WorldWideScience

Sample records for plate mantle sunda

  1. How mantle slabs drive plate tectonics.

    Science.gov (United States)

    Conrad, Clinton P; Lithgow-Bertelloni, Carolina

    2002-10-04

    The gravitational pull of subducted slabs is thought to drive the motions of Earth's tectonic plates, but the coupling between slabs and plates is not well established. If a slab is mechanically attached to a subducting plate, it can exert a direct pull on the plate. Alternatively, a detached slab may drive a plate by exciting flow in the mantle that exerts a shear traction on the base of the plate. From the geologic history of subduction, we estimated the relative importance of "pull" versus "suction" for the present-day plates. Observed plate motions are best predicted if slabs in the upper mantle are attached to plates and generate slab pull forces that account for about half of the total driving force on plates. Slabs in the lower mantle are supported by viscous mantle forces and drive plates through slab suction.

  2. Plate tectonics: Delayed response to mantle pull

    Science.gov (United States)

    Nedimović, Mladen R.

    2016-08-01

    At mid-ocean ridges, the directions in which plates spread and the underlying mantle flows were thought to broadly align. A synthesis of results from ridges that spread at a variety of rates reveals that instead there may be a systematic skew.

  3. Slab detachment of subducted Indo-Australian plate beneath Sunda arc, Indonesia

    Indian Academy of Sciences (India)

    Bhaskar Kundu; V K Gahalaut

    2011-04-01

    Necking, tearing, slab detachment and subsequently slab loss complicate the subduction zone processes and slab architecture. Based on evidences which include patterns of seismicity, seismic tomography and geochemistry of arc volcanoes, we have identified a horizontal slab tear in the subducted Indo-Australian slab beneath the Sunda arc. It strongly reflects on trench migration, and causes along-strike variations in vertical motion and geochemically distinct subduction-related arc magmatism. We also propose a model for the geodynamic evolution of slab detachment.

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

    Science.gov (United States)

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

    2015-01-01

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

  5. Lasting mantle scars lead to perennial plate tectonics.

    Science.gov (United States)

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

    2016-06-10

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

  6. Lasting mantle scars lead to perennial plate tectonics

    Science.gov (United States)

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

    2016-06-01

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

  7. Lasting mantle scars lead to perennial plate tectonics

    OpenAIRE

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

    2016-01-01

    Mid-ocean ridges, transform faults, subduction and continental collisions form the conventional theory of plate tectonics to explain non-rigid behaviour at plate boundaries. However, the theory does not explain directly the processes involved in intraplate deformation and seismicity. Recently, damage structures in the lithosphere have been linked to the origin of plate tectonics. Despite seismological imaging suggesting that inherited mantle lithosphere heterogeneities are ubiquitous, their p...

  8. Seismic anisotropy: tracing plate dynamics in the mantle.

    Science.gov (United States)

    Park, Jeffrey; Levin, Vadim

    2002-04-19

    Elastic anisotropy is present where the speed of a seismic wave depends on its direction. In Earth's mantle, elastic anisotropy is induced by minerals that are preferentially oriented in a directional flow or deformation. Earthquakes generate two seismic wave types: compressional (P) and shear (S) waves, whose coupling in anisotropic rocks leads to scattering, birefringence, and waves with hybrid polarizations. This varied behavior is helping geophysicists explore rock textures within Earth's mantle and crust, map present-day upper-mantle convection, and study the formation of lithospheric plates and the accretion of continents in Earth history.

  9. Origin of azimuthal seismic anisotropy in oceanic plates and mantle

    Science.gov (United States)

    Becker, Thorsten W.; Conrad, Clinton P.; Schaeffer, Andrew J.; Lebedev, Sergei

    2014-09-01

    Seismic anisotropy is ubiquitous in the Earth's mantle but strongest in its thermo-mechanical boundary layers. Azimuthal anisotropy in the oceanic lithosphere and asthenosphere can be imaged by surface waves and should be particularly straightforward to relate to well-understood plate kinematics and large-scale mantle flow. However, previous studies have come to mixed conclusions as to the depth extent of the applicability of paleo-spreading and mantle flow models of anisotropy, and no simple, globally valid, relationships exist. Here, we show that lattice preferred orientation (LPO) inferred from mantle flow computations produces a plausible global background model for asthenospheric anisotropy underneath oceanic lithosphere. The same is not true for absolute plate motion (APM) models. A ˜200 km thick layer where the flow model LPO matches observations from tomography lies just below the ˜1200 °C isotherm of a half-space cooling model, indicating strong temperature-dependence of the processes that control the development of azimuthal anisotropy. We infer that the depth extent of shear, and hence the thickness of a relatively strong oceanic lithosphere, can be mapped this way. These findings for the background model, and ocean-basin specific deviations from the half-space cooling pattern, are found in all of the three recent and independent tomographic models considered. Further exploration of deviations from the background model may be useful for general studies of oceanic plate formation and dynamics as well as regional-scale tectonic analyses.

  10. Nazca plate subduction, mantle flow and Cordilleras formation

    Science.gov (United States)

    Capitanio, Fabio A.

    2013-04-01

    The Nazca-South America convergence represents a unique natural laboratory to probe our understanding of subduction, mantle flow and stress coupling at Andean-type margins. Here, it is shown that the most fundamental balance of forces associated with the downgoing slab, the upper plates and the mantle can account for the Nazca plate motions, although it does not adequately explain the variations of the Cordilleran tectonics found along the ~6000 km wide margin. Using three-dimensional numerical models it is shown that trench-parallel gradients in both the driving and resisting forces are an essential component of the force balance, and necessary to reproduce the macroscopic features observed. When along-trench buoyancy variations similar to the Nazca plate's are included, the slab dips and upper plate deformations observed in the Nazca slab, in the Cordilleras and South American continent interiors can be reproduced. The models show that gradients in the resisting shear force along the trench can be as relevant, as they modulate the trench retreat to form the concave Bolivian Orocline. Pressure gradients in the mantle follow the Nazca buoyancy gradients, and effectively rearrange the flow introducing a trench-parallel component, similar to what suggested by seismic anisotropy in this area. Although they introduce only secondary variations to the primary subduction and mantle flow dynamics, the regional features of the Nazca and South American plates exert a primary control at the margin-local scale. This suggests that far-field forces, e.g. from spreading Atlantic or large-scale convection, should play a minor role in the formation of the Cordilleras.

  11. Linear volcanic segments in the Sunda Arc, Indonesia: Implications for arc lithosphere control upon volcano distribution

    Science.gov (United States)

    Macpherson, C. G.; Pacey, A.; McCaffrey, K. J.

    2012-12-01

    The overall curvature of many subduction zones is immediately apparent and the term island arc betrays the common assumption that subduction zone magmatism occurs in curved zones. This assumption can be expressed by approximating island arcs as segments of small circles on the surface of a sphere. Such treatments predict that the location of arc volcanoes is related to their vertical separation from the slab (in fact, the depth to seismicity in the slab) and require that the primary control on the locus of magmatism lies either within the subducted slab or the mantle wedge that separates the subducted and overriding lithospheric plates. The concept of curved arcs ignores longstanding observations that magmatism in many subduction systems occurs as segments of linearly arranged volcanic centres. Further evidence for this distribution comes from the close relationship between magmatism and large scale, arc-parallel fabrics in some arcs. Similarly, exposures of deep arc crust or mantle often reveal elongation of magmatic intrusions sub-parallel to the inferred trend of the arc. The Sunda Arc forms the Indonesian islands from Sumatra to Alor and provides an important test for models of volcano distribution for several reasons. First, Sunda has hosted abundant historic volcanic activity. Second, with the notable exception of Krakatau, every volcano in the arc is subaerial from base to cone and, therefore, can be readily identified where there is a suitable extent of local mapping that can be used to ground-truth satellite imagery. Third, there are significant changes in the stress regime along the length of the arc, allowing the influence of the upper plate to be evaluated by comparison of different arc segments. Finally, much of the Sunda Arc has proved difficult to accommodate in models that try to relate volcano distribution to the depth to the subducted slab. We apply an objective line-fitting protocol; the Hough Transform, to explore the distribution of volcanoes

  12. Towards implementing plate tectonics in 3D mantle convection simulations

    Science.gov (United States)

    Bollada, Peter; Davies, Huw

    2010-05-01

    One of the great challenges in numerical mantle convection simulations is to achieve models that naturally develop plate tectonic like behaviour at the surface. In this work we are looking to achieve such models by investigating the set of models where a single consistent rheology is used for the whole model. We have started by investigating a viscoelastic rheology, related to the Oldroyd-B model from the field of polymers. The goal will be to have the parameter that controls the relaxation between elastic and viscous behaviour to depend upon temperature, pressure and strain-rate. With an appropriate choice of this dependence we have, on the near surface, high viscous/elastic regions interfaced with lower, pure viscous, regions of high strain-rate; while it also becomes more viscous at depth in the interior. In this way we hope to obtain plate like behaviour at the surface which naturally progresses to viscous convective behaviour in the interior. We have started to implement this model in the established mantle 3D finite element spherical mantle convection code TERRA (Baumgardner, 1984). Some parts of the model have been implemented as a force (to be combined with the gravitational body force) on the right hand side. The work has required us to develop and code in TERRA: (i) methods to overcome the continuity problem of the stress field stemming from the fact that the velocity field is represented by linear finite elements; (ii) new operators to handle stress and its gradients; (iii) methods to analyse plate-like behaviour at the surface (iv) the necessary functional dependence of viscosity and elastic relaxation time on temperature, strain-rate and pressure We will present the background to the work, its implementation and results.

  13. Mantle convection and plate tectonics on Earth-like exoplanets

    Science.gov (United States)

    Sotin, C.; Schubert, G.

    2009-12-01

    The likelihood of plate tectonics on exoplanets larger than Earth can be assessed using either scaling laws or numerical models describing mantle thermal convection. We investigate the parameters which control the ratio of convective driving forces to lithosphere resisting forces. Two papers, Valencia et al. (AstroPhys. J., 670, L45-L48, 2007) and O’Neill and Lenardic (Geophys. Res. Lett., 34, L19204, 2007), came to opposite conclusions based on scaling laws and numerical calculations, respectively. The different assumptions and parameters used in each study are compared. The definition of thermal boundary layer and lithosphere and the use of their characteristics in the scaling laws are clarified. We show that Valencia et al. (2007) overestimate the ratio of driving forces to resistive forces because they infer too large values for both the thickness of the thermal boundary layer and the length of the plate and too small a value for the yield strength. We show that this ratio is so weakly dependent on the size of an Earth-like planet that other parameters such as presence of water, heating per unit mass, upper mantle thickness, etc., may actually determine the occurrence or not of plate tectonics. The numerical calculations of O’Neill and Lenardic (2007) show the importance of 2D simulations for determining the values of the velocity below the lithosphere, the convective stresses, and the plate dimensions. It demonstrates the need for 3D spherical numerical simulations. Their conclusion that super-Earths would not have plate tectonics depends on a number of assumptions including the constancy of heat-flux as a function of planetary size. We present a 3D spherical scaling including the increase of heat flux with the size of a planet showing that larger Earth-like planets would be marginally in the mobile lid convection regime reinforcing our caution that other factors may tip the balance. The present study points out the importance of the distance between

  14. Mantle convection and plate tectonics: toward an integrated physical and chemical theory

    Science.gov (United States)

    Tackley

    2000-06-16

    Plate tectonics and convection of the solid, rocky mantle are responsible for transporting heat out of Earth. However, the physics of plate tectonics is poorly understood; other planets do not exhibit it. Recent seismic evidence for convection and mixing throughout the mantle seems at odds with the chemical composition of erupted magmas requiring the presence of several chemically distinct reservoirs within the mantle. There has been rapid progress on these two problems, with the emergence of the first self-consistent models of plate tectonics and mantle convection, along with new geochemical models that may be consistent with seismic and dynamical constraints on mantle structure.

  15. The dynamics of plate tectonics and mantle flow: from local to global scales.

    Science.gov (United States)

    Stadler, Georg; Gurnis, Michael; Burstedde, Carsten; Wilcox, Lucas C; Alisic, Laura; Ghattas, Omar

    2010-08-27

    Plate tectonics is regulated by driving and resisting forces concentrated at plate boundaries, but observationally constrained high-resolution models of global mantle flow remain a computational challenge. We capitalized on advances in adaptive mesh refinement algorithms on parallel computers to simulate global mantle flow by incorporating plate motions, with individual plate margins resolved down to a scale of 1 kilometer. Back-arc extension and slab rollback are emergent consequences of slab descent in the upper mantle. Cold thermal anomalies within the lower mantle couple into oceanic plates through narrow high-viscosity slabs, altering the velocity of oceanic plates. Viscous dissipation within the bending lithosphere at trenches amounts to approximately 5 to 20% of the total dissipation through the entire lithosphere and mantle.

  16. Whole-mantle convection with tectonic plates preserves long-term global patterns of upper mantle geochemistry.

    Science.gov (United States)

    Barry, T L; Davies, J H; Wolstencroft, M; Millar, I L; Zhao, Z; Jian, P; Safonova, I; Price, M

    2017-05-12

    The evolution of the planetary interior during plate tectonics is controlled by slow convection within the mantle. Global-scale geochemical differences across the upper mantle are known, but how they are preserved during convection has not been adequately explained. We demonstrate that the geographic patterns of chemical variations around the Earth's mantle endure as a direct result of whole-mantle convection within largely isolated cells defined by subducting plates. New 3D spherical numerical models embedded with the latest geological paleo-tectonic reconstructions and ground-truthed with new Hf-Nd isotope data, suggest that uppermost mantle at one location (e.g. under Indian Ocean) circulates down to the core-mantle boundary (CMB), but returns within ≥100 Myrs via large-scale convection to its approximate starting location. Modelled tracers pool at the CMB but do not disperse ubiquitously around it. Similarly, mantle beneath the Pacific does not spread to surrounding regions of the planet. The models fit global patterns of isotope data and may explain features such as the DUPAL anomaly and long-standing differences between Indian and Pacific Ocean crust. Indeed, the geochemical data suggests this mode of convection could have influenced the evolution of mantle composition since 550 Ma and potentially since the onset of plate tectonics.

  17. Role of plate-driven mantle flow in distribution of the global heat flow

    Institute of Scientific and Technical Information of China (English)

    叶正仁; 安镇文

    1999-01-01

    Heat flow in the Earth, from its hot interior to its relatively cool exterior, is the primary energy flow responsible for the dynamic nature of our planet. The motion of the plates excites a forced convective motion in the mantle, and this plate-driven mantle flow will strongly modulate the temperature field in the mantle because of the relatively high Peeler number of the mantle dynamic system. Here the role of the plate-driven mantle flow in the observed global heat flow is examined. The result reveals that the main feature of the distribution of the observed heat flow at the surface of the Earth matches well with the prediction and nearly one half of the average heat flow can be attributed to the thermal effect of the plate-driven mantle flow.

  18. Testing Absolute Plate Reference Frames and the Implications for the Generation of Geodynamic Mantle Heterogeneity Structure

    Science.gov (United States)

    Shephard, G. E.; Bunge, H.; Schuberth, B. S.; Müller, D.; Talsma, A.; Moder, C.

    2010-12-01

    Several absolute reference frames for Cretaceous-Tertiary plate tectonic reconstructions have been proposed over the last decade. They include reference frames based on hotspot tracks displaying age progression, and assuming either fixed or moving hotspots, as well as palaeomagnetically-based reference frames, a subduction reference frame and hybrid reference frames. All these alternative reference frames imply a particular history of the location of subduction zones through time, the associated subduction history, and the evolution of mantle heterogeneity via the mixing of subducted slab material with the mantle. Therefore it is possible to evaluate the observed distribution of subducted slab material in the mantle versus that predicted by a forward geodynamic model in which the plate kinematic history given by a particular absolute plate is coupled with a mantle convection model. We present a comparison of five alternative absolute plate motion models in terms of their consequences for global deep mantle structure by utilizing the 3-D spherical finite element mantle convection code TERRA, coupled with the global plate tectonic reconstruction software GPlates. We impose global palaeo-plate boundaries and plate velocities back to 140 Ma as surface boundary conditions for each absolute rotation model and forward model the associated subduction history. The correlation of seismic tomography with the predicted present-day mantle structure from each of plate models is then assessed using well-imaged slabs. We will present and discuss a comparison of geodynamically predicted mantle heterogeneity and seismic tomography to infer the robustness of each absolute reference frame through time, thus providing additional constraints for the integration of plate tectonics and mantle dynamics.

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

    Science.gov (United States)

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

    2015-12-01

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

  20. Stability of active mantle upwelling revealed by net characteristics of plate tectonics.

    Science.gov (United States)

    Conrad, Clinton P; Steinberger, Bernhard; Torsvik, Trond H

    2013-06-27

    Viscous convection within the mantle is linked to tectonic plate motions and deforms Earth's surface across wide areas. Such close links between surface geology and deep mantle dynamics presumably operated throughout Earth's history, but are difficult to investigate for past times because the history of mantle flow is poorly known. Here we show that the time dependence of global-scale mantle flow can be deduced from the net behaviour of surface plate motions. In particular, we tracked the geographic locations of net convergence and divergence for harmonic degrees 1 and 2 by computing the dipole and quadrupole moments of plate motions from tectonic reconstructions extended back to the early Mesozoic era. For present-day plate motions, we find dipole convergence in eastern Asia and quadrupole divergence in both central Africa and the central Pacific. These orientations are nearly identical to the dipole and quadrupole orientations of underlying mantle flow, which indicates that these 'net characteristics' of plate motions reveal deeper flow patterns. The positions of quadrupole divergence have not moved significantly during the past 250 million years, which suggests long-term stability of mantle upwelling beneath Africa and the Pacific Ocean. These upwelling locations are positioned above two compositionally and seismologically distinct regions of the lowermost mantle, which may organize global mantle flow as they remain stationary over geologic time.

  1. 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

  2. Supercontinent Pangea, Mantle Dynamics, and Reference Frame of Global Plate Motions

    Science.gov (United States)

    Zhong, S.; Rudolph, M. L.; Liu, X.

    2014-12-01

    Arguably the most important and challenging goal in geodynamics is to understand the two-way dynamics between tectonic plates and mantle convection. While it has long been recognized that the present-day degree-2 mantle structure as imaged seismically is closely related to the plate motions (Hager and O'Connell, 1981) and their history (500 Ma (Torsvik et al., 2014), although its statistical significance has been challenged (Austermann et al., 2013). The proposals of the spatially stable Africa and Pacific LLSVPs and of the LIP eruptions along their edges have also been exploited in attempts to build global plate motion models since the Pangea assembly by providing a plate motion reference frame or inferring true polar wander (TPW) corrections to the plate motions (Torsvik et al., 2014). Second, mantle dynamics studies indicate that degree-1 mantle convection, which is expected with realistic lithospheric and mantle viscosity, may be needed for assembly of a supercontinent (e.g., Pangea) (Zhong et al., 2007). This suggests that the present degree-2 mantle structure may have been formed only after the Pangea assembly from an initially degree-1 structure - a scenario that is consistent with convection calculations with a proxy plate motion model that considers Pangea process (Zhang et al., 2010). In this presentation, in addition to critically reviewing these arguments, we will discuss calculations of long-wavelength geoid for the mantle with thermochemical piles and LLSVPs and their potential effects on TPW determinations and hence reconstruction of plate motion (i.e., net lithospheric rotation). We will also present additional calculations of mantle structure evolution using different plate motion history models.

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

    Science.gov (United States)

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

    2013-12-01

    Eastern New Guinea lies within the rapidly obliquely converging Australian (AUS)- Pacific (PAC) plate boundary zone and is characterized by transient plate boundaries, rapidly rotating microplates and a globally significant geoid high. As the AUS plate moved northward in the Cenozoic, its leading edge has been a zone of subduction and arc accretion. The variety of tectonic settings in this region permits assessment of the complex interplay among mantle dynamics, plate tectonics, and surface processes. Importantly, the timescale of tectonic events (e.g., subduction, (U)HP exhumation, seafloor spreading) are within the valid bounds of mantle convection models. A record of changes in bathymetry and topography are preserved in high standing mountain belts, exhumed extensional gneiss domes and core complexes, uplifted coral terraces, and marine sedimentary basins. Global seismic tomography models indicate accumulation of subducted slabs beneath eastern New Guinea at the bottom of the upper mantle (i.e., 250-300 km). Preliminary global-scale backward advected mantle convection models, driven by density inferred from joint seismic-geodynamic tomography models, exhibit large-scale flow associated with these subducted slab remnants and predict the timing and magnitude (up to 1500 m) of dynamic topography change (both subsidence and uplift) since the Oligocene. In this talk we will explore the effects of large-scale background mantle flow and plate tectonics on the evolution of topography and bathymetry in eastern New Guinea, and discuss possible mechanisms to explain basin subsidence and surface uplift in the region.

  4. Gaya Pedalangan Sunda

    Directory of Open Access Journals (Sweden)

    Cahya Cahya

    2013-11-01

    Full Text Available Memahami gaya pedalangan Sunda pada dasarnya adalah sebuah upaya penjelajahan dan pemetaan jagatpedalangan Sunda yang kaya dengan nilai-nilai tradisi dan permasalahan-permasalahan uniknya. Salah satunyaadalah permasalahan gaya pedalangan yang identik dengan keberadaan paguron-paguron dalang dengan tokohtokohdalang yang mencirikan warna paguronnya masing-masing. Berkaitan dengan gaya pedalangan itulah, maka pada akhirnya mucul bentuk gaya mendalang perseorangan yang lazim disebut gaya mandiri. Penelitian ini membahas berbagai gaya mandiri yang berkembang di wilayah Jawa Barat.Kata Kunci: wayang golek, gaya pedalangan, paguron dalangABSTRACTSundanese Puppetry Style. Understanding Sundanese puppetry style is basically venturing and mapping Sundanesepuppetry world which is rich of traditional values and distinctive problems. One of the problems is related to puppetrystyle in which the puppet masters are characterized by their mainstream or school. Such style has later developed intoindependent styles of Sundanese puppetry. This research discusses various independent styles of Sundanese puppetry.Key words: Sundanese wayang, wodden puppet

  5. The temporal evolution of a subducting plate in the lower mantle

    Science.gov (United States)

    Loiselet, C.; Grujic, D.; Braun, J.; Fullsack, P.; Thieulot, C.; Yamato, P.

    2009-04-01

    It is now widely accepted that some subducting slabs may cross the lower/upper mantle boundary to ground below the 660 km discontinuity. Indeed, geophysical data underline long and narrow traces of fast materials, associated with subducting slabs, from the upper mantle transition zone to mid-mantle depths that are visible beneath North and South America and southern Asia (Li et al, 2008). Furthermore, seismic tomography data (Van der Hilst et al., 1997; Karason and van der Hilst, 2000, 2001) show a large variety of slab geometries and of mantle flow patterns around subducting plate boundaries (e.g. the slab geometry in the lower mantle in the Tonga subduction zone). However, seismic tomography does not elucidate the temporal evolution of the slab behaviour and geometry during its descent through the upper and lower mantle. In this work, we therefore propose to study the deformation of a thin plate (slab) falling in a viscous fluid (mantle) by means of both analogue and numerical modelling. The combination of both analogue and numerical experiments provides important insights into the shape and attitude evolution of subducting slabs. Models bring information into the controls exerted by the rheology of the slab and the mantle and other physical parameters such as the density contrast between the slab and the surrounding mantle, on the rate at which this deformation takes place. We show that in function of a viscosity ratios between the plate and the surrounding fluid, the plate will acquire a characteristic shape. For the isoviscous case, the plate shape tends toward a bubble with long tails: a "jellyfish" form. The time necessary for the plate to acquire this shape is a function of the viscosity and density contrast between the slab and the mantle. To complete our approach, we have developed a semi-analytical model based on the solution of the Hadamar-Rybinski equations for the problem of a dense, yet isoviscous and thus deforming sphere. This model helps to better

  6. Uppermost mantle Pn Velocity of the Arabian Plate, a Preliminary study

    Science.gov (United States)

    Al-Lazki, A. I.; Al-Damegh, K. S.; Al-Enizi, A.; Elhusain, I.; Al-Mahrooqi, I.

    2005-12-01

    The Arabian plate represents a unique tectonic setup. The uniqueness of this plate is its boundaries that constitute the three known types of plate boundaries. The Red Sea and the Gulf of Aden represent the south and southwest plate boundary with Africa plate. Farther north the Dead Sea Fault system represents the remainder of the northwestern boundary with Africa plate. Continent-continent collision along the Bitlis-Zagros Suture zones represents the northern and northeastern boundary with Eurasia plate. Farther south the convergent plate boundary is manifested by the Makran Subduction Zone. Finally, the Owen and Murray Transform Faults represent the southeast boundary of Arabia with India plate. The broad objective of this study is to map uppermost mantle Pn velocity and anisotropy within the Arabian plate and around its boundaries. Zones that are along the north and the northeast boundaries of Arabia plate historically and in recent years has been effected by devastating earthquakes, a recent example is the Bam earthquake on December, 2003. In this region, accurate earthquake location is essential to delineate seismically active zones, where, without proper velocity models for the region, located earthquake may have large location error. In this preliminary study we present uppermost mantle Pn velocity tomography results of the north and northeastern regions of Arabia plate. We used in this study Pn phase data from the bulletins of Oman Seismic Network, Saudi Seismic Network, Kuwait Seismic Network, International Seismological Center and the National Earthquake Information Center,USA.

  7. Mantle Convection, Plate Tectonics, and the Asthenosphere: A Bootstrap Model of the Earth's Internal Dynamics

    Science.gov (United States)

    Lenardic, A.; Hoink, T.

    2008-12-01

    Several studies have highlighted the role of a low viscosity asthenosphere in promoting plate-like behavior in mantle convection models. It has also been argued that the asthenosphere is fed by mantle plumes (Phipps- Morgan et al. 1993; Deffeyes 1972) and that the existence of the specific plume types required for this depends on plate subduction (Lenardic and Kaula 1995; Jellinek et al. 2002). Independent of plumes, plate subduction can generate a non-adiabatic temperature gradient which, together with temperature dependent mantle viscosity, leads to a low viscosity near surface region. The above suggests a conceptual model in which the asthenosphere can not be defined solely in terms of material properties but must also be defined in terms of an active process, plate tectonics, which both maintains it and is maintained by it. The bootstrap aspect of the model is its circular causality between plates and the asthenosphere, neither being more fundamental than the other and the existence of each depending on the other. Several of the feedbacks key to the conceptual model will be quantified. The implications for modeling mantle convection in a plate-tectonic mode will also be discussed: 1) A key is to get numerical simulations into the bootstrap mode of operation and this is dependent on assumed initial conditions; 2) The model implies potentially strong hysteresis effects (e.g., transition between convection states, associated with variable yield stress, will occur at different values depending on whether the yield stress is systematically lowered or raised between successive models).

  8. Tectonic plates, D (double prime) thermal structure, and the nature of mantle plumes

    Science.gov (United States)

    Lenardic, A.; Kaula, W. M.

    1994-01-01

    It is proposed that subducting tectonic plates can affect the nature of thermal mantle plumes by determining the temperature drop across a plume source layer. The temperature drop affects source layer stability and the morphology of plumes emitted from it. Numerical models are presented to demonstrate how introduction of platelike behavior in a convecting temperature dependent medium, driven by a combination of internal and basal heating, can increase the temperature drop across the lower boundary layer. The temperature drop increases dramatically following introduction of platelike behavior due to formation of a cold temperature inversion above the lower boundary layer. This thermal inversion, induced by deposition of upper boundary layer material to the system base, decays in time, but the temperature drop across the lower boundary layer always remains considerably higher than in models lacking platelike behavior. On the basis of model-inferred boundary layer temperature drops and previous studies of plume dynamics, we argue that generally accepted notions as to the nature of mantle plumes on Earth may hinge on the presence of plates. The implication for Mars and Venus, planets apparently lacking plate tectonics, is that mantle plumes of these planets may differ morphologically from those of Earth. A corollary model-based argument is that as a result of slab-induced thermal inversions above the core mantle boundary the lower most mantle may be subadiabatic, on average (in space and time), if major plate reorganization timescales are less than those acquired to diffuse newly deposited slab material.

  9. Partial melting and the efficiency of mantle outgasing in one-plate planets

    Science.gov (United States)

    Plesa, Ana-Catalina; Breuer, Doris

    2013-04-01

    The generation of partial melting can have a major impact on the thermo-chemical evolution of a terrestrial body by the depletion of the mantle material in incompatible elements such as radioactive elements and volatiles, crust formation and volcanic outgassing. During some period in the thermal history of a terrestrial planet, the temperature in regions of the upper mantle, either below tectonic plates or a stagnant lid, rises above the solidus - the temperature at which the mineral with the lowest melting temperature among those that form the silicate mantle mixture starts to melt. The melt than rises toward the surface, forms the crust, and releases volatiles into the atmosphere. In case of one-plate (stagnant lid) planets the thickness of the present-day crust can 'tell' us already about the efficiency of mantle melting and mantle degassing - the thicker the crust the more mantle material experienced melting and thus the more efficient can be the outgassing. However, it has been shown with parameterized convection models [1] but also 2-3D convection models [2] that crustal delamination is a common process in one-plate planets. Crustal delamination allows that possibly much more crust is produced during the entire evolution (and thus more mantle material experienced differentiation) than what is observed today, implying also more efficient outgassing than expected. Crustal delamination is therefore a process that may help to generate a substantial planetary atmosphere. In the present work we investigate the influence of partial melt on mantle dynamics and the volcanic outgassing of one-plate planets using the mantle convection code GAIA [3] in a 2D cylindrical geometry. We consider the depletion of the mantle, redistribution of radioactive heat sources between mantle and crust, as well as mantle dehydration and volcanic outgassing [4]. When melt is extracted to form the crust, the mantle material left behind is more buoyant than its parent material and depleted

  10. Mapping the subducted Nazca plate in the lower mantle beneath South America

    Science.gov (United States)

    Contenti, S. M.; Gu, Y. J.; Okeler, A.

    2009-12-01

    Recent improvements in data coverage have enabled high-resolution imaging of the morphology of subduction zones and mantle plumes. In this study, we migrate the SS precursors from over 5000 seismograms to obtain a detailed map of mid- and upper-mantle reflectors beneath the northern portion of the South American subduction zone, where the oceanic Nazca plate is descending below the South American plate. In addition to an elevated 410 and depressed 660 (as expected for a subduction zone), strong mid-mantle reflectors at 800-1100 km depth are also apparent. The amplitudes of these steeply dipping reflectors are comparable to that of the 660-kilometer discontinuity. This anomaly outlines a high-velocity (therefore presumably cold) region present in recent finite-frequency based mantle velocity models, suggesting the extension of slab material into the lower mantle. The strength of the reflection is interpreted to be caused by a relatively sharp velocity change, likely due to a strong temperature gradient in combination with mineral phase transitions, the presence of water, or other chemical heterogeneities. Significant mass and heat exchange is therefore expected between the upper- and lower-mantle beneath the study region.

  11. Permanent upper plate deformation in western Myanmar during the great 1762 earthquake: Implications for neotectonic behavior of the northern Sunda megathrust

    Science.gov (United States)

    Wang, Yu; Shyu, J. Bruce H.; Sieh, Kerry; Chiang, Hong-Wei; Wang, Chung-Che; Aung, Thura; Lin, Yu-Nung Nina; Shen, Chuan-Chou; Min, Soe; Than, Oo; Lin, Kyaw Kyaw; Tun, Soe Thura

    2013-03-01

    The 1762 Arakan earthquake resulted from rupture of the northern Sunda megathrust and is one of those rare preinstrumental earthquakes for which early historical accounts document ground deformations. In order to obtain more comprehensive and detailed measurements of coseismic uplift, we conducted comprehensive field investigations and geochronological analyses of marine terraces on the two largest islands in western Myanmar. We confirm 3-4 m of coseismic coastal emergence along southwestern Cheduba Island, diminishing northeastward to less than 1 m. Farther northeast, uplift associated with the earthquake ranges from slightly more than 1 m to 5-6 m along the western coast of Ramree Island but is insignificant along the island's eastern coast. This double-hump pattern of uplift coincides with the long-term anticlinal growth of these two islands. Thus, we propose that the 1762 earthquake resulted from slip on splay faults under the islands, in addition to rupture of the megathrust. Elastic modeling implies that fault slip during the 1762 earthquake ranges from about 9 to 16 m beneath the islands and corresponds to a magnitude of Mw 8.5 if the rupture length of the megathrust is ~500 km. The island's uplift histories suggest recurrence intervals of such events of about 500-700 years. Additional detailed paleoseismological studies would add significant additional detail to the history of large earthquakes in this region.

  12. Past Plate Motions and The Evolution of Earth's Lower Mantle: Relating LLSVPs and Plume Distribution

    Science.gov (United States)

    Bull, A. L.; Torsvik, T. H.; Shephard, G. E.

    2015-12-01

    Seismic tomography elucidates broad, low shear-wave velocity structures in the lower mantle beneath Africa and the central Pacific with uncertain physical and compositional origins. The anomalously slow areas, which cover nearly 50% of the core-mantle boundary, are often referred to as Large Low Shear Velocity Provinces (LLSVPs) due to the reduced velocity of seismic waves passing through them. Several hypotheses have arisen to explain the LLSVPs in the context of large-scale mantle convection. One end-member scenario infers a spatial correlation between LLSVP margins at depth and the reconstructed surface eruption sites of hotspots, kimberlites, and Large Igneous Provinces. Such a correlation has been explained by the preferential triggering of plumes at LLSVP margins by impingement of the subducting lithosphere upon the lower thermal boundary layer at the interface between ambient mantle and the higher density structures. This scenario propounds that Earth's plate motion history plays a controlling role in plume development, and that the location, geometry and morphology of plumes may be influenced by the movement of subducting slabs. Here, we investigate what is necessary to create such a pattern of plume distribution in relation to LLSVPs. We consider what effect past plate motions may have had on the evolution of Earth's lower mantle, and discuss the development of mantle plumes in terms of subduction dynamics. We integrate plate tectonic histories and numerical models of mantle convection to investigate the role that subduction history plays in the development and evolution of plumes in the presence of LLSVPs. To test whether an interaction exists between the surface location of subduction and plume eruption sites, and if so, to what degree over time, we apply varying shifts to the absolute reference frame of the plate reconstruction. With this method, we are able to change the location of subduction at the surface and thus the global flow field. This in turn

  13. Asymmetric Mid-Ocean ridges: Interplay Between Plate and Mantle Processes and Consequences for Melting

    Science.gov (United States)

    Montesi, L.; Bai, H.

    2014-12-01

    Mid-ocean ridges constitute a fundamental component of the global plate tectonic system. The classical view of ridges is of symmetric system, where plates diverge, generating a mostly passive upwelling immediately underneath the ridge axis. However, observations of mid-ocean ridges draw quite a different picture. At the Southern East Pacific Rise, plate subsidence (related to plate age) occurs at different rates on the Pacific and Nazca plates, implying different rates of accretion on each side of the ridge. At greater depth, the melting region extends much further beneath the Pacific plate than the Nazca plate. Asymmetry is also evident in slow spreading center. For examples, at the 13°N segment of the Mid-Atlantic Ridge, isochrons are more widely spaced on the American side than the European side. Core complexes along the axis are another manifestation of asymmetric accretion at that location. In this contribution, we seek to understand how is the melting system affected by ridge asymmetry. First, we discuss the different ways that an asymmetric ridge may develop. We present an analytical solution of mantle flow in the mantle underneath spreading centers that considers 1) different rates of accretion in on the two plates; 2) migration of the ridge system with respect to the underlying mantle (Couette flow in the asthenosphere); 3) mantle wind (Poiseuille flow in the asthenosphere); 4) different slopes of the lithosphere underneath each plate; and 5) any combination of the above. These solutions assume an isoviscous mantle underneath the lithosphere. Asymmetry in mantle flow is observed in each case. The temperature field associated with each case implies that melting is suppressed by the asymmetric accretion, although deeper processes have little effect on melting. As asymmetric accretion is thought to develop when melt flux to the axis is reduced, there is the possibility of a positive feedback that forces segments to switch between symmetric and asymmetric

  14. Integrating Geochemical and Geodynamic Numerical Models of Mantle Evolution and Plate Tectonics

    Science.gov (United States)

    Tackley, P. J.; Xie, S.

    2001-12-01

    The thermal and chemical evolution of Earth's mantle and plates are inextricably coupled by the plate tectonic - mantle convective system. Convection causes chemical differentiation, recycling and mixing, while chemical variations affect the convection through physical properties such as density and viscosity which depend on composition. It is now possible to construct numerical mantle convection models that track the thermo-chemical evolution of major and minor elements, and which can be used to test prospective models and hypotheses regarding Earth's chemical and thermal evolution. Model thermal and chemical structures can be compared to results from seismic tomography, while geochemical signatures (e.g., trace element ratios) can be compared to geochemical observations. The presented, two-dimensional model combines a simplified 2-component major element model with tracking of the most important trace elements, using a tracer method. Melting is self-consistently treated using a solidus, with melt placed on the surface as crust. Partitioning of trace elements occurs between melt and residue. Decaying heat-producing elements and secular cooling of the mantle and core provide the driving heat sources. Pseudo-plastic yielding of the lithosphere gives a first-order approximation of plate tectonics, and also allows planets with a rigid lid or intermittent plate tectonics to be modeled simply by increasing the yield strength. Preliminary models with an initially homogeneous mantle show that regions with a HIMU-like signature can be generated by crustal recycling, and regions with high 3He/4He ratios can be generated by residuum recycling. Outgassing of Argon is within the observed range. Models with initially layered mantles will also be investigated. In future it will be important to include a more realistic bulk compositional model that allows continental crust as well as oceanic crust to form, and to extend the model to three dimensions since toroidal flow may alter

  15. The efficiency of plate tectonics and nonequilibrium dynamical evolution of planetary mantles

    Science.gov (United States)

    Moore, W. B.; Lenardic, A.

    2015-11-01

    Consideration of the structure of dynamical equilibria in terrestrial planets using simplified descriptions of the relevant heat transport processes (rigid-lid convection, plate tectonics, and heat pipe volcanism) reveals that if the efficiency of plate tectonic heat transport decreases at higher mantle temperature, then it cannot govern quasi-equilibrium dynamical evolution, and the system is always evolving away from the plate tectonic regime. A planet on which plate tectonics is less efficient at higher temperature stays in heat pipe mode longer, spends less time undergoing plate tectonics, and has a low and ever-decreasing Urey number during this phase. These conclusions are based solely on the structure of the equilibria in a system with less efficient plate tectonics in the past and are independent of the mechanisms leading to this behavior. Commonly used quasi-equilibrium approaches to planetary thermal evolution are likely not valid for planets in which heat transport becomes less efficient at higher temperature.

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

    Science.gov (United States)

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

    2014-12-01

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

  17. Effect of plate bending on the Urey ratio and the thermal evolution of the mantle

    Science.gov (United States)

    Davies, Geoffrey F.

    2009-10-01

    The bending of tectonic plates as they subduct causes resistance to plate motions and mantle convection. It has been proposed that this effect could keep plate velocities relatively constant with time, and it would imply relatively high mantle temperatures through much of Earth history and relatively rapid cooling at present. It also implies a low Urey ratio, compatible with that inferred from cosmochemistry. Here it is confirmed that bending resistance only plays a significant role if plate thickness is determined mainly by dehydration stiffening accompanying melting, rather than by conductive cooling. Even then the bending resistance is quite sensitive to the radius of curvature of the subducting plate. Observed radii are generally larger than the 200 km assumed in some studies, ranging up to 600 km or more. Furthermore radii of curvature tend to adjust so as to prevent bending resistance from becoming large. When these factors are accounted for, calculations show that bending resistance is unlikely to have been a large factor through Earth history, and the thermal evolution of the mantle is unlikely to have been affected very much. The resolution of the Urey ratio problem should then be sought elsewhere.

  18. Supercontinents, mantle dynamics and plate tectonics: A perspective based on conceptual vs. numerical models

    Science.gov (United States)

    Yoshida, Masaki; Santosh, M.

    2011-03-01

    The periodic assembly and dispersal of supercontinents through the history of the Earth had considerable impact on mantle dynamics and surface processes. Here we synthesize some of the conceptual models on supercontinent amalgamation and disruption and combine it with recent information from numerical studies to provide a unified approach in understanding Wilson Cycle and supercontinent cycle. Plate tectonic models predict that superdownwelling along multiple subduction zones might provide an effective mechanism to pull together dispersed continental fragments into a closely packed assembly. The recycled subducted material that accumulates at the mantle transition zone and sinks down into the core-mantle boundary (CMB) provides the potential fuel for the generation of plumes and superplumes which ultimately fragment the supercontinent. Geological evidence related to the disruption of two major supercontinents (Columbia and Gondwana) attest to the involvement of plumes. The re-assembly of dispersed continental fragments after the breakup of a supercontinent occurs through complex processes involving 'introversion', 'extroversion' or a combination of both, with the closure of the intervening ocean occurring through Pacific-type or Atlantic-type processes. The timescales of the assembly and dispersion of supercontinents have varied through the Earth history, and appear to be closely linked with the processes and duration of superplume genesis. The widely held view that the volume of continental crust has increased over time has been challenged in recent works and current models propose that plate tectonics creates and destroys Earth's continental crust with more crust being destroyed than created. The creation-destruction balance changes over a supercontinent cycle, with a higher crustal growth through magmatic influx during supercontinent break-up as compared to the tectonic erosion and sediment-trapped subduction in convergent margins associated with supercontinent

  19. Upper mantle structure of the Pacific and Philippine Sea plates revealed by seafloor seismic array observations

    Science.gov (United States)

    Isse, Takehi; Shiobara, Hajime; Suetsugu, Daisuke; Sugioka, Hiroko; Ito, Aki

    2016-04-01

    Seismic tomography studies have revealed the structure and dynamics of Earth's interior since the 1980s. However, the spatial resolution of the oceanic region is not good enough caused by sparse distribution of the seismic stations. The observations with broadband ocean-bottom seismographs (BBOBSs) since the 2000s enabled us to obtain seismic tomography models with higher spatial resolution. Our Japanese BBOBS group deployed more than 100 BBOBSs in the Pacific Ocean and obtained a high-resolution (300-500 km) three-dimensional shear wave velocity structure in the upper mantle beneath northwestern and south Pacific Ocean by using surface wave tomography technique. In the northwestern Pacific Ocean, where the Pacific plate subducts beneath the Philippine Sea plate, we found that the shear wave structure in the Philippine sea plate is well correlated with the seafloor age in the upper 120 km, three separate slow anomalies in the mantle wedge at depth shallower than 100 km beneath the Izu-Bonin-Mariana arc, which have a close relationship with the three groups of frontal and rear arc volcanoes having distinct Sr, Nd, and Pb isotope ratios, and that the Philippine Sea plate, which is a single plate, shows very large lateral variations in azimuthal and radial anisotropies compared with the Pacific plate. In the South Pacific Ocean, where midplate hotspots are concentrated, we found that the localized slow anomalies are found near hotspots in the upper mantle, estimated thickness of the lithosphere is about 90 km in average and is thinned by ~20 km in the vicinity of hotspots, which may represent thermal erosion due to mantle plumes.

  20. The role of the heating mode of the mantle in intermittent reorganization of the plate velocity field

    Science.gov (United States)

    Lowman, Julian P.; King, Scott D.; Gable, Carl W.

    2003-02-01

    The geological record indicates that stages of relatively steady plate motion have been punctuated by comparatively brief periods in which plate velocities have reorganized. The distribution of buoyancy sources in the mantle has generally been regarded as evolving too slowly to explain these rapid transitions in plate velocity. We investigate the feedback between mantle convection and plate velocity using 2-D and 3-D mantle convection models that incorporate mobile dynamic plates. We focus on the influence of internal heating in the mantle and consider the effect of mantle viscosity stratification and different plate geometries on the plate velocity time dependence. As either the Rayleigh number or the internal heating rate is increased to magnitudes approaching mantle values, the record of the plate motion from our calculations becomes characterized by intermittent changes in direction. This behaviour is a result of the influence of plates on heat loss from the inherently unsteady, internally heated convecting system. Plate motion instills a pattern of organization on the underlying convection that reflects the plate geometry and results in the formation of sheet-like downwelling structures at convergent plate boundaries in both 2-D and 3-D calculations (in contrast, upwellings in 3-D models are not sheet-like). The role of the sheet-like downwellings is critical in the observed episodic reorganization of the plate velocities. Warm material below the plates is entrained by plate motion into regions enveloping the downwelling sheets. During periods of fairly steady plate motion, buoyancy associated with the build-up of heat around the downwelling sheets leads to the creation of an unstable convection pattern. This build-up of heat is dramatic in calculations with mantle-like internal heating rates and resists continued long-term plate motion towards mature downwellings. When there are limitations on the degree of freedom of the direction of plate movement, such as

  1. Cascadia subducting plate fluids channelled to fore-arc mantle corner: ETS and silica deposition

    Science.gov (United States)

    Hyndman, R. D.; McCrory, P. A.; Wech, A.; Kao, H.; Ague, J.

    2015-06-01

    In this study we first summarize the constraints that on the Cascadia subduction thrust, there is a 70 km gap downdip between the megathrust seismogenic zone and the Episodic Tremor and Slip (ETS) that lies further landward; there is not a continuous transition from unstable to conditionally stable sliding. Seismic rupture occurs mainly offshore for this hot subduction zone. ETS lies onshore. We then suggest what does control the downdip position of ETS. We conclude that fluids from dehydration of the downgoing plate, focused to rise above the fore-arc mantle corner, are responsible for ETS. There is a remarkable correspondence between the position of ETS and this corner along the whole margin. Hydrated mineral assemblages in the subducting oceanic crust and uppermost mantle are dehydrated with downdip increasing temperature, and seismic tomography data indicate that these fluids have strongly serpentinized the overlying fore-arc mantle. Laboratory data show that such fore-arc mantle serpentinite has low permeability and likely blocks vertical expulsion and restricts flow updip within the underlying permeable oceanic crust and subduction shear zone. At the fore-arc mantle corner these fluids are released upward into the more permeable overlying fore-arc crust. An indication of this fluid flux comes from low Poisson's Ratios (and Vp/Vs) found above the corner that may be explained by a concentration of quartz which has exceptionally low Poisson's Ratio. The rising fluids should be silica saturated and precipitate quartz with decreasing temperature and pressure as they rise above the corner.

  2. Deep Structures and Initiation of Plate Tectonics in Thermochemical Mantle Convection Models

    Science.gov (United States)

    Hansen, U.; Stein, C.

    2015-12-01

    Recently deep thermochemical structures have been studied intensively. The observed large anomalies with reduced seismic velocities (LLSVPs) beneath Africa and the Pacific are obtained in numerical models as an initial dense layer at the core-mantle boundary (CMB) is pushed up to piles by the convective flow (e.g., McNamara et al., EPSL 229, 1-9, 2010). Adding a dense CMB layer to a model featuring active plate tectonics, Trim et al. (EPSL 405, 1-14, 2014) find that surface mobility is strongly hindered by the dense material and can even vanish completely for a CMB layer that has a too high density or too large a volume.In a further study we employed a fully rheological model in which oceanic plates form self-consistently. We observe that an initial dense CMB layer strongly affects the formation of plates and therefore the onset time of plate tectonics. We present a systematic 2D parameter study exploring the time of plate initiation and discuss the resulting deep thermal and thermochemical structures in a self-consistent thermochemical mantle convection system.

  3. The benefits of extended plate motion history in mantle circulation models

    Science.gov (United States)

    Webb, Peter; Davies, Huw; Davies, Rhodri; Hochard, Cyril; Stampfli, Gerard

    2010-05-01

    Mantle Circulation Models (MCMs) are mantle convection simulations conditioned with plate motion history. Due to difficulties in reconstructing plate motions beyond ≈ 120 Ma, MCMs often only incorporate the most recent 120 Myr of plate tectonic evolution. We find that such models are strongly influenced by initial conditions. The development of a new series of tectonic reconstructions extending back to the Triassic (230 Ma) and including careful reconstruction of the oceanic parts of the plates (modified from Stampfli and Borel, 2004, Stampfli et al. 2008 and references therein) should prove to be of huge importance to MCMs. In this study we present a comparison between the traditionally used 120 Myr and the latest 230 Myr plate motion histories. We use the three-dimensional spherical mantle convection code TERRA (Bunge et al., 2003) to simulate convection at Earth like vigour. Here we apply the plate motion history as a surface velocity boundary condition to drive the internal convection of an already well-mixed system. The forward models from a chosen starting point to present day yield information on mantle temperature (as well as pressure, velocity and material properties) throughout the volume. One of the ways to validate our results is to compare these with tomographic models. Seismic tomography provides us with a snapshot of Earth's mantle at present day. Assuming that the mantle is driven largely by thermal convection, we can assume that the seismically fast regions are associated with cooler, denser material. The most significant of these can be interpreted as remnants of subducted slabs (Hafkenscheid et al 2006, van der Meer et al. 2010). We convert the temperatures predicted by the MCM to seismic velocities using the latest techniques (e.g. Cobden et al., 2008) and compare the calculated velocities to a range of seismic tomography models (both P and S wave). This way we can examine the validity of the surface velocity boundary condition and identify

  4. Effect of Rheology on Mantle Dynamics and Plate Tectonics in Super-Earths

    Science.gov (United States)

    Tackley, P. J.; Ammann, M. W.; Brodholt, J. P.; Dobson, D. P.; Valencia, D. C.

    2011-12-01

    The discovery of extra-solar "super-Earth" planets with sizes up to twice that of Earth has prompted interest in their possible lithosphere and mantle dynamics and evolution. Simple scalings [1,2] suggest that super-Earths are more likely than an equivalent Earth-sized planet to be undergoing plate tectonics. Generally, viscosity and thermal conductivity increase with pressure while thermal expansivity decreases, resulting in lower convective vigor in the deep mantle, which, if extralopated to the largest super-Earths might, according to conventional thinking, result a very low effective Rayleigh number in their deep mantles and possibly no convection there. Here we evaluate this. (i) As the mantle of a super-Earth is made mostly of post-perovskite we here extend the density functional theory (DFT) calculations of post-perovskite activation enthalpy of [3] to a pressure of 1 TPa. The activation volume for diffusion creep becomes very low at very high pressure, but nevertheless for the largest super-Earths the viscosity along an adiabat may approach 10^30 Pa s in the deep mantle, which would be too high for convection. (ii) We use these DFT-calculated values in numerical simulations of mantle convection and lithosphere dynamics of planets with up to ten Earth masses. The models assume a compressible mantle including depth-dependence of material properties and plastic yielding induced plate-like lithospheric behavior, solved using StagYY [4]. Results confirm the likelihood of plate tectonics and show a novel self-regulation of deep mantle temperature. The deep mantle is not adiabatic; instead internal heating raises the temperature until the viscosity is low enough to facilitate convective loss of the radiogenic heat, which results in a super-adiabatic temperature profile and a viscosity increase with depth of no more than ~3 orders of magnitude, regardless of what is calculated for an adiabat. It has recently been argued [5] that at very high pressures, deformation

  5. The effect of plate motion history on the longevity of deep mantle heterogeneities

    Science.gov (United States)

    Bull, Abigail L.; Domeier, Mathew; Torsvik, Trond H.

    2014-09-01

    Understanding the first-order dynamical structure and evolution of Earth's mantle is a fundamental goal in solid-earth geophysics. Tomographic observations reveal a lower mantle characterised by higher-than-average shear-wave speeds beneath Asia and encircling the Pacific, consistent with cold slabs beneath regions of ancient subduction, and lower-than-average shear-wave speeds in broad regional areas beneath Africa and the Central Pacific (termed LLSVPs). The LLSVPs are not well understood from a dynamical perspective and their origin and evolution remain enigmatic. Some numerical studies propose that the LLSVP beneath Africa is post-Pangean in origin, formed as a result of return flow in the mantle due to circum-Pangean subduction, countered by an older Pacific LLSVP, suggested to have formed during the break up of Rodinia. This propounds that, prior to the formation of Pangea, the lower mantle was dominated by a degree-1 convection pattern with a major upwelling centred close to the present-day Pacific LLSVP and subduction concentrated mainly in the antipodal hemisphere. In contrast, palaeomagnetic observations which proffer a link between the reconstructed eruption sites of Phanerozoic kimberlites and Large Igneous Provinces with regions on the margins of the present-day LLSVPs suggest that the anomalies may have remained stationary for at least the last 540 Myr and further that the anomalies were largely insensitive to the formation and subsequent break-up of Pangea. Here we investigate the evolution and long-term stability of LLSVP-like structures in Earth's mantle by integrating plate tectonics and numerical models of global thermochemical mantle dynamics. We explore the possibility that either one or both LLSVPs existed prior to the formation of Pangea and improve upon previous studies by using a new, true polar wander-corrected global plate model to impose surface velocity boundary conditions for a time interval that spans the amalgamation and subsequent

  6. Upper Mantle Flow Beneath the Subducted Nazca Plate: Slab Contortions and Flattening (Invited)

    Science.gov (United States)

    Russo, R. M.

    2010-12-01

    The form of asthenospheric flow beneath subducted lithospheric slabs can be discerned using splitting of shear waves emanating from earthquakes in the slabs themselves. However, the subducted Nazca plate’s abrupt changes in morphology from a planar slab dipping 30° ENE beneath the central Andes to large areas of flat-lying slab beneath Peru, to the north, and Argentina, to the south, are a potential complication to the sub-slab mantle flow. S waves from earthquakes in the Nazca slab reveal details of the upper mantle flow field below and in the vicinity of the slab. Nazca slab earthquakes large enough to be well recorded (M > 5.4, typically), and deep enough to separate S from pS and sS (30-40 km or more), are suitable for such study, and, for events between 1990 and 2010, recording stations are mostly well-distributed azimuthally about the source event. The S waves were recorded at seismic stations at teleseismic distances from the events, and were corrected for known sub-station seismic anisotropy. Thus, the shear wave splitting engendered during their passage through the asthenospheric upper mantle beneath the slab was isolated, and asthenospheric deformation fabrics resulting from plastic flow beneath the slab mapped in some detail. Shear wave splitting fast directions and upper mantle flow beneath the Nazca plate are most often trench-parallel, consistent with trench-parallel upper mantle flow beneath the slab. Fast splitting polarizations at high angle to the strike of the slab occur in the transition regions from flat to normally dipping slab. Upper mantle flow beneath the slab in these regions appears to be channeled by the slab contortion. Upper mantle flow oceanward of the Nazca slab also appears to change abruptly from trends at a high angle to the Peru-Chile trench to trench-parallel as the top of the Nazca slab attains a depth of around 75 km. Trench-parallel sub-slab flow appears to develop once the asthenosphere beneath the Nazca plate is affected

  7. PENERAPAN ANIMASI INTERAKTIF DALAM PENGENALAN AKSARA SUNDA

    Directory of Open Access Journals (Sweden)

    Siti Maria Holida

    2016-03-01

    Full Text Available Abstract - Sundanese script is the work of Sundanese orthography to be maintained and preserved, because the Sundanese script is a cultural heritage that is priceless. Socialization of Sundanese script is very minimal done, although West Java government has to take legal actions in the form of regional regulations No. 5 of 2003 and the Governor's Decree no. 434 / SK.614 / dis-pk / 1999. Along with the increasing sophistication of technology, the use of interactive animations introduction Sundanese script can be used to promote literacy by explaining the meaning of the Sundanese, Sundanese script, history Sundanese script, how to write Sundanese script, as well as Sundanese script puzzle games as testing and entertainment. Application of interactive animation is the best solution which is very helpful in Sundanese script publicizes to the community, especially people of sundanese to be more interested in learning Sundanese script that became cultural heritage. Keywords : Interactive Animation , Script Sundanese Abstrak - Aksara Sunda merupakan hasil karya ortografi masyarakat Sunda yang harus dipelihara dan dilestarikan, karena aksara Sunda adalah warisan budaya yang tidak ternilai harganya. Sosialisasi aksara Sunda masih sangat minim dilakukan, meskipun pemerintah Jawa barat sudah melakukan upaya hukum dalam bentuk Peraturan daerah (Perda no.5 tahun 2003 dan Surat Keputusan Gubernur no. 434/SK.614/dis-pk/1999. Seiring dengan semakin canggihnya tekhnologi, penggunaan animasi interaktif pengenalan aksara sunda dapat digunakan untuk mensosialisasikan aksara Sunda dengan menjelaskan mengenai pengertian aksara Sunda, sejarah aksara Sunda, cara penulisan aksara Sunda, serta game puzzle aksara Sunda sebagai pengujian dan hiburannya. Penerapan animasi interaktif merupakan solusi terbaik yang sangat membantu dalam mensosialisakan aksara Sunda kepada masyarakat khususnya masyarakat Sunda agar lebih berminat mempelajari aksara Sunda yang menjadi warisan

  8. The life cycle of continental rifts: Numerical models of plate tectonics and mantle convection.

    Science.gov (United States)

    Ulvrova, Martina; Brune, Sascha; Williams, Simon

    2017-04-01

    Plate tectonic processes and mantle convection form a self-organized system whose surface expression is characterized by repeated Wilson cycles. Conventional numerical models often capture only specific aspects of plate-mantle interaction, due to imposed lateral boundary conditions or simplified rheologies. Here we study continental rift evolution using a 2D spherical annulus geometry that does not require lateral boundary conditions. Instead, continental extension is driven self-consistently by slab pull, basal drag and trench suction forces. We use the numerical code StagYY to solve equations of conservation of mass, momentum and energy and transport of material properties. This code is capable of computing mantle convection with self-consistently generated Earth-like plate tectonics using a pseudo-plastic rheology. Our models involve an incompressible mantle under the Boussinesq approximation with internal heat sources and basal heating. Due to the 2D setup, our models allow for a comparably high resolution of 10 km at the mantle surface and 15 km at the core mantle boundary. Viscosity variations range over 7 orders of magnitude. We find that the causes for rift initiation are often related to subduction dynamics. Some rifts initiate due to increasing slab pull, others because of developing trench suction force, for instance by closure of an intra-oceanic back-arc basin. In agreement with natural settings, our models reproduce rifts forming in both young and old collision zones. Our experiments show that rift dynamics follow a characteristic evolution, which is independent of the specific setting: (1) continental rifts initiate during tens of million of years at low extension rates (few millimetres per year) (2) the extension velocity increases during less than 10 million years up to several tens of millimetres per year. This speed-up takes place before lithospheric break-up and affects the structural architecture of rifted margins. (3) high divergence rates

  9. Heat transport in the Hadean mantle: From heat pipes to plates

    Science.gov (United States)

    Kankanamge, Duminda G. J.; Moore, William B.

    2016-04-01

    Plate tectonics is a unique feature of Earth, and it plays a dominant role in transporting Earth's internally generated heat. It also governs the nature, shape, and the motion of the surface of Earth. The initiation of plate tectonics on Earth has been difficult to establish observationally, and modeling of the plate breaking process has not consistently accounted for the nature of the preplate tectonic Earth. We have performed numerical simulations of heat transport in the preplate tectonic Earth to understand the transition to plate tectonic behavior. This period of time is dominated by volcanic heat transport called the heat pipe mode of planetary cooling. These simulations of Earth's mantle include heat transport by melting and melt segregation (volcanism), Newtonian temperature-dependent viscosity, and internal heating. We show that when heat pipes are active, the lithosphere thickens and lithospheric isotherms are kept flat by the solidus. Both of these effects act to suppress plate tectonics. As volcanism wanes, conduction begins to control lithospheric thickness, and large slopes arise at the base of the lithosphere. This produces large lithospheric stress and focuses it on the thinner regions of the lithosphere resulting in plate breaking events.

  10. Tracking the evolution of mantle sources with incompatible element ratios in stagnant-lid and plate-tectonic planets

    Science.gov (United States)

    Condie, Kent C.; Shearer, Charles K.

    2017-09-01

    The distribution of high field strength incompatible element ratios Zr/Nb, Nb/Th, Th/Yb and Nb/Yb in terrestrial oceanic basalts prior to 2.7 Ga suggests the absence or near-absence of an enriched mantle reservoir. Instead, most oceanic basalts reflect a variably depleted mantle source similar in composition to primitive mantle. In contrast, basalts from hydrated mantle sources (like those associated with subduction) exist from 4 Ga onwards. The gradual appearance of enriched mantle between 2 and 3 Ga may reflect the onset and propagation of plate tectonics around the globe. Prior to 3 Ga, Earth may have been in a stagnant-lid regime with most basaltic magmas coming from a rather uniform, variably depleted mantle source or from a non-subduction hydrated mantle source. It was not until the extraction of continental crust and accompanying propagation of plate tectonics that ;modern type; enriched and depleted mantle reservoirs developed. Consistent with the absence of plate tectonics on the Moon is the near absence of basalts derived from depleted (DM) and enriched (EM) mantle reservoirs as defined by the four incompatible element ratios of this study. An exception are Apollo 17 basalts, which may come from a mixed source with a composition similar to primitive mantle as one end member and a high-Nb component as the other end member. With exception of Th, which requires selective enrichment in at least parts of the martian mantle, most martian meteorites can be derived from sources similar to terrestrial primitive mantle or by mixing of enriched and depleted mantle end members produced during magma ocean crystallization. Earth, Mars and the Moon exhibit three very different planetary evolution paths. The mantle source regions for Mars and the Moon are ancient and have HFS element signatures of magma ocean crystallization well-preserved, and differences in these signatures reflect magma ocean crystallization under two distinct pressure regimes. In contrast, plate

  11. The Effect of Plate Motion History on the Longevity of Deep Mantle Heterogeneities

    Science.gov (United States)

    Bull, Abigail; Domeier, Mathew; Torsvik, Trond

    2014-05-01

    Numerical studies of mantle convection have attempted to explain tomographic observations that reveal a lower mantle dominated by broad regional areas of lower-than-average shear-wave speeds beneath Africa and the Central Pacific. The anomalous regions, termed LLSVPs ("large low shear velocity provinces"), are inferred to be thermochemical structures encircled by regions of higher-than-average shear-wave speeds associated with Mesozoic and Cenozoic subduction zones. The origin and long-term evolution of the LLSVPs remains enigmatic. It has been proposed that the LLSVP beneath Africa was not present before 240 Ma, prior to which time the lower mantle was dominated by a degree-1 convection pattern with a major upwelling centred close to the present-day Pacific LLSVP and subduction concentrated mainly in the antipodal hemisphere. The African LLSVP would thus have formed during the time-frame of the supercontinent Pangea as a result of return flow in the mantle due to circum-Pacific subduction. An opposing hypothesis, which propounds a more long-term stability for both the African and Pacific LLSVPs, is suggested by recent palaeomagnetic plate motion models that propose a geographic correlation between the surface eruption sites of Phanerozoic kimberlites, major hotspots and Large Igneous Provinces to deep regions of the mantle termed "Plume Generation Zones" (PGZs), which lie at the margins of the LLSVPs. If the surface volcanism was sourced from the PGZs, such a link would suggest that both LLSVPs may have remained stationary for at least the age of the volcanics. i.e., 540 Myr. To investigate these competing hypotheses for the evolution of LLSVPs in Earth's mantle, we integrate plate tectonic histories and numerical models of mantle dynamics and perform a series of 3D spherical thermochemical convection calculations with Earth-like boundary conditions. We improve upon previous studies by employing a new, TPW-corrected global plate motion model to impose surface

  12. Cascadia subducting plate fluids channelled to fore-arc mantle corner: ETS and silica deposition

    Science.gov (United States)

    Hyndman, Roy D; McCrory, Patricia A.; Wech, Aaron; Kao, Han; Ague, Jay j

    2015-01-01

    In this study we first summarize the constraints that on the Cascadia subduction thrust, there is a 70 km gap downdip between the megathrust seismogenic zone and the Episodic Tremor and Slip (ETS) that lies further landward; there is not a continuous transition from unstable to conditionally stable sliding. Seismic rupture occurs mainly offshore for this hot subduction zone. ETS lies onshore. We then suggest what does control the downdip position of ETS. We conclude that fluids from dehydration of the downgoing plate, focused to rise above the fore-arc mantle corner, are responsible for ETS. There is a remarkable correspondence between the position of ETS and this corner along the whole margin. Hydrated mineral assemblages in the subducting oceanic crust and uppermost mantle are dehydrated with downdip increasing temperature, and seismic tomography data indicate that these fluids have strongly serpentinized the overlying fore-arc mantle. Laboratory data show that such fore-arc mantle serpentinite has low permeability and likely blocks vertical expulsion and restricts flow updip within the underlying permeable oceanic crust and subduction shear zone. At the fore-arc mantle corner these fluids are released upward into the more permeable overlying fore-arc crust. An indication of this fluid flux comes from low Poisson's Ratios (and Vp/Vs) found above the corner that may be explained by a concentration of quartz which has exceptionally low Poisson's Ratio. The rising fluids should be silica saturated and precipitate quartz with decreasing temperature and pressure as they rise above the corner.

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

    Science.gov (United States)

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

    2016-05-01

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

  14. Mantle-derived peridotites in southwestern Oregon: relation to plate tectonics.

    Science.gov (United States)

    Medaris, L G; Dott, R H

    1970-09-04

    A group of peridotites in southwestern Oregon contains high-pressure mineral assemblages reflecting recrystallization at high temperatures (1100 degrees to 1200 degrees C) over a range of pressure decreasing from 19 to 5 kilobars. It is proposed that the peridotites represent upper-mantle material brought from depth along the ancestral Gorda-Juan de Fuca ridge system, transported eastward by the spreading Gorda lithosphere plate, and then emplaced by thrust-faulting in the western margin of the Cordillera during late Mesozoic time.

  15. Assessing the role of slab rheology in coupled plate-mantle convection models

    Science.gov (United States)

    Bello, Léa; Coltice, Nicolas; Tackley, Paul J.; Dietmar Müller, R.; Cannon, John

    2015-11-01

    Reconstructing the 3D structure of the Earth's mantle has been a challenge for geodynamicists for about 40 yr. Although numerical models and computational capabilities have substantially progressed, parameterizations used for modeling convection forced by plate motions are far from being Earth-like. Among the set of parameters, rheology is fundamental because it defines in a non-linear way the dynamics of slabs and plumes, and the organization of lithosphere deformation. In this study, we evaluate the role of the temperature dependence of viscosity (variations up to 6 orders of magnitude) and the importance of pseudo-plasticity on reconstructing slab evolution in 3D spherical models of convection driven by plate history models. Pseudo-plasticity, which produces plate-like behavior in convection models, allows a consistent coupling between imposed plate motions and global convection, which is not possible with temperature-dependent viscosity alone. Using test case models, we show that increasing temperature dependence of viscosity enhances vertical and lateral coherence of slabs, but leads to unrealistic slab morphologies for large viscosity contrasts. Introducing pseudo-plasticity partially solves this issue, producing thin laterally and vertically more continuous slabs, and flat subduction where trench retreat is fast. We evaluate the differences between convection reconstructions employing different viscosity laws to be very large, and similar to the differences between two models with the same rheology but using two different plate histories or initial conditions.

  16. Structures in the Deep Mantle: Implications for the Onset of Plate Tectonics and the Viscosity Structure

    Science.gov (United States)

    Stein, Claudia; Hansen, Ulrich

    2016-04-01

    Recently deep structures have been studied intensively. The observed large anomalies with reduced seismic velocities (LLSVPs) beneath Africa and the Pacific are obtained in numerical models as an initial dense layer at the core-mantle boundary (CMB) is pushed up to piles by the convective flow (e.g., McNamara et al., EPSL 229, 1-9, 2010). Adding a dense CMB layer to a model featuring active plate tectonics, Trim et al. (EPSL 405, 1-14, 2014) find that surface mobility is strongly hindered by the dense material and can even vanish completely for a CMB layer that has a too high density or too large a volume. In a further study we employed a fully rheological model in which oceanic plates form self-consistently. We observe that an initial dense CMB layer strongly affects the formation of plates and therefore the onset time of plate tectonics. In a systematic 2D parameter study of thermochemical convection we discuss the resulting viscosity structure and time of plate initiation.

  17. Crustal and upper mantle seismic structure of the Australian Plate, South Island, New Zealand

    Science.gov (United States)

    Melhuish, Anne; Holbrook, W. Steven; Davey, Fred; Okaya, David A.; Stern, Tim

    2005-01-01

    Seismic reflection and refraction data were collected west of New Zealand's South Island parallel to the Pacific-Australian Plate boundary. The obliquely convergent plate boundary is marked at the surface by the Alpine Fault, which juxtaposes continental crust of each plate. The data are used to study the crustal and uppermost mantle structure and provide a link between other seismic transects which cross the plate boundary. Arrival times of wide-angle reflected and refracted events from 13 recording stations are used to construct a 380-km long crustal velocity model. The model shows that, beneath a 2-4-km thick sedimentary veneer, the crust consists of two layers. The upper layer velocities increase from 5.4-5.9 km/s at the top of the layer to 6.3 km/s at the base of the layer. The base of the layer is mainly about 20 km deep but deepens to 25 km at its southern end. The lower layer velocities range from 6.3 to 7.1 km/s, and are commonly around 6.5 km/s at the top of the layer and 6.7 km/s at the base. Beneath the lower layer, the model has velocities of 8.2-8.5 km/s, typical of mantle material. The Mohorovicic discontinuity (Moho) therefore lies at the base of the second layer. It is at a depth of around 30 km but shallows over the south-central third of the profile to about 26 km, possibly associated with a southwest dipping detachment fault. The high, variable sub-Moho velocities of 8.2 km/s to 8.5 km/s are inferred to result from strong upper mantle anisotropy. Multichannel seismic reflection data cover about 220 km of the southern part of the modelled section. Beneath the well-layered Oligocene to recent sedimentary section, the crustal section is broadly divided into two zones, which correspond to the two layers of the velocity model. The upper layer (down to about 7-9 s two-way travel time) has few reflections. The lower layer (down to about 11 s two-way time) contains many strong, subparallel reflections. The base of this reflective zone is the Moho. Bi

  18. Tsunamigenik di Selat Sunda: Kajian terhadap katalog Tsunami Soloviev

    Directory of Open Access Journals (Sweden)

    Yudhicara Yudhicara

    2014-06-01

    Full Text Available http://dx.doi.org/10.17014/ijog.vol3no4.20086Tsunamigenic is a natural phenomena which is potential to generate a tsunami, such as water dis- turbance due to the presence of activities of volcanism, earthquakes, coastal and sub marine landslidse, or other causal factors . Historically, the Sunda Strait has experienced several tsunami events recorded in the tsunami catalog. Those tsunamies were caused by some geological phenomena such as eruptions of Krakatau submarine volcano in 416, 1883, and 1928; earthquakes in 1722, 1852, and 1958; and other causes which were suggested as a mass failure of coastal and submarine landslide in 1851, 1883, and 1889. Tectonic condition of the Sunda Strait is very complicated, because this region is located at the boundary of Indian-Australian and Eurasian Plates, where a unique island arc system occurs with its association such as trench, accretionary zone, volcanic arc and back-arc basin. Sunda trench as a plate boundary is the most potential region to produce big earthquakes. Existence of a seismic gap in the region can cause a stress accumulation and store energy, then it will be released any time as a big earthquake to generate a tsunami. Along eruption history, Krakatau volcanic arc has four stages of reconstruction and three stages of destruction, and every destruction stage produces tsunami which is suggested to be potentially repeated in the future in a period between 2500 to 2700. Seafloor of the Sunda Strait has an unstable geological condition due to geological structure development, which creates grabens and also enable to produce submarine landslides triggered by earthquake. Coastal condition around the Semangko and Lampung Bays consisting of steep topography with high intensity of weathering, is another factor to contribute landslide, particularly in the case of triggering be heavy rainfall between December to Februari. Furthermore, if landslide materials tumble into the water, even very small and

  19. A New Comprehensive Model for Crustal and Upper Mantle Structure of the European Plate

    Science.gov (United States)

    Morelli, A.; Danecek, P.; Molinari, I.; Postpischl, L.; Schivardi, R.; Serretti, P.; Tondi, M. R.

    2009-12-01

    We present a new comprehensive model of crustal and upper mantle structure of the whole European Plate — from the North Atlantic ridge to Urals, and from North Africa to the North Pole — describing seismic speeds (P and S) and density. Our description of crustal structure merges information from previous studies: large-scale compilations, seismic prospection, receiver functions, inversion of surface wave dispersion measurements and Green functions from noise correlation. We use a simple description of crustal structure, with laterally-varying sediment and cristalline layers thickness and seismic parameters. Most original information refers to P-wave speed, from which we derive S speed and density from scaling relations. This a priori crustal model by itself improves the overall fit to observed Bouguer anomaly maps, as derived from GRACE satellite data, over CRUST2.0. The new crustal model is then used as a constraint in the inversion for mantle shear wave speed, based on fitting Love and Rayleigh surface wave dispersion. In the inversion for transversely isotropic mantle structure, we use group speed measurements made on European event-to-station paths, and use a global a priori model (S20RTS) to ensure fair rendition of earth structure at depth and in border areas with little coverage from our data. The new mantle model sensibly improves over global S models in the imaging of shallow asthenospheric (slow) anomalies beneath the Alpine mobile belt, and fast lithospheric signatures under the two main Mediterranean subduction systems (Aegean and Tyrrhenian). We map compressional wave speed inverting ISC travel times (reprocessed by Engdahl et al.) with a non linear inversion scheme making use of finite-difference travel time calculation. The inversion is based on an a priori model obtained by scaling the 3D mantle S-wave speed to P. The new model substantially confirms images of descending lithospheric slabs and back-arc shallow asthenospheric regions, shown in

  20. Preliminary result of 3-D attenuation tomography beneath Sunda Strait and western part of Java

    Science.gov (United States)

    Anshori, Muhajir; Nugraha, Andri Dian; Puspito, Nanang T.

    2017-07-01

    Sunda strait lies in the transition zone of two different subduction system that is almost perpendicular to the subduction in southern Java and oblique subduction in western Sumatra. The series of major disasters such as earthquakes and volcanic eruptions is a manifestation of its tectonic setting complexity. We used selected waveform data from724 earthquakes that occurred around the Sunda strait and western part of Java from 2009 - 2015 recorded by 21 MCGA network stations to construct three dimensional image of seismic attenuation. Frequency independent attenuation operators (t*) was determined using spectral fitting method for P and S wave arrivals, respectively. The inversion was performed using simul2000 algorithm to image the lateral and vertical variations of Qp and Qs value in the Sunda Strait and western part of Java. Some interesting features such as subducting slab, mantle wedge, magma chamber under volcanos and fault zones can be imaged well.

  1. Reconstructing the Cenozoic evolution of the mantle: Implications for mantle plume dynamics under the Pacific and Indian plates

    Science.gov (United States)

    Glišović, Petar; Forte, Alessandro M.

    2014-03-01

    The lack of knowledge of the initial thermal state of the mantle in the geological past is an outstanding problem in mantle convection. The resolution of this problem also requires the modelling of 3-D mantle evolution that yields maximum consistency with a wide suite of geophysical constraints. Quantifying the robustness of the reconstructed thermal evolution is another major concern. To solve and estimate the robustness of the time-reversed (inverse) problem of mantle convection, we analyse two different numerical techniques: the quasi-reversible (QRV) and the backward advection (BAD) methods. Our investigation extends over the 65 Myr interval encompassing the Cenozoic era using a pseudo-spectral solution for compressible-flow thermal convection in 3-D spherical geometry. We find that the two dominant issues for solving the inverse problem of mantle convection are the choice of horizontally-averaged temperature (i.e., geotherm) and mechanical surface boundary conditions. We find, in particular, that the inclusion of thermal boundary layers that yield Earth-like heat flux at the top and bottom of the mantle has a critical impact on the reconstruction of mantle evolution. We have developed a new regularisation scheme for the QRV method using a time-dependent regularisation function. This revised implementation of the QRV method delivers time-dependent reconstructions of mantle heterogeneity that reveal: (1) the stability of Pacific and African ‘large low shear velocity provinces’ (LLSVP) over the last 65 Myr; (2) strong upward deflections of the CMB topography at 65 Ma beneath: the North Atlantic, the south-central Pacific, the East Pacific Rise (EPR) and the eastern Antarctica; (3) an anchored deep-mantle plume ascending directly under the EPR (Easter and Pitcairn hotspots) throughout the Cenozoic era; and (4) the appearance of the transient Reunion plume head beneath the western edge of the Deccan Plateau at 65 Ma. Our reconstructions of Cenozoic mantle

  2. Is the Juan Fernandez Ridge (nazca Plate) a Deep-Mantle Hot SPOT Trail?

    Science.gov (United States)

    Lara, L. E.; Selles, D.; Díaz, A.; Piña-Gauthier, M.

    2011-12-01

    The Juan Fernández Ridge on the oceanic Nazca plate is thought to be a classic hot spot trail because of the apparent westward rejuvenation of the eruptive ages. Geochronological data is still scarce to prove this is the case, and other hypothesis should be taken into account. There are a few constrains, like the ca. 9 Ma Ar-Ar age of the O'Higgins seamount (115 km from the Chile-Perú trench), published K-Ar ages of ca. 3-4 Ma in Robinson Crusoe island (580 km from the trench) and ca. 1 Ma in Alejandro Selkirk (180 km further west). New reconnaissance K-Ar ages in Robinson Crusoe yield ca. 1-3 Ma, which partially overlap with the age of Alejandro Selkirk, breaking the expected age progression given that the Nazca plate moves eastwards at ca. 6-8 cm/yr. New geological mapping also shows a sharp unconformity between the older, strongly altered sequences and more recent, post-erosional volcanic piles, where only the vent facies have disappeared. A fixed deep-mantle plume origin for Pacific hot spots has been widely debated and concurrent phenomena arose as a possible explanation for non-linear age progressions and/or long-lived volcanic activity. In fact, intraplate regional tectonics, plume displacement, and mantle heterogeneities could be the main factor of the ridge architecture or the mask for a first-order linear trend. An ongoing mapping and dating effort is aimed to understand the evolution of the Juan Fernández Ridge, testing the main hypothesis. Fondecyt grant 110966 is acknowledged for financial support.

  3. Understanding seismic heterogeneities in the lower mantle beneath the Americas from seismic tomography and plate tectonic history

    NARCIS (Netherlands)

    Ren, Y.; Stutzmann, E.; Hilst, R.D. van der; Besse, J.

    2007-01-01

    We combine results from seismic tomography and plate motion history to investigate slabs of subducted lithosphere in the lower mantle beneath the Americas. Using broadband waveform cross correlation, we measured 37,000 differential P and S traveltimes, 2000 PcP-P and ScS-S times along a wide corrido

  4. Understanding seismic heterogeneities in the lower mantle beneath the Americas from seismic tomography and plate tectonic history

    NARCIS (Netherlands)

    Ren, Y.; Stutzmann, E.; Hilst, R.D. van der; Besse, J.

    2007-01-01

    We combine results from seismic tomography and plate motion history to investigate slabs of subducted lithosphere in the lower mantle beneath the Americas. Using broadband waveform cross correlation, we measured 37,000 differential P and S traveltimes, 2000 PcP-P and ScS-S times along a wide corrido

  5. 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

  6. Azimuthal seismic anisotropy in the Earth's upper mantle and the thickness of tectonic plates

    Science.gov (United States)

    Schaeffer, A. J.; Lebedev, S.; Becker, T. W.

    2016-11-01

    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. Here, we present a new global, azimuthally anisotropic model of the crust, upper mantle and transition zone. Two versions of this new model are computed: the rough SL2016svAr and the smooth SL2016svA. Both are constrained by a very large data set of waveform fits (˜750 000 vertical component seismogram fits). Automated, multimode waveform inversion was used to extract structural information from surface and S wave forms in broad period ranges (dominantly from 11 to 450 s, with the best global sampling in the 20-350 s range), yielding resolving power from the crust down to the transition zone. In our global tomographic inversion, regularization of anisotropy is implemented to more uniformly recover the amplitude and orientation of anisotropy, including near the poles. Our massive waveform data set, with complementary large global networks and high-density regional array data, produces improved resolution of global azimuthal anisotropy patterns. We show that regional scale variations, related to regional lithospheric deformation and mantle flow, can now be resolved by the global models, in particular in densely sampled regions. For oceanic regions, we compare quantitatively the directions of past and present plate motions and the fast-propagation orientations of anisotropy. By doing so, we infer the depth of the boundary between the rigid, high-viscosity lithosphere (preserving ancient, frozen fabric) and the rheologically weak asthenosphere (characterized by fabric developed recently). The average depth of thus inferred rheological lithosphere-asthenosphere boundary (LAB) beneath the world's oceans is ˜115 km. The LAB depth displays a clear dependence on the age of the oceanic

  7. 100 Ma: the new frontier for quantitative global models of the coupled brittle-plates/viscous-mantle system.

    Science.gov (United States)

    Stotz, Ingo; Iaffaldano, Giampiero; Davies, Rhodri

    2014-05-01

    Over recent decades the body of geophysical datasets has grown substantially and rapidly. Ocean-floor observations now allow one to unravel past plate motions (for instance, in the North Atlantic and Indian Ocean over the past 20 Myr) at the unprecedented temporal resolution of about 1 Myr; and more data is anticipated in the near future. Similarly, our knowledge of continental evolution has grown due to advances in interpreting the records of orogeny and sedimentation. Altogether, these ever-growing datasets allow us to reconstruct the past evolution of Earth's lithospheric plates in greater detail than previously achieved. This is key to unravel the dynamics of geological processes, because reconstructed plate motions and their temporal changes are a powerful probe into the evolving balance of shallow- and deep-rooted forces. Such progress, however, is not yet matched by the ability to quantitatively model past plate-motion changes and, therefore to test hypotheses on the dominant geological controls. The main technical challenge is simulating the rheological behaviour of the plates/mantle system, which varies significantly from viscous to brittle. Classically, computer models for viscous mantle flow and for the piecewise motions of the brittle lithosphere have been developed separately. In recent years, coupling of these two independent classes of models has been pioneered, but only for neo-tectonic scenarios (i.e. past few Myr), and with some limitations as to accounting for the impact of evolving mantle-flow on plate motions. It is now timely to further advance the technical ability to simulate the coupled plates/mantle system through geological time (for instance throughout the Cenozoic and possibly the Cretaceous), and to use the growing body of geophysical data as a primary constraint on these quantitative models. In this project, we take steps in this direction. We build on previous work aimed at coupling two advanced codes for mantle flow and lithosphere

  8. The effect of plumes and a free surface on mantle dynamics with continents and self-consistent plate tectonics

    Science.gov (United States)

    Jain, Charitra; Rozel, Antoine; Tackley, Paul

    2014-05-01

    Rolf et al. (EPSL, 2012) and Coltice et al. (Science, 2012) investigated the thermal and dynamical influences of continents on plate tectonics and the thermal state of Earth's mantle, but they did not explicitly consider the influence of mantle plumes. When present, strong mantle plumes arising from the deep mantle can impose additional stresses on the continents, thereby facilitating continental rifting (Storey, Nature 1995; Santosh et al., Gondwana Research 2009) and disrupting the supercontinent cycle (Philips and Bunge, Geology 2007). In recent years, several studies have characterized the relation between the location of the plumes and the continents, but with contradicting observations. While Heron and Lowman (GRL, 2010; Tectonophysics, 2011) propose regions where downwelling has ceased (irrespective of overlying plate) as the preferred location for plumes, O'Neill et al. (Gondwana Research, 2009) show an anti-correlation between the average positions of subducting slabs at continental margins, and mantle plumes at continental/oceanic interiors. Continental motion is attributed to the viscous stresses imparted by the convecting mantle and the extent of this motion depends on the heat budget of the mantle. Core-mantle boundary (CMB) heat flux, internal heating from decay of radioactive elements, and mantle cooling contribute to this heat budget. Out of these sources, CMB heat flux is not well defined; however, the recent determination that the core's thermal conductivity is much higher than previously thought requires a CMB heat flow of at least 12 TW (de Koker et al., PNAS 2012; Pozzo et al., Nature 2012; Gomi et al., PEPI 2013), much higher than early estimates of 3-4 TW (Lay et al., Nature 2008). Thus, it is necessary to characterize the effect of increased CMB heat flux on mantle dynamics. In almost all mantle convection simulations, the top boundary is treated as a free-slip surface whereas Earth's surface is a deformable free surface. With a free

  9. Development of three dimensional Eulerian numerical procedure toward plate-mantle simulation: accuracy test by the fluid rope coiling

    Science.gov (United States)

    Furuichi, M.; Kameyama, M.; Kageyama, A.

    2007-12-01

    Reproducing a realistic plate tectonics with mantle convection simulation is one of the greatest challenges in computational geophysics. We have developed a three dimensional Eulerian numerical procedure toward plate-mantle simulation, which includes a finite deformation of the plate in the mantle convection. Our method, combined with CIP-CSLR (Constrained Interpolation Profile method-Conservative Semi-Lagrangian advection scheme with Rational function) and ACuTE method, enables us to solve advection and force balance equations even with a large and sharp viscosity jump, which marks the interface between the plates and surrounding upper mantle materials. One of the typical phenomena represented by our method is a fluid rope coiling event, where a stream of viscous fluid is poured onto the bottom plane from a certain height. This coiling motion is due to delicate balances between bending, twisting and stretching motions of fluid rope. In the framework of the Eulerian scheme, the fluid rope and surrounding air are treated as a viscosity profile which differs by several orders of magnitude. Our method solves the complex force balances of the fluid rope and air, by a multigrid iteration technique of ACuTE algorithm. In addition, the CIP-CSLR advection scheme allows us to obtain a deforming shape of the fluid rope, as a low diffusive solution in the Eulerian frame of reference. In this presentation, we will show the simulation result of the fluid rope coiling as an accuracy test for our simulation scheme, by comparing with the simplified numerical solution for thin viscous jet.

  10. Quantifying melt production and degassing rate at mid-ocean ridges from global mantle convection models with plate motion history

    Science.gov (United States)

    Li, Mingming; Black, Benjamin; Zhong, Shijie; Manga, Michael; Rudolph, Maxwell L.; Olson, Peter

    2016-07-01

    The Earth's surface volcanism exerts first-order controls on the composition of the atmosphere and the climate. On Earth, the majority of surface volcanism occurs at mid-ocean ridges. In this study, based on the dependence of melt fraction on temperature, pressure, and composition, we compute melt production and degassing rate at mid-ocean ridges from three-dimensional global mantle convection models with plate motion history as the surface velocity boundary condition. By incorporating melting in global mantle convection models, we connect deep mantle convection to surface volcanism, with deep and shallow mantle processes internally consistent. We compare two methods to compute melt production: a tracer method and an Eulerian method. Our results show that melt production at mid-ocean ridges is mainly controlled by surface plate motion history, and that changes in plate tectonic motion, including plate reorganizations, may lead to significant deviation of melt production from the expected scaling with seafloor production rate. We also find a good correlation between melt production and degassing rate beneath mid-ocean ridges. The calculated global melt production and CO2 degassing rate at mid-ocean ridges varies by as much as a factor of 3 over the past 200 Myr. We show that mid-ocean ridge melt production and degassing rate would be much larger in the Cretaceous, and reached maximum values at ˜150-120 Ma. Our results raise the possibility that warmer climate in the Cretaceous could be due in part to high magmatic productivity and correspondingly high outgassing rates at mid-ocean ridges during that time.

  11. Geological evidence for the geographical pattern of mantle return flow and the driving mechanism of plate tectonics

    Energy Technology Data Exchange (ETDEWEB)

    Alvarez, W.

    1982-08-10

    Tectonic features at the earth's surface can be used to test models for mantle return flow and to determine the geographic pattern of this flow. A model with shallow return and deep continental roots places the strongest constraints on the geographical pattern of return flow and predicts recognizable surface manifestations. Because of the progressive shrinkage of the Pacific (averaging 0.5 km/sup 2//yr over the last 180 m.y.) this model predicts upper mantle outflow through the three gaps in the chain of continents rimming the Pacific (Carribbean, Drake Passage, Australian-Antartic gap). In this model, upper mantle return flow streams originating at the western Pacific trenches and at the Java Trench meet south of Australia, filling in behind this rapidly northward-moving continent and provding an explanation for the negative bathymetric and gravity anomalies of the 'Australian-Antarctic-Discordance'. The long-continued tectonic movements toward the east that characterize the Caribbean and the eastenmost Scotia Sea may be produced by viscous coupling to the predicted Pacific outflow through the gaps, and the Caribbean floor slopes in the predicted direction. If mantle outflow does not pass through the gaps in the Pacific perimeter, it must pass beneath three seismic zones (Central America, Lesser Antiles, Scotia Sea); none of these seismic zones shows foci below 200 km. Mantle material flowing through the Caribbean and Drake Passage gaps would supply the Mid-Atlantic Ridge, while the Java Trench supplies the Indian Ocean ridges, so that deep-mantle upwellings need not be centered under spreading ridges and therefore are not required to move laterally to follow ridge migrations. The analysis up to this point suggests that upper mantle return flow is a response to the motion of the continents. The second part of the paper suggest driving mechanism for the plate tectonic process which may explain why the continents move.

  12. Time variability in Cenozoic reconstructions of mantle heat flow: plate tectonic cycles and implications for Earth's thermal evolution.

    Science.gov (United States)

    Loyd, S J; Becker, T W; Conrad, C P; Lithgow-Bertelloni, C; Corsetti, F A

    2007-09-04

    The thermal evolution of Earth is governed by the rate of secular cooling and the amount of radiogenic heating. If mantle heat sources are known, surface heat flow at different times may be used to deduce the efficiency of convective cooling and ultimately the temporal character of plate tectonics. We estimate global heat flow from 65 Ma to the present using seafloor age reconstructions and a modified half-space cooling model, and we find that heat flow has decreased by approximately 0.15% every million years during the Cenozoic. By examining geometric trends in plate reconstructions since 120 Ma, we show that the reduction in heat flow is due to a decrease in the area of ridge-proximal oceanic crust. Even accounting for uncertainties in plate reconstructions, the rate of heat flow decrease is an order of magnitude faster than estimates based on smooth, parameterized cooling models. This implies that heat flow experiences short-term fluctuations associated with plate tectonic cyclicity. Continental separation does not appear to directly control convective wavelengths, but rather indirectly affects how oceanic plate systems adjust to accommodate global heat transport. Given that today's heat flow may be unusually low, secular cooling rates estimated from present-day values will tend to underestimate the average cooling rate. Thus, a mechanism that causes less efficient tectonic heat transport at higher temperatures may be required to prevent an unreasonably hot mantle in the recent past.

  13. Water Release from Cold Serpentinized Forearc Mantle During Subduction Associated with Changes in Incoming Oceanic Plate Thermal Structure and Plate Boundary Kinematics: New Insights

    Science.gov (United States)

    Kirby, S. H.

    2015-12-01

    Kirby, Wang, and Brocher (Earth Planets and Space, 2014) recently showed how the change in kinematics of the California margin from subduction motion to continental transform motion with the birth and growth of the San Andreas Fault System (SAFS) beginning at about 33 Ma BP likely led to a warming of the former forearc mantle and the release of water by serpentinite dehydration. Such discharges from serpentinized mantle increase fluid pressures along the SAFS under the Coast Ranges and this gives insights into both the low sliding resistance for the SAFS and the mobilization and ascent of some serpentinized mantle peridotites through the crust. Thermal modeling by others has also shown that changes in the incoming plate age and subduction rate can also lead to warming of the forearc mantle during subduction. This development gives insights into the Mesozoic and Paleogene ages of emplacement of some, but not all, California serpentinites. Recent mineralogical and geochemical observations of serpentinized blocks in serpentinize mélange bodies in the San Francisco Bay Area (Uno and Kirby, 2015; Lewis and Kirby, 2015, this session) suggest that these rocks sustained multiple stages of serpentinization that are broadly consistent with the model of Kirby et al. (2014). Previous studies of localized late-stage silica-carbonate-water alteration of serpentinite bodies in California by carbonated water suggest that this alteration occurred largely in Neogene time when the highest rate of water release from the former forearc mantle probably happened. I also suggest that the occurrence of serpentinite belts emplaced in Cenozoic time during changing plate-boundary kinematics, such as the Cenozoic closing of the Tethys Ocean bordering Eurasia and arc reversal and decreasing convergence rates under the Greater Antilles, may give insights into the serpentinite belts in those regions.

  14. Mantle plume related dynamic uplift and plate kinematics: The NE Atlantic case with global implications.

    Science.gov (United States)

    Skogseid, Jakob; Khabbaz Ghazian, Reza; Lunt, Ian

    2014-05-01

    At present a pronounced residual depth anomaly (RDA), centred on Iceland, is characterizing the bathymetry of the NE Atlantic region. For the oceanic lithosphere this anomaly represents a 2500 m elevation difference compared to 'normal' oceanic lithosphere. The observed depth anomaly has since Cochran and Talwani (1978) been ascribed to a 200 -300 km thick moderate thermal anomaly beneath the oceanic lithosphere, the existence of which today has been proven by a sizable low velocity zone on seismic tomography data. The sub-lithosphere low velocities are, however, not limited to the oceanic domain, but also underlie the adjacent continental lithosphere, thus causing a similar magnitude anomalous elevation of the continental shelves and landmasses. The thermal anomaly is presumed to relate to the arrival of the Iceland mantle plume demonstrated by excess Paleocene and Early Eocene magmatism and the formation of the North Atlantic Volcanic Province (NAVP), and subsequent volcanic margin formation. The present width of the RDA compares with the size of the regions that experienced excess magmatism during rifting and breakup, which implies that the sub-lithospheric thermally anomalous body was emplaced in Paleocene time, but still resides in the area. This presentation aims to describe the temporal and spatial development of uplift based on combining plate kinematic modeling with models of lithospheric and plume body thickness development through Late Cretaceous-Paleocene extension, and subsequent seafloor spreading. The model prediction of uplift compares well with descriptions of erosional episodes and depositional sequences off Greenland, in the Northern North Sea, off mid-Norway and in the SW Barents Sea, and represents a mechanism that explains the present elevation of East Greenland as well as western Norway. In a global perspective the close correlation between Large Igneous Provinces (LIP's), the arrival of known mantle plumes and formation of volcanic margins

  15. The Nature of Mantle Sources for Perm-Triassic Traps of Western Siberian Plate and Siberian Platform

    Science.gov (United States)

    Sharapov, V.; Perepechko, Y.; Rakhmenkulova, I.

    2007-12-01

    This work deals with the consistent dynamics for the development of melting zones due to convection in the upper mantle and the adjacent melting zones in inhomogeneous lithosphere. This model is studied for magma systems of Western Siberian Plate and Siberian Platform (SP). The results of numerical modeling allow us to conclude the following: 1. Structural and petrochemical zoning for Perm-Triassic trap magmatism of the Siberian Platform can be explained due to two-level melting of mantle rocks over hotspots (McKenzie, 1984). An alternative approach to explain mechanism of trap magmatism because of hydrodynamic evolution of magma under inhomogeneous lithosphere (King, Anderson, 1995) does not allow us to obtain voluminous melting of the mantle rocks for the lithosphere. 2. Main volumes of tholeiitic magmas (which compose both the intrusives in the SP platform cover and SP profiles of lava shield) are due to melting of mantle rocks in the thinned parts of the lithosphere over a number of spread hotspots. 3. The area of partial melting in the lithosphere is appearing after the zone of decompressing melting developed to its maximum extent, under the conditions of convection in the upper mantle. The melting zone appearing at the depth about 70-100 km has a plate-like shape, thickness up to ~20-30 km and horizontal extent coexistent with the sizes of the lava shield. This research was supported by the President's grants NSh-1573.2003.5, and by the Russian Ministry Science and Education grant RNP.2.1.1.702.

  16. A source-sink model of the generation of plate tectonics from non-Newtonian mantle flow

    Science.gov (United States)

    Bercovici, David

    1995-01-01

    A model of mantle convection which generates plate tectonics requires strain rate- or stress-dependent rheology in order to produce strong platelike flows with weak margins as well as strike-slip deformation and plate spin (i.e., toroidal motion). Here, we employ a simple model of source-sink driven surface flow to determine the form of such a rheology that is appropriate for Earth's present-day plate motions. In this model, lithospheric motion is treated as shallow layer flow driven by sources and sinks which correspond to spreading centers and subduction zones, respectively. Two plate motion models are used to derive the source sink field. As originally implied in the simpler Cartesian version of this model, the classical power law rheologies do not generate platelike flows as well as the hypothetical Whitehead-Gans stick-slip rheology (which incorporates a simple self-lubrication mechanism). None of the fluid rheologies examined, however, produce more than approximately 60% of the original maximum shear. For either plate model, the viscosity fields produced by the power law rheologies are diffuse, and the viscosity lows over strike-slip shear zones or pseudo-margins are not as small as over the prescribed convergent-divergent margins. In contrast, the stick-slip rheology generates very platelike viscosity fields, with sharp gradients at the plate boundaries, and margins with almost uniformly low viscosity. Power law rheologies with high viscosity contrasts, however, lead to almost equally favorable comparisons, though these also yield the least platelike viscosity fields. This implies that the magnitude of toroidal flow and platelike strength distributions are not necessarily related and thus may present independent constraints on the determination of a self-consistent plate-mantle rheology.

  17. Development of Stokes flow solver against a large contrast in viscosity: toward plate-mantle simulation with free surface

    Science.gov (United States)

    Furuichi, M.

    2009-12-01

    We are interested in solving a large-scale plate-mantle simulation enables capture of the large and complex deformation of a subducting plate. In our earlier study (Furuichi, et al 2008), we developed a numerical method toward plate-mantle simulation especially for the highly parallel vector supercomputer system (e.g. Earth Simulator). Our scheme is based on the finite volume method combines (i) the multigrid technique together with ACuTE smoother algorithm (Kameyama et al., 2005), and (ii) the low diffusive CIP-CSLR advection. The validity test of our simulation code by using a fluid rope coiling event (Furuichi, et al 2009) showed that our method enable us to reproduce large non-linear deformation problems of a rigid plate surrounded by soft material without serious quantitative errors. Then as a next step, I am trying to create a Stokes flow solver scalable against a large jump in a viscosity profile, for moving surface (geometrically free boundary) problems. It is for solving the Stokes flow motion under the same condition as real earth. In this presentation, I propose to apply BFBt preconditioner and AMG techniques for the problems of large viscosity contrast and moving free surface boundary condition respectively. I would like to show some numerical experiments for a self-gravitating motion of the layered Stokes flow.

  18. A Review of the Isotopic and Trace Element Evidence for Mantle and Crustal Processes in the Hadean and Archean: implications for the Onset of Plate Tectonic Subduction

    Science.gov (United States)

    Smart, Katie A.; Tappe, Sebastian; Stern, Richard A.; Webb, Susan J.; Ashwal, Lewis D.

    2016-03-01

    Plate tectonics plays a vital role in the evolution of our planet. Geochemical analysis of Earth’s oldest continental crust suggests that subduction may have begun episodically about 3.8 to 3.2 billion years ago, during the early Archaean or perhaps more than 3.8 billion years ago, during the Hadean. Yet, mantle rocks record evidence for modern-style plate tectonics beginning only in the late Archaean, about 3 billion years ago. Here we analyse the nitrogen abundance, as well as the nitrogen and carbon isotopic signatures of Archaean placer diamonds from the Kaapvaal craton, South Africa, which formed in the upper mantle 3.1 to 3.5 billion years ago. We find that the diamonds have enriched nitrogen contents and isotopic compositions compared with typical mantle values. This nitrogen geochemical fingerprint could have been caused by contamination of the mantle by nitrogen-rich Archaean sediments. Furthermore, the carbon isotopic signature suggests that the diamonds formed by reduction of an oxidized fluid or melt. Assuming that the Archaean mantle was more reduced than the modern mantle, we argue that the oxidized components were introduced to the mantle by crustal recycling at subduction zones. We conclude, on the basis of evidence from mantle-derived diamonds, that modern-style plate tectonics operated as early as 3.5 billion years ago.

  19. Wayang dalam Tari Sunda Gaya Priangan

    Directory of Open Access Journals (Sweden)

    Iyus Rusliana

    2017-03-01

    ABSTRAK   Tulisan ini merupakan kajian terhadap potensi wayang dalam lingkup budaya Sunda subkultur Priangan, khususnya seni tari. Awalnya kata wayang diartikan untuk menyebut boneka dari kayu yang dimainkan dalang dalam pertunjukan seni pedalangan atau untuk menunjukkan ceritanya dalam pertunjukan seni padalangan, dan juga bisa secara langsung untuk menyebut seni padalangan Wayang Golek. Selanjutnya potensi wayang ini berpengaruh kuat ke dalam beberapa aspek kehidupan yang berbau kepercayaan dan juga kesenian, termasuk ke tari Sunda gaya Priangan. Karena wayang mengandung makna religius yang tersirat dalam isi ceritanya, maka wayang dalam tari Sunda gaya Priangan tidaklah lepas dari misi atau pesan moral ke arah tuntunan hidup. Lahirnya Wayang Wong Priangan, terungkap sebagai bentuk dramatari berdialog dengan membawakan cerita wayang secara utuh atau sebagian, dan senantiasa adanya pertentangan antara tokoh wayang yang jahat dengan yang menumpas kejahatan.   Kata kunci: subkultur Priangan, Tari Wayang, gaya Priangan

  20. Kreativitas Mang Koko dalam Karawitan Sunda

    Directory of Open Access Journals (Sweden)

    Tardi Ruswandi

    2016-03-01

    ABSTRAK   Penelitian ini terfokus pada kreativitas Mang Koko dalam menciptakan lagu-lagu dan gending sebagai pengiring lagu. Kreativitas Mang Koko dianalisis dengan menggunakan teori Dedi Supriadi (1994:7 yang menjelaskan bahwa kreativitas merupakan kemampuan seseorang untuk melahirkan sesuatu yang baru, baik berupa gagasan maupun karya nyata, yang relatif   berbeda dengan apa yang telah ada sebelumnya. Mang Koko merupakan seniman kreatif dan produktif dalam berkarya yang hingga saat ini masih diperhitungkan. Dalam mengembangkan karawitan Sunda dan melahirkan genre baru, Mang Koko terilhami oleh beberapa jenis karawitan Sunda dan terinspirasi oleh pola-pola musik Barat sehingga proses kreatifnya berpijak pada aspek penggalian dan penciptaan. Hasil kreativitas Mang koko dikelompokkan menjadi Sekar Jenaka, lagu-lagu Kawih (anggana dan rampak sekar, Gamelan Wanda Anyar, Kacapian, Etude Kacapi, dan Drama Suara (Gending Karesmen.   Kata kunci: Mang Koko, Kreativitas, Karawitan Sunda

  1. The avifauna of Flores (Lesser Sunda Islands)

    NARCIS (Netherlands)

    Mees, G.F.

    2006-01-01

    The avifauna of the island of Flores (Lesser Sunda Islands) is reviewed. Introductory sections, which include a chapter on the history of ornithological discovery, are followed by the main part, a systematic account in which each species and subspecies known from Flores is treated separately. A disc

  2. Mantle Convection, Plate Tectonics, and Volcanism on Hot Exo-Earths

    CERN Document Server

    van Summeren, Joost; Gaidos, Eric

    2011-01-01

    Recently discovered exoplanets on close-in orbits should have surface temperatures of 100's to 1000's of K. They are likely tidally locked and synchronously rotating around their parent stars and, if an atmosphere is absent, have surface temperature contrasts of many 100's to 1000's K between permanent day and night sides. We investigated the effect of elevated surface temperature and strong surface temperature contrasts for Earth-mass planets on the (i) pattern of mantle convection, (ii) tectonic regime, and (iii) rate and distribution of partial melting, using numerical simulations of mantle convection with a composite viscous/pseudo-plastic rheology. Our simulations indicate that, if a close-in rocky exoplanet lacks an atmosphere to redistribute heat, a >~ 400 K surface temperature contrast can maintain an asymmetric degree 1 pattern of mantle convection in which the surface of the planet moves preferentially toward subduction zones on the cold night side. The planetary surface features a hemispheric dicho...

  3. On the relationship between tectonic plates and thermal mantle plume morphology

    Science.gov (United States)

    Lenardic, A.; Kaula, W. M.

    1993-01-01

    Models incorporating plate-like behavior, i.e., near uniform surface velocity and deformation concentrated at plate boundaries, into a convective system, heated by a mix of internal and basal heating and allowing for temperature dependent viscosity, were constructed and compared to similar models not possessing plate-like behavior. The simplified numerical models are used to explore how plate-like behavior in a convective system can effect the lower boundary layer from which thermal plumes form. A principal conclusion is that plate-like behavior can significantly increase the temperature drop across the lower thermal boundary layer. This temperature drop affects the morphology of plumes by determining the viscosity drop across the boundary layer. Model results suggest that plumes on planets possessing plate-like behavior, e.g., the Earth, may differ in morphologic type from plumes on planets not possessing plate-like behavior, e.g., Venus and Mars.

  4. Fenomena Gender dalam Dongkari Lagu-Lagu Tembang Sunda Cianjuran

    Directory of Open Access Journals (Sweden)

    Deni Hermawan

    2016-02-01

    ABSTRAK   Tulisan ini, “Fenomena Gender dalam Dongkari Lagu-lagu Tembang Sunda Cainjuran,” merupakan bagian kecil dari disertasi penulis berjudul “Gender dalam Tembang Sunda Cianjuran,” yang kemudian diolah kembali sesuai dengan tema tulisan ini. Tulisan ini ber- maksud untuk mengkaji fenomena gender dalam salah satu unsur tembang sunda cianjuran tersebut, yaitu dongkari. Sejauh mana ideologi gender dalam kehidupan masyarakat ber- pengaruh terhadap pertunjukan tembang sunda cianjuran, khususnya dalam menggunakan dongkari lagu-lagu tembang sunda cianjuran; dan sebaliknya. Dari kajian tersebut diperoleh kesimpulan yang menyatakan bahwa fenomena gender dapat ditemukan dalam ornamen/ dongkari. Hal ini ditunjukkan oleh adanya ornamen/dongkari yang bersifat maskulin dan feminin yang masing-masing biasa digunakan oleh penembang pria dan wanita dalam menembangkan lagu-lagu tembang sunda cianjuran. Kendatipun demikian, hal tersebut tidak terlepas dari fenomena cross-gender yang senantiasa hadir menyertainya sehingga dalam kasus-kasus tertentu, ornamen/dongkari yang bersifat maskulin bisa pula digunakan oleh penembang wanita; dan demikian pula sebaliknya. Keterkaitan antara fenomena gen- der yang ditemukan dalam ornamen/dongkari dan penggunaannya oleh penembang pria dan wanita dalam praktik pertunjukan tembang sunda cianjuran menunjukkan adanya sa- ling keterkaitan dan saling memengaruhi antara ideologi gender yang melekat dalam ke- hidupan masyarakat Sunda dan pertunjukan musik—tembang sunda cianjuran.   Kata kunci: gender, tembang sunda cianjuran, ornamen/dongkari

  5. Water Release from Cold Serpentinized Forearc Mantle During Subduction Associated with Changes in Incoming Oceanic Plate Thermal Structure and Plate Boundary Kinematics: New Insights into Serpentinite Belts and Plate-Boundary Rheology

    Science.gov (United States)

    Kirby, Stephen

    2016-04-01

    Kirby, Wang, and Brocher (Earth Planets and Space, 2014) recently showed how the change in kinematics of the California margin from subduction motion to continental transform motion with the birth and growth of the San Andreas Fault System (SAFS) beginning at about 33 Ma BP likely led to a warming of the former forearc mantle and the release of water from serpentinized mantle by dehydration and a likely increase in fluid pressures along the SAFS. Such a mantle source of pressurized water gives insights into both the low sliding resistance for the SAFS and the mobilization and ascent of some serpentinized mantle peridotites through the crust. Thermal modeling by others has also shown that changes in the incoming plate age and subduction rate can also lead to warming of the forearc mantle during subduction. This development gives insights into the Mesozoic and Paleogene ages of emplacement of some, but not all, California serpentinites. Recent mineralogical and geochemical observations of serpentinite blocks in serpentinize mélange bodies in the San Francisco Bay Area (Uno and Kirby, 2014 AGU Meeting and Lewis and Kirby, 2015 AGU Meeting) suggest that these rocks sustained multiple stages of serpentinization that are broadly consistent with the model of Kirby et al. (2014). A new development comes from interpretation of investigations in the literature of localized late-stage silica-carbonate-water alteration of serpentinite bodies in California that this alteration occurred largely in Neogene time when the highest rates of water release from the former forearc mantle probably occurred. This presentation also suggests that the occurrence of serpentinite belts emplaced in Cenozoic time during changing plate-boundary kinematics, such as the Cenozoic closing of the Tethys Ocean bordering Eurasia by subduction and collision and arc reversal and decreasing convergence rates under the Greater Antilles and Colombia and New Guinea, may give insights into the serpentinite

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

    Science.gov (United States)

    Sharkov, E. V.

    2015-12-01

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

  7. Mixing in mantle convection models with self-consistent plate tectonics and melting and crustal production: Application to mixing in the early Earth

    Science.gov (United States)

    Tackley, Paul

    2016-04-01

    It is generally thought that the early Earth's mantle was hotter than today, which using conventional convective scalings should have led to vigorous convection and mixing. Geochemical observations, however, suggest that mixing was not as rapid as would be expected, leading to the suggestion that early Earth had stagnant lid convection (Debaille et al., EPSL 2013). Additionally, the mantle's thermal evolution is difficult to explain using conventional scalings because early heat loss would have been too rapid, which has led to the hypothesis that plate tectonics convection does not follow the conventional convective scalings (Korenaga, GRL 2003). One physical process that could be important in this context is partial melting leading to crustal production, which has been shown to have the major effects of buffering mantle temperature and carrying a significant fraction of the heat from hot mantle (Nakagawa and Tackley, EPSL 2012), making plate tectonics easier (Lourenco et al., submitted), and causing compositional differentiation of the mantle that can buffer core heat loss (Nakagawa and Tackley, GCubed 2010). Here, the influence of this process on mantle mixing is examined, using secular thermo-chemical models that simulate Earth's evolution over 4.5 billion years. Mixing is quantified both in terms of how rapidly stretching occurs, and in terms of dispersion: how rapidly initially close heterogeneities are dispersed horizontally and vertically through the mantle. These measures are quantified as a function of time through Earth's evolution. The results will then be related to geochemically-inferred mixing rates.

  8. Towards absolute plate motions constrained by lower-mantle slab remnants

    NARCIS (Netherlands)

    Meer, D.G. van der; Spakman, W.; Hinsbergen, D.J.J. van; Amaru, M.L.; Torsvik, T.H.

    2010-01-01

    Since the first reconstruction of the supercontinent Pangaea, key advances in plate tectonic reconstructions have been made1. Although the movement of tectonic plates since the start of the mid-Cretaceous period (~100 million years (Myr) ago) is relatively well understood1, 2, the longitudinal posit

  9. The Earth's Mantle Is Solid: Teachers' Misconceptions About the Earth and Plate Tectonics.

    Science.gov (United States)

    King, Chris

    2000-01-01

    Discusses the misconceptions revealed by the teachers' answers and outlines more accurate answers and explanations based on established evidence and uses these to provide a more complete understanding of plate tectonic process and the structure of Earth. (Author/YDS)

  10. The Earth's Mantle Is Solid: Teachers' Misconceptions About the Earth and Plate Tectonics.

    Science.gov (United States)

    King, Chris

    2000-01-01

    Discusses the misconceptions revealed by the teachers' answers and outlines more accurate answers and explanations based on established evidence and uses these to provide a more complete understanding of plate tectonic process and the structure of Earth. (Author/YDS)

  11. Mantle amphibole control on arc and within-plate chemical signatures: Quaternary lavas from Kurdistan Province, Iran

    Science.gov (United States)

    Kheirkhah, M.; Allen, M. B.; Neill, I.; Emami, M. H.; McLeod, C.

    2012-04-01

    New analyses of Quaternary lavas from Kurdistan Province in west Iran shed light on the nature of collision zone magmatism. The rocks are from the Turkish-Iranian plateau within the Arabia-Eurasia collision. Compositions are typically basanite, hawaiite and alkali basalt. Sr-Nd isotope values are close to BSE, which is similar to Quaternary alkali basalts of NW Iran, but distinct from a depleted source melting under Mount Ararat. The chemical signatures suggests variable melting of two distinct sources. One inferred source produced melts with La/Nb from~3.5 to~1.2, which we model as the result of depletion of amphibole during ≤1% melting in the garnet stability field. We infer phlogopite in the source of potassic lavas from Takab. Lithosphere delamination or slab break-off mechanisms for triggering melting are problematic, as the lithosphere is~150-200km thick. It is possible that the negative dT/dP section of the amphibole peridotite solidus was crossed as a result of lithospheric thickening in the collision zone. This explanation is conditional upon the mantle source being weakly hydrated and so only containing a small proportion of amphibole, which can be exhausted during small degrees of partial melting. Our model maybe viable for other magmatic areas within orogenic plateaux, e.g. northern Tibet. Depletion of mantle amphibole may also help explain larger scale transitions from arc to within-plate chemistry in orogens, such as the Palaeogene Arabia-Eurasia system.

  12. Mantle heterogeneities beneath the Northeast Indian Ocean as sampled by intra-plate volcanism at Christmas Island

    Science.gov (United States)

    Taneja, Rajat; Rushmer, Tracy; Blichert-Toft, Janne; Turner, Simon; O'Neill, Craig

    2016-10-01

    The intra-plate region of the Northeast Indian Ocean, located between the Ninetyeast Ridge and the North West Shelf of Australia, contains numerous submerged seamounts and two sub-aerially exposed volcanic island groups. While the Cocos (Keeling) Archipelago is a coral atoll, Christmas Island is the only sub-aerially exposed volcanic island and contains Late Cretaceous, Eocene and Pliocene lavas. The lavas are predominantly basaltic in composition, except for one sampled flow that is trachytic. Although the evolution of the western margin of Australia, and the seismicity in the intra-plate region, has received considerable attention, the origin of the seamount province in the Northeast Indian Ocean is still a matter of debate. In order to constrain the origin of volcanism on Christmas Island and the associated Seamount Province we analysed 14 Christmas Island samples for major and trace element abundances and 12 of these for Nd, Hf and Pb isotope compositions. The trace element patterns of the lavas are similar to many ocean island basalts, while high 208Pb/204Pb and 207Pb/204Pb at a given 206Pb/204Pb suggest affiliation with the DUPAL anomaly. The reconstructed position of Christmas Island during the Eocene (44-37 Ma) places the island in close proximity to the (present-day) upper mantle low-seismic velocity anomalies. Moreover, an enriched mantle (EM-2) type component in addition to the DUPAL anomaly is observed in the Eocene volcanic phase. The younger Pliocene (~ 4 Ma) sequences at Christmas Island are inferred to be the product of partial melting of existing material induced by lithospheric flexure.

  13. 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...

  14. Comparative Seismotectonic Conditions Along the Sunda and Aleutian Arcs from Broadband Analysis of Earthquake Energetics

    Science.gov (United States)

    Choy, G. L.; Kirby, S. H.; Hayes, G. P.

    2014-12-01

    In the digital era, the Sunda arc has been the site of sixteen large and great (MW>7.0) earthquakes that generated oftimes devastating tsunamis. In contrast, the largest tsunami earthquakes along the Aleutian arc occurred in the pre-digital era. Given the tectonic and geological commonalities between the two arcs, such as oblique plate convergence and long sediment-rich sections of trench, it is natural to ask whether the numerous and well-recorded Sunda events can serve as analogs to the more sparse Aleutian events for insight into seismic and tsunami potential. The large earthquakes are examined in the context of moderate-sized earthquakes (5.5assess maturity of the faults. In the Sunda arc, energy release for moderate events was predominantly along the peripheries of the rupture zones of large events. Rather than on the slab interface, they often occurred on splay faults in the overriding plate, on perturbations of the slab interface under the outer-arc high or alongside obliquely subducted ridges and fracture zones. High strength regions (identified by high energy-release faults) resisted rupture during large earthquakes. Other splays seemed tsunami-capable. The greatest tsunamis came from earthquakes with rupture confined to the shallow forearc seaward of the outer-arc high, while greater seismic damage came from earthquakes confined to the deep forearc behind the outer-arc high. For the Aleutians, only two large events occurred during the same time period. But, like Sunda, the numerous moderate-sized events tended to demarcate the periphery of the rupture zone of past large events. Some splays with tsunami potential were observed, but the majority of events occurred at slab bends and around subducting fracture zones and seamounts, rather than about the subdued outer-arc high.

  15. New evidences of rupture of crust and mantle in the subducted Nazca plate at intermediate-depth

    Science.gov (United States)

    Spagnotto, Silvana L.; Triep, Enrique G.; Giambiagi, Laura B.; Nacif, Silvina V.; Álvarez, Orlando

    2015-03-01

    Between 33°-36°S, the Nazca plate subducts below South American plate with an angle of ˜30°, and it is seismically active until ˜200-280 km depth. At 33.5°S, the seismicity decreases drastically at 120 km depth, just below the volcanic arc. In this paper, we studied a pair of associated earthquakes located in the area where the frequency of seismicity changes. The hypocenters of the Mw = 6.4, June 16th, 2000 and Mw = 5.7 January 7th, 2003 earthquakes were found nearby, adjacent to the oceanic Moho, closely associated with each other. The slip on the plane of the 2000 event produced Coulomb stress changes on the fault plane of 2003, both westward dipping, with a variation from ˜1 bar near the hypocenter of the latter to ˜0.1 bars in the deepest part of the plane. The two earthquakes combined process describes a normal focal mechanism, which cuts through the crust and breaks the mantle, reaching depths of ˜40 km below the Moho. The composed fault plane of the 2000 and 2003 events corresponds to a west-dipping normal fault with strike and dip consistent with those of the outer ridge faults. Thus, these events could be related to a preexisting fault originated in that environment reactivated at depth. The slip on the composed fault plane is consistent with the bending produced by the slab pull. Dehydration could be associated to these events.

  16. What can seafloor fabric tell us about the nature of the 50 Ma plate-mantle event?

    Science.gov (United States)

    Müller, R. D.; Matthews, K. J.

    2011-12-01

    Several different mechanisms have been proposed to account for the 50 Ma plate-mantle event, including India-Eurasia collision, the time dependence of the Reunion plume-push force, the subduction of the Izanagi-Pacific mid-ocean ridge, and transient ridge capture of the Hawaiian plume. We use a recent digital global seafloor tectonic fabric map derived from vertical gravity gradients together with magnetic anomaly identifications to analyse the geometry and timing of Late Cretaceous-Early Cenozoic fracture zone (FZ) bends. Two sets of closely spaced FZ bends in the North Atlantic, Weddell Sea and at the Southwest Indian Ridge between Antarctica and Africa produce an S-shape in the seafloor fabric. The older spreading ridge reorganisation initiated close to 70 Ma, and was completed around 55 Ma. The younger FZ bends are sharper, were initiated approximately 55-49 Ma and completed around 40-42 Ma, after which time spreading returned to its pre-S-bend azimuth. Additionally there is a distinct increase in seafloor roughness at the mid-Atlantic ridge at about 70 Ma reflecting a decrease in spreading rate. Seafloor fabric indicators of plate motion change produced at around 70 Ma coincide with emplacement of the Reunion plume and are restricted to parts of the Atlantic-Indian realm. The Pacific domain appears unaffected by the mechanism that drove plate motion changes in the Atlantic and Indian Oceans at this time. Yet, from ~55-40 Ma Pacific FZ bends and other oceanic and plate margin events are widespread. Along with formation of the younger part of the Atlantic-Indian S-bends, FZ bends and changes in FZ morphology in the northeast Pacific signify a reorientation of the Pacific-Farallon spreading ridge, a northward propagation of the Pacific-Antarctic ridge, increases in spreading rates at the Australia-Pacific ridge and a change in the direction of plate motion, with spreading terminating in the Tasman Sea. And initiation of Izu-Bonin-Mariana subduction. This

  17. 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

  18. Mantle contamination and the Izu-Bonin-Mariana (IBM) 'high-tide mark': evidence for mantle extrusion caused by Tethyan closure

    Science.gov (United States)

    Flower, M. F. J.; Russo, R. M.; Tamaki, K.; Hoang, N.

    2001-04-01

    Western Pacific basins are characterized by three remarkable attributes: (1) complex kinematic histories linked to global-scale plate interactions; (2) DUPAL-like contaminated mantle; and (3) rapid post-Mesozoic rollback of the confining arc-trench systems. The coincidence of slab steepening, extreme arc curvature, and vigorous basin opening associated with the Mariana convergent margin suggests that rollback continues in response to an east-directed mantle 'wind'. Against a backdrop of conflicting kinematic and genetic interpretations we explore the notion that eastward asthenospheric flow driven by diachronous Tethyan closure caused stretching of eastern Eurasia and concomitant opening of western Pacific basins. Marking the eastern boundary of the latter, the Izu-Bonin-Mariana forearc may be regarded as a litho-tectonic 'high-tide mark' comprising igneous and metamorphic products from successive episodes (since ca. 45 Ma.) of arc sundering and backarc basin opening. The forearc also forms an isotopic boundary separating contaminated western Pacific mantle from the N-MORB Pacific Ocean reservoir. While the isotopic composition of western Pacific mantle resembles that feeding Indian Ocean hotspot and spreading systems, its spatial-temporal variation and the presence of subduction barriers to the south appear to preclude northward flow of Indian Ocean mantle and require an endogenous origin for sub-Eurasian contaminated mantle. It is concluded that the extrusion of Tethyan asthenosphere, contaminated by sub-Asian cratonic lithosphere, was a major cause of western Pacific arc rollback and basin opening. The model is consistent with paleomagnetic and geologic evidence supporting independent kinematic histories for constituent parts of the Philippine Sea and Sunda plates although interpretation of these is speculative. Compounded by effects of the Australia-Indonesia collision, late-Tethyan mantle extrusion appears to have produced the largest DUPAL domain in the

  19. Effects of crystal preferred orientation on upper-mantle flow near plate boundaries: rheologic feedbacks and seismic anisotropy

    Science.gov (United States)

    Blackman, D. K.; Boyce, D. E.; Castelnau, O.; Dawson, P. R.; Laske, G.

    2017-09-01

    Insight into upper-mantle processes can be gained by linking flow-induced mineral alignment to regional deformation and seismic anisotropy patterns. Through a series of linked micro-macro scale numerical experiments, we explore the rheologic effects of crystal preferred orientation (CPO) and evaluate the magnitude of possible impacts on the pattern of flow and associated seismic signals for mantle that includes a cooling, thickening young oceanic lithosphere. The CPO and associated anisotropic rheology, computed by a micromechanical polycrystal model, are coupled with a large scale flow model (Eulerian Finite Element method) via a local viscosity tensor field, which quantifies the stress:strain rate response of a textured polycrystal. CPO is computed along streamlines throughout the model space and the corresponding viscosity tensor field at each element defines the local properties for the next iteration of the flow field. Stable flow and CPO distributions were obtained after several iterations for the two dislocation glide cases tested: linear and nonlinear stress:strain rate polycrystal behaviour. The textured olivine polycrystals are found to have anisotropic viscosity tensors in a significant portion of the model space. This directional dependence in strength impacts the pattern of upper-mantle flow. For background asthenosphere viscosity of ˜1020 Pa s and a rigid lithosphere, the modification of the corner flow pattern is not drastic but the change could have geologic implications. Feedback in the development of CPO occurs, particularly in the region immediately below the base of the lithosphere. Stronger fabric is predicted below the flanks of a spreading centre for fully coupled, power-law polycrystals than was determined using prior linear, intermediate coupling polycrystal models. The predicted SKS splitting is modestly different (˜0.5 s) between the intermediate and fully coupled cases for oceanic plates less than 20 Myr old. The magnitude of azimuthal

  20. WACANA KEMADJOEAN DI KELOMPOK ETNIS SUNDA AWAL ABAD 20

    Directory of Open Access Journals (Sweden)

    Holy Rafika Dhona

    2016-02-01

    Kemadjoean menjadi istilah kunci bagi semua gerakan sosial pribumi Hindia Belanda di awal abad 20. Tulisan ini meyakini bahwa wacana kemajuan dipraktikkan berbeda dalam tiap komunitas kultural. Tulisan ini membahas bagaimana kemajuan dipahami, didiskusikan dan dinegosiasikan oleh kelompok etnis Sunda pada dekade awal abad 20. Menggunakan analisis wacana Foucauldian pada teks Surat Kabar Papaes Nonoman (1914-1917, penelitian ini menemukan bahwa selain kemajuan dipahami sebagai ‘usaha menjadi Belanda’-sebagaimana umumnya terjadi di Hindia Belanda, kemajuan secara khusus dipahami oleh etnis Sunda sebagai pembebasan budaya Sunda dari dominasi budaya etnis Jawa.

  1. Toroidal, Counter-Toroidal, and Upwelling Flow in the Mantle Wedge of the Rivera and Cocos Plates: Implications for IOB Geochemistry in the Trans-Mexican Volcanic Belt

    Science.gov (United States)

    Neumann, Florian; Vásquez-Serrano, Alberto; Tolson, Gustavo; Negrete-Aranda, Raquel; Contreras, Juan

    2016-10-01

    We carried out analog laboratory modeling at a scale 1:4,000,000 and computer rendering of the flow patterns in a simulated western Middle American subduction zone. The scaled model consists of a transparent tank filled with corn syrup and housing two conveyor belts made of polyethylene strips. One of the strips dips 60° and moves at a velocity of 30 mm/min simulating the Rivera plate. The other one dips 45°, moves at 90 mm/min simulating the subduction of the Cocos plate. Our scaled subduction zone also includes a gap between the simulated slabs analogous to a tear recently observed in shear wave tomography studies. An acrylic plate 3 mm thick floats on the syrup in grazing contact with the polyethylene strips and simulates the overriding North America plate. Our experiments reveal a deep toroidal flow of asthenospheric mantle through the Cocos-Rivera separation. The flow is driven by a pressure gradient associated with the down-dip differential-motion of the slabs. Similarly, low pressure generated by the fast-moving Cocos plate creates a shallow counter-toroidal flow in the uppermost 100 km of the mantle wedge. The flow draws mantle beneath the western Trans-Mexican Volcanic Belt to the Jalisco block, then plunges into the deep mantle by the descending poloidal cell of the Cocos slab. Moreover, our model suggests a hydraulic jump causes an ~250 km asthenosphere upwelling around the area where intra-arc extensional systems converge in western Mexico. The upwelling eventually merges with the shallow counter-toroidal flow describing a motion in 3D space similar to an Archimedes' screw. Our results indicate the differential motion between subducting slabs drives mixing in the mantle wedge of the Rivera plate and allows the slab to steepen and retreat. Model results are in good agreement with seismic anisotropy studies and the geochemistry of lavas erupted in the Jalisco block. The model can explain the eruption of OIB lavas in the vicinity of the City of

  2. Toroidal, Counter-Toroidal, and Upwelling Flow in the Mantle Wedge of the Rivera and Cocos Plates: Implications for IOB Geochemistry in the Trans-Mexican Volcanic Belt

    Science.gov (United States)

    Neumann, Florian; Vásquez-Serrano, Alberto; Tolson, Gustavo; Negrete-Aranda, Raquel; Contreras, Juan

    2015-12-01

    We carried out analog laboratory modeling at a scale 1:4,000,000 and computer rendering of the flow patterns in a simulated western Middle American subduction zone. The scaled model consists of a transparent tank filled with corn syrup and housing two conveyor belts made of polyethylene strips. One of the strips dips 60° and moves at a velocity of 30 mm/min simulating the Rivera plate. The other one dips 45°, moves at 90 mm/min simulating the subduction of the Cocos plate. Our scaled subduction zone also includes a gap between the simulated slabs analogous to a tear recently observed in shear wave tomography studies. An acrylic plate 3 mm thick floats on the syrup in grazing contact with the polyethylene strips and simulates the overriding North America plate. Our experiments reveal a deep toroidal flow of asthenospheric mantle through the Cocos-Rivera separation. The flow is driven by a pressure gradient associated with the down-dip differential-motion of the slabs. Similarly, low pressure generated by the fast-moving Cocos plate creates a shallow counter-toroidal flow in the uppermost 100 km of the mantle wedge. The flow draws mantle beneath the western Trans-Mexican Volcanic Belt to the Jalisco block, then plunges into the deep mantle by the descending poloidal cell of the Cocos slab. Moreover, our model suggests a hydraulic jump causes an ~250 km asthenosphere upwelling around the area where intra-arc extensional systems converge in western Mexico. The upwelling eventually merges with the shallow counter-toroidal flow describing a motion in 3D space similar to an Archimedes' screw. Our results indicate the differential motion between subducting slabs drives mixing in the mantle wedge of the Rivera plate and allows the slab to steepen and retreat. Model results are in good agreement with seismic anisotropy studies and the geochemistry of lavas erupted in the Jalisco block. The model can explain the eruption of OIB lavas in the vicinity of the City of

  3. DUA KEBENARAN DALAM NASKAH SUNDA CARIOS TAMIM

    Directory of Open Access Journals (Sweden)

    Rohim Rohim

    2015-02-01

    Full Text Available Artikel ini bertujuan menghadirkan teks naskah Sunda Carios Tamim yangberbentuk wawacan melalui suntingan teks dan analisis struktur. Selainsuntingan teks dan analisis struktur, untuk mengetahui keterpaduanperistiwa dalam mengeksplorasi tokoh digunakan teori aktan dan modelfungsional yang dikembangkan oleh Greimas. Dari hasil pembahasandiperoleh simpulan bahwa struktur formal Carios Tamim menggunakan 14jenis pupuh dengan 390 bait, 2644 larik dengan tiga unsur pembangun ceritayaitu manggala, isi cerita, dan penutup. Hasil analisis struktur teks naratifCarios Tamim ditemukan jalinan erat alur, tokoh, penokohan, dan latar sehingga terungkap tema cerita yaitu tegaknya kebenaran di antara duakebenaran. Kebenaran dalam teks Carios Tamim berhubungan denganmasalah munâkahah (pernikahan.  Berdasarkan uraian aktan dan modelfungsional  yang diajukan oleh Greimas, tokoh Tamim Ibnu Habib Al-Dâridan istrinya sebagai subjek berhasil memperoleh objek berkat peristiwa yangdialami keduanya saling berkaitan dalam hubungan sebab akibat.

  4. Preliminary results of characteristic seismic anisotropy beneath Sunda-Banda subduction-collision zone

    Science.gov (United States)

    Wiyono, Samsul H.; Nugraha, Andri Dian

    2015-04-01

    Determining of seismic anisotropy allowed us for understanding the deformation processes that occured in the past and present. In this study, we performed shear wave splitting to characterize seismic anisotropy beneath Sunda-Banda subduction-collision zone. For about 1,610 XKS waveforms from INATEWS-BMKG networks have been analyzed. From its measurements showed that fast polarization direction is consistent with trench-perpendicular orientation but several stations presented different orientation. We also compared between fast polarization direction with absolute plate motion in the no net rotation and hotspot frame. Its result showed that both absolute plate motion frame had strong correlation with fast polarization direction. Strong correlation between the fast polarization direction and the absolute plate motion can be interpreted as the possibility of dominant anisotropy is in the asthenosphere..

  5. Preliminary results of characteristic seismic anisotropy beneath Sunda-Banda subduction-collision zone

    Energy Technology Data Exchange (ETDEWEB)

    Wiyono, Samsul H., E-mail: samsul.wiyono@bmkg.go.id [Study Program of Earth Sciences, Faculty of Earth Sciences and Technology, Institute of Technology Bandung, Bandung 40132 (Indonesia); Indonesia’s Agency for Meteorology Climatology and Geophysics, Jakarta 10610 (Indonesia); Nugraha, Andri Dian, E-mail: nugraha@gf.itb.ac.id [Indonesia’s Agency for Meteorology Climatology and Geophysics, Jakarta 10610 (Indonesia); Global Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institute of Technology Bandung, Bandung 40132, Indonesia, Phone: +62-22 2534137 (Indonesia)

    2015-04-24

    Determining of seismic anisotropy allowed us for understanding the deformation processes that occured in the past and present. In this study, we performed shear wave splitting to characterize seismic anisotropy beneath Sunda-Banda subduction-collision zone. For about 1,610 XKS waveforms from INATEWS-BMKG networks have been analyzed. From its measurements showed that fast polarization direction is consistent with trench-perpendicular orientation but several stations presented different orientation. We also compared between fast polarization direction with absolute plate motion in the no net rotation and hotspot frame. Its result showed that both absolute plate motion frame had strong correlation with fast polarization direction. Strong correlation between the fast polarization direction and the absolute plate motion can be interpreted as the possibility of dominant anisotropy is in the asthenosphere.

  6. Contamination of the Convecting Mantle in Eastern Tethyan 'Subduction Factories'

    Science.gov (United States)

    Flower, M. F.; Nguyen, T. H.

    2003-04-01

    As subduction gives way to collision at the end of a Wilson Cycle the associated magmatic activity becomes increasingly enriched in potassium and other large-ion lithophile elements. This is usually attributed to the addition of continental crust-derived material to the convecting mantle wedge. Corresponding depletions in high-field strength elements (Ti and Nb) are more commonly explained in terms of accessory phase buffering or protracted reaction of melts with mantle wallrock. It is increasingly apparent that mantle wedge magmatic sources range from 'fertile' (lherzolitic) to 'refractory' (harzburgitic) although the extent to which this corresponds to the LILE and HFSE variation is unclear. Mantle wedge mass balances clearly hold clues to enrichment-depletion histories of the convecting asthenosphere with respect to both the overriding and subducting plates. With a view to better understanding these effects we have used the MELTS algorithm to calculate hypothetical partial melt compositions as a function of source fertility and H2O content, in the pressure range, 0-1.0 GPa as a basis comparison for natural partial melts. Primitive magmas characterizing the Mariana (western Pacific) and Sunda-Banda (Indonesia) arcs, and the northeastern syntaxis of the India-Asia collision suture (Yunnan) appear to resemble calculated equilibrium melts of refractory (basalt-depleted) peridotite, variably enriched in lithophile and light rare earth elements. These comparisons lead to three observations. 1) HFSE and Fe abundances in primitive MORB, calcalkaline, and boninite magmas, and their respective high-potassium variants are consistent with those implied by phase equilibria associated with partial melting and fractionation, suggesting accessory phases, wall-rock reaction, and slab contamination are probably not important as causes of HFSE depletions. 2) Magmatic sources at convergent and colliding margins are typically refractory (basalt-depleted) compared to those yielding

  7. Mantle enrichment by volatiles as the Nazca plate subducts beneath the Payenia backarc of the Southern Volcanic Zone, Argentina

    DEFF Research Database (Denmark)

    Brandt, Frederik Ejvang

    , minerals, fluid and melt inclusions from the Payenia backarc province of the Andean Southern Volcanic Zone. Major emphasis has been on olivine hosted melt inclusions. The study gives evidence for the role of fluids in the metasomatism of the backarc mantle, and outlines the trend of the variation...... of the metasomatism in Payenia, which is also characterized by a variation in oxidation state and other geochemical parameters of the melt inclusions, and is moreover related to mantle lithological variations. The mantle metasomatism by melts of subducted crust and fluid-borne enrichment is quantitatively modelled...

  8. Three-dimensional numerical modeling of temperature and mantle flow fields associated with subduction of the Philippine Sea plate, southwest Japan

    Science.gov (United States)

    Ji, Yingfeng; Yoshioka, Shoichi; Matsumoto, Takumi

    2016-06-01

    We investigated temperature and mantle flow distributions associated with subduction of the Philippine Sea (PHS) plate beneath southwest Japan, by constructing a three-dimensional parallelepiped model incorporating a past clockwise rotation, the bathymetry of the Philippine Sea plate, and distribution of the subducting velocity within its slab. The geometry of the subducting plate was inferred from contemporary seismic studies and was used as a slab guide integrated with historical plate rotation into the 3-D simulation. Using the model, we estimated a realistic and high-resolution temperature field on the subduction plate interface, which was constrained by a large number of heat flow data, and attempted to clarify its relationship with occurrences of megathrust earthquakes, long-term slow slip events (L-SSEs), and nonvolcanic low-frequency earthquakes (LFEs). Results showed that the oblique subduction coupled with the 3-D geometry of subducting PHS plate was a key factor affecting the interplate and intraplate temperature distributions, leading to a cold anomaly in the plate interface beneath western Shikoku, the Bungo Channel, and the Kii Peninsula. Temperatures in the slab core in these regions at a depth near the continental Moho were nearly 200°C lower than that in eastern Shikoku, indicating a high thermal lateral heterogeneity within the subducting plate. The geothermal control of the LFEs beneath western Shikoku was estimated to be within a range from 400 to 700°C, and the interplate temperature for the L-SSEs with a slip larger than 15 cm beneath the Bungo Channel was estimated to be approximately 350-500°C. A large horizontal temperature gradient of 2.5 ~ °C/km was present where the LFEs occurred repeatedly. The steep temperature change was likely to be related to the metamorphic phase transformation from lawsonite or blueschist to amphibolite of hydrous minerals of the mid-ocean ridge basalt of the subducting PHS plate.

  9. Cocos Plate Seamounts offshore NW Costa Rica and SW Nicaragua: Implications for large-scale distribution of Galápagos plume material in the upper mantle

    Science.gov (United States)

    Herbrich, Antje; Hoernle, Kaj; Werner, Reinhard; Hauff, Folkmar; Bogaard, Paul v. d.; Garbe-Schönberg, Dieter

    2015-01-01

    The origin of intraplate volcanism not directly part of a hotspot track, such as diffuse seamount provinces, and the extent of mantle plume influence on the upper mantle remain enigmatic. Here we present new 40Ar/39Ar age data and geochemical (major and trace-element and Sr-Nd-Pb isotopic) data from seamounts on the Cocos Plate presently located offshore of NW Costa Rica and SW Nicaragua. The seamounts (~ 7-24 Ma) require mixing of an enriched ocean island basalt composition, similar to that of the Northern Galápagos Domain, with two depleted components. One of the depleted components is similar to East Pacific Rise normal mid-ocean ridge basalt and the other has more depleted incompatible elements, either reflecting secondary melting of MORB or a depleted Galápagos plume component. Seamounts with ages significantly younger than the ocean crust formed in an intraplate setting and can be explained by northward transport of Galápagos plume material along the base of the Cocos Plate up to 900 km away from the hotspot and 250-500 km north of the Galápagos hotspot track. We propose that melting occurs due to decompression as the mantle upwells to shallower depth as it flows northwards, either due to changes in lithospheric thickness or as a result of upwelling at the edge of a viscous plug of accumulated plume material at the base of the lithosphere. The tholeiitic to alkaline basalt compositions of the Cocos Plate Seamounts compared to the more silica under-saturated compositions of Hawaiian rejuvenated and arch (alkali basalts to nephelinites) lavas are likely to reflect the significant difference in age (< 25 vs ~ 90 Ma) and thus thickness of the lithosphere on which the lavas were erupted.

  10. Towards Crustal Structure of Java Island (Sunda Arc) from Ambient Seismic Noise Tomography

    Science.gov (United States)

    Widiyantoro, Sri; Zulhan, Zulfakriza; Martha, Agustya; Saygin, Erdinc; Cummins, Phil

    2015-04-01

    In our previous studies, P- and S-wave velocity structures beneath the Sunda Arc were successfully imaged using a global data set and a nested regional-global tomographic method was employed. To obtain more detailed P- and S-wave velocity structures beneath Java, in the central part of the Sunda Arc, we then used local data sets, i.e. newline from the MErapi AMphibious EXperiment (MERAMEX) and the Meteorological, Climatological and Geophysical Agency (MCGA), as well as employed a double-difference technique for tomographic imaging. The results of the imaging show e.g. that P- and S-wave velocities are significantly reduced in the uppermost mantle beneath central Java. In order to obtain detailed crustal structure information beneath Java, the Ambient Noise Tomography (ANT) method was used. The application of this method to the MERAMEX data has produced a good crustal model beneath central Java. We continue our experiment to image crustal structure of eastern Java. We have used seismic waveform data recorded by 22 MCGA stationary seismographic stations and 25 portable seismographs installed for 2 to 8 weeks. The data were processed to obtain waveforms of cross-correlated noise between pairs of seismographic stations. Our preliminary results presented here indicate that the Kendeng zone, an area of low gravity anomaly, is associated with a low velocity zone. On the other hand, the southern mountain range, which has a high gravity anomaly, is related to a high velocity anomaly (as shown by our tomographic images). In future work we will install more seismographic stations in eastern Java as well as in western Java to conduct ANT imaging for the whole of Java Island. The expected result combined with the mantle velocity models resulting from our body wave tomography will allow for accurate location of earthquake hypocenters and determination of regional tectonic structures. Both of these are valuable for understanding seismic hazard in Java, the most densely populated

  11. Importance of the Small-Scale Processes Melting, Plate Boundary Formation and Mineralogy on the Large-Scale, Long-Term Thermo-Chemical Evolution of Earth's Mantle-Plate System

    Science.gov (United States)

    Tackley, P.

    2015-12-01

    Seismic observations of the deep Earth reveal the presence of two large low shear velocity provinces (LLSVPs) that are typically inferred to be dense chemically-distinct material, as well as discontinuities that are typically linked to the post-perovskite (pPv) phase transition. Several possible origins of chemically-dense material have been proposed, including recycling of mid-ocean ridge basalt (MORB), primordial differentiation events, crystallisation of a basal magma ocean, or some combination of these creating a basal melange (BAM; Tackley 2012 Earth Sci. Rev.). Each of these possibilities would result in a different composition hence different mineralogy. In order to constrain this we have been running calculations of thermo-chemical mantle evolution over 4.5 billion years that include melting-induced differentiation, plate tectonics induced by strongly temperature-dependent viscosity and plastic yielding, core cooling and compressibility with reasonable assumptions about the pressure-dependence of other material properties. Some of our simulations start from a magma ocean state so initial layering is developed self-consistently. Already-published results (Nakagawa et al., 2009 GCubed, 2010 PEPI, 2012 GCubed) already indicate the importance of exact MORB composition on the amount of MORB segregating above the CMB, which in turn influences mantle thermal structure and the evolution of the core and geodynamo. In more recent results we have been additionally including primordial material. We find that melting-induced differentiation has several first-order effects on the dynamics, including (i) making plate tectonics easier (through stresses associated with lateral variations in crustal thickness) and (ii) reducing heat flux through the CMB (due to the build-up of dense material above the CMB); also (iii) tectonic mode (continuous plate tectonics, episodic lid or stagnant lid) also makes a first-order difference to mantle structure and dynamics. This emphasises

  12. Zoned mantle convection.

    Science.gov (United States)

    Albarède, Francis; Van Der Hilst, Rob D

    2002-11-15

    We review the present state of our understanding of mantle convection with respect to geochemical and geophysical evidence and we suggest a model for mantle convection and its evolution over the Earth's history that can reconcile this evidence. Whole-mantle convection, even with material segregated within the D" region just above the core-mantle boundary, is incompatible with the budget of argon and helium and with the inventory of heat sources required by the thermal evolution of the Earth. We show that the deep-mantle composition in lithophilic incompatible elements is inconsistent with the storage of old plates of ordinary oceanic lithosphere, i.e. with the concept of a plate graveyard. Isotopic inventories indicate that the deep-mantle composition is not correctly accounted for by continental debris, primitive material or subducted slabs containing normal oceanic crust. Seismological observations have begun to hint at compositional heterogeneity in the bottom 1000 km or so of the mantle, but there is no compelling evidence in support of an interface between deep and shallow mantle at mid-depth. We suggest that in a system of thermochemical convection, lithospheric plates subduct to a depth that depends - in a complicated fashion - on their composition and thermal structure. The thermal structure of the sinking plates is primarily determined by the direction and rate of convergence, the age of the lithosphere at the trench, the sinking rate and the variation of these parameters over time (i.e. plate-tectonic history) and is not the same for all subduction systems. The sinking rate in the mantle is determined by a combination of thermal (negative) and compositional buoyancy and as regards the latter we consider in particular the effect of the loading of plates with basaltic plateaux produced by plume heads. Barren oceanic plates are relatively buoyant and may be recycled preferentially in the shallow mantle. Oceanic plateau-laden plates have a more pronounced

  13. Slab-rollback induced upper mantle upwelling near lateral slab edges: A new mechanism for generating intra-plate magmatism in the central Mediterranean

    Science.gov (United States)

    Schellart, W. P.

    2010-12-01

    Most volcanism on Earth is associated with plate boundaries and can thus be explained in a plate tectonic framework. Intra-plate volcanism, however, cannot directly be explained with plate tectonic theory. Intraplate volcanism is frequently explained with the plume model, in which a relatively fixed buoyant plume rises from the lower mantle to the surface and, as the overlying plate moves with respect to the plume source, produces a linear hotspot track along which the age of volcanoes progressively changes. This model has been applied to linear volcanic chains such as the Hawaii-Emperor Ridge in the Pacific and the Walvis Ridge in the Atlantic Ocean. Other intra-plate volcanism that does not occur in linear chains and does not show a preferred age progression in a specific geographical direction is more difficult to explain with the plume model, and might require an alternative explanation. There are several examples of intraplate volcanism on Earth located close to lateral slab edges, suggesting that they might be genetically related to these slab edges. One example of such volcanism is located in Sicily in the Mediterranean, which took place at ~7.0-1.1 Ma on the Iblean plateau and at 0.5 Ma to Present to form Mount Etna. The volcanics are located in close proximity but are laterally offset with respect to the Eolian magmatic arc and the Calabrian subduction zone, where Ionian oceanic lithosphere is subducting west-northwestward below Calabria. The volcanics in Sicily can therefore not be interpreted as arc volcanism. Previous work, primarily based on the geochemistry and petrology of the volcanics, suggests that the volcanism resulted from a plume. The volcanics in Sicily and surrounding seas, however, do not align along a linear chain and show no lateral age progression. Here it is proposed that Mount Etna and the Iblean volcanics are related to decompression melting of upper mantle material that is flowing around the southern Ionian slab edge to accommodate

  14. Combined effects of Eurasia/Sunda oblique convergence and East-Tibetan crustal flow on the active tectonics of Burma

    Science.gov (United States)

    Rangin, Claude; Maurin, Thomas; Masson, Frederic

    2013-10-01

    It is widely accepted that deformation of the India/Sunda plate is the result of partitioned hyper oblique convergence. Presently, sub-meridian dextral strike slip faulting accommodates this India/Sunda motion in a buffer zone, the Burma platelet. This wide dextral strike slip shear zone is complicated by the side effect of the Tibet plateau collapse that can be described in term of crustal flow and gravity tectonics. The loss of potential energy related to this plateau collapse affects most of the Burmese platelet particularly in its northernmost part. Interaction of these two distinct geodynamic processes is recorded in the GPS based regional strain field, the analysis of seismic focal mechanism but also from direct geologic observations both onshore and offshore Myanmar and Bangladesh. We propose the apparent E-W shortening component of this so called partitioned hyper-oblique subduction is only the effect of regional gravitational forces related to the Tibet plateau collapse whereas the NS strike slip faulting accommodates the India/Sunda motion.

  15. Mantle enrichment by volatiles as the Nazca plate subducts beneath the Payenia backarc of the Sourthern Volcanic Zone, Argentina

    DEFF Research Database (Denmark)

    Brandt, Frederik Ejvang

    , minerals, fluid and melt inclusions from the Payenia backarc province of the Andean Southern Volcanic Zone. Major emphasis has been on olivine hosted melt inclusions. The study gives evidence for the role of fluids in the metasomatism of the backarc mantle, and outlines the trend of the variation...

  16. 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

  17. Seismotectonic pattern and the source region of volcanism in the central part of Sunda Arc

    Science.gov (United States)

    Špičák, Aleš; Hanuš, Václav; Vaněk, Jiří

    2005-07-01

    The seismotectonic pattern in the central part of the Sunda Arc (Java, Nusa Tenggara) was studied in relation to the distribution of active calc-alkaline volcanoes, using global seismological data. Hypocentral determinations of the International Seismological Centre from the period 1964-1999, as relocated by Engdahl, and Harvard Centroid Moment Tensor Solutions from the period 1976-2003 were used. The following phenomena, which could assist the location of the source region of primary magma for island arc calc-alkaline volcanism, were observed: (1) An aseismic gap without any strong teleseismically recorded earthquakes was found in the Wadati-Benioff zone of the subducting slab along the whole investigated region of the Sunda Arc, forming a continuous strip of laterally variable depth and shape, at depths between 100 and 200 km. The absence of strong earthquakes (with mb>4.0) indicates a significant change in the mechanical properties of the subducting slab at intermediate depths. All active calc-alkaline volcanoes in the Sunda Arc are located above this gap. (2) The majority of earthquakes occurring in the lithospheric wedge of the Eurasian Plate above the subducted slab could be attributed to several deep-rooted seismically active fracture zones of regional extent. All delineated active fracture zones display a thrust tectonic regime as shown by the available fault plane solutions. (3) Clusters of earthquakes were found beneath active volcanoes of western Java, Bali and Nusa Tenggara in the lithospheric wedge above the slab and identified as seismically active columns. These clusters occur only beneath the volcanoes that are located at the outcrops of seismically active fracture zones. We interpret the earthquakes in these clusters beneath volcanoes as events induced by magma transport through the medium of the lithospheric wedge that has been subcritically pre-stressed by the process of plate convergence. (4) Beneath the volcanoes of central Java no seismically

  18. KEARIFAN LOKAL ADAT MASYARAKAT SUNDA DALAM HUBUNGAN DENGAN LINGKUNGAN ALAM

    Directory of Open Access Journals (Sweden)

    Ira Indrawardana

    2013-04-01

    Full Text Available Tujuan penelitian ini adalah untuk mendiskusikan kearifan lokal adat masyarakat Sunda dalam hubungan dengan lingkungan alam. Penelitian dilakukan secara kualitatif terhadap masyarakat Sunda Kanekes. Penelitian ini menghasilkan temuan bahwa pada dasarnya kearifan lokal masyarakat Sunda Kanekes disarikan dari pengalaman masyarakat Sunda lama yang sangat akrab dengan lingkungannya dan sudah lama hidup dalam budaya masyarakat peladang. Kearifan lokal adat, suatu kondisi sosial dan budaya yang didalamnya terkandung khasanah nilai-nilai budaya yang menghargai dan adaptif dengan alam sekitar, dan tertata secara ajeg dalam suatu tatanan adat istiadat suatu masyarakat. Walau sering dianggap kuno, nilai-nilai yang mereka ajarkan dan praktek yang mereka jalankan masih merupakan cara yang terbaik untuk memelihara lingkungan di zaman post-modern. The objective of this study is to discuss the wisdom of indigenous traditional Sundanese community in relation to natural environment. The research is done qualitatively in Kanekes Sundanese traditional community. The research found that the distinguished Kanekes local knowledge regarding to the environment is creatively developed by the community from their everyday exepriences of living with natures, being friends with nature and their experience as farming communities. The local wisdom of Kanekes community, which contains cultural values of respect and adaptive to the environment, and life based upon traditional norms. Though often stereotyped as primitive, their living values and practices of life are still the best instrument to conserve environment in post-modern age.

  19. Tasawuf Sunda dalam Naskah Asmarandana Ngagurit Kaburu Burit (OR. 7876

    Directory of Open Access Journals (Sweden)

    Jajang A. Rohmana

    2015-03-01

    Full Text Available Abstract:   The spread of Islam in the Archipelago was closely tied to the roles of Sufi ulama. The circulation of Sufi work in Nusantara proves a strong connection between this region and the Middle East. In West Java, a number of these work expose Sufi teachings in the form of Sundanese Sufi literature, such as the work by Haji Hasan Mustafa. He is considered the greatest Sundanese poet whose work features strong influences of wahdat al-wujud. This paper aims to examine Sundanese Sufism expressed in Mustafa’s work of Asmarandana Ngagurit Kaburu Burit. This study shows that this work contains Sufi’s path that explores the self and its encounters with Supreme Being and the self’s diffusion, where there is no longer existence except the One. Mustafa called his Sufi poetry imperfect suluk because it was written in late afternoon. His work reveals local Sufi accommodation to wah}dat al-wujud in Sundanese language and culture.Abstrak:   Seiringan dengan perkembangan Islam di Nusantara adalah beredarnya naskah-naskah tasawuf membuktikan adanya hubungan kuat tradisi tasawuf lokal dan Timur Tengah. Di tatar Sunda, sejumlah naskah tasawuf mengekspresikan ajarannya ke dalam bentuk sastra sufistik Sunda (dangding, guguritan. Artikel ini bertujuan untuk mengkaji ekspresi pengalaman tasawuf Sunda dalam naskah Asmarandana Ngagurit Kaburu Burit (Cod. Or. 7876 karya Haji Hasan Mustapa (1852-1930, sufi sekaligus pujangga Sunda yang dipengaruhi ajaran wa╪dah al-wujūd. Dalam naskah itu tergerai ungkapan perjalanan sufistik (susulukan sang penulisnya. Bermula pada tahap pencarian diri saat hingga mengalami pertemuan (pasamoan, sapatemon. Puncaknya adalah pengalaman membaurnya eksistensi diri (fanā’, pakula-kula dalam kesejatian sempurna di alam jatnika. Karya Mustapa ini mencirikan kreativitas lokal dalam menyerap pengaruh tasawuf wa╪dah al-wujud yang diekspresikan dengan bahasa sastra dan alam Sunda.

  20. Potassic volcanic rocks and adakitic intrusions in southern Tibet: Insights into mantle-crust interaction and mass transfer from Indian plate

    Science.gov (United States)

    Liu, Dong; Zhao, Zhidan; DePaolo, Donald J.; Zhu, Di-Cheng; Meng, Fan-Yi; Shi, Qingshang; Wang, Qing

    2017-01-01

    Elucidating geodynamic processes at depth relies on a correct interpretation of petrological and geochemical features in magmatic records. In southern Tibet, both potassic volcanic rocks and adakitic intrusions exhibit high Sr/Y and La/Yb, and low Y and Yb concentrations. But these two rock types have contrasting temporal-spatial distributions and isotopic variations. Here we present a systematic study on the postcollisional potassic and adakitic rocks in order to investigate their petrogenetic links with the coeval mantle-derived ultrapotassic rocks and shed light on the potential input from underthrusted Indian continental crust. We found that adakitic intrusions with higher K2O/Na2O tend to display lower Y and higher SiO2, suggesting that the mantle-derived ultrapotassic melts, showing relatively high Y and Yb concentrations, only played a minor role in adakitic magmatism. Therefore, the unradiogenic 143Nd/144Nd and the dramatic decrease of zircon εHf(t) values since 35 Ma shown by postcollisional adakites should be interpreted as reflecting the crustal input from Indian plate. Unlike adakitic intrusions in southern Lhasa subterrane, potassic volcanic rocks share similar spatial distributions with ultrapotassic rocks, and their isotopic discrepancy is diminishing with volcanic activity becomes younger and migrates eastward. Evidence from whole-rock Pb and zircon Hf isotopes further indicates that potassic volcanic rocks are more likely to originate from partial melting of the overthickened and isotopically heterogeneous Lhasa terrane crust rather than the underthrusted Indian continental crust. The elevated Rb/Sr and varying Sr/CaO in potassic volcanic rocks provide an argument for sanidine + plagioclase + clinopyroxene as the major fractionating phases during magmatic differentiation. These findings not only highlight the significance of potassic and adakitic rocks in providing constraints on the geodynamic processes beneath southern Tibet, but also imply that

  1. The SOUTHERN PUNA Seismic Experiment: Shape of the Subducting Nazca Plate, Areas of Concentrated Mantle and Crustal Earthquakes, and Crustal Focal Mechanisms

    Science.gov (United States)

    Mulcahy, P.; Chen, C.; Kay, S. M.; Brown, L. D.; Alvarado, P. M.; Sandvol, E. A.; Heit, B.; Yuan, X.

    2010-12-01

    The SOUTHERN PUNA Seismic Experiment in the Central Andes between 25° - 28°S and 70° - 65°W recorded data in a 74-instrument array from Dec 07 to Nov 09 with the purpose of evaluating the structure and seismic character of the mantle and crust at the southern end of the Puna-Antiplano Plateau. Hypocenter locations for local and regional mantle earthquakes from 16 months of continuous recording confirm the persistence of the backarc teleseismic Antofalla Gap in intermediate depth mantle seismicity between 25.5° and 27.5°S consistent with the interpretation of a hot mantle wedge under this region. The best located Wadati Benioff Zone events agree with the subducting Nazca Plate contours of Cahill and Isacks (1992) north of 27°S, but show a more abrupt southward shallowing of contours in agreement with the Anderson et al. (2007) contours outlining the projected path of the already subducted Juan Fernandez Ridge. Another prominent feature in the data is the concentration of hypocenters in the Pipanaco nest to the south of the Antofalla Gap between 27° and 29°S. New PUNA results together with available HCMT solutions indicate NW oriented normal and strike-slip faulting in three general clusters within this nest at ~130km, 150km and 180km depth. Hypocenter locations and fault solutions for the Pipanaco Nest suggest flexure associated with steepening of the subducting slab consistent with the revised Wadati Benioff Zone contours. In an area of little to no crustal seismicity in global catalogs over the same time period, hundreds of well-located crustal earthquakes at depths less than 15km were recorded by the PUNA array. Among these earthquakes are three distinct clusters near relatively young volcanic centers. One cluster defines a nest northeast of the < 1 Ma Cerro Blanco caldera. The other two clusters are characterized by large quantities of earthquakes within 24-36 hours (swarms) near the Cerro Galan caldera that last erupted at ~2 Ma and near a ~1 Ma or

  2. Keterwakilan Etnis di Politik Nasional: Kasus Etnis Sunda di Republik Indonesia

    Directory of Open Access Journals (Sweden)

    Iwan Gardono Sujatmiko

    2014-01-01

    Full Text Available Artikel ini bertujuan untuk membuat sebuah model analisis untuk menjelaskan mengapa kehadiran tokoh politik Sunda di tingkat nasional relatif rendah walaupunmereka merupakan kelompok mayoritas terbesar kedua di Indonesia. Model analisis ini difokuskan pada faktor sejarah, jaringan sosial, budaya, dan peran Pemda sertamasyarakat. Faktor sejarah berguna untuk mengetahui sejauh mana pentingnya posisi orang Sunda dan Bandung sebagai pusatnya dalam hubungan sosial politiknya denganJakarta. Faktor jaringan sosial dapat menganalisis keterkaitan antara jaringan Sunda dengan jaringan nasional. Sementara itu faktor budaya berguna untuk melihat pengaruhnilai dan perilaku orang Sunda dalam berpolitik. Model ini juga mencakup peran Pemda dan masyarakat Sunda dalam mendukung orang Sunda untuk meningkatkan kehadiran tokoh politik mereka ditingkat nasional.

  3. Producing Appropriation: Negotiating Islam-Sunda in Terebang Sejak

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    Neneng Yanti Khozanatu Lahpan

    2015-04-01

    Full Text Available This article is an ethnographic account of my research on negotiating Islam and Sunda in Islamic Sundanese music. By taking special case of Terebang Sejak, I draw my attention on the issue based on my fieldwork in Cikeusal village, TasikMalaya, West Java. Observations and interviews are the main tools I used in gathering information. By presenting particularity of Terebang Sejak, this paper aims to present complexity and negotiations that are formed from the interaction between Islam and Sunda in the music in the village. In this context, presenting the idea of the truism of marginalizing Islam on local culture is in accordance with the idea of Indonesian modernity, which has parallelism with the mission of modernist Islam. While many scholars describe Islam in Indonesia with the idea of syncretism to depict the religion as ‘not really Islam’, in this article I provide different interpretation of localizing Islam by which people produce their own interpretation and appropriation in response to social and political changes in their environs. This interpretation will contribute to new understanding in addressing the particularity of meanings based on local knowledge, among Cikeusal people that forms what coded as ‘identity’ of being Muslim-Sunda. Here, Islamic text of Kitab Mulud in the music has played an agentive role to acknowledge the music as Islamic, thus continues to be part of ritual. 

  4. Sunda Shelf Seas: flushing rates and residence times

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    B. Mayer

    2015-05-01

    Full Text Available The region of the Sunda Shelf has an average depth of approx. 48 m and is subject to many physical and biogeochemical processes with a strong impact from human activities. For the investigation of marine environmental water properties and quality, it is helpful to have an idea about exchange rates of water masses in the different parts of this region. Four numerical models, the global hydrodynamical model MPI-OM, the global hydrological model MPI-HM, the regional hydrodynamical model HAMSOM and a Lagrangian tracer model have been utilized to estimate the flushing rates and residence times in different seas on the Sunda Shelf. Using decadal averaged monthly transports, the commonly used flushing rate formula gives rates for the different months of approximately 40 to 70 days for the entire Sunda Shelf. For most parts of it (Malacca Strait, southern South China Sea, Java Sea, the results are similar, while for the Gulf of Thailand, the flushing rates amount to 80 to 170 days. The tracer model provides quite different but very detailed 3-D pictures with residence times of below 30 days to more than two years, depending on the location within the region, on the starting layer and on the season.

  5. Elastic plate flexure above mantle plumes explains the upstream offset of volcanic activity at la Réunion and Hawaii

    Science.gov (United States)

    Gerbault, Muriel; Fontaine, Fabrice; Rabinowicz, Michel; Bystricky, Micha

    2017-04-01

    Surface volcanism at la Réunion and Hawaii occurs with an offset of 150-180 km upstream to the plume axis with respect to the plate motion. This striking observation raises questions about the forcing of plume-lithosphere thermo-mechanical interactions on melt trajectories beneath these islands. Based on visco-elasto-plastic numerical models handled at kilometric resolution, we propose to explain this offset by the development of compressional stresses at the base of the lithosphere, that result from elastic plate bending above the upward load exerted by the plume head. This horizontal compression adopts a disc shape centered around the plume axis, 20 km thick and 150 km in radius, at 50-70 km depth where the temperature varies from 600°C to 750°C. It lasts for 5 to 10 My in an oceanic plate of age greater than 70 My, a timing that is controlled by the visco-elastic relaxation time at 50-70 km depth. This period of time exceeds the time during which both the Somalian/East-African and Pacific plates drift over the Reunion and Hawaii plumes, respectively, thus rendering this basal compression a persistent feature. It is inferred that the buoyant melts percolating in the plume head pond below this zone of compression and eventually spread laterally until the most compressive principal elastic stresses reverse to the vertical, i.e., 150 km away from the plume head. There, melts propagate through dikes upwards to 35 km depth, where the plate curvature reverses and ambient compression diminishes. This 30-35 km depth may thus host magmatic reservoirs where melts pond, until further differentiation can relaunch ascension up to the surface and form a volcanic edifice. In a second stage, as the volcano grows because of melt accumulation at the top of the plate, the lithosphere is flexed downwards, inducing extra tensile stress at 30-35 km depth and compression at 15 km depth. It implies that now the melts pond at 15 km and form another magmatic reservoir lying just

  6. Landslide tsunami hazard in the Indonesian Sunda Arc

    Directory of Open Access Journals (Sweden)

    S. Brune

    2010-03-01

    Full Text Available The Indonesian archipelago is known for the occurrence of catastrophic earthquake-generated tsunamis along the Sunda Arc. The tsunami hazard associated with submarine landslides however has not been fully addressed. In this paper, we compile the known tsunamigenic events where landslide involvement is certain and summarize the properties of published landslides that were identified with geophysical methods. We depict novel mass movements, found in newly available bathymetry, and determine their key parameters. Using numerical modeling, we compute possible tsunami scenarios. Furthermore, we propose a way of identifying landslide tsunamis using an array of few buoys with bottom pressure units.

  7. PLATE

    DEFF Research Database (Denmark)

    Kling, Joyce; Hjulmand, Lise-Lotte

    2008-01-01

    ’s level of English is sufficient for the increasing number of courses offered in English each semester. This paper addresses these concerns and describes a pilot project initiated in 2003 at CBS to gauge the overall English language proficiency of those teaching content courses in English. Through......Copenhagen Business School (CBS) finds itself needing to address the issue of English-medium instruction for its increasing number of foreign exchange and full degree students. With internationalisation as a main pillar of the institution’s agenda, there are concerns whether the teaching faculty...... the Project in Language Assessment for Teaching in English (PLATE) language professionals from CBS’s Language Center observe teachers and provide feedback using evaluation criteria from the Common European Framework for Reference (CEFR) supplemented by some additional criteria which take the LSP nature...

  8. PLATE

    DEFF Research Database (Denmark)

    Kling, Joyce; Hjulmand, Lise-Lotte

    2008-01-01

    Copenhagen Business School (CBS) finds itself needing to address the issue of English-medium instruction for its increasing number of foreign exchange and full degree students. With internationalisation as a main pillar of the institution’s agenda, there are concerns whether the teaching faculty......’s level of English is sufficient for the increasing number of courses offered in English each semester. This paper addresses these concerns and describes a pilot project initiated in 2003 at CBS to gauge the overall English language proficiency of those teaching content courses in English. Through...... the Project in Language Assessment for Teaching in English (PLATE) language professionals from CBS’s Language Center observe teachers and provide feedback using evaluation criteria from the Common European Framework for Reference (CEFR) supplemented by some additional criteria which take the LSP nature...

  9. Karakteristik Iket Sunda di Bandung dan Sumedang Periode Tahun 1968-2006

    Directory of Open Access Journals (Sweden)

    Suciati Suciati

    2008-11-01

    Full Text Available The study discusses the design of Iket Sunda as it is related to the life of Sundanese people and their associated culture. Iket is a type of traditional head-attire of Sunda, in which through its use we may grasp the function and status of those who wears it. Unfortunately, the use of traditional iket Sunda is no longer common and no one seems to wear it in daily basis. Yet, iket Sunda carries more than just fashion, as it also represent distinct identity amongst diverse ethnic cultures of Indonesia. This study exposes the knowledge behind iket Sunda, from the embedded aesthetic values, the associated behavior of the people who wears it, and its inter-related historical background. To address the purpose, this study applied qualitative approach based on cultural transformation theory, in order to understand the undergone changes that may relate to the design of iket-Sunda.  Results indicate that iket Sunda is not completely washed out of use in today’s living, as a small group of Sundanese societies in Bandung and Sumedang still wear it on a daily basis. However, some Sundanese people only wear it as part of complete traditional attire in certain events, including dance costumes and other performance activities, therefore most are not aware of the various styles of iket-Sunda. Study found that through times, iket Sunda has undergone changes on the shape, use of clothes, size, decorations, colors, and way of wearing. As rare as it may be, iket Sunda represents the true identity of Sundanese people and their associated culture.

  10. Along-arc geochemical and isotopic variations in Javanese volcanic rocks: 'crustal' versus 'source' contamination at the Sunda arc, Indonesia

    Science.gov (United States)

    Handley, H.; Blichert-Toft, J.; Turner, S.; Macpherson, C. G.

    2012-12-01

    Understanding the genesis of volcanic rocks in subduction zone settings is complicated by the multitude of differentiation processes and source components that exert control on lava geochemistry. Magma genesis and evolution at the Sunda arc is controlled and influenced by 1) along arc changes in the composition and thickness of the overriding Eurasian plate, 2) the variable age of the subducting oceanic crust and, 3) changes in the type and amount of sediment deposited on the subducting plate. Along-arc changes in geochemistry have long been recognised in the Sunda arc (Whitford, 1975), but debate still prevails over the cause of such variations and the relative importance of shallow (crustal) versus deep (subduction) contamination at the Sunda arc, Indonesia. Detailed study of individual Sunda arc volcanic centres is, therefore, a prerequisite in order to establish the relative importance and contributions of various potential source components and composition modifying differentiation processes at individual volcanoes, prior to an along arc comparative petrogenetic investigation. We present new radiogenic isotope data for Javanese volcanoes, which is combined with our recently published (Handley et al., 2007; Handley et al., 2008, Handley et al., 2010; Handley et al., 2011) geochemical and isotopic data of Javanese volcanic rocks along with data from other detailed geochemical studies to establish whether variable contributions from the subducting slab, or a change in crustal architecture of the overriding plate, best explain along-arc variations in isotope ratios and trace element characteristics. In West and Central Java Sr isotope ratios of the volcanic rocks broadly correlate with inferred lithospheric thickness implicating a shallow level control on isotopic composition. However, key trace element ratios combined with Hf isotope data indicate that the subducted slab and slab thermal regime also exert major control on the composition of the erupted Javanese

  11. Archimedean Proof of the Physical Impossibility of Earth Mantle Convection

    CERN Document Server

    Herndon, J Marvin

    2010-01-01

    Eight decades ago, Arthur Holmes introducted the idea of mantle convection as a mechanism for continental drift. Five decades ago, continental drift was modified to become plate tectonics theory, which included mantle convection as an absolutely critical component. Using the submarine design and operation concept of "neutral buoyancy", which follows from Archimedes' discoveries, the concept of mantle convection is proven to be incorrect, concomitantly refuting plate tectonics, refuting all mantle convection models, and refuting all models that depend upon mantle convection.

  12. Desain Kebaya Sunda Abad Ke-20 Studi Kasus di Bandung Tahun 1910-1980

    Directory of Open Access Journals (Sweden)

    Irma Russanti

    2007-08-01

    Full Text Available The female traditional outfits of Sunda are varied according to geography, history, social life, economy, and cultural transformations that have taken place for centuries. The similarity in both cultures and historical background had resulted in the similarity on structural design of the various female outfits in this area. This study focuses to identify various styles of kebaya Sunda that shared similarity of features. The word Sunda itself was used as a collective term, and apparently had a relation with the original place and culture of the kebaya wearers – female Sundanese. Given wide geographical area and historical richness of Sunda, the study focuses on the area of Bandung during the period of 1910–1980. The study employed a descriptive analysis that was based on the historical approach, in an attempt to describe the cultural transformation of kebaya as the traditional female outfit that had taken place in Sunda area. To identify design features of kebaya Sunda, the study employed both synchronic and diachronic approaches. To analyze the effect of modernization toward aesthetical shift and changes of design in kebaya Sunda during 1910-1980, the study employed aesthetical approach. In addition, the study also looks into the influence of social stratification upon the classification of the designs in kebaya Sunda. Results suggest that: (1 Design features of the kebaya Sunda had accumulated into five different styles (V neckline, wide samleh, small samleh, cowak, and triangle bef, (2 The modern education and the changes of thinking pattern, trend mode and textile, and the technological development of pattern making had greatly influenced the aesthetical shift of the kebaya Sunda design, thus greatly affecting their design changes (sleeve shape, collars, necklines, proportions, textures, silhouettes, constructions, and decoration varieties, (3 The influence of the social stratification to the design classification of kebaya Sunda in

  13. Crustal strain partitioning and the associated earthquake hazard in the eastern Sunda-Banda Arc

    Science.gov (United States)

    Koulali, A.; Susilo, S.; McClusky, S.; Meilano, I.; Cummins, P.; Tregoning, P.; Lister, G.; Efendi, J.; Syafi'i, M. A.

    2016-03-01

    We use Global Positioning System (GPS) measurements of surface deformation to show that the convergence between the Australian Plate and Sunda Block in eastern Indonesia is partitioned between the megathrust and a continuous zone of back-arc thrusting extending 2000 km from east Java to north of Timor. Although deformation in this back-arc region has been reported previously, its extent and the mechanism of convergence partitioning have hitherto been conjectural. GPS observations establish that partitioning occurs via a combination of anticlockwise rotation of an arc segment called the Sumba Block, and left-lateral movement along a major NE-SW strike-slip fault west of Timor. We also identify a westward extension of the back-arc thrust for 300 km onshore into East Java, accommodating slip of ˜6 mm/yr. These results highlight a major new seismic threat for East Java and draw attention to the pronounced seismic and tsunami threat to Bali, Lombok, Nusa Tenggara, and other coasts along the Flores Sea.

  14. Distribution of the Sunda Colugo (Galeopterus variegatus) in Malaysia (Peninsular, Sabah, Sarawak)

    OpenAIRE

    Nasir, Muhammad Dzulhelmi Muhammad; Abdullah, Mohd Tajuddin

    2010-01-01

    There is not much information available on the distribution of the Sunda colugo (Galeopterus variegates) in Malaysia, despite it being one of only two known species in the order Dermoptera. Data on the presence of the Sunda colugo and the vernacular names used by various ethnic groups throughout Malaysia were collected and compiled from various primary and secondary sources. There were 27 locations from Peninsular, 11 locations from Sabah and 34 locations from Sarawak that reported the presen...

  15. Mantle constraints on the plate tectonic evolution of the Tonga-Kermadec-Hikurangi subduction zone and the South Fiji Basin region

    NARCIS (Netherlands)

    Schellart, W.P.; Spakman, W.

    2012-01-01

    The Tonga–Kermadec–Hikurangi subduction zone is a major plate boundary in the Southwest Pacific region, where the Pacific plate subducts westward underneath the Australian plate. Considerable controversy exists regarding the Cenozoic evolution of this subduction zone, its connection with

  16. Delineating Biophysical Environments of the Sunda Banda Seascape, Indonesia

    Directory of Open Access Journals (Sweden)

    Mingshu Wang

    2015-01-01

    Full Text Available The Sunda Banda Seascape (SBS, located in the center of the Coral Triangle, is a global center of marine biodiversity and a conservation priority. We proposed the first biophysical environmental delineation of the SBS using globally available satellite remote sensing and model-assimilated data to categorize this area into unique and meaningful biophysical classes. Specifically, the SBS was partitioned into eight biophysical classes characterized by similar sea surface temperature, chlorophyll a concentration, currents, and salinity patterns. Areas within each class were expected to have similar habitat types and ecosystem functions. Our work supplemented prevailing global marine management schemes by focusing in on a regional scale with finer spatial resolution. It also provided a baseline for academic research, ecological assessments and will facilitate marine spatial planning and conservation activities in the area. In addition, the framework and methods of delineating biophysical environments we presented can be expanded throughout the whole Coral Triangle to support research and conservation activities in this important region.

  17. IMPACT OF CLIMATE ANOMALY ON CATCH COMPOSITION OF NERITIC TUNA IN SUNDA STRAIT

    Directory of Open Access Journals (Sweden)

    Khairul Amri

    2013-12-01

    Full Text Available Tongkol komo/kawakawa (Euthynnus affinis and tenggiri (Scomberomerus guttatus are commonly caught by mini purseiners operated in Sunda Straits and landed in Labuan, West Java. This species inhabits coastal water and has preference staying in relatively warm water. Oceanography parameters commonly influencing the distribution of Euthynnus affinis are temperature, current, and salinity. The oceanography of Sunda Strait is influenced by water masses coming from the north that mainly originated from the Java Sea and water masses from the south mainly originated from Indian Ocean. The internal oceanography of Sunda Strait is also influenced by upwelling and monsoon as regional climate anomaly (ENSO and Indian Ocean Dipole Mode. This paper describes the influence of Dipole Mode (positive and negative event and ENSO (El- Nino/La-Nina to the catch dynamics of neritic tuna particularly in Sunda Straits waters. The results shown that regional climate anomaly influenced neritic tuna catch and its composition. The catches Euthynnus affinis in phase negative dipole mode or La-Nina were higher and dominated the catch composition of pelagic fishes of Sunda Strait. Similar situation also is showen by Scomberomorus commerson.

  18. Tradisi Wuku Taun sebagai B entuk Integrasi Agama Islam dengan Budaya Sunda pada Masyarakat Adat Cikondang

    Directory of Open Access Journals (Sweden)

    Deni Miharja

    2015-01-01

    Full Text Available This article write starts from some phenomena of the relation between religions and local cultures. Such relation is interesting to do research that interpretations of the relation between religion and local cultures to certain societies are various. The interaction between Islam and local cultures also undergoes variuos form of relation. Variety of the form of relation between Islam and local cultures in a society depends upon their understanding and interpretation of Islamic teachings itself. One of the forms of relation between Islam and local cultures can be found in traditional society of Cikondang. The form of relation between Islam and local cultures was occurred in traditional society in Cikondang tends to be the form of integration wich certain pattern. Therefore, the focus of this writer article is to describe relation between Islam and Sundanese cultures in form of integration with wuku taun. Based on data of research the tradisional society of Cikondang represents the part of Sundanese society in wich all of them are muslims. This goes hand in hand with the statement that Islam is Sunda and Sunda is Islam. Sundanese people are Muslims before Islam comes to Sundanese society.Tulisan artikel ini berangkat dari fenomena hubungan agama dengan budaya lokal. Dimana hubungan agama dengan budaya lokal pada suatu masyarakat, mengalami bentuk hubungan yang beragam. Begitu pun hubungan agama Islam dengan budaya lokal mengalami bentuk hubungan yang beragam pula. Beragamnya bentuk hubungan agama Islam dengan budaya lokal pada suatu masyarakat tergantung dari penghayatan terhadap ajaran Islam itu sendiri. Bentuk hubungan agama Islam dengan budaya lokal bisa ditemukan salah satunya pada masyarakat adat Cikondang. Bentuk hubungan yang terjadi antara Islam dengan budaya Sunda pada masyarakat adat Cikondang cenderung dalam bentuk integrasi dengan pola tertentu, sehingga fokus penulisan artikel ini adalah untuk mengungkap hubungan agama Islam dengan

  19. Coupling dynamic mechanisms between plate tectonics evolution and mantle convection of south and north Tianshan%天山南北地块构造演化与地幔对流耦合动力机制

    Institute of Scientific and Technical Information of China (English)

    刘玉虎; 刘兴旺; 郑建京; 赵丹丹; 杨鑫; 王亚东

    2011-01-01

    inquiry of the five kinds of mantle convection patterns, based on whole-mantle convection and small-scale upper mantle convection model, we propose that the dynamic mechanism of plate tectonic evolution coupled with the mantle convection in the Tianshan region totally presented as "Start-Sync-Transcendence-Subtractive" mode, and the middle course of the dynamic model with micro-oscillation cycle forward. This model can be compared with the classic Wilsoncycle while the current traces of the plate tectonic evolution in the deep crust and the numerical simulation of themantle convection also supports this niode to sone extent. In short of a unified dynamic model combing the history and evolution of plate teconies and mantle convection,it will be of great significance for future stuty of coupling andintcraction between all the subsystems of the Earth.

  20. Large-scale retreat and advance of shallow seas in Southeast Asia driven by mantle flow

    Science.gov (United States)

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

    2016-04-01

    the active margin, leading to slab breakoff and a weakened mantle down-welling acting on the overriding plate, which resulted in regional dynamic uplift and emergence from a ~10-15 Myr-long subduction hiatus along the Sunda active margin. This explains the absence of sediment deposition across Sundaland and the emergence of Sundaland between ~80-60 Ma. Renewed subduction from ~60 Ma reinitiated dynamic subsidence of Sundaland, leading to submergence from ~40 Ma despite falling long-term global sea levels. Our results highlight a complete 'down-up-down' dynamic topography cycle experienced by Sundaland over 100 million years, with the transience of topography revealed in sedimentary basin stratigraphy punctuated with regional unconformities. Subduction-driven mantle convection models are now able to transform the geological record of basins into a dynamic surface history, enabling a deeper understanding of mechanisms that control landscape evolution across spatial and temporal scales.

  1. Tomography, the geoid and plate motions

    Science.gov (United States)

    Gable, Carl W.; O'Connell, Richard J.

    1991-01-01

    The dynamics of the earth's mantle and its relationship to mantle structure as revealed by seismic tomography, the geoid, and plate motions are discussed in a critical review of U.S. research from the period 1987-1990. Sections are devoted to plates and mantle convection; seismic anomalies, flow, and the geoid; subducted slabs and the 670-km discontinuity; the physical properties of the mantle; plumes; and computational and experimental modeling efforts. Also included is a comprehensive bibliography for the period.

  2. Electrical conductivity of old oceanic mantle in the northwestern Pacific I: 1-D profiles suggesting differences in thermal structure not predictable from a plate cooling model

    Science.gov (United States)

    Baba, Kiyoshi; Tada, Noriko; Matsuno, Tetsuo; Liang, Pengfei; Li, Ruibai; Zhang, Luolei; Shimizu, Hisayoshi; Abe, Natsue; Hirano, Naoto; Ichiki, Masahiro; Utada, Hisashi

    2017-08-01

    Seafloor magnetotelluric (MT) experiments were recently conducted in two areas of the northwestern Pacific to investigate the nature of the old oceanic upper mantle. The areas are far from any tectonic activity, and "normal" mantle structure is therefore expected. The data were carefully analyzed to reduce the effects of coastlines and seafloor topographic changes, which are significant boundaries in electrical conductivity and thus distort seafloor MT data. An isotropic, one-dimensional electrical conductivity profile was estimated for each area. The profiles were compared with those obtained from two previous study areas in the northwestern Pacific. Between the four profiles, significant differences were observed in the thickness of the resistive layer beyond expectations based on cooling of homogeneous oceanic lithosphere over time. This surprising feature is now further clarified from what was suggested in a previous study. To explain the observed spatial variation, dynamic processes must be introduced, such as influence of the plume associated with the formation of the Shatsky Rise, or spatially non-uniform, small-scale convection in the asthenosphere. There is significant room of further investigation to determine a reasonable and comprehensive interpretation of the lithosphere-asthenosphere system beneath the northwestern Pacific. The present results demonstrate that electrical conductivity provides key information for such investigation.[Figure not available: see fulltext.

  3. A new subspecies of Accipiter virgatus (Temminck) from Flores, Lesser Sunda Islands, Indonesia (Aves: Accipitridae)

    NARCIS (Netherlands)

    Mees, G.F.

    1984-01-01

    A new subspecies of Accipiter virgatus (Temminck) is described from Flores (Lesser Sunda Islands). In addition some notes are given on the distribution of A. virgatus in south-eastern Burma and adjacent parts of Thailand, supplementary to an earlier paper (Mees, 1981).

  4. Revision of the Euagathis species (Hymenoptera: Braconidae: Bassinae) from the Sunda Islands

    NARCIS (Netherlands)

    Simbolotti, G.; Achterberg, van C.

    1994-01-01

    The species of the genus Euagathis Szépligeti, 1900 (Braconidae: Bassinae (= Agathidinae)) from the Greater and Lesser Sunda Islands (including West Malaysia) are revised and keyed. The subfamily name Bassinae Nees, 1812, is used because it is senior to the commonly used subfamily name Agathidinae

  5. Global correlation of lower mantle structure and past subduction

    NARCIS (Netherlands)

    Domeier, M.; Doubrovine, Pavel V.; Torsvik, Trond H.; Spakman, W.|info:eu-repo/dai/nl/074103164; Bull, A.L.

    2016-01-01

    Advances in global seismic tomography have increasingly motivated identification of subducted lithosphere in Earth's deep mantle, creating novel opportunities to link plate tectonics and mantle evolution. Chief among those is the quest for a robust subduction reference frame, wherein the mantle asse

  6. Geological Features Inferred from Local Seismic Tomography in the Sunda Strait and West Java regions, Indonesia

    Science.gov (United States)

    Nugraha, A. D.; Sakti, A. P.; Rohadi, S.; Widiyantoro, S.

    2012-12-01

    We have conducted seismic tomographic inversions to obtain a P-wave seismic velocity structure beneath the Sunda Strait and West Java regions, Indonesia. The Sunda Strait is located in a complex geological system i.e. in the transition from the oblique subduction beneath Sumatra to the nearly perpendicular subduction below Java. The Krakatau active volcano is located in the Sunda Strait. In this study, we have used selected P-wave arrival times from the data catalogs of the SeisComP-BMKG network (from 2009 to 2011) and the BMKG BALAI II network (from 1992 to 2011) compiled by Badan Meteorologi,Klimatologi dan Geofisika (BMKG), Indonesia. In total, there are 1,598 local earthquakes and 10,366 P-wave phases from 25 seismographic stations that have been used for the tomographic inversions. We have also relocated the hypocenter locations along with velocity inversions simultaneously. Our preliminary results depict some prominent geological features that include: (1) a low velocity anomaly beneath north of the Ujung Kulon region, which coincides with a low gravity anomaly resulting from a previous study, (2) a low velocity anomaly alignment beneath the Krakatau volcano in the Sunda Strait, (3) a sharp contrast in velocity anomalies extending from Pelabuhan Ratu towards Jakarta with a strike of SW-NE, and (4) a low velocity anomaly in the offshore of Pelabuhan Ratu that may be correlated with the continuation of the Cimandiri fault zone. More detailed information will be presented during the meeting. Keywords: tomography, Sunda Strait, West Java, velocity anomaly

  7. Archimedean Proof of the Physical Impossibility of Earth Mantle Convection

    OpenAIRE

    Herndon, J. Marvin

    2010-01-01

    Eight decades ago, Arthur Holmes introducted the idea of mantle convection as a mechanism for continental drift. Five decades ago, continental drift was modified to become plate tectonics theory, which included mantle convection as an absolutely critical component. Using the submarine design and operation concept of "neutral buoyancy", which follows from Archimedes' discoveries, the concept of mantle convection is proven to be incorrect, concomitantly refuting plate tectonics, refuting all ma...

  8. The records of coastline changes reflected by mangroves on the Sunda Shelf since the last 40 ka

    Institute of Scientific and Technical Information of China (English)

    WANG XiaoMei; SUN XiangJun; WANG PinXian; Karl Stattegger

    2008-01-01

    This paper presents a 40000-year-long high-resolution mangrove record from sediments of Core 18300,18302 and 18323 on the continental shelf of the southern South China Sea and reconstructs the coast-line changes on Sunda Shelf since the last 40000 years.In the period Marine Isotope 3,the old Sunda Shelf had low sea level,and it was partly exposed.Flourishing vegetations grew on the exposed old land.Mangroves developed along the coastline.On the Last Glacial Maximum,the sea level dropped greatly,coastline moved from inner shelf to outer shelf,the Old Sunda Land exposed further,and the lowering sea level induced the gradual disappearing of mangroves from the inner Sunda Shelf to the outer Sunda Shelf.And pioneer vegetation ferns covered the broadly exposed old land immediately.At the time of the last Deglaciation,sea level rose greatly,the coastline moved to the sea and the Sunda Shelf was drown again.Mangroves were emergent again from outer shelf to inner shelf and developed quickly.

  9. ANALISA ANOMALI GAYABERAT TERHADAP KONDISI TATANAN TEKTONIK ZONA SUBDUKSI SUNDA MEGATHRUST DI SEBELAH BARAT PULAU SUMATERA

    Directory of Open Access Journals (Sweden)

    Anita Thea Saraswati

    2015-02-01

    Full Text Available Aktivitas tektonik yang terjadi di bumi merupakan hal yang masih terus diteliti sampai sekarang. Sumatera yang terletak pada area Sunda Megathrust, yang merupakan zona subduksi Lempeng Indo-Australia dan Lempeng Eurasia, mengakibatkan daerah ini rentan dengan aktivitas seismogenic. Salah satu akibat dari adanya pergerakan kedua lempeng ini adalah terbentuknya tatanan tektonik di wilayah Sumatera. GOCE (Gravity field and steady-state Ocean Circulation Explorer menawarkan metode yang cepat dengan cakupan global untuk mendapatkan data gayaberat bumi. Dengan memanfaatkan hitungan dari spherical harmonic coeffisien (SHC serta dilengkapi dengan data Digital Elevation Model (DEM, dapat diketahui nilai anomali gayaberat pada suatu wilayah. Distribusi anomali gayaberat mampu mencerminkan kondisi tektonik di suatu area. Variasi spasial dari anomali gayaberat menunjukkan bahwa pada palung yang terbentuk akibat subduksi kedua lempeng memiliki nilai anomali gayaberat negatif dengan nilai rata-rata sebesar -42.8729 mgal. Forearc ridge yang terbentuk akibat konvergensi lempeng memiliki nilai anomali gayaberat positif, sedangkan forearc basin yang merupakan cekungan diantara backarc dan forearc ridge, memiliki nilai anomali gayaberat negatif yang lebih kuat daripada yang terdapat pada Sunda Megathrust. Variasi temporal yang teramati menunjukkan bahwa distribusi anomali gayaberat positif yang terdapat pada prisma akresi di kedua tepian palung bergerak semakin mendekati Sunda Megathrust pada tiap seri pengamatannya, sedangkan distribusi anomali gayaberat negatif pada palung laut dan forearc basin membentuk suatu  pola distribusi yang semakin menyempit sehingga menyebabkan semakin curamnya gradient anomali gayaberat pada area di sekitarnya.

  10. The effect of water to mantle rheology and convection

    Science.gov (United States)

    Brändli, Stefan

    2016-04-01

    Water has a significant influence to mantle rheology and therefore also to the convection of the mantle and the plate tectonics. The viscosity of the mantle can be decreased by up to two orders of magnitude when water is present. Another effect of the water is the change in the solidus of the mantle and therefore the melting regime. These two effects of water in the mantle have a significant influence on mantle convection and plate tectonics. The influx of water to the mantle is driven by plate tectonics as wet oceanic lithosphere is subducted into the mantle, then water is brought back to the lithosphere and the surface by MOR-, arc- and hotspot volcanism. Studies show that the amount of water in the mantle is about three times bigger than the water in the oceans. To model this water cycle multiple additions to our simulation code StagYY are necessary. A water diffusion to complement the water transport due to advection, and water dependent viscosity law are implemented. This additions to StagYY will be followed by implementations of a pressure-temperature law for maximum water content, additional transport mechanisms for water, water dependent solidus functions and the implementation of recent values for plate velocities and water capacities in subducting slabs. This will allow us to research the influence of water to the mantle convection and rheology over the past 200Ma.

  11. Tectonics: Changing of the plates

    Science.gov (United States)

    Brandon, Alan

    2016-10-01

    The composition of Earth's crust depends on the style of plate tectonics and of the melting regimes in the mantle. Analyses of the oldest identified rocks suggest that these styles and the resulting crust have changed over Earth's history.

  12. Compositional Evolution of the Mantle

    Science.gov (United States)

    Bennett, V. C.

    2003-12-01

    are also considered. Understanding the origin of chemical heterogeneity in the Earth's mantle remains a fundamental focus in Earth science. Thus, the second part of this chapter is devoted to the implications of these observations for some of the key questions in mantle geochemistry such as, what are the major chemical reservoirs, when did they form, and how do they interact with each other? Was the Archean mantle substantially different from the modern mantle? How much, if any, of what we see in the modern mantle is a result of early planetary differentiation processes such as those inferred for the Moon and Mars, and how much is a result of the prolonged effects of plate tectonic processes? Has the mantle become more or less chemically heterogeneous with time? All of these questions remain active areas of research, and the intention of this chapter is primarily to present an overview of the current "state of play," which will undoubtedly evolve rapidly with further study.

  13. Sources characteristics and Afterslip of Great Earthquakes in the Western Sunda Subduction Zone

    Science.gov (United States)

    Chlieh, M.; Avouac, J.; Sieh, K.; Natawidjaja, D. H.

    2006-12-01

    We determine coseismic and the first-month postseismic deformation associated with the Sumatra-Andaman earthquake of December 26, 2004 from near-field Global Positioning System (GPS) surveys in northwestern Sumatra and along the Nicobar-Andaman islands, continuous and campaign GPS measurements from Thailand and Malaysia, and in-situ and remotely sensed observations of the vertical motion of coral reefs. The coseismic model shows that the Sunda subduction megathrust ruptured over a distance of about 1500 km and a width of less than 150 km, releasing a total moment of 6.7-7.0 1022 Nm, equivalent to a magnitude Mw~9.15. The latitudinal distribution of released moment in our model has three distinct peaks around 4°N, 7° and 9°N, which compares well to the latitudinal variations seen in the seismic inversion and of the analysis of radiated T-waves. Our coseismic model is also consistent with interpretation of normal modes and with the amplitude of very long period surface waves. The tsunami predicted from this model fits relatively well the altimetric measurements made by the JASON and TOPEX satellites. Neither slow nor delayed slip is needed to explain the normal modes and the tsunami wave. The near-field geodetic data that encompass both coseismic deformation and up to 40 days of postseismic deformation require that slip must have continued on the plate interface after the 500s long seismic rupture releasing a moment equivalent to 2.5 1022 Nm (Mw~8.8). The Mw8.6 Nias-Simeulue earthquake of March 28, 2005, ruptured the southern adjacent segment of the Sumatra-Andaman earthquake. This event occurred within an array of continuous GPS stations and produced measurable vertical displacement of the fringing coral reefs above the fault rupture. Source models obtained from the joint inversion of various combinations of the teleseismic body waves and geodetic data indicate a relatively slow average rupture velocity of 1.5 to 2.5km/s and long average rise time of up to 20s

  14. Analysis of spatiotemporal variation in b-value for the Sunda arc using high precision earthquake location

    Science.gov (United States)

    Nugraha, Andri Dian; Shiddiqi, Hasbi Ash; Widiyantoro, Sri; Sutiyono, Handayani, Titi

    2016-05-01

    The Sunda arc is one of the most active tectonic regions, which has a complex tectonic setting due to different tectonic regimes and subduction geometry along this arc. We analyzed variation in b-value for this region in order to obtain better information regarding the state of stress in this region. For the first step, we relocated earthquake hypocenters taken from the BMKG catalog for the period 2009 - 2015 by employing a teleseismic double-difference (DD) relocation method and using a 3D velocity model. There are 10,440 earthquakes that were successfully relocated with greatly reduced residual errors. Based on its tectonic feature and earthquake distribution, we divided the study area into 8 regions, i.e. northern Sumatra, central Sumatra, southern Sumatra, Sunda strait, western Java, eastern Java, lesser Sunda islands, and Sunda-Banda transition zone. For b-value analysis we combined the BMKG catalog with the International Seismological Centre (ISC) catalog from 2006 to 2009 to obtain a longer time period. We analyzed the spatial variation in b-value for western sunda arc and found a low b-value that matches well with earthquake locations.

  15. Crustal structure beneath two seismic stations in the Sunda-Banda arc transition zone derived from receiver function analysis

    Energy Technology Data Exchange (ETDEWEB)

    Syuhada, E-mail: hadda9@gmail.com [Graduate Research on Earthquake and Active Tectonics (GREAT), Bandung Institute of Technology, Jalan Ganesha 10, Bandung 40132 (Indonesia); Research Centre for Physics - Indonesian Institute of Sciences (LIPI), Kompleks Puspiptek Serpong, Tangsel 15314, Banten Indonesia (Indonesia); Hananto, Nugroho D.; Handayani, Lina [Research Centre for Geotechnology - Indonesian Institute of Sciences (LIPI), Jl. Sangkuriang (Kompleks LIPI) Bandung 40135 (Indonesia); Puspito, Nanang T; Yudistira, Tedi [Faculty of Mining and Petroleum Engineering ITB, Jalan Ganesha 10, Bandung 40132 (Indonesia); Anggono, Titi [Research Centre for Physics - Indonesian Institute of Sciences (LIPI), Kompleks Puspiptek Serpong, Tangsel 15314, Banten Indonesia (Indonesia)

    2015-04-24

    We analyzed receiver functions to estimate the crustal thickness and velocity structure beneath two stations of Geofon (GE) network in the Sunda-Banda arc transition zone. The stations are located in two different tectonic regimes: Sumbawa Island (station PLAI) and Timor Island (station SOEI) representing the oceanic and continental characters, respectively. We analyzed teleseismic events of 80 earthquakes to calculate the receiver functions using the time-domain iterative deconvolution technique. We employed 2D grid search (H-κ) algorithm based on the Moho interaction phases to estimate crustal thickness and Vp/Vs ratio. We also derived the S-wave velocity variation with depth beneath both stations by inverting the receiver functions. We obtained that beneath station PLAI the crustal thickness is about 27.8 km with Vp/Vs ratio 2.01. As station SOEI is covered by very thick low-velocity sediment causing unstable solution for the inversion, we modified the initial velocity model by adding the sediment thickness estimated using high frequency content of receiver functions in H-κ stacking process. We obtained the crustal thickness is about 37 km with VP/Vs ratio 2.2 beneath station SOEI. We suggest that the high Vp/Vs in station PLAI may indicate the presence of fluid ascending from the subducted plate to the volcanic arc, whereas the high Vp/Vs in station SOEI could be due to the presence of sediment and rich mafic composition in the upper crust and possibly related to the serpentinization process in the lower crust. We also suggest that the difference in velocity models and crustal thicknesses between stations PLAI and SOEI are consistent with their contrasting tectonic environments.

  16. Crustal structure beneath two seismic stations in the Sunda-Banda arc transition zone derived from receiver function analysis

    Science.gov (United States)

    Syuhada, Hananto, Nugroho D.; Puspito, Nanang T.; Anggono, Titi; Handayani, Lina; Yudistira, Tedi

    2015-04-01

    We analyzed receiver functions to estimate the crustal thickness and velocity structure beneath two stations of Geofon (GE) network in the Sunda-Banda arc transition zone. The stations are located in two different tectonic regimes: Sumbawa Island (station PLAI) and Timor Island (station SOEI) representing the oceanic and continental characters, respectively. We analyzed teleseismic events of 80 earthquakes to calculate the receiver functions using the time-domain iterative deconvolution technique. We employed 2D grid search (H-κ) algorithm based on the Moho interaction phases to estimate crustal thickness and Vp/Vs ratio. We also derived the S-wave velocity variation with depth beneath both stations by inverting the receiver functions. We obtained that beneath station PLAI the crustal thickness is about 27.8 km with Vp/Vs ratio 2.01. As station SOEI is covered by very thick low-velocity sediment causing unstable solution for the inversion, we modified the initial velocity model by adding the sediment thickness estimated using high frequency content of receiver functions in H-κ stacking process. We obtained the crustal thickness is about 37 km with VP/Vs ratio 2.2 beneath station SOEI. We suggest that the high Vp/Vs in station PLAI may indicate the presence of fluid ascending from the subducted plate to the volcanic arc, whereas the high Vp/Vs in station SOEI could be due to the presence of sediment and rich mafic composition in the upper crust and possibly related to the serpentinization process in the lower crust. We also suggest that the difference in velocity models and crustal thicknesses between stations PLAI and SOEI are consistent with their contrasting tectonic environments.

  17. Upper and mid mantle fabric developing during subduction-induced mantle flow

    Science.gov (United States)

    Faccenda, Manuele

    2013-04-01

    Subduction zones are convergent margins where the rigid lithosphere sinks into the Earth's mantle inducing complex 3D flow patterns. Seismic anisotropy generated by strain-induced lattice/crystal preferred orientation (LPO/CPO) of intrinsically anisotropic minerals is commonly used to study flow in the mantle and its relations with plate motions. We computed the seismic anisotropy of the upper and mid mantle due to strain-induced LPO in 3D mechanical models of dynamic subduction by using, respectively, D-Rex and Underworld. Subsequently, FSTRACK was used to compute seismogram synthetics and SKS splitting patterns. Strong anisotropy develops in the upper mantle, while weak or null seismic anisotropy is formed in the upper transition zone/lower mantle and lower transition zone, respectively. The distribution of the fabric in the mantle depends on the distribution and amount of the deformation, and not on the rate at which the slab subducts. The SKS splitting patterns are controlled by the anisotropy in the upper mantle because SKS waves are more sensitive to the anisotropy in the shallowest layers. Horizontally propagating shear waves in the mid mantle originating from local earthquakes are characterized by significant splitting that is mostly due to the fabric in the uppermost lower mantle. We discuss the implications of our results for real subduction settings like Tonga, where a discrete amount of observations have been collected in the past 10 years on the anisotropy in the upper and mid mantle.

  18. Numerical modeling of mantle plume diffusion

    Science.gov (United States)

    Krupsky, D.; Ismail-Zadeh, A.

    2004-12-01

    To clarify the influence of the heat diffusion on the mantle plume evolution, we develop a two-dimensional numerical model of the plume diffusion and relevant efficient numerical algorithm and code to compute the model. The numerical approach is based on the finite-difference method and modified splitting algorithm. We consider both von Neumann and Direchlet conditions at the model boundaries. The thermal diffusivity depends on pressure in the model. Our results show that the plume is disappearing from the bottom up - the plume tail at first and its head later - because of the mantle plume geometry (a thin tail and wide head) and higher heat conductivity in the lower mantle. We study also an effect of a lateral mantle flow associated with the plate motion on the distortion of the diffusing mantle plume. A number of mantle plumes recently identified by seismic tomography seem to disappear in the mid-mantle. We explain this disappearance as the effect of heat diffusion on the evolution of mantle plume.

  19. Kontinuitas dan Perubahan Sawer Panganten dalam Upacara Perkawinan Adat Sunda Kontemporer

    Directory of Open Access Journals (Sweden)

    Cepi Irawan

    2014-11-01

    Full Text Available Penelitian ini bertujuan untuk memahami peristiwa saweran yang terjadi dalammasyarakat Sunda kontemporer. Penelitian dilakukan dengan pengamatan terlibatpada upacara perkawinan yang berlangsung dalam masyarakat Sunda yang tinggaldi kota. Peristiwa nyawer atau sawer dilaksanakan pada waktu upacara perkawinanadat Sunda setelah akad nikah. Upacara ini dilengkapi dengan benda-benda simbolikyang mempunyai nilai ritual seperti mantera atau rajah. Sawer yang bentukaktivitasnya berupa penyampaian nasihat kepada mempelai melalui lagu-lagu yangdinyanyikan oleh juru sawer dengan seni mamaos sebagai sarananya. Sawer ataunyawer mempunyai arti air jatuh memercik, sesuai dengan praktek juru sawer yangmenabur-naburkan perlengkapan nyawer seolah-olah memercikkan air kepadamempelai serta kepada semua yang hadir dan ikut menyaksikan di sekelilingnya.Acara seperti ini disebut nyawer karena dilakukan di panyaweran atau taweuranatau cucuran atap. berdasarkan pengamatan, dapat disimpulkan bahwa pada saatini telah terjadi perubahan-perubahan, baik dari segi tempat pertunjukan, waktupelaksanaan, materi lagu yang dibawakan, dan juru sawer yang melaksanakannya.Meskipun demikian, acara sawer ini sampai sekarang masih terus dilaksanakan olehmasyarakat Sunda kontemporer. Continuity and Change of Sawer Art in the Sundanese Tradition WeddingCeremony. The sawer art is a kind of song that has a free meter, accompanied by themusical instruments of kacapi (both the kacapi indung and the kacapi rincik and eitherthe flute or the rebab (a two-stringed musical instrument. One of the functions of thisart is to become a part of the ceremonial activities in the Sundanese wedding ceremony.It is performed after the marriage ceremony. In this case, the sawer art is carried out byusing a technique served with beverage refreshment (ditambul or songs sung withoutany musical accompaniments. Marriage is considered to be sunnah (optional and it isdetermined by human beings based on the spiritual

  20. Geophysical and geochemical constraints on geoneutrino fluxes from Earth's mantle

    CERN Document Server

    Šrámek, Ondřej; Kite, Edwin S; Lekić, Vedran; Dye, Steve; Zhong, Shijie

    2012-01-01

    Knowledge of the amount and distribution of radiogenic heating in the mantle is crucial for understanding the dynamics of the Earth, including its thermal evolution, the style and planform of mantle convection, and the energetics of the core. Although the flux of heat from the surface of the planet is robustly estimated, the contributions of radiogenic heating and secular cooling remain poorly defined. Constraining the amount of heat-producing elements in the Earth will provide clues to understanding nebula condensation and planetary formation processes in early Solar System. Mantle radioactivity supplies power for mantle convection and plate tectonics, but estimates of mantle radiogenic heat production vary by a factor of up to 30. Recent experimental results demonstrate the potential for direct assessment of mantle radioactivity through observations of geoneutrinos, which are emitted by naturally occurring radionuclides. Predictions of the geoneutrino signal from the mantle exist for several established est...

  1. Model Pergerakan Tumpahan Minyak di Perairan Selat Sunda dengan Gnome Analysis

    Directory of Open Access Journals (Sweden)

    Agus Salim

    2016-03-01

    Full Text Available Sunda Strait is an area of strait that has potential for enormous natural wealth. However, this potential is threatened by oil spills that occurred due to the activities of transportation and storage of crude oil. A study of ecological risk assessment of oil spills was conducted to measure the magnitude of the threat of oil spills and to have preemptive strategies to minimize the impact if a large-scale oil spills occur in the future. From the analysis of the trajectory, it can be concluded that the areas that are vulnerable to the impact of the oil spill were Panimbang Beach, Wells Island, Coastal Cigeulis, Cimanggu, Selat Panaitan, Cilegon, Anyer, Mediation, and Jabung Sragi. The applicability of the trajectory final data can be used as a reference in determining the risk level of oil particles which expose to ecosystems around the Sunda Strait and the foremost result was that it would be used to minimize the impact of the oil spills in the future.

  2. The black flies (Diptera: Simuliidae) of the Lesser Sunda Archipelago, Indonesia.

    Science.gov (United States)

    Takaoka, Hiroyuki; Sofian-Azirun, Mohd; Ya'cob, Zubaidah; Chen, Chee Dhang; Lau, Koon Weng; Low, Van Lun; Suana, I Wayan

    2017-05-01

    Surveys of pupae and larvae of black flies were carried out in Bali, Lombok, Sumbawa and Flores in the Lesser Sunda Archipelago, Indonesia, where 10 species were known. A total of 14 simuliid species including four new species and five new records of the genus Simulium were collected, bringing the number of species from the Lesser Sunda Archipelago to 19. They are classified into four subgenera: two in Nevermannia, nine in Gomphostilbia, seven in Simulium and one in Wallacellum. One of four new species, Simulium (Simulium) baliense, is described based on females, males, pupae and larvae from Bali and Lombok. This new species, which is placed in the Simulium striatum species-group of the subgenus Simulium, is closely related to S. (S.) argyrocinctum De Meijere from Java and Sumatra, but it is distinguished from the latter species by the smaller number of the male enlarged upper-eye facets and larval abdomen lacking dorsal pairs of conical protuberances. The distribution record of S. (S.) upikae Takaoka & Davies from Flores is corrected as that of S. (S.) eximium De Meijere. Some aberrant characters of the pupal gill filaments of S. (G.) atratum De Meijere, S. (G.) floresense Takaoka, Hadi & Sigit and S. (G.) sunapii Takaoka, Sofian-Azirun & Suana are illustrated. Characteristics of the fauna of black flies in this archipelago are briefly noted. Keys to all 19 species are provided for females, males, pupae and larvae. Copyright © 2017 Elsevier B.V. All rights reserved.

  3. Obliquity along plate boundaries

    Science.gov (United States)

    Philippon, Mélody; Corti, Giacomo

    2016-12-01

    Most of the plate boundaries are activated obliquely with respect to the direction of far field stresses, as roughly only 8% of the plate boundaries total length shows a very low obliquity (ranging from 0 to 10°, sub-orthogonal to the plate displacement). The obliquity along plate boundaries is controlled by (i) lateral rheological variations within the lithosphere and (ii) consistency with the global plate circuit. Indeed, plate tectonics and magmatism drive rheological changes within the lithosphere and consequently influence strain localization. Geodynamical evolution controls large-scale mantle convection and plate formation, consumption, and re-organization, thus triggering plate kinematics variations, and the adjustment and re-orientation of far field stresses. These geological processes may thus result in plate boundaries that are not perpendicular but oblique to the direction of far field stresses. This paper reviews the global patterns of obliquity along plate boundaries. Using GPlate, we provide a statistical analysis of present-day obliquity along plate boundaries. Within this framework, by comparing natural examples and geological models, we discuss deformation patterns and kinematics recorded along oblique plate boundaries.

  4. Global Plate Driving Forces at 50Ma

    Science.gov (United States)

    Butterworth, N. P.; Quevedo, L. E.; Müller, R. D.

    2011-12-01

    We apply a novel workflow utilising the BEM-Earth geodynamic software to analyse the global coupled plate-mantle dynamics at 50 Ma. A subduction history model based on kinematic data going as far back as 80 Ma was developed using the GPlates software. Advection of the plates into the mantle takes into account the absolute plate motions and lithospheric thickness derived from its age to produce an estimated density heterogeneity initial model condition in the upper mantle. The resulting global model consists of regions of a mantle viscosity and density structure that is post-processed to ensure smooth non-overlapping 3D surfaces. BEM-Earth is then free to evolve the model toward the 50 Ma solution. The evolution of the model is driven by self-consistent buoyancy driven mantle dynamics. We use the model velocity output to quantify changes in forces driving the plates before and after 50 Ma. We analyse the rapid change in plate motion of India, Africa and plates in the Pacific Ocean basin by considering slab-pull, ridge-push and mantle drag/suction forces that naturally result from such top-down driven mantle flow. We compare the results with plate kinematic reconstructions and other geological observations.

  5. Thermoconvective waves in the earth's mantle

    Science.gov (United States)

    Birger, B. I.

    1980-06-01

    The thermoconvective instability of the Earth's mantle is analysed. The mantle is modelled as an infinite horizontal layer with a free upper surface, heated from below. The creep in the mantle is supposed to be transient when strains are small. This transient creep is described by Lomnitz's law modified by Jeffreys (1958a). It is shown that disturbances, in the form of thermoconvective waves with a period of 10 8 - 10 9y and wavelength of the order 10 3 km, can propagate through the mantle without attenuation. These waves induce oscillations of the Earth's surface. The pattern of flows differs greatly from that suggested by plate tectonics. An attempt is made to give a new explanation for the linear magnetic anomalies over oceanic ridges.

  6. Linking mantle upwelling with the lithosphere descent [corrected] and the Japan Sea evolution: a hypothesis.

    Science.gov (United States)

    Ismail-Zadeh, Alik; Honda, Satoru; Tsepelev, Igor

    2013-01-01

    Recent seismic tomography studies image a low velocity zone (interpreted as a high temperature anomaly) in the mantle beneath the subducting Pacific plate near the Japanese islands at the depth of about 400 km. This thermal feature is rather peculiar in terms of the conventional view of mantle convection and subduction zones. Here we present a dynamic restoration of the thermal state of the mantle beneath this region assimilating geophysical, geodetic, and geological data up to 40 million years. We hypothesise that the hot mantle upwelling beneath the Pacific plate partly penetrated through the subducting plate into the mantle wedge and generated two smaller hot upwellings, which contributed to the rapid subsidence in the basins of the Japan Sea and to back-arc spreading. Another part of the hot mantle migrated upward beneath the Pacific lithosphere, and the presently observed hot anomaly is a remnant part of this mantle upwelling.

  7. Jaipongan: Genre Tari Generasi Ketiga dalam Perkembangan Seni Pertunjukan Tari Sunda

    Directory of Open Access Journals (Sweden)

    Lalan Ramlan

    2013-09-01

    Full Text Available ABSTRAK Seni pertunjukan tari Sunda hingga saat ini telah diisi dengan tiga genre tari yang diciptakan oleh tiga tokoh pembaharu tari Sunda, yaitu Rd. Sambas Wirakusumah yang menciptakan genre tari Keurseus sekitar tahun 1920- an, Rd. Tjetje Somantri yang menciptakan genre tari Kreasi Baru sekitar tahun 1950-an, dan Gugum Gumbira Tirasondjaya yang menciptakan genre tari Jaipongan pada awal tahun 1980-an. Ketiga genre tari tersebut memiliki citra estetiknya sendiri-sendiri sesuai latar budaya generasinya masing-masing. Genre tari Jaipongan yang kini sudah lebih dari 30 tahun belum tergantikan di dalamnya menunjukkan nilai-nilai yang mengakar dalam kehidupan masyarakat Sunda. Untuk mengekplanasi berbagai aspek penting yang melengkapi pembentukan sebuah genre tari ini digunakan metode kualitatif dengan pendekatan fenomenologi. Berdasarkan penelitian disimpulkan bahwa genre tari Jaipongan dibentuk oleh konsep dasar etika dan estetik egaliter dengan menghasilkan struktur koreografi yang simpel dan fl eksibel yang terdiri dari empat ragam gerak, yaitu bukaan, pencugan, nibakeun, dan mincid. Kata kunci: Gugum Gunbira, genre tari, dan Jaipongan   ABSTRACT Jaipongan: The Genre of Third Dancing Generation in the Development of Sundanese Dance Performing Arts. Sundanese dancing performance art recently has been fi lled with three dancing genres created by three prominent reformers of Sundanese dances, namely Rd. Sambas Wirakusumah who created the dance genre of Keurseus around 1920, Rd. Tjetje Somantri who created the dance genre of Kreasi Baru (New Creation 1950s, and Gugum Gumbira Tirasondjaya who created the dance genre of Jaipongan in the early 1980s. The three genres of the dances have their own aesthetic image based on their cultural background respectively. The Jaipongan dance genre which now has been more than 30 years and not yet been changed shows the values rooted in Sundanese community life. To explain various important aspects which complete

  8. Sediment velocities from sonobuoys: Bengal Fan, Sunda Trench, Andaman Basin, and Nicobar Fan

    Energy Technology Data Exchange (ETDEWEB)

    Hamilton, E.L.; Bachman, R.T.; Curray, J.R.; Moore, D.G.

    1977-07-10

    New measurements of interval compressional wave velocities were made in the first sediment layer using the sonobuoy technique during two expeditions in the Bay of Bengal, in the Andaman Sea, and over the Nicobar Fan and Sunda Trench. Sediment interval velocities from these areas were added to those previously reported, and revised diagrams and regression equations of instantaneous and mean velocity versus one-way travel time are furnished for four areas of the Bengal Fan, and for the Anadman Basin, Nicobar Fan, Sunda Trench. The velocity gradients directly below the sea floor were used to separate the Bengal Fan into four geoacoustic provinces. In the north and west the velocity gradients are 0.86 and 1.28 s/sup -1/, respectively, whereas in the central part of the fan the gradient is 1.87 s/sup -1/. These variations indicate lesser increases of velocity with depth in the sea floor in the north and west, and they are probably due to more rapid deposition, less consolidation, and less lithification near the riverine source areas of the sediments. The near-surface velocity gradients in the other areas are the Andaman Basin, 1.53 s/sup -1/, the Nicobar Fan 1.63 s/sup -1/, and the Sunda Trench, 1.41 s/sup -1/. The linear velocity gradients (from the sediment surface to a given travel time) in 17 areas of the Indian Ocean, Pacific area, Atlantic Ocean, and Gulf of Mexico were averaged at each 0.1 s from 0 to 0.5 s of one-way travel time. These averaged gradients ranged from 1.32 s/sup -1/ at t=0 to 0.76 s/sup -1/ at t=0.5 s. The regression equation for the velocity gradients a, in s/sup -1/, as a function of one-way travel time t, in seconds, is a=1.316-1.117t (for use from t=0 to 0.5 s). These average velocity gradients can be used with sediment surface velocities and one-way travel times (measured from reflection records) to compute sediment layer thickness in areas of turbidites lacking interval velocity measurements in the first sediment layer.

  9. Mantle plumes and continental tectonics.

    Science.gov (United States)

    Hill, R I; Campbell, I H; Davies, G F; Griffiths, R W

    1992-04-10

    Mantle plumes and plate tectonics, the result of two distinct modes of convection within the Earth, operate largely independently. Although plumes are secondary in terms of heat transport, they have probably played an important role in continental geology. A new plume starts with a large spherical head that can cause uplift and flood basalt volcanism, and may be responsible for regional-scale metamorphism or crustal melting and varying amounts of crustal extension. Plume heads are followed by narrow tails that give rise to the familiar hot-spot tracks. The cumulative effect of processes associated with tail volcanism may also significantly affect continental crust.

  10. Evidence for the 1762 Tsunamigenic Earthquake in an Extremely Sedimented Segment of the Sunda Subduction/Collision Boundary, SE Bangladesh

    Science.gov (United States)

    McHugh, C. M.; Mansfield, V.; Mondal, D. R.; Seeber, L.; Steckler, M. S.; Mustaque, S.; Ahkter, S. H.

    2015-12-01

    After the catastrophic 2004 Sumatra earthquake and tsunami, attention focussed on the segment of the Sunda subduction system along the heavily populated region of the Bay of Bengal. Here the Indian plate is converging obliquely with the Burma arc at GPS rates of 14mm/yr. The extremely thick sediments (~20km) of the Ganges-Brahmaputra Delta (GBD) are accreted into a very wide thrust-fold belt. Despite some likely aseismic deformation, the great 1762 earthquake proves the seismogenic potential of this boundary. Evidence is mounting that the earthquake ruptured 700km of the boundary from the Bengal Fan to the GBD shelf along Myanmar and Bangladesh. Recent U-Th ages and GPS measurements in Saint Martin Island, an anticline in the outer part of the accretion belt on the shelf, showed that corals died and were uplifted 2.5m coseismically during the 1762 earthquake. Historic accounts and modelling predicted a 1762 tsunami, but geologic evidence for it was not previously reported. We found in both Saint Martin and ~20km north on the Teknaf coast strong evidence for tsunami emplacement. In Saint Martin we discovered a shelly sand layer that extends ~4km in the center of the island. The layer contains shallow water foraminifers, coral fragments and molluscs. Twenty C-14 ages from the shell layer range 1440-1753 cal yrs AD and average 1600 cal yrs AD. We also studied a shell layer that extends for 16,500 m2 on top of a terrace that is now 2m above present sea level and pre-1762 earthquake elevation. Ten C14 ages obtained from the shell bed range 1689-1875 cal yrs AD and average 1753 cal yrs AD. This bed is 1.2m thick and composed of molluscs and foraminifers of intertidal and subtidal origin currently found in shelf depths of 0-100 m. The layer is composed of cobble to mud size sediment and although chaotic, we identified at least three pulses of coarse sediment within an overall fining-upwards unit. The studied 1762 shoreline uplift is likely to partly include coseiesmic

  11. Tides and their dynamics over the Sunda Shelf of the southern South China Sea

    DEFF Research Database (Denmark)

    Daryabor, Farshid; Ooi, See Hai Ooi; Samah, Azizan Abu

    2016-01-01

    A three-dimensional Regional Ocean Modelling System is used to study the tidal characteristics and their dynamics in the Sunda Shelf of the southern South China Sea. In this model, the outer domain is set with a 25 km resolution and the inner one, with a 9 km resolution. Calculations are performed...... on the inner domain. The model is forced at the sea surface by climatological monthly mean wind stress, freshwater (evaporation minus precipitation), and heat fluxes. Momentum and tracers (such as temperature and salinity) are prescribed in addition to the tidal heights and currents extracted from the Oregon...... State University TOPEX/Poseidon Global Inverse Solution (TPXO7.2) at the open boundaries. The results are validated against observed tidal amplitudes and phases at 19 locations. Results show that the mean average power energy spectrum (in unit m2/s/cph) for diurnal tides at the southern end of the East...

  12. Primary magmas and mantle temperatures through time

    Science.gov (United States)

    Ganne, Jérôme; Feng, Xiaojun

    2017-03-01

    Chemical composition of mafic magmas is a critical indicator of physicochemical conditions, such as pressure, temperature, and fluid availability, accompanying melt production in the mantle and its evolution in the continental or oceanic lithosphere. Recovering this information has fundamental implications in constraining the thermal state of the mantle and the physics of mantle convection throughout the Earth's history. Here a statistical approach is applied to a geochemical database of about 22,000 samples from the mafic magma record. Potential temperatures (Tps) of the mantle derived from this database, assuming melting by adiabatic decompression and a Ti-dependent (Fe2O3/TiO2 = 0.5) or constant redox condition (Fe2+/∑Fe = 0.9 or 0.8) in the magmatic source, are thought to be representative of different thermal "horizons" (or thermal heterogeneities) in the ambient mantle, ranging in depth from a shallow sublithospheric mantle (Tp minima) to a lower thermal boundary layer (Tp maxima). The difference of temperature (ΔTp) observed between Tp maxima and minima did not change significantly with time (˜170°C). Conversely, a progressive but limited cooling of ˜150°C is proposed since ˜2.5 Gyr for the Earth's ambient mantle, which falls in the lower limit proposed by Herzberg et al. [2010] (˜150-250°C hotter than today). Cooling of the ambient mantle after 2.5 Ga is preceded by a high-temperature plateau evolution and a transition from dominant plumes to a plate tectonics geodynamic regime, suggesting that subductions stabilized temperatures in the Archaean mantle that was in warming mode at that time.abstract type="synopsis">Plain Language SummaryThe Earth's upper mantle constitutes a major interface between inner and outer envelops of the planet. We explore at high resolution its thermal state evolution (potential temperature of the ambient mantle, Tp) in depth and time using a multi-dimensional database of mafic lavas chemistry (>22,000 samples formed in

  13. Earth's Decelerating Tectonic Plates

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-08-22

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

  14. Earth's Decelerating Tectonic Plates

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-08-22

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

  15. Global-scale water circulation in the Earth's mantle: Implications for the mantle water budget in the early Earth

    Science.gov (United States)

    Nakagawa, Takashi; Spiegelman, Marc W.

    2017-04-01

    We investigate the influence of the mantle water content in the early Earth on that in the present mantle using numerical convection simulations that include three processes for redistribution of water: dehydration, partitioning of water into partially molten mantle, and regassing assuming an infinite water reservoir at the surface. These models suggest that the water content of the present mantle is insensitive to that of the early Earth. The initial water stored during planetary formation is regulated up to 1.2 OMs (OM = Ocean Mass; 1.4 ×1021 kg), which is reasonable for early Earth. However, the mantle water content is sensitive to the rheological dependence on the water content and can range from 1.2 to 3 OMs at the present day. To explain the evolution of mantle water content, we computed water fluxes due to subducting plates (regassing), degassing and dehydration. For weakly water dependent viscosity, the net water flux is almost balanced with those three fluxes but, for strongly water dependent viscosity, the regassing dominates the water cycle system because the surface plate activity is more vigorous. The increased convection is due to enhanced lubrication of the plates caused by a weak hydrous crust for strongly water dependent viscosity. The degassing history is insensitive to the initial water content of the early Earth as well as rheological strength. The degassing flux from Earth's surface is calculated to be approximately O (1013) kg /yr, consistent with a coupled model of climate evolution and mantle thermal evolution.

  16. Submergence and Uplift Associated to Paleoearthquakes in the Northern Sunda Subduction System: Implications for Future Earthquakes.

    Science.gov (United States)

    Mondal, D. R.; McHugh, C. M.; Mortlock, R. A.; Steckler, M. S.; Seeber, L.; Goodbred, S. L., Jr.; Akhter, S. H.; Mustaque, S.

    2015-12-01

    Recent studies documented that the northern part of the Sunda subduction zone ruptured several times in the past 1500 years including one in 1762. To better understand megathrust surface ruptures and the hazards associated to them, we surveyed the SE coast of Bangladesh along the Teknaf peninsula and the Saint Martin anticline by dating coral microatolls of Porites lutea species by the U-Th dating method. Porites luteagrows a few centimeters below the low tide level creating a 5-12 mm thick skeletal band per year, which makes them a good indicator of relative sea level change that might be caused during tectonic submergence and uplift. U-Th ages were obtained from coral slabs and their growth bands interpreted from x-rays. The corals and marine terraces uplift were measured with high precision RTK GPS and modeled with high resolution DEM. The coral microatolls along the St. Martin anticline were dated to be ~ 250, 800 and 1300 years old. Since storm and other climatic phenomenon cannot cause uplift, we interpret that 2.5 m uplift was caused by 1762 earthquake that killed the coral microatolls. The coral slabs show three growth interruptions, where skeletal growth bands continued to grow onlapping the older growth bands. These growth onlaps could be the result of smaller uplift events after 1762 that did not result in coral mortality. The subsidence history extracted from vertical growth of the slabs suggests that the island is submerging at a rate of 11 mm/year. Corals growing 250 m from the dead coral colony post date the 1762 earthquake. Today living Porites lutea can be found 2.5 m below the dead coral heads and 9 cm above the spring low tide. The elevation of marine terraces (T1, T2 and T3) along the Teknaf coast is 2.5 m, 5-7 m and 11-13 m above sea level, respectively. A shell bed on top of T1 was dated at 1763 (dated by C14). This and the other two terraces could have been uplifted during the three earthquakes dated from coral microatolls. Considering the

  17. The Sedimentary System and Evolution of the Early Tertiary in the Sunda Basin, Indonesia

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The Sunda basin is located at the north of the Sunda Strait situated between Sumatra and Java islands, Indonesia. It is an early Tertiary typical half-graben basin, in which developed a series of terrigenous clastic sedimentation. Previous work suggested that the early Tertiary sediments were alluvial, fluvial, lacustrine and swamp deposits, of which the Banuwati formation was alluvial and lacustrine deposits, the Zelda member fluvial deposits, and Gita member fluvial and swamp deposits. In this paper, based on the integrated research on core lithology (including lithology succession and structure), well log shape, and seismic reflection characteristics, a more detailed sedimentation system was set up as follows: 1) In addition to the alluvial, lacustrine, fluvial and the swamp deposits presented in previous work, subaqeous fan, shore-shallow lacustrine, deep lacustrine and turbidite fan, fan delta and delta deposits also developed in this basin. 2) Alluvial fan, subaqeous fan and fan delta deposits occurred on the steep slope adjacent to the synrift boundary fault; while the deltaic depositional system usually distributed on the gentle slope of the basins. 3) The Zelda member that was interpreted as a fluvial deposit in previous work is now interpreted as a subaqueous fan, fan delta, delta and lacustrine deposit system. 4) From the point of view of sedimentology, the evolution of basin could be divided into four stages: the initial subsidence (matching the Banuwati formation), the rapid subsidence (matching the low Zelda member of Talang Akar formation), the steady subsidence or fluctuation (matching the middle Zelda member of Talang Akar formation), and the uplifting (matching the upper Zelda member and the Gita member of Talang Akar formation). At the initial subsidence stage, the alluvial fan, flood plain, braided stream deposits developed, and then subaqeous fan sedimentation; at the rapid subsidence stage, shore-shallow lacustrine and deep lacustrine deposits

  18. 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.

  19. Mapping mantle flow during retreating subduction: Laboratory models analyzed by feature tracking

    Science.gov (United States)

    Funiciello, F.; Moroni, M.; Piromallo, C.; Faccenna, C.; Cenedese, A.; Bui, H. A.

    2006-03-01

    Three-dimensional dynamically consistent laboratory models are carried out to model the large-scale mantle circulation induced by subduction of a laterally migrating slab. A laboratory analogue of a slab-upper mantle system is set up with two linearly viscous layers of silicone putty and glucose syrup in a tank. The circulation pattern is continuously monitored and quantitatively estimated using a feature tracking image analysis technique. The effects of plate width and mantle viscosity/density on mantle circulation are systematically considered. The experiments show that rollback subduction generates a complex three-dimensional time-dependent mantle circulation pattern characterized by the presence of two distinct components: the poloidal and the toroidal circulation. The poloidal component is the answer to the viscous coupling between the slab motion and the mantle, while the toroidal one is produced by lateral slab migration. Spatial and temporal features of mantle circulation are carefully analyzed. These models show that (1) poloidal and toroidal mantle circulation are both active since the beginning of the subduction process, (2) mantle circulation is intermittent, (3) plate width affects the velocity and the dimension of subduction induced mantle circulation area, and (4) mantle flow in subduction zones cannot be correctly described by models assuming a two-dimensional steady state process. We show that the intermittent toroidal component of mantle circulation, missed in those models, plays a crucial role in modifying the geometry and the efficiency of the poloidal component.

  20. Crustal anisotropy along the Sunda-Banda arc transition zone from shear wave splitting measurements

    Science.gov (United States)

    Syuhada, Syuhada; Hananto, Nugroho D.; Abdullah, Chalid I.; Puspito, Nanang T.; Anggono, Titi; Yudistira, Tedi; Ramdhan, Mohamad

    2017-01-01

    We analyse shear wave splitting derived from the local earthquakes recorded at 13 seismic stations to investigate crustal anisotropy over varied geological regimes of the Sunda-Banda arc transition zone. We determine high-quality splitting measurements for 262 event-station pairs. The orientations of fast polarisation for the stations located in the oceanic regime are generally parallel or sub-parallel to the directions of the principal compressional strain-rate axes with a lack of dependency of delay time δt on increasing depth. The results suggest that anisotropy in this domain is primarily due to the influence of stress induced anisotropy on the upper crust. On the other hand, the average fast polarisations show more scattered for the stations located around Sumba Island and in the collision regime, implying a mix of anisotropy causes. Thus, anisotropy in this region is not only controlled by preferentially aligned cracks due to tectonic stress, but also by preferential mineral alignment and macro-scale faults associated with the regional tectonic deformation. We also perform further analysis to search possible temporal variations of splitting parameters associated with the stress changes excited by large earthquakes. The association between variation in splitting parameters and earthquake activity observed in this study might provide useful information about accumulation of stress before large events, and thus might be considered as an earthquake-forecasting tool in the future.

  1. Membangun Karakter Sadar Wisata Masyarakat Di Destinasi Melalui Kearifan Lokal Sunda

    Directory of Open Access Journals (Sweden)

    Oda I.B Haryanto

    2017-05-01

    ABSTRACT Sadar Wisata Program has been launched since 2003, but isn’t show changes and significant results as expected, by the community or the Government. Especially for tourists who travel to the destinations, it can be seen the competitiveness index based on tourism and travel, Indonesia ranks 70th out of 140 countries. A rating is still low when compared with Singapore, Malaysia, Thailand, although Indonesia has a wealth of beautiful natural and cultural glamour. Although there have been many programs and campaign done like visa-free visits to Indonesia and visit Indonesia year. 70th rank obtained by Indonesia because while some things still are lacking such as clean, as well as the security and safety service, Aware of this research is focused on finding and implementation of local wisdom in building a character aware of Tourism on communities in the destinations. Research used descriptive qualitative research methods with a multidisciplinary approach to research, the reason this is done naturally by using a variety of methods, theories, techniques and instruments. The goal is to get factual data in the field, thus producing an accurate and valid research. The results of this study in particular can be a reference to regional destinations in West Java in building character aware tourist communities in the destinations through the local wisdom of sundanese, and in General for the destnation in Indonesia. Keywords: Conscious tourism, building character and local wisdom of Sunda

  2. Initial Feasibility Study to Drill and Core the Ocean Mantle

    OpenAIRE

    2011-01-01

    An initial feasibility study (Pilisi and Whitney, 2011) of drilling through the Mohorovičić discontinuity (Moho) into the oceanic mantle specifically focused on future requirements for planning, drilling and coring a hole 500 m into the oceanic mantle from three candidate locations in the Pacific Ocean (Cocos Plate, Baja California, and offshore Hawaii). The study points out some of the critical issues that need to be resolved before embarking upon such a challengingproject. It was conducted ...

  3. Numerical modeling of mantle wedge processes and exhumation of UHP mantle in subduction zones

    Science.gov (United States)

    Gorczyk, W.; Gerya, T. V.; Guillot, S.; Connolly, J. A.; Yuen, D.

    2007-12-01

    The upwelling of subduction generated partially molten rocks is potentially a mechanism for the exhumation of UHP rocks through the mantle wedge. We investigated this processes using a 2-D coupled petrological- thermomechanical model that incorporates slab dehydration and water transport as well as partial melting of mantle and crustal rocks. This approach allows us to study the dynamics of mantle wedge processes including evolution of partially molten plumes and their interaction with surrounding dry mantle. To study the internal structure of the plumes we used ultra-high resolution numerical simulations with 10 billion active markers to detail the internal structure of natural plumes originating from the slab. The plumes consist of partially molten hydrated peridotite, dry solid mantle and subducted oceanic crust, which may comprise up to 12 volume % of the plume. As the plumes grow and mature these materials mix chaotically resulting in attenuation and duplication of the original layering on scales of 1-1000 m. Comparison of numerical results with geological observations from the Horoman ultramafic complex in Japan suggests that mixing and differentiation processes related to development of partially molten plumes above slabs may be responsible for strongly layered lithologically mixed (marble cake) structure of asthenospheric mantle wedges. The recent discovery of garnet bearing peridotites in the subduction zone of the Great Antilles in Hispaniola has raised questions about the process that leads to their exhumation. To evaluate whether upwelling plumes are a plausible exhumation mechanism we investigated the dynamics of subduction of slow spreading ridges. The results show that subduction of strongly serpentinized oceanic plate causes strong dehydration of the slab and leads to a rheological weakening of the interface between subducting and overriding plate. This weakening triggers trench retreat and massive asthenospheric upwelling into the gap between the

  4. Global correlation of lower mantle structure and past subduction

    Science.gov (United States)

    Domeier, Mathew; Doubrovine, Pavel V.; Torsvik, Trond H.; Spakman, Wim; Bull, Abigail L.

    2016-05-01

    Advances in global seismic tomography have increasingly motivated identification of subducted lithosphere in Earth's deep mantle, creating novel opportunities to link plate tectonics and mantle evolution. Chief among those is the quest for a robust subduction reference frame, wherein the mantle assemblage of subducted lithosphere is used to reconstruct past surface tectonics in an absolute framework anchored in the deep Earth. However, the associations heretofore drawn between lower mantle structure and past subduction have been qualitative and conflicting, so the very assumption of a correlation has yet to be quantitatively corroborated. Here we show that a significant, time-depth progressive correlation can be drawn between reconstructed subduction zones of the last 130 Myr and positive S wave velocity anomalies at 600-2300 km depth, but that further correlation between greater times and depths is not presently demonstrable. This correlation suggests that lower mantle slab sinking rates average between 1.1 and 1.9 cm yr-1.

  5. Shear wave splitting and subcontinental mantle deformation

    Science.gov (United States)

    Silver, Paul G.; Chan, W. Winston

    1991-09-01

    We have made measurements of shear wave splitting in the phases SKS and SKKS at 21 broadband stations in North America, South America, Europe, Asia, and Africa. Measurements are made using a retrieval scheme that yields the azimuth of the fast polarization direction ϕ and delay time δt of the split shear wave plus uncertainties. Detectable anisotropy was found at most stations, suggesting that it is a general feature of the subcontinental mantle. Delay times range from 0.65 s to 1.70 s and average about 1 s. Somewhat surprisingly, the largest delay time is found in the 2.7 b.y.-old Western Superior Province of the Canadian Shield. The splitting observations are interpreted in terms of the strain-induced lattice preferred orientation of mantle minerals, especially olivine. We consider three hypotheses concerning the origin of the continental anisotropy: (1) strain associated with absolute plate motion, as in the oceanic upper mantle, (2) crustal stress, and (3) the past and present internal deformation of the subcontinental upper mantle by tectonic episodes. It is found that the last hypothesis is the most successful, namely that the most recent significant episode of internal deformation appears to be the best predictor of ϕ. For stable continental regions, this is interpreted as "fossil" anisotropy, whereas for presently active regions, such as Alaska, the anisotropy reflects present-day tectonic activity. In the stable portion of North America there is a good correlation between delay time and lithospheric thickness; this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant. The acceptance of this hypothesis has several implications for subcontinental mantle deformation. First, it argues for coherent deformation of the continental lithosphere (crust and mantle) during orogenies. This implies that the anisotropic portion of the lithosphere was present since the

  6. Horizontal versus vertical plate motions

    Directory of Open Access Journals (Sweden)

    M. Cuffaro

    2006-07-01

    Full Text Available We review both present and past motions at major plate boundaries, which have the horizontal component in average 10 to 100 times faster (10–100 mm/yr than the vertical component (0.01–1 mm/yr in all geodynamic settings. The steady faster horizontal velocity of the lithosphere with respect to the upward or downward velocities at plate boundaries supports dominating tangential forces acting on plates. This suggests a passive role of plate boundaries with respect to far field forces determining the velocity of plates. The forces acting on the lithosphere can be subdivided in coupled and uncoupled, as a function of the shear at the lithosphere base. Higher the asthenosphere viscosity, more significant should be the coupled forces, i.e., the mantle drag and the trench suction. Lower the asthenosphere viscosity, more the effects of uncoupled forces might result determinant, i.e., the ridge push, the slab pull and the tidal drag. Although a combination of all forces acting on the lithosphere is likely, the decoupling between lithosphere and mantle suggests that a torque acts on the lithosphere independently of the mantle drag. Slab pull and ridge push are candidates for generating this torque, but, unlike these boundary forces, the advantage of the tidal drag is to be a volume force, acting simultaneously on the whole plates, and being the decoupling at the lithosphere base controlled by lateral variations in viscosity of the low-velocity layer.

  7. Superweak asthenosphere in light of upper mantle seismic anisotropy

    Science.gov (United States)

    Becker, Thorsten W.

    2017-05-01

    Earth's upper mantle includes a ˜200 km thick asthenosphere underneath the plates where viscosity and seismic velocities are reduced compared to the background. This zone of weakness matters for plate dynamics and may be required for the generation of plate tectonics itself. However, recent seismological and electromagnetic studies indicate strong heterogeneity in thinner layers underneath the plates which, if related to more extreme, global viscosity reductions, may require a revision of our understanding of mantle convection. Here, I use dynamically consistent mantle flow modeling and the constraints provided by azimuthal seismic anisotropy as well as plate motions to explore the effect of a range of global and local viscosity reductions. The fit between mantle flow model predictions and observations of seismic anisotropy is highly sensitive to radial and lateral viscosity variations. I show that moderate suboceanic viscosity reductions, to ˜0.01-0.1 times the upper mantle viscosity, are preferred by the fit to anisotropy and global plate motions, depending on layer thickness. Lower viscosities degrade the fit to azimuthal anisotropy. Localized patches of viscosity reduction, or layers of subducted asthenosphere, however, have only limited additional effects on anisotropy or plate velocities. This indicates that it is unlikely that regional observations of subplate anomalies are both continuous and indicative of dramatic viscosity reduction. Locally, such weak patches may exist and would be detectable by regional anisotropy analysis, for example. However, large-scale plate dynamics are most likely governed by broad continent-ocean asthenospheric viscosity contrasts rather than a thin, possibly high melt fraction layer.

  8. A case for mantle plumes

    Institute of Scientific and Technical Information of China (English)

    Geoffrey F. Davies

    2005-01-01

    The existence of at least several plumes in the Earth's mantle can be inferred with few assumptions from well-established observations. As well, thermal mantle plumes can be predicted from well-established and quantified fluid dynamics and a plausible assumption about the Earth's early thermal state. Some additional important observations, especially of flood basalts and rift-related magmatism, have been shown to be plausibly consistent with the physical theory. Recent claims to have detected plumes using seismic tomography may comprise the most direct evidence for plumes, but plume tails are likely to be difficult to resolve definitively and the claims need to be well tested. Although significant questions remain about its viability, the plume hypothesis thus seems to be well worth continued investigation. Nevertheless there are many non-plate-related magmatic phenomena whose association with plumes is unclear or unlikely. Compositional buoyancy has recently been shown potentially to substantially complicate the dynamics of plumes, and this may lead to explanations for a wider range of phenomena, including "headless" hotspot tracks, than purely thermal plumes.

  9. Plate tectonics conserves angular momentum

    Directory of Open Access Journals (Sweden)

    C. Bowin

    2009-03-01

    Full Text Available A new combined understanding of plate tectonics, Earth internal structure, and the role of impulse in deformation of the Earth's crust is presented. Plate accelerations and decelerations have been revealed by iterative filtering of the quaternion history for the Euler poles that define absolute plate motion history for the past 68 million years, and provide an unprecedented precision for plate angular rotation variations with time at 2-million year intervals. Stage poles represent the angular rotation of a plate's motion between adjacent Euler poles, and from which the maximum velocity vector for a plate can be determined. The consistent maximum velocity variations, in turn, yield consistent estimates of plate accelerations and decelerations. The fact that the Pacific plate was shown to accelerate and decelerate, implied that conservation of plate tectonic angular momentum must be globally conserved, and that is confirmed by the results shown here (total angular momentum ~1.4 E+27 kgm2s−1. Accordingly, if a plate decelerates, other plates must increase their angular momentums to compensate. In addition, the azimuth of the maximum velocity vectors yields clues as to why the "bend" in the Emperor-Hawaiian seamount trend occurred near 46 Myr. This report summarizes processing results for 12 of the 14 major tectonic plates of the Earth (except for the Juan de Fuca and Philippine plates. Plate accelerations support the contention that plate tectonics is a product of torques that most likely are sustained by the sinking of positive density anomalies due to phase changes in subducted gabbroic lithosphere at depth in the upper lower mantle (above 1200 km depth. The tectonic plates are pulled along by the sinking of these positive mass anomalies, rather than moving at near constant velocity on the crests of convection cells driven by rising heat. These results imply that spreading centers are primarily passive reactive

  10. Seismic determination of elastic anisotropy and mantle flow.

    Science.gov (United States)

    Park, J; Yu, Y

    1993-08-27

    When deformed, many rocks develop anisotropic elastic properties. On many seismic records, a long-period (100 to 250 seconds), "quasi-Love" wave with elliptical polarization arrives slightly after the Love wave but before the Rayleigh wave. Mantle anisotropy is sufficient to explain these observations qualitatively as long as the "fast" axis of symmetry is approximately horizontal. Quasi-Love observations for several propagation paths near Pacific Ocean subduction zones are consistent with either flow variations in the mantle within or beneath subducting plates or variations in the direction of fossil spreading in older parts of the Pacific plate.

  11. Tides and Their Dynamics over the Sunda Shelf of the Southern South China Sea

    Science.gov (United States)

    Ooi, See Hai; Abu Samah, Azizan; Akbari, Abolghasem

    2016-01-01

    A three-dimensional Regional Ocean Modelling System is used to study the tidal characteristics and their dynamics in the Sunda Shelf of the southern South China Sea. In this model, the outer domain is set with a 25 km resolution and the inner one, with a 9 km resolution. Calculations are performed on the inner domain. The model is forced at the sea surface by climatological monthly mean wind stress, freshwater (evaporation minus precipitation), and heat fluxes. Momentum and tracers (such as temperature and salinity) are prescribed in addition to the tidal heights and currents extracted from the Oregon State University TOPEX/Poseidon Global Inverse Solution (TPXO7.2) at the open boundaries. The results are validated against observed tidal amplitudes and phases at 19 locations. Results show that the mean average power energy spectrum (in unit m2/s/cph) for diurnal tides at the southern end of the East Coast of Peninsular Malaysia is approximately 43% greater than that in the East Malaysia region located in northern Borneo. In contrast, for the region of northern Borneo the semidiurnal power energy spectrum is approximately 25% greater than that in the East Coast of Peninsular Malaysia. This implies that diurnal tides are dominant along the East Coast of Peninsular Malaysia while both diurnal and semidiurnal tides dominate almost equally in coastal East Malaysia. Furthermore, the diurnal tidal energy flux is found to be 60% greater than that of the semidiurnal tides in the southern South China Sea. Based on these model analyses, the significant tidal mixing frontal areas are located primarily off Sarawak coast as indicated by high chlorophyll-a concentrations in the area. PMID:27622552

  12. Characteristics of Mineralized Volcanic Centers in Javanese Sunda Island Arc, Indonesia

    Science.gov (United States)

    Setijadji, L. D.; Imai, A.; Watanabe, K.

    2007-05-01

    The subduction-related arc magmatism in Java island, Sunda Arc, Indonesia might have started in earliest Tertiary period, but the distinctively recognizable volcanic belts related with Java trench subduction occurred since the Oligocene. We compiled geoinformation on volcanic centers of different epochs, distribution of metallic mineral deposits, petrochemistry of volcanic rocks, geologic structures, and regional gravity image in order to elucidate characteristics of the known mineralized volcanic centers. Metallic deposits are present in various styles from porphyry-related, high-sulfidation, and low-sulfidation epithermal systems; all related with subaerial volcanism and subvolcanic plutonism. Only few and small occurrences of volcanigenic massive sulfides deposits suggest that some mineralization also occurred in a submarine environment. Most locations of mineral deposits can be related with location of Tertiary volcanic centers along the volcanic arcs (i.e. volcanoes whose genetic link with subduction is clear). On the other side there is no mineralization has been identified to occur associated with backarc magmatism whose genetic link with subduction is under debate. There is strong evidence that major metallic deposit districts are located within compressive tectonic regime and bound by coupling major, deep, and old crustal structures (strike-slip faults) that are recognizable from regional gravity anomaly map. So far the most economical deposits and the only existing mines at major industry scale are high-grade epithermal gold deposits which are young (Upper Miocene to Upper Pliocene), concentrated in Bayah dome complex in west Java, and are associated with alkalic magmatism-volcanism. On the other hand, known porphyry Cu-Au deposits are associated with old (Oligocene to Upper Miocene) stocks, and except for one case, all deposits are located in east Java. Petrochemical data suggest a genetic relationship between porphyry mineralization with low- to

  13. Vertical velocity of mantle flow of East Asia and adjacent areas

    Institute of Scientific and Technical Information of China (English)

    CHENG Xianqiong; ZHU Jieshou; CAI Xuelin

    2007-01-01

    Based on the high-resolution body wave tomo- graphic image and relevant geophysical data, we calculated the form and the vertical and tangential velocities of mantle flow. We obtained the pattern of mantle convection for East Asia and the West Pacific. Some important results and under- standings are gained from the images of the vertical velocity of mantle flow for East Asia and the West Pacific. There is an upwelling plume beneath East Asia and West Pacific, which is the earth's deep origin for the huge rift valley there. We have especially outlined the tectonic features of the South China Sea, which is of the "工" type in the upper mantle shield type in the middle and divergent in the lower; the Siberian clod downwelling dives from the surface to near Core and mantle bounary (CMB), which is convergent in the upper mantle and divergent in the lower mantle; the Tethyan subduction region, centered in the Qinghai-Tibet plateau, is visible from 300 to 2 000 km, which is also convergent in the upper mantle and divergent in the lower mantle. The three regions of mantle convection beneath East Asia and the West Pacific are in accordance with the West Pacific, Ancient Asia and the Tethyan structure regions. The mantle upwelling orig- inates from the core-mantle boundary and mostly occurs in the middle mantle and the lower part of the upper mantle. The velocities of the vertical mantle flow are about 1-4 cm per year and the tangential velocities are 1-10 cm per year. The mantle flow has an effect on controlling the movement of plates and the distributions of ocean ridges, subduction zones and collision zones. The mantle upwelling regions are clearly related with the locations ofhotspots on the earth's surface.

  14. Insights from Pb and O isotopes into along-arc variations in subduction inputs and crustal assimilation for volcanic rocks in Java, Sunda arc, Indonesia

    Science.gov (United States)

    Handley, Heather K.; Blichert-Toft, Janne; Gertisser, Ralf; Macpherson, Colin G.; Turner, Simon P.; Zaennudin, Akhmad; Abdurrachman, Mirzam

    2014-08-01

    New Pb isotope data are presented for Gede Volcanic Complex, Salak and Galunggung volcanoes in West Java, Merbabu and Merapi volcanoes in Central Java and Ijen Volcanic Complex in East Java of the Sunda arc, Indonesia. New O isotope data for Merbabu and new geochemical and radiogenic isotope data (Sr-Nd-Hf-Pb) for three West Javanese, upper crustal, Tertiary sedimentary rocks are also presented. The data are combined with published geochemical and isotopic data to constrain the relative importance of crustal assimilation and subducted input of crustal material in petrogenesis in Java. Also discussed are the significance of limestone assimilation in controlling the geochemical and isotopic characteristics of erupted Javanese rocks and the geochemical impact upon central and eastern Javanese arc rocks due to the subduction of Roo Rise between 105 and 109°E. The negative correlation between Pb isotopes and SiO2, combined with mantle-like δ18O values in Gede Volcanic Complex rocks, West Java, are most likely explained by assimilation of more isotopically-primitive arc rocks and/or ophiolitic crust known to outcrop in West Java. The negative Pb isotope-SiO2 trend cannot be explained by assimilation of the known compositions of the upper crustal rocks. A peak in δ18O whole-rock and mineral values in Central Javanese volcanic rocks (Merbabu and Merapi) combined with along-arc trends in Sr isotope ratios suggest that a different or additional crustal assimilant exerts control on the isotopic composition of Central Javanese volcanic rocks. This assimilant (likely carbonate material) is characterised by high δ18O and high Sr isotope ratio but is not particularly elevated in its Pb isotopic ratio. Once the effects of crustal assimilation are accounted for, strong East to West Java regional variations in Ba concentration, Ba/Hf ratio and Pb isotopic composition are evident. These differences are attributed to heterogeneity in the subducted source input component along the

  15. Importance of Mantle Viscosity in Interseismic Deformation

    Science.gov (United States)

    Wang, K.; He, J.; Hu, Y.

    2012-12-01

    The role of mantle viscosity in subduction earthquake cycles was postulated when the plate tectonics theory had just gained wide acceptance. The process was described using Elsasser's 1-D model for diffusion of stress from the subduction boundary to the plate interior. Main features of interseismic surface deformation predicted by this elegantly simple model were later verified by GPS observations following giant subduction earthquakes. However, and intriguingly, the vast majority of interseismic deformation models developed in the era of space geodesy assume an elastic Earth, incorrectly regarding interseismic deformation as a subdued mirror image of coseismic deformation. The reason is four-fold. (1) The 1-D model and subsequent 2-D viscoelastic models failed to recognize the role of rupture length in the strike direction and could not self-consistently explain deformation following medium and small earthquakes. (2) Based on global mantle viscosity models derived from glacial isostatic adjustment studies, the viscoelastic mantle should indeed behave elastically in earthquake cycles of a few hundred years. (3) The effect of viscous mantle deformation can often be equivalently described by deep fault creep in a purely elastic Earth. (4) The use of an elastic model provides convenience in inverting geodetic data to determine fault locking and creep. Here we use 3D finite element models to show that the main characteristics of surface deformation following subduction earthquakes of all sizes can be explained with a viscoelastic Earth in which the mantle wedge is less viscous than global upper-mantle average of 1020 - 1021 Pa s by one to two orders of magnitude. Following giant earthquakes, such as 1700 Cascadia, 1960 Chile, 1964 Alaska, 2004 Sumatra, and 2011 Japan, upper-plate land deformation undergoes phases of wholesale seaward motion, opposing motion of coastal and inland areas, and wholesale landward motion. The "speed" of the evolution scales inversely with

  16. Subduction History and the Evolution of Earth's Lower Mantle

    Science.gov (United States)

    Bull, Abigail; Shephard, Grace; Torsvik, Trond

    2016-04-01

    Understanding the complex structure, dynamics and evolution of the deep mantle is a fundamental goal in solid Earth geophysics. Close to the core-mantle boundary, seismic images reveal a mantle characterised by (1) higher than average shear wave speeds beneath Asia and encircling the Pacific, consistent with sub ducting lithosphere beneath regions of ancient subduction, and (2) large regions of anomalously low seismic wavespeeds beneath Africa and the Central Pacific. The anomalously slow areas are often referred to as Large Low Shear Velocity Provinces (LLSVPs) due to the reduced velocity of seismic waves passing through them. The origin, composition and long-term evolution of the LLSVPs remain enigmatic. Geochemical inferences of multiple chemical reservoirs at depth, strong seismic contrasts, increased density, and an anticorrelation of shear wave velocity to bulk sound velocity in the anomalous regions imply that heterogeneities in both temperature and composition may be required to explain the seismic observations. Consequently, heterogeneous mantle models place the anomalies into the context of thermochemical piles, characterised by an anomalous component whose intrinsic density is a few percent higher relative to that of the surrounding mantle. Several hypotheses have arisen to explain the LLSVPs in the context of large-scale mantle convection. One end member scenario suggests that the LLSVPs are relatively mobile features over short timescales and thus are strongly affected by supercontinent cycles and Earth's plate motion history. In this scenario, the African LLSVP formed as a result of return flow in the mantle due to circum-Pangean subduction (~240 Ma), contrasting a much older Pacific LLSVP, which may be linked to the Rodinia supercontinent and is implied to have remained largely unchanged since Rodinian breakup (~750-700 Ma). This propounds that Earth's plate motion history plays a controlling role in LLSVP development, suggesting that the location

  17. Mantle Convection Models Constrained by Seismic Tomography

    Science.gov (United States)

    Durbin, C. J.; Shahnas, M.; Peltier, W. R.; Woodhouse, J. H.

    2011-12-01

    Although available three dimensional models of the lateral heterogeneity of the mantle, based upon the latest advances in seismic tomographic imaging (e.g. Ritsema et al., 2004, JGR) have provided profound insights into aspects of the mantle general circulation that drives continental drift, the compatibility of the tomography with explicit models of mantle mixing has remained illusive. For example, it remains a significant issue as to whether hydrodynamic models of the mixing process alone are able to reconcile the observed detailed pattern of surface plate velocities or whether explicit account must be taken of elastic fracture processes to account for the observed equipartition of kinetic energy between the poloidal and toroidal components of the surface velocity pattern (e.g. Forte and Peltier, 1987, JGR). It is also an issue as to the significance of the role of mantle chemical heterogeneity in determining the buoyancy distribution that drives mantle flow, especially given the expected importance of the spin transition of iron that onsets in the mid-lower mantle, at least in the ferropericlase component of the mineralogy. In this paper we focus upon the application of data assimilation techniques to the development of a model of mantle mixing that is consistent with a modern three dimensional tomography based model of seismic body wave heterogeneity. Beginning with the simplest possible scenario, that chemical heterogeneity is irrelevant to first order, we employ a three dimensional version of the recently published control volume based convection model of Shahnas and Peltier (2010, JGR) as the basis for the assimilation of a three dimensional density field inferred from our preferred tomography model (Ritsema et al., 2004, JGR). The convection model fully incorporates the dynamical influence of the Olivine-Spinel and Spinel-Perovskite+Magnesiowustite solid-solid phase transformations that bracket the mantle transition zone as well as the recently discovered

  18. Oceanic mantle alteration in the trench-outer rise region of the Japan trench

    Science.gov (United States)

    Fujie, G.; Takahashi, T.; Kodaira, S.; Obana, K.; Yamada, T.

    2014-12-01

    Dehydration processes and the expulsion of the water from the subducting oceanic plate affect various subduction-zone processes, including arc volcanism and generation of earthquakes and tremor. Since the amount of chemically bound water in the oceanic plate is highest in serpentinized mantle, it is important to reveal the degree of oceanic mantle serpentinization prior to subduction.In 2009 and 2013, to reveal the structural evolution of the incoming oceanic plate prior to subduction, we conducted wide-angle seismic structural surveys in the trench-outer rise region of the Japan trench. We found P-wave velocity (Vp) within the oceanic crust and mantle gradually decreases toward the trench axis, especially beneath the well-developed horst and grabens. Generally, reduction of Vp suggests two possibilities; one is a fracturing (dry mechanism) and the other is fracturing and water penetration (wet mechanism). The Vp/Vs ratio is a key to distinguish these two possibilities. Using P-to-S converted phases, we successfully modeled Vs within the oceanic crust by the travel-time inversion, and we found the Vp/Vs ratio within the oceanic crust gradually increases toward the trench, suggesting the water infiltration into the oceanic crust. However, it is not straightforward to determine Vs within the oceanic mantle because signal-to-noise ratio of S-wave mantle refraction was too poor to pick arrival times. Therefore, we calculated S-wave mantle refractions by assuming wide variety of Vp/Vs ratio within the oceanic mantle and compared with the observed horizontal data. Although S-wave mantle refraction was observed at only limited number of OBSs, we found that Vp/Vs ratio within the oceanic mantle did not change even in the area where mantle Vp become lower. This implies that the mantle Vp reduction in our seismic profile is mainly governed by the "dry mechanism" or mantle hydration might be confined in only topmost mantle.

  19. Volatile cycling and the thermal evolution of planetary mantle

    Science.gov (United States)

    Sandu, Constantin

    The thermal histories of terrestrial planets are investigated using two parameterized mantle convection models for either Earth like planets and planets with no active plate tectonics. Using parameterized models of mantle convection, we performed computer simulations of planetary cooling and volatile cycling. The models estimate the amount of volatile in mantle reservoir, and calculate the outgassing and regassing rates. A linear model of volatile concentration-dependent is assumed for the activation energy of the solid-state creep in the mantle. The kinematic viscosity of the mantle is thus dynamically affected by the activation energy through a variable concentration in volatile. Mantle temperature and heat flux is calculated using a model derived from classic thermal boundary layer theory of a single layered mantle with temperature dependent viscosity. The rate of volatile exchanged between mantle and surface is calculated by balancing the amount of volatiles degassed in the atmosphere by volcanic and spreading related processes and the amount of volatiles recycled back in the mantle by the subduction process. In the cases that lack plate tectonics, the degassing efficiency is dramatically reduced and the regassing process is absent. The degassing effect is dependent on average spreading rate of tectonic plates and on the amount of volatile in the melt extract in the transition zone between mantle and upper boundary laver. The regassing effect is dependent on the subduction rate and on the amount of volatile present on a hydrated layer on top of the subducting slab. The degassing and regassing parameters are all related to the intensity of the convection in the mantle and to the surface temperature of the planet, and they are regulated by the amount of volatiles in reservoir. Comparative study with the previous models display significant differences and improve the versatility of the model. The optimum efficiency factors found are in the range of 0.01--0.06 for

  20. Mantle updrafts and mechanisms of oceanic volcanism

    Science.gov (United States)

    Anderson, Don L.; Natland, James H.

    2014-10-01

    Convection in an isolated planet is characterized by narrow downwellings and broad updrafts-consequences of Archimedes' principle, the cooling required by the second law of thermodynamics, and the effect of compression on material properties. A mature cooling planet with a conductive low-viscosity core develops a thick insulating surface boundary layer with a thermal maximum, a subadiabatic interior, and a cooling highly conductive but thin boundary layer above the core. Parts of the surface layer sink into the interior, displacing older, colder material, which is entrained by spreading ridges. Magma characteristics of intraplate volcanoes are derived from within the upper boundary layer. Upper mantle features revealed by seismic tomography and that are apparently related to surface volcanoes are intrinsically broad and are not due to unresolved narrow jets. Their morphology, aspect ratio, inferred ascent rate, and temperature show that they are passively responding to downward fluxes, as appropriate for a cooling planet that is losing more heat through its surface than is being provided from its core or from radioactive heating. Response to doward flux is the inverse of the heat-pipe/mantle-plume mode of planetary cooling. Shear-driven melt extraction from the surface boundary layer explains volcanic provinces such as Yellowstone, Hawaii, and Samoa. Passive upwellings from deeper in the upper mantle feed ridges and near-ridge hotspots, and others interact with the sheared and metasomatized surface layer. Normal plate tectonic processes are responsible both for plate boundary and intraplate swells and volcanism.

  1. Deep Mantle Cycling of Oceanic Crust: Evidence from Diamonds and Their Mineral Inclusions

    Science.gov (United States)

    Walter, M. J.; Kohn, S. C.; Araujo, D.; Bulanova, G. P.; Smith, C. B.; Gaillou, E.; Wang, J.; Steele, A.; Shirey, S. B.

    2011-10-01

    A primary consequence of plate tectonics is that basaltic oceanic crust subducts with lithospheric slabs into the mantle. Seismological studies extend this process to the lower mantle, and geochemical observations indicate return of oceanic crust to the upper mantle in plumes. There has been no direct petrologic evidence, however, of the return of subducted oceanic crustal components from the lower mantle. We analyzed superdeep diamonds from Juina-5 kimberlite, Brazil, which host inclusions with compositions comprising the entire phase assemblage expected to crystallize from basalt under lower-mantle conditions. The inclusion mineralogies require exhumation from the lower to upper mantle. Because the diamond hosts have carbon isotope signatures consistent with surface-derived carbon, we conclude that the deep carbon cycle extends into the lower mantle.

  2. Deep mantle forces and the uplift of the Colorado Plateau

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-06-23

    Since the advent of plate tectonics, it has been speculated that the northern extension of the East Pacific Rise, specifically its mantle source, has been over-ridden by the North American Plate in the last 30 Myrs. Consequently, it has also been postulated that the opening of the Gulf of California, the extension in the Basin and Range province, and the uplift of the Colorado Plateau are the resulting continental expressions of the over-ridden mantle source of the East Pacific Rise. However, only qualitative models based solely on surface observations and heuristic, simplified conceptions of mantle convection have been used in support or against this hypothesis. We introduce a quantitative model of mantle convection that reconstructs the detailed motion of a warm mantle upwelling over the last 30 Myrs and its relative advance towards the interior of the southwestern USA. The onset and evolution of the crustal uplift in the central Basin and Range province and the Colorado Plateau is determined by tracking the topographic swell due to this mantle upwelling through time. We show that (1) the extension and magmatism in the central Basin and Range province between 25 and 10 Ma coincides with the reconstructed past position of this focused upwelling, and (2) the southwestern portion of the Colorado Plateau experienced significant uplift between 10 Ma and 5 Ma that progressed towards the northeastern portion of the plateau. These uplift estimates are consistent with a young, ca. 6 Ma, Grand Canyon model and the recent commencement of mafic magmatism.

  3. Oceanic crust recycling and the formation of lower mantle heterogeneity

    Science.gov (United States)

    van Keken, Peter E.; Ritsema, Jeroen; Haugland, Sam; Goes, Saskia; Kaneshima, Satoshi

    2016-04-01

    The Earth's lower mantle is heterogeneous at multiple scales as demonstrated for example by the degree-2 distribution of LLSVPs seen in global tomography and widespread distribution of small scale heterogeneity as seen in seismic scattering. The origin of this heterogeneity is generally attributed to leftovers from Earth's formation, the recycling of oceanic crust, or a combination thereof. Here we will explore the consequences of long-term oceanic crust extraction and recycling by plate tectonics. We use geodynamical models of mantle convection that simulate plates in an energetically consistent manner. The recycling of oceanic crust over the age of the Earth produces persistent lower mantle heterogeneity while the upper mantle tends to be significantly more homogeneous. We quantitatively compare the predicted heterogeneity to that of the present day Earth by tomographic filtering of the geodynamical models and comparison with S40RTS. We also predict the scattering characteristics from S-P conversions and compare these to global scattering observations. The geophysical comparison shows that lower mantle heterogeneity is likely dominated by long-term oceanic crust recycling. The models also demonstrate reasonable agreement with the geochemically observed spread between HIMU-EM1-DMM in ocean island basalts as well as the long-term gradual depletion of the upper mantle as observed in Lu-Hf systematics.

  4. Where is mantle's carbon?

    Science.gov (United States)

    Oganov, A. R.; Ono, S.; Ma, Y.

    2008-12-01

    Due to the strongly reducing conditions (the presence of metallic iron was suggested both by experiments [1] and theory [2]), diamond was believed to be the main host of carbon through most of the lower mantle [3]. We showed [4] that cementite Fe3C is another good candidate to be the main host of "reduced" carbon in the mantle, reinforcing an earlier hypothesis [5]. The fate of "oxidised" carbon (in subducted slabs) is of particular importance - if carbonates decompose producing fluid CO2, this would have important implications for the chemistry and rheology of the mantle. Knowledge of crystal structures and phase diagrams of carbonates is crucial here. The high-pressure structures of CaCO3 were predicted [6] and subsequently verified by experiments. For MgCO3, Isshiki et al. [7] found a new phase above 110 GPa, and several attempts were made to solve it [8,9]. Here [4], using an evolutionary algorithm for crystal structure prediction [10], we show that there are two post-magnesite phases at mantle-relevant pressure range, one stable at 82-138 GPa, and the other from 138 GPa to ~160 GPa. Both are based on threefold rings of CO4-tetrahedra and are more favourable than all previously proposed structures. We show that through most of the P-T conditions of the mantle, MgCO3 is the major host of oxidized carbon in the Earth. We predict the possibility of CO2 release at the very bottom of the mantle (in SiO2-rich basaltic part of subducted slabs), which could enhance partial melting of rocks and be related to the geodynamical differences between the Earth and Venus. 1.Frost D.J., Liebske C., Langenhorst F., McCammon C.A., Tronnes R.G., Rubie D.C. (2004). Experimental evidence for the existence of iron-rich metal in the Earth's lower mantle. Nature 428, 409-412. 2.Zhang F., Oganov A.R. (2006). Valence and spin states of iron impurities in mantle-forming silicates. Earth Planet. Sci. Lett. 249, 436-443. 3.Luth R.W. (1999). Carbon and carbonates in the mantle. In: Mantle

  5. The effect of a power-law mantle viscosity on trench retreat rate

    Science.gov (United States)

    Holt, Adam F.; Becker, Thorsten W.

    2017-01-01

    The subduction of lithospheric plates is partitioned between subducting plate motion and lateral slab migration (i.e. trench retreat and advance). We use 3-D, dynamic models of subduction to address the role of a power-law mantle viscosity on subduction dynamics and, in particular, rates of trench retreat. For all numerical models tested, we find that a power-law rheology results in reduced rates of trench retreat, and elevated slab dip angles, relative to the equivalent isoviscous mantle model. We analyse the asthenospheric pressure distribution and the style of mantle flow, which exhibits only limited variability as a function of mantle rheology, in order to compute estimates of the mantle forces associated with subduction. The inclusion of a power-law rheology reduces the mantle shear force (which resists subducting plate motion) to a greater degree than it reduces the dynamic pressure gradient across the slab (which resists trench retreat). Therefore, the inclusion of a power-law mantle rheology favours a shift towards a subduction mode with a reduced trench retreat component, typically a relative reduction of order 25 per cent in our 3-D models. We suggest that this mechanism may be of importance for reducing the high trench retreat rates observed in many previous models to levels more in line with the average subduction partitioning observed on Earth at present (i.e. trench velocity ≤ plate velocity), for most absolute plate motion reference frames.

  6. New interpretation of the deep mantle structure beneath eastern China

    Science.gov (United States)

    Ma, Pengfei; Liu, Shaofeng; Lin, Chengfa; Yao, Xiang

    2016-04-01

    Recent study of high resolution seismic tomography presents a large mass of high velocity abnormality beneath eastern China near the phase change depth, expanding more than 1600km-wide in East-west cross-section across the North China plate. This structure high is generally believed to be the subducted slab of Pacific plate beneath the Eurasia continent, while its origin and dynamic effect on the Cenozoic tectonic evolution of eastern China remain to be controversial. We developed a subduction-driven geodynamic mantle convection model that honors a set of global plate reconstruction data since 230Ma to help understand the formation and evolution of mantle structure beneath eastern China. The assimilation of plate kinematics, continuous evolving plate margin, asymmetric subduction zone, and paleo seafloor age data enables the spatial and temporal consistency between the geologic data and the mantle convection model, and guarantees the conservation of the buoyancy flux across the lithosphere and subducted slabs. Our model achieved a first order approximation between predictions and the observed data. Interestingly, the model suggests that the slab material stagnated above discontinuity didn't form until 15Ma, much later than previous expected, and the fast abnormality in the mid-mantle further west in the tomographic image is interpreted to be the remnants of the Mesozoic Izanagi subduction. Moreover, detailed analysis suggests that the accelerated subduction of Philippine Sea plate beneath Eurasia plate along the Ryukyu Trench and Nankai Trough since 15Ma may largely contribute to extending feature above 670km discontinuity. The long distance expansion of the slab material in the East-west direction may be an illusion caused by the approximate spatial perpendicularity between the cross-section and the subduction direction of the Philippine Sea plate. Our model emphasizes the necessity of the re-examination on the geophysical observation and its tectonic and

  7. 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

  8. Seismic anisotropy of upper mantle in eastern China

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Based on the polarization analysis of teleseismic SKS waveform data recorded at 65 seismic stations which respectively involved in the permanent and temporary broadband seismograph networks deployed in eastern China, the SKS fast-wave direction and the delay time between the fast and slow shear waves at each station were determined by use of SC method and the stacking analysis method, and then the image of upper mantle anisotropy in eastern China was acquired. In the study region, from south to north, the fast-wave polarization directions are basically EW in South China, gradually clockwise rotate to NWW-SEE in North China, then to NW-SE in Northeast China. The delay time falls into the interval [0.41 s, 1.52 s]. Anisotropic characteristics in eastern China indicate that the upper mantle anisotropy is possibly caused by both the collision between the Indian and Eurasian Plates and the subduction from the Pacific and Philippine Sea Plates to the Eurasian Plate. The collision between two plates made the crust of western China thickening and uplifting and the material eastwards extruding, and then caused the upper mantle flow eastwards and southeastwards. The subduction of Pacific Plate and Philippine Sea Plate has resulted in the lithosphere and the asthenosphere deformation in eastern China, and made the alignment of upper mantle peridotite lattice parallel to the deformation direction. The fast-wave polarization direction is consistent with the direction of lithosphere extension and the GPS velocity direction, implying that the crust-upper mantle deformation is possibly a vertically coherent deformation.

  9. Seismic anisotropy of upper mantle in eastern China

    Institute of Scientific and Technical Information of China (English)

    CHANG LiJun; WANG ChunYong; Ding ZhiFeng

    2009-01-01

    Based on the polarization analysis of teleseismic SKS waveform data recorded at 65 seismic stations which respectively involved in the permanent and temporary broadband seismograph networks de-ployed in eastern China,the SKS fast-wave direction and the delay time between the fast and slow shear waves at each station were determined by use of SC method and the stacking analysis method,and then the image of upper mantle anisotropy in eastern China was acquired.In the study region,from south to north,the fast-wave polarization directions are basically EW in South China,gradually clock-wise rotate to NWW-SEE in North China,then to NW-SE in Northeast China.The delay time falls into the Interval [0.41 s,1.52 s].Anisotropic characteristics in eastern China indicate that the upper mantle anisotropy is possibly caused by both the collision between the Indian and Eurasian Plates and the subduction from the Pacific and Philippine Sea Plates to the Eurasian Plate.The collision between two plates made the crust of western China thickening and uplifting and the material eastwards extruding,and then caused the upper mantle flow eastwards and southeastwards.The subduction of Pacific Plate and Philippine Sea Plate has resulted in the lithosphere and the asthenosphere deformation in eastern China,and made the alignment of upper mantle peridotite lattice parallel to the deformation direction.The fast-wave polarization direction is consistent with the direction of lithosphere extension and the GPS velocity direction,implying that the crust-upper mantle deformation is possibly a vertically co-herent deformation.

  10. Westward migration of oceanic ridges and related asymmetric upper mantle differentiation

    Science.gov (United States)

    Chalot-Prat, Françoise; Doglioni, Carlo; Falloon, Trevor

    2017-01-01

    Combining geophysical, petrological and structural data on oceanic mantle lithosphere, underlying asthenosphere and oceanic basalts, an alternative oceanic plate spreading model is proposed in the framework of the westward migration of oceanic spreading ridges relative to the underlying asthenosphere. This model suggests that evolution of both the composition and internal structure of oceanic plates and underlying upper mantle strongly depends at all scales on plate kinematics. We show that the asymmetric features of lithospheric plates and underlying upper asthenosphere on both sides of oceanic spreading ridges, as shown by geophysical data (seismic velocities, density, thickness, and plate geometry), reflect somewhat different mantle compositions, themselves related to various mantle differentiation processes (incipient to high partial melting degree, percolation/reaction and refertilization) at different depths (down to 300 km) below and laterally to the ridge axis. The fundamental difference between western and eastern plates is linked to the westward ridge migration inducing continuing mantle refertilization of the western plate by percolation-reaction with ascending melts, whereas the eastern plate preserves a barely refertilized harzburgitic residue. Plate thickness on both sides of the ridge is controlled both by cooling of the asthenospheric residue and by the instability of pargasitic amphibole producing a sharp depression in the mantle solidus as it changes from vapour-undersaturated to vapour-saturated conditions, its intersection with the geotherm at 90 km, and incipient melt production right underneath the lithosphere-asthenosphere boundary (LAB). Thus the intersection of the geotherm with the vapour-saturated lherzolite solidus explains the existence of a low-velocity zone (LVZ). As oceanic lithosphere is moving westward relative to asthenospheric mantle, this partially molten upper asthenosphere facilitates the decoupling between lower asthenosphere

  11. Ins and outs of a complex subduction zone: C cycling along the Sunda margin, Indonesia

    Science.gov (United States)

    House, B. M.; Bebout, G. E.; Hilton, D. R.

    2016-12-01

    Subduction of C in marine sediments and altered oceanic crust is the main mechanism for reintroducing C into the deep earth and removing it from communication with the ocean and atmosphere. However, detailed studies of individual margins - which are necessary to understanding global C cycling - are sparse. The thick, C-rich sediment column along the Sunda margin, Indonesia makes understanding this margin crucial for constructing global C cycling budgets. Furthermore it is an ideal location to compare cycling of organic and carbonate C due to the abrupt transition from carbonate-dominated sediments in the SE to sediments rich in organic C from the Nicobar Fan in the NW. To quantify and characterize C available for subduction, we analyzed samples from DSDP 211, 260, 261, and ODP 765, all outboard of the trench, as well as piston and gravity cores of locally-sourced terrigenous trench fill. We created a 3-D model of overall sediment thickness and the thicknesses of geochemically distinct sedimentary units using archived and published seismic profiles to infer unit thicknesses at and along the 2500 km trench. This model vastly improves estimates of the C available for subduction and also reveals that the Christmas Island Seamount Province serves as a barrier to turbidite flow, dividing the regions of the trench dominated by organic and inorganic C input. Incorporating best estimates for the depth of the decollement indicates that the terrigenous trench fill, with up to 1.5 wt % organic C, is entirely accreted as is the thick section of carbonate-rich turbidites that dominate the southeastern portion of the margin (DSDP 261/ODP 765). Organic C accounts for most of the C bypassing the accretionary complex NW of the Christmas Island Seamount Province, and C inputs to the trench are lower there than to the SE where carbonate units near the base of the sediment column are the dominant C source. Release of C from altered oceanic crust - a C reservoir up to 10 times greater

  12. DESENVOLVIMENTO DE IOGURTE TIPO SUNDAE SABOR MARACUJA FEITO A PARTIR DE LEITE DE CABRA

    Directory of Open Access Journals (Sweden)

    Tatiane F. Araújo,

    2012-02-01

    Full Text Available O objetivo desse estudo foi verificar a viabilidade do leite de cabra na fabricação de iogurte como alternativa ao consumo de derivados lácteos fabricados com este leite. Foram fabricados dois iogurtes, variando-se a matéria láctea base: leite de cabra e leite de vaca. Os dois tipos de iogurtes foram fabricados em três bateladas, em ocasiões diferentes. As variáveis avaliadas foram: pH, acidez titulável (% de ácido lático, gordura e perfil de textura (firmeza, mastigabilidade, coesividade e gomosidade. Na análise sensorial, os testes de aceitação foram realizados em duas sessões, nas quais se avaliou a impressão global das amostras. Na primeira sessão os provadores (n=50 avaliaram as amostras codificadas com números de três dígitos aleatórios (teste cego, ou seja, os mesmos não tinham informação a respeito do iogurte que estavam avaliando; na segunda sessão, a amostra foi servida com a informação (iogurte de leite de cabra. Os dados foram avaliados estatisticamente utilizando-se análise de variância (ANOVA. Para comparação de médias utilizou-se o teste de Tukey. As análises físico-químicas demonstraram alta similaridade nas variáveis avaliadas entre os iogurtes feitos com leite de cabra e leite de vaca. No entanto, o iogurte de leite de vaca apresentou maior teor de gordura (p<0,05. Ambos os iogurtes apresentaram perfil de textura similar. A análise sensorial indicou a mesma aceitação para os dois tipos de iogurtes. A informação «feito com leite de cabra» não influenciou na aceitação do respectivo iogurte. Conclui-se que a produção de iogurte tipo sundae sabor maracujá constitui uma alternativa viável para a colocação no mercado de produtos lácteos fermentados derivados do leite de cabra.

  13. AVALIAÇÃO SENSORIAL DE IOGURTE DE AÇAÍ (EUTERPE OLERACEA MART TIPO "SUNDAE"

    Directory of Open Access Journals (Sweden)

    Pedro Danilo De Oliveira,

    2011-06-01

    Full Text Available Diversos produtos de leites fermentados são atualmente produzidos, em diferentes países, entretanto, o iogurte é provavelmente o leite fermentado mais popular e considerado um dos mais importantes derivados lácteos para a alimentação humana. O objetivo deste trabalho foi o estudo da viabilidade da elaboração de um iogurte sabor açaí, tipo "sundae", bem como sua aceitação. As matérias-primas utilizadas, leite e açaí, foram caracterizadas físico quimicamente, através de determinação de pH, acidez, umidade, proteínas, resíduo mineral fixo e lipídios. Durante o processo fermentativo foram retiradas amostras do produto, a cada 20 minutos, para determinação de pH e acidez. O tempo de fermentação, três horas e 20 minutos, foi considerado necessário para o produto atingir pH 4,6. O produto foi estocado, em copos de plástico, a 4ºC e, após 1, 8, 15 e 21 dias de fabricação, foram avaliados quanto ao pH e acidez. Após a fabricação os iogurtes foram analisados para sólidos totais, proteína, gordura, carboidrato, e cinzas. O produto final, também, foi avaliado microbiologicamente, com análises de bolores e leveduras, coliformes fecais e totais e salmonella, e os resultados mostraram que o produto foi manipulado em condições higiênicosanitárias satisfatórias e apto para consumo. A análise sensorial mostrou que o produto foi bem aceito pelos consumidores, com 86,9% de aceitação.

  14. Ninety-eight new species of Trigonopterus weevils from Sundaland and the Lesser Sunda Islands.

    Science.gov (United States)

    Riedel, Alexander; Tänzler, Rene; Balke, Michael; Rahmadi, Cahyo; Suhardjono, Yayuk R

    2014-01-01

    The genus Trigonopterus Fauvel, 1862 is highly diverse in Melanesia. Only one species, Trigonopterusamphoralis Marshall, 1925 was so far recorded West of Wallace's Line (Eastern Sumatra). Based on focused field-work the fauna from Sundaland (Sumatra, Java, Bali, Palawan) and the Lesser Sunda Islands (Lombok, Sumbawa, Flores) is here revised. We redescribe Trigonopterusamphoralis Marshall and describe an additional 98 new species: Trigonopterusacuminatus sp. n., Trigonopterusaeneomicans sp. n., Trigonopterusalaspurwensis sp. n., Trigonopterusallopatricus sp. n., Trigonopterusallotopus sp. n., Trigonopterusangulicollis sp. n., Trigonopterusargopurensis sp. n., Trigonopterusarjunensis sp. n., Trigonopterusasper sp. n., Trigonopterusattenboroughi sp. n., Trigonopterusbaliensis sp. n., Trigonopterusbatukarensis sp. n., Trigonopterusbawangensis sp. n., Trigonopterusbinodulus sp. n., Trigonopterusbornensis sp. n., Trigonopteruscahyoi sp. n., Trigonopteruscostipennis sp. n., Trigonopteruscuprescens sp. n., Trigonopteruscupreus sp. n., Trigonopterusdacrycarpi sp. n., Trigonopterusdelapan sp. n., Trigonopterusdentipes sp. n., Trigonopterusdiengensis sp. n., Trigonopterusdimorphus sp. n., Trigonopterusdisruptus sp. n., Trigonopterusdua sp. n., Trigonopterusduabelas sp. n., Trigonopterusechinatus sp. n., Trigonopterusempat sp. n., Trigonopterusenam sp. n., Trigonopterusfissitarsis sp. n., Trigonopterusflorensis sp. n., Trigonopterusfoveatus sp. n., Trigonopterusfulgidus sp. n., Trigonopterusgedensis sp. n., Trigonopterushalimunensis sp. n., Trigonopterushonjensis sp. n., Trigonopterusijensis sp. n., Trigonopterusjavensis sp. n., Trigonopteruskalimantanensis sp. n., Trigonopteruskintamanensis sp. n., Trigonopterusklatakanensis sp. n., Trigonopteruslampungensis sp. n., Trigonopteruslatipes sp. n., Trigonopteruslima sp. n., Trigonopteruslombokensis sp. n., Trigonopterusmerubetirensis sp. n., Trigonopterusmesehensis sp. n., Trigonopterusmicans sp. n., Trigonopterusmisellus sp. n

  15. 3D Thermochemical Numerical Model of a Convergent Zone With an Overriding Plate

    Science.gov (United States)

    Mason, W. G.; Moresi, L.; Betts, P. G.

    2008-12-01

    We have created a new three dimensional thermochemical numerical model of a convergent zone, in which a viscoplastic oceanic plate subducts beneath a viscous overriding plate, using the finite element Geoscience research code Underworld. Subduction is initiated by mantle flow induced by the gravitational instability of a slab tip, and buoyancy of the overriding plate. A cold thermal boundary layer envelopes both plates, and is partially dragged into the mantle along with the subducting slab. The trench rolls back as the slab subducts, and the overriding plate follows the retreating trench without being entrained into the upper mantle. The model is repeated with the overriding plate excluded, to analyse the influence of the overriding plate. The overriding plate retards the rate of subduction. Maximum strain rates, evident along the trench in the absence of an overriding plate, extend to a greater depth within the subducted portion of the slab in the presence of an overriding plate.

  16. Large gem diamonds from metallic liquid in Earth's deep mantle.

    Science.gov (United States)

    Smith, Evan M; Shirey, Steven B; Nestola, Fabrizio; Bullock, Emma S; Wang, Jianhua; Richardson, Stephen H; Wang, Wuyi

    2016-12-16

    The redox state of Earth's convecting mantle, masked by the lithospheric plates and basaltic magmatism of plate tectonics, is a key unknown in the evolutionary history of our planet. Here we report that large, exceptional gem diamonds like the Cullinan, Constellation, and Koh-i-Noor carry direct evidence of crystallization from a redox-sensitive metallic liquid phase in the deep mantle. These sublithospheric diamonds contain inclusions of solidified iron-nickel-carbon-sulfur melt, accompanied by a thin fluid layer of methane ± hydrogen, and sometimes majoritic garnet or former calcium silicate perovskite. The metal-dominated mineral assemblages and reduced volatiles in large gem diamonds indicate formation under metal-saturated conditions. We verify previous predictions that Earth has highly reducing deep mantle regions capable of precipitating a metallic iron phase that contains dissolved carbon and hydrogen.

  17. Estimating Upper Mantle Hydration from In Situ Electrical Conductivity

    Science.gov (United States)

    Behrens, J.; Constable, S.; Heinson, G.; Everett, M.; Weiss, C.; Key, K.

    2004-12-01

    The electrical conductivity of 35-40 Ma Pacific plate has been measured in situ; one robust result is the presence of bulk anisotropy in the lithospheric upper mantle. We interpret this anisotropy to be a result of hydrothermal circulation into the upper mantle along spreading-ridge-parallel normal faults: the associated zones of serpentinized peridotite provide the pathways of enhanced electrical conductivity required by the data. Our modeling bounds the range of possible anisotropic ratios, which are then used to estimate the amount of water required to serpentinize the requisite amounts of peridotite. These data sets, however, do not indicate anisotropy in the bulk conductivity of the crust, nor in the asthenospheric mantle. This second point is significant, as recent measurements of sub-continental asthenospheric conductivity have been interpreted to indicate anisotropy aligned with present plate motion, with the diffusion of hydrogen through olivine advanced as an explanation.

  18. Mantle structure beneath the western edge of the Colorado Plateau

    Science.gov (United States)

    Sine, C.R.; Wilson, D.; Gao, W.; Grand, S.P.; Aster, R.; Ni, J.; Baldridge, W.S.

    2008-01-01

    Teleseismic traveltime data are inverted for mantle Vp and Vs variations beneath a 1400 km long line of broadband seismometers extending from eastern New Mexico to western Utah. The model spans 600 km beneath the moho with resolution of ???50 km. Inversions show a sharp, large-magnitude velocity contrast across the Colorado Plateau-Great Basin transition extending ???200 km below the crust. Also imaged is a fast anomaly 300 to 600 km beneath the NW portion of the array. Very slow velocities beneath the Great Basin imply partial melting and/or anomalously wet mantle. We propose that the sharp contrast in mantle velocities across the western edge of the Plateau corresponds to differential lithospheric modification, during and following Farallon subduction, across a boundary defining the western extent of unmodified Proterozoic mantle lithosphere. The deep fast anomaly corresponds to thickened Farallon plate or detached continental lithosphere at transition zone depths. Copyright 2008 by the American Geophysical Union.

  19. Ensemble data assimilation for the reconstruction of mantle circulation

    Science.gov (United States)

    Bocher, Marie; Coltice, Nicolas; Fournier, Alexandre; Tackley, Paul

    2016-04-01

    The surface tectonics of the Earth is the result of mantle dynamics. This link between internal and surface dynamics can be used to reconstruct the evolution of mantle circulation. This is classically done by imposing plate tectonics reconstructions as boundary conditions on numerical models of mantle convection. However, this technique does not account for uncertainties in plate tectonics reconstructions and does not allow any dynamical feedback of mantle dynamics on surface tectonics to develop. Mantle convection models are now able to produce surface tectonics comparable to that of the Earth to first order. We capitalize on these convection models to propose a more consistent integration of plate tectonics reconstructions into mantle convection models. For this purpose, we use the ensemble Kalman filter. This method has been developed and successfully applied to meteorology, oceanography and even more recently outer core dynamics. It consists in integrating sequentially a time series of data into a numerical model, starting from an ensemble of possible initial states. The initial ensemble of states is designed to represent an approximation of the probability density function (pdf) of the a priori state of the system. Whenever new observations are available, each member of the ensemble states is corrected considering both the approximated pdf of the state, and the pdf of the new data. Between two observation times, each ensemble member evolution is computed independently, using the convection model. This technique provides at each time an approximation of the pdf of the state of the system, in the form of a finite ensemble of states. We perform synthetic experiments to assess the efficiency of this method for the reconstruction of mantle circulation.

  20. Limited latitudinal mantle plume motion for the Louisville hotspot

    Science.gov (United States)

    Koppers, Anthony A. P.; Yamazaki, Toshitsugu; Geldmacher, Jörg; Gee, Jeffrey S.; Pressling, Nicola; Koppers, Anthony A. P.; Yamazaki, Toshitsugu; Geldmacher, Jörg; Gee, Jeffrey S.; Pressling, Nicola; Hoshi, Hiroyuki; Anderson, L.; Beier, C.; Buchs, D. M.; Chen, L.-H.; Cohen, B. E.; Deschamps, F.; Dorais, M. J.; Ebuna, D.; Ehmann, S.; Fitton, J. G.; Fulton, P. M.; Ganbat, E.; Hamelin, C.; Hanyu, T.; Kalnins, L.; Kell, J.; Machida, S.; Mahoney, J. J.; Moriya, K.; Nichols, A. R. L.; Rausch, S.; Sano, S.-I.; Sylvan, J. B.; Williams, R.

    2012-12-01

    Hotspots that form above upwelling plumes of hot material from the deep mantle typically leave narrow trails of volcanic seamounts as a tectonic plate moves over their location. These seamount trails are excellent recorders of Earth's deep processes and allow us to untangle ancient mantle plume motions. During ascent it is likely that mantle plumes are pushed away from their vertical upwelling trajectories by mantle convection forces. It has been proposed that a large-scale lateral displacement, termed the mantle wind, existed in the Pacific between about 80 and 50 million years ago, and shifted the Hawaiian mantle plume southwards by about 15° of latitude. Here we use 40Ar/39Ar age dating and palaeomagnetic inclination data from four seamounts associated with the Louisville hotspot in the South Pacific Ocean to show that this hotspot has been relatively stable in terms of its location. Specifically, the Louisville hotspot--the southern hemisphere counterpart of Hawai'i--has remained within 3-5° of its present-day latitude of about 51°S between 70 and 50 million years ago. Although we cannot exclude a more significant southward motion before that time, we suggest that the Louisville and Hawaiian hotspots are moving independently, and not as part of a large-scale mantle wind in the Pacific.

  1. Mantle flow and dynamic topography associated with slab window opening

    Science.gov (United States)

    Guillaume, Benjamin; Moroni, Monica; Funiciello, Francesca; Martinod, Joseph; Faccenna, Claudio

    2010-05-01

    A slab window is defined as an 'hole' in the subducting lithosphere. In the classical view, slab windows develop where a spreading ridge intersects a subduction zone. The main consequences of this phenomenon are the modifications of the physical, chemical and thermal conditions in the backarc mantle that in turn affect the tectonic and magmatic evolution of the overriding plate. In this work, we perform dynamically self-consistent mantle-scale laboratory models, to evaluate how the opening of a window in the subducting panel influences the geometry and the kinematics of the slab, the mantle circulation pattern and, finally, the overriding plate dynamic topography. The adopted setup consists in a two-layer linearly viscous system simulating the roll-back of a fixed subducting plate (simulated using silicone putty) into the upper mantle (simulated using glucose syrup). Our experimental setting is also characterized by a constant-width rectangular window located at the center of a laterally confined slab, modeling the case of the interaction of a trench-parallel spreading ridge with a wide subduction zone. We find that the geometry and the kinematics of the slab are only minorly affected by the opening of a slab window. On the contrary, slab induced mantle circulation, quantified using Feature Tracking image analysis technique, is strongly modified and produces a peculiar non-isostatic topographic signal on the overriding plate. Assuming that our modeling results can be representative of the natural behavior of subduction zones, we compare them to the Patagonian subduction zone finding that anomalous backarc volcanism that developed since middle Miocene could result from the lateral flowage of subslab mantle, and that part of the Patagonian uplift could be dynamically supported.

  2. The tectonic emplacement of Sumba in the Sunda-Banda Arc: paleomagnetic and geochemical evidence from the early Miocene Jawila volcanics

    NARCIS (Netherlands)

    Wensink, H.; Bergen, M.J. van

    1995-01-01

    The island of Sumba is a continental fragment in the fore-arc region near the transition between the Sunda Arc and Banda Arc in southeastern Indonesia. Paleomagnetic and geochemical evidence from the early Miocene volcanics of the Jawila Formation in western Sumba constrain the final drift stage

  3. Seismicity of the Earth 1900-2012 Philippine Sea plate and vicinity

    Science.gov (United States)

    Smoczyk, Gregory M.; Hayes, Gavin P.; Hamburger, Michael W.; Benz, Harley M.; Villaseñor, Antonio; Furlong, Kevin P.

    2013-01-01

    The complex tectonics surrounding the Philippine Islands are dominated by the interactions of the Pacific, Sunda, and Eurasia plates with the Philippine Sea plate (PSP). The latter is unique because it is almost exclusively surrounded by zones of plate convergence. At its eastern and southeastern edges, the Pacific plate is subducted beneath the PSP at the Izu-Bonin, Mariana, and Yap trenches. Here, the subduction zone exhibits high rates of seismic activity to depths of over 600 km, though no great earthquakes (M>8.0) have been observed, likely because of weak coupling along the plate interface. In the northeast, the PSP subducts beneath Japan and the eastern margin of the Eurasia plate at the Nankai and Ryukyu trenches, extending westward to Taiwan. The Nankai portion of this subduction zone has hosted some of the largest earthquakes along the margins of the PSP, including a pair of Mw8.1 megathrust events in 1944 and 1946. Along its western margin, the convergence of the PSP and the Sunda plate is responsible for a broad and active plate boundary system extending along both sides of the Philippine Islands chain. The region is characterized by opposite-facing subduction systems on the east and west sides of the islands, and the archipelago is cut by a major transform structure: the Philippine Fault. Subduction of the Philippine Sea plate occurs at the eastern margin of the islands along the Philippine Trench and its northern extension, the East Luzon Trough. On the west side of Luzon, the Sunda Plate subducts eastward along a series of trenches, including the Manila Trench in the north, the smaller Negros Trench in the central Philippines, and the Sulu and Cotabato trenches in the south. Twentieth and early twentyfirst century seismic activity along the boundaries of the Philippine Sea plate has produced seven great (M>8.0) earthquakes and 250 large (M>7) events. Among the most destructive events were the 1923 Kanto, the 1948 Fukui, and the 1995 Kobe, Japan

  4. Finding the patterns in mantle convection

    Science.gov (United States)

    Atkins, Suzanne; Rozel, Antoine; Valentine, Andrew; Tackley, Paul; Trampert, Jeannot

    2016-04-01

    Inverting mantle flow for past configurations is one of the great outstanding problems in geodynamics. We demonstrate a new method for probabilistic inversion of present-day Earth observations for mantle properties and history. Convection is a non-linear and chaotic, thwarting most standard inversion methods. Because of its chaotic and unpredictable nature, small errors in initial conditions, parameter selection, and computational precision can all significantly change the results produced by mantle convection simulations. However, some patterns and statistics of convection contain the signature of the parameters used in the simulations over long time-scales. Geodynamical studies often vary these parameters to investigate their effects on the patterns produced. We show that with a large enough set of simulations, we can investigate the relationship between input parameters and convection patterns in a more rigorous way. Probabilistic inversion is the only way to approach highly non-linear problems. We use neural networks to represent the probability density function linking convection simulation input parameters and the patterns they produce. This allows us to find input parameters, whilst taking into account all of the uncertainties that are inherent in the inversion of any Earth system: how well do we understand the physics of the process; what do we already know about the input parameters; and how certain are our observations? We show that the mantle structures produced by 4.5 Gyr of convection simulations contain enough information on yield stress, viscosity coefficients, mantle heating rate, and the initial state of primordial material that we can infer them directly without requiring any other information, such as plate velocity.

  5. STRUCTURE OF THE LITHOSPHERE AND SEISMOTECTONIC DEFORMATIONS IN CONTACT ZONE OF LITHOSPHERIC PLATES IN THE SUMATRA ISLAND REGION

    Directory of Open Access Journals (Sweden)

    O. A. Kuchay

    2015-09-01

    Full Text Available The inversion seismic tomography algorithm (ITS was used to calculate 3D seismic anomalies models for velocities of P- and S-waves in the zone of the Sunda arc, Indonesia. In the area under study, strong earthquakes (M>4.8 are clustered in the zone of high P-wave velocities. Earthquake hypocenters are located in zones of both high and low velocity anomalies of S-waves. The giant Sumatra earthquake (December 26, 2004, Mw=9.0 ruptured the greatest fault length of any recorded earthquake, and the rupture started in the area wherein the sign of P-wave velo­city anomalies is abruptly changed. We calculated seismotectonic deformations (STD from data on mechanisms of 2227 earthquakes recorded from 1977 to 2013, and our calculations show that the STD component, that controls vertical extension of rocks, is most stable through all the depth levels. In the marginal regions at the western and eastern sides of the Sunda arc, the crustal areas (depths from 0 to 35 km are subject to deformations which sign is opposite to that of deformations in the central part. Besides, at depths from 70 to 150 km beneath the Sumatra earthquake epicentre area, the zone is subject to deformations which sign is opposite to that of deformations in the studied part of the Sunda arc. For earthquakes that may occur in the crust in the Sunda arc in the contact zone of the plates, maximum magnitudes depend on the direction of pressure imposed by the actively subducting plate, which is an additional criteria for determining the limit magnitude for the region under study. 

  6. Relationship between plume and plate tectonics

    Science.gov (United States)

    Puchkov, V. N.

    2016-07-01

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

  7. Seismic anisotropy of upper mantle in eastern Tibetan Plateau and related crust-mantle coupling pattern

    Institute of Scientific and Technical Information of China (English)

    Paul; SILVER; Lucy; FLESCH

    2007-01-01

    By using the polarization analysis of teleseismic SKS waveform data recorded at 116 seismic stations which respectively involved in China National Digital Seismograph Network, and Yunnan, Sichuan, Gansu and Qinghai regional digital networks, and portable broadband seismic networks deployed in Sichuan, Yunnan and Tibet, we obtained the SKS fast-wave direction and the delay time between fast and slow waves of each station by use of the stacking analysis method, and finally acquired the fine image of upper mantle anisotropy in the eastern Tibetan Plateau and its adjacent regions. We analyzed the crust-mantle coupling deformation on the basis of combining the GPS observation results and the upper mantle anisotropy distribution in the study area. The Yunnan region out of the plateau has dif-ferent features of crust-mantle deformation from the inside plateau. There exists a lateral transitional zone of crust-mantle coupling in the eastern edge of the Tibetan Plateau, which is located in the region between 26° and 27°N in the west of Sichuan and Yunnan. To the south of transitional zone, the fast-wave direction is gradually turned from S60°―70°E in southwestern Yunnan to near EW in south-eastern Yunnan. To the north of transitional zone in northwestern Yunnan and the south of western Sichuan, the fast-wave direction is nearly NS. From crust to upper mantle, the geophysical parameters (e.g. the crustal thickness, the Bouguer gravity anomaly, and tectonic stress direction) show the feature of lateral variation in the transitional zone, although the fault trend on the ground surface is inconsis-tent with the fast-wave direction. This transitional zone is close by the eastern Himalayan syntaxis, and it may play an important role in the plate boundary dynamics.

  8. Seismic anisotropy of upper mantle in eastern Tibetan Plateau and related crust-mantle coupling pattern

    Institute of Scientific and Technical Information of China (English)

    WANG ChunYong; CHANG LiJun; L(U) ZhiYong; QIN JiaZheng; SU Wei; Paul SILVER; Lucy FLESCH

    2007-01-01

    By using the polarization analysis of teleseismic SKS waveform data recorded at 116 seismic stations which respectively involved in China National Digital Seismograph Network, and Yunnan, Sichuan,Gansu and Qinghai regional digital networks, and portable broadband seismic networks deployed in Sichuan, Yunnan and Tibet, we obtained the SKS fast-wave direction and the delay time between fast and slow waves of each station by use of the stacking analysis method, and finally acquired the fine image of upper mantle anisotropy in the eastern Tibetan Plateau and its adjacent regions. We analyzed the crust-mantle coupling deformation on the basis of combining the GPS observation results and the upper mantle anisotropy distribution in the study area. The Yunnan region out of the plateau has different features of crust-mantle deformation from the inside plateau. There exists a lateral transitional zone of crust-mantle coupling in the eastern edge of the Tibetan Plateau, which is located in the region between 26° and 27°N in the west of Sichuan and Yunnan. To the south of transitional zone, the fast-wave direction is gradually turned from S60°-70°E in southwestern Yunnan to near EW in southeastern Yunnan. To the north of transitional zone in northwestern Yunnan and the south of western Sichuan, the fast-wave direction is nearly NS. From crust to upper mantle, the geophysical parameters(e.g. the crustal thickness, the Bouguer gravity anomaly, and tectonic stress direction) show the feature of lateral variation in the transitional zone, although the fault trend on the ground surface is inconsistent with the fast-wave direction. This transitional zone is close by the eastern Himalayan syntaxis, and it may play an important role in the plate boundary dynamics.

  9. Lithology and temperature: How key mantle variables control rift volcanism

    Science.gov (United States)

    Shorttle, O.; Hoggard, M.; Matthews, S.; Maclennan, J.

    2015-12-01

    Continental rifting is often associated with extensive magmatic activity, emplacing millions of cubic kilometres of basalt and triggering environmental change. The lasting geological record of this volcanic catastrophism are the large igneous provinces found at the margins of many continents and abrupt extinctions in the fossil record, most strikingly that found at the Permo-Triassic boundary. Rather than being considered purely a passive plate tectonic phenomenon, these episodes are frequently explained by the involvement of mantle plumes, upwellings of mantle rock made buoyant by their high temperatures. However, there has been debate over the relative role of the mantle's temperature and composition in generating the large volumes of magma involved in rift and intra-plate volcanism, and even when the mantle is inferred to be hot, this has been variously attributed to mantle plumes or continental insulation effects. To help resolve these uncertainties we have combined geochemical, geophysical and modelling results in a two stage approach: Firstly, we have investigated how mantle composition and temperature contribute to melting beneath Iceland, the present day manifestation of the mantle plume implicated in the 54Ma break up of the North Atlantic. By considering both the igneous crustal production on Iceland and the chemistry of its basalts we have been able to place stringent constraints on the viable temperature and lithology of the Icelandic mantle. Although a >100°C excess temperature is required to generate Iceland's thick igneous crust, geochemistry also indicates that pyroxenite comprises 10% of its source. Therefore, the dynamics of rifting on Iceland are modulated both by thermal and compositional mantle anomalies. Secondly, we have performed a global assessment of the mantle's post break-up thermal history to determine the amplitude and longevity of continental insulation in driving excess volcanism. Using seismically constrained igneous crustal

  10. Predicting lower mantle heterogeneity from 4-D Earth models

    Science.gov (United States)

    Flament, Nicolas; Williams, Simon; Müller, Dietmar; Gurnis, Michael; Bower, Dan J.

    2016-04-01

    The Earth's lower mantle is characterized by two large-low-shear velocity provinces (LLSVPs), approximately ˜15000 km in diameter and 500-1000 km high, located under Africa and the Pacific Ocean. The spatial stability and chemical nature of these LLSVPs are debated. Here, we compare the lower mantle structure predicted by forward global mantle flow models constrained by tectonic reconstructions (Bower et al., 2015) to an analysis of five global tomography models. In the dynamic models, spanning 230 million years, slabs subducting deep into the mantle deform an initially uniform basal layer containing 2% of the volume of the mantle. Basal density, convective vigour (Rayleigh number Ra), mantle viscosity, absolute plate motions, and relative plate motions are varied in a series of model cases. We use cluster analysis to classify a set of equally-spaced points (average separation ˜0.45°) on the Earth's surface into two groups of points with similar variations in present-day temperature between 1000-2800 km depth, for each model case. Below ˜2400 km depth, this procedure reveals a high-temperature cluster in which mantle temperature is significantly larger than ambient and a low-temperature cluster in which mantle temperature is lower than ambient. The spatial extent of the high-temperature cluster is in first-order agreement with the outlines of the African and Pacific LLSVPs revealed by a similar cluster analysis of five tomography models (Lekic et al., 2012). Model success is quantified by computing the accuracy and sensitivity of the predicted temperature clusters in predicting the low-velocity cluster obtained from tomography (Lekic et al., 2012). In these cases, the accuracy varies between 0.61-0.80, where a value of 0.5 represents the random case, and the sensitivity ranges between 0.18-0.83. The largest accuracies and sensitivities are obtained for models with Ra ≈ 5 x 107, no asthenosphere (or an asthenosphere restricted to the oceanic domain), and a

  11. Insights on slab-driven mantle flow from advances in three-dimensional modelling

    Science.gov (United States)

    Jadamec, Margarete A.

    2016-10-01

    The wealth of seismic observations collected over the past 20 years has raised intriguing questions about the three-dimensional (3D) nature of the mantle flow field close to subduction zones and provided a valuable constraint for how the plate geometry may influence mantle flow proximal to the slab. In geodynamics, there has been a new direction of subduction zone modelling that has explored the 3D nature of slab-driven mantle flow, motivated in part by the observations from shear wave splitting, but also by the observed variations in slab geometries worldwide. Advances in high-performance computing are now allowing for an unprecedented level of detail to be incorporated into numerical models of subduction. This paper summarizes recent advances from 3D geodynamic models that reveal the complex nature of slab-driven mantle flow, including trench parallel flow, toroidal flow around slab edges, mantle upwelling at lateral slab edges, and small scale convection within the mantle wedge. This implies slab-driven mantle deformation zones occur in the asthenosphere proximal to the slab, wherein the mantle may commonly flow in a different direction and rate than the surface plates, implying laterally variable plate-mantle coupling. The 3D slab-driven mantle flow can explain, in part, the lateral transport of geochemical signatures in subduction zones. In addition, high-resolution geographically referenced models can inform the interpretation of slab structure, where seismic data are lacking. The incorporation of complex plate boundaries into high-resolution, 3D numerical models opens the door to a new avenue of research in model construction, data assimilation, and modelling workflows, and gives 3D immersive visualization a new role in scientific discovery.

  12. On the validity of Epeorella Ulmer, 1939 (Ephemeroptera, Heptageniidae with general considerations on the Heptageniidae of the Sunda Islands

    Directory of Open Access Journals (Sweden)

    Michel Sartori

    2014-10-01

    Full Text Available The type material of Epeorella borneonia Ulmer, 1939, the sole species of the genus Epeorella Ulmer, 1939 is reinvestigated and a lectotype (male imago is designated. Based on several morphological structures, the synonymy with Epeorus Eaton, 1881 (Rhithrogeninae is rejected. Epeorella stat. prop., known only at the winged stages, belongs to the subfamily Ecdyonurinae, and is a probable endemic of the island of Borneo. The newly erected genus Darthus Webb & McCafferty, 2007, also endemic to Borneo and only known by one species at the nymphal stage, is shown to be a junior subjective synonym of Epeorella. The new combination Epeorella vadora (Webb & McCafferty, 2007 is proposed for the species. The distribution of known heptageniid species from the Sunda Islands is discussed.

  13. The Elephants' Graveyard: Constraints from Mantle Plumes on the Fate of Subducted Slabs and Implications for the Style of Mantle Convection

    Science.gov (United States)

    Lassiter, J. C.

    2007-12-01

    The style of mantle convection (e.g., layered- vs. whole-mantle convection) is one of the most hotly contested questions in the Geological Sciences. Geochemical arguments for and against mantle layering have largely focused on mass-balance evidence for the existence of "hidden" geochemical reservoirs. However, the size and location of such reservoirs are largely unconstrained, and most geochemical arguments for mantle layering are consistent with a depleted mantle comprising most of the mantle mass and a comparatively small volume of enriched, hidden material either within D" or within seismically anomalous "piles" beneath southern Africa and the South Pacific. The mass flux associated with subduction of oceanic lithosphere is large and plate subduction is an efficient driver of convective mixing in the mantle. Therefore, the depth to which oceanic lithosphere descends into the mantle is effectively the depth of the upper mantle in any layered mantle model. Numerous geochemical studies provide convincing evidence that many mantle plumes contain material which at one point resided close to the Earth's surface (e.g., recycled oceanic crust ± sediments, possibly subduction-modified mantle wedge material). Fluid dynamic models further reveal that only the central cores of mantle plumes are involved in melt generation. The presence of recycled material in the sources of many ocean island basalts therefore cannot be explained by entrainment of this material during plume ascent, but requires that recycled material resides within or immediately above the thermo-chemical boundary layer(s) that generates mantle plumes. More recent Os- isotope studies of mantle xenoliths from OIB settings reveal the presence not only of recycled crust in mantle plumes, but also ancient melt-depleted harzburgite interpreted to represent ancient recycled oceanic lithosphere [1]. Thus, there is increasing evidence that subducted slabs accumulate in the boundary layer(s) that provide the source

  14. The challenge of installing a tsunami early warning system in the vicinity of the Sunda Arc, Indonesia

    Directory of Open Access Journals (Sweden)

    J. Lauterjung

    2010-04-01

    Full Text Available Indonesia is located along the most prominent active continental margin in the Indian Ocean, the so-called Sunda Arc and, therefore, is one of the most threatened regions of the world in terms of natural hazards such as earthquakes, volcanoes, and tsunamis. On 26 December 2004 the third largest earthquake ever instrumentally recorded (magnitude 9.3, Stein and Okal, 2005 occurred off-shore northern Sumatra and triggered a mega-tsunami affecting the whole Indian Ocean. Almost a quarter of a million people were killed, as the region was not prepared either in terms of early-warning or in terms of disaster response.

    In order to be able to provide, in future, a fast and reliable warning procedure for the population, Germany, immediately after the catastrophe, offered during the UN World Conference on Disaster Reduction in Kobe, Hyogo/Japan in January 2005 technical support for the development and installation of a tsunami early warning system for the Indian Ocean in addition to assistance in capacity building in particular for local communities. This offer was accepted by Indonesia but also by other countries like Sri Lanka, the Maldives and some East-African countries. Anyhow the main focus of our activities has been carried out in Indonesia as the main source of tsunami threat for the entire Indian Ocean. Challenging for the technical concept of this warning system are the extremely short warning times for Indonesia, due to its vicinity to the Sunda Arc. For this reason the German Indonesian Tsunami Early Warning System (GITEWS integrates different modern and new scientific monitoring technologies and analysis methods.

  15. Satellite estimate of freshwater exchange between the Indonesian Seas and the Indian Ocean via the Sunda Strait

    Science.gov (United States)

    Potemra, James T.; Hacker, Peter W.; Melnichenko, Oleg; Maximenko, Nikolai

    2016-07-01

    The straits in Indonesia allow for low-latitude exchange of water between the Pacific and Indian Oceans. Collectively known as the Indonesian Throughflow (ITF), this exchange is thought to occur primarily via the Makassar Strait and downstream via Lombok Strait, Ombai Strait, and Timor Passage. The Sunda Strait, between the islands of Sumatra and Java, is a very narrow (≈10 km) and shallow (≈20 m) gap, but it connects the Java Sea directly to the Indian Ocean. Flow through this strait is presumed to be small, given the size of the passage; however, recent observations from the Aquarius satellite indicate periods of significant freshwater transport, suggesting the Sunda Strait may play a more important role in Pacific to Indian Ocean exchange. The nature of this exchange is short-duration (several days) bursts of freshwater injected into the eastern Indian Ocean superimposed on a mean seasonal cycle. The mean volume transport is small averaging about 0.1 Sv toward the Indian Ocean, but the freshwater transport is nonnegligible (estimated at 5.8 mSv). Transport through the strait is hydraulically controlled and directly correlates to the along-strait pressure difference. The episodic low-salinity plumes observed by Aquarius do not, however, appear to be forced by this same mechanism but are instead controlled by convergence of flow at the exit of the Strait in the Indian Ocean. Numerical model results show the fate of this freshwater plume varies with season and is either advected to the northwest along the coast of Sumatra or southerly into the ITF pathway.

  16. Plate tectonics and planetary habitability: current status and future challenges.

    Science.gov (United States)

    Korenaga, Jun

    2012-07-01

    Plate tectonics is one of the major factors affecting the potential habitability of a terrestrial planet. The physics of plate tectonics is, however, still far from being complete, leading to considerable uncertainty when discussing planetary habitability. Here, I summarize recent developments on the evolution of plate tectonics on Earth, which suggest a radically new view on Earth dynamics: convection in the mantle has been speeding up despite its secular cooling, and the operation of plate tectonics has been facilitated throughout Earth's history by the gradual subduction of water into an initially dry mantle. The role of plate tectonics in planetary habitability through its influence on atmospheric evolution is still difficult to quantify, and, to this end, it will be vital to better understand a coupled core-mantle-atmosphere system in the context of solar system evolution. © 2012 New York Academy of Sciences.

  17. Implications of εNd—La/Nb,Ba/Nb,Nb/Th Diagrams to Mantle Heterogeneity—Classification of Island—arc Basalts and Decomposition of EMII Component

    Institute of Scientific and Technical Information of China (English)

    李曙光

    1995-01-01

    A group of εNd/Nb,Ba/Nb,Nb/Th diagrams are used to study mantle heterogeneity.Island-arc basalts(IAB) are distributed in a triangle of these diagrams. Three end-member components (the MORB-type depleted mantle, the fluid released from subducted oceanic crust and the sediments from the continental crust) of the source of IAB may be displayed in these diagrams. Two types of IAB are identified .They are of the two-component type (with little continental sediments), such as the basalts from Aletians and New Britain ,and the three-compeonent type, such as those from Sunda, Lesser Antilles and Andes. In addition ,the EMII type mantle-derived rocks may also be divided into two groups. One is exemplified by continental flood basalts and some peridotite xenoliths, similar to IAB, with high La/Nb and Ba/Nb and low Nb/Th ratios, The other includes the Samoa-type oceanic island basalts, with low La/Nb and Ba/Nb and high Nb/Th ratios. The corresponding two sub-components of EMII are EMIIM, which is related to the metasomatism of lithosphere mantle by fluids released from the subducted oceanic crust, and EMIISR, related to the intervention of recycling continental sediments into the convective mantle.

  18. Measurements of upper mantle shear wave anisotropy from a permanent network in southern Mexico

    NARCIS (Netherlands)

    van Benthem, S.A.C.; Valenzuela, R.W.; Ponce, G.J.

    2013-01-01

    Upper mantle shear wave anisotropy under stations in southern Mexico was measured using records of SKS phases. Fast polarization directions where the Cocos plate subducts subhorizontally are oriented in the direction of the relative motion between the Cocos and North American plates, and are trench-

  19. Measurements of upper mantle shear wave anisotropy from a permanent network in southern Mexico

    NARCIS (Netherlands)

    van Benthem, S.A.C.; Valenzuela, R.W.; Ponce, G.J.

    2013-01-01

    Upper mantle shear wave anisotropy under stations in southern Mexico was measured using records of SKS phases. Fast polarization directions where the Cocos plate subducts subhorizontally are oriented in the direction of the relative motion between the Cocos and North American plates, and are

  20. Mantle Structure Beneath Central South America

    Science.gov (United States)

    Vandecar, J. C.; Silver, P. G.; James, D. E.; Assumpcao, M.; Schimmel, M.; Zandt, G.

    2003-12-01

    Making use of 60 digital broadband seismic stations that have operated across central South America in recent years, we have undertaken an inversion for the upper- and uppermost lower-mantle P- and S-wave velocity structures beneath the region. We have combined data from four portable PASSCAL-type experiments as well as the 3 GTSN permanent stations (LPAZ, BDFB and CPUP) and 1 Geoscope station (SPB) located in the region. The portable data were deployed at various times between 1992 and 1999 and include: 28 sites from the Brazilian Lithosphere Seismic Project (BLSP: Carnegie Institution of Washington and Universidade de Sao Paulo), 16 sites from the Broadband ANdean JOint experiment (BANJO: Carnegie Institution of Washington and University of Arizona), 8 sites from the Seismic Exploration of the Deep Altiplano project (SEDA: Lawrence Livermore National Laboratory) and 4 sites from the University of Brasilia. The P- and S-wave relative delay times are independently obtained via a multi-channel cross correlation of band-passed waveforms for each teleseismic event. These data are then inverted using an iterative, robust, non-linear scheme which parameterizes the 3-D velocity variations as splines under tension constrained at over 120,000 nodes across South America between latitudes of 15 and 30 degrees South. Amongst other features, we robustly image the high-velocity subducting Nazca plate penetrating into the lower mantle and the high-velocity root of the ~3.2 Gyr old Sao Francisco Craton extending to depths of 200-300 km. We will discuss the consistency between our tomographic models and predictions of dynamic mantle models based on plate tectonic reconstructions of subduction.

  1. Trans-Pacific whole mantle structure

    Science.gov (United States)

    Liu, Lijun; Tan, Ying; Sun, Daoyuan; Chen, Min; Helmberger, Don

    2011-04-01

    Recent reports on modeling USArray data reveal mostly vertical microplates with little resemblance to preliminary reference Earth model (PREM). Such complexity at plate boundaries makes it difficult to form reliable images of ocean basins using global paths. Here, we report on modeling stacked seismograms obtained from the first broadband array (TriNet) situated on the edge of the Pacific Plate, southern California, with no major subduction zone blocking its view. Extended records, including multi-S and ScS waves up to four bounces from 18 Tonga-Fiji deep events (140 to 620 km) are analyzed to check the validity of existing models and derive the whole mantle shear velocity structure along this corridor. Synthetics generated from 3-D tomographic models do not fit the upper mantle triplication data or the mantle reverberations associated with the ScS multiples as well as the 1-D model PAC06. We construct a hybrid model (HPAC), which remains one dimensional down to 800 km (PAC06). The lower portion of HPAC is essentially the tomography model S20RTS with velocity variation inflated by a factor of 2 for the lowermost 600 km. Thus, the mid-Pacific large low shear velocity province (LLSVP) has a lower shear velocity of about 2% relative to PREM and extends into the midmantle, similar to that beneath South Africa. Moreover, rapid changes in the differential (ScS-S) and (ScS2-S) times as a function of distance suggest ultra low velocity zones near the eastern edge and under the LLSVP, again similar to that found beneath Africa.

  2. Plate Motions Predicted from Global Dynamic Models and Seismic Tomography: The Problem of North American Plate Motion

    Science.gov (United States)

    Liu, S.; King, S. D.; Adam, C. M.

    2016-12-01

    Seismic tomography is a snapshot of the mantle convection system and provides important constraints on Earth's internal dynamics. An increasing number of global seismic tomography models along with various rheological structures have been used to compute mantle flow pattern and the resulting surface expressions, including dynamic topography and geoid. Accurately predicting the plate motion from the mantle dynamic models is a challenge particularly with the newest generation of seismic tomography models (e.g., S40RTS, SAVANI), especially for the North American plate which only has a little subduction along it's boundary. The difficulties include the uncertainty of the velocity-to-density scaling, discrepancies between different seismic tomography models, and the computational technology to solve for global mantle flow with observationally constrained high resolution models. We use the code ASPECT (Advanced Solver for Problems in Earth CovecTion) to make a series of tests to derive mantle flow pattern from different global seismic tomography models and rheological structures. We further make a quantitative statistical comparison between the modeled and observed plate motions in terms of flow magnitude, flow direction, and plateness within each plate area. We investigate how the velocity-to-density scaling, the features of seismic tomography models, and the lateral rheological structures of the lithosphere and upper mantle influence the modeled plate motions. We find that the velocity-to-density scaling mainly changes the flow magnitude and has little impact on the flow direction. The results of different seismic tomography models are similar broadly but can be quite different in some regions. The presence of lateral viscosity variations including stiff cratons, weak plate boundary zones, and high viscosity slabs along with density variations from seafloor age and subducting slabs can improve the fit to observed plate motions. With a very small fraction of subduction

  3. New observational and experimental evidence for a plume-fed asthenosphere boundary layer in mantle convection

    Science.gov (United States)

    Morgan, J. P.; Hasenclever, J.; Shi, C.

    2013-03-01

    The textbook view is that the asthenosphere is the place beneath the tectonic plates where competing temperature and pressure effects on mantle rheology result in the lowest viscosity region of Earth's mantle. We think the sub-oceanic asthenosphere exists for a different reason, that instead it is where rising plumes of hot mantle stall and spread out beneath the strong tectonic plates. Below this plume-fed asthenosphere is a thermal and density inversion with cooler underlying average-temperature mantle. Here we show several recent seismic studies that are consistent with a plume-fed asthenosphere. These include the seismic inferences that asthenosphere appears to resist being dragged down at subduction zones, that a sub-oceanic thermal inversion ∼250-350 km deep is needed to explain the seismic velocity gradient there for an isochemical mantle, that a fast 'halo' of shear-wave travel-times surrounds the Hawaiian plume conduit, and that an apparent seismic reflector is found ∼300 km beneath Pacific seafloor near Hawaii. We also present 2D axisymmetric and 3D numerical experiments that demonstrate these effects in internally consistent models with a plume-fed asthenosphere. If confirmed, the existence of a plume-fed asthenosphere will change our understanding of the dynamics of mantle convection and melting, and the links between surface plate motions and mantle convection.

  4. Experimental evidence supports mantle partial melting in the asthenosphere

    Science.gov (United States)

    Chantel, Julien; Manthilake, Geeth; Andrault, Denis; Novella, Davide; Yu, Tony; Wang, Yanbin

    2016-01-01

    The low-velocity zone (LVZ) is a persistent seismic feature in a broad range of geological contexts. It coincides in depth with the asthenosphere, a mantle region of lowered viscosity that may be essential to enabling plate motions. The LVZ has been proposed to originate from either partial melting or a change in the rheological properties of solid mantle minerals. The two scenarios imply drastically distinct physical and geochemical states, leading to fundamentally different conclusions on the dynamics of plate tectonics. We report in situ ultrasonic velocity measurements on a series of partially molten samples, composed of mixtures of olivine plus 0.1 to 4.0 volume % of basalt, under conditions relevant to the LVZ. Our measurements provide direct compressional (VP) and shear (VS) wave velocities and constrain attenuation as a function of melt fraction. Mantle partial melting appears to be a viable origin for the LVZ, for melt fractions as low as ~0.2%. In contrast, the presence of volatile elements appears necessary to explaining the extremely high VP/VS values observed in some local areas. The presence of melt in LVZ could play a major role in the dynamics of plate tectonics, favoring the decoupling of the plate relative to the asthenosphere. PMID:27386548

  5. Experimental evidence supports mantle partial melting in the asthenosphere.

    Science.gov (United States)

    Chantel, Julien; Manthilake, Geeth; Andrault, Denis; Novella, Davide; Yu, Tony; Wang, Yanbin

    2016-05-01

    The low-velocity zone (LVZ) is a persistent seismic feature in a broad range of geological contexts. It coincides in depth with the asthenosphere, a mantle region of lowered viscosity that may be essential to enabling plate motions. The LVZ has been proposed to originate from either partial melting or a change in the rheological properties of solid mantle minerals. The two scenarios imply drastically distinct physical and geochemical states, leading to fundamentally different conclusions on the dynamics of plate tectonics. We report in situ ultrasonic velocity measurements on a series of partially molten samples, composed of mixtures of olivine plus 0.1 to 4.0 volume % of basalt, under conditions relevant to the LVZ. Our measurements provide direct compressional (V P) and shear (V S) wave velocities and constrain attenuation as a function of melt fraction. Mantle partial melting appears to be a viable origin for the LVZ, for melt fractions as low as ~0.2%. In contrast, the presence of volatile elements appears necessary to explaining the extremely high V P/V S values observed in some local areas. The presence of melt in LVZ could play a major role in the dynamics of plate tectonics, favoring the decoupling of the plate relative to the asthenosphere.

  6. Subduction-controlled mantle flow and seismic anisotropy in South America

    Science.gov (United States)

    Hu, Jiashun; Faccenda, Manuele; Liu, Lijun

    2017-07-01

    Seismic anisotropy records both the past and present deformation inside the solid Earth. In the mantle, seismic anisotropy is mainly attributed to the lattice preferred orientation (LPO) of mineral fabrics, caused by the shear deformation due to mantle flow. However, contributions from different tectonic processes remain debated, and a single geodynamic model that simultaneously explains the observed mantle structures and various seismic anisotropy measurements is still lacking. Here, we present a model for the Cenozoic subduction history in South America using a geodynamic simulation constrained by both past plate reconstructions and present mantle seismic structures. With a recently developed software package DRexS, we further predict azimuthal seismic anisotropy at different depths and generate synthetic shear wave splitting (SWS) measurements using the resulting mantle flow. Our results provide a good match to both depth-dependent surface wave anisotropy and various land-based SWS records. We find that the dominant control on seismic anisotropy in South America comes from subduction-induced mantle flow, where anisotropy below the subducting Nazca Plate aligns with plate-motion-induced Couette flow and that below the overriding South American Plate follows slab-induced Poiseuille flow. This large-scale mantle flow can be diverted by secondary slabs, such as that below the Antilles subduction zone. In contrast, the contribution to SWS from fossil continental anisotropy and from the effects due to mantle flow modulation by lithosphere thickness variation are minor. Upper-mantle fast seismic anomalies beneath the southern Atlantic margin should have close-to-neutral buoyancy in order to satisfy the observed seismic anisotropy.

  7. Plate tectonics, damage and inheritance.

    Science.gov (United States)

    Bercovici, David; Ricard, Yanick

    2014-04-24

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

  8. Relations between plate kinematics, slab geometry and overriding plate deformation in subduction zones: insights from statistical observations and laboratory modelling

    Science.gov (United States)

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

    2005-12-01

    3-D laboratory models have been performed in order to investigate the way plates kinematics (subducting and overriding plate absolute motions and the resulting plate convergence rate) influences the geometry of the slab and the overriding plate deformation in subduction zones. In the experiments a viscous plate of silicone (subducting plate) is pushed beneath another plate, which is itself pushed toward or pulled away from the trench (overriding plate), and sinks into a viscous layer of glucose syrup (upper mantle). The subducting and overriding plate velocities explored the variability field of natural subduction plates kinematics. The overriding plate motion exerts a primary role in the control of slab geometries and overriding plate deformation rates. The experiments have revealed two different subduction behaviours: (Style I) the overriding plate moves toward the trench and shortens at high rates, the slab is flat and deflected when reaching the bottom of the box in a forward direction; (Style II) the overriding plates moves away from the trench and shortens at low rates the slab is steep and deflected on the box bottom in a backward direction. To a lesser extent, increasing subducting plate motion is associated to increasing slab dips and overriding plate shortening. Slab geometry and overriding plate deformation are less sensitive to the overall plate convergence rate. These laboratory models behaviours are consistent with statistical analysis performed on natural subduction zones, and enlighten the first order control exerted by the overriding plate absolute motion, on the geometry adopted by the slab and the way the overriding plate deforms.

  9. Continent-sized anomalous zones with low seismic velocity at the base of Earth's mantle

    Science.gov (United States)

    Garnero, Edward J.; McNamara, Allen K.; Shim, Sang-Heon

    2016-07-01

    Seismic images of Earth's interior reveal two massive anomalous zones at the base of the mantle, above the core, where seismic waves travel slowly. The mantle materials that surround these anomalous regions are thought to be composed of cooler rocks associated with downward advection of former oceanic tectonic plates. However, the origin and composition of the anomalous provinces is uncertain. These zones have long been depicted as warmer-than-average mantle materials related to convective upwelling. Yet, they may also be chemically distinct from the surrounding mantle, and potentially partly composed of subducted or primordial material, and have therefore been termed thermochemical piles. From seismic, geochemical and mineral physics data, the emerging view is that these thermochemical piles appear denser than the surrounding mantle materials, are dynamically stable and long-lived, and are shaped by larger-scale mantle flow. Whether remnants of a primordial layer or later accumulations of more-dense materials, the composition of the piles is modified over time by stirring and by chemical reactions with material from the surrounding mantle, underlying core and potentially from volatile elements transported into the deep Earth by subducted plates. Upwelling mantle plumes may originate from the thermochemical piles, so the unusual chemical composition of the piles could be the source of distinct trace-element signatures observed in hotspot lavas.

  10. Plate tectonics and hotspots: the third dimension.

    Science.gov (United States)

    Anderson, D L; Tanimoto, T; Zhang, Y S

    1992-06-19

    High-resolution seismic tomographic models of the upper mantle provide powerful new constraints on theories of plate tectonics and hotspots. Midocean ridges have extremely low seismic velocities to a depth of 100 kilometers. These low velocities imply partial melting. At greater depths, low-velocity and high-velocity anomalies record, respectively, previous positions of migrating ridges and trenches. Extensional, rifting, and hotspot regions have deep (> 200 kilometers) low-velocity anomalies. The upper mantle is characterized by vast domains of high temperature rather than small regions surrounding hotspots; the asthenosphere is not homogeneous or isothermal. Extensive magmatism requires a combination of hot upper mantle and suitable lithospheric conditions. High-velocity regions of the upper 200 kilometers of the mantle correlate with Archean cratons.

  11. Crustal thickness controlled by plate tectonics

    DEFF Research Database (Denmark)

    Artemieva, Irina M.; Meissner, Rolf

    2012-01-01

    The continental crust on Earth cannot be extracted directly from the mantle, and the primary crust extracted directly from an early magma ocean is not preserved on Earth. We review geophysical and geochemical aspects of global crust–mantle material exchange processes and examine the processes which...... magmatism. While both subduction and delamination recycle crustal material into the mantle, mafic magmatism transports mantle material upward and participates in growth of newoceanic and continental crusts and significant structural and chemicalmodification of the latter. We discuss the role of basalt....../gabbro–eclogite phase transition in crustal evolution and the links between lithosphere recycling, mafic magmatism, and crustal underplating. We advocate that plate tectonics processes, togetherwith basalt/gabbro–eclogite transition, limit crustal thickness worldwide by providing effective mechanisms of crustal...

  12. Tomography images of the Alpine roots and surrounding upper mantle

    Science.gov (United States)

    Plomerova, Jaroslava; Babuska, Vladislav

    2017-04-01

    Teleseismic body-wave tomography represents powerful tool to study regional velocity structure of the upper mantle and to image velocity anomalies, such as subducted lithosphere plates in collisional zones. In this contribution, we recapitulate 3D models of the upper mantle beneath the Alps, which developed at a collision zone of the Eurasian and African plates. Seismic tomography studies indicate a leading role of the rigid mantle lithosphere that functioned as a major stress guide during the plate collisions. Interactions of the European lithosphere with several micro-plates in the south resulted in an arcuate shape of this mountain range on the surface and in a complicated geometry of the Alpine subductions in the mantle. Early models with one bended lithosphere root have been replaced with more advanced models showing two separate lithosphere roots beneath the Western and Eastern Alps (Babuska et al., Tectonophysics 1990; Lippitsch et al., JGR 2003). The standard isotropic velocity tomography, based on pre-AlpArray data (the currently performed passive seismic experiment in the Alps and surroundings) images the south-eastward dipping curved slab of the Eurasian lithosphere in the Western Alps. On the contrary, beneath the Eastern Alps the results indicate a very steep northward dipping root that resulted from the collision of the European plate with the Adriatic microplate. Dando et al. (2011) interpret high-velocity heterogeneities at the bottom of their regional tomographic model as a graveyard of old subducted lithospheres. High density of stations, large amount of rays and dense ray-coverage of the volume studied are not the only essential pre-requisites for reliable tomography results. A compromise between the amount of pre-processed data and the high-quality of the tomography input (travel-time residuals) is of the high importance as well. For the first time, the existence of two separate roots beneath the Alps has been revealed from carefully pre

  13. Subduction controls the distribution and fragmentation of Earth’s tectonic plates.

    Science.gov (United States)

    Mallard, Claire; Coltice, Nicolas; Seton, Maria; Müller, R Dietmar; Tackley, Paul J

    2016-07-07

    The theory of plate tectonics describes how the surface of Earth is split into an organized jigsaw of seven large plates of similar sizes and a population of smaller plates whose areas follow a fractal distribution. The reconstruction of global tectonics during the past 200 million years suggests that this layout is probably a long-term feature of Earth, but the forces governing it are unknown. Previous studies, primarily based on the statistical properties of plate distributions, were unable to resolve how the size of the plates is determined by the properties of the lithosphere and the underlying mantle convection. Here we demonstrate that the plate layout of Earth is produced by a dynamic feedback between mantle convection and the strength of the lithosphere. Using three-dimensional spherical models of mantle convection that self-consistently produce the plate size–frequency distribution observed for Earth, we show that subduction geometry drives the tectonic fragmentation that generates plates. The spacing between the slabs controls the layout of large plates, and the stresses caused by the bending of trenches break plates into smaller fragments. Our results explain why the fast evolution in small back-arc plates reflects the marked changes in plate motions during times of major reorganizations. Our study opens the way to using convection simulations with plate-like behaviour to unravel how global tectonics and mantle convection are dynamically connected.

  14. Subduction controls the distribution and fragmentation of Earth’s tectonic plates

    Science.gov (United States)

    Mallard, Claire; Coltice, Nicolas; Seton, Maria; Müller, R. Dietmar; Tackley, Paul J.

    2016-07-01

    The theory of plate tectonics describes how the surface of Earth is split into an organized jigsaw of seven large plates of similar sizes and a population of smaller plates whose areas follow a fractal distribution. The reconstruction of global tectonics during the past 200 million years suggests that this layout is probably a long-term feature of Earth, but the forces governing it are unknown. Previous studies, primarily based on the statistical properties of plate distributions, were unable to resolve how the size of the plates is determined by the properties of the lithosphere and the underlying mantle convection. Here we demonstrate that the plate layout of Earth is produced by a dynamic feedback between mantle convection and the strength of the lithosphere. Using three-dimensional spherical models of mantle convection that self-consistently produce the plate size-frequency distribution observed for Earth, we show that subduction geometry drives the tectonic fragmentation that generates plates. The spacing between the slabs controls the layout of large plates, and the stresses caused by the bending of trenches break plates into smaller fragments. Our results explain why the fast evolution in small back-arc plates reflects the marked changes in plate motions during times of major reorganizations. Our study opens the way to using convection simulations with plate-like behaviour to unravel how global tectonics and mantle convection are dynamically connected.

  15. Trench migration, net rotation and slab mantle coupling

    Science.gov (United States)

    Funiciello, F.; Faccenna, C.; Heuret, A.; Lallemand, S.; Di Giuseppe, E.; Becker, T. W.

    2008-07-01

    Laboratory models have been conducted to improve our understanding of the role that the resistance of the slab to bending and its coupling to the ambient mantle play in subduction dynamics over geological time scales. Our models are set up with a viscous plate of silicone (lithosphere) subducting under negative buoyancy in a viscous layer of glucose syrup (mantle). For our study, the lithosphere/upper mantle viscosity contrast has been systematically varied, from ~ 10 to ~ 10 5 in order to explore the parameter space between weak and strong slab dynamics. We found that subduction is characterized by a retreating mode for viscosity ratios > 10 4, by the coexistence of a retreating mode and an advancing mode for viscosity ratios between ~ 10 4 and ~ 10 2, and quasi-stationary, Rayleigh-Taylor like behaviour for ratios < 10 2. By combining our experimental results and kinematic data from current subduction zones in four reference frames which differ in the amount of net rotation, we infer that a lithosphere/upper mantle viscosity contrast of 150-500 is necessary to obtain realistic trench/subducting plate velocity ratios as well as the variability of subduction styles observed in nature.

  16. Mantle hydrocarbons: abiotic or biotic?

    Science.gov (United States)

    Sugisaki, R; Mimura, K

    1994-06-01

    Analyses of 227 rocks from fifty localities throughout the world showed that mantle derived rocks such as tectonized peridotites in ophiolite sequences (tectonites) arid peridotite xenoliths in alkali basalts contain heavier hydrocarbons (n-alkanes), whereas igneous rocks produced by magmas such as gabbro arid granite lack them. The occurrence of hydrocarbons indicates that they were not derived either from laboratory contamination or from held contamination; these compounds found in the mantle-derived rocks are called here "mantle hydrocarbons." The existence of hydrocarbons correlates with petrogenesis. For example, peridotite cumulates produced by magmatic differentiation lack hydrocarbons whereas peridotite xenoliths derived from the mantle contain them. Gas chromatographic-mass spectrometric records of the mantle hydrocarbons resemble those of aliphatics in meteorites and in petroleum. Features of the hydrocarbons are that (a) the mantle hydrocarbons reside mainly along grain boundaries and in fluid inclusions of minerals; (b) heavier isoprenoids such as pristane and phytane are present; and (c) delta 13C of the mantle hydrocarbons is uniform (about -27%). Possible origins for the mantle hydrocarbons are as follows. (1) They were in organically synthesized by Fischer-Tropsch type reaction in the mantle. (2) They were delivered by meteorites and comets to the early Earth. (3) They were recycled by subduction. The mantle hydrocarbons in the cases of (1) and (2) are abiogenic and those in (3) are mainly biogenic. It appears that hydrocarbons may survive high pressures and temperatures in the mantle, but they are decomposed into lighter hydrocarbon gases such as CH4 at lower pressures when magmas intrude into the crust; consequently, peridotite cumulates do not contain heavier hydrocarbons but possess hydrocarbon gases up to C4H10.

  17. Lunar maria - result of mantle plume activity?

    Science.gov (United States)

    Sharkov, E.

    It is generally accepted that lunar maria are the result of catastrophic impact events. However, comparative studying of the Earth's and the Moon's tectonomagmatic evolution could evidence about another way of these specific structures origin. Such studies showed that the both planetary bodies evolved on the close scenario: their geological development began after solidification of global magmatic oceans which led to appearance of their primordial crusts: granitic on the Earth and anorthositic - on the Moon. The further evolution of the both bodies occurred in two stages. For their first stages, lasted ˜2.5 mlrd. years on the Earth and ˜1.5 mlrd. years on the Moon, were typical melts, generated in depleted mantle (Bogatikov et al., 2000). However, at the boundary 2.2-2.0 Ga ago on the Earth and 3.9-3.8 Ga on the Moon another type of magmas appeared: geochemical enriched Fe-Ti picrites and basalts, characteristic for the terrestrial Phanerozoic plume-related situations, and basaltic mare magmatism with high-Ti varieties on the Moon. It suggests that evolution of the Earth's magmatism was linked with ascending of mantle plumes (superplumes) of two generation: (1) generated in the mantle, depleted during solidification of magmatic ocean and Archean magmatic activity, and (2) generated at the core-mantle boundary (CMB). The latter were enriched in the mantle fluid components (Fe, Ti, alkalies, etc); this lighter material could ascend to shallower depths, leading to change of tectonic processes, in particular, to appearance of plate tectonics as the major type of tectonomagmatic activity till now (Bogatikov et al., 2000). By analogy to the Earth, magmatism of the Moon was also linked with ascending of mantle plumes: (1) generated in the depleted mantle (magnesian suite) and (2) generated at the lunar CMB with liquid at that time metallic core (mare basalt and picrites with high-Ti varieties). Like on the Earth, these plumes were lighter than the older plumes, and

  18. 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.

  19. The initiation, temporal evolution and dynamics of deep mantle heterogeneities

    Science.gov (United States)

    Bull-Aller, Abigail; Torsvik, Trond; Domeier, Mathew; Doubrovine, Pavel

    2013-04-01

    80% of all kimberlites erupted in the past 542 Myr lay, at the time of their eruption, above the edges of the African and Pacific LLSVPs. Such a finding requires both LLSVPs to be stationary in their present-day positions for at least the past 500 Ma, and thus be insensitive, to first-order, to the formation and subsequent break-up of the Pangean supercontinent. In this work, we investigate the temporal evolution and possible long-term persistence of LLSVPs by integrating plate tectonics into numerical models of mantle dynamics. We improve upon previous studies by employing a new palaeomagnetically-derived global plate motion data set to impose surface velocity boundary conditions for a time period which encompasses the creation and subsequent break-up of the Pangean supercontinent. We aim to understand the role that Earth's plate motion history plays on the development of LLSVPs within Earth's mantle. Specifically, we investigate the effect of plate history on the degree-2 structure of the mantle and explore the possibility that both LLSVPs existed prior to the Pangean supercontinent.

  20. History and Evolution of Precambrian plate tectonics

    Science.gov (United States)

    Fischer, Ria; Gerya, Taras

    2014-05-01

    Plate tectonics is a global self-organising process driven by negative buoyancy at thermal boundary layers. Phanerozoic plate tectonics with its typical subduction and orogeny is relatively well understood and can be traced back in the geological records of the continents. Interpretations of geological, petrological and geochemical observations from Proterozoic and Archean orogenic belts however (e.g., Brown, 2006), suggest a different tectonic regime in the Precambrian. Due to higher radioactive heat production the Precambrian lithosphere shows lower internal strength and is strongly weakened by percolating melts. The fundamental difference between Precambrian and Phanerozoic tectonics is therefore the upper-mantle temperature, which determines the strength of the upper mantle (Brun, 2002) and the further tectonic history. 3D petrological-thermomechanical numerical modelling experiments of oceanic subduction at an active plate at different upper-mantle temperatures show these different subduction regimes. For upper-mantle temperatures buckling and also lithospheric delamination and drip-offs. For upper-mantle temperatures > 250 K above the present day value no subduction occurs any more. The whole lithosphere is delaminating and due to strong volcanism and formation of a thicker crust subduction is inhibited. This stage of 200-250 K higher upper mantle temperature which corresponds roughly to the early Archean (Abbott, 1994) is marked by strong volcanism due to sublithospheric decompression melting which leads to an equal thickness for both oceanic and continental plates. As a consequence subduction is inhibited, but a compressional setup instead will lead to orogeny between a continental or felsic terrain and an oceanic or mafic terrain as well as internal crustal convection. Small-scale convection with plume shaped cold downwellings also in the upper mantle is of increased importance compared to the large-scale subduction cycle observed for present temperature

  1. Simple scaling relations in geodynamics:the role of pressure in mantle convection and plume formation

    Institute of Scientific and Technical Information of China (English)

    Don L. Anderson

    2004-01-01

    Scaling relations are important in extrapolating laboratory experiments to the Earth's mantle. In planetary interiors, compression becomes an important parameter and it is useful to explore scalings that involve volume. I use simple volume scaling relations that allow one to extrapolate laboratory experiments and upper mantle behavior, in a thermodynamically self-consistent way, to predict lower mantle behavior. The relations are similar to the quasi- harmonic approximation. Slabs and plates have characteristic dimensions of hundreds of kilometers and time constants of 100 million years, but the volume scalings predict order of magnitude higher values in the deep mantle. The scaling relations imply that the deep mantle is a sluggish system with ancient features. They imply irreversible chemical stratification and do not favor the plume hypothesis.

  2. Triggers and sources of volatile-bearing plumes in the mantle transition zone

    Institute of Scientific and Technical Information of China (English)

    Inna Safonova; Konstantin Litasov; Shigenori Maruyama

    2015-01-01

    The paper discusses generation of volatile-bearing plumes in the mantle transition zone (MTZ) in terms of mineral-fluid petrology and their related formation of numerous localities of intra-plate bimodal volcanic series in Central and East Asia. The plume generation in the MTZ can be triggered by the tectonic erosion of continental crust at Pacific-type convergent margins and by the presence of water and carbon dioxide in the mantle. Most probable sources of volatiles are the hydrated/carbonated sediments and basalts and serpentinite of oceanic slabs, which can be subducted down to the deep mantle. Tectonic erosion of continental crust supplies crustal material enriched in uranium and thorium into the mantle, which can serve source of heat in the MTZ. The heating in the MTZ induces melting of subducted slabs and continental crust and mantle upwelling, to produce OIB-type mafic and felsic melts, respectively.

  3. Triggers and sources of volatile-bearing plumes in the mantle transition zone

    Directory of Open Access Journals (Sweden)

    Inna Safonova

    2015-09-01

    Full Text Available The paper discusses generation of volatile-bearing plumes in the mantle transition zone (MTZ in terms of mineral-fluid petrology and their related formation of numerous localities of intra-plate bimodal volcanic series in Central and East Asia. The plume generation in the MTZ can be triggered by the tectonic erosion of continental crust at Pacific-type convergent margins and by the presence of water and carbon dioxide in the mantle. Most probable sources of volatiles are the hydrated/carbonated sediments and basalts and serpentinite of oceanic slabs, which can be subducted down to the deep mantle. Tectonic erosion of continental crust supplies crustal material enriched in uranium and thorium into the mantle, which can serve source of heat in the MTZ. The heating in the MTZ induces melting of subducted slabs and continental crust and mantle upwelling, to produce OIB-type mafic and felsic melts, respectively.

  4. Mantle Dynamics in Super-Earths: Post-Perovskite Rheology and Self-Regulation of Viscosity

    CERN Document Server

    Tackley, Paul J; Brodholt, John P; Dobson, David P; Valencia, Diana

    2012-01-01

    Simple scalings suggest that super-Earths are more likely than an equivalent Earth-sized planet to be undergoing plate tectonics. Generally, viscosity and thermal conductivity increase with pressure while thermal expansivity decreases, resulting in lower convective vigor in the deep mantle. According to conventional thinking, this might result in no convection in a super-Earth's deep mantle. Here we evaluate this. First, we here extend the density functional theory (DFT) calculations of post-perovskite activation enthalpy of to a pressure of 1 TPa. The activation volume for diffusion creep becomes very low at very high pressure, but nevertheless for the largest super-Earths the viscosity along an adiabat may approach 1030 Pa s in the deep mantle. Second, we use these calculated values in numerical simulations of mantle convection and lithosphere dynamics of planets with up to ten Earth masses. The models assume a compressible mantle including depth-dependence of material properties and plastic yielding induce...

  5. Trench-parallel flow beneath the nazca plate from seismic anisotropy.

    Science.gov (United States)

    Russo, R M; Silver, P G

    1994-02-25

    Shear-wave splitting of S and SKS phases reveals the anisotropy and strain field of the mantle beneath the subducting Nazca plate, Cocos plate, and the Caribbean region. These observations can be used to test models of mantle flow. Two-dimensional entrained mantle flow beneath the subducting Nazca slab is not consistent with the data. Rather, there is evidence for horizontal trench-parallel flow in the mantle beneath the Nazca plate along much of the Andean subduction zone. Trench-parallel flow is attributale utable to retrograde motion of the slab, the decoupling of the slab and underlying mantle, and a partial barrier to flow at depth, resulting in lateral mantle flow beneath the slab. Such flow facilitates the transfer of material from the shrinking mantle reservoir beneath the Pacific basin to the growing mantle reservoir beneath the Atlantic basin. Trenchparallel flow may explain the eastward motions of the Caribbean and Scotia sea plates, the anomalously shallow bathymetry of the eastern Nazca plate, the long-wavelength geoid high over western South America, and it may contribute to the high elevation and intense deformation of the central Andes.

  6. The language attitude of border peoples Insular Riau, West Kalimantan, East Kalimantan, North Sulawesi, and the Eastern Sunda Islands

    Directory of Open Access Journals (Sweden)

    Dendy Sugono

    2011-04-01

    Full Text Available This research aims at describing (1 the language use of border area societies (Insular Riau, West Kalimantan, East Kalimantan, North Sulawesi, and the Eastern Sunda Islands in terms of local language (BD, Indonesian (BI, and foreign language (BA in the domains of family, society, and occupation, (2 language activity of border area societies relating to news observation, language attention, and language constraints in mass media, (3 language attitude of border area societies towards BD, BI, and BA. The findings are as follows. First, within the family and society at large, BD is more frequently used than BI and BA. This shows that BD functions in non-formal situations. In the professional field, however, BI is more frequently used than BD. Second, people in border provinces widely observe mass media, whether printed or electronic. They also often pay attention to the language the mass media uses. Third, border societies have a positive attitude towards BD as is shown (agree/totally agree by the answers to eight questions relating to BD. The language attitude of border societies towards BI is positive based on the answers (agree/totally agree to seven questions concerning BI. This also means that BI is prestigious for border people, especially in formal communication. The language attitude of border societies towards BA is mixed. In as far as it is negative it implies a positive evaluation of BD and BI because people appreciate them as part of their local and national identities.

  7. New insights into regional tectonics of the Sunda-Banda Arcs region from integrated magnetic and gravity modelling

    Science.gov (United States)

    Zubaidah, Teti; Korte, Monika; Mandea, Mioara; Hamoudi, Mohamed

    2014-02-01

    The Lombok Island (Indonesia), situated along the Sunda-Banda Arcs transition region, lies between zones characterized by very large intensity magnetic anomalies. These anomalies have been noted as being part of the eight most important ones seen on the 1st edition of the World Digital Magnetic Anomaly Map. Unfortunately, only marine magnetic data of surroundings are available, and no regional high-resolution magnetic surveys of this island had been done. Since 2004, we have carried out several geomagnetic ground surveys in this region. Here, we present modelling results for a new geological and tectonic interpretation of the magnetic anomalies. The new results confirm the general pattern of contiguous negative-positive anomalies, revealing two active Quaternary normal faults and a magmatic arc related to a subduction region. This outcome agrees with earlier results in surrounding areas obtained by satellite, aeromagnetic, and marine platforms, and provides a more detailed picture of strong anomalies on this island. Considering both magnetic anomalies and gravity models, it is possible to suggest an extension of the Flores Thrust zone (reaching the northwest off the Lombok Island). The Flores Thrust zone may be considered as a mature subduction in the back arc region, showing a tendency of progressive subduction during last decades.

  8. Scent marking in Sunda clouded leopards (Neofelis diardi): novel observations close a key gap in understanding felid communication behaviours

    Science.gov (United States)

    Allen, Maximilian L.; Wittmer, Heiko U.; Setiawan, Endro; Jaffe, Sarah; Marshall, Andrew J.

    2016-01-01

    Intraspecific communication is integral to the behavioural ecology of solitary carnivores, but observing and quantifying their communication behaviours in natural environments is difficult. Our systematic literature review found that basic information on scent marking is completely lacking for 23% of all felid species, and information on 21% of other felid species comes solely from one study of captive animals. Here we present results of the first systematic investigation of the scent marking behaviours of Sunda clouded leopards in the wild. Our observations using motion-triggered video cameras in Indonesian Borneo are novel for clouded leopards, and contrary to previous descriptions of their behaviour. We found that clouded leopards displayed 10 distinct communication behaviours, with olfaction, scraping, and cheek rubbing the most frequently recorded. We also showed that males make repeated visits to areas they previously used for marking and that multiple males advertise and receive information at the same sites, potentially enhancing our ability to document and monitor clouded leopard populations. The behaviours we recorded are remarkably similar to those described in other solitary felids, despite tremendous variation in the environments they inhabit, and close a key gap in understanding and interpreting communication behaviours of clouded leopards and other solitary felids. PMID:27739507

  9. The mantle transition zone beneath the Afar Depression and adjacent regions: implications for mantle plumes and hydration

    Science.gov (United States)

    Reed, C. A.; Gao, S. S.; Liu, K. H.; Yu, Y.

    2016-06-01

    The Afar Depression and its adjacent areas are underlain by an upper mantle marked by some of the world's largest negative velocity anomalies, which are frequently attributed to the thermal influences of a lower-mantle plume. In spite of numerous studies, however, the existence of a plume beneath the area remains enigmatic, partially due to inadequate quantities of broad-band seismic data and the limited vertical resolution at the mantle transition zone (MTZ) depth of the techniques employed by previous investigations. In this study, we use an unprecedented quantity (over 14 500) of P-to-S receiver functions (RFs) recorded by 139 stations from 12 networks to image the 410 and 660 km discontinuities and map the spatial variation of the thickness of the MTZ. Non-linear stacking of the RFs under a 1-D velocity model shows robust P-to-S conversions from both discontinuities, and their apparent depths indicate the presence of an upper-mantle low-velocity zone beneath the entire study area. The Afar Depression and the northern Main Ethiopian Rift are characterized by an apparent 40-60 km depression of both MTZ discontinuities and a normal MTZ thickness. The simplest and most probable interpretation of these observations is that the apparent depressions are solely caused by velocity perturbations in the upper mantle and not by deeper processes causing temperature or hydration anomalies within the MTZ. Thickening of the MTZ on the order of 15 km beneath the southern Arabian Plate, southern Red Sea and western Gulf of Aden, which comprise the southward extension of the Afro-Arabian Dome, could reflect long-term hydration of the MTZ. A 20 km thinning of the MTZ beneath the western Ethiopian Plateau is observed and interpreted as evidence for a possible mantle plume stem originating from the lower mantle.

  10. Seismic velocity variations beneath central Mongolia: Evidence for upper mantle plumes?

    Science.gov (United States)

    Zhang, Fengxue; Wu, Qingju; Grand, Stephen P.; Li, Yonghua; Gao, Mengtan; Demberel, Sodnomsambuu; Ulziibat, Munkhuu; Sukhbaatar, Usnikh

    2017-02-01

    Central Mongolia is marked by wide spread recent volcanism as well as significant topographic relief even though it is far from any plate tectonic boundaries. The cause of the recent magmatism and topography remains uncertain partially because little is known of the underlying mantle seismic structure due to the lack of seismic instrumentation in the region. From August 2011 through August 2013, 69 broadband seismic stations were deployed in central Mongolia. Teleseismic traveltime residuals were measured using waveform correlation and were inverted to image upper mantle P and S velocity variations. Significant lateral variations in seismic velocity are imaged in the deep upper mantle (100 to 800 km depth). Most significant are two continuous slow anomalies from the deep upper mantle to near the surface. One slow feature has been imaged previously and may be a zone of deep upwelling bringing warm mantle to beneath the Hangay Dome resulting in uplift and magmatism including the active Khanuy Gol and Middle Gobi volcanoes. The second, deep low velocity anomaly is seen in the east from 800 to 150 km depth. The anomaly ends beneath the Gobi Desert that is found to have fast shallow mantle indicating a relatively thick lithosphere. We interpret the second deep slow anomaly as a mantle upwelling that is deflected by the thick Gobi Desert lithosphere to surrounding regions such as the Hentay Mountains to the north. The upwellings are a means of feeding warmer than normal asthenospheric mantle over a widely distributed region beneath Mongolia resulting in distributed volcanic activity and uplift. There is no indication that the upwellings are rooted in the deep lower mantle i.e. classic plumes. We speculate the upwellings may be related to deep subduction of the Pacific and Indian plates and are thus plumes anchored in the upper mantle.

  11. Mantle flow and dynamic topography associated with slab window opening: Insights from laboratory models

    Science.gov (United States)

    Guillaume, Benjamin; Moroni, Monica; Funiciello, Francesca; Martinod, Joseph; Faccenna, Claudio

    2010-12-01

    We present dynamically self-consistent mantle-scale laboratory models that have been conducted to improve our understanding of the influence of slab window opening on subduction dynamics, mantle flow and associated dynamic topography over geological time scales. The adopted setup consists of a two-layer linearly viscous system simulating the subduction of a fixed plate of silicone (lithosphere) under negative buoyancy in a viscous layer of glucose syrup (mantle). Our experimental setting is also characterized by a constant-width rectangular window located at the center of a laterally confined slab, modeling the case of the interaction of a trench-parallel spreading ridge with a wide subduction zone. We found that the opening of a slab window does not produce consistent changes of the geometry and the kinematics of the slab. On the contrary, slab-induced mantle circulation, quantified both in the vertical and horizontal sections using the Feature Tracking image analysis technique, is strongly modified. In particular, rollback subduction and the opening of the slab window generate a complex mantle circulation pattern characterized by the presence of poloidal and toroidal components, with the importance of each evolving according to kinematic stages. Mantle coming from the oceanic domain floods through the slab window, indenting the supra-slab mantle zone and producing its deformation without any mixing between mantle portions. The opening of the slab window and the upwelling of sub-slab mantle produce a regional-scale non-isostatic topographic uplift of the overriding plate that would correspond to values ranging between ca. 1 and 5 km in nature. Assuming that our modeling results can be representative of the natural behavior of subduction zones, we compared them to the tectonics and volcanism of the Patagonian subduction zone. We found that the anomalous backarc volcanism that has been developing since the middle Miocene could result from the lateral flow of sub

  12. Faulting within the Pacific plate at the Mariana Trench: Implications for plate interface coupling and subduction of hydrous minerals

    OpenAIRE

    Emry, E.L; Wiens, D.A; García-Castellanos, Daniel

    2014-01-01

    We investigate faulting within the incoming Pacific plate at the Mariana subduction trench to understand stresses within the bending plate, regional stresses acting upon the plate interface, and the extent of possible faulting-induced mantle serpentinization. We determine accurate depths by inverting teleseismic P and SH waveforms for earthquakes occurring during 1990-2011 with Global Centroid Moment Tensor (GCMT) solutions. For earthquakes with Mw 5.0+, we determine centroid depths and sourc...

  13. Geometry of the Cocos Plate Under North American Plate

    Science.gov (United States)

    Perez-Campos, X.

    2015-12-01

    The Cocos plate subducts under the North American plate with a complex geometry, and previous seismicity studies revealed some of this complexity. However, details of the geometry and the depth that the plate penetrates werelargely unknown. Since 2004, temporary experiments and the expansion of the permanent network of the Servicio Sismológico Nacional (SSN, Mexican National Seismological Service) have improved resolution of the plate geometry and have helped to map its descent into the upper mantle. Going from northwest to southeast, the Cocos plate appears to be fragmenting into north and south segments. The north segment subducts with an angle of ~30º and the south with an angle of ~10-15º. The transition is smooth near the trench and progresses to a tear at depth; this coincides with the projection of the Orozco Fracture Zone to depth. Also, this transition marks the limit of the presence to the south of an ultra slow velocity layer (USL) on top of the slab.South of this transition, the Cocos plate subducts horizontally , underplating the North American plate for a distance of ~140 to ~300 km from the trench. Along this horizontal region, silent slow events (SSE) and tectonic tremor (TT) have been observed. At a distance of 300 km from the trench (beneath central Mexico), the plate dives into the mantle with an angle of 76º to a depth of 500 km. This geometry changes abruptly to the south, marking the eastern limit of the USL. This change seems to be also characterized by a tear on the slab. Finally to the south, the Cocos plate subducts with a constant angle of 26º. This presentation summarizes the work of many contributors including A. Arciniega-Ceballos, M. Brudzinski, E. Cabral-Cano, T. Chen, R. Clayton,F. Cordoba-Montiel,P. Davis,S. Dougherty,F. Green, M. Gurnis, D. V. Helmberger, A. Husker,A. Iglesias, Y. Kim, V. Manea, D. Melgar, M. Rodríguez-Domínguez,S. K. Singh, T.-R. A. Song, C. M. Valdés-González, D. Valencia-Cabrera

  14. Spatial and Temporal Variability in the Circulation and Thermal Evolution of the Mantle in Subduction Zones: Insights From 3-D Laboratory Experiments.

    Science.gov (United States)

    Kincaid, C.; Griffiths, R. W.

    2003-12-01

    The subduction of oceanic lithosphere plays a key role in plate tectonics, the thermal evolution of the mantle and recycling processes between Earth's interior and surface. The majority of subduction models are two-dimensional (2-D), assuming limited variability in the direction parallel to the trench. Observationally based models increasingly appeal to three-dimensional (3-D) flow associated with trench migration and the sinking of oceanic plates with a translational component of motion (rollback). We report results from laboratory experiments that reveal fundamental differences in 3-D mantle circulation and temperature structure in response to subduction with and without a rollback component. In our experiments the upper mantle is simulated with glucose syrup and the subducting plate is represented with a Phenolic sheet that is forced to sink into the glucose along prescribed trajectories. An array of 40 thermisters embedded within the plate is used to monitor slab surface temperatures (SSTs). We vary the relative magnitude of downdip and translational components of slab motion and also consider cases where the plate steepens with time. Another parameter is the initial thickness of the thermal boundary layer (TBL) beneath the overriding plate. Without rollback motion, flow in the mantle wedge is sluggish, there is no mass flux around the plate, and plate edges heat up faster than plate centers. Rollback subduction drives flow around and beneath the sinking plate, velocities increase within the mantle wedge and are focussed towards the center of the plate and the surface of the plate heats more along the centerline. In addition to lateral variability in flow and mantle temperatures, results highlight temporal variability in SSTs and 3-D mantle flow trajectories associated with the initiation of subduction and variations between periods of predominantly downdip versus rollback sinking.

  15. Iron geochemistry of the mantle

    Science.gov (United States)

    Humayun, M.; Campbell, T. J.; Brandon, A. D.; Davis, F. A.; Hirschmann, M. M.

    2011-12-01

    The Fe/Mg ratio is an important constraint on the compositionally controlled density of the mantle. However, this ratio cannot be inferred from erupted lavas from OIB or MORB sources, but must be determined directly from mantle peridotites. Recently, the Fe/Mn ratio of erupted lavas has been used as an indicator of potential Fe variability in the mantle driven by core-mantle interaction, recycled oceanic crust, or even variations in the temperature of mantle melting. The classic compilation of McDonough & Sun (1995) provided the currently accepted Fe/Mn ratio of the upper mantle, 60±10. The uncertainty on this ratio allows for 15-30% variability in mantle iron abundances, which is equivalent to a density variation larger than observed by seismic tomography in the mantle. To better understand the relationship between mantle peridotites and erupted lavas, and to search for real variability in the Fe/Mn ratio of mantle peridotites, we report precise new ICP-MS measurements of the transition element geochemistry of suites of mantle xenoliths that have known Fe/Mg ratios. For 12 Kilbourne Hole xenoliths, we observe a clear correlation between Fe/Mn and MgO (or Fe/Mg) over an Fe/Mn range of 59-72. Extrapolation of this trend to a Primitive Mantle (PM) MgO content of 37.8 yields an Fe/Mn of 59±1 for the PM. Our new analyses of KLB-1 powder and fused glass beads yield an Fe/Mn of 61.4 for both samples, which plots on the Kilbourne Hole Fe/Mn vs. MgO trend. A set of ten xenoliths from San Carlos yield a wide range of Fe/Mn (56-65) not correlated with MgO content. The San Carlos xenoliths may have experienced a metasomatic effect that imprinted variable Fe/Mn. A clinopyroxene-rich lithology from San Carlos yields an Fe/Mn of 38, which plots on an extension of the Kilbourne Hole Fe/Mn vs. MgO trend. These new results, and those from other xenolith localities being measured in our lab, provide new constraints on the compositional variability of the Earth's upper mantle. Mc

  16. Water contents in pyroxenes of intraplate lithospheric mantle

    Science.gov (United States)

    Bonadiman, C.; Hao, Y.-T.; Coltorti, M.; Dallai, L.; Faccini, B.; Hu, H.; Qunke, X.

    2009-04-01

    Water contents of clinopyroxene and orthopyroxene in mantle peridotites from various xenolith occurrences in intraplate settings (both oceanic and continental) were determined by Fourier Transform Infrared Spectroscopy (FTIR). The localities are as follow: Sal Island (Cape Verde Archipelago); Baker Rocks and Greene Point (Northern Victoria Land, Antarctica); Panshishan and Lianshan (Subei Basin, Eastern China). They represent well-known localities where detailed petrographical and geochemical studies have already been carried out or areas which are currently under investigation. The water incorporated in these pyroxenes is low (cpx, 37-399ppm; opx: 9-166ppm)(or very low as in Greene Point, Antarctica; cpx, 5-16ppm; opx: 9-16ppm) and, among each population, no clear correlation with melting parameters (MgO contents) in single mineral is evident. Results are compared with the available literature data on water contents in mantle pyroxene which includes peridotites from on-craton (hosted by kimberlitic-type magmas) and off-craton (hosted by alkaline basic magmas), as well as subarc mantle settings. The "relatively dry" (cpx: 140-528 ppm; opx: 38-280 ppm) sub-arc mantle xenoliths (Peslier et al., 2002) are shown to be wetter than the intraplate (off-craton) xenoliths. Cratonic mantle pyroxenes are only represented by a few determinations on garnet peridotites and eclogite from Kaapvaal and Colorado Plateau. They record the highest water contents (cpx: 342-1012 ppm; opx: 180-491 ppm) so far measured in mantle pyroxenes from various tectonic settings. Despite the limited data set, the indication that the cratonic mantle is strongly hydrated is compelling. Rehydration for the Colorado Plateau craton may be due to the Farallon plate subduction (Li et al., 2008), while for Kaapvaal Craton it might be related to young (<100Ma) metasomatic enrichments (Griffin et al., 2003a; Kobussen et al., 2008). If this is the case then the Archean mantle water content needs to be

  17. A great thermal divergence in the mantle beginning 2.5 Ga: Geochemical constraints from greenstone basalts and komatiites

    Directory of Open Access Journals (Sweden)

    Kent C. Condie

    2016-07-01

    Full Text Available Greenstone basalts and komatiites provide a means to track both mantle composition and magma generation temperature with time. Four types of mantle are characterized from incompatible element distributions in basalts and komatiites: depleted, hydrated, enriched and mantle from which komatiites are derived. Our most important observation is the recognition for the first time of what we refer to as a Great Thermal Divergence within the mantle beginning near the end of the Archean, which we ascribe to thermal and convective evolution. Prior to 2.5 Ga, depleted and enriched mantle have indistinguishable thermal histories, whereas at 2.5–2.0 Ga a divergence in mantle magma generation temperature begins between these two types of mantle. Major and incompatible element distributions and calculated magma generation temperatures suggest that Archean enriched mantle did not come from mantle plumes, but was part of an undifferentiated or well-mixed mantle similar in composition to calculated primitive mantle. During this time, however, high-temperature mantle plumes from dominantly depleted sources gave rise to komatiites and associated basalts. Recycling of oceanic crust into the deep mantle after the Archean may have contributed to enrichment of Ti, Al, Ca and Na in basalts derived from enriched mantle sources. After 2.5 Ga, increases in Mg# in basalts from depleted mantle and decreases in Fe and Mn reflect some combination of growing depletion and cooling of depleted mantle with time. A delay in cooling of depleted mantle until after the Archean probably reflects a combination of greater radiogenic heat sources in the Archean mantle and the propagation of plate tectonics after 3 Ga.

  18. 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.

  19. Episodic plate tectonics on Venus

    Science.gov (United States)

    Turcotte, Donald

    1992-01-01

    Studies of impact craters on Venus from the Magellan images have placed important constraints on surface volcanism. Some 840 impact craters have been identified with diameters ranging from 2 to 280 km. Correlations of this impact flux with craters on the Moon, Earth, and Mars indicate a mean surface age of 0.5 +/- 0.3 Ga. Another important observation is that 52 percent of the craters are slightly fractured and only 4.5 percent are embayed by lava flows. These observations led researchers to hypothesize that a pervasive resurfacing event occurred about 500 m.y. ago and that relatively little surface volcanism has occurred since. Other researchers have pointed out that a global resurfacing event that ceased about 500 MYBP is consistent with the results given by a recent study. These authors carried out a series of numerical calculations of mantle convection in Venus yielding thermal evolution results. Their model considered crustal recycling and gave rapid planetary cooling. They, in fact, suggested that prior to 500 MYBP plate tectonics was active in Venus and since 500 MYBP the lithosphere has stabilized and only hot-spot volcanism has reached the surface. We propose an alternative hypothesis for the inferred cessation of surface volcanism on Venus. We hypothesize that plate tectonics on Venus is episodic. Periods of rapid plate tectonics result in high rates of subduction that cool the interior resulting in more sluggish mantle convection.

  20. A possible relict mantle wedge:Geochemical evidence from Paleogene volcanics in North China

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The major and trace element and isotopic composition were analyzed for the Paleogene volcanics in North China dated by the K-Ar method. The geochemical data show that most volcanics are in caic-alkaline series and the minor is in alkaline series. They differ obviously from Neogene and Quaternary volcanics in geochemistry. In particular, the Paleogene volcanics from the southern part of North China were derived from enriched lithospheric mantle (EMⅡ), which were likely to be a relict mantle wedge formed during the subduction of the Yangtze plate into the North China plate in late Triassic (Indo- Sinian).

  1. Mapping the mass distribution of Earth's mantle using satellite-derived gravity gradients

    Science.gov (United States)

    Panet, Isabelle; Pajot-Métivier, Gwendoline; Greff-Lefftz, Marianne; Métivier, Laurent; Diament, Michel; Mandea, Mioara

    2014-02-01

    The dynamics of Earth's mantle are not well known. Deciphering mantle flow patterns requires an understanding of the global distribution of mantle density. Seismic tomography has been used to derive mantle density distributions, but converting seismic velocities into densities is not straightforward. Here we show that data from the GOCE (Gravity field and steady-state Ocean Circulation Explorer) mission can be used to probe our planet's deep mass structure. We construct global anomaly maps of the Earth's gravitational gradients at satellite altitude and use a sensitivity analysis to show that these gravitational gradients image the geometry of mantle mass down to mid-mantle depths. Our maps highlight north-south-elongated gravity gradient anomalies over Asia and America that follow a belt of ancient subduction boundaries, as well as gravity gradient anomalies over the central Pacific Ocean and south of Africa that coincide with the locations of deep mantle plumes. We interpret these anomalies as sinking tectonic plates and convective instabilities between 1,000 and 2,500km depth, consistent with seismic tomography results. Along the former Tethyan Margin, our data also identify an east-west-oriented mass anomaly likely in the upper mantle. We suggest that by combining gravity gradients with seismic and geodynamic data, an integrated dynamic model for Earth can be achieved.

  2. The crustal and upper mantle structure around the Gulf of California, inferred from surface wave data and receiver functions

    NARCIS (Netherlands)

    de Vos, D.

    2016-01-01

    This thesis reports on studies that have been carried out to better image the crustal and upper mantle shear velocity structure around the Gulf of California, Mexico. The Gulf of California forms a part of the plate boundary between the Pacific and North-American plates, where transform motion in th

  3. Anatomy of mantle plumes: hot heads and cold stems

    Science.gov (United States)

    Davaille, A. B.; Kumagai, I.; Vatteville, J.; Touitou, F.; Brandeis, G.

    2012-12-01

    Recent petrological studies show evidences for secular cooling in mantle plumes: the source temperature of oceanic plateaus could be 100°C hotter than the source temperature of volcanic island chains (Herzberg and Gazel, Nature, 2009). In terms of mantle plumes, it would mean that the temperature of the plume head is hotter than that of the plume stem. This is at odd with a model where a plume head would entrain so much ambient mantle on its journey towards the Earth's surface that it would end up being considerably colder than its narrow stem. So we revisited the problem using laboratory experiments and new visualization techniques to measure in situ simultaneously the temperature, velocity and composition fields. At time t=0, a hot instability is created by heating a patch of a given radius at constant power or constant temperature. The fluids are mixtures of sugar syrups , with a strongly temperature-dependent viscosity, and salt. Rayleigh numbers were varied from 104 to 108, viscosity ratios between 1.8 and 4000, and buoyancy ratios between 0 and 2. After a stage where heat transport is by conduction only, the hot fluid gathers in a sphere and begins to rise, followed by a stem anchored on the hot patch. In all cases, temperatures in the head start with higher values than in the subsequent stem. This is also the case for the thermal instabilities rising from a infinite plate heated uniformly. However, the head also cools faster than the stem as they rise, so that they will eventually have the same temperature if the mantle is deep enough. Moreover, all the material sampled by partial melting in the plume head or stem would be coming from the heated area around the deep source, and very little entrainment from the ambient mantle is predicted. The difference in temperature between head and stem strongly depends on the mantle depth, the viscosity ratio and the buoyancy ratio. Our scaling laws predict that Earth's mantle plumes can indeed have hot heads and colder

  4. Importance of initial buoyancy field on evolution of mantle thermal structure: Implications of surface boundary conditions

    Directory of Open Access Journals (Sweden)

    Petar Glišović

    2015-01-01

    Full Text Available Although there has been significant progress in the seismic imaging of mantle heterogeneity, the outstanding issue that remains to be resolved is the unknown distribution of mantle temperature anomalies in the distant geological past that give rise to the present-day anomalies inferred by global tomography models. To address this question, we present 3-D convection models in compressible and self-gravitating mantle initialised by different hypothetical temperature patterns. A notable feature of our forward convection modelling is the use of self-consistent coupling of the motion of surface tectonic plates to the underlying mantle flow, without imposing prescribed surface velocities (i.e., plate-like boundary condition. As an approximation for the surface mechanical conditions before plate tectonics began to operate we employ the no-slip (rigid boundary condition. A rigid boundary condition demonstrates that the initial thermally-dominated structure is preserved, and its geographical location is fixed during the evolution of mantle flow. Considering the impact of different assumed surface boundary conditions (rigid and plate-like on the evolution of thermal heterogeneity in the mantle we suggest that the intrinsic buoyancy of seven superplumes is most-likely resolved in the tomographic images of present-day mantle thermal structure. Our convection simulations with a plate-like boundary condition reveal that the evolution of an initial cold anomaly beneath the Java-Indonesian trench system yields a long-term, stable pattern of thermal heterogeneity in the lowermost mantle that resembles the present-day Large Low Shear Velocity Provinces (LLSVPs, especially below the Pacific. The evolution of subduction zones may be, however, influenced by the mantle-wide flow driven by deeply-rooted and long-lived superplumes since Archean times. These convection models also detect the intrinsic buoyancy of the Perm Anomaly that has been identified as a unique

  5. Reaction-induced rheological weakening enables oceanic plate subduction

    Science.gov (United States)

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

    2016-08-01

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

  6. Whole planet coupling between climate, mantle, and core: Implications for rocky planet evolution

    Science.gov (United States)

    Foley, Bradford J.; Driscoll, Peter E.

    2016-05-01

    Earth's climate, mantle, and core interact over geologic time scales. Climate influences whether plate tectonics can take place on a planet, with cool climates being favorable for plate tectonics because they enhance stresses in the lithosphere, suppress plate boundary annealing, and promote hydration and weakening of the lithosphere. Plate tectonics plays a vital role in the long-term carbon cycle, which helps to maintain a temperate climate. Plate tectonics provides long-term cooling of the core, which is vital for generating a magnetic field, and the magnetic field is capable of shielding atmospheric volatiles from the solar wind. Coupling between climate, mantle, and core can potentially explain the divergent evolution of Earth and Venus. As Venus lies too close to the sun for liquid water to exist, there is no long-term carbon cycle and thus an extremely hot climate. Therefore, plate tectonics cannot operate and a long-lived core dynamo cannot be sustained due to insufficient core cooling. On planets within the habitable zone where liquid water is possible, a wide range of evolutionary scenarios can take place depending on initial atmospheric composition, bulk volatile content, or the timing of when plate tectonics initiates, among other factors. Many of these evolutionary trajectories would render the planet uninhabitable. However, there is still significant uncertainty over the nature of the coupling between climate, mantle, and core. Future work is needed to constrain potential evolutionary scenarios and the likelihood of an Earth-like evolution.

  7. Expansion dating: calibrating molecular clocks in marine species from expansions onto the Sunda Shelf Following the Last Glacial Maximum.

    Science.gov (United States)

    Crandall, Eric D; Sbrocco, Elizabeth J; Deboer, Timery S; Barber, Paul H; Carpenter, Kent E

    2012-02-01

    The rate of change in DNA is an important parameter for understanding molecular evolution and hence for inferences drawn from studies of phylogeography and phylogenetics. Most rate calibrations for mitochondrial coding regions in marine species have been made from divergence dating for fossils and vicariant events older than 1-2 My and are typically 0.5-2% per lineage per million years. Recently, calibrations made with ancient DNA (aDNA) from younger dates have yielded faster rates, suggesting that estimates of the molecular rate of change depend on the time of calibration, decaying from the instantaneous mutation rate to the phylogenetic substitution rate. aDNA methods for recent calibrations are not available for most marine taxa so instead we use radiometric dates for sea-level rise onto the Sunda Shelf following the Last Glacial Maximum (starting ∼18,000 years ago), which led to massive population expansions for marine species. Instead of divergence dating, we use a two-epoch coalescent model of logistic population growth preceded by a constant population size to infer a time in mutational units for the beginning of these expansion events. This model compares favorably to simpler coalescent models of constant population size, and exponential or logistic growth, and is far more precise than estimates from the mismatch distribution. Mean rates estimated with this method for mitochondrial coding genes in three invertebrate species are elevated in comparison to older calibration points (2.3-6.6% per lineage per million years), lending additional support to the hypothesis of calibration time dependency for molecular rates.

  8. Redox conditions for mantle plumes

    Science.gov (United States)

    Heister, L. E.; Lesher, C. E.

    2005-12-01

    The vanadium to scandium ratio (V/Sc) for basalts from mid-ocean ridge (MOR) and arc environments has been proposed as a proxy for fO2 conditions during partial melting (e.g. [1] and [2]). Contrary to barometric measurements of the fO2 of primitive lavas, the V/Sc ratio of the upper mantle at mid-ocean ridges and arcs is similar, leading previous authors to propose that the upper mantle has uniform redox potential and is well-buffered. We have attempted to broaden the applicability of the V/Sc parameter to plume-influenced localities (both oceanic and continental), where mantle heterogeneities associated with recycled sediments, mafic crust, and metasomatized mantle, whether of shallow or deep origin, exist. We find that primitive basalts from the North Atlantic Igneous Province (NAIP), Hawaii (both the Loa and Kea trends), Deccan, Columbia River, and Siberian Traps show a range of V/Sc ratios that are generally higher (average ~9) than those for MOR (average ~ 6.7) or arc (average ~7) lavas. Based on forward polybaric decompression modeling, we attribute these differences to polybaric melting and melt segregation within the garnet stability field rather than the presence of a more oxidized mantle in plume-influenced settings. Like MORB, the V/Sc ratios for plume-influenced basalts can be accounted for by an oxidation state approximately one log unit below the Ni-NiO buffer (NNO-1). Our analysis suggests that source heterogeneities have little, if any, resolvable influence on mantle redox conditions, although they have significant influence on the trace element and isotopic composition of mantle-derived melts. We suggest that variations in the redox of erupted lavas is largely a function of shallow lithospheric processes rather than intrinsic to the mantle source, regardless of tectonic setting. [1] Li and Lee (2004) EPSL, [2] Lee et al. (2005) J. of Petrology

  9. The influence of deep mantle heterogeneity on the rhythms and scales of surface topography evolution

    Science.gov (United States)

    Arnould, Maëlis; Coltice, Nicolas; Flament, Nicolas

    2016-04-01

    Earth's surface, the interface between external processes and internal dynamics (lithosphere motions and mantle convection), is continuously reorganised. A large part of Earth's topography is generated by mantle motions and lithospheric stresses [1], which impacts for instance the global sea-level, the dynamics of sedimentary basins and the geoid. Studying how surface topography evolves in both space and time thus not only provides information on the rhythms and scales of evolution of those processes, but would also be a tool for the study of the mantle motions and properties from which it originates [2]. In this study, we propose to characterise the spatial and temporal scales of evolution of surface topography in 2D spherical annulus numerical models of mantle convection developing a plate-like behaviour. We use the geodynamical code StagYY [3] to first determine a mantle convection regime generating a surface topography with Earth-like amplitudes and realistic mantle dynamics at first order (e.g. high Rayleigh number, reasonable lithosphere thickness, pseudo-plastic lithosphere rheology generating plate tectonics). We then use this convection regime to investigate how the presence of stable deep-rooted thermochemical heterogeneities influence the rhythms of evolution of surface topography. We analyse our results to identify how the timescales of evolution are connected with the lengthscales of topography, in light of the tectonic histories produced by the models. References: [1] M. Gurnis, Long-term controls of eustatic and epeirogenic motions by mantle convection, GSA Today, 2(7):141-157, 1992. [2] B.H. Hager, R.W. Clayton, M.A. Richards, R.P. Comer, and A.M. Dziewonski, Lower mantle heterogeneity, dynamic topography and the geoid, Nature, 313:541-545, 1985. [3] J.W. Hernlund and P.J. Tackley, Modeling mantle convection in the spherical annulus, Phys. Earth Planet. Interiors, 171(1):48-54, 2008.

  10. Passive margins getting squeezed in the mantle convection vice

    Science.gov (United States)

    Husson, Laurent; Yamato, Philippe; Becker, Thorsten; Pedoja, Kevin

    2013-04-01

    Quaternary coastal geomorphology reveals that passive margins underwent wholesale uplift at least during the glacial cycle. In addition, these not-so-passive margins often exhibit long term exhumation and tectonic inversion, which suggest that compression and tectonic shortening could be the mechanism that triggers their overall uplift. We speculate that the compression in the lithosphere gradually increased during the Cenozoic. The many mountain belts at active margins that accompany this event readily witness this increase. Less clear is how that compression increase affects passive margins. In order to address this issue, we design minimalist 2D viscous models to quantify the impact of plate collision on the stress regime. In these models, a sluggish plate is disposed on a less viscous mantle. It is driven by a "mantle conveyor belt" alternatively excited by lateral shear stresses that represent a downwelling on one side, an upwelling on the other side, or both simultaneously. The lateral edges of the plate are either free or fixed, respectively representing the cases of free convergence and collision. In practice, it dramatically changes the upper boundary condition for mantle circulation and subsequently, for the stress field. The flow pattern transiently evolves almost between two end-members, starting from a situation close to a Couette flow to a pattern that looks like a Poiseuille flow with an almost null velocity at the surface (though in the models, the horizontal velocity at the surface is not strictly null, as the lithosphere deforms). In the second case, the lithosphere is highly stressed horizontally and deforms. For an equivalent bulk driving force, compression increases drastically at passive margins if upwellings are active because they push plates towards the collision. Conversely, if only downwellings are activated, compression occurs on one half of the plate and extension on the other half, because only the downwelling is pulling the plate

  11. Outer rise seismicity of the subducting Nazca Plate: Plate stress distribution, fault orientation and plate hydration

    Science.gov (United States)

    Barama, Louisa

    Subduction of the Nazca plate beneath the South American plate drives frequent and sometimes large magnitude earthquakes. During the past 40 years, significant numbers of outer rise earthquakes have occurred in the offshore regions of Colombia and Chile. In this study, we investigate the distribution of stress due to lithospheric bending and the extent of faults within the subducting plate. To calculate more accurate epicenters and to constrain which earthquakes occurred within the outer rise, we use hypocentroidal decomposition to relocate earthquakes with Global Centroid Moment Tensor (GCMT) solutions occurring after 1976 offshore Colombia and Chile. We determine centroid depths of outer rise earthquakes by inverting teleseismic P-, SH-, and SV- waveforms for earthquakes occurring from 1993 to 2014 with Mw ≥ 5.5. In order to further constrain the results of the waveform inversion, we estimate depths by comparing earthquake duration, amplitude, and arrival times for select stations with waveforms with good signal to noise ratios. Our results indicate that tensional earthquakes occur at depths down to 13 km and 24 km depth beneath the surface in the Colombia and Chile regions, respectively. Since faulting within the outer rise can make the plate susceptible to hydration and mantle serpentinization, we therefore infer the extent of possible hydration of the Nazca plate to extend no deeper than the extent of tensional outer rise earthquakes.

  12. Mantle Volatiles - Distribution and Consequences

    Science.gov (United States)

    Luth, R. W.

    2003-12-01

    Volatiles in the mantle have, for many years, been the subject of intensive study from a number of perspectives. They are of interest because of their potential effects on melting relationships, on transport of major and trace elements, and on the rheological and other physical properties of the mantle. By convention, "volatiles" in this context are constituents that are liquid or gaseous at normal Earth surface conditions. This review will look at the behavior of C-O-H-S-halogen volatiles, beginning with H2O and C-O volatiles.There have been tremendous strides made recently towards understanding how volatiles in general and water in particular is transported and stored in the mantle. This progress is based on research on a number of fronts: studies of mantle-derived samples have provided insight into the nature and occurrence of hydrous phases such as amphibole, mica, and chlorite, and have provided constraints on the capacity of nominally anhydrous minerals (NAMs) such as olivine, pyroxenes, and garnet to contain "water" by a variety of substitution mechanisms. Experimental studies on mantle-derived magmas have provided constraints on volatile contents in their source regions. Other studies have constrained the pressure, temperature, and composition conditions over which hydrous phases are stable in the mantle.Fundamental questions remain about the geochemical cycling of volatiles in the mantle, and between the mantle and the surface. Much attention has focused on the capability of hydrous phases such as amphibole, mica, serpentine, chlorite, and a family of "dense hydrous magnesian silicates" (DHMSs) to act as carriers of water in subducting slabs back into the mantle. It has been clear since the work of Ito et al. (1983) that there is a discrepancy between the amount of volatiles subducted into the mantle and those returned to the surface by arc magmatism. A recent overview of volatile cycling in subduction systems by Bebout (1996) suggests that 5-15% of the H2

  13. The Large-scale Component of Mantle Convection

    Science.gov (United States)

    Cserepes, L.

    Circulation in the Earth's mantle occurs on multiple spatial scales: this review dis- cusses the character of its large-scale or global components. Direct and strong evi- dence concerning the global flow comes, first of all, from the pattern of plate motion. Further indirect observational data which can be transformed into flow velocities by the equation of motion are the internal density heterogeneities revealed by seismic to- mography, and the geoid can also be used as an observational constraint. Due to their limited spatial resolution, global tomographic data automatically filter out the small- scale features and are therefore relevant to the global flow pattern. Flow solutions obtained from tomographic models, using the plate motion as boundary condition, re- veal that subduction is the downwelling of the global mantle circulation and that the deep-rooted upwellings are concentrated in 2-3 superplumes. Spectral analysis of the tomographic heterogeneities shows that the power of global flow appears dominantly in the lowest spherical harmonic orders 2-5. Theoretical convection calculations con- tribute substantially to the understanding of global flow. If basal heating of the mantle is significant, numerical models can reproduce the basic 2 to 5 cell pattern of con- vection even without the inclusion of surface plates. If plates are superimposed on the solution with their present arrangement and motion, the dominance of these low spherical harmonic orders is more pronounced. The cells are not necessarily closed, rather they show chaotic time-dependence, but they are normally bordered by long downwelling features, and they have usually a single superplume in the cell interior. Swarms of small plumes can develop in the large cells, especially when convection is partially layered due to an internal boundary such as the 670 km discontinuity (source of small plumes). These small plumes are usually tilted by the background large-scale flow which shows that they are

  14. Mantle xenoliths from Marosticano area (Northern Italy): a comparison with Veneto Volcanic Province lithospheric mantle

    Science.gov (United States)

    Brombin, Valentina; Bonadiman, Costanza; Coltorti, Massimo

    2016-04-01

    The Tertiary Magmatic Province of Veneto, known as Veneto Volcanic Province (VVP), in the North-East of Italy, represents the most important volcanic distric of Adria Plate. It is composed by five volcanic bodies: Val d'Adige, Marosticano, Mts. Lessini, Berici Hills and Euganean Hills. Most of the volcanic products are relatively undifferentiated lavas and range in composition from nephelinites to tholeiites. Often VVP nephelinites and basanites carry mantle xenoliths (mainly harzburgites and lherzolite). This study reports petrological comparison between Marosticano xenoliths (new outcrop) and xenoliths from the Lessinean and Val d'Adige areas already studied by many Authors (Siena & Coltorti 1989; Beccaluva et al., 2001, Gasperini et al., 2006). Mineral major elements analyses show that the Marosticano lherzolites and harzburgites reflect "more restitic" composition than the mantle domain beneath the other VVP districts (Lessini Mts. and Val d'Adige). In fact, olivine and pyroxene of Marosticano xenoliths have the highest mg# values of the entire district (Marosticano→90-93; literature→86-92). At comparable mg# (45-85 wt%) Marosticano spinels tend to be higher in Cr2O3 (23-44 wt%) contents with respect to the other VVP sp (7-25 wt%). It is worth noting that, Ni contents of Marosticano olivines in both harzburgites and lherzolites are higher (2650-3620 ppm) than those of the Lessinean xenoliths (1500- 3450 ppm), and similar to that of Val d'Adige lherzolites (3000-3500 ppm), approaching the contents of Archean cratonic mantle (Kelemen, 1998). In turn, Lessinean olivines properly fall in the Ni-mg# Phanerozoic field. At fixed pressure of 15 kbar, the equilibration temperature of Marosticano xenoliths are similar (Brey & Köhler: 920-1120°C) to those of Lessini (O'Neill & Wall: 990-1110°C; Beccaluva et al., 2007), but higher than those of Val d'Adige (Wells: 909-956°C; Gasperini et al., 2006). Finally, Marosticano mantle fragment show similar relatively high

  15. Kinematics and dynamics of the East Pacific Rise linked to a stable, deep-mantle upwelling.

    Science.gov (United States)

    Rowley, David B; Forte, Alessandro M; Rowan, Christopher J; Glišović, Petar; Moucha, Robert; Grand, Stephen P; Simmons, Nathan A

    2016-12-01

    Earth's tectonic plates are generally considered to be driven largely by negative buoyancy associated with subduction of oceanic lithosphere. In this context, mid-ocean ridges (MORs) are passive plate boundaries whose divergence accommodates flow driven by subduction of oceanic slabs at trenches. We show that over the past 80 million years (My), the East Pacific Rise (EPR), Earth's dominant MOR, has been characterized by limited ridge-perpendicular migration and persistent, asymmetric ridge accretion that are anomalous relative to other MORs. We reconstruct the subduction-related buoyancy fluxes of plates on either side of the EPR. The general expectation is that greater slab pull should correlate with faster plate motion and faster spreading at the EPR. Moreover, asymmetry in slab pull on either side of the EPR should correlate with either ridge migration or enhanced plate velocity in the direction of greater slab pull. Based on our analysis, none of the expected correlations are evident. This implies that other forces significantly contribute to EPR behavior. We explain these observations using mantle flow calculations based on globally integrated buoyancy distributions that require core-mantle boundary heat flux of up to 20 TW. The time-dependent mantle flow predictions yield a long-lived deep-seated upwelling that has its highest radial velocity under the EPR and is inferred to control its observed kinematics. The mantle-wide upwelling beneath the EPR drives horizontal components of asthenospheric flows beneath the plates that are similarly asymmetric but faster than the overlying surface plates, thereby contributing to plate motions through viscous tractions in the Pacific region.

  16. Decoupled crust-mantle accommodation of Africa-Eurasia convergence in the NW Moroccan margin

    OpenAIRE

    Jiménez-Munt, Ivone; Fernandez, Manel; Vergés, Jaume; García-Castellanos, Daniel; Fullea, J.; M. Pérez-Gussinyé; Afonso, Juan Carlos

    2011-01-01

    The extent of the area accommodating convergence between the African and Iberian plates, how this convergence is partitioned between crust and mantle, and the role of the plate boundary in accommodating deformation are not well-understood subjects. We calculate the structure of the lithosphere derived from its density distribution along a profile running from the Tagus Abyssal Plain to the Sahara Platform and crossing the Gorringe Bank, the NW Moroccan margin, and the Atlas Mountains. The mod...

  17. A model for the evolution of the Earth's mantle structure since the Early Paleozoic

    Science.gov (United States)

    Zhang, Nan; Zhong, Shijie; Leng, Wei; Li, Zheng-Xiang

    2010-06-01

    Seismic tomography studies indicate that the Earth's mantle structure is characterized by African and Pacific seismically slow velocity anomalies (i.e., superplumes) and circum-Pacific seismically fast anomalies (i.e., a globally spherical harmonic degree 2 structure). However, the cause for and time evolution of the African and Pacific superplumes and the degree 2 mantle structure remain poorly understood with two competing proposals. First, the African and Pacific superplumes have remained largely unchanged for at least the last 300 Myr and possibly much longer. Second, the African superplume is formed sometime after the formation of Pangea (i.e., at 330 Ma) and the mantle in the African hemisphere is predominated by cold downwelling structures before and during the assembly of Pangea, while the Pacific superplume has been stable for the Pangea supercontinent cycle (i.e., globally a degree 1 structure before the Pangea formation). Here, we construct a proxy model of plate motions for the African hemisphere for the last 450 Myr since the Early Paleozoic using the paleogeographic reconstruction of continents constrained by paleomagnetic and geological observations. Coupled with assumed oceanic plate motions for the Pacific hemisphere, this proxy model for the plate motion history is used as time-dependent surface boundary condition in three-dimensional spherical models of thermochemical mantle convection to study the evolution of mantle structure, particularly the African mantle structure, since the Early Paleozoic. Our model calculations reproduce well the present-day mantle structure including the African and Pacific superplumes and generally support the second proposal with a dynamic cause for the superplume structure. Our results suggest that while the mantle in the African hemisphere before the assembly of Pangea is predominated by the cold downwelling structure resulting from plate convergence between Gondwana and Laurussia, it is unlikely that the bulk of

  18. Coupling between mantle and surface processes: Insights from analogue modelling

    Science.gov (United States)

    Király, Ágnes; Sembroni, Andrea; Faccenna, Claudio; Funiciello, Francesca

    2014-05-01

    Thermal or density anomalies located beneath the lithosphere are thought to generate dynamic topography. Such a topographic signal compensates the viscous stresses originating from the anomaly driven mantle flow. It has been demonstrated that the erosion modulates the dynamic signal of topography changing the uplift rate by unload. The characteristic time for adjustments of dynamic topography due to surface erosion is likely similar to post-glacial rebound time (10000 - 50000 years). Here we present preliminary results of a new set of analogue models realized to study and quantify the contribution given by erosion to dynamic topography, during a process specifically driven by a positively buoyant deep anomaly. The adopted set up consists of a Plexiglas box (40x40x50 cm3) filled with glucose syrup as analogue upper mantle. A silicon plate positioned on the top of the syrup simulates the lithosphere. On the silicone plate is placed a thin layer of a high viscous glucose syrup which reproduces the upper, erodible layer of the crust. To simulate the positively buoyant anomaly we used an elastic, undeformable silicon ball free to rise by buoyancy in the syrup until the floating silicone plate is hit. The changes in topography have been monitored by using a 3D laser scan, while a side-view camera recorded the position of the rising ball in time. Data have been post-processed with image analysis techniques (e.g., Particle Image Velocimetry) in order to obtain the evolution of topography, uplift rate, erosion patterns of the top layer, bulge width and mantle circulation during the experiment. We ran experiments with and without the shallow, erodible crustal layer in order to quantify the effect of erosion on dynamic topography. Preliminary results showed that both the maximum topography and uplift rate are inversely proportional to the lithospheric thickness. The maximum uplift rate and the deformation of the lithospheric plate occurred just before the arrival of the

  19. A window for plate tectonics in terrestrial planet evolution?

    Science.gov (United States)

    O'Neill, Craig; Lenardic, Adrian; Weller, Matthew; Moresi, Louis; Quenette, Steve; Zhang, Siqi

    2016-06-01

    The tectonic regime of a planet depends critically on the contributions of basal and internal heating to the planetary mantle, and how these evolve through time. We use viscoplastic mantle convection simulations, with evolving core-mantle boundary temperatures, and radiogenic heat decay, to explore how these factors affect tectonic regime over the lifetime of a planet. The simulations demonstrate (i) hot, mantle conditions, coming out of a magma ocean phase of evolution, can produce a "hot" stagnant-lid regime, whilst a cooler post magma ocean mantle may begin in a plate tectonic regime; (ii) planets may evolve from an initial hot stagnant-lid condition, through an episodic regime lasting 1-3 Gyr, into a plate-tectonic regime, and finally into a cold, senescent stagnant lid regime after ∼10 Gyr of evolution, as heat production and basal temperatures wane; and (iii) the thermal state of the post magma ocean mantle, which effectively sets the initial conditions for the sub-solidus mantle convection phase of planetary evolution, is one of the most sensitive parameters affecting planetary evolution - systems with exactly the same physical parameters may exhibit completely different tectonics depending on the initial state employed. Estimates of the early Earth's temperatures suggest Earth may have begun in a hot stagnant lid mode, evolving into an episodic regime throughout most of the Archaean, before finally passing into a plate tectonic regime. The implication of these results is that, for many cases, plate tectonics may be a phase in planetary evolution between hot and cold stagnant states, rather than an end-member.

  20. Large gem diamonds from metallic liquid in Earth’s deep mantle

    Science.gov (United States)

    Smith, Evan M.; Shirey, Steven B.; Nestola, Fabrizio; Bullock, Emma S.; Wang, Jianhua; Richardson, Stephen H.; Wang, Wuyi

    2016-12-01

    The redox state of Earth’s convecting mantle, masked by the lithospheric plates and basaltic magmatism of plate tectonics, is a key unknown in the evolutionary history of our planet. Here we report that large, exceptional gem diamonds like the Cullinan, Constellation, and Koh-i-Noor carry direct evidence of crystallization from a redox-sensitive metallic liquid phase in the deep mantle. These sublithospheric diamonds contain inclusions of solidified iron-nickel-carbon-sulfur melt, accompanied by a thin fluid layer of methane ± hydrogen, and sometimes majoritic garnet or former calcium silicate perovskite. The metal-dominated mineral assemblages and reduced volatiles in large gem diamonds indicate formation under metal-saturated conditions. We verify previous predictions that Earth has highly reducing deep mantle regions capable of precipitating a metallic iron phase that contains dissolved carbon and hydrogen.

  1. Initial Feasibility Study to Drill and Core the Ocean Mantle

    Directory of Open Access Journals (Sweden)

    Nicolas Pilisi

    2011-09-01

    Full Text Available An initial feasibility study (Pilisi and Whitney, 2011 of drilling through the Mohorovičić discontinuity (Moho into the oceanic mantle specifically focused on future requirements for planning, drilling and coring a hole 500 m into the oceanic mantle from three candidate locations in the Pacific Ocean (Cocos Plate, Baja California, and offshore Hawaii. The study points out some of the critical issues that need to be resolved before embarking upon such a challengingproject. It was conducted on the basis of data provided by the Integrated Ocean Drilling Program–Management International (IODP-MI, the Center for Deep Earth Exploration (CDEX operating the drilling vessel Chikyu within IODP, public domain information, and past experience that Blade Energy Partners (hereafter mentioned as “Blade”; http://www.blade-energy.com/ has had with frontier projects in the offshore deepwater oil and gas and geothermal industries.

  2. Sinking of spherical slablets through a non-Newtonian mantle

    Science.gov (United States)

    Crameri, Fabio; Stegman, Dave; Petersen, Robert; Tackley, Paul

    2014-05-01

    The dominant driving force for plate tectonics is slab pull, in which sinking slabs pull the trailing plate. Forward plate velocities are typically similar in magnitude (7 cm/yr) as estimates for sinking velocities of slabs through the upper mantle. However, these estimates are based on data for slabs that are coherent into the transition zone as well as models that considered the upper mantle to be entirely Newtonian. Dislocation creep in the upper mantle can strongly influence mantle flow, and is likely activated for flow around vertically sinking slabs in the uppermost mantle. Thus, it is possible that in some scenarios, a non-Newtonian mantle will have an influence on plate motions but it is unclear to what degree. To address this question, we investigate how the non-Newtonian rheology modifies the sinking velocities of slablets (spherical, negatively buoyant and highly viscous blobs). The model set-up is similar to a Stokes sphere sinking, but is in 2-D cartesian with temperature-and stress-dependent rheology. For these numerical models, we use the Stag-YY code (e.g., Tackley 2008) and apply a pseudo-free surface using the 'sticky-air' approach (Matsumoto and Tomoda 1983; Schmeling et al, 2008, Crameri et al., 2012). The sinking blob is both highly viscous and compositionally dense, but is the same temperature as the background fluid which eliminates thermal diffusion and associated variations in thermal buoyancy. The model domain is 2x1 or 4x1 and allows enough distance to the sidewalls so that sinking velocities are not influenced by the boundary conditions. We compare our results with those previously obtained for salt diapirs rising through a power-law rheology mantle/crust (Weinberg, 1993; Weinberg and Podladchikov, 1994), which provided both numerical and analytic results. Previous results indicate a speed-up of an order of magnitude is possible. Finally, we then extend the models and analysis to mantle convection systems that include for single

  3. Energy of plate tectonics calculation and projection

    Directory of Open Access Journals (Sweden)

    N. H. Swedan

    2013-02-01

    Full Text Available Mathematics and observations suggest that the energy of the geological activities resulting from plate tectonics is equal to the latent heat of melting, calculated at mantle's pressure, of the new ocean crust created at midocean ridges following sea floor spreading. This energy varies with the temperature of ocean floor, which is correlated with surface temperature. The objective of this manuscript is to calculate the force that drives plate tectonics, estimate the energy released, verify the calculations based on experiments and observations, and project the increase of geological activities with surface temperature rise caused by climate change.

  4. The fate of the slabs interacting with a density/viscosity hill in the mid-mantle

    Science.gov (United States)

    Morra, G.; Yuen, D. A.; Boschi, L.; Chatelain, P.; Koumoutsakos, P.; Tackley, P. J.

    2010-06-01

    In the last two decades it has been proposed several times that a non-monotonic profile might fit the average lower mantle radial viscosity. Most proposed profiles consist in a more or less broad viscosity hill in the middle of the mantle, at a depth roughly between 1200 km and 2000 km. Also many tomographic models display strong signals of the presence of "fast" material lying at mid mantle depths and a recent spectral analysis of seismic tomography shows a very clear transition for degree up to around 16 at a less than 1500 km depth. Finally latest works, both theoretical and experimental, on the high-to-low-spin transition for periclase, have suggested that the high-spin to low-spin transition of Fe++ might lie at the heart of all these observations. To verify the dynamical compatibility between possible mantle profile and observed tomographic images and compare them with possible mineral physics scenarios, such as the spin transition, we employ here a recently developed Fast Multipole-accelerated Boundary Element Method (FMM-BEM), a numerical approach for solving the viscous momentum equation in a global spherical setting, for simulating the interaction of an individual slab with a mid mantle smooth discontinuity in density and viscosity. We have focused on the complexities induced to the behaviour of average and very large plates O (2000-10,000 km), characteristic of the Farallon, Tethys and Pacific plate subducting during the Cenozoic, demonstrating that the a mid mantle density and/or viscosity discontinuity produces a strong alteration of the sinking velocity and an intricate set of slab morphologies. We also employ the Kula-Farallon plate system subducting at 60 Ma as a paradigmatic case, which reveals the best high resolution tomography models and clearly suggests an interaction with a strong and/or denser layer in the mantle. Our 38 models show that a plate might or might not penetrate into the lowest mantle and might stall in the mid lower mantle for

  5. Melt transport rates in heterogeneous mantle beneath mid-ocean ridges

    CERN Document Server

    Weatherley, Samuel M

    2015-01-01

    Recent insights to melt migration beneath ridges suggest that channelized flow is a consequence of melting of a heterogeneous mantle, and that spreading rate modulates the dynamics of the localized flow. A corollary of this finding is that both mantle het- erogeneity and spreading rate have implications for the speed and time scale of melt migration. Here, we investigate these implications using numerical models of magma flow in heterogeneous mantle beneath spreading plates. The models predict that a broad distribution of magma flow speeds is characteristic of the sub-ridge mantle. Within the melting region, magmatic flow is fastest in regions of average fusibility; surprisingly, magmas from sources of above-average fusibility travel to the ridge in a longer time. Spreading rate has comparatively simple consequences, mainly resulting in faster segregation speeds at higher spreading rates. The computed time scales are short enough to preserve deep origin 230Th disequilibria and, under favourable parameter regi...

  6. Fine scale heterogeneity in the Earth's upper mantle - observation and interpretation

    DEFF Research Database (Denmark)

    Thybo, Hans

    2014-01-01

    can be correlated to main plate tectonic features, such as oceanic spreading centres, continental rift zones and subducting slabs. Much seismological mantle research is now concentrated on imaging fine scale heterogeneity, which may be detected and imaged with high-resolution seismic data with dense......High resolution seismic data has over the last decade provided significant evidence for pronounced fine scale heterogeneity in the Earth’s mantle at an unprecedented detail. Seismic tomography developed tremendously during the last 20-30 years. The results show overall structure in the mantle which...... station spacing and at high frequency, e.g. from the Russian Peaceful Nuclear Explosion (PNE) data set and array recordings of waves from natural seismic sources. Mantle body waves indicate pronounced heterogeneity at three depth levels whereas other depth intervals appear transparent, at least...

  7. Deformation and melt in natural mantle rocks: The Hilti Massif (Oman) and the Othris Massif (Greece)

    NARCIS (Netherlands)

    Dijkstra, A.H.

    2001-01-01

    For a full understanding of plate tectonics, one of the central paradigms in Earth Sciences, it is critical to know the mechanical properties of the material of which the earth's upper mantle consists, i.e., peridotite. The cold outer shell of the Earth, the lithosphere, is broken up into strong and

  8. Seismic Anisotropy and Mantle Flow Driven by the Cocos Slab Under Southern Mexico

    Science.gov (United States)

    Bernal-López, Leslie A.; Garibaldi, Berenice R.; León Soto, Gerardo; Valenzuela, Raúl W.; Escudero, Christian R.

    2016-10-01

    Shear wave splitting measurements were made using SKS and SKKS waves recorded by the Meso-American Subduction Experiment, which was deployed in southern Mexico starting at the coast of the Pacific Ocean and running north toward the Gulf of Mexico. In this segment of the Middle America Trench the oceanic Cocos plate subducts under the continental North American plate. The active volcanic arc is located at the southern end of the Trans-Mexican Volcanic Belt. Unlike most subduction zones, however, the volcanic arc is not subparallel to the trench. In the fore-arc, between the trench and the Trans-Mexican Volcanic Belt, the Cocos slab subducts subhorizontally. Beneath the volcanic belt, however, the slab dives steeply into the mantle. A marked difference in the orientation of the fast polarization directions is observed between the fore-arc and the back-arc. In the fore-arc the fast axes determined using SKS phases are oriented NE-SW, in the same direction as the relative motion between the Cocos and North American plates, and are approximately perpendicular to the trench. Physical conditions in the subslab mantle are consistent with the existence of A-type olivine and consequently entrained mantle flow is inferred. Strong coupling between the slab and the surrounding mantle is observed. In the back-arc SKS fast polarization directions are oriented N-S and are perpendicular to the strike of the slab. Given the high temperatures in the mantle wedge tip, the development of A-type, or similar, olivine fabric throughout the mantle wedge is expected. The orientation of the fast axes is consistent with corner flow in the mantle wedge.

  9. The 2016 Case for Mantle Plumes and a Plume-Fed Asthenosphere (Augustus Love Medal Lecture)

    Science.gov (United States)

    Morgan, Jason P.

    2016-04-01

    The process of science always returns to weighing evidence and arguments for and against a given hypothesis. As hypotheses can only be falsified, never universally proved, doubt and skepticism remain essential elements of the scientific method. In the past decade, even the hypothesis that mantle plumes exist as upwelling currents in the convecting mantle has been subject to intense scrutiny; from geochemists and geochronologists concerned that idealized plume models could not fit many details of their observations, and from seismologists concerned that mantle plumes can sometimes not be 'seen' in their increasingly high-resolution tomographic images of the mantle. In the place of mantle plumes, various locally specific and largely non-predictive hypotheses have been proposed to explain the origins of non-plate boundary volcanism at Hawaii, Samoa, etc. In my opinion, this debate has now passed from what was initially an extremely useful restorative from simply 'believing' in the idealized conventional mantle plume/hotspot scenario to becoming an active impediment to our community's ability to better understand the dynamics of the solid Earth. Having no working hypothesis at all is usually worse for making progress than having an imperfect and incomplete but partially correct one. There continues to be strong arguments and strong emerging evidence for deep mantle plumes. Furthermore, deep thermal plumes should exist in a mantle that is heated at its base, and the existence of Earth's (convective) geodynamo clearly indicates that heat flows from the core to heat the mantle's base. Here I review recent seismic evidence by French, Romanowicz, and coworkers that I feel lends strong new observational support for the existence of deep mantle plumes. I also review recent evidence consistent with the idea that secular core cooling replenishes half the mantle's heat loss through its top surface, e.g. that the present-day mantle is strongly bottom heated. Causes for

  10. Evidence for multiple magma ocean outgassing and atmospheric loss episodes from mantle noble gases

    CERN Document Server

    Tucker, Jonathan M

    2014-01-01

    The energy associated with giant impacts is large enough to generate global magma oceans during Earth's accretion. However, geochemical evidence requiring a terrestrial magma ocean is scarce. Here we present evidence for at least two separate magma ocean outgassing episodes on Earth based on the ratio of primordial 3He to 22Ne in the present-day mantle. We demonstrate that the depleted mantle 3He/22Ne ratio is at least 10 while a more primitive mantle reservoir has a 3He/22Ne ratio of 2.3 to 3. The 3He/22Ne ratios of the mantle reservoirs are higher than possible sources of terrestrial volatiles, including the solar nebula ratio of 1.5. Therefore, a planetary process must have raised the mantle's 3He/22Ne ratio. We show that long-term plate tectonic cycling is incapable of raising the mantle 3He/22Ne ratio and may even lower it. However, ingassing of a gravitationally accreted nebular atmosphere into a magma ocean on the proto-Earth explains the 3He/22Ne and 20Ne/22Ne ratios of the primitive mantle reservoir....

  11. Mantle plumes in the vicinity of subduction zones

    Science.gov (United States)

    Mériaux, C. A.; Mériaux, A.-S.; Schellart, W. P.; Duarte, J. C.; Duarte, S. S.; Chen, Z.

    2016-11-01

    We present three-dimensional deep-mantle laboratory models of a compositional plume within the vicinity of a buoyancy-driven subducting plate with a fixed trailing edge. We modelled front plumes (in the mantle wedge), rear plumes (beneath the subducting plate) and side plumes with slab/plume systems of buoyancy flux ratio spanning a range from 2 to 100 that overlaps the ratios in nature of 0.2-100. This study shows that 1) rising side and front plumes can be dragged over thousands of kilometres into the mantle wedge, 2) flattening of rear plumes in the trench-normal direction can be initiated 700 km away from the trench, and a plume material layer of lesser density and viscosity can ultimately almost entirely underlay a retreating slab after slab/plume impact, 3) while side and rear plumes are not tilted until they reach ∼600 km depth, front plumes can be tilted at increasing depths as their plume buoyancy is lessened, and rise at a slower rate when subjected to a slab-induced downwelling, 4) rear plumes whose buoyancy flux is close to that of a slab, can retard subduction until the slab is 600 km long, and 5) slab-plume interaction can lead to a diversity of spatial plume material distributions into the mantle wedge. We discuss natural slab/plume systems of the Cascadia/Bowie-Cobb, and Nazca/San Felix-Juan Fernandez systems on the basis of our experiments and each geodynamic context and assess the influence of slab downwelling at depths for the starting plumes of Java, Coral Sea and East Solomon. Overall, this study shows how slab/plume interactions can result in a variety of geological, geophysical and geochemical signatures.

  12. Transcurrent reactivation of Australia's western passive margin: An example of intraplate deformation from the central Indo-Australian plate

    Science.gov (United States)

    Hengesh, J. V.; Whitney, B. B.

    2016-05-01

    Australia's northwestern passive margin intersects the eastern termination of the Java trench segment of the Sunda arc subduction zone and the western termination of Timor trough along the Banda arc tectonic collision zone. Differential relative motion between the Sunda arc subduction zone and the Banda arc collision zone has reactivated the former rifted margin of northwestern Australia evidenced by Pliocene to Quaternary age deformation along a 1400 km long offshore fault system. The fault system has higher rates of seismicity than the adjacent nonextended crustal terranes, has produced the largest historical earthquake in Australia (1941 ML 7.3 Meeberrie event), and is dominated by focal mechanism solutions consistent with dextral motion along northeast trending fault planes. The faults crosscut late Miocene unconformities that are eroded across middle Miocene inversion structures suggesting multiple phases of Neogene and younger fault reactivation. Onset of deformation is consistent with the timing of the collision of the Scott Plateau part of the passive continental margin with the former Banda trench between 3.0 Ma and present. The range of estimated maximum horizontal slip rates across the zone is ~1.4 to 2.6 mm yr-1, at the threshold of geodetically detectable motion, yet significant with respect to an intraplate tectonic setting. The folding and faulting along this part of the continental margin provides an example of intraplate deformation resulting from kinematic transitions along a distant plate boundary and demonstrates the presence of a youthful evolving intraplate fault system within the Indo-Australian plate.

  13. Rogue mantle helium and neon.

    Science.gov (United States)

    Albarède, Francis

    2008-02-15

    The canonical model of helium isotope geochemistry describes the lower mantle as undegassed, but this view conflicts with evidence of recycled material in the source of ocean island basalts. Because mantle helium is efficiently extracted by magmatic activity, it cannot remain in fertile mantle rocks for long periods of time. Here, I suggest that helium with high 3He/4He ratios, as well as neon rich in the solar component, diffused early in Earth's history from low-melting-point primordial material into residual refractory "reservoir" rocks, such as dunites. The difference in 3He/4He ratios of ocean-island and mid-ocean ridge basalts and the preservation of solar neon are ascribed to the reservoir rocks being stretched and tapped to different extents during melting.

  14. Numerical modelling of volatiles in the deep mantle

    Science.gov (United States)

    Eichheimer, Philipp; Thielmann, Marcel; Golabek, Gregor J.

    2017-04-01

    The transport and storage of water in the mantle significantly affects several material properties of mantle rocks and thus water plays a key role in a variety of geodynamical processes (tectonics, magmatism etc.). The processes driving transport and circulation of H2O in subduction zones remain a debated topic. Geological and seismological observations suggest different inflow mechanisms of water e.g. slab bending, thermal cracking and serpentinization (Faccenda et al., 2009; Korenaga, 2017), followed by dehydration of the slab. On Earth both shallow and steep subduction can be observed (Li et al., 2011). However most previous models (van Keken et al., 2008; Wilson et al., 2014) did not take different dip angles and subduction velocities of slabs into account. To which extent these parameters and processes influence the inflow of water still remains unclear. We present 2D numerical models simulating the influence of the various water inflow mechanisms on the mantle with changing dip angle and subduction velocity of the slab over time. The results are used to make predictions regarding the rheological behavior of the mantle wedge, dehydration regimes and volcanism at the surface. References: van Keken, P. E., et al. A community benchmark for subduction zone modeling. Phys. Earth Planet. Int. 171, 187-197 (2008). Faccenda, M., T.V. Gerya, and L. Burlini. Deep slab hydration induced by bending-related variations in tectonic pressure. Nat. Geosci. 2, 790-793 (2009). Korenaga, J. On the extent of mantle hydration caused by plate bending. Earth Planet. Sci. Lett. 457, 1-9 (2017). Wilson, C. R., et al. Fluid flow in subduction zones: The role of solid rheology and compaction pressure. Earth Planet. Sci. Lett. 401, 261-274 (2014). Li, Z. H., Z. Q. Xu, and T. V. Gerya. Flat versus steep subduction: Contrasting modes for the formation and exhumation of high- to ultrahigh-pressure rocks in continental collision zones. Earth Planet. Sci. Lett. 301, 65-77 (2011).

  15. Along-strike variation in subducting plate velocity induced by along-strike variation in overriding plate structure: Insights from 3D numerical models

    Science.gov (United States)

    Rodríguez-González, Juan; Billen, Magali I.; Negredo, Ana M.; Montesi, Laurent G. J.

    2016-10-01

    Subduction dynamics can be understood as the result of the balance between driving and resisting forces. Previous work has traditionally regarded gravitational slab pull and viscous mantle drag as the main driving and resistive forces for plate motion respectively. However, this paradigm fails to explain many of the observations in subduction zones. For example, subducting plate velocity varies significantly along-strike in many subduction zones and this variation is not correlated to the age of subducting lithosphere. Here we present three-dimensional and time-dependent numerical models of subduction. We show that along-strike variations of the overriding plate thermal structure can lead to along-strike variations in subducting plate velocity. In turn, velocity variations lead to significant migration of the Euler pole over time. Our results show that the subducting plate is slower beneath the colder portion of the overriding plate due to two related mechanisms. First, the mantle wedge beneath the colder portion of the overriding plate is more viscous, which increases mantle drag. Second, where the mantle wedge is more viscous, hydrodynamic suction increases, leading to a lower slab dip. Both factors contribute to decreasing subducting plate velocity in the region; therefore, if the overriding plate is not uniform, the resulting velocity varies significantly along-strike, which causes the Euler pole to migrate closer to the subducting plate. We present a new mechanism to explain observations of subducting plate velocity in the Cocos and Nazca plates. These results shed new light on the balance of forces that control subduction dynamics and prove that future studies should take into consideration the three-dimensional structure of the overriding plate.

  16. Alignment between seafloor spreading directions and absolute plate motions through time

    Science.gov (United States)

    Williams, Simon E.; Flament, Nicolas; Müller, R. Dietmar

    2016-02-01

    The history of seafloor spreading in the ocean basins provides a detailed record of relative motions between Earth's tectonic plates since Pangea breakup. Determining how tectonic plates have moved relative to the Earth's deep interior is more challenging. Recent studies of contemporary plate motions have demonstrated links between relative plate motion and absolute plate motion (APM), and with seismic anisotropy in the upper mantle. Here we explore the link between spreading directions and APM since the Early Cretaceous. We find a significant alignment between APM and spreading directions at mid-ocean ridges; however, the degree of alignment is influenced by geodynamic setting, and is strongest for mid-Atlantic spreading ridges between plates that are not directly influenced by time-varying slab pull. In the Pacific, significant mismatches between spreading and APM direction may relate to a major plate-mantle reorganization. We conclude that spreading fabric can be used to improve models of APM.

  17. Continental tectonics in the aftermath of plate tectonics

    Science.gov (United States)

    Molnar, Peter

    1988-01-01

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

  18. Continental tectonics in the aftermath of plate tectonics

    Science.gov (United States)

    Molnar, Peter

    1988-01-01

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

  19. When Did Plate Tectonics Begin

    Science.gov (United States)

    Brown, M.

    2015-12-01

    Present-day plate tectonics on Earth is characterized by asymmetric (one-sided) subduction, but how do we recognize the imprint of subduction in the geologic record? How do we weigh global (commonly younger) vs local (commonly older) datasets or distinguish initiation from episodic from continuous subduction? How reliable are data gaps? Characteristics of the Paleozoic record of subduction include calc-alkaline magmatism, blueschist/UHP metamorphism and collisional orogenesis, and ophiolites as representatives of former ocean lithosphere. Are these characteristic rocks preserved in Proterozoic, Archean and Hadean crust? Does a hotter mantle, higher heat production and weaker lithosphere modify or eliminate these features? What preceded subduction and how do we recognize that regime? Are rock associations or geochemical fingerprints reliable? Does reworking and overprinting modify geochemical fingerprints? Proposals for the start of plate tectonics have been based on: persistence of isotope anomalies/fractionated chemical domains in the mantle; changes in chemistry of magmatic rocks, rates of crustal growth vs reworking, and sites of growth; the metamorphic record, particularly the first appearance of contrasting thermal gradients or eclogite (including evidence from mineral inclusions in diamonds) or UHP metamorphic rocks; stabilization of cratonic lithosphere and formation of supercratons, and the beginning of the Proterozoic supercontinent cycle; the end of the flat Earth, emergence of continents, development of significant topography, changes in the style of orogeny and the rise in atmospheric oxygen; and, the appearance of passive margins and changes in the style of sedimentation. Estimates of the timing have varied from the Hadean to Neoproterozoic. I will summarize evidence for a growing consensus that the late Mesoarchean to early Paleoproterozoic was a 700 Myr long period of transition to continuous (?) subduction and global (?) mobile-lid plate tectonics.

  20. Imaging variations in the central Andean mantle and the subducting Nazca slab with teleseismic tomography

    Science.gov (United States)

    Scire, Alissa

    The Nazca-South America convergent margin is marked by the presence of the Andean mountain belt, which stretches along the 8000-km long western margin of the South American plate. The subduction zone is characterized by significant along-strike changes in both upper plate structure and slab geometry that make it an ideal region to study the relationship between the subducting slab, the surrounding mantle, and the overriding plate. This dissertation summarizes the results of three finite frequency teleseismic tomography studies of the central Nazca-South America subduction zone which improve our understanding of how along-strike variations in the Andean mountain belt and the subducting Nazca plate interact with each other and with the surrounding mantle. This is accomplished by first focusing on two smaller adjacent regions of the central Andes to explore upper mantle variations and then by using a combined dataset, which covers a larger region, to image the deeply subducted Nazca slab to investigate the fate of the slab. The first study focuses on the central Andean upper mantle under the Altiplano-Puna Plateau where normally dipping subduction of the Nazca plate is occurring (18° to 28°S). The shallow mantle under the Eastern Cordillera is generally fast, consistent with either underthrusting of the Brazilian cratonic lithosphere from the east or a localized "curtain" of delaminating material. Additional evidence for delamination is seen in the form of high amplitude low velocities under the Puna Plateau, consistent with proposed asthenospheric influx following lithospheric removal. In the second study, we explore the transition between normal and flat subduction along the north edge of the Altiplano Plateau (8° to 21°S). We find that the Peruvian flat slab extends further inland along the projection of the Nazca Ridge than was previously proposed and that when re-steepening of the slab occurs, the slab dips very steeply (˜70°) down through the mantle

  1. Long-term preservation of early formed mantle heterogeneity by mobile lid convection: Importance of grainsize evolution

    Science.gov (United States)

    Foley, Bradford J.; Rizo, Hanika

    2017-10-01

    The style of tectonics on the Hadean and Archean Earth, particularly whether plate tectonics was in operation or not, is debated. One important, albeit indirect, constraint on early Earth tectonics comes from observations of early-formed geochemical heterogeneities: 142Nd and 182W anomalies recorded in Hadean to Phanerozoic rocks from different localities indicate that chemically heterogeneous reservoirs, formed during the first ∼500 Myrs of Earth's history, survived their remixing into the mantle for over 1 Gyrs. Such a long mixing time is difficult to explain because hotter mantle temperatures, expected for the early Earth, act to lower mantle viscosity and increase convective vigor. Previous studies found that mobile lid convection typically erases heterogeneity within ∼100 Myrs under such conditions, leading to the hypothesis that stagnant lid convection on the early Earth was responsible for the observed long mixing times. However, using two-dimensional Cartesian convection models that include grainsize evolution, we find that mobile lid convection can preserve heterogeneity at high mantle temperature conditions for much longer than previously thought, because higher mantle temperatures lead to larger grainsizes in the lithosphere. These larger grainsizes result in stronger plate boundaries that act to slow down surface and interior convective motions, in competition with the direct effect temperature has on mantle viscosity. Our models indicate that mobile lid convection can preserve heterogeneity for ≈0.4-1 Gyrs at early Earth mantle temperatures when the initial heterogeneity has the same viscosity as the background mantle, and ≈1-4 Gyrs when the heterogeneity is ten times more viscous than the background mantle. Thus, stagnant lid convection is not required to explain long-term survival of early formed geochemical heterogeneities, though these heterogeneities having an elevated viscosity compared to the surrounding mantle may be essential for their

  2. Mantle superplumes induce geomagnetic superchrons

    Directory of Open Access Journals (Sweden)

    Peter eOlson

    2015-07-01

    Full Text Available We use polarity reversal systematics from numerical dynamos to quantify the hypothesis that the modulation of geomagnetic reversal frequency, including geomagnetic superchrons, results from changes in core heat flux related to growth and collapse of lower mantle superplumes. We parameterize the reversal frequency sensitivity from numerical dynamos in terms of average core heat flux normalized by the difference between the present-day core heat flux and the core heat flux at geomagnetic superchron onset. A low-order polynomial fit to the 0-300 Ma Geomagnetic Polarity Time Scale (GPTS reveals that a decrease in core heat flux relative to present-day of approximately 30% can account for the Cretaceous Normal Polarity and Kiaman Reverse Polarity Superchrons, whereas the hyper-reversing periods in the Jurassic require a core heat flux equal to or higher than present-day. Possible links between GPTS transitions, large igneous provinces (LIPs, and the two lower mantle superplumes are explored. Lower mantle superplume growth and collapse induce GPTS transitions by increasing and decreasing core heat flux, respectively. Age clusters of major LIPs postdate transitions from hyper-reversing to superchron geodynamo states by 30-60 Myr, suggesting that superchron onset may be contemporaneous with LIP-forming instabilities produced during collapses of lower mantle superplumes.

  3. Upper Mantle Discontinuity Structure Beneath the Western Atlantic Ocean and Eastern North America from SS Precursors

    Science.gov (United States)

    Schmerr, N. C.; Beghein, C.; Kostic, D.; Baldridge, A. M.; West, J. D.; Nittler, L. R.; Bull, A. L.; Montesi, L.; Byrne, P. K.; Hummer, D. R.; Plescia, J. B.; Elkins-Tanton, L. T.; Lekic, V.; Schmidt, B. E.; Elkins, L. J.; Cooper, C. M.; ten Kate, I. L.; Van Hinsbergen, D. J. J.; Parai, R.; Glass, J. B.; Ni, J.; Fuji, N.; McCubbin, F. M.; Michalski, J. R.; Zhao, C.; Arevalo, R. D., Jr.; Koelemeijer, P.; Courtier, A. M.; Dalton, H.; Waszek, L.; Bahamonde, J.; Schmerr, B.; Gilpin, N.; Rosenshein, E.; Mach, K.; Ostrach, L. R.; Caracas, R.; Craddock, R. A.; Moore-Driskell, M. M.; Du Frane, W. L.; Kellogg, L. H.

    2015-12-01

    Seismic discontinuities within the mantle arise from a wide range of mechanisms, including changes in mineralogy, major element composition, melt content, volatile abundance, anisotropy, or a combination of the above. In particular, the depth and sharpness of upper mantle discontinuities at 410 and 660 km depth are attributed to solid-state phase changes sensitive to both mantle temperature and composition, where regions of thermal heterogeneity produce topography and chemical heterogeneity changes the impedance contrast across the discontinuity. Seismic mapping of this topography and sharpness thus provides constraint on the thermal and compositional state of the mantle. The EarthScope USArray is providing unprecedented access to a wide variety of new regions previously undersampled by the SS precursors. This includes the boundary between the oceanic plate in the western Atlantic Ocean and continental margin of eastern North America. Here we use a seismic array approach to image the depth, sharpness, and topography of the upper mantle discontinuities, as well as other possible upper mantle reflectors beneath this region. This array approach utilizes seismic waves that reflect off the underside of a mantle discontinuity and arrive several hundred seconds prior to the SS seismic phase as precursory energy. In this study, we collected high-quality broadband data SS precursors data from shallow focus (ocean lithosphere to underlying continental lithosphere, as while deeper reflectors are associated with the subduction of the ancient Farallon slab. A comparison of the depth of upper mantle discontinuities to changes in seismic velocity and anisotropy will further quantify the relationship to mantle flow, compositional layering, and phases changes.

  4. Peridotite-melt interaction: A key point for the destruction of cratonic lithospheric mantle

    Institute of Scientific and Technical Information of China (English)

    ZHANG HongFu

    2009-01-01

    This paper presents an overview of recent studies dealing with different ages of mantle peridotitic xenoliths and xenocrysts from the North China Craton, with aim to provide new ideas for further study on the destruction of the North China Craton. Re-Os isotopic studies suggest that the lithospheric mantle of the North China Craton is of Archean age prior to its thinning. The key reason why such a low density and highly refractory Archean lithospheric mantle would be thinned is changes in composition, thermal regime, and physical properties of the lithospheric mantle due to interaction of peridotites with melts of different origins. Inward subducUon of circum craton plates and collision with the North China Craton provided not only the driving force for the destruction of the craton, but also continuous melts derived from partial melting of subducted continental or oceanic crustal materials that resulted in the compositional change of the lithospheric mantle. Regional thermal anomaly at ca. 120 Ma led to the melting of highly modified iithospheric mantle. At the same time or subsequently lithospheric extension and asthenospheric upwelling further reinforced the melting and thinning of the lithospheric mantle. Therefore, the destruction and thinning of the North China Craton is a combined result of peridotite-melt interaction (addition of volatile), enhanced regional thermal anomaly (temperature increase) and lithospheric extension (decompression). Such a complex geological process finally produced a "mixed" lithospheric mantle of highly chemical heterogeneity during the Mesozoic and Cenozoic. It also resulted in significant difference in the composition of mantle peridotitic xenoliths between different regions and times.

  5. GyPSuM: A Detailed Tomographic Model of Mantle Density and Seismic Wave Speeds

    Energy Technology Data Exchange (ETDEWEB)

    Simmons, N A; Forte, A M; Boschi, L; Grand, S P

    2010-03-30

    GyPSuM is a tomographic model fo mantle seismic shear wave (S) speeds, compressional wave (P) speeds and detailed density anomalies that drive mantle flow. the model is developed through simultaneous inversion of seismic body wave travel times (P and S) and geodynamic observations while considering realistic mineral physics parameters linking the relative behavior of mantle properties (wave speeds and density). Geodynamic observations include the (up to degree 16) global free-air gravity field, divergence of the tectonic plates, dynamic topography of the free surface, and the flow-induced excess ellipticity of the core-mantle boundary. GyPSuM is built with the philosophy that heterogeneity that most closely resembles thermal variations is the simplest possible solution. Models of the density field from Earth's free oscillations have provided great insight into the density configuration of the mantle; but are limited to very long-wavelength solutions. Alternatively, simply scaling higher resolution seismic images to density anomalies generates density fields that do not satisfy geodynamic observations. The current study provides detailed density structures in the mantle while directly satisfying geodynamic observations through a joint seismic-geodynamic inversion process. Notable density field observations include high-density piles at the base of the superplume structures, supporting the fundamental results of past normal mode studies. However, these features are more localized and lower amplitude than past studies would suggest. When we consider all seismic anomalies in GyPSuM, we find that P and S-wave speeds are strongly correlated throughout the mantle. However, correlations between the high-velocity S zones in the deep mantle ({approx} 2000 km depth) and corresponding P-wave anomalies are very low suggesting a systematic divergence from simplified thermal effects in ancient subducted slab anomalies. Nevertheless, they argue that temperature variations are

  6. Create Your Plate

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    Full Text Available ... A A A Listen En Español Create Your Plate Create Your Plate is a simple and effective ... and that your options are endless. Create Your Plate! Click on the plate sections below to add ...

  7. Plate tectonics in the late Paleozoic

    Directory of Open Access Journals (Sweden)

    Mathew Domeier

    2014-05-01

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

  8. Plate tectonics in the late Paleozoic

    Institute of Scientific and Technical Information of China (English)

    Mathew Domeier; Trond H. Torsvik

    2014-01-01

    As the chronicle of plate motions through time, paleogeography is fundamental to our understanding of plate tectonics and its role in shaping the geology of the present-day. To properly appreciate the history of tectonicsdand its influence on the deep Earth and climatedit is imperative to seek an accurate and global model of paleogeography. However, owing to the incessant loss of oceanic lithosphere through subduction, the paleogeographic reconstruction of‘full-plates’ (including oceanic lithosphere) becomes increasingly challenging with age. Prior to 150 Ma w60% of the lithosphere is missing and re-constructions are developed without explicit regard for oceanic lithosphere or plate tectonic principles;in effect, reflecting the earlier mobilistic paradigm of continental drift. Although these ‘continental’ re-constructions have been immensely useful, the next-generation of mantle models requires global plate kinematic descriptions with full-plate reconstructions. Moreover, in disregarding (or only loosely applying) plate tectonic rules, continental reconstructions fail to take advantage of a wealth of additional information in the form of practical constraints. Following a series of new developments, both in geo-dynamic theory and analytical tools, it is now feasible to construct full-plate models that lend themselves to testing by the wider Earth-science community. Such a model is presented here for the late Paleozoic (410e250 Ma) together with a review of the underlying data. Although we expect this model to be particularly useful for numerical mantle modeling, we hope that it will also serve as a general framework for understanding late Paleozoic tectonics, one on which future improvements can be built and further tested.

  9. Upper- and mid-mantle interaction between the Samoan plume and the Tonga–Kermadec slabs

    Science.gov (United States)

    Chang, Sung-Joon; Ferreira, Ana M. G.; Faccenda, Manuele

    2016-01-01

    Mantle plumes are thought to play a key role in transferring heat from the core–mantle boundary to the lithosphere, where it can significantly influence plate tectonics. On impinging on the lithosphere at spreading ridges or in intra-plate settings, mantle plumes may generate hotspots, large igneous provinces and hence considerable dynamic topography. However, the active role of mantle plumes on subducting slabs remains poorly understood. Here we show that the stagnation at 660 km and fastest trench retreat of the Tonga slab in Southwestern Pacific are consistent with an interaction with the Samoan plume and the Hikurangi plateau. Our findings are based on comparisons between 3D anisotropic tomography images and 3D petrological-thermo-mechanical models, which self-consistently explain several unique features of the Fiji–Tonga region. We identify four possible slip systems of bridgmanite in the lower mantle that reconcile the observed seismic anisotropy beneath the Tonga slab (VSH>VSV) with thermo-mechanical calculations. PMID:26924190

  10. Upper- and mid-mantle interaction between the Samoan plume and the Tonga-Kermadec slabs

    Science.gov (United States)

    Chang, Sung-Joon; Ferreira, Ana M. G.; Faccenda, Manuele

    2016-02-01

    Mantle plumes are thought to play a key role in transferring heat from the core-mantle boundary to the lithosphere, where it can significantly influence plate tectonics. On impinging on the lithosphere at spreading ridges or in intra-plate settings, mantle plumes may generate hotspots, large igneous provinces and hence considerable dynamic topography. However, the active role of mantle plumes on subducting slabs remains poorly understood. Here we show that the stagnation at 660 km and fastest trench retreat of the Tonga slab in Southwestern Pacific are consistent with an interaction with the Samoan plume and the Hikurangi plateau. Our findings are based on comparisons between 3D anisotropic tomography images and 3D petrological-thermo-mechanical models, which self-consistently explain several unique features of the Fiji-Tonga region. We identify four possible slip systems of bridgmanite in the lower mantle that reconcile the observed seismic anisotropy beneath the Tonga slab (VSH>VSV) with thermo-mechanical calculations.

  11. Upper- and mid-mantle interaction between the Samoan plume and the Tonga-Kermadec slabs.

    Science.gov (United States)

    Chang, Sung-Joon; Ferreira, Ana M G; Faccenda, Manuele

    2016-02-29

    Mantle plumes are thought to play a key role in transferring heat from the core-mantle boundary to the lithosphere, where it can significantly influence plate tectonics. On impinging on the lithosphere at spreading ridges or in intra-plate settings, mantle plumes may generate hotspots, large igneous provinces and hence considerable dynamic topography. However, the active role of mantle plumes on subducting slabs remains poorly understood. Here we show that the stagnation at 660 km and fastest trench retreat of the Tonga slab in Southwestern Pacific are consistent with an interaction with the Samoan plume and the Hikurangi plateau. Our findings are based on comparisons between 3D anisotropic tomography images and 3D petrological-thermo-mechanical models, which self-consistently explain several unique features of the Fiji-Tonga region. We identify four possible slip systems of bridgmanite in the lower mantle that reconcile the observed seismic anisotropy beneath the Tonga slab (V(SH)>V(SV)) with thermo-mechanical calculations.

  12. Plate tectonics, habitability and life

    Science.gov (United States)

    Spohn, Tilman; Breuer, Doris

    2016-04-01

    The role of plate tectonics in defining habitability of terrestrial planets is being increasingly discussed (e.g., Elkins-Tanton, 2015). Plate tectonics is a significantly evolved concept with a large variety of aspects. In the present context, cycling of material between near surface and mantle reservoirs is most important. But increased heat transport through mixing of cold lithosphere with the deep interior and formation of continental crust may also matter. An alternative mechanism of material cycling between these reservoirs is hot-spot volcanism combined with crust delamination. Hot-spot volcanism will transport volatiles to the atmosphere while delamination will mix crust, possibly altered by sedimentation and chemical reactions, with the mantle. The mechanism works as long as the stagnant lithosphere plate has not grown thicker than the crust and as long as volcanic material is added onto the crust. Thermal evolution studies suggest that the mechanism could work for the first 1-2 Ga of planetary evolution. The efficiency of the mechanism is limited by the ratio of extrusive to intrusive volcanism, which is thought to be less than 0.25. Plate tectonics would certainly have an advantage by working even for more evolved planets. A simple, most-used concept of habitability requires the thermodynamic stability of liquid water on the surface of a planet. Cycling of CO2between the atmosphere, oceans and interior through subduction and surface volcanism is an important element of the carbonate-silicate cycle, a thermostat feedback cycle that will keep the atmosphere from entering into a runaway greenhouse. Calculations for a model Earth lacking plate tectonics but degassing CO2, N, and H2O to form a surface ocean and a secondary atmosphere (Tosi et al, 2016) suggest that liquid water can be maintained on the surface for 4.5Ga. The model planet would then qualify as habitable. It is conceivable that the CO2 buffering capability of its ocean together with silicate

  13. Effects of change in slab geometry on the mantle flow and slab fabric in Southern Peru

    Science.gov (United States)

    Knezevic Antonijevic, Sanja; Wagner, Lara S.; Beck, Susan L.; Long, Maureen D.; Zandt, George; Tavera, Hernando

    2016-10-01

    The effects of complex slab geometries on the surrounding mantle flow field are still poorly understood. Here we combine shear wave velocity structure with Rayleigh wave phase anisotropy to examine these effects in southern Peru, where the slab changes its geometry from steep to flat. To the south, where the slab subducts steeply, we find trench-parallel anisotropy beneath the active volcanic arc that we attribute to the mantle wedge and/or upper portions of the subducting plate. Farther north, beneath the easternmost corner of the flat slab, we observe a pronounced low-velocity anomaly. This anomaly is caused either by the presence of volatiles and/or flux melting that could result from southward directed, volatile-rich subslab mantle flow or by increased temperature and/or decompression melting due to small-scale vertical flow. We also find evidence for mantle flow through the tear north of the subducting Nazca Ridge. Finally, we observe anisotropy patterns associated with the fast velocity anomalies that reveal along strike variations in the slab's internal deformation. The change in slab geometry from steep to flat contorts the subducting plate south of the Nazca Ridge causing an alteration of the slab petrofabric. In contrast, the torn slab to the north still preserves the primary (fossilized) petrofabric first established shortly after plate formation.

  14. Magnetodynamo Lifetimes for Rocky, Earth-Mass Exoplanets with Contrasting Mantle Convection Regimes

    CERN Document Server

    van Summeren, Joost; Conrad, Clinton P

    2013-01-01

    We used a thermal model of an iron core to calculate magnetodynamo evolution in Earth-mass rocky planets to determine the sensitivity of dynamo lifetime and intensity to planets with different mantle tectonic regimes, surface temperatures, and core properties. The heat flow at the core-mantle boundary (CMB) is derived from numerical models of mantle convection with a viscous/pseudo-plastic rheology that captures the phenomenology of plate-like tectonics. Our thermal evolution models predict a long-lived (~8 Gyr) field for Earth and similar dynamo evolution for Earth-mass exoplanets with plate tectonics. Both elevated surface temperature and pressure-dependent mantle viscosity reduce the CMB heat flow but produce only slightly longer-lived dynamos (~8-9.5 Gyr). Single-plate ("stagnant lid") planets with relatively low CMB heat flow produce long-lived (~10.5 Gyr) dynamos. These weaker dynamos can cease for several billions of years and subsequently reactivate due to the additional entropy production associated ...

  15. 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...

  16. 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).

  17. 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).

  18. Decoupled crust-mantle accommodation of Africa-Eurasia convergence in the NW Moroccan margin

    Science.gov (United States)

    JiméNez-Munt, I.; Fernã Ndez, M.; VergéS, J.; Garcia-Castellanos, D.; Fullea, J.; PéRez-Gussinyé, M.; Afonso, J. C.

    2011-08-01

    The extent of the area accommodating convergence between the African and Iberian plates, how this convergence is partitioned between crust and mantle, and the role of the plate boundary in accommodating deformation are not well-understood subjects. We calculate the structure of the lithosphere derived from its density distribution along a profile running from the Tagus Abyssal Plain to the Sahara Platform and crossing the Gorringe Bank, the NW Moroccan margin, and the Atlas Mountains. The model is based on the integration of gravity, geoid, elevation, and heat flow data and on the crustal structure across the NW Moroccan margin derived from reflection and wide-angle seismic data. The resulting mantle density anomalies suggest important variations of the lithosphere-asthenosphere boundary (LAB) topography, indicating prominent lithospheric mantle thickening beneath the margin (LAB > 200 km depth) followed by thinning beneath the Atlas Mountains (LAB ˜90 km depth). At crustal levels the Iberia-Africa convergence is sparsely accommodated in a ˜950 km wide area and localized in the Atlas and Gorringe regions, with an inferred shortening of ˜50 km. In contrast, mantle thickening accommodates a 400 km wide region, thus advocating for a decoupled crustal-mantle mechanical response. A combination of mantle underthrusting due to oblique convergence, together with a viscous dripping fed by lateral mantle dragging, can explain the imaged lithospheric structure. The model is consistent with crustal shortening estimates and with the accommodation of part of the Iberia-Africa convergence farther NW of the Gorringe Bank and/or off the strike of the profile.

  19. Al-'Arābīyah and Basa Sunda: Ideologies of Translation and Interpretation among the Muslim of West Java

    Directory of Open Access Journals (Sweden)

    Benjamin G. Zimmer

    2014-03-01

    Full Text Available This article reflects on these questions as they relate to the Sundanese-speaking population of western Java, Indonesia's second largest ethnic group. "Sundaneseness" is to a great extent defined by vernacular usage of the local language, basa Sunda, which is related to but distinct from Javanese, Indonesian, and the other Austronesian languages of the region. Speakers of Sundanese currently number more than 30 million, rivaling the populations of such countries as Canada, Morocco, and Kenya (and twice the population of their erstwhile colonizers, the Netherlands, yet Western scholarly literature on "Java" has paid them scant attention. Ethnographic studies of the island's Muslim communities, from Geertz's Religion of Java to Woodward's Islam in Java, have been similarly skewed towards the dominant Javanese ethno linguistic group inhabiting central and eastern Java.Copyright (c 2014 by SDI. All right reserved.DOI: 10.15408/sdi.v7i3.702

  20. Ridge-spotting: A new test for Pacific absolute plate motion models

    Science.gov (United States)

    Wessel, Paul; Müller, R. Dietmar

    2016-06-01

    Relative plate motions provide high-resolution descriptions of motions of plates relative to other plates. Yet geodynamically, motions of plates relative to the mantle are required since such motions can be attributed to forces (e.g., slab pull and ridge push) acting upon the plates. Various reference frames have been proposed, such as the hot spot reference frame, to link plate motions to a mantle framework. Unfortunately, both accuracy and precision of absolute plate motion models lag behind those of relative plate motion models. Consequently, it is paramount to use relative plate motions in improving our understanding of absolute plate motions. A new technique called "ridge-spotting" combines absolute and relative plate motions and examines the viability of proposed absolute plate motion models. We test the method on six published Pacific absolute plate motions models, including fixed and moving hot spot models as well as a geodynamically derived model. Ridge-spotting reconstructs the Pacific-Farallon and Pacific-Antarctica ridge systems over the last 80 Myr. All six absolute plate motion models predict large amounts of northward migration and monotonic clockwise rotation for the Pacific-Farallon ridge. A geodynamic implication of our ridge migration predictions is that the suggestion that the Pacific-Farallon ridge may have been pinned by a large mantle upwelling is not supported. Unexpected or erratic ridge behaviors may be tied to limitations in the models themselves or (for Indo-Atlantic models) discrepancies in the plate circuits used to project models into the Pacific realm. Ridge-spotting is promising and will be extended to include more plates and other ocean basins.

  1. The tectonic emplacement of Sumba in the Sunda-Banda Arc: paleomagnetic and geochemical evidence from the early Miocene Jawila volcanics

    Science.gov (United States)

    Wensink, Hans; van Bergen, Manfred J.

    1995-11-01

    The island of Sumba is a continental fragment in the fore-arc region near the transition between the Sunda Arc and Banda Arc in southeastern Indonesia. Paleomagnetic and geochemical evidence from the early Miocene volcanics of the Jawila Formation in western Sumba constrain the final drift stage and tectonic emplacement of the island. The lavas range from predominantly andesites to dacites, and display textural evidence for a weak metamorphism. Rock magnetic and mineral chemical data point to pseudo-single- to multi-domain (titano)magnetite (Fe 2.5-3Ti 0.5-0O 3), with grain sizes up to 10 μm, as the main carrier of remanence. The Jawila Formation reveals a ChRM direction with declination = 4.6°, inclination = - 19.2°, α95 = 9.9° and a paleolatitude of 9.9°S, which corroborates earlier results (Chamalaun and Sunata, 1982). Taking paleomagnetic evidence from other formations on the island into account, we conclude that the Sumba fragment has occupied approximately its present position since the Miocene. The calc-alkaline affinity and trace-element signatures of the lavas point to an origin in an arc environment. This occurrence of subduction-related volcanic activity in the early Miocene on Sumba implies that a volcanic arc existed south of the present-day East Sunda Arc, or that the island was located within the latter arc between Sumbawa and eastern Flores, and still had a minor southward drift to cover.

  2. Variation of thermal conductivity and heat flux at the Earth's core mantle boundary

    Science.gov (United States)

    Ammann, Michael W.; Walker, Andrew M.; Stackhouse, Stephen; Wookey, James; Forte, Alessandro M.; Brodholt, John P.; Dobson, David P.

    2014-03-01

    The two convective systems that dominate Earth's internal dynamics meet at the boundary between the rocky mantle and metallic liquid core. Energy transfer between processes driving plate tectonics and the geodynamo is controlled by thermal conduction in the lowermost mantle (D″). We use atomic scale simulations to determine the thermal conductivity of MgSiO3 perovskite and post-perovskite under D″ conditions and probe how these two convective systems interact. We show that the thermal conductivity of post-perovskite (∼12 W/mK) is 50% larger than that of perovskite under the same conditions (∼8.5 W/mK) and is anisotropic, with conductivity along the a-axis being 40% higher than conductivity along the c-axis. This enhances the high heat flux into cold regions of D″ where post-perovskite is stable, strengthening the feedback between convection in the core and mantle. Reminiscent of the situation in the lithosphere, there is potential for deformation induced texturing associated with mantle convection to modify how the mantle is heated from below. We test this by coupling our atomic scale results to models of texture in D″ and suggest that anisotropic thermal conductivity may help to stabilise the roots of mantle plumes over their protracted lifetime.

  3. Triggers and sources of volatile-bearing plumes in the mantle transition zone

    OpenAIRE

    Inna Safonova; Konstantin Litasov; Shigenori Maruyama

    2015-01-01

    The paper discusses generation of volatile-bearing plumes in the mantle transition zone (MTZ) in terms of mineral-fluid petrology and their related formation of numerous localities of intra-plate bimodal volcanic series in Central and East Asia. The plume generation in the MTZ can be triggered by the tectonic erosion of continental crust at Pacific-type convergent margins and by the presence of water and carbon dioxide in the mantle. Most probable sources of volatiles are the hydrated/carbona...

  4. Mantle Response to a Slab Gap and Three-dimensional Slab Interaction in Central America

    Science.gov (United States)

    Jadamec, M. A.; Fischer, K. M.

    2013-12-01

    Seismically constrained global slab geometries suggest the Middle America-South American subduction system contains a gap on the order of 500 km separating the east-dipping Cocos and Nazca slabs at depth (Gudmundsson and Sambridge, 1998; Syracuse and Abers, 2006; Hayes et al., 2012). The location of the gap correlates with tectonic features impinging on the Pacific side of the Middle America trench, in particular the incoming young buoyant oceanic lithosphere and oceanic ridges associated with the Galapagos hotspot and Cocos-Nazca spreading center (Protti et al., 1994; Mann et al., 2007; Muller et al., 2008). Moreover, geochemical studies focusing on the arc chemistry in the Central American volcanic front argue for a slab window of some kind in this region (Johnston and Thorkelson, 1997; Abratis and Worner, 2001; Hoernle et al., 2008). We use high-resolution, three-dimensional (3D) geodynamic modeling of the Middle America-South American subduction system to investigate the role of the incoming young oceanic lithosphere and a gap between the Cocos and Nazca slabs in controlling mantle flow velocity and geochemical signatures beneath Central America. The geodynamic models are geographically referenced with the geometry and thermal structure for the overriding and subducting plates based on geological and geophysical observables and constructed with the multi-plate subduction generator code, SlabGenerator (Jadamec and Billen, 2010; Jadamec et al., 2012; Jadamec and Billen, 2012). The viscous flow simulations are solved using the mantle convection finite-element code, CitcomCU (Zhong, 2006), modified by Jadamec and Billen (2010) to take into account the experimentally derived flow law for olivine and allow for variable 3D plate interface geometries and magnitudes of inter-plate coupling. The 3D numerical models indicate the gap between the Cocos and Nazca slabs serves as a conduit for Pacific-Cocos mantle to pass into the Caribbean, with toroidal flow around the

  5. Importance of initial buoyancy field on evolution of mantle thermal structure:Implications of surface boundary conditions

    Institute of Scientific and Technical Information of China (English)

    Petar Glisovic; Alessandro M. Forte

    2015-01-01

    Although there has been significant progress in the seismic imaging of mantle heterogeneity, the outstanding issue that remains to be resolved is the unknown distribution of mantle temperature anomalies in the distant geological past that give rise to the present-day anomalies inferred by global tomography models. To address this question, we present 3-D convection models in compressible and self-gravitating mantle initialised by different hypothetical temperature patterns. A notable feature of our forward convection modelling is the use of self-consistent coupling of the motion of surface tectonic plates to the underlying mantle flow, without imposing prescribed surface velocities (i.e., plate-like boundary condition). As an approximation for the surface mechanical conditions before plate tectonics began to operate we employ the no-slip (rigid) boundary condition. A rigid boundary condition dem-onstrates that the initial thermally-dominated structure is preserved, and its geographical location is fixed during the evolution of mantle flow. Considering the impact of different assumed surface boundary conditions (rigid and plate-like) on the evolution of thermal heterogeneity in the mantle we suggest that the intrinsic buoyancy of seven superplumes is most-likely resolved in the tomographic images of present-day mantle thermal structure. Our convection simulations with a plate-like boundary condition reveal that the evolution of an initial cold anomaly beneath the Java-Indonesian trench system yields a long-term, stable pattern of thermal heterogeneity in the lowermost mantle that resembles the present-day Large Low Shear Velocity Provinces (LLSVPs), especially below the Pacific. The evolution of sub-duction zones may be, however, influenced by the mantle-wide flow driven by deeply-rooted and long-lived superplumes since Archean times. These convection models also detect the intrinsic buoyancy of the Perm Anomaly that has been identified as a unique slow feature

  6. Subduction to the lower mantle – a comparison between geodynamic and tomographic models

    Directory of Open Access Journals (Sweden)

    B. Steinberger

    2012-07-01

    Full Text Available It is generally believed that subduction of lithospheric slabs is a major contribution to thermal heterogeneity in Earth's entire mantle and provides a main driving force for mantle flow. Mantle structure can, on the one hand, be inferred from plate tectonic models of subduction history and geodynamic models of mantle flow. On the other hand, seismic tomography models provide important information on mantle heterogeneity. Yet, the two kinds of models are only similar on the largest (1000s of km scales and are quite different in their detailed structure. Here, we provide a quantitative assessment how good a fit can be currently achieved with a simple viscous flow geodynamic model. The discrepancy between geodynamic and tomography models can indicate where further model refinement could possibly yield an improved fit. Our geodynamical model is based on 300 Myr of subduction history inferred from a global plate reconstruction. Density anomalies are inserted into the upper mantle beneath subduction zones, and flow and advection of these anomalies is calculated with a spherical harmonic code for a radial viscosity structure constrained by mineral physics and surface observations. Model viscosities in the upper mantle beneath the lithosphere are ~1020 Pas, and viscosity increases to ~1023 Pas in the lower mantle above D". Comparison with tomography models is assessed in terms of correlation, both overall and as a function of depth and spherical harmonic degree. We find that, compared to previous geodynamic and tomography models, correlation is improved significantly, presumably because of improvements in both plate reconstructions and mantle flow computation. However, high correlation is still limited to lowest spherical harmonic degrees. An important ingredient to achieve high correlation – in particular at spherical harmonic degree two – is a basal chemical layer. Subduction shapes this layer into two rather stable hot but

  7. Subduction to the lower mantle – a comparison between geodynamic and tomographic models

    Directory of Open Access Journals (Sweden)

    T. W. Becker

    2012-11-01

    Full Text Available It is generally believed that subduction of lithospheric slabs is a major contribution to thermal heterogeneity in Earth's entire mantle and provides a main driving force for mantle flow. Mantle structure can, on the one hand, be inferred from plate tectonic models of subduction history and geodynamic models of mantle flow. On the other hand, seismic tomography models provide important information on mantle heterogeneity. Yet, the two kinds of models are only similar on the largest (1000 s of km scales and are quite different in their detailed structure. Here, we provide a quantitative assessment how good a fit can be currently achieved with a simple viscous flow geodynamic model. The discrepancy between geodynamic and tomography models can indicate where further model refinement could possibly yield an improved fit. Our geodynamical model is based on 300 Myr of subduction history inferred from a global plate reconstruction. Density anomalies are inserted into the upper mantle beneath subduction zones, and flow and advection of these anomalies is calculated with a spherical harmonic code for a radial viscosity structure constrained by mineral physics and surface observations. Model viscosities in the upper mantle beneath the lithosphere are ~1020 Pas, and viscosity increases to ~1023 Pas in the lower mantle above D". Comparison with tomography models is assessed in terms of correlation, both overall and as a function of depth and spherical harmonic degree. We find that, compared to previous geodynamic and tomography models, correlation is improved, presumably because of advances in both plate reconstructions and mantle flow computations. However, high correlation is still limited to lowest spherical harmonic degrees. An important ingredient to achieve high correlation – in particular at spherical harmonic degree two – is a basal chemical layer. Subduction shapes this layer into two rather stable hot but chemically dense "piles

  8. Mantle Dynamics of Australia-Banda Arc Collision as Inferred from Shear Wave Splitting Analysis of Teleseismic and Local Slab Events

    Science.gov (United States)

    Harris, C. W.; Miller, M. S.; O'Driscoll, L.; Porritt, R. W.; Roosmawati, N.; Widiyantoro, S.

    2015-12-01

    Arc-continent collision is an important factor in continent building, orogensis, and ocean closure, yet the details associated with it are not fully understood. East-Timor and the Nusa Tenggara Timur region of Indonesia provide a unique setting to study a young arc-continent collision (~8 Ma) and incipient orogenesis. The NSF funded Banda Arc project affords a rare opportunity to investigate unconstrained processes such as active continental subduction and slab rupture beneath a regional deployment of broadband seismometers. We use data from 35 broadband sensors to analyze seismic anisotropy through measuring shear wave splitting. These stations span the roughly east-west transition from normal oceanic subduction at the Sunda Arc to collision at the Banda Arc, and cross areas associated with back-arc thrusting, arc volcanism, extinct volcanism and a rapidly exhuming forearc. Thirty of the sensors used in the analysis are temporary stations installed by our research team in 2014 and will remain in the field until 2016 or later. The remaining stations are part of the open-access GFZ GEOFON global seismic network. We present preliminary shear wave splitting results for teleseismic (*KS core phases) and local (direct S phase) arrivals in order to inspect the sub-slab mantle and the supra-slab mantle wedge for anisotropic patterns related to olivine flow fabric. These results can be used to assess regional strain linked to ongoing collision and may elucidate any slab tearing that has resulted from the (partial) subduction of buoyant continental material of Australian affinity. Presently, we observe a trend of primarily trench-parallel sub-slab fast polarization directions and perhaps more complicated anisotropy in the mantle wedge. Relative to the trench, there appears to be more spatial variation in fast axis orientation for direct arrivals than teleseismic phases. We discuss how the interpretation of our initial results provides insight into the mantle dynamics of the

  9. Faulting within the Pacific plate at the Mariana Trench: Implications for plate interface coupling and subduction of hydrous minerals

    Science.gov (United States)

    Emry, Erica L.; Wiens, Douglas A.; Garcia-Castellanos, Daniel

    2014-04-01

    We investigate faulting within the incoming Pacific plate at the Mariana subduction trench to understand stresses within the bending plate, regional stresses acting upon the plate interface, and the extent of possible faulting-induced mantle serpentinization. We determine accurate depths by inverting teleseismic P and SH waveforms for earthquakes occurring during 1990-2011 with Global Centroid Moment Tensor (GCMT) solutions. For earthquakes with Mw 5.0+, we determine centroid depths and source time functions and refine the fault parameters. Results from Central Mariana indicate that all earthquakes are extensional and occur at centroid depths down to 11 km below the Moho. At the Southern Mariana Trench, extensional earthquakes continue to 5 km below the Moho. One compressional earthquake at 34 km below the seafloor suggests stronger plate interface coupling here. In addition, we model the stress distribution within the Pacific plate along two bathymetric profiles extending seaward from the Mariana subduction trench axis to better understand whether our earthquake depth solutions match modeled scenarios for plate bending under applied external forces. Results from our flexure models match the locations of extensional and compressional earthquakes and suggest that the Pacific plate at Southern Mariana is experiencing larger, compressional stresses, possibly due to greater interplate coupling. Additionally, we conclude that if extensional faulting promotes the infiltration of water into the subducting plate mantle, then the top 5-15 km of the Pacific plate mantle are partially serpentinized, and a higher percentage of serpentinization is located near the Central Mariana trench where extensional events extend deeper.

  10. How stratified is mantle convection?

    Science.gov (United States)

    Puster, Peter; Jordan, Thomas H.

    1997-04-01

    We quantify the flow stratification in the Earth's mid-mantle (600-1500 km) in terms of a stratification index for the vertical mass flux, Sƒ (z) = 1 - ƒ(z) / ƒref (z), in which the reference value ƒref(z) approximates the local flux at depth z expected for unstratified convection (Sƒ=0). Although this flux stratification index cannot be directly constrained by observations, we show from a series of two-dimensional convection simulations that its value can be related to a thermal stratification index ST(Z) defined in terms of the radial correlation length of the temperature-perturbation field δT(z, Ω). ST is a good proxy for Sƒ at low stratifications (SƒUniformitarian Principle. The bound obtained here from global tomography is consistent with local seismological evidence for slab flux into the lower mantle; however, the total material flux has to be significantly greater (by a factor of 2-3) than that due to slabs alone. A stratification index, Sƒ≲0.2, is sufficient to exclude many stratified convection models still under active consideration, including most forms of chemical layering between the upper and lower mantle, as well as the more extreme versions of avalanching convection governed by a strong endothermic phase change.

  11. Modeling Continental Growth and Mantle Hydration in Earth's Evolution and the Impact of Life

    Science.gov (United States)

    Höning, Dennis; Spohn, Tilman

    2016-04-01

    The evolution of planets with plate tectonics is significantly affected by several intertwined feedback cycles. On Earth, interactions between atmosphere, hydrosphere, biosphere, crust, and interior determine its present day state. We here focus on the feedback cycles including the evolutions of mantle water budget and continental crust, and investigate possible effects of the Earth's biosphere. The first feedback loop includes cycling of water into the mantle at subduction zones and outgassing at volcanic chains and mid-ocean ridges. Water is known to reduce the viscosity of mantle rock, and therefore the speed of mantle convection and plate subduction will increase with the water concentration, eventually enhancing the rates of mantle water regassing and outgassing. A second feedback loop includes the production and erosion of continental crust. Continents are formed above subduction zones, whose total length is determined by the total size of the continents. Furthermore, the total surface area of continental crust determines the amount of eroded sediments per unit time. Subducted sediments affect processes in subduction zones, eventually enhancing the production rate of new continental crust. Both feedback loops affect each other: As a wet mantle increases the speed of subduction, continental production also speeds up. On the other hand, the total length of subduction zones and the rate at which sediments are subducted (both being functions of continental coverage) affect the rate of mantle water regassing. We here present a model that includes both cycles and show how the system develops stable and unstable fixed points in a plane defined by mantle water concentration and surface of continents. We couple these feedback cycles to a parameterized thermal evolution model that reproduces present day observations. We show how Earth has been affected by these feedback cycles during its evolution, and argue that Earth's present day state regarding its mantle water

  12. Mid-mantle heterogeneities and iron spin transition in the lower mantle: Implications for mid-mantle slab stagnation

    Science.gov (United States)

    Shahnas, M. H.; Yuen, D. A.; Pysklywec, R. N.

    2017-01-01

    Recent high pressure experimental results reveal that the elastic and transport properties of mantle materials are impacted by the electronic spin transition in iron under lower mantle pressure and temperature conditions. The electronic transition in ferropericlase (Fp), the second major constituent mineral of the lower mantle material, is associated with a smooth increase in density starting from the mid-mantle depth to the core-mantle boundary (CMB). The transition also yields softening in the elastic moduli and an increase in the thermal expansivity over the transition zone in the lower mantle. Although there is not yet robust experimental evidence for spin-transition induced density change in the perovskite (Pv) phase (the major constituent mineral in the lower mantle), the spin transition in the octahedral (B) site in Al-free perovskite causes a bulk modulus hardening (increase in the bulk modulus) in the mineral. We have incorporated these physical processes into high resolution 3D-spherical control volume models for mantle convection. A series of numerical experiments explore how the electronic spin transition in iron modifies the mantle flow, and in particular the fate of sinking cold slabs. Such mid-mantle stagnations are prevalent globally in seismic tomographic inversions, but previous explanations for their existence are not satisfactory. Employing density anomalies from the iron spin transition in ferropericlase and density anomaly models for perovskite, we study the influence of the spin transition in the minerals of the lower mantle on mantle flow. Our model results reveal that while the spin transition-induced property variations in ferropericlase enhance mixing in the lower depths of the mantle, the density anomaly arising from the hardening in the bulk modulus of Al-free perovskite can be effective in slowing the descent of slabs and may cause stagnation at mid-mantle levels. A viscosity hill in the lower mantle may further enhance the stagnation

  13. Composition of the continental plates

    Science.gov (United States)

    Gilluly, J.

    1954-01-01

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

  14. Scaling of plate-tectonic convection with pseudoplastic rheology

    CERN Document Server

    Korenaga, Jun

    2010-01-01

    The scaling of plate-tectonic convection is investigated by simulating thermal convection with pseudoplastic rheology and strongly temperature-dependent viscosity. The effect of mantle melting is also explored with additional depth-dependent viscosity. Heat-flow scaling can be constructed with only two parameters, the internal Rayleigh number and the lithospheric viscosity contrast, the latter of which is determined entirely by rheological properties. The critical viscosity contrast for the transition between plate-tectonic and stagnant-lid convection is found to be proportional to the square root of the internal Rayleigh number. The relation between mantle temperature and surface heat flux on Earth is discussed on the basis of these scaling laws, and the inverse relationship between them, as previously suggested from the consideration of global energy balance, is confirmed by this fully dynamic approach. In the presence of surface water to reduce the effective friction coefficient, the operation of plate tec...

  15. Mantle wedge serpentinization effects on slab dips

    Directory of Open Access Journals (Sweden)

    Eh Tan

    2017-01-01

    Full Text Available The mechanical coupling between a subducting slab and the overlying mantle wedge is an important factor in controlling the subduction dip angle and the flow in mantel wedge. This paper investigates the role of the amount of mantle serpentinization on the subduction zone evolution. With numerical thermos-mechanical models with elasto-visco-plastic rheology, we vary the thickness and depth extent of mantle serpentinization in the mantle wedge to control the degree of coupling between the slab and mantle wedge. A thin serpentinized mantle layer is required for stable subduction. For models with stable subduction, we find that the slab dip is affected by the down-dip extent and the mantle serpentinization thickness. A critical down-dip extent exists in mantle serpentinization, determined by the thickness of the overriding lithosphere. If the down-dip extent does not exceed the critical depth, the slab is partially coupled to the overriding lithosphere and has a constant dip angle regardless of the mantle serpentinization thickness. However, if the down-dip extent exceeds the critical depth, the slab and the base of the overriding lithosphere would be separated and decoupled by a thick layer of serpentinized peridotite. This allows further slab bending and results in steeper slab dip. Increasing mantle serpentinization thickness will also result in larger slab dip. We also find that with weak mantle wedge, there is no material flowing from the asthenosphere into the serpentinized mantle wedge. All of these results indicate that serpentinization is an important ingredient when studying the subduction dynamics in the mantle wedge.

  16. Episodic kinematics in continental rifts modulated by changes in mantle melt fraction

    Science.gov (United States)

    Lamb, Simon; Moore, James D. P.; Smith, Euan; Stern, Tim

    2017-07-01

    Oceanic crust is created by the extraction of molten rock from underlying mantle at the seafloor ‘spreading centres’ found between diverging tectonic plates. Modelling studies have suggested that mantle melting can occur through decompression as the mantle flows upwards beneath spreading centres, but direct observation of this process is difficult beneath the oceans. Continental rifts, however—which are also associated with mantle melt production—are amenable to detailed measurements of their short-term kinematics using geodetic techniques. Here we show that such data can provide evidence for an upwelling mantle flow, as well as information on the dimensions and timescale of mantle melting. For North Island, New Zealand, around ten years of campaign and continuous GPS measurements in the continental rift system known as the Taupo volcanic zone reveal that it is extending at a rate of 6-15 millimetres per year. However, a roughly 70-kilometre-long segment of the rift axis is associated with strong horizontal contraction and rapid subsidence, and is flanked by regions of extension and uplift. These features fit a simple model that involves flexure of an elastic upper crust, which is pulled downwards or pushed upwards along the rift axis by a driving force located at a depth greater than 15 kilometres. We propose that flexure is caused by melt-induced episodic changes in the vertical flow forces that are generated by upwelling mantle beneath the rift axis, triggering a transient lower-crustal flow. A drop in the melt fraction owing to melt extraction raises the mantle flow viscosity and drives subsidence, whereas melt accumulation reduces viscosity and allows uplift—processes that are also likely to occur in oceanic spreading centres.

  17. Intra Plate Stresses Using Finite Element Modelling

    Directory of Open Access Journals (Sweden)

    Jayalakshmi S.

    2016-10-01

    Full Text Available One of the most challenging problems in the estimation of seismic hazard is the ability to quantify seismic activity. Empirical models based on the available earthquake catalogue are often used to obtain activity of source regions. The major limitation with this approach is the lack of sufficient data near a specified source. The non-availability of data poses difficulties in obtaining distribution of earthquakes with large return periods. Such events recur over geological time scales during which tectonic processes, including mantle convection, formation of faults and new plate boundaries, are likely to take place. The availability of geometries of plate boundaries, plate driving forces, lithospheric stress field and GPS measurements has provided numerous insights on the mechanics of tectonic plates. In this article, a 2D finite element model of Indo-Australian plate is developed with the focus of representing seismic activity in India. The effect of large scale geological features including sedimentary basins, fold belts and cratons on the stress field in India is explored in this study. In order to address long term behaviour, the orientation of stress field and tectonic faults of the present Indo-Australian plate are compared with a reconstructed stress field from the early Miocene (20 Ma.

  18. The development of slabs in the upper mantle: Insights from numerical and laboratory experiments

    Science.gov (United States)

    Becker, Thorsten W.; Faccenna, Caludio; O'Connell, Richard J.; Giardini, Domenico

    1999-07-01

    We have performed numerical and laboratory experiments to model subduction of oceanic lithosphere in the upper mantle from its beginnings as a gravitational instability to the fully developed slab. A two-dimensional finite element code is applied to model Newtonian creep in the numerical experiments. Scaled analog media are used in the laboratory, a sand mixture models the brittle crust, silicone putty simulates creep in the lower crust and mantle lithosphere, and glucose syrup is the asthenosphere analog. Both model approaches show similar results and reproduce first-order observations of the subduction process in nature based on density and viscosity heterogeneities in a Stokes flow model. Subduction nucleates slowly and a pronounced slab forms only when the viscosity contrast between oceanic plate and mantle is below a threshold. We find that the subduction velocity and angle are time-dependent and increase roughly exponentially over tens of millions of years before the slab reaches the 670-km discontinuity. The style of subduction is controlled by the prescribed velocity of convergence, the density contrast between the plates, and the viscosity contrast between the oceanic plate and the mantle. These factors can be combined in the buoyancy number F which expresses the ratio between driving slab pull and resisting viscous dissipation in the oceanic plate. Variations in F control the stress in the plates, the speed and the dip of subduction, and the rate of trench retreat, reproducing the contrasting styles of subduction observed in nature. The subduction rate is strongly influenced by the work of bending the lithosphere as it subducts.

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

    Science.gov (United States)

    Clark, Marin Kristen

    2012-02-29

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

  20. Thermochemical and phase structure of the D"-Region constrained by 3-D spherical mantle convection and seismic tomography

    Science.gov (United States)

    Wu, B.; Olson, P.

    2011-12-01

    Results of time-dependent 3-D spherical mantle convection simulations with Newtonian rheology, solid-state phase transitions, and multiple composition as well as imposed plate motion back to 120 Ma are compared with observed lower mantle seismic heterogeneity to interpret structure in the D"-region. Synthetic seismic tomography images are created from the simulated temperature, composition, and phase change heterogeneity, which are then compared to the global seismic tomography models in terms of pattern and statistical properties. Several models are found that match the seismic tomography in terms of their RMS variation, Gaussian-like frequency distribution, and spherical harmonic degree-2 pattern for global-scale low velocity and high velocity regions. For these best-fitting models the heat flow at the CMB and the mantle heat flow at the surface are about 13.1 ~ 14.7 TW and 31 TW, respectively, and the Urey ratio is in range of 0.36 ~ 0.58. 3-D mantle convection constrained by plate motion history explains the statistics and the global pattern of lower mantle seismic heterogeneity provided that thermal, chemical and phase change heterogeneity is included in the mantle D"-region, and predicts large temporal and spatial variations in heat transport across the CMB.

  1. The subduction dichotomy of strong plates and weak slabs

    Science.gov (United States)

    Petersen, Robert I.; Stegman, Dave R.; Tackley, Paul J.

    2017-03-01

    A key element of plate tectonics on Earth is that the lithosphere is subducting into the mantle. Subduction results from forces that bend and pull the lithosphere into the interior of the Earth. Once subducted, lithospheric slabs are further modified by dynamic forces in the mantle, and their sinking is inhibited by the increase in viscosity of the lower mantle. These forces are resisted by the material strength of the lithosphere. Using geodynamic models, we investigate several subduction models, wherein we control material strength by setting a maximum viscosity for the surface plates and the subducted slabs independently. We find that models characterized by a dichotomy of lithosphere strengths produce a spectrum of results that are comparable to interpretations of observations of subduction on Earth. These models have strong lithospheric plates at the surface, which promotes Earth-like single-sided subduction. At the same time, these models have weakened lithospheric subducted slabs which can more easily bend to either lie flat or fold into a slab pile atop the lower mantle, reproducing the spectrum of slab morphologies that have been interpreted from images of seismic tomography.

  2. Radioactivity released from burning gas lantern mantles.

    Science.gov (United States)

    Luetzelschwab, J W; Googins, S W

    1984-04-01

    Gas lantern mantles contain thorium to produce incandescence when lantern fuel is burned on the mantle. Although only thorium is initially present on the mantle, the thorium daughters build up, some over a period of weeks and some over a period of years, and significant quantities of these daughters are present when the mantle is used. Some of these daughters are released when the lantern fuel is burned on the mantle. The amounts of radioactivity released during burning is studied by measuring the gamma radiation emitted by the daughters. Results of this study show that some of the radium (224Ra and 228Ra) and more than half the 212Pb and 212Bi is released during the first hour of a burn. The actual amounts release depend on the age of the mantle.

  3. Models of convection-driven tectonic plates - A comparison of methods and results

    Science.gov (United States)

    King, Scott D.; Gable, Carl W.; Weinstein, Stuart A.

    1992-01-01

    Recent numerical studies of convection in the earth's mantle have included various features of plate tectonics. This paper describes three methods of modeling plates: through material properties, through force balance, and through a thin power-law sheet approximation. The results obtained are compared using each method on a series of simple calculations. From these results, scaling relations between the different parameterizations are developed. While each method produces different degrees of deformation within the surface plate, the surface heat flux and average plate velocity agree to within a few percent. The main results are not dependent upon the plate modeling method and herefore are representative of the physical system modeled.

  4. LOWLID FORMATION AND PLATE TECTONICS ON EXOPLANETS

    Science.gov (United States)

    Stamenkovic, V.; Noack, L.; Breuer, D.

    2009-12-01

    The last years of astronomical observation have opened the doors to a universe filled with extrasolar planets. Detection techniques still only offer the possibility to detect mainly Super-Earths above five Earth masses. But detection techniques do steadily improve and are offering the possibility to detect even smaller planets. The observations show that planets seem to exist in many possible sizes just as the planets and moons of our own solar system do. It is only a natural question to ask if planetary mass has an influence on some key habitability factors such as on plate tectonics, allowing us to test which exoplanets might be more likely habitable than others, and allowing us to understand if plate tectonics on Earth is a stable or a critical, instable process that could easily be perturbed. Here we present results derived from 1D parameterized thermal evolution and 2D/3D computer models, showing how planetary mass influences the propensity of plate tectonics for planets with masses ranging from 0.1 to 10 Earth masses. Lately [2, 3] studied the effect of planetary mass on the ability to break plates and hence initiate plate tectonics - but both derived results contradictory to the other. We think that one of the reasons why both studies [2, 3] are not acceptable in their current form is partly due to an oversimplification. Both treated viscosity only temperature-dependent but neglected the effect pressure has on enlarging the viscosity in the deep mantle. More massive planets have therefore a stronger pressure-viscosity-coupling making convection at high pressures sluggish or even impossible. For planets larger than two Earth masses we observe that a conductive lid (termed low-lid) forms above the core-mantle boundary and thus reduces the effective convective part of the mantle when including a pressure-dependent term into the viscosity laws as shown in [1]. Moreover [2, 3] use time independent steady state models neglecting the fact that plate tectonics is a

  5. Mantle convection, tectonics and the evolution of the Tethyan subduction zone

    Science.gov (United States)

    Jolivet, Laurent; Sternai, Pietro; Menant, Armel; Faccenna, Claudio; Becker, Thorsten; Burov, Evguenii

    2014-05-01

    Mantle convection drives plate tectonics and the size, number and thermotectonic age of plates codetermines the convection pattern. However, the degree of coupling of surface deformation and mantle flow is unclear. Most numerical models of lithospheric deformation are designed such that strain is a consequence of kinematic boundary conditions, and rarely account for basal stresses due to mantle flow. On the other hand, convection models often treat the lithosphere as a single-layer stagnant lid with vertically undeformable surface. There is thus a gap between convection models and lithospheric-scale geodynamic models. The transmission of stresses from the flowing mantle to the crust is a complex process. The presence of a ductile lower crust inhibits the upward transmission of stresses but a highly extended crust in a hot environment such as a backarc domain, with no lithospheric mantle and a ductile lower crust in direct contact with asthenosphere, will be more prone to follow the mantle flow than a thick and stratified lithosphere. We review geological observations and present reconstructions of the Aegean and Middle East and discuss the possible role played by basal drag in governing lithospheric deformation. In Mediterranean backarc regions, lithosphere-mantle coupling is effective on geological time scale as shown by the consistency of SKS fast orientations in the mantle with stretching directions in the crust. The long-term geological history of the Tethyan convergent zone suggests that asthenospheric flow has been an important player. The case of Himalaya and Tibet strongly supports a major contribution of a northward asthenospheric push, with no persistent slab that could drive India after collision, large thrust planes being then decoupling zones between deep convection and surface tectonics. The African plate repeatedly fragmented during its northward migration with the separation of Apulia and Arabia. Indeed, extension has been active on the northern

  6. Deep Drilling into a Mantle Plume Volcano: The Hawaii Scientific Drilling Project

    Directory of Open Access Journals (Sweden)

    Donald M. Thomas

    2009-03-01

    Full Text Available Oceanic volcanoes formed by mantle plumes, such as those of Hawaii and Iceland, strongly influence our views about the deep Earth (Morgan, 1971; Sleep, 2006. These volcanoes are the principal geochemical probe into the deep mantle, a testing ground for understanding mantle convection, plate tectonics and volcanism, and an archive of information on Earth’s magnetic field and lithospheredynamics. Study of the petrology, geochemistry, and structure of oceanic volcanoes has contributed immensely to our present understanding of deep Earth processes, but virtually all of this study has been concentrated on rocks available at the surface. In favorable circumstances, surface exposures penetrate to a depth of a few hundred meters, which is a small fraction of the 10- to 15-kilometer height of Hawaiian volcanoes above the depressed seafloor (Moore, 1987; Watts, 2001.

  7. The amount of recycled crust in sources of mantle-derived melts.

    Science.gov (United States)

    Sobolev, Alexander V; Hofmann, Albrecht W; Kuzmin, Dmitry V; Yaxley, Gregory M; Arndt, Nicholas T; Chung, Sun-Lin; Danyushevsky, Leonid V; Elliott, Tim; Frey, Frederick A; Garcia, Michael O; Gurenko, Andrey A; Kamenetsky, Vadim S; Kerr, Andrew C; Krivolutskaya, Nadezhda A; Matvienkov, Vladimir V; Nikogosian, Igor K; Rocholl, Alexander; Sigurdsson, Ingvar A; Sushchevskaya, Nadezhda M; Teklay, Mengist

    2007-04-20

    Plate tectonic processes introduce basaltic crust (as eclogite) into the peridotitic mantle. The proportions of these two sources in mantle melts are poorly understood. Silica-rich melts formed from eclogite react with peridotite, converting it to olivine-free pyroxenite. Partial melts of this hybrid pyroxenite are higher in nickel and silicon but poorer in manganese, calcium, and magnesium than melts of peridotite. Olivine phenocrysts' compositions record these differences and were used to quantify the contributions of pyroxenite-derived melts in mid-ocean ridge basalts (10 to 30%), ocean island and continental basalts (many >60%), and komatiites (20 to 30%). These results imply involvement of 2 to 20% (up to 28%) of recycled crust in mantle melting.

  8. Compositional layering within the large low shear-wave velocity provinces (LLSVPs) in the lower mantle

    Science.gov (United States)

    Ballmer, Maxim; Lekic, Vedran; Schumacher, Lina; Ito, Garrett; Thomas, Christine

    2016-04-01

    to entrain basaltic material that has evolved in the lower mantle. Long-lived "primary" plumes rise from LLSVP margins and entrain a mix of materials, including small fractions of primordial mantle material. These predictions address the geochemical and geochronological record of intraplate hotspot volcanism on the Pacific plate. In general, the parameter range spanned by models that are able to reconcile observations provides a constraint for the intrinsic density anomaly (or composition) of DDDs. We use this constraint to evaluate a possible origin of DDDs from (basal) magma ocean cumulates. The study of LLSVP compositional layering has indeed important implications for our understanding of heat and material fluxes through mantle reservoirs, as well as bulk Earth chemistry and evolution.

  9. The role of harzburgite layers in the morphology of subducting plates and the behavior of oceanic crustal layers

    Science.gov (United States)

    Yoshida, Masaki

    2014-05-01

    Previous numerical studies of mantle convection focusing on subduction dynamics have indicated that the viscosity contrast between the subducting plate and the surrounding mantle have a primary effect on the behavior of subducting plates. The seismically observed plate stagnation at the base of the mantle transition zone (MTZ) under the Western Pacific and Eastern Eurasia is considered to mainly result from a viscosity increase at the ringwoodite to perovskite + magnesiowüstite (Rw→Pv+Mw) phase decomposition boundary, i.e., the boundary between the upper and lower mantle. The harzburgite layer, which is sandwiched between basaltic crust and depleted peridotite (lherzolite) layers, is a key component of highly viscous, cold oceanic plates. However, the possible sensitivity of the effective viscosity of harzburgite layers in the morphology of subducting plates that are flattened in the MTZ and/or penetrated in the lower mantle has not been examined systematically in previous three-dimensional (3D) numerical modeling studies that consider the viscosity increase at the boundary between the upper and lower mantle. In this study, in order to investigate the role of harzburgite layers in the morphology of subducting plates and the behavior of oceanic crustal layers, I performed a series of numerical simulations of mantle convection with semi-dynamic plate subduction in 3D regional spherical-shell geometry. The results show that a buckled crustal layer is observed under the "heel" of the stagnant slab that begins to penetrate into the lower mantle, regardless of the magnitude of the viscosity contrast between the harzburgite layer and the underlying mantle, when the factor of viscosity increase at the boundary of the upper and lower mantle is larger than 60-100. As the viscosity contrast between the harzburgite layer and the underlying mantle increases, the curvature of buckling is larger. When the viscosity increase at the boundary of the upper and lower mantle and the

  10. Thermal Stratification in Vertical Mantle Tanks

    DEFF Research Database (Denmark)

    Knudsen, Søren; Furbo, Simon

    2001-01-01

    It is well known that it is important to have a high degree of thermal stratification in the hot water storage tank to achieve a high thermal performance of SDHW systems. This study is concentrated on thermal stratification in vertical mantle tanks. Experiments based on typical operation conditions...... are carried out to investigate how the thermal stratification is affected by different placements of the mantle inlet. The heat transfer between the solar collector fluid in the mantle and the domestic water in the inner tank is analysed by CFD-simulations. Furthermore, the flow pattern in the vertical mantle...... tank is investigated....

  11. Diamond growth in mantle fluids

    Science.gov (United States)

    Bureau, Hélène; Frost, Daniel J.; Bolfan-Casanova, Nathalie; Leroy, Clémence; Esteve, Imène; Cordier, Patrick

    2016-11-01

    In the upper mantle, diamonds can potentially grow from various forms of media (solid, gas, fluid) with a range of compositions (e.g. graphite, C-O-H fluids, silicate or carbonate melts). Inclusions trapped in diamonds are one of the few diagnostic tools that can constrain diamond growth conditions in the Earth's mantle. In this study, inclusion-bearing diamonds have been synthesized to understand the growth conditions of natural diamonds in the upper mantle. Diamonds containing syngenetic inclusions were synthesized in multi-anvil presses employing starting mixtures of carbonates, and silicate compositions in the presence of pure water and saline fluids (H2O-NaCl). Experiments were performed at conditions compatible with the Earth's geotherm (7 GPa, 1300-1400 °C). Results show that within the timescale of the experiments (6 to 30 h) diamond growth occurs if water and carbonates are present in the fluid phase. Water promotes faster diamond growth (up to 14 mm/year at 1400 °C, 7 GPa, 10 g/l NaCl), which is favorable to the inclusion trapping process. At 7 GPa, temperature and fluid composition are the main factors controlling diamond growth. In these experiments, diamonds grew in the presence of two fluids: an aqueous fluid and a hydrous silicate melt. The carbon source for diamond growth must be carbonate (CO32) dissolved in the melt or carbon dioxide species in the aqueous fluid (CO2aq). The presence of NaCl affects the growth kinetics but is not a prerequisite for inclusion-bearing diamond formation. The presence of small discrete or isolated volumes of water-rich fluids is necessary to grow inclusion-bearing peridotitic, eclogitic, fibrous, cloudy and coated diamonds, and may also be involved in the growth of ultradeep, ultrahigh-pressure metamorphic diamonds.

  12. Large Scale, High Resolution, Mantle Dynamics Modeling

    Science.gov (United States)

    Geenen, T.; Berg, A. V.; Spakman, W.

    2007-12-01

    To model the geodynamic evolution of plate convergence, subduction and collision and to allow for a connection to various types of observational data, geophysical, geodetical and geological, we developed a 4D (space-time) numerical mantle convection code. The model is based on a spherical 3D Eulerian fem model, with quadratic elements, on top of which we constructed a 3D Lagrangian particle in cell(PIC) method. We use the PIC method to transport material properties and to incorporate a viscoelastic rheology. Since capturing small scale processes associated with localization phenomena require a high resolution, we spend a considerable effort on implementing solvers suitable to solve for models with over 100 million degrees of freedom. We implemented Additive Schwartz type ILU based methods in combination with a Krylov solver, GMRES. However we found that for problems with over 500 thousend degrees of freedom the convergence of the solver degraded severely. This observation is known from the literature [Saad, 2003] and results from the local character of the ILU preconditioner resulting in a poor approximation of the inverse of A for large A. The size of A for which ILU is no longer usable depends on the condition of A and on the amount of fill in allowed for the ILU preconditioner. We found that for our problems with over 5×105 degrees of freedom convergence became to slow to solve the system within an acceptable amount of walltime, one minute, even when allowing for considerable amount of fill in. We also implemented MUMPS and found good scaling results for problems up to 107 degrees of freedom for up to 32 CPU¡¯s. For problems with over 100 million degrees of freedom we implemented Algebraic Multigrid type methods (AMG) from the ML library [Sala, 2006]. Since multigrid methods are most effective for single parameter problems, we rebuild our model to use the SIMPLE method in the Stokes solver [Patankar, 1980]. We present scaling results from these solvers for 3D

  13. Anisotropy from SKS splitting across the Pacific-North America plate boundary offshore southern California

    Science.gov (United States)

    Ramsay, Joseph; Kohler, Monica D.; Davis, Paul M.; Wang, Xinguo; Holt, William; Weeraratne, Dayanthie S.

    2016-10-01

    SKS arrivals from ocean bottom seismometer (OBS) data from an offshore southern California deployment are analysed for shear wave splitting. The project involved 34 OBSs deployed for 12 months in a region extending up to 500 km west of the coastline into the oceanic Pacific plate. The measurement process consisted of removing the effects of anisotropy using a range of values for splitting fast directions and delay times to minimize energy along the transverse seismometer axis. Computed splitting parameters are unexpectedly similar to onland parameters, exhibiting WSW-ENE fast polarization directions and delays between 0.8 and 1.8 s, even for oceanic plate sites. This is the first SKS splitting study to extend across the entire boundary between the North America and Pacific plates, into the oceanic part of the Pacific plate. The splitting results show that the fast direction of anisotropy on the Pacific plate does not align with absolute plate motion (APM), and they extend the trend of anisotropy in southern California an additional 500 km west, well onto the oceanic Pacific plate. We model the finite strain and anisotropy within the asthenosphere associated with density-buoyancy driven mantle flow and the effects of APM. In the absence of plate motion effects, such buoyancy driven mantle flow would be NE-directed beneath the Pacific plate observations. The best-fit patterns of mantle flow are inferred from the tomography-based models that show primary influences from foundering higher-density zones associated with the history of subduction beneath North America. The new offshore SKS measurements, when combined with measurements onshore within the plate boundary zone, indicate that dramatic lateral variations in density-driven upper-mantle flow are required from offshore California into the plate boundary zone in California and western Basin and Range.

  14. Upper mantle seismic structure beneath southwest Africa from finite-frequency P- and S-wave tomography

    DEFF Research Database (Denmark)

    Soliman, Mohammad Youssof Ahmad; Yuan, Xiaohui; Tilmann, Frederik

    2015-01-01

    , probably related to surficial suture zones and the presence of fertile material. A shallower depth extent of the lithospheric plate of ∼100 km was observed beneath the ocean, consistent with plate-cooling models. In addition to tomographic images, the seismic anisotropy measurements within the upper mantle....... Utilizing 3D sensitivity kernels, we invert traveltime residuals to image velocity perturbations in the upper mantle down to 1000 km depth. To test the robustness of our tomographic image we employed various resolution tests which allow us to evaluate the extent of smearing effects and help defining...... the optimum inversion parameters (i.e. damping and smoothness) used during the regularization of inversion process. Resolution assessment procedure includes also a detailed investigation of the effect of the crustal corrections on the final images, which strongly influenced the resolution for the mantle...

  15. Flat-slab subduction, topography, and mantle dynamics in southwestern Mexico

    Science.gov (United States)

    Gérault, Mélanie; Husson, Laurent; Miller, Meghan S.; Humphreys, Eugene D.

    2015-09-01

    Topography above subduction zones arises from the isostatic contribution of crustal and lithospheric buoyancy, as well as the dynamic contribution from slab-driven mantle flow. We evaluate those effects in southwestern Mexico, where a segment of the Cocos slab subducts horizontally. The eastern part of the volcanic arc—the Trans-Mexican Volcanic Belt—stands at an average elevation of 2.3 km, nearly 1.3 km above the fore-arc. Lateral changes in bulk crustal density are relatively small, and seismic imaging shows that there is little variation in crustal thickness between these two regions. Thus, the elevation difference between the arc and the fore-arc should arise from differences in mantle properties. We present finite element models of flat-slab subduction that provide a simultaneous match to topography, plate velocities, and stress state in the overriding plate. We find that the dynamic effects are primarily controlled by the amount of coupling at the subduction interface and in the mantle wedge, the lack of slab anchoring into the lower mantle, and the absence of continental mantle lithosphere. With a mantle wedge and a subduction interface that are, respectively, 2 and 4 orders of magnitude weaker than the asthenosphere, the flat slab exerts a downward pull that can explain most of the elevation difference between the fore-arc and the arc. We infer that lateral viscosity variations play a significant role in shaping dynamic topography in complex tectonic settings and that sublithospheric dynamics can influence the topography at wavelengths that are significantly shorter than previously recognized.

  16. Water Content in the SW USA Mantle Lithosphere: FTIR Analysis of Dish Hill and Kilbourne Hole Pyroxenites

    Science.gov (United States)

    Gibler, Robert; Peslier, Anne H.; Schaffer, Lillian Aurora; Brandon, Alan D.

    2014-01-01

    Kilbourne Hole (NM, USA) and Dish Hill (CA, USA) mantle xenoliths sample continental mantle in two different tectonic settings. Kilbourne Hole (KH) is located in the Rio Grande rift. Dish Hill (DH) is located in the southern Mojave province, an area potentially affected by subduction of the Farallon plate beneath North America. FTIR analyses were obtained on well characterized pyroxenite, dunite and wehrlite xenoliths, thought to represent crystallized melts at mantle depths. PUM normalized REE patterns of the KH bulk-rocks are slightly LREE enriched and consistent with those of liquids generated by 6% melting of a spinel peridotite source. Pyroxenite pyroxenes have no detectable water but one DH wehrlite, which bulk-rock is LREE enriched, has 4 ppm H2O in orthopyroxene and 2 Ga. The Farallon subduction appears to have enriched in water the southwestern United States lithospheric mantle further east than DH, beneath the Colorado plateau.

  17. Seismic Evidence for Widespread Serpentinized Forearc Upper Mantle Along the Cascadia Margin

    Science.gov (United States)

    Brocher, T. M.; Parsons, T.; Trehu, A. M.; Snelson, C. M.; Fisher, M. A.

    2002-12-01

    Petrologic models for subducting slabs suggest that metamorphism of such slabs releases water that serpentinizes the overlying forearc mantle wedge. We use controlled-source-seismic and earthquake-tomography data from Cascadia to test the hypothesis that a narrow wedge of low velocity, serpentinized upper mantle extends along the Cascadia forearc from Vancouver Island to the Mendocino triple junction. The primary evidence for this wedge is low upper mantle (Pn) velocities (<7.8 km/s) and/or absent or low-amplitude wide-angle reflections from the top of the upper mantle (PmP) in a narrow belt (about 50 to 70 km wide) beneath the Georgia Strait, Puget Lowland, Willamette Valley, and the northern Great Valley. These results are compatible with a recent teleseismic model from central Oregon showing a weak and even inverted velocity contrast across the forearc Moho. Tomography models from Georgia Strait and the northern Puget Lowland show low upper mantle velocities. The absence of near-vertical and wide-angle PmP reflections from the top of the upper mantle in the SHIPS data from Puget Lowland are consistent with a weak continental Moho contrast there. Similarly, wide-angle reflections from the continental Moho (PmP) along a 1995 SW Washington seismic profile are discontinuous in the forearc. No clear PmP reflections or upper mantle refractions are observed from the North America plate, above the subducting Gorda plate, along Line 6 from the 1993 Mendocino seismic experiment. Local seismic reflectivity within the forearc upper mantle wedge may indicate, among other possibilities, that these low-velocity rocks have undergone extensive shearing. These observations are consistent with the suggestion that this wedge of low-velocity, rheologically-weak, serpentinized rocks facilitates slow slip events on the megathrust by lubricating the megathrust and/or accommodating some of the interplate deformation. The presence of a low-velocity forearc upper mantle wedge in Cascadia

  18. Three-dimensional shear wave velocity structure in the Atlantic upper mantle

    Science.gov (United States)

    James, Esther Kezia Candace

    Oceanic lithosphere constitutes the upper boundary layer of the Earth's convecting mantle. Its structure and evolution provide a vital window on the dynamics of the mantle and important clues to how the motions of Earth's surface plates are coupled to convection in the mantle below. The three-dimensional shear-velocity structure of the upper mantle beneath the Atlantic Ocean is investigated to gain insight into processes that drive formation of oceanic lithosphere. Travel times are measured for approximately 10,000 fundamental-mode Rayleigh waves, in the period range 30-130 seconds, traversing the Atlantic basin. Paths with >30% of their length through continental upper mantle are excluded to maximize sensitivity to the oceanic upper mantle. The lateral distribution of Rayleigh wave phase velocity in the Atlantic upper mantle is explored with two approaches. One, phase velocity is allowed to vary only as a function of seafloor age. Two, a general two-dimensional parameterization is utilized in order to capture perturbations to age-dependent structure. Phase velocity shows a strong dependence on seafloor age, and removing age-dependent velocity from the 2-D maps highlights areas of anomalously low velocity, almost all of which are proximal to locations of hotspot volcanism. Depth-dependent variations in vertically-polarized shear velocity (Vsv) are determined with two sets of 3-D models: a layered model that requires constant VSV in each depth layer, and a splined model that allows VSV to vary continuously with depth. At shallow depths (˜75 km) the seismic structure shows the expected dependence on seafloor age. At greater depths (˜200 km) high-velocity lithosphere is found only beneath the oldest seafloor; velocity variations beneath younger seafloor may result from temperature or compositional variations within the asthenosphere. The age-dependent phase velocities are used to constrain temperature in the mantle and show that, in contrast to previous results for

  19. 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

  20. A Model for Earth's Mantle Dynamic History for The Last 500 Ma and Its Implications for Continental Vertical Motions and Geomagnetism

    Science.gov (United States)

    Zhong, S.; Olson, P.; Zhang, N.

    2012-12-01

    Seismic tomography studies indicate that the Earth's mantle structure is characterized by African and Pacific seismically slow velocity anomalies (i.e., thermochemical piles) and circum Pacific seismically fast anomalies (i.e., degree 2) in the lower mantle. Mantle convection calculations including plate motion history for the last 120 Ma suggest that these degree 2 thermochemical structures result from plate subduction history (e.g., McNamara and Zhong, 2005). Given the important controls of mantle structure and dynamics on surface tectonics and volcanism and geodynamo in the core, an important question is the long-term evolution of mantle structures, for example, was the mantle structure in the past similar to the present-day's degree 2 structure, or significantly different from the present day? To address this question, we constructed a proxy model of plate motions for the African hemisphere for the last 450 Ma using the paleogeographic reconstruction of continents constrained by paleomagnetic and geological observations (e.g., Pangea assembly and breakup). Coupled with assumed oceanic plate motions for the Pacific hemisphere before 120 Ma, this proxy model for the plate motion history is used in three dimensional spherical models of mantle convection to study the evolution of mantle structure since the Early Paleozoic. Our model calculations reproduce well the present day degree 2 mantle structure including the African and Pacific thermochemical piles, and present-day surface heat flux, bathymetry and dynamic topography. Our results suggest that while the mantle in the African hemisphere before the assembly of Pangea is dominated by the cold downwelling structure resulting from plate convergence between Gondwana and Laurussia, it is unlikely that the bulk of the African superplume structure can be formed before ˜230 Ma. Particularly, the last 120 Ma plate motion plays an important role in generating the African thermochemical pile. We reconstruct temporal

  1. Mantle flow and deformation of subducting slab at the junction of Tohoku-Kurile arc

    Science.gov (United States)

    Morishige, M.; Honda, S.

    2012-12-01

    Geophysical studies of the plate junction reveal possible evidence of the presence of 3D mantle flow and deformation of subducting slabs. The junction of the Tohoku-Kurile is one of the best studied junctions in the world. The Pacific plate subducts under the North American plate in a direction almost perpendicular to Japan trench, while it subducts obliquely along the Kurile arc. Analysis of seismic anisotropy in this region shows the trench-normal fast polarization direction of S-wave splitting in the back arc even where the oblique subduction occurs. The angle of subduction varies along the strike of the trench, that is, it is smallest near the plate junction and becomes large beneath Kurile arc. There is also an important distinction in the slab behavior. The slab beneath Tohoku stagnates in the transition zone, whereas the slab beneath the Kurile arc penetrates into the lower mantle. In this presentation, we show the dynamic effects of the junction using a numerical model of mantle convection with a realistic curved shape of the trench in spherical geometry. The model is set so that it becomes similar to the geometry of the surface plate boundary in the Tohoku-Kurile arc. In order to enable one-sided subduction, the velocities are imposed both on the surface and in the small 3D boundary region around the trench. We obtain 3D flow in the mantle wedge which is consistent with the observation of seismic anisotropy including the oblique subduction zone. The flow and hence the fast polarization direction in the subslab mantle is almost 2D. We also find that the angle of subduction varies along-strike, which agrees with the observations. This variation can be explained by a torque balance acting on subducting slabs in the case of oblique subduction. This along-arc variation of the angle of subduction partly contributes to the different behavior of slab stagnation in the Tohoku-Kurile arc. Our results show that the shape of the trench is an important factor which

  2. Mantle hydration and Cl-rich fluids in the subduction forearc

    Science.gov (United States)

    Reynard, Bruno

    2016-12-01

    In the forearc region, aqueous fluids are released from the subducting slab at a rate depending on its thermal state. Escaping fluids tend to rise vertically unless they meet permeability barriers such as the deformed plate interface or the Moho of the overriding plate. Channeling of fluids along the plate interface and Moho may result in fluid overpressure in the oceanic crust, precipitation of quartz from fluids, and low Poisson ratio areas associated with tremors. Above the subducting plate, the forearc mantle wedge is the place of intense reactions between dehydration fluids from the subducting slab and ultramafic rocks leading to extensive serpentinization. The plate interface is mechanically decoupled, most likely in relation to serpentinization, thereby isolating the forearc mantle wedge from convection as a cold, potentially serpentinized and buoyant, body. Geophysical studies are unique probes to the interactions between fluids and rocks in the forearc mantle, and experimental constrains on rock properties allow inferring fluid migration and fluid-rock reactions from geophysical data. Seismic velocities reveal a high degree of serpentinization of the forearc mantle in hot subduction zones, and little serpentinization in the coldest subduction zones because the warmer the subduction zone, the higher the amount of water released by dehydration of hydrothermally altered oceanic lithosphere. Interpretation of seismic data from petrophysical constrain is limited by complex effects due to anisotropy that needs to be assessed both in the analysis and interpretation of seismic data. Electrical conductivity increases with increasing fluid content and temperature of the subduction. However, the forearc mantle of Northern Cascadia, the hottest subduction zone where extensive serpentinization was first demonstrated, shows only modest electrical conductivity. Electrical conductivity may vary not only with the thermal state of the subduction zone, but also with time for

  3. Pn anisotropic tomography and mantle dynamics beneath China

    Science.gov (United States)

    Zhou, Zhigang; Lei, Jianshe

    2016-08-01

    We present a new high-resolution Pn anisotropic tomographic model of the uppermost mantle beneath China inferred from 52,061 Pn arrival-time data manually picked from seismograms recorded at provincial seismic stations in China and temporary stations in Tibet and the Tienshan orogenic belt. Significant features well correlated with surface geology are revealed and provide new insights into the deep dynamics beneath China. Prominent high Pn velocities are visible under the stable cratonic blocks (e.g., the Tarim, Junngar, and Sichuan basins, and the Ordos block), whereas remarkable low Pn velocities are observed in the tectonically active areas (e.g., Pamir, the Tienshan orogenic belt, central Tibet and the Qilian fold belt). A distinct N-S trending low Pn velocity zone around 86°E is revealed under the rift running from the Himalayan block through the Lhasa block to the Qiangtang block, which indicates the hot material upwelling due to the breaking-off of the subducting Indian slab. Two N-S trending low Pn velocity belts with an approximate N-S Pn fast direction along the faults around the Chuan-Dian diamond block suggest that these faults may serve as channels of mantle flow from Tibet. The fast Pn direction changes from N-S in the north across 27°N to E-W in the south, which may reflect different types of mantle deformation. The anisotropy in the south could be caused by the asthenospheric flow resulted from the eastward subduction of the Indian plate down to the mantle transition zone beneath the Burma arc. Across the Talas-Fergana fault in the Tienshan orogenic belt, an obvious difference in velocity and anisotropy is revealed. To the west, high Pn velocities and an arc-shaped fast Pn direction are observed, implying the Indo-Asian collision, whereas to the east low Pn velocities and a range-parallel Pn fast direction are imaged, reflecting the northward underthrusting of the Tarim lithosphere and the southward underthrusting of the Kazakh lithosphere. In

  4. Western US intermountain seismicity caused by changes in upper mantle flow.

    Science.gov (United States)

    Becker, Thorsten W; Lowry, Anthony R; Faccenna, Claudio; Schmandt, Brandon; Borsa, Adrian; Yu, Chunquan

    2015-08-27

    Understanding the causes of intraplate earthquakes is challenging, as it requires extending plate tectonic theory to the dynamics of continental deformation. Seismicity in the western United States away from the plate boundary is clustered along a meandering, north-south trending 'intermountain' belt. This zone coincides with a transition from thin, actively deforming to thicker, less tectonically active crust and lithosphere. Although such structural gradients have been invoked to explain seismicity localization, the underlying cause of seismicity remains unclear. Here we show results from improved mantle flow models that reveal a relationship between seismicity and the rate change of 'dynamic topography' (that is, vertical normal stress from mantle flow). The associated predictive skill is greater than that of any of the other forcings we examined. We suggest that active mantle flow is a major contributor to seismogenic intraplate deformation, while gravitational potential energy variations have a minor role. Seismicity localization should occur where convective changes in vertical normal stress are modulated by lithospheric strength heterogeneities. Our results on deformation processes appear consistent with findings from other mobile belts, and imply that mantle flow plays a significant and quantifiable part in shaping topography, tectonics, and seismic hazard within intraplate settings.

  5. Destruction geodynamics of the North China Craton and its Paleoproterozoic plate tectonics

    Institute of Scientific and Technical Information of China (English)

    ZHU RiXiang; ZHENG TianYu

    2009-01-01

    Much attention has been paid in the last two decades to the physical and chemical processes as well as temporal-spatial variations of the lithospheric mantle beneath the North China Craton. In order to provide insights into the geodynamics of this variation, it is necessary to thoroughly study the state and structure of the lithospheric crust and mantle of the North China Craton and its adjacent regions as an integrated unit. Based on the velocity structure of the crust and upper mantle constrained from seismological studies, this paper presents various available geophysical results regarding the lithosphere thickness, the nature of crust-mantle boundary, the upper mantle structure and deformation characteristics as well as their tectonic features and evolution systematics. Combined with the obtained data from petrology and geochemistry, a mantle flow model is proposed for the tectonic evolution of the North China Craton during the Mesozoic-Cenozoic. We suggest that subduction of the Pacific plate made the mantle underneath the eastern Asian continent unstable and able to flow faster. Such a regional mantle flow system would cause an elevation of melt/fluid content in the upper mantle of the North China Craton and the lithospheric softening, which, subsequently resulted in destruction of the North China Craton in different ways of delamination and thermal erosion in Yanshan, Taihang Mountains and the Tan-Lu Fault zone. Multiple lines of evidence recorded in the crust of the North China Craton, such as the amalgamation of the Archean eastern and western blocks, the subduction of Paleo-oceanic crust and Paleo-continental residue, indicate that the Earth in the Paleoproterozoic had already evolved into the plate tectonic system similar to the present plate tectonics.

  6. Crustal thickness controlled by plate tectonics

    DEFF Research Database (Denmark)

    Artemieva, Irina M.; Meissner, Rolf

    2012-01-01

    /gabbro–eclogite phase transition in crustal evolution and the links between lithosphere recycling, mafic magmatism, and crustal underplating. We advocate that plate tectonics processes, togetherwith basalt/gabbro–eclogite transition, limit crustal thickness worldwide by providing effective mechanisms of crustal...... (lithosphere) recycling. The processes of crust–mantle interaction have created very dissimilar crustal styles in Europe, as seen by its seismic structure, crustal thickness, and average seismic velocities in the basement. Our special focus is on processes responsible for the formation of the thin crust...

  7. Small-scale upper mantle flow during the initiation of craton destruction

    Science.gov (United States)

    Zhao, Liang; Wang, Kun; Xu, Xiaobing

    2017-04-01

    The North China Craton (NCC) is an old craton which has experienced multi-episodic tectonism with surrounding plates. Bordered to the north by Xing'an-Mongolian Orogenic Belt, to the south by Qingling-Dabie-Sulu Orogen and to the far-east by (Paleo-) Pacific plate, the NCC has lost the cratonic properties within its eastern part. Evidently, the initiation and mechanism of craton destruction attract tremendous attention and remain hot debated. During the Mesozoic to the Cenozoic, the northeastern part of the NCC has been intensively revoked, along with the transition from NE shortening to NW-SE extension. The subduction of Paleo-Pacific plate becomes the prime suspect due to the same kinematic direction. Here we present a hybrid shear wave splitting measurement to investigate the mantle deformation of the NCC, and intend to constrain geodynamic process during the initiation of craton destruction. The SKS waveform data is recorded from 60 broadband stations with an average spacing of 15 km. We employ the traditional routine method to obtain fast polarization directions (FPDs, Φ) and delay times (δt) for the teleseismic events with epicenter range in 85°-115°. One may often have troubles in delimiting SKS and S wave with regard to the events at distances NCC, the east-end nearly E-W FPD is possibly owing to the fossil anisotropy in the lithosphere during the N-S shortening in Jurassic. The other is located in the Solonker suture zone beneath where the Moho and lithosphere and asthenosphere boundary (LAB) have sharp variation in depth. It suggests that the subduction of Pacific plate apparently reactivates the upper mantle of the north edge of the NCC but has minor effects westwards. The inconsistency in FPDs may result from small-scale mantle flow in the upper mantle, which could be the dominant operating mode of the Pacific subduction during the initiation of cratonic destruction.

  8. The role of viscoelasticity in subducting plates

    Science.gov (United States)

    Farrington, R. J.; Moresi, L.-N.; Capitanio, F. A.

    2014-11-01

    of tectonic plates into Earth's mantle occurs when one plate bends beneath another at convergent plate boundaries. The characteristic time of deformation at these convergent boundaries approximates the Maxwell relaxation time for olivine at lithospheric temperatures and pressures, it is therefore by definition a viscoelastic process. While this is widely acknowledged, the large-scale features of subduction can, and have been, successfully reproduced assuming the plate deforms by a viscous mechanism alone. However, the energy rates and stress profile within convergent margins are influenced by viscoelastic deformation. In this study, viscoelastic stresses have been systematically introduced into numerical models of free subduction, using both the viscosity and shear modulus to control the Maxwell relaxation time. The introduction of an elastic deformation mechanism into subduction models produces deviations in both the stress profile and energy rates within the subduction hinge when compared to viscous only models. These variations result in an apparent viscosity that is variable throughout the length of the plate, decreasing upon approach and increasing upon leaving the hinge. At realistic Earth parameters, we show that viscoelastic stresses have a minor effect on morphology yet are less dissipative at depth and result in an energy transfer between the energy stored during bending and the energy released during unbending. We conclude that elasticity is important during both bending and unbending within the slab hinge with the resulting stress loading and energy profile indicating that slabs maintain larger deformation rates at smaller stresses during bending and retain their strength during unbending at depth.

  9. Ultraslow, slow, or fast spreading ridges: Arm wrestling between mantle convection and far-field tectonics

    Science.gov (United States)

    Husson, Laurent; Yamato, Philippe; Bezos, Antoine

    2016-04-01

    Oceanic spreading rates are highly variable, and these variations are known to correlate to a variety of surface observables, like magmatic production, heat flow or bathymetry. This correlation lead to classify ridges into fast and slow spreading ridges, but also into the more peculiar ultraslow spreading regime. Here we explore the dynamic relationships between spreading ridges, plate tectonics and mantle flow. We first focus on the thermal signature of the mantle, that we infer from the global S-wave seismic tomography model of Debayle and Ricard (2012). We show that the thermal structure of ridges gradually departs from the half-space cooling model for slow, and above all ultraslow spreading ridges. We also infer that the sublithospheric mantle temperature decreases by more than 150 degrees C from fast to ultraslow spreading regimes. Both observations overall indicate that the mantle convection pattern is increasingly chaotic underneath slow and ultraslow spreading ridges. We suggest that this is due to far-field tectonics at the other ends of lithospheric plates: not only it modulates the spreading rates but it also alters the convection regime by obstructing the circulation of plates, which in turn modifies the surface kinematic conditions for the convecting mantle. We test this hypothesis using a thermo-mechanical model that represents a convection cell carrying a continental lithosphere atop. The continent gradually drifts away from the spreading ridge, from which the oceanic lithosphere grows and cools while the continent eventually collides at the opposite side. In turn, this event drastically modifies the upper kinematic condition for the convecting mantle that evolves from a mobile lid regime to an almost stagnant lid regime. Implications on spreading ridges are prominent: heat advection decreases with respect to thermal conduction, which causes the oceanic lithosphere to thicken faster; the oceanic plates get compressed and destabilized by a growing

  10. Mantle convection modeling of the supercontinent cycle:Introversion, extroversion, or a combination?

    Institute of Scientific and Technical Information of China (English)

    Masaki Yoshida; M. Santosh

    2014-01-01

    The periodic assembly and dispersal of continental fragments, referred to as the supercontinent cycle, bear close relation to the evolution of mantle convection and plate tectonics. Supercontinent formation involves complex processes of “introversion” (closure of interior oceans), “extroversion” (closure of exterior oceans), or a combination of these processes in uniting dispersed continental fragments. Recent developments in numerical modeling and advancements in computation techniques enable us to simulate Earth’s mantle convection with drifting continents under realistic convection vigor and rheology in Earth-like geometry (i.e., 3D spherical-shell). We report a numerical simulation of 3D mantle convection, incorporating drifting deformable continents, to evaluate supercontinent processes in a realistic mantle convection regime. Our results show that supercontinents are assembled by a combi-nation of introversion and extroversion processes. Small-scale thermal heterogeneity dominates deep mantle convection during the supercontinent cycle, although large-scale upwelling plumes intermit-tently originate under the drifting continents and/or the supercontinent.

  11. The Cascadia Paradox: Mantle flow and slab fragmentation in the Cascadia subduction system

    Science.gov (United States)

    Long, Maureen D.

    2016-12-01

    The pattern of mantle flow in subduction systems and the processes that control the mantle flow field represent fundamental but still poorly understood aspects of subduction dynamics. The Cascadia subduction zone is a compelling system in which to understand the controls on mantle flow, especially given the dense geophysical observations recently provided by EarthScope, GeoPRISMS, the Cascadia Initiative, and related efforts. Observations of seismic anisotropy, which provide relatively direct constraints on mantle flow, are particularly intriguing in Cascadia because they seem to yield contradictory views of the mantle flow field in different parts of the system. Specifically, observations of seismic anisotropy on the overriding plate, notably in the central portion of the backarc, apparently require a significant component of three-dimensional, toroidal flow around the slab edge. In contrast, new observations from offshore stations are compellingly explained with a simple two-dimensional entrained flow model. Recent evidence from seismic tomography for the likely fragmentation of the Cascadia slab at depth provides a further puzzle: how does a fragmented slab provide a driving force for either two-dimensional entrained flow or three-dimensional toroidal flow due to slab rollback? Resolution of this apparent paradox will require new imaging strategies as well as the integration of constraints from seismology, geodynamics, and geochemistry.

  12. Compositional and temperature variations of the Pacific upper mantle since the Cretaceous

    Institute of Scientific and Technical Information of China (English)

    ZHANG Guoliang

    2016-01-01

    The geological evolution of the Earth during the mid-Cretaceous were shown to be anomalous, e.g., the pause of the geomagnetic field, the global sea level rise, and increased intra-plate volcanic activities, which could be attributed to deep mantle processes. As the anomalous volcanic activities occurred mainly in the Cretaceous Pacific, here we use basalt chemical compositions from the oceanic drilling (DSDP/ODP/IODP) sites to investigate their mantle sources and melting conditions. Based on locations relative to the Pacific plateaus, we classified these sites as oceanic plateau basalts, normal mid-ocean ridge basalts, and near-plateau seafloor basalts. This study shows that those normal mid-ocean ridge basalts formed during mid-Cretaceous are broadly similar in average Na8, La/Sm and Sm/Yb ratios and Sr-Nd isotopic compositions to modern Pacific spreading ridge (the East Pacific Rise). The Ontong Java plateau (125–90 Ma) basalts have distinctly lower Na8 and 143Nd/144Nd, and higher La/Sm and87Sr/86Sr than normal seafloor basalts, whereas those for the near-plateau seafloor basalts are similar to the plateau basalts, indicating influences from the Ontong Java mantle source. The super mantle plume activity that might have formed the Ontong Java plateau influenced the mantle source of the simultaneously formed large areas of seafloor basalts. Based on the chemical data from normal seafloor basalts, I propose that the mantle compositions and melting conditions of the normal mid-ocean ridges during the Cretaceous are similar to the fast spreading East Pacific Rise. Slight variations of mid-Cretaceous normal seafloor basalts in melting conditions could be related to the local mantle source and spreading rate.

  13. Constraining mantle convection models with palaeomagnetic reversals record and numerical dynamos

    Science.gov (United States)

    Choblet, G.; Amit, H.; Husson, L.

    2016-11-01

    We present numerical models of mantle dynamics forced by plate velocities history in the last 450 Ma. The lower-mantle rheology and the thickness of a dense basal layer are systematically varied and several initial procedures are considered for each case. For some cases, the dependence on the mantle convection vigour is also examined. The resulting evolution of the CMB heat flux is analysed in terms of criteria to promote or inhibit reversals inferred from numerical dynamos. Most models present a rather dynamic lower mantle with the emergence of two thermochemical piles towards present-day. Only a small minority of models present two stationary piles over the last 450 Myr. At present-day, the composition field obtained in our models is found to correlate better with tomography than the temperature field. In addition, the temperature field immediately at the CMB (and thus the heat flux pattern) slightly differs from the average temperature field over the 100-km thick mantle layer above it. The evolution of the mean CMB heat flux or of the amplitude of heterogeneity seldom presents the expected correlation with the evolution of the palaeomagnetic reversal frequency suggesting these effects cannot explain the observations. In contrast, our analysis favours `inertial control' on the geodynamo associated with polar cooling and in some cases break of Taylor columns in the outer core as sources of increased reversal frequency. Overall, the most likely candidates among our mantle dynamics models involve a viscosity increase in the mantle equal or smaller than 30: models with a discontinuous viscosity increase at the transition zone tend to agree better at present-day with observations of seismic tomography, but models with a gradual viscosity increase agree better with some of the criteria proposed to affect reversal frequency.

  14. Constraining mantle convection models with paleomagnetic reversals record and numerical dynamos

    Science.gov (United States)

    Choblet, G.; Amit, H.; Husson, L.

    2016-09-01

    We present numerical models of mantle dynamics forced by plate velocities history in the last 450 Ma. The lower mantle rheology and the thickness of a dense basal layer are systematically varied and several initial procedures are considered for each case. For some cases, the dependence on the mantle convection vigor is also examined. The resulting evolution of the CMB heat flux is analyzed in terms of criteria known to promote or inhibit reversals inferred from numerical dynamos. Most models present a rather dynamic lower mantle with the emergence of two thermochemical piles towards present-day. Only a small minority of models present two stationary piles over the last 450 Myr. At present-day, the composition field obtained in our models is found to correlate better with tomography than the temperature field. In addition, the temperature field immediately at the CMB (and thus the heat flux pattern) slightly differs from the average temperature field over the 100-km thick mantle layer above it. The evolution of the mean CMB heat flux or of the amplitude of heterogeneities seldom presents the expected correlation with the evolution of the paleomagnetic reversal frequency suggesting these effects cannot explain the observations. In contrast, our analysis favors either 'inertial control' on the geodynamo associated to polar cooling and in some cases break of Taylor columns in the outer core as sources of increased reversal frequency. Overall, the most likely candidates among our mantle dynamics models involve a viscosity increase in the mantle equal or smaller than 30: models with a discontinuous viscosity increase at the transition zone tend to agree better at present-day with observations of seismic tomography, but models with a gradual viscosity increase agree better with some of the criteria proposed to affect reversal frequency.

  15. Development of seismic anisotropy during subduction-induced 3D mantle flow

    Science.gov (United States)

    Faccenda, M.; capitanio, F. A.

    2012-12-01

    Subduction zones are convergent margins where the rigid lithosphere sinks into the Earth's mantle inducing complex 3D flow patterns. Seismic anisotropy generated by strain-induced lattice/crystal preferred orientation (LPO/CPO) of intrinsically anisotropic minerals is commonly used to study flow in the mantle and its relations with plate motions. As the development of seismic anisotropy due to upper and lower plate motions occurs at depths and timescales such that it is not directly observable, numerical modelling provides a useful tool to investigate these processes. We computed the seismic anisotropy of dry olivine-enstatite aggregates due to strain-induced LPO in 3D mechanical models of dynamic subduction by using, respectively, D-Rex and Underworld. Subsequently, FSTRACK was used to compute seismogram synthetics and SKS splitting patterns. We found that for relatively narrow subducting plates, retreat motions are maximized producing strong subslab trench-parallel anisotropy. Here, synthetic data reproduce quite well the observations in analogous subduction systems like Calabria and South Sandwich, where the fast azimuths orients parallel to the trench in the forearc and follow the toroidal flow patterns on the slab edges. Furthermore, we found that the amount of anisotropy is proportional to the amount of subduction, while it does not depend on the rate at which the plate subducts. On the other hand, larger subducting plates subducts mainly by plate advance, favoring poloidal motions and trench-perpendicular anisotropy. Additional Earth-like plate geometries involving along-trench variation of the subducting plate age that induces differential slab retreat motions are considered. We also tested different olivine fabrics (A, B, C, E type), yielding distinct SKS splitting patterns that may help to constrain the composition of the upper mantle. Although more sophisticated numerical modelling taking into account temperature-dependent mantle rock rheologies and P

  16. Intraplate deformation, stress in the lithosphere and the driving mechanism for plate motions

    Science.gov (United States)

    Albee, Arden L.

    1993-01-01

    The initial research proposed was to use the predictions of geodynamical models of mantle flow, combined with geodetic observations of intraplate strain and stress, to better constrain mantle convection and the driving mechanism for plate motions and deformation. It is only now that geodetic observations of intraplate strain are becoming sufficiently well resolved to make them useful for substantial geodynamical inference to be made. A model of flow in the mantle that explains almost 90 percent of the variance in the observed longwavelength nonhydrostatic geoid was developed.

  17. Deep Mantle Seismic Modeling and Imaging

    Science.gov (United States)

    Lay, Thorne; Garnero, Edward J.

    2011-05-01

    Detailed seismic modeling and imaging of Earth's deep interior is providing key information about lower-mantle structures and processes, including heat flow across the core-mantle boundary, the configuration of mantle upwellings and downwellings, phase equilibria and transport properties of deep mantle materials, and mechanisms of core-mantle coupling. Multichannel seismic wave analysis methods that provide the highest-resolution deep mantle structural information include network waveform modeling and stacking, array processing, and 3D migrations of P- and S-wave seismograms. These methods detect and identify weak signals from structures that cannot be resolved by global seismic tomography. Some methods are adapted from oil exploration seismology, but all are constrained by the source and receiver distributions, long travel paths, and strong attenuation experienced by seismic waves that penetrate to the deep mantle. Large- and small-scale structures, with velocity variations ranging from a fraction of a percent to tens of percent, have been detected and are guiding geophysicists to new perspectives of thermochemical mantle convection and evolution.

  18. Heat transfer correlations in mantle tanks

    DEFF Research Database (Denmark)

    Furbo, Simon; Knudsen, Søren

    2005-01-01

    Small solar domestic hot water systems are best designed as low flow systems based on vertical mantle tanks. Theoretical investigations of the heat transfer in differently designed vertical mantle tanks during different operation conditions have been carried out. The investigations are based...... of the inner hot water tank and the domestic water in all levels of the tank. The heat transfer analysis showed that the heat transfer near the mantle inlet port between the solar collector fluid in the mantle and the walls surrounding the mantle is in the mixed convection regime, and as the distance from...... the inlet increases, natural convection starts to dominate. The heat transfer between the wall of the inner hot water tank and the domestic water is governed by natural convection. The results of the CFD-calculations are used to determine improved heat transfer correlations based on dimensionless analysis...

  19. Viscosity jump in Earth's mid-mantle.

    Science.gov (United States)

    Rudolph, Maxwell L; Lekić, Vedran; Lithgow-Bertelloni, Carolina

    2015-12-11

    The viscosity structure of Earth's deep mantle affects the thermal evolution of Earth, the ascent of mantle plumes, settling of subducted oceanic lithosphere, and the mixing of compositional heterogeneities in the mantle. Based on a reanalysis of the long-wavelength nonhydrostatic geoid, we infer viscous layering of the mantle using a method that allows us to avoid a priori assumptions about its variation with depth. We detect an increase in viscosity at 800- to 1200-kilometers depth, far greater than the depth of the mineral phase transformations that define the mantle transition zone. The viscosity increase is coincident in depth with regions where seismic tomography has imaged slab stagnation, plume deflection, and changes in large-scale structure and offers a simple explanation of these phenomena.

  20. Geodynamic evolution and mantle structure

    NARCIS (Netherlands)

    de Jonge, M.R.

    1995-01-01

    With the advent of plate tectonic theory a framework has become available in which many observed features of the structure of the Earth can be understood. The theory can explain the geological processes that have resulted in terranes as diverse as oceans, mid-oceanic ridges, mountain belts, and intr

  1. Processless offset printing plates

    Directory of Open Access Journals (Sweden)

    Sanja Mahović Poljaček

    2015-06-01

    Full Text Available With the implementation of platesetters in the offset printing plate making process, imaging of the printing plate became more stable and ensured increase of the printing plate quality. But as the chemical processing of the printing plates still highly influences the plate making process and the graphic reproduction workflow, development of printing plates that do not require chemical processing for offset printing technique has been one of the top interests in graphic technology in the last few years. The main reason for that came from the user experience, where majority of the problems with plate making process could be connected with the chemical processing of the printing plate. Furthermore, increased environmental standards lead to reducing of the chemicals used in the industrial processes. Considering these facts, different types of offset printing plates have been introduced to the market today. This paper presents some of the processless printing plates.

  2. Dynamics and Upper Mantle Structure Beneath the Northwestern Andes: Subduction Segments, Moho Depth, and Possible Relationships to Mantle Flow

    Science.gov (United States)

    Monsalve, G.; Yarce, J.; Becker, T. W.; Porritt, R. W.; Cardona, A.; Poveda, E.; Posada, G. A.

    2014-12-01

    The northwestern South American plate shows a complex tectonic setting whose causes and relationship to mantle structure are still debated. We combine different techniques to elucidate some of the links between slabs and surface deformation in Colombia. Crustal structure beneath the Northern Andes was inferred from receiver functions where we find thicknesses of nearly 60 km beneath the plateau of the Eastern Cordillera and underneath the southern volcanic area of the Central Cordillera. We infer that such crustal thickening resulted from shortening, magmatic addition, and accretion-subduction. Analyses of relative teleseismic travel time delays and estimates of residual surface topography based on our new crustal model suggest that there are at least two subduction segments underneath the area. The Caribbean slab lies at a low angle beneath northernmost Colombia and steepens beneath the Eastern Cordillera. Such steepening is indicated by negative travel time relative residuals in the area of the Bucaramanga Nest, implying a cold anomaly in the upper mantle, and by positive residual topography just off the east of this area, perhaps generated by slab-associated return flow. Results for the western Andes and the Pacific coastal plains are consistent with "normal" subduction of the Nazca plate: travel time relative residuals there are predominantly positive, and the residual topography shows an W-E gradient, going from positive at the Pacific coastline to negative at the Magdalena Valley, which separates the eastern cordillera from the rest of the Colombian Andean system. Azimuthal analysis of relative travel time residuals further suggests the presence of seismically slow materials beneath the central part of the Eastern Cordillera. Azimuthal anisotropy from SKS splitting in that region indicates that seismically fast orientations do not follow plate convergence, different from what we find for the western Colombian Andes and the Caribbean and Pacific coastal plains

  3. Plate Tectonics as a Far-From-Equilibrium Self-Organized Dissipative System

    Science.gov (United States)

    Anderson, D. L.

    2001-12-01

    A fluid above the critical Rayleigh number is far from equilibrium and spontaneously organizes itself into patterns involving the collective motion of large numbers of molecules which are resisted by the viscosity of the fluid. No external template is involved in forming the pattern. In 1928 Pearson showed that Bénard's experiments were driven by variations in surface tension at the top of the fluid and the surface motions drove convection in the fluid. In this case, the surface organized itself AND the underlying fluid. Both internal buoyancy driven flow and flow driven by surface forces can be far-from-equilibrium self-organized open systems that receive energy and matter from the environment. In the Earth, the cold thermal boundary layer at the surface drives plate tectonics and introduces temperature, shear and pressure gradients into the mantle that drive mantle convection. The mantle provides energy and material but may not provide the template. Plate tectonics is therefore a candidate for a far-from-equilibrium dissipative self-organizing system. Alternatively, one could view mantle convection as the self-organized system and the plates as simply the surface manifestation. Lithospheric architecture also imposes lateral temperature gradients onto the mantle which can drive and organize flow. Far-from-equilibrium self-organization requires; an open system, interacting parts, nonlinearities or feedbacks, an outside steady source of energy or matter, multiple possible states and a source of dissipation. In uniform fluids viscosity is the source of dissipation. Sources of dissipation in the plate system include bending, breaking, folding, shearing, tearing, collision and basal drag. These can change rapidly, in contrast to plate driving forces, and introduce the sort of fluctuations that can reorganize far-from-equilibrium systems. Global plate reorganizations can alternatively be thought of as convective overturns of the mantle, or thermal weakening of plates

  4. Strain Partitioning and the Geometry of Oblique Plate Convergence

    Science.gov (United States)

    Guzman-Speziale, M.

    2004-05-01

    Strain partitioning occurs at convergent margins where oblique subduction takes place, a fact that has been known for a number of years. The geometry of plate subduction controls strain-partitioning mode in the forearc region. Deformation in the forearc depends on the direction of relative plate convergence, earthquake slip vectors, and trench-normal direction. Two basic angles are derived from these vectors: obliquity of plate convergence, the angle of plate motion direction and trench normal, and slip partitioning which is the angle between the earthquake slip vector and trench normal. Traditionally, oblique convergence models consider the trench (convergent margin) a straight line on a flat Earth. This is correct for small-scale (in the order of a few kilometers) models. However, earthquakes along convergent margins often have fault lengths of tens and even hundreds (for magnitude 7 or greater) of kilometers. On the other hand, the direction normal to the trench is usually calculated averaging contiguous points along the deepest part of the digitized bathymetry, yielding the local trend of the trench. The direction normal to the trench thus calculated varies greatly along a specific trench. In this work we propose an alternate treatment of the geometry of the trench. On a spherical Earth, trench segments form arcs of small circles. Usually, a trench of interest will contain a few (three-five) such segments, which can be fitted (in a least-squares sense) with small circles with a known center of curvature (or pole) on the surface of the Earth. Also known are the initial and final points. Instead of the standard direction normal to the trench, we use the average azimuth from the segment of small circle to its corresponding pole. We use this direction instead of trench normal and calculate obliquity of plate convergence. We test our model along the western Sunda arc, from the eastern Himalayan sintaxis to Sumatra. Five contiguos small circles were fitted to the

  5. High-Resolution Imaging of the Mantle Flow Field Beneath Western North America

    Science.gov (United States)

    Fouch, M. J.; West, J. D.

    2008-12-01

    The goal of this study is to provide an improved understanding the nature of deformation in the crust and lithospheric mantle and its relationship to the mantle flow field beneath western North America. We utilize broadband data from regional and portable seismic arrays, including EarthScope's USArray Transportable Array and the ~120 stations of the High Lava Plains seismic array to image seismic anisotropy in the crust and mantle to constrain deformation in the crust, mantle lithosphere, and asthenosphere across the region. Regional shear wave splitting parameters show clear variations with geologic terrane. In the Pacific Northwest, splitting times are large (2.25+ sec) and fast directions are ~E-W with limited variability. Beneath the southern Basin and Range/Colorado Plateau region, splitting times are also large (~1.75+ sec) and fast directions are oriented ~NE-SW (similar to absolute plate motion). Stations near the San Andreas fault exhibit more variability between measurements at individual stations, but regionally exhibit a general rotation toward NW-SE for stations closer to the fault. Analyses from a dense array across the fault near Parkfield exhibit fast direction variations of ~30 degrees over ~15 km, indicating that uppermost crustal structure plays a significant role in some regions. Away from the Pacific-North American plate boundary, and sandwiched between broad regions of simple (i.e., regionally similar fast directions) and strong (i.e., large splitting times) azimuthal anisotropy, stations within the Great Basin exhibit significant complexity. Fast directions show a clear rotation from E-W in the northern Great Basin, to N-S in the eastern Great Basin, to NE-SW in the southeastern Great Basin. Splitting times reduce dramatically, approaching zero within the central Great Basin. At many stations within the Great Basin, particularly those that have been in operation for many years, we observe backazimuthal variations in splitting parameters that

  6. A Model of Continental Growth and Mantle Degassing Comparing Biotic and Abiotic Worlds

    Science.gov (United States)

    Höning, D.; Hansen-Goos, H.; Spohn, T.

    2012-12-01

    While examples for interaction of the biosphere with the atmosphere can be easily cited (e.g., production and consumption of O2), interaction between the biosphere and the solid planet and its interior is much less established. It has been argued (e.g., Rosing et al. 2006; Sleep et al, 2012) that the formation of continents could be a consequence of bioactivity harvesting solar energy through photosynthesis to help build the continents and that the mantle should carry a chemical biosignature. We present an interaction model that includes mantle convection, mantle water vapor degassing at mid-oceanic ridges and regassing through subduction zones, continental crust formation and erosion and water storage and transport in a porous oceanic crust that includes hydrous mineral phases. The mantle viscosity in this model depends on the water concentration in the mantle. We use boundary layer theory of mantle convection to parameterize the mantle convection flow rate and assume that the plate speed equals the mantle flow rate. The biosphere enters the calculation through the assumption that the continental erosion rate is enhanced by a factor of several through bioactivity and through an assumed reduction of the kinetic barrier to diagenetic and metamorphic reactions (e.g., Kim et al. 2004) in the sedimentary basins in subduction zones that would lead to increased water storage capacities. We further include a stochastic model of continent-to-continent interactions that limits the effective total length of subduction zones. We use present day parameters of the Earth and explore a phase plane spanned by the percentage of surface coverage of the Earth by continents and the total water content of the mantle. We vary the ratio of the erosion rate in a postulated abiotic Earth to the present Earth, as well as the activation barrier to diagenetic and metamorphic reactions that affect the water storage capacity of the subducting crust. We find stable and unstable fixed points in

  7. Taxonomic Notes on Nasutitermes and Bulbitermes (Termitidae, Nasutitermitinae from the Sunda region of Southeast Asia based on morphological and molecular characters

    Directory of Open Access Journals (Sweden)

    Syaukani Syaukani

    2011-11-01

    Full Text Available The Sunda region of Southeastern Asia is rich in termite fauna, but termites from this region have been poorly described. In this study, we described eight species from two diverse genera from this region, and from the family Termitidae. We describe Bulbitermes 4 spp. and Nasutitermes 4 spp. from new field collections. Where possible we examine original holotype specimens, and describe the essential morphological characters for soldier and worker castes. We devise two new bifurcating keys to guide the field identification of each species. In addition, we develop a nucleotide sequence profile for the COI gene. From this molecular character matrix, we use Neighbour-Joining analysis to test the monophyly of each morphospecies and genus. We find that the morphological and molecular characters are highly concordant, whereby all taxa appear to represent distinct molecular clades. For termites, there is therefore agreement between the morphological taxonomic characters used to sort species from a bifurcating key and the molecular taxonomic characters used to sort species on a bifurcating tree. This joint analysis suggests that DNA barcoding holds considerable promise for termite taxonomy, especially for diverse clades like Bulbitermes and Nasutitermes for which a global morphological key would be intractable.

  8. KARAKTERISTIK LINGKUNGAN DAN ASPEK SOSIAL DEMOGRAFI DALAM KAITANNYA DENGAN PENYAKIT INFEKSI HANTAVIRUS DI WILAYAH PELABUHAN TANJUNG PRIOK DAN SUNDA KELAPA, JAKARTA UTARA

    Directory of Open Access Journals (Sweden)

    Kasnodihardjo Kasnodihardjo

    2012-11-01

    Full Text Available Epidemiological study on hantavirus infection diseases in the area of Tanjung Priok and Sunda Kelapa Harbours has been conducted in the year of 1997; Considering a harbour may become a very potential port d'antre of diseases between islands, regions and countries. Hantavirus infection is well known as haemorrhagic fever with renal syndrome (HFRS, cause by some species of genus Hantavirus and transmitted to human by air droplet contaminated by urine, saliva or faeces of infected rodents. This is toreport a part of the study which is stress on sociocultural aspects, especially character of demography and community perceptions to hantavirus infection diseases. The data were collected by interviewing using questionaires and field observations. Sample population were household (HH while family members above 13 year of age including head of HH (Kepala Rumah Tangga were chosen as individual respondents and become analitical units. In total the number of samples were 113 HH, consisting 58 HH in Kelurahan Koja and 55 HH in Kelurahan Ancol. The number of individual respondents were 410 people. The results showed that most of respondents work as a labor in the harbours. In general they have low level formal education, mostly only elementary school graduated. The relatively low of their formal education they have might influence their wrong perceptions to any disease. The wrong community perceptions in the two areas mistaken hantavirus infection diseases with typhoid diseases.

  9. Diapir versus along-channel ascent of crustal material during plate convergence: Constrained by the thermal structure of subduction zones

    Science.gov (United States)

    Liu, Ming-Qi; Li, Zhong-Hai; Yang, Shao-Hua

    2017-09-01

    Subduction channel processes are crucial for understanding the material and energy exchange between the Earth's crust and mantle. Crustal rocks can be subducted to mantle depths, interact with the mantle wedge, and then exhume to the crustal depth again, which is generally considered as the mechanism for the formation of ultrahigh-pressure metamorphic rocks in nature. In addition, the crustal rocks generally undergo dehydration and melting at subarc depths, giving rise to fluids that metasomatize and weaken the overlying mantle wedge. There are generally two ways for the material ascent from subarc depths: one is along subduction channels; the other is through the mantle wedge by diapir. In order to study the conditions and dynamics of these contrasting material ascent modes, systematic petrological-thermo-mechanical numerical models are constructed with variable thicknesses of the overriding and subducting continental plates, ages of the subducting oceanic plate, as well as the plate convergence rates. The model results suggest that the thermal structures of subduction zones control the thermal condition and fluid/melt activity at the slab-mantle interface in subcontinental subduction channels, which further strongly affect the material transportation and ascent mode. The thick overriding continental plate and the low-angle subduction style induced by young subducting oceanic plate both contribute to the formation of relatively cold subduction channels with strong overriding mantle wedge, where the along-channel exhumation occurs exclusively to result in the exhumation of HP-UHP metamorphic rocks. In contrast, the thin overriding lithosphere and the steep subduction style induced by old subducting oceanic plate are the favorable conditions for hot subduction channels, which lead to significant hydration and metasomatism, melting and weakening of the overriding mantle wedge and thus cause the ascent of mantle wedge-derived melts by diapir through the mantle wedge

  10. Choosing an adequate FEM grid for global mantle convection modelling

    Science.gov (United States)

    Thieulot, Cedric

    2016-04-01

    Global numerical models of mantle convection are typically run on a grid which represents a hollow sphere. In the context of using the Finite Element method, there are many ways to discretise a hollow sphere by means of cuboids in a regular fashion (adaptive mesh refinement is here not considered). I will here focus on the following two: the cubed sphere [1], which is a quasi-uniform mapping of a cube to a sphere (considering both equidistant and equiangular projections), and the 12-block grid used for instance in CITCOM [2]. By means of simple experiments, I will show that at comparable resolutions (and all other things being equal), the 12-block grid is surprisingly vastly superior to the cubed-sphere grid, when used in combination with trilinear velocity - constant pressure elements, while being more difficult to build/implement. [1] C. Ronchi, R. Iacono, and P. S. Paolucci, The "Cubed Sphere": A New Method for the Solution of Partial Differential Equations in Spherical Geometry, Journal of Computational Physics, 124, p93-114 (1996). [2] S. Zhong and M.T. Zuber and L.N. Moresi and M. Gurnis, Role of temperature-dependent viscosity and surface plates in spherical shell models of mantle convection, Journal of Geophysical Research, 105 (B5), p 11,063-11,082 (2000).

  11. Study provides data on active plate tectonics in southeast Asia region

    Science.gov (United States)

    Wilson, P.; Rais, J.; Reigber, Ch.; Reinhart, E.; Ambrosius, B. A. C.; Le Pichon, X.; Kasser, M.; Suharto, P.; Majid, Dato'Abdul; Yaakub, Dato'Paduka Awang Haji Othman Bin Haji; Almeda, R.; Boonphakdee, C.

    A major geodynamic study has provided significant new information about the location of active plate boundaries in and around Southeast Asia, as well as deformation processes in the Sulawesi region of Indonesia and tectonic activity in the Philippine archipelago. Results also have confirmed the existence of the so-called Sunda Block, which appears to be rotating with respect to adjacent plates.The study, known as the Geodynamics of South and South-East Asia (GEODYSSEA) project, has been a joint venture of the European Commission and the Association of South- East Asian Nations. It began in 1991 and involved a large team of European and Asian scientists and technicians studying the complex geodynamic processes and natural hazards of the region from the Southeast Asia mainland to the Philippines to northern Australia. Earthquakes, volcanic eruptions, tsunamis, and tectonically induced landslides endanger the lives of millions of people in the region, and the tectonic activity behind these natural hazards results from the convergence and collision of the Eurasian, Philippine, and Indo-Australian Plates at relative velocities of up to 10 cm per year.

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

    Science.gov (United States)

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

    2007-04-01

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

  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. Mantle wedge dynamics from seismic anisotropy (Invited)

    Science.gov (United States)

    Long, M. D.; Wirth, E. A.

    2013-12-01

    The mantle wedge above subducting slabs plays a critical role in many of the physical processes associated with subduction, including water transport into the upper mantle and the generation and transport of melts. Our understanding of mantle wedge dynamics is incomplete; in particular, the mantle flow field above subducting slabs remains poorly understood. Because seismic anisotropy is a consequence of deformation, observations of anisotropy (such as shear wave splitting and P-to-SH converted waves) can constrain the geometry of the wedge flow field. Additionally, because the presence of water (either in nominally anhydrous minerals or as hydrous phases) can have a large effect on anisotropic structure, a detailed understanding of mantle wedge anisotropy can help to constrain processes related to water cycling in subduction systems. We present a global, synoptic view of anisotropy observations in subduction zone mantle wedges, compiled from a large number of individual studies, with the goal of understanding the first-order controls on wedge anisotropy and flow patterns. This compilation allows us to explicitly test the predictions made by many different conceptual models for wedge anisotropy, as well as to explore the relationships between observed anisotropy parameters and other parameters that describe subduction. We find that no simple model can explain all of the trends observed in the global data set. Mantle wedge flow is likely controlled by a combination of downdip motion of the slab, trench migration, ambient mantle flow, small-scale convection, proximity to slab edges, and slab morphology, with the relative contributions of these in any given subduction system controlled by the subduction kinematics and mantle rheology. There is also a likely contribution from B-type olivine and/or serpentinite fabric in many subduction zones, governed by the local thermal structure and volatile distribution.

  15. Partial melting in one-plate planets: Implications for thermo-chemical and atmospheric evolution

    Science.gov (United States)

    Plesa, A.-C.; Breuer, D.

    2014-08-01

    In the present work, we investigate the influence of partial melting on mantle dynamics, crustal formation, and volcanic outgassing of a one-plate planet using a 2D mantle convection code. When melt is extracted to form crust, the mantle material left behind is more buoyant than its parent material and depleted in radioactive heat sources. The extracted heat-producing elements are then enriched in the crust, which also has an insulating effect due to its lower thermal conductivity compared to the mantle. In addition, partial melting can influence the mantle rheology through the dehydration (water depletion) of the mantle material by volcanic outgassing. As a consequence, the viscosity of water-depleted regions increases more than two orders of magnitude compared to water-saturated rocks resulting in slower cooling rates. The most important parameter influencing the thermo-chemical evolution is the assumed density difference between the primitive and the depleted mantle material (i.e., between peridotite and harzburgite). With small or negligible values of compositional buoyancy, crustal formation including crustal delamination is very efficient, also resulting in efficient processing and degassing of the mantle. The convecting mantle below the stagnant lid depletes continuously with time. In contrast, with increasing compositional buoyancy, crustal formation and mantle degassing are strongly suppressed although partial melting is substantially prolonged in the thermal evolution. The crust shows strong lateral variations in thickness, and crustal delamination is reduced and occurs only locally. Furthermore, two to four different mantle reservoirs can form depending on the initial temperature distribution. Two of these reservoirs can be sustained during the entire evolution - a scenario possibly valid for Mars as it may explain the isotope characteristic of the Martian meteorites.

  16. Hunting for the Tristan mantle plume - An upper mantle tomography around the volcanic island of Tristan da Cunha

    Science.gov (United States)

    Schlömer, Antje; Geissler, Wolfram H.; Jokat, Wilfried; Jegen, Marion

    2017-03-01

    The active volcanic island Tristan da Cunha, located at the southwestern and youngest end of the Walvis Ridge - Tristan/Gough hotspot track, is believed to be the surface expression of a huge thermal mantle anomaly. While several criteria for the diagnosis of a classical hotspot track are met, the Tristan region also shows some peculiarities. Consequently, it is vigorously debated if the active volcanism in this region is the expression of a deep mantle plume, or if it is caused by shallow plate tectonics and the interaction with the nearby Mid-Atlantic Ridge. Because of a lack of geophysical data in the study area, no model or assumption has been completely confirmed. We present the first amphibian P-wave finite-frequency travel time tomography of the Tristan da Cunha region, based on cross-correlated travel time residuals of teleseismic earthquakes recorded by 24 ocean-bottom seismometers. The data can be used to image a low velocity structure southwest of the island. The feature is cylindrical with a radius of ∼100 km down to a depth of 250 km. We relate this structure to the origin of Tristan da Cunha and name it the Tristan conduit. Below 250 km the low velocity structure ramifies into narrow veins, each with a radius of ∼50 km. Furthermore, we imaged a linkage between young seamounts southeast of Tristan da Cunha and the Tristan conduit.

  17. Magma genesis, plate tectonics, and chemical differentiation of the Earth

    OpenAIRE

    Wyllie, Peter J.

    1988-01-01

    Magma genesis, migration, and eruption have played prominent roles in the chemical differentiation of the Earth. Plate tectonics has provided the framework of tectonic environments for different suites of igneous rocks and the dynamic mechanisms for moving masses of rock into melting regions. Petrology is rooted in geophysics. Petrological and geophysical processes are calibrated by the phase equilibria of the materials. The geochemistry of basalts and mantle xenoliths demonstrates that the m...

  18. Seismic Anisotropy from the Core-Mantle Boundary to the Surface

    Science.gov (United States)

    Lynner, Colton Lee

    Subduction systems are vitally important to plate tectonics and mantle convection, but questions remain about many aspects of subduction dynamics, particularly the nature of sub-slab mantle flow. Observations of seismic anisotropy can shed light on the pattern of mantle flow in subduction systems. Understanding the sub-slab mantle is the focus of my first three chapters as well as my last chapter. In Chapters 1 and 2, I examine the sub-slab anisotropy beneath the Caribbean, Scotia, Central America, Alaska-Aleutians, Sumatra, Ryukyu, and IzuBonin-Japan-Kurile subduction systems. I find that measured fast splitting directions in these regions generally fall into two broad categories, aligning either with the strike of the trench or with the motion of the subducting slab relative to the overriding plate. In theses systems, there is a correlation between fast direction and age of the subducting lithosphere; older lithosphere (> 95 Ma) is associated with trench parallel splitting while younger lithosphere (studies of source-side splitting studies to test the predictions of a number of recently proposed conceptual models for the dynamics of the sub-slab mantle. I find that a model in which fast splitting directions are determined by slab age matches the observations better than either the 3D-return flow or radial anisotropic models. Based on this observation, I propose that the sub-slab mantle is characterized by two distinct anisotropic and mantle flow regimes. Beneath younger lithosphere ( 95 Ma), the entrained layer is thin and effectively serves as decoupling layer; the dynamics of the sub-slab region beneath old lithosphere is therefore dominated by three-dimensional return flow. In Chapters 4 and 5, I focus on the dynamics of lowermost mantle. Shear wave splitting of SK(K)S phases is often used to examine upper mantle anisotropy. In specific cases, however, splitting of these phases may reflect anisotropy in the lowermost mantle. In both Chapters 4 and 5, I present

  19. Towards adjoint-based inversion of time-dependent mantle convection with non-linear viscosity

    Science.gov (United States)

    Li, Dunzhu; Gurnis, Michael; Stadler, Georg

    2017-01-01

    We develop and study an adjoint-based inversion method for the simultaneous recovery of initial temperature conditions and viscosity parameters in time-dependent mantle convection from the current mantle temperature and historic plate motion. Based on a realistic rheological model with temperature- and strain rate-dependent viscosity, we formulate the inversion as a PDE-constrained optimization problem. The objective functional includes the misfit of surface velocity (plate motion) history, the misfit of the current mantle temperature, and a regularization for the uncertain initial condition. The gradient of this functional with respect to the initial temperature and the uncertain viscosity parameters is computed by solving the adjoint of the mantle convection equations. This gradient is used in a preconditioned quasi-Newton minimization algorithm. We study the prospects and limitations of the inversion, as well as the computational performance of the method using two synthetic problems, a sinking cylinder and a realistic subduction model. The subduction model is characterized by the migration of a ridge toward a trench whereby both plate motions and subduction evolve. The results demonstrate: (1) for known viscosity parameters, the initial temperature can be well recovered, as in previous initial condition-only inversions where the effective viscosity was given; (2) for known initial temperature, viscosity parameters can be recovered accurately, despite the existence of trade-offs due to ill-conditioning; (3) for the joint inversion of initial condition and viscosity parameters, initial condition and effective viscosity can be reasonably recovered, but the high dimension of the parameter space and the resulting ill-posedness may limit recovery of viscosity parameters.

  20. High-Resolution Imaging of Structure and Dynamics of the Lowermost Mantle

    Science.gov (United States)

    Zhao, Chunpeng

    This research investigates Earth structure in the core-mantle boundary (CMB) region, where the solid rocky mantle meets the molten iron alloy core. At long wavelengths, the lower mantle is characterized by two nearly antipodal large low shear velocity provinces (LLSVPs), one beneath the Pacific Ocean the other beneath Africa and the southern Atlantic Ocean. However, fine-scale LLSVP structure as well as its relationship with plate tectonics, mantle convection, hotspot volcanism, and Earth's outer core remains poorly understood. The recent dramatic increase in seismic data coverage due to the EarthScope experiment presents an unprecedented opportunity to utilize large concentrated datasets of seismic data to improve resolution of lowermost mantle structures. I developed an algorithm that identifies anomalously broadened seismic waveforms to locate sharp contrasts in shear velocity properties across the margins of the LLSVP beneath the Pacific. The result suggests that a nearly vertical mantle plume underlies Hawaii that originates from a peak of a chemically distinct reservoir at the base of the mantle, some 600-900 km above the CMB. Additionally, acute horizontal Vs variations across and within the northern margin of the LLSVP beneath the central Pacific Ocean are inferred from forward modeling of differential travel times between S (and Sdiff) and SKS, and also between ScS and S. I developed a new approach to expand the geographic detection of ultra-low velocity zones (ULVZs) with a new ScS stacking approach that simultaneously utilizes the pre- and post-cursor wavefield. Strong lateral variations in ULVZ thicknesses and properties are found across the LLSVP margins, where ULVZs are thicker and stronger within the LLSVP than outside of it, consistent with convection model predictions. Differential travel times, amplitude ratios, and waveshapes of core waves SKKS and SKS are used to investigate CMB topography and outermost core velocity structure. 1D and 2D

  1. Geodynamically Consistent Interpretation of Seismic Tomography for Thermal and Thermochemical Mantle Plumes

    Science.gov (United States)

    Samuel, H.; Bercovici, D.

    2006-05-01

    Recent theoretical developments as well as increased data quality and coverage have allowed seismic tomographic imaging to better resolve narrower structures at both shallow and deep mantle depths. However, despite these improvements, the interpretation of tomographic images remains problematic mainly because of: (1) the trade off between temperature and composition and their different influence on mantle flow; (2) the difficulty in determining the extent and continuity of structures revealed by seismic tomography. We present two geodynamic studies on mantle plumes which illustrate the need to consider both geodynamic and mineral physics for a consistent interpretation of tomographic images in terms of temperature composition and flow. The first study aims to investigate the coupled effect of pressure and composition on thermochemical plumes. Using both high resolution 2D numerical modeling and simple analytical theory we show that the coupled effect of composition and pressure have a first order impact on the dynamics of mantle thermochemical plumes in the lower mantle: (1) For low Si enrichment of the plume relative to a reference pyrolitic mantle, an oscillatory behavior of the plume head is observed; (2) For Si-enriched plume compositions, the chemical density excess of the plume increases with height, leading to stagnation of large plume heads at various depths in the lower mantle. As a consequence, these thermochemical plumes may display broad (~ 1200 km wide and more) negative seismic velocity anomalies at various lower mantle depths, which may not necessarily be associated with upwelling currents. The second study focuses on the identification of thermal mantle plumes by seismic tomography beneath the Hawaiian hot spot: we performed a set of 3D numerical experiments in a spherical shell to model a rising plume beneath a moving plate. The thermal structure obtained is converted into P and S wave seismic velocities using mineral physics considerations. We

  2. Spreading continents kick-started plate tectonics.

    Science.gov (United States)

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

    2014-09-18

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

  3. Characteristics of Vertical Mantle Heat Exchangers for Solar Water Heaters

    DEFF Research Database (Denmark)

    Shah, Louise Jivan; Morrison, G.L.; Behnia, M.

    1999-01-01

    exchangers was also developed for detailed evaluation of the heat flux distribution over the mantle surface. Both the experimental and simulation results indicate that distribution of the flow around the mantle gap is governed by buoyancy driven recirculation in the mantle. The operation of the mantle...

  4. Seismic Anisotropy due to Crust and Uppermost Mantle Deformation Beneath Southern Peru and Bolivia: Constraints from Receiver Functions

    Science.gov (United States)

    Bar, N.; Long, M. D.; Wagner, L. S.; Beck, S. L.; Tavera, H.

    2016-12-01

    Subduction systems play a key role in plate tectonics, but the deformation of the crust and uppermost mantle during subduction and orogenesis in continental subduction systems remains poorly understood. Observations of seismic anisotropy can provide important constraints on dynamic processes in the crust and uppermost mantle in subduction systems. The subduction zone beneath Peru and Bolivia, where the Nazca plate subducts beneath South America, represents a particularly interesting location to study subduction-related deformation, given the complex slab morphology and the along-strike transition from flat to normally dipping subduction. In particular, understanding the structure and deformation of the crust and mantle will yield insight into the relationship between the flat slab and the overriding continental lithosphere. In this study we constrain seismic anisotropy within and above the subducting slab (including the mantle wedge and the overriding plate) beneath southern Peru and Bolivia using transverse component receiver functions. Because anisotropic receiver function analysis can constrain the depth distribution of anisotropy, this analysis is complementary to previous studies of shear wave splitting in this region. We examine data from two dense lines of seismometers from the PULSE and CAUGHT deployments in Peru and Bolivia, each anchored by a long-running permanent station. The northern line overlies the Peru flat slab, while the southern line overlies the normally dipping slab beneath Bolivia. Beneath Peru, our investigation of anisotropic structure along the flat slab will help test the recently suggested hypothesis of a slab tear; beneath Bolivia, we aim to characterize the pattern of flow in the mantle wedge as well as the nature of deformation in the lower crust of the overriding plate.

  5. Trace-element geochemistry of mantle olivine and application to mantle petrogenesis and geothermobarometry

    OpenAIRE

    De Hoog, Cees-Jan; Gall, Louise; Cornell, David H.

    2010-01-01

    Trace-element compositions of olivine from 75 mantle rocks of diverse origin, including xenoliths from kimberlites, basaltic lavas and orogenic peridotites, were determined by laser ablation ICP-MS to study systematic variations between mantle lithologies, partitioning mechanisms in olivine and their potential for geothermobarometry and unravelling mantle processes. Samples were selected to cover a wide range of forsterite contents (89.1-93.4), equilibration temperatures and pressures (750-14...

  6. Can mantle convection be self-regulated?

    Science.gov (United States)

    Korenaga, Jun

    2016-08-01

    The notion of self-regulating mantle convection, in which heat loss from the surface is constantly adjusted to follow internal radiogenic heat production, has been popular for the past six decades since Urey first advocated the idea. Thanks to its intuitive appeal, this notion has pervaded the solid earth sciences in various forms, but approach to a self-regulating state critically depends on the relation between the thermal adjustment rate and mantle temperature. I show that, if the effect of mantle melting on viscosity is taken into account, the adjustment rate cannot be sufficiently high to achieve self-regulation, regardless of the style of mantle convection. The evolution of terrestrial planets is thus likely to be far from thermal equilibrium and be sensitive to the peculiarities of their formation histories. Chance factors in planetary formation are suggested to become more important for the evolution of planets that are more massive than Earth.

  7. MODELLING MANTLE TANKS FOR SDHW SYSTEMS USING PIV AND CFD

    DEFF Research Database (Denmark)

    Shah, Louise Jivan; Morrison, G.L.; Behnia, Masud

    1999-01-01

    Characteristics of vertical mantle heat exchanger tanks for SDHW systems have been investigated experimentally and theoretically using particle image velocimetry (PIV) and CFD modelling. A glass model of a mantle heat exchanger tank was constructed so that the flow distribution in the mantle could...... be studied using the PIV test facility. Two transient three-dimensional CFD-models of the glass model mantle tank were developed using the CFD-programmes CFX and FLUENT.The experimental results illustrate that the mantle flow structure in the mantle is complicated and the distribution of flow in the mantle...

  8. Comparisons between radioactive and non-radioactive gas lantern mantles.

    Science.gov (United States)

    Furuta, E; Yoshizawa, Y; Aburai, T

    2000-12-01

    Gas lantern mantles containing radioactive thorium have been used for more than 100 years. Although thorium was once believed to be indispensable for giving a bright light, non-radioactive mantles are now available. From the radioactivities of the daughter nuclides, we estimated the levels of radioactivity of 232Th and 228Th in 11 mantles. The mantles contained various levels of radioactivity from background levels to 1410 +/- 140 Bq. Our finding that radioactive and non-radioactive mantles are equally bright suggests that there is no advantage in using radioactive mantles. A remaining problem is that gas lantern mantles are sold without any information about radioactivity.

  9. The link between Hawaiian mantle plume composition, magmatic flux, and deep mantle geodynamics

    Science.gov (United States)

    Harrison, Lauren N.; Weis, Dominique; Garcia, Michael O.

    2017-04-01

    Oceanic island basalts sample mantle reservoirs that are isotopically and compositionally heterogeneous. The Hawaiian-Emperor chain represents ∼85 Myr of volcanism supplied by a deep mantle plume. Two geographically and geochemically delineated trends, Kea and Loa, are well documented within the Hawaiian Islands. Enriched Loa compositions originate from subduction recycled or primordial material stored in deep mantle reservoirs such as the large low shear velocity province (LLSVP) below Hawai'i. Loa compositions have not been observed along the Emperor Seamounts (>50 Ma), whereas lavas on the Hawaiian Islands (chain and the Hawaiian Islands record the geochemical evolution of the Hawaiian mantle plume over a time period when many geophysical parameters (volcanic propagation rate, magmatic flux, mantle potential temperature) increased significantly. Along the NWHR, the Loa geochemical component appears ephemerally, which we link to the sampling of different lower mantle compositional domains by the Hawaiian mantle plume. The plume initially sampled only the deep Pacific mantle (Kea component) from outside the LLSVP during the formation of the Emperor Seamounts. Southward migration and anchoring of the plume on the LLSVP led to entrainment of increasing amounts of LLSVP material (Loa component) along the NWHR as documented by an increase in 208Pb*/206Pb* with decreasing age. The correlation between 208Pb*/206Pb* and magmatic flux suggests source composition affects the magmatic flux, and explains why the Hawaiian mantle plume has dramatically strengthened through time.

  10. Create Your Plate

    Medline Plus

    Full Text Available ... steps to get started: Using your dinner plate, put a line down the middle of the plate. ... vegetables . Now in one of the small sections, put grains and starchy foods. See this list of ...

  11. Create Your Plate

    Medline Plus

    Full Text Available ... Your Plate It's simple and effective for both managing diabetes and losing weight. Creating your plate lets ... 2016 Articles from Diabetes Forecast® magazine: wcie-meal-planning, In this section Food Planning Meals Diabetes Meal ...

  12. Create Your Plate

    Medline Plus

    Full Text Available ... Your Plate Gluten Free Diets Meal Planning for Vegetarian Diets Cook with Heart-Healthy Foods Holiday Meal ... Healthy Diet Create Your Plate Meal Planning for Vegetarian Diets Gluten Free Diets Holiday Meal Planning Cook ...

  13. Food guide plate

    Science.gov (United States)

    ... chips or cookies. VEGETABLES: MAKE HALF OF YOUR PLATE FRUITS AND VEGETABLES Vegetables can be raw, fresh, ... as a snack. FRUITS: MAKE HALF OF YOUR PLATE FRUITS AND VEGETABLES Fruits can be fresh, canned, ...

  14. Growth Plate Fractures

    Science.gov (United States)

    ... the most widely used by doctors is the Salter-Harris system, described below. Type I Fractures These ... incidence of growth plate fractures peaks in adolescence. Salter-Harris classification of growth plate fractures. AAOS does ...

  15. Create Your Plate

    Medline Plus

    Full Text Available ... Planning Meals Diabetes Meal Plans Create Your Plate Gluten Free Diets Meal Planning for Vegetarian Diets Cook ... Create Your Plate Meal Planning for Vegetarian Diets Gluten Free Diets Holiday Meal Planning Cook with Heart- ...

  16. Create Your Plate

    Medline Plus

    Full Text Available ... Planning Meals Diabetes Meal Plans Create Your Plate Gluten Free Diets Meal Planning for Vegetarian Diets Cook ... Create Your Plate Meal Planning for Vegetarian Diets Gluten Free Diets Holiday Meal Planning Cook with Heart- ...

  17. Create Your Plate

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    Full Text Available ... Your Plate It's simple and effective for both managing diabetes and losing weight. Creating your plate lets you still choose the foods you want, but changes the portion sizes so you are getting larger ...

  18. Create Your Plate

    Medline Plus

    Full Text Available ... Your Plate It's simple and effective for both managing diabetes and losing weight. Creating your