune of grid searches. The fault system contains three faults, labeled F1 (89°/289° for dip/strike), F2 (74°/20°) and F3 (60°/310°). The inversion indicates that the main rupture consisted of a cascade of high stress drop asperities (up to 30MPa), extending as deep as 50 km. The rupture propagated smoothly from one fault to the next (F1, F2 and F3 in sequence) with rupture velocities of 2.0-2.5 km/s. The whole process lasted about 200s and the major moment release (>70%) took place on the N-S oriented F2. The Mw8.2 aftershock happened about 2hrs later on a N-S oriented fault with a relatively short duration (~60s) and also ruptured as deep as 50km. The slip distributions suggest that the earthquake sequence was part of a broad left-lateral shear zone between the Australian and Indian plates, and ruptured the whole lithosphere. These earthquakes apparently reactivated existing fracture zones and were probably triggered by unclamping of the great Sumatran earthquake of 2004.

  3. Modeling the 2012 Wharton basin earthquakes off-Sumatra: Complete lithospheric failure

    Science.gov (United States)

    Wei, Shengji; Helmberger, Don; Avouac, Jean-Philippe

    2013-07-01

    sequence of large strike-slip earthquakes occurred west of Sunda Trench beneath the Wharton Basin. First reports indicate that the main shock was extremely complex, involving three to four subevents (Mw > 8) with a maze of aftershocks. We investigate slip models of the two largest earthquakes by joint inversion of regional and teleseismic waveform data. Using the Mw7.2 foreshock, we developed hybrid Green's Functions for the regional stations to approximate the mixture of oceanic and continental paths. The main shock fault geometry is defined based on the back projection results, point-source mechanisms, aftershock distribution, and fine tune of grid searches. The fault system contains three faults, labeled F1 (89°/289° for dip/strike), F2 (74°/20°), and F3 (60°/310°). The inversion indicates that the main rupture consisted of a cascade of high-stress drop asperities (up to 30 MPa), extending as deep as 50 km. The rupture propagated smoothly from one fault to the next (F1, F2, and F3 in sequence) with rupture velocities of 2.0-2.5 km/s. The whole process lasted about 200 s, and the major moment release (>70%) took place on the N-S oriented F2. The Mw8.2 aftershock happened about 2 h later on a N-S oriented fault with a relatively short duration (~60 s) and also ruptured as deep as 50 km. The slip distributions suggest that the earthquake sequence was part of a broad left-lateral shear zone between the Australian and Indian plates and ruptured the whole lithosphere. These earthquakes apparently reactivated existing fracture zones and were probably triggered by unclamping of the great Sumatran earthquake of 2004.

  4. Full waveform tomography for lithospheric imaging: results from a blind test in a realistic crustal model

    Science.gov (United States)

    Brenders, A. J.; Pratt, R. G.

    2007-01-01

    observed near the edges of the images due to the limited ray coverage inherent to the footprint of the survey geometry. Several aspects of the waveform tomography strategy were critical to the success of the acoustic method with realistic, synthetic, viscoelastic data: (i) the accuracy of the starting model from traveltime tomography, (ii) implementation in the frequency domain, (iii) the use of complex-valued frequencies to effect time damping of the data residuals, (iv) the selection of a suitable subset of data and data frequencies, (v) progressive inversion of low- to high-frequency components of the data, (vi) initial, pre-inversion matching of the amplitudes between observed and modelled data, and (vii) sufficient preconditioning of both the data and the update images. Combined, these strategies were effectively equivalent to a multiscale approach that mitigated the non-linearity of the seismic inverse problem. During the inversion we carried out repeated forward modelling to ensure our modelled waveforms matched the observed data as closely as possible in both frequency and time domains. The synthetic data set used in this paper provides a benchmark for future testing of modelling, inversion, and imaging algorithms for wide-angle lithospheric imaging.

  5. Shallow and buoyant lithospheric subduction : causes and implications from thermo-chemical numerical modeling

    OpenAIRE

    2002-01-01

    Where two lithospheric plates converge on the Earth, one of them disappears into the mantle. The dominant driving mechanism for plate motion is regarded to be `slab pull': the subducted plate, the slab, exerts a pulling force on the attached plate at the surface. However, what has been puzzling geodynamicists since their discovery in the seventies, is that shallow, almost horizontal subduction, as occurring below Peru or Central Chile, does not fit into this simple picture. This forms the mot...

  6. A preliminary model for 3-D rheological structure of the lithosphere in North China

    Institute of Scientific and Technical Information of China (English)

    ZANG; Shaoxian; (臧绍先); LI; Chang; (李昶); NING; Jieyuan; (宁杰远); WEI; Rongqiang; (魏荣强)

    2003-01-01

    3-D structures of velocity and temperature are obtained using the dataof P-wave velocity and heat flow in North China (105°E-124°E, 30°N-42°N).Taking into account the effect of three main rheological mechanisms, namely friction sliding, brittle fracture and creep in the lithosphere, the 3-D structuresof the rheological strength and viscosity in the lithosphere in North China arecalculated. The results show that the strength and viscosity in the lithospherehave layering characteristics. Under the strain rate of 10-15 s-1, the upper part of the upper crust is in the brittle region and the lower part of the upper crust may be in the ductile region dominated by creep; the middle crust can be inthe brittle region dominated by brittle fracture, or the upper layer of brittlefracture and lower layer of creep ductile; the lower crust almost is in the creep region dominated by creep. In addition, the strength varies horizontally, which has a close relationship with geotectonics. The influence of velocity structure and temperature structure on the rheological structure is discussed and some suggestions to improve the study of lithospheric rheological structure are put forward.

  7. How are we behaving?

    CERN Multimedia

    2012-01-01

    It’s almost two years since CERN introduced a Code of Conduct. The results may not be immediately measurable, but I’d like to think it’s made the lab a better place to be. The Code of Conduct is based on values that most of us immediately identify with, and so implementing it comes as second nature. Nevertheless, in an organisation of over 10,000 people, it’s useful to have a set of guidelines and there have been occasions on which it’s been necessary to remind people of them.   I use the figure of 10,000 advisedly since the Code of Conduct applies to us all, those on the CERN payroll as well as users of the lab’s facilities and people working for CERN contractors, as long as they are acting on CERN’s behalf. The Code also applies to us whether we are on the CERN site or anywhere else. CERN is a major presence in the region. The way we behave can have a significant influence on how our neighbours perceive us, and how the la...

  8. Viscous model of lithosphere rheology, stress distribution, integrated strength, and bulk failure: application to and implications from examples of intracratonic rifts and inversion structures

    Science.gov (United States)

    Stephenson, R. A.; Ershov, A.

    2001-12-01

    One way in which theoretical rheological models of the lithosphere can be constrained by geological data is through estimations of the lithosphere's integrated strength. When an applied force exceeds this, then the lithosphere should lose its integrity and undergo irreversible deformation (WLF - "whole lithosphere failure"). The geological expression of this kind of deformational regime is the development of rifts (in extension) and inverted structures (in compression). By considering intracratonic structures rather than marginal ones it is possible to exclude additional extraneous influences and infer the net effect of intraplate stresses. Here, actual intraplate structures are considered in terms of a rheological model in which the non-brittle part of the lithosphere deforms viscously (by creep) in response to applied forces. This is in contrast to conventional estimations of total lithosphere strength based on "yield stress envelopes" in which "ductile" deformation is taken to be time-invariant (plastic). Taking into account the implications of adopting a viscous rheology in place of a plastic one in evaluating the "strength" of the lithosphere, it is necessary to incorporate the time-dependence of stresses, strains and strain rates and also the dependence of the bulk strain rate on the total applied force. This means that the duration of loading of tectonic forces prior to eventual rifting or inversion is also an important model variable. The mechanism that controls strain rate and stress distribution in the lithosphere prior to WLF in the model is one of stress redistribution from ductile deformation zones into elastic ones, as determined by stress relaxation in the former and stress amplification in the latter given an assumed constant applied boundary force. A stable equilibrium regime of deformation occurs when, at each point within the lithosphere, the stress reduction effected by viscous relaxation equals the stress increase effected by the applied force

  9. Paraná-Etendeka lithosphere modeling according to GOCE observations and geophysical constraints: improvement of PERLA project

    Science.gov (United States)

    Mariani, Patrizia; Braitenberg, Carla

    2015-04-01

    One of the challenges of the European Space Agency (ESA) is to improve knowledge of physical properties and geodynamic processes of the lithosphere and the Earth's deep interior, and their relationship to the Earth-surface changes. PERLA project is a part of the challenge of ESA's Living Planet program to investigate the Solid Earth, and in particular the lithosphere of the Paraná-Etendeka Large Igneous Province (LIP). At the present stage the study is focusing on the upper mantle, the source of the magma. The aim is to motivate the asymmetry of the shallow volcanic effusion of the Early Cretaceous tholeiitic magmatism, that in Paraná is wide, thick and represented by the basaltic layer of Serra Geral Formation, while in Etendeka it is rare and spanned. Viceversa the alkaline magmatism shows similar effusions along the region with dyke swarms and associated alkaline and alkaline-carbonatite complexes from Early Creataceous to Paleogene age. ESA's Living Planet program offers a suite of scientific satellites, the Earth Explorers, and in this context PERLA adopts the newest GOCE satellite mission products. The Marussi tensor field and especially its vertical component show a positive anomaly along the coastline sector of both the western and eastern Atlantic Ocean. Positive anomalies are also related to the deeper Moho under the northern part of Paraná basin, in South America (SAM) and the Etendeka continental part. Here we aim to define the detail of masses between crust and upper mantle by modeling the Marussi Tensor components and the invariants. The invariants are easier to understand because they are independent of the reference system. The forward model uses Tesseroids. The density model is compared with recent seismologic models, and is performed according to the results provided by the physical laws governing rock densities and seismic velocity of lithosphere in function of temperature and pressure combined with laboratory measurements of a great number of

  10. Lithospheric structure of the Eastern Iranian plateau from integrated geophysical modeling: A transect from Makran to the Turan platform

    Science.gov (United States)

    Entezar-Saadat, Vahid; Motavalli-Anbaran, Seyed-Hani; Zeyen, Hermann

    2017-05-01

    We present a 2D profile of density and temperature distribution in the lithosphere across Iran along a more than 1600 km long profile extending from the Oman Gulf in the South to the Kopeh-Dagh and the Turan platform in the North. Gravity, geoid, topography and surface heat flow data were used for modeling, assuming local isostatic equilibrium. As much as possible, crustal structure has been constrained by seismic data. Crustal thickening is found under the Taftan-Bazman volcanic-arc (up to 47 km), under the Binalud foreland (∼54 km) and beneath the Kopeh-Dagh mountains (up to 50 km) whereas thin crust has been obtained under the Oman Gulf (20 km). Moho depth under the Lut block and the Turan platform is about 40 km. The lithospheric thickness is ∼90 km under the Oman Gulf and increases slightly until the Jazmourian depression. Then the lithospheric-asthenospheric boundary (LAB) bends significantly and sinks to ∼260 km under the Taftan-Bazman volcanic-arc. The LAB depth is about 190 km beneath the Lut block. A slight increase of LAB depth under the Binalud foreland towards the North may indicate a suture zone. Under the Turan platform, the LAB depth reaches ∼210 km. We also modeled two possible positions of the deep suture zone in NE Iran (along the main Kopeh-Dagh fault or along the Atrak River) and concluded that, when the suture zone is along the Atrak River, we obtained the better fit between calculated and measured data.

  11. The new strains Brucella inopinata BO1 and Brucella species 83-210 behave biologically like classic infectious Brucella species and cause death in murine models of infection.

    Science.gov (United States)

    Jiménez de Bagüés, María P; Iturralde, María; Arias, Maykel A; Pardo, Julián; Cloeckaert, Axel; Zygmunt, Michel S

    2014-08-01

    Recently, novel atypical Brucella strains isolated from humans and wild rodents have been reported. They are phenotypically close to Ochrobactrum species but belong to the genus Brucella, based on genetic relatedness, although genetic diversity is higher among the atypical Brucella strains than between the classic species. They were classified within or close to the novel species Brucella inopinata. However, with the exception of Brucella microti, the virulence of these novel strains has not been investigated in experimental models of infection. The type species B. inopinata strain BO1 (isolated from a human) and Brucella species strain 83-210 (isolated from a wild Australian rodent) were investigated. A classic infectious Brucella reference strain, B. suis 1330, was also used. BALB/c, C57BL/6, and CD1 mice models and C57BL/6 mouse bone-marrow-derived macrophages (BMDMs) were used as infection models. Strains BO1 and 83-210 behaved similarly to reference strain 1330 in all mouse infection models: there were similar growth curves in spleens and livers of mice and similar intracellular replication rates in BMDMs. However, unlike strain 1330, strains BO1 and 83-210 showed lethality in the 3 mouse models. The novel atypical Brucella strains of this study behave like classic intracellular Brucella pathogens. In addition, they cause death in murine models of infection, as previously published for B. microti, another recently described environmental and wildlife species. © The Author 2014. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

  12. Late Miocene Pacific plate kinematic change explained with coupled global models of mantle and lithosphere dynamics

    DEFF Research Database (Denmark)

    Stotz, Ingo Leonardo; Iaffaldano, Giampiero; Davies, DR

    2017-01-01

    and the consequent subduction polarity reversal. The uncertainties associated with the timing of this event, however, make it difficult to quantitatively demonstrate a dynamical association. Here, we first reconstruct the Pacific plate's absolute motion since the mid-Miocene (15 Ma), at high-temporal resolution....../lithosphere system to test hypotheses on the dynamics driving this change. These indicate that the arrival of the OJP at the Melanesian arc, between 10 and 5 Ma, followed by a subduction polarity reversal that marked the initiation of subduction of the Australian plate underneath the Pacific realm, were the key...

  13. Why does shear banding behave like first-order phase transitions? Derivation of a potential from a mechanical constitutive model.

    Science.gov (United States)

    Sato, K; Yuan, X-F; Kawakatsu, T

    2010-02-01

    Numerous numerical and experimental evidence suggest that shear banding behavior looks like first-order phase transitions. In this paper, we demonstrate that this correspondence is actually established in the so-called non-local diffusive Johnson-Segalman model (the DJS model), a typical mechanical constitutive model that has been widely used for describing shear banding phenomena. In the neighborhood of the critical point, we apply the reduction procedure based on the center manifold theory to the governing equations of the DJS model. As a result, we obtain a time evolution equation of the flow field that is equivalent to the time-dependent Ginzburg-Landau (TDGL) equations for modeling thermodynamic first-order phase transitions. This result, for the first time, provides a mathematical proof that there is an analogy between the mechanical instability and thermodynamic phase transition at least in the vicinity of the critical point of the shear banding of DJS model. Within this framework, we can clearly distinguish the metastable branch in the stress-strain rate curve around the shear banding region from the globally stable branch. A simple extension of this analysis to a class of more general constitutive models is also discussed. Numerical simulations for the original DJS model and the reduced TDGL equation is performed to confirm the range of validity of our reduction theory.

  14. Quantitative Modelling of Multiphase Lithospheric Stretching and Deep Thermal History of Some Tertiary Rift Basins in Eastern China

    Institute of Scientific and Technical Information of China (English)

    林畅松; 张燕梅; 李思田; 刘景彦; 仝志刚; 丁孝忠; 李喜臣

    2002-01-01

    The stretching process of some Tertiary rift basins in eastern China is characterized by multiphase rifting. A multiple instantaneous uniform stretching model is proposed in this paper to simulate the formation of the basins as the rifting process cannot be accurately described by a simple (one episode) stretching model. The study shows that the multiphase stretching model, combined with the back-stripping technique, can be used to reconstruct the subsidence history and the stretching process of the lithosphere, and to evaluate the depth to the top of the asthenosphere and the deep thermal evolution of the basins. The calculated results obtained by applying the quantitative model to the episodic rifting process of the Tertiary Qiongdongnan and Yinggehai basins in the South China Sea are in agreement with geophysical data and geological observations. This provides a new method for quantitative evaluation of the geodynamic process of multiphase rifting occurring during the Tertiary in eastern China.

  15. Importance of the temperature field and its uncertainties in modeling ductile deformation of the southern California lithosphere

    Science.gov (United States)

    Thatcher, W. R.; Chapman, D. S.; Williams, C. F.; Hearn, E. H.

    2015-12-01

    Temperature is arguably the most important parameter controlling ductile deformation in tectonically active regions. Laboratory measurements at lower crust and upper mantle conditions define the mechanisms controlling ductile deformation and constrain quantitative rules relating stress and strain rate. Exhumed ductily deformed rocks reveal the micromechanics of deformation, supplying ground truth that can be compared with lab results. However, even if the mechanism and ductile deformation rules are accepted at face value, strain rates are exquisitely dependent on temperature. Here we critically assess observational data relevant to constraining the southern California lithospheric temperature field. Our goal is to improve estimates of the 3D temperature field and its real uncertainties and apply them to regional deformation modeling. We use a phased approach to estimating geotherms, beginning with simple 1D steady state conductive models. We identify the most important parameters and disaggregate them, separately examining the effects of varying radiogenic heat source concentration, rock type, crust and lithosphere thickness and asthenosphere solidus. We assess geotherm uncertainties by assigning realistic error bounds on all input quantities, propagate these uncertainties by Monte Carlo sampling and determine probability density functions for the geotherm. We find that although other parameter uncertainties contribute, variability in heat sources produces the largest variation in model-predicted geotherms. Because heat production depends strongly on rock type, better characterization of crustal lithology using refined seismic imaging results now becoming available beneath southern California is likely to produce the largest improvements in thermal models. Nonetheless, substantial uncertainty will remain, arguing for adoption of one or a few standard thermal models as common starting points for regional deformation modeling in southern California and elsewhere.

  16. Lithospheric deformation in the Africa-Iberia plate boundary: Improved neotectonic modeling testing a basal-driven Alboran plate

    Science.gov (United States)

    Neres, M.; Carafa, M. M. C.; Fernandes, R. M. S.; Matias, L.; Duarte, J. C.; Barba, S.; Terrinha, P.

    2016-09-01

    We present an improved neotectonic numerical model of the complex NW Africa-SW Eurasia plate boundary segment that runs from west to east along the Gloria Fault up to the northern Algerian margin. We model the surface velocity field and the ongoing lithospheric deformation using the most recent version of the thin-shell code SHELLS and updated lithospheric model and fault map of the region. To check the presence versus the absence of an independently driven Alboran domain, we develop two alternative plate models: one does not include an Alboran plate; another includes it and determines the basal shear tractions necessary to drive it with known velocities. We also compare two alternative sets of Africa-Eurasia velocity boundary conditions, corresponding to geodetic and geological-scale averages of plate motion. Finally, we perform an extensive parametric study of fault friction coefficient, trench resistance, and velocities imposed in Alboran nodes. The final run comprises 5240 experiments, each scored to geodetic velocities (estimated for 250 stations and here provided), stress direction data, and seismic strain rates. The model with the least discrepancy to the data includes the Alboran plate driven by a basal WSW directed shear traction, slightly oblique to the westward direction of Alboran motion. We provide estimates of long-term strain rates and slip rates for the modeled faults, which can be useful for further hazard studies. Our results support that a mechanism additional to the Africa-Eurasia convergence is required to drive the Alboran domain, which can be related to subduction processes occurring within the mantle.

  17. Lithospheric velocity model of Texas and implications for the Ouachita orogeny and the opening of the Gulf of Mexico

    Science.gov (United States)

    Yao, Yao; Li, Aibing

    2016-12-01

    A 3-D shear wave velocity model of Texas has been developed from Rayleigh wave phase velocities by using ambient noise data recorded at the USArray stations. In the upper crust, the Ouachita front separates high velocity in the Laurentia to its west from low velocity in the east and south Texas basins. The Ouachita belt is characterized as a high-velocity zone with local maximums coinciding with known uplifts, which we interpret as accreted island arcs during the Ouachita orogeny. Our model evidences a strong Ouachita lithosphere that helped to buffer crust thinning from the Mesozoic rifting. A significantly low-velocity anomaly is present in southeast Texas in the lower crust and upper mantle. We associate this anomaly with a past asthenosphere upwelling that likely originated from the edge of the subducted slab during the Ouachita collision and was potentially responsible for the opening of the Gulf of Mexico.

  18. Modeling and optimization of microbial hyaluronic acid production by Streptococcus zooepidemicus using radial basis function neural network coupling quantum-behaved particle swarm optimization algorithm.

    Science.gov (United States)

    Liu, Long; Sun, Jun; Xu, Wenbo; Du, Guocheng; Chen, Jian

    2009-01-01

    Hyaluronic acid (HA) is a natural biopolymer with unique physiochemical and biological properties and finds a wide range of applications in biomedical and cosmetic fields. It is important to increase HA production to meet the increasing HA market demand. This work is aimed to model and optimize the amino acids addition to enhance HA production of Streptococcus zooepidemicus with radial basis function (RBF) neural network coupling quantum-behaved particle swarm optimization (QPSO) algorithm. In the RBF-QPSO approach, RBF neural network is used as a bioprocess modeling tool and QPSO algorithm is applied to conduct the optimization with the established RBF neural network black model as the objective function. The predicted maximum HA yield was 6.92 g/L under the following conditions: arginine 0.062 g/L, cysteine 0.036 g/L, and lysine 0.043 g/L. The optimal amino acids addition allowed HA yield increased from 5.0 g/L of the control to 6.7 g/L in the validation experiments. Moreover, the modeling and optimization capacity of the RBF-QPSO approach was compared with that of response surface methodology (RSM). It was indicated that the RBF-QPSO approach gave a slightly better modeling and optimization result compared with RSM. The developed RBF-QPSO approach in this work may be helpful for the modeling and optimization of the other multivariable, nonlinear, time-variant bioprocesses.

  19. Mechanical heterogeneities and lithospheric extension

    Science.gov (United States)

    Duretz, Thibault; Petri, Benoit; Mohn, Geoffroy; Schenker, Filippo L.; Schmalholz, Stefan

    2016-04-01

    Detailed geological and geophysical studies of passive margins have highlighted the multi-stage and depth-dependent aspect of lithospheric thinning. Lithospheric thinning involves a variety of structures (normal faults, low angle detachments, extensional shear zones, extraction faults) and leads to a complex architecture of passive margins (with e.g. necking zone, mantle exhumation, continental allochthons). The processes controlling the generation and evolution of these structures as well as the impact of pre-rift inheritance are so far incompletely understood. In this study, we investigate the impact of pre-rift inheritance on the development of rifted margins using two-dimensional thermo-mechanical models of lithospheric thinning. To first order, we represent the pre-rift mechanical heterogeneities with lithological layering. The rheologies are kept simple (visco-plastic) and do not involve any strain softening mechanism. Our models show that mechanical layering causes multi-stage and depth-dependent extension. In the initial rifting phase, lithospheric extension is decoupled: as the crust undergoes thinning by brittle (frictional-plastic) faults, the lithospheric mantle accommodates extension by symmetric ductile necking. In a second rifting phase, deformation in the crust and lithospheric mantle is coupled and marks the beginning of an asymmetric extension stage. Low angle extensional shear zones develop across the lithosphere and exhume subcontinental mantle. Furthemore, crustal allochthons and adjacent basins develop coevally. We describe as well the thermal evolution predicted by the numerical models and discuss the first-order implications of our results in the context of the Alpine geological history.

  20. Structure of the lithosphere of the northeastern part of the Indian Ocean according to results of two-dimensional structural-density modeling

    Science.gov (United States)

    Bulychev, A. A.; Gilod, D. A.; Dubinin, E. P.

    2016-05-01

    From a gravitational field analysis, the lithosphere was regionalized and a structural schematic map of the eastern part of the Indian Ocean was compiled. The area adjacent to the western margin of Australia was studied. The region is characterized by a complex lithospheric structure. It includes heterogeneous blocks of varying age, framed by structures with different morphological and geophysical expression and varying genesis. To clarify the peculiarities of tectonic structures of various genetic types, structural-density modeling was performed. This made it possible to establish certain gravimetric indicators characteristic of structures of various genesis.

  1. Lithospheric structure of the westernmost Mediterranean inferred from finite frequency Rayleigh wave tomography S-velocity model.

    Science.gov (United States)

    Palomeras, Imma; Villasenor, Antonio; Thurner, Sally; Levander, Alan; Gallart, Josep; Harnafi, Mimoun

    2016-04-01

    The Iberian Peninsula and Morocco, separated by the Alboran Sea and the Algerian Basin, constitute the westernmost Mediterranean. From north to south this region consists of the Pyrenees, the result of interaction between the Iberian and Eurasian plates; the Iberian Massif, a region that has been undeformed since the end of the Paleozoic; the Central System and Iberian Chain, regions with intracontinental Oligocene-Miocene deformation; the Gibraltar Arc (Betics, Rif and Alboran terranes) and the Atlas Mountains, resulting from post-Oligocene subduction roll-back and Eurasian-Nubian plate convergence. In this study we analyze data from recent broad-band array deployments and permanent stations on the Iberian Peninsula and in Morocco (Spanish IberArray and Siberia arrays, the US PICASSO array, the University of Munster array, and the Spanish, Portuguese, and Moroccan National Networks) to characterize its lithospheric structure. The combined array of 350 stations has an average interstation spacing of ~60 km, comparable to USArray. We have calculated the Rayleigh waves phase velocities from ambient noise for short periods (4 s to 40 s) and teleseismic events for longer periods (20 s to 167 s). We inverted the phase velocities to obtain a shear velocity model for the lithosphere to ~200 km depth. The model shows differences in the crust for the different areas, where the highest shear velocities are mapped in the Iberian Massif crust. The crustal thickness is highly variable ranging from ~25 km beneath the eastern Betics to ~55km beneath the Gibraltar Strait, Internal Betics and Internal Rif. Beneath this region a unique arc shaped anomaly with high upper mantle velocities (>4.6 km/s) at shallow depths (Gibraltar arc to ~55 km depth. Low upper mantle velocities (<4.2 km/s) are observed beneath the Atlas, the northeastern end of the Betic Mountains and the Late Cenozoic volcanic fields in Iberia and Morocco, indicative of high temperatures at relatively shallow depths

  2. Plate Tectonic Consequences of competing models for the origin and history of the Banda Sea subducted oceanic lithosphere

    CERN Document Server

    Heine, Christian; McKay, Hamish; Müller, R Dietmar

    2012-01-01

    The Banda Arc, situated west of Irian Jaya and in the easternmost extension of the Sunda subduction zone system, reveals a characteristic bowl-shaped geometry in seismic tomographic images. This indicates that the oceanic lithosphere still remains attached to the surrounding continental margins of northern Australia and the Bird's Head microcontinent. Major controversies exist between authors proposing an allochthonous or autochthonous origin of the Bird's Head block. Either scenario has important implications for plate kinematic models aiming to reconstruct the tectonic evolution of the region and the late Jurassic seaoor spreading geometry of this now subducted Argo-Tanimbar-Seram (ATS) ocean basin. Wider implications affect the tectonic conguration of the Tethyan-Pacic realm, the distribution of plate boundaries as well as the shape and size of continental blocks which have been rifted off the northeastern Gondwana margin during the Late Jurassic and are now accreted to the SE Asia margin. We apply structu...

  3. LITHO1.0 - An Updated Crust and Lithospheric Model of the Earth Developed Using Multiple Data Constraints

    Science.gov (United States)

    Pasyanos, M. E.; Masters, G.; Laske, G.; Ma, Z.

    2012-12-01

    Models such as CRUST2.0 (Bassin et al., 2000) have proven very useful to many seismic studies on regional, continental, and global scales. We have developed an updated, higher resolution model called LITHO1.0 that extends deeper to include the lithospheric lid, and includes mantle anisotropy, potentially making it more useful for a wider variety of applications. The model is evolving away from the crustal types strongly used in CRUST5.1 (Mooney et al., 1998) to a more data-driven model. This is accomplished by performing a targeted grid search with multiple data inputs. We seek to find the most plausible model which is able to fit multiple constraints, including updated sediment and crustal thickness models, upper mantle velocities derived from travel times, and surface wave dispersion. The latter comes from a new, very large, global surface wave dataset built using a new, efficient measurement technique that employs cluster analysis (Ma et al., 2012), and includes the group and phase velocities of both Love and Rayleigh waves. We will discuss datasets and methodology, highlight significant features of the model, and provide detailed information on the availability of the model in various formats.

  4. Anatomy of lithosphere necking during orthogonal rifting

    Science.gov (United States)

    Nestola, Yago; Cavozzi, Cristian; Storti, Fabrizio

    2013-04-01

    The evolution of lithosphere necking is a fundamental parameter controlling the structural architecture and thermal-state of rifted margin. The necking shape depends on several parameters, including the extensional strain-rate and thermal layering of the lithosphere. Despite a large number of analogue and numerical modelling studies on lithosphere extension, a quantitative description of the evolution of necking through time is still lacking. We used analogue modelling to simulate in three-dimension the progression of lithosphere thinning and necking during orthogonal rifting. In our models we simulated a typical "cold and young" 4-layer lithosphere stratigraphy: brittle upper crust (loose quartz sand), ductile lower crust (silicon-barite mixture), brittle upper mantle (loose quartz sand), and ductile lower mantle (silicon-barite mixture). The experimental lithosphere rested on a glucose syrup asthenosphere. We monitored model evolution by periodic and coeval laser scanning of both the surface topography and the lithosphere base. After model completion, each of the four layers was removed and the top of the underlying layer was scanned. This technical approach allowed us to quantify the evolution in space and time of the thinning factors for both the whole lithosphere (βz) and the crust (γ). The area of incremental effective stretching (βy) parallel to the extensional direction was obtained from the βz maps.

  5. The Development of Training Model Based on Theory of Planned Behavior and Willingness to Behave Higienic Practices for The Food Handler at Foodcourt Baseball in Unesa Surabaya

    Directory of Open Access Journals (Sweden)

    Sri Handajani

    2015-01-01

    Full Text Available Training is not always change the personal behavior. According to the theory of planned behavior (Ajzen, 2005, the behavior intention is influence by three factors including the attitude, the subjective norms and the perceived behavior control (PBC. Willingness is the independent concept of the presumption behavior and influenced by intention as well. The aim of  this study was to develop training model based on the theory of planned behavior and and willingness to higienic behavior for the food handler at foodcourt Baseball in Unesa Surabaya and implementation analysis of the development of training model. The development of the training model is using preliminary investigation phase, design phase and implementation. Partial Least Square (PLS was performed. The effectiveness of training model was analyzed by using t test with two paired samples (paired t - test. The result of food handlers hygienic behavioral analisys showed: PBC had contributed the most to the intentions through the willingness to behave hygienic practices, compared to the contribution of the attitude, subjective norm and PBC directly against the intention. These results could be used to develop a model of training for food handlers at the venue. The training was significantly effective (paired t test, p <0,05 in increasing the knowledge, practicing the hygienic behavior, attitude, subjective norm, PBC, intention and willingness of hygienic behavior of food handlers. The practicality of evaluation model was obtained by instructor assessment activities in very good result (88,42, 96% of trainees could participate well, and 89% of trainees responded well to the training. This training model was effectively proven to be used in increasing the intention of hygienic behavior of food handlers.

  6. 3D modelling of non-linear visco-elasto-plastic crustal and lithospheric processes using LaMEM

    Science.gov (United States)

    Popov, Anton; Kaus, Boris

    2016-04-01

    LaMEM (Lithosphere and Mantle Evolution Model) is a three-dimensional thermo-mechanical numerical code to simulate crustal and lithospheric deformation. The code is based on a staggered finite difference (FDSTAG) discretization in space, which is a stable and very efficient technique to solve the (nearly) incompressible Stokes equations that does not suffer from spurious pressure modes or artificial compressibility (a typical feature of low-order finite element techniques). Higher order finite element methods are more accurate than FDSTAG methods under idealized test cases where the jump in viscosity is exactly aligned with the boundaries of the elements. Yet, geodynamically more realistic cases involve evolving subduction zones, nonlinear rheologies or localized plastic shear bands. In these cases, the viscosity pattern evolves spontaneously during a simulation or even during nonlinear iterations, and the advantages of higher order methods disappear and they all converge with approximately first order accuracy, similar to that of FDSTAG [1]. Yet, since FDSTAG methods have considerably less degrees of freedom than quadratic finite element methods, they require about an order of magnitude less memory for the same number of nodes in 3D which also implies that every matrix-vector multiplication is significantly faster. LaMEM is build on top of the PETSc library and uses the particle-in-cell technique to track material properties, history variables which makes it straightforward to incorporate effects like phase changes or chemistry. An internal free surface is present, together with (simple) erosion and sedimentation processes, and a number of methods are available to import complex geometries into the code (e.g, http://geomio.bitbucket.org). Customized Galerkin coupled geometric multigrid preconditioners are implemented which resulted in a good parallel scalability of the code (we have tested LaMEM on 458'752 cores [2]). Yet, the drawback of using FDSTAG

  7. Thermal-rheological structure of lithosphere beneath the northern flank of Tarim Basin, western China:Implications for geodynamics

    Institute of Scientific and Technical Information of China (English)

    LIU; Shaowen; WANG; Liangshu; LI; Cheng; LI; Hua; HAN; Yong

    2004-01-01

    Based on the data of geo-temperature and thermophysical parameters of rocks in the Kuqa Depression and the Tabei Uplift, northern flank of the Tarim Basin, in terms of the analytical solution of 1-D heat transfer equation, the thermal structure of the lithosphere under this region is determined. Our results show that the average surface heat flow of the northern flank of the Tarim Basin is 45 mW/m2, and the mantle heat flow is between 20 and 23 mW/m2; the temperature at crust-mantle boundary (Moho) ranges from 514℃ to 603℃ and the thermal lithosphere where the heat conduction dominates is 138-182 km thick. Furthermore, in combination with the P wave velocity structure resulting from the deep seismic sounding profile across this region and rheological modeling, we have studied the local composition of the lithosphere and its rheological profile, as well as the strength distribution. We find that the rheological stratification of the lithosphere in this region is apparent. The lowermost of the lower crust is ductile; however,the uppermost of the mantle and the upper and middle parts of the crust are both brittle layers,which is typically the so-called sandwich-like structure. Lithospheric strength is also characterized by the lateral variation, and the uplift region is stronger than the depression region. The lithospheric strength of the northem flank of the Tarim Basin decreases gradually from south to north; the Kuqa Depression has the lowest strength and the south of the Tabei Uplift is strongest.The total lithospheric strength of this region is 4.77× 1012-5.03 × 1013 N/m under extension, and 6.5 × 1012-9.4× 1013 N/m under compression. The lithospheric brittle-ductile transition depth is between 20 km and 33 km. In conclusion, the lithosphere of the northern flank of the Tarim Basin is relatively cold with higher strength, so it behaves rigidly and deforms as a whole, which is also supported by the seismic activity in this region. This rigidity of the

  8. Electrical conductivity of continental lithospheric mantle from integrated geophysical and petrological modeling: Application to the Kaapvaal Craton and Rehoboth Terrane, southern Africa

    OpenAIRE

    Fullea, J.; Muller, M.R.; Jones, A. G.

    2011-01-01

    The electrical conductivity of mantle minerals is highly sensitive to parameters that characterize the structure and state of the lithosphere and sublithospheric mantle, and mapping its lateral and vertical variations gives insights into formation and deformation processes. We review state-of-the-art conductivity models based on laboratory studies for the most relevant upper mantle minerals and define a bulk conductivity model for the upper mantle that accounts for temperature, pressure, and ...

  9. A random-walk algorithm for modeling lithospheric density and the role of body forces in the evolution of the Midcontinent Rift

    Science.gov (United States)

    Levandowski, William Brower; Boyd, Oliver; Briggs, Richard; Gold, Ryan D.

    2015-01-01

    This paper develops a Monte Carlo algorithm for extracting three-dimensional lithospheric density models from geophysical data. Empirical scaling relationships between velocity and density create a 3D starting density model, which is then iteratively refined until it reproduces observed gravity and topography. This approach permits deviations from uniform crustal velocity-density scaling, which provide insight into crustal lithology and prevent spurious mapping of crustal anomalies into the mantle.

  10. Implementing a Matrix-free Analytical Jacobian to Handle Nonlinearities in Models of 3D Lithospheric Deformation

    Science.gov (United States)

    Kaus, B.; Popov, A.

    2015-12-01

    The analytical expression for the Jacobian is a key component to achieve fast and robust convergence of the nonlinear Newton-Raphson iterative solver. Accomplishing this task in practice often requires a significant algebraic effort. Therefore it is quite common to use a cheap alternative instead, for example by approximating the Jacobian with a finite difference estimation. Despite its simplicity it is a relatively fragile and unreliable technique that is sensitive to the scaling of the residual and unknowns, as well as to the perturbation parameter selection. Unfortunately no universal rule can be applied to provide both a robust scaling and a perturbation. The approach we use here is to derive the analytical Jacobian for the coupled set of momentum, mass, and energy conservation equations together with the elasto-visco-plastic rheology and a marker in cell/staggered finite difference method. The software project LaMEM (Lithosphere and Mantle Evolution Model) is primarily developed for the thermo-mechanically coupled modeling of the 3D lithospheric deformation. The code is based on a staggered grid finite difference discretization in space, and uses customized scalable solvers form PETSc library to efficiently run on the massively parallel machines (such as IBM Blue Gene/Q). Currently LaMEM relies on the Jacobian-Free Newton-Krylov (JFNK) nonlinear solver, which approximates the Jacobian-vector product using a simple finite difference formula. This approach never requires an assembled Jacobian matrix and uses only the residual computation routine. We use an approximate Jacobian (Picard) matrix to precondition the Krylov solver with the Galerkin geometric multigrid. Because of the inherent problems of the finite difference Jacobian estimation, this approach doesn't always result in stable convergence. In this work we present and discuss a matrix-free technique in which the Jacobian-vector product is replaced by analytically-derived expressions and compare results

  11. Are Girls Behaving like Boys?

    Science.gov (United States)

    Arnott, Rosie

    2008-01-01

    This article explores some of the issues that have given rise to the perception of an increase in aggressive behaviour by females. It asserts that merely comparing girls' behaviour with that of boys, especially the claim that "girls are behaving like boys", trivialises the very real issues associated with females and aggression. This paper will…

  12. Gravity and magnetic modelling of North Sea basins[Marine and Onshore North Sea Acquisition for Lithospheric Seismic Analysis

    Energy Technology Data Exchange (ETDEWEB)

    Lyngsie, S.B.; Thybo, H. [Copenhagen Univ., Geological Inst. (Denmark)

    2003-07-01

    One of the primary sources of information for interpretation of subsurface geology and large scale tectonic features is potential field data. Gravity and magnetic data may reveal large and small scale features such as basement type, intrusions into the crust, volcanic roks, basement furface, faults and salt structures. As such, this type of data provides an invaluable source of information, which is cimplimentary to seismic data. We are currently conducting a project on interpretation of basins in the North Sea Based on potential field data, constrained by the wealth of existing seismic data. High resolution modelling of gravimetric and magnetic anomalies constrained by seismic P-wave velocity models and normal incidence reflection seismic data may reveal intrinsic details of upper- and lower Palaeozoic basin formation and changes in crustal domains in the Danish North Sea area. The MONA LISA (Marine and Onshore North Sea Acquisition for Lithospheric Seismic Analysis) data set from the south-eastern North Sea (MONA LISA Working Group, 1997) consists of four deep seismic normal incidence reflection profiles recorded to 26 s (twt) and coincident wide-angle reflection/refraction data recorded on 26 onshore mobile seismometers and 29 ocean bottom hydrophones (OBH's) placed along profiles 1,2 and 3. The east-west trending MONA LISA profile 3 traverses the basement high of the Mid North Sea - Ringkoebing Fyn High (MSRFH) and crosses the N-S striking Central Graben (CG) and Horn Graven (HG). (au)

  13. New model of the mantle lithosphere beneath Kuoyka kimberlite field Yakutia.

    Science.gov (United States)

    Ashchepkov, Igor; Kostrovitsky, Sergey; Ovchinnikov, Yury; Tychkov, Nikolai; Khmelnikova, Olga; Palessky, Stanislav

    2013-04-01

    New data for the 11 pipes from Kuoyka field show that high Cr2O3 garnets to 10- 12% as well as high Cr chromites (to 64%Cr2O3) are found in several more pipes Zaozernaya, Seraya, Slyudyanka, Vodorasdelnaya, Titan, Lusya in addition to Djanga pipe. All garnets belong o lherzolite field and not less than 1/3 are TiO rich. The TiO2 rich chromites are dominating in the Cr- rich population. Metasomatic Cr2O3- rich (to 6%) ilmenites pre in the MgO and TiO2- part of the variation diagrams. The Cr- diopside variations show high variations of Fe and Na content to 4 % suggesting the hybridic origin similar to the Cr- pyroxeneis from Obnazhennaya pyroxenites (Taylor et al ., 2003). Omphicites (to 7 % Na2O) are rare. Cr-amphiboles (pargasites and hornblendes) are common in the upper part of the SCLM as well as in the Anabar and Kharamai region. Reconstructions of the mantle sections show the deep lithospheric roots beneath the Zosernaya pipe (7.5 GPa) traced by the PT conditions for Opx, Cpx, Gar, Cr and Ilm. SCLM is divided in to 4 sections and Ilm trace tow intervals in lower and upper part form 4 GPa. Th HT branch is sporadically found from 7 GPa to the Moho. In other pipes ilmenite and garnet PT estimates are more common in the lower part o mantle section while the Cpx trace mainly middle part of SCLM similar to the Obnazhennaya pip. It seems that kimberlites captured mainly the walls of feeders traced by Cr- low garnets and ilmenites in the lower part of SCLM while peridotitic mantle column was captured starting from the middle part of SCLM. The NS transsect of the Kuoyka field show more fertile mantle sections in the NNW part of the field. The TRE determined for the minerals from Kuoyka field show rather rounded patterns for REE of garnets with high variations in HREE part and small elevation in LREE . The depleted compositions reval the inflection in Eu TRE spidergrams well as relatively small Sr minima. Many of them show Ta peak, relatively small Pb elevation and Th

  14. Influence of the inherited lithospheric structure on the interaction between the Kenyan and Ethiopian rifts across the Turkana depression: analog and numerical models

    Science.gov (United States)

    Corti, Giacomo; Brune, Sascha; Ranalli, Giorgio

    2017-04-01

    Rifting processes result from the application of extensional stresses to a pre-deformed, and thus already structured, anisotropic lithosphere; consequently, the pre-rift lithospheric rheological structure and its along-axis variations play a major role in controlling the evolution and architecture of continental rifts. The East African Rift is a classic example of this process. The rift system developed within a region that has experienced several deformation events, which have given rise to significant variations in the rheological structure of the lithosphere. These variations -in turn- have played a major role on rift evolution, as clearly testified by the localisation and propagation of major rift segments within weak Proterozoic mobile belts surrounding cratonic areas. Linkage and mechanical interaction between adjacent rift segments typically occurred in correspondence to transverse pre-existing fabrics, where structurally complex areas (transfer zones) allowed significant along-axis variations in subsidence of grabens and elevation of uplifted flanks. One of these complex areas is the Turkana depression where the Ethiopian and Kenyan rifts interact. The region is characterised by anomalous morphology and distribution of deformation with respect to the rift valleys in Kenya and Ethiopia. In this work we investigate whether these anomalies result from the presence of a pre-existing Mesozoic graben, transverse to the trend of the rift valleys and characterized by thin crust and lithosphere. To this aim, we integrate crustal-scale, isothermal analog experiments with lithospheric-scale, thermo-mechanical numerical models. The two different methodologies generate very similar results, reproducing the along-axis transition from narrow rift valleys in Ethiopia/Kenya to a distributed deformation within the Turkana depression. Modeling results indicate that this variation results from the inherited distribution of lithospheric strength and -in particular- from the

  15. Resolution of direction of oceanic magnetic lineations by the sixth-generation lithospheric magnetic field model from CHAMP satellite magnetic measurements

    Science.gov (United States)

    Maus, S.; Yin, F.; Lühr, H.; Manoj, C.; Rother, M.; Rauberg, J.; Michaelis, I.; Stolle, C.; Müller, R. D.

    2008-07-01

    The CHAMP satellite continues to provide highly accurate magnetic field measurements from decreasing orbital altitudes (<350 km) at solar minimum conditions. Using the latest 4 years (2004-2007) of readings from the CHAMP fluxgate magnetometer, including an improved scalar data product, we have estimated the lithospheric magnetic field to spherical harmonic degree 120, corresponding to 333 km wavelength resolution. The data were found to be sensitive to crustal field variations up to degree 150 (down to 266 km wavelength), but a clean separation of the lithospheric signal from ionospheric and magnetospheric noise sources was achieved only to degree 120. This new MF6 model is the first satellite-based magnetic model to resolve the direction of oceanic magnetic lineations, revealing the age structure of oceanic crust.

  16. DECOUPLED ACCOMMODATION OF CONVERGENCE BETWEEN AFRICA AND EURASIA. MODELLING THE LITHOSPHERIC STRUCTURE ACROSS THE GORRINGE BANK AND THE NW MOROCCAN MARGIN

    Science.gov (United States)

    Jimenez-Munt, I.; Fernandez, M.; Verges, J.; Garcia-Castellanos, D.; Perez-Gussinye, M.; Afonso, J.; Fullea, J.

    2009-12-01

    We have modelled the lithospheric structure across the NW Moroccan margin using an integrated methodology that combines elevation, heat flow, gravity, geoid and seismic data. The modelled profile is 1360 km long and extends NW-SE from the Iberian Abyssal Plane to the Sahara Platform, crossing the Gorringe Bank, the west Iberian-Africa plate boundary, the Moroccan continental margin, and the Atlas Mountains. Offshore, the profile coincides with the IAM-4 and SISMAR-04 deep seismic profiles whereas onshore, where no seismic data are available, it follows previous modelled lithospheric profiles. The present configuration of the Gorringe Bank is explained by a subcrustal NW-directed thrust carrying exhumed upper mantle rocks and transitional African crust on top of flexed-down Eurasian oceanic crust along the Tagus Abyssal Plain. This is the result of a long-lasting evolution related to the African and Eurasian plate boundary characterized by: (1) Late Jurassic-Early Cretaceous extension with mantle exhumation, intrusion of gabbros, and mantle serpentinization; (2) early Miocene compression, which produced ~20 km of NW-directed thrusting of serpentinized upper mantle rocks and African transitional crust on top of the Eurasian oceanic crust and sedimentary cover. In the Moroccan continental margin, the most outstanding result is a prominent lithospheric thickening with thickness values of around 210 km. This thickening is the result of applying the crustal and density structure proposed from SISMAR survey. Assuming that this thickening is gained by plate convergence, our calculations predict a minimum shortening of 140 km in the lithospheric mantle affecting a 400 km wide region. Meanwhile, at crustal levels, the Africa-Iberia convergence has been accommodated in a wider area (at least of 900 km) with an observed shortening of only ~ 60 km. This model shows a clear decoupled accommodation of the Africa-Eurasia convergence and put additional constraints on the regional

  17. Understanding the interplays between Earth's shallow- and deep- rooted processes through global, quantitative model of the coupled brittle-lithosphere/viscous mantle system

    Science.gov (United States)

    Stotz, Ingo; Iaffaldano, Giampiero; Rhodri Davies, D.

    2016-04-01

    The volume of geophysical datasets has grown substantially, over recent decades. Our knowledge of continental evolution has increased due to advances in interpreting the records of orogeny and sedimentation. Ocean-floor observations now allow one to resolve past plate motions (e.g. in the North Atlantic and Indian Ocean over the past 20 Myr) at temporal resolutions of about 1 Myr. Altogether, these ever-growing datasets permit reconstructing the past evolution of Earth's lithospheric plates in greater detail. This is key to unravelling the dynamics of geological processes, because plate motions and their temporal changes are a powerful probe into the evolving force balance between shallow- and deep-rooted processes. However, such a progress is not yet matched by the ability to quantitatively model past plate-motion changes and, therefore, to test hypotheses on the dominant controls. The main technical challenge is simulating the rheological behaviour of the lithosphere/mantle system, which varies significantly from viscous to brittle. Traditionally computer models for viscous mantle flow and on the one hand, and for the motions of the brittle lithosphere on the other hand, have been developed separately. Coupling of these two independent classes of models has been accomplished only for neo-tectonic scenarios and with some limitations as to accounting for the impact of time-evolving mantle-flow and lithospheric slabs. Here we present results in this direction that permit simulating the coupled plates/mantle system through geological time. We build on previous work aimed at coupling two sophisticated codes for mantle flow and lithosphere dynamics: TERRA and SHELLS. TERRA is a global spherical finite-element code for mantle convection. It has been developed by Baumgardner (1985) and Bunge et al. (1996), and further advanced by Yang (1997; 2000) and Davies et al. (2013), among others. SHELLS is a thin-sheet finite-element code for lithosphere dynamics, developed by

  18. Rifting Thick Lithosphere - Canning Basin, Western Australia

    Science.gov (United States)

    Czarnota, Karol; White, Nicky

    2016-04-01

    The subsidence histories and architecture of most, but not all, rift basins are elegantly explained by extension of ~120 km thick lithosphere followed by thermal re-thickening of the lithospheric mantle to its pre-rift thickness. Although this well-established model underpins most basin analysis, it is unclear whether the model explains the subsidence of rift basins developed over substantially thick lithosphere (as imaged by seismic tomography beneath substantial portions of the continents). The Canning Basin of Western Australia is an example where a rift basin putatively overlies lithosphere ≥180 km thick, imaged using shear wave tomography. Subsidence modelling in this study shows that the entire subsidence history of the Canning Basin is adequately explained by mild Ordovician extension (β≈1.2) of ~120 km thick lithosphere followed by post-rift thermal subsidence. This is consistent with the established model, described above, albeit with perturbations due to transient dynamic topography support which are expressed as basin-wide unconformities. In contrast the Canning Basin reveals an almost continuous period of normal faulting between the Ordovician and Carboniferous (βCanning Basin to rifting of thick lithosphere beneath the eastern part, verified by the presence of ~20 Ma diamond-bearing lamproites intruded into the basin depocentre. In order to account for the observed subsidence, at standard crustal densities, the lithospheric mantle is required to be depleted in density by 50-70 kg m-3, which is in line with estimates derived from modelling rare-earth element concentrations of the ~20 Ma lamproites and global isostatic considerations. Together, these results suggest that thick lithosphere thinned to > 120 km is thermally stable and is not accompanied by post-rift thermal subsidence driven by thermal re-thickening of the lithospheric mantle. Our results show that variations in lithospheric thickness place a fundamental control on basin architecture

  19. Seismic anisotropy of the lithosphere and asthenosphere beneath southern Madagascar from teleseismic shear wave splitting analysis and waveform modeling

    Science.gov (United States)

    Reiss, M. C.; Rümpker, G.; Tilmann, F.; Yuan, X.; Giese, J.; Rindraharisaona, E. J.

    2016-09-01

    Madagascar occupies a key position in the assembly and breakup of the supercontinent Gondwana. It has been used in numerous geological studies to reconstruct its original position within Gondwana and to derive plate kinematics. Seismological observations in Madagascar to date have been sparse. Using a temporary, dense seismic profile across southern Madagascar, we present the first published study of seismic anisotropy from shear wave splitting analyses of teleseismic phases. The splitting parameters obtained show significant small-scale variation of fast polarization directions and delay times across the profile, with fast polarization rotating from NW in the center to NE in the east and west of the profile. The delay times range between 0.4 and 1.5 s. A joint inversion of waveforms at each station is applied to derive hypothetical one-layer splitting parameters. We use finite-difference, full-waveform modeling to test several hypotheses about the origin and extent of seismic anisotropy. Our observations can be explained by asthenospheric anisotropy with a fast polarization direction of 50°, approximately parallel to the absolute plate motion direction, in combination with blocks of crustal anisotropy. Predictions of seismic anisotropy as inferred from global mantle flow models or global anisotropic surface wave tomography are not in agreement with the observations. Small-scale variations of splitting parameters require significant crustal anisotropy. Considering the complex geology of Madagascar, we interpret the change in fast-axis directions as a 150 km wide zone of ductile deformation in the crust as a result of the intense reworking of lithospheric material during the Pan-African orogeny. This fossil anisotropic pattern is underlain by asthenospheric anisotropy induced by plate motion.

  20. Lithosphere tectonics and thermo-mechanical properties: An integrated modeling approach for enhanced geothermal systems exploration in Europe

    NARCIS (Netherlands)

    Wees, J.D. van; Cloetingh, S.; Ziegler, P.A.; Lenkey, L.; Beekman, F.; Tesauro, M.; Förster, A.; Norden, B.; Kaban, M.; Hardebol, N.; Voorde, M.T.; Willingshofer, E.; Cornu, T.; Bonté, D.

    2009-01-01

    For geothermal exploration and the development of enhanced geothermal systems (EGS) knowlegde of temperature at drillable depth is a prerequisite for site selection. Equally important is the thermo-mechanical signature of the lithosphere and crust which allow to obtain critical constraints for the c

  1. Lithosphere tectonics and thermo-mechanical properties: An integrated modeling approach for enhanced geothermal systems exploration in Europe

    NARCIS (Netherlands)

    Wees, J.D. van; Cloetingh, S.; Ziegler, P.A.; Lenkey, L.; Beekman, F.; Tesauro, M.; Förster, A.; Norden, B.; Kaban, M.; Hardebol, N.; Voorde, M.T.; Willingshofer, E.; Cornu, T.; Bonté, D.

    2009-01-01

    For geothermal exploration and the development of enhanced geothermal systems (EGS) knowlegde of temperature at drillable depth is a prerequisite for site selection. Equally important is the thermo-mechanical signature of the lithosphere and crust which allow to obtain critical constraints for the c

  2. LITHO1.0: An Updated Crust and Lithosphere Model of the Earth

    Science.gov (United States)

    2010-09-01

    A. M., S. Bloch, and M. Landisman (1969). A technique for the analysis of transient seismic signals. Bull. Seism . Soc. Am. 59: 427^44. Durek, J. and...G. Ekstrom (1996). A radial model of anelasticity consistent with long-period surface-wave attenuation, Bull. Seism . Soc. Am. 86: 144 158. Goes, S...Peculiarities of surface wave propagation across central Eurasia, Bull. Seism . Soc. Am. 82: 2464 2493. Levshin, A. L., M. H. Ritzwoller, and J. Resovsky

  3. MAIN REGULARITIES OF FAULTING IN LITHOSPHERE AND THEIR APPLICATION (BASED ON PHYSICAL MODELLING RESULTS

    Directory of Open Access Journals (Sweden)

    S. A. Bornyakov

    2015-09-01

    Full Text Available Results of long-term experimental studies and modelling of faulting are briefly reviewed, and research methods and the-state-of-art issues are described. The article presents the main results of faulting modelling with the use of non-transparent elasto-viscous plastic and optically active models. An area of active dynamic influence of fault (AADIF is the term introduced to characterise a fault as a 3D geological body. It is shown that AADIF's width (М is determined by thickness of the layer wherein a fault occurs (Н, its viscosity (η and strain rate (V. Multiple correlation equations are proposed to show relationships between AADIF's width (М, H, η and V for faults of various morphological and genetic types. The irregularity of AADIF in time and space is characterised in view of staged formation of the internal fault structure of such areas and geometric and dynamic parameters of AADIF which are changeable along the fault strike. The authors pioneered in application of the open system conception to find explanations of regularities of structure formation in AADIFs. It is shown that faulting is a synergistic process of continuous changes of structural levels of strain, which differ in manifestation of specific self-similar fractures of various scales. Such levels are changeable due to self-organization processes of fracture systems. Fracture dissipative structures (FDS is the term introduced to describe systems of fractures that are subject to self-organization. It is proposed to consider informational entropy and fractal dimensions in order to reveal FDS in AADIF. Studied are relationships between structure formation in AADIF and accompanying processes, such as acoustic emission and terrain development above zones wherein faulting takes place. Optically active elastic models were designed to simulate the stress-and-strain state of AADIF of main standard types of fault jointing zones and their analogues in nature, and modelling results are

  4. Earthquake focal parameters and lithospheric structure of the anatolian plateau from complete regional waveform modeling

    Energy Technology Data Exchange (ETDEWEB)

    Rodgers, A

    2000-12-28

    This is an informal report on preliminary efforts to investigate earthquake focal mechanisms and earth structure in the Anatolian (Turkish) Plateau. Seismic velocity structure of the crust and upper mantle and earthquake focal parameters for event in the Anatolian Plateau are estimated from complete regional waveforms. Focal mechanisms, depths and seismic moments of moderately large crustal events are inferred from long-period (40-100 seconds) waveforms and compared with focal parameters derived from global teleseismic data. Using shorter periods (10-100 seconds) we estimate the shear and compressional velocity structure of the crust and uppermost mantle. Results are broadly consistent with previous studies and imply relatively little crustal thickening beneath the central Anatolian Plateau. Crustal thickness is about 35 km in western Anatolia and greater than 40 km in eastern Anatolia, however the long regional paths require considerable averaging and limit resolution. Crustal velocities are lower than typical continental averages, and even lower than typical active orogens. The mantle P-wave velocity was fixed to 7.9 km/s, in accord with tomographic models. A high sub-Moho Poisson's Ratio of 0.29 was required to fit the Sn-Pn differential times. This is suggestive of high sub-Moho temperatures, high shear wave attenuation and possibly partial melt. The combination of relatively thin crust in a region of high topography and high mantle temperatures suggests that the mantle plays a substantial role in maintaining the elevation.

  5. Lithospheric deformation and mantle/crust coupling related to slab roll-back and tearing processes: the role of magma-related rheological weakening highlighted by 3D numerical modeling

    Science.gov (United States)

    Menant, Armel; Jolivet, Laurent; Guillou-Frottier, Laurent; Sternai, Pietro; Gerya, Taras

    2016-04-01

    Active convergent margins are the locus of various large-scale lithospheric processes including subduction, back-arc opening, lithospheric delamination, slab tearing and break-off. Coexistence of such processes results in a complex lithospheric deformation pattern through the rheological stratification of the overriding lithosphere. In this context, another major feature is the development of an intense arc- and back-arc-related magmatism whose effects on lithospheric deformation by rheological weakening are largely unknown. Quantifying this magma-related weakening effect and integrating the three-dimensional (3D) natural complexity of subduction system is however challenging because of the large number of physico-chemical processes involved (e.g. heat advection, dehydration of subducted material, partial melting of the mantle wedge). We present here a set of 3D high-resolution petrological and thermo-mechanical numerical experiments to assess the role of low-viscosity magmatic phases on lithospheric deformation associated with coeval oceanic and continental subduction, followed by slab retreat and tearing processes. Results in terms of crustal kinematics, patterns of lithospheric deformation and distribution and composition of magmatic phases are then compared to a natural example displaying a similar geodynamical evolution: the eastern Mediterranean subduction zone. Our modeling results suggest that the asthenospheric flow controls the ascending trajectories of mantle-derived magmatic sources developed in the mantle wedge in response to dehydration of oceanic slab. Once stored at the base of the overriding continental crust, low-viscosity mantle- and crustal-derived magmatic phases allow to decrease the lithospheric strength. This weakening then enhances the propagation of localized extensional and strike-slip deformation in response to slab roll-back and extrusion tectonics respectively. In addition, we show that storage of large amounts of low-viscosity magmas

  6. Lithospheric Structure and Active Deformation in the Salton Trough from Coseismic and Postseismic Models of the 2010 Mw 7.2 El Mayor-Cucapah Earthquake

    Science.gov (United States)

    Fielding, E. J.; Huang, M. H.; Dickinson, H.; Freed, A. M.; Burgmann, R.; Gonzalez-Ortega, J. A.; Andronicos, C.

    2016-12-01

    The 4 April 2010 Mw 7.2 El Mayor-Cucapah (EMC) Earthquake ruptured about 120 km along several NW-striking faults to the west of the Cerro Prieto Fault in the Salton Trough of Baja California, Mexico. We analyzed interferometric synthetic aperture radar (SAR), SAR and optical pixel offsets, and continuous and campaign GPS data to optimize an EMC coseismic rupture model with 9 fault segments, which fits the complex structure of the faults. Coseismic slip inversion with a layered elastic model shows that largely right-lateral slip is confined to upper 10 km with strong variations along strike. Near-field GPS measures slip on a north-striking normal fault that ruptured at the beginning of the earthquake, previously inferred from seismic waveforms. EMC Earthquake postseismic deformation shows the Earth's response to the large coseismic stress changes. InSAR shows rapid shallow afterslip at the north and south ends of the main ruptures. Continuous GPS from the Plate Boundary Observatory operated by UNAVCO measures the first six years of postseismic deformation, extremely rapid near the rupture. Afterslip on faults beneath the coseismic rupture cannot explain far-field displacements that are best explained by viscoelastic relaxation of the lower crust and upper mantle. We built a viscoelastic 3D finite element model of the lithosphere and asthenosphere based on available data for the region with the EMC coseismic faults embedded inside. Coseismic slip was imposed on the model, allowed to relax for 5 years, and then compared to the observed surface deformation. Systematic exploration of the viscoelastic parameters shows that horizontal and vertical heterogeneity is required to fit the postseismic deformation. Our preferred viscoelastic model has weaker viscosity layers beneath the Salton Trough than adjacent blocks that are consistent with the inferred differences in the geotherms. Defining mechanical lithosphere as rocks that have viscosities greater than 10^19 Pa s (able

  7. Electrical Conductivity Model of the Mantle Lithosphere of the Slave Craton (NW Canada) and its tectonic interpretation in the context of Geochemical Results

    Science.gov (United States)

    Lezaeta, P.; Chave, A.; Evans, R.; Jones, A. G.; Ferguson, I.

    2002-12-01

    The Slave Craton, northwestern Canada, contains the oldest known rocks on Earth, with exposed outcrop over an area of about 600x400 km2. The discovery of economic diamondiferous kimberlite pipes during the early 1990s motivated extensive research in the region. Over the last six years, four types of deep-probing magnetotelluric (MT) surveys were conducted within the framework of diverse geoscientific programs, aimed at determining the regional-scale electrical structures of the craton. Two of the surveys involved novel acquisition; one through frozen lake ice along ice roads during winter, and the second deploying ocean-bottom instrumentation from float planes during summer. The latter surveys required one year of recording between summers, thus allowing long period transfer functions that lead to mantle penetration depths of over 300 km. Two-dimensional modeling of the MT data from along the winter road showed the existence of a high conductivity zone at depths of 80-120 km beneath the central Slave craton. This anomalous region is spatially coincident with an ultradepleted harzburgitic layer in the upper mantle that was interpreted by others to be related to a subducted slab emplaced during the mid-Archean. A 3-D electrical conductivity model of the Slave lithosphere has been obtained, by trial and error, to fit the magnetic transfer and MT response functions from the lake experiments. This 3-D model traces the central Slave conductor as a NE-SW oriented mantle structure. Its NE-SW orientation coincides with that of a late fold belt system, with the first phase of craton-wide plutonism at ca 2630-2590 Ma, three-part subdivision of the craton based on SKS results, and with a G10 (garnet) geochemical mantle boundaries. All of these highlight a NE-SW structural grain to the lithospheric mantle of the craton, in sharp contrast to the N-S grain of the crust. Constraints on the depth range and lateral extension of the electrical conductive structure are obtained

  8. Water based on a molecular model behaves like a hard-sphere solvent for a nonpolar solute when the reference interaction site model and related theories are employed

    Science.gov (United States)

    Hayashi, Tomohiko; Oshima, Hiraku; Harano, Yuichi; Kinoshita, Masahiro

    2016-09-01

    For neutral hard-sphere solutes, we compare the reduced density profile of water around a solute g(r), solvation free energy μ, energy U, and entropy S under the isochoric condition predicted by the two theories: dielectrically consistent reference interaction site model (DRISM) and angle-dependent integral equation (ADIE) theories. A molecular model for water pertinent to each theory is adopted. The hypernetted-chain (HNC) closure is employed in the ADIE theory, and the HNC and Kovalenko-Hirata (K-H) closures are tested in the DRISM theory. We also calculate g(r), U, S, and μ of the same solute in a hard-sphere solvent whose molecular diameter and number density are set at those of water, in which case the radial-symmetric integral equation (RSIE) theory is employed. The dependences of μ, U, and S on the excluded volume and solvent-accessible surface area are analyzed using the morphometric approach (MA). The results from the ADIE theory are in by far better agreement with those from computer simulations available for g(r), U, and μ. For the DRISM theory, g(r) in the vicinity of the solute is quite high and becomes progressively higher as the solute diameter d U increases. By contrast, for the ADIE theory, it is much lower and becomes further lower as d U increases. Due to unphysically positive U and significantly larger |S|, μ from the DRISM theory becomes too high. It is interesting that μ, U, and S from the K-H closure are worse than those from the HNC closure. Overall, the results from the DRISM theory with a molecular model for water are quite similar to those from the RSIE theory with the hard-sphere solvent. Based on the results of the MA analysis, we comparatively discuss the different theoretical methods for cases where they are applied to studies on the solvation of a protein.

  9. A comparison of surface wave tomography in the Atlantic Ocean with the plate model: mismatches and implications for the lithosphere-asthenosphere system

    Science.gov (United States)

    Fishwick, S.; Crosby, A. G.

    2009-12-01

    The oceans should be one of the most straightforward regions within which to investigate the lithosphere-asthenosphere boundary, because their thermal structure appears to be so simple. However, this assertion assumes our present understanding of the oceanic lithosphere is correct, which is derived principally from observations of heat flow and subsidence beneath the ocean floor. These observations show large positive deviations from half-space cooling models after 60-80 Ma, which indicate that conductive cooling does not continue forever as the plate moves away from the ridge. Instead, data from the oldest ocean floor are better fit by a thermal plate model with a thickness of 90-100 km, which is gently modulated by convection within the upper mantle. The physical interpretation of the fixed temperature basal boundary condition is that heat is supplied to the base of the plate by small-scale convection in the thermal boundary layer underlying the rigid lid. We compare the expected shear velocities given the plate cooling model with the velocities observed from surface wave tomography. Tomographic data sets for both Africa and South America have been combined to place constraints on the velocity structure beneath the Atlantic Ocean. The velocities observed in the tomography are faster than expected at lithospheric depths, and an age-velocity relationship continues to around 125km - a depth at which the plate model predicts uniform temperatures. Some aspect of these discrepancies could be due to the vertical parameterisation and smearing within the surface wave tomography. To test this possibility, we compare the dispersion characteristics for the theoretical model with the surface wave dispersion data, and also observe a similar mismatch. A more likely source of error is the conversion between velocity and temperature, particularly given our limited knowledge of the attenuation structure of the region. These results have important implications for our understanding

  10. Crustal response to lithosphere evolution

    DEFF Research Database (Denmark)

    Artemieva, Irina; Thybo, Hans; Cherepanova, Yulia;

    2012-01-01

    We present a new model for the structure of the crust in an area which stretches from the North Atlantic region in the west to the Verkhoyansk Ridge in the east and encompasses Greenland, Iceland, most of Europe, West Siberian basin, and the Siberian cratons. The model is based on critically...... such as lower crust/lithospheric mantle delamination in the Variscan Europe and large-scale rifting across the entire West Siberian basin. The results are summarized in a series of maps of lateral variations in crustal properties, including the depth to the basement and to the Moho, average crustal velocity......, thicknesses of different crustal layers, and Pn seismic velocities....

  11. Lithospheric cooling as a basin forming mechanism within accretionary crust.

    Science.gov (United States)

    Holt, P. J.; Allen, M.; van Hunen, J.; Björnseth, H. M.

    2009-04-01

    Widely accepted basin forming mechanisms are limited to flexure of the lithosphere, lithospheric stretching, lithospheric cooling following rifting and, possibly, dynamic topography. In this work forward models have been used to investigate lithospheric growth due to cooling beneath accretionary crust, as a new basin forming mechanism. Accretionary crust is formed from collision of island arcs, accretionary complexes and fragments of reworked older crust at subduction zones, and therefore has thin lithosphere due to melting and increased convection. This is modeled using a 1D infinite half space cooling model similar to lithospheric cooling models for the oceans. The crustal composition and structure used in the models has been varied around average values of accretionary crust to represent the heterogeneity of accretionary crust. The initial mantle lithosphere thickness used in the model was 20 km. The model then allows the lithosphere to thicken as it cools and calculates the subsidence isostatically. The model produces sediment loaded basins of 2-7 km for the various crustal structures over 250 Myrs. Water-loaded tectonic subsidence curves from the forward models were compared to tectonic subsidence curves produced from backstripping wells from the Kufrah and Ghadames basins, located on the accretionary crust of North Africa. A good match between the subsidence curves for the forward model and backstripping is produced when the best estimates for the crustal structure, composition and the present day thickness of the lithosphere for North Africa are used as inputs for the forward model. This shows that lithospheric cooling provides a good method for producing large basins with prolonged subsidence in accretionary crust without the need for initial extension.

  12. A lithospheric cross-section in the eastern Iberian Peninsula and its margins. Modelling the physical properties of the upper mantle; Corte litosferico al Este de la Peninsula Iberica y sus margenes. Modelizacion de las propiedades fisicas del manto superior

    Energy Technology Data Exchange (ETDEWEB)

    Carballo, A.; Fernandez, M.; Jimenez-Munt, I.

    2011-07-01

    We study the lithosphere structure along a 1700 km transect crossing the Aquitaine basin, Pyrenees, Ebro basin, Catalan Costal Ranges, Valencia Trough, Balearic Promontory, and Sudbalearic basin, and Kabyles, Tell, Atlas, and Saharan Platform in Africa. The objective is to characterize the structure and composition of the lthospheric mantle in the region, using a method (LitMod) that combines elevation, gravity, geoid, surface heat flow, seismic and petrological data. Using this method we can identify along the profile different mantle composition, derived from geochemical analysis and age. This is the main different with the previous model done in the same area, where lithospheric mantle density just varied with temperature. The results obtained with the LitMod methodology show important differences in geometry and depth of the lithosphere-asthenosphere boundary with the previous model. In the present study we had to consider four different lithopheric mantle compositions in order to fit all the observables. (Author) 18 refs.

  13. The lithospheric-scale 3D structural configuration of the North Alpine Foreland Basin constrained by gravity modelling and the calculation of the 3D load distribution

    Science.gov (United States)

    Przybycin, Anna M.; Scheck-Wenderoth, Magdalena; Schneider, Michael

    2014-05-01

    The North Alpine Foreland Basin is situated in the northern front of the European Alps and extends over parts of France, Switzerland, Germany and Austria. It formed as a wedge shaped depression since the Tertiary in consequence of the Euro - Adriatic continental collision and the Alpine orogeny. The basin is filled with clastic sediments, the Molasse, originating from erosional processes of the Alps and underlain by Mesozoic sedimentary successions and a Paleozoic crystalline crust. For our study we have focused on the German part of the basin. To investigate the deep structure, the isostatic state and the load distribution of this region we have constructed a 3D structural model of the basin and the Alpine area using available depth and thickness maps, regional scale 3D structural models as well as seismic and well data for the sedimentary part. The crust (from the top Paleozoic down to the Moho (Grad et al. 2008)) has been considered as two-parted with a lighter upper crust and a denser lower crust; the partition has been calculated following the approach of isostatic equilibrium of Pratt (1855). By implementing a seismic Lithosphere-Asthenosphere-Boundary (LAB) (Tesauro 2009) the crustal scale model has been extended to the lithospheric-scale. The layer geometry and the assigned bulk densities of this starting model have been constrained by means of 3D gravity modelling (BGI, 2012). Afterwards the 3D load distribution has been calculated using a 3D finite element method. Our results show that the North Alpine Foreland Basin is not isostatically balanced and that the configuration of the crystalline crust strongly controls the gravity field in this area. Furthermore, our results show that the basin area is influenced by varying lateral load differences down to a depth of more than 150 km what allows a first order statement of the required compensating horizontal stress needed to prevent gravitational collapse of the system. BGI (2012). The International

  14. Lithospheric strength and elastic thickness of the Barents Sea and Kara Sea region

    Science.gov (United States)

    Gac, Sébastien; Klitzke, Peter; Minakov, Alexander; Faleide, Jan Inge; Scheck-Wenderoth, Magdalena

    2016-11-01

    Interpretation of tomography data indicates that the Barents Sea region has an asymmetric lithospheric structure characterized by a thin and hot lithosphere in the west and a thick and cold lithosphere in the east. This suggests that the lithosphere is stronger in the east than in the west. This asymmetric lithosphere strength structure may have a strong control on the lithosphere response to tectonic and surface processes. In this paper, we present computed strength and effective elastic thickness maps of the lithosphere of the Barents Sea and Kara Sea region. Those are estimated using physical parameters from a 3D lithospheric model of the Barents Sea and Kara Sea region. The lithospheric strength is computed assuming a temperature-dependent ductile and brittle rheology for sediments, crust and mantle lithosphere. Results show that lithospheric strength and elastic thickness are mostly controlled by the lithosphere thickness. The model generally predicts much larger lithospheric strength and elastic thickness for the Proterozoic parts of the East Barents Sea and Kara Sea. Locally, the thickness and lithology of the continental crust disturb this general trend. At last, the gravitational potential energy (GPE) is computed. Our results show that the difference in GPE between the Barents Sea and the Mid-Atlantic Ridge provides a net horizontal force large enough to cause contraction in the western and central Barents Sea.

  15. BASE Flexible Array Preliminary Lithospheric Structure Analysis

    Science.gov (United States)

    Yeck, W. L.; Sheehan, A. F.; Anderson, M. L.; Siddoway, C. S.; Erslev, E.; Harder, S. H.; Miller, K. C.

    2009-12-01

    The Bighorns Arch Seismic Experiment (BASE) is a Flexible Array experiment integrated with EarthScope. The goal of BASE is to develop a better understanding of how basement-involved foreland arches form and what their link is to plate tectonic processes. To achieve this goal, the crustal structure under the Bighorn Mountain range, Bighorn Basin, and Powder River Basin of northern Wyoming and southern Montana are investigated through the deployment of 35 broadband seismometers, 200 short period seismometers, 1600 “Texan” instruments using active sources and 800 “Texan” instruments monitoring passive sources, together with field structural analysis of brittle structures. The novel combination of these approaches and anticipated simultaneous data inversion will give a detailed structural crustal image of the Bighorn region at all levels of the crust. Four models have been proposed for the formation of the Bighorn foreland arch: subhorizontal detachment within the crust, lithospheric buckling, pure shear lithospheric thickening, and fault blocks defined by lithosphere-penetrating thrust faults. During the summer of 2009, we deployed 35 broadband instruments, which have already recorded several magnitude 7+ teleseismic events. Through P wave receiver function analysis of these 35 stations folded in with many EarthScope Transportable Array stations in the region, we present a preliminary map of the Mohorovicic discontinuity. This crustal map is our first test of how the unique Moho geometries predicted by the four hypothesized models of basement involved arches fit seismic observations for the Bighorn Mountains. In addition, shear-wave splitting analysis for our first few recorded teleseisms helps us determine if strong lithospheric deformation is preserved under the range. These analyses help lead us to our final goal, a complete 4D (3D spatial plus temporal) lithospheric-scale model of arch formation which will advance our understanding of the mechanisms

  16. Subduction Stability: Lithospheric Strength and Roll-back

    Science.gov (United States)

    Patel, P. I.; Lavier, L.; Grand, S.

    2007-12-01

    In exploring the issue of subduction zone stability, we ran a series of simulations representing subduction systems consisting of simple 2D representations of oceanic lithosphere subducting beneath continental lithosphere. Our modelling software utilizes temperature dependent visco-elasto-plastic rheologies as well as a few proxies for significant chemical processes such as ecologitization and hydration. With externally imposed convergence rates, these models evolve from a contrived subduction initiation state to "normal-looking" subduction within approximately 10 million years. The simulations are then allowed to continue to evolve for up to 30 million more years. From our early results, we note that while most systems start with similar subduction geometries, they may deviate from each other over time. Notably, subduction initiated at "cooler" (and therefore stronger) junctures tend to form very stable subduction zones which maintain normal-looking geometries throughout the life of the simulation. However, subduction initiated at warmer margins tend to result in slab rollback relatively quickly. Systems with junctures of intermediate temperature also tend to subduct stably for a substantial amount of time, yet they too eventually result in rollback as the subducting slab entrains and removes some of the cooler lithosphere near the juncture, allowing hotter asthenospheric material into the contact region between the plates. The hot, low-viscosity material sharply reduces the fluid-dynamically derived suction force that partially supports the stable subduction geometry, facilitating the retreat of the subducting slab as well as the rifting of the over-riding slab. These simulations incorporate a variety of approximations and assumptions which may not reflect the actual conditions within the Earth. However, they do offer a chance to observe how a system that at least appears geometrically similar to observed Earth systems may behave when subjected to varying

  17. CHAMP, SWARM, and WDMAM magnetic data; three reasons for further developing techniques for modeling the lithospheric magnetic field at regional scales

    Science.gov (United States)

    Thebault, E.; Vervelidou, F.

    2012-04-01

    The spatial resolution of all available data monitoring the Earth's lithospheric magnetic field range from thousands to few kilometers at the regional spatial scale. The data type and measurement platforms covering these various wavelengths are in general different. For instance, Low Earth Orbiting satellites, such as CHAMP and the forthcoming SWARM, measure the vector field and are sensitive to large-scale and deep lithospheric magnetic field structures, while aeromagnetic and marine data or grids, like the World Digital Magnetic Anomaly Map (WDMAM), which are mostly scalar, in general fetch better shallow and small spatial scale signals. For quantitative geophysical interpretations, there is therefore a need for methodologies allowing for the reconstruction of the full magnetic field spectrum. During the last decades, various methodologies have been proposed in an effort to merge all kinds of magnetic data available over particular regions. We first briefly review the methods proposed by the scientific community and will more specifically focus on new progresses in developing the Revised Spherical Cap modeling approach. In particular, we will discuss the concept of spectrum with this formalism and its applicability in the framework of geomagnetism. Since a regional modeling approach can only be applied on high quality data we then propose some strategies to first obtain a better signal to noise ratio in satellite data and second to better account for its nature. We will illustrate our conclusions with issues faced with the data processing of single satellite missions such as CHAMP. Finally, we discuss how a constellation such as the Swarm mission will alleviate some of, so far, unresolved problems and how important it is to have the metadata information about the aeromagnetic and marine anomaly data.

  18. Lateral heterogeneity and vertical stratification of cratonic lithospheric keels: examples from Europe, Siberia, and North America

    DEFF Research Database (Denmark)

    Artemieva, Irina; Cherepanova, Yulia; Herceg, Matija;

    The presentation summarizes geophysical models for Precambrian cratons, including the structure of the crust and the lithospheric mantle. A particular focus is on thermo-compositional heterogeneity of the lithospheric mantle as constrained by different geophysical data sets: (i) thermal structure...... by an increase in mantle density as compared to light and strongly depleted lithospheric mantle of the Archean nuclei....

  19. Lithospheric cooling and thickening as a basin forming mechanism

    Science.gov (United States)

    Holt, Peter J.; Allen, Mark B.; van Hunen, Jeroen; Bjørnseth, Hans Morten

    2010-12-01

    Widely accepted basin forming mechanisms are limited to flexure of the lithosphere, and lithospheric stretching followed by cooling and thermal subsidence. Neither of these mechanisms works for a group of large basins, sometimes known as "intracontinental sags". In this paper we investigate cooling and thickening of initially thin lithosphere as a basin forming mechanism, by a combination of forward modelling and a backstripping study of two Palaeozoic North African basins: Ghadames and Al Kufrah. These are two of a family of basins, once unified, which lie over the largely accretionary crust of North Africa and Arabia. Such accretionary crust tends to be juvenile, consisting of amalgamated island arcs, accretionary prisms and melanges, and typically has near-normal crustal thicknesses but initially thin mantle lithosphere. Post-accretion subsidence is modelled using a plate cooling model similar to cooling models for oceanic lithosphere. The crustal composition and thickness used in the models are varied around average values of accretionary crust to represent likely heterogeneity. The model allows the lithosphere to thicken as it cools and calculates the resulting isostatic subsidence. Water-loaded tectonic subsidence curves from these forward models are compared to tectonic subsidence curves produced from backstripped wells from Al Kufrah and Ghadames Basins. A good match between the subsidence curves for the forward model and backstripping is produced when the best estimates for the crustal structure, composition and the present day thickness of the lithosphere for North Africa are used as inputs for the forward model. The model produces sediment loaded basins of 2-7 km thickness for the various crustal assemblies over ~ 250 Myr. This shows that lithospheric cooling provides a viable method for producing large basins with prolonged subsidence, without the need for initial extension, provided the condition of initially thin mantle lithosphere is met.

  20. Folded Lithospheric Basins in Central Asia: Altai-Sayan and Tien Shan basins in a folding lithosphere

    Science.gov (United States)

    Delvaux, Damien; Cloetingh, Sierd; Beekman, Fred; Sokoutis, Dimitrios; Burov, Evguenii; Buslov, Misha; Abdrakhmatov, Kanatbeck

    2014-05-01

    Central Asia is a classic example for continental lithospheric folding. In particular, the Altay-Sayan belt in South-Siberia and the Kyrgyz Tien Shan display a special mode of lithospheric deformation, involving decoupled lithospheric mantle folding and upper crustal folding and faulting. A review of the paleostress data and tectono-stratigraphic evolution of the Kurai-Chuya basin in Siberian Altai, Zaisan basin in Kazakh South Altai and Issyk-Kul basin in Kyrgyz Tien Shan suggests that these basins were initiated in an extensional context and later inverted by a combination of fault-controlled deformation and flexural folding. They deformed by a combination of lithospheric buckling inducing surface tilting, uplift and subsidence, together with upper crustal fault-controlled deformation. They are good examples of Folded Lithospheric Basins (FLB) which typically form in a buckling lithosphere. Their characteristic basin fill and symmetry, inner structure, folding wavelength and amplitude, thermal regime and time frame are examined in relation to basement structure, stress field, strain rate, timing of deformation, and compared to existing modelling results. Both regions of active lithospheric folding have a heterogeneous crust with a long history of accretion-collision, subsequently reactivated as a far-field effect of the Indian-Eurasian collision. Thanks to the youthfulness of the tectonic deformation in this region (peak deformation in late Pliocene - early Pleistocene), the surface expression of lithospheric deformation is well documented by the surface topography and superficial tectonic structures.

  1. Layering of the lithospheric mantle beneath the Siberian Craton: Modeling using thermobarometry of mantle xenolith and xenocrysts

    Science.gov (United States)

    Ashchepkov, I. V.; Vladykin, N. N.; Ntaflos, T.; Kostrovitsky, S. I.; Prokopiev, S. A.; Downes, H.; Smelov, A. P.; Agashev, A. M.; Logvinova, A. M.; Kuligin, S. S.; Tychkov, N. S.; Salikhov, R. F.; Stegnitsky, Yu. B.; Alymova, N. V.; Vavilov, M. A.; Minin, V. A.; Babushkina, S. A.; Ovchinnikov, Yu. I.; Karpenko, M. A.; Tolstov, A. V.; Shmarov, G. P.

    2014-11-01

    Single-grain thermobarometric studies of xenocrysts were used to compile local SCLM transects through the major regions of kimberlite magmatism in Siberia and longer transects through the subcontinental mantle lithosphere (SCLM) beneath the Siberian craton. The mantle structure was obtained using P-Fe#, Ca in garnets, oxygen fugacity values fO2 and calculated temperatures T°C. The most detail transect obtained for the Daldyn field on the Udachnaya-Zarnitsa reveals layering showing an inclination of > 35° to Udachnaya. Mantle layering beneath the Alakit field determined from the Krasnopresnenskaya-Sytykanskaya transect shows a moderate inclination from N to S. The inflection near Yubileinaya-Aykhal is also supported by the extreme depletion in peridotites with low-Fe sub-Ca garnets. Beneath the Malo-Botuobinsky field the sharply layered mantle section starts from 5.5 GPa and reveals step-like P-Fe#Ol trends for garnets and ilmenites. The deeper part of SCLM in this field was originally highly depleted but has been regenerated by percolation of protokimberlites and hybrid melts especially beneath Internationalnaya pipe. The three global transects reveal flat layering in granite-greenstone terranes and fluctuations in the granulite-orthogneiss Daldyn collision terranes. The mantle layering beneath the Daldyn - Alakite region may have been created by marginal accretion. Most of southern fields including the Malo-Botuobinsky field reveal flat layering. The primary subduction layering is smoothed beneath the Alakit field. Lower Jurassic kimberlites from the Kharamai-Anabar kimberlite fields reveal a small decrease of the thickness of the SCLM and heating of its base. The Jurassic Kuoyka field shows an uneven base of the SCLM inclined from west to east. SCLM sequences sampled at this time started mainly from depths of 130 km, but some pipes still showed mantle roots to 250 km. The garnet series demonstrates an inclined straight line pyroxenite P-Fe# trend due to

  2. Allergenic lipid transfer proteins from plant-derived foods do not immunologically and clinically behave homogeneously: the kiwifruit LTP as a model.

    Directory of Open Access Journals (Sweden)

    Maria Livia Bernardi

    Full Text Available BACKGROUND: Food allergy is increasingly common worldwide. Tools for allergy diagnosis measuring IgE improved much since allergenic molecules and microarrays started to be used. IgE response toward allergens belonging to the same group of molecules has not been comprehensively explored using such approach yet. OBJECTIVE: Using the model of lipid transfer proteins (LTPs from plants as allergens, including two new structures, we sought to define how heterogeneous is the behavior of homologous proteins. METHODS: Two new allergenic LTPs, Act d 10 and Act c 10, have been identified in green (Actinidia deliciosa and gold (Actinidia chinensis kiwifruit (KF, respectively, using clinically characterized allergic patients, and their biochemical features comparatively evaluated by means of amino acid sequence alignments. Along with other five LTPs from peach, mulberry, hazelnut, peanut, mugwort, KF LTPs, preliminary tested positive for IgE, have been immobilized on a microarray, used for IgE testing 1,003 allergic subjects. Comparative analysis has been carried out. RESULTS: Alignment of Act d 10 primary structure with the other allergenic LTPs shows amino acid identities to be in a narrow range between 40 and 55%, with a number of substitutions making the sequences quite different from each other. Although peach LTP dominates the IgE immune response in terms of prevalence, epitope recognition driven by sequence heterogeneity has been recorded to be distributed in a wide range of behaviors. KF LTPs IgE positive results were obtained in a patient subset IgE positive for the peach LTP. Anyhow, the negative results on homologous molecules allowed us to reintroduce KF in patients' diet. CONCLUSION: The biochemical nature of allergenic molecule belonging to a group of homologous ones should not be taken as proof of immunological recognition as well. The availability of panels of homologous molecules to be tested using microarrays is valuable to address the

  3. Subduction-driven recycling of continental margin lithosphere.

    Science.gov (United States)

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

    2014-11-13

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

  4. The lithosphere structure of Northeast China

    Institute of Scientific and Technical Information of China (English)

    ZHANG Xingzhou; YANG Baojun; WU Fuyuan; LIU Guoxing

    2007-01-01

    The lithosphere of northeastern China is composed of the Erguna, Xingan, Songnen, Jiamusi blocks and Mesozoic Wandashan accretionary complex from west to east. Nd isotope model ages indicate that the Xingan and Songnen blocks have the same Nd model ages ranging from 500 to 1 000 Ma. These are obviously younger than those of the Jiamusi block (1 500-2 000 Ma) and the Erguna block (1 500-1 700 Ma), reflecting the different evolutions of indi- vidual blocks in the early times. Geochemical tracing analysis shows that the Nd model ages of Paleozoic supercrustal rocks in the four blocks are dominantly Mesoproterozoic, while those of Mesozoic granites are mainly Neoproterozoic. It is shown that the crust ages of the region are characterized by being younger in the lower part and older in the upper part. The Os isotope analysis also indicates that the lithosphere mantle of the region is characteristic of a younger age. The P-wave velocities of the region show more complicated struc- tures in lithosphere and asthenosphere. First of all, notably different from traditional concept of the seismic lithosphere, the low velocity zone of the lithosphere beneath the region has no persistent and continuous top interface which is highly varied in depth and intersected with the high velocity layers, forming sharp velocity discontinuities beneath major tectonic belts, even up to the Moho beneath some tectonic units. But the bottom interface of the low velocity zone is relatively per- sistent, occurring at a depth of 230-240 km. Another feature is that the lithosphere is characterized by an "overpass type" velocity structure vertically, in which the contoured velocity is distributed in the NE trending within the crust, in a nearly NS trending in the lithosphere mantle from a depth of 45 to 90 km, in a nearly EW trending in the upper part of the asthe- nosphere from 90 to 170 km and in a ring-like distribution with a diameter of about 300 km in the lower part of the asthenosphere from

  5. FEM Modeling of Lithospheric Rheology of Taiwan from GPS and PSInSAR Observations of Postseismic Deformation of the 1999 Chi-Chi Earthquake

    Science.gov (United States)

    Lin, G.; Chang, W. L.; Chang, C. P.

    2015-12-01

    Postseismic deformation following large earthquakes can persist from years to decades. Since the 1999 Chi-Chi earthquake (Mw=7.6), more than a decade of GPS records reveal postseismic deformation across Taiwan and have been used for afterslip and lithospheric rheology studies. Previous researches show that this earthquake has experienced rapid afterslip on deeper part of Chelungpu fault with slip rates decreased within years [Hsu et al., 2002 and 2007]. Other postseismic deformation signals were modeled by assumed Maxwell viscoelastic relaxation with heterogeneous lower crust and upper mantle [Rousset et al., 2012; Tang et al., 2015], which suggest that the pattern of vertical displacements is more sensitive to the geometry of heterogeneous viscoelastic lithospheric structure. To improve the spatial coverage of observation, this study processed both ERS and Envisat SAR images from 1999-2008 with PSInSAR techniques, and the result provide a better illustration of Line-Of-Sight (LOS) deformation field which is near to vertical. Both GPS and PSInSAR results reveal that the surface displacement rates (horizontal or vertical?) of eastern Taiwan are higher than interseismic rates after a decade, and this feature may reveal the importance of low viscosity zone beneath central range of Taiwan. With the benefits from GPS and PSInSAR data, we intend to test other posssible viscosity and the geometry of viscoelastic structure. We adopt coseismic fault geometry and slip distribution of the Chi-Chi earthquake based on previous studies, and build a set of 2D rheological models with an elastic upper-crust layer overlain a viscoelastic lower-crust layer and a viscoelastic upper mantle. The depths of the two layer boundaries are determined according to subsurface tectonic and velocity structures inferred by previous literatures. We employ the finite element method (FEM), Pylith, to estimate the postseismic surface deformation corresponding to different viscosities. Benefit from the

  6. Rejuvenation of the lithosphere by the Hawaiian plume.

    Science.gov (United States)

    Li, Xueqing; Kind, Rainer; Yuan, Xiaohui; Wölbern, Ingo; Hanka, Winfried

    2004-02-26

    The volcanism responsible for creating the chain of the Hawaiian islands and seamounts is believed to mark the passage of the oceanic lithosphere over a mantle plume. In this picture hot material rises from great depth within a fixed narrow conduit to the surface, penetrating the moving lithosphere. Although a number of models describe possible plume-lithosphere interactions, seismic imaging techniques have not had sufficient resolution to distinguish between them. Here we apply the S-wave 'receiver function' technique to data of three permanent seismic broadband stations on the Hawaiian islands, to map the thickness of the underlying lithosphere. We find that under Big Island the lithosphere is 100-110 km thick, as expected for an oceanic plate 90-100 million years old that is not modified by a plume. But the lithosphere thins gradually along the island chain to about 50-60 km below Kauai. The width of the thinning is about 300 km. In this zone, well within the larger-scale topographic swell, we infer that the rejuvenation model (where the plume thins the lithosphere) is operative; however, the larger-scale topographic swell is probably supported dynamically.

  7. Global strength and elastic thickness of the lithosphere

    NARCIS (Netherlands)

    Tesauro, M.; Kaban, M.K.; Cloetingh, S.A.P.L.

    2012-01-01

    Thestrengthand effective elasticthickness (Te) ofthelithosphere control its response to tectonic and surface processes. Here, we present the first globalstrengthand effective elasticthickness maps, which are determined using physical properties from recent crustal and lithospheric models. Pronounced

  8. Decoupling of surface and subsurface sutures in the Dabie orogen and a continent-collisional lithospheric-wedging model:Sr-Nd-Pb isotopic evidences of Mesozoic igneous rocks in eastern China

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    There are significant differences of Nd and Pb isotopic compositions between Mesozoic mafic igneous rocks from the North China Block (NCB) and the South China Block (SCB). Mesozoic mantle-derived igneous rocks from the North China Block have very low εNd values (-15 to -21), and 206Pb/204Pb ratios ( -10 and 206Pb/204Pb > 18.3. The very low εNd values (-16 to -20) and 206Pb/204Pb ratios (< 17.3) of the early Cretaceous mafic-ultramafic intrusions developed in the north part of the Dabie orogen (NDZ) suggest that the deep lithosphere underneath the NDZ belongs to the NCB but not the SCB. Therefore, although the surface suture between the NCB and SCB is located on the north side of the NDZ, the subsurface suture between the NCB and SCB should be located to the south side of the NDZ. This is consistent with the previous suggestion that the subsurface suture in the Sulu terrane east of the Tanlu fault was the south displacement, but contradictory to northward continental subduction of the SCB. A continent-collisional lithospheric- wedging model can interpret the decoupling of the surface and subsurface sutures in the Dabie-Sulu orogen. After slab break-off, the continuing convergence of two continental blocks must increase the compression force acting on the suture zone, which might induce the lithosphere splitting of SCB. Thus, the lower crust and lithospheric mantle on the south margin of the NCB can wedge into the north margin of the lithosphere of the SCB along the Dabie-Sulu collision zone. This process caused the overthrust of the mid-upper continental crust with exhumed ultrahigh pressure metamorphic (UHPM) rocks and underthrust of the deep lithosphere of the SCB. It could be an important mechanism responsible for the second rapid cooling and uplifting of the UHPM rocks and lithospheric delamination as well as the corresponding magmatism in Jurassic in the Dabie orogen. The southward movement of subsurface suture in the Dabie-Sulu orogen may also provide a

  9. The longevity of subcontinental lithospheric mantle beneath Jiangsu-Anhui Region ——The Os isotope model age of mantle-derived peridotite xenoliths

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The basalt-borne peridotite xenoliths from Jiangsu-Anhui provinces were analyzed for whole rock Os isotopic compositions in two laboratories of USTC, China and CRPG, France, respectively. The 187Os/188Os ratio of the sample set ranges from 0.119 to 0.129 (25 samples, USTC)and from 0.117 to 0.131 (17 samples, CRPG). The Os isotopic compositions of most samples are less than 0.129 and depleted relatively to the primitive mantle, showing a good correlation with the major element compositions. With the 187Os/188Os-Al2O3 alumichron, the samples yield a model age of 2.5 ± 0.1 Ga (data of USTC) and 1.9 ± 0.1 Ga (data of CRPG), late Archean to early Proterozoic, The two samples with the lowest 187Os/188Os ratio (0.119 and 0.117) have the TRD (Re depleted age) of 1.1 Ga (USTC) and 1.4 Ga (CRPG), mid-Proterozoic. The Os isotope model age shows that the peridotite xenoliths from Cenozoic alkali basalt in Jiangsu-Anhui provinces have an old formation age (early- to mid- Proterozoic). They are not newly produced mantle after the Phanerozoic replacement of the lithosphere mantle, but residual fractions of Proterozoic mantle.

  10. NSF Continental Lithosphere Program

    Science.gov (United States)

    Mayhew, Michael; MacGregor, Ian

    For several months the Continental Lithosphere Program (CL) of the National Science Foundation has been subject to a major review. The process was stimulated by a series of budget setbacks over the past few years. Although Presidential budget requests have been very favorable for the Division of Earth Sciences (EAR), and there has been strong support within the National Science Foundation and Congress, actual appropriations by Congress have been disappointing.In each year the final allocation to EAR has been affected by external factors beyond the control of the Foundation. In the four fiscal years from 1986 through 1989 the factors include reductions tied to the Gramm-Rudman deficit reduction measures, congressional reaction to the October 1987 stock market crash, and two years of protection for the Ocean Sciences part of the NSF budget that was paid for from the budgets of the Atmospheric and Earth Sciences divisions.

  11. Flexure and rheology of Pacific oceanic lithosphere

    Science.gov (United States)

    Hunter, Johnny; Watts, Tony

    2016-04-01

    The idea of a rigid lithosphere that supports loads through flexural isostasy was first postulated in the late 19th century. Since then, there has been much effort to investigate the spatial and temporal variation of the lithosphere's flexural rigidity, and to understand how these variations are linked to its rheology. We have used flexural modelling to first re-assess the variation in the rigidity of oceanic lithosphere with its age at the time of loading, and then to constrain mantle rheology by testing the predictions of laboratory-derived flow laws. A broken elastic plate model was used to model trench-normal, ensemble-averaged profiles of satellite-derived gravity at the trench-outer rise system of circum-Pacific subduction zones, where an inverse procedure was used to find the best-fit Te and loading conditions. The results show a first-order increase in Te with plate age, which is best fit by the depth to the 400 ± 35°C plate-cooling isotherm. Fits to the observed gravity are significantly improved by an elastic plate that weakens landward of the outer rise, which suggests that bending-induced plate weakening is a ubiquitous feature of circum-Pacific subduction zones. Two methods were used to constrain mantle rheology. In the first, the Te derived by modelling flexural observations was compared to the Te predicted by laboratory-derived yield strength envelopes. In the second, flexural observations were modelled using elastic-plastic plates with laboratory-derived, depth-dependent yield strength. The results show that flow laws for low-temperature plasticity of dry olivine provide a good fit to the observations at circum-Pacific subduction zones, but are much too strong to fit observations of flexure in the Hawaiian Islands region. We suggest that this discrepancy can be explained by differences in the timescale of loading combined with moderate thermal rejuvenation of the Hawaiian lithosphere.

  12. The principal characteristics of the lithosphere of China

    Institute of Scientific and Technical Information of China (English)

    Tingdong Li

    2010-01-01

    The lithospheric structure of China and its adjacent area is very complex and is marked by several prominent characteristics. Firstly, China's continental crust is thick in the west but thins to the east, and thick in the south but thins to the north. Secondly, the continental crust of the Qinghai-Tibet Plateau has an average thickness of 60-65 km with a maximum thickness of 80 km, whereas in eastern China the average thickness is 30-35 kin, with a minimum thickness of only 5 km in the center of the South China Sea. The average thickness of continental crust in China is 47.6 km, which greatly exceeds the global average thickness of 39.2 km. Thirdly, as with the crust, the lithosphere of China and its adjacent areas shows a general pattern of thicker in the west and south, and thinner in the east and north. The lithosphere of the Qinghai-Tibet Plateau and northwestern China has an average thickness of 165 kin,with a maximum thickness of 180-200 km in the central and eastern parts of the Tarim Basin, Pamir,and Changdu areas. In contrast, the vast areas to the east of the Da Hinggan Ling-Taihang-Wuling Mountains, including the marginal seas, are characterized by lithospheric thicknesses of only 50-85 km. Fourthly, in western China the lithosphere and asthenosphere behave as a "layered structure",reflecting their dynamic background of plate collision and convergence. The lithosphere and asthenosphere in eastern China display a "block mosaic structure", where the lithosphere is thin and the asthenosphere is very thick, a pattern reflecting the consequences of crustal extension and an upsurge of asthenospheric materials. The latter is responsible for a huge low velocity anomaly at a depth of 85-250 km beneath East Asia and the western Pacific Ocean. Finally, in China there is an age structure of "older in the upper layers and younger in the lower layers" between both the upper and lower crusts and between the crust and the lithospheric mantle.

  13. The effects of lithospheric thickness and density structure on Earth's stress field

    Science.gov (United States)

    Naliboff, J. B.; Lithgow-Bertelloni, C.; Ruff, L. J.; de Koker, N.

    2012-01-01

    Lithospheric density and thickness variations are important contributors to the state of stress of the plates. The relationship between the lithosphere's isostatic state, subcrustal structure and stress field, however, remains unresolved due to the uncertainties on its thickness, composition and rheology. To study the influence of lithospheric structure on intraplate stresses, we use a new model of global lithospheric structure (TDL) that accounts for the presence of depleted mantle to explore the effects of isostatic compensation, mantle density structure, lithospheric thickness (base depth) and mechanical coupling within the lithosphere on wavelengths >200 km. We compute the mean lithostatic stress (Ω) of 2°× 2° lithospheric columns and then solve for the resulting global 'tectonic' stress field for a homogeneous elastic lithosphere with the finite element package ABAQUS. For a 100 km base depth, a historically common value for lithospheric thickness, tectonic stress patterns are largely insensitive to mantle density structure and match patterns in the world stress map, for both isostatically compensanted and non-compensated lithospheric structure. Increasing the base depth up to 250 km to account for thick continental roots, however, leads to sharp variations in the stress field between isostatic lithospheric structure models and TDL as the mantle portion of the lithosphere dominates Ω. Decreasing the model base depths up to 25 km as a proxy for vertical strength variations due to low viscosity channels within the crust or lithosphere as a whole, strongly alters stresses in magnitude, azimuth and regime, as the influence of topography and shallow crustal structure increases. We find that restricting spatial changes in Ω to a specified region to mimic lateral variations in strength also has a large effect on the resulting stresses, which leads us to conclude that regional models may not always be adequate for modelling the stress field. Strong deviations

  14. From the Alpine region to the Central Apennines (Italy): 3d upper lithospheric P-velocity model with controlled source seismology data

    Science.gov (United States)

    di Stefano, R.; Tondi, R.; de Luca, L.; Lippitsch, R.; Sandoval, S.; Kissling, E.

    2003-04-01

    The complex lithosphere structure of the Italian region leads to difficulties in uniquely interpreting the results obtained with geophysical investigation methods. Relating to P waves velocity models, the geometry of the moho is the main first order structure influencing the interpretation of controlled source seismology (CSS) profile data and results from local earthquake tomography (LET). Moreover, the crustal structures complexities, though poorly resolved by teleseismic tomography, strongly distort teleseismic wave fronts and thus influence teleseismic traveltimes. In 1996 a method was developed by F. Waldhauser to determine the 3D topography and lateral continuity of seismic interfaces using 2D-derived controlled-source seismic reflector data. This method has been successfully applied to retrieve the moho geometry in the complex Alpine region with the aim to obtain the simplest possible 3D structure consistent with all reflector data and error estimates. For the Alpine region a 3D crustal P-wave velocity model has been thus developed from comparative use of published information from active and passive sources surveys. Here we present the extension of this map to the Italian peninsula to include Northern and Central Apennines. Information from the CROP project and from other CSS experiments performed in the past 40 years, both on land and offshore, has been included to cover the whole area. The first order features of Adriatic and Tyrrhenian moho have been recovered and a Vp crustal velocity model has been produced. For the Northern Apennines we compare the newly derived crustal model with the 3D structure of the crust obtained by the inversion of P-wave first arrivals picked on the CSS data, and of gravity data collected on land and off-shore (see Tondi et al., session SM3).

  15. How thick is the lithosphere?

    Science.gov (United States)

    Kanamori, H; Press, F

    1970-04-25

    A rapid decrease in shear velocity in the suboceanic mantle is used to infer the thickness of the lithosphere. It is proposed that new and highly precise group velocity data constrain the solutions and imply a thickness near 70 km.

  16. A Novel Distributed Quantum-Behaved Particle Swarm Optimization

    Directory of Open Access Journals (Sweden)

    Yangyang Li

    2017-01-01

    Full Text Available Quantum-behaved particle swarm optimization (QPSO is an improved version of particle swarm optimization (PSO and has shown superior performance on many optimization problems. But for now, it may not always satisfy the situations. Nowadays, problems become larger and more complex, and most serial optimization algorithms cannot deal with the problem or need plenty of computing cost. Fortunately, as an effective model in dealing with problems with big data which need huge computation, MapReduce has been widely used in many areas. In this paper, we implement QPSO on MapReduce model and propose MapReduce quantum-behaved particle swarm optimization (MRQPSO which achieves parallel and distributed QPSO. Comparisons are made between MRQPSO and QPSO on some test problems and nonlinear equation systems. The results show that MRQPSO could complete computing task with less time. Meanwhile, from the view of optimization performance, MRQPSO outperforms QPSO in many cases.

  17. Geodynamic inversion to constrain the nonlinear rheology of the lithosphere

    Science.gov (United States)

    Baumann, Tobias; Kaus, Boris

    2015-04-01

    A common method to determine the strength of the lithosphere is through estimating its effective elastic thickness from the coherence between gravity and topography. This method assumes a priori that the lithosphere is a thin elastic plate floating on a viscous mantle. Whereas this seems to work well with oceanic plates, it has given controversial results in continental collision zones. Usually, continental collisions zones are well-studied areas for which additional geophysical datasets such as receiver functions and seismic tomography exist that constrain the geometry of the lithosphere and often show that it is rather complex. Yet, lithospheric geometry by itself is insufficient to understand the dynamics of the lithosphere, as this also requires knowledge of the rheology of the lithosphere. Experimental results show significant variability between various rock types and there are large uncertainties in extrapolating laboratory values to nature, which leaves room for speculation. An independent approach is thus required to better understand the rheology and dynamics of the lithosphere in collision zones. Our method combines numerical thermo-mechanical forward models of the present-day lithosphere with a massively parallel Bayesian inversion approach. The geometry of the forward models is part of the a priori knowledge and is constructed from seismological data. We jointly invert topography, gravity, horizontal and vertical surface velocities to constrain the unknown rheological material parameters of the forward models in a probabilistic sense. The model rheology is described with experimentally determined viscous creep laws and other parameters describing the plastic behaviour. As viscosity is temperature dependent, the temperature structure of the forward models is parameterised as well. We apply the method to cross-sections of the India-Asia collision system. In this case, we deal with 17 to 20 model parameters, which requires solving up to 2 × 106 forward

  18. Lithospheric Architecture Beneath Hudson Bay

    Science.gov (United States)

    Porritt, R. W.; Miller, M. S.; Darbyshire, F. A.

    2015-12-01

    Hudson Bay overlies some of the thickest Precambrian lithosphere on Earth, whose internal structures contain important clues to the earliest workings of plate formation. The terminal collision, the Trans-Hudson Orogen, brought together the Western Churchill craton to the northwest and the Superior craton to the southeast. These two Archean cratons along with the Paleo-Proterozoic Trans-Hudson internides, form the core of the North American craton. We use S to P converted wave imaging and absolute shear velocity information from a joint inversion of P to S receiver functions, new ambient noise derived phase velocities, and teleseismic phase velocities to investigate this region and determine both the thickness of the lithosphere and the presence of internal discontinuities. The lithosphere under central Hudson Bay approaches 􏰂350 km thick but is thinner (􏰂200-250 km) around the periphery of the Bay. Furthermore, the amplitude of the lithosphere-asthenosphere boundary (LAB) conversion from the S receiver functions is unusually large for a craton, suggesting a large thermal contrast across the LAB, which we interpret as direct evidence of the thermal insulation effect of continents on the asthenosphere. Within the lithosphere, midlithospheric discontinuities, significantly shallower than the base of the lithosphere, are often imaged, suggesting the mechanisms that form these layers are common. Lacking time-history information, we infer that these discontinuities reflect reactivation of formation structures during deformation of the craton.

  19. Lithosphere types in North China: Evidence from geology and geophysics

    Institute of Scientific and Technical Information of China (English)

    QIU; Ruizhao; DENG; Jinfu; ZHOU; Su; LI; Jinfa; XIAO; Qingh

    2005-01-01

    On the basis of the characteristics of geology and geophysics in North China, three types of lithosphere, namely, the cratonic, the orogenic and the rift lithospheres can be classified. In terms of petrological method (based on the information from Precambrian rock assemblages, igneous activities, deep-seated enclaves, etc.) and the relationship between seismic velocity and rock compositions, the crust-mantle petrological and chemical structure models can be set up. Researching results indicate that the geology and geophysics of North China platform bears the similar characteristics in comparison with those of the global typical cratons. The Eerduosi(Ordos) block located in the west of the North China Platform is a remnant of cratonic lithosphere after the North China platform had undergone "activation" in Mesozoic and "reconstruction" in Cenozoic times. The continental crust consists mainly of TTG rock assemblage while the subcontinental lithosphere mantle mainly consists of strongly depleted harzburgite. The craton was finally formed in late Archaean and early Proterozoic, and has been kept in stability up to present; its crustal-mantle petrological structures of lithosphere can be set up as a reference for the study of North China craton and even Sino-Korean craton. In the Mesozoic period, the middle and east areas of North China platform were activated in the Yanshanian orogenic process, the continental crust was reformed by material and heat-transfer of convective mantle and the original crustal TTG component was reconstructed to be granitic crust, and the subcontinental lithosphere mantle was replaced by the Yanshanian harzburgite-lherzolite. The Yanshan-Taihang Mountains were the remnants of orogenic lithosphere after the rifting in eastern North China in Cenozoic. The present thickness of continental crust and lithosphere in the Yanshan-Taihang Mountains is not equal to their thickness during the Yanshanian orogenic movement because they had undergone the

  20. Integrated geophysical-petrological modeling of lithosphere-asthenosphere boundary in central Tibet using electromagnetic and seismic data

    OpenAIRE

    Vozar, Jan; Jones, Alan G.; Fullea, Javier; Agius, Matthew R.; LEBEDEV, Sergei; Le Pape, Florian; Wei, Wenbo

    2014-01-01

    We undertake a petrologically driven approach to jointly model magnetotelluric (MT) and seismic surface wave dispersion (SW) data from central Tibet, constrained by topographic height. The approach derives realistic temperature and pressure distributions within the upper mantle and characterizes mineral assemblages of given bulk chemical compositions as well as water content. This allows us to define a bulk geophysical model of the upper mantle based on laboratory and xenolith data for the mo...

  1. Effect of Upper Mantle Heterogeneities on Lithosphere Stresses and Topography

    Science.gov (United States)

    Osei Tutu, A.; Steinberger, B.; Rogozhina, I.; Sobolev, S. V.

    2016-12-01

    The orientation and magnitude of lithosphere stresses give us knowledge about most of the processes within the Earth that are not easy to observe. It has been established (Steinberger, Schmeling, and Marquart 2001) that large contribution of the forces producing lithosphere stresses have their source origination from the buoyancies of both the upper and lower mantle acting beneath the lithosphere. The contribution of the crustal thickness to the stresses has been estimated to be less than 10% (Steinberger et al. 2001) in most region and increases in areas with high gravitational potential energy like the Himalayas. In most of these studies, the effect of the crust was determined separately by computing the gravitational potential energy from the crust (Ghosh et al. 2013) and applied as correction. (Artyushkov 1973) showed that the inhomogeneous nature of the crust contribute to the stresses observed as against using constant lithosphere thickness in most studies, due to the complexities for implementing a variable lithosphere. We seek extend the approach of Ghosh et al. (2013) by coupling the Crust 1.0 (Laske et al. 2013) to a varaible lithosphere thickness in our numerical method. Using a 3D global lithosphere-asthenosphere model (Popov and Sobolev 2008) with visco-elasto-plastic rheology, coupled at 300 km depth to a mantle modeled with a spectral technique (Hager and O'Connell, 1981), we compute lithosphere stresses and topography. we compare our model with observations; the World Stress Map, Global Strain Rate Map and the observed topgraphy. We use S40RTS seismic tomography below 300 km depth, with radial viscosity distribution (Steinberger et al 2006). To account for all the heterogeneities in the upper mantle (300 km) we used different 3D temperatures models setups. The first model is the thermal lithosphere model (Artemieva and Mooney, 2001) in continental regions and assumes half-space cooling of sea floor with age (Müller et al. 2008) for oceans. For the

  2. Numerical modelling of thermochemically driven fluid flow with non-Newtonian rheology : applied to the earth's lithosphere and mantle

    NARCIS (Netherlands)

    van Keken, P.E.

    1993-01-01

    In the 25 years after the general acceptance of the concept of plate tectonics we have witnessed large progress in observational, laboratory, forward modelling and inversion techniques. These provide a clear view of the immense complexities that are facing us when studying the dynamics of the interi

  3. Formation of Oceanic Lithosphere by Basal Magma Accretion

    Science.gov (United States)

    Hamza, V. M.; Cardoso, R. R.; Alexandrino, C. H.

    2009-12-01

    The thermal models of the lithosphere proposed to date have failed to provide satisfactory accounts of some of the important features in large-scale variations of ocean floor bathymetry and heat flow. The systematic difference between model calculations and observational data have given rise to the so-called “oceanic heat flow paradox”, for which no satisfactory solution has been found for over the last forty years. In the present work, we point out that this paradox is a consequence of the assumption that lateral temperature variations are absent in the sub-lithospheric mantle. In the present work we propose a simple magma accretion model and examine its implications for understanding the thermal field of oceanic lithosphere. The new model (designated VBA) assumes existence of lateral variations in magma accretion rates and temperatures at the boundary zone between the lithosphere and the asthenosphere, similar in character to those observed in magma solidification processes in the upper crust. However, unlike the previous thermal models of the lithosphere, the ratio of advection to conduction heat transfer (the Peclet number) is considered a space dependent variable. The solution to the problem of variable basal heat input has been obtained by the method of integral transform. The results of VBA model simulations reveal that the thickness of the young lithosphere increases with distance from the ridge axis, at rates faster than those predicted by Half-Space Cooling and Plate models. Another noteworthy feature of the new model is its ability to account for the main observational features in the thermal behavior of both young and old oceanic lithosphere. Thus, heat flow and bathymetry variations calculated on the basis of the VBA model provide vastly improved fits to respective observational datasets. More importantly, the improved fits to bathymetry and heat flow have been achieved for the entire age range of oceanic lithosphere and without the need to invoke

  4. Rheological benchmark of silicone oils used for analog modeling of short- and long-term lithospheric deformation

    Science.gov (United States)

    Rudolf, Michael; Boutelier, David; Rosenau, Matthias; Schreurs, Guido; Oncken, Onno

    2016-08-01

    Analog models of tectonic processes at various scales commonly use silicone polymers to simulate viscous flow in the lower crust and mantle. To achieve dynamic similarity with the natural prototype and to improve comparability between analog models, better knowledge of the rheology of commonly used silicones is required. In this study, we present a rheological benchmark of silicones used in various laboratories. Rheometric tests, including rotational and oscillatory tests, were performed and the viscoelastic behavior of silicone is quantitatively described. We found that silicone oils show a transition from Newtonian viscous to power-law, shear thinning behavior around shear rates of 10- 2 to 10- 1 s- 1. The viscosity of chemically similar silicones varied between 2 and 3 × 104 Pa s. Maxwell relaxation times are about 0.1-0.2 s. Such a behavior is able to mimic slow to fast deformation mechanisms in the ductile regime, such as diffusion and dislocation creep as well as viscoelastic relaxation processes. Temperature and aging effects are verified, but can be considered minor with respect to the uncertainty in rheological properties in the natural prototype. Nevertheless, to assure comparability between models and proper scaling the exact properties and conditions should be reported.

  5. Adakites from collision-modified lithosphere

    Science.gov (United States)

    Haschke, M.; Ben-Avraham, Z.

    2005-08-01

    Adakitic melts from Papua New Guinea (PNG) show adakitic geochemical characteristics, yet their geodynamic context is unclear. Modern adakites are associated with hot-slab melting and/or remelting of orogenic mafic underplate at convergent margins. Rift-propagation over collision-modified lithosphere may explain the PNG adakite enigma, as PNG was influenced by rapid creation and subduction of oceanic microplates since Mesozoic times. In a new (rift) tectonic regime, decompressional rift melts encountered and melted remnant mafic eclogite and/or garnet-amphibolite slab fragments in arc collisional-modified mantle, and partially equilibrated with metasomatized mantle. Alternatively, hot-slab melting in a proposed newborn subduction zone along the Trobriand Trough could generate adakitic melts, but recent seismic P-wave tomographic models lack evidence for subducting oceanic lithosphere in the adakite melt region; however they do show deep subduction zone remnants as a number of high P-wave anomalies at lithospheric depths, which supports our proposed scenario.

  6. Global map of lithosphere thermal thickness on a 1 deg x 1 deg grid - digitally available

    DEFF Research Database (Denmark)

    Artemieva, Irina

    2014-01-01

    than 250 km) lithosphere is restrictedsolely to young Archean terranes (3.0–2.6 Ga), while in old Archean cratons (3.6–3.0 Ga) lithospheric roots donot extend deeper than 200–220 km.The TC1 model is presented by a set of maps, which show significant thermal heterogeneity within continentalupper mantle......This presentation reports a 1 deg 1 deg global thermal model for the continental lithosphere (TC1). The modelis digitally available from the author’s web-site: www.lithosphere.info.Geotherms for continental terranes of different ages (early Archean to present) are constrained by reliabledata...

  7. Complex structure of the lithospheric slab beneath the Banda arc, eastern Indonesia depicted by a seismic tomographic model

    Directory of Open Access Journals (Sweden)

    Sri Widiyantoro

    2011-10-01

    Full Text Available Seismic tomography with a non-linear approach has been successfully applied to image the P-wave velocity structure beneath the Banda arc in detail. Nearly one million compressional phases including the surfacereflected depth phases pP and pwP from events within the Indonesian region have been used. The depth phases have been incorporated in order to improve the sampling of the uppermantle structure, particularly below the Banda Sea in the back-arc regions. For the model parameterization, we have combined a highresolution regional inversion with a low-resolution global inversion to allow detailed images of slab structures within the study region and to minimize the mapping of distant aspherical mantle structure into the volume under study. In this paper, we focus our discussion on the upper mantle and transition zone structure beneath the curved Banda arc. The tomographic images confirm previous observations of the twisting of the slab in the upper mantle, forming a spoon-shaped structure beneath the Banda arc. A slab lying flat on the 660 km discontinuity beneath the Banda Sea is also well imaged. Further interpretations of the resulting tomograms and seismicity data support the scenario of the Banda arc subduction rollback.

  8. A kinematic model for Afar Depression lithospheric thinning and its implications for hominid evolution: an exercise in plate-tectonic paleoanthropology

    Science.gov (United States)

    Redfield, T.; Often, M.; Wheeler, W. H.

    2002-12-01

    We present a detailed Nubia-Arabia-Somalia (NU-AR-SOM) kinematic reconstruction based on magnetic sea floor isochrons in the Gulf of Aden and Red Sea and piercing points along the Red Sea margins. The reconstruction is combined with digital topographic and depth-to-Moho data to constrain in 4D the Late Oligocene to present-day evolution of the Afar supra-Moho crust. Opposite end-member models for crustal evolution are described. We conclude that less than 20% of the present-day Afar supra-Moho crust was constructed by magmatic processes such as diking and underplating. The reconstructions indicate that the greater percentage of crustal thinning (extension) occurred before 6.2 Ma. We model the thinning of the effective elastic lithosphere that accompanied extension, and show that the regional-scale topographic development of the Afar depression was virtually complete by Mid Pliocene time. The plate-tectonic model has paleoanthropological implications. Prior to 6.2 Ma the proximal positions of NU-SOM, AR, and the Danakil block suggest subaerial conditions prevailed between Yemen and Ethiopia. Uninhibited Africa-Eurasia faunal exchange through Afar and Arabia (corroborated by isotopic and paleontologic data) was tectonically permissible until the time of the earliest hominids. Continued stretching caused the Afar land bridge(s) to disappear during Early to Mid Pliocene time. Primitive hominid populations living within the Afar Depression became isolated from AR sometime before ~3.2 Ma. With the plateau becoming less habitable due to long-term Late Neogene cooling, hominids that remained in the Afar Depression were required to adapt to a smaller range that was effectively bounded by the already well-developed NU-SOM escarpments and the newly opened Straits of Bab el Mandeb. The combination of high quality habitat,topographic confinement, and a gradual (tectonic) reduction in range, exacerbated by potentially severe fluctuations in local climate (well documented by land

  9. Lithospheric structure and continental geodynamics

    Institute of Scientific and Technical Information of China (English)

    许忠淮; 石耀霖

    2003-01-01

    This paper briefly reviews main progress in the research on lithospheric structure and continental geodynamics made by Chinese geophysicists during last 4 years since 22nd IUGG general assembly in July 1999. The research mainly covers the following fields: investigations on regional lithospheric structure, DSS survey of crust and upper mantle velocity structure, study on present-day inner movement and deformation of Chinese mainland by analyzing GPS observations, geodynamics of Qingzang plateau, geophysical survey of the Dabie-Sulu ultra-high pressure metamorphic belt and probing into its formation mechanism, geophysical observations in sedimentary basins and study on their evolution process, and plate dynamics, etc.

  10. Descending lithosphere slab beneath the Northwest Dinarides from teleseismic tomography

    Science.gov (United States)

    Šumanovac, Franjo; Dudjak, Darko

    2016-12-01

    The area of study covers the marginal zone between the Adriatic microplate (African plate) and the Pannonian segment (Eurasian plate). We present a tomography model for this area, with special emphasis on the northwest Dinarides. A dense distribution of temporary seismic stations in the area of the Northern Dinarides along with permanent seismic stations located in the area, allowed us to construct this P-wave tomographic model. We assembled our travel-time dataset based on 26 seismic stations were used to collect the dataset. Teleseismic events were recorded for a period of 18 months and a set of 76 distant earthquakes were used to calculate the P-wave travel-time residuals. We calculated relative rather than absolute arrival-time residuals in the inversion to obtain depths of 0-400 km. We imaged a pronounced fast velocity anomaly below the NW Dinarides which directly indicates a lithosphere slab downgoing beneath the Dinarides. This fast anomaly extends towards the NW direction to at least 250 km depth, and we interpreted it as a descending lithosphere slab. The thrusting of the Adriatic microplate may be brought about by sub-lithosphere rising movement beneath the Pannonian region, along with a push from African plate. In our interpretation, the Adriatic lower lithosphere has been detached from the crust, and steeply sinks beneath the Dinarides. A lithosphere model of the contact between the Adriatic microplate and Pannonian tectonic segment was constructed based on the tomographic velocity model and results of previous crustal studies.

  11. Model Investigations of Lithospheric Propagation

    Science.gov (United States)

    1988-05-01

    O ol e " -160 - 20logloEjO(p,O,z)I (incident field) ×[1 - z’/L) 2]Ii 2 cos ), (78) 20l0.. ,olE p(pO,z)l (S ,,O red field) where K,(0) and 0N(O) are...configurations of perimetrical metal quency source and the mechanisms of data acquisition in the sheets including the vertical one directly tre-ated by theory...This means that the lateral- !hr I ’t in Fig. 4. The measured field is shown by the wave field B1 0(p. 0) is the same when D, >> :,,, as %hen nui,. red

  12. Deflection rheoevolution of lithosphere under subduction

    Institute of Scientific and Technical Information of China (English)

    韩玉英; 王维襄

    1997-01-01

    Along the continental margin, the tectonic system consisting of trench, island arc, back arc basin and outer rise is often known as a convergent transitional belt between the oceanic lithosphere and the continental litho-sphere. The occurrence, development and activity of trench and outer rise bear closely on the underthrusting process of the oceanic lithosphere. A generalized analytical theory of deflection rheoevolution of lithosphere under subduction is established, and solutions with universal significance have been obtained.

  13. Temporal evolution of continental lithospheric strength in actively deforming regions

    Science.gov (United States)

    Thatcher, W.; Pollitz, F.F.

    2008-01-01

    It has been agreed for nearly a century that a strong, load-bearing outer layer of earth is required to support mountain ranges, transmit stresses to deform active regions and store elastic strain to generate earthquakes. However the dept and extent of this strong layer remain controversial. Here we use a variety of observations to infer the distribution of lithospheric strength in the active western United States from seismic to steady-state time scales. We use evidence from post-seismic transient and earthquake cycle deformation reservoir loading glacio-isostatic adjustment, and lithosphere isostatic adjustment to large surface and subsurface loads. The nearly perfectly elastic behavior of Earth's crust and mantle at the time scale of seismic wave propagation evolves to that of a strong, elastic crust and weak, ductile upper mantle lithosphere at both earthquake cycle (EC, ???10?? to 103 yr) and glacio-isostatic adjustment (GIA, ???103 to 104 yr) time scales. Topography and gravity field correlations indicate that lithosphere isostatic adjustment (LIA) on ???106-107 yr time scales occurs with most lithospheric stress supported by an upper crust overlying a much weaker ductile subtrate. These comparisons suggest that the upper mantle lithosphere is weaker than the crust at all time scales longer than seismic. In contrast, the lower crust has a chameleon-like behavior, strong at EC and GIA time scales and weak for LIA and steady-state deformation processes. The lower crust might even take on a third identity in regions of rapid crustal extension or continental collision, where anomalously high temperatures may lead to large-scale ductile flow in a lower crustal layer that is locally weaker than the upper mantle. Modeling of lithospheric processes in active regions thus cannot use a one-size-fits-all prescription of rheological layering (relation between applied stress and deformation as a function of depth) but must be tailored to the time scale and tectonic

  14. Cratonic lithospheric mantle: Is anything subducted?

    Institute of Scientific and Technical Information of China (English)

    William L. Griffin; Suzanne Y. O'ReiUy

    2007-01-01

    @@ If the subcontinental lithospheric mantle (SCLM) formed through the repeated underthrusting of oceanic slabs, peridotitic SCLM should resemble oceanic peridotites, and mafic rocks (eclogites, s.l.) should be distributed throughout the SCLM. However, cratonic peridotites (both exposed massifs and xenoliths) differ markedly from oceanic and ophiolitic peridotites in their Fe-Cr-Al relationships and abundances of trace elements (Li and B) diagnostic of subduction. "Typical"cratonic peridotites have experienced extensive metaso matism; modelling of their refractory protoliths indicates high-degree melting at high P, perhaps a uniquely Archean process.

  15. Continental collision with a sandwiched accreted terrane: Insights into Himalayan-Tibetan lithospheric mantle tectonics?

    Science.gov (United States)

    Kelly, Sean; Butler, Jared P.; Beaumont, Christopher

    2016-12-01

    Many collisional orogens contain exotic terranes that were accreted to either the subducting or overriding plate prior to terminal continent-continent collision. The ways in which the physical properties of these terranes influence collision remain poorly understood. We use 2D thermomechanical finite element models to examine the effects of prior 'soft' terrane accretion to a continental upper plate (retro-lithosphere) on the ensuing continent-continent collision. The experiments explore how the style of collision changes in response to variations in the density and viscosity of the accreted terrane lithospheric mantle, as well as the density of the pro-lithospheric mantle, which determines its propensity to subduct or compress the accreted terrane and retro-lithosphere. The models evolve self-consistently through several emergent phases: breakoff of subducted oceanic lithosphere; pro-continent subduction; shortening of the retro-lithosphere accreted terrane, sometimes accompanied by lithospheric delamination; and, terminal underthrusting of pro-lithospheric mantle beneath the accreted terrane crust or mantle. The modeled variations in the properties of the accreted terrane lithospheric mantle can be interpreted to reflect metasomatism during earlier oceanic subduction beneath the terrane. Strongly metasomatized (i.e., dense and weak) mantle is easily removed by delamination or entrainment by the subducting pro-lithosphere, and facilitates later flat-slab underthrusting. The models are a prototype representation of the Himalayan-Tibetan orogeny in which there is only one accreted terrane, representing the Lhasa terrane, but they nonetheless exhibit processes like those inferred for the more complex Himalayan-Tibetan system. Present-day underthrusting of the Tibetan Plateau crust by Indian mantle lithosphere requires that the Lhasa terrane lithospheric mantle has been removed. Some of the model results support previous conceptual interpretations that Tibetan

  16. The structural evolution of the deep continental lithosphere

    Science.gov (United States)

    Cooper, C. M.; Miller, Meghan S.; Moresi, Louis

    2017-01-01

    Continental lithosphere houses the oldest and thickest regions of the Earth's surface. Locked within this deep and ancient rock record lies invaluable information about the dynamics that has shaped and continue to shape the planet. Much of that history has been dominated by the forces of plate tectonics which has repeatedly assembled super continents together and torn them apart - the Wilson Cycle. While the younger regions of continental lithosphere have been subject to deformation driven by plate tectonics, it is less clear whether the ancient, stable cores formed and evolved from similar processes. New insight into continental formation and evolution has come from remarkable views of deeper lithospheric structure using enhanced seismic imaging techniques and the increase in large volumes of broadband data. Some of the most compelling observations are that the continental lithosphere has a broad range in thicknesses ( 300 km), has complex internal structure, and that the thickest portion appears to be riddled with seismic discontinuities at depths between 80 and 130 km. These internal structural features have been interpreted as remnants of lithospheric formation during Earth's early history. If they are remnants, then we can attempt to investigate the structure present in the deep lithosphere to piece together information about early Earth dynamics much as is done closer to the surface. This would help delineate between the differing models describing the dynamics of craton formation, particularly whether they formed in the era of modern plate tectonics, a transitional mobile-lid tectonic regime, or are the last fragments of an early, stagnant-lid planet. Our review paper (re)introduces readers to the conceptual definitions of the lithosphere and the complex nature of the upper boundary layer, then moves on to discuss techniques and recent seismological observations of the continental lithosphere. We then review geodynamic models and hypotheses for the formation

  17. Lithosphere-mantle coupling and the dynamics of the Eurasian Plate

    NARCIS (Netherlands)

    Warners-Ruckstuhl, K.N.; Govers, R.; Wortel, R.

    2012-01-01

    Mechanical equilibrium of tectonic plates implies that lithospheric edge and body forces are balanced by forces arising from interaction with the underlying mantle. We use this quantitative physical relation to integrate existing modelling approaches of lithosphere dynamics and mantle flow into a ne

  18. Density heterogeneity of the cratonic lithosphere

    DEFF Research Database (Denmark)

    Cherepanova, Yulia; Artemieva, Irina

    2015-01-01

    Using free-board modeling, we examine a vertically-averaged mantle density beneath the Archean-Proterozoic Siberian craton in the layer from the Moho down to base of the chemical boundary layer (CBL). Two models are tested: in Model 1 the base of the CBL coincides with the LAB, whereas in Model 2...... the base of the CBL is at a 180 km depth. The uncertainty of density model is density structure of the Siberian lithospheric mantle with a strong...... correlation between mantle density variations and the tectonic setting. Three types of cratonic mantle are recognized from mantle density anomalies. 'Pristine' cratonic regions not sampled by kimberlites have the strongest depletion with density deficit of 1.8-3.0% (and SPT density of 3.29-3.33 t/m3...

  19. Fossilized Dipping Fabrics in Continental Mantle Lithosphere as Possible Remnants of Stacked Oceanic Paleosubductions

    Science.gov (United States)

    Babuska, V.; Plomerova, J.; Vecsey, L.; Munzarova, H.

    2015-12-01

    We have examined seismic anisotropy within the mantle lithosphere of Archean, Proterozoic and Phanerozoic provinces of Europe by means of shear-wave splitting and P-wave travel-time deviations of teleseismic waves observed at dense arrays of seismic stations (e.g., Vecsey et al., Tectonophys. 2007). Lateral variations of seismic-wave anisotropy delimit domains of the mantle lithosphere, each of them having a consistent fabric. The domains, modeled in 3D by olivine aggregates with dipping lineation a, or foliation (a,c), represent microplates or their fragments that preserved their pre-assembly fossil fabrics in the mantle lithosphere. Evaluating seismic anisotropy in 3D, as well as mapping boundaries of the domains helps to decipher processes of the lithosphere formation. Systematically dipping mantle fabrics and other seismological findings seem to support a model of continental lithosphere built from systems of paleosubductions of plates of ancient oceanic lithosphere (Babuska and Plomerova, AGU Geoph. Monograph 1989), or by stacking of the plates (Helmstaedt and Schulze, Geol. Soc. Spec. Publ. 1989). Seismic anisotropy in the oceanic mantle lithosphere, explained mainly by the olivine A- or D-type fabric (Karato et al., Annu. Rev. Earth Planet. Sci. 2008), was discovered a half century ago (Hess, Nature 1964). Field observations and laboratory experiments indicate the oceanic olivine fabric might be preserved in the subducting lithosphere to a depth of at least 200-300 km. We thus interpret the dipping anisotropic fabrics in domains of the European mantle lithosphere as systems of "frozen" paleosubductions (Babuska and Plomerova, PEPI 2006), and the lithosphere base as a boundary between a fossil anisotropy in the lithospheric mantle and an underlying seismic anisotropy related to present-day flow in the asthenosphere (Plomerova and Babuska, Lithos 2010).

  20. Implications for anomalous mantle pressure and dynamic topography from lithospheric stress patterns in the North Atlantic Realm

    DEFF Research Database (Denmark)

    Schiffer, Christian; Nielsen, Søren Bom

    2016-01-01

    -established thin sheet model in a global finite element representation. We adjust the lithospheric thickness and the sub-lithospheric pressure iteratively, comparing modelled in plane stress with the observations of the World Stress Map. We find that an anomalous mantle pressure associated with the Iceland...... of a buoyancy anomaly at the base of the North Atlantic lithosphere at or slightly before continental breakup, relatively fast dissipation of the fringes of this, and continued melt generation below Iceland....

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

    Science.gov (United States)

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

    2015-08-01

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

  2. Global distribution of the lithosphere-asthenosphere boundary: a new look

    Directory of Open Access Journals (Sweden)

    V. M. Hamza

    2012-02-01

    Full Text Available New global maps of the depth to the boundary between the lithosphere and the asthenosphere are presented. The maps are based on updated global databases for heat flow and crustal structure. For continental regions the estimates of lithospheric thickness are based on determinations of subcrustal heat flow, after corrections for contributions of radiogenic heat in crustal layers. For oceanic regions the estimates of lithospheric thickness are based on the newly proposed finite half-space (FHS model. Unlike the half-space cooling (HSC and the Plate models the FHS model takes into account effects of buffered solidification at the lower boundary of the lithosphere and assumes that vertical domain for downward growth of boundary layer have an asymptotic limit. Results of numerical simulations reveal that theoretical values derived from FHS model provide vastly improved fits to observational data for heat flow and bathymetry than can be achieved with HSC and Plate models. Also, the data fits are valid for the entire age range of the oceanic lithosphere. Hence estimates of depths to lithosphere – asthenosphere boundary (LAB based on FHS model, are believed to provide more reliable estimates than those reported in previous thermal models. The global maps of depths to LAB derived in the present work reveal several features in regional variations of lithosphere thicknesses that have not been identified in earlier studies. For example, regions of ocean floor with ages less than 55 Ma are characterized by relatively rapid thickening of the lithosphere. Also there is better resolution in mapping the transition from oceanic to continental lithosphere, as most of the latter ones are characterized by lithospheric thickness greater than 150 km. As expected the plate spreading centers in oceanic regions as well as areas of recent magmatic activity in continental regions are characterized by relatively thin lithosphere, with LAB depths of less than 50 km. On the

  3. Thin elastic shells with variable thickness for lithospheric flexure of one-plate planets

    CERN Document Server

    Beuthe, Mikael

    2007-01-01

    Planetary topography can either be modeled as a load supported by the lithosphere, or as a dynamical effect due to lithospheric flexure caused by mantle convection. In both cases the response of the lithosphere to external forces can be calculated with the theory of thin elastic plates or shells. On one-plate planets the spherical geometry of the lithospheric shell plays an important role in the flexure mechanism. So far the equations governing the deformations and stresses of a spherical shell have only been derived under the assumption of a shell of constant thickness. However local studies of gravity and topography data suggest large variations in the thickness of the lithosphere. In this article we obtain the scalar flexure equations governing the deformations of a thin spherical shell with variable thickness or variable Young's modulus. The resulting equations can be solved in succession, except for a system of two simultaneous equations, the solutions of which are the transverse deflection and an associ...

  4. Dipping fossil fabrics of continental mantle lithosphere as tectonic heritage of oceanic paleosubductions

    Science.gov (United States)

    Babuska, Vladislav; Plomerova, Jaroslava; Vecsey, Ludek; Munzarova, Helena

    2016-04-01

    Subduction and orogenesis require a strong mantle layer (Burov, Tectonophys. 2010) and our findings confirm the leading role of the mantle lithosphere. We have examined seismic anisotropy of Archean, Proterozoic and Phanerozoic provinces of Europe by means of shear-wave splitting and P-wave travel-time deviations of teleseismic waves observed at dense arrays of seismic stations (e.g., Vecsey et al., Tectonophys. 2007). Lateral variations of seismic-velocity anisotropy delimit domains of the mantle lithosphere, each of them having its own consistent fabric. The domains, modeled in 3D by olivine aggregates with dipping lineation a, or foliation (a,c), represent microplates or their fragments that preserved their pre-assembly fossil fabrics. Evaluating seismic anisotropy in 3D, as well as mapping boundaries of the domains helps to decipher processes of the lithosphere formation. Systematically dipping mantle fabrics and other seismological findings seem to support a model of continental lithosphere built from systems of paleosubductions of plates of ancient oceanic lithosphere (Babuska and Plomerova, AGU Geoph. Monograph 1989), or from stacking of the plates (Helmstaedt and Schulze, Geol. Soc. Spec. Publ. 1989). Seismic anisotropy in the oceanic mantle lithosphere, explained mainly by the olivine A- or D-type fabric (Karato et al., Annu. Rev. Earth Planet. Sci. 2008), was discovered a half century ago (Hess, Nature 1964). Field observations and laboratory experiments indicate the oceanic olivine fabric might be preserved in the subducting lithosphere to a depth of at least 200-300 km. We thus interpret the dipping anisotropic fabrics in domains of the European mantle lithosphere as systems of "frozen" paleosubductions (Babuska and Plomerova, PEPI 2006) and the lithosphere base as a boundary between the fossil anisotropy in the lithospheric mantle and an underlying seismic anisotropy related to present-day flow in the asthenosphere (Plomerova and Babuska, Lithos 2010).

  5. Challenges (and Promise) of In-Situ Lithospheric Rheology from Isostatic Strength Analyses

    Science.gov (United States)

    Lowry, Anthony R.; Becker, Thorsten W.; Buehler, Janine S.; Miller, Meghan S.; Pérez-Gussinyé, Marta; Schutt, Derek L.; Seunarine, Lisa L.

    2013-04-01

    Measurements of effective elastic thickness, Te, from flexural isostatic modeling are sensitive to flow rheology of the lithosphere. Nevertheless Te has not been widely used to estimate in-situ rheology, partly owing to methodological questions regarding the measurement of Te and partly because of uncertainties in other in-situ properties of temperature, composition, water content and state-of-stress of the lithosphere. Dense seismic and other geophysical arrays such as EarthScope's USArray are providing a wealth of new information about physical state of the lithosphere, however, and the relationships of these data to Te promises new insights into lithospheric rheology and deformation processes. For example, new estimates of subsurface mass distributions derived from seismic data enable us to examine various controversial assumptions about the nature of lithospheric loads. Variations in crustal composition evident in bulk crustal velocity ratio, vP-vS, contribute a surprisingly large fraction of total loading, and elevation models better match observations if Moho flexure is not forced to match surface flexure, indicating that lower crustal flow and other crustal mass transfer processes are significant. Perhaps the most interesting new information on physical state derives from imaging of uppermost mantle velocities using refracted mantle phases, Pn and Sn, and depths to negative velocity gradients imaged as converted phases in receiver functions (seismic lithosphere-asthenosphere boundary, "LAB"). We will compare Te measurements to thermal models derived from these seismic fields, and discuss their implications for lithospheric rheological controls and thermal processes.

  6. Utilizing thermal isostasy to estimate sub-lithospheric heat flow and anomalous crustal radioactivity

    Science.gov (United States)

    Hasterok, D.; Gard, M.

    2016-09-01

    While surface heat flow relates to the heat loss through the lithosphere, it can be difficult to quantify and separate the heat produced internally through radiogenic decay from the heat transferred across the base of the lithosphere by mantle convection. In this study, we apply a thermo-isostatic analysis to Australia and estimate the sub-lithospheric and radiogenic heat flow components by employing a simple 1-D conservation of energy model. We estimate an anomalous radiogenic heat production across much of eastern Australia generally accounting for >50 mW m-2, while western Australia appears to have high crustal compositionally corrected elevation, possibly related to chemical buoyancy of the mantle lithosphere. A moderately high sub-lithospheric heat flow (∼40 mW m-2) along the eastern and southeastern coast, including Tasmania, is coincident with locations of Cenozoic volcanism and supports an edge-driven convection hypothesis. However, the pattern of sub-lithospheric heat flow along the margin does not support the existence of hotspot tracks. Thermo-isostatic models such as these improve our ability to identify and quantify crustal from mantle sources of heat loss and add valuable constraints on tectonic and geodynamic models of the continental lithosphere's physical state and evolution.

  7. Continental Rifts: Lithospheric Weakness and Strength Contrasts as Triggers for Necking Instabilities

    Science.gov (United States)

    Wenker, S.; Beaumont, C.

    2014-12-01

    Rifted margin geometry is too complex and diverse to be explained by simple kinematic models. Instead, we consider the effects of strain localization and the growth of necking instabilities as they apply to rifted margins. The intrinsic layering of the lithosphere will affect the growth rate of necking instabilities, leading to depth-dependent extension. In addition, continents are far from homogeneous after multiple cycles of collision, strike-slip motion and rifting. The resulting inherited heterogeneities may serve to localize strain and initiate necking instabilities. We use 2D finite element models containing embedded finite weak zones in the crust and/or mantle as well as a vertical lithospheric boundary across which lithospheric layering changes resulting in an overall strength contrast. We show that there are two controls on the style of rifting: Control 1, the stiff/pliable nature of the lithospheric layers and; Control 2, the distribution of the background strain rate in the lithosphere. Control 1 depends on the lithospheric rheology, such that necking instabilities grow faster in a stiff, dominantly plastic, layer than in equivalent layers with a pliable, mostly viscous, rheology. Control 2 is important where a strength contrast at a lithospheric boundary influences the distribution of the background strain rate. Necking is a mechanism that amplifies the background strain rate, which implies faster necking in parts of the lithosphere where background strain rates are highest. In a laterally homogeneous lithosphere, the background strain rate will be uniform in each layer and Control 1 will dominate giving necking in stiff layers. However, juxtaposed lithospheres with different strengths will distribute strain giving the weaker lithosphere the higher strain rate, implying the fastest necking may occur under Control 2 in pliable layers with the higher strain rate. An end-member case is where strong lithosphere acts as a rigid block. Here, no necking

  8. Global map of lithosphere thermal thickness on a 1 deg x 1 deg grid - digitally available

    Science.gov (United States)

    Artemieva, Irina

    2014-05-01

    This presentation reports a 1 deg ×1 deg global thermal model for the continental lithosphere (TC1). The model is digitally available from the author's web-site: www.lithosphere.info. Geotherms for continental terranes of different ages (early Archean to present) are constrained by reliable data on borehole heat flow measurements (Artemieva and Mooney, 2001), checked with the original publications for data quality, and corrected for paleo-temperature effects where needed. These data are supplemented by cratonic geotherms based on xenolith data. Since heat flow measurements cover not more than half of the continents, the remaining areas (ca. 60% of the continents) are filled by the statistical numbers derived from the thermal model constrained by borehole data. Continental geotherms are statistically analyzed as a function of age and are used to estimate lithospheric temperatures in continental regions with no or low quality heat flow data. This analysis requires knowledge of lithosphere age globally. A compilation of tectono-thermal ages of lithospheric terranes on a 1 deg × 1 deg grid forms the basis for the statistical analysis. It shows that, statistically, lithospheric thermal thickness z (in km) depends on tectono-thermal age t (in Ma) as: z=0.04t+93.6. This relationship formed the basis for a global thermal model of the continental lithosphere (TC1). Statistical analysis of continental geotherms also reveals that this relationship holds for the Archean cratons in general, but not in detail. Particularly, thick (more than 250 km) lithosphere is restricted solely to young Archean terranes (3.0-2.6 Ga), while in old Archean cratons (3.6-3.0 Ga) lithospheric roots do not extend deeper than 200-220 km. The TC1 model is presented by a set of maps, which show significant thermal heterogeneity within continental upper mantle. The strongest lateral temperature variations (as large as 800 deg C) are typical of the shallow mantle (depth less than 100 km). A map of the

  9. A preliminary study on the lithospheric thermal-rheological structure of the East Qinling orogenic belt

    Institute of Scientific and Technical Information of China (English)

    CHENG Shunyou; ZHANG Guowei; DIAO Bo; GUO Anlin; YU Xiangni

    2007-01-01

    This paper considers the lithospheric rheological structure of the East Qinling orogenic belt to explore its geodynamics. The lithospheric rheological structure was calculated by the constraints of the lithospheric temperature structure. The thermal-rheological stratification structures of the lithosphere in the East Qinling orogenic belt present different features from each other within different tectonic units. The hinterland fault-bounded fold zone (HLZ) and the North Qinling thick-skinned imbricated thrust zone (NQL) in the northern half part of the Qinling orogen, with a tempera-ture of 305℃ for the Moho boundary, are characterized by "cold" geotherm, thickened lithosphere and the model C for rheological stratification structure. The South Qinling tectonic zone (SQL), with a mean temperature of 642℃ and a high temperature of 826℃ for the Moho boundary, has obvious features with the model H of"hot" geotherm, thinned lithosphere and intensive rheological behavior within moderate-lower crust and top of the upper mantle. During post-orogenesis, the NQL, being the convergent frontal region of continental subduction beneath the Qinling orogen by both the North China craton (NC) and Yangtze craton (YZ), is in a coexistence period of a dominantly thickened lithosphere and an initial delamination, and the SQL, proba-bly under pluming, has been developing new delamination and underplating and partial melting within the crust in its axel area and recycling for mass and energy (in the forms of heat transfer and convection) between the crust and mantle.

  10. The Lithospheric Structure of Madagascar

    Science.gov (United States)

    Wysession, M. E.; Pratt, M. J.; Andriampenomanana Ny Ony, F. S. T.; Tsiriandrimanana, R.; Nyblade, A.; Aleqabi, G. I.; Shore, P.; Tucker, R.; Wiens, D. A.; Rambolamanana, G.

    2016-12-01

    The lithosphere of Madagascar is revealed for the first time from a combination of studies using data from the 2011-2013 MACOMO (Madagascar, the Comoros, and Mozambique) broadband seismic array from the IRIS PASSCAL program (funded by NSF, with additional data from the RHUM-RUM and Madagascar Seismic Profile projects). Methods include seismicity locations, body-wave receiver functions, Pn tomography, body-wave tomography, and ambient-noise and two-plane-wave earthquake surface-wave analyses. Madagascar's crustal thickness varies greatly, from 20 to 45 km, in good agreement with its past tectonic history of rifting from the mainland and having India break away to the north. The crust is thickest along the central spine of the island, along a ridge of mountains, but unusually high elevations suggest some amount f thermal buoyancy in the mantle. Crust is also thick along the east coast, where archean terranes were severed from India. Crust is thinnest along the west coast, where thick sedimentary basins up to 8 km thick are found on top of unusually thinned basement crust (about 12 km thick), a remnant of rifting away from Africa 130-160 Ma ago. Madagascar has an unusually high level of intraplate seismicity, with 918 earthquakes located during the 2-year period. Seismicity shows interesting correlations with paleotectonic features, but much is located in the central regions of the island, associated with normal faulting along several graben structures. This region also corresponds to the central of three regions within Madagascar (north, central, and southwest) that display strong lithospheric seismic low-velocity anomalies that underlie regions of current or recent volcanic activity. Surface waves show that these low-velocity zones (LVZs) extending down into the asthenosphere, and body-wave tomography shows them extending even deeper. Pn tomography shows that the width of the central LVZ is only about 100-200 km in diameter at the top of the mantle, indicative of

  11. The role of elasticity in normal faulting and the development of axial topography in the oceanic lithosphere

    Science.gov (United States)

    Olive, J. L.; Behn, M. D.; Mittelstaedt, E. L.; Ito, G.

    2012-12-01

    In this study we compare 2D numerical simulations of lithospheric extension with and without elasticity in order to investigate its role on the development of normal faults and axial topography at oceanic spreading centers. Specifically, we use a finite difference / marker-in-cell technique to model visco-elasto-plastic (VEP) and visco-plastic (VP) deformation of the lithosphere under extension. Simulated fault zones form spontaneously as the system evolves and the associated strain localization is achieved by reducing the cohesion in proportion to the accumulated plastic strain in regions undergoing yielding. We investigate the development of different fault modes (e.g. growth of multiple faults vs. a single large-offset fault) both in a VP and a VEP lithosphere for a range of lithospheric thicknesses, spreading rates, and rates of cohesion loss. In our simulations, fault-induced bending of a VP lithosphere occurs on a larger wavelength and with less overall vertical deflection than in a VEP lithosphere. Flexural rotation of long-lived, initially steep faults does not require elasticity, but appears to have a strain-rate-dependent wavelength in a VP lithosphere. We find that thinner lithosphere and rapid weakening promote the growth of large-offset faults in both a VEP and a VP lithosphere. The effect of neglecting elasticity appears greater in thicker lithosphere, where a VP rheology favors the growth of multiple steep faults instead of a few large-offset faults. We also note that a VP lithosphere requires more total extension to achieve the same faulting pattern as a VEP lithosphere. This may be due to distributed viscous deformation taking up a portion of the extension in the VP case. To further quantify our numerical results, we develop scaling relations describing the build-up of topographic and bending stresses in a faulted VP lithosphere and compare them to those previously derived for a VEP lithosphere. These relations are then implemented in a force

  12. Toward robotic socially believable behaving systems

    CERN Document Server

    Jain, Lakhmi

    2016-01-01

    This volume is a collection of research studies on the modeling of emotions in complex autonomous systems. Several experts in the field are reporting their efforts and reviewing the literature in order to shed lights on how the processes of coding and decoding emotional states took place in humans, which are the physiological, physical, and psychological variables involved, invent new mathematical models and algorithms to describe them, and motivate these investigations in the light of observable societal changes and needs, such as the aging population and the cost of health care services. The consequences are the implementation of emotionally and socially believable machines, acting as helpers into domestic spheres, where emotions drive behaviors and actions. The contents of the book are highly multidisciplinary since the modeling of emotions in robotic socially believable systems requires a holistic perspective on topics coming from different research domains such as computer science, engineering, sociology...

  13. Melt-rich channel observed at the lithosphere-asthenosphere boundary.

    Science.gov (United States)

    Naif, S; Key, K; Constable, S; Evans, R L

    2013-03-21

    The lithosphere-asthenosphere boundary (LAB) separates rigid oceanic plates from the underlying warm ductile asthenosphere. Although a viscosity decrease beneath this boundary is essential for plate tectonics, a consensus on its origin remains elusive. Seismic studies identify a prominent velocity discontinuity at depths thought to coincide with the LAB but disagree on its cause, generally invoking either partial melting or a mantle dehydration boundary as explanations. Here we use sea-floor magnetotelluric data to image the electrical conductivity of the LAB beneath the edge of the Cocos plate at the Middle America trench offshore of Nicaragua. Underneath the resistive oceanic lithosphere, the magnetotelluric data reveal a high-conductivity layer confined to depths of 45 to 70 kilometres. Because partial melts are stable at these depths in a warm damp mantle, we interpret the conductor to be a partially molten layer capped by an impermeable frozen lid that is the base of the lithosphere. A conductivity anisotropy parallel to plate motion indicates that this melt has been sheared into flow-aligned tube-like structures. We infer that the LAB beneath young plates consists of a thin, partially molten, channel of low viscosity that acts to decouple the overlying brittle lithosphere from the deeper convecting mantle. Because this boundary layer has the potential to behave as a lubricant to plate motion, its proximity to the trench may have implications for subduction dynamics.

  14. To Teach "Vikings" to Behave among "Mandarins"

    DEFF Research Database (Denmark)

    Søndergaard, Mikael; Lemmergaard, Jeanette

    2002-01-01

    The objective of this paper is to report from interactive teaching situations that involve a number of cross-cultural puzzles and to report on the construct value of a model in progress on bribery in China. The paper reports from eight simulations. It is a cross-disciplinary case involving joint ...

  15. Deformation in the continental lithosphere

    Science.gov (United States)

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

  16. Global map of lithosphere thermal thickness on a 1 deg x 1 deg grid - digitally available

    DEFF Research Database (Denmark)

    Artemieva, Irina

    2014-01-01

    than 250 km) lithosphere is restrictedsolely to young Archean terranes (3.0–2.6 Ga), while in old Archean cratons (3.6–3.0 Ga) lithospheric roots donot extend deeper than 200–220 km.The TC1 model is presented by a set of maps, which show significant thermal heterogeneity within continentalupper mantle......This presentation reports a 1 deg 1 deg global thermal model for the continental lithosphere (TC1). The modelis digitally available from the author’s web-site: www.lithosphere.info.Geotherms for continental terranes of different ages (early Archean to present) are constrained by reliabledata...... of the continents, the remaining areas (ca. 60% ofthe continents) are filled by the statistical numbers derived from the thermal model constrained by boreholedata. Continental geotherms are statistically analyzed as a function of age and are used to estimate lithospherictemperatures in continental regions...

  17. Matching Lithosphere velocity changes to the GOCE gravity signal

    Science.gov (United States)

    Braitenberg, Carla

    2016-07-01

    Authors: Carla Braitenberg, Patrizia Mariani, Alberto Pastorutti Department of Mathematics and Geosciences, University of Trieste Via Weiss 1, 34100 Trieste Seismic tomography models result in 3D velocity models of lithosphere and sublithospheric mantle, which are due to mineralogic compositional changes and variations in the thermal gradient. The assignment of density is non-univocal and can lead to inverted density changes with respect to velocity changes, depending on composition and temperature. Velocity changes due to temperature result in a proportional density change, whereas changes due to compositional changes and age of the lithosphere can lead to density changes of inverted sign. The relation between velocity and density implies changes in the lithosphere rigidity. We analyze the GOCE gradient fields and the velocity models jointly, making simulations on thermal and compositional density changes, using the velocity models as constraint on lithosphere geometry. The correlations are enhanced by applying geodynamic plate reconstructions to the GOCE gravity field and the tomography models which places today's observed fields at the Gondwana pre-breakup position. We find that the lithosphere geometry is a controlling factor on the overlying geologic elements, defining the regions where rifting and collision alternate and repeat through time. The study is carried out globally, with focus on the conjugate margins of the African and South American continents. The background for the study can be found in the following publications where the techniques which have been used are described: Braitenberg, C., Mariani, P. and De Min, A. (2013). The European Alps and nearby orogenic belts sensed by GOCE, Boll. Bollettino di Geofisica Teorica ed Applicata, 54(4), 321-334. doi:10.4430/bgta0105---- Braitenberg, C. and Mariani, P. (2015). Geological implications from complete Gondwana GOCE-products reconstructions and link to lithospheric roots. Proceedings of 5th

  18. Time-dependent rotational stability of dynamic planets with viscoelastic lithospheres

    Science.gov (United States)

    Moore, K. M.; Chan, N.-H.; Daradich, A.; Mitrovica, J. X.

    2017-06-01

    We extend previous work to derive a non-linear rotational stability theory governing true polar wander (TPW) of terrestrial planets with viscoelastic lithospheres. We demonstrate, analytically and using numerical examples, that our expressions are consistent with previous results in the limiting cases of low and infinite (i.e., purely elastic) viscosity lithospheres. To illustrate the stability theory, we compute TPW on Mars driven by a simple, prescribed mass loading. Our calculations demonstrate that on short time scales relative to the relaxation time of the viscoelastic lithosphere, the rotation axis follows a constrained path that reflects stabilization by remnant strength in the lithosphere, but that on long times scales this stabilization disappears and the load ultimately reaches the equator. Earlier work based on the assumption of a permanent remnant bulge in the case of a purely elastic lithosphere has suggested that Martian TPW would not persist for any significant time after a load is emplaced, and thus an equilibrium stability theory is sufficient to model long-term (order 1 Myr or longer) polar motion of the planet. Our results suggest, in contrast, that TPW on Mars can continue over time scales on the order of the relaxation time of the lithosphere after load emplacement; for sufficiently high lithospheric viscosities, this time scale may be comparable to the age of the planet.

  19. Big insights from tiny peridotites: Evidence for persistence of Precambrian lithosphere beneath the eastern North China Craton

    Science.gov (United States)

    Liu, Jingao; Rudnick, Roberta L.; Walker, Richard J.; Xu, Wen-liang; Gao, Shan; Wu, Fu-yuan

    2015-05-01

    Previous studies have shown that the eastern North China Craton (NCC) lost its ancient lithospheric mantle root during the Phanerozoic. The temporal sequence, spatial extent, and cause of the lithospheric thinning, however, continue to be debated. Here we report olivine compositions, whole-rock Re-Os isotopic systematics, and platinum-group element abundances of small ( 92) lithospheric mantle is largely absent. Osmium isotopic data suggest the Wudi peridotites experienced melt depletion primarily during the Paleoproterozoic (~ 1.8 Ga), although an Archean Os model age for one xenolith indicates incorporation of a minor component of Archean lithospheric mantle. These data suggest that a previously unrecognized Paleoproterozoic orogenic event removed and replaced the original Archean lithospheric mantle beneath the sedimentary basin at the southern edge of the Bohai Sea. By contrast, the Fuxin peridotites, entrained in Cretaceous basalts that crop out along the northern edge of the eastern NCC, document the coexistence of both ancient (≥ 2.3 Ga) and modern lithospheric mantle components. Here, the original Late Archean-Early Paleoproterozoic lithospheric mantle was, at least partially, removed and replaced prior to 100 Ma. Combined with literature data, our results show that removal of the original Archean lithosphere occurred within Proterozoic collisional orogens, and that replacement of Precambrian lithosphere during the Mesozoic may have been spatially associated with the collisional boundaries and the strike-slip Tan-Lu fault, as well as the onset of Paleo-Pacific plate subduction.

  20. The lithosphere-asthenosphere Italy and surroundings

    CERN Document Server

    Panza, G F; Chimera, G; Pontevivo, A; Raykova, R

    2003-01-01

    The velocity-depth distribution of the lithosphere-asthenosphere in the Italian region and surroundings is imaged, with a lateral resolution of about 100 km, by surface wave velocity tomography and non-linear inversion. Maps of the Moho depth, of the thickness of the lithosphere and of the shear-wave velocities, down to depths of 200 km and more, are constructed. A mantle wedge, identified in the uppermost mantle along the Apennines and the Calabrian Arc, underlies the principal recent volcanoes, and partial melting can be relevant in this part of the uppermost mantle. In Calabria a lithospheric doubling is seen, in connection with the subduction of the Ionian lithosphere. The asthenosphere is shallow in the Southern Tyrrhenian Sea. High velocity bodies, cutting the asthenosphere, outline the Adria-lonian subduction in the Tyrrhenian Sea and the deep-reaching lithospheric root in the Western Alps. Less deep lithospheric roots are seen in the Central Apennines. The lithosphere-asthenosphere properties delineat...

  1. Rheology of the lithosphere: selected topics.

    Science.gov (United States)

    Kirby, S.H.; Kronenberg, A.K.

    1987-01-01

    Reviews recent results concerning the rheology of the lithosphere with special attention to the following topics: 1) the flexure of the oceanic lithosphere, 2) deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins, 3) the rheological stratification of the continents, 4) strain localization and shear zone development, and 5) strain-induced crystallographic preferred orientations and anisotropies in body-wave velocities. We conclude with a section citing the 1983-1986 rock mechanics literature by category.-Authors

  2. Dynamic topography as constraints on stress and viscosity in the mantle and lithosphere

    Science.gov (United States)

    Zhong, S.

    2015-12-01

    Mantle convection generates stress in the mantle and lithosphere. The lithosphere stress is responsible for localized deformation including seismic deformation at plate boundaries, and localized stress highs in lithosphere are also suggested to cause dynamically self-consistent generation of plate tectonics and continental lithosphere instability, as the stress exceeds a threshold or yield stress. Modeling load-induced deformation at oceanic islands (e.g., Hawaii) constrains lithospheric stress at 100-200 MPa in the plate interiors, leading to a lower limit on lithospheric yield stress (Zhong and Watts, 2013). However, convection-induced lithospheric stress is poorly understood, ranging from 500 MPa to tens of MPa as reported in mantle convection studies. The magnitude and distribution of lithospheric and mantle stress depend critically on buoyancy and viscosity, particularly the latter. Unfortunately, lithospheric and mantle viscosity is also poorly constrained. For example, the inferred lower mantle viscosity from post-glacial rebound and geoid modeling studies ranges from 1023 Pas to 1022 Pas (e.g., Mitrovica and Forte, 2004; Simons and Hager, 1996; Paulson et al., 2007). In addition to the stress, the lower mantle viscosity may also affect the time evolution of mantle structure including sinking rate of slabs and formation of the degree-2 mantle seismic structure. Therefore, it is important to develop independent constraints on mantle viscosity and convection-induced stress. In this study, I demonstrate that dynamic topography can be used to place first-order constraints on both lithospheric stress and mantle viscosity. For a given superadiabatic temperature difference across the mantle (e.g., 2500 K), a larger mantle viscosity (or a smaller Rayleigh number) leads to a larger lithospheric stress and a larger dynamic topography. To be consistent with the inferred dynamic topography, the lower mantle viscosity is constrained to be significantly smaller than 1023

  3. Geodynamic inversion to constrain the rheology of the lithosphere: What is the effect of elasticity?

    Science.gov (United States)

    Baumann, Tobias; Kaus, Boris; Thielmann, Marcel

    2016-04-01

    The concept of elastic thickness (T_e) is one of the main methods to describe the integrated strength of oceanic lithosphere (e.g. Watts, 2001). Observations of the Te are in general agreement with yield strength envelopes estimated from laboratory experiments (Burov, 2007, Goetze & Evans 1979). Yet, applying the same concept to the continental lithosphere has proven to be more difficult (Burov & Diament, 1995), which resulted in an ongoing discussion on the rheological structure of the lithosphere (e.g. Burov & Watts, 2006, Jackson, 2002; Maggi et al., 2000). Recently, we proposed a new approach, which constrains rheological properties of the lithosphere directly from geophysical observations such as GPS-velocity, topography and gravity (Baumann & Kaus, 2015). This approach has the advantage that available data sets (such as Moho depth) can be directly taken into account without making the a-priori assumption that the lithosphere is thin elastic plate floating on the mantle. Our results show that a Bayesian inversion method combined with numerical thermo-mechanical models can be used as independent tool to constrain non-linear viscous and plastic parameters of the lithosphere. As the rheology of the lithosphere is strongly temperature dependent, it is even possible to add a temperature parameterisation to the inversion method and constrain the thermal structure of the lithosphere in this manner. Results for the India-Asia collision zone show that existing geophysical data require India to have a quite high effective viscosity. Yet, the rheological structure of Tibet less well constrained and a number of scenarios give a nearly equally good fit to the data. Yet, one of the assumptions that we make while doing this geodynamic inversion is that the rheology is viscoplastic, and that elastic effects do not significantly alter the large-scale dynamics of the lithosphere. Here, we test the validity of this assumption by performing synthetic forward models and retrieving

  4. Alpine Lithosphere and Upper Mantle Passive Seismic Monitoring

    OpenAIRE

    Brückl, Ewald; Hausmann, Helmut; Behm, Michael; Lippitsch, Regina; Mitterbauer, Ulrike; Institute of Geodesy and Geophysics Vienna University of Technology (Hrsg.)

    2008-01-01

    The project ALPASS is a passive seismic monitoring project aiming to reveal upper mantle, lower lithosphere, and asthenosphere beneath the wider Eastern Alpine region, including the Bohemian Massive, the Carpathians, the Pannonian Basin, and the Dinarides. A 3D seismic model which will provide crustal corrections to the seismic travel times has been generated in this area down to the Moho and the uppermost mantle from data of former projects CELEBRATION 2000 and ALP 2002. ALPASS will yield in...

  5. The Arctic lithosphere: an overview

    Science.gov (United States)

    Drachev, S.; Pease, V.; Stephenson, R.

    2012-04-01

    The Arctic is comprised of three deepwater oceanic basins, the Norwegian-Greenland, Eurasia, and Amerasia basins, surrounded by continental masses of the Achaean to Early Proterozoic North American, Baltica and Siberian cratons and intervening Neoproterozoic and Phanerozoic fold belts. Though the tectonic history of the Arctic continental realm spans almost three billions of years, the formation of the Arctic began with the creation of Pangaea-II supercontinent at end of Permian epoch. Between 250 and 150 Ma the Proto-Arctic was represented by the Anyui Ocean, or Angayuchum Sea - a Paleo-Pacific embayment into Pangaea II. During the Mesozoic Pangaea II was destroyed and the Anyi Ocean was isolated from the Paleo-Pacific, finally leading to the separation of Arctic Alaska-Chukchi Microcontinent from the North American side of Laurasia; the collision of this microplate with the Siberian margin occurred at ca. 125 Ma in association with the opening of the Canada Basin. The final stage of the Arctic formation took place in the Cenozoic, and was related to the propagation of the divergent Atlantic lithospheric plate boundary between North America and Baltica with the separation of the Lomonosov continental sliver from the Eurasian margin and opening of the Eurasia oceanic basin between 56 and 0 Ma. The present-day Arctic, especially its shelves and oceanic basins, is one of the least studied places on the Earth. Though we know the geology of the surrounding continental masses, there are still many questions remaining about major lithospheric divides beneath the Arctic seas, such as: • Where are the plate boundaries associated with the Amerasia Basin? • How and when did the Canada Basin open? • What was the pre-drift setting of the Chukchi Borderland? • Which tectonic processes formed the East Siberian shelves? • How and when did the major ridges in the Amerasia Basin form? • Where are the Early Tertiary plate boundaries in the Arctic? • What is the

  6. Lithospheric Rheology Constrained by Loading of the Hawaiian Islands and its Implications for the Dynamics of Plate Tectonics

    Science.gov (United States)

    Zhong, S.; Watts, A. B.

    2013-12-01

    Lithospheric rheology is important for understanding crustal and lithospheric dynamics, and the conditions for plate tectonics. For example, numerical modeling studies suggest that plate tectonics emerge from the dynamics of mantle convection when a small coefficient of friction (significantly to match the observations, together with frictional coefficient in the range from 0.1 to 0.7. However, the small coefficient of friction weakens the shallow part of the lithosphere so much that it causes the minima in strain rate and stress to occur at too large depths to be consistent with the depth distribution of seismicity at Hawaii. Our results therefore suggest that the coefficient of friction is between 0.25 and 0.7. Finally, maximum lithospheric stress under Hawaiian loads is about 100-200 MPa for models that match the observations, and this stress may be viewed as the largest lithospheric stress on the Earth.

  7. Seismic structure of the lithosphere beneath the ocean islands near the mid-oceanic ridges

    Science.gov (United States)

    Haldar, C.; Kumar, P.; Kumar, M. Ravi

    2013-10-01

    Deciphering the seismic character of the young lithosphere near the mid-oceanic ridges (MOR) is a challenging endeavor. In this study, we determine the seismic structure of the oceanic plate near the MORs, using the P-to-s conversions isolated from good quality data recorded at 5 broadband seismological stations situated on the ocean Islands in their vicinity. Estimates of the crustal and lithospheric thickness values from waveform modeling of the P receiver function stacks reveal that the crustal thickness varies between 6 and 8 km with the corresponding depths to the lithosphere asthenosphere boundary (LAB) varying between 43 and 68 km. However, the depth to the LAB at Macquire Island is intriguing in view of the observation of a thick (~ 87 km) lithosphere beneath a relatively young crust. At three other stations i.e., Ascension Island, Sao Jorge and Easter Island, we find evidence for an additional deeper low velocity layer probably related to the presence of a hotspot.

  8. Lithospheric Stress and Geodynamics: History, Accomplishments and Challenges

    Science.gov (United States)

    Richardson, R. M.

    2016-12-01

    The kinematics of plate tectonics was established in the 1960s, and shortly thereafter the Earth's stress field was recognized as an important constraint on the dynamics of plate tectonics. Forty years ago the 1976 Chapman Conference on the Stress in the Lithosphere, which I was fortunate to attend as a graduate student, and the ensuing 1977 PAGEOPH Stress in the Earth publication's 28 articles highlighted a range of datasets and approaches that established fertile ground for geodynamic research ever since. What are the most useful indicators of stress? Do they measure residual or tectonic stresses? Local or far field sources? What role does rheology play in concentrating deformation? Great progress was made with the first World Stress Map in 1991 by Zoback and Zoback, and the current version (2016 release with 42,348 indicators) remains a tremendous resource for geodynamic research. Modeling sophistication has seen significant progress over the past 40 years. Early applications of stress to dynamics involved simple lithospheric flexure, particularly at subduction zones, Hawaii, and continental foreland basin systems. We have progressed to full 3-D finite element models for calculating the flexure and stress associated with loads on a crust and mantle with realistic non-linear viscoelastic rheology, including frictional sliding, low-temperature plasticity, and high-temperature creep. Initial efforts to use lithospheric stresses to constrain plate driving forces focused on a "top-down" view of the lithosphere. Such efforts have evolved to better include asthenosphere-lithosphere interactions, have gone from simple to complicated rheologies, from 2-D to 3-D, and seek to obtain a fully thermo-mechanical model that avoids relying on artificial boundary conditions to model plate dynamics. Still, there are a number of important issues in geodynamics, from philosophy (when are more complicated models necessary? can one hope to identify "the" answer with modeling, or only

  9. Metasomatized lithosphere and the origin of alkaline lavas.

    Science.gov (United States)

    Pilet, Sébastien; Baker, Michael B; Stolper, Edward M

    2008-05-16

    Recycled oceanic crust, with or without sediment, is often invoked as a source component of continental and oceanic alkaline magmas to account for their trace-element and isotopic characteristics. Alternatively, these features have been attributed to sources containing veined, metasomatized lithosphere. In melting experiments on natural amphibole-rich veins at 1.5 gigapascals, we found that partial melts of metasomatic veins can reproduce key major- and trace-element features of oceanic and continental alkaline magmas. Moreover, experiments with hornblendite plus lherzolite showed that reaction of melts of amphibole-rich veins with surrounding lherzolite can explain observed compositional trends from nephelinites to alkali olivine basalts. We conclude that melting of metasomatized lithosphere is a viable alternative to models of alkaline basalt formation by melting of recycled oceanic crust with or without sediment.

  10. South China Sea crustal thickness and lithosphere thinning from satellite gravity inversion incorporating a lithospheric thermal gravity anomaly correction

    Science.gov (United States)

    Kusznir, Nick; Gozzard, Simon; Alvey, Andy

    2016-04-01

    The distribution of ocean crust and lithosphere within the South China Sea (SCS) are controversial. Sea-floor spreading re-orientation and ridge jumps during the Oligocene-Miocene formation of the South China Sea led to the present complex distribution of oceanic crust, thinned continental crust, micro-continents and volcanic ridges. We determine Moho depth, crustal thickness and continental lithosphere thinning (1- 1/beta) for the South China Sea using a gravity inversion method which incorporates a lithosphere thermal gravity anomaly correction (Chappell & Kusznir, 2008). The gravity inversion method provides a prediction of ocean-continent transition structure and continent-ocean boundary location which is independent of ocean isochron information. A correction is required for the lithosphere thermal gravity anomaly in order to determine Moho depth accurately from gravity inversion; the elevated lithosphere geotherm of the young oceanic and rifted continental margin lithosphere of the South China Sea produces a large lithosphere thermal gravity anomaly which in places exceeds -150 mGal. The gravity anomaly inversion is carried out in the 3D spectral domain (using Parker 1972) to determine 3D Moho geometry and invokes Smith's uniqueness theorem. The gravity anomaly contribution from sediments assumes a compaction controlled sediment density increase with depth. The gravity inversion includes a parameterization of the decompression melting model of White & McKenzie (1999) to predict volcanic addition generated during continental breakup lithosphere thinning and seafloor spreading. Public domain free air gravity anomaly, bathymetry and sediment thickness data are used in this gravity inversion. 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, rift orientation and sea-floor spreading trajectory. SCS conjugate margins

  11. The State of Lithospheric Stress in Greater Thailand

    Science.gov (United States)

    Meyers, B.; Furlong, K. P.; Pananont, P.; Pornsopin, P.

    2013-12-01

    Thailand and its surrounding regions occupy an important, but often overlooked, location in terms of plate tectonics and lithospheric deformation. The lateral extrusion of Tibet southeastward and eastward along deep strike slip faults to the north and the Sumatra-Andaman subduction zone to the south and west bound the region of greater Thailand. While it is adjacent to some of the most seismically active plate boundaries and intra-plate regions on Earth, this region has experienced only a low level of background seismicity. Thus, the long-term seismic potential of greater Thailand remains highly uncertain. Although historic seismicity is one indicator for future seismicity it is not the only tool we have for determining seismic hazard; we can assess the state of lithospheric stress. The stress conditions in this apparent aseismic region will be controlled by the forces acting on it boundaries. We can analyze those conditions through a study of fault structure, earthquake activity, and kinematics in the boundary area. Using Global Seismic Network (GSN) data augmented with Thai seismic network data to constrain the kinematics, and numerical finite element modeling of crustal and lithospheric deformation of the region, we are able to determine to overall stress conditions. This stress model can be compared to the known fault states in Thailand to assess the potential for earthquake activity.

  12. The rheological structure of the lithosphere in the Eastern Marmara region, Turkey

    Science.gov (United States)

    Oruç, Bülent; Sönmez, Tuba

    2017-05-01

    The aim of this work is to propose the geometries of the crustal-lithospheric mantle boundary (Moho) and lithosphere-asthenosphere boundary (LAB) and the 1D thermal structure of the lithosphere, in order to establish a rheological model of the Eastern Marmara region. The average depths of Moho and LAB are respectively 35 km and 51 km from radially averaged amplitude spectra of EGM08 Bouguer anomalies. The geometries of Moho and LAB interfaces are estimated from the Parker-Oldenburg gravity inversion algorithm. Our results show the Moho depth varies from 31 km at the northern part of North Anatolian Fault Zone (NAFZ) to 39 km below the mountain belt in the southern part of the NAFZ. The depth to the LAB beneath the same parts of the region ranges from 45 km to 55 km. Having lithospheric strength and thermal boundary layer structure, we analyzed the conditions of development of lithosphere thinning. A two-dimensional strength profile has been estimated for rheology model of the study area. Thus we suggest that the rheological structure consists of a strong upper crust, a weak lower crust, and a partly molten upper lithospheric mantle.

  13. Continental growth by successive accretion of oceanic lithosphere: Evidence from tilted seismic anisotropy

    Science.gov (United States)

    Babuska, V.; Plomerova, J.; Karato, S. I.

    2012-04-01

    Although many studies indicate that subduction-related accretion, subduction-driven magmatism and tectonic stacking are major crustal-growth mechanisms, how the mantle lithosphere forms remains enigmatic. Cook (AGU Geod. Series 1986) published a model of continental 'shingling' based on seismic reflection data indicating dipping structures in the deep crust of accreted terranes. Helmstaedt and Gurney (J. Geoch. Explor. 1995) and Hart et al. (Geology 1997) suggest that the Archean continental lithosphere consists of alternating layers of basalt and peridotite derived from subducted and obducted Archean oceanic lithosphere. Peridotite xenoliths from the Mojavian mantle lithosphere (Luffi et al., JGR 2009), as well as xenoliths of eclogites underlying the Sierra Nevada batholith in California (Horodynskij et al., EPSL 2007), are representative for oceanic slab fragments successively attached to the continent. Recent seismological findings also seem to support a model of continental lithosphere built from systems of paleosubductions of plates of ancient oceanic lithosphere (Babuska and Plomerova, AGU Geoph. Monograph 1989), or by stacking of the plates (Helmstaedt and Schulze, Geol. Soc. Aust. Spec. Publ. 1989). Seismic anisotropy in the oceanic mantle lithosphere, explained mainly by the olivine A- (or D-) type fabric (Karato et al., Annu. Rev. Earth Planet. Sci. 2008), was discovered almost a half century ago (Hess, Nature 1964). Though it is difficult to determine seismic anisotropy within an active subducting slab (e.g., Healy et al., EPSL 2009; Eberhart-Phillips and Reyners, JGR 2009), field observations and laboratory experiments indicate the oceanic olivine fabric might be preserved there to a depth of at least 200-300 km. Dipping anisotropic fabrics in domains of the European mantle lithosphere were interpreted as systems of 'frozen' paleosubductions (Babuska and Plomerova, PEPI 2006), and the lithosphere base as a boundary between a fossil anisotropy in the

  14. Constraining lithosphere deformation modes during continental breakup for the Iberia-Newfoundland conjugate rifted margins

    Science.gov (United States)

    Jeanniot, Ludovic; Kusznir, Nick; Mohn, Geoffroy; Manatschal, Gianreto; Cowie, Leanne

    2016-06-01

    A kinematic model of lithosphere and asthenosphere deformation has been used to investigate lithosphere stretching and thinning modes during continental rifting leading to breakup and seafloor spreading. The model has been applied to two conjugate profiles across the Iberia-Newfoundland rifted margins and quantitatively calibrated using observed present-day water loaded subsidence and crustal thickness, together with observed mantle exhumation, subsidence and melting generation histories. The kinematic model uses an evolving prescribed flow-field to deform the lithosphere and asthenosphere leading to lithospheric breakup from which continental crustal thinning, lithosphere thermal evolution, decompression melt initiation and subsidence are predicted. We explore the sensitivity of model predictions to extension rate history, deformation migration and buoyancy induced upwelling. The best fit calibrated models of lithosphere deformation evolution for the Iberia-Newfoundland conjugate margins require; (1) an initial broad region of lithosphere deformation with passive upwelling, (2) lateral migration of deformation, (3) an increase in extension rate with time, (4) focussing of the deformation and (5) buoyancy induced upwelling. The model prediction of exhumed mantle at the Iberia-Newfoundland margins, as observed, requires a critical threshold of melting to be exceeded before melt extraction. The preferred calibrated models predict faster extension rates and earlier continental crustal separation and mantle exhumation for the Iberia Abyssal Plain-Flemish Pass conjugate margin profile than for the Galicia Bank-Flemish Cap profile to the north. The predicted N-S differences in the deformation evolution give insights into the 3D evolution of Iberia-Newfoundland margin crustal separation.

  15. Constraining lithosphere deformation mode evolution for the Iberia-Newfoundland rifted margins

    Science.gov (United States)

    Jeanniot, Ludovic; Kusznir, Nick; Mohn, Geoffroy; Manatschal, Gianreto

    2015-04-01

    The deformation of lithosphere and asthenosphere and its evolution during continental rifting leading to breakup and seafloor spreading initiation is poorly understood. The resulting margin architecture and OCT structure is complex and diverse, and observations at magma poor margins includes hyper-extended continental crust and lithosphere, detachments faults, exhumed mantle, continental slivers and scattered embryonic oceanic crust. A coupled kinematic-dynamic model of lithosphere and asthenosphere deformation has been used to investigate the sequence of lithosphere deformation modes for 2 conjugate margin profiles for the Iberia-Newfoundland rifted margins. We use the observed water-loaded subsidence and crustal thickness, together with subsidence history and the age of melt generation, to test and constrain lithosphere and asthenosphere deformation models. A sequence of lithosphere deformation modes is represented by a succession of flow-fields, which are generated by a 2D finite element viscous flow model (FE-Margin), and is used to advect lithosphere and asthenosphere temperature and material. FE-Margin is kinematically driven by divergent deformation in the upper 15-20 km of the lithosphere inducing passive upwelling below. Buoyancy enhanced upwelling (e.g. Braun et al. 2000) is also kinematically included. The methodology of Katz et al., 2003 is used to predict melt generation by decompressional melting. The magnitude of extension used in the modelling is consistent with that proposed by Sutra et al (2013). The best fit calibrated models of lithosphere deformation evolution for the Iberia-Newfoundland conjugate margins require (i) an initial broad region of lithosphere deformation and passive upwelling, (ii) lateral migration of deformation, (iii) an increase in extension rate with time, (iv) focussing of deformation and (v) buoyancy induced upwelling. The preferred calibrated models predict faster extension rates and earlier continental crustal rupture and

  16. Magnetic tracking of eye position in freely behaving chickens

    Directory of Open Access Journals (Sweden)

    Jason S Schwarz

    2013-11-01

    Full Text Available Research on the visual system of non-primates, such as birds and rodents, is increasing. Evidence that neural responses can differ dramatically between head-immobilized and freely behaving animals underlines the importance of studying visual processing in ethologically relevant contexts. In order to systematically study visual responses in freely behaving animals, an unobtrusive system for monitoring eye-in-orbit position in real time is essential. We describe a novel system for monitoring eye position that utilizes a head-mounted magnetic displacement sensor coupled with an eye-implanted magnet. This system is small, lightweight, and offers high temporal and spatial resolution in real time. We use the system to demonstrate the stability of the eye and the stereotypy of eye position during two different behavioral tasks in chickens. This approach offers a viable alternative to search coil and optical eye tracking techniques for high resolution tracking of eye-in-orbit positions in behaving animals.

  17. Magnetic tracking of eye position in freely behaving chickens

    Science.gov (United States)

    Schwarz, Jason S.; Sridharan, Devarajan; Knudsen, Eric I.

    2013-01-01

    Research on the visual system of non-primates, such as birds and rodents, is increasing. Evidence that neural responses can differ dramatically between head-immobilized and freely behaving animals underlines the importance of studying visual processing in ethologically relevant contexts. In order to systematically study visual responses in freely behaving animals, an unobtrusive system for monitoring eye-in-orbit position in real time is essential. We describe a novel system for monitoring eye position that utilizes a head-mounted magnetic displacement sensor coupled with an eye-implanted magnet. This system is small, lightweight, and offers high temporal and spatial resolution in real time. We use the system to demonstrate the stability of the eye and the stereotypy of eye position during two different behavioral tasks in chickens. This approach offers a viable alternative to search coil and optical eye tracking techniques for high resolution tracking of eye-in-orbit position in behaving animals. PMID:24312023

  18. Visualizing the Structure of the Earth’s Lithosphere on the Google Earth Virtual-Globe Platform

    Directory of Open Access Journals (Sweden)

    Liangfeng Zhu

    2016-03-01

    Full Text Available While many of the current methods for representing the existing global lithospheric models are suitable for academic investigators to conduct professional geological and geophysical research, they are not suited to visualize and disseminate the lithospheric information to non-geological users (such as atmospheric scientists, educators, policy-makers, and even the general public as they rely on dedicated computer programs or systems to read and work with the models. This shortcoming has become more obvious as more and more people from both academic and non-academic institutions struggle to understand the structure and composition of the Earth’s lithosphere. Google Earth and the concomitant Keyhole Markup Language (KML provide a universal and user-friendly platform to represent, disseminate, and visualize the existing lithospheric models. We present a systematic framework to visualize and disseminate the structure of the Earth’s lithosphere on Google Earth. A KML generator is developed to convert lithospheric information derived from the global lithospheric model LITHO1.0 into KML-formatted models, and a web application is deployed to disseminate and visualize those models on the Internet. The presented framework and associated implementations can be easily exported for application to support interactively integrating and visualizing the internal structure of the Earth with a global perspective.

  19. Water in the Cratonic Mantle Lithosphere

    Science.gov (United States)

    Peslier, A. H.

    2016-01-01

    The fact that Archean and Proterozoic cratons are underlain by the thickest (>200 km) lithosphere on Earth has always puzzled scientists because the dynamic convection of the surrounding asthenosphere would be expected to delaminate and erode these mantle lithospheric "keels" over time. Although density and temperature of the cratonic lithosphere certainly play a role in its strength and longevity, the role of water has only been recently addressed with data on actual mantle samples. Water in mantle lithologies (primarily peridotites and pyroxenites) is mainly stored in nominally anhydrous minerals (olivine, pyroxene, garnet) where it is incorporated as hydrogen bonded to structural oxygen in lattice defects. The property of hydrolytic weakening of olivine [4] has generated the hypothesis that olivine, the main mineral of the upper mantle, may be dehydrated in cratonic mantle lithospheres, contributing to its strength. This presentation will review the distribution of water concentrations in four cratonic lithospheres. The distribution of water contents in olivine from peridotite xenoliths found in kimberlites is different in each craton (Figure 1). The range of water contents of olivine, pyroxene and garnet at each xenolith location appears linked to local metasomatic events, some of which occurred later then the Archean and Proterozoic when these peridotites initially formed via melting. Although the low olivine water contents ( 6 GPa at the base of the Kaapvaal cratonic lithosphere may contribute to its strength, and prevent its delamination, the wide range of those from Siberian xenoliths is not compatible with providing a high enough viscosity contrast with the asthenophere. The water content in olivine inclusions from Siberian diamonds, on the other hand, have systematically low water contents (water contents. The olivine inclusions, however, may have been protected from metasomatism by their host diamond and record the overall low olivine water content of

  20. Was the magnitude (M = 9.0R) of the mega-earthquake of Japan (11th of March, 2011) predictable? An analysis based on the Lithospheric Seismic Energy Flow Model (LSEFM)

    CERN Document Server

    Thanassoulas, C; Verveniotis, G

    2012-01-01

    The Tohoku EQ (11th of March, 2011, M = 9.0) in Japan falsified the proposed EQ magnitude range (M = 7.0 - 8.5) of the same seismogenic regional area that had been determined by the compiled hazard maps, study of historical data, or other probabilistic methods while a larger magnitude (M > 9.0) had been proposed for all subduction zones. The observed discrepancy between the proposed EQ magnitude range and the actual one of the Tohoku EQ is studied in this work in terms of the cumulative seismic energy release of the study area and by the use of the Lithospheric Seismic Energy Flow Model (LSEFM). The results indicate that the Tohoku mega-earthquake magnitude could be predicted quite accurately provided that a long past seismic history had been available for use by the LSEFM procedure. Moreover, the presence, of the missing historic 1855 EQ (7.0 < M < 8.0) from seismic catalogs, was predicted backwards by the LSEFM method and its existence was verified by the Ishibashi (2004) work on Japanese historic sei...

  1. Seismic anisotropy of Precambrian lithosphere: Insights from Rayleigh wave tomography of the eastern Superior Craton

    Science.gov (United States)

    Petrescu, Laura; Darbyshire, Fiona; Bastow, Ian; Totten, Eoghan; Gilligan, Amy

    2017-05-01

    The thick, seismically fast lithospheric keels underlying continental cores (cratons) are thought to have formed in the Precambrian and resisted subsequent tectonic destruction. A consensus is emerging from a variety of disciplines that keels are vertically stratified, but the processes that led to their development remain uncertain. Eastern Canada is a natural laboratory to study Precambrian lithospheric formation and evolution. It comprises the largest Archean craton in the world, the Superior Craton, surrounded by multiple Proterozoic orogenic belts. To investigate its lithospheric structure, we construct a frequency-dependent anisotropic seismic model of the region using Rayleigh waves from teleseismic earthquakes recorded at broadband seismic stations across eastern Canada. The joint interpretation of phase velocity heterogeneity and azimuthal anisotropy patterns reveals a seismically fast and anisotropically complex Superior Craton. The upper lithosphere records fossilized Archean tectonic deformation: anisotropic patterns align with the orientation of the main tectonic boundaries at periods ≤110 s. This implies that cratonic blocks were strong enough to sustain plate-scale deformation during collision at 2.5 Ga. Cratonic lithosphere with fossil anisotropy partially extends beneath adjacent Proterozoic belts. At periods sensitive to the lower lithosphere, we detect fast, more homogenous, and weakly anisotropic material, documenting postassembly lithospheric growth, possibly in a slow or stagnant convection regime. A heterogeneous, anisotropic transitional zone may also be present at the base of the keel. The detection of multiple lithospheric fabrics at different periods with distinct tectonic origins supports growing evidence that cratonization processes may be episodic and are not exclusively an Archean phenomenon.

  2. High-resolution lithospheric structure beneath Mainland China from ambient noise and earthquake surface-wave tomography

    Science.gov (United States)

    Bao, X.; Song, X.; Li, J.

    2016-12-01

    We present a new high-resolution shear-velocity model of the lithosphere (down to about 160 km) beneath China using Rayleigh-wave tomography. We combined ambient noise and earthquake data recorded at 1316 seismic stations, the largest number used for the region to date. More than 700,000 dispersion curves were measured to generate group and phase velocity maps at periods of 10-140s. The resolution of our model is significantly improved over previous models with about 1-2°in eastern China and 2-3°in western China. We also derived models of the study region for crustal thickness and averaged S velocities for upper and mid-lower crust and uppermost mantle. These models reveal important lithospheric features beneath China and provide a fundamental data set for understanding continental dynamics and evolution. Different geological units show distinct features in the Moho depth, lithospheric thickness, and shear velocity. In particular, the North China Craton (NCC) lithosphere shows strong east-west structural variations with thin and low-velocity lithosphere in eastern NCC and thick and high-velocity lithosphere beneath western NCC and the lithosphere of the Ordos Block seems to have undergone strong erosion. The results support the progressive destruction of the NCC lithosphere from east to west at least partly caused by the thermal-chemical erosion of the cratonic lithosphere from the asthenosphere. Another pronounced feature of our model is the strong lateral variations of the mantle lithosphere beneath the Tibetan Plateau (TP). The Indian lithosphere beneath the TP shows variable northward advancement with nearly flat subduction in western and eastern TP and steep subduction in central TP with evidence for the tearing of Indian lithosphere beneath central TP, which may be important for the riftings at the surface in Himalayas and southern TP. The low-velocity zone in northern TP shows strong correlation with the region of the mid-Miocene to Quaternary potassic

  3. Microearthquake activity, lithospheric structure, and deformation modes at an amagmatic ultraslow spreading Southwest Indian Ridge segment

    Science.gov (United States)

    Schmid, Florian; Schlindwein, Vera

    2016-07-01

    While nascent oceanic lithosphere at slow to fast spreading mid-ocean ridges (MOR) is relatively well studied, much less is known about the lithospheric structure and properties at ultraslow MORs. Here we present microearthquake data from a 1 year ocean bottom seismometer deployment at the amagmatic, oblique supersegment of the ultraslow spreading Southwest Indian Ridge. A refraction seismic experiment was performed to constrain upper lithosphere P-velocities and results were used to construct a 1D velocity model for earthquake location. Earthquake foci were located individually and subsequently relocated relative to each other to sharpen the image of seismically active structures. Frequent earthquake activity extends to 31 km beneath the seafloor, indicating an exceptionally thick brittle lithosphere and an undulating brittle-ductile transition that implies significant variations in the along-axis thermal structure of the lithosphere. We observe a strong relation between petrology, microseismicity distribution, and topography along the ridge axis: Peridotite-dominated areas associate with deepest hypocenters, vast volumes of lithosphere that deforms aseismically as a consequence of alteration, and the deepest axial rift valley. Areas of basalt exposure correspond to shallower hypocenters, shallower and more rugged axial seafloor. Focal mechanisms deviate from pure extension and are spatially variable. Earthquakes form an undulating band of background seismicity and do not delineate discrete detachment faults as common on slow spreading ridges. Instead, the seismicity band sharply terminates to the south, immediately beneath the rift boundary. Considering the deep alteration, large steep boundary faults might be present but are entirely aseismic.

  4. Depth-dependent extension, two-stage breakup and depleted lithospheric counterflow at rifted margins

    Science.gov (United States)

    Huismans, Ritske S.; Beaumont, Christopher

    2014-05-01

    Uniform lithospheric extension predicts basic properties of non-volcanic rifted margins but fails to explain other important characteristics. Significant discrepancies are observed at 'type I' margins (such as the Iberia-Newfoundland conjugates), where large tracts of continental mantle lithosphere are exposed at the sea floor, and 'type II' margins (such as some ultrawide central South Atlantic margins), where thin continental crust spans wide regions below which continental lower crust and mantle lithosphere have apparently been removed. Neither corresponds to uniform extension. Instead, either crust or mantle lithosphere has been preferentially removed. Using dynamical models, we demonstrate that these margins are opposite end members: in type I, depth-dependent extension results in crustal-necking breakup before mantle-lithosphere breakup and in type II, the converse is true. These two-layer, two-stage breakup behaviours explain the discrepancies and have implications for the styles of the associated sedimentary basins. Laterally flowing lower-mantle lithosphere may underplate both type I and type II margins, thereby contributing to their anomalous characteristics.

  5. A sharp lithosphere-asthenosphere boundary imaged beneath eastern North America.

    Science.gov (United States)

    Rychert, Catherine A; Fischer, Karen M; Rondenay, Stéphane

    2005-07-28

    Plate tectonic theory hinges on the concept of a relatively rigid lithosphere moving over a weaker asthenosphere, yet the nature of the lithosphere-asthenosphere boundary remains poorly understood. The gradient in seismic velocity that occurs at this boundary is central to constraining the physical and chemical properties that create differences in mechanical strength between the two layers. For example, if the lithosphere is simply a thermal boundary layer that is more rigid owing to colder temperatures, mantle flow models indicate that the velocity gradient at its base would occur over tens of kilometres. In contrast, if the asthenosphere is weak owing to volatile enrichment or the presence of partial melt, the lithosphere-asthenosphere boundary could occur over a much smaller depth range. Here we use converted seismic phases in eastern North America to image a very sharp seismic velocity gradient at the base of the lithosphere-a 3-11 per cent drop in shear-wave velocity over a depth range of 11 km or less at 90-110 km depth. Such a strong, sharp boundary cannot be reconciled with a purely thermal gradient, but could be explained by an asthenosphere that contains a few per cent partial melt or that is enriched in volatiles relative to the lithosphere.

  6. Pre-subduction metasomatic enrichment of the oceanic lithosphere induced by plate flexure

    Science.gov (United States)

    Pilet, S.; Abe, N.; Rochat, L.; Kaczmarek, M.-A.; Hirano, N.; Machida, S.; Buchs, D. M.; Baumgartner, P. O.; Müntener, O.

    2016-12-01

    Oceanic lithospheric mantle is generally interpreted as depleted mantle residue after mid-ocean ridge basalt extraction. Several models have suggested that metasomatic processes can refertilize portions of the lithospheric mantle before subduction. Here, we report mantle xenocrysts and xenoliths in petit-spot lavas that provide direct evidence that the lower oceanic lithosphere is affected by metasomatic processes. We find a chemical similarity between clinopyroxene observed in petit-spot mantle xenoliths and clinopyroxene from melt-metasomatized garnet or spinel peridotites, which are sampled by kimberlites and intracontinental basalts respectively. We suggest that extensional stresses in oceanic lithosphere, such as plate bending in front of subduction zones, allow low-degree melts from the seismic low-velocity zone to percolate, interact and weaken the oceanic lithospheric mantle. Thus, metasomatism is not limited to mantle upwelling zones such as mid-ocean ridges or mantle plumes, but could be initiated by tectonic processes. Since plate flexure is a global mechanism in subduction zones, a significant portion of oceanic lithospheric mantle is likely to be metasomatized. Recycling of metasomatic domains into the convecting mantle is fundamental to understanding the generation of small-scale mantle isotopic and volatile heterogeneities sampled by oceanic island and mid-ocean ridge basalts.

  7. GAS BUBBLE-FACILITATED TRANSPORT OF METALS IN LITHOSPHERE

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    A physicochemical model for transport of mobile forms of occurrence of elements by gas bubbles in porous medium-gas bubble-facilitated transport of metals in the lithosphere is proposed and its corresponding mathematical model is discussed. The physico-chemical model consists of three phases: water with dissolved metallic elements, gas bubbles and solid matrix of the porous medium. In the model the gas bubbles act as carriers to transport the elements in the pore water from the depth in the lithosphere to the Earth's surface. In the process of transportation the elements dissipate in porous rocks and consequently a new kind of geochemical halo-jet halo of dispersion is formed in the rocks. In order to describe the transport and fate of the elements in the porous rocks a nonlinear quasiconvection mathematical model is developed, in which the transport of elements is modeled by a quasiconvection of gas bubbles with the elements and the interaction of elements with the porous medium is represented by a second-order chemical kinetics. A finite difference scheme is provided to solve the nonlinear quasiconvection model. From the numerical solutions a stabilization effect of concentration front in the transportation of elements in the porous medium is discovered. The sensitivities of the stabilization effect to model parameters are analyzed. To verify the reality of the mathematical model, physicochemical modeling experiments are conducted. The obtained experimental data support the proposed model in this work.

  8. Constraints on lithospheric thermal structure for the Indian Ocean from depth and heat flow data

    Science.gov (United States)

    Shoberg, Tom; Stein, Carol A.; Stein, Seth

    1993-06-01

    Models for the thermal evolution of oceanic lithosphere are primarily constrained by variations in seafloor depth and heat flow with age. These models have been largely based on data from the Pacific and Atlantic Ocean basins. We construct seafloor age relations for the Indian Ocean which we combine with bathymetric, sediment isopach and heat flow data to derive curves for depth and heat flow versus age. Comparison of these curves with predictions from three thermal models shows that they are better fit by the shallower depths and higher heat flow for the GDH1 model, which is characterized by a thinner and hotter lithosphere than previous models.

  9. Magnetic mineralogy of the Mercurian lithosphere

    Science.gov (United States)

    Strauss, B. E.; Feinberg, J. M.; Johnson, C. L.

    2016-11-01

    Mercury and Earth are the only inner solar system planets with active, internally generated dynamo magnetic fields. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission recently detected magnetic fields on Mercury that are consistent with lithospheric magnetization. We investigate the physical and chemical environment of Mercury's lithosphere, past and present, to establish the conditions under which magnetization may have been acquired and modified. Three factors are particularly crucial to the determination of crustal composition and iron mineralogy: redox conditions in the planet's crust and mantle, the iron content of the lithosphere, and, for any remanent magnetization, the temperature profile of the lithosphere and its evolution over time. We explore potential mechanisms for remanence acquisition and alteration on Mercury, whose surface environment is both hot and highly reducing. The long-term thermal history of Mercury's crust plays an important role in the longevity of any remanent crustal magnetization, which may be subject to remagnetization through thermal, viscous, and shock mechanisms. This thermal and compositional framework is used both to constrain plausible candidate minerals that could carry magnetic remanence on Mercury and to evaluate their capacity to acquire and retain sufficient magnetization to be detectable from satellite orbit. We propose that iron metal and its alloys are likely to be the dominant contributors to induced and remanent magnetization in Mercury's lithosphere, with additional contributions from iron silicides, sulfides, and carbides.

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

    Science.gov (United States)

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

    2014-12-01

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

  11. Thermal-rheological structure of the lithosphere beneath Jiyang Depression: Its implications for geodynamics

    Institute of Scientific and Technical Information of China (English)

    LIU Shaowen; WANG Liangshu; GONG Yuling; LI Cheng; LI Hua; HAN Yongbing

    2005-01-01

    Jiyang Depression, located in the southeast Bohai Bay Basin, has the geomorphologic framework of multiple uplifts intervening with sags. Combined the abundant geo-temperature data and thermo-physical parameters of rock samples derived from oil and gas exploration during the past years, with geothermal approaches, here we investigate the lithospheric thermal regime of this depression. Consequently, based on the obtained thermal structure of the lithosphere, along with rheological modeling, the lithospheric rheological profiles of Jiyang Depression are then determined. Our results show that the temperature at the bottom of sedimentary cover within depression varies from 129℃ to 298℃, accompanied with the basement heat flow ranging between 54.3 and 60.5 mW/m2; and 406℃-436℃ for temperature at the bottom of the upper crust, along with heat flow varying from 47.7 to 52.6 mW/m2; while the temperature at the bottom of the middle crust is between 537℃ and 572℃, as well as heat flow ranging from 41.3 to 56.3 mW/m2. The temperature at Moho ranges from 669℃ to 721℃, the heat flow derived from mantle is between 38.1 and 43.1 mW/m2, and calculated thickness of the thermal lithosphere beneath depression varies from 71 to 90 km. Lithospheric thermal regime is a close correlation with such factors as crustal thickness and surface heat flow, etc. Usually, the larger the surface heat flow, the larger the deep temperature and heat flow within lithosphere, and the thinner the thermal lithospheric thickness. This high thermal regime of the lithosphere in Jiyang Depression is thought to be related to Cenozoic back-arc spreading during the western Pacific plate subduction into Eurasian continent. Lithospheric rheological modeling shows that the lithosphere in Jiyang Depression is characterized by its distinct rheological stratification as follows: The upper and most part of the middle crust are of brittle, while the lower crust and the lower part of middle crust are all

  12. Lithospheric stress patterns: A global view

    Science.gov (United States)

    Zoback, Mary Lou; Burke, Kevin

    The present-day lithospheric stress state is the result of a variety of forces that act on and within the tectonic plates forming the Iithosphere. Knowledge of this stress state provides important constraints on forces acting at a variety of scales and, hence, helps to solve scientific problems of interest to a wide spectrum of scientists and engineers.Six years of effort by scientists from all over the world (listed at end of article) brought together under the International Lithosphere Program (ILP) of the joint International Union of Geodesy and Geophysics/International Union of Geological Sciences (IUGG/IUGS) Interunion Commission on the Lithosphere culminated in the July 1992 publication of the World Stress Map and nineteen accompanying research papers in a special issue of the Journal of Geophysical Research-Solid Earth (volume 87, number B8). Figure 1 shows a reduced version of the published 1:40,000,000 color map.

  13. Lithospheric structure in the Pacific geoid

    Science.gov (United States)

    Marsh, B. D.; Hinojosa, J. H.

    1985-01-01

    The high degree and order SEASAT geoid in the central Pacific correlates closely with the structure of the cooling lithosphere. Relative changes in plate age across major fracture zones in relatively young seafloor frame the east-west trending pattern formed by the geoid anomalies. The field removal in bathymetry corresponds to removal of some of the low degree and order geoidal components, the step like structure across fracture zones is also removed. The regional thermal subsidence was removed from the bathymetry by subtracting a mean subsidence surface from the observed bathymetry. This produces a residual bathymetry map analogous to the usual residual depth anomaly maps. The residual bathymetry obtained in this way contains shallow depths for young seafloor, and larger depths for older seafloor, thus retaining the structure of the lithosphere while removing the subsidence of the lithosphere.

  14. Time-dependent thermal state of the lithosphere in the foreland of the Eastern Carpathians bend. Insights from new geothermal measurements and modelling results

    DEFF Research Database (Denmark)

    Demetrescu, Crisan; Wilhelm, H.; Tumanian, M.

    2007-01-01

    and geological information on structure, lithology and time evolution of the sedimentary pile have been used to model the thermal evolution by means of a 2-D finite element model which includes sedimentation history, sediment compaction, lateral and vertical variation of thermal properties of sediments...

  15. Hydration of marginal basins and compositional variations within the continental lithospheric mantle inferred from a new global model of shear and compressional velocity

    DEFF Research Database (Denmark)

    Tesoniero, Andrea; Auer, Ludwig; Boschi, Lapo;

    2015-01-01

    We present a new global model of shear and compressional wave speeds for the entire mantle, partly based on the data set employed for the shear velocity model savani. We invert Rayleigh and Love surface waves up to the sixth overtone in combination with major P and S body wave phases. Mineral...

  16. The Effect of Heterogeneous Lithospheric Structure on Surface Stress and Tectonics on Mercury

    Science.gov (United States)

    Rosenburg, M. A.; Williams, J.; Aharonson, O.

    2008-12-01

    Observations of Mercury's surface from the Mariner 10 and MESSENGER spacecraft reveal a planet-wide distribution of lobate scarps, which are interpreted to be the surface expression of thrust faults due to global contraction. Statistical analysis of scarps mapped in images from both missions suggests that the orientations of these features are not consistent with a uniform distribution, the expected outcome for a contracting lithosphere of constant thickness. One possible explanation for this observation considers Mercury's thermal state, which is driven by the insolation pattern. Mercury's 3:2 spin-orbit resonance, in concert with its substantial orbital eccentricity of e = 0.20, causes long-wavelength surface temperature variations of more than 130 K. Corresponding variations in lithospheric thickness are hence expected. If the contraction occurred while Mercury was in this dynamical state, the resulting stress distribution recorded on the surface during global cooling and inner core solidification may reflect this heterogeneity. We seek to determine whether contraction of a lithosphere with lateral thickness variations can explain the observed lobate scarp orientations on Mercury's surface. We employ the three-dimensional, viscoelastic, finite element model CitcomSVE along with a thermal evolution model to study Mercury's response to cooling, inner core formation, and lithosphere growth and to track the accumulation of stress in the lithosphere. The resulting stress pattern can then be compared to the orientations and distribution of scarps mapped on the surface of Mercury. Preliminary results indicate systematic variations between the expected orientation of faults in the "cold poles," where the lithosphere is thicker and the "hot poles," where the lithosphere is weaker. As MESSENGER returns more data, comparisons between model results and surface features will be refined.

  17. Lithosphere Response to Intracratonic Rifting: Examples from Europe and Siberia

    DEFF Research Database (Denmark)

    Artemieva, I. M.; Thybo, H.; Herceg, M.

    2012-01-01

    is based on critically assessed results from various seismic studies, including reflection and refraction profiles and receiver function studies. We also use global shear-wave tomography models, gravity constraints based on GOCE data, and thermal models for the lithosphere to speculate on thermo...... of basaltic magmas and consequently in a change in mantle density and seismic velocities. Although kimberlite magmatism is commonly not considered as a rifting events, its deep causes may be similar to the mantle-driven rifting and, as a consequence, modification of mantle density and velocity structure may...... in it seismic wave velocity and density structure....

  18. Lithosphere-asthenosphere system in the Mediterranean region in the framework of polarized plate tectonics

    CERN Document Server

    Raykova, Reneta Blagoeva; Doglioni, Carlo

    2015-01-01

    Velocity structure of the lithosphere-asthenosphere system, to the depth of about 350 km, is obtained for almost 400 cells, sized 1 degree by 1 degree in the Mediterranean region. The models are obtained by the following sequence of methods and tools: surface-wave dispersion measurements and collection; 2D tomography of dispersion relations; non-linear inversion of cellular dispersion relations; smoothing optimization method to select a preferred model for each cell. The 3D velocity model, that satisfies Occam razor principle, is obtained as a juxtaposition of selected cellular models. The reconstructed picture of the lithosphere-asthenosphere system evidences the, globally well known, asymmetry between the W- and E-directed subduction zones, attributed to the westward drift of the lithosphere relative to the mantle. Different relationship between slabs and mantle dynamics cause strong compositional differences in the upper mantle, as shown by large variations of seismic waves velocity, consistent with Polari...

  19. Earth's lithospheric magnetic field determined to spherical harmonic degree 90 from CHAMP satellite measurements

    DEFF Research Database (Denmark)

    Maus, S.; Rother, M.; Hemant, K.;

    2006-01-01

    The CHAMP magnetic field mission is providing highly reliable measurements from which the global lithospheric magnetic field can be determined in unprecedented resolution and accuracy. Using almost 5 yr of data, we derive our fourth generation lithospheric field model termed MF4, which is expanded...... to spherical harmonic degree and order 90. After subtracting from the full magnetic field observations predicted fields from an internal field model up to degree 15, an external field model up to degree two, and the predicted magnetic field signatures for the eight dominant ocean tidal constituents, we fit...... of the lithospheric field down to an altitude of about 50 km at lower latitudes, with reduced accuracy in the polar regions. Crustal features come out significantly sharper than in previous models. In particular, bands of magnetic anomalies along subduction zones become visible by satellite for the first time....

  20. Thermal cooling of the oceanic lithosphere from geoid height data

    Science.gov (United States)

    Cazenae, A.

    1985-01-01

    Another type of geophysical observation has proved to be very useful in the study of thermal cooling of the oceanic lithosphere. It is the geoid height derivative with respect to plate age, a quantity computed from the short wavelength geoid step across fracture zones measured by altimeter satellites. Two categories of simples models are proposed to describe cooling and contraction of the oceanic lithosphere with age. Both plate model and half space model, give almost similar results up to ages of 50 to 70 ma, but predict quite distinct behavior of seafloor depth, heat flow and other parameters in old basins. Tests of thermal models are based on heat flow and topography data. However, heat flow is not very sensitive to the form of the thermal model. Large areas of the ocean floor are particularly shallow, and as a result topography data may not be very appropriate to discriminate between plate and half space models, and no clear concensus on a preferred model yet exists.

  1. Lithospheric thinning beneath rifted regions of Southern California.

    Science.gov (United States)

    Lekic, Vedran; French, Scott W; Fischer, Karen M

    2011-11-11

    The stretching and break-up of tectonic plates by rifting control the evolution of continents and oceans, but the processes by which lithosphere deforms and accommodates strain during rifting remain enigmatic. Using scattering of teleseismic shear waves beneath rifted zones and adjacent areas in Southern California, we resolve the lithosphere-asthenosphere boundary and lithospheric thickness variations to directly constrain this deformation. Substantial and laterally abrupt lithospheric thinning beneath rifted regions suggests efficient strain localization. In the Salton Trough, either the mantle lithosphere has experienced more thinning than the crust, or large volumes of new lithosphere have been created. Lack of a systematic offset between surface and deep lithospheric deformation rules out simple shear along throughgoing unidirectional shallow-dipping shear zones, but is consistent with symmetric extension of the lithosphere.

  2. Gravity and multichannel seismic reflection constraints on the lithospheric structure of the Canary Swell

    Science.gov (United States)

    Ranero, C. R.; Torne, M.; Banda, E.

    1995-12-01

    Deep penetrating multichannel seismic reflection and gravity data have been used to study the lithospheric structure of the Canary Swell. The seismic reflection data show the transition from undisturbed Jurassic oceanic crust, away from the Canary Islands, to an area of ocean crust strongly modified by the Canary volcanism (ACV). Outside the ACV the seismic records image a well layered sedimentary cover, underlined by a bright reflection from the top of the igneous basement and also relatively continuous reflections from the base of the crust. In the ACV the definition of the boundary between sedimentary cover and igneous basement and the crust-mantle boundary remains very loose. Two-dimensional gravity modelling in the area outside the influence of the Canary volcanism, where the reflection data constrain the structure of the ocean crust, suggests a thinning of the lithosphere. The base of the lithosphere rises from 100 km, about 400 km west of the ACV, to 80 km at the outer limit of the ACV. In addition, depth conversion of the seismic reflection data and unloading of the sediments indicate the presence of a regional depth anomaly of an extension similar to the lithospheric thinning inferred from gravity modelling. The depth anomaly associated with the swell, after correction for sediment weight, is about 500 m. We interpret the lithospheric thinning as an indication of reheating of old Mesozoic lithosphere beneath the Canary Basin and along with the depth anomaly as indicating a thermal rejuvenation of the lithosphere. We suggest that the most likely origin for the Canary Islands is a hot spot.

  3. Olivine anisotropy suggests Gutenberg discontinuity is not the base of the lithosphere.

    Science.gov (United States)

    Hansen, Lars N; Qi, Chao; Warren, Jessica M

    2016-09-20

    Tectonic plates are a key feature of Earth's structure, and their behavior and dynamics are fundamental drivers in a wide range of large-scale processes. The operation of plate tectonics, in general, depends intimately on the manner in which lithospheric plates couple to the convecting interior. Current debate centers on whether the transition from rigid lithosphere to flowing asthenosphere relates to increases in temperature or to changes in composition such as the presence of a small amount of melt or an increase in water content below a specified depth. Thus, the manner in which the rigid lithosphere couples to the flowing asthenosphere is currently unclear. Here we present results from laboratory-based torsion experiments on olivine aggregates with and without melt, yielding an improved database describing the crystallographic alignment of olivine grains. We combine this database with a flow model for oceanic upper mantle to predict the structure of the seismic anisotropy beneath ocean basins. Agreement between our model and seismological observations supports the view that the base of the lithosphere is thermally controlled. This model additionally supports the idea that discontinuities in velocity and anisotropy, often assumed to be the base of the lithosphere, are, instead, intralithospheric features reflecting a compositional boundary established at midocean ridges, not a rheological boundary.

  4. Thermal erosion of cratonic lithosphere as a potential trigger for mass-extinction.

    Science.gov (United States)

    Guex, Jean; Pilet, Sebastien; Müntener, Othmar; Bartolini, Annachiara; Spangenberg, Jorge; Schoene, Blair; Sell, Bryan; Schaltegger, Urs

    2016-03-24

    The temporal coincidence between large igneous provinces (LIPs) and mass extinctions has led many to pose a causal relationship between the two. However, there is still no consensus on a mechanistic model that explains how magmatism leads to the turnover of terrestrial and marine plants, invertebrates and vertebrates. Here we present a synthesis of ammonite biostratigraphy, isotopic data and high precision U-Pb zircon dates from the Triassic-Jurassic (T-J) and Pliensbachian-Toarcian (Pl-To) boundaries demonstrating that these biotic crises are both associated with rapid change from an initial cool period to greenhouse conditions. We explain these transitions as a result of changing gas species emitted during the progressive thermal erosion of cratonic lithosphere by plume activity or internal heating of the lithosphere. Our petrological model for LIP magmatism argues that initial gas emission was dominated by sulfur liberated from sulfide-bearing cratonic lithosphere before CO2 became the dominant gas. This model offers an explanation of why LIPs erupted through oceanic lithosphere are not associated with climatic and biotic crises comparable to LIPs emitted through cratonic lithosphere.

  5. Olivine anisotropy suggests Gutenberg discontinuity is not the base of the lithosphere

    Science.gov (United States)

    Hansen, Lars N.; Qi, Chao; Warren, Jessica M.

    2016-09-01

    Tectonic plates are a key feature of Earth’s structure, and their behavior and dynamics are fundamental drivers in a wide range of large-scale processes. The operation of plate tectonics, in general, depends intimately on the manner in which lithospheric plates couple to the convecting interior. Current debate centers on whether the transition from rigid lithosphere to flowing asthenosphere relates to increases in temperature or to changes in composition such as the presence of a small amount of melt or an increase in water content below a specified depth. Thus, the manner in which the rigid lithosphere couples to the flowing asthenosphere is currently unclear. Here we present results from laboratory-based torsion experiments on olivine aggregates with and without melt, yielding an improved database describing the crystallographic alignment of olivine grains. We combine this database with a flow model for oceanic upper mantle to predict the structure of the seismic anisotropy beneath ocean basins. Agreement between our model and seismological observations supports the view that the base of the lithosphere is thermally controlled. This model additionally supports the idea that discontinuities in velocity and anisotropy, often assumed to be the base of the lithosphere, are, instead, intralithospheric features reflecting a compositional boundary established at midocean ridges, not a rheological boundary.

  6. Lithospheric thermal structure of the North China Craton and its geodynamic implications

    Science.gov (United States)

    Liu, Qiongying; Zhang, Linyou; Zhang, Chao; He, Lijuan

    2016-12-01

    We conduct 2-D numerical modeling of the lithospheric thermal structure of the North China Craton (NCC) on basis of twenty-four crustal velocity structure profiles. About five hundred heat flow data constitute the principal constraints for our modeling. The modeling results demonstrate marked lateral variations in thermal regime of the crust-lithosphere system in the NCC. The average mantle heat flow decreases from 38 ± 5 mW m-2 under the Bohai Bay Basin in the eastern NCC to 27 ± 4 mW m-2 under the Ordos Basin in the western NCC, characterized by a 'cold crust but hot mantle' structure and a 'hot crust but cold mantle' structure, respectively. Thermal lithospheric thickness varies from ∼65 km beneath the Tan-Lu Fault zone to ∼160 km beneath the western and northern Ordos Basin, with similar trend to the seismic lithosphere. However, the disparities in thickness between the thermal and seismic lithosphere are within 20 km beneath the Bohai Bay Basin, but 30-90 km beneath the Shanxi-Weihe Graben and 50-120 km beneath the Ordos Basin. This may imply a westward thickening trend of the rheological boundary layer, which might be attributed to the reducing of asthenosphere viscosity due to hydrous fluid released by dehydration of the subducting Pacific Plate under the eastern NCC. Combined with other pieces of evidence, we suggest that vigorous mantle processes may occur beneath the eastern NCC, whereas the western NCC is relatively stable.

  7. Lithosphere Response to Intracratonic Rifting: Examples from Europe and Siberia

    DEFF Research Database (Denmark)

    Artemieva, I. M.; Thybo, H.; Herceg, M.;

    2012-01-01

    . The pattern of is controlled by the pre-existing tectonic setting and the intensity of lithosphere-mantle interaction. The results are summarized in a series of maps of lateral variations in lithosphere structure, including the depth to the LAB and compositional heterogeneity of the lithosphere as reflected...

  8. Volcanism, Earth Degassing and Replenished Lithosphere Mantle

    Science.gov (United States)

    Bailey, D. K.

    1980-07-01

    Volcanism that pierces plate interiors is characteristically rich in alkalis and volatiles, and its cause and persistence are essentially expressions of the Earth's outgassing. The general balance of mobile elements (such as H, C, F and Cl) rules out recycling of sea floor, hydrosphere, sediments or atmosphere: furthermore, it is not in accord with accepted planet degassing budgets. The typical eruptive mode of volatile-rich magmatism means that the observed regional chemical variations, and even differences between adjacent volcanoes, must largely reflect source heterogeneity. In a broader context, this magmatism is also at odds with a concept of continental crust underlain by strongly depleted (refractory) mantle. Repetition of activity along crustal zones of weakness shows that the lithosphere mantle (a) is structurally complex and (b) still holds continuing (or continual) rich reserves of mobile elements. Unbroken lithosphere muffles the evolutionary escape of volatiles from the deep mantle: any lesion that appears then offers easy escape channels, whereby volatiles are drained from a large mantle region and funnelled through the plate. Horizontal movement of thick continental lithosphere releases volatiles from deep sources, imparting some of the special chemical characteristics of the stable continental magmatism. Present evidence requires consideration of the continental lithosphere as a site of primordial heterogeneity that has been accentuated rather than diminished by geological processes.

  9. The lithospheric mantle below southern West Greenland

    DEFF Research Database (Denmark)

    Sand, Karina Krarup; Waight, Tod Earle; Pearson, D. Graham

    2009-01-01

    Geothermobarometry of primarily garnet lherzolitic xenoliths from several localities in southern West Greenland is applied to address the diamond potential, pressure and temperature distribution and the stratigraphy of the subcontinental lithospheric mantle ~600 Ma ago. The samples are from kimbe...... into the reworked Archean North of the Naqssugtoqidian deformation front....

  10. Geodynamic inversion to constrain the non-linear rheology of the lithosphere

    Science.gov (United States)

    Baumann, T. S.; Kaus, Boris J. P.

    2015-08-01

    One of the main methods to determine the strength of the lithosphere is by estimating it's effective elastic thickness. This method assumes that the lithosphere is a thin elastic plate that floats on the mantle and uses both topography and gravity anomalies to estimate the plate thickness. Whereas this seems to work well for oceanic plates, it has given controversial results in continental collision zones. For most of these locations, additional geophysical data sets such as receiver functions and seismic tomography exist that constrain the geometry of the lithosphere and often show that it is rather complex. Yet, lithospheric geometry by itself is insufficient to understand the dynamics of the lithosphere as this also requires knowledge of the rheology of the lithosphere. Laboratory experiments suggest that rocks deform in a viscous manner if temperatures are high and stresses low, or in a plastic/brittle manner if the yield stress is exceeded. Yet, the experimental results show significant variability between various rock types and there are large uncertainties in extrapolating laboratory values to nature, which leaves room for speculation. An independent method is thus required to better understand the rheology and dynamics of the lithosphere in collision zones. The goal of this paper is to discuss such an approach. Our method relies on performing numerical thermomechanical forward models of the present-day lithosphere with an initial geometry that is constructed from geophysical data sets. We employ experimentally determined creep-laws for the various parts of the lithosphere, but assume that the parameters of these creep-laws as well as the temperature structure of the lithosphere are uncertain. This is used as a priori information to formulate a Bayesian inverse problem that employs topography, gravity, horizontal and vertical surface velocities to invert for the unknown material parameters and temperature structure. In order to test the general methodology

  11. Lithospheric radial anisotropy beneath the Gulf of Mexico

    Science.gov (United States)

    Chu, Risheng; Ko, Justin Yen-Ting; Wei, Shengji; Zhan, Zhongwen; Helmberger, Don

    2017-05-01

    The Lithosphere-Asthenosphere Boundary (LAB), where a layer of low viscosity asthenosphere decouples with the upper plate motion, plays an essential role in plate tectonics. Most dynamic modeling assumes that the shear velocity can be used as a surrogate for viscosity which provides key information about mantle flow. Here, we derive a shear velocity model for the LAB structure beneath the Gulf of Mexico allowing a detailed comparison with that beneath the Pacific (PAC) and Atlantic (ATL). Our study takes advantage of the USArray data from the March 25th, 2013 Guatemala earthquake at a depth of 200 km. Such data is unique in that we can observe a direct upward traveling lid arrival which remains the first arrival ahead of the triplications beyond 18°. This extra feature in conjunction with upper-mantle triplication sampling allows good depth control of the LAB and a new upper-mantle seismic model ATM, a modification of ATL, to be developed. ATM has a prominent low velocity zone similar to the structure beneath the western Atlantic. The model contains strong radial anisotropy in the lid where VSH is about 6% faster than VSV. This anisotropic feature ends at the bottom of the lithosphere at about the depth of 175 km in contrast to the Pacific where it extends to over 300 km. Another important feature of ATM is the weaker velocity gradient from the depth of 175 to 350 km compared to Pacific models, which may be related to differences in mantle flow.

  12. Evolution of the East African rift: Drip magmatism, lithospheric thinning and mafic volcanism

    Science.gov (United States)

    Furman, Tanya; Nelson, Wendy R.; Elkins-Tanton, Linda T.

    2016-07-01

    The origin of the Ethiopian-Yemeni Oligocene flood basalt province is widely interpreted as representing mafic volcanism associated with the Afar mantle plume head, with minor contributions from the lithospheric mantle. We reinterpret the geochemical compositions of primitive Oligocene basalts and picrites as requiring a far more significant contribution from the metasomatized subcontinental lithospheric mantle than has been recognized previously. This region displays the fingerprints of mantle plume and lithospheric drip magmatism as predicted from numerical models. Metasomatized mantle lithosphere is not dynamically stable, and heating above the upwelling Afar plume caused metasomatized lithosphere with a significant pyroxenite component to drip into the asthenosphere and melt. This process generated the HT2 lavas observed today in restricted portions of Ethiopia and Yemen now separated by the Red Sea, suggesting a fundamental link between drip magmatism and the onset of rifting. Coeval HT1 and LT lavas, in contrast, were not generated by drip melting but instead originated from shallower, dominantly anhydrous peridotite. Looking more broadly across the East African Rift System in time and space, geochemical data support small volume volcanic events in Turkana (N. Kenya), Chyulu Hills (S. Kenya) and the Virunga province (Western Rift) to be derived ultimately from drip melting. The removal of the gravitationally unstable, metasomatized portion of the subcontinental lithospheric mantle via dripping is correlated in each case with periods of rapid uplift. The combined influence of thermo-mechanically thinned lithosphere and the Afar plume together thus controlled the locus of continental rift initiation between Africa and Arabia and provide dynamic support for the Ethiopian plateau.

  13. Lithosphere versus asthenosphere mantle sources at the Big Pine Volcanic Field, California

    Science.gov (United States)

    Gazel, Esteban; Plank, Terry; Forsyth, Donald W.; Bendersky, Claire; Lee, Cin-Ty A.; Hauri, Erik H.

    2012-06-01

    Here we report the first measurements of the H2O content of magmas and mantle xenoliths from the Big Pine Volcanic Field (BPVF), California, in order to constrain the melting process in the mantle, and the role of asthenospheric and lithospheric sources in this westernmost region of the Basin and Range Province, western USA. Melt inclusions trapped in primitive olivines (Fo82-90) record surprisingly high H2O contents (1.5 to 3.0 wt.%), while lithospheric mantle xenoliths record low H2O concentrations (whole rock 500 ka, to cooler (˜1220°C) and shallower melting (˜1 GPa) conditions in younger magmas. The estimated depth of melting correlates strongly with some trace element ratios in the magmas (e.g., Ce/Pb, Ba/La), with deeper melts having values closer to upper mantle asthenosphere values, and shallower melts having values more typical of subduction zone magmas. This geochemical stratification is consistent with seismic observations of a shallow lithosphere-asthenosphere boundary (˜55 km depth). Combined trace element and cryoscopic melting models yield self-consistent estimates for the degree of melting (˜5%) and source H2O concentration (˜1000 ppm). We suggest two possible geodynamic models to explain small-scale convection necessary for magma generation. The first is related to the Isabella seismic anomaly, either a remnant of the Farallon Plate or foundered lithosphere. The second scenario is related to slow extension of the lithosphere.

  14. Imaging the continental lithosphere: Perspectives from global and regional anisotropic seismic tomography

    Science.gov (United States)

    Lebedev, Sergei; Schaeffer, Andrew

    2016-04-01

    Azimuthal seismic anisotropy, the dependence of seismic wave speeds on propagation azimuth, is largely due to fabrics within the Earth's crust and mantle, produced by deformation. It thus provides constraints on the distribution and evolution of deformation within the upper mantle. Lateral variations in isotropic-average seismic velocities reflect variations in the temperature of the rocks at depth. Seismic tomography thus also provides a proxy for lateral changes in the temperature and thickness of the lithosphere. It can map the deep boundaries between tectonic blocks with different properties and age of the lithosphere. Our new global, anisotropic, 3D tomographic models of the upper mantle and the crust are constrained by an unprecedentedly large global dataset of broadband waveform fits (over one million seismograms) and provide improved resolution of the lithosphere at the global scale, compared to other available models. The most prominent high-velocity anomalies, seen down to around 200 km depths, indicate the cold, thick, stable mantle lithosphere beneath Precambrian cratons. The tomography resolves the deep boundaries of the cratons even where they are not exposed and difficult to map at the surface. Our large waveform dataset, with complementary large global networks and high-density regional array data, also produces improved resolution of azimuthal anisotropy patterns, so that regional-scale variations related to lithospheric deformation and mantle flow can be resolved, in particular in densely sampled regions. The depth of the boundary between the cold, rigid lithosphere (preserving ancient, frozen anisotropic fabric) and the rheologically weak asthenosphere (characterized by fabric developed recently) can be inferred from the depth layering of seismic anisotropy and its comparison to the past and present plate motions. Beneath oceans, the lithosphere-asthenosphere boundary (LAB) is defined clearly by the layering of anisotropy, with a dependence on

  15. Electrical conductivity in the precambrian lithosphere of western canada

    Science.gov (United States)

    Boerner; Kurtz; Craven; Ross; Jones; Davis

    1999-01-29

    The subcrustal lithosphere underlying the southern Archean Churchill Province (ACP) in western Canada is at least one order of magnitude more electrically conductive than the lithosphere beneath adjacent Paleoproterozoic crust. The measured electrical properties of the lithosphere underlying most of the Paleoproterozoic crust can be explained by the conductivity of olivine. Mantle xenolith and geological mapping evidence indicate that the lithosphere beneath the southern ACP was substantially modified as a result of being trapped between two nearly synchronous Paleoproterozoic subduction zones. Tectonically induced metasomatism thus may have enhanced the subcrustal lithosphere conductivity of the southern ACP.

  16. Thermal erosion of cratonic lithosphere as a potential trigger for mass-extinction

    Science.gov (United States)

    Pilet, Sebastien; Guex, Jean; Muntener, Othmar; Bartolini, Annachiara; Spangenberg, Jorge; Schoene, Blair; Schaltegger, Urs

    2016-04-01

    The temporal coincidence between large igneous provinces (LIPs) and mass extinctions has led many to pose a causal relationship between the two. However, there is still no consensus on a mechanistic model that explains how magmatism leads to the turnover of terrestrial and marine plants, invertebrates and vertebrates. Here, we present a synthesis of stratigraphic constraints on the Triassic-Jurassic (T-J) and Pliensbachian-Toarcian (Pl-To) boundaries combined with geochronological data in order to establish the sequence of events that initiate two of the major mass extinctions recorded in Earth's history. This synthesis demonstrates that these biotic crises are both associated with rapid change from an initial cool period to greenhouse conditions. The initial regressive events recorded at T-J and Pl-To boundaries seem difficult to reconcile either with large initial CO2 degassing associated with plume activity or by volatile-release (CO2, CH4, Cl2) from deep sedimentary reservoirs during contact metamorphism associated to dykes and sills intrusion because massive CO2 degassing is expected to produce super greenhouse conditions. We evaluate, here, an alternative suggesting that the initial cooling could be due to gas release during the initial thermal erosion of the cratonic lithosphere due to emplacement of the CAMP and Karoo-Ferrar volcanic provinces. Petrological constraints on primary magmas indicate that the mantle is hotter and melts more extensively to produce LIP lavas than for current oceanic islands basalts. However, available data suggest that the Karoo and CAMP areas were underlain by thick lithosphere (>200 km) prior to continental break up. The presence of thick lithosphere excludes significant melting of the asthenospheric mantle without initial stage of thermal erosion of the cratonic lithosphere. This initial step of thermal erosion / thermal heating of the cratonic lithosphere is critical to understand the volatile budget associated with LIPs while

  17. In-Situ Lithospheric Rheology Measurement Using Isostatic Response and Geophysical State

    Science.gov (United States)

    Lowry, A. R.; Becker, T. W.; Buehler, J. S.; ma, X.; Miller, M. S.; Perez-Gussinye, M.; Ravat, D.; Schutt, D.

    2013-12-01

    Measurements of effective elastic thickness, Te, from flexural isostatic modeling are sensitive to flow rheology of the lithosphere. Nevertheless, Te has not been widely used to estimate in-situ rheology. Past methodological controversies regarding Te measurement are partly to blame for under-utilization of isostatic response in rheology studies, but these controversies are now largely resolved. The remaining hurdles include uncertainties in properties of geophysical state such as temperature, lithology, and water content. These are ambiguous in their relative contributions to total strength, and the unknown state-of-stress adds to ambiguity in the rheology. Dense seismic and other geophysical arrays such as EarthScope's USArray are providing a wealth of new information about physical state of the lithosphere, however, and these data promise new insights into rheology and deformation processes. For example, new estimates of subsurface mass distributions derived from seismic data enable us to examine controversial assumptions about the nature of lithospheric loads. Variations in crustal lithology evident in bulk crustal velocity ratio, vP/vS, contribute a surprisingly large fraction of total loading. Perhaps the most interesting new information on physical state derives from imaging of uppermost mantle velocities using refracted mantle phases, Pn and Sn, and depths to negative velocity gradients imaged as converted phases in receiver functions (so-called seismic lithosphere-asthenosphere boundary, 'LAB', and mid-lithosphere discontinuity, 'MLD'). Imaging of the ~580°C isotherm associated with the phase transition from alpha- to beta-quartz affords another exciting new avenue for investigation, in part because the transition closely matches the Curie temperature thought to control magnetic bottom in some continental crust. Reconciling seismic estimates of temperature variations with measurements of Te and upper-mantle negative velocity gradients in the US requires

  18. The Lithosphere-Asthenosphere System in the Calabrian Arc and Surrounding Seas Southern Italy

    Science.gov (United States)

    Pontevivo, Antonella; Panza, Giuliano Francesco

    2006-08-01

    A fairly detailed structural model of the lithosphere-asthenosphere system (thickness, S- and P-wave velocities of the crust and of the uppermost mantle layers) has been defined in the Calabrian Arc region (Southern Tyrrhenian Sea, Calabria and the northwestern part of the Ionian Sea) in Southern Italy using seismic data from literature as a priori constraints of the nonlinear inversion of surface-wave data. The main features identified by this study are: (1) A very shallow (less then 10 km deep) crust-mantle transition in the Southern Tyrrhenian Sea and a very low vs just below a very thin lid, in correspondence of the submarine volcanic bodies Magnaghi, Marsili and Vavilov, while the vs in the lid is quite high in the area that separates Marsili from Magnaghi-Vavilov; (2) a shallow and very low vs layer in the uppermost mantle in the areas of the Aeolian Islands, Vesuvius, Phlegraean Fields and Ischia, which represents their shallow-mantle magma source; (3) a thickened continental crust and lithospheric doubling in Calabria; (4) a crust about 25-km thick and a mantle velocity profile versus depth consistent with the presence of a continental rifted lithosphere, now thermally relaxed, in the investigated part of the Ionian Sea; (5) the subduction towards northwest of the Ionian lithosphere below the Southern Tyrrhenian Sea; (6) the subduction of the Adriatic/Ionian lithosphere underneath the Vesuvius and Phlegraean Fields.

  19. Interactions of multi-scale heterogeneity in the lithosphere: Australia

    Science.gov (United States)

    Kennett, B. L. N.; Yoshizawa, K.; Furumura, T.

    2017-10-01

    Understanding the complex heterogeneity of the continental lithosphere involves a wide variety of spatial scales and the synthesis of multiple classes of information. Seismic surface waves and multiply reflected body waves provide the main constraints on broad-scale structure, and bounds on the extent of the lithosphere-asthenosphere transition (LAT) can be found from the vertical gradients of S wavespeed. Information on finer-scale structures comes through body wave studies, including detailed seismic tomography and P-wave reflectivity extracted from stacked autocorrelograms of continuous component records. With the inclusion of deterministic large-scale structure and realistic medium-scale stochastic features fine-scale variations are subdued. The resulting multi-scale heterogeneity model for the Australian region gives a good representation of the character of observed seismograms and their geographic variations and matches the observations of P-wave reflectivity. P reflections in the 0.5-3.0 Hz band in the uppermost mantle suggest variations on vertical scales of a few hundred metres with amplitudes of the order of 1%. Interference of waves reflected or converted at sequences of such modest variations in physical properties produce relatively simple behaviour for lower frequencies, which can suggest simpler structures than are actually present. Vertical changes in the character of fine-scale heterogeneity can produce apparent discontinuities. In Central Australia a 'mid-lithospheric discontinuity' can be tracked via changes in frequency content of station reflectivity, with links to the broad-scale pattern of wavespeed gradients and, in particular, the gradients of radial anisotropy. Comparisons with xenolith results from southeastern Australia indicate a strong tie between geochemical stratification and P-wave reflectivity.

  20. Extremely depleted lithospheric mantle and diamonds beneath the southern Zimbabwe Craton

    Science.gov (United States)

    Smith, Chris B.; Pearson, D. Graham; Bulanova, Galina P.; Beard, Andrew D.; Carlson, Richard W.; Wittig, Nadine; Sims, Keith; Chimuka, Lovemore; Muchemwa, Ellah

    2009-11-01

    Inclusion-bearing diamonds, mantle xenoliths, and kimberlite concentrates from the Cambrian-aged Murowa and Sese kimberlites have been studied to characterise the nature of the lithospheric mantle beneath the southern Zimbabwe Craton. The diamonds are mostly octahedral, moderately rich in nitrogen with moderate to high aggregation, and contain mainly dunite-harzburgite mineral inclusions. Similarly, dunite xenoliths predominate over harzburgite and lherzolite and carry olivines with Mg/Mg + Fe (Mg#) values of 0.92-0.95, spanning the average signatures for Kaapvaal Craton peridotites. Eclogitic xenoliths are extremely rare, in contrast to the Kaapvaal mantle lithosphere. The Zimbabwe mantle assemblage has been only slightly affected by later silicic metasomatism and re-fertilisation with re-introduction of pyroxenes in contrast to the Kaapvaal and many cratonic lithospheric blocks elsewhere where strong metasomatism and re-fertilisation is widespread. Pyroxene, garnet and spinel thermobarometry suggests an ambient 40 mW m - 2 geotherm, with the lithosphere extending down to 210 km at the time of kimberlite eruption. Whole rock peridotite Re-Os isotope analyses yield T RD model ages of 2.7 to 2.9 Ga, providing minimum estimates of the time of melt depletion, are slightly younger in age than the basement greenstone formation. These model ages coincide with the mean T RD age of > 200 analyses of Kaapvaal Craton peridotites, whereas the average Re-Os model age for the Zimbabwe peridotites is 3.2 Ga. The Os data and low Yb n/Lu n ratios suggest a model whereby thick lithospheric mantle was stabilised during the early stages of crustal development by shallow peridotite melting required for formation of residues with sufficiently high Cr/Al to stabilise chromite which then transforms to low Ca, high Cr garnet. Sulphide inclusions in diamond produce minimum T RD model ages of 3.4 Ga indicating that parts of the lithosphere were present at the earliest stages of crust

  1. Crustal seismicity and the earthquake catalog maximum moment magnitudes (Mcmax) in stable continental regions (SCRs): correlation with the seismic velocity of the lithosphere

    Science.gov (United States)

    Mooney, Walter D.; Ritsema, Jeroen; Hwang, Yong Keun

    2012-01-01

    A joint analysis of global seismicity and seismic tomography indicates that the seismic potential of continental intraplate regions is correlated with the seismic properties of the lithosphere. Archean and Early Proterozoic cratons with cold, stable continental lithospheric roots have fewer crustal earthquakes and a lower maximum earthquake catalog moment magnitude (Mcmax). The geographic distribution of thick lithospheric roots is inferred from the global seismic model S40RTS that displays shear-velocity perturbations (δVS) relative to the Preliminary Reference Earth Model (PREM). We compare δVS at a depth of 175 km with the locations and moment magnitudes (Mw) of intraplate earthquakes in the crust (Schulte and Mooney, 2005). Many intraplate earthquakes concentrate around the pronounced lateral gradients in lithospheric thickness that surround the cratons and few earthquakes occur within cratonic interiors. Globally, 27% of stable continental lithosphere is underlain by δVS≥3.0%, yet only 6.5% of crustal earthquakes with Mw>4.5 occur above these regions with thick lithosphere. No earthquakes in our catalog with Mw>6 have occurred above mantle lithosphere with δVS>3.5%, although such lithosphere comprises 19% of stable continental regions. Thus, for cratonic interiors with seismically determined thick lithosphere (1) there is a significant decrease in the number of crustal earthquakes, and (2) the maximum moment magnitude found in the earthquake catalog is Mcmax=6.0. We attribute these observations to higher lithospheric strength beneath cratonic interiors due to lower temperatures and dehydration in both the lower crust and the highly depleted lithospheric root.

  2. The lithosphere of the Appalachian orogen and Atlantic passive margin

    Science.gov (United States)

    Fischer, K. M.; MacDougall, J. G.; Hawman, R. B.; Parker, E. H.; Wagner, L. S.

    2012-12-01

    The lithosphere of the Appalachian orogen and Atlantic passive margin has recorded repeated episodes of continental collision and break-up. Improved resolution of crust and mantle structure in this region holds promise for better understanding of orogenesis, rifting and passive margin development. At a broad scale, tomographic models manifest a decrease in lithospheric thickness from the central U.S. craton into the Appalachian orogen. Migration of Sp scattered waves indicates that a significant drop in shear-wave velocity typically occurs at depths of 80-120 km in the eastern U.S., and where these phases fall within the transition from high velocity lid to lower velocity mantle obtained from tomography, they are interpretable as the seismological lithosphere-asthenosphere boundary. Beneath the Appalachians and coastal plain, Sp-derived lithospheric thicknesses are larger than those found in the tectonically active western U.S. where values range from 40-90 km. The vertical shear velocity gradients required to produce the observed Sp phases are sharp (drops of 4-10% over governed solely by temperature, but they may be explained by small amounts of partial melt or enhanced volatile content in the asthenosphere. While an asthenospheric low velocity zone appears to be ubiquitous beneath the continent, minimum velocities (and likely viscosities) within the eastern U.S. asthenosphere are not as low as those in the western U.S. At smaller scales, Sp imaging hints at lithospheric thickness variations that are correlated with tectonic features (e.g. orogenic boundaries, failed rifts) but resolution will be vastly improved with analysis of data from USArray Transportable and Flexible Arrays. The goal of the Southeastern Suture of the Appalachian Margin Experiment (SESAME) is to better understand lithospheric structures produced by accretion and rifting processes, with a particular focus on the Laurentia-Gondwana suture proposed in southern Georgia, adjacent regions of

  3. Colorado Plateau magmatism and uplift by warming of heterogeneous lithosphere.

    Science.gov (United States)

    Roy, Mousumi; Jordan, Thomas H; Pederson, Joel

    2009-06-18

    The forces that drove rock uplift of the low-relief, high-elevation, tectonically stable Colorado Plateau are the subject of long-standing debate. While the adjacent Basin and Range province and Rio Grande rift province underwent Cenozoic shortening followed by extension, the plateau experienced approximately 2 km of rock uplift without significant internal deformation. Here we propose that warming of the thicker, more iron-depleted Colorado Plateau lithosphere over 35-40 Myr following mid-Cenozoic removal of the Farallon plate from beneath North America is the primary mechanism driving rock uplift. In our model, conductive re-equilibration not only explains the rock uplift of the plateau, but also provides a robust geodynamic interpretation of observed contrasts between the Colorado Plateau margins and the plateau interior. In particular, the model matches the encroachment of Cenozoic magmatism from the margins towards the plateau interior at rates of 3-6 km Myr(-1) and is consistent with lower seismic velocities and more negative Bouguer gravity at the margins than in the plateau interior. We suggest that warming of heterogeneous lithosphere is a powerful mechanism for driving epeirogenic rock uplift of the Colorado Plateau and may be of general importance in plate-interior settings.

  4. Lithospheric structure of the Western Iberian Atlantic Margin

    Science.gov (United States)

    Tunini, Lavinia; Vergés, Jaume; Fernandez, Manel; Jiménez-Munt, Ivone; Torne, Montserrat

    2017-04-01

    The Western Iberia Atlantic margin has been the object of multiple geophysical surveys in the last two decades, which highlight the crustal architecture of a hyperextended, magma-poor passive margin with a wide transition zone of exhumed mantle peridotites and anomalously small magma fractions. However, studies dealing with its lithospheric structure are lacking. We present a 2D model of the present-day lithospheric structure along a 530-km transect of the Western Iberian Margin, from the Southern Iberian Abyssal Plain to the Lusitanian Basin. The model combines seismic and geological data, mantle petrology, mineral physics and geophysical observables (gravity, geoid, topography, mantle seismic velocities and heat flow) within a self-consistent thermodynamic framework. Results show that the crustal thickness decreases gradually from 30 km below the Lusitanian Basin onshore to 11 km in the Abyssal Plain, 250 km further oceanwards, while the LAB rises from 140 km to 110 km, respectively. Furthermore, our results favour a 22% degree of serpentinization of the exhumed mantle which represents a 4.4% of water content. The study is supported by project ALPIMED (PIE-CSIC-201530E082)

  5. Mechanical strength of extended continental lithosphere: Constraints from the Western Rift System, East Africa

    Science.gov (United States)

    Ebinger, Cynthia J.; Karner, Garry D.; Weissel, Jeffrey K.

    1991-12-01

    Although regional isostasy generally is associated with continental lithospheric compression and foreland basin formation, local isostatic compensation commonly is assumed in models of extensional basin formation. The assumption of negligible lithospheric strength during rifting often is justified on the basis of: (1) high heat flow and temperatures produced by elevating the lithosphere - asthenosphere boundary and (2) fracturing of the crust and lithosphere by normal faults. By modeling the development of rift basins within the Western rift system of East Africa and their associated free air gravity anomalies, we assess the role of basin-producing normal faults in modifying the flexural strength of extended lithosphere. Heat flow and seismicity data from the East African plateau region indicate that the Western rift system located on the western side of the plateau developed in old, cold continental lithosphere. These relatively narrow (40-70 km wide), but deep, basins are bounded along one side by high-angle border faults that penetrate to lower crustal levels, as indicated by seismicity data. Along the length of the Western rift system, depth to pre-rift basement and rift flank topography vary between basins from 1 to 8 km and from 1 to 2 km respectively, with deeper basins generally correlating with higher flanks. Comparison of model predictions with topography and free air gravity profiles reveals that the basin depth and the flank height in the majority of the Western rift basins studied can be explained simply by small heaves (3-10 km) across the border fault and with significant flexural strength of the lithosphere maintained during extension. Where both observed basin depth and flank height could not be reproduced, basins were located adjacent to eruptive volcanic centers active in Miocene-Recent times. In these areas, basin depth, rift flank elevation, and free air gravity anomaly may be modified by magmatic underplating of the crust. Estimates of

  6. Pn Anisotropy in Old Pacific Lithosphere

    Science.gov (United States)

    Shintaku, N.; Forsyth, D. W.; Weeraratne, D. S.

    2012-12-01

    Pn is the high frequency, scattered P phase guided for great distances within old oceanic lithosphere, which is also known as Po. Two arrays of ocean bottom seismometers were deployed on old (~150-160Ma) seafloor in the northwestern Pacific south of Shatsky Rise for the PLATE experiment (Pacific Lithosphere Anisotropy and Thickness Experiment). More than 5 or 6 Pn phases per day are recorded on these ocean bottom seismometers generated by earthquakes in western Pacific subduction zones during one year of deployment; we used 512 Pn phases from earthquakes with locations reported in routine bulletins. Each array was deployed on a separate limb of a magnetic bight, formed at a ridge-ridge-ridge triple junction. The spreading rates on both limbs were ~ 70mm/yr, and the current plate motion direction in the hotspot coordinate frame is WNW. Our overall goal is to identify the pattern of fossil anisotropy in the old oceanic lithosphere, and dynamically generated anisotropy in underlying asthenosphere using both body waves and surface waves. Using high frequency waves (3-10 Hz), we look at variations of Pn velocities as a function of backazimuth. In the western array, where the spreading direction is parallel to the absolute plate motion direction, we find clear Pn anisotropy with velocities varying from ~8.5 km/s in the spreading direction to ~ 8.0 km/s perpendicular to the spreading direction. However, in the eastern array where the fossil spreading direction is perpendicular to the current plate motion, the velocity variations as a function of backazimuth are much less obvious. This may be due to heterogeneity of anisotropy in the oceanic lithosphere, with the fast direction changing from the fossil direction at shallow levels to the absolute direction at greater depth.

  7. Gravity, geoid and the oceanic lithosphere

    Science.gov (United States)

    Watts, A. B.

    1985-01-01

    Plate tectonics and its contribution to progress in studies of the Earth's gravitational field is discussed. In acquisition, the development of forced feedback accelerometers, satellite navigation, and satellite radar altimetry significantly improved the accuracy and coverage of gravity data over the oceans. In interpretation, gravity and geoid anomalies are used to determine information on the thermal and mechanical properties of the oceanic lithosphere and the forces that drive plate motions.

  8. Understanding lithospheric stresses: systematic analysis of controlling mechanisms with applications to the African Plate

    Science.gov (United States)

    Medvedev, Sergei

    2016-06-01

    Many mechanisms control the state of stress within Earth plates. First-order well-known mechanisms include stresses induced by lateral variations of lithospheric density structure, sublithospheric tractions, ridge push, and subduction pull. In this study, we attempt to quantify the influence of these mechanisms to understand the origin of stresses in the lithosphere, choosing the African plate (TAP) as an example. A finite-element based suite, Proshell, was developed to combine several data sets, to estimate the gravitational potential energy (GPE) of the lithosphere, and to calculate stresses acting on the real (non-planar) geometry of TAP. We introduce several quantitative parameters to measure the degree of fit between the model and observations. Our modelling strategy involves nine series of numerical experiments. We start with the simplest possible model and then, step by step, build it up to be a more physically realistic model, all the while discussing the influence of each additional component. The starting (oversimplified) model series (1) is based on the CRUST2 data set for the crust, and a half-space-cooling approximation of the lithospheric mantle. We then describe models (series 2-5) that account for lithospheric mantle density heterogeneities to build a more reliable GPE model. The consecutive series involve basal traction from the convective mantle (series A, C), and the rheological heterogeneity of the TAP via variations in its effective elastic thickness (series B, C). The model quality reflects the increase in complexity between series with an improving match toobserved stress regimes and directions. The most complex model (series D) also accounts for the bending stresses in the elastic lithosphere and achieves a remarkably good fit to observations. All of our experiments were based on the iteration of controlling parameters in order to achieve the best fit between modelled and observed stresses, always considering physically feasible values. This

  9. Paleoproterozoic Collisional Structures in the Hudson Bay Lithosphere Constrained by Multi-Observable Probabilistic Inversion

    Science.gov (United States)

    Darbyshire, F. A.; Afonso, J. C.; Porritt, R. W.

    2015-12-01

    The Paleozoic Hudson Bay intracratonic basin conceals a Paleoproterozoic Himalayan-scale continental collision, the Trans-Hudson Orogen (THO), which marks an important milestone in the assembly of the Canadian Shield. The geometry of the THO is complex due to the double-indentor geometry of the collision between the Archean Superior and Western Churchill cratons. Seismic observations at regional scale show a thick, seismically fast lithospheric keel beneath the entire region; an intriguing feature of recent models is a 'curtain' of slightly lower wavespeeds trending NE-SW beneath the Bay, which may represent the remnants of more juvenile material trapped between the two Archean continental cores. The seismic models alone, however, cannot constrain the nature of this anomaly. We investigate the thermal and compositional structure of the Hudson Bay lithosphere using a multi-observable probabilistic inversion technique. This joint inversion uses Rayleigh wave phase velocity data from teleseismic earthquakes and ambient noise, geoid anomalies, surface elevation and heat flow to construct a pseudo-3D model of the crust and upper mantle. Initially a wide range of possible mantle compositions is permitted, and tests are carried out to ascertain whether the lithosphere is stratified with depth. Across the entire Hudson Bay region, low temperatures and a high degree of chemical depletion characterise the mantle lithosphere. Temperature anomalies within the lithosphere are modest, as may be expected from a tectonically-stable region. The base of the thermal lithosphere lies at depths of >250 km, reaching to ~300 km depth in the centre of the Bay. Lithospheric stratification, with a more-depleted upper layer, is best able to explain the geophysical data sets and surface observables. Some regions, where intermediate-period phase velocities are high, require stronger mid-lithospheric depletion. In addition, a narrow region of less-depleted material extends NE-SW across the Bay

  10. Radial anisotropy beneath northeast Tibet, implications for lithosphere deformation at a restraining bend in the Kunlun fault and its vicinity

    Science.gov (United States)

    Li, Lun; Li, Aibing; Murphy, Michael A.; Fu, Yuanyuan V.

    2016-09-01

    Three-dimensional shear wave velocity and radial anisotropy models of the crust and upper mantle beneath the NE Tibetan plateau are constructed from new measurements of Love wave dispersions (20-77s) and previously obtained Rayleigh wave dispersions (20-87s) using a two-plane-wave method. The mid-lower crust is characterized with positive anisotropy (VSH > VSV) with large strength beneath the Qinling and Qilian Mountains and small values beneath the Anyemaqen Mountain. The large positive anisotropy can be explained by horizontal alignment of anisotropic minerals in the mid-lower crust due to crustal flow. The mantle lithosphere above 90 km is largely isotropic while weak positive anisotropy appears beneath 90 km, which probably marks the lithosphere-asthenosphere boundary (LAB). A low shear wave velocity anomaly and relatively negative radial anisotropy are imaged in the entire lithosphere beneath the restraining bend in the eastern Kunlun fault, consistent with a weak lithosphere experiencing vertical thickening under horizontal compression. The asthenosphere at the restraining bend is characterized by significant low velocity and positive radial anisotropy, reflecting that the asthenosphere here is probably hotter, has more melts, and deforms more easily than the surrounding region. We propose that the lithosphere at the restraining bend was vertically thickened and subsequently delaminated locally, and induced asthenosphere upwelling. This model explains the observations of velocity and anisotropy anomalies in the lithosphere and asthenosphere as well as geological observations of rapid rock uplift at the restraining bend of the Kunlun fault.

  11. The evolution of fault geometry and lithosphere mechanical response to faulting during lithosphere hyper-extension at magma-poor rifted margins

    Science.gov (United States)

    Gómez Romeu, Júlia; Kusznir, Nick; Manatschal, Gianreto; Roberts, Alan

    2016-04-01

    The geometry of upper lithosphere extensional faulting and the mechanical response of the lithosphere during continental breakup are controversial. The lithosphere response to extensional faulting at magma-poor rifted margins controls the distribution of thinned continental crust, exhumed mantle, continental allochthons and syn-tectonic sediments leading to the complexity of heterogeneous structure of hyper-extended domain at these margins. In order to better understand the evolving fault geometry and lithosphere mechanics during magma-poor rifted margin formation, we investigate extensional faulting for the tectonic end-members of continental rifting and slow sea-floor spreading. We presume that these end-members faulting styles both contribute to lithosphere thinning during rifted margin evolution as continental rifting evolves into sea-floor spreading. For continental rifting, large extensional faults that rupture the seismogenic brittle upper lithosphere have been shown to be planar and steeply dipping by earthquake seismology and geodesy (Stein and Barrientos 1985; Jackson 1987). These results are supported by seismic reflection imaging and structural modelling of rift basins (Kusznir et al., 1991, 1995). Individual fault heaves for continental rifting seldom exceeds approximately 10 km. The effective elastic thickness, used to parameterize lithosphere flexural strength for syn-tectonic response to extensional faulting during continental rifting, are typically between 1.5 and 3 km. For slow-spreading ocean ridges we examine extensional fault geometry and lithosphere flexural response to cumulative faulting. We focus on the TAG area (deMartin et al., 2007) and the 15°N area (Schroeder et al., 2007) of the Mid-Atlantic Ridge using a flexural isostatic extensional faulting model (Buck 1988; Kusznir et al., 1991). Modelling of fault controlled bathymetry at slow-spreading ocean ridges shows that active extensional faults at depth have a steep dip (50° - 70

  12. Reflection Character of the Continental Lithosphere and Crustal Evolution

    Science.gov (United States)

    Brown, L. D.

    2015-12-01

    Reflection images represent the high-frequency end member of the suite of seismological tools commonly used to probe the lithosphere. The global inventory of deep reflection profiles has documented reflection characters as varied as the surface geology that provides the primary boundary condition for the interpretation of reflection images. Past reviews of reflection results have stressed similarities in reflection patterns between various geographic regions and attempted to associate these patterns with specific tectonic processes. Examples include: laminated sequences (shear fabrics formed during extension or collision), reflective Mohos (mafic underplating), bright spots (contemporary and fossil magma bodies), dipping mantle reflections rooted in the lower crust (fossil subduction zones) and subhorizontal mantle reflections (phase changes in the lower lithosphere). Here I focus on relating reflection character to the inversion and/or interpretation of results from broadband techniques such as receiver functions, body wave and surface wave tomography. Among the underappreciated aspects of reflectivity are its dependence upon density as well as velocity, and the limitations of 2D images in a 3D world. A core consideration is the need to meaningfully relate integrated physical properties (e.g. velocity inferred from refraction and surface wave measurements) with the differential physical properties (e.g. reflection coefficients) to which reflection images are primarily sensitive. Examples from Tibet and Eurasia are used to illustrate examples of successful integration of controlled (active) and natural (passive) source observations to constrain models of crustal evolution.

  13. Offshore Southern California lithospheric velocity structure from noise cross-correlation functions

    Science.gov (United States)

    Bowden, D. C.; Kohler, M. D.; Tsai, V. C.; Weeraratne, D. S.

    2016-05-01

    A new shear wave velocity model offshore Southern California is presented that images plate boundary deformation including both thickening and thinning of the crustal and mantle lithosphere at the westernmost edge of the North American continent. The Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment (ALBACORE) ocean bottom seismometer array, together with 65 stations of the onshore Southern California Seismic Network, is used to measure ambient noise correlation functions and Rayleigh wave dispersion curves which are inverted for 3-D shear wave velocities. The resulting velocity model defines the transition from continental lithosphere to oceanic, illuminating the complex history and deformation in the region. A transition to the present-day strike-slip regime between the Pacific and North American Plates resulted in broad deformation and capture of the now >200 km wide continental shelf. Our velocity model suggests the persistence of the uppermost mantle volcanic processes associated with East Pacific Rise spreading adjacent to the Patton Escarpment, which marks the former subduction of Farallon Plate underneath North America. The most prominent of these seismic structures is a low-velocity anomaly underlying the San Juan Seamount, suggesting ponding of magma at the base of the crust, resulting in thickening and ongoing adjustment of the lithosphere due to the localized loading. The velocity model also provides a robust framework for future earthquake location determinations and ground-shaking simulations for risk estimates.

  14. Tectonic implications of tomographic images of subducted lithosphere beneath northwestern South America

    NARCIS (Netherlands)

    Hilst, R.D. van der; Mann, P.

    1994-01-01

    We used seismic tomography to investigate the complex structure of the upper mantle below northwestern South America. Images of slab structure not delineated by previous seismicity studies help us to refine existing tectonic models of subducted Caribbean-Pacific lithosphere beneath the study area. B

  15. 3-D seismic tomography of the lithosphere and its geodynamic implications beneath the northeast India region

    Science.gov (United States)

    Raoof, J.; Mukhopadhyay, S.; Koulakov, I.; Kayal, J. R.

    2017-05-01

    We have evolved 3-D seismic velocity structures in northeast India region and its adjoining areas to understand the geodynamic processes of Indian lithosphere that gently underthrusts under the Himalayas and steeply subducts below the Indo-Burma Ranges. The region is tectonically buttressed between the Himalayan arc to the north and the Indo-Burmese arc to the east. The tomographic image shows heterogeneous structure of lithosphere depicting different tectonic blocks. Though our results are limited to shallower depth (0-90 km), it matches well with the deeper continuation of lithospheric structure obtained in an earlier study. We observe low-velocity structure all along the Eastern Himalayas down to 70 km depth, which may be attributed to deeper roots/thicker crust developed by underthrusting of Indian plate. Parallel to this low-velocity zone lies a high-velocity zone in foredeep region, represents the Indian lithosphere. The underthrusting Indian lithosphere under the Himalayas as well as below the Indo-Burma Ranges is well reflected as a high-velocity dipping structure. The buckled up part of bending Indian plate in study region, the Shillong Plateau-Mikir Hills tectonic block, is marked as a high-velocity structure at shallower depth. The Eastern Himalayan Syntaxis, tectonic block where the two arcs meet, is identified as a high-velocity structure. The Bengal Basin, tectonic block to the south of Shillong Plateau, shows low velocity due to its thicker sediments. Based on the tomographic image, a schematic model is presented to elucidate the structure and geodynamics of Indian lithosphere in study region.

  16. COMPOSITIONAL AND THERMAL DIFFERENCES BETWEEN LITHOSPHERIC AND ASTHENOSPHERIC MANTLE AND THEIR INFLUENCE ON CONTINENTAL DELAMINATION

    Directory of Open Access Journals (Sweden)

    A. I. Kiselev

    2015-09-01

    Full Text Available The lower part of lithosphere in collisional orogens may delaminate due to density inversion between the asthenosphere and the cold thickened lithospheric mantle. Generally, standard delamination models have neglected density changes within the crust and the lithospheric mantle, which occur due to phase transitions and compositional variations upon changes of P-T parameters. Our attention is focused on effects of phase and density changes that may be very important and even dominant when compared with the effect of a simple change of the thermal mantle structure. The paper presents the results of numerical modeling for eclogitization of basalts of the lower crust as well as phase composition changes and density of underlying peridotite resulted from tectonic thickening of the lithosphere and its foundering into the asthenosphere. As the thickness of the lower crust increases, the mafic granulite (basalt passes into eclogite, and density inversion occurs at the accepted crust-mantle boundary (P=20 kbar because the newly formed eclogite is heavier than the underlying peridotite by 6 % (abyssal peridotite, according to [Boyd, 1989]. The density difference is a potential energy for delamination of the eclogitic portion of the crust. According to the model, P=70 kbar and T=1300 °C correspond to conditions at the lower boundary of the lithosphere. Assuming the temperature adiabatic distribution within the asthenosphere, its value at the given parameters ranges from 1350 °C to 1400 °C. Density inversion at dry conditions occurs with the identical lithospheric and asthenospheric compositions at the expense of the temperature difference at 100 °C with the density difference of only 0.0022 %. Differences of two other asthenospheric compositions (primitive mantle, and lherzolite KH as compared to the lithosphere (abyssal peridotite are not compensated for by a higher temperature. The asthenospheric density is higher than that of the lithospheric base

  17. Foundering lithosphere imaged beneath the southern Sierra Nevada, California, USA.

    Science.gov (United States)

    Boyd, Oliver S; Jones, Craig H; Sheehan, Anne F

    2004-07-30

    Seismic tomography reveals garnet-rich crust and mantle lithosphere descending into the upper mantle beneath the southeastern Sierra Nevada. The descending lithosphere consists of two layers: an iron-rich eclogite above a magnesium-rich garnet peridotite. These results place descending eclogite above and east of high P wave speed material previously imaged beneath the southern Great Valley, suggesting a previously unsuspected coherence in the lithospheric removal process.

  18. The long-term rotational stability of terrestrial planets with viscoelastic lithospheres: A new theory with application to Mars

    Science.gov (United States)

    Moore, K.; Chan, N. H.; Daradich, A.; Mitrovica, J. X.

    2016-12-01

    The long-term rotational stability of terrestrial planets is a classic problem in geophysics and planetary science. Modern theoretical treatments stem from Gold (1955) and Goldreich and Toomre (1969) who: (1) argued that the rotation axis orientation of terrestrial planets is inherently unstable since any stabilization due to the rotational bulge is transient; and (2) established conditions for rapid, large-scale reorientation of the axis relative to the surface geography (true polar wander, TPW). Willemann (1984) and Matsuyama et al. (2006) extended this work, demonstrating that an elastic lithosphere stabilizes the rotation axis through elastic stresses induced in the lithosphere by planetary reorientation. In this case, the magnitude of load-induced TPW can be significantly more muted. The above studies describe equilibrium theories concerned with the final state of the rotation axis. More recent studies (e.g., Ricard et al., 1993; Tsai & Stevenson, 2007; Harada, 2012; Chan et al., 2014) incorporate time dependence into the governing theory. We build on this earlier work to derive a new theory of time-dependent TPW on terrestrial planets with viscoelastic lithospheres. Our formalism more realistically models the time evolution of TPW by bridging the two end-member cases: an infinite viscosity (elastic) lithosphere; and a fully relaxed, finite viscosity lithosphere that provides no stabilization. On short timescales the rotation axis is stabilized by the lithosphere (the Willemann case), but on timescales longer than the relaxation time of the lithosphere the axis becomes unstable (the Gold case). We illustrate our theory with numerical simulations for Mars. Published work suggests that Martian TPW would not continue for any significant time after the addition of a load, and thus that an equilibrium theory is adequate. Our results demonstrate, in contrast, that the slow relaxation of a high viscosity lithosphere can lead to TPW on Mars that continues for billions

  19. Imaging the Italian Lithosphere based on Adjoint Tomography

    Science.gov (United States)

    Magnoni, F.; Casarotti, E.; Komatitsch, D.; Melini, D.; Michelini, A.; Piersanti, A.; Tape, C.; Tromp, J.

    2016-12-01

    We exploit the powerful European computational resources awarded to our PRACE project IMAGINE_IT ("3D full-wave tomographic IMAGINg of the Entire ITalian lithosphere") to develop a reference, high-resolution 3D seismic wavespeed model for the Italian lithosphere. The inversion procedure consists of iterative improvements of an initial 3D traveltime tomographic model of the region constrained by a large number of full, high-quality observed seismic waveforms. The final model images the regional structure at unprecedented resolution ( 10 s) minimizing the misfit between recorded and synthetic data. Numerical wavefield simulations at high frequency are performed using a spectral-element method (code SPECFEM3D) that allows us to implement all complexities that characterize the studied region (lateral heterogeneity, topography, attenuation). This method is then efficiently combined with an adjoint technique to perform the 3D full-wave tomographic inversion. The Italian peninsula is characterized by very heterogeneous features resulting from complex tectonic evolution of the region mainly dominated by the interaction of Tyrrhenian, Adria and European plates. Our inversion includes 163 earthquakes that occurred in Italy and neighboring areas between 2005 and 2014, and a dense seismological network of 400 seismic recording stations. We perform 25 iterations of our iterative tomographic inversion process, as well as moment tensor inversions for the considered events. The resolution capabilities of our model are also explored based on point spread function analyses and calculation of the approximate Hessian. Thanks to our project IMAGINE_IT, at present the first application of adjoint tomography for the whole Italian region, we are able to constrain Vp as well as Vs at unprecedented resolution; the complex plate relationships start to be accurately modeled, and other inferences on the Italian geodynamical evolution or on fluid (such as CO2) distribution become possible.

  20. Pn anisotropy in Mesozoic western Pacific lithosphere

    Science.gov (United States)

    Shintaku, Natsumi; Forsyth, Donald W.; Hajewski, Christina J.; Weeraratne, Dayanthie S.

    2014-04-01

    Pn is the high-frequency, scattered P phase guided for great distances within the old oceanic lithosphere. Two arrays of ocean bottom seismometers were deployed on old (150-160 Ma) seafloor in the northwestern Pacific south of Shatsky Rise for the Pacific Lithosphere Anisotropy and Thickness Experiment. We use Pn phases from 403 earthquakes during the 1 year of deployment to measure apparent velocities across the arrays. Each array was deployed on a separate limb of a magnetic bight, formed near a fast-spreading, ridge-ridge-ridge triple junction. Using high-frequency waves (5-10 Hz), we look at variations of Pn velocities as a function of azimuth. In the western array, we find Pn anisotropy with velocities ranging from ~8.7 km/s in the back azimuth (θ) direction of 310° to ~7.7 km/s at ~350°. In the eastern array, the velocity ranges from ~8.5 km/s in back azimuth direction of ~210° to ~7.7 km/s at 260° and ~310°. We observe rapid velocity changes with azimuth in the both arrays requiring sinusoidal variations of roughly equal amplitude as a function of both 2θ and 4θ, which is not expected for the orthorhombic symmetry of olivine or orthopyroxene. The fastest directions on the two limbs are roughly orthogonal to each other suggesting the dominance of fossil anisotropy, but the fast directions of the 2θ components are skewed counterclockwise from the spreading directions. We speculate that the rapid azimuthal variations may be caused by vertical stratification with changing anisotropy with depth in the oceanic lithosphere.

  1. Updating the thermo-mechanical structure of the European lithosphere with subsurface temperature data

    Science.gov (United States)

    Limberger, Jon; van Wees, Jan-Diederik; Tesauro, Magdala; Bonté, Damien; Lipsey, Lindsay; Smit, Jeroen; Beekman, Fred; Cloetingh, Sierd

    2016-04-01

    As part of the EU FP7-funded Integrated Methods for Advanced Geothermal Exploration (IMAGE) project we developed a methodology to obtain an improved, physics-based thermal model of the European lithosphere. On the basis of geophysical data, the model is divided into a four layer geometry consisting of sediments, upper crust, lower crust and lithospheric mantle. The horizontal resolution is 10 by 10 km, while the vertical one is 250 m. The prior steady-state temperature distribution is calculated using vertical heat flow only. imposing as boundary conditions fixed temperatures at the surface and at the base of the lithosphere, respectively. Thermal properties, including radiogenic heat production and temperature- and pressure-dependent bulk thermal conductivity, are assigned on the base of the broad-scale lithological variation within the European crust. Further improvements of the thermal model, aiming at consistency between temperatures and heat flow observations and tectonic model predictions, are obtained by applying data assimilation. An Ensemble Kalman Filter (EnKF) is used to assimilate temperature data and improve the prior estimates of the thermal properties and the thermal field. One of the advantages of EnKF is that multiple model realisations yield uncertainties for both the thermal properties and the thermal field. Borehole temperature data are directly used for this procedure, when publically available. Regional thermal models - originally based on borehole data - are used for areas lacking any (public) borehole temperature data. A larger error is assigned to the temperature values derived from these models, in order to account for the higher uncertainty compared to direct-measured temperatures. The thermal model is also used together with compositional data to estimate the integrated strength of the lithosphere. The result is an updated thermo-mechanical model of the European lithosphere with estimated uncertainties for the thermal properties and the

  2. Constraints on Lithospheric Rheology from Observations of Coronae on Venus

    Science.gov (United States)

    O'Rourke, Joseph G.; Smrekar, Suzanne; Moresi, Louis N.

    2016-10-01

    Coronae are enigmatic, quasi-circular features found in myriad geological environments. They are primarily distinguished as rings of concentric fractures superimposed on various topographic profiles with at least small-scale volcanism. Mantle plumes may produce coronae with interior rises, whereas coronae with central depressions are often attributed to downwellings like Rayleigh-Taylor instabilities. For almost three decades, modelers have attempted to reproduce the topographic and gravity profiles measured at coronae. Until recently, few studies also considered tectonic deformation and melt production. In particular, "Type 2" coronae have complete topographic rims but arcs of fractures extending less than 180°, signifying both brittle and ductile deformation. Only a narrow range of rheological parameters like temperature and volatile content may be compatible with these observations. Ultimately, identifying how lithospheric properties differ between Earth and Venus is critical to understanding what factors permit plate tectonics on rocky, Earth-sized planets.Here we present a hierarchical approach to study the formation of coronae. First, we discuss an observational survey enabled by a new digital elevation model derived from stereo topography for ~20% of the surface of Venus, which offers an order-of-magnitude improvement over the horizontal resolution (10 to 20 kilometers) of altimetry data from NASA's Magellan mission. Next, we search this new dataset for signs of lithospheric flexure around small coronae. Simple, thin-elastic plate models were fit to topographic profiles of larger coronae in previous studies, but data resolution impeded efforts to apply this method to the entire coronae population. Finally, we show simulations of the formation of coronae using Underworld II, an open-source code adaptable to a variety of geodynamical problems. We benchmark our code using models of pure Rayleigh-Taylor instabilities and then investigate the influence of

  3. Constraining deformation at the lithosphere-asthenosphere boundary beneath the San Andreas fault with Sp phases

    Science.gov (United States)

    Fischer, K. M.; Ford, H. A.; Lekic, V.

    2013-12-01

    The geometry of deformation in the deep mantle lithosphere beneath strike-slip plate boundaries has been enigmatic, with models ranging from localized shear zones that are deep extensions of individual crustal faults to broad zones of diffuse, distributed shear with widths of hundreds of kilometers. Using seismic phases that convert from shear to compressional motion (Sp) at the base of the lithosphere beneath California, we find evidence for strike-slip deformation in the deepest mantle lithosphere beneath the central San Andreas fault that occurs over a horizontal width of 50 km or less. This study is based on over 135,000 Sp receiver functions from 730 seismic stations, including the Northern and Southern California Seismic Networks and the NSF EarthScope Transportable and Flexible Arrays. Individual Sp receiver functions were calculated using an extended-time multi-taper method and were migrated and stacked according to their three-dimensional conversion point locations using a model for crust (Lowry and Pérez-Gussinyé, 2011) and mantle (Obrebski et al., 2010 and 2011) velocity structure beneath each station and a spline-function representation of the Sp Fresnel zone. Sp conversion points at lithosphere-asthenosphere boundary depths are very dense on both sides of the San Andreas fault, and we interpreted the Sp common conversion point stack only at those nodes with information from more than 300 receiver functions. To the east of the plate boundary, a strong coherent Sp phase, indicative of a decrease in shear-wave velocity with depth, is present in the depth range where tomographic studies image the transition from high velocity lithosphere to low velocity asthenosphere. This phase, interpreted as the seismological lithosphere-asthenosphere boundary, has systematically lower amplitudes on the western side of the plate boundary, indicating that the drop in shear velocity from lithosphere to asthenosphere is either smaller or is distributed over a larger

  4. Delamination of sub-crustal lithosphere beneath the Isthmus of Tehuantepec, Mexico

    Science.gov (United States)

    Manea, Marina; Constantin Manea, Vlad; Ferrari, Luca; Orozco-Esquivel, Maria Teresa

    2015-04-01

    Recent seismic data from a dense seismic array (VEOX), as well as from the permanent broadband network of the Mexican National Seismological Service (SSN), revealed several anomalous structures in the Isthmus of Tehuantepec. Seismic tomography imaged a high velocity body dipping ~30° from the Gulf of Mexico southward. Analysis of seismic noise detected a large well-defined low-velocity anomaly on top of this structure in the vicinity of the Late Miocene-Quaternary Los Tuxtlas volcanic field. The current interpretation of these observations propose the presence of a southward dipping slab resulting from the subduction of oceanic lithosphere prior to the collision of the Yucatán Block with Mexico ~12 Ma ago. However this interpretation contradicts many aspects of well-established models of Caribbean tectonics. Additionally such model does not explain how the southward dipping structure remained at a relatively low dipping angle (~30°) over the last 12 Ma, and why it is not seismically active. We propose an alternative model that reconciles the seismic observations with the tectonic evolution of the region. The south dipping seismic structure is the result of lithospheric delamination produced by a thermal anomaly that migrated upwards through a slab gap in the Cocos slab located at ~200 km depth. Using high-resolution two-dimensional coupled petrological-thermomechanical numerical simulations of subduction, we show that hot and buoyant asthenospheric material flowing through a slab gap in the Cocos plate may have produced a rapid delamination of the lithosphere once it reached its base. The model geometry of the delaminated lithosphere is similar to the observed seismic anomaly, and the hot material from the plume impact is consistent with the low-velocity anomaly located at the north of the Isthmus of Tehuantepec, which feeds the Los Tuxtla volcanic field. Additionally our simulations show that the temperature of the delaminated lithosphere is above 700

  5. Role of orthopyroxene in rheological weakening of the lithosphere via dynamic recrystallization.

    Science.gov (United States)

    Farla, Robert J M; Karato, Shun-Ichiro; Cai, Zhengyu

    2013-10-01

    For plate tectonics to operate on a terrestrial planet, the surface layer (the lithosphere) must have a modest strength (Earth, ≤ 200 MPa), but a standard strength profile based on olivine far exceeds this threshold value. Consequently, it is essential to identify mechanisms that reduce the strength of the lithosphere on Earth. Here we report results of high-strain laboratory deformation experiments on a representative olivine-orthopyroxene composition that show the addition of orthopyroxene substantially reduces the strength in the ductile regime within a certain temperature window. The reduction in strength is associated with the formation of small orthopyroxene and olivine grains. Our samples show heterogeneous microstructures similar to those observed in natural peridotites in shear zones: fine-grained regions containing both orthopyroxene and olivine that form interconnected bands where a large fraction of strain is accommodated. A model is developed to apply these results to geological conditions. Such a model, combined with our experimental observations, suggests that orthopyroxene may play a key role in the plastic deformation of the lithosphere in a critical temperature range, leading to long-term weakening associated with strain localization in the lithosphere.

  6. Power law olivine crystal size distributions in lithospheric mantle xenoliths

    Science.gov (United States)

    Armienti, P.; Tarquini, S.

    2002-12-01

    Olivine crystal size distributions (CSDs) have been measured in three suites of spinel- and garnet-bearing harzburgites and lherzolites found as xenoliths in alkaline basalts from Canary Islands, Africa; Victoria Land, Antarctica; and Pali Aike, South America. The xenoliths derive from lithospheric mantle, from depths ranging from 80 to 20 km. Their textures vary from coarse to porphyroclastic and mosaic-porphyroclastic up to cataclastic. Data have been collected by processing digital images acquired optically from standard petrographic thin sections. The acquisition method is based on a high-resolution colour scanner that allows image capturing of a whole thin section. Image processing was performed using the VISILOG 5.2 package, resolving crystals larger than about 150 μm and applying stereological corrections based on the Schwartz-Saltykov algorithm. Taking account of truncation effects due to resolution limits and thin section size, all samples show scale invariance of crystal size distributions over almost three orders of magnitude (0.2-25 mm). Power law relations show fractal dimensions varying between 2.4 and 3.8, a range of values observed for distributions of fragment sizes in a variety of other geological contexts. A fragmentation model can reproduce the fractal dimensions around 2.6, which correspond to well-equilibrated granoblastic textures. Fractal dimensions >3 are typical of porphyroclastic and cataclastic samples. Slight bends in some linear arrays suggest selective tectonic crushing of crystals with size larger than 1 mm. The scale invariance shown by lithospheric mantle xenoliths in a variety of tectonic settings forms distant geographic regions, which indicate that this is a common characteristic of the upper mantle and should be taken into account in rheological models and evaluation of metasomatic models.

  7. Seismic structure of the oceanic lithosphere inferred from guided wave

    Science.gov (United States)

    Shito, A.; Suetsugu, D.; Furumura, T.; Sugioka, H.; Ito, A.

    2012-12-01

    Characteristic seismic waves are observed by seismological experiment using Broad-Band Ocean Bottom Seismometers (BBOBSs) conducted in the northwestern Pacific from 2007 to 2008 and from 2010 to 2011. The seismic waves have low frequency onset (phases (2.5-10 Hz). The high frequency later phases have large amplitude and long duration for both P and S waves. The seismic waves are observed commonly at the BBOBS array from events in the subducting Pacific plate. To investigate generation and propagation mechanisms of the seismic wave will help us to understand the seismic structure and the origin of the oceanic lithosphere. High frequency phases travelling efficiently through the oceanic lithosphere more than 3000 km are well known phenomenon. These phases were previously called as Po/So waves. Po/So waves were observed as early as 1935, and were studied actively from the 1970s to 1990s. However, the mechanism of generation and propagation of the phases are still controversial. The guided waves propagating in subducting plate are also common phenomenon in the subduction zone. The waves are generally characterized by separation of low frequency and high frequency components. In order to explain the separation, Martin and Rietbrock [2003] considered the trapping of waves in the waveguide formed by thin low velocity former oceanic crust at the top of the plate. However, large amplitude and long duration of the high frequency component cannot be achieved by the model. From the analysis of waveform observed at the eastern seaboard of northern Japan and numerical simulation of seismic wave propagation, Furumura and Kennet [2005] demonstrate that the guided wave travelling in the subducting plate is produced by multiple forward scattering of high-frequency seismic waves due to small-scale random heterogeneity in the plate structure. We apply the method proposed by Furumura and Kennett [2005] to reproduce the seismograms recorded by the BBOBS array. We conduct 2D numerical

  8. The correct mechanism of lithospheric plates movement

    Science.gov (United States)

    Ostrihansky, L.

    2016-12-01

    Imagination that lithospheric plates move above low-viscous seismic low-velocity zone contradicts to reality but alternating movement of variations of the Earth's rotation deform plastic mantle. Because these deformations never return to original position and solidified ascending magma in mid-ocean ridge prevents return, the lithospheric plates move plunging to mantle by their own weight and move westward pushed by force of tidal friction enlarged by alternating movement of heavy and large-volume mantle. This imagination has been proven by calculating azimuths of Moon and opposite tidal bulging in a moment of earthquake. They resulted occurring on local eastern horizon when earthquake was triggered and also calculated tidal torques in their maximums coincided with earthquakes. To distinguish these tidal properties the earthquakes in Hindu Kush in westward moving Eurasian plate were examined and also in northward moving Indian plate. LOD graph has shown that in Hindu Kush tidal friction triggers earthquake almost every day and large earthquakes are triggered in large positive LOD anomalies corresponding to deceleration. In the Indian plate the calculated maximum tidal torques corresponding to accelerations (LOD minimums) coincided with the greatest earthquakes: with the Great Sumatra 2004, largest Nepal earthquake 1934, large earthquake Nepal 2015 evoked by resonance effect and others.

  9. Lithosphere destabilization by melt percolation during pre-oceanic rifting: Evidence from Alpine-Apennine ophiolitic peridotites

    Science.gov (United States)

    Piccardo, Giovanni; Ranalli, Giorgio

    2017-04-01

    conditions. This indicates that thermal advection by percolation of hot asthenospheric melts significantly heated the lithospheric mantle column above the melting asthenosphere. Numerical and analogue models show that infiltration of melts results in considerable softening of mantle rocks. Total ithospheric strength can be decreased from 10 to 1 TN m-1 as orders of magnitude and the sin-rift thermo-mechanical erosion of the lithospheric mantle induces significant rheological softening along the axial zone of extension (Corti et al., 2007; Ranalli et al., 2007). Softening of the lithospheric mantle may lead to whole lithospheric failure and consequently to transition from continental extension to oceanic spreading. Therefore, rheological softening caused destabilization of the lithospheric mantle between the future continental margins (Piccardo et al., 2014; Piccardo, 2016) of the Ligurian Tethys. The wedge of destabilized lithosphere favored faster divergence of the continental blocks and enhanced doming and thermal buoyancy of deeper/hotter asthenosphere that rose between the future continental margins and originated aggregated MORB melts (i.e., the oceanic magmatism that formed olivine-gabbro intrusions and pillowed basalt extrusions). Lithosphere destabilization by melt percolation can play a fundamental role in the geodynamic evolution of lithosphere extension causing transition from continental extension to continental break-up to oceanic spreading. Corti, G., Bonini, M., Innocenti, F., Manetti, P., Piccardo, G.B., Ranalli, G., 2007. Journal of Geodynamics, 43, 465-483. Piccardo, G.B., Padovano, M., Guarnieri, L. 2014. Earth-Science Reviews, 138, 409-434. Piccardo, G.B., 2016. Gondwana Research, 39, 230-249. Piccardo, G.B., Vissers, R.L.M., 2007. Journal of Geodynamics, 43, 417-449. Piccardo, G.B., Guarnieri, L., 2011. Lithos, 124, 210-214. Ranalli, G., Piccardo, G.B., Corona-Chavez, P., 2007. Journal of Geodynamics, 43, 450-464.

  10. Rheology, tectonics, and the structure of the Venus lithosphere

    Science.gov (United States)

    Zuber, M. T.

    1994-01-01

    Given the absence of ground truth information on seismic structure, heat flow, and rock strength, or short wavelength gravity or magnetic data for Venus, information on the thermal, mechanical and compositional nature of the shallow interior must be obtained by indirect methods. Using pre-Magellan data, theoretical models constrained by the depths of impact craters and the length scales of tectonic features yielded estimates on the thickness of Venus' brittle-elastic lithosphere and the allowable range of crustal thickness and surface thermal gradient. The purpose of this study is to revisit the question of the shallow structure of Venus based on Magellan observations of the surface and recent experiments that address Venus' crustal rheology.

  11. Estimating the stresses within the lithosphere: parameter check with applications to the African Plate

    Science.gov (United States)

    Medvedev, Sergei; Werner, Stephanie; Steinberger, Bernhard; "African Plate" Working Group

    2010-05-01

    Several mechanisms control the state of stress within plates on Earth. The list is rather long, but well-known and includes ridge push, mantle drag, stresses invoked by lateral variations of lithospheric density structure and subduction processes. We attempt to quantify the influence of these mechanisms and to construct a reliable model to understand modern and palaeo-stresses using the African plate (TAP) as an example. Previous studies explained stress patterns and their evolution solely by assigning different rheological properties to sub-domains and their boundaries. Such an approach often leads to unrealistically high variations of properties within a modeled plate. In our approach we find the best possible agreement with observations before differentiating between sub-domains of TAP. The finite-element based suite ProShell was utilized to calculate stresses on the real geometry of TAP (non-planar). The approach allows us to combine several data sets and to estimate stresses caused by lateral and vertical distribution of properties within the lithosphere, to quantify the in-plane and bending stresses, to account for forces due to ridge push and mantle heterogeneities and mantle flow. The modeled results are tested and iterated to match the observed stress pattern and potential fields as good as possible. The starting model is based on the CRUST2 data set to construct the model crust and half-space cooling model to approximate properties of the lithospheric mantle. The results however, are not satisfactory, and might be related to oversimplifications in the uniform model of lithosphere or/and to the unrealistic representation of the CRUST2 model in certain areas of TAP. The latter was also shown by simple evaluation using gravity forward modeling of the model boundaries. The model implementation of the crustal structure calculated from simple gravity inversion or derived through isostatical considerations agree better to today's observed stress pattern.

  12. The effect of bimineralic composition on extensional processes at lithospheric scale

    Science.gov (United States)

    Jammes, Suzon; Lavier, Luc L.

    2016-08-01

    We investigate how lithospheric scale compositional heterogeneities affect kilometric scale deformation processes. To this end, we perform numerical experiments of lithospheric extension in which we vary the Moho temperature and the mineralic composition of the mantle and the crust. In both the crust and the mantle, we use an explicit bimineralic composition by randomly distributing two mineral phases in the materials. Comparison of our models to simulations using an implicit bimineralic composite (one average viscous flow laws for a two-phase aggregate) crust and mantle demonstrates that an explicit bimineralic composition assimilated to heterogeneities succeeds in explaining observations related to the formation of rifted margins such a: (1) the absence of a sharp deformation zone at the brittle ductile transition (BDT), (2) the initiation of the rifting process as a wide delocalized rift system with multiple normal faults dipping in both directions; (3) the development of anastomosing shear zones in the middle/lower crust and the upper lithospheric mantle similar to the crustal scale anastomosing patterns observed in the field or in seismic data; (4) the preservation of undeformed lenses of material leading to lithospheric scale boudinage structure and resulting in the formation of continental ribbons as observed along the Iberian-Newfoundland margin.

  13. Interplay of variable thermal conductivity and expansivity on the thermal structure of oceanic lithosphere II

    Science.gov (United States)

    Honda, S.; Yuen, D. A.

    2004-04-01

    We have extended our previous analysis of the effects of constant vs. variable, i.e., pressure and temperature dependent thermal conductivity (k) and constant thermal expansivity (a) on the thermal structure of the oceanic lithosphere. We apply our analysis to the actual data set including information on the geoid slope. The heat flow and ocean floor depth data constrain the thermal expansivity (a ≍ 3 × 10-5 1/°C). Including geoid slope data may loosely constrain both the thermal expansivity and the thermal conductivity. The probable value of thermal conductivity is ≍ 3 W/m/°C for the constant k case and ≍ 4 W/m/°C (at ambient conditions) for the variable k case. These a and k are generally consistent with laboratory data of appropriate lithospheric materials. Our analysis supports the plate model with thin lithosphere and high bottom temperature, such as GDH1 (95 km; 1450°C). Variable k case requires slightly thinner and higher temperature lithosphere (≍ 85 km and ≍ 1500°C) and gives a slightly better fit to the geoid slope data.

  14. The crust and lithosphere thicknesses of Greenland revisited: what do recent gravity data tell us?

    Science.gov (United States)

    Steffen, Rebekka; Lund, Björn

    2016-04-01

    Crustal and lithospheric thicknesses are nowadays extensively studied and several datasets exist for most parts of the Earth; however, for some regions only a few estimations are available. For high resolution models of glacial isostatic adjustment (GIA), the thickness of the crust and lithosphere beneath the glaciated regions are very important as they affect the calculation of past and future sea level changes. Greenland, with its decreasing ice sheet and rapidly retreating outlet glaciers, is one such region where the GIA estimation is important but where the ice sheet itself prevents extensive studies of the crustal and lithospheric thicknesses. Most of the thickness estimates have so far been obtained from seismological studies, which depend on the density of the station networks. We will present newly obtained crustal and lithospheric thickness maps, which are estimated from gravity data using the Parker-Oldenburg inversion algorithm. The gravity dataset will be presented together with all the necessary corrections which have to be applied before the inversion procedure. The obtained thickness maps will be compared to former results of seismological and gravimetric studies and differences will be discussed, also from a geodynamic point of view.

  15. Macroscopic strength of oceanic lithosphere revealed by ubiquitous fracture-zone instabilities

    Science.gov (United States)

    Cadio, Cécilia; Korenaga, Jun

    2016-09-01

    The origin of plate tectonics is one of the most fundamental issues in earth and planetary sciences. Laboratory experiments indicate that the viscosity of silicate rocks is so strongly temperature-dependent that the entire surface of the Earth should be one immobile rigid plate. The rheology of oceanic lithosphere is, however, still poorly understood, and there exist few constraints on the temperature dependency of viscosity on the field scale. Here we report a new kind of observational constraint based on the geoid along oceanic fracture zones. We identify a large number of conspicuous small-scale geoid anomalies, which cannot be explained by the standard evolution model of oceanic lithosphere, and estimate their source density perturbations using a new Bayesian inversion method. Our results suggest that they are caused most likely by small-scale convection involving temperature perturbations of ∼ 300 K ± 100 K. Such thermal contrast requires the activation energy of mantle viscosity to be as low as 100 ± 50 kJmol-1 in case of diffusion creep, and 225 ± 112 kJmol-1 in case of dislocation creep, substantially reducing the thickness of the stiffest part of oceanic lithosphere. Oceanic lithosphere may thus be broken and bent much more easily than previously thought, facilitating the operation of plate tectonics.

  16. Pre-plate tectonics and structure of the Archean mantle lithosphere imaged by seismic anisotropy - inferences from the LAPNET array in northern Fennoscandia

    Science.gov (United States)

    Plomerova, Jaroslava; Vecsey, Ludek; Babuska, Vladislav; Lapnet Working Group

    2013-04-01

    Various studies of seismic anisotropy clearly demonstrate the Archean mantle lithosphere consists of domains with different fabrics reflecting fossil anisotropic structures. We detect anisotropic signal both in the P-wave travel-time deviations and shear-wave splitting recorded by the LAPNET array (2007-2009) in the Archean craton of Fennoscandia (Plomerova et al., 2011). The anisotropic parameters change across the array and stations with similar characteristics form groups. The geographical variations of seismic-wave anisotropy delimit individual sharply bounded domains of the mantle lithosphere, each of them having a consistent fabric. The domains can be modelled in 3D by peridotite aggregates with dipping lineation a, or foliation (a,c). Also radial anisotropy of the Archean lithosphere derived from surface waves indicates inclined structure of all the cratonic regions of the continents, though with less detailed lateral resolution in comparison with body-wave anisotropy. These findings allow us to interpret the domains as micro-plate fragments retaining fossil fabrics in the mantle lithosphere, reflecting thus an olivine LPO created before the micro-plates assembled. Successive subductions of oceanic lithosphere is a mechanism which can work in modern-style plate tectonics as we know it now, being considered as widespread since 2.7 Ga. Though the modern plate tectonics is the most distinct tectonic style acting up to now, we have to consider a mechanism creating oriented structures (fabrics) in a pre-plate-tectonic style. The early lithosphere formed in dynamic conditions far from simple cooling which would result in sub-horizontal layered structure of the lithosphere. Earlier tectonic modes in a hotter and more dynamic Earth might be similar in some respects to those of the modern-plate tectonics. Basaltic "rockbergs" on convecting magma ocean in the Hadean Earth are supposed to turn to either proto-plate tectonics with platelets and supercratonal, or, to

  17. Water and its influence on the lithosphere-asthenosphere boundary.

    Science.gov (United States)

    Green, David H; Hibberson, William O; Kovács, István; Rosenthal, Anja

    2010-09-23

    The Earth has distinctive convective behaviour, described by the plate tectonics model, in which lateral motion of the oceanic lithosphere of basaltic crust and peridotitic uppermost mantle is decoupled from the underlying mechanically weaker upper mantle (asthenosphere). The reason for differentiation at the lithosphere-asthenosphere boundary is currently being debated with relevant observations from geophysics (including seismology) and geochemistry (including experimental petrology). Water is thought to have an important effect on mantle rheology, either by weakening the crystal structure of olivine and pyroxenes by dilute solid solution, or by causing low-temperature partial melting. Here we present a novel experimental approach to clarify the role of water in the uppermost mantle at pressures up to 6 GPa, equivalent to a depth of 190 km. We found that for lherzolite in which a water-rich vapour is present, the temperature at which a silicate melt first appears (the vapour-saturated solidus) increases from a minimum of 970 °C at 1.5 GPa to 1,350 °C at 6 GPa. We have measured the water content in lherzolite to be approximately 180 parts per million, retained in nominally anhydrous minerals at 2.5 and 4 GPa at temperatures above and below the vapour-saturated solidus. The hydrous mineral pargasite is the main water-storage site in the uppermost mantle, and the instability of pargasite at pressures greater than 3 GPa (equivalent to more than about 90 km depth) causes a sharp drop in both the water-storage capacity and the solidus temperature of fertile upper-mantle lherzolite. The presence of interstitial melt in mantle with more than 180 parts per million of water at pressures greater than 3 GPa alters mantle rheology and defines the lithosphere-asthenosphere boundary. Modern asthenospheric mantle acting as the source for mid-oceanic ridge basalts has a water content of 50-200 parts per million (refs 3-5). We show that this matches the

  18. Effect of the lithospheric thermal state on the Moho interface: A case study in South America

    Science.gov (United States)

    Bagherbandi, Mohammad; Bai, Yongliang; Sjöberg, Lars E.; Tenzer, Robert; Abrehdary, Majid; Miranda, Silvia; Alcacer Sanchez, Juan M.

    2017-07-01

    Gravimetric methods applied for Moho recovery in areas with sparse and irregular distribution of seismic data often assume only a constant crustal density. Results of latest studies, however, indicate that corrections for crustal density heterogeneities could improve the gravimetric result, especially in regions with a complex geologic/tectonic structure. Moreover, the isostatic mass balance reflects also the density structure within the lithosphere. The gravimetric methods should therefore incorporate an additional correction for the lithospheric mantle as well as deeper mantle density heterogeneities. Following this principle, we solve the Vening Meinesz-Moritz (VMM) inverse problem of isostasy constrained by seismic data to determine the Moho depth of the South American tectonic plate including surrounding oceans, while taking into consideration the crustal and mantle density heterogeneities. Our numerical result confirms that contribution of sediments significantly modifies the estimation of the Moho geometry especially along the continental margins with large sediment deposits. To account for the mantle density heterogeneities we develop and apply a method in order to correct the Moho geometry for the contribution of the lithospheric thermal state (i.e., the lithospheric thermal-pressure correction). In addition, the misfit between the isostatic and seismic Moho models, attributed mainly to deep mantle density heterogeneities and other geophysical phenomena, is corrected for by applying the non-isostatic correction. The results reveal that the application of the lithospheric thermal-pressure correction improves the RMS fit of the VMM gravimetric Moho solution to the CRUST1.0 (improves ∼ 1.9 km) and GEMMA (∼1.1 km) models and the point-wise seismic data (∼0.7 km) in South America.

  19. Understanding the lithosphere in complex tectonic scenarios by integrating geophysical data: The Pyrenees case study

    Science.gov (United States)

    Campanyà, Joan; Fullea, Javier; Ledo, Juanjo; Queralt, Pilar; Marcuello, Alex; Liesa, Montserrat; Muñoz, Josep Anton

    2016-04-01

    Tectonic processes dominate the development of the outermost layer of the Earth over a timescale of millions of years. The locations where these processes take place provide a great opportunity for Earth scientists to study and understand the dynamics and properties of the lithosphere. The Pyrenees are a particular case of continental collision formed as a result of the collision between the Iberian and European plates, which caused the subduction of the Iberian lower crust below the European crust. Large amounts of geophysical data have been acquired in the area providing spectacular images of lithospheric subduction beneath the Western and Central Pyrenees, confirming the occurrence of this generally well-understood process. The Eastern Pyrenees, however, are a most puzzling part of the orogen and the geodynamical evolution of this area cannot be understood without the influence of the Neogene Mediterranean rifting, following the continental collision. The complexity of this area and the controversy of the geophysical results set in debate concepts well recognized in the other parts of the Pyrenees such as the subduction of the Iberian lower crust and the depth of the lithosphere-asthenosphere boundary. The aims of this study are to characterise major tectonic and geophysical variations along the Pyrenean mountain range at a lithospheric-scale and constrain the causes of the observed lateral variations. A preliminary model of the lithospheric configuration and dynamics, based on magnetotelluric geophysical results, has been developed and constrained using independent and available geophysical, geological and geochemical data. Computational petrology methods, using Litmod, were used for integrated modelling of all data.

  20. Thermo-chemical structure of the North China Craton from multi-observable probabilistic inversion: extent and causes of cratonic lithosphere modification

    Science.gov (United States)

    Guo, Z.; Afonso, J. C.; Qashqai, M.; Yang, Y.; Chen, J.

    2016-12-01

    Although the North China Craton (NCC) is one of the best documented cases of cratonic lithosphere modification, the actual causes, processes, and extent of lithospheric modification still are a matter of debate. Here, we present the first thermo-chemical model of the NCC from the surface down to 350 km by jointly inverting surface wave phase velocity data, geoid height, surface heat flow and absolute elevation with a novel multi-observable probabilistic inversion method. Our model reveals a thin ( 65-100 km) and chemically fertile lithosphere (8790) lithospheric mantle is imaged beneath the central TNCO and Ordos Block, reaching depths > 260 km. This lithospheric "keel" is surrounded to the east by a high-temperature sublithospheric anomaly that originates at depths > 280 km. The spatial distribution of this anomaly and its correlation with the location of recent volcanism in the region suggest that the anomaly represents a deep mantle upwelling being diverted by the cratonic keel and spreading onto regions of shallow lithosphere. Our results indicate that the present-day thermochemical structure beneath the NCC is the result of a complex interaction between a large-scale return flow associated with the subduction of the Pacific slab and the shallow lithospheric structure.

  1. Highly CO2-supersaturated melts in the Pannonian lithospheric mantle - A transient carbon reservoir?

    Science.gov (United States)

    Créon, Laura; Rouchon, Virgile; Youssef, Souhail; Rosenberg, Elisabeth; Delpech, Guillaume; Szabó, Csaba; Remusat, Laurent; Mostefaoui, Smail; Asimow, Paul D.; Antoshechkina, Paula M.; Ghiorso, Mark S.; Boller, Elodie; Guyot, François

    2017-08-01

    Subduction of carbonated crust is widely believed to generate a flux of carbon into the base of the continental lithospheric mantle, which in turn is the likely source of widespread volcanic and non-volcanic CO2 degassing in active tectonic intracontinental settings such as rifts, continental margin arcs and back-arc domains. However, the magnitude of the carbon flux through the lithosphere and the budget of stored carbon held within the lithospheric reservoir are both poorly known. We provide new constraints on the CO2 budget of the lithospheric mantle below the Pannonian Basin (Central Europe) through the study of a suite of xenoliths from the Bakony-Balaton Highland Volcanic Field. Trails of secondary fluid inclusions, silicate melt inclusions, networks of melt veins, and melt pockets with large and abundant vesicles provide numerous lines of evidence that mantle metasomatism affected the lithosphere beneath this region. We obtain a quantitative estimate of the CO2 budget of the mantle below the Pannonian Basin using a combination of innovative analytical and modeling approaches: (1) synchrotron X-ray microtomography, (2) NanoSIMS, Raman spectroscopy and microthermometry, and (3) thermodynamic models (Rhyolite-MELTS). The three-dimensional volumes reconstructed from synchrotron X-ray microtomography allow us to quantify the proportions of all petrographic phases in the samples and to visualize their textural relationships. The concentration of CO2 in glass veins and pockets ranges from 0.27 to 0.96 wt.%, higher than in typical arc magmas (0-0.25 wt.% CO2), whereas the H2O concentration ranges from 0.54 to 4.25 wt.%, on the low end for estimated primitive arc magmas (1.9-6.3 wt.% H2O). Trapping pressures for vesicles were determined by comparing CO2 concentrations in glass to CO2 saturation as a function of pressure in silicate melts, suggesting pressures between 0.69 to 1.78 GPa. These values are generally higher than trapping pressures for fluid inclusions

  2. Does urothelial cancer of bladder behave differently in young patients?

    Institute of Scientific and Technical Information of China (English)

    WANG Zhi-hua; LI You-yuan; HU Zhi-quan; ZHU Hui; ZHUANG Qian-yuan; QI Yong; YE Zhang-qun

    2012-01-01

    Background Bladder urothelial cancer has been diagnosed at an increasing rate among young adults in China while the clinical outcomes remain highly controversial.To optimize the management of young patients with bladder cancer,we examined whether bladder urothelial cancer in young patients behaved differently from that in the elder patients.Methods From 1994 to 2008,a database of bladder urothelial cancer patients at a major tertiary medical center was retrospectively reviewed.The clinical and pathological parameters of patients who were less than 40 years of age and a series of patients older than 40 years of age as the control group during the same period were compared.A survival analysis was performed using the Kaplan-Meier method and log-rank test,and Cox regression was performed to identify clinical parameters that affected the clinic outcomes.Results Young bladder cancer patients had a lower male-to-female ratio and were less likely to have advanced stages and high-grade cancers at the initial diagnosis.Tumors in young bladder cancer patients tended to be less multifocal at diagnosis.In addition,young patients had a lower recurrence rate and longer recurrence interval than older patients.The Kaplan-Meier curve and Log-rank test showed that young patients had significantly better cancer specific survival than old patients.The univariats and multivariate Cox regression analysis revealed that tumor grade is the sole predictor for tumor recurrence in young patients.Conclusions Young patients with bladder cancer have favorable pathological features and clinical outcomes than older patients.These findings argue for more conservative management approaches for young patients with bladder cancer.

  3. Three-dimensional density structure of the lunar upper lithosphere

    Science.gov (United States)

    Liang, Q.; Du, J.; Chen, C.; Li, Y.

    2011-12-01

    The lithosphere of the Moon has a thickness over 1200 km according to the seismology studies. It records the giant impact events during the processes of solidification. The upper lithosphere including the crust and the upper mantle was thought to be a nonuniform layer in thickness and seismic velocity, yet the lateral density structure remains poorly understood. The global gravity data thus provides a significant constraint on the three-dimensional (3-D) density structure of the Moon. Previous studies assumed that the crust and the mantle have constant density the gravity anomalies are only produced by the variations of interface between the crust and the mantle. Therefore, the constant density may give overestimation or underestimation of the Moho depth. In contrast, we apply a 3-D inverse method in spherical coordinate to the lunar gravity anomaly. It is a direct way in recovering the density structures beneath mascon basins or the lateral density heterogeneities in the upper lithosphere. The gravity anomaly we use in this study is the Bouguer gravity anomaly calculated at 1750 km radius relative to the reference radius, 1737.153 km[1], from the newly gravity field model SGM100i[2] and the topography model LRO_LTM02[1]. In order to understand the global feature of density variation, we truncate the long wavelength anomaly up to the order of 30 to reconstruct the density distribution above the depth of 100 km in the Moon. With the inverse technique, we obtain a global 3-D density structure of the lunar lithosphere down to 100 km depth. The major features are dominated by the mascons with dense materials and the broad region of the farside highland with relative low density mass. From this structure, the huge mass concentrations are found beneath the South Pole-Aitken (SPA) basin, meaning that the oblique impact not only excavated the SPA basin into deep but also made the mantle uplifted close to a depth of 30 km (relative to a 1738 km radius). We suggest here that

  4. Lithospheric bending at subduction zones based on depth soundings and satellite gravity

    Science.gov (United States)

    Levitt, Daniel A.; Sandwell, David T.

    1995-01-01

    A global study of trench flexure was performed by simultaneously modeling 117 bathymetric profiles (original depth soundings) and satellite-derived gravity profiles. A thin, elastic plate flexure model was fit to each bathymetry/gravity profile by minimization of the L(sub 1) norm. The six model parameters were regional depth, regional gravity, trench axis location, flexural wavelength, flexural amplitude, and lithospheric density. A regional tilt parameter was not required after correcting for age-related trend using a new high-resolution age map. Estimates of the density parameter confirm that most outer rises are uncompensated. We find that flexural wavelength is not an accurate estimate of plate thickness because of the high curvatures observed at a majority of trenches. As in previous studies, we find that the gravity data favor a longer-wavelength flexure than the bathymetry data. A joint topography-gravity modeling scheme and fit criteria are used to limit acceptable parameter values to models for which topography and gravity yield consistent results. Even after the elastic thicknesses are converted to mechanical thicknesses using the yield strength envelope model, residual scatter obscures the systematic increase of mechanical thickness with age; perhaps this reflects the combination of uncertainties inherent in estimating flexural wavelength, such as extreme inelastic bending and accumulated thermoelastic stress. The bending moment needed to support the trench and outer rise topography increases by a factor of 10 as lithospheric age increases from 20 to 150 Ma; this reflects the increase in saturation bending moment that the lithosphere can maintain. Using a stiff, dry-olivine rheology, we find that the lithosphere of the GDH1 thermal model (Stein and Stein, 1992) is too hot and thin to maintain the observed bending moments. Moreover, the regional depth seaward of the oldest trenches (approximately 150 Ma) exceeds the GDH1 model depths by about 400 m.

  5. Trench curvature and deformation of the subducting lithosphere

    Science.gov (United States)

    Schettino, Antonio; Tassi, Luca

    2012-01-01

    The subduction of oceanic lithosphere is generally accompanied by downdip and lateral deformation. The downdip component of strain is associated with external forces that are applied to the slab during its sinking, namely the gravitational force and the mantle resistance to penetration. Here, we present theoretical arguments showing that a tectonic plate is also subject to a predictable amount of lateral deformation as a consequence of its bending along an arcuate trench zone, independently from the long-term physical processes that have determined the actual curvature of the subduction zone. In particular, we show that the state of lateral strain and the lateral strain rate of a subducting slab depend from geometric and kinematic parameters, such as trench curvature, dip function and subduction velocity. We also demonstrate that the relationship between the state of lateral strain in a subducting slab and the geometry of bending at the corresponding active margin implies a small component of lateral shortening at shallow depths, and may include large extensional lateral deformation at intermediate depths, whereas a state of lateral mechanical equilibrium can only represent a localized exception. Our formulation overcomes the flaws of the classic 'ping-pong ball' model for the bending of the lithosphere at subduction zones, which lead to severe discrepancies with the observed geometry and style of deformation of the modern subducting slabs. A study of the geometry and seismicity of eight modern subduction zones is performed, to assess the validity of the theoretical relationship between trench curvature, slab dip function, and lateral strain rate. The strain pattern within the eight present-day slabs, which is reconstructed through an analysis of Harvard CMT solutions, shows that tectonic plates cannot be considered as flexible-inextensible spherical caps, whereas the lateral intraslab deformation which is accommodated through seismic slip can be explained in terms

  6. On a family of well behaved perfect fluid balls as astrophysical objects in general relativity

    Science.gov (United States)

    Maurya, S. K.; Gupta, Y. K.

    2011-07-01

    A family of well behaved perfect fluid balls has been derived starting with the metric potential g 44= B(1+ Cr 2) n for all positive integral values of n. For n≥4, the members of this family are seen to satisfy the various physical conditions e.g. c 2 ρ≥ p≥0, dp/ dr1. Also the pressure, energy density, velocity of sound and ratio of pressure and energy density are of monotonically decreasing towards the pressure free interface ( r= a). The fluid balls join smoothly with the Schwarzschild exterior model at r= a. The well behaved perfect fluid balls so obtained are utilised to construct the superdense star models with their surface density 2×1014 gm/cm3. We have found that the maximum mass of the fluid balls corresponding to various values of n are decreasing with the increasing values of n. Over all maximum mass for the whole family turns out to be 4.1848 M Θ and the corresponding radius as 19.4144 km while the red shift at the centre and red shift at surface as Z 0=1.6459 and Z a =0.6538 respectively this all happens for n=4. It is interesting to note that for higher values of n viz n≥170, the physical data start merging with that of Kuchowicz superdense star models and hence the family of fluid models tends to the Kuchowicz fluid models as n→∞. Consequently the maximum mass of the family of solution can not be less than 1.6096 M Θ which is the maximum mass occupied by the Kuchowicz superdense ball. Hence each member of the family for n≥4 provides the astrophysical objects like White dwarfs, Quark star, typical neutron star.

  7. Intraplate seismicity in SE Brazil: stress concentration in lithospheric thin spots

    Science.gov (United States)

    Assumpção, Marcelo; Schimmel, Martin; Escalante, Christian; Roberto Barbosa, José; Rocha, Marcelo; Barros, Lucas V.

    2004-10-01

    Intraplate seismicity has generally poor correlation with surface geological patterns. Except for major extensional features, such as aborted continental rifts, which may act as weak zones, it is usually difficult to find simple geology based models to explain differences in seismic activity in stable continental regions. Seismicity in Brazil is clearly not uniform and a few areas of higher activity have been identified. However, the seismic areas show almost no correlation with the main geological provinces, which is typical of other intraplate settings. A recent upper-mantle tomography study in SE and central Brazil, using approximately 8500 P-wave and 2000 PKP-wave arrivals recorded in 59 sites since 1992, has mapped P-wave velocity anomalies from lithospheric depths down to 1300 km. In this region, higher seismic activity occurs preferentially in areas with low P-wave velocities at 150-250 km depth. The low P-wave velocities are interpreted as shallower asthenosphere. In such areas, a hotter geotherm will reduce the strength of the lithospheric upper mantle causing most of the intraplate forces to be concentrated in the brittle upper crust. The low-velocity anomalies coincide with Late Cretaceous provinces of alkaline intrusions. The proposed ponding of the Trindade plume head beneath lithospheric thin spots is consistent with our tomography results, suggesting that plume effects may have helped to preserve lithosphere/asthenosphere topography. Although other factors are also important, the present data show that stress concentrations resulting from lithosphere/asthenosphere topography should play an important role in explaining the intraplate seismicity in the Brazilian platform.

  8. Electrical Conductivity and Anisotropy in Pacific Lithosphere: CSEM Results from APPLE

    Science.gov (United States)

    Behrens, J.; Constable, S.; Everett, M.; MacGregor, L.

    2003-12-01

    Strain associated with plate formation at mid-ocean ridge spreading centers may influence electrical conductivity at various depths in the lithosphere, and may leave an anisotropic fabric frozen in place. By measuring lithospheric electrical conductivity and anisotropy, insight may be gained regarding the formation and evolution of oceanic crust and mantle. Controlled-source electromagnetic (CSEM) sounding of 35 Ma Pacific lithosphere was undertaken as part of the Anisotropy and Physics of the Pacific Lithosphere Experiment (APPLE), carried out approximately 1000 km west of San Diego. The transmitter (DASI), with a 100 m horizontal electric dipole antenna, was deep-towed in a 30 km radius circle around an array of receivers. A radial tow to 70 km total range and a 15 km radius semi-circular tow supplemented the geometry of the main tow. DASI transmitted a 4 Hz square wave throughout the CSEM phase of the experiment. Smooth (and layered) inversions of short-offset (2-20 km) data, using 1-D isotropic modeling, generate models with upper-crustal resistivities ˜1 Ω m, varying by about an order of magnitude across the survey area. Lower crustal resistivities are on the order of 103 Ω m. Smooth inversion of the long radial tow data indicates upper mantle resistivities of ˜104 Ω m, with an increase in conductivity below 20 km depth. This may be due to thermally-activated olivine conduction, indicating that the base of the lithosphere has been detected. The integrated resistivity-thickness product for the top 100 km of our model is 1.1 x 109 Ω m2. The electric field is characterized in terms of the polarization ellipse parameters. During the circular tow, the maximum axis varies by a factor of two, while the minimum axis varies by a factor of 5. Forward calculations were run on models with a uniaxially anisotropic layer sandwiched between two isotropic layers. Simulated data from models with increased conductivity perpendicular to the paleo-spreading direction in the

  9. Lithosphere Thickness, Heat Flow and Moho Depth in The South of Portugal

    Science.gov (United States)

    Rosa Duque, Maria

    2016-10-01

    In the last years, several models have been presented trying to obtain lithosphere and Moho thickness in the Iberian Peninsula, using data related to geoid elevation and topography, gravity, seismicity and thermal analysis. The results obtained show a decrease in the thickness of the crust and the lithosphere in the SW part of the Iberian Peninsula. Density anomalies in the crust are also referred. Data obtained in the region was collected and deviations from average values used were detected. In this work, models were made taking into account the specific characteristics of the region. Heat flow, thermal conductivity, heat production, topography, gravity, seismic and geological data available for the region, were used to adjust the model. The results show that this region is different from other parts of the Iberian Peninsula and a special attention must be given to it. This work shows the importance of trying to know and understand the thermal structure of the region.

  10. The biology of habitat dominance; can microbes behave as weeds?

    Science.gov (United States)

    Cray, Jonathan A; Bell, Andrew N W; Bhaganna, Prashanth; Mswaka, Allen Y; Timson, David J; Hallsworth, John E

    2013-09-01

    Competition between microbial species is a product of, yet can lead to a reduction in, the microbial diversity of specific habitats. Microbial habitats can resemble ecological battlefields where microbial cells struggle to dominate and/or annihilate each other and we explore the hypothesis that (like plant weeds) some microbes are genetically hard-wired to behave in a vigorous and ecologically aggressive manner. These 'microbial weeds' are able to dominate the communities that develop in fertile but uncolonized--or at least partially vacant--habitats via traits enabling them to out-grow competitors; robust tolerances to habitat-relevant stress parameters and highly efficient energy-generation systems; avoidance of or resistance to viral infection, predation and grazers; potent antimicrobial systems; and exceptional abilities to sequester and store resources. In addition, those associated with nutritionally complex habitats are extraordinarily versatile in their utilization of diverse substrates. Weed species typically deploy multiple types of antimicrobial including toxins; volatile organic compounds that act as either hydrophobic or highly chaotropic stressors; biosurfactants; organic acids; and moderately chaotropic solutes that are produced in bulk quantities (e.g. acetone, ethanol). Whereas ability to dominate communities is habitat-specific we suggest that some microbial species are archetypal weeds including generalists such as: Pichia anomala, Acinetobacter spp. and Pseudomonas putida; specialists such as Dunaliella salina, Saccharomyces cerevisiae, Lactobacillus spp. and other lactic acid bacteria; freshwater autotrophs Gonyostomum semen and Microcystis aeruginosa; obligate anaerobes such as Clostridium acetobutylicum; facultative pathogens such as Rhodotorula mucilaginosa, Pantoea ananatis and Pseudomonas aeruginosa; and other extremotolerant and extremophilic microbes such as Aspergillus spp., Salinibacter ruber and Haloquadratum walsbyi. Some microbes

  11. Quantum Behaved Particle Swarm Optimization Algorithm Based on Artificial Fish Swarm

    OpenAIRE

    Dong Yumin; Zhao Li

    2014-01-01

    Quantum behaved particle swarm algorithm is a new intelligent optimization algorithm; the algorithm has less parameters and is easily implemented. In view of the existing quantum behaved particle swarm optimization algorithm for the premature convergence problem, put forward a quantum particle swarm optimization algorithm based on artificial fish swarm. The new algorithm based on quantum behaved particle swarm algorithm, introducing the swarm and following activities, meanwhile using the a...

  12. Structure, seismicity, and instrumentation of stable North American lithosphere

    Science.gov (United States)

    Wolin, Emily Lynne Gregonis

    The work in this thesis covers a number of different fields in seismology. These can be divided into three parts. In the first, I discuss earthquakes that occur along the North American passive margin. In the second, I investigate the noise characteristics of Superior Rifting Earthscope Experiment (SPREE) seismic stations. In the third, I evaluate the predictions of pre-existing tomographic models, expand raypath coverage in eastern North America by fitting waveforms, and produce an updated tomographic model focusing on the structure of stable North American lithosphere. First, I explore the rare, but moderate-to-large earthquakes that occur along the passive margin of North America, such as the August 2011 Mineral, Virginia earthquake. I discuss the tectonic setting, possible causes, and challenges of studying such earthquakes and propose directions for their future study. Examining the seismicity of the regions surrounding the 1929 Grand Banks and 1933 Baffin Bay earthquakes, I conclude that the aftershocks of these events continue today due to low strain rates along the margin. Second, I characterize the long-period noise characteristics of SPREE stations. At periods greater than 20 seconds, horizontal noise levels at SPREE stations vary seasonally and diurnally. I find that SPREE stations in sandy soil have the most consistent noise levels. Stations in fine-grained soil become extremely noisy during summer days, but very quiet when the surrounding soil freezes solid in winter. Finally, I evaluate previous generations of tomographic models and develop my own. I calculate synthetic seismograms for three tomographic models and compare them to new observed seismograms from earthquakes in stable North America. I find that adding data to a tomographic model does not necessarily improve predictions of regional S and Rayleigh waveforms. With this in mind, I apply the method of partitioned waveform inversion to derive constraints on S-velocity structure. I add these

  13. Imaging the Dynamics of Neocortical Population Activity in Behaving and Freely Moving Mammals.

    Science.gov (United States)

    Grinvald, Amiram; Petersen, Carl C H

    2015-01-01

    The development of functional imaging techniques applicable to neuroscience and covering a wide range of spatial and temporal scales has greatly facilitated the exploration of the relationships between cognition, behaviour and electrical brain activity. For mammals, the neocortex plays a particularly profound role in generating sensory perception, controlling voluntary movement, higher cognitive functions and planning goal-directed behaviours. Since these remarkable functions of the neocortex cannot be explored in simple model preparations or in anesthetised animals, the neural basis of behaviour must be explored in awake behaving subjects. Because neocortical function is highly distributed across many rapidly interacting regions, it is essential to measure spatiotemporal dynamics of cortical activity in real-time. Extensive work in anesthetised mammals has shown that in vivo Voltage-Sensitive Dye Imaging (VSDI) reveals the neocortical population membrane potential dynamics at millisecond temporal resolution and subcolumnar spatial resolution. Here, we describe recent advances indicating that VSDI is also already well-developed for exploring cortical function in behaving monkeys and mice. The first animal model, the non-human primate, is well-suited for fundamental exploration of higher-level cognitive function and behavior. The second animal model, the mouse, benefits from a rich arsenal of molecular and genetic technologies. In the monkey, imaging from the same patch of cortex, repeatedly, is feasible for a long period of time, up to a year. In the rodent, VSDI is applicable to freely moving and awake head-restrained mice. Interactions between different cortical areas and different cortical columns can therefore now be dynamically mapped through VSDI and related to the corresponding behaviour. Thus by applying VSDI to mice and monkeys one can begin to explore how behaviour emerges from neuronal activity in neuronal networks residing in different cortical areas.

  14. Seismic Structure and Geodynamic Evolution of the Lithosphere and Upper Mantle in the Pannonian - Carpathian Region

    Science.gov (United States)

    Houseman, G.; Stuart, G.; Dando, B.; Hetenyi, G.; Lorinczi, P.; Brueckl, E.; Hegedus, E.; Radovanovic, S.; Brisbourne, A.

    2009-04-01

    The Pannonian Basin is the largest of a group of Miocene-age extensional basins within the arc of the Alpine-Carpathian Mountain Ranges. These basins are extensional in origin, but the surrounding Carpathians result from sustained convergence during and since the period of active extension. A significant part of the mantle lithosphere here has been replaced, as gravitational instability caused an overturn of the upper mantle. The Carpathian Basins Project (CBP) is a major international broadband seismology experiment, supported by geodynamical modelling and designed to improve our understanding of the structure and evolution of the lithosphere and upper mantle beneath the Pannonian and Vienna Basins. Between 2005 and 2007 we deployed 56 portable broadband seismic stations in Austria, Hungary and Serbia, spanning the Vienna Basin and the western part of the Pannonian Basin. Arrival time residuals from teleseismic earthquakes are delayed by about 0.8 sec in the Vienna Basin and early by a similar amount in southwest Hungary. Tomographic inversion of the travel time residuals shows relatively fast P-wave velocities in the upper mantle beneath the western Pannonian Basin and slow P-wave velocities beneath the West Carpathians. Seismic anisotropy (SKS) measurements reveal an intriguing pattern of lithospheric anisotropy: in the north-west the fast direction is generally elongated EW, perpendicular to the shortening direction across the Alps. Across the Vienna Basin the fast direction is NW-SE, perpendicular to the major bounding fault systems. Across the Pannonian Basin the dominant fast direction is EW, but in several locations the vectors are rotated toward NW-SE. The Mid-Hungarian Line, a major strike-slip structure already clearly identified in the gravity field, also is associated with abrupt changes in the azimuth of lithospheric anisotropy. Receiver function analysis of the seismic discontinuity at 670 km shows significant structure on scales of order 100 km, and

  15. Lithospheric analysis of satellite geopotential anomalies of East Asia

    Science.gov (United States)

    Tan, Li

    Satellite gravity and magnetic anomalies are used to study the lithosphere of East Asia. Free-air gravity anomalies are decomposed into terrain-correlated, mantle/core and intracrustal components by spectral correlation analysis of the free-air gravity anomalies and terrain gravity effects. Compensated terrain gravity anomalies are obtained by removing the terrain-correlated free-air gravity anomalies. They are used to estimate the Moho undulation and crustal thickness by Gauss-Legendre quadrature (GLQ) inversion techniques assuming a Airy-Heiskanen model of crustal compensation. These results are used to develop enhanced reduction procedures to generate an improved Magsat magnetic anomaly map for East Asia. A degree 12 core field is removed from the data that are updated for the crustal components in the core field differences between degree 14 and 12. These components are estimated by using spectral correlation analysis to compare the Magsat anomalies to the magnetic effect of the crust that is available from the first vertical derivative of the terrain-correlated free-air gravity anomalies via Poisson's theorem. External field effects are separated using pass-by-pass correlation analysis of the dusk and dawn data sets and their spectral reconstruction. Coherent components in the dusk and dawn maps are combined to estimate the magnetic anomalies of the lithosphere. Long wavelength magnetic features related to lower crustal thickness variations are converted into effective magnetization contrasts by a new GLQ inversion technique. Effective magnetization contrasts of the lower crust range over ±4 A/m in accordance petrological studies. Finally, a new GLQ integration formula for triangular wedge sources is derived for modeling of satellite-altitude geopotential field anomalies from arbitrarily shaped sources. Detailed magnetization and density contrasts for central India, the Tibetan Plateau, and the Bengal Gulf region are modeled by this new formula. Positive

  16. The lithosphere of Ellesmere Island and adjacent northwestern Greenland (CALE “A” transect onshore)

    DEFF Research Database (Denmark)

    Stephenson, Randell Alexander; Schiffer, Christian; Oakey, Gordon

    to the lithosphere model. The most recent tectonic event governing the geological and physiographic character of Ellesmere Island is the Eurekan Orogeny, an intraplate orogeny that developed as a consequence of North Atlantic-Arctic plate reorganisations and the resulting convergence of Greenland against Ellesmere...... vertical structural differences in in the central part of Ellesmere Island, which are absent in the north and south. The lithosphere model is interpreted in the context of plate convergence processes in the Palaeozoic and large-scale intraplate shortening in the Cenozoic with extensional tectonics......Ellesmere Island, in Canada’s Arctic, comprises a series of ~SW-NE trending tectonic provinces, the crustal structure and geological expression of which represent a combination of interplate, accretionary orogenesis in the Palaeozoic (Caledonian equivalent and Ellesmerian orogenies) and intraplate...

  17. Lithospheric imaging from teleseismic data by frequency-domain elastic full-waveform tomography

    Science.gov (United States)

    Pageot, D.; Operto, S.; Vallée, M.; Brossier, R.; Virieux, J.; Seiscope

    2010-12-01

    Teleseismic data recorded by dense multicomponent surveys are potentially amenable to multichannel processing such as full waveform inversion to develop high-resolution lithospheric models. In this study, 2D frequency-domain full waveform tomography (FWT) is tailored to suit teleseismic geometries. Frequency-domain FWT seeks to estimate the elastic properties of the Earth by minimizing a misfit function between recorded and modeled full wavefields. FWT is designed to invert few discrete frequencies by proceeding hierarchically from the low frequencies to the higher ones, following a multiscale approach useful to mitigate the inversion nonlinearity. In teleseismic framework, seismic sources are planar incident wavefields impinging the base of the lithosphere with arbitrary incidence and obliquity angles. The full wavefield is computed using a scattered-field formulation in the frequency domain. First, an analytical wavefield is computed in a homogeneous background model with free surface on the topside for an incident compressional plane wave. Then, a scattering source is formed by the product of the analytical planewave with the difference of the forward problem operators associated with the homogeneous background and lithospheric models. The scattered wavefield is then computed by performing a simulation in the lithospheric model using the scattering source, and, finally, the full wavefield is built by summation of the analytical wavefield and of the scattered wavefield. The 2D P-SV wave modeling is performed with a finite element discontinuous Galerkin method allowing for unstructured triangular meshes. Teleseismic experiments are characterized by a narrow illumination of aperture angles because of the limited number of planewave sources related to the teleseismic earthquake distribution. This narrow aperture bandwith requires the use of finely-sampled frequencies to prevent spatial aliasing in the reconstructed FWT models. Moreover, planewave propagation from

  18. Global thermochemical imaging of the lithosphere using satellite and terrestrial observations

    Science.gov (United States)

    Fullea, Javier; Lebedev, Sergei; Martinec, Zdenek; Celli, Nicolas

    2017-04-01

    Conventional methods of seismic tomography, topography, gravity and electromagnetic data analysis and geodynamic modelling constrain distributions of seismic velocity, density, electrical conductivity, and viscosity at depth, all depending on temperature and composition of the rocks within the Earth. However, modelling and interpretation of multiple data sets provide a multifaceted image of the true thermochemical structure of the Earth that needs to be appropriately and consistently integrated. A simple combination of gravity, electromagnetic, geodynamics, petrological and seismic models alone is insufficient due to the non-uniqueness and different sensitivities of these models, and the internal consistency relationships that must connect all the intermediate parameters describing the Earth involved. Thermodynamic and petrological links between seismic velocities, density, electrical conductivity, viscosity, melt, water, temperature, pressure and composition within the Earth can now be modelled accurately using new methods of computational petrology and data from laboratory experiments. The growth of very large terrestrial and satellite (e.g., Swarm and GOCE ESA missions) geophysical data sets over the last few years, together with the advancement of petrological and geophysical modelling techniques, now present an opportunity for global, thermochemical and deformation 3D imaging of the lithosphere and underlying upper mantle with unprecedented resolution. This project combines state-of-the-art seismic waveform tomography (using both surface and body waves), newly available global gravity satellite data (geoid and gravity anomalies and new gradiometric measurements from ESA's GOCE mission) and surface heat flow and elevation within a self-consistent thermodynamic framework. The aim is to develop a method for detailed and robust global thermochemical image of the lithosphere and underlying upper mantle. In a preliminary study, we convert a state-of-the-art global

  19. Post glacial rebounds measure the viscosity of the lithosphere

    CERN Document Server

    Garai, J

    2003-01-01

    The observed higher uplift rates before the end of deglaciation requires the existence of a low viscosity channel or layer. The uplifts observed after the end of deglaciation does not show any contribution from this low viscosity channel and a homogeneous viscosity model fits very well to the observed uplift. Most of the researchers therefore prefer the homogeneous model and suggest that the higher uplift rate before the end of deglaciation is the result of elastic contamination. It has been shown that the elastic deformation of the lithosphere is far too small to be responsible for the observed extra uplift; therefore, the homogeneous viscosity model should be discredited. The homogeneous viscosity of the postglacial period and the high uplift rate of the late glacial period can be explained with a model which has an upper layer determining the homogeneous viscosity and the layer below it which has a low viscosity. The contribution to the uplift of this low viscosity layer is indistinguishable from an instan...

  20. 'Behaving well': the transition to respectable womanhood in rural South Africa.

    Science.gov (United States)

    Sennott, Christie; A Mojola, Sanyu

    2016-12-09

    Few studies of the transition to adulthood in Africa analyse young people's own definitions of the events that confer adult status, and how adulthood is actually attained. This paper examines the experience of transitioning to womanhood in rural Mpumalanga Province, South Africa, drawing on interviews with 18 women aged 18-39. Three primary experiences characterised this transition: puberty and emerging body awareness, spending time with boys, and having a child. More important than the timing of these experiences, however, was whether women 'behaved well' and maintained respectability as they transitioned to adulthood. Behavioural standards reinforcing ideal femininity were focused on dress, manner and talk, and were particularly stringent for mothers. Findings emphasise the value of emic models of adulthood for understanding how youth experience this transition and provide an important counter-narrative to the literature focused primarily on the risk African youth face during this period of change in the life course.

  1. A rapid method to map the crustal and lithospheric thickness using elevation, geoid anomaly and thermal analysis. Application to the Gibraltar Arc System, Atlas Mountains and adjacent zones

    Science.gov (United States)

    Fullea, J.; Fernàndez, M.; Zeyen, H.; Vergés, J.

    2007-02-01

    We present a method based on the combination of elevation and geoid anomaly data together with thermal field to map crustal and lithospheric thickness. The main assumptions are local isostasy and a four-layered model composed of crust, lithospheric mantle, sea water and the asthenosphere. We consider a linear density gradient for the crust and a temperature dependent density for the lithospheric mantle. We perform sensitivity tests to evaluate the effect of the variation of the model parameters and the influence of RMS error of elevation and geoid anomaly databases. The application of this method to the Gibraltar Arc System, Atlas Mountains and adjacent zones reveals the presence of a lithospheric thinning zone, SW-NE oriented. This zone affects the High and Middle Atlas and extends from the Canary Islands to the eastern Alboran Basin and is probably linked with a similarly trending zone of thick lithosphere constituting the western Betics, eastern Rif, Rharb Basin, and Gulf of Cadiz. A number of different, even mutually opposite, geodynamic models have been proposed to explain the origin and evolution of the study area. Our results suggest that a plausible slab-retreating model should incorporate tear and asymmetric roll-back of the subducting slab to fit the present-day observed lithosphere geometry. In this context, the lithospheric thinning would be caused by lateral asthenospheric flow. An alternative mechanism responsible for lithospheric thinning is the presence of a hot magmatic reservoir derived from a deep ancient plume centred in the Canary Island, and extending as far as Central Europe.

  2. The nature of cratonic lithosphere: Combining constraints from seismology, mineral physics, and petrology

    Science.gov (United States)

    Dalton, Colleen; Faul, Ulrich; Hirsch, Aaron

    2014-05-01

    In recent years, the prevailing notion of Precambrian continental lithosphere as a thick boundary layer (~200-300 km) with a very depleted composition and temperature structure controlled by steady-state conductive cooling has been challenged by several lines of seismological evidence. One, profiles of shear velocity with depth beneath cratons exhibit lower wave speed at shallow depths and higher wave speed at greater depths than can be explained by temperature alone. These profiles are also characterized by positive or flat velocity gradients with depth in the uppermost mantle and anomalously high attenuation, both of which are difficult to reconcile with the low temperatures and large thermal gradient expected in the thermal boundary layer. Two, body-wave receiver-function studies have detected a mid-lithospheric discontinuity that requires a large and abrupt velocity decrease with depth in cratonic regions that cannot be achieved by thermal gradients alone. We have used a forward-modeling approach to identify the suite of shear-velocity profiles that are consistent with phase-velocity observations made for Rayleigh waves traversing cratons in North America, Africa, and Australia. We have also calculated the range of lithospheric temperatures and compositions that are consistent with the elastic and anelastic seismological models, using laboratory measurements on the sensitivity of velocity and attenuation to temperature, major-element composition, and mineralogy. Finally, we consider the implications of the models for the long-term stability of cratons.

  3. Lithospheric instability beneath the Transverse Ranges of California

    OpenAIRE

    Houseman, Gregory A.; Neil, Emily A.; Kohler, Monica D.

    2000-01-01

    Recent high-resolution seismic experiments reveal that the crust beneath the San Gabriel Mountains portion of the Transverse Ranges thickens by 10–15 km (contrary to earlier studies). Associated with the Transverse Ranges, there is an anomalous ridge of seismically fast upper mantle material extending at least 200 km into the mantle. This high-velocity anomaly has previously been interpreted as a lithospheric downwelling. Both lithospheric downwelling and crustal thickening are associated wit...

  4. The elastic properties of the lithosphere beneath Scotian basin

    Science.gov (United States)

    Zheng, Ying; Arkani-Hamed, Jafar

    2002-02-01

    To assess the possibility that the North Atlantic Ocean may subduct at Scotian basin east of Canada, we investigate the present compensation state of this deep basin. A Fourier domain analysis of the bathymetry, depth to basement and observed gravity anomalies over the oceanic area east of Nova Scotia indicates that the basin is not isostatically compensated. Moreover, the analysis emphasizes that in addition to the sediments, density perturbations exist beneath the basin. The load produced by the sediments and these density perturbations must have been supported by the lithosphere. We simulate the flexure of the lithosphere under this load by that of a thin elastic plate overlying an inviscid interior. It is shown that a plate with a uniform rigidity does not adequately represent the lithosphere beneath the basin as well as the oceanic lithosphere far from the basin, rather the rigidity of the lithosphere directly beneath the basin is about one to two orders of magnitude smaller than elsewhere. We relate this weakening to the thermal blanketing effects of the thick sediments and the fact that the lithosphere has a temperature-dependent rheology. We suggest that this weak zone would have a controlling effect on the reactivation of normal faults at the hinge zone of the basin, that were formed during the break-up of Africa and North America and were locked in the early stages after the break-up. The weak zone would facilitate reactivation of the faults if tensional stresses were produced by possible reorientation of the spreading direction of the North Atlantic Ocean in the future. The reactivation of the faults would create a free boundary condition at the hinge zone, allowing further bending of the lithosphere beneath the basin and juxtaposition of this lithosphere to the mantle beneath the continent. This may provide a favorable situation for initiation of slow subduction due to subsequent compressional forces.

  5. Implications for anomalous mantle pressure and dynamic topography from lithospheric stress patterns in the North Atlantic Realm

    Science.gov (United States)

    Schiffer, Christian; Nielsen, Søren Bom

    2016-08-01

    With convergent plate boundaries at some distance, the sources of the lithospheric stress field of the North Atlantic Realm are mainly mantle tractions at the base of the lithosphere, lithospheric density structure and topography. Given this, we estimate horizontal deviatoric stresses using a well-established thin sheet model in a global finite element representation. We adjust the lithospheric thickness and the sub-lithospheric pressure iteratively, comparing modelled in plane stress with the observations of the World Stress Map. We find that an anomalous mantle pressure associated with the Iceland and Azores melt anomalies, as well as topography are able to explain the general pattern of the principle horizontal stress directions. The Iceland melt anomaly overprints the classic ridge push perpendicular to the Mid Atlantic ridge and affects the conjugate passive margins in East Greenland more than in western Scandinavia. The dynamic support of topography shows a distinct maximum of c. 1000 m in Iceland and amounts Greenland. Considering that large areas of the North Atlantic Realm have been estimated to be sub-aerial during the time of break-up, two components of dynamic topography seem to have affected the area: a short-lived, which affected a wider area along the rift system and quickly dissipated after break-up, and a more durable in the close vicinity of Iceland. This is consistent with the appearance of a buoyancy anomaly at the base of the North Atlantic lithosphere at or slightly before continental breakup, relatively fast dissipation of the fringes of this, and continued melt generation below Iceland.

  6. Imaging neuronal populations in behaving rodents: paradigms for studying neural circuits underlying behavior in the mammalian cortex.

    Science.gov (United States)

    Chen, Jerry L; Andermann, Mark L; Keck, Tara; Xu, Ning-Long; Ziv, Yaniv

    2013-11-06

    Understanding the neural correlates of behavior in the mammalian cortex requires measurements of activity in awake, behaving animals. Rodents have emerged as a powerful model for dissecting the cortical circuits underlying behavior attributable to the convergence of several methods. Genetically encoded calcium indicators combined with viral-mediated or transgenic tools enable chronic monitoring of calcium signals in neuronal populations and subcellular structures of identified cell types. Stable one- and two-photon imaging of neuronal activity in awake, behaving animals is now possible using new behavioral paradigms in head-fixed animals, or using novel miniature head-mounted microscopes in freely moving animals. This mini-symposium will highlight recent applications of these methods for studying sensorimotor integration, decision making, learning, and memory in cortical and subcortical brain areas. We will outline future prospects and challenges for identifying the neural underpinnings of task-dependent behavior using cellular imaging in rodents.

  7. Imaging the Lithospheric - Asthenosphere Boundary Structure of the Westernmost Mediterranean Using S Receiver Functions

    Science.gov (United States)

    Butcher, A.; Miller, M. S.; Diaz Cusi, J.

    2013-12-01

    The Iberian microcontinent, in the westernmost portion of the Mediterranean is comprised of the Betic Cordillera Zone, the South Portuguese Zone, the Ossa-Morena Zone, the Central Iberian Zone, the Galicia-Tras Os Montes Zone, the West Asturian-Leonese Zone, and the Cantabrian Zone. These zones were created as a result of three primary stages of Iberian evolution, with the last being the collision of Iberia with in the Late Cretaceous. In northeastern Africa, Neogene convergence between the European and African plates created the Alboran System: comprised of the Gibraltar Arc, Rif-Betics, Atlas Mountains, and Alboran Sea. The primary purpose of this study is to advance our understanding of the structure and evolution of the lithosphere, as well as the lithosphere - asthenosphere boundary (LAB) of the Iberian microcontinent and surrounding areas. Of particular interest is improving our understanding of the evolution from ocean subduction to continental collision that has been taking place in the late stage convergence of this part of the Mediterranean., The region is a particularly complex three-dimensional settings and, several models have been suggested to explain the tectonics of this system including: continental lithospheric delamination and drips, slab breakoff, and subducting slab rollback. Here we use broadband seismic data from 272 broadband instruments deployed in Morocco and Spain as part of the PICASSO and IBERArray (Díaz, J., et al., 2009) projects to constrain lithospheric structure via identification of S-to-p conversions from S receiver functions (SRF). We use SRFs to image the characteristics and structure in terms of seismic velocity discontinuities, including the crust-mantle boundary (Moho) and the lithosphere-asthenosphere boundary (LAB) beneath the region. Our SRFs agree with previous work that suggests that the lithospheric thickness is shallow (~65 km) beneath the Atlas and thickest (~120 km) beneath the Rif. Additionally, LAB structures

  8. Gravity and lithospheric stress on the terrestrial planets with reference to the Tharsis region of Mars

    Science.gov (United States)

    Sleep, N. H.; Phillips, R. J.

    1985-01-01

    On Mars and Venus, a strong positive correlation is found between geoid height and topography. The Tharsis region of Mars provides an exhibition of this correlation. Several hypotheses have been proposed regarding the origin of Tharsis. For purposes of explanation, three end-member dynamic hypotheses are considered. A hypothesis that the flexural doming of Tharsis resulted from uplift caused by some force acting on the base of the lithosphere can be rejected. According to another hypothesis, Tharsis is associated with a lithospheric load, while a third one considers that Tharsis is primarily isostatically compensated. In the present study, improved stress models for isostatic compensation on Mars are obtained. The strains inferred from fracture patterns on Mars are compared with the stresses predicted by the isostatic theory. It is found that the computed stresses are in reasonable agreement with tectonic features on Mars.

  9. Decoding of intentional actions from scalp electroencephalography (EEG) in freely-behaving infants.

    Science.gov (United States)

    Hernandez, Zachery R; Cruz-Garza, Jesus; Tse, Teresa; Contreras-Vidal, Jose L

    2014-01-01

    The mirror neuron system (MNS) in humans is thought to enable an individual's understanding of the meaning of actions performed by others and the potential imitation and learning of those actions. In humans, electroencephalographic (EEG) changes in sensorimotor a-band at central electrodes, which desynchronizes both during execution and observation of goal-directed actions (i.e., μ suppression), have been considered an analog to MNS function. However, methodological and developmental issues, as well as the nature of generalized μ suppression to imagined, observed, and performed actions, have yet to provide a mechanistic relationship between EEG μ-rhythm and MNS function, and the extent to which EEG can be used to infer intent during MNS tasks remains unknown. In this study we present a novel methodology using active EEG and inertial sensors to record brain activity and behavioral actions from freely-behaving infants during exploration, imitation, attentive rest, pointing, reaching and grasping, and interaction with an actor. We used 5-band (1-4Hz) EEG as input to a dimensionality reduction algorithm (locality-preserving Fisher's discriminant analysis, LFDA) followed by a neural classifier (Gaussian mixture models, GMMs) to decode the each MNS task performed by freely-behaving 6-24 month old infants during interaction with an adult actor. Here, we present results from a 20-month male infant to illustrate our approach and show the feasibility of EEG-based classification of freely occurring MNS behaviors displayed by an infant. These results, which provide an alternative to the μ-rhythm theory of MNS function, indicate the informative nature of EEG in relation to intentionality (goal) for MNS tasks which may support action-understanding and thus bear implications for advancing the understanding of MNS function.

  10. Introduction of sub-lithospheric component into melted lithospheric base by propagating crack: Case study of migrated Quaternary volcanoes in Wudalianchi, China

    Science.gov (United States)

    Chuvashova, Irina; Sun, Yi-min

    2016-04-01

    mutual convergence of trends, obtained in the diagrams of initial (87Sr/86Sr) versus 1/Sr and initial (87Sr/86Sr) versus 206Pb/204Pb, the common sub-lithospheric composition of volcanic rocks was defined at the initial values (87Sr/86Sr) = 0.7052 and 206Pb/204Pb = 17.5. From model calculations, the erupted liquids were examined as generated through melting of the lithospheric material with minor sub-lithospheric admixture, which did not exceed 9 % (Chuvashova et al., 2009; Rasskazov et al., 2014). In terms of space-time activity and variations of rock compositions obtained on basis of the new representative sampling, we distinguish three groups of the Wudalianchi volcanoes: north-western (Northern and Southern Gelaquishan), central (Wohushan, Bijiashan, Laoheishan, Huoshaoshan), and eastern (Yaoquanshan, Weishan, Western and Eastern Jiaodebushan, Xiaogoshan, Western and Eastern Longmenshan, and Molabushan). Randomly distributed rocks of the north-western and eastern groups, as well as the Erkeshan volcanoes, we examine as a result of background volcanic activity. These rocks show a limited range of compositions dominated by lithospheric material: SiO2 51-55 wt.%, K2O 5-6 wt.%, CaO 5.3-6.8 wt.%, MgO 5.3-7.0 wt.%, CaO/Al2O3 0.35-0.45, and CaO/Sr 31-45. On the contrary, the central group of the Wudalianchi volcanoes reveals persistent northeastward shift of eruptions along the volcanic line Wohushan - Bijiashan - Laoheishan - Huoshaoshan in the past 1.3 Ma. Initial rocks from the Wohushan volcano are compositionally close to rocks of background activity. Over time, the compositions of rocks from the migrated volcanoes have changed due to admixture of the sub-lithospheric component with decreasing SiO2 to 49 wt.%, K2O to 3.2 wt .% and increasing CaO to 8.1 wt.%, MgO to 8.3 wt.%, CaO/Al2O3 to 0.65, CaO/Sr to 65. We infer that the background eruptions in the Wudalianchi and Erkeshan volcanic fields were due to overall melting at the base of the heterogeneous lithospheric

  11. Observatory geoelectric fields induced in a two-layer lithosphere during magnetic storms

    Science.gov (United States)

    Love, Jeffrey J.; Swidinsky, Andrei

    2015-01-01

    We report on the development and validation of an algorithm for estimating geoelectric fields induced in the lithosphere beneath an observatory during a magnetic storm. To accommodate induction in three-dimensional lithospheric electrical conductivity, we analyze a simple nine-parameter model: two horizontal layers, each with uniform electrical conductivity properties given by independent distortion tensors. With Laplace transformation of the induction equations into the complex frequency domain, we obtain a transfer function describing induction of observatory geoelectric fields having frequency-dependent polarization. Upon inverse transformation back to the time domain, the convolution of the corresponding impulse-response function with a geomagnetic time series yields an estimated geoelectric time series. We obtain an optimized set of conductivity parameters using 1-s resolution geomagnetic and geoelectric field data collected at the Kakioka, Japan, observatory for five different intense magnetic storms, including the October 2003 Halloween storm; our estimated geoelectric field accounts for 93% of that measured during the Halloween storm. This work demonstrates the need for detailed modeling of the Earth’s lithospheric conductivity structure and the utility of co-located geomagnetic and geoelectric monitoring.

  12. Experimental constraints on the electrical anisotropy of the lithosphere-asthenosphere system.

    Science.gov (United States)

    Pommier, Anne; Leinenweber, Kurt; Kohlstedt, David L; Qi, Chao; Garnero, Edward J; Mackwell, Stephen J; Tyburczy, James A

    2015-06-11

    The relative motion of lithospheric plates and underlying mantle produces localized deformation near the lithosphere-asthenosphere boundary. The transition from rheologically stronger lithosphere to weaker asthenosphere may result from a small amount of melt or water in the asthenosphere, reducing viscosity. Either possibility may explain the seismic and electrical anomalies that extend to a depth of about 200 kilometres. However, the effect of melt on the physical properties of deformed materials at upper-mantle conditions remains poorly constrained. Here we present electrical anisotropy measurements at high temperatures and quasi-hydrostatic pressures of about three gigapascals on previously deformed olivine aggregates and sheared partially molten rocks. For all samples, electrical conductivity is highest when parallel to the direction of prior deformation. The conductivity of highly sheared olivine samples is ten times greater in the shear direction than for undeformed samples. At temperatures above 900 degrees Celsius, a deformed solid matrix with nearly isotropic melt distribution has an electrical anisotropy factor less than five. To obtain higher electrical anisotropy (up to a factor of 100), we propose an experimentally based model in which layers of sheared olivine are alternated with layers of sheared olivine plus MORB or of pure melt. Conductivities are up to 100 times greater in the shear direction than when perpendicular to the shear direction and reproduce stress-driven alignment of the melt. Our experimental results and the model reproduce mantle conductivity-depth profiles for melt-bearing geological contexts. The field data are best fitted by an electrically anisotropic asthenosphere overlain by an isotropic, high-conductivity lowermost lithosphere. The high conductivity could arise from partial melting associated with localized deformation resulting from differential plate velocities relative to the mantle, with subsequent upward melt percolation

  13. Formation of lithospheric shear zones: Effect of temperature on two-phase grain damage

    Science.gov (United States)

    Mulyukova, Elvira; Bercovici, David

    2017-09-01

    Shear localization in the lithosphere is a characteristic feature of plate tectonic boundaries, and is evident in the presence of small grain mylonites. Localization and mylonitization in the ductile portion of the lithosphere can arise when its polymineralic material deforms by a grain-size sensitive rheology in combination with Zener pinning, which can impede, or possibly even reverse, grain growth and thus promotes a self-softening feedback mechanism. However, the efficacy of this mechanism is not ubiquitous and depends on lithospheric conditions such as temperature and stress. Therefore, we explore the conditions under which self-weakening takes place, and, in particular, the effect of temperature and deformation state (stress or strain-rate) on these conditions. In our model, the lithosphere-like polymineralic material is deformed in a two-dimensional simple shear driven by constant stress or strain rate. The mineral grains evolve to a stable size, which is obtained when the rate of coarsening by normal grain growth and the rate of grain size reduction by damage are in balance. Damage involves processes by which some of the deformational energy gets transferred into surface energy. This can happen by (i) dynamic recrystallization (grain damage) and (ii) stretching, deforming and stirring the material interface (interface damage). The influence of temperature enters through rheological laws (which govern the rate of work and damage), grain growth kinetics, and the damage partitioning fraction, which is the fraction of deformational work that goes into creating new surface energy. We demonstrate that a two-phase damage model, in which the partitioning fraction depends on both temperature and roughness of the interface between the phases, can successfully match the field data, including the reported correlation of grain size and temperature, the increasing dominance of dislocation creep at higher temperatures and a large range of grain sizes observed across the

  14. Long wavelength gravity anomalies over India: Crustal and lithospheric structures and its flexure

    Science.gov (United States)

    Tiwari, V. M.; Ravi Kumar, M.; Mishra, D. C.

    2013-07-01

    Long wavelength gravity anomalies over India were obtained from terrestrial gravity data through two independent methods: (i) wavelength filtering and (ii) removing crustal effects. The gravity fields due to the lithospheric mantle obtained from two methods were quite comparable. The long wavelength gravity anomalies were interpreted in terms of variations in the depth of the lithosphere-asthenosphere boundary (LAB) and the Moho with appropriate densities, that are constrained from seismic results at certain points. Modeling of the long wavelength gravity anomaly along a N-S profile (77°E) suggest that the thickness of the lithosphere for a density contrast of 0.05 g/cm3 with the asthenosphere is maximum of ˜190 km along the Himalayan front that reduces to ˜155 km under the southern part of the Ganga and the Vindhyan basins increasing to ˜175 km south of the Satpura Mobile belt, reducing to ˜155-140 km under the Eastern Dharwar craton (EDC) and from there consistently decreasing south wards to ˜120 km under the southernmost part of India, known as Southern Granulite Terrain (SGT). The crustal model clearly shows three distinct terrains of different bulk densities, and thicknesses, north of the SMB under the Ganga and the Vindhyan basins, and south of it the Eastern Dharwar Craton (EDC) and the Southern Granulite Terrain (SGT) of bulk densities 2.87, 2.90 and 2.96 g/cm3, respectively. It is confirmed from the exposed rock types as the SGT is composed of high bulk density lower crustal rocks and mafic/ultramafic intrusives while the EDC represent typical granite/gneisses rocks and the basement under the Vindhyan and Ganga basins towards the north are composed of Bundelkhand granite massif of the lower density. The crustal thickness along this profile varies from ˜37-38 km under the EDC, increasing to ˜40-45 km under the SGT and ˜40-42 km under the northern part of the Ganga basin with a bulge up to ˜36 km under its southern part. Reduced lithospheric and

  15. Risk and Geodynamically active areas of Carpathian lithosphere

    Directory of Open Access Journals (Sweden)

    Lubomil Pospíšil

    2007-01-01

    Full Text Available This paper illustrates an application of multidisciplinary data analysis to the Carpathian–Pannonian region and presents a verification of a Complex model of the Carpathian - Pannonian lithosphere by recent data sets and geophysical data analyses and its utilization for the determination of risk and active geodynamic and tectonic zones of Ist order . This model can be used for the analysing any Carpathian area from the point of view of the seismic risk, hazards and geodynamic activity, which is important to know for the building of a repository for the radioactive wasted material. Besides the traditionally used geological (sedimentological and volcanological data and geomorphological data (Remote Sensing, an emphasis was laid on geodetic, grav/mag data, seismic, seismological and other geophysical data (magnetotelluric, heat flow, paleomagnetic etc.. All available geonomic (geologic, geodetic, geophysical, geomorphological data were verified and unified on the basis of the same scale and in the Western Carpathians on the Remote Sensing data. The paper concentrates on two problematic areas – the so call “rebounding area” in the Eastern Carpathians and the Raba – Muran - Malcov tectonic systems.

  16. Variations in Crustal Structure, Lithospheric Flexural Strength, and Isostatic Compensation Mechanisms of Mars

    Science.gov (United States)

    Ding, M.; Lin, J.; Zuber, M. T.

    2014-12-01

    We analyze gravity and topography of Mars to investigate the spatial variations in crustal thickness, lithospheric strength, and mechanisms of support of prominent topographic features on Mars. The latest gravity model JGMRO110c (released in 2012) from the Mars Reconnaissance Orbiter mission has a spatial block size resolution of ~97 km (corresponding to degree-110), enabling us to resolve crustal structures at higher spatial resolution than those determined from previous degree-80 and 85 gravity models [Zuber et al., 2000; McGovern et al., 2002, 2004; Neumann et al., 2004; Belleguic et al., 2005]. Using the latest gravity data, we first inverted for a new version of crustal thickness model of Mars assuming homogeneous crust and mantle densities of 2.9 and 3.5 g/cm3. We calculated "isostatic" topography for the Airy local isostatic compensation mechanism, and "non-isostatic" topography after removing the isostatic part. We find that about 92% of the Martian surface is in relatively isostatic state, indicating either relatively small lithospheric strength and/or small vertical loading. Relatively isostatic regions include the hemispheric dichotomy, Hellas and Argyre Planitia, Noachis and Arabia Terra, and Terra Cimmeria. In contrast, regions with significant amount of non-isostatic topography include the Olympus, Ascraeus, Arsia, Pavonis, Alba, and Elysium Mons, Isidis Planitia and Valles Marineris. Their relatively large "non-isostatc topography" implies relatively strong lithospheric strength and large vertical loading. Spectral analysis of the admittance and correlation relationship between gravity and topography were conducted for the non-isostatic regions using the localized spectra method [Wieczorek and Simons, 2005, 2007] and thin-shell lithospheric flexural approximation [Forsyth, 1985; McGovern et al., 2002, 2004]. The best-fitting models reveal significant variations in the effective lithospheric thickness with the greatest values for the Olympus Mon

  17. Long-wavelength Folding on Mercury: Lithospheric Boudinage in the Caloris Basin?

    Science.gov (United States)

    Klimczak, C.; Byrne, P. K.; Solomon, S. C.; Ernst, C. M.; Watters, T. R.; Murchie, S. L.; Preusker, F.; Oberst, J.

    2012-12-01

    Both laser altimetric and stereo photogrammetric datasets returned by the MESSENGER spacecraft in orbit about Mercury reveal impact craters whose floors show systematic tilts away from topographically high regions. Such tilted craters indicate that Mercury's lithosphere has been affected by large-scale folding that, when mapped, is manifest as several long-wavelength and low-amplitude rises and troughs, interpreted as anticlines and synclines, that cross the planet. Topographic profiles across the syn- and anticlines show that folding can be described as more or less harmonic with wavelengths of 800 to 1300 km and amplitudes of 1.5 to 3 km. These dimensions show that folding accommodated shortening strains of only ~0.002%. Several syn- and anticlines are found in the region in and around the Caloris basin, the largest recognized impact basin on the planet. The topography within the basin is characterized by two anticlines, each trending approximately east-west and having crests that rise more than 2 km above a low-lying region near the basin center. Fault displacement analysis of several radial graben and circumferential ridges, together with crater excavation depths of spectrally distinct materials, yields stratigraphic information on the uppermost smooth volcanic plains in the basin's interior, revealing a pinch-and-swell structure to these units. Specifically, the plains are thicker in the vicinity of the topographic highs and thinner at the topographic low. We used numerical simulations with the two-dimensional module of the finite-element modeling code ADELI to explore how folding of the lithosphere on Mercury and the pinching and swelling might have been accommodated for a range of assumed boundary conditions and properties of the lithosphere and mantle, informed by recent geophysical data returned by MESSENGER. We find that continuing lithospheric folding with periodic emplacement of volcanic plains units can account for the observed topography and

  18. Oh, Behave! Behavior as an Interaction between Genes & the Environment

    Science.gov (United States)

    Weigel, Emily G.; DeNieu, Michael; Gall, Andrew J.

    2014-01-01

    This lesson is designed to teach students that behavior is a trait shaped by both genes and the environment. Students will read a scientific paper, discuss and generate predictions based on the ideas and data therein, and model the relationships between genes, the environment, and behavior. The lesson is targeted to meet the educational goals of…

  19. Oh, Behave! Behavior as an Interaction between Genes & the Environment

    Science.gov (United States)

    Weigel, Emily G.; DeNieu, Michael; Gall, Andrew J.

    2014-01-01

    This lesson is designed to teach students that behavior is a trait shaped by both genes and the environment. Students will read a scientific paper, discuss and generate predictions based on the ideas and data therein, and model the relationships between genes, the environment, and behavior. The lesson is targeted to meet the educational goals of…

  20. Recycling of Oceanic Lithosphere: Water, fO2 and Fe-isotope Constraints

    Science.gov (United States)

    Bizmis, M.; Peslier, A. H.; McCammon, C. A.; Keshav, S.; Williams, H. M.

    2014-01-01

    Spinel peridotite and garnet pyroxenite xenoliths from Hawaii provide important clues about the composition of the oceanic lithosphere, and can be used to assess its contribution to mantle heterogeneity upon recycling. The peridotites have lower bulk H2O (approximately 70-114 ppm) than the MORB source, qualitatively consistent with melt depletion. The garnet pyroxenites (high pressure cumulates) have higher H2O (200-460 ppm, up to 550 ppm accounting for phlogopite) and low H2O/Ce ratios (less than 100). The peridotites have relatively light Fe-isotopes (delta Fe -57 = -0.34 to 0.13) that decrease with increasing depletion, while the pyroxenites are significantly heavier (delta Fe-57 up to 0.3). The observed xenolith, as well as MORB and OIB total Fe-isotope variability is larger that can be explained by existing melting models. The high H2O and low H2O/Ce ratios of pyroxenites are similar to estimates of EM-type OIB sources, while their heavy delta Fe-57 are similar to some Society and Cook-Austral basalts. Therefore, recycling of mineralogically enriched oceanic lithosphere (i.e. pyroxenites) may contribute to OIB sources and mantle heterogeneity. The Fe(3+)/Sigma? systematics of these xenoliths also suggest that there might be lateral redox gradients within the lithosphere, between juxtaposed oxidized spinel peridotites (deltaFMQ = -0.7 to 1.6, at 15 kb) and more reduced pyroxenites (deltaFMQ = -2 to -0.4, at 20-25kb). Such mineralogically and compositionally imposed fO2 gradients may generate local redox melting due to changes in fluid speciation (e.g. reduced fluids from pyroxenite encountering more oxidized peridotite). Formation of such incipient, small degree melts could further contribute to metasomatic features seen in peridotites, mantle heterogeneity, as well as the low velocity and high electrical conductivity structures near the base of the lithosphere and upper mantle.

  1. Lithospheric deformation in the Canadian Appalachians: evidence from shear wave splitting

    Science.gov (United States)

    Gilligan, Amy; Bastow, Ian D.; Watson, Emma; Darbyshire, Fiona A.; Levin, Vadim; Menke, William; Lane, Victoria; Hawthorn, David; Boyce, Alistair; Liddell, Mitchell V.; Petrescu, Laura

    2016-08-01

    Plate-scale deformation is expected to impart seismic anisotropic fabrics on the lithosphere. Determination of the fast shear wave orientation (φ) and the delay time between the fast and slow split shear waves (δt) via SKS splitting can help place spatial and temporal constraints on lithospheric deformation. The Canadian Appalachians experienced multiple episodes of deformation during the Phanerozoic: accretionary collisions during the Palaeozoic prior to the collision between Laurentia and Gondwana, and rifting related to the Mesozoic opening of the North Atlantic. However, the extent to which extensional events have overprinted older orogenic trends is uncertain. We address this issue through measurements of seismic anisotropy beneath the Canadian Appalachians, computing shear wave splitting parameters (φ, δt) for new and existing seismic stations in Nova Scotia and New Brunswick. Average δt values of 1.2 s, relatively short length scale (≥100 km) splitting parameter variations, and a lack of correlation with absolute plate motion direction and mantle flow models, demonstrate that fossil lithospheric anisotropic fabrics dominate our results. Most fast directions parallel Appalachian orogenic trends observed at the surface, while δt values point towards coherent deformation of the crust and mantle lithosphere. Mesozoic rifting had minimal impact on our study area, except locally within the Bay of Fundy and in southern Nova Scotia, where fast directions are subparallel to the opening direction of Mesozoic rifting; associated δt values of >1 s require an anisotropic layer that spans both the crust and mantle, meaning the formation of the Bay of Fundy was not merely a thin-skinned tectonic event.

  2. Lithospheric thermal-rheological structures of the continental margin in the northern South China Sea

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Thermal structures of three deep seismic profiles in the continental margin in the northern South China Sea are calculated, their "thermal" lithospheric thicknesses are evaluated based on the basalt dry solidus, and their rheological structures are evaluated with linear frictional failure criterion and power-law creep equation. "Thermal" lithosphere is about 90 km in thickness in shelf area, and thins toward the slope, lowers to 60-65 km in the lower slope, ocean crust and Xisha Trough. In the mid-west of the studied area, the lithospheric rheological structure in shelf area and Xisha Islands is of four layers: brittle, ductile, brittle and ductile. Because of uprising of heat mantle and thinning of crust and lithosphere in Xisha Trough, the bottom of the upper brittle layer is only buried at 16 km. In the eastern area, the bottom of the upper brittle layer in the north is buried at 20 km or so, while in lower slope and ocean crust, the rheological structure is of two layers of brittle and ductile, and crust and uppermost mantle form one whole brittle layer whose bottom is buried at 30-32 km. Analyses show that the characteristics of rheological structure accord with the seismic result observed. The character of rheological stratification implies that before the extension of the continent margin, there likely was a ductile layer in mid-lower crust. The influence of the existence of ductile layer to the evolution of the continent margin and the different extensions of ductile layer and brittle layer should not be overlooked. Its thickness, depth and extent in influencing continent margin's extension and evolution should be well evaluated in building a dynamic model for the area.

  3. Flexural anisotropy in the continental lithosphere: How robust are our estimates?

    Science.gov (United States)

    Kalnins, Lara; Simons, Frederik; Kirby, Jon; Wang, Dong; Olhede, Sofia

    2015-04-01

    In addition to considering the magnitude and lateral variation of the long-term strength of the lithosphere, we must also consider its directional variation, its anisotropy. Many geological materials and processes are themselves anisotropic; this might lead to a natural expectation of widespread anisotropy in lithosphere strength, which both modulates and is modulated by many key tectonic processes. Cratons, with their long, complex geological histories, and orogenic belts, the result of extremely anisotropy processes, might seem especially likely to show anisotropy in their flexural rigidity. The observed coherence between gravity and topography remains the most popular metric for the analysis of flexural rigidity, and, indeed, it is frequently anisotropic. However, does this correspond to anisotropy in the actual mechanical strength of the lithosphere? Using coherence, we should only reject the null hypothesis of isotropy when there is significant anisotropy in both the observed coherence and the resulting flexural strength. In addition, the anisotropy should not arise purely from marginal (in the statistical sense) anisotropy in the topography and gravity data themselves. We use wholly isotropic synthetic models to test two common methods for estimating coherence, multitapers and wavelets, and find widespread spurious anisotropy using both methods. Using a series of statistical and geophysical tests developed to identify and remove such spurious directionality, our global reanalysis shows sparse evidence for meaningful anisotropy in the mechanical strength of the lithosphere. Although the geological argument for anisotropy in these regions and its role in tectonic cycles remains highly plausible, this anisotropy has not yet been convincingly verified by any cross-spectral method.

  4. Lithosphere-asthenosphere system in shield areas of North America and Europe

    Directory of Open Access Journals (Sweden)

    P. Pierri

    1997-06-01

    Full Text Available In previous papers surface dispersion data have been combined with the results of deep seismic refraction data to derive a regionalization of the lithosphere-asthenosphere system and to investigate the presence of significant heterogeneity down to depths of 350 km along two profiles in the North European Fennoscandian area; a regionalized upper mantle model for the whole area down to more than 400 km is given as cross sections. We have extended that approach to North America. The older part of the shield shows lid thickness up to more than 100 km with, if any, weak shear velocity contrast to the underlying layer. The surrounding areas are characterized by a thinner lid; a stronger low-velocity zone to lid contrast may be found in peripheral areas. A map of the lithosphere-asthenosphere system has been derived, permitting a better regional resolution of the shear-wave velocity distribution with depth beneath different regions of North America. The correlation between the lithosphere-asthenosphere system structure and other geophysical data is commented as well as the results for North America and those obtained for the corresponding North European area, in order to outline the geophysical characteristics of shield areas that might give useful constraints for the geodynamic behaviour of the plates to which they belong.

  5. Grain size in lithospheric-scale shear zones: Chicken or Egg?

    Science.gov (United States)

    Thielmann, M.; Rozel, A.; Kaus, B. J. P.; Ricard, Y.

    2012-04-01

    Lithospheric-scale shear zones are commonly defined as regions inhomogeneous and localized deformation. Strain softening has been demonstrated to be necessary for localization in those shear zones, but there is still debate about the physical cause of this softening. As natural shear zones typically have a significantly reduced grain size, it has been proposed that grain size reduction provides the necessary strain softening to localize deformation. As grain size reduces, the dominant deformation mechanism switches from dislocation to diffusion creep, thus requiring less stress to deform the rock. Until recently, the equilibrium grain size has been thought to follow a piezometric relationship, thus indicating the stress under which a shear zone deformed. More recent work (Austin and Evans (2007), Rozel et. al. (2011)) suggests that the equilibrium grain size is not dependent on stress, but rather on the deformational work. Using this relationship, we use numerical models to investigate the effect of grain size evolution on lithospheric deformation. We focus on the question if grain size provides sufficient weakening to effectively localize deformation under lithospheric conditions or if it's effect is rather passive and as such a marker for the deformational work done in a shear zone. We then compare the localization potential of grain size reduction to shear heating and investigate the interplay between the two weakening mechanisms.

  6. Evidence for recycled Archaean oceanic mantle lithosphere in the Azores plume.

    Science.gov (United States)

    Schaefer, Bruce F; Turner, Simon; Parkinson, Ian; Rogers, Nick; Hawkesworth, Chris

    2002-11-21

    The compositional differences between mid-ocean-ridge and ocean-island basalts place important constraints on the form of mantle convection. Also, it is thought that the scale and nature of heterogeneities within plumes and the degree to which heterogeneous material endures within the mantle might be reflected in spatial variations of basalt composition observed at the Earth's surface. Here we report osmium isotope data on lavas from a transect across the Azores archipelago which vary in a symmetrical pattern across what is thought to be a mantle plume. Many of the lavas from the centre of the plume have lower 187Os/188Os ratios than most ocean-island basalts and some extend to subchondritic 187Os/188Os ratios-lower than any yet reported from ocean-island basalts. These low ratios require derivation from a depleted, harzburgitic mantle, consistent with the low-iron signature of the Azores plume. Rhenium-depletion model ages extend to 2.5 Gyr, and we infer that the osmium isotope signature is unlikely to be derived from Iberian subcontinental lithospheric mantle. Instead, we interpret the osmium isotope signature as having a deep origin and infer that it may be recycled, Archaean oceanic mantle lithosphere that has delaminated from its overlying oceanic crust. If correct, our data provide evidence for deep mantle subduction and storage of oceanic mantle lithosphere during the Archaean era.

  7. The Cenozoic mantle magmatism and motion of lithosphere on the north margin of the Tibetan Plateau

    Institute of Scientific and Technical Information of China (English)

    罗照华; 肖序常; 曹永清; 莫宣学; 苏尚国; 邓晋福; 张文会

    2001-01-01

    Geodynamic properties and evolution of the lithosphere on the north margin of the Tibetan Plateau are recently hot topics to geoscientists in the world. Have the northern plates been subducting underneath the Plateau? It is still an unsolved problem. One of the keys to solving this problem is to understand the genetic processes of Cenozoic magmas on the north margin of the Tibetan Plateau. However, there is no enough evidence supporting the subduction model. In contrast, a series of evidence indicates that collision-induced huge shearing faults and large-scale crust shortening played a main role in lithosphere motion on the north margin of the Tibetan Plateau. The mantle-derived igneous rocks strictly distribute at the intersections of large strike-slip faults on the north margin of the Plateau. Generation of magmas may be related to local exten-sional condition induced by strike-slipping faults, which lead to lithosphere gravitational instability and collapse, as well as upwelling of the deep hot materi

  8. Lithospheric Thermal Isostasy of North Continental Margin of the South China Sea

    Institute of Scientific and Technical Information of China (English)

    Chen Shi; Zhang Jian; Sun Yujun; Shi Yaolin

    2009-01-01

    Accompanied with rifting and detaching of the north continental margin of the South China Sea,the ernst and the lithosphere become thinner away from the continental margin resulting from the tectonic activities,such as tensile deformation,thermal uplift,and cooling subsidence,etc..Integrated with thermal,gravimetric,and isostatic analysis techniques,based on the seismic interpretation of the deep penetration seismic soundings across the northern margin of the South China Sea,we reconstructed the lithospheric thermal structure and derived the variation of the crust boundary in the east and west parts of the seismic profde by using gravity anomaly data.We mainly studied the thermal isostasy problems using the bathymetry of the profiles and calculated the crust thinning effect due to the thermal variety in the rifting process.The results Indicate that the thermal isostasy may reach 2.5 kin,and the compositional variations in the ilthospheric density and thickness may produce a variation of 4.0 kin.Therefore,the compositional isostatic correction is very important to recover the relationship between surface heat flow and topography.Moreover,because of the high heat flow characteristic of the continental margin,building the model of lithospheric geotherm in this region is of great importan for studying the Cenozoic tectonic thermal evolution of the north passive continental margin of the South China Sea.

  9. Rheological properties of deep subducted oceanic lithosphere and their geodynamic implications

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    According to the experimental studies on the rheology of two important mantle rocks (eclogite and harzburgite), the rheological properties of the deep subducted oceanic lithosphere are investigated by assuming a simplified harzburgite type slab model with moderate thickness of basaltic layer. When the mantle convergence rate is small or the subducting slab has been trapped in the mantle for an enough long time, the strength profile of the slab is characterized by a strong subducting crustal component lying on a weak subducting upper mantle. However, if the convergence rate is large enough, the subducting slab will be featured only by a rigid cold center. Our study suggests that the detachment of the subducting crust component from the underlying upper mantle is only likely to happen in hot slow subducting slabs, but not the cold fast subducting lithosphere. Rheological properties of the harzburgitic and the eclogitic upper mantle vary with depths. The eclogitic upper mantle is stronger than the peridotitic upper mantle across the upper mantle. Transition zone is the high strength and high viscosity layer in the upper mantle except the lithosphere.

  10. Nature and Evolution of the lithospheric mantle beneath the Hoggar swell (Algeria): a record from mantle xenoliths.

    Science.gov (United States)

    Kourim, Fatna; Bodinier, Jean-Louis; Alard, Olivier; Bendaoud, Abderrahmane; Vauchez, Alain; Dautria, Jean-Marie

    2013-04-01

    The mantle xenoliths sampled by the Quaternary alkaline volcanics from the Tahalgha district (Central Hoggar) represent the subcontinental lithospheric mantle beneath the boundary between two major structural domains of the Tuareg Shield: the "Polycyclic Central Hoggar" to the East and the "Western Hoggar", or "Pharusian Belt", to the West. Samples were collected from volcanic centres located on both sides of the 4°10, a major lithospheric shear zone separating these two domains. Although showing substantial variations in their deformation microstructures, equilibrium temperatures, and modal and chemical compositions, the studied samples do not display systematic variations of these features across the 4°10. The observed variations rather record small-scale heterogeneities distributed throughout the whole studied area and mostly related to the asthenosphere-lithosphere interaction events associated with the evolution of the Hoggar swell, in the Cenozoic. These features include partial annealing of pre-existing deformation microstructures, post-deformation metasomatic reactions, and trace-element enrichment, coupled with heating from 750-900°C (low-temperature lherzolites) to 900-1150°C (intermediate-T lherzolites and high-T harzburgites and wehrlites). Trace element modelling confirms that the whole range of REE fractionation observed in the Tahalgha xenoliths may be accounted for by reactive porous flow involving a single stage of basaltic melt infiltration into a LREE-depleted protolith. The striking correlations between equilibrium temperatures and trace-element enrichments favor a scenario whereby the high-temperature peridotites record advective heat transport along melt conduits while the intermediate- and low-temperature lherzolites would represent more conductive heating of the host Mechanical Boundary Layer. This indicates that the lithosphere did not reach thermal equilibrium, suggesting that the inferred heating event was transient and rapidly erased

  11. DEFORMATION WAVES AS A TRIGGER MECHANISM OF SEISMIC ACTIVITY IN SEISMIC ZONES OF THE CONTINENTAL LITHOSPHERE

    Directory of Open Access Journals (Sweden)

    S. I. Sherman

    2015-09-01

    fault zones, a brief description of the method for assessment of spatial and temporal regularities in locations of earthquake epicentres in zones of dynamic influence of faults is provided. The method can be applied to estimate a dominating direction of movement of the epicentres, which corresponds to the phase velocity of the deformation wave disturbing meta-stability of the fault-block medium, leading to displacement of neighbouring blocks and thus causing a seismic event (Fig. 14. By integration of vectors of migration of epicentres at active faults, it is possible to demonstrate a pattern of vectors of movements of the deformation waves in the seismic zones of the continental lithosphere (Fig. 18.Regional and trans-regional deformation waves are analyzed. For seismic zones of Central Asia, vectors of deformation waves are established, a scheme showing regional orientations of the waves is developed, and main wave parameters (length and time period are estimated (Fig. 19. Three depth levels of deformation waves are distinguished: the whole lithosphere, the upper brittle part of the lithosphere, and the top part of the brittle layer (Fig. 20.It is concluded that the leading factor of gradual accumulation of earthquake foci, which takes place regularly in space and time in seismic zones, are deformation waves that influence the geophysical medium. This understanding of the fundamental basis of seismic process needs to be more thoroughly justified with application of modern concepts, its revised phenomenological concept and development of a model representing a seismic zones as a geologically and geophysically independent structure of the lithosphere, which has its specific properties, based on which testing of the lithosphere becomes possible for purposes of potential earthquake prediction.

  12. An investigation into why macroscopic systems behave classically

    OpenAIRE

    Hallwood, David W.; Burnett, Keith; Dunningham, Jacob

    2006-01-01

    We study why it is quite so hard to make a superposition of superfluid flows in a Bose-Einstein condensate. To do this we initially investigate the quantum states of $N$ atoms trapped in a 1D ring with a barrier at one position and a phase applied around it. We show how macroscopic superpositions can in principle be produced and investigate factors which affect the superposition. We then use the Bose-Hubbard model to study an array of Bose-Einstein condensates trapped in optical potentials an...

  13. The first magnetotelluric image of the lithospheric-scale geological architecture in central Svalbard, Arctic Norway

    Directory of Open Access Journals (Sweden)

    Thomas I. Beka

    2015-12-01

    Full Text Available Magnetotelluric data, collected from 30 stations on Spitsbergen as part of a reconnaissance geothermal resource assessment along a profile with 0.5–3-km spacing in 0.003–1000-s period range, were used to develop a lithospheric-scale two-dimensional (2D resistivity model, heretofore unavailable for the region. Inverting the determinant of the impedance tensor in 2D, we found the smoothest model fitting the data within a specified tolerance level. We justified the model by perturbing it, performing sensitivity analysis and re-running the inversion with a different algorithm and starting models. From our final model, we constructed a crustal-scale stratigraphic framework, using it to estimate the depth of major geological features and to locate structural deformations. The 2D resistivity model indicates a shallow low resistive (1000 Ωm east of the Billefjorden Fault Zone. Underneath, a (possibly Devonian basin is imaged as a thick conductive anomaly stretching >15 km downwards. Beneath a deformed Paleozoic–Mesozoic successions, an uplifted pre-Devonian shallow basement (>3000 Ωm is revealed. We estimated a thin lithosphere, in the range of ca. 55–100 km thick, that could explain the area's elevated surface heat flow (ca. 60–90 mW/m2, consistent with the calculated depth of thermal lithosphere heat-base boundaries for a partially melting mantle. The model indicates a possible replenishment pathway of upward heat transport from the shallow convective mantle to the composite crustal conductive units. This is encouraging for low-enthalpy geothermal development.

  14. A Novel Gas Turbine Engine Health Status Estimation Method Using Quantum-Behaved Particle Swarm Optimization

    Directory of Open Access Journals (Sweden)

    Xinyi Yang

    2014-01-01

    Full Text Available Accurate gas turbine engine health status estimation is very important for engine applications and aircraft flight safety. Due to the fact that there are many to-be-estimated parameters, engine health status estimation is a very difficult optimization problem. Traditional gas path analysis (GPA methods are based on the linearized thermodynamic engine performance model, and the estimation accuracy is not satisfactory on conditions that the nonlinearity of the engine model is significant. To solve this problem, a novel gas turbine engine health status estimation method has been developed. The method estimates degraded engine component parameters using quantum-behaved particle swarm optimization (QPSO algorithm. And the engine health indices are calculated using these estimated component parameters. The new method was applied to turbine fan engine health status estimation and is compared with the other three representative methods. Results show that although the developed method is slower in computation speed than GPA methods it succeeds in estimating engine health status with the highest accuracy in all test cases and is proven to be a very suitable tool for off-line engine health status estimation.

  15. Seeing the whole picture: A comprehensive imaging approach to functional mapping of circuits in behaving zebrafish.

    Science.gov (United States)

    Feierstein, C E; Portugues, R; Orger, M B

    2015-06-18

    In recent years, the zebrafish has emerged as an appealing model system to tackle questions relating to the neural circuit basis of behavior. This can be attributed not just to the growing use of genetically tractable model organisms, but also in large part to the rapid advances in optical techniques for neuroscience, which are ideally suited for application to the small, transparent brain of the larval fish. Many characteristic features of vertebrate brains, from gross anatomy down to particular circuit motifs and cell-types, as well as conserved behaviors, can be found in zebrafish even just a few days post fertilization, and, at this early stage, the physical size of the brain makes it possible to analyze neural activity in a comprehensive fashion. In a recent study, we used a systematic and unbiased imaging method to record the pattern of activity dynamics throughout the whole brain of larval zebrafish during a simple visual behavior, the optokinetic response (OKR). This approach revealed the broadly distributed network of neurons that were active during the behavior and provided insights into the fine-scale functional architecture in the brain, inter-individual variability, and the spatial distribution of behaviorally relevant signals. Combined with mapping anatomical and functional connectivity, targeted electrophysiological recordings, and genetic labeling of specific populations, this comprehensive approach in zebrafish provides an unparalleled opportunity to study complete circuits in a behaving vertebrate animal.

  16. Anatomical and functional neuroimaging in awake, behaving marmosets.

    Science.gov (United States)

    Silva, Afonso C

    2017-03-01

    The common marmoset (Callithrix jacchus) is a small New World monkey that has gained significant recent interest in neuroscience research, not only because of its compatibility with gene editing techniques, but also due to its tremendous versatility as an experimental animal model. Neuroimaging modalities, including anatomical (MRI) and functional magnetic resonance imaging (fMRI), complemented by two-photon laser scanning microscopy and electrophysiology, have been at the forefront of unraveling the anatomical and functional organization of the marmoset brain. High-resolution anatomical MRI of the marmoset brain can be obtained with remarkable cytoarchitectonic detail. Functional MRI of the marmoset brain has been used to study various sensory systems, including somatosensory, auditory, and visual pathways, while resting-state fMRI studies have unraveled functional brain networks that bear great correspondence to those previously described in humans. Two-photon laser scanning microscopy of the marmoset brain has enabled the simultaneous recording of neuronal activity from thousands of neurons with single cell spatial resolution. In this article, we aim to review the main results obtained by our group and by our colleagues in applying neuroimaging techniques to study the marmoset brain. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 373-389, 2017.

  17. Computation in spinal circuitry: lessons from behaving primates.

    Science.gov (United States)

    Harel, Ran; Asher, Itay; Cohen, Oren; Israel, Zvi; Shalit, Uri; Yanai, Yuval; Zinger, Nofya; Prut, Yifat

    2008-12-12

    Performing voluntary motor actions requires the translation of motor commands into a specific set of muscle activation. While it is assumed that this process is carried out via cooperative interactions between supraspinal and spinal neurons, the unique contribution of each of these areas to the process is still unknown. Many studies have focused on the neuronal representation of the motor command, mostly in the motor cortex. Nonetheless, to execute these commands there must be a mechanism that can translate this representation into a sustained drive to the spinal motoneurons (MNs). Here we review different candidate mechanisms for activating MNs and their possible role in voluntary movements. We discuss recent studies which directly estimate the contribution of segmental INs to the transmission of cortical command to MNs, both in terms of functional connectivity and as a computational link. Finally, we suggest a conceptual framework in which the cortical motor command is processed simultaneously via MNs and INs. In this model, the motor cortex provides a transient signal which is important for initiating new patterns of recruited muscles, whereas the INs translate this command into a sustained, amplified and muscle-based signal which is necessary to maintain ongoing muscle activity.

  18. A global view of the lithosphere-asthenosphere boundary.

    Science.gov (United States)

    Rychert, Catherine A; Shearer, Peter M

    2009-04-24

    The lithosphere-asthenosphere boundary divides the rigid lid from the weaker mantle and is fundamental in plate tectonics. However, its depth and defining mechanism are not well known. We analyzed 15 years of global seismic data using P-to-S (Ps) converted phases and imaged an interface that correlates with tectonic environment, varying from 95 +/- 4 kilometers beneath Precambrian shields and platforms to 81 +/- 2 kilometers beneath tectonically altered regions and 70 +/- 4 kilometers at oceanic island stations. High-frequency Ps observations require a sharp discontinuity; therefore, this interface likely represents a boundary in composition, melting, or anisotropy, not temperature alone. It likely represents the lithosphere-asthenosphere boundary under oceans and tectonically altered regions, but it may constitute another boundary in cratonic regions where the lithosphere-asthenosphere boundary is thought to be much deeper.

  19. Properties of the lithosphere and asthenosphere deduced from geoid observations

    Science.gov (United States)

    Turcotte, D. L.

    1985-01-01

    Data from the GEOS-3 and SEASAT Satellites provided a very accurate geoid map over the oceans. Broad bathymetric features in the oceans such as oceanic swells and plateaus are fully compensated. It is shown that the geoid anomalies due to the density structures of the lithosphere are proportional to the first moment of the density distribution. The deepening of the ocean basins is attributed to thermal isostasy. The thickness of the oceanic lithosphere increases with age due to the loss of heat to the sea floor. Bathymetry and the geoid provide constraints on the extent of this heat loss. Offsets in the geoid across major fracture zones can also be used to constrain this problem. Geoid bathymetry correlations show that the Hawaiian and Bermuda swells and the Cape Verde Rise are probably due to lithospheric thinning.

  20. Improved quantum-behaved particle swarm optimization with local search strategy

    Directory of Open Access Journals (Sweden)

    Maolong Xi

    2017-03-01

    Full Text Available Quantum-behaved particle swarm optimization, which was motivated by analysis of particle swarm optimization and quantum system, has shown compared performance in finding the optimal solutions for many optimization problems to other evolutionary algorithms. To address the problem of premature, a local search strategy is proposed to improve the performance of quantum-behaved particle swarm optimization. In proposed local search strategy, a super particle is presented which is a collection body of randomly selected particles’ dimension information in the swarm. The selected probability of particles in swarm is different and determined by their fitness values. To minimization problems, the fitness value of one particle is smaller; the selected probability is more and will contribute more information in constructing the super particle. In addition, in order to investigate the influence on algorithm performance with different local search space, four methods of computing the local search radius are applied in local search strategy and propose four variants of local search quantum-behaved particle swarm optimization. Empirical studies on a suite of well-known benchmark functions are undertaken in order to make an overall performance comparison among the proposed methods and other quantum-behaved particle swarm optimization. The simulation results show that the proposed quantum-behaved particle swarm optimization variants have better advantages over the original quantum-behaved particle swarm optimization.

  1. Modes of continental extension in a lithospheric wedge

    Science.gov (United States)

    Wu, G.; Lavier, L. L.; Choi, E.

    2014-12-01

    We studied extension of a lithospheric wedge as an approximation to an orogenic belt or a continental margin. We ran a series of numerical models to quantify the effects of the strength of the lower crust and a mid-crustal shear zone (MCSZ) on the extension processes. When the MCSZ is present, we found that the regional lower crustal flow plays a critical role in controlling the modes of extension. The compensation is long-wavelength when the lower crust flows from the highest to the lowest elevation in order to compensate upper crustal thinning. In response to this motion, the mantle flows towards the highest elevation in order to balance for the lower crust leaving the area under the highest topography. For weak (wet quartz regime with partial melting) or intermediate (wet quartz regime), or strong (dry quartz regime) lower crust, we recognized three predominantly decoupled modes of extension characterized by 1) significant lower crustal exhumation exemplified as a large massif, 2) formation of core complexes and detachment faults, and 3) distributive domino faulting, respectively. Without the MCSZ, however, the lower crustal flow is essentially subdued with predominantly coupled extension. For weak or intermediate, or strong lower crust, we recognized three coupled modes characterized by 1) localized generally symmetric crustal exhumation, 2) distributed grabens and narrow rifts, and 3) wide continental margins, respectively. The MCSZ controls the degree of decoupling of the lower crustal flow such that a frictionally stronger MCSZ does not change the behaviors of the models but results in a more distributed extension. Due to the long-wavelength compensation, subhorizontal Moho is achieved where intensive extension occurred for all the decoupled models with a MCSZ. Natural counterparts for each mode may be easily identified, for instance, in the Basin and Range or the Aegean.

  2. Subduction initiation, recycling of Alboran lower crust, and intracrustal emplacement of subcontinental lithospheric mantle in the Westernmost Mediterranean

    Science.gov (United States)

    Varas-Reus, María Isabel; Garrido, Carlos J.; Bosch, Delphine; Marchesi, Claudio; Hidas, Károly; Booth-Rea, Guillermo; Acosta-Vigil, Antonio

    2015-04-01

    sediments strongly support Alboran geodynamic models that envisage slab roll-back as the tectonic mechanism responsible for Miocene lithospheric thinning, and consistent with a scenario where back-arc inversion leading to subduction initiation of crustal units at the front of the Alboran wedge

  3. Heterogeneity of Water Concentrations in the Mantle Lithosphere Beneath Hawaii

    Science.gov (United States)

    Bizimis, M.; Peslier, A. H.; Clague, D.

    2017-01-01

    The amount and distribution of water in the oceanic mantle lithosphere has implications on its strength and of the role of volatiles during plume/lithosphere interaction. The latter plays a role in the Earth's deep water cycle as water-rich plume lavas could re-enrich an oceanic lithosphere depleted in water at the ridge, and when this heterogeneous lithosphere gets recycled back into the deep mantle. The main host of water in mantle lithologies are nominally anhydrous minerals like olivine, pyroxene and garnet, where hydrogen (H) is incorporated in mineral defects by bonding to structural oxygen. Here, we report water concentrations by Fourier transform infrared spectrometry (FTIR) on olivine, clino- and orthopyroxenes (Cpx & Opx) from spinel peridotites from the Pali vent and garnet pyroxenite xenoliths from Aliamanu vent, both part of the rejuvenated volcanism at Oahu (Hawaii). Pyroxenes from the Aliamanu pyroxenites have high water concentrations, similar to the adjacent Salt Lake Crater (SLC) pyroxenites (Cpx 400-500 ppm H2O, Opx 200 ppm H2O). This confirms that pyroxenite cumulates form water-rich lithologies within the oceanic lithosphere. In contrast, the Pali peridotites have much lower water concentrations than the SLC ones (10% modal Cpx and low spinel Cr# (0.09-0.10). The contrast between the two peridotite suites is also evident in their trace elements and radiogenic isotopes. The Pali Cpx are depleted in light REE, consistent with minimal metasomatism. Those of SLC have enriched light REE patterns and Nd and Hf isotopes consistent with metasomatism by alkaline melts. These observations are consistent with heterogeneous water distribution in the oceanic lithosphere that may be related to metasomatism, as well as relatively dry peridotites cross-cut by narrow (?) water-rich melt reaction zones.

  4. Satellite tidal magnetic signals constrain oceanic lithosphere-asthenosphere boundary

    DEFF Research Database (Denmark)

    Grayver, Alexander V.; Schnepf, Neesha R.; Kuvshinov, Alexey V.

    2016-01-01

    , there are no reports that these signals have been used to infer subsurface structure. We use satellite-detected tidal magnetic fields to image the global electrical structure of the oceanic lithosphere and upper mantle down to a depth of about 250 km. Themodel derived from more than 12 years of satellite data reveals...... a ≈72-km-thick upper resistive layer followed by a sharp increase in electrical conductivity likely associated with the lithosphere-asthenosphere boundary, which separates colder rigid oceanic plates from the ductile and hotter asthenosphere....

  5. Seismic imaging of the downwelling Indian lithosphere beneath central Tibet.

    Science.gov (United States)

    Tilmann, Frederik; Ni, James

    2003-05-30

    A tomographic image of the upper mantle beneath central Tibet from INDEPTH data has revealed a subvertical high-velocity zone from approximately 100- to approximately 400-kilometers depth, located approximately south of the Bangong-Nujiang Suture. We interpret this zone to be downwelling Indian mantle lithosphere. This additional lithosphere would account for the total amount of shortening in the Himalayas and Tibet. A consequence of this downwelling would be a deficit of asthenosphere, which should be balanced by an upwelling counterflow, and thus could explain the presence of warm mantle beneath north-central Tibet.

  6. Remobilization in the cratonic lithosphere recorded in polycrystalline diamond

    Science.gov (United States)

    Jacob; Viljoen; Grassineau; Jagoutz

    2000-08-18

    Polycrystalline diamonds (framesites) from the Venetia kimberlite in South Africa contain silicate minerals whose isotopic and trace element characteristics document remobilization of older carbon and silicate components to form the framesites shortly before kimberlite eruption. Chemical variations within the garnets correlate with carbon isotopes in the diamonds, indicating contemporaneous formation. Trace element, radiogenic, and stable isotope variations can be explained by the interaction of eclogites with a carbonatitic melt, derived by remobilization of material that had been stored for a considerable time in the lithosphere. These results indicate more recent formation of diamonds from older materials within the cratonic lithosphere.

  7. Control of high velocity lithosphere roots on crustal scale density variations seen in Gondwana reconstructions

    Science.gov (United States)

    Braitenberg, C. F.; Mariani, P.

    2015-12-01

    The GOCE gravity field is globally homogeneous at the resolution of about 80km or better allowing for the first time to identify tectonic structures at continental scale. The large scale structures are presumably controlled by the rheology of the underlying crust down to the base of the lithosphere. Seismic tomography identifies the presence of the deep lithosphere roots by increased velocity. The joint analysis of the tomography results and the GOCE gravity reveals that at global scale the two data have some common patterns. The correlations are enhanced by applying geodynamic plate reconstructions to the GOCE gravity field and to the tomography models which places today's observed fields at the Gondwana pre-breakup position. There are several examples for which it is found that the deep lithospheric roots, as those found below cratons, control the position of the positive gravity values outboard of the deep roots. This could be explained by the deep lithospheric roots focusing asthenospheric upwelling outboard of the root protecting the overlying craton from magmatic intrusions. Over several of the deep roots the gravity is systematically negative, which could be due to a compositional effect, with deep roots of increased velocity having reduced density. The study is carried out globally, with focus on the African and South American continents. The background for the study can be found in the following publications where the techniques which have been used are described: Braitenberg, C., Mariani, P. and De Min, A. (2013). The European Alps and nearby orogenic belts sensed by GOCE, Boll. Bollettino di Geofisica Teorica ed Applicata, 54(4), 321-334. doi:10.4430/bgta0105 Braitenberg, C. and Mariani, P. (2015). Geological implications from complete Gondwana GOCE-products reconstructions and link to lithospheric roots. Proceedings of 5th International GOCE User Workshop, 25 - 28 November 2014. Braitenberg, C. (2015). Exploration of tectonic structures with GOCE in

  8. A Preliminary Study on the Lithosphere-Asthenosphere Boundary beneath the South China Sea

    Science.gov (United States)

    Lee, T. T. Y.; Chen, C. W.

    2014-12-01

    The lithosphere-asthenosphere boundary (LAB) is an important boundary at which the rigid lithosphere translates coherently upon the viscous asthenosphere. New observations have been made on LAB through detailed seismic analysis, especially that from receiver functions. Previous studies have found LAB depth varies significantly, systematically getting shallower from continental to oceanic lithosphere. In smaller scale, the depth and sharpness of LAB also differ from region to region, suggesting the effects of a combination of thermal and compositional origins. In this study, we investigate the LAB beneath the South China Sea, a region poorly instrumented that conventional seismological are less effective and impractical. The South China Sea is on the Sunda Plate, which is considered to be once the southeastern part of the Eurasia Plate before separating with a distinct moving direction from that of India-Eurasia continental collision. The South China Sea is Phanerozoic in age and continental in nature, but the striped magnetic anomalies observed from the sea floor have suggested multiple spreading events since early Miocene, indicating the presence of latter formed oceanic lithosphere. Previous seismic studies of this region focused mainly on shallow basin structure pertaining to petroleum exploration. The lithospheric structure, particularly the LAB, remains elusive, while it provides important insight into the complex tectonic history in this region. To image the LAB, we use the precursor of SS phase. The precursor bounces at the LAB discontinuity at depth would appear before the SS and presents a signal amenable to analysis for depth and properties. We collect seismic waveform data recorded mainly at Japan and Cocos Islands of corresponding teleseismic events from Southern Sumatera and Japan, with SS and potential precursors bouncing beneath the South China Sea. We employ an analysis technique, velocity spectral analysis (vespagrams), to identify precursory

  9. Constraining the Lithospheric Structure of the Central Andes Using P- and S- wave Receiver Functions

    Science.gov (United States)

    Ryan, J. C.; Beck, S. L.; Zandt, G.; Wagner, L. S.; Minaya, E.; Tavera, H.

    2014-12-01

    The Central Andean Plateau (CAP) has elevations in excess of 3 km, and is part of the Andean Cordillera that resulted in part from shortening along the western edge of South America as it was compressed between the subducting Nazca plate and underthrusting Brazilian cratonic lithosphere. We calculated P- and S-wave receiver functions for the Central Andean Uplift and Geodynamics of High Topography (CAUGHT) temporary deployment of broadband seismometers in the Bolivian orocline (12°-20°S) region to investigate crustal thickness and lithospheric structure. Migration of the receiver functions is done using common conversion point (CCP) stacks through a 3D shear velocity model from ambient noise tomography (Ward et al., 2013). The P- and S-wave receiver functions provide similar estimates of the depth to Moho under the CAP. Crustal thicknesses include 60-65 km thick crust underneath the Bolivian Altiplano, crust that varies from ~70 km to ~50 km underneath the Eastern Cordillera and Interandean zone, and thins to 50 to 40 km crust in the Subandes and the edge of the foreland. The variable crustal thickness of the Eastern Cordillera and Interandean zone ranges from >70 km associated with the Los Frailes volcanic field at 19°-20°S to ~55 km beneath the 6 km peaks of the Cordillera Real at ~16°S. From our S-wave receiver functions, that have no multiples that can interfere with deeper structure, we also identify structures below the Moho. Along a SW-NE line that runs near La Paz where we have our highest station density, the S-wave CCP receiver-function stacks show a strong negative polarity arrival at a depth of ~120 km from the eastern edge of the Altiplano to the Subandean zone. We suggest this may be a good candidate for the base of the CAP lithosphere. In addition, above this depth the mantle is strongly layered, suggesting that there is not a simple high velocity mantle lithosphere associated with the continental lithosphere underthrusting the Andean orogen

  10. Deformation of the Pannonian lithosphere and related tectonic topography: a depth-to-surface analysis

    NARCIS (Netherlands)

    Dombrádi, E.

    2012-01-01

    Fingerprints of deep-seated, lithospheric deformation are often recognised on the surface, contributing to topographic evolution, drainage organisation and mass transport. Interactions between deep and surface processes were investigated in the Carpathian-Pannonian region. The lithosphere beneath th

  11. Deformation of the Pannonian lithosphere and related tectonic topography: a depth-to-surface analysis

    NARCIS (Netherlands)

    Dombrádi, E.

    2012-01-01

    Fingerprints of deep-seated, lithospheric deformation are often recognised on the surface, contributing to topographic evolution, drainage organisation and mass transport. Interactions between deep and surface processes were investigated in the Carpathian-Pannonian region. The lithosphere beneath th

  12. Shallow and deep lithosphere slabs beneath the Dinarides from teleseismic tomography as the result of the Adriatic lithosphere downwelling

    Science.gov (United States)

    Šumanovac, Franjo; Markušić, Snježana; Engelsfeld, Tihomir; Jurković, Klaudia; Orešković, Jasna

    2017-08-01

    The study area covers the Dinarides and southwestern part of the Pannonian basin as the marginal zone between the Adriatic microplate (African plate) and the Pannonian tectonic segment (Eurasian plate). We created a three-dimensional seismic velocity model to 450 km depth using teleseismic tomography. Our travel-time dataset was collected by means of 40 seismic stations from the ORFEUS database and Croatian Seismological Survey database. A set of 90 teleseismic earthquakes were selected in the time range 2014-2015, and relative P-wave travel-time residuals were calculated. For the first time the seismic P-wave velocity model of a relatively high resolution on the entire Dinaridic mountain belt was obtained. Based on this model, a more reliable insight in the relations of the lithosphere plates has been achieved. We imaged a fast velocity anomaly extending underneath the entire Dinaridic mountain belt which indicates cold, rigid materials. The anomaly is steeply sloping towards the northeast and directly indicates the sinking of the Adriatic microplate underneath the Pannonian tectonic segment. In the Northern Dinarides the anomaly extends to the depth of 250 km, whereas in the Southern Dinarides it covers greater depths, up to 450 km. The shallow Adriatic slab extends along the External Dinarides, while the deep Adriatic slab extends beneath the Internal Dinarides and ophiolite zones in the area of central and southern Dinarides. Different slab depths are interpreted as the faster convergence of the plate in the southern Dinarides than in the northern, or the convergence of the plates had started in the southern part and systematically developed to the north.

  13. The story of a craton from heart to margins: illuminating cratonic lithosphere with Rayleigh wave phase velocities in Eastern Canada

    Science.gov (United States)

    Petrescu, L.; Darbyshire, F. A.; Gilligan, A.; Bastow, I. D.; Totten, E. J.

    2015-12-01

    Cratons are Precambrian continental nuclei that are geologically distinct from modern continental regions and are typically underlain by seismically fast lithospheric roots (keels) to at least 200 km depth. Both plate and non-plate tectonic origin theories such as stacking of subducted slabs or multiple mantle plume underplating have been proposed to explain keel growth.Eastern Canada is an ideal continental region to investigate cratonization processes and the onset of plate tectonics. It comprises part of the largest Archean craton in the world, the Superior Province, flanked by a ~1.1 Ga Himalayan-scale orogenic belt, the Grenville Province, and the 500-300 Ma old Appalachian orogenic province, following the same general SW-NE axial trend. The region is also cross-cut by the Great Meteor Hotspot track, providing an excellent opportunity to study the interaction of hotspot tectonism with progressively younger lithospheric domains.We investigate the lithospheric structure of Precambrian Eastern Canada using teleseismic earthquake data recorded at permanent and temporary networks. We measure interstation dispersion curves of Rayleigh wave phase velocities between ~15 and 220 s, and compare the results to standard continental and cratonic reference models. We combine the dispersion curves via a tomographic inversion which solves for isotropic phase velocity heterogeneity and azimuthal anisotropy across the region at a range of periods. The phase velocity maps indicate variations in lithospheric properties from the heart of the Superior craton to the SE Canadian coast.The new regional-scale models will help to understand the processes that generated, stabilized and reworked the cratonic roots through their billion-year tectonic history. We investigate how surface tectonic boundaries relate to deeper lithospheric structural changes, and consider the effects of the multiple Wilson cycles that affected Laurentia.

  14. Activity of Caudate Nucleus Neurons in a Visual Fixation Paradigm in Behaving Cats.

    Directory of Open Access Journals (Sweden)

    Tamás Nagypál

    Full Text Available Beside its motor functions, the caudate nucleus (CN, the main input structure of the basal ganglia, is also sensitive to various sensory modalities. The goal of the present study was to investigate the effects of visual stimulation on the CN by using a behaving, head-restrained, eye movement-controlled feline model developed recently for this purpose. Extracellular multielectrode recordings were made from the CN of two cats in a visual fixation paradigm applying static and dynamic stimuli. The recorded neurons were classified in three groups according to their electrophysiological properties: phasically active (PAN, tonically active (TAN and high-firing (HFN neurons. The response characteristics were investigated according to this classification. The PAN and TAN neurons were sensitive primarily to static stimuli, while the HFN neurons responded primarily to changes in the visual environment i.e. to optic flow and the offset of the stimuli. The HFNs were the most sensitive to visual stimulation; their responses were stronger than those of the PANs and TANs. The majority of the recorded units were insensitive to the direction of the optic flow, regardless of group, but a small number of direction-sensitive neurons were also found. Our results demonstrate that both the static and the dynamic components of the visual information are represented in the CN. Furthermore, these results provide the first piece of evidence on optic flow processing in the CN, which, in more general terms, indicates the possible role of this structure in dynamic visual information processing.

  15. Basin evolution in a folding lithosphere: Altai-Sayan and Tien Shan belts in Central Asia

    NARCIS (Netherlands)

    Delvaux, D.; Cloetingh, S.; Beekman, F.; Sokoutis, D.; Burov, E.; Buslov, M.M.; Abdrakhmatov, K.E.

    2013-01-01

    Central Asia is a classical example for continental lithospheric folding. In particular, the Altay–Sayan belt in South-Siberia and the Kyrgyz Tien Shan display a special mode of lithospheric deformation, involving decoupled lithospheric mantle folding and upper crustal folding and faulting. Both are

  16. The crust and lithosphere thicknesses in South America: trying to find the lithosphere- asthenosphere boundary

    Science.gov (United States)

    Heit, B.; Sodoudi, F.; Yuan, X.; Bianchi, M.; Kind, R.

    2007-05-01

    During the past years, a series of seismological investigations have been carried out to study the crustal and mantle structures all over the world. In South America, this investigation has not been an easy task as there are different regions where the geodynamics involves the subduction of an oceanic plate, the building of a mountain range as the Andes, the interaction with older lithosphere as the Brazilian Shield and the presence of active deformation fronts between the last two regions. In order to investigate the thickness of the lithosphere in such a complex context we have performed S-wave receiver function analysis (Vinnik and Farra, 2000; Li et al., 2004). The S receiver function technique looks for the S-to-P converted waves at seismic discontinuities beneath a station in the same way as the conventional P receiver function method that deals with P-to-S conversions. The S receiver function technique have proved to be useful to map the Moho and the LAB in many regions where other methods (i.e. surface waves) failed to provide reliable information (e.g. Li et al., 2004; Kumar et al., 2004a, 2004b; Sodoudi et al., 2006). We present here the results of S receiver function technique that has been applied to all the available temporary seismic experiments (e.g. BANJO, SEDA, REFUCA, BLSP) and the permanent stations from the IRIS network. We have been able to investigate the upper mantle discontinuities at all the depths beneath the stations and obtained coherent Moho depths along the entire Andes and in other South American continental regions. The LAB has been clearly detected below some stations, particularly those that are located far away from the subduction zone. By comparing our results with those from the P receiver functions, we have been able to further constrain the thicknesses of the crust and LAB in different regions including shields, mobile belts, basins and mountain ranges. At many stations we have also been able to map the upper mantle

  17. Petrological imaging of the Cordilleran lithosphere beneath Craven Lake, NCVP, BC, Canada: local evidence for a texturally diverse, hydrous lithosphere

    Science.gov (United States)

    Miller, Christine; Edwards, Benjamin R.; Russell, James K.; Peterson, Nils

    2010-05-01

    Peridotite and pyroxenite xenoliths from the glaciovolcanic Craven Lake center (Edwards et al., 2006) provide local evidence for a texturally diverse, hydrous lithosphere beneath the Stikine terrane, in the Canadian Cordilleran lithosphere. Although the xenolith suite is dominated by spinel lherzolite, websterite and Ol websterite xenoliths also occur. Veins of amphibole, with local apatite, have so far been found in one spinel lherzolite and one websterite xenolith. Although interstitial amphibole has been reported from at least two localities in the northern Cordillera, we believe that this is the first documented occurrence of an amphibole vein in lithospheric peridotite and pyroxenite. Textural analysis shows that the xenoliths from Craven Lake are on average finer grained (~2.0 mm) and less equigranular than xenolith suites from localities to the north (e.g. Harder and Russell, 2005) or to the south (e.g. Peslier et al., 2002). Clinopyroxene-orthopyroxene geothermometry of a peridotite sample indicates that the temperatures of equilibration (964-1022C at 0.1 GPa) are well within the established stability limits of amphibole at lithospheric pressures. Observations on the Craven Lake suite have important implications for the petrology of the Cordilleran lithosphere. Textural observations confirm that the lithosphere beneath the accreted terranes in British Columbia is distinctly heterogeneous, which is consistent with at least local lithospheric variation that could be due in part to tectonism during Mesozoic terrane accretion. Documentation of veins of amphibole plus apatite in the Cordilleran lithosphere is consistent with the Francis and Ludden (1995) hypothesis that the veins could be lithospheric sources for volumetrically minor but spatially wide-spread nephelinite throughout the Canadian Cordilleran, which were remelted during Neogene to Recent, extension-related magmatism. The formation of the veins may be linked to Mesozoic subduction zone metasomatism

  18. A lithospheric perspective on structure and evolution of Precambrian cratons

    DEFF Research Database (Denmark)

    Artemieva, Irina

    2012-01-01

    the roots of the continents, and moves together with continental plates. Depending on geophysical techniques (and physical properties measured), the lithosphere has different practical definitions. Most of them (i.e., seismic, electrical) are on the basis of a sharp change in temperature-dependent physical...

  19. Seismicity in Romania--evidence for the sinking lithosphere.

    Science.gov (United States)

    Roman, C

    1970-12-19

    The revision of Romanian earthquakes shows a distribution suggesting a sinking lithosphere under the Carpathian arc. Thermal and gravitational anomalies, as well as petrological and tectonic features, provide further evidence on the cause and character of intermediate earthquakes of Romania. This is consistent with the theory of plate tectonics in south-east Europe.

  20. Upper mantle viscosity and lithospheric thickness under Iceland

    NARCIS (Netherlands)

    Barnhoorn, A.; Wal, W. van der; Drury, M.R.

    2011-01-01

    Deglaciation during the Holocene on Iceland caused uplift due to glacial isostatic adjustment. Relatively low estimates for the upper mantle viscosity and lithospheric thickness result in rapid uplift responses to the deglaciation cycles on Iceland. The relatively high temperatures of the upper mant

  1. European Lithospheric Mantle; geochemical, petrological and geophysical processes

    Science.gov (United States)

    Ntaflos, Th.; Puziewicz, J.; Downes, H.; Matusiak-Małek, M.

    2017-04-01

    The second European Mantle Workshop occurred at the end of August 2015, in Wroclaw, Poland, attended by leading scientists in the study the lithospheric mantle from around the world. It built upon the results of the first European Mantle Workshop (held in 2007, in Ferrara, Italy) published in the Geological Society of London Special Publication 293 (Coltorti & Gregoire, 2008).

  2. A lithospheric perspective on structure and evolution of Precambrian cratons

    DEFF Research Database (Denmark)

    Artemieva, Irina

    2012-01-01

    the roots of the continents, and moves together with continental plates. Depending on geophysical techniques (and physical properties measured), the lithosphere has different practical definitions. Most of them (i.e., seismic, electrical) are on the basis of a sharp change in temperature-dependent physical...

  3. Density and P-wave velocity structure beneath the Paraná Magmatic Province: Refertilization of an ancient lithospheric mantle

    Science.gov (United States)

    Chaves, Carlos; Ussami, Naomi; Ritsema, Jeroen

    2016-08-01

    We estimate density and P-wave velocity perturbations in the mantle beneath the southeastern South America plate from geoid anomalies and P-wave traveltime residuals to constrain the structure of the lithosphere underneath the Paraná Magmatic Province (PMP) and conterminous geological provinces. Our analysis shows a consistent correlation between density and velocity anomalies. The P-wave speed and density are 1% and 15 kg/m3 lower, respectively, in the upper mantle under the Late Cretaceous to Cenozoic alkaline provinces, except beneath the Goiás Alkaline Province (GAP), where density (+20 kg/m3) and velocity (+0.5%) are relatively high. Underneath the PMP, the density is higher by about 50 kg/m3 in the north and 25 kg/m3 in the south, to a depth of 250 - 300 km. These values correlate with high-velocity perturbations of +0.5% and +0.3%, respectively. Profiles of density perturbation versus depth in the upper mantle are different for the PMP and the adjacent Archean São Francisco (SFC) and Amazonian (AC) cratons. The Paleoproterozoic PMP basement has a high-density root. The density is relatively low in the SFC and AC lithospheres. A reduction of density is a typical characteristic of chemically depleted Archean cratons. A more fertile Proterozoic and Phanerozoic subcontinental lithospheric mantle has a higher density, as deduced from density estimates of mantle xenoliths of different ages and composition. In conjunction with Re-Os isotopic studies of the PMP basalts, chemical and isotopic analyses of peridodite xenoliths from the GAP in the northern PMP, and electromagnetic induction experiments of the PMP lithosphere, our density and P-wave speed models suggest that the densification of the PMP lithosphere and flood basalt generation are related to mantle refertilization. Metasomatic refertilization resulted from the introduction of asthenospheric components from the mantle wedge above Proterozoic subduction zones, which surrounded the Paraná lithosphere

  4. On the relation between lithospheric strength and ridge push transmission in the Nazca plate

    Science.gov (United States)

    Mahatsente, R.; Ranalli, G.; Bolte, D.; Götze, H.-J.

    2012-01-01

    The ridge push force and the total lithospheric strength of the Nazca plate are compared along an East-West transect from the East Pacific Rise to the Peru-Chile trench at latitude 12°S. The thermal structure of the plate is estimated from the plate cooling model and constrained by heat flow, bathymetry, and geoid height data. The best fitting thermal model has a basal temperature of ˜1600 K and an asymptotic plate thickness (not reached because of the relatively young age of the plate at the trench) of ˜101 km. The ridge push force, also determined from the plate cooling model, is of the order of 1.5 TN m -1 at the trench. The total lithospheric strength as a function of age is estimated for a possible range of conditions (compressional/extensional intraplate tectonic regime, wet/dry rheology). A comparison of ridge push force with lithospheric strength, extended beyond the Nazca plate by considering different spreading rates and ages, shows that oceanic plates with dry rheology have strengths higher than the ridge push force at any age if the tectonic regime is compressional, and comparable if the regime is extensional. On the other hand, oceanic plates with wet rheology have strengths lower than the ridge push force, especially if the tectonic regime is extensional. Therefore, if the rheology is wet and mantle drag at the base of the plate is sufficiently strong, the ridge push force may result in intraplate deformation and be partly dissipated within the plate.

  5. Lithospheric Convergence Preceded Extension in the Pannonian-Carpathian System

    Science.gov (United States)

    Houseman, Gregory; Stuart, Graham; Dando, Ben; Hetenyi, Gyorgy; Lorinczi, Piroska; Hegedus, Endre; Brueckl, Ewald

    2010-05-01

    The continuing collision of the Adriatic block with European continental lithosphere has its clearest expression now in the Alpine collision zone. Recent tomographic images of the upper mantle beneath the eastern Alps and western Pannonian Basin support the interpretation that in the Early Miocene the collision zone extended further east: a steeply dipping seismically fast structure stretches downward beneath the Eastern Alps reaching to the base of the transition zone, consistent with the long history of convergence in this region. This high velocity structure also extends eastward beneath the extensional Pannonian Basin. The high velocity anomaly beneath the Basin is strongly developed in transition zone depths (410 to 660 km) but the anomaly weakens upward. High velocities beneath the center of the extensional basin are unexpected because there is substantive evidence that the onset of extension in the Pannonian domain at around 17 Ma produced rapid extension of the lithosphere and replacement of the lower part of the lithosphere by hot asthenosphere. These deeper structures, however, must be explained by the long history of convergence that preceded the extension of the basin. Further evidence of a history of sustained convergence in the present Pannonian region is found in the depression of the 660 km seismic discontinuity beneath the Alps (Lombardi et al., EPSL, 2009) and also beneath the Pannonian Basin (Hetenyi et al., GRL, 2009). The 660 km discontinuity in both places is depressed by as much as 40 km, whereas the 410 km discontinuity is at approximately nominal depths. Evidently in both regions relatively dense material derived from the mid-Miocene collision sits stagnant on top of the 660 km discontinuity, where further descent is obstructed by the negative Clapeyron slope of the spinel-to-perovskite phase transition and/or the high viscosity of the lower mantle. The rapid extension of the Intra-Carpathian Basins in the Mid-Miocene (between about 17 and

  6. Geodynamic and Seismic Constraints on the Evolution of the Oceanic Lithosphere and Asthenosphere

    Science.gov (United States)

    Fahy, E. H.; Hall, P. S.; Dalton, C. A.; Faul, U.

    2011-12-01

    We report on a series of numerical geodynamic experiments undertaken to investigate the evolution the oceanic lithosphere and the characteristics of the underlying asthenosphere. In particular, we used the CitcomCU finite element package to model mantle flow beneath an oceanic plate. Experiments incorporated deformation by both diffusion creep and dislocation creep mechanisms, with experimentally constrained constants used for the relevant flow laws. We find that the use of flow laws appropriate for wet olivine aggregates leads to the formation of instabilities at the base of the thermal boundary layer corresponding to the lithosphere, which are not found in the experiments employing flow laws for dry olivine. These instabilities effectively thin the older portions of the thermal boundary layer, resulting in an average temperature structure closely resembling the GDH1 plate model [Stein and Stein, 1992] within the model domain. In contrast, the thermal structure of experiments in which instabilities do not form resembles resembles that of a half-space cooling model. Comparison of experimental results to seismic models of variations in shear wave velocity and shear attenuation with both depth and age within the oceanic upper mantle indicates that experiments in which instabilities occur provide a better match to seismic observations than do experiments without such instabilities.

  7. Gravity anomalies and lithospheric flexure around the Longmen Shan deduced from combinations of in situ observations and EGM2008 data

    Science.gov (United States)

    She, Yawen; Fu, Guangyu; Wang, Zhuohua; Liu, Tai; Xu, Changyi; Jin, Honglin

    2016-10-01

    The current work describes the combined data of three field campaigns, spanning 2009-2013. Their joint gravity and GPS observations thoroughly cover the sites of lithospheric flexure between the Sichuan Basin and the Eastern Tibetan Plateau. The study area's free-air gravity anomalies (FGAs) are updated by using a remove-and-restore algorithm which merges EGM2008 data with in situ observations. These new FGAs show pairs of positive and negative anomalies along the eastern edges of the Tibetan Plateau. The FGAs are used to calculate effective elastic thickness ( T e) and load ratios ( F) of the lithosphere. Admittance analysis indicates the T e of Longmen Shan (LMS) to be 6 km, and profile analysis indicates that the T e of the Sichuan Basin excesses 30 km. The load ratio ( F 1 = 1) confirms that the lithospheric flexure of the LMS area can be attributed solely to the surface load of the crust. [Figure not available: see fulltext. Caption: The current work describes the combined data of three field campaigns, spanning 2009-2013. Their joint gravity and GPS observations thoroughly cover the sites of lithospheric flexure between the Sichuan Basin and the Eastern Tibetan Plateau. The study area's free-air gravity anomalies (FGAs) are updated by using a remove-and-restore algorithm which merges EGM2008 data with in situ observations. With the new FGAs data, the lithospheric strength of the study area is studied by the authors, and they also give a combined model to illustrate the uplift mechanism of this area.

  8. Seismic constraints on the lithosphere-asthenosphere boundary

    Science.gov (United States)

    Rychert, Catherine A.

    2014-05-01

    The basic tenet of plate tectonics is that a rigid plate, or lithosphere, moves over a weaker asthenospheric layer. However, the exact location and defining mechanism of the boundary at the base of the plate, the lithosphere-asthenosphere boundary (LAB) is debated. The oceans should represent a simple scenario since the lithosphere is predicted to thicken with seafloor age if it thermally defined, whereas a constant plate thickness might indicate a compositional definition. However, the oceans are remote and difficult to constrain, and studies with different sensitivities and resolutions have come to different conclusions. Hotspot regions lend additional insight, since they are relatively well instrumented with seismic stations, and also since the effect of a thermal plume on the LAB should depend on the defining mechanism of the plate. Here I present new results using S-to-P receiver functions to image upper mantle discontinuity structure beneath volcanically active regions including Hawaii, Iceland, Galapagos, and Afar. In particular I focus on the lithosphere-asthenosphere boundary and discontinuities related to the base of melting, which can be used to highlight plume locations. I image a lithosphere-asthenosphere boundary in the 50 - 95 km depth range beneath Hawaii, Galapagos, and Iceland. Although LAB depth variations exist within these regions, significant thinning is not observed in the locations of hypothesized plume impingement from receiver functions (see below). Since a purely thermally defined lithosphere is expected to thin significantly in the presence of a thermal plume anomaly, a compositional component in the definition of the LAB is implied. Beneath Afar, an LAB is imaged at 75 km depth on the flank of the rift, but no LAB is imaged beneath the rift itself. The transition from flank of rift is relatively abrupt, again suggesting something other than a purely thermally defined lithosphere. Melt may also exist in the asthenosphere in these regions

  9. The role of lithospheric processes on the development of linear volcanic ridges in the Azores

    Science.gov (United States)

    Neves, M. C.; Miranda, J. M.; Luis, J. F.

    2013-11-01

    Linear volcanic ridges (LVRs) are widespread along the Azores plateau and are often used as a tectonic marker of the surface stress field. Nevertheless, the mechanisms that drive the emplacement and development of these structures are not well established and they have been attributed to the plateau diffuse deformation, off-rift extension or the result of the interaction between a hotspot and the brittle lithosphere. This study hypothesizes that linear volcanic ridges are the result of magma emplacement into pre-existing damaged lithosphere, using a 3D finite-element representation of the brittle lithosphere and underlying ductile mantle, and assuming that the deformation is driven by plate boundary forces applied at the edges, as describe by global plate kinematic models. The brittle layer is described by an elastoplastic rheology with progressive damage, where fractures are assumed to be analogous to localized shear bands. The ductile mantle underneath is modeled as a viscoelastic layer that exerts a shear drag at the base of the brittle layer. The modeling shows that lithospheric processes alone can justify the spatial distribution of linear volcanic ridges, and even the development of the Faial Ridge. The factors controlling the fracturing pattern are the plate geometry and velocity boundary conditions, the shearing introduced at the East Azores Fracture Zone/Gloria fault limit and the interaction between the viscous mantle and the spatially varying brittle plate thickness. Along the Terceira Rift the predicted fractures match the orientation of the LVRs in the second (~ N135°-N140°) and third (N150° to N-S) sectors and provide an explanation for the arcuate shape of the rift itself. The brittle plate thickness variations are crucial for the development of the more recent LVRs, which are predicted to occur along the Faial Ridge. In the best fit model the top mantle viscosity is 1 × 1022 Pa s at 5-15 km depth, and the present-day fracture network takes ~ 3

  10. First scalar magnetic anomaly map from CHAMP satellite data indicates weak lithospheric field

    DEFF Research Database (Denmark)

    Maus, S.; Rother, M.; Holme, R.;

    2002-01-01

    Satellite magnetic anomaly maps derived by different techniques from Magsat/POGO data vary by more than a factor of 2 in the deduced strength of the lithospheric magnetic field. Here, we present a first anomaly map from new CHAMP scalar magnetic field data. After subtracting a recent Ørsted main...... and external field model, we remove remaining unmodeled large-scale external contributions from 120 track segments by subtracting a best-fitting uniform field. In order to preserve N/S trending features, the data are not filtered along-track. Direct integration of the spherically gridded data yields the final...

  11. Project Hotspot - The Snake River Scientific Drilling Project - Investigating the Interactions of Mantle Plumes and Continental Lithosphere

    Science.gov (United States)

    Shervais, J. W.

    2008-12-01

    the crust by adding mafic material to the lower and middle crust, and by transferring fusible components from the lower crust to the upper crust as rhyolite lavas and ignimbrites. We further hypothesize that the structure, composition, age and thickness of continental lithosphere influence the chemical and isotopic evolution of plume-derived magmas, and localizes where they erupt on the surface. We propose to test these hypotheses by addressing two fundamental questions: (1) Are the chemical and isotopic compositions of the basaltic and rhyolitic magmas a function of lithosphere thickness, composition and age at the locality where they erupted? (2) Are the eruptive flux and mantle source signatures consistent with the mantle plume model for the Snake River-Yellowstone volcanic system? To address these fundamental questions, we plan a transect of the continental margin that begins with lavas erupted through Mesozoic-Paleozoic accreted terranes of oceanic provenance that lie west of the craton margin, as defined by the Sr=0.706 line, and continues through progressively thicker and older lithosphere of Proterozoic to Archean age. The rationale is to examine how basalt chemistry varied through time at different locations along this transect in response to changes in the thickness, age, and composition of the underlying mantle lithosphere and the age of the erupted basalt. We will leverage this transect with samples from existing drill holes that intercept basalt at critical locations across the plain and with three new deep drill holes. This strategy will result in the recovery of the complete sequence of SRP basalts at relatively low cost.

  12. Preseismic Lithosphere-Atmosphere-Ionosphere Coupling

    Science.gov (United States)

    Kamogawa, Masashi

    hardly verified so far, a statistical approach has been unique way to promote the research. After the 2000s, several papers showing robust statistical results have arisen. In this paper, we focus on publications satisfying the following identification criteria: 1) A candidate of precursor, namely anomaly, is quantitatively defied. 2) Two time-series of anomalies and earthquake are constructed within the fixed thresholds such as a minimum magnitude, a region, and a lead-time. 3) To obtain a statistical correlation, a statistical process which includes four relations considering all combination among earthquake - no earthquake versus anomaly and no anomalies is applied, e. g., phi correlation. 4) For correlations under various thresholds the results keep consistency. 5) Large anomalies appear before large earthquakes. One of papers based on the identification criteria, which concerns preseismic geoelectrically anomalies, is introduced as an educative example. VAN method in Greece, i. e., Geo-electric potential difference measurement for precursor study in Greece, has been often discussed in the point of view of success and failure performance for practical prediction [Varotsos et al, Springer, 2011] to show a correlation and then less number of papers shows the statistical correlation with satisfying the identification criteria [Geller (ed.), GRL, 1996], so that the phenomena had been controversial. However, recent related study in Kozu-Island, Japan which satisfied the criteria showed the robust correlation [Orihara and Kamogawa et al., PNAS, 2012]. Therefore, the preseismic geoelectric anomalies are expected to be a precursor. Preseismic lithosphere-atmosphere-ionosphere coupling has been intensively discussed [Kamogawa, Eos, 2006]. According to review based on the identification criteria with considering recent publications, plausible precursors have been found, which are tropospheric anomaly [Fujiwara and Kamogawa, GRL, 2004], daytime electron depletion in F region

  13. Lithospheric Mantle heterogeneities beneath northern Santa Cruz province, Argentina

    Science.gov (United States)

    Mundl, Andrea; Ntaflos, Theodoros; Bjerg, Ernesto

    2013-04-01

    interstitial clinopyroxene appears to be of metasomatic origin. The clinopyroxene from cumulate dunites has depleted LREE abundances and low HREE indicating that they have been formed from residual melts. In contrast, clinopyroxene from mantle dunites has enriched LREE (10 x PM) and LILE suggesting that the metasomatic agent was fluid-rich silicate melt. Calculated equilibrium conditions cover a wide range, from 800 to 1100 °C. Considering the crustal thickness in the area being around 35 km, a pressure between 12 and 17 kbar can be assumed as reasonable, indicating that xenoliths were extracted from shallow depths, in the order of 40 to 60 km. Model calculations have shown that the Lithospheric Mantle beneath Don Camilo is fertile and that spinel peridotites experienced low degrees of partial melting (2-8% batch melting in the spinel peridotite field). The metasomatic agent was a fluid rich silicate melt presumably similar to that which affected the xenoliths from Cerro Clark locality, north of Don Camilo. The clinopyroxenes with the highest Sr and lowest Nd isotopic signatures suggest that the metasomatism was an old event apparently not associated to the interaction of the Lithospheric Mantle in southern Patagonia with downgoing Nazca and Antarctic plates.

  14. Age differences in how consumers behave following exposure to DTC advertising.

    Science.gov (United States)

    DeLorme, Denise E; Huh, Jisu; Reid, Leonard N

    2006-01-01

    This study was conducted to provide additional evidence on how consumers behave following direct-to-consumer (DTC) advertising exposure and to determine if there are differences in ad-prompted acts (drug inquiry and drug requests) between different age groups (i.e., older, mature, and younger adults). The results suggest that younger, mature, and older consumers are all moved to act by DTC drug ads, but that each age group behaves in different ways. Somewhat surprisingly, age was not predictive of ad-prompted behavior. DTC advertising was no more effective at moving older consumers to behave than their younger counterparts. These results suggest that age does not matter that much when it comes to the "moving power" of prescription drug advertising, even though research indicates that older consumers are more vulnerable to the persuasive effects of communication.

  15. Action potential waveform variability limits multi-unit separation in freely behaving rats.

    Directory of Open Access Journals (Sweden)

    Peter Stratton

    Full Text Available Extracellular multi-unit recording is a widely used technique to study spontaneous and evoked neuronal activity in awake behaving animals. These recordings are done using either single-wire or multiwire electrodes such as tetrodes. In this study we have tested the ability of single-wire electrodes to discriminate activity from multiple neurons under conditions of varying noise and neuronal cell density. Using extracellular single-unit recording, coupled with iontophoresis to drive cell activity across a wide dynamic range, we studied spike waveform variability, and explored systematic differences in single-unit spike waveform within and between brain regions as well as the influence of signal-to-noise ratio (SNR on the similarity of spike waveforms. We also modelled spike misclassification for a range of cell densities based on neuronal recordings obtained at different SNRs. Modelling predictions were confirmed by classifying spike waveforms from multiple cells with various SNRs using a leading commercial spike-sorting system. Our results show that for single-wire recordings, multiple units can only be reliably distinguished under conditions of high recording SNR (≥ 4 and low neuronal density (≈ 20,000/ mm(3. Physiological and behavioural changes, as well as technical limitations typical of awake animal preparations, reduce the accuracy of single-channel spike classification, resulting in serious classification errors. For SNR <4, the probability of misclassifying spikes approaches 100% in many cases. Our results suggest that in studies where the SNR is low or neuronal density is high, separation of distinct units needs to be evaluated with great caution.

  16. Lithosphere structure and upper mantle characteristics below the Bay of Bengal

    Science.gov (United States)

    Rao, G. Srinivasa; Radhakrishna, M.; Sreejith, K. M.; Krishna, K. S.; Bull, J. M.

    2016-07-01

    The oceanic lithosphere in the Bay of Bengal (BOB) formed 80-120 Ma following the breakup of eastern Gondwanaland. Since its formation, it has been affected by the emplacement of two long N-S trending linear aseismic ridges (85°E and Ninetyeast) and by the loading of ca. 20-km of sediments of the Bengal Fan. Here, we present the results of a combined spatial and spectral domain analysis of residual geoid, bathymetry and gravity data constrained by seismic reflection and refraction data. Self-consistent geoid and gravity modelling defined by temperature-dependent mantle densities along a N-S transect in the BOB region revealed that the depth to the lithosphere-asthenosphere boundary (LAB) deepens steeply from 77 km in the south to 127 km in north, with the greater thickness being anomalously thick compared to the lithosphere of similar-age beneath the Pacific Ocean. The Geoid-Topography Ratio (GTR) analysis of the 85°E and Ninetyeast ridges indicate that they are compensated at shallow depths. Effective elastic thickness (Te) estimates obtained through admittance/ coherence analysis as well as the flexural modelling along these ridges led to the conclusions: (i) 85°E Ridge was emplaced in off-ridge environment (Te = 10-15 km); (ii) the higher Te values of ˜25 km over the Afanasy Nikitin Seamount (ANS) reflect the secondary emplacement of the seamount peaks in off-ridge environment, (iii) that the emplacement of the Ninetyeast Ridge north of 2°N occurred in an off-ridge environment as indicated by higher Te values (25-30 km). Furthermore, the admittance analysis of geoid and bathymetry revealed that the admittance signatures at wavelengths >800 km are compensated by processes related to upper mantle convection.

  17. Magnetotelluric investigations of the lithosphere beneath the central Rae craton, mainland Nunavut, Canada

    Science.gov (United States)

    Spratt, Jessica E.; Skulski, Thomas; Craven, James A.; Jones, Alan G.; Snyder, David B.; Kiyan, Duygu

    2014-03-01

    New magnetotelluric soundings at 64 locations throughout the central Rae craton on mainland Nunavut constrain 2-D resistivity models of the crust and lithospheric mantle beneath three regional transects. Responses determined from colocated broadband and long-period magnetotelluric recording instruments enabled resistivity imaging to depths of > 300 km. Strike analysis and distortion decomposition on all data reveal a regional trend of 45-53°, but locally the geoelectric strike angle varies laterally and with depth. The 2-D models reveal a resistive upper crust to depths of 15-35 km that is underlain by a conductive layer that appears to be discontinuous at or near major mapped geological boundaries. Surface projections of the conductive layer coincide with areas of high grade, Archean metasedimentary rocks. Tectonic burial of these rocks and thickening of the crust occurred during the Paleoproterozoic Arrowsmith (2.3 Ga) and Trans-Hudson orogenies (1.85 Ga). Overall, the uppermost mantle of the Rae craton shows resistivity values that range from 3000 Ω m in the northeast (beneath Baffin Island and the Melville Peninsula) to 10,000 Ω m beneath the central Rae craton, to >50,000 Ω m in the south near the Hearne Domain. Near-vertical zones of reduced resistivity are identified within the uppermost mantle lithosphere that may be related to areas affected by mantle melt or metasomatism associated with emplacement of Hudsonian granites. A regional decrease in resistivities to values of 500 Ω m at depths of 180-220 km, increasing to 300 km near the southern margin of the Rae craton, is interpreted as the lithosphere-asthenosphere boundary.

  18. Lithospheric flexure under the Hawaiian volcanic load: Internal stresses and a broken plate revealed by earthquakes

    Science.gov (United States)

    Klein, Fred W.

    2016-04-01

    Several lines of earthquake evidence indicate that the lithospheric plate is broken under the load of the island of Hawai`i, where the geometry of the lithosphere is circular with a central depression. The plate bends concave downward surrounding a stress-free hole, rather than bending concave upward as with past assumptions. Earthquake focal mechanisms show that the center of load stress and the weak hole is between the summits of Mauna Loa and Mauna Kea where the load is greatest. The earthquake gap at 21 km depth coincides with the predicted neutral plane of flexure where horizontal stress changes sign. Focal mechanism P axes below the neutral plane display a striking radial pattern pointing to the stress center. Earthquakes above the neutral plane in the north part of the island have opposite stress patterns; T axes tend to be radial. The M6.2 Honomu and M6.7 Kiholo main shocks (both at 39 km depth) are below the neutral plane and show radial compression, and the M6.0 Kiholo aftershock above the neutral plane has tangential compression. Earthquakes deeper than 20 km define a donut of seismicity around the stress center where flexural bending is a maximum. The hole is interpreted as the soft center where the lithospheric plate is broken. Kilauea's deep conduit is seismically active because it is in the ring of maximum bending. A simplified two-dimensional stress model for a bending slab with a load at one end yields stress orientations that agree with earthquake stress axes and radial P axes below the neutral plane. A previous inversion of deep Hawaiian focal mechanisms found a circular solution around the stress center that agrees with the model. For horizontal faults, the shear stress within the bending slab matches the slip in the deep Kilauea seismic zone and enhances outward slip of active flanks.

  19. Practical Conditions for Well-behaved-ness of Anisotropic Voronoi Diagrams

    CERN Document Server

    Canas, Guillermo D

    2012-01-01

    Recently, simple conditions for well-behaved-ness of anisotropic Voronoi diagrams have been proposed. While these conditions ensure well-behaved-ness of two types of practical anisotropic Voronoi diagrams, as well as the geodesic-distance one, in any dimension, they are both prohibitively expensive to evaluate, and not well-suited for typical problems in approximation or optimization. We propose simple conditions that can be efficiently evaluated, and are better suited to practical problems of approximation and optimization. The practical utility of this analysis is enhanced by the fact that orphan-free anisotropic Voronoi diagrams have embedded triangulations as duals.

  20. Unraveling African plate structure from elevation, geoid and geology data: implications for the impact of mantle flow and sediment transfers on lithospheric deformation

    Science.gov (United States)

    Bajolet, Flora; Robert, Alexandra; Chardon, Dominique; Rouby, Delphine

    2017-04-01

    The aim of our project is to simulate the long-wavelength, flexural isostatic response of the African plate to sediment transfers due to Meso-Cenozoic erosion - deposition processes in order to extract the residual topography driven by mantle dynamics. The first step of our project consists in computing crustal and lithospheric thickness maps of the African plate considering its main geological components (cratons, mobile belts, basins, rifts and passive margins of various ages and strengths). In order to consider these heterogeneities, we compute a 2D distribution of crustal densities and thermal parameters from geological data and use it as an input of our modeling. We combine elevation and geoid anomaly data using a thermal analysis, following the method of Fullea et al. (2007) in order to map crustal and lithospheric thicknesses. In this approach, we assume local isostasy and consider a four-layer model made of crust and lithospheric mantle plus seawater and asthenosphere. In addition, we compare our results with crustal and lithospheric thickness datasets compiled from bibliography and existing global models. The obtained crustal thicknesses range from 28 to 42km, with the thickest crust confined to the northern part of the West African Craton, the Kaapvaal craton, and the Congo cuvette. The crust in the East African Rift appears unrealistically thick (40-45 km) as it is not isotatically compensated, highlighting the dynamic effect of the African superswell. The thinnest crust (28-34km) follows a central East-West trend coinciding with Cretaceous rifts and the Cameroon volcanic line. The lithosphere reaches 220 km beneath the Congo craton, but remains globally thin (ca. 120-180 km) compared to tomographic models and considering the age of most geological provinces. As for the crust, the thinnest lithosphere is located in areas of Cretaceous-Jurassic rifting, suggesting that the lithosphere did not thermally recover from Mesozoic rifting. A new elastic

  1. Parameters driving strain localization in the lithosphere are highly scale-dependent

    Science.gov (United States)

    Jolivet, Laurent

    2016-04-01

    Modelling lithospheric deformation requires specifying mechanisms that promote strain localization. This can be done in different ways, such as the inclusion of weaker zones in the model setup (to initiate subduction or slab tearing, for instance) or using various sorts of weakening processes depending upon temperature, grain-size, fluid content or metamorphic reactions, among others. In most cases, this choice is ad hoc because the relevant parameters are largely unknown, especially at the scale of geodynamic models. Two lines of research have been developed, a traditional one which seeks to determine the rheological parameters of natural or synthetic rocks experimentally, and a more recent one, promoted by the development of fast computing, which aims at reproducing a natural tectonic or rheological evolution through time, not only geometries. The latter requires that the parameters allowing this reproduction are significant at the scale of the model, and which may be different from those obtained in the experimental lab, thus questioning the extrapolation through a wide range of scales of experimental parameters. This apparent discrepancy is due to the intrinsic complexity of the lithosphere, and even more so for the continental lithosphere with its highly heterogeneous crust and its long tectonic history, which implies the co-existence of many different parameters active in nature. In this presentation, we review the main localizing factors and look to the range of scales in which they are significant. Small-scale processes such as grain-size reduction, coexistence of several mineralogical phases with different strength and rheological behaviour, fluid-rock interactions and/or metamorphic reactions, often cannot initiate strain localization in nature but are all efficient to locally reduce the strength of rock material once localization has started. Some exceptions to this rule, however, exist, such as the mixing of ductile and brittle behaviour in the same

  2. The EarthChem Deep Lithosphere Dataset: Digital Access to Mantle Xenolith Petrological Data

    Science.gov (United States)

    Block, K. A.; Lehnert, K. A.; Walker, J. D.; Fishman, A.; McDonough, W. F.

    2006-12-01

    Establishment of a geologic framework for the USArray mission of EarthScope largely depends on community efforts that facilitate the integration of seismic data with petrologic, gravity, structural, and other geologic data. The EarthChem federation of interoperable databases (www.earthchem.org) provides cyberinfrastructure in which large geochemical data collections are assembled and curated to maximize data usability and accessibility. In an effort to address the needs of the GeoFrame/USArray community, EarthChem is developing the Deep Lithosphere Petrological Dataset to provide easy access to an integrated, comprehensive, global set of petrological data from upper mantle and lower crustal rocks. The initial focus for EarthChem's Deep Lithosphere dataset is xenolith data from geographic locations identified by GeoFrame as relevant to the USArray mission. Data are compiled in a relational database that complements the data collections of NAVDAT, GEOROC, and PetDB, and which together can be accessed and downloaded through the EarthChem Portal. The web interface permits the user to query by sample location, rock type, mineral, inclusion, author, major oxide, trace element and isotopic composition to build customized datasets. Additionally, radiometric age, host rock information, and model data such as pressure and temperature, including information about the geobarometer/geothermometer used by authors in their calculations, are included in the dataset to provide the perspective of geochemical modeling on the nature of the sub-continental mantle and lower crust for correlation with seismic imaging and geodynamic modeling.

  3. Lithospheric expression of cenozoic subduction, mesozoic rifting and the Precambrian Shield in Venezuela

    Science.gov (United States)

    Masy, Jeniffer; Niu, Fenglin; Levander, Alan; Schmitz, Michael

    2015-01-01

    We have combined surface wave tomography with Ps and Sp receiver-function images based on common-conversion-point (CCP) stacking to study the upper mantle velocity structure, particularly the lithosphere-asthenosphere boundary (LAB), beneath eastern and central Venezuela. Rayleigh phase velocities in the frequency range of 0.01-0.05 Hz (20-100 s in period) were measured using the two-plane-wave method and finite-frequency kernels, and then inverted on a 0.5° × 0.5° grid. The phase velocity dispersion data at grid points were inverted for 1D shear velocity profiles using initial crust-mantle velocity models constructed from previous studies. The 3D velocity model and receiver-function images were interpreted jointly to determine the depth of the LAB and other upper mantle features. The tomographic images revealed two high velocity anomalies extending to more than ∼200 km depth. One corresponds to the top of the subducting Atlantic plate beneath the Serrania del Interior. The other anomaly is a highly localized feature beneath the Maturin Basin. The LAB depth varies significantly in the study region: It is located at ∼110 km depth beneath the Guayana Shield, and reaches ∼130 km at the northern edge of the Maturin Basin, which might be related to the downward flexural bending due to thrust loading of the Caribbean plate and pull from the subducting Atlantic plate. Immediately to the west, the lithosphere is thin (∼50-60 km) along the NE-SW trending Espino Graben from the Cariaco basin to the Orinoco River at the northern edge of the craton. The LAB in this region is the top of a pronounced low velocity zone. Westward, the lithosphere deepens to ∼80 km depth beneath the Barinas Apure Basin, and to ∼90 km beneath the Neogene Merida Andes and Maracaibo block. Both upper mantle velocity structure and lithosphere thickness correlate well with surface geology and are consistent with northern South American tectonics.

  4. Differing presynaptic contributions to LTP and associative learning in behaving mice

    Directory of Open Access Journals (Sweden)

    Noelia Madroñal

    2009-05-01

    Full Text Available The hippocampal CA3-CA1 synapse is an excellent experimental model for studying the interactions between short- and long-term plastic changes taking place following high-frequency stimulation (HFS of Schaffer collaterals and during the acquisition and extinction of a classical eyeblink conditioning in behaving mice. Input/output curves and a full-range paired-pulse study enabled determining the optimal intensities and inter-stimulus intervals for evoking paired-pulse facilitation (PPF or depression (PPD at the CA3-CA1 synapse. Long-term potentiation (LTP induced by HFS lasted ≈ 10 days. HFS-induced LTP evoked an initial depression of basal PPF. Recovery of PPF baseline values was a steady and progressive process lasting ≈ 20 days, i.e., longer than the total duration of the LTP. In a subsequent series of experiments, we checked whether PPF was affected similarly during activity-dependent synaptic changes. Animals were conditioned using a trace paradigm, with a tone as a conditioned stimulus (CS and an electrical shock to the trigeminal nerve as an unconditioned stimulus (US. A pair of pulses (40 ms interval was presented to the Schaffer collateral-commissural pathway to evoke field EPSPs (fEPSPs during the CS-US interval. Basal PPF decreased steadily across conditioning sessions (i.e., in the opposite direction to that during LTP, reaching a minimum value during the 10th conditioning session. Thus, LTP and classical eyeblink conditioning share some presynaptic mechanisms, but with an opposite evolution. Furthermore, PPF and PPD might play a homeostatic role during long-term plastic changes at the CA3-CA1 synapse.

  5. Riding on the fast lane: how sea turtles behave in post-nesting migration

    Science.gov (United States)

    Wang, Y.-H.; Cheng, I.-J.; Centurioni, L.

    2014-07-01

    Sea turtles are known as powerful swimmers. How do they behave when riding in strong currents during their migrations? In this study, three, satellite-tagged, post-nesting green turtles travelled from Lanyu Island, east of Taiwan, partly within the Kuroshio to their foraging sites approximately 1000 km away in the Ryukyu Archipelago. Their swimming behaviors were analyzed by comparing their migration velocities estimated from Argos tag data with ocean currents derived from a data simulation model and from AVISO advection estimates. Results suggest that the turtles take advantage of Kuroshio during the initial portion of their migration routes. They must then make a great effort to swim eastward, at speeds over 1 m s-1, toward their foraging sites to avoid being carried off course by the strong current. The cues that might cause the change in swimming direction were evaluated with a Principle Component Analysis. The factors considered are ambient current velocity, wind, eddy activity (vorticity), magnetic field (latitude) and water temperature. The analysis shows that the ambient current and water temperature are negatively correlated with the eastward swimming velocity. This suggests that the changes in ocean current and a drop of water temperature, likely due to eddies impinging on the Kuroshio, may trigger the eastward swimming. Despite the differences among migratory routes of three Argos-tagged turtles after leaving the Kuroshio, they all reached foraging sites in the same general area. That suggests there may be more complex cues that guide the turtles to their foraging sites during their post-nesting migrations.

  6. Imaging and Interpreting Lithospheric Structure in the Southern Appalachians using the SESAME Broadband Array

    Science.gov (United States)

    Verellen, D.; Alberts, E.; Parker, H., Jr.; Hawman, R. B.; Fischer, K. M.; Wagner, L. S.

    2016-12-01

    The Southeastern Suture of the Appalachian Margin Experiment (SESAME) was designed to investigate the role of crustal and subcrustal deformation associated with Alleghanian collision and Mesozoic extension of the lithosphere across the southeastern United States. It involved the deployment of three profiles with a total length of 1300 kilometers. In this study, we use zero-offset reflections generated by the global seismic phase PKIKP as a virtual source to image structure within the lithosphere. Together with Consortium for Continental Reflection Profiling (COCORP) surveys, these data allow us to study the nature of the Moho and other discontinuities over a wide range of scales. A major objective of this work is to track variations in the detailed structure of the crust-mantle transition from Grenville basement beneath the Valley & Ridge to accreted terranes beneath the Coastal Plain and across the boundary between Laurentian and Gondwanan lithosphere. We also investigate the scale of layering in the uppermost mantle and its possible relation to contrasts in anisotropy in relation to shearing. Preliminary findings for a single earthquake (mb=6.1) recorded along a profile trending northwest across the Carolina Terrane, Inner Piedmont, and Blue Ridge show dipping reflectors at a depth of approximately 15-20 km in the crust, and layered, relatively flat-lying reflectors at a depth of roughly 70 km in the upper mantle. Ongoing work includes stacking of waveforms for multiple events in order to enhance signal-to-noise levels and construction of images for two additional north-south trending profiles across the Coastal Plain, where deep structure is more difficult to image due to reverberations within low-velocity sediments. The resulting broadband images of P-wave reflectivity will be used in combination with models of S-wave reflectivity derived by other methods to provide insight into the complex deformational history of the southern Appalachian system.

  7. Mechanically, the shoot apical meristem of Arabidopsis behaves like a shell inflated by a pressure of about 1 MPa

    Directory of Open Access Journals (Sweden)

    Léna eBeauzamy

    2015-11-01

    Full Text Available In plants, the shoot apical meristem contains the stem cells and is responsible for the generation of all aerial organs. Mechanistically, organogenesis is associated with an auxin-dependent local softening of the epidermis. This has been proposed to be sufficient to trigger outgrowth, because the epidermis is thought to be under tension and stiffer than internal tissues in all the aerial part of the plant. However, this has not been directly demonstrated in the shoot apical meristem. Here we tested this hypothesis in Arabidopsis using indentation methods and modeling. We considered two possible scenarios: either the epidermis does not have unique properties and the meristem behaves as a homogeneous linearly-elastic tissue, or the epidermis is under tension and the meristem exhibits the response of a shell under pressure. Large indentation depths measurements with a large tip (~size of the meristem were consistent with a shell-like behavior. This also allowed us to deduce a value of turgor pressure, estimated at 0.82 ± 0.16 MPa. Indentation with atomic force microscopy provided local measurements of pressure in the epidermis, further confirming the values obtained from large deformations. Altogether, our data demonstrate that the Arabidopsis shoot apical meristem behaves like a shell under a MPa range pressure and support a key role for the epidermis in shaping the shoot apex.

  8. Hippocampal activity during transient respiratory events in the freely behaving cat

    DEFF Research Database (Denmark)

    Poe, G R; Kristensen, Morten Pilgaard; Rector, D M;

    1996-01-01

    We measured dorsal hippocampal activity accompanying sighs and apnea using reflectance imaging and electrophysiologic measures in freely behaving cats. Reflected 660-nm light from a 1-mm2 area of CA1 was captured during sighs and apnea at 25 Hz through a coherent image conduit coupled to a charge...

  9. A family of well-behaved Karmarkar spacetimes describing interior of relativistic stars

    Energy Technology Data Exchange (ETDEWEB)

    Singh, K. Newton [National Defence Academy, Department of Physics, Pune (India); Pant, Neeraj [National Defence Academy, Department of Mathematics, Pune (India)

    2016-10-15

    We present a family of new exact solutions for relativistic anisotropic stellar objects by considering a four-dimensional spacetime embedded in a five-dimensional pseudo Euclidean space, known as Class I solutions. These solutions are well behaved in all respects, satisfy all energy conditions, and the resulting compactness parameter is also within Buchdahl limit. The well-behaved nature of the solutions for a particular star solely depends on the index n. We have discussed the solutions in detail for the neutron star XTE J1739-285 (M = 1.51M {sub CircleDot}, R = 10.9 km). For this particular star, the solution is well behaved in all respects for 8 ≤ n ≤ 20. However, the solutions with n < 8 possess an increasing trend of the sound speed and the solutions belonging to n > 20 disobey the causality condition. Further, the well-behaved nature of the solutions for PSR J0348+0432 (2.01M {sub CircleDot}, 11 km), EXO 1785-248 (1.3M {sub CircleDot}, 8.85 km), and Her X-1 (0.85M {sub CircleDot}, 8.1 km) are specified by the index n with limits 24 ≤ n ≤ 54, 1.5 ≤ n ≤ 4, and 0.8 ≤ n ≤ 2.7, respectively. (orig.)

  10. A family of well-behaved Karmarkar spacetime describing interior of relativistic stars

    CERN Document Server

    Singh, Ksh Newton

    2016-01-01

    We are presenting a family of new exact solutions for relativistic anisotropic stellar objects by considering four dimensional spacetime embedded in five dimensional Pseudo Euclidean space known as Class I solutions. These solutions are well-behaved in all respects and free from central singularities. It also satisfies all energy conditions and the resulting compactness parameter is within Buchdahl limit. Here we discovered that the mass of compact stars represented by these solution depends on the parameter n and the radius rb. The well-behaved nature of the solutions depends on mass and radius of the chosen stars. We have discussed the solutions in detail for the neutron star XTE J1739-217 (M = 1.51$M_\\odot$, R = 10.9 km). For the particle star, the solution is well behaved in all respects for n = 8 to n = 20, where the solutions with n 20 disobeyed causality condition. However, for PSR J0348+0432 (2.01$M_\\odot$, 11km), the parameter n may approach upto 25 and the solution is well-behaved.

  11. The Gutenberg discontinuity: melt at the lithosphere-asthenosphere boundary.

    Science.gov (United States)

    Schmerr, Nicholas

    2012-03-23

    The lithosphere-asthenosphere boundary (LAB) beneath ocean basins separates the upper thermal boundary layer of rigid, conductively cooling plates from the underlying ductile, convecting mantle. The origin of a seismic discontinuity associated with this interface, known as the Gutenberg discontinuity (G), remains enigmatic. High-frequency SS precursors sampling below the Pacific plate intermittently detect the G as a sharp, negative velocity contrast at 40- to 75-kilometer depth. These observations lie near the depth of the LAB in regions associated with recent surface volcanism and mantle melt production and are consistent with an intermittent layer of asthenospheric partial melt residing at the lithospheric base. I propose that the G reflectivity is regionally enhanced by dynamical processes that produce melt, including hot mantle upwellings, small-scale convection, and fluid release during subduction.

  12. Physico-chemical constraints on cratonic lithosphere discontinuities

    Science.gov (United States)

    Aulbach, Sonja; Rondenay, Stéphane; Huismans, Ritske

    2014-05-01

    The origins of the mid-lithospheric discontinuity (MLD) and lithosphere-asthenosphere boundary (LAB) have received much attention over the recent years. Peculiarities of cratonic lithosphere construction - compositional and rheological stratification due to thickening in collisional settings or by plume subcretion, multiple metasomatic overprints due to longevity - offer a variety of possibilities for the generation of discontinuities. Interconnected small degrees of conductive partial melt (carbonate-rich melts, such as carbonatites and kimberlites, or highly alkaline melts) at the cratonic LAB, which produce seismic discontinuities, may be generated in the presence of volatiles. These depress the peridotite solidus sufficiently to intersect the mantle adiabat at depths near the cratonic LAB at ~160-220 km, i.e. above the depth of metal saturation where carbonatite becomes unstable. The absence of agreement between the different seismic and magnetotelluric estimates for the depth of the LAB beneath Kaapvaal may be due to impingement of a plume, leading to a pervasively, but heterogeneously metasomatised ('asthenospherised') hot and deep root. Such a root and hot sublithosphere may yield conflicting seismic-thermal-geochemical depths for the LAB. The question arises whether the chemical boundary layer should be defined as above or below the asthenospherised part of the SCLM, which has preserved isotopic, compositional (non-primitive olivine forsterite content) and physical evidence (e.g. from teleseismic tomography and receiver functions) for a cratonic heritage and which therefore is still distinguishable from the asthenospheric mantle. If cratonic lithosphere overlies anomalously hot mantle for extended periods of time, the LAB may be significantly thinned, aided by penetration of relatively high-degree Fe-rich partial melts, as has occurred beneath the Tanzanian craton. Xenoliths from the deep Slave craton show little evidence for 'asthenospherisation'. Its root

  13. Plate tectonics on the early Earth: Limitations imposed by strength and buoyancy of subducted lithosphere

    Science.gov (United States)

    van Hunen, Jeroen; van den Berg, Arie P.

    2008-06-01

    The tectonic style and viability of modern plate tectonics in the early Earth is still debated. Field observations and theoretical arguments both in favor and against the uniformitarian view of plate tectonics back until the Archean continue to accumulate. Here, we present the first numerical modeling results that address for a hotter Earth the viability of subduction, one of the main requirements for plate tectonics. A hotter mantle has mainly two effects: 1) viscosity is lower, and 2) more melt is produced, which in a plate tectonic setting will lead to a thicker oceanic crust and harzburgite layer. Although compositional buoyancy resulting from these thick crust and harzburgite might be a serious limitation for subduction initiation, our modeling results show that eclogitization significantly relaxes this limitation for a developed, ongoing subduction process. Furthermore, the lower viscosity leads to more frequent slab breakoff, and sometimes to crustal separation from the mantle lithosphere. Unlike earlier propositions, not compositional buoyancy considerations, but this lithospheric weakness could be the principle limitation to the viability of plate tectonics in a hotter Earth. These results suggest a new explanation for the absence of ultrahigh-pressure metamorphism (UHPM) and blueschists in most of the Precambrian: early slabs were not too buoyant, but too weak to provide a mechanism for UHPM and exhumation.

  14. Dome and Keel dynamics in the hot Archean lithosphere: a numerical approach

    Science.gov (United States)

    Duclaux, G.; Thebaud, N.; Gessner, K.; Doublier, M.

    2012-12-01

    The long-term interactions between greenstone belts and adjacent granitoids domes is key for understanding hot lithosphere rheology, crustal evolution and major ore deposits formation in Archean terrains. Some few tectonic processes have been proposed to explain both local and regional granite/greenstone finite deformation patterns observed in Archean terrains such as the West Australian Pilbara or Yilgarn cratons, including crustal extension following gravitational collapse, metamorphic core complex formation, folding interferences, and gravity driven deformation associated with exhumation of granitoids relative to a supracrustal cover. We propose to assess gravity driven deformation processes from simplified 2-D and 3-D thermo-mechanical numerical experiments using Underworld. A series of visco-plastic experiments under controlled boundary conditions have allowed us to identify three distinct stages in the hot lithosphere tectonic evolution: (1) an internal heating phase, (2) an inversion phase where dense mafic materials fall toward the lower crust while mid-crustal granitoids raise toward the surface, and (3) a freezing phase where the system stops. The relative duration of these phases is dependent on models initial geometries and inherited structures, materials thermal properties and rheologies, and the rheological contrast between granitoids and greenstones. We compare our experimental results with field observations and geophysical data from the Yilgarn craton in order to validate the gravity driven tectonic model, and eventually constrain the range of thermal and mechanical parameters that best capture Archean crustal dynamics.

  15. Planetary Lithosphere-Outer Core-Inner Core-Mantle Coupled Evolution Over the Entire Age of the Solar System

    Science.gov (United States)

    Tackley, P. J.; Nakagawa, T.; Louro Lourenço, D. J.; Rozel, A.

    2016-12-01

    Core evolution is determined by the heat flux extracted by the mantle as a function of time, which is itself dependent on the tectonic mode of the lithosphere and its evolution with time (Nakagawa & Tackley, 2015), as well as other factors. Thus, lithosphere, mantle and core must be treated as a coupled system in order to understand long-term core evolution. We have performed coupled modelling of mantle and core using a 2D or 3D mantle convection code with parameterized core. By plastic yielding the lithosphere may develop plate tectonics, stagnant lid, or episodic lid modes of tectonics, and the mode can change with time. Our recent models demonstrate that crustal production arising from partial melting plays a major role in facilitating plate tectonics; when this is included plate tectonics or episodic lithospheric overturn can occur even when purely thermal models predict a stagnant lithosphere (Lourenco et al, 2016). These models also demonstrate transitions between tectonic models as the planet cools. Considering Earth's core evolution, there is only a limited parameter range in which the heat extracted from the core is large enough at all times for a geodynamo to exist, but small enough that the core did not cool more than observed, a balance that becomes even more difficult if the core thermal conductivity is as high as recently thought (Nakagawa & Tackley, 2013). Models typically predict too much core cooling, which can be reduced by dense layering above the CMB: in particular such a dense, compositionally-distinct layer existing from early times is important for avoiding early too-rapid core cooling (Nakagawa & Tackley, 2014). Our latest models treat Earth evolution from the magma ocean phase to the present day (Lourenco et al., presented at this meeting). In these models an initially very hot core cools extremely rapidly until it reaches the rheological transition of mantle rock ( 40% melt fraction). Therefore, it is difficult for the core temperature at

  16. Three-dimensional lithospheric deformation and gravity anomalies associated with oblique continental collision in South Island, New Zealand

    Science.gov (United States)

    Scherwath, Martin; Stern, Tim; Davey, Fred; Davies, Rob

    2006-11-01

    Isostatic considerations exhibit differences between the northern, central and southern parts of the Pacific-Australian plate collision in South Island, New Zealand. In the northern part mean elevations are moderate and the gravity low is small; the central part contains the highest elevations, and gravity and elevations correspond to each other relatively well; and in the southern part the gravity low is strongest whereas the mean elevations are moderate again. These differences indicate changes in the character of the isostatic compensation and are explained by increased thickening and widening of the crustal root from north to south, and also by the long wavelength gravity response to a mantle density anomaly that increases towards the south. A simple 3-D gravity model is derived that includes the detailed crustal structures from the South Island GeopHysical Transect (SIGHT) experiment as well as a high-density anomaly in the mantle inferred from teleseismic data. The model indicates that cold and, therefore, dense upper mantle material penetrates the asthenosphere to a greater extent in the south, similar to the behaviour of an apparently highly ductile lower crust. As plate reconstruction suggests more lithospheric shortening in the north, our model corresponds to lithospheric material escaping laterally to the south, almost perpendicular to the compression caused by lithospheric shortening of the mantle. Therefore, in addition to the prevailing mantle shear in New Zealand, there may also be a component of extrusional mantle creep beneath the Southern Alps orogen, which could have caused some of the observed large seismic anisotropy in this region. We may have also found evidence for submerged Eocene-Miocene oceanic lithosphere beneath the southeastern part of South Island that has been unaccounted for after plate reconstruction.

  17. Seismic structure of the North American lithosphere and upper mantle imaged using Surface and S waveform tomography

    Science.gov (United States)

    Schaeffer, A. J.; Lebedev, S.

    2010-12-01

    The evolution, stability, and dynamics of continental lithosphere remain a central focus of Earth Science research. The continued deployment of the US Array is producing a massive new dataset that samples North America at scales from tectonic units to continent-wide domains and enables resolution of structure and deformation of the lithosphere previously possible only at regional scales. With this resolving power come new challenges relating to efficient management and processing of such large data volumes. In this study, we have assembled a dataset comprising over 3.5 million three-component broadband seismic waveforms from more than 3000 stations. We augment available US Array stations with ~600 additional North American stations of the GSN and affiliates, Canadian National Seismograph Network, regional arrays, past PASSCAL experiments, and other stations from Iceland, Greenland, Central and South America, the Caribbean, and several Mid-Atlantic Islands. We exploit the resolving power of this unprecedentedly large dataset using the Automated Multimode Inversion of surface- and S-wave forms. The waveforms are inverted for path-averaged linear constraints on elastic structure along the source-receiver paths. The linear equations are then simultaneously solved for a high-resolution 3D upper mantle shear velocity model of the continent. We present a model of the North American continent's and the surrounding Ocean's (Pacific, Atlantic, Gulf of Mexico) upper mantle structure down to the 660 km discontinuity. Clearly identifiable boundaries between different tectonic features such as basins and relic mountain ranges are readily observable. For example, a strong correlation between the Hudson Bay geoid anomaly can be identified with an underlying domain of particularily cold cratonic lithosphere. Our model also includes the 3D distribution of azimuthal anisotropy within these structures, which provides new insight into past and present dynamics of the lithosphere and

  18. A Top to Bottom Lithospheric Study of Africa and Arabia

    Energy Technology Data Exchange (ETDEWEB)

    Pasyanos, M

    2006-10-31

    We study the lithospheric structure of Africa, Arabia and adjacent oceanic regions with fundamental-mode surface waves over a wide period range. Including short period group velocities allows us to examine shallower features than previous studies of the whole continent. In the process, we have developed a crustal thickness map of Africa. Main features include crustal thickness increases under the West African, Congo, and Kalahari cratons. We find crustal thinning under Mesozoic and Cenozoic rifts, including the Benue Trough, Red Sea, and East, Central, and West African rift systems. Crustal shear wave velocities are generally faster in oceanic regions and cratons, and slower in more recent crust and in active and formerly active orogenic regions. Deeper structure, related to the thickness of cratons and modern rifting, is generally consistent with previous work. Under cratons we find thick lithosphere and fast upper mantle velocities, while under rifts we find thinned lithosphere and slower upper mantle velocities. There are no consistent effects in areas classified as hotspots, indicating that there seem to be numerous origins for these features. Finally, it appears that the African Superswell has had a significantly different impact in the north and the south, indicating specifics of the feature (temperature, time of influence, etc.) to be dissimilar between the two regions. Factoring in other information, it is likely that the southern portion has been active in the past, but that shallow activity is currently limited to the northern portion of the superswell.

  19. Constrained inversion as a hypothesis testing tool, what can we learn about the lithosphere?

    Science.gov (United States)

    Moorkamp, Max; Stewart, Fishwick; Jones, Alan G.

    2017-04-01

    Inversion of geophysical data constrained by a reference model is typically used to guide the inversion of low resolution data towards a geologically plausible solution. For example, a migrated seismic section can provide the location of lithological boundaries for potential field inversions. Here we consider the inversion of long-period magnetotelluric data constrained by models generated through surface wave inversion. In this case, we do not consider the surface wave model inherently better in any sense and want to guide the magnetotelluric inversion towards this model, but we want to test the hypothesis that both datasets can be explained by models with similar structure. If the hypothesis test is successful, i.e. we can fit the observations with a conductivity model with structural similarity to the seismic model, we have found an alternative explanation compared to the individual inversion and can use the differences to learn about the resolution of the magnetotelluric data and can improve our interpretation. Conversely, if the test refutes our hypothesis of coincident structure, we have found features in the models that are sensed fundamentally different by both methods which is potentially instructive on the nature of the anomalies. We use a MT dataset acquired in central Botswana over the Okwa terrane and the adjacent Kaapvaal and Zimbabwe Cratons together with a tomographic model for the region to illustrate and test this approach. Here, various conductive structures have been identified that bridge the Moho. Furthermore, the thickness of the lithosphere inferred from the different methods differs. In both cases the question is in how far this is a result of the ill-posed nature of inversion and in how far these differences can be reconciled. Thus this dataset is an ideal test case for our hypothesis testing approach. Finally, we will demonstrate how we can use the results of the constrained inversion to extract conductivity-velocity relationships in the

  20. Multi-Layer Strain Rate Field Controlled by Netlike Plastic-Flow in the Lithosphere in Central-Eastern Asia

    Institute of Scientific and Technical Information of China (English)

    Wang Sheng-zu

    2006-01-01

    According to the "Netlike Plastic-Flow (NPF)" continental dynamics model, the transition of the deformation regime from brittle in shallow layers to ductile in deep layers in the lithosphere, and the controlling effect of NPF in the lower lithosphere result in intraplate multilayer tectonic deformation. NPF is a viscous (plastic) flow accompanied by shear strain localization, forming a plastic-flow network in the lower lithosphere. The strain rates in the seismogenic layer can be estimated using the "earthquake-recurrence-interval" method, in which the strain rate is calculated in terms of the recurrence interval of two sequential carthquakes and the seismic probability of the second earthquake. The strains in the lower lithosphere are estimated using the "conjugate-angle" method, which takes the relationship between the conjugate angles and the compressive strains of the network, and calculates the characteristic strain rates in this layer from the strains and the durations of deformation inferred. The contour map of characteristic maximum principal compressive strain rates in the lower lithosphere in central-eastern Asia given in the paper shows strain rates with magnitudes on the order of 10-15 ~ 10-14/s in this region. The strain rates within the plastic-flow belts,which control seismic activities in the seismogenic layer, are greater than the characteristic strain rates of the network and, in addition, the strain rates and seismic activities in the seismogenic layer are also influenced by other factors, including the directive action of driving boundary along the upper crust, the effects of plastic-flow waves and the existence of the transitional weak layer distributed discontinuously between the upper and lower layers. The comparison between the strain rates in the seismogenic layer and the characteristic strain rates in the lower lithosphere for 11 potential hypocenter areas in the region from the Qinghai-Xizang (Tibet) plateau to the North China plain

  1. The elusive lithosphere-asthenosphere boundary (LAB) beneath cratons

    Science.gov (United States)

    Eaton, David W.; Darbyshire, Fiona; Evans, Rob L.; Grütter, Herman; Jones, Alan G.; Yuan, Xiaohui

    2009-04-01

    The lithosphere-asthenosphere boundary (LAB) is a first-order structural discontinuity that accommodates differential motion between tectonic plates and the underlying mantle. Although it is the most extensive type of plate boundary on the planet, its definitive detection, especially beneath cratons, is proving elusive. Different proxies are used to demarcate the LAB, depending on the nature of the measurement. Here we compare interpretations of the LAB beneath three well studied Archean regions: the Kaapvaal craton, the Slave craton and the Fennoscandian Shield. For each location, xenolith and xenocryst thermobarometry define a mantle stratigraphy, as well as a steady-state conductive geotherm that constrains the minimum pressure (depth) of the base of the thermal boundary layer (TBL) to 45-65 kbar (170-245 km). High-temperature xenoliths from northern Lesotho record Fe-, Ca- and Ti-enrichment, grain-size reduction and globally unique supra-adiabatic temperatures at 53-61 kbar (200-230 km depth), all interpreted to result from efficient advection of asthenosphere-derived melts and heat into the TBL. Using a recently compiled suite of olivine creep parameters together with published geotherms, we show that beneath cratons the probable deformation mechanism near the LAB is dislocation creep, consistent with widely observed seismic and electrical anisotropy fabrics. If the LAB is dry, it is probably diffuse (> 50 km thick) and high levels of shear stress (> 2 MPa or > 20 bar) are required to accommodate plate motion. If the LAB is wet, lower shear stress is required to accommodate plate motion and the boundary may be relatively sharp (≤ 20 km thick). The seismic LAB beneath cratons is typically regarded as the base of a high-velocity mantle lid, although some workers infer its location based on a distinct change in seismic anisotropy. Surface-wave inversion studies provide depth-constrained velocity models, but are relatively insensitive to the sharpness of the LAB

  2. Anisotropic Shear-Velocity Structure of the Lithosphere-Asthenosphere System in the Central Pacific from the NoMelt Experiment

    Science.gov (United States)

    Lin, P.; Gaherty, J. B.; Jin, G.; Collins, J. A.; Lizarralde, D.; Evans, R. L.; Hirth, G.

    2014-12-01

    Recent theoretical models of the seismic properties of mantle rocks predict seismic velocity profiles for mature oceanic lithosphere that are fundamentally inconsistent with the best observations of seismic velocities in two ways. Observations of strong positive velocity gradients with depth, and a very sharp and very shallow low-velocity asthenosphere boundary (LAB), both suggest that non-thermal factors such as bulk composition, mineral fabric, grain size, and dehydration play important roles in controlling the formation of the lithosphere, and thus the underlying LAB. There is little consensus on which of these factors are dominant, in part because observations of detailed lithosphere structure are limited. To address this discrepancy, we conducted the NoMelt experiment on ~70 Ma Pacific lithosphere between the Clarion & Clipperton fracture zones. The experiment consists of a 600x400 km array of broad-band ocean bottom seismometers (OBS) and magnetotelluric instruments, and an active-source reflection/refraction experiment. Here we characterize the shear-velocity structure and its seismic anisotropy across the lithosphere-asthenosphere system beneath the array using surface-wave dispersion. Of the 27 deployed instruments, 21 were recovered, all of which produced useful data on the seismometer and the differential pressure gauge in the 20-200 s period band. Energetic, high S/N Rayleigh waves and useful love waves are observ