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Sample records for prevent deep mantle

  1. Kinematics and flow patterns in deep mantle and upper mantle subduction models : Influence of the mantle depth and slab to mantle viscosity ratio

    NARCIS (Netherlands)

    Schellart, W. P.

    Three-dimensional fluid dynamic laboratory simulations are presented that investigate the subduction process in two mantle models, an upper mantle model and a deep mantle model, and for various subducting plate/mantle viscosity ratios (ηSP/ηM = 59-1375). The models investigate the mantle flow field,

  2. Solid-liquid iron partitioning in Earth's deep mantle.

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    Andrault, Denis; Petitgirard, Sylvain; Lo Nigro, Giacomo; Devidal, Jean-Luc; Veronesi, Giulia; Garbarino, Gaston; Mezouar, Mohamed

    2012-07-18

    Melting processes in the deep mantle have important implications for the origin of the deep-derived plumes believed to feed hotspot volcanoes such as those in Hawaii. They also provide insight into how the mantle has evolved, geochemically and dynamically, since the formation of Earth. Melt production in the shallow mantle is quite well understood, but deeper melting near the core-mantle boundary remains controversial. Modelling the dynamic behaviour of deep, partially molten mantle requires knowledge of the density contrast between solid and melt fractions. Although both positive and negative melt buoyancies can produce major chemical segregation between different geochemical reservoirs, each type of buoyancy yields drastically different geodynamical models. Ascent or descent of liquids in a partially molten deep mantle should contribute to surface volcanism or production of a deep magma ocean, respectively. We investigated phase relations in a partially molten chondritic-type material under deep-mantle conditions. Here we show that the iron partition coefficient between aluminium-bearing (Mg,Fe)SiO(3) perovskite and liquid is between 0.45 and 0.6, so iron is not as incompatible with deep-mantle minerals as has been reported previously. Calculated solid and melt density contrasts suggest that melt generated at the core-mantle boundary should be buoyant, and hence should segregate upwards. In the framework of the magma oceans induced by large meteoritic impacts on early Earth, our results imply that the magma crystallization should push the liquids towards the surface and form a deep solid residue depleted in incompatible elements.

  3. Compositional stratification in the deep mantle

    NARCIS (Netherlands)

    Kellogg, louise H.; Hager, Bradford H.; Hilst, R.D. van der

    1999-01-01

    A boundary between compositionally distinct regions at a depth of about 1600 kilometers may explain the seismological observations pertaining to Earth's lower mantle, produce the isotopic signatures of mid-ocean ridge basalts and oceanic island basalts, and reconcile the discrepancy between the

  4. Toward a coherent model for the melting behavior of the deep Earth's mantle

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    Andrault, D.; Bolfan-Casanova, N.; Bouhifd, M. A.; Boujibar, A.; Garbarino, G.; Manthilake, G.; Mezouar, M.; Monteux, J.; Parisiades, P.; Pesce, G.

    2017-04-01

    Knowledge of melting properties is critical to predict the nature and the fate of melts produced in the deep mantle. Early in the Earth's history, melting properties controlled the magma ocean crystallization, which potentially induced chemical segregation in distinct reservoirs. Today, partial melting most probably occurs in the lowermost mantle as well as at mid upper-mantle depths, which control important aspects of mantle dynamics, including some types of volcanism. Unfortunately, despite major experimental and theoretical efforts, major controversies remain about several aspects of mantle melting. For example, the liquidus of the mantle was reported (for peridotitic or chondritic-type composition) with a temperature difference of ∼1000 K at high mantle depths. Also, the Fe partitioning coefficient (DFeBg/melt) between bridgmanite (Bg, the major lower mantle mineral) and a melt was reported between ∼0.1 and ∼0.5, for a mantle depth of ∼2000 km. Until now, these uncertainties had prevented the construction of a coherent picture of the melting behavior of the deep mantle. In this article, we perform a critical review of previous works and develop a coherent, semi-quantitative, model. We first address the melting curve of Bg with the help of original experimental measurements, which yields a constraint on the volume change upon melting (ΔVm). Secondly, we apply a basic thermodynamical approach to discuss the melting behavior of mineralogical assemblages made of fractions of Bg, CaSiO3-perovskite and (Mg,Fe)O-ferropericlase. Our analysis yields quantitative constraints on the SiO2-content in the pseudo-eutectic melt and the degree of partial melting (F) as a function of pressure, temperature and mantle composition; For examples, we find that F could be more than 40% at the solidus temperature, except if the presence of volatile elements induces incipient melting. We then discuss the melt buoyancy in a partial molten lower mantle as a function of pressure

  5. Dehydrogenation of goethite in Earth's deep lower mantle

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    Hu, Qingyang; Kim, Duck Young; Liu, Jin; Meng, Yue; Yang, Liuxiang; Zhang, Dongzhou; Mao, Wendy L.; Mao, Ho-kwang

    2017-02-01

    The cycling of hydrogen influences the structure, composition, and stratification of Earth’s interior. Our recent discovery of pyrite-structured iron peroxide (designated as the P phase) and the formation of the P phase from dehydrogenation of goethite FeO2H implies the separation of the oxygen and hydrogen cycles in the deep lower mantle beneath 1,800 km. Here we further characterize the residual hydrogen, x, in the P-phase FeO2Hx. Using a combination of theoretical simulations and high-pressure-temperature experiments, we calibrated the x dependence of molar volume of the P phase. Within the current range of experimental conditions, we observed a compositional range of P phase of 0.39 hydrogen and lower x, suggesting that dehydrogenation could be approaching completion at the high-temperature conditions of the lower mantle over extended geological time. Our observations indicate a fundamental change in the mode of hydrogen release from dehydration in the upper mantle to dehydrogenation in the deep lower mantle, thus differentiating the deep hydrogen and hydrous cycles.

  6. Deep mantle seismic heterogeneities in Western Pacific subduction zones

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    Bentham, H. L. M.; Rost, S.

    2012-04-01

    In recent years array seismology has been used extensively to image the small scale (~10 km) structure of the Earth. In the mantle, small scale structure likely represents chemical heterogeneity and is essential in our understanding of mantle convection and especially mantle mixing. As subduction is the main source of introducing crustal material into the Earth's mantle, it is of particular interest to track the transport of subducted crust through the mantle to resolve details of composition and deformation of the crust during the subduction process. Improved knowledge of subduction can help provide constraints on the mechanical mixing process of crustal material into the ambient mantle, as well as constraining mantle composition and convection. This study uses seismic array techniques to map seismic heterogeneities associated with Western Pacific subduction zones, where a variety of slab geometries have been previously observed. We use seismic energy arriving prior to PP, a P-wave underside reflection off the Earth's surface halfway between source and receiver, to probe the mantle for small-scale heterogeneities. PP precursors were analysed at Eielson Array (ILAR), Alaska using the recently developed Toolkit for Out-of-Plane Coherent Arrival Tracking (TOPCAT) algorithm. The approach combines the calculated optimal beampower and an independent semblance (coherency) measure, to improve the signal-to-noise ratio of coherent arrivals. 94 earthquakes with sufficient coherent precursory energy were selected and directivity information of the arrivals (i.e. slowness and backazimuth) was extracted from the data. The scattering locations for 311 out-of-plane precursors were determined by ray-tracing and minimising the slowness, backazimuth and differential travel time misfit. Initial analyses show that deep scattering (>1000 km) occurs beneath the Izu-Bonin subduction zone, suggesting that subducted crust does continue into the lower mantle in this location. Other

  7. Deep and persistent melt layer in the Archaean mantle

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    Andrault, Denis; Pesce, Giacomo; Manthilake, Geeth; Monteux, Julien; Bolfan-Casanova, Nathalie; Chantel, Julien; Novella, Davide; Guignot, Nicolas; King, Andrew; Itié, Jean-Paul; Hennet, Louis

    2018-02-01

    The transition from the Archaean to the Proterozoic eon ended a period of great instability at the Earth's surface. The origin of this transition could be a change in the dynamic regime of the Earth's interior. Here we use laboratory experiments to investigate the solidus of samples representative of the Archaean upper mantle. Our two complementary in situ measurements of the melting curve reveal a solidus that is 200-250 K lower than previously reported at depths higher than about 100 km. Such a lower solidus temperature makes partial melting today easier than previously thought, particularly in the presence of volatiles (H2O and CO2). A lower solidus could also account for the early high production of melts such as komatiites. For an Archaean mantle that was 200-300 K hotter than today, significant melting is expected at depths from 100-150 km to more than 400 km. Thus, a persistent layer of melt may have existed in the Archaean upper mantle. This shell of molten material may have progressively disappeared because of secular cooling of the mantle. Crystallization would have increased the upper mantle viscosity and could have enhanced mechanical coupling between the lithosphere and the asthenosphere. Such a change might explain the transition from surface dynamics dominated by a stagnant lid on the early Earth to modern-like plate tectonics with deep slab subduction.

  8. Numerical modelling of volatiles in the deep mantle

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    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).

  9. Numerical Modeling of Deep Mantle Flow: Thermochemical Convection and Entrainment

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    Mulyukova, Elvira; Steinberger, Bernhard; Dabrowski, Marcin; Sobolev, Stephan

    2013-04-01

    One of the most robust results from tomographic studies is the existence of two antipodally located Large Low Shear Velocity Provinces (LLSVPs) at the base of the mantle, which appear to be chemically denser than the ambient mantle. Results from reconstruction studies (Torsvik et al., 2006) infer that the LLSVPs are stable, long-lived, and are sampled by deep mantle plumes that rise predominantly from their margins. The origin of the dense material is debated, but generally falls within three categories: (i) a primitive layer that formed during magma ocean crystallization, (ii) accumulation of a dense eclogitic component from the recycled oceanic crust, and (iii) outer core material leaking into the lower mantle. A dense layer underlying a less dense ambient mantle is gravitationally stable. However, the flow due to thermal density variations, i.e. hot rising plumes and cold downwelling slabs, may deform the layer into piles with higher topography. Further deformation may lead to entrainment of the dense layer, its mixing with the ambient material, and even complete homogenisation with the rest of the mantle. The amount of the anomalous LLSVP-material that gets entrained into the rising plumes poses a constraint on the survival time of the LLSVPs, as well as on the plume buoyancy, on the lithospheric uplift associated with plume interaction and geochemical signature of the erupted lavas observed at the Earth's surface. Recent estimates for the plume responsible for the formation of the Siberian Flood Basalts give about 15% of entrained dense recycled oceanic crust, which made the hot mantle plume almost neutrally buoyant (Sobolev et al., 2011). In this numerical study we investigate the mechanics of entrainment of a dense basal layer by convective mantle flow. We observe that the types of flow that promote entrainment of the dense layer are (i) upwelling of the dense layer when it gets heated enough to overcome its stabilizing chemical density anomaly, (ii

  10. Long-Lived Mantle Plumes Sample Multiple Deep Mantle Geochemical Domains: The Example of the Hawaiian-Emperor Chain

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    Harrison, L.; Weis, D.

    2017-12-01

    Oceanic island basalts provide the opportunity for the geochemist to study the deep mantle source removed from continental sources of contamination and, for long-lived systems, the evolution of mantle sources with time. In the case of the Hawaiian-Emperor (HE) chain, formation by a long-lived (>81 Myr), deeply-sourced mantle plume allows for insight into plume dynamics and deep mantle geochemistry. The geochemical record of the entire chain is now complete with analysis of Pb-Hf-Nd-Sr isotopes and elemental compositions of the Northwest Hawaiian Ridge (NWHR), which consists of 51 volcanoes spanning 42 Ma between the bend in the chain and the Hawaiian Islands. This segment of the chain previously represented a significant data gap where Hawaiian plume geochemistry changed markedly, along with magmatic flux: only Kea compositions have been observed on Emperor seamounts (>50 Ma), whereas the Hawaiian Islands (drift through different lower mantle geohemical domains.

  11. Signal restoration through deconvolution applied to deep mantle seismic probes

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    Stefan, W.; Garnero, E.; Renaut, R. A.

    2006-12-01

    We present a method of signal restoration to improve the signal-to-noise ratio, sharpen seismic arrival onset, and act as an empirical source deconvolution of specific seismic arrivals. Observed time-series gi are modelled as a convolution of a simpler time-series fi, and an invariant point spread function (PSF) h that attempts to account for the earthquake source process. The method is used on the shear wave time window containing SKS and S, whereby using a Gaussian PSF produces more impulsive, narrower, signals in the wave train. The resulting restored time-series facilitates more accurate and objective relative traveltime estimation of the individual seismic arrivals. We demonstrate the accuracy of the reconstruction method on synthetic seismograms generated by the reflectivity method. Clean and sharp reconstructions are obtained with real data, even for signals with relatively high noise content. Reconstructed signals are simpler, more impulsive, and narrower, which allows highlighting of some details of arrivals that are not readily apparent in raw waveforms. In particular, phases nearly coincident in time can be separately identified after processing. This is demonstrated for two seismic wave pairs used to probe deep mantle and core-mantle boundary structure: (1) the Sab and Scd arrivals, which travel above and within, respectively, a 200-300-km-thick, higher than average shear wave velocity layer at the base of the mantle, observable in the 88-92 deg epicentral distance range and (2) SKS and SPdiff KS, which are core waves with the latter having short arcs of P-wave diffraction, and are nearly identical in timing near 108-110 deg in distance. A Java/Matlab algorithm was developed for the signal restoration, which can be downloaded from the authors web page, along with example data and synthetic seismograms.

  12. Subduction of the primordial crust into the deep mantle

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    Hiroki Ichikawa

    2017-03-01

    Full Text Available The primordial crust on the Earth formed from the crystallization of the surface magma ocean during the Hadean. However, geological surveys have found no evidence of rocks dating back to more than 4 Ga on the Earth's surface, suggesting the Hadean crust was lost due to some processes. We investigated the subduction of one of the possible candidates for the primordial crust, anorthosite and KREEP crust similar to the Moon, which is also considered to have formed from the crystallization of the magma ocean. Similar to the present Earth, the subduction of primordial crust by subduction erosion is expected to be an effective way of eliminating primordial crust from the surface. In this study, the subduction rate of the primordial crust via subduction channels is evaluated by numerical simulations. The subduction channels are located between the subducting slab and the mantle wedge and are comprised of primordial crust materials supplied mainly by subduction erosion. We have found that primordial anorthosite and KREEP crust of up to ∼50 km thick at the Earth's surface was able to be conveyed to the deep mantle within 0.1-2 Gy by that mechanism.

  13. Effect of phase transformations on microstructures in deep mantle materials

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    Merkel, Sébastien; Langrand, Christopher; Rosa, Angelika; Hilairet, Nadège

    2017-04-01

    Phase transformations induce microstructural changes in deep Earth materials, including changes in grain size and orientation distribution. The effect of phase transformations on mineral microstructures is usually studied using electron microscopy on quench products from high P/T experiments. The method allows for a precise evaluation of the microscopic mechanisms involved. It is limited, however, to samples that can be quenched to ambient conditions and allows for investigations at a single P/T point for each experiment. In recent years, we extended the use of multigrain crystallography to samples inside diamond anvil cells under mantle P/T conditions. The method allows for monitoring the orientations of hundreds of grains and grain size variations during various physical processes, such as plastic deformation and successions of phase transformations (Rosa et al 2015, Langrand et al 2017). Here, we will show results concerning hydrous Mg2SiO4 during the series of α-β-γ phase transformations up to 40 GPa and 850 °C. Such results are important to understand the descending behaviour of subducted slabs, observations of seismic anisotropy, and polarity changes for seismic waves reflected of deep Earth interfaces. The data is used to asses the effect of the transformation on grain orientation and grain sizes. In particular, we do not observe orientation relationships between the parent α-phase and the daughter β-phase phase, suggesting an incoherent growth. We also observe significant grain size reductions and only little grain growth within the newly formed phases (Rosa et al 2016). These new results are important for understanding the mechanical behavior of subducting slabs, seismic anisotropy in the Earth's mantle, and phase transformation mechanisms in olivine. Now that it is validated, the method can also be applied to other phases that can not be studied using electron microscopy, such as perovskite and post-perovskite. Langrand, Hilairet, Nisr, Roskosz, Rib

  14. Preventing Deep Vein Thrombosis

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    ... you may wear special elastic stockings or inflatable boots. These devices squeeze the muscles to help keep ... Special stockings that compress the legs below the knee may help prevent blood clots from forming. However, ...

  15. THE VELOCITY STRUCTURE OF THE UPPER MANTLE AND REGIONAL DEEP THERMODYNAMICS OF THE BAIKAL RIFT ZONE

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    Alexander V. Pospeev

    2012-01-01

    Full Text Available The article is aimed at discussion of geological and geophysical aspects of the ‘asthenospheric’ interpretation of the ‘anomalous’ mantle layer that is revealed in the Baikal rift zone by deep seismic sounding (DSS methods. Based on the analysis of the geoelectrical model, estimations of rheological properties, regional geothermal and deep petrological data, it is concluded that the ‘anomalous’ mantle phenomenon should be interpreted within the framework of solid-phase models. It is shown that the actual minimum depth to the top of the asthenosphere is about 60–70 km in the region under study, and temperatures at the surface of the Earth’s mantle varies from 600 to 900 °С. It is most probable that velocities are reduced in the ‘anomalous’ mantle layer due to the presence of hightemperature spinel-pyroxene facies of the mantle rocks.

  16. Redox freezing and melting in the Earth's deep mantle resulting from carbon-iron redox coupling.

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    Rohrbach, Arno; Schmidt, Max W

    2011-04-14

    Very low seismic velocity anomalies in the Earth's mantle may reflect small amounts of melt present in the peridotite matrix, and the onset of melting in the Earth's upper mantle is likely to be triggered by the presence of small amounts of carbonate. Such carbonates stem from subducted oceanic lithosphere in part buried to depths below the 660-kilometre discontinuity and remixed into the mantle. Here we demonstrate that carbonate-induced melting may occur in deeply subducted lithosphere at near-adiabatic temperatures in the Earth's transition zone and lower mantle. We show experimentally that these carbonatite melts are unstable when infiltrating ambient mantle and are reduced to immobile diamond when recycled at depths greater than ∼250 kilometres, where mantle redox conditions are determined by the presence of an (Fe,Ni) metal phase. This 'redox freezing' process leads to diamond-enriched mantle domains in which the Fe(0), resulting from Fe(2+) disproportionation in perovskites and garnet, is consumed but the Fe(3+) preserved. When such carbon-enriched mantle heterogeneities become part of the upwelling mantle, diamond will inevitably react with the Fe(3+) leading to true carbonatite redox melting at ∼660 and ∼250 kilometres depth to form deep-seated melts in the Earth's mantle.

  17. Spin Transition in the Lower Mantle: Deep Learning and Pattern Recognition of Superplumes from the Mid-mantle and Mid-mantle Slab Stagnation

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    Yuen, D. A.; Shahnas, M. H.; De Hoop, M. V.; Pysklywec, R.

    2016-12-01

    The broad, slow seismic anomalies under Africa and Pacific cannot be explained without ambiguity. There is no well-established theory to explain the fast structures prevalent globally in seismic tomographic images that are commonly accepted to be the remnants of fossil slabs at different depths in the mantle. The spin transition from high spin to low spin in iron in ferropericlase and perovskite, two major constituents of the lower mantle can significantly impact their physical properties. We employ high resolution 2D-axisymmetric and 3D-spherical control volume models to reconcile the influence of the spin transition-induced anomalies in density, thermal expansivity, and bulk modulus in ferropericlase and perovskite on mantle dynamics. The model results reveal that the spin transition effects increase the mixing in the lower regions of mantle. Depending on the changes of bulk modulus associated with the spin transition, these effects may also cause both stagnation of slabs and rising plumes at mid-mantle depths ( 1600 km). The stagnation may be followed by downward or upward penetration of cold or hot mantle material, respectively, through an avalanche process. The size of these mid-mantle plumes reaches 1500 km across with a radial velocity reaching 20 cm/yr near the seismic transition zone and plume heads exceeding 2500 km across. We will employ a deep-learning algorithm to formulate this challenge as a classification problem where modelling/computation aids in the learning stage for detecting the particular patterns.The parameters based on which the convection models are developed are poorly constrained. There are uncertainties in initial conditions, heterogeneities and boundary conditions in the simulations, which are nonlinear. Thus it is difficult to reconstruct the past configuration over long time scales. In order to extract information and better understand the parameters in mantle convection, we employ deep learning algorithm to search for different

  18. Tomographic and Geodynamic Constraints on Convection-Induced Mixing in Earth's Deep Mantle

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    Hafter, D. P.; Forte, A. M.; Bremner, P. M.; Glisovic, P.

    2017-12-01

    Seismological studies reveal two large low-shear-velocity provinces (LLSVPs) in the lowermost mantle (e.g., Su et al. 1994; Wang & Wen 2007; He & Wen 2012), which may represent accumulations of subducted slabs at the CMB (Tan & Gurnis 2005; Christensen & Hoffman 1994) or primordial material generated in the early differentiation of Earth (e.g. Li et al. 2014). The longevity or stability of these large-scale heterogeneities in the deep mantle depends on the vigor and spatial distribution of the convective circulation, which is in turn dependent on the distribution of mantle buoyancy and viscosity (e.g. Glisovic & Forte 2015). Here we explore the state of convective mixing in the mantle using the ASPECT convection code (Kronbichler et al. 2012). A series of experiments are conducted to consider the geochemical and dynamical contributions of LLSVPs to deep-mantle upwellings and corresponding plume-sourced volcanism. The principal feature of these experiments is the use of particle tracers to track geochemical changes in the LLSVPs and mantle plumes in addition to identifying those parts of the mantle that may remain unmixed. We employ 3-D mantle density anomalies derived from joint inversions of seismic, geodynamic and mineral physics constraints and geodynamically-constrained viscosity distributions (Glisovic et al. 2015) to ensure that the predicted flow fields yield a good match to key geophysical constraints (e.g. heat flow, global gravity anomalies and plate velocities).

  19. Subduction of oceanic crust into the deep mantle imaged by a new seismic migration

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    Kito, T.; Korenaga, J.

    2009-12-01

    The behavior of subducted materials in the deep mantle may be a key issue to understand chemical evolution of the Earth’s mantle. Although recent tomographic images imply that subducted slabs may penetrate into the lower mantle in some regions, the remixing process of slab materials remains poorly understood. To investigate the fate of the subducted slabs beneath Central America, we analyzed USArray data from intermediate- and deep-earthquakes in South America. To suppress artifacts and noise, and obtain a high-resolution image, we applied a newly developed seismic migration method called cross-correlation weighted migration (CCWM) that weights migrated energy based on coherency of waveforms. The migrated seismic energy was then evaluated using bootstrap resampling to determine statistically significant seismic signals. The observed scattered waves may be explained by the subducted former oceanic lithosphere (MORB) in the deep mantle, which provides independent evidence for slab penetration into the lower mantle and mass transportation across the mantle transition zone, at least in this region.

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

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    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.

  1. The Interaction Between Supercontinent Cycles and Compositional Variations in the Deep Mantle

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    Lowman, J. P.; Trim, S. J.

    2015-12-01

    Earth is the only planet known to currently feature active plate tectonics. Two features that may influence the Earth's ability to sustain plate-like surface motion are the presence of continents and the inferred chemical piles lying on the core mantle boundary. In our previous study that modelled thermochemical convection in the mantle with evolving plates, it was shown that upwellings that form on top of chemical piles are relatively weak and make a diminished contribution to lithospheric stress. Yet, surface yielding is required in order to maintain plate tectonics and form new plate boundaries. Consequently an intrinsically dense layer in the lower mantle can decrease the vigour of convection and the likelihood of surface failure. In contrast to the mantle upwellings that form above the chemically dense provinces in our models, particularly vigorous plumes form where the ambient mantle lies adjacent to the core mantle boundary and at the edges of the chemically dense piles. Continents also affect surface mobility, due to their inherent buoyancy and their distinct yield strength. In this study we employ numerical models of mantle convection featuring both tectonic plates and compositional variation in the mantle and lithosphere. Plate-like surface motion is dynamically modelled using a force-balance method that determines plate velocities based upon lithospheric stresses. Oceanic and continental margins evolve in response to the plate velocities and specified lithospheric yield stresses. Compositional variations in the deep mantle are tracked using the tracer ratio method. For a range of ratios of the ambient mantle density to the density of the compositionally enriched material, we examine the the impact of mantle compositional variation on plate evolution, the effect of continents on planetary surface mobility and the frequency of supercontinent assembly versus the mobility of compositional provinces.

  2. Deep mantle structure as a reference frame for movements in and on the Earth.

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    Torsvik, Trond H; van der Voo, Rob; Doubrovine, Pavel V; Burke, Kevin; Steinberger, Bernhard; Ashwal, Lewis D; Trønnes, Reidar G; Webb, Susan J; Bull, Abigail L

    2014-06-17

    Earth's residual geoid is dominated by a degree-2 mode, with elevated regions above large low shear-wave velocity provinces on the core-mantle boundary beneath Africa and the Pacific. The edges of these deep mantle bodies, when projected radially to the Earth's surface, correlate with the reconstructed positions of large igneous provinces and kimberlites since Pangea formed about 320 million years ago. Using this surface-to-core-mantle boundary correlation to locate continents in longitude and a novel iterative approach for defining a paleomagnetic reference frame corrected for true polar wander, we have developed a model for absolute plate motion back to earliest Paleozoic time (540 Ma). For the Paleozoic, we have identified six phases of slow, oscillatory true polar wander during which the Earth's axis of minimum moment of inertia was similar to that of Mesozoic times. The rates of Paleozoic true polar wander (Earth's mantle may have operated throughout the entire Phanerozoic.

  3. Rock species formation due to deep-mantle melting

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    Fomin, Ilya; Tackley, Paul

    2017-04-01

    Melting and melting migration are processes leading to chemically distinct rock species from a homogeneous substrate in the Earth mantle. Iron-rich melts and corresponding rock species are proposed to result from magma ocean progressive crystallization [Labrosse et al., 2007], and modern geophysical models of ULVZ (e.g. [Beuchert & Schmeling, 2013]) discuss their presence at around the CMB today. We perform long-term (tens of millions of years) numerical simulations of the Earth's mantle for a plausible range of CMB temperatures to understands the possibility of melting and it's consequences. Our model of melting is based on experimental data and ab initio simulations. Physical properties (liquid-solid density differences) are adjusted with data of [de Koker et al., 2013; Mosenfelder et al., 2007; Stixrude & Lithgow-Bertelloni, 2011; Thomas & Asimow, 2013]. This model is included in StagYY numerical code (e.g. [Tackley, 2008]) to simulate mass and thermal fluxes within the Earth mantle. Melt segregation (rocks' permeability and velocities) is considered using equations listed in [Abe, 1995; Solomatov, Stevenson, 1993; Martin & Nokes, 1989]. Thermal effects (adiabatic heating and viscous dissipation) are considered. Viscous dissipation term includes Darcy flux term, but omits highly non-linear Brinkman contribution [Nield, 2007]. Modeling predicts formation of melt if temperature at CMB exceeds 4000-4050K. It's segregation and reequilibration results in sufficient volumes of slightly iron-enriched melt lighter than solid counterpart and moving upward. However, it's propagation is strongly controlled by temperature. Partial melting atop the molten layer results in formation of refractory iron-poor restite which delaminates and sink down, so that a layer of iron-depleted material forms underneath the molten layer. Our model applied to homogeneous pyrolitic mantle results in formation of layers of iron-depleted material with average FeO around 4.6 mol.% and iron

  4. Continuous subduction of oceanic crust into the deep mantle beneath central America

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    Kito, T.; Korenaga, J.

    2008-12-01

    Recent tomographic images imply that subducted slabs may penetrate into the lower mantle in some regions. However the behavior of the subducted materials around and below the mantle transition zone remains poorly understood. In order to investigate the fate of the subducted slab beneath central America, we have analyzed broadband teleseismic data from intermediate- and deep-earthquakes in south America recorded at several Californian seismic networks. To suppress artifacts and obtain a high resolution image, we have applied seismic migration method called Slowness Back azimuth Weighted Migration (SBWM) which utilizes not only travel time but also slowness and back azimuth information in the wavefield. We have observed reflected/scattered waves from heterogeneities associated with subduction processes. The migrated seismic energy has then been evaluated using the jackknife algorithm to determine statistically significant seismic signals. The observed reflected seismic waves can be explained by the subducted former oceanic lithosphere (MORB) in the deep mantle, which provides independent evidence for slab penetration into the lower mantle and mass transportation across the mantle transition zone, at least in this region.

  5. The Role of Deep Mantle Flow in Shaping the Hawaiian-Emperor Bend

    Science.gov (United States)

    Hassan, R.; Müller, D.; Gurnis, M.; Williams, S.; Flament, N. E.

    2016-12-01

    Age-progressive volcanic hotspot tracks are typical surface expressions of plate tectonic movement on top of narrow plumes of hot material within Earth's mantle. Seismic imaging reveals that these plumes can be of deep origin, potentially rooted on thermochemical structures in the lower mantle. Although palaeomagnetic and radiometric age data suggest that mantle flow can advect plume conduits laterally, the flow dynamics underlying the formation of the sharp bend occurring only in the Hawaiian-Emperor hotspot track in the Pacific Ocean remains enigmatic. The north Pacific features long-lasting subduction systems, unlike those in the south Pacific. We present palaeogeographically-constrained numerical models of thermochemical convection demonstrating that flow in the deep lower mantle under the north Pacific was anomalously vigorous between 100 Ma and 50 Ma. These models show a sharp bend in the Hawaiian-Emperor hotspot track arising from the interplay of plume tilt and the lateral advection of plume sources. We show that the different trajectories of the Hawaiian and Louisville hotspot tracks arise from asymmetric deformation of thermochemical structures under the Pacific between 100 Ma and 50 Ma. This asymmetric deformation waned just before the Hawaiian-Emperor bend developed, owing to flow in the deepest lower mantle associated with slab descent in the north and south Pacific.

  6. A rapid burst in hotspot motion through the interaction of tectonics and deep mantle flow

    Science.gov (United States)

    Hassan, Rakib; Müller, R. Dietmar; Gurnis, Michael; Williams, Simon E.; Flament, Nicolas

    2016-05-01

    Volcanic hotspot tracks featuring linear progressions in the age of volcanism are typical surface expressions of plate tectonic movement on top of narrow plumes of hot material within Earth’s mantle. Seismic imaging reveals that these plumes can be of deep origin—probably rooted on thermochemical structures in the lower mantle. Although palaeomagnetic and radiometric age data suggest that mantle flow can advect plume conduits laterally, the flow dynamics underlying the formation of the sharp bend occurring only in the Hawaiian-Emperor hotspot track in the Pacific Ocean remains enigmatic. Here we present palaeogeographically constrained numerical models of thermochemical convection and demonstrate that flow in the deep lower mantle under the north Pacific was anomalously vigorous between 100 million years ago and 50 million years ago as a consequence of long-lasting subduction systems, unlike those in the south Pacific. These models show a sharp bend in the Hawaiian-Emperor hotspot track arising from the interplay of plume tilt and the lateral advection of plume sources. The different trajectories of the Hawaiian and Louisville hotspot tracks arise from asymmetric deformation of thermochemical structures under the Pacific between 100 million years ago and 50 million years ago. This asymmetric deformation waned just before the Hawaiian-Emperor bend developed, owing to flow in the deepest lower mantle associated with slab descent in the north and south Pacific.

  7. Earth's Deep Carbon Cycle Constrained by Partial Melting of Mantle Peridotite and Eclogite

    Science.gov (United States)

    Dasgupta, R.; Hirschmann, M. M.; Withers, A. C.

    2006-05-01

    The mass of carbon in the mantle is thought to exceed that in all Earth's other reservoirs combined1 and large fluxes of carbon are cycled into and out of the mantle via subduction and volcanic emission. Devolatilization is known to release water in the mantle wedge, but release of carbon could be delayed if the relevant decarbonation reactions or solidi of oceanic crust are not encountered along P-T path of subduction. Outgassing of CO2 from the mantle also has a critical influence on Earth's climate for time scales of 108-109 yr1. The residence time for carbon in the mantle is thought to exceed the age of the Earth1,2, but it could be significantly shorter owing to pervasive deep melting beneath oceanic ridges. The dominant influx of carbon is via carbonate in altered ocean-floor basalts, which survives decarbonation during subduction. Our experiments demonstrate that solidi of carbonated eclogite remain hotter than average subduction geotherms at least as deep as transition zone3, and thus significant subducted C is delivered to the deep Earth, rather than liberated in the shallow mantle by melting. Flux of CO2 into the mantle, assuming average estimate of carbon in altered ocean crust of 0.21 wt. % CO24, can amount to 0.15 × 1015 g/yr. In upwelling mantle, however, partial melting of carbonated eclogite releases calcio-dolomitic carbonatite melt at depths near ~400 km and metasomatically implants carbonate to surrounding peridotite. Thus, volcanic release of CO2 to basalt source regions is likely controlled by the solidus of carbonated peridotite. Our recent experiments with nominally anhydrous, carbonate-bearing garnet lherzolite indicate that the solidus of peridotite with a trace amount of CO2 is ~500 °C lower than that of volatile-free peridotite at 10 GPa5. In upwelling mantle the solidus of carbonated lherzolite is ~100-200 km shallower than that of eclogite+CO2, but beneath oceanic ridges, initial melting occurs as deep as 300-330 km. For peridotite

  8. Gondwana subduction-modified mantle domain prevents magmatic seafloor generation in the Central Indian Ridge

    Science.gov (United States)

    Morishita, T.; Nakamura, K.; Senda, R.; Suzuki, K.; Kumagai, H.; Sato, H.; Sato, T.; Shibuya, T.; Minoguchi, K.; Okino, K.

    2013-12-01

    The creation of oceanic crust at mid-ocean ridges is essential to understanding the genesis of oceanic plate and the evolution of the Earth. Detailed bathymetric measurements coupled with dense sample recovery at mid-ocean ridge revealed a wide range of variations in the ridge and seafloor morphologies, which cannot be simply explained by a spreading rate, but also by ridge geometry, mantle compositions and thermal structure (Dick et al., 2003 Nature; Cannat et al. 2006 Geology). It is now widely accepted that very limited magmatic activity with tectonic stretching generates oceanic core complex and/or smooth seafloor surface in the slow to ultraslow-spreading ridges, where serpentinized peridotite and gabbros are expected to be exposed associated with detachment faults (Cann et al., 1997 Nature; Cannat et al., 2006), although magmatism might be an essential role for the formation of oceanic core complexes (Buck et al., 2005 Nature; Tucholke et al 2008 JGR). A rising question is why magmatic activity is sometimes prevented during the oceanic plate formation. Ancient melting domain, that are too refractory to melt even in adiabatically upwelling to the shallow upper mantle, might cause the amagmatic spreading ridges (Harvey et al., 2006 EPSL, Liu et al.,2008 Nature). Its origin and effect on seafloor generations are, however, not well understood yet. We report an oceanic hill as an example of an ancient subduction-modified mantle domain, probably formed at continental margin of the Gondwanaland~Pangea supercontinent, existing beneath the Central Indian Ridge. This domain is the most likely to have prevented magmatic seafloor generation, resulting in creation of very deep oceanic valley and serpentine diaper (now the studied oceanic hill) at the present Central Indian ridge.

  9. Gravity inversion of deep-crust and mantle interfaces in the Three Gorges area

    Directory of Open Access Journals (Sweden)

    Wang Jian

    2012-11-01

    Full Text Available To better understand the heterogeneity of deep-crust and mantle interfaces in the region of the Three Gorges, China, we used the Parker-Oldenburg iterative inversion method to invert existing Bouguer gravity data from the Three Gorges area (1 : 500000, a new gravity map of the Three Gorges Dam (1 : 200000, and the results of deep seismic soundings. The inversion results show a Moho depth of 42 km between Badong and Zigui and the depth of the B2 lower-crustal interface beneath the Jianghan Plain and surrounding areas at 21–25 km. The morphology of crustal interfaces and the surface geology present an overpass structure. The mid-crust beneath the Three Gorges Dam is approximately 9 km thick, which is the thinnest in the Three Gorges area and may be related to the shallow low-density body near the Huangling anticline. The upper crust is seismogenic, and there is a close relationship between seismicity and the deep-crust and mantle interfaces. For example, the M5. 1 Zigui earthquake occurred where the gradients of the Moho and the B2 interface are the steepest, showing that deep structure has a very important effect on regional seismicity.

  10. Seismic characteristics of central Brazil crust and upper mantle: A deep seismic refraction study

    Science.gov (United States)

    Soares, J.E.; Berrocal, J.; Fuck, R.A.; Mooney, W.D.; Ventura, D.B.R.

    2006-01-01

    A two-dimensional model of the Brazilian central crust and upper mantle was obtained from the traveltime interpretation of deep seismic refraction data from the Porangatu and Cavalcante lines, each approximately 300 km long. When the lines were deployed, they overlapped by 50 km, forming an E-W transect approximately 530 km long across the Tocantins Province and western Sa??o Francisco Craton. The Tocantins Province formed during the Neoproterozoic when the Sa??o Francisco, the Paranapanema, and the Amazon cratons collided, following the subduction of the former Goia??s ocean basin. Average crustal VP and VP/VS ratios, Moho topography, and lateral discontinuities within crustal layers suggest that the crust beneath central Brazil can be associated with major geological domains recognized at the surface. The Moho is an irregular interface, between 36 and 44 km deep, that shows evidences of first-order tectonic structures. The 8.05 and 8.23 km s-1 P wave velocities identify the upper mantle beneath the Porangatu and Cavalcante lines, respectively. The observed seismic features allow for the identification of (1) the crust has largely felsic composition in the studied region, (2) the absence of the mafic-ultramafic root beneath the Goia??s magmatic arc, and (3) block tectonics in the foreland fold-and-thrust belt of the northern Brasi??lia Belt during the Neoproterozoic. Seismic data also suggested that the Bouguer gravimetric discontinuities are mainly compensated by differences in mass distribution within the lithospheric mantle. Finally, the Goia??s-Tocantins seismic belt can be interpreted as a natural seismic alignment related to the Neoproterozoic mantle domain. Copyright 2006 by the American Geophysical Union.

  11. Theoretical Prediction of Melting Relations in the Deep Mantle: the Phase Diagram Approach

    Science.gov (United States)

    Belmonte, D.; Ottonello, G. A.; Vetuschi Zuccolini, M.; Attene, M.

    2016-12-01

    Despite the outstanding progress in computer technology and experimental facilities, understanding melting phase relations in the deep mantle is still an open challenge. In this work a novel computational scheme to predict melting relations at HP-HT by a combination of first principles DFT calculations, polymer chemistry and equilibrium thermodynamics is presented and discussed. The adopted theoretical framework is physically-consistent and allows to compute multi-component phase diagrams relevant to Earth's deep interior in a broad range of P-T conditions by a convex-hull algorithm for Gibbs free energy minimisation purposely developed for high-rank simplexes. The calculated phase diagrams are in turn used as a source of information to gain new insights on the P-T-X evolution of magmas in the deep mantle, providing some thermodynamic constraints to both present-day and early Earth melting processes. High-pressure melting curves of mantle silicates are also obtained as by-product of phase diagram calculation. Application of the above method to the MgO-Al2O3-SiO2 (MAS) ternary system highlights as pressure effects are not only able to change the nature of melting of some minerals (like olivine and pyroxene) from eutectic to peritectic (and vice versa), but also simplify melting relations by drastically reducing the number of phases with a primary phase field at HP-HT conditions. It turns out that mineral phases like Majorite-Pyrope garnet and Anhydrous Phase B (Mg14Si5O24), which are often disregarded in modelling melting processes of mantle assemblages, are stable phases at solidus or liquidus conditions in a P-T range compatible with the mantle transition zone (i.e. P = 16 - 23 GPa and T = 2200 - 2700 °C) when their thermodynamic and thermophysical properties are properly assessed. Financial support to the Senior Author (D.B.) during his stay as Invited Scientist at the Institut de Physique du Globe de Paris (IPGP, Paris) is warmly acknowledged.

  12. Geochemical Consequence of Extraction of Incipient CO2-rich melts from Earth's Deep Upper Mantle

    Science.gov (United States)

    Dasgupta, R.; Withers, A. C.; McDonough, W. F.; Hirschmann, M. M.

    2007-12-01

    The initiation of partial melting beneath mid-oceanic ridges and ocean islands likely produces incipient carbonatitic melts. These highly mobile melts generated at great depth may not only affect geophysical properties of deep upper mantle but can also influence Earth's geochemical evolution by releasing incompatible parent and/or daughter elements, heat producing elements, and volatiles. But constraints on the fractionation of the key trace elements between the peridotitic residue and carbonatitic melts are lacking at conditions of initiation of partial melting beneath ridges.Experiments at 6.6-8.6 GPa and 1265-1470 °C on carbonated peridotite doped with a blend of trace elements produced cpx + garnet + magnesite ± opx ± olivine + carbonatitic melt (cbL) similar in composition to that expected at the solidus of carbonated peridotite (Ca# = 0.52 at 6.6 GPa and 0.45 at 8.6 GPa; Na2O = ~4 wt.% at 6.6 GPa and ~2.5 wt.% at 8.6 GPa). Compared to previous studies at lower pressures (2.0-4.6 GPa), Dcpx/cbL from the present study are smaller for elements substituting into the cpx M2 site, especially trivalent cations ( DLu = 0.17, DLa = 0.006). Dcpx/cbL for U (0.001) and Th (0.002) are also noticeably lower than the previous estimates. In contrast, Dgarnet/cbL values are higher for REEs ( DLu = 4.6, DLa = 0.039) and HFSEs, U (0.023) and Th (0.017).Our estimate of Dperidotite/cbL indicates that incipient carbonatite extraction from the deep upper mantle will produce a residue with a more depleted Rb/Sr, U/Pb, Th/U, and enriched Sm/Nd, which may evolve to produce the most common of the mantle end member components, PREMA. Metasomatic implantation of deep carbonatitic melt into the lithosphere can generate a high-μ (238U/204Pb) signature, whereas mixing of carbonatite with elevated Th/U can contribute to the observed 230Th-excesses in MORBs. However, carbonatites derived by incipient melting of depleted (DMM) mantle have limited trace element enrichments, ~10-100

  13. Deep Mantle Layering by Post-Perovskite Dissociation at 0.9 TPa in GJ876d Super Earth

    Science.gov (United States)

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

    2017-12-01

    The processes in the interior of the exoplanets are poorly known. This is due to the uncertainties in the pressure- and temperature-dependence of the mantle properties, as well as the circumstances under which the mantle processes such as phase and spin transitions and structural changes in the mantle minerals occur. Recent advances in high pressure mineral physics as well as some recent theoretical studies have yielded new insights into our understanding of mantle dynamics. MgSiO3 post-perovskite (pPv) dissociates into MgO and MgSi2O5 at 0.9 TPa, and MgSi2O5 dissociates into MgO and SiO2 at 2.1 TPa. Both dissociations are endothermic and the first dislocation with a large Clapeyron slope of -12 MPa/K is expected to occur close to the bottom of the mantle in GJ876d super-Earth which is 7.5 times more massive than the Earth. Employing 3D-spherical control volume compressible models we perform a systematic investigation on the combined impact of the deep mantle dissociation of post-perovskite and the mantle conductivity and the viscosity, on the mixing, cooling and the style of the convection in GJ876d super Earth. Our model results reveal that in the presence of deep mantle dissociation of post-perovskite into MgO and MgSi2O5 at 0.9 TP, the mean mantle temperature decreases which is associated with the viscosity increase. However, while this deep mantle endothermic process for high viscosities ( 1023 Pa.s) does not cause layering in the bottom of mantle, for viscosities 1022 Pa.s and below, a layering of thickness 500 km develops above the CMB. The mean temperature and heat flow decrease in the presence of pPv dissociation-induced layering and the impact of the viscosity on mean mantle temperature is enhanced. In the layered models while the upper layer is cooling mainly by conduction; there may exist a vigorous convection in the lower layer above the CMB depending on the strength of the viscosity.

  14. A comparison of peridotites from the Molloy Deep and the Gakkel Ridge with mantle xenolites from Spitsbergen

    Science.gov (United States)

    Hansen, H. E.; Amundsen, H. E. F.; Snow, J. E.; Pedersen, R. B.

    2003-04-01

    Along the Arctic ridges, mantle peridotites are tectonically exposed in the Molloy Deep and along the Gakkel Ridge. In the Arctic region, mantel peridotites are also present as xenolites in Quaternary volcanoes in the Bockfjord area on Spitsbergen -- approximately 150 km east of the Molloy Deep. These volcanic centres contain up to 15--20% of xenolites that comprise: Cr-diopside lherzolites, wehrlites, meta-pyroksenites and granulites. The Sr and Nd isotopic composition of clinopyroxenes from lherzolite xenolites have been analysed and compared with the isotopic composition of clinopyroxenes extracted from mantle peridotites from the Molloy Deep and the Gakkel Ridge, as well as with the isotopic compositions of basalts dredged from the Mohns and the Knipovich Ridges. Preliminary results show that a group of lherzolite xenolites from Spitsbergen have Sr-Nd isotopic compositions similar to the enriched end member of the Mohns-Knipovich trend. Other xenolites show much more depleted Nd-isotopic compositions. These xenolites have Sm-Nd model ages ranging from 900 Ma to 1700 Ma suggesting that parts of the sub-continental mantle in the region experienced Precambrian melt extraction. The peridotites from the Molloy Deep have similar Nd-isotopic compositions as the least depleted mantle xenolites from Spitsbergen, and plot also at the enriched end of the Mohns-Knipovich trend. The peridotites analysed from the Gakkel Ridge show, however, significantly higher 143Nd/144Nd ratios than the peridotites from the Molloy Deep.

  15. Mission Moho: Rationale for drilling deep through the ocean crust into the upper mantle

    Science.gov (United States)

    Ildefonse, B.; Abe, N.; Kelemen, P. B.; Kumagai, H.; Teagle, D. A. H.; Wilson, D. S.; Moho Proponents, Mission

    2009-04-01

    Sampling a complete section of the ocean crust to the Moho was the original inspiration for scientific ocean drilling, and remains the main goal of the 21st Century Mohole Initiative in the IODP Science Plan. Fundamental questions about the composition, structure, and geophysical characteristics of the ocean lithosphere, and about the magnitude of chemical exchanges between the mantle, crust and oceans remain unresolved due to the absence of in-situ samples and measurements. The geological nature of the Mohorovičić discontinuity itself remains poorly constrained. "Mission Moho" is a proposal that was submitted to IODP in April 2007, with the ambition to drill completely through intact oceanic crust formed at a fast spreading rate, across the Moho and into the uppermost mantle. Although, eventually, no long-term mission was approved by IODP, the scientific objectives related to deep drilling in the ocean crust remain essential to our understanding of the Earth. These objectives are to : - Determine the geological meaning of the Moho in different oceanic settings, determine the in situ composition, structure and physical properties of the uppermost mantle, and understand mantle melt migration, - Determine the bulk composition of the oceanic crust to establish the chemical links between erupted lavas and primary mantle melts, understand the extent and intensity of seawater hydrothermal exchange with the lithosphere, and estimate the chemical fluxes returned to the mantle by subduction, - Test competing hypotheses of the ocean crust accretion at fast spreading mid-ocean ridges, and quantify the linkages and feedbacks between magma intrusion, hydrothermal circulation and tectonic activity, - Calibrate regional seismic measurements against recovered cores and borehole measurements, and understand the origin of marine magnetic anomalies, - Establish the limits of life in the ocean lithosphere. The "MoHole" was planned as the final stage of Mission Moho, which requires

  16. Deep vein thrombosis: diagnosis, treatment, and prevention

    Energy Technology Data Exchange (ETDEWEB)

    Stewart, W.P.; Youngswick, F.D.

    Deep vein thrombosis (DVT) is a dangerous complication that may present after elective foot surgery. Because of the frequency with which DVT occurs in the elderly patient, as well as in the podiatric surgical population, the podiatrist should be acquainted with this entity. A review of the diagnosis, treatment, prevention, and the role of podiatry in the management of DVT is discussed in this paper.

  17. Effects of iron on the lattice thermal conductivity of Earth's deep mantle and implications for mantle dynamics.

    Science.gov (United States)

    Hsieh, Wen-Pin; Deschamps, Frédéric; Okuchi, Takuo; Lin, Jung-Fu

    2018-04-17

    Iron may critically influence the physical properties and thermochemical structures of Earth's lower mantle. Its effects on thermal conductivity, with possible consequences on heat transfer and mantle dynamics, however, remain largely unknown. We measured the lattice thermal conductivity of lower-mantle ferropericlase to 120 GPa using the ultrafast optical pump-probe technique in a diamond anvil cell. The thermal conductivity of ferropericlase with 56% iron significantly drops by a factor of 1.8 across the spin transition around 53 GPa, while that with 8-10% iron increases monotonically with pressure, causing an enhanced iron substitution effect in the low-spin state. Combined with bridgmanite data, modeling of our results provides a self-consistent radial profile of lower-mantle thermal conductivity, which is dominated by pressure, temperature, and iron effects, and shows a twofold increase from top to bottom of the lower mantle. Such increase in thermal conductivity may delay the cooling of the core, while its decrease with iron content may enhance the dynamics of large low shear-wave velocity provinces. Our findings further show that, if hot and strongly enriched in iron, the seismic ultralow velocity zones have exceptionally low conductivity, thus delaying their cooling.

  18. Nitrogen solubility in the deep mantle and the origin of Earth's primordial nitrogen budget

    Science.gov (United States)

    Yoshioka, Takahiro; Wiedenbeck, Michael; Shcheka, Svyatoslav; Keppler, Hans

    2018-04-01

    be modeled. Such models show that if the magma ocean coexisted with a primordial atmosphere having a nitrogen partial pressure of just a few bars, several times the current atmospheric mass of nitrogen must have been trapped in the deep mantle. It is therefore plausible that the apparent depletion of nitrogen relative to other volatiles in the near-surface reservoirs reflects the storage of a larger reservoir of nitrogen in the solid Earth. Dynamic exchange between these reservoirs may have induced major fluctuations of bulk atmospheric pressure over Earth's history.

  19. Subduction recycling of continental sediments and the origin of geochemically enriched reservoirs in the deep mantle

    Energy Technology Data Exchange (ETDEWEB)

    Rapp, R.P.; Irifune, T.; Shimizu, N.; Nishiyama, N.; Norman, M.D.; Inoue, T. (Ehime U); (WHOI); (UC); (ANU)

    2008-10-08

    Isotopic and trace element geochemical studies of ocean island basalts (OIBs) have for many years been used to infer the presence of long-lived ({approx} 1-2 Ga old) compositional heterogeneities in the deep mantle related to recycling of crustal lithologies and marine and terrigenous sediments via subduction [e.g., Zindler, A., Hart, S.R., 1986. Chemical geodynamics. Annu. Rev. Earth Planet. Sci. 14, 493-571; Weaver, B.L., 1991. The origin of ocean island basalt end-member compositions: trace element and isotopic constraints. Earth Planet. Sci. Lett. 104, 381-397; Chauvel, C., Hofmann, A.W., Vidal, P., 1992. HIMU-EM: the French Polynesian connection. Earth Planet. Sci. Lett. 110, 99-119; Hofmann, A.W., 1997. Mantle geochemistry: the message from oceanic volcanism. Nature 385, 219-229; Willbold, M., Stracke, A., 2006. Trace element composition of mantle end-members: Implications for recycling of oceanic and upper and lower continental crust. Geochem. Geophys. Geosyst. Q04004. 7, doi:10.1029/2005GC001005]. In particular, models for the EM-1 type ('enriched mantle') OIB reservoir have invoked the presence of subducted, continental-derived sediment to explain high {sup 87}Sr/{sup 86}Sr ratios, low {sup 143}Nd/{sup 144}Nd and {sup 206}Pb/{sup 204}Pb ratios, and extreme enrichments in incompatible elements observed in OIB lavas from, for example, the Pitcairn Island group in the South Pacific [Woodhead, J.D., McCulloch, M.T., 1989; Woodhead, J.D., Devey, C.W., 1993. Geochemistry of the Pitcairn seamounts, I: source character and temporal trends. Earth Planet. Sci. Lett. 116, 81-99; Eisele, J., Sharma, M., Galer, S.J.G., Blichert-Toft, J., Devey, C.W., Hofmann, A.W., 2002. The role of sediment recycling in EM-1 inferred from Os, Pb, Hf, Nd, Sr isotope and trace element systematics of the Pitcairn hotspot. Earth Planet. Sci. Lett. 196, 197-212]. More recently, ultrapotassic, mantle-derived lavas (lamproites) from Gaussberg, Antarctica have been interpreted as

  20. Messengers from the deep: Fossil wadsleyite-chromite microstructures from the Mantle Transition Zone.

    Science.gov (United States)

    Satsukawa, Takako; Griffin, William L; Piazolo, Sandra; O'Reilly, Suzanne Y

    2015-11-13

    Investigations of the Mantle Transition Zone (MTZ; 410-660 km deep) by deformation experiments and geophysical methods suggest that the MTZ has distinct rheological properties, but their exact cause is still unclear due to the lack of natural samples. Here we present the first direct evidence for crystal-plastic deformation by dislocation creep in the MTZ using a chromitite from the Luobusa peridotite (E. Tibet). Chromite grains show exsolution of diopside and SiO2, suggesting previous equilibration in the MTZ. Electron backscattered diffraction (EBSD) analysis reveals that olivine grains co-existing with exsolved phases inside chromite grains and occurring on chromite grain boundaries have a single pronounced crystallographic preferred orientation (CPO). This suggests that olivine preserves the CPO of a high-pressure polymorph (wadsleyite) before the high-pressure polymorph of chromite began to invert and exsolve. Chromite also shows a significant CPO. Thus, the fine-grained high-pressure phases were deformed by dislocation creep in the MTZ. Grain growth in inverted chromite produced an equilibrated microstructure during exhumation to the surface, masking at first sight its MTZ deformation history. These unique observations provide a window into the deep Earth, and constraints for interpreting geophysical signals and their geodynamic implications in a geologically robust context.

  1. Numerical Modeling of Deep Mantle Convection: Advection and Diffusion Schemes for Marker Methods

    Science.gov (United States)

    Mulyukova, Elvira; Dabrowski, Marcin; Steinberger, Bernhard

    2013-04-01

    Thermal and chemical evolution of Earth's deep mantle can be studied by modeling vigorous convection in a chemically heterogeneous fluid. Numerical modeling of such a system poses several computational challenges. Dominance of heat advection over the diffusive heat transport, and a negligible amount of chemical diffusion results in sharp gradients of thermal and chemical fields. The exponential dependence of the viscosity of mantle materials on temperature also leads to high gradients of the velocity field. The accuracy of many numerical advection schemes degrades quickly with increasing gradient of the solution, while the computational effort, in terms of the scheme complexity and required resolution, grows. Additional numerical challenges arise due to a large range of length-scales characteristic of a thermochemical convection system with highly variable viscosity. To examplify, the thickness of the stem of a rising thermal plume may be a few percent of the mantle thickness. An even thinner filament of an anomalous material that is entrained by that plume may consitute less than a tenth of a percent of the mantle thickness. We have developed a two-dimensional FEM code to model thermochemical convection in a hollow cylinder domain, with a depth- and temperature-dependent viscosity representative of the mantle (Steinberger and Calderwood, 2006). We use marker-in-cell method for advection of chemical and thermal fields. The main advantage of perfoming advection using markers is absence of numerical diffusion during the advection step, as opposed to the more diffusive field-methods. However, in the common implementation of the marker-methods, the solution of the momentum and energy equations takes place on a computational grid, and nodes do not generally coincide with the positions of the markers. Transferring velocity-, temperature-, and chemistry- information between nodes and markers introduces errors inherent to inter- and extrapolation. In the numerical scheme

  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. Probing the oxidation state of iron in the deep mantle using high P,T Mössbauer spectroscopy

    Science.gov (United States)

    McCammon, C. A.; Kupenko, I.; Sinmyo, R.; Cerantola, V.; Potapkin, V.; Chumakov, A. I.; Kantor, A.; Rüffer, R.; Dubrovinsky, L. S.

    2014-12-01

    The bulk of the Earth's interior is not directly accessible, yet redox processes occurring deep within drive many of the events observed at its surface. Laboratory studies of the relevant minerals at the appropriate pressure and temperature conditions have been pivotal in advancing our understanding of the Earth's interior. Iron plays an important role because it is the only major element with multiple electronic configurations (oxidation and spin state); however most of our knowledge regarding the oxidation state of iron in deep mantle phases is based on measurements of samples quenched from high temperature and sometimes also from high pressure. Mössbauer spectroscopy has been a key player in such studies and results on quenched samples have shown that the oxidation state of iron varies considerably through the mantle, from predominantly ferrous iron in upper mantle and transition zone phases to roughly 50% ferric iron in silicate perovskite (bridgmanite) due to the strong affinity of ferric iron for that phase in the presence of trivalent aluminium. Mössbauer measurements at pressures and temperatures along the geotherm are impractical using conventional radioactive sources due to their low brightness and the extremely limited possibilities for focusing in a laboratory setting. To address these limitations, we have developed an energy domain Synchrotron Mössbauer Source (SMS) on beamline ID18 at the European Synchrotron Radiation Facility that enables rapid collection of high quality energy domain Mössbauer spectra, and coupled with a portable double-sided laser heating system, SMS spectra can be collected on iron-containing mantle phases at pressures and temperatures up to those near the Earth's core in only a few hours (or less). The presentation will showcase recent results documenting in situ determination of iron oxidation state in lower mantle phases and discuss their implications for redox sensitive processes taking place throughout the Earth

  4. Fluids of the lower crust and upper mantle: deep is different

    Science.gov (United States)

    Manning, C. E.

    2017-12-01

    Deep fluids are important for the evolution and properties of the lower crust and upper mantle in tectonically active settings. Uncertainty about their chemistry has led past workers to use upper crustal fluids as analogues. However, recent results show that fluids at >15 km differ fundamentally from shallow fluids and help explain high-pressure metasomatism and resistivity patterns. Deep fluids are comprised of four components: H2O, non-polar gases (chiefly CO2), salts (mostly alkali chlorides), and rock-derived solutes (dominated by aluminosilicates and related components). The first three generally define the solvent properties of the fluid, and models must account for observations that H2O activity may be quite low. The contrasting behavior of H2O-gas and H2O-salt mixtures yields immiscibility in the ternary system, which can lead to separation of two phases with fundamentally different chemical and transport properties. Thermodynamic modeling of equilibrium between rocks and H2O using simple ionic species known from shallow-crustal systems yields solutions possessing total dissolved solids and ionic strength that are too low to be consistent with experiments and resistivity surveys. Addition of CO2 further lowers bulk solubility and conductivity. Therefore, additional species must be present in H2O, and H2O-salt solutions likely explain much of the evidence for fluid action in high-P settings. At low salinity, H2O-rich fluids are powerful solvents for aluminosilicate rock components that are dissolved as previously unrecognized polymerized clusters. Experiments show that, near H2O-saturated melting, Al-Si polymers comprise >80% of solutes. The stability of these species facilitates critical critical mixing in rock-H2O systems. Addition of salt (e.g., NaCl) changes solubility patterns, but aluminosilicate contents remain high. Thermodynamic models indicate that the ionic strength of fluids with Xsalt = 0.05 to 0.4 and equilibrated with model crustal rocks have

  5. The depth of sub-lithospheric diamond formation and the redistribution of carbon in the deep mantle

    Science.gov (United States)

    Beyer, Christopher; Frost, Daniel J.

    2017-03-01

    respectively. Macroscopic diamond formation in rocks with pyroxenite compositions are likely facilitated in the deep mantle by higher average oxidation states and low mineral H2 O solubility compared to the surrounding mantle, which aid the mobility of C-O-H volatile species. The apparent lack of inclusions with a peridotite affinity may result from generally low oxygen fugacities in such lithologies, which reduces carbon mobility, and the lack of a suitable oxidising agent to allow diamonds to form from CH4. This glimpse of deep carbon cycle processes implies that heterogeneities in the carbon content, redox state and chemical composition of the mantle may be strongly coupled.

  6. Mantle fluids ascent in the regions of strong earthquake sources and large deep fault zones: geochemical evidences

    International Nuclear Information System (INIS)

    Kopnichev, Yu.F.; Sokolova, I.N.

    2005-01-01

    Data on variations of a ratio of the helium isotope content (parameter R= 3 He/ 4 He) near the sources of strong earthquakes and some large fault zones (in the regions of Tien Shan, Mongolia, California, Central Japan and Central Apennines) are being analyzed. It was shown that in many cases R values regularly diminish with the distance from epicenters and large regional faults. This testifies to the ascent of mantle fluids into the earth's crust after strong earthquakes and in some deep fault zones, which are characterized by superhigh permeability and their further migration in horizontal direction. (author)

  7. The relationship between mantle pH and the deep nitrogen cycle

    Science.gov (United States)

    Mikhail, Sami; Barry, Peter H.; Sverjensky, Dimitri A.

    2017-07-01

    Nitrogen is distributed throughout all terrestrial geological reservoirs (i.e., the crust, mantle, and core), which are in a constant state of disequilibrium due to metabolic factors at Earth's surface, chemical weathering, diffusion, and deep N fluxes imposed by plate tectonics. However, the behavior of nitrogen during subduction is the subject of ongoing debate. There is a general consensus that during the crystallization of minerals from melts, monatomic nitrogen behaves like argon (highly incompatible) and ammonium behaves like potassium and rubidium (which are relatively less incompatible). Therefore, the behavior of nitrogen is fundamentally underpinned by its chemical speciation. In aqueous fluids, the controlling factor which determines if nitrogen is molecular (N2) or ammonic (inclusive of both NH4+ and NH30) is oxygen fugacity, whereas pH designates if ammonic nitrogen is NH4+ or NH30. Therefore, to address the speciation of nitrogen at high pressures and temperatures, one must also consider pH at the respective pressure-temperature conditions. To accomplish this goal we have used the Deep Earth Water Model (DEW) to calculate the activities of aqueous nitrogen from 1-5 GPa and 600-1000 °C in equilibrium with a model eclogite-facies mineral assemblage of jadeite + kyanite + quartz/coesite (metasediment), jadeite + pyrope + talc + quartz/coesite (metamorphosed mafic rocks), and carbonaceous eclogite (metamorphosed mafic rocks + elemental carbon). We then compare these data with previously published data for the speciation of aqueous nitrogen across these respective P-T conditions in equilibrium with a model peridotite mineral assemblage (Mikhail and Sverjensky, 2014). In addition, we have carried out full aqueous speciation and solubility calculations for the more complex fluids in equilibrium with jadeite + pyrope + kyanite + diamond, and for fluids in equilibrium with forsterite + enstatite + pyrope + diamond. Our results show that the pH of the fluid is

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

    Science.gov (United States)

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

    2013-12-04

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

  9. Long-Term Stability of Plate-Like Behavior Caused by Hydrous Mantle Convection and Water Absorption in the Deep Mantle

    Science.gov (United States)

    Nakagawa, Takashi; Iwamori, Hikaru

    2017-10-01

    We investigate the cycling of water (regassing, dehydration, and degassing) in mantle convection simulations as a function of the strength of the oceanic lithosphere and its influence on the evolution of mantle water content. We also consider pseudo-plastic yielding with a friction coefficient for simulating brittle behavior of the plates and the water-weakening effect of mantle materials. This model can generate long-term plate-like behavior as a consequence of the water-weakening effect of mantle minerals. This finding indicates that water cycling plays an essential role in generating tectonic plates. In vigorous plate motion, the mantle water content rapidly increases by up to approximately 4-5 ocean masses, which we define as the "burst" effect. A burst is related to the mantle temperature and water solubility in the mantle transition zone. When the mantle is efficiently cooled down, the mantle transition zone can store water transported by the subducted slabs that can pass through the "choke point" of water solubility. The onset of the burst effect is strongly dependent on the friction coefficient. The burst effect of the mantle water content could have significantly influenced the evolution of the surface water if the burst started early, in which case the Earth's surface cannot preserve the surface water over the age of the Earth.

  10. Sulfide-Sulfate Equilibria in Subducted Lithosphere, Mantle Redox and the Deep Earth Sulfur Cycle in Space and Time

    Science.gov (United States)

    Canil, D.

    2016-12-01

    The redox budget during subduction affects the deep-earth S cycle, and is tied to the evolution of oxygen and biogeochemical cycles on Earth's surface over time. One component in the deep S cycle and its redox is the sedimentary veneer that sits atop the subducted oceanic basalt crust. The conversion of subducted sulfide to sulfate (or vice versa) is an eight-electron change in redox state, with significant oxidation/ reduction capacity of mantle sources for magmas, and for controlling the mobility or extraction of chalcophile metals from the arc mantle. I calculate buffers on sulfate - sulfide stability in subducted oceanic crust within the eclogite facies, and their disposition relative to other redox couples in the mantle along both `hot' and `warm' P-T trajectories for subducted lithosphere. To a first order, sulfide stability in subducted crust passing through the eclogite facies beneath an arc is shifted 0.5-1 logfO2 units by variations in the bulk Ca/Fe of the subducting crust alone. Because sulfate is highly soluble, its liberation from subducted crust by either melting or fluid flow into the arc source region can vary in space or time, depending on bulk composition of subducted crust or on variations in subduction P-T trajectories. The released sulfate may be one cause of the increase in the fO2 of the arc mantle. Experimental data on melts of subducted sediment show the control of sulfide-sulfate stability on the solubility of chalcophile metals (Cu, As, Mo, Pb). By assuming the normalized abundances of Cu as a proxy for S, the effect of variable subducted sediment composition on sulfide-sulfate stability and release of chalcophiles beneath convergent margins can be recognized in arc basalts and andesites from several modern subduction zones. The release of S and chalcophiles in the convergent margin setting may have changed with time, however, simply due to changes in the nature of sedimentation in the oceans over the course of earth history.

  11. Mixing and Progressive Melting of Deep and Shallow Mantle Sources in the NE Atlantic and Arctic

    DEFF Research Database (Denmark)

    Trønnes, Reidar; Debaille, Vincianne; Erambert, M.

    2013-01-01

    and the Southern Volcanic Flank Zone in Iceland, via 1.2 at the Snæfellsnes peninsula, Western Rift Zone and Mid-Icelandic Belt and 0.7 at Jan Mayen and the Kolbeinsey, Mohns and Knipovich Ridges to less than 0.2 in Spitsbergen and along the Gakkel Ridge. These ratios might be slightly overestimated due......, Mohns, Knipovich and Gakkel Ridges reflects the young, narrow and slow-spreading character of the corresponding oceanic basins. These ridges appear to sample mantle sources with higher proportions of locally derived SCLM-material than other mid-ocean ridges....

  12. Long-term, deep-mantle support of the Ethiopia-Yemen Plateau

    Science.gov (United States)

    Sembroni, Andrea; Faccenna, Claudio; Becker, Thorsten W.; Molin, Paola; Abebe, Bekele

    2016-04-01

    Ethiopia is a key site to investigate the interactions between mantle dynamics and surface processes because of the presence of the Main Ethiopian Rift (MER), Cenozoic continental flood basalt volcanism, and plateau uplift. The role of mantle plumes in causing Ethiopia's flood basalts and tectonics has been commonly accepted. However, the location and number of plumes and their impact on surface uplift are still uncertain. Here, we present new constraints on the geological and topographic evolution of the Ethiopian Plateau (NW Ethiopia) prior to and after the emplacement of the large flood basalts (40-20 Ma). Using geological information and topographic reconstructions, we show that the large topographic dome that we see today is a long-term feature, already present prior the emplacement of the flood basalts. We also infer that large-scale doming operated even after the emplacement of the flood basalts. Using a comparison with the present-day topographic setting we show that an important component of the topography has been and is presently represented by a residual, non-isostatic, dynamic contribution. We conclude that the growth of the Ethiopian Plateau is a long-term, probably still active, dynamically supported process. Our arguments provide constraints on the processes leading to the formation of one of the largest igneous plateaus on Earth.

  13. High-resolution investigation of reflections from a deep mantle slab

    Science.gov (United States)

    Schumacher, Lina; Thomas, Christine

    2010-05-01

    Subduction zones form dominant tectonic features on the Earth and it is clear that there is significant three-dimensional structure and complexity within them. Tomographic inversions for P- and S-wave seismic velocities in the Earth's mantle suggest that in several places, subducted oceanic lithosphere descends through the mantle transition zone and penetrates into the lower mantle. But tomography is not able to make a statement concerning structural differences within the slab and its behavior with depth. The main objective of this study is to investigate the geometry, physical parameters and structural differences of subducted slabs by closely investigating seismic P-wave arrivals that reflect off the base of the slab (e.g. the polarity, amplitude, frequency and waveforms of the reflected waves). We are focusing primarily on the Cocos plate that is subducted beneath the Caribbean, since previous migration results show reflections in the slab region from a reflector at the base of the subducted lithosphere. Yet, at that time, a high-resolution investigation of physical parameters was not possible. This is done now by using South American earthquakes recorded by North American networks (e.g. USArray and California broadband seismometers). The data cover a period from 1991-2009 with a minimum magnitude of 5.9 Mw and depths below 100 km. The great circle paths of the source-receiver combinations used here do not intersect the slab and serve as reference. We are looking for reflections from the slab region that would arrive at the stations with different backazimuth. These arrivals can be observed in slowness-backazimuth diagrams as stacked energy of waves traveling out of plane. Information on slowness, backazimuth and travel time is used to backtrack the wave to its reflection point and can be compared to the results of previous migration results and tomography studies. In addition, beamforming for the observed slowness and backazimuth of the out of plane

  14. Deep Sources: New constraints on the tectonic origin of the Klyuchevskoy Group upper mantle anomaly

    Science.gov (United States)

    Bourke, J. R.; Nikulin, A.; Levin, V. L.

    2017-12-01

    Volcanoes of the Klyuchevskoy Group (KG) form one of the most active volcanic clusters on the planet, yet its position relative to the subducting Pacific Plate seems to be in violation of the understood principles of the flux-induced arc volcanism. Positioned at 170km above the accepted subduction contact, the KG is seemingly outside the maximum fluid flux release zone of 100km, as observed across global subduction zone environments. Past geophysical studies indicate presence of a planar seismic anomaly 110km below the KG, and it has been noted that the KG lavas exhibit anomalous geochemical signatures, possibly associated with two separate melt generation regions. This interpretation was largely based on receiver function analysis of seismic data recorded by 3 stations of the Partnership in International Research and Education (PIRE) network, done prior to this data becoming publically available. We present results of receiver function and a teleseismic, regional, and local source shear wave splitting study, focused on datasets obtained by the full PIRE network of 12 stations, as well as a hybrid summation of all stations. We present our findings in the form of depth migrated receiver function images convolved with a three-dimensional model of the subduction zone and shear-wave splitting measurements. Our results vastly increase the resolution of the previously identified upper mantle anomaly, further constraining its geometry both vertically and laterally. We complement our observations with a forward modeling effort aimed at assessing the geological nature of the anomaly. Specifically, we test three scenarios that were previously invoked to explain the presence of the low-velocity anomaly in the upper mantle below the KG: a 3D flow of mantle material around the corner of the subducting Pacific Plate, a sinking paleoslab left behind as a result of subduction rollback, and a plume of sediments from the subducting plate. We show that presence of remnant paleoslab

  15. Deep Vein Thrombosis: Risk Factors and Prevention in Surgical ...

    African Journals Online (AJOL)

    BACKGROUND: Deep vein thrombosis (DVT) is a cause of preventable morbidity and mortality in hospitalized surgical patients. The occurrence of the disease is related to presence of risk factors, which are related primarily to trauma, venous stasis and hyper-coagulability. DVT seems not to be taken seriously by many ...

  16. Deep global cycling of carbon constrained by the solidus of anhydrous, carbonated eclogite under upper mantle conditions

    Science.gov (United States)

    Dasgupta, Rajdeep; Hirschmann, Marc M.; Withers, Anthony C.

    2004-10-01

    We present partial melting experiments that constrain the near solidus phase relations of carbonated eclogite from 2 to 8.5 GPa. The starting material was prepared by adding 5 wt.% CO 2 in the form of a mixture of Fe-Mg-Ca-Na-K carbonates to an eclogite from Salt Lake crater, Oahu, Hawaii and is a reasonable approximation of carbonated oceanic crust from which siliceous hydrous fluids have been extracted during subduction. Melt-present versus melt-absent conditions are distinguished based on textural criteria. Garnet and clinopyroxene appear in all the experiments. Between 2 and 3 GPa, the subsolidus assemblage also includes ilmenite±calcio-dolomite ss±CO 2, whereas above the solidus (1050-1075 °C at 3 GPa) calcio-dolomitic liquid appears. From 3 to 4.5 GPa, dolomite ss is stable at the solidus and the near-solidus melt becomes increasingly dolomitic. The appearance of dolomite above 3 GPa is accompanied by a negative Clapeyron slope of the solidus, with a minimum located between 995 and 1025 °C at ca. 4 GPa. Above 4 GPa, the solidus rises with increasing pressure to 1245±35 °C at 8.5 GPa and magnesite becomes the subsolidus carbonate. Dolomitic melt coexists with magnesite+garnet+cpx+rutile along the solidus from 5 to 8.5 GPa. Comparison of our results to other recent experimental studies [T. Hammouda, High-pressure melting of carbonated eclogite and experimental constraints on carbon recycling and storage in the mantle, Earth Planet. Sci. Lett. 214 (2003) 357-368; G.M. Yaxley, G.P. Brey, Phase relations of carbonate-bearing eclogite assemblages from 2.5 to 5.5 GPa: implications for petrogenesis of carbonatites, Contrib. Mineral. Petrol. 146 (2004) 606-619] shows that carbonate minerals are preserved in anhydrous or slightly hydrous carbonated eclogite to temperatures >1100 and >1200 °C at 5 and 9 GPa, respectively. Thus, deep subduction of carbonate is expected along any plausible subduction geotherm. If extrapolated to higher pressures, the carbonated

  17. Deep long-period earthquakes west of the volcanic arc in Oregon: evidence of serpentine dehydration in the fore-arc mantle wedge

    Science.gov (United States)

    Vidale, John E.; Schmidt, David A.; Malone, Stephen D.; Hotovec-Ellis, Alicia J.; Moran, Seth C.; Creager, Kenneth C.; Houston, Heidi

    2014-01-01

    Here we report on deep long-period earthquakes (DLPs) newly observed in four places in western Oregon. The DLPs are noteworthy for their location within the subduction fore arc: 40–80 km west of the volcanic arc, well above the slab, and near the Moho. These “offset DLPs” occur near the top of the inferred stagnant mantle wedge, which is likely to be serpentinized and cold. The lack of fore-arc DLPs elsewhere along the arc suggests that localized heating may be dehydrating the serpentinized mantle wedge at these latitudes and causing DLPs by dehydration embrittlement. Higher heat flow in this region could be introduced by anomalously hot mantle, associated with the western migration of volcanism across the High Lava Plains of eastern Oregon, entrained in the corner flow proximal to the mantle wedge. Alternatively, fluids rising from the subducting slab through the mantle wedge may be the source of offset DLPs. As far as we know, these are among the first DLPs to be observed in the fore arc of a subduction-zone system.

  18. S-to-P Conversions from Mid-mantle Slow Scatterers in Slab Regions: Observations of Deep/Stagnated Oceanic Crust?

    Science.gov (United States)

    He, Xiaobo; Zheng, Yixian

    2018-02-01

    The fate of a subducted slab is a key ingredient in the context of plate tectonics, yet it remains enigmatic especially in terms of its crustal component. In this study, our efforts are devoted to resolve slab-related structures in the mid-mantle below eastern Indonesia, the Izu-Bonin region, and the Peru area by employing seismic array analysing techniques on high-frequency waveform data from F-net in Japan and the Alaska regional network and the USArray in North America. A pronounced arrival after the direct P wave is observed in the recordings of four deep earthquakes (depths greater than 400 km) from three subduction systems including the Philippines, the Izu-Bonin, and the Peru. This later arrival displays a slightly lower slowness compared to the direct P wave and its back-azimuth deviates somewhat from the great-circle direction. We explain it as an S-to-P conversion at a deep scatterer below the sources in the source region. In total, five scatterers are seen at depths ranging from 930 to 1500 km. Those scatterers appear to be characterised by an 7 km-thick low-velocity layer compared to the ambient mantle. Combined evidence from published mineral physical analysis suggests that past subducted oceanic crust, possibly fragmented, is most likely responsible for these thin-layer compositional heterogeneities trapped in the mid-mantle beneath the study regions. Our observations give a clue to the potential fate of subducted oceanic crust.

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

    Science.gov (United States)

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

    2016-04-01

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

  20. Neutron activation analysis of the rare earth elements in rocks from the earth's upper mantle and deep crust

    International Nuclear Information System (INIS)

    Stosch, H.-G.; Koetz, J.; Herpers, U.

    1986-01-01

    Three techniques for analyzing rare earth elements (REE) in geological materials are described, i.e. instrumental neutron activation analysis (INAA), neutron activation analysis with pre-irradiation chemical REE separation (PCS-NAA) and radiochemical neutron activation analysis (RNAA). The knowledge of REE concentrationd in eclogites, peridotites and minerals from the earth's lower crust and upper mantle is very useful in constraining their petrogenetic history. (author)

  1. Mantle transition zone beneath central-eastern Greenland: Possible evidence for a deep tectosphere from receiver functions

    Science.gov (United States)

    Kraft, Helene Anja; Vinnik, Lev; Thybo, Hans

    2018-03-01

    We investigate the mantle of central-eastern Greenland by using recordings with data from 24 local broad-band seismograph stations. We apply P wave receiver function technique and evaluate the difference in the arrival times of seismic phases that are formed by P to SV mode conversion at the 410-km and 660-km seismic discontinuities. These boundaries mark the top and bottom of the mantle transition zone (MTZ). The difference in the arrival time of the phases from the 410-km and 660-km discontinuities is sensitive to the thickness of the MTZ and relatively insensitive to volumetric velocity anomalies above the 410-km discontinuity. Near the east coast of Greenland in the region of the Skaergaard basalt intrusions we find two regions where the differential time is reduced by more than 2 s. The 410-km discontinuity in these regions is depressed by more than 20 km. The depression may be explained by a temperature elevation of 150 °C. We hypothesize that the basaltic intrusions and the temperature anomalies at a depth of 400 km are, at least partly, effects of the passage of Greenland over the Iceland hotspot at about 55 Ma. This explanation is consistent with the concept of tectosphere and implies that the upper mantle to a depth of 400 km translates coherently with the Greenland plate.

  2. Nebular Volatiles in Earth's Deep Mantle from Neon Isotope Systematics of Plume-influenced South Atlantic MORBs

    Science.gov (United States)

    Williams, C. D.; Mukhopadhyay, S.

    2017-12-01

    The origin and acquisition of volatiles within planetary interiors remains a significant challenge in planet formation models. Two common hypotheses are [1] incorporation of nebular volatiles with later addition of chondritic materials or [2] the accretion of solar wind irradiated materials1. Here we use the neon isotopic composition of plume-influenced mid-ocean ridge basalts (MORBs) from the south Atlantic, along with ratios of primordial argon to neon (36Ar/22Ne), to distinguish between these two potential sources of volatiles. Maximum measured 20Ne/22Ne ratios of 12.99 ± 0.03 are significantly higher than the MORB source ratio2 of 12.49 ± 0.04. Mixing between the plume source and the MORB source indicate a lower mantle source region characterized by a 20Ne/22Ne ratio of 13.32 ± 0.17, indistinguishable from an estimate of 13.36 ± 0.09 for nebular gas3. Conversely, the MORB source 20Ne/22Ne and 36Ar/22Ne ratios trend towards chondritic materials. These results support a scenario in which at least two sources, nebular gas and later addition of chondritic materials, contributed volatiles to the mantle during Earth's accretion. Acquisition of nebular volatiles places strong constraints on planet formation models including accretion timescales and the H2 budget of the early Earth. The nebular volatiles are likely sequestered in the large low shear-wave velocity provinces (LLSVPs) at the bottom of the mantle as primordial helium isotopic compositions associated with high 20Ne/22Ne ratio samples display a strong correlation with LLSVPs when deflection of plume conduits is considered. Consequently, LLSVPs are chemically distinct reservoirs sitting atop the core-mantle boundary and contain material with a memory of the nebular disk. 1Moreira, M. 2013. Geochemical Perspectives 2, 229-403. 2Holland, G. & Ballentine, C. J. 2006. Nature 441, 186-191. 3Heber, V. S. et al., 2012. The Astrophysical Journal 759, 121.

  3. Variation of Seismic Velocity Structure around the Mantle Transition Zone and Conjecture of Deep Water Transport by Subducted Slabs

    Science.gov (United States)

    Tajima, F. C.; Stahler, S. C.; Ohtani, E.; Yoshida, M.; Sigloch, K.

    2011-12-01

    Seismic tomography models published in the past two decades determined common long-wavelength features of subducting plates as high velocity anomalies and upwelling plumes as low velocity anomalies, and have led to a new class of high-resolution three-dimensional (3D) modeling of global mantle convection with a link to tomography models [e.g., Becker and Boschi, 2002; Ritsema et al., 2007; Schuberth et al., 2009a,b]. However, even such high resolution numerical models do not account for the variation associated with different behaviors of subducting plates as they enter the mantle transition zone (MTZ), i.e., some flatten to form stagnant slabs with a large lateral extent and others descend further into the lower mantle. There are conventional interpretations applied for the cause of variation of the subducted slab behaviors, i.e., temperature difference due to different plate age, different geochemical compositions, different water content and subsequent possible reduction of viscosity etc., which could be taken as non-unique and somewhat equivocal. These parameters and conditions have been tested in two-dimensional numerical simulations, while the water content in the MTZ or the mechanisms of hydration and dehydration through subduction process are still in the realm of conjecture. Recent models of seismic P- and SH-wave velocities derived for the mantle structure beneath northeast China [Wang and Niu, 2010; Ye et al., 2011] using reflectivity synthetics with data from the dense Chinese networks of broadband seismic instruments, show a broader 660 km discontinuity (by about 30 to 70 km) and slower shear velocities above the MTZ than a global standard model iasp91 (Kennett and Engdahl, 1991). These features were interpreted with a mixture of different chemical properties which show delayed phase transformation, and effects of water above the flattened slab. Nonetheless, the SH-wave model has a structure similar to model TNA above the MTZ, which was derived for the

  4. Dismantling the Deep Earth: Geochemical Constraints from Hotspot Lavas for the Origin and Lengthscales of Mantle Heterogeneity

    Science.gov (United States)

    2008-02-01

    a mixed reservoir in mantle plames, Nature 424, 57 59. ofoceaic basalts and mantie evolution. Natare 296. 821 825. q6A 942 SiL Y ., in press. Global...e p t e d b y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ../_ _r Prof. Bradford H. Hager Co-Chair, Joint Committee for Marine...we measure intensities FOZ( (li,cu Loe , hgh iHe, low , Sr 5 ’Sri, ott masses 82 through 88. Raw data are exported to ant PHElrM (Primitive I/e.ium

  5. Clinopyroxenite dykes within a banded unit in the basal mantle section of the northern part of the Oman ophiolite: A record of the latest deep-seated magmatism

    Science.gov (United States)

    Ishimaru, Satoko; Arai, Shoji; Tamura, Akihiro

    2017-11-01

    We found clinopyroxenite dykes in a banded harzburgite block within the Sumeini area in the uppermost part of the metamorphic sole of the northern part of the Oman ophiolite. The dykes clearly cut the deformational structure of the harzburgite and contain its fragments, indicating dyke formation during obduction of the ophiolite. The Mg# [= Mg / (Mg + total Fe)] of clinopyroxenes in the dykes ranges from 0.81 to 0.91, and increases up to 0.93 proximal to harzburgite fragments. Mantle minerals in the harzburgite fragments were modified chemically through interaction with the magma that formed the dyke, yielding lower clinopyroxene and spinel Mg#, and spinels with higher TiO2 contents than those in the unaltered harzburgite. These geochemical features indicate that the clinopyroxenite dykes are cumulates derived from a relatively deep-seated primitive magma enriched in light rare earth elements (LREE) with an ocean island basalt (OIB)-like affinity, geochemically similar to the V3 lavas of an off-ridge origin. Combining these data with geological observations suggests that the clinopyroxenite dykes represent root system of the V3 lavas. Our analyses of the clinopyroxenite dykes testify to the external nature of the V3 magmas, which was added to the sliced oceanic lithosphere from the outside. It is likely that the V3 magma underwent deep-seated crystallization of clinopyroxene and had limited interaction with mantle peridotite en route to the surface. The mode of occurrence of the Sumeini clinopyroxenites (i.e., emplaced into a banded harzburgite block surrounded by garnet amphibolite) is consistent with the generation of OIB-like magmas (V3 lava) beneath the Oman ophiolite resulting from the break-off of the "subducting slab" and subsequent infiltration of hot asthenospheric mantle. This view is consistent with the limited distribution of V3-related rocks in the Oman ophiolite. The production of such OIB-like magmas during ophiolite obduction is not a rare event

  6. Interaction of extended mantle plume head with ancient lithosphere: evidence from deep-seated xenoliths in basalts and lamprophyre diatremes in Western Syria

    Science.gov (United States)

    Sharkov, Evgenii

    2016-04-01

    . Formation of clinopyroxene-hornblende rocks (analogs of the "black series" of mantle xenoliths in basalt) occurred at close P-T parameters: 12.6 kbar, 1100°C. Judging from the absence of deformations in the rocks, their parental melts were intruded into the stabilized lower crust. Hence, it follows that the ancient continental lower crust existed there in the mid-Cretaceous, but in the Late Cenozoic it was replaced by the spreading mantle plume head. In other words, the deep structure of the region was reconstructed radically in the Late Cenozoic, and only the uppermost horizon of the ancient lithosphere (sialic crust) was not changed. According to the geological and petrological data, the heads of mantle plumes reached the base of the upper sialic crust, and the level of the lower crust of the continents (30-40 km) is optimal for abundant adiabatic melting of the mantle plume head. If this level was not reached, melting was limited, and an excess of volatile components appeared, which resulted in the formation of lamprophyric and even kimberlitic diatremes. The work was supported by grant RFBR # 14-05-00468 and Project of ONZ RAS # 8.

  7. How to Spot and Prevent Deep Vein Thrombosis

    Science.gov (United States)

    ... May Help More People After Stroke Transplant Reverses Sickle Cell Disease Avoiding Anemia When Blood Cells Bend Wise Choices Clues of a Clot Seek treatment if you have these symptoms. They may signal a deep vein clot or ...

  8. Upper mantle diapers, lower crustal magmatic underplating, and lithospheric dismemberment of the Great Basin and Colorado Plateau regions, Nevada and Utah; implications from deep MT resistivity surveying

    Science.gov (United States)

    Wannamaker, P. E.; Doerner, W. M.; Hasterok, D. P.

    2005-12-01

    In the rifted Basin and Range province of the southwestern U.S., a common faulting model for extensional basins based e.g. on reflection seismology data shows dominant displacement along master faults roughly coincident with the main topographic scarp. On the other hand, complementary data such as drilling, earthquake focal mechanisms, volcanic occurrences, and trace indicators such as helium isotopes suggest that there are alternative geometries of crustal scale faulting and material transport from the deep crust and upper mantle in this province. Recent magnetotelluric (MT) profiling results reveal families of structures commonly dominated by high-angle conductors interpreted to reflect crustal scale fault zones. Based mainly on cross cutting relationships, these faults appear to be late Cenozoic in age and are of low resistivity due to fluids or alteration (including possible graphitization). In the Ruby Mtns area of north-central Nevada, high angle faults along the margins of the core complex connect from near surface to a regional lower crustal conductor interpreted to contain high-temperature fluids and perhaps melts. Such faults may exemplify the high angle normal faults upon which the major earthquakes of the Great Basin appear to nucleate. A larger-scale transect centered on Dixie Valley shows major conductive crustal-scale structures connecting to conductive lower crust below Dixie Valley, the Black Rock desert in NW Nevada, and in east-central Nevada in the Monitor-Diamond Valley area. In the Great Basin-Colorado Plateau transition of Utah, the main structures revealed are a series of nested low-angle detachment structures underlying the incipient development of several rift grabens. All these major fault zones appear to overlie regions of particularly conductive lower crust interpreted to be caused by recent basaltic underplating. In the GB-CP transition, long period data show two, low-resistivity upper mantle diapirs underlying the concentrated

  9. The mantle-plume model, its feasibility and consequences

    NARCIS (Netherlands)

    Calsteren, van P.W.C.

    1981-01-01

    High beat-flow foci on the Earth have been named ‘hot-spots’ and are commonly correlated with ‘mantle-plumes’ in the deep. A mantle plume may be described as a portion of mantle material with a higher heat content than its surroundings. The intrusion of a mantle-plume is inferred to be similar to

  10. The Mechanism and Application of Deep-Hole Precracking Blasting on Rockburst Prevention

    Directory of Open Access Journals (Sweden)

    Zhenhua Ouyang

    2015-01-01

    Full Text Available The mechanism of preventing rockburst through deep-hole precracking blasting was studied based on experimental test, numerical simulation, and field testing. The study results indicate that the deep-hole precracking could change the bursting proneness and stress state of coal-rock mass, thereby preventing the occurrence of rockburst. The bursting proneness of the whole composite structure could be weakened by the deep-hole precracking blasting. The change of stress state in the process of precracking blasting is achieved in two ways: (1 artificially break the roof apart, thus weakening the continuity of the roof strata, effectively inducing the roof caving while reducing its impact strength; and (2 the dynamic shattering and air pressure generated by the blasting can structurally change the properties of the coal-rock mass by mitigating the high stress generation and high elastic energy accumulation, thus breaking the conditions of energy transfer and rock burst occurrence.

  11. Treatment of superficial vein thrombosis to prevent deep vein thrombosis and pulmonary embolism: a systematic review

    NARCIS (Netherlands)

    Wichers, Iris M.; Di Nisio, Marcello; Büller, Harry R.; Middeldorp, Saskia

    2005-01-01

    The aim of this systematic review was to summarize the evidence from randomized controlled trials (RCT) concerning the efficacy and safety of medical or surgical treatments of superficial vein thrombosis (SVT) for the prevention of deep venous thrombosis (DVT) and pulmonary embolism (PE). A

  12. Docosahexaenoic Acid Supplementation Early in Pregnancy May Prevent Deep Placentation Disorders

    Directory of Open Access Journals (Sweden)

    Jorge A. Carvajal

    2014-01-01

    Full Text Available Uteroplacental ischemia may cause preterm birth, either due to preterm labor, preterm premature rupture of membranes, or medical indication (in the presence of preeclampsia or fetal growth restriction. Uteroplacental ischemia is the product of defective deep placentation, a failure of invasion, and transformation of the spiral arteries by the trophoblast. The failure of normal placentation generates a series of clinical abnormalities nowadays called “deep placentation disorders”; they include preeclampsia, fetal growth restriction, preterm labor, preterm premature rupture of membranes, in utero fetal death, and placental abruption. Early reports suggested that a LC-PUFAs (long chain polyunsaturated fatty acids rich diet reduces the incidence of deep placentation disorders. Recent randomized controlled trials are inconsistent to show the benefit of docosahexaenoic acid (DHA supplementation during pregnancy to prevent deep placentation disorders, but most of them showed that DHA supplementation was associated with lower risk of early preterm birth. We postulate that DHA supplementation, early in pregnancy, may reduce the incidence of deep placentation disorders. If our hypothesis is correct, DHA supplementation, early in pregnancy, will become a safe and effective strategy for primary prevention of highly relevant pregnancy diseases, such as preterm birth, preeclampsia, and fetal growth restriction.

  13. Mantle plumes and hotspot geochemistry

    Science.gov (United States)

    Jackson, M. G.; Becker, T. W.; Konter, J.

    2017-12-01

    Ever improving global seismic models, together with expanding databases of mantle derived hotspot lavas, herald advances that relate the geochemistry of hotspots with low seismic shear-wave velocity conduits (plumes) in the mantle. Early efforts linked hotspot geochemistry with deep mantle large low velocity provinces (LLVPs) [1]. More recently, Konter and Becker (2012) [2] observed that the proportion of the C mantle component (inferred from Sr-Nd-Pb isotopes) in hotspot lavas shows an inverse relationship with seismic S-wave velocity anomalies in the shallow mantle (200 km) beneath each hotspot. They proposed that these correlations should also be made based on 3He/4He. Thus, we compare 3He/4He versus seismic S-wave velocity anomalies at 200 km depth. We find that plume-fed hotspots with the highest maximum 3He/4He (i.e., which host more of the C component) have higher hotspot buoyancy fluxes and overlie regions of lower seismic S-wave velocity (interpreted to relate to hotter mantle temperatures) at 200 km depth than hotspots that have only low 3He/4He [3]. This result complements recent work that shows an inverse relationship between maximum 3He/4He and seismic S-wave velocity anomalies in the mantle beneath the western USA [4]. The relationship between 3He/4He, shallow mantle seismic S-wave velocity anomalies, and buoyancy flux is most easily explained by a model where hotter plumes are more buoyant and entrain more of a deep, dense high 3He/4He reservoir than cooler plumes that underlie low 3He/4He hotspots. If the high 3He/4He domain is denser than other mantle components, it will be entrained only by the hottest, most buoyant plumes [3]. Such a deep, dense reservoir is ideally suited to preserving early-formed Hadean domains sampled in modern plume-fed hotspots. An important question is whether, like 3He/4He, seismic S-wave velocity anomalies in the mantle are associated with distinct heavy radiogenic isotopic compositions. C signatures are related to hot

  14. Investigating melting induced mantle heterogeneities in plate driven mantle convection models

    Science.gov (United States)

    Price, M.; Davies, H.; Panton, J.

    2017-12-01

    Observations from geochemistry and seismology continue to suggest a range of complex heterogeneity in Earth's mantle. In the deep mantle, two large low velocity provinces (LLVPs) have been regularly observed in seismic studies, with their longevity, composition and density compared to the surrounding mantle debated. The cause of these observed LLVPs is equally uncertain, with previous studies advocating either thermal or thermo-chemical causes. There is also evidence that these structures could provide chemically distinct reservoirs within the mantle, with recent studies also suggesting there may be additional reservoirs in the mantle, such as bridgmanite-enriched ancient mantle structures (BEAMS). One way to test these hypotheses is using computational models of the mantle, with models that capture the full 3D system being both complex and computationally expensive. Here we present results from our global mantle model TERRA. Using our model, we can track compositional variations in the convecting mantle that are generated by self-consistent, evolving melting zones. Alongside the melting, we track trace elements and other volatiles which can be partitioned during melting events, and expelled and recycled at the surface. Utilising plate reconstruction models as a boundary condition, the models generate the tectonic features observed at Earth's surface, while also organising the lower mantle into recognisable degree-two structures. This results in our models generating basaltic `oceanic' crusts which are then brought into the mantle at tectonic boundaries, providing additional chemical heterogeneity in the mantle volume. Finally, by utilising thermodynamic lookup tables to convert the final outputs from the model to seismic structures, together with resolution filters for global tomography models, we are able to make direct comparisons between our results and observations. By varying the parameters of the model, we investigate a range of current hypotheses for

  15. The Earth's heterogeneous mantle a geophysical, geodynamical, and geochemical perspective

    CERN Document Server

    Khan, Amir

    2015-01-01

    This book highlights and discusses recent developments that have contributed to an improved understanding of observed mantle heterogeneities and their relation to the thermo-chemical state of Earth's mantle, which ultimately holds the key to unlocking the secrets of the evolution of our planet. This series of topical reviews and original contributions address 4 themes. Theme 1 covers topics in geophysics, including global and regional seismic tomography, electrical conductivity and seismic imaging of mantle discontinuities and heterogeneities in the upper mantle, transition zone and lower mantle. Theme 2 addresses geochemical views of the mantle including lithospheric evolution from analysis of mantle xenoliths, composition of the deep Earth and the effect of water on subduction-zone processes. Theme 3 discusses geodynamical perspectives on the global thermo-chemical structure of the deep mantle. Theme 4 covers application of mineral physics data and phase equilibrium computations to infer the regional-scale ...

  16. Dynamical geochemistry of the mantle

    Directory of Open Access Journals (Sweden)

    G. F. Davies

    2011-09-01

    oceanic crust. Residence times in D" are longer, so the hybrid pyroxenite there would be less degassed. Plumes would sample both the degassed, enriched old oceanic crust and the gassy, less enriched hybrid pyroxenite and deliver them to OIBs. These findings can account quantitatively for the main He, Ne and Ar isotopic observations.

    It has been commonly inferred that the MORB source is strongly depleted of incompatible elements. However it has recently been argued that conventional estimates of the MORB source composition fail to take full account of mantle heterogeneity, and in particular focus on an ill-defined "depleted" mantle component while neglecting less common enriched components. Previous estimates have also been tied to the composition of peridotites, but these probably do not reflect the full complement of incompatible elements in the heterogeneous mantle. New estimates that account for enriched mantle components suggest the MORB source complement of incompatibles could be as much as 50–100 % larger than previous estimates.

    A major difficulty has been the inference that mass balances of incompatible trace elements could only be satisfied if there is a deep enriched layer in the mantle, but the Earth's topography precludes such a layer. The difficulty might be resolved if either the Earth is depleted relative to chondritic or the MORB source is less depleted than previous estimates. Together these factors can certainly resolve the mass balance difficulties.

  17. Comparison of Efficacy Compressive Stockings with Heparin in Prevention of Deep Vein Thrombosis in Stroke Patients

    Directory of Open Access Journals (Sweden)

    Nastaran Majdi-Nasab

    2013-04-01

    Full Text Available Background: The present study is carried out to make a comparison between two pharmacological (heparin and physical (compression stockings in the prevention of deep vein thrombosis in lower limb of the patients suffered from acute stroke. Materials and Methods: In this investigation as a clinical trial, the effectiveness of the above methods on 100 patients with the stroke was compared in two groups of 50 persons. Results: Three patients in physical group and two patients in pharmacological group got deep vein thrombosis that showed no significant difference between two groups.Conclusion: In spite of no significant relationship and due to less incurrence of thrombosis in heparin group, it is more reasonable to use pharmacological methods.

  18. Mantle dynamics following supercontinent formation

    Science.gov (United States)

    Heron, Philip J.

    This thesis presents mantle convection numerical simulations of supercontinent formation. Approximately 300 million years ago, through the large-scale subduction of oceanic sea floor, continental material amalgamated to form the supercontinent Pangea. For 100 million years after its formation, Pangea remained relatively stationary, and subduction of oceanic material featured on its margins. The present-day location of the continents is due to the rifting apart of Pangea, with supercontinent dispersal being characterized by increased volcanic activity linked to the generation of deep mantle plumes. The work presented here investigates the thermal evolution of mantle dynamics (e.g., mantle temperatures and sub-continental plumes) following the formation of a supercontinent. Specifically, continental insulation and continental margin subduction are analyzed. Continental material, as compared to oceanic material, inhibits heat flow from the mantle. Previous numerical simulations have shown that the formation of a stationary supercontinent would elevate sub-continental mantle temperatures due to the effect of continental insulation, leading to the break-up of the continent. By modelling a vigorously convecting mantle that features thermally and mechanically distinct continental and oceanic plates, this study shows the effect of continental insulation on the mantle to be minimal. However, the formation of a supercontinent results in sub-continental plume formation due to the re-positioning of subduction zones to the margins of the continent. Accordingly, it is demonstrated that continental insulation is not a significant factor in producing sub-supercontinent plumes but that subduction patterns control the location and timing of upwelling formation. A theme throughout the thesis is an inquiry into why geodynamic studies would produce different results. Mantle viscosity, Rayleigh number, continental size, continental insulation, and oceanic plate boundary evolution are

  19. Petrologic evaluation of Pliocene basaltic volcanism in Eastern Anatolian region, Turkey: Evidence for mixing of melts derived from both shallow and deep mantle sources

    Science.gov (United States)

    Oyan, Vural; Özdemir, Yavuz; Keskin, Mehmet; Güleç, Nilgün

    2017-04-01

    Collision-related Neogene volcanism in the Eastern Anatolia region (EAR) began after the continent-continent collision between the Arabia and the Eurasia plates, and spreads in a wide zone from the Erzurum-Kars Plateau in the northeast to the Karacadaǧ in the south. Volcanic activity in the EAR started 15 Ma ago (Middle Miocene) in the south of the region. Voluminous basaltic lavas from local eruption centers formed basaltic lava plateaus and volcanic cones as a result of high production level of volcanism during the Pliocene time interval. Our dating results (Ar-Ar and K-Ar) indicate that age of this Late Miocene-Pliocene magmatic activity range between 6 and 3.5 Ma. Volcanic products contain alkaline and subalkaline lavas, ranging in composition from basalts to andesites and trachyandesites. Our EC-AFC and AFC modeling, based on trace element and Sr, Nd, Pb isotopic compositions, suggests about 2-7 % crustal contamination in the evolved andesites and trachyandesites. MORB and primitive mantle normalized patterns of the lavas and isotopic compositions imply that alkaline and subalkaline basalts erupted in Pliocene time interval in the EAR could have been derived from a mantle source that had previously been enriched by a clear subduction component. A partial melting model was conducted to evaluate partial melting processes in the mantle source of the Pliocene basalts. Our melting model calculations suggest that basaltic melts in the EAR could have been produced by melting of mantle sources containing spinel, garnet and amphibole with melting degree in the range of 0.7-7%. The products of mixing of these derivative melts are the Pliocene basaltic lavas of the Eastern Anatolian Region.

  20. Deep brain stimulation during early adolescence prevents microglial alterations in a model of maternal immune activation.

    Science.gov (United States)

    Hadar, Ravit; Dong, Le; Del-Valle-Anton, Lucia; Guneykaya, Dilansu; Voget, Mareike; Edemann-Callesen, Henriette; Schweibold, Regina; Djodari-Irani, Anais; Goetz, Thomas; Ewing, Samuel; Kettenmann, Helmut; Wolf, Susanne A; Winter, Christine

    2017-07-01

    In recent years schizophrenia has been recognized as a neurodevelopmental disorder likely involving a perinatal insult progressively affecting brain development. The poly I:C maternal immune activation (MIA) rodent model is considered as a neurodevelopmental model of schizophrenia. Using this model we and others demonstrated the association between neuroinflammation in the form of altered microglia and a schizophrenia-like endophenotype. Therapeutic intervention using the anti-inflammatory drug minocycline affected altered microglia activation and was successful in the adult offspring. However, less is known about the effect of preventive therapeutic strategies on microglia properties. Previously we found that deep brain stimulation of the medial prefrontal cortex applied pre-symptomatically to adolescence MIA rats prevented the manifestation of behavioral and structural deficits in adult rats. We here studied the effects of deep brain stimulation during adolescence on microglia properties in adulthood. We found that in the hippocampus and nucleus accumbens, but not in the medial prefrontal cortex, microglial density and soma size were increased in MIA rats. Pro-inflammatory cytokine mRNA was unchanged in all brain areas before and after implantation and stimulation. Stimulation of either the medial prefrontal cortex or the nucleus accumbens normalized microglia density and soma size in main projection areas including the hippocampus and in the area around the electrode implantation. We conclude that in parallel to an alleviation of the symptoms in the rat MIA model, deep brain stimulation has the potential to prevent the neuroinflammatory component in this disease. Copyright © 2016 Elsevier Inc. All rights reserved.

  1. The viscosity of Earth's lower mantle inferred from sinking speed of subducted lithosphere

    NARCIS (Netherlands)

    Čížková, H.; van den Berg, A.P.; Spakman, W.; Matyska, C.

    2012-01-01

    The viscosity of the mantle is indispensable for predicting Earth's mechanical behavior at scales ranging from deep mantle material flow to local stress accumulation in earthquakes zones. But, mantle viscosity is not well determined. For the lower mantle, particularly, only few constraints result

  2. Facilitating atmosphere oxidation through mantle convection

    Science.gov (United States)

    Lee, K. K. M.; Gu, T.; Creasy, N.; Li, M.; McCammon, C. A.; Girard, J.

    2017-12-01

    Earth's mantle connects the surface with the deep interior through convection, and the evolution of its redox state will affect the distribution of siderophile elements, recycling of refractory isotopes, and the oxidation state of the atmosphere through volcanic outgassing. While the rise of oxygen in the atmosphere, i.e., the Great Oxidation Event (GOE) occurred 2.4 billion years ago (Ga), multiple lines of evidence point to oxygen production in the atmosphere well before 2.4 Ga. In contrast to the fluctuations of atmospheric oxygen, vanadium in Archean mantle lithosphere suggests that the mantle redox state has been constant for 3.5 Ga. Indeed, the connection between the redox state of the deep Earth and the atmosphere is enigmatic as is the effect of redox state on mantle dynamics. Here we show a redox-induced density contrast affects mantle convection and may potentially cause the oxidation of the upper mantle. We compressed two synthetic enstatite chondritic samples with identical bulk compositions but formed under different oxygen fugacities (fO2) to lower mantle pressures and temperatures and find Al2O3 forms its own phase separate from the dominant bridgmanite phase in the more reduced composition, in contrast to a more Al-rich, bridgmanite-dominated assemblage for a more oxidized starting composition. As a result, the reduced material is 1-1.5% denser than the oxidized material. Subsequent experiments on other plausible mantle compositions, which differ only in redox state of the starting glass materials, show similar results: distinct mineral assemblages and density contrasts up to 4%. Our geodynamic simulations suggest that such a density contrast causes a rapid ascent and accumulation of oxidized material in the upper mantle, with descent of the denser reduced material to the core-mantle boundary. The resulting heterogeneous redox conditions in Earth's interior may have contributed to the large low-shear velocity provinces in the lower mantle and the

  3. Deep data science to prevent and treat growth faltering in Maya children.

    Science.gov (United States)

    Varela-Silva, M I; Bogin, B; Sobral, J A G; Dickinson, F; Monserrat-Revillo, S

    2016-06-01

    The Maya people are descended from the indigenous inhabitants of southern Mexico, Guatemala and adjacent regions of Central America. In Guatemala, 50% of infants and children are stunted (very low height-for-age), and some rural Maya regions have >70% children stunted. A large, longitudinal, intergenerational database was created to (1) provide deep data to prevent and treat somatic growth faltering and impaired neurocognitive development, (2) detect key dependencies and predictive relations between highly complex, time-varying, and interacting biological and cultural variables and (3) identify targeted multifactorial intervention strategies for field testing and validation. Contributions to this database included data from the Universidad del Valle de Guatemala Longitudinal Study of Child and Adolescent Development, child growth and intergenerational studies among the Maya in Mexico and studies about Maya migrants in the United States.

  4. Is the track of the Yellowstone hotspot driven by a deep mantle plume? -- Review of volcanism, faulting, and uplift in light of new data

    Science.gov (United States)

    Pierce, Kenneth L.; Morgan, Lisa A.

    2009-01-01

    Geophysical imaging of a tilted mantle plume extending at least 500 km beneath the Yellowstone caldera provides compelling support for a plume origin of the entire Yellowstone hotspot track back to its inception at 17 Ma with eruptions of flood basalts and rhyolite. The widespread volcanism, combined with a large volume of buoyant asthenosphere, supports a plume head as an initial phase. Estimates of the diameter of the plume head suggest it completely spanned the upper mantle and was fed from sources beneath the transition zone, We consider a mantle–plume depth to at least 1,000 km to best explain the large scale of features associated with the hotspot track. The Columbia River–Steens flood basalts form a northward-migrating succession consistent with the outward spreading of a plume head beneath the lithosphere. The northern part of the inferred plume head spread (pancaked) upward beneath Mesozoic oceanic crust to produce flood basalts, whereas basalt melt from the southern part intercepted and melted Paleozoic and older crust to produce rhyolite from 17 to 14 Ma. The plume head overlapped the craton margin as defined by strontium isotopes; westward motion of the North American plate has likely "scraped off" the head from the plume tail. Flood basalt chemistries are explained by delamination of the lithosphere where the plume head intersected this cratonic margin. Before reaching the lithosphere, the rising plume head apparently intercepted the east-dipping Juan de Fuca slab and was deflected ~ 250 km to the west; the plume head eventually broke through the slab, leaving an abruptly truncated slab. Westward deflection of the plume head can explain the anomalously rapid hotspot movement of 62 km/m.y. from 17 to 10 Ma, compared to the rate of ~ 25 km/m.y. from 10 to 2 Ma.

  5. Prevention of deep venous thrombosis in patients with acute spinal cord injuries: use of rotating treatment tables

    Energy Technology Data Exchange (ETDEWEB)

    Becker, D.M.; Gonzalez, M.; Gentili, A.; Eismont, F.; Green, B.A.

    1987-05-01

    A randomized clinical trial of 15 patients with acute spinal cord injuries was performed to test the hypothesis that rotating treatment tables prevent deep venous thrombosis in this population. Four of 5 control (nonrotated) patients developed distal and proximal thrombi, assessed by /sup 125/I fibrinogen leg scans and impedance plethysmography. In comparison, only 1 of 10 treated (rotated) patients developed both distal and proximal thrombosis. These results suggest but do not prove that rotating treatment tables prevent the development of proximal deep venous thrombosis in spinal cord-injured patients. Larger clinical trials are needed to confirm this heretofore undocumented benefit of rotating treatment tables.

  6. Prevention of deep venous thrombosis in patients with acute spinal cord injuries: use of rotating treatment tables

    International Nuclear Information System (INIS)

    Becker, D.M.; Gonzalez, M.; Gentili, A.; Eismont, F.; Green, B.A.

    1987-01-01

    A randomized clinical trial of 15 patients with acute spinal cord injuries was performed to test the hypothesis that rotating treatment tables prevent deep venous thrombosis in this population. Four of 5 control (nonrotated) patients developed distal and proximal thrombi, assessed by 125 I fibrinogen leg scans and impedance plethysmography. In comparison, only 1 of 10 treated (rotated) patients developed both distal and proximal thrombosis. These results suggest but do not prove that rotating treatment tables prevent the development of proximal deep venous thrombosis in spinal cord-injured patients. Larger clinical trials are needed to confirm this heretofore undocumented benefit of rotating treatment tables

  7. Preservation of deep inferior epigastric artery at kidney transplantation prevents atrophy of lower rectus abdominis muscle.

    Science.gov (United States)

    Iwami, Daiki; Harada, Hiroshi; Morita, Ken; Oba, Koji; Fukuzawa, Nobuyuki; Hotta, Kiyohiko; Sasaki, Hajime; Miyazaki, Chihoko; Nonomura, Katsuya

    2012-05-27

    The deep inferior epigastric artery (DIEA), which feeds the lower rectus abdominis muscle (lower RAM), is usually transected in kidney transplantation. In this study, we investigated whether preservation of DIEA can prevent lower RAM atrophy. Two hundred and forty-five kidney transplant recipients (150 men and 95 women) were enrolled in the study (mean age 39.9 years) and were divided into two groups according to whether DIEA was transected (group A, n = 175) or preserved (group B, n = 70). The extent of lower RAM atrophy calculated in computed tomography (performed 1 year after transplantation) and incidence of lower RAM atrophy were compared between the two groups. The most predictive factors for lower RAM atrophy were assessed using a multivariate logistic regression model. The extent of lower RAM atrophy was significantly lower in group B (15.0 ± 18.5%) than that in group A (38.9 ± 25.4%, P = 0.003). The incidence of lower RAM atrophy was less prevalent in group B (20.0%) compared with that in group A (62.9%, P DIEA was the only independent predictive factor for lower RAM atrophy (P DIEA during kidney transplant can prevent lower RAM atrophy.

  8. Is the track of the Yellowstone hotspot driven by a deep mantle plume? - Review of volcanism, faulting, and uplift in light of new data

    Science.gov (United States)

    Pierce, K.L.; Morgan, L.A.

    2009-01-01

    Geophysical imaging of a tilted mantle plume extending at least 500??km beneath the Yellowstone caldera provides compelling support for a plume origin of the entire Yellowstone hotspot track back to its inception at 17??Ma with eruptions of flood basalts and rhyolite. The widespread volcanism, combined with a large volume of buoyant asthenosphere, supports a plume head as an initial phase. Estimates of the diameter of the plume head suggest it completely spanned the upper mantle and was fed from sources beneath the transition zone, We consider a mantle-plume depth to at least 1,000 km to best explain the large scale of features associated with the hotspot track. The Columbia River-Steens flood basalts form a northward-migrating succession consistent with the outward spreading of a plume head beneath the lithosphere. The northern part of the inferred plume head spread (pancaked) upward beneath Mesozoic oceanic crust to produce flood basalts, whereas basalt melt from the southern part intercepted and melted Paleozoic and older crust to produce rhyolite from 17 to 14??Ma. The plume head overlapped the craton margin as defined by strontium isotopes; westward motion of the North American plate has likely "scraped off" the head from the plume tail. Flood basalt chemistries are explained by delamination of the lithosphere where the plume head intersected this cratonic margin. Before reaching the lithosphere, the rising plume head apparently intercepted the east-dipping Juan de Fuca slab and was deflected ~ 250??km to the west; the plume head eventually broke through the slab, leaving an abruptly truncated slab. Westward deflection of the plume head can explain the anomalously rapid hotspot movement of 62??km/m.y. from 17 to 10??Ma, compared to the rate of ~ 25??km/m.y. from 10 to 2??Ma. A plume head-to-tail transition occurred in the 14-to-10-Ma interval in the central Snake River Plain and was characterized by frequent (every 200-300??ka for about 2??m.y. from 12.7 to 10

  9. Pilot study evaluating the efficacy of exergaming for the prevention of deep venous thrombosis.

    Science.gov (United States)

    Rahemi, Hadi; Chung, Jayer; Hinko, Vanessa; Hoeglinger, Simon; Martinek, Wendy A; Montero-Baker, Miguel; Mills, Joseph L; Najafi, Bijan

    2018-03-01

    Current prophylactic protocols fail to prevent deep venous thrombosis (DVT) in a significant minority of patients, and it remains one of the leading causes of preventable death. We therefore quantified the efficacy of novel game-based exercises (exergaming) to augment femoral venous parameters relative to ankle movement and muscle flexion. Healthy volunteers were recruited to perform a series of ankle and foot exercises using a wireless foot sensor (LEGSys; BioSensics LLC, Watertown, Mass) to navigate a computer cursor sequentially on a screen to the center of 200 circular targets. A single ultrasound technician (W.A.M.) measured each patient's mean flow volume, peak flow velocity, mean flow velocity, and cross-sectional area of the right femoral vein at baseline and obtained immediate postexercise (PEX), 5-minute PEX, and 15-minute PEX measurements. Electromyography (EMG) was performed at baseline and during the exercise. Baseline demographics and medical and surgical comorbidities were also recorded. The primary end point was the difference between baseline and immediate PEX mean flow volume estimates. We secondarily explored the association of baseline characteristics and EMG measurements with femoral vein parameters. Fifteen healthy subjects (53% male; 28.1 ± 4.6 years) completed the exergaming task within a mean of 4 minutes, 2 ± 21 seconds. Immediately after exercise, the femoral vein mean flow volume, mean velocity, and peak systolic velocity increased by 49%, 53%, and 48%, respectively (P  .05). Subgroup analysis revealed that women (P peak plantar flexion velocities (P peak systolic velocity within the femoral vein by approximately 50% above baseline. Exergaming represents a novel and potentially attractive method of DVT prevention by augmenting femoral vein mean volume flow and capitalizing on biofeedback. Less forceful but more uniform contractions were found to be most effective at augmenting venous blood flow. Exergaming will require further

  10. Determining resolvability of mantle plumes with synthetic seismic modeling

    Science.gov (United States)

    Maguire, R.; Van Keken, P. E.; Ritsema, J.; Fichtner, A.; Goes, S. D. B.

    2014-12-01

    Hotspot volcanism in locations such as Hawaii and Iceland is commonly thought to be associated with plumes rising from the deep mantle. In theory these dynamic upwellings should be visible in seismic data due to their reduced seismic velocity and their effect on mantle transition zone thickness. Numerous studies have attempted to image plumes [1,2,3], but their deep mantle origin remains unclear. In addition, a debate continues as to whether lower mantle plumes are visible in the form of body wave travel time delays, or whether such delays will be erased due to wavefront healing. Here we combine geodynamic modeling of mantle plumes with synthetic seismic waveform modeling in order to quantitatively determine under what conditions mantle plumes should be seismically visible. We model compressible plumes with phase changes at 410 km and 670 km, and a viscosity reduction in the upper mantle. These plumes thin from greater than 600 km in diameter in the lower mantle, to 200 - 400 km in the upper mantle. Plume excess potential temperature is 375 K, which maps to seismic velocity reductions of 4 - 12 % in the upper mantle, and 2 - 4 % in the lower mantle. Previous work that was limited to an axisymmetric spherical geometry suggested that these plumes would not be visible in the lower mantle [4]. Here we extend this approach to full 3D spherical wave propagation modeling. Initial results using a simplified cylindrical plume conduit suggest that mantle plumes with a diameter of 1000 km or greater will retain a deep mantle seismic signature. References[1] Wolfe, Cecily J., et al. "Seismic structure of the Iceland mantle plume." Nature 385.6613 (1997): 245-247. [2] Montelli, Raffaella, et al. "Finite-frequency tomography reveals a variety of plumes in the mantle." Science 303.5656 (2004): 338-343. [3] Schmandt, Brandon, et al. "Hot mantle upwelling across the 660 beneath Yellowstone." Earth and Planetary Science Letters 331 (2012): 224-236. [4] Hwang, Yong Keun, et al

  11. One hundred million years of mantle geochemical history suggest the retiring of mantle plumes is premature

    Science.gov (United States)

    Konter, Jasper G.; Hanan, Barry B.; Blichert-Toft, Janne; Koppers, Anthony A. P.; Plank, Terry; Staudigel, Hubert

    2008-11-01

    Linear chains of intraplate volcanoes and their geochemistry provide a record of mantle melting through geological time. The isotopic compositions of their lavas characterize their mantle sources, and their ages help backtrack these volcanoes to their original, eruptive source regions. Such data may shed light on a much-debated issue in Earth Sciences: the origin of intraplate volcanism and its underlying mantle and lithosphere dynamics. We show here that three major Western Pacific Seamount groups, ˜ 50-100 million years in age, display distinct Sr, Nd, Hf, and Pb isotopic signatures that can be traced back in time, both geographically and geochemically, to three separate, recently-active intraplate volcanoes in the South Pacific Cook-Austral Islands. Their unique 100 million year history, which shows a persistent geochemical fingerprint, suggests formation from large volumes of laterally fixed, long-lived source regions. Such longevity is unlikely to be attained in the relatively dynamic upper mantle. Therefore, these sources are likely anchored deep in the mantle, isolated from homogenization by mantle convection, and imply a primary origin from deep mantle plumes rather than resulting from lithosphere extension.

  12. Upper mantle fluids evolution, diamond formation, and mantle metasomatism

    Science.gov (United States)

    Huang, F.; Sverjensky, D. A.

    2017-12-01

    During mantle metasomatism, fluid-rock interactions in the mantle modify wall-rock compositions. Previous studies usually either investigated mineral compositions in xenoliths and xenocrysts brought up by magmas, or examined fluid compositions preserved in fluid inclusions in diamonds. However, a key study of Panda diamonds analysed both mineral and fluid inclusions in the diamonds [1] which we used to develop a quantitative characterization of mantle metasomatic processes. In the present study, we used an extended Deep Earth Water model [2] to simulate fluid-rock interactions at upper mantle conditions, and examine the fluids and mineral assemblages together simultaneously. Three types of end-member fluids in the Panda diamond fluid inclusions include saline, rich in Na+K+Cl; silicic, rich in Si+Al; and carbonatitic, rich in Ca+Mg+Fe [1, 3]. We used the carbonatitic end-member to represent fluid from a subducting slab reacting with an excess of peridotite + some saline fluid in the host environment. During simultaneous fluid mixing and reaction with the host rock, the logfO2 increased by about 1.6 units, and the pH increased by 0.7 units. The final minerals were olivine, garnet and diamond. The Mg# of olivine decreased from 0.92 to 0.85. Garnet precipitated at an early stage, and its Mg# also decreased with reaction progress, in agreement with the solid inclusions in the Panda diamonds. Phlogopite precipitated as an intermediate mineral and then disappeared. The aqueous Ca, Mg, Fe, Si and Al concentrations all increased, while Na, K, and Cl concentrations decreased during the reaction, consistent with trends in the fluid inclusion compositions. Our study demonstrates that fluids coming from subducting slabs could trigger mantle metasomatism, influence the compositions of sub-lithospherc cratonic mantle, precipitate diamonds, and change the oxygen fugacity and pH of the upper mantle fluids. [1] Tomlinson et al. EPSL (2006); [2] Sverjensky, DA et al., GCA (2014

  13. Electrical stimulation using sine waveform prevents unloading-induced muscle atrophy in the deep calf muscles of rat.

    Science.gov (United States)

    Tanaka, Minoru; Hirayama, Yusuke; Fujita, Naoto; Fujino, Hidemi

    2014-09-01

    The aim of this study was to compare the effects of electrical stimulation by using rectangular and sine waveforms in the prevention of deep muscle atrophy in rat calf muscles. Rats were randomly divided into the following groups: control, hindlimb unloading (HU), and HU plus electrical stimulation (ES). The animals in the ES group were electrically stimulated using rectangular waveform (RS) on the left calves and sine waveform (SS) on the right calves, twice a day, for 2 weeks during unloading. HU for 2 weeks resulted in a loss of the muscle mass, a decrease in the cross-sectional area of the muscle fibers, and overexpression of ubiquitinated proteins in the gastrocnemius and soleus muscles. In contrast, electrical stimulation with RS attenuated the HU-induced reduction in the cross-sectional area of muscle fibers and the increase of ubiquitinated proteins in the gastrocnemius muscle. However, electrical stimulation with RS failed to prevent muscle atrophy in the deep portion of the gastrocnemius and the soleus muscles. Nevertheless, electrical stimulation with SS attenuated the HU-induced muscle atrophy and the up-regulation of ubiquitinated proteins in both gastrocnemius and soleus muscles. This indicates that SS was more effective in the prevention of deep muscle atrophy than RS. Since the skin muscle layers act like the plates of a capacitor, separated by the subcutaneous adipose layer, the SS can pass through this capacitor more easily than the RS. Hence, SS can prevent the progressive loss of muscle fibers in the deep portion of the calf muscles. Copyright © 2014 Elsevier GmbH. All rights reserved.

  14. Evolution of the earliest mantle caused by the magmatism-mantle upwelling feedback: Implications for the Moon and the Earth

    Science.gov (United States)

    Ogawa, M.

    2017-12-01

    The two most important agents that cause mantle evolution are magmatism and mantle convection. My earlier 2D numerical models of a coupled magmatism-mantle convection system show that these two agents strongly couple each other, when the Rayleigh number Ra is sufficiently high: magmatism induced by a mantle upwelling flow boosts the upwelling flow itself. The mantle convection enhanced by this positive feedback (the magmatism-mantle upwelling, or MMU, feedback) causes vigorous magmatism and, at the same time, strongly stirs the mantle. I explored how the MMU feedback influences the evolution of the earliest mantle that contains the magma ocean, based on a numerical model where the mantle is hot and its topmost 1/3 is partially molten at the beginning of the calculation: The evolution drastically changes its style, as Ra exceeds the threshold for onset of the MMU feedback, around 107. At Ra 107, however, the mantle remains compositionally more homogeneous in spite of the widespread magmatism, and the deep mantle remains hotter than the shallow mantle, because of the strong convective stirring caused by the feedback. The threshold value suggests that the mantle of a planet larger than Mars evolves in a way substantially different from that in the Moon does. Indeed, in my earlier models, magmatism makes the early mantle compositionally stratified in the Moon, but the effects of strong convective stirring overwhelms that of magmatism to keep the mantle compositionally rather homogeneous in Venus and the Earth. The MMU feedback is likely to be a key to understanding why vestiges of the magma ocean are so scarce in the Earth.

  15. Dihedral angle of carbonatite melts in mantle residue near the upper mantle and transition zone

    Science.gov (United States)

    Ghosh, S. K.; Rohrbach, A.; Schmidt, M. W.

    2015-12-01

    Carbonate melts are thought to be ideal metasomatic agents in the deep upper mantle (Green & Wallace, 1988) and these melts are low in viscosities (10-1-10-3 Pa·s) compared to primitive basalt (101-102 Pa·s), furthermore the ability to form an interconnected grain-edge melt network at low melt fractions (3 GPa (Dasgupta et al. 2006, Ghosh et al., 2009), dissolve a number of geochemically incompatible elements much better than silicate melts (Blundy and Dalton, 2000). Previous studies of carbonate melt dihedral angles in olivine-dominated matrices yielded 25-30oat 1-3 GPa, relatively independent of melt composition (Watson et al., 1990) and temperature (Hunter and McKenzie, 1989). Dihedral angles of carbonate melts in contact with deep mantle silicate phases (e.g. garnet, wadsleyite, and ringwoodite) which constitute more than 70 % of the deep upper mantle and transition zone have not been studied yet. We have performed multi-anvil experiments on carbonate-bearing peridotites with 5.0 wt% CO2 from 13.5 to 20 GPa 1550 oC to investigate the dihedral angle of magnesio-carbonatite melts in equilibrium with garnet, olivine (and its high-pressure polymorphs), and clinoenstatite. The dihedral angle of carbonate melts in the deep upper mantle and transition zone is ~30° for majorite garnet and olivine (and its polymorphs) dominated matrices. It does not change with increasing pressure in the range 13.5-20 GPa. Our results suggest that very low melt fractions of carbonatite melt forming in the deep upper mantle and transition zone are interconnected at melt fractions less than 0.01. Consistent with geophysical observations, this could possibly explain low velocity regions in the deep mantle and transition zone.

  16. Comparison of premodulated interferential and pulsed current electrical stimulation in prevention of deep muscle atrophy in rats.

    Science.gov (United States)

    Tanaka, Minoru; Hirayama, Yusuke; Fujita, Naoto; Fujino, Hidemi

    2013-04-01

    The goal of this study was to compare the effects of electrical stimulation using pulsed current (PC) and premodulated interferential current (IC) on prevention of muscle atrophy in the deep muscle layer of the calf. Rats were randomly divided into 3 treatment groups: control, hindlimb unloading for 2 weeks (HU), and HU plus electrical stimulation for 2 weeks. The animals in the electrical stimulation group received therapeutic stimulation of the left (PC) or right (IC) calf muscles twice a day during the unloading period. Animals undergoing HU for 2 weeks exhibited significant loss of muscle mass, decreased cross-sectional area (CSA) of muscle fibers, and increased expression of ubiquitinated proteins in the gastrocnemius and soleus muscles compared with control animals. Stimulation with PC attenuated the effects on the muscle mass, fiber CSA, and ubiquitinated proteins in the gastrocnemius muscle. However, PC stimulation failed to prevent atrophy of the deep layer of the gastrocnemius muscle and the soleus muscle. In contrast, stimulation with IC inhibited atrophy of both the gastrocnemius and soleus muscles. In addition, the IC protocol inhibited the HU-induced increase in ubiquitinated protein expression in both gastrocnemius and soleus muscles. These results suggest that electrical stimulation with IC is more effective than PC in preventing muscle atrophy in the deep layer of limb muscles.

  17. Choline and Geranate Deep Eutectic Solvent as a Broad-Spectrum Antiseptic Agent for Preventive and Therapeutic Applications.

    Science.gov (United States)

    Zakrewsky, Michael; Banerjee, Amrita; Apte, Sanjana; Kern, Theresa L; Jones, Mattie R; Sesto, Rico E Del; Koppisch, Andrew T; Fox, David T; Mitragotri, Samir

    2016-06-01

    Antiseptic agents are the primary arsenal to disinfect skin and prevent pathogens spreading within the host as well as into the surroundings; however the Food and Drug Administration published a report in 2015 requiring additional validation of nearly all current antiseptic agents before their continued use can be allowed. This vulnerable position calls for urgent identification of novel antiseptic agents. Recently, the ability of a deep eutectic, Choline And Geranate (CAGE), to treat biofilms of Pseudomonas aeruginosa and Salmonella enterica was demonstrated. Here it is reported that CAGE exhibits broad-spectrum antimicrobial activity against a number of drug-resistant bacteria, fungi, and viruses including clinical isolates of Mycobacterium tuberculosis, Staphylococcus aureus, and Candida albicans as well as laboratory strains of Herpes Simplex Virus. Studies in human keratinocytes and mice show that CAGE affords negligible local or systemic toxicity, and an ≈180-14 000-fold improved efficacy/toxicity ratio over currently used antiseptic agents. Further, CAGE penetrates deep into the dermis and treats pathogens located in deep skin layers as confirmed by the ability of CAGE in vivo to treat Propionibacterium acnes infection. In combination, the results clearly demonstrate CAGE holds promise as a transformative platform antiseptic agent for preventive as well as therapeutic applications. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Noble Gases And Changing Models Of Mantle Evolution

    Science.gov (United States)

    Ballentine, C. J.; van Keken, P. E.; Porcelli, D.; Hauri, E. H.

    2003-04-01

    The noble gas isotopes recorded in Ocean Island Basalts (OIB) and Mid Ocean Ridge Basalts (MORB) combined with an estimate of ^3He concentration in the upper mantle have played a defining role in the development of models describing the geochemical evolution of the mantle. The three most cited noble gas constraints on a layered mantle system are the Heat/He discrepancy, 40Ar mass balance, and low ^3He concentration (relative to U+Th) in the upper mantle. These are all equally dependant on the validity of integrating the mantle ^3He flux into the oceans (t_frac{1}{2} ˜ 10^3 years) with the record of ocean floor generation (t_frac{1}{2} ˜ 5x10^6 years) to obtain the mantle ^3He concentration. A ^3He concentration 3.5 times higher in the mantle than currently accepted removes these noble gas constraints. A deep reservoir would then no longer be required to: i) trap ^4He produced by U+Th decay but let the associated heat escape; ii) provide a reservoir for the 'missing' 40Ar generated by K decay; and iii) provide a flux of ^3He to balance the ^3He/^4He ratio and U+Th content of the upper mantle. Numerical models simulating whole mantle convection show that natural fluctuations in the Heat/He ratio due to different extraction methods can accommodate the difference between predicted and observed values, while these same models illustrate that the efficiency of mantle 40Ar degassing is low enough to account for the 'missing' 40Ar within the context of whole mantle convection. The simple observation that ^3He/^4He ratios in OIB are higher than MORB nevertheless demands that there is a high ^3He reservoir in the mantle and that the model 'zero paradox' concentration remains the upper limit reference value. While higher upper mantle ^3He concentrations remove the need for a layer at the 670km boundary, mantle models satisfying the noble gases must still provide a system that separates radiogenic Heat from Helium production, preserves a region of the mantle with higher 40Ar

  19. Formation of mantle "lone plumes" in the global downwelling zone - A multiscale modelling of subduction-controlled plume generation beneath the South China Sea

    Science.gov (United States)

    Zhang, Nan; Li, Zheng-Xiang

    2018-01-01

    It has been established that almost all known mantle plumes since the Mesozoic formed above the two lower mantle large low shear velocity provinces (LLSVPs). The Hainan plume is one of the rare exceptions in that instead of rising above the LLSVPs, it is located within the broad global mantle downwelling zone, therefore classified as a "lone plume". Here, we use the Hainan plume example to investigate the feasibility of such lone plumes being generated by subducting slabs in the mantle downwelling zone using 3D geodynamic modelling. Our geodynamic model has a high-resolution regional domain embedded in a relatively low resolution global domain, which is set up in an adaptive-mesh-refined, 3D mantle convection code ASPECT (Advanced Solver for Problems in Earth's ConvecTion). We use a recently published plate motion model to define the top mechanical boundary condition. Our modelling results suggest that cold slabs under the present-day Eurasia, formed from the Mesozoic subduction and closure of the Tethys oceans, have prevented deep mantle hot materials from moving to the South China Sea from regions north or west of the South China Sea. From the east side, the Western Pacific subduction systems started to promote the formation of a lower-mantle thermal-chemical pile in the vicinity of the future South China Sea region since 70 Ma ago. As the top of this lower-mantle thermal-chemical pile rises, it first moved to the west, and finally rested beneath the South China Sea. The presence of a thermochemical layer (possible the D″ layer) in the model helps stabilizing the plume root. Our modelling is the first implementation of multi-scale mesh in the regional model. It has been proved to be an effective way of modelling regional dynamics within a global plate motion and mantle dynamics background.

  20. Differential motion between upper crust and lithospheric mantle in the central Basin and Range

    Science.gov (United States)

    Schulte-Pelkum, Vera; Biasi, Glenn; Sheehan, Anne; Jones, Craig

    2011-09-01

    Stretching of the continental crust in the Basin and Range, western USA, has more than doubled the surface area of the central province. But it is unknown whether stretching affects the entire column of lithosphere down to the convecting mantle, if deep extension occurs offset to the side, or if deeper layers are entirely decoupled from the upper crust. The central Basin and Range province is unusual, compared with its northern and southern counterparts: extension began later; volcanism was far less voluminous; and the unique geochemistry of erupted basalts suggests a long-preserved mantle source. Here we use seismic data and isostatic calculations to map lithospheric thickness in the central Basin and Range. We identify an isolated root of ancient mantle lithosphere that is ~125km thick, providing geophysical confirmation of a strong, cold mantle previously inferred from geochemistry. We suggest that the root caused the later onset of extension and prevented the eruption of voluminous volcanism at the surface. We infer that the root initially pulled away from the Colorado Plateau along with the crust, but then was left behind intact during extension across Death Valley to the Sierra Nevada. We conclude that the upper crust is now decoupled from and moving relative to the root.

  1. Methods of medical prevention of borderline states and maintaining capacity to work in miners at deep coal mines

    Energy Technology Data Exchange (ETDEWEB)

    Kobets, G.P.; Perederii, G.S.; Tkachenko, L.N.; Ivanov, V.V.; Kiva, A.I. (Institut Gigieny Truda i Profzabolevanii, Donetsk (USSR))

    1990-01-01

    Describes the procedures used to identify and treat borderline states in coal miners working in deep mines in the Donbass. Timely preventive treatment helps to maintain the condition of the miners and reduce time lost through sickness. Diagnosis is performed on the basis of a number of physical indices coupled with a subjective assessment marked on a points scale. The types of treatment available at sanatoria are outlined: they include physiotherapy, mud and carbon dioxide baths, various types of massage, etc. Courses last 2-3 weeks and are followed by 3-8 days of rehabilitation at work, depending on occupation and working conditions. 6 refs.

  2. The Efficacy of Blue-Green Infrastructure for Pluvial Flood Prevention under Conditions of Deep Uncertainty

    Science.gov (United States)

    Babovic, Filip; Mijic, Ana; Madani, Kaveh

    2017-04-01

    Urban areas around the world are growing in size and importance; however, cities experience elevated risks of pluvial flooding due to the prevalence of impermeable land surfaces within them. Urban planners and engineers encounter a great deal of uncertainty when planning adaptations to these flood risks, due to the interaction of multiple factors such as climate change and land use change. This leads to conditions of deep uncertainty. Blue-Green (BG) solutions utilise natural vegetation and processes to absorb and retain runoff while providing a host of other social, economic and environmental services. When utilised in conjunction with Decision Making under Deep Uncertainty (DMDU) methodologies, BG infrastructure provides a flexible and adaptable method of "no-regret" adaptation; resulting in a practical, economically efficient, and socially acceptable solution for flood risk mitigation. This work presents the methodology for analysing the impact of BG infrastructure in the context of the Adaptation Tipping Points approach to protect against pluvial flood risk in an iterative manner. An economic analysis of the adaptation pathways is also conducted in order to better inform decision-makers on the benefits and costs of the adaptation options presented. The methodology was applied to a case study in the Cranbrook Catchment in the North East of London. Our results show that BG infrastructure performs better under conditions of uncertainty than traditional grey infrastructure.

  3. Alkaline Phosphatase for the Prevention of Intestinal and Renal Injury in a Rat Model of Cardiopulmonary Bypass with Deep Hypothermic Circulatory Arrest

    Science.gov (United States)

    2017-09-01

    AWARD NUMBER: W81XWH-16-1-0090 TITLE: Alkaline Phosphatase for the Prevention of Intestinal and Renal Injury in a Rat Model of Cardiopulmonary...TYPE Annual 3. DATES COVERED 8/15/2016—8/14/2017 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Alkaline Phosphatase for the Prevention of Intestinal... prevention of intestinal and kidney injury after pediatric cardiopulmonary bypass with deep hypothermic circulatory arrest. In this model, we place 5-10kg

  4. Investigating Late Cenozoic Mantle Dynamics beneath Yellowstone

    Science.gov (United States)

    Zhou, Q.; Liu, L.

    2015-12-01

    Recent tomography models (Sigloch, 2011; Schmandt & Lin, 2014) reveal unprecedented details of the mantle structure beneath the United States (U.S.). Prominent slow seismic anomalies below Yellowstone, traditionally interpreted as due to a mantle plume, are restricted to depths either shallower than 200 km or between 500 and 1000 km, but a continuation to greater depth is missing. Compared to fast seismic anomalies, which are usually interpreted as slabs or delaminated lithosphere, origin of deep slow seismic anomalies, especially those in the vicinity of subduction zones, is more enigmatic. As a consequence, both the dynamics and evolution of these slow anomalies remain poorly understood. To investigate the origin and evolution of the Yellowstone slow anomaly during the past 20 Myr, we construct a 4D inverse mantle convection model with a hybrid data assimilation scheme. On the one hand, we use the adjoint method to recover the past evolution of mantle seismic structures beyond the subduction zones. On the other hand, we use a high-resolution forward model to simulate the subduction of the oceanic (i.e., Farallon) plate. During the adjoint iterations, features from these two approaches are blended together at a depth of ~200 km below the subduction zone. In practice, we convert fast and slow seismic anomalies to effective positive and negative density heterogeneities. Our preliminary results indicate that at 20 Ma, the present-day shallow slow anomalies beneath the western U.S. were located inside the oceanic asthenosphere, which subsequently entered the mantle wedge, through the segmented Farallon slab. The eastward encroachment of the slow anomaly largely followed the Yellowstone hotspot track migration. The present deep mantle Yellowstone slow anomaly originated at shallower depths (i.e. transition zone), and was then translated down to the lower mantle accompanying the sinking fast anomalies. The temporal evolution of the slow anomalies suggests that the deep

  5. Tracing recycled volatiles in a heterogeneous mantle with boron isotopes

    Science.gov (United States)

    Walowski, Kristina; Kirstein, Linda; de Hoog, Cees-Jan; Elliot, Tim; Savov, Ivan; Devey, Colin

    2016-04-01

    Recycling of oceanic lithosphere drives the chemical evolution of the Earth's mantle supplying both solids and volatiles to the Earth's interior. Yet, how subducted material influences mantle composition remains unclear. A perfect tracer for slab recycling should be only fractionated at the Earth's surface, have a strong influence on mantle compositions but be resistant to perturbations en route back to the surface. Current understanding suggests that boron concentrations linked to B isotope determinations fulfil all these requirements and should be an excellent tracer of heterogeneity in the deep mantle. Here, we present the trace element, volatile and the B isotope composition of basaltic glasses and melt inclusions in olivine from distinct end-member ocean island basalts (OIB) to track the fate of recycled lithosphere and ultimately document how recycling contributes to mantle heterogeneity. The chosen samples represent the different end member OIB compositions and include: EMI (Pitcairn), EMII (MacDonald), HIMU (St. Helena), and FOZO (Cape Verde & Reunion). The data is derived from both submarine and subaerial deposits, with B isotope determination of both basaltic glass and melt inclusions from each locality. Preliminary results suggest OIB have B isotopic compositions that overlap the MORB array (-7.5‰±0.7; Marschall et al., 2015) but extend to both lighter and heavier values. These results suggest that B isotopes will be useful for resolving mantle source heterogeneity at different ocean islands and contribute to our understanding of the volatile budget of the deep mantle.

  6. Prevention of deep vein thrombosis after total knee arthroplasty. Coumadin versus pneumatic calf compression.

    Science.gov (United States)

    Hodge, W A

    1991-10-01

    The rate of deep vein thrombosis (DVT) after total knee arthroplasty (TKA) without prophylaxis has been reported as high as 84%. Coumadin anticoagulation and pneumatic calf compression (PCC) boots are two current therapies that have been thought to be effective in reducing this high rate of DVT. To investigate these two methods, a nonrandomized prospective study was designed. The first group involved treating 48 consecutive knee arthroplasties with a regimen of coumadin anticoagulation. The second group involved 81 consecutive knee arthroplasties treated with sequential PCC boots. Bilateral lower extremity venography was performed between the eighth and tenth hospital postoperative days. The overall incidence of DVT in the coumadin group was 33%, with 29% having calf thrombi and 6% having thigh thrombi. The overall incidence of DVT in the boot group was 31%, with 27% having calf thrombi and 6% having thigh thrombi. In both groups, there were no treatment-related complications. Cost analysis of the administration of each type of therapy showed coumadin to be approximately 50% more expensive than PCC boots. Although coumadin and PCC boot therapy are safe and effective in reducing the incidence of DVT after TKA, there are economic factors that make the latter a more favorable option.

  7. 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

  8. Understanding the nature of mantle upwelling beneath East-Africa

    Science.gov (United States)

    Civiero, Chiara; Hammond, James; Goes, Saskia; Ahmed, Abdulhakim; Ayele, Atalay; Doubre, Cecile; Goitom, Berhe; Keir, Derek; Kendall, Mike; Leroy, Sylvie; Ogubazghi, Ghebrebrhan; Rumpker, Georg; Stuart, Graham

    2014-05-01

    The concept of hot upwelling material - otherwise known as mantle plumes - has long been accepted as a possible mechanism to explain hotspots occurring at Earth's surface and it is recognized as a way of removing heat from the deep Earth. Nevertheless, this theory remains controversial since no one has definitively imaged a plume and over the last decades several other potential mechanisms that do not require a deep mantle source have been invoked to explain this phenomenon, for example small-scale convection at rifted margins, meteorite impacts or lithospheric delamination. One of the best locations to study the potential connection between hotspot volcanism at the surface and deep mantle plumes on land is the East African Rift (EAR). We image seismic velocity structure of the mantle below EAR with higher resolution than has been available to date by including seismic data recorded by stations from many regional networks ranging from Saudi Arabia to Tanzania. We use relative travel-time tomography to produce P- velocity models from the surface down into the lower mantle incorporating 9250 ray-paths in our model from 495 events and 402 stations. We add smaller earthquakes (4.5 image structures of ~ 100-km length scales to ~ 1000 km depth beneath the northern East-Africa rift (Ethiopia, Eritrea, Djibouti, Yemen) with good resolution also in the transition zone and uppermost lower mantle. Our observations provide evidence that the shallow mantle slow seismic velocities continue trough the transition zone and into the lower mantle. In particular, the relatively slow velocity anomaly beneath the Afar Depression extends up to depths of at least 1000 km depth while another low-velocity anomaly beneath the Main Ethiopian Rift seems to be present in the upper mantle only. These features in the lower mantle are isolated with a diameter of about 400 km indicating deep multiple sources of upwelling that converge in broader low-velocity bodies along the rift axis at shallow

  9. Moho vs crust-mantle boundary: Evolution of an idea

    Science.gov (United States)

    O'Reilly, Suzanne Y.; Griffin, W. L.

    2013-12-01

    The concept that the Mohorovicic Discontinuity (Moho) does not necessarily coincide with the base of the continental crust as defined by rock-type compositions was introduced in the early 1980s. This had an important impact on understanding the nature of the crust-mantle boundary using information from seismology and from deep-seated samples brought to the surface as xenoliths in magmas, or as tectonic terranes. The use of empirically-constrained P-T estimates to plot the locus of temperature vs depth for xenoliths defined a variety of geotherms depending on tectonic environment. The xenolith geotherms provided a framework for constructing lithological sections through the deep lithosphere, and revealed that the crust-mantle boundary in off-craton regions commonly is transitional over a depth range of about 5-20 km. Early seismic-reflection data showed common layering near the Moho, correlating with the petrological observation of multiple episodes of basaltic intrusion around the crust-mantle boundary. Developments in seismology, petrophysics and experimental petrology have refined interpretation of lithospheric domains. The expansion of in situ geochronology (especially zircon U-Pb ages and Hf-isotopes; Os isotopes of mantle sulfides) has defined tectonic events that affected whole crust-mantle sections, and revealed that the crust-mantle boundary can change in depth through time. However, the nature of the crust-mantle boundary in cratonic regions remains enigmatic, mainly due to lack of key xenoliths or exposed sections. The observation that the Moho may lie significantly deeper than the crust-mantle boundary has important implications for modeling the volume of the crust. Mapping the crust using seismic techniques alone, without consideration of the petrological problems, may lead to an overestimation of crustal thickness by 15-30%. This will propagate to large uncertainties in the calculation of elemental mass balances relevant to crust-formation processes

  10. Efficacy of prophylactic inferior vena caval filters in prevention of pulmonary embolism in the absence of deep venous thrombosis.

    Science.gov (United States)

    Davies, Mark G; Hart, Joseph P; El-Sayed, Hosam F

    2016-01-01

    There is an increasing use of inferior vena caval filters (IVCFs) as prophylactic activity in the absence of a deep venous thrombosis (DVT) to prevent pulmonary embolism (PE) in high-risk patients. These devices are effective in preventing PE in the presence of lower extremity DVT, when anticoagulation is contraindicated or has failed. An electronic databases search of MEDLINE, PubMed, The Cochrane Library, and Google Scholar for relevant articles listed between January 2000 and December 2014 was performed. The review was confined to patients without a history of previous venous thromboembolism and no evidence of changes on venous duplex imaging suggestive of previous DVT. At present, the use of prophylactic IVCF is predominantly in the trauma, orthopedic, and bariatric surgical populations. Currently, no class I studies exist to support insertion of an IVCF in a patient without an established DVT or PE. However, there is a body of class II and class III evidence that would support the use of IVCFs in certain "high-risk" patients who do not have a documented DVT or the occurrence of a PE. Widespread use of prophylactic IVCFs is not supported by evidence and should be discouraged. Copyright © 2016 Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.

  11. Deep sea water prevents balloon angioplasty-induced hyperplasia through MMP-2: an in vitro and in vivo study.

    Directory of Open Access Journals (Sweden)

    Pei-Chuan Li

    Full Text Available Major facts about the development of restenosis include vascular smooth muscle cells (VSMCs proliferation and migration. A previous study showed that in vitro treatment with magnesium chloride has the potential to affect the proliferation and migration of VSMCs. Magnesium is the major element in deep sea water (DSW and is a biologically active mineral. It is unclear whether DSW intake can prevent abnormal proliferation and migration of VSMCs as well as balloon angioplasty-induced neointimal hyperplasia. Thus, we attempted to evaluate the anti-restenotic effects of DSW and its possible molecular mechanisms. Several concentrations of DSW, based on the dietary recommendations (RDA for magnesium, were applied to a model of balloon angioplasty in SD rats. The results showed that DSW intake markedly increased magnesium content within the vascular wall and reduced the development of neointimal hyperplasia. The immunohistochemical analysis also showed that the expression of proteins associated with cell proliferation and migration were decreased in the balloon angioplasty groups with DSW supplement. Furthermore, in vitro treatment with DSW has a dose-dependent inhibitory effect on serum-stimulated proliferation and migration of VSMCs, whose effects might be mediated by modulation of mitogen-activated protein kinase (MAPK signaling and of the activity of matrix metalloproteinase-2 (MMP-2. Our study suggested that DSW intake can help prevent neointimal hyperplasia (or restenosis, whose effects may be partially regulated by magnesium and other minerals.

  12. Experimental investigation of mantle melting in the presence of carbonates

    Science.gov (United States)

    Dasgupta, Rajdeep

    High pressure-temperature experiments are performed at pressures of 2 to 10 GPa and temperatures of 900 to 1600 °C to constrain partial melting of carbonate bearing mantle eclogite and peridotite. Eclogite and peridotite in the presence of CO2 is observed to produce carbonatitic melts at their respective solidi for most parts of Earth's upper mantle. The solidus of carbonated eclogite at 3 GPa is observed to vary significantly with bulk Ca/Mg and Na2O content. But the appropriate solidus of carbonated ocean crust remains hotter than the subduction geotherms up to 260 km, indicating subduction of carbon, in the form of magnesite-eclogite, deep into the mantle. Upwelling mantle eclogite, on the other hand, must release carbonatite at depths >350 km. From experiments at 3 GPa, it is found that carbonated eclogite can generate silicate partial melts that can give rise to silica-undersaturated ocean island lavas. Solidus of carbonated peridotite from 3 to 10 GPa indicates that along an oceanic geotherm, the onset of partial melting happens shallower than that of carbonated eclogite, but still as deep as 300-330 km beneath ridges. Extraction of incipient carbonatite from deep mantle implies efficient removal of highly incompatible trace elements, including carbon, from the mantle. This deep melting likely creates a vast mantle residue that is depleted and fractionated in important trace elements and also might explain many geophysical features of Earth's deep upper mantle. Experiments with peridotite of variable carbonate concentrations also indicate that increasing CO2, unlike H2O, does not cause the isobaric solidus of carbonated peridotite to decrease. Using a new method of iterative sandwich experiments, the detailed composition of near-solidus melt from carbonated peridotite is determined at 6.6 GPa. Near-solidus melt of peridotite + CO2 at a depth of ˜200 km is Fe-Na bearing magnesio-dolomitic carbonatite. Transition from near-solidus carbonatite to carbonated

  13. Tectonic Stacking of HP/LT Metamorphic Rocks in Accretionary Wedges and the Role of Shallowing Slab-Mantle Decoupling

    Science.gov (United States)

    Aygül, Mesut; Oberhänsli, Roland

    2017-11-01

    High-pressure/low-temperature (HP/LT) chloritoid-bearing micaschists crop out widely in the central part of northern Turkey and represent deep-seated subduction-accretionary complexes. Three peak metamorphic assemblages are identified in the area studied: (1) garnet-chloritoid-glaucophane with pseudomorphs after lawsonite; (2) chloritoid with pseudomorphs after glaucophane; and (3) chloritoid with pseudomorphs after jadeite in addition to phengite, paragonite, quartz, chlorite, rutile, and apatite. The latter is interpreted as transformation of a chloritoid + glaucophane assemblage to chloritoid + jadeite with increasing pressure; PT modeling indicates 17 and 22-25 kbars for the two peak parageneses. The diversity of peak metamorphic assemblages and the PT estimates suggest that basal accretion occurred at different depths within the wedge. The depth of the basal accretion is possibly controlled by the slab-mantle decoupling depth. Stretching and thinning of the lithospheric fore arc induced by the slab rollback possibly caused shallowing of the slab-mantle decoupling depth which limited depth of the basal accretion from 70-80 km to 55 km within the subduction channel. A slab-mantle coupling depth-controlled basal accretion may also explain the scarcity of eclogite and high-grade blueschist facies metamorphic rocks in active intraoceanic subduction zones. Because the overriding plate is young and hot in intraoceanic subductions, the slab and mantle are coupled at a relatively shallow depth before eclogitization of the oceanic crust. This prevents accretion and exhumation of eclogite along the subduction channel.

  14. Selective cerebral perfusion prevents abnormalities in glutamate cycling and neuronal apoptosis in a model of infant deep hypothermic circulatory arrest and reperfusion.

    Science.gov (United States)

    Kajimoto, Masaki; Ledee, Dolena R; Olson, Aaron K; Isern, Nancy G; Robillard-Frayne, Isabelle; Des Rosiers, Christine; Portman, Michael A

    2016-11-01

    Deep hypothermic circulatory arrest is often required for the repair of complex congenital cardiac defects in infants. However, deep hypothermic circulatory arrest induces neuroapoptosis associated with later development of neurocognitive abnormalities. Selective cerebral perfusion theoretically provides superior neural protection possibly through modifications in cerebral substrate oxidation and closely integrated glutamate cycling. We tested the hypothesis that selective cerebral perfusion modulates glucose utilization, and ameliorates abnormalities in glutamate flux, which occur in association with neuroapoptosis during deep hypothermic circulatory arrest. Eighteen infant male Yorkshire piglets were assigned randomly to two groups of seven (deep hypothermic circulatory arrest or deep hypothermic circulatory arrest with selective cerebral perfusion for 60 minutes at 18℃) and four control pigs without cardiopulmonary bypass support. Carbon-13-labeled glucose as a metabolic tracer was infused, and gas chromatography-mass spectrometry and nuclear magnetic resonance were used for metabolic analysis in the frontal cortex. Following 2.5 h of cerebral reperfusion, we observed similar cerebral adenosine triphosphate levels, absolute levels of lactate and citric acid cycle intermediates, and carbon-13 enrichment among three groups. However, deep hypothermic circulatory arrest induced significant abnormalities in glutamate cycling resulting in reduced glutamate/glutamine and elevated γ-aminobutyric acid/glutamate along with neuroapoptosis, which were all prevented by selective cerebral perfusion. The data suggest that selective cerebral perfusion prevents these modifications in glutamate/glutamine/γ-aminobutyric acid cycling and protects the cerebral cortex from apoptosis. © The Author(s) 2016.

  15. Circulation of carbon dioxide in the mantle: multiscale modeling

    Science.gov (United States)

    Morra, G.; Yuen, D. A.; Lee, S.

    2012-12-01

    Much speculation has been put forward on the quantity and nature of carbon reservoirs in the deep Earth, because of its involvement in the evolution of life at the surface and inside planetary interiors. Carbon penetrates into the Earth's mantle mostly during subduction of oceanic crust, which contains carbonate deposits [1], however the form that it assumes at lower mantle depths is scarcely understood [2], hampering our ability to estimate the amount of carbon in the entire mantle by orders of magnitude. We present simulations of spontaneous degassing of supercritical CO2 using in-house developed novel implementations of the Fast-Multipole Boundary Element Method suitable for modeling two-phase flow (here mantle mineral and free CO2 fluid) through disordered materials such as porous rocks. Because the mutual interaction of droplets immersed either in a fluid or a solid matrix and their weakening effect to the host rock alters the strength of the mantle rocks, at the large scale the fluid phases in the mantle may control the creeping of mantle rocks [3]. In particular our study focuses on the percolation of supercritical CO2, estimated through the solution of the Laplace equation in a porous system, stochastically generated through a series of random Karhunen-Loeve decomposition. The model outcome is employed to extract the transmissivity of supercritical fluids in the mantle from the lowest scale up to the mantle scale and in combination with the creeping flow of the convecting mantle. The emerging scenarios on the global carbon cycle are finally discussed. [1] Boulard, E., et al., New host for carbon in the deep Earth. Proceedings of the National Academy of Sciences, 2011. 108(13): p. 5184-5187. [2] Walter, M.J., et al., Deep Mantle Cycling of Oceanic Crust: Evidence from Diamonds and Their Mineral Inclusions. Science, 2011. 334(6052): p. 54-57. [3] Morra, G., et al., Ascent of Bubbles in Magma Conduits Using Boundary Elements and Particles. Procedia Computer

  16. Water Distribution in the Continental and Oceanic Upper Mantle

    Science.gov (United States)

    Peslier, Anne H.

    2015-01-01

    Nominally anhydrous minerals such as olivine, pyroxene and garnet can accommodate tens to hundreds of ppm H2O in the form of hydrogen bonded to structural oxygen in lattice defects. Although in seemingly small amounts, this water can significantly alter chemical and physical properties of the minerals and rocks. Water in particular can modify their rheological properties and its distribution in the mantle derives from melting and metasomatic processes and lithology repartition (pyroxenite vs peridotite). These effects will be examined here using Fourier transform infrared spectrometry (FTIR) water analyses on minerals from mantle xenoliths from cratons, plume-influenced cratons and oceanic settings. In particular, our results on xenoliths from three different cratons will be compared. Each craton has a different water distribution and only the mantle root of Kaapvaal has evidence for dry olivine at its base. This challenges the link between olivine water content and survival of Archean cratonic mantle, and questions whether xenoliths are representative of the whole cratonic mantle. We will also present our latest data on Hawaii and Tanzanian craton xenoliths which both suggest the intriguing result that mantle lithosphere is not enriched in water when it interacts with melts from deep mantle upwellings (plumes).

  17. Continental flood basalts derived from the hydrous mantle transition zone.

    Science.gov (United States)

    Wang, Xuan-Ce; Wilde, Simon A; Li, Qiu-Li; Yang, Ya-Nan

    2015-07-14

    It has previously been postulated that the Earth's hydrous mantle transition zone may play a key role in intraplate magmatism, but no confirmatory evidence has been reported. Here we demonstrate that hydrothermally altered subducted oceanic crust was involved in generating the late Cenozoic Chifeng continental flood basalts of East Asia. This study combines oxygen isotopes with conventional geochemistry to provide evidence for an origin in the hydrous mantle transition zone. These observations lead us to propose an alternative thermochemical model, whereby slab-triggered wet upwelling produces large volumes of melt that may rise from the hydrous mantle transition zone. This model explains the lack of pre-magmatic lithospheric extension or a hotspot track and also the arc-like signatures observed in some large-scale intracontinental magmas. Deep-Earth water cycling, linked to cold subduction, slab stagnation, wet mantle upwelling and assembly/breakup of supercontinents, can potentially account for the chemical diversity of many continental flood basalts.

  18. Mantle structure and tectonic history of SE Asia

    Science.gov (United States)

    Hall, Robert; Spakman, Wim

    2015-09-01

    Seismic travel-time tomography of the mantle under SE Asia reveals patterns of subduction-related seismic P-wave velocity anomalies that are of great value in helping to understand the region's tectonic development. We discuss tomography and tectonic interpretations of an area centred on Indonesia and including Malaysia, parts of the Philippines, New Guinea and northern Australia. We begin with an explanation of seismic tomography and causes of velocity anomalies in the mantle, and discuss assessment of model quality for tomographic models created from P-wave travel times. We then introduce the global P-wave velocity anomaly model UU-P07 and the tectonic model used in this paper and give an overview of previous interpretations of mantle structure. The slab-related velocity anomalies we identify in the upper and lower mantle based on the UU-P07 model are interpreted in terms of the tectonic model and illustrated with figures and movies. Finally, we discuss where tomographic and tectonic models for SE Asia converge or diverge, and identify the most important conclusions concerning the history of the region. The tomographic images of the mantle record subduction beneath the SE Asian region to depths of approximately 1600 km. In the upper mantle anomalies mainly record subduction during the last 10 to 25 Ma, depending on the region considered. We interpret a vertical slab tear crossing the entire upper mantle north of west Sumatra where there is a strong lateral kink in slab morphology, slab holes between c.200-400 km below East Java and Sumbawa, and offer a new three-slab explanation for subduction in the North Sulawesi region. There is a different structure in the lower mantle compared to the upper mantle and the deep structure changes from west to east. What was imaged in earlier models as a broad and deep anomaly below SE Asia has a clear internal structure and we argue that many features can be identified as older subduction zones. We identify remnants of slabs

  19. Diagnosis prevention and treatment for PICC-related upper extremity deep vein thrombosis in breast cancer patients.

    Science.gov (United States)

    Xing, Lei; Adhikari, Vishnu Prasad; Liu, Hong; Kong, Ling Quan; Liu, Sheng Chun; Li, Hong Yuan; Ren, Guo Sheng; Luo, Feng; Wu, Kai Nan

    2012-09-01

    To study the incidence, diagnosis, prevention and treatment of peripherally inserted central catheter (PICC)-related upper extremity deep vein thrombosis (DVT) in breast cancer patients using a PICC catheter for chemotherapy. The data of the incidence, diagnosis and treatment of PICC-related upper extremity DVT in 187 breast cancer patients using a PICC catheter for chemotherapy, from August 2009 to July 2011 were retrospectively analyzed. In total 188 PICC were inserted between August 2009 and July 2011 and followed up for a total of 14 399 catheter-days (median placement, 76.6 days; range, 1 to 170 days). Four (2.1%) of 188 PICC were removed as a result of PICC-related upper extremity DVT in 14 to 112 catheter-days, at a rate of 0.28/1000 catheter-days. The use of PICCs in breast cancer patients for chemotherapy is safe and effective. However, some patients may develop catheter-related upper extremity DVT. In order to minimize complications, we should pay attention to its early symptoms and signs, as well as the timely removal of the catheter and appropriate anti-coagulant treatment. © 2012 Wiley Publishing Asia Pty Ltd.

  20. Seismic Evidence for Lower Mantle Plume Under the Yellowstone Hotspot

    Science.gov (United States)

    Nelson, P.; Grand, S.

    2017-12-01

    The mantle plume hypothesis for the origin of intraplate volcanism has been controversial since its inception in the 1970s. The hypothesis proposes hot narrow upwelling of rock rooted at the core mantle boundary (CMB) rise through the mantle and interact with the base of the lithosphere forming linear volcanic systems such as Hawaii and Yellowstone. Recently, broad lower mantle (>500 km in diameter) slow velocity conduits, most likely thermochemical in origin, have been associated with some intraplate volcanic provinces (French and Romanowicz, 2015). However, the direct detection of a classical thin thermal plume in the lower mantle using travel time tomography has remained elusive (Anderson and Natland, 2014). Here we present a new shear wave tomography model for the mantle beneath the western United States that is optimized to find short wavelength, sub-vertical structures in the lower mantle. Our approach uses carefully measured SKS and SKKS travel times recorded by dense North American seismic networks in conjunction with finite frequency kernels to build on existing tomography models. We find the presence of a narrow ( 300 km diameter) well isolated cylindrically shaped slow anomaly in the lower most mantle which we associate with the Yellowstone Hotspot. The conduit has a 2% reduction in shear velocity and is rooted at the CMB near the California/Arizona/Nevada border. A cross sectional view through the anomaly shows that it is slightly tilted toward the north until about 1300 km depth where it appears to weaken and deflect toward the surficial positon of the hotspot. Given the anomaly's strength, proximity to the Yellowstone Hotspot, and morphology we argue that a thermal plume interpretation is the most reasonable. Our results provide strong support for a lower mantle plume origin of the Yellowstone hotspot and more importantly the existence of deep thermal plumes.

  1. Stagnant lids and mantle overturns: Implications for Archaean tectonics, magmagenesis, crustal growth, mantle evolution, and the start of plate tectonics

    Directory of Open Access Journals (Sweden)

    Jean H. Bédard

    2018-01-01

    probability that oceanic crustal segments could founder in an organized way, producing a gradual evolution of pre-subduction convergent margins into modern-style active subduction systems around 2.5 Ga. Plate tectonics today is constituted of: (1 a continental drift system that started in the Early Archaean, driven by deep mantle currents pressing against the Archaean-age sub-continental lithospheric mantle keels that underlie Archaean cratons; (2 a subduction-driven system that started near the end of the Archaean.

  2. The origin of volatiles in the Earth's mantle

    Science.gov (United States)

    Hier-Majumder, Saswata; Hirschmann, Marc M.

    2017-08-01

    The Earth's deep interior contains significant reservoirs of volatiles such as H, C, and N. Due to the incompatible nature of these volatile species, it has been difficult to reconcile their storage in the residual mantle immediately following crystallization of the terrestrial magma ocean (MO). As the magma ocean freezes, it is commonly assumed that very small amounts of melt are retained in the residual mantle, limiting the trapped volatile concentration in the primordial mantle. In this article, we show that inefficient melt drainage out of the freezing front can retain large amounts of volatiles hosted in the trapped melt in the residual mantle while creating a thick early atmosphere. Using a two-phase flow model, we demonstrate that compaction within the moving freezing front is inefficient over time scales characteristic of magma ocean solidification. We employ a scaling relation between the trapped melt fraction, the rate of compaction, and the rate of freezing in our magma ocean evolution model. For cosmochemically plausible fractions of volatiles delivered during the later stages of accretion, our calculations suggest that up to 77% of total H2O and 12% of CO2 could have been trapped in the mantle during magma ocean crystallization. The assumption of a constant trapped melt fraction underestimates the mass of volatiles in the residual mantle by more than an order of magnitude.Plain Language SummaryThe Earth's deep interior contains substantial amounts of volatile elements like C, H, and N. How these elements got sequestered in the Earth's interior has long been a topic of debate. It is generally assumed that most of these elements escaped the interior of the Earth during the first few hundred thousand years to create a primitive atmosphere, leaving the mantle reservoir nearly empty. In this work, we show that the key to this paradox involves the very early stages of crystallization of the mantle from a global magma ocean. Using numerical models, we show

  3. 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

    of mantle plumes, as suggested 25 years ago by Hofmann & White [2]. Determination of the depth of origin of mantle plumes would provide a 1st-order constraint on the depth of plate subduction and the volume of the "upper" mantle. Improved seismic techniques and deployment of OBS arrays may soon allow robust imaging of mantle plumes in the deep mantle, although preliminary results are controversial [3]. Detection of a conclusive geochemical signature of core/mantle interaction would also provide strong evidence for a deep origin of mantle plumes, although there is considerable debate as to what such a signature would entail. In summary, determination of the depth of origin of mantle plumes may provide the key to deciphering the fate of subducted slabs and the overall style of mantle convection. Although this problem remains unresolved after several decades of work, recent developments in both geophysics and geochemistry provide hope for a final resolution within the next 10 years. [1] M Bizimis, M Griselin, JC Lassiter, VJM Salters, G Sen, EPSL 257, 259-293, 2007. [2] AW Hofmann, WM White, EPSL 57, 421-436, 1982. [3] R Montelli, G Nolet, F Dahlens, G Masters, E Engdahl, S-H Hung, Science 303, 338-343, 2004.

  4. An application of GOCE satellite gravity to resolve mantle heterogeneity in Europe

    DEFF Research Database (Denmark)

    Herceg, Matija; Artemieva, Irina; Thybo, Hans

    2015-01-01

    The aim of this study is to obtain new information on the density structure of the European upper mantle by incorporating the state-of-the-art global gravity data derived from the GOCE satellite gravity mission and recently released seismic model for the crustal structure, EUNAseis. The residual...... mantle gravity anomalies are derived from the GOCE data, from which gravitational effects of the deep mantle and the crust are removed. Our model of mantle density structure has lateral resolution of ca. 100 km, which allows to distinguish small-scale mantle anomalies and to link them to regional...... geodynamic processes. Given a relatively small range of expected density variations in the lithospheric mantle, knowledge on the uncertainties associated with incomplete knowledge of density structure of the crust is of utmost importance for further progress in density heterogeneity studies. Therefore...

  5. Pillars of the Mantle

    KAUST Repository

    Pugmire, David

    2017-07-05

    In this work, we investigate global seismic tomographic models obtained by spectral-element simulations of seismic wave propagation and adjoint methods. Global crustal and mantle models are obtained based on an iterative conjugate-gradient type of optimization scheme. Forward and adjoint seismic wave propagation simulations, which result in synthetic seismic data to make measurements and data sensitivity kernels to compute gradient for model updates, respectively, are performed by the SPECFEM3D-GLOBE package [1] [2] at the Oak Ridge Leadership Computing Facility (OLCF) to study the structure of the Earth at unprecedented levels. Using advances in solver techniques that run on the GPUs on Titan at the OLCF, scientists are able to perform large-scale seismic inverse modeling and imaging. Using seismic data from global and regional networks from global CMT earthquakes, scientists are using SPECFEM3D-GLOBE to understand the structure of the mantle layer of the Earth. Visualization of the generated data sets provide an effective way to understand the computed wave perturbations which define the structure of mantle in the Earth.

  6. A >100 Ma Mantle Geochemical Record: Retiring Mantle Plumes may be Premature

    Science.gov (United States)

    Konter, J. G.; Hanan, B. B.; Blichert-Toft, J.; Koppers, A. A.; Plank, T.; Staudigel, H.

    2006-12-01

    component. Thus, shallow mantle material sampled by lithospheric extension is unlikely to both supply geochemically similar material over 100 m.y., and allow the source to mature undisturbed for 0.6 Ga, given upper mantle dynamics. Instead, the persistent eruption of chemical anomalies is consistent with a model of individual, geochemically distinct deep-sourced hotspots evolving in the South Pacific. Furthermore, the size of the clusters requires at least some plume motion likely due to mantle wind, which may explain the disturbed age progressions in the WPSP and Gilbert Ridge as well as the presence of only short seamount trail segments in these regions.

  7. Pristine MORB mantle from Gakkel Ridge

    Science.gov (United States)

    Snow, J. E.; Hellebrand, E.

    2010-12-01

    altered samples comprise tectonites, from porphyroclastic peridotites to peridotite mylonites, including samples with significant bulk weathering and porosity presumably generated during weathering. This suggests that the mylonites concentrated the mass flux of water through the system, at low temperatures, preserving the still fresh protogranular peridotites. The samples represent a significant analog for the types of fresh mantle samples that might be encountered in any mantle deep drilling project. Fresh protogranular abyssal peridotite from Gakkel Ridge, Dredge PS 66: 238

  8. Tectonic predictions with mantle convection models

    Science.gov (United States)

    Coltice, Nicolas; Shephard, Grace E.

    2018-04-01

    Over the past 15 yr, numerical models of convection in Earth's mantle have made a leap forward: they can now produce self-consistent plate-like behaviour at the surface together with deep mantle circulation. These digital tools provide a new window into the intimate connections between plate tectonics and mantle dynamics, and can therefore be used for tectonic predictions, in principle. This contribution explores this assumption. First, initial conditions at 30, 20, 10 and 0 Ma are generated by driving a convective flow with imposed plate velocities at the surface. We then compute instantaneous mantle flows in response to the guessed temperature fields without imposing any boundary conditions. Plate boundaries self-consistently emerge at correct locations with respect to reconstructions, except for small plates close to subduction zones. As already observed for other types of instantaneous flow calculations, the structure of the top boundary layer and upper-mantle slab is the dominant character that leads to accurate predictions of surface velocities. Perturbations of the rheological parameters have little impact on the resulting surface velocities. We then compute fully dynamic model evolution from 30 and 10 to 0 Ma, without imposing plate boundaries or plate velocities. Contrary to instantaneous calculations, errors in kinematic predictions are substantial, although the plate layout and kinematics in several areas remain consistent with the expectations for the Earth. For these calculations, varying the rheological parameters makes a difference for plate boundary evolution. Also, identified errors in initial conditions contribute to first-order kinematic errors. This experiment shows that the tectonic predictions of dynamic models over 10 My are highly sensitive to uncertainties of rheological parameters and initial temperature field in comparison to instantaneous flow calculations. Indeed, the initial conditions and the rheological parameters can be good enough

  9. Water in the Cratonic Mantle Lithosphere

    Science.gov (United States)

    Peslier, A. H.

    2016-01-01

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

  10. A New Carbonate Chemistry in the Earth's Lower Mantle

    Science.gov (United States)

    Boulard, E.; Gloter, A.; Corgne, A.; Antonangeli, D.; Auzende, A.; Perrillat, J.; Guyot, F. J.; Fiquet, G.

    2010-12-01

    The global geochemical carbon cycle involves exchange between the Earth’s mantle and the surface. Carbon (C) is recycled into the mantle via subduction and released to the atmosphere via volcanic outgassing. Carbonates are the main C-bearing minerals that are transported deep in the Earth’s mantle via subduction of the oceanic lithosphere [1]. The way C is recycled and its contribution to the lower mantle reservoir is however largely unknown [ e.g 2, 3]. In this respect, it is important to assess if carbonates can be preserved in the deep mantle, or if decarbonatation, melting or reduction play a role in the deep carbon cycle. To clarify the fate of carbonates in the deep mantle, we carried out high-pressure and high-temperature experiments up to 105 GPa and 2850 K. Natural Fe-Mg carbonates or oxide mixtures of (Mg,Fe)O + CO2 were loaded into laser heated diamond anvil cells. In situ characterizations were done by X-ray Diffraction (XRD) using synchrotron radiation at the high-pressure beamline ID27 of the European Synchrotron Radiation Facility. A focused ion beam technique was then used to prepare the recovered samples for electron energy loss spectroscopy in a dedicated scanning transmission electron microscope (EELS-STEM) and scanning transmission X-ray microscopy (STXM). In situ XRD clearly shows the transformation of the initial carbonate phase into a new Mg-Fe high pressure carbonate phase at lower mantle conditions. We also provide direct evidence for recombination of CO2 with (Mg,Fe)O to form this new carbonate structure. In addition, subsequent EELS-STEM and STXM spectroscopies carried out on recovered samples yields C K-edge and stoechiometry characteristic to this new carbonate structure. This new high pressure phase concentrates a large amount of Fe(III), as a result of redox reactions within the siderite-rich carbonate. The oxidation of iron is balanced by partial reduction of carbon into CO groups and/or diamond. These reactions may provide an

  11. Diamond growth in mantle fluids

    OpenAIRE

    Bureau, Hélène; Frost, Daniel J.; Bolfan-casanova, Nathalie; Leroy, Clémence; Esteve, Imène; Cordier, Patrick

    2016-01-01

    International audience; 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 ...

  12. Prevention of deep vein thrombosis after hip replacement: randomised comparison between unfractionated heparin and low molecular weight heparin

    NARCIS (Netherlands)

    Leyvraz, P. F.; Bachmann, F.; Hoek, J.; Büller, H. R.; Postel, M.; Samama, M.; Vandenbroek, M. D.

    1991-01-01

    To evaluate the efficacy and safety of two subcutaneous prophylactic regimens for postoperative deep vein thrombosis after total hip replacement. Prospective open randomised multicentre trial. 28 European departments of orthopaedic surgery. All patients had bilateral phlebography 10 days after

  13. Tracing Mantle Plumes: Quantifying their Morphology and Behavior from Seismic Tomography

    Science.gov (United States)

    O'Farrell, K. A.; Eakin, C. M.; Jones, T. D.; Garcia, E.; Robson, A.; Mittal, T.; Lithgow-Bertelloni, C. R.; Jackson, M. G.; Lekic, V.; Rudolph, M. L.

    2016-12-01

    Hotspot volcanism provides a direct link between the deep mantle and the surface, but the location, depth and source of the mantle plumes that feed hotspots are highly controversial. In order to address this issue it is important to understand the journey along which plumes have travelled through the mantle. The general behavior of plumes in the mantle also has the potential to tell us about the vigor of mantle convection, net rotation of the mantle, the role of thermal versus chemical anomalies, and important bulk physical properties of the mantle such as the viscosity profile. To address these questions we developed an algorithm to trace plume-like features in shear-wave (Vs) seismic tomographic models based on picking local minima in velocity and searching for continuous features with depth. We apply this method to several of the latest tomographic models and can recover 30 or more continuous plume conduits that are >750 km long. Around half of these can be associated with a known hotspot at the surface. We study the morphology of these plume chains and find that the largest lateral deflections occur near the base of the lower mantle and in the upper mantle. We analyze the preferred orientation of the plume deflections and their gradient to infer large scale mantle flow patterns and the depth of viscosity contrasts in the mantle respectively. We also retrieve Vs profiles for our traced plumes and compare with velocity profiles predicted for different mantle adiabat temperatures. We use this to constrain the thermal anomaly associated with these plumes. This thermal anomaly is then converted to a density anomaly and an upwelling velocity is derived. We compare this to buoyancy fluxes calculated at the surface and use this in conjunction with our measured plume tilts/deflections to estimate the strength of the "mantle wind".

  14. Deep structure and origin of active volcanoes in China

    Directory of Open Access Journals (Sweden)

    Dapeng Zhao

    2010-10-01

    Full Text Available We synthesize significant recent results on the deep structure and origin of the active volcanoes in mainland China. Magmatism in the western Pacific arc and back-arc areas is caused by dehydration of the subducting slab and by corner flow in the mantle wedge, whereas the intraplate magmatism in China has different origins. The active volcanoes in Northeast China (such as the Changbai and Wudalianchi are caused by hot upwelling in the big mantle wedge (BMW above the stagnant slab in the mantle transition zone and deep slab dehydration as well. The Tengchong volcano in Southwest China is caused by a similar process in the BMW above the subducting Burma microplate (or Indian plate. The Hainan volcano in southernmost China is a hotspot fed by a lower-mantle plume which may be associated with the Pacific and Philippine Sea slabs’ deep subduction in the east and the Indian slab’s deep subduction in the west down to the lower mantle. The stagnant slab finally collapses down to the bottom of the mantle, which can trigger the upwelling of hot mantle materials from the lower mantle to the shallow mantle beneath the subducting slabs and may cause the slab–plume interactions.

  15. Outcomes of inferior vena cava filter insertion in patients with lower extremity deep vein thrombosis for prevention of pulmonary thromboembolism: A single center retrospective analysis

    International Nuclear Information System (INIS)

    Park, Byung Jin; Kim, Jae Kyu; Yim, Nam Yeol; Kim, Hyoung Ook; Kang, Yang Jun

    2017-01-01

    To evaluate the mid- and long-term outcomes of inferior vena cava (IVC) filter insertion in patients with underlying deep vein thrombosis for prevention of pulmonary thromboembolism, based on a single center experience. A total of 166 IVC filter insertion procedures in 160 patients, between February 2004 and December 2014, were retrospectively reviewed. Severity of deep vein thrombosis, indwelling time of the IVC filter, retrieval rate, and complication rate depending on the type of IVC filter were analyzed based on the patients' radiologic findings and medical records. IVC filter insertion procedures were successfully performed in all patients. Among the 99 attempts at filter retrieval, 91 trials succeeded (91.9%, 91/99) and 8 trials failed. Indwelling time of the IVC filter showed a positive correlation with failure of filter retrieval (p = 0.01). There was no procedure-related complication after all IVC filter insertion procedures. Eight delayed complications (5.0%, 8/160 patients with IVC filter insertion) were observed [caval thrombosis below the IVC filter (n = 7) and IVC penetration (n = 1)]. Günther Tulip filter was associated with a significant incidence of complication (p = 0.036). IVC filter insertion in patients with lower extremity deep vein thrombosis for prevention of pulmonary thromboembolism can be regarded as a safe treatment modality with an acceptable complication rate

  16. Outcomes of inferior vena cava filter insertion in patients with lower extremity deep vein thrombosis for prevention of pulmonary thromboembolism: A single center retrospective analysis

    Energy Technology Data Exchange (ETDEWEB)

    Park, Byung Jin; Kim, Jae Kyu; Yim, Nam Yeol; Kim, Hyoung Ook [Dept. of Radiology, Chonnam National University Hospital, Gwangju (Korea, Republic of); Kang, Yang Jun [Dept. of Radiology, Chonnam National University Hwasun Hospital, Hwasun (Korea, Republic of)

    2017-07-15

    To evaluate the mid- and long-term outcomes of inferior vena cava (IVC) filter insertion in patients with underlying deep vein thrombosis for prevention of pulmonary thromboembolism, based on a single center experience. A total of 166 IVC filter insertion procedures in 160 patients, between February 2004 and December 2014, were retrospectively reviewed. Severity of deep vein thrombosis, indwelling time of the IVC filter, retrieval rate, and complication rate depending on the type of IVC filter were analyzed based on the patients' radiologic findings and medical records. IVC filter insertion procedures were successfully performed in all patients. Among the 99 attempts at filter retrieval, 91 trials succeeded (91.9%, 91/99) and 8 trials failed. Indwelling time of the IVC filter showed a positive correlation with failure of filter retrieval (p = 0.01). There was no procedure-related complication after all IVC filter insertion procedures. Eight delayed complications (5.0%, 8/160 patients with IVC filter insertion) were observed [caval thrombosis below the IVC filter (n = 7) and IVC penetration (n = 1)]. Günther Tulip filter was associated with a significant incidence of complication (p = 0.036). IVC filter insertion in patients with lower extremity deep vein thrombosis for prevention of pulmonary thromboembolism can be regarded as a safe treatment modality with an acceptable complication rate.

  17. MANTLE SOURCES OF GENERATION OF HYDROCARBONS: GEOLOGY-PHYSICAL SIGNS AND FORECAST-SEARCHING CRITERIONS OF MAPPING; REGULARITY OF AN OIL-AND-GAS-BEARING CAPACITY AS UNLOADING REFLEX OF MANTLE HYDROCARBON-SYSTEMS IN THE CRUST OF THE EARTH

    OpenAIRE

    Тімурзіїв, А.І.

    2017-01-01

    In the conditions of the developed uncertainty concerning the nature of primary sources (donors) and the generation focal (reactionary chambers) of deep hydrocarbons, questions of the nature of donors and the sources of generation of deep hydrocarbons systems, the mechanism and ways of generation and in-source mobilization of hydrocarbons in the top mantle of the Earth and evacuation (vertical migration) of hydrocarbon-systems from the generation sources in the mantle of the Earth into the ac...

  18. Linking lowermost mantle structure, core-mantle boundary heat flux and mantle plume formation

    Science.gov (United States)

    Li, Mingming; Zhong, Shijie; Olson, Peter

    2018-04-01

    The dynamics of Earth's lowermost mantle exert significant control on the formation of mantle plumes and the core-mantle boundary (CMB) heat flux. However, it is not clear if and how the variation of CMB heat flux and mantle plume activity are related. Here, we perform geodynamic model experiments that show how temporal variations in CMB heat flux and pulses of mantle plumes are related to morphologic changes of the thermochemical piles of large-scale compositional heterogeneities in Earth's lowermost mantle, represented by the large low shear velocity provinces (LLSVPs). We find good correlation between the morphologic changes of the thermochemical piles and the time variation of CMB heat flux. The morphology of the thermochemical piles is significantly altered during the initiation and ascent of strong mantle plumes, and the changes in pile morphology cause variations in the local and the total CMB heat flux. Our modeling results indicate that plume-induced episodic variations of CMB heat flux link geomagnetic superchrons to pulses of surface volcanism, although the relative timing of these two phenomena remains problematic. We also find that the density distribution in thermochemical piles is heterogeneous, and that the piles are denser on average than the surrounding mantle when both thermal and chemical effects are included.

  19. A diffusion mechanism for core-mantle interaction.

    Science.gov (United States)

    Hayden, Leslie A; Watson, E Bruce

    2007-11-29

    Understanding the geochemical behaviour of the siderophile elements--those tending to form alloys with iron in natural environments--is important in the search for a deep-mantle chemical 'fingerprint' in upper mantle rocks, and also in the evaluation of models of large-scale differentiation of the Earth and terrestrial planets. These elements are highly concentrated in the core relative to the silicate mantle, but their concentrations in upper mantle rocks are higher than predicted by most core-formation models. It has been suggested that mixing of outer-core material back into the mantle following core formation may be responsible for the siderophile element ratios observed in upper mantle rocks. Such re-mixing has been attributed to an unspecified metal-silicate interaction in the reactive D'' layer just above the core-mantle boundary. The siderophile elements are excellent candidates as indicators of an outer-core contribution to the mantle, but the nature and existence of possible core-mantle interactions is controversial. In light of the recent findings that grain-boundary diffusion of oxygen through a dry intergranular medium may be effective over geologically significant length scales and that grain boundaries can be primary storage sites for incompatible lithophile elements, the question arises as to whether siderophile elements might exhibit similar (or greater) grain-boundary mobility. Here we report experimental results from a study of grain-boundary diffusion of siderophile elements through polycrystalline MgO that were obtained by quantifying the extent of alloy formation between initially pure metals separated by approximately 1 mm of polycrystalline MgO. Grain-boundary diffusion resulted in significant alloying of sink and source particles, enabling calculation of grain-boundary fluxes. Our computed diffusivities were high enough to allow transport of a number of siderophile elements over geologically significant length scales (tens of kilometres

  20. Atlas of the underworld: Slab remnants in the mantle, their sinking history, and a new outlook on lower mantle viscosity

    Science.gov (United States)

    van der Meer, Douwe G.; van Hinsbergen, Douwe J. J.; Spakman, Wim

    2018-01-01

    Across the entire mantle we interpret 94 positive seismic wave-speed anomalies as subducted lithosphere and associate these slabs with their geological record. We document this as the Atlas of the Underworld, also accessible online at www.atlas-of-the-underworld.org, a compilation comprising subduction systems active in the past 300 Myr. Deeper slabs are correlated to older geological records, assuming no relative horizontal motions between adjacent slabs following break-off, using knowledge of global plate circuits, but without assuming a mantle reference frame. The longest actively subducting slabs identified reach the depth of 2500 km and some slabs have impinged on Large Low Shear Velocity Provinces in the deepest mantle. Anomously fast sinking of some slabs occurs in regions affected by long-term plume rising. We conclude that slab remnants eventually sink from the upper mantle to the core-mantle boundary. The range in subduction-age versus - depth in the lower mantle is largely inherited from the upper mantle history of subduction. We find a significant depth variation in average sinking speed of slabs. At the top of the lower mantle average slab sinking speeds are between 10 and 40 mm/yr, followed by a deceleration to 10-15 mm/yr down to depths around 1600-1700 km. In this interval, in situ time-stationary sinking rates suggest deceleration from 20 to 30 mm/yr to 4-8 mm/yr, increasing to 12-15 mm/yr below 2000 km. This corroborates the existence of a slab deceleration zone but we do not observe long-term (> 60 My) slab stagnation, excluding long-term stagnation due to compositional effects. Conversion of slab sinking profiles to viscosity profiles shows the general trend that mantle viscosity increases in the slab deceleration zone below which viscosity slowly decreases in the deep mantle. This is at variance with most published viscosity profiles that are derived from different observations, but agrees qualitatively with recent viscosity profiles suggested

  1. Hydrogen in the Deep Earth

    Science.gov (United States)

    Mookherjee, M.; Hermann, A.; Bajgain, S.; Shukla, G.

    2017-12-01

    Water is crucial for the sustenance of planetary activities. For instance, water reduces melting temperatures and affects the density and elasticity of minerals and melts. It also influences the transport properties of minerals and melts, including their diffusion, electrical conductivity, and rheology. The solid-state mantle convection for the water-free, dry silicate mantle is likely to be extremely sluggish and may not be sustainable over geological timescales. Therefore, it is important to identify the potential hosts for water and estimate the size of the hidden reservoir of water in the deep Earth. Also, it is important to correlate how the deep Earth water reservoir, i.e., the degree of mantle hydration, influences the global sea level over geological time scales. Constraining the degree of mantle hydration is not straightforward. It requires understanding and linking atomistic scale behavior of minerals and melts to large-scale geophysical and geochemical observations. High-pressure experiments and first-principles simulations based on density functional theory (DFT) have been crucial in enhancing our understanding of hydrogen bearing mineral phases that are likely to be present in the Earth's mantle and subduction zone settings. In this study we present DFT results on hydrous phases and provide constraints on the crystal structure, thermodynamic stability, elasticity, and transport properties of proton bearing mineral phases. Acknowledgements: MM acknowledges US NSF awards EAR-1639552 and EAR-1634422.

  2. 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.

  3. Nanodiamond Finding in the Hyblean Shallow Mantle Xenoliths

    OpenAIRE

    Simakov, S. K.; Kouchi, A.; Mel?nik, N.N.; Scribano, V.; Kimura, Y.; Hama, T.; Suzuki, N.; Saito, H.; Yoshizawa, T.

    2015-01-01

    Most of Earth?s diamonds are connected with deep-seated mantle rocks; however, in recent years, ?m-sized diamonds have been found in shallower metamorphic rocks, and the process of shallow-seated diamond formation has become a hotly debated topic. Nanodiamonds occur mainly in chondrite meteorites associated with organic matter and water. They can be synthesized in the stability field of graphite from organic compounds under hydrothermal conditions. Similar physicochemical conditions occur in ...

  4. Prevention

    Science.gov (United States)

    ... Error processing SSI file About Heart Disease & Stroke Prevention Heart disease and stroke are an epidemic in ... secondhand smoke. Barriers to Effective Heart Disease & Stroke Prevention Many people with key risk factors for heart ...

  5. 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

  6. The clinical efficacy of the local, deep insufflation of an oxygen-ozone mixture in the prevention and treatment of infections in the locomotor system.

    Science.gov (United States)

    Białoszewski, D; Kowalewski, M

    2001-01-01

    Background. Ozone therapy - i.e. the treatment of patients by a mixture of oxygen and ozone - has been used for many years as a method ancillary to basic treatment, especially in those cases in which traditional treatment methods do not give satisfactory results, e.g. skin loss in non-healing wounds, ulcers, pressure sores, fistulae, etc. Material and methods. In the Orthopedic and Rehabilitation Department of the Medical Faculty No. 2 and the Department of the Orthopedics and Traumatology of the Locomotor System at the Medical Academy of Warsaw in the period from January 2000 until November 2001, 49 patients with extensive injuries to the locomotor system and septic complications after surgical procedures were treated with ozone. The ozone therapy was administered using an authorial technique of deep ozone application. Two groups of patients were treated: posttraumatic patients at risk for primary deep infections (e.g. open fractures without skin losses) and patients with declared postoperative infections in the locomotor system. The first group involved 31 patients; the second group, 18. Results. In the first group, three patients had septic complications despite mixed treatment, including one case of osteomyelitis. In the second group, all the patients experienced much faster than normal wound healing with inhibition of septic processes. In two cases, the septic process was reactivated after 6 and 9 months respectively, and these patients are still undergoing treatment. Conclusions. Our data confirm the advantages resulting from the deep application of ozone in the prevention and combined treatment for septic complications in the locomotor system. Our technique of deep ozone application makes it possible to reduce the risk of posttraumatic infections and promotes quicker healing of post-surgical complications and chronic septic infections. This method also lowers the cost of antibiotic therapy and is sometimes the only available auxiliary technique to support

  7. Prevention of deep vein thrombosis in potential neurosurgical patients. A randomized trial comparing graduated compression stockings alone or graduated compression stockings plus intermittent pneumatic compression with control

    Energy Technology Data Exchange (ETDEWEB)

    Turpie, A.G.; Hirsh, J.; Gent, M.; Julian, D.; Johnson, J.

    1989-03-01

    In a randomized trial of neurosurgical patients, groups wearing graduated compression stockings alone (group 1) or graduated compression stockings plus intermittent pneumatic compression (IPC) (group 2) were compared with an untreated control group in the prevention of deep vein thrombosis (DVT). In both active treatment groups, the graduated compression stockings were continued for 14 days or until hospital discharge, if earlier. In group 2, IPC was continued for seven days. All patients underwent DVT surveillance with iodine 125-labeled fibrinogen leg scanning and impedance plethysmography. Venography was carried out if either test became abnormal. Deep vein thrombosis occurred in seven (8.8%) of 80 patients in group 1, in seven (9.0%) of 78 patients in group 2, and in 16 (19.8%) of 81 patients in the control group. The observed differences among these rates are statistically significant. The results of this study indicate that graduated compression stockings alone or in combination with IPC are effective methods of preventing DVT in neurosurgical patients.

  8. Prevention of deep vein thrombosis in potential neurosurgical patients. A randomized trial comparing graduated compression stockings alone or graduated compression stockings plus intermittent pneumatic compression with control

    International Nuclear Information System (INIS)

    Turpie, A.G.; Hirsh, J.; Gent, M.; Julian, D.; Johnson, J.

    1989-01-01

    In a randomized trial of neurosurgical patients, groups wearing graduated compression stockings alone (group 1) or graduated compression stockings plus intermittent pneumatic compression (IPC) (group 2) were compared with an untreated control group in the prevention of deep vein thrombosis (DVT). In both active treatment groups, the graduated compression stockings were continued for 14 days or until hospital discharge, if earlier. In group 2, IPC was continued for seven days. All patients underwent DVT surveillance with iodine 125-labeled fibrinogen leg scanning and impedance plethysmography. Venography was carried out if either test became abnormal. Deep vein thrombosis occurred in seven (8.8%) of 80 patients in group 1, in seven (9.0%) of 78 patients in group 2, and in 16 (19.8%) of 81 patients in the control group. The observed differences among these rates are statistically significant. The results of this study indicate that graduated compression stockings alone or in combination with IPC are effective methods of preventing DVT in neurosurgical patients

  9. Universal single grain amphibole thermobarometer for mantle rocks - preliminary calibration.

    Science.gov (United States)

    Ashchepkov, Igor

    2017-04-01

    SCLM and the third group refer to richterites form the depleted manle peridotites. In SCLM beneat the Sytykanskaya they are more frequent and trace through all the mantle layers. In SCLM beneat the Aykhal they mostly are from the lower and in Komsomolskaya from the middle SCLM parts. In Daldyn field rare amdphibles from Dalnaya are Fe- enriched pargasites belonging to the Ilm bearing peridotites in middle SCLM part as well as in SCLM beneath thr Udachnaya. But there are Fe- low amphiboles substitutng the orthopyroxenes. In Zarnitsa the Cr - hornblendes occur in shallow garnet pyroxenites. One deep seated richterite substitute garnet grains. Rare amphiboles were detedted in Mirninsky filed in Internatiolnaya pipe and reffer to the resorbed and deformed granets from the Garnet -Spinel facies and from 4.0 GPa boundary. Amphiboles are frequent in the SCLM from the northern part of Siberian craton. In SCLM beneath the Kharmai the Fe- encriched varietes are from the Moho boundary. Common Cr-pargasite occurs to 3 GPa in Obnazhennay, pipe, Kharamai field In mantle SCLM beneath Obnazhennaya pipe and circum Anabr region friquent Cr- pargasies and horblendes refer to the relatively hot branch of mantle lithosphere and probably corresponds to the Triassic mantle reactivation. Mantle Cr- hornbleneds occurs on most upper part of the mantle column beneath Quaternary mujeritic Bartoy vocanoes in Transbaikal. The pargasites and kaersutites in this locality refer to more heated conditions and could be found to 2.0 GPa. Grant RFBR 16.-05-000860

  10. Seismic Imaging of Mantle Plumes

    Science.gov (United States)

    Nataf, Henri-Claude

    The mantle plume hypothesis was proposed thirty years ago by Jason Morgan to explain hotspot volcanoes such as Hawaii. A thermal diapir (or plume) rises from the thermal boundary layer at the base of the mantle and produces a chain of volcanoes as a plate moves on top of it. The idea is very attractive, but direct evidence for actual plumes is weak, and many questions remain unanswered. With the great improvement of seismic imagery in the past ten years, new prospects have arisen. Mantle plumes are expected to be rather narrow, and their detection by seismic techniques requires specific developments as well as dedicated field experiments. Regional travel-time tomography has provided good evidence for plumes in the upper mantle beneath a few hotspots (Yellowstone, Massif Central, Iceland). Beneath Hawaii and Iceland, the plume can be detected in the transition zone because it deflects the seismic discontinuities at 410 and 660 km depths. In the lower mantle, plumes are very difficult to detect, so specific methods have been worked out for this purpose. There are hints of a plume beneath the weak Bowie hotspot, as well as intriguing observations for Hawaii. Beneath Iceland, high-resolution tomography has just revealed a wide and meandering plume-like structure extending from the core-mantle boundary up to the surface. Among the many phenomena that seem to take place in the lowermost mantle (or D''), there are also signs there of the presence of plumes. In this article I review the main results obtained so far from these studies and discuss their implications for plume dynamics. Seismic imaging of mantle plumes is still in its infancy but should soon become a turbulent teenager.

  11. Eutectic melting temperature of the lowermost Earth's mantle

    Science.gov (United States)

    Andrault, D.; Lo Nigro, G.; Bolfan-Casanova, N.; Bouhifd, M.; Garbarino, G.; Mezouar, M.

    2009-12-01

    Partial melting of the Earth's deep mantle probably occurred at different stages of its formation as a consequence of meteoritic impacts and seismology suggests that it even continues today at the core-mantle boundary. Melts are important because they dominate the chemical evolution of the different Earth's reservoirs and more generally the dynamics of the whole planet. Unfortunately, the most critical parameter, that is the temperature profile inside the deep Earth, remains poorly constrained accross the planet history. Experimental investigations of the melting properties of materials representative of the deep Earth at relevant P-T conditions can provide anchor points to refine past and present temperature profiles and consequently determine the degree of melting at the different geological periods. Previous works report melting relations in the uppermost lower mantle region, using the multi-anvil press [1,2]. On the other hand, the pyrolite solidus was determined up to 65 GPa using optical observations in the laser-heated diamond anvil cell (LH-DAC) [3]. Finally, the melting temperature of (Mg,Fe)2SiO4 olivine is documented at core-mantle boundary (CMB) conditions by shock wave experiments [4]. Solely based on these reports, experimental data remain too sparse to draw a definite melting curve for the lower mantle in the relevant 25-135 GPa pressure range. We reinvestigated melting properties of lower mantle materials by means of in-situ angle dispersive X-ray diffraction measurements in the LH-DAC at the ESRF [5]. Experiments were performed in an extended P-T range for two starting materials: forsterite and a glass with chondrite composition. In both cases, the aim was to determine the onset of melting, and thus the eutectic melting temperatures as a function of pressure. Melting was evidenced from drastic changes of diffraction peak shape on the image plate, major changes in diffraction intensities in the integrated pattern, disappearance of diffraction rings

  12. Early episodes of high-pressure core formation preserved in plume mantle

    Science.gov (United States)

    Jackson, Colin R. M.; Bennett, Neil R.; Du, Zhixue; Cottrell, Elizabeth; Fei, Yingwei

    2018-01-01

    The decay of short-lived iodine (I) and plutonium (Pu) results in xenon (Xe) isotopic anomalies in the mantle that record Earth’s earliest stages of formation. Xe isotopic anomalies have been linked to degassing during accretion, but degassing alone cannot account for the co-occurrence of Xe and tungsten (W) isotopic heterogeneity in plume-derived basalts and their long-term preservation in the mantle. Here we describe measurements of I partitioning between liquid Fe alloys and liquid silicates at high pressure and temperature and propose that Xe isotopic anomalies found in modern plume rocks (that is, rocks with elevated 3He/4He ratios) result from I/Pu fractionations during early, high-pressure episodes of core formation. Our measurements demonstrate that I becomes progressively more siderophile as pressure increases, so that portions of mantle that experienced high-pressure core formation will have large I/Pu depletions not related to volatility. These portions of mantle could be the source of Xe and W anomalies observed in modern plume-derived basalts. Portions of mantle involved in early high-pressure core formation would also be rich in FeO, and hence denser than ambient mantle. This would aid the long-term preservation of these mantle portions, and potentially points to their modern manifestation within seismically slow, deep mantle reservoirs with high 3He/4He ratios.

  13. Experimental investigation of the stability of Fe-rich carbonates in the lower mantle

    Science.gov (United States)

    Boulard, E.; Menguy, N.; Auzende, A.; Benzerara, K.; Bureau, H.; Antonangeli, D.; Corgne, A.; Morard, G.; Siebert, J.; Perrillat, J.; Guyot, F. J.; Fiquet, G.

    2011-12-01

    Carbonates are the main C-bearing minerals that are transported deep in the Earth's mantle via subduction of the oceanic lithosphere [1]. The fate of carbonates at mantle conditions plays a key role in the deep carbon cycle. Decarbonation, melting or reduction of carbonates will affect the extent and the way carbon is recycled into the deep Earth. To clarify the fate of carbonates in the deep mantle, high-pressure high-temperature experiments were carried out up to 105 GPa and 2850 K on oxide assemblages of (Mg,Fe)O + CO2. The presence of Fe(II) in starting materials induces redox reactions from which Fe(II) is oxidized and a part of the carbon is reduced. This leads to an assemblage of magnetite, diamonds, and carbonates or, pressure depending, their newly discovered Fe(III)-bearing high-pressure polymorphs based on a silicate-like chemistry with tetrahedrally coordinated carbon [2]. Our results show the possibility for carbon to be recycled in the lowermost mantle and provide evidence of a possible coexistence of reduced and oxidized carbon at lower mantle conditions. [1] Sleep, N. H., and K. Zahnle (2001) J. Geophys. Res.-Planets 106(E1), 1373-1399. [2] Boulard et al. (2011) PNAS, 108, 5184-5187.

  14. Mapping the mantle transition zone beneath Hawaii from Ps receiver functions: Evidence for a hot plume and cold mantle downwellings

    Science.gov (United States)

    Agius, Matthew R.; Rychert, Catherine A.; Harmon, Nicholas; Laske, Gabi

    2017-09-01

    Hawaii is the archetypal example of hotspot volcanism. Classic plume theory suggests a vertical plume ascent from the core-mantle boundary to the surface. However, recently it has been suggested that the plume path may be more complex. Determining the exact trajectory of the Hawaiian plume seismic anomaly in the mantle has proven challenging. We determine P-to-S (Ps) receiver functions to illuminate the 410- and 660-km depth mantle discontinuities beneath the Hawaiian Islands using waveforms recorded on land and ocean-bottom seismometers, applying new corrections for tilt and coherence to the ocean bottom data. Our 3-D depth-migrated maps provide enhanced lateral resolution of the mantle transition zone discontinuities. The 410 discontinuity is characterised by a deepened area beneath central Hawaii, surrounded by an elevated shoulder. At the 660 discontinuity, shallow topography is located to the north and far south of the islands, and a deep topographic anomaly is located far west and east. The transition zone thickness varies laterally by ±13 km depth: thin beneath north-central Hawaii and thick farther away in a horseshoe-like feature. We infer that at 660-km depth a broad or possibly a double region of upwelling converges into a single plume beneath central Hawaii at 410-km depth. As the plume rises farther, uppermost mantle melting and flow results in the downwelling of cold material, down to at least 410 km surrounding the plume stem. This result in the context of others supports complex plume dynamics including a possible non-vertical plume path and adjacent mantle downwellings.

  15. Effects of torpedo blasting on rockburst prevention during deep coal seam mining in the Upper Silesian Coal Basin

    Czech Academy of Sciences Publication Activity Database

    Wojtecki, Ł.; Koníček, Petr; Schreiber, J.

    2017-01-01

    Roč. 9, č. 4 (2017), s. 694-701 ISSN 1674-7755 Institutional support: RVO:68145535 Keywords : rockburst prevention * torpedo blasting * seismic effect * Upper Silesian Coal Basin (USCB) Subject RIV: DH - Mining , incl. Coal Mining OBOR OECD: Mining and mineral processing http://www.sciencedirect.com/science/article/pii/S1674775517300896

  16. Effectiveness and Safety of the Tempofilter II to Prevent the Occurrence of Pulmonary Thromboembolism in Patients with Lower Extremity Deep Vein Thrombosis

    Energy Technology Data Exchange (ETDEWEB)

    Baek, Byung Hyun; Jung, Min Young; Oh, Hyun Jun; Kim, Jae Kyu; Lee, Ho Kyun [Chonnam National University College of Medicine, Gwangju (Korea, Republic of); Jang, Nam Kyu [Chonnam National University Hospital, Hwasun (Korea, Republic of)

    2010-04-15

    To evaluate the efficacy and safety of the Tempofilter II for the prevention of a pulmonary thromboembolism (PTE) in patients with lower extremity deep vein thrombosis (DVT). Between January 2007 and December 2008, thirteen patients with lower extremity DVT whom were implanted with the Tempofilter II to prevent PTE were analyzed. A chest CT was compared before and after filter placement, to evaluate effectiveness of preventing PTE. Clinical symptoms of PTE were checked. Fluoroscopy and a plain radiograph were examined to evaluate filter status. The tempofilter II was successfully inserted in 13 patients. Nine patients underwent endovascular treatment after filter insertion. Trapping of thrombus was evaluated by following CT, venography, and filter retrieval. Trapped thrombus was detected in four patients by CT or retrieved filter. Two patients showed a decrease in thrombus in a follow-up chest CT. Not all patients showed symptoms of PTE. One filter was surgically removed due to the detachment of the anchoring device. The placement and retrieval of the Tempofilter II is feasible and effective for the prophylaxis of PTE in patients with lower extremity DVT; especially for patients that underwent subsequent endovascular treatment

  17. Transition region of the earth's upper mantle

    Science.gov (United States)

    Anderson, D. L.; Bass, J. D.

    1986-01-01

    The chemistry of the earth's mantle is discussed using data from cosmochemistry, geochemistry, petrology, seismology, and mineral physics. The chondritic earth, the upper mantle and the 400-km discontinuity, the transition region, lower mantle mineralogy, and surface wave tomography are examined. Three main issues are addressed: (1) whether the mantle is homogeneous in composition or chemically stratified, (2) whether the major element chemistry of the mantle is more similar to upper mantle peridotites or to chondrites, and (3) the nature of the composition of the source region of basalts erupted at midocean ridges.

  18. Prevention

    Science.gov (United States)

    ... Contact Aging & Health A to Z Find a Geriatrics Healthcare Professional Medications & Older Adults Making Your Wishes ... Prevention Hearing Loss Heart Attack High Blood Pressure Nutrition Osteoporosis Shingles Skin Cancer Related News Quitting Smoking, ...

  19. Retrievable Günther Tulip Vena Cava Filter in the prevention of pulmonary embolism in patients with acute deep venous thrombosis in perinatal period.

    Science.gov (United States)

    Köcher, Martin; Krcova, Vera; Cerna, Marie; Prochazka, Martin

    2009-04-01

    To evaluate the feasibility and efficacy of the retrievable Günther Tulip Vena Cava Filter in the prevention of pulmonary embolism in patients with acute deep vein thrombosis in the perinatal period and to discuss the technical demands associated with the filter's implantation and retrieval. Between 1996 until 2007, eight women (mean age 27.4 years, range 20-42 years) with acute deep iliofemoral venous thrombosis in the perinatal period of pregnancy and increased risk of pulmonary embolism during delivery were indicated for retrievable Günther Tulip Vena Cava Filter implantation. All filters were inserted and removed under local anesthesia from the jugular approach. The Günther Tulip Vena Cava Filter was implanted suprarenally in all patients on the day of caesarean delivery. In follow-up cavograms performed just before planned filter removal, no embolus was seen in the filter in any patient. In all patients the filter was retrieved without complications on the 12th day after implantation. Retrievable Günther Tulip Vena Cava Filters can be inserted and removed in patients during the perinatal period without major complications.

  20. Retrievable Guenther Tulip Vena Cava Filter in the prevention of pulmonary embolism in patients with acute deep venous thrombosis in perinatal period

    International Nuclear Information System (INIS)

    Koecher, Martin; Krcova, Vera; Cerna, Marie; Prochazka, Martin

    2009-01-01

    Objectives: To evaluate the feasibility and efficacy of the retrievable Guenther Tulip Vena Cava Filter in the prevention of pulmonary embolism in patients with acute deep vein thrombosis in the perinatal period and to discuss the technical demands associated with the filter's implantation and retrieval. Methods: Between 1996 until 2007, eight women (mean age 27.4 years, range 20-42 years) with acute deep iliofemoral venous thrombosis in the perinatal period of pregnancy and increased risk of pulmonary embolism during delivery were indicated for retrievable Guenther Tulip Vena Cava Filter implantation. All filters were inserted and removed under local anesthesia from the jugular approach. Results: The Guenther Tulip Vena Cava Filter was implanted suprarenally in all patients on the day of caesarean delivery. In follow-up cavograms performed just before planned filter removal, no embolus was seen in the filter in any patient. In all patients the filter was retrieved without complications on the 12th day after implantation. Conclusions: Retrievable Guenther Tulip Vena Cava Filters can be inserted and removed in patients during the perinatal period without major complications.

  1. Retrievable Guenther Tulip Vena Cava Filter in the prevention of pulmonary embolism in patients with acute deep venous thrombosis in perinatal period

    Energy Technology Data Exchange (ETDEWEB)

    Koecher, Martin [Department of Radiology, University Hospital, I.P. Pavlova 6, 775 20 Olomouc (Czech Republic)], E-mail: martin.kocher@seznam.cz; Krcova, Vera [Department of Hematooncology, University Hospital, I.P. Pavlova 6, 775 20 Olomouc (Czech Republic); Cerna, Marie [Department of Radiology, University Hospital, I.P. Pavlova 6, 775 20 Olomouc (Czech Republic); Prochazka, Martin [Department of Obstetrics and Gynaecology, University Hospital, I.P. Pavlova 6, 775 20 Olomouc (Czech Republic)

    2009-04-15

    Objectives: To evaluate the feasibility and efficacy of the retrievable Guenther Tulip Vena Cava Filter in the prevention of pulmonary embolism in patients with acute deep vein thrombosis in the perinatal period and to discuss the technical demands associated with the filter's implantation and retrieval. Methods: Between 1996 until 2007, eight women (mean age 27.4 years, range 20-42 years) with acute deep iliofemoral venous thrombosis in the perinatal period of pregnancy and increased risk of pulmonary embolism during delivery were indicated for retrievable Guenther Tulip Vena Cava Filter implantation. All filters were inserted and removed under local anesthesia from the jugular approach. Results: The Guenther Tulip Vena Cava Filter was implanted suprarenally in all patients on the day of caesarean delivery. In follow-up cavograms performed just before planned filter removal, no embolus was seen in the filter in any patient. In all patients the filter was retrieved without complications on the 12th day after implantation. Conclusions: Retrievable Guenther Tulip Vena Cava Filters can be inserted and removed in patients during the perinatal period without major complications.

  2. The efficacy and safety of enoxaparin versus unfractionated heparin for prevention of deep vein thrombosis in elective cancer surgery. A double blind randomized multicentre trail with venographic assesment

    DEFF Research Database (Denmark)

    Bergkvist, A; Eldor, A; Thorlacius-Ussing, O.

    1997-01-01

    three times daily. METHODS: Patients included were over 40 years of age and undergoing planned elective curative abdominal or pelvic surgery for cancer. The study was designed as a prospective double-blind randomized multicentre trial with participating departments from ten countries. Primary outcome...... severe thrombocytopenia. There were no differences in mortality at either 30 days or 3 months. CONCLUSION: Enoxaparin, 40 mg once daily, is as safe and effective as unfractionated heparin three times daily in preventing venous thromboembolism in patients undergoing major elective surgery for abdominal......BACKGROUND: Surgery for malignant disease carries a high risk of deep vein thrombosis. The aim of this study was to evaluate the prophylactic effect of a low molecular weight heparin, enoxaparin, 40 mg once daily, beginning 2 h before surgery, compared with that of unfractionated low-dose heparin...

  3. Slab melting as a barrier to deep carbon subduction.

    Science.gov (United States)

    Thomson, Andrew R; Walter, Michael J; Kohn, Simon C; Brooker, Richard A

    2016-01-07

    Interactions between crustal and mantle reservoirs dominate the surface inventory of volatile elements over geological time, moderating atmospheric composition and maintaining a life-supporting planet. While volcanoes expel volatile components into surface reservoirs, subduction of oceanic crust is responsible for replenishment of mantle reservoirs. Many natural, 'superdeep' diamonds originating in the deep upper mantle and transition zone host mineral inclusions, indicating an affinity to subducted oceanic crust. Here we show that the majority of slab geotherms will intersect a deep depression along the melting curve of carbonated oceanic crust at depths of approximately 300 to 700 kilometres, creating a barrier to direct carbonate recycling into the deep mantle. Low-degree partial melts are alkaline carbonatites that are highly reactive with reduced ambient mantle, producing diamond. Many inclusions in superdeep diamonds are best explained by carbonate melt-peridotite reaction. A deep carbon barrier may dominate the recycling of carbon in the mantle and contribute to chemical and isotopic heterogeneity of the mantle reservoir.

  4. Effects of torpedo blasting on rockburst prevention during deep coal seam mining in the Upper Silesian Coal Basin

    Directory of Open Access Journals (Sweden)

    Ł. Wojtecki

    2017-08-01

    Full Text Available In the Upper Silesian Coal Basin (USCB, coal seams are exploited under progressively more difficult geological and mining conditions (greater depth, higher horizontal stress, more frequent occurrence of competent rock layers, etc.. Mining depth, dislocations and mining remnants in coal seams are the most important factors responsible for the occurrence of rockburst hazards. Longwall mining next to the mining edges of neighbouring coal seams is particularly disadvantageous. The levels of rockburst hazards are minimised via the use of rockburst prevention methods. One active prevention method is torpedo blasting in roof rocks. Torpedo blastings are performed in order to decrease local stress concentrations in rock masses and to fracture the roof rocks to prevent or minimise the impact of high-energy tremors on excavations. The estimation of the effectiveness of torpedo blasting is particularly important when mining is under difficult geological and mining conditions. Torpedo blasting is the main form of active rockburst prevention in the assigned colliery in the Polish part of the USCB. The effectiveness of blasting can be estimated using the seismic effect method, in which the seismic monitoring data and the mass of explosives are taken into consideration. The seismic effect method was developed in the Czech Republic and is always being used in collieries in the Czech part of the coal basin. Now, this method has been widely adopted for our selected colliery in the Polish part of the coal basin. The effectiveness of torpedo blastings in the faces and galleries of the assigned longwall in coal seam 506 has been estimated. The results show that the effectiveness of torpedo blastings for this longwall was significant in light of the seismic effect method, which corresponds to the in situ observations. The seismic effect method is regularly applied to estimating the blasting effectiveness in the selected colliery.

  5. The geobiological nitrogen cycle: From microbes to the mantle.

    Science.gov (United States)

    Zerkle, A L; Mikhail, S

    2017-05-01

    Nitrogen forms an integral part of the main building blocks of life, including DNA, RNA, and proteins. N 2 is the dominant gas in Earth's atmosphere, and nitrogen is stored in all of Earth's geological reservoirs, including the crust, the mantle, and the core. As such, nitrogen geochemistry is fundamental to the evolution of planet Earth and the life it supports. Despite the importance of nitrogen in the Earth system, large gaps remain in our knowledge of how the surface and deep nitrogen cycles have evolved over geologic time. Here, we discuss the current understanding (or lack thereof) for how the unique interaction of biological innovation, geodynamics, and mantle petrology has acted to regulate Earth's nitrogen cycle over geologic timescales. In particular, we explore how temporal variations in the external (biosphere and atmosphere) and internal (crust and mantle) nitrogen cycles could have regulated atmospheric pN 2 . We consider three potential scenarios for the evolution of the geobiological nitrogen cycle over Earth's history: two in which atmospheric pN 2 has changed unidirectionally (increased or decreased) over geologic time and one in which pN 2 could have taken a dramatic deflection following the Great Oxidation Event. It is impossible to discriminate between these scenarios with the currently available models and datasets. However, we are optimistic that this problem can be solved, following a sustained, open-minded, and multidisciplinary effort between surface and deep Earth communities. © 2017 The Authors Geobiology Published by John Wiley & Sons Ltd.

  6. Mantle viscosity structure constrained by joint inversions of seismic velocities and density

    Science.gov (United States)

    Rudolph, M. L.; Moulik, P.; Lekic, V.

    2017-12-01

    The viscosity structure of Earth's deep mantle affects the thermal evolution of Earth, the ascent of mantle upwellings, sinking of subducted oceanic lithosphere, and the mixing of compositional heterogeneities in the mantle. Modeling the long-wavelength dynamic geoid allows us to constrain the radial viscosity profile of the mantle. Typically, in inversions for the mantle viscosity structure, wavespeed variations are mapped into density variations using a constant- or depth-dependent scaling factor. Here, we use a newly developed joint model of anisotropic Vs, Vp, density and transition zone topographies to generate a suite of solutions for the mantle viscosity structure directly from the seismologically constrained density structure. The density structure used to drive our forward models includes contributions from both thermal and compositional variations, including important contributions from compositionally dense material in the Large Low Velocity Provinces at the base of the mantle. These compositional variations have been neglected in the forward models used in most previous inversions and have the potential to significantly affect large-scale flow and thus the inferred viscosity structure. We use a transdimensional, hierarchical, Bayesian approach to solve the inverse problem, and our solutions for viscosity structure include an increase in viscosity below the base of the transition zone, in the shallow lower mantle. Using geoid dynamic response functions and an analysis of the correlation between the observed geoid and mantle structure, we demonstrate the underlying reason for this inference. Finally, we present a new family of solutions in which the data uncertainty is accounted for using covariance matrices associated with the mantle structure models.

  7. Quantifying mantle structure and dynamics using plume tracing in seismic tomography

    Science.gov (United States)

    O'Farrell, K. A.; Eakin, C. M.; Jackson, M. G.; Jones, T. D.; Lekic, V.; Lithgow-Bertelloni, C. R.

    2017-12-01

    Directly linking deep mantle processes with surface features and dynamics is a complex problem. Hotspot volcanism gives us surface observables of mantle signatures, but the depth and source of the mantle plumes feeding these hotspots are highly debated. To address these issues, it is necessary to consider the entire journey of a plume through the mantle. By analyzing the behavior of mantle plumes we can constrain the vigor of mantle convection, the net rotation of the mantle and the role of thermal versus chemical anomalies as well as the bulk physical properties such as the viscosity profile. To do this, we developed a new algorithm to trace plume-like features in shear-wave (Vs) seismic tomography models based on picking local minima in the velocity and searching for continuous features with depth. We applied this method to recent tomographic models and find 60+ continuous plume conduits that are > 750 km long. Approximately a third of these can be associated with known hotspots at the surface. We analyze the morphology of these continuous conduits and infer large scale mantle flow patterns and properties. We find the largest lateral deflections in the conduits occur near the base of the lower mantle and in the upper mantle (near the thermal boundary layers). The preferred orientation of the plume deflections show large variability at all depths and indicate no net mantle rotation. Plate by plate analysis shows little agreement in deflection below particular plates, indicating these deflected features might be long lived and not caused by plate shearing. Changes in the gradient of plume deflection are inferred to correspond with viscosity contrasts in the mantle and found below the transition zone as well as at 1000 km depth. From this inferred viscosity structure, we explore the dynamics of a plume through these viscosity jumps. We also retrieve the Vs profiles for the conduits and compare with the velocity profiles predicted for different mantle adiabat

  8. 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...... on calculations with a CFD-model, which has earlier been validated by means of experiments. The CFD-model is used to determine the heat transfer between the solar collector fluid in the mantle and the walls surrounding the mantle in all levels of the mantle as well as the heat transfer between the wall...... 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...

  9. Prevention

    DEFF Research Database (Denmark)

    Halken, S; Høst, A

    2001-01-01

    , breastfeeding should be encouraged for 4-6 months. In high-risk infants a documented extensively hydrolysed formula is recommended if exclusive breastfeeding is not possible for the first 4 months of life. There is no evidence for preventive dietary intervention neither during pregnancy nor lactation...... populations. These theories remain to be documented in proper, controlled and prospective studies. Breastfeeding and the late introduction of solid foods (>4 months) is associated with a reduced risk of food allergy, atopic dermatitis, and recurrent wheezing and asthma in early childhood. In all infants....... Preventive dietary restrictions after the age of 4-6 months are not scientifically documented....

  10. 182W evidence from flood basalt lavas for the long-term survival of primordial mantle

    Science.gov (United States)

    Rizo Garza, H. L.; Walker, R. J.; Carlson, R.; Horan, M. F.; Mukhopadhyay, S.; Francis, D.; Jackson, M. G.

    2016-12-01

    How much of the chemical heterogeneity present in mantle today dates to processes that occurred during Earth's planetary formation stage remains an unanswered question. Geochemical observations obtained from short-lived radiogenic isotope systems, however, provide important insights. Tungsten isotope data for flood basalt lavas from two large igneous provinces, the North Atlantic Igneous Province ( 60 Ma) and the Ontong Java Plateau ( 120 Ma), show well resolved 182W excesses, compared with terrestrial standards that are presumed to be representative of the present bulk mantle. These W isotope results, thus, indicate that one or more mantle domains formed very early in Earth history and have been preserved well into the Phanerozoic eon. The flood basalts from Baffin Bay contain among the highest 3He/4He ratios ever measured, as well as Pb and 143Nd isotopic compositions, and D/H ratios consistent with a chemically primitive, un-degassed mantle source. Ontong Java is the Earth's largest known volcanic province and shares chemical and isotopic similarities with the Baffin Bay lavas, indicative of a similarly primitive mantle source. The 182W-enriched nature of the mantle sources of rocks from both locations indicates that their primitive characteristics were likely isolated in a deep mantle reservoir within the first 50 Ma of Solar System history. The correlation between large low seismic shear velocity provinces (LLSVPs) and the distribution of reconstructed eruption sites of these large igneous provinces makes the LLSVPs possible candidate domains for the required primitive and un-degassed reservoirs.

  11. Analysis of PKP scattering using mantle mixing simulations and axisymmetric 3D waveforms

    Science.gov (United States)

    Haugland, Samuel M.; Ritsema, Jeroen; van Keken, Peter E.; Nissen-Meyer, Tarje

    2018-03-01

    The scattering of PKP waves in the lower mantle produces isolated signals before the PKIKP phase. We explore whether these so-called PKIKP precursors can be related to wave scattering off mid ocean ridge basalt (MORB) fragments that have been advected in the deep mantle throughout geologic time. We construct seismic models of small-scale (>20 km) heterogeneity in the lower mantle informed by mantle mixing simulations from Brandenburg et al. (2008) and generate PKIKP precursors using 3D, axisymmetric waveform simulations up to 0.75 Hz. We consider two end-member geodynamic models with fundamentally different distributions of MORB in the lower mantle. Our results suggest that the accumulation of MORB at the base of the mantle is a viable hypothesis for the origin of PKP scattering. We find that the strength of the PKIKP precursor amplitudes is consistent with P wave speed heterogeneity of 0.1-0.2%, as reported previously. The radial distribution of MORB has a profound effect on the strength of PKIKP precursors. Simulation of PKIKP precursors for models with an increasing MORB concentration in the lowermost 500 km of the mantle appears to reproduce most accurately the strength of PKIKP precursors in Global Seismic Network waveforms. These models assume that MORB has an excess density of at least 7%. Additional simulations of more complex geodynamic models will better constrain the geodynamic conditions to explain the significant variability of PKP scattering strength.

  12. Pulses of earthquake activity in the mantle wedge track the route of slab fluid ascent

    Science.gov (United States)

    White, Lloyd; Rawlinson, Nicholas; Lister, Gordon; Tanner, Dominique; Macpherson, Colin; Morgan, Jason

    2016-04-01

    Earthquakes typically record the brittle failure of part of the Earth at a point in space and time. These almost invariably occur within the crust or where the upper surface of subducting lithosphere interacts with the overriding mantle. However, there are also reports of rare, enigmatic earthquakes beneath rifts, above mantle plumes or very deep in the mantle. Here we report another type of mantle earthquake and present three locations where earthquake clusters occur in the mantle wedge overlying active subduction zones. These earthquake clusters define broadly circular to ellipsoidal columns that are 50 km or greater in diameter from depths between ~150 km and the surface. We interpret these rare pulses of earthquakes as evidence of near vertical transport of fluids (and associated flux-melts) from the subducted lithosphere through the mantle wedge. Detailed temporal analysis shows that most of these earthquakes occur over two-year periods, with the majority of events occurring in discrete month-long flurries of activity. As the time and location of each earthquake is recorded, pulses of seismic activity may provide information about the rate of magma ascent from the dehydrated subducted slab to sub-arc/backarc crust. This work indicates that fluids are not transported through the mantle wedge by diapirism, but through sub-vertical pathways facilitated by fracture networks and dykes on monthly to yearly time scales. These rare features move us toward solving what has until now represented a missing component of the subduction factory.

  13. Geoelectromagnetic investigation of the earth’s crust and mantle

    CERN Document Server

    Rokityansky, Igor I

    1982-01-01

    Electrical conductivity is a parameter which characterizes composition and physical state of the Earth's interior. Studies of the state equations of solids at high temperature and pressure indicate that there is a close relation be­ tween the electrical conductivity of rocks and temperature. Therefore, measurements of deep conductivity can provide knowledge of the present state and temperature of the Earth's crust and upper mantle matter. Infor­ mation about the temperature of the Earth's interior in the remote past is derived from heat flow data. Experimental investigation of water-containing rocks has revealed a pronounced increase of electrical conductivity in the temperature range D from 500 to 700 DC which may be attributed to the beginning of fractional melting. Hence, anomalies of electrical conductivity may be helpful in identitying zones of melting and dehydration. The studies of these zones are perspective in the scientific research of the mobile areas of the Earth's crust and upper mantle where t...

  14. A New Global Model Of Plates Motion Over The Mantle For The Last 300MA: Link Between Mantle Structures, Volcanism and Plate Tectonics.

    Science.gov (United States)

    Jean, B.; Sophie, V. D. G.; Greff-Lefftz, M.; Frizon de Lamotte, D.; Lescanne, M.; Leparmentier, F.

    2017-12-01

    We compare several models of hot spot reference frames published in the litterature retracing the kinematics of the lithosphere over the mantle for the last 120Ma. We then propose a new model between 130 and 300Ma, based on the comparison of various surface indicators (geological, thermal data from boreholes and compilation of global surface volcanism), a reassessment of hot spots classification and paleomagnetic data. We discuss the implication of our model on the location and timing of several types of surface volcanism (subductions, intracontinental volcanism, rifting and LIPS, kimberlites) that we link to deep structures interpreted from tomographic images. A clear degree two permanent organization of mantle convection during this period of time is obvious, and the subduction rate appears to be episodic. We finally deduce from our model mantle TPW (True Polar Wander), the shifting of the entire mantle relative to the earth's spin axis over the last 300 million years. The inferred global motion of the mantle deduced occurs around a Euler pole which axis is close to the earth equator but varies significantly in longitude with respect to time showing complex tridimensional mass reorganizations in the mantle, probably linked to both LLSVPs and slabs effect.

  15. Traditional Chinese and western medicine for the prevention of deep venous thrombosis after lower extremity orthopedic surgery: a meta-analysis of randomized controlled trials.

    Science.gov (United States)

    Zhu, Shibai; Song, Yi; Chen, Xi; Qian, Wenwei

    2018-04-10

    Chinese herbal medicine has traditionally been considered to promote blood circulation to remove obstruction in the channels and clear pathogenic heat to drain dampness effects. We conducted this meta-analysis to evaluate its benefits for the prevention of deep venous thrombosis (DVT) after lower extremity orthopedic surgery. Relevant, published studies were identified using the following keywords: lower extremity orthopedic surgery, arthroplasty, joint replacement, fracture, traditional Chinese and western medicine, Chinese herbal medicine, deep venous thrombosis (DVT), and Venous thromboembolism (VTE). The following databases were used to identify the literature consisting of RCTs with a date of search of 31 May 2017: PubMed, Cochrane Library, Web of knowledge, the Chinese National Knowledge Infrastructure Database, the Chongqing VIP Database, the Chinese Biomedical Database, and the Wanfang Database (including three English and four Chinese databases). All relevant data were collected from studies meeting the inclusion criteria. The outcome variables were the incidence rate of DVT, activated partial thromboplastin time (APTT), prothrombin time (PT), and D-dimer; subcutaneous hematoma; and other reported outcomes. RevMan5.2. software was adopted for the meta-analysis. A total of 20 published studies (1862 cases) met the inclusion criteria. The experimental group, 910 patients (48.87%), received the Chinese herbal medicine or traditional Chinese and western medicine for prevention of DVT; the control group, 952 patients (51.13%), received the standard western treatment. The meta-analysis showed that traditional Chinese and western medicine therapy reduced the incidence rates of DVT significantly when compared with controls (risk ratio [RR] = 0.40; 95% CI, 0.30 to 0.54; P < 0.00001), and the D-dimer was lower in the experimental group (P = 0.01). Besides, the incidence rate of subcutaneous hematoma was lower in the experimental group (P < 0

  16. AND THEIR IMPLICATIONS TO MANTLE DYNAMICS

    African Journals Online (AJOL)

    ... the southwest Indian ridge appears to be tapping the same portion of mantle as did the Central Indian ridge. These results have important thermo-chemical implications, such as variations in the extent of melting and mineralogicalcomposition of the mantle beneath diflerent ridges, which may influence mantle dynamics.

  17. Komatiites constrain molybdenum isotope composition of the Earth's mantle

    Science.gov (United States)

    Greber, Nicolas D.; Puchtel, Igor S.; Nägler, Thomas F.; Mezger, Klaus

    2015-07-01

    In order to estimate the Mo isotope composition and Mo abundance in the Bulk Silicate Earth (BSE), a total of thirty komatiite samples from five localities on three continents were analyzed using an isotope dilution double spike technique. Calculated Mo concentrations of the emplaced komatiite lavas range from 25 ± 3 to 66 ± 22 ng /g, and the inferred Mo concentrations in the deep mantle sources of the komatiites range between 17 ± 4 and 30 ± 12 ng /g, with an average value of 23 ± 7 ng /g (2SE). This average value represents our best estimate for the Mo concentration in the BSE; it is identical, within the uncertainty, to published previous estimates of 39 ± 16 ng /g, but is at least a factor of 2 more precise. The Mo isotope compositions of the komatiite mantle sources overlap within uncertainty and range from δ98Mo = - 0.04 ± 0.28 to 0.11 ± 0.10 ‰, with an average of 0.04 ± 0.06 ‰ (2SE). This value is analytically indistinguishable from published Mo isotope compositions of ordinary and enstatite chondrites and represents the best estimate for the Mo isotope composition of the BSE. The inferred δ98Mo for the BSE is therefore lighter than the suggested average of the upper continental crust (0.3 to 0.4‰). Thus, from the mass balance standpoint, a reservoir with lighter Mo isotope composition should exist in the Earth's mantle; this reservoir can potentially be found in subducted oceanic crust. The similarity of δ98Mo between chondritic meteorites and estimates for the BSE from this study indicates that during the last major equilibration between Earth's core and mantle, i.e., the one that occurred during the giant impact that produced the Moon, chemical and isotopic equilibrium of Mo between Fe metal of the core and the silicate mantle was largely achieved.

  18. Melting behavior of Earth's lower mantle minerals at high pressures

    Science.gov (United States)

    Fu, S.; Yang, J.; Prakapenka, V. B.; Zhang, Y.; Greenberg, E.; Lin, J. F.

    2017-12-01

    Melting behavior of the most abundant lower mantle minerals, bridgmanite and ferropericlase, at high pressure-temperature (P-T) conditions is of critical importance to understand the dynamic evolution of the early Earth and to explain the seismological and geochemical signatures in the present lowermost mantle. Theoretical calculations [1] and geodynamical models [2] suggested that partial melting of early Earth among MgO-FeO-SiO2 ternary could be located at the eutectic point where a pyrolitic composition formed for the Earth's lower mantle and the eutectic crystallization process could provide a plausible mechanism to the origin of the ultra-low velocity zones (ULVZs) near the core-mantle boundary. Here we have investigated the melting behavior of ferropericlase and Al,Fe-bearing bridgmanite in laser-heated diamond anvil cells coupled with in situ X-ray diffraction up to 120 GPa. Together with chemical and texture characterizations of the quenched samples, these results are analyzed using thermodynamic models to address the effects of iron on the liquidus and solidus temperatures as well as solid-liquid iron partitioning and the eutectic point in ferropericlase-bridgmanite existing system at lower-mantle pressure. In this presentation, we discuss the application of these results to better constrain the seismic observations of the deep lowermost mantle such as large low shear wave velocity provinces (LLSVPs) and ULVZs. We will also discuss the geochemical consequences of the ferropericlase-bridgmanite melting due to the changes in the electronic spin and valence states of iron in the system. ADDIN EN.REFLIST 1. Boukaré, C.E., Y. Ricard, and G. Fiquet, Thermodynamics of the MgO-FeO-SiO2 system up to 140 GPa: Application to the crystallization of Earth's magma ocean. Journal of Geophysical Research: Solid Earth, 2015. 120(9): p. 6085-6101. 2. Labrosse, S., J. Hernlund, and N. Coltice, A crystallizing dense magma ocean at the base of the Earth's mantle. Nature, 2007

  19. Intracontinental mantle plume and its implications for the Cretaceous tectonic history of East Asia

    Science.gov (United States)

    Ryu, In-Chang; Lee, Changyeol

    2017-12-01

    A-type granitoids, high-Mg basalts (e.g., picrites), adakitic rocks, basin-and-range-type fault basins, thinning of the North China Craton (NCC), and southwest-to-northeast migration of the adakites and I-type granitoids in southern Korea and southwestern Japan during the Cretaceous are attributed to the passive upwelling of deep asthenospheric mantle or ridge subduction. However, the genesis of these features remains controversial. Furthermore, the lack of ridge subduction during the Cretaceous in recently suggested plate reconstruction models poses a problem because the Cretaceous adakites in southern Korea and southwestern Japan could not have been generated by the subduction of the old Izanagi oceanic plate. Here, we speculate that plume-continent (intracontinental plume-China continent) and subsequent plume-slab (intracontinental plume-subducted Izanagi oceanic plate) interactions generated the various intracontinental magmatic and tectonic activities in eastern China, Korea, and southwestern Japan. We support our proposal using three-dimensional numerical models: 1) An intracontinental mantle plume is dragged into the mantle wedge by corner flow of the mantle wedge, and 2) the resultant channel-like flow of the mantle plume in the mantle wedge apparently migrated from southwest to northeast because of the northeast-to-southwest migration of the East Asian continental blocks with respect to the Izanagi oceanic plate. Our model calculations show that adakites and I-type granitoids can be generated by increased slab-surface temperatures because of the channel-like flow of the mantle plume in the mantle wedge. We also show that the southwest-to-northeast migration of the adakites and I-type granitoids in southern Korea and southwestern Japan can be attributable to the opposite migration of the East Asian continental blocks with respect to the Izanagi oceanic plate. This correlation implies that an intracontinental mantle plume existed in eastern China during the

  20. U-Series Disequilibria across the New Southern Ocean Mantle Province, Australian-Antarctic Ridge

    Science.gov (United States)

    Scott, S. R.; Sims, K. W. W.; Park, S. H.; Langmuir, C. H.; Lin, J.; Kim, S. S.; Blichert-Toft, J.; Michael, P. J.; Choi, H.; Yang, Y. S.

    2017-12-01

    Mid-ocean ridge basalts (MORB) provide a unique window into the temporal and spatial scales of mantle evolution. Long-lived radiogenic isotopes in MORB have demonstrated that the mantle contains many different chemical components or "flavors". U-series disequilibria in MORB have further shown that different chemical components/lithologies in the mantle contribute differently to mantle melting processes beneath mid-ocean ridges. Recent Sr, Nd, Hf, and Pb isotopic analyses from newly collected basalts along the Australian-Antarctic Ridge (AAR) have revealed that a large distinct mantle province exists between the Australian-Antarctic Discordance and the Pacific-Antarctic Ridge, extending from West Antarctica and Marie Byrd Land to New Zealand and Eastern Australia (Park et al., submitted). This southern mantle province is located between the Indian-type mantle and the Pacific-type mantle domains. U-series measurements in the Southeast Indian Ridge and East Pacific Rise provinces show distinct signatures suggestive of differences in melting processes and source lithology. To examine whether the AAR mantle province also exhibits different U-series systematics we have measured U-Th-Ra disequilibria data on 38 basalts from the AAR sampled along 500 km of ridge axis from two segments that cross the newly discovered Southern Ocean Mantle province. We compare the data to those from nearby ridge segments show that the AAR possesses unique U-series disequilibria, and are thus undergoing distinct mantle melting dynamics relative to the adjacent Pacific and Indian ridges. (230Th)/(238U) excesses in zero-age basalts (i.e., those with (226Ra)/(230Th) > 1.0) range from 1.3 to 1.7, while (226Ra)/(230Th) ranges from 1.0 to 2.3. (226Ra)/(230Th) and (230Th)/(238U) are negatively correlated, consistent with the model of mixing between deep and shallow melts. The AAR data show higher values of disequilibria compared to the Indian and Pacific Ridges, which can be explained by either

  1. Dynamical links between small- and large-scale mantle heterogeneity: Seismological evidence

    Science.gov (United States)

    Frost, Daniel A.; Garnero, Edward J.; Rost, Sebastian

    2018-01-01

    We identify PKP • PKP scattered waves (also known as P‧ •P‧) from earthquakes recorded at small-aperture seismic arrays at distances less than 65°. P‧ •P‧ energy travels as a PKP wave through the core, up into the mantle, then scatters back down through the core to the receiver as a second PKP. P‧ •P‧ waves are unique in that they allow scattering heterogeneities throughout the mantle to be imaged. We use array-processing methods to amplify low amplitude, coherent scattered energy signals and resolve their incoming direction. We deterministically map scattering heterogeneity locations from the core-mantle boundary to the surface. We use an extensive dataset with sensitivity to a large volume of the mantle and a location method allowing us to resolve and map more heterogeneities than have previously been possible, representing a significant increase in our understanding of small-scale structure within the mantle. Our results demonstrate that the distribution of scattering heterogeneities varies both radially and laterally. Scattering is most abundant in the uppermost and lowermost mantle, and a minimum in the mid-mantle, resembling the radial distribution of tomographically derived whole-mantle velocity heterogeneity. We investigate the spatial correlation of scattering heterogeneities with large-scale tomographic velocities, lateral velocity gradients, the locations of deep-seated hotspots and subducted slabs. In the lowermost 1500 km of the mantle, small-scale heterogeneities correlate with regions of low seismic velocity, high lateral seismic gradient, and proximity to hotspots. In the upper 1000 km of the mantle there is no significant correlation between scattering heterogeneity location and subducted slabs. Between 600 and 900 km depth, scattering heterogeneities are more common in the regions most remote from slabs, and close to hotspots. Scattering heterogeneities show an affinity for regions close to slabs within the upper 200 km of the

  2. 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

  3. Carbon-dioxide-rich silicate melt in the Earth's upper mantle.

    Science.gov (United States)

    Dasgupta, Rajdeep; Mallik, Ananya; Tsuno, Kyusei; Withers, Anthony C; Hirth, Greg; Hirschmann, Marc M

    2013-01-10

    The onset of melting in the Earth's upper mantle influences the thermal evolution of the planet, fluxes of key volatiles to the exosphere, and geochemical and geophysical properties of the mantle. Although carbonatitic melt could be stable 250 km or less beneath mid-oceanic ridges, owing to the small fraction (∼0.03 wt%) its effects on the mantle properties are unclear. Geophysical measurements, however, suggest that melts of greater volume may be present at ∼200 km (refs 3-5) but large melt fractions are thought to be restricted to shallower depths. Here we present experiments on carbonated peridotites over 2-5 GPa that constrain the location and the slope of the onset of silicate melting in the mantle. We find that the pressure-temperature slope of carbonated silicate melting is steeper than the solidus of volatile-free peridotite and that silicate melting of dry peridotite + CO(2) beneath ridges commences at ∼180 km. Accounting for the effect of 50-200 p.p.m. H(2)O on freezing point depression, the onset of silicate melting for a sub-ridge mantle with ∼100 p.p.m. CO(2) becomes as deep as ∼220-300 km. We suggest that, on a global scale, carbonated silicate melt generation at a redox front ∼250-200 km deep, with destabilization of metal and majorite in the upwelling mantle, explains the oceanic low-velocity zone and the electrical conductivity structure of the mantle. In locally oxidized domains, deeper carbonated silicate melt may contribute to the seismic X-discontinuity. Furthermore, our results, along with the electrical conductivity of molten carbonated peridotite and that of the oceanic upper mantle, suggest that mantle at depth is CO(2)-rich but H(2)O-poor. Finally, carbonated silicate melts restrict the stability of carbonatite in the Earth's deep upper mantle, and the inventory of carbon, H(2)O and other highly incompatible elements at ridges becomes controlled by the flux of the former.

  4. Processes and consequences of deep subduction

    NARCIS (Netherlands)

    Rubie, David C.; Hilst, R.D. van der

    2001-01-01

    Subduction of slabs of oceanic lithosphere into the deep mantle involves a wide range of geophysical and geochemical processes and is of major importance for the physical and chemical evolution of the Earth. For example, subduction and subduction-related volcanism are major processes through

  5. 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...... transfer correlations are suitable as input for a detailed simulation model for mantle tanks. The heat transfer correlations determined in this study are somewhat different from previous reported heat transfer correlations. The reason is that this study includes more mantle tank designs and operation...... 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...

  6. Iron speciation and redox state of mantle eclogites: Implications for ancient volatile cycles during mantle melting and oceanic crust subduction

    Science.gov (United States)

    Aulbach, Sonja; Woodand, Alan; Vasilyev, Prokopiy; Viljoen, Fanus

    2017-04-01

    (exclusion of TiO2 and REE). NMORB-normalised Nd/Yb, as a proxy of partial melt loss from subducting oceanic crust (1), shows no relationship with Fe3+/ΣFe. ΔFMQ, calculated using recently calibrated oxybarometers [2,4], broadly decreases with increasing pressure, which is ascribed to increasing garnet modes in metabasalts into which Fe3+ can be sequestered, similar to peridotite. The very low Fe3+/ΣFe, like V/Sc, appears to be a relatively robust indicator of low-pressure igneous processes and, potentially, the redox state of the ambient convecting mantle source to the protoliths of mantle eclogites. In contrast, Fe-based fO2 predominantly reflects pressure and bulk composition, and controls the speciation and mobility of volatiles in mafic heterogeneities during subduction and after emplacement in the cratonic mantle. The highly reduced nature of Archaean oceanic crust combined with further reduction upon pressure increase suggests that refractory graphite/diamond will be the stable carbon species. This may have prevented significant carbon output in Archaean subduction zones. [1] Aulbach and Jacob (2016) Lithos 262: 586-605; [2] Stagno et al. (2015) Contrib Mineral Petrol 42: 207-219; [3] Aulbach and Stagno (2016) Geology 44: 751-754; [4] Vasilyev (2016) PhD Thesis, Australian Nat Univ

  7. Selective cerebral perfusion prevents abnormalities in glutamate cycling and neuronal apoptosis in a model of infant deep hypothermic circulatory arrest and reperfusion

    Energy Technology Data Exchange (ETDEWEB)

    Kajimoto, Masaki; Ledee, Dolena R.; Olson, Aaron K.; Isern, Nancy G.; Robillard-Frayne, Isabelle; Des Rosiers, Christine; Portman, Michael A.

    2016-10-01

    Rationale: Deep hypothermic circulatory arrest (DHCA) is often required for the repair of complex congenital cardiac defects in infants. However, DHCA induces neuroapoptosis associated with later development of neurocognitive abnormalities. Selective cerebral perfusion (SCP) theoretically provides superior neural protection possibly through modifications in cerebral substrate oxidation and closely integrated glutamate cycling. Objectives: We tested the hypothesis that SCP modulates glucose entry into the citric acid cycle, and ameliorates abnormalities in glutamate flux which occur in association neuroapoptosis during DHCA. Methods and Results: Eighteen male Yorkshire piglets (age 34-44 days) were assigned randomly to 2 groups of 7 (DHCA or DHCA with SCP for 60 minutes at 18 °C) and 4 control pigs without cardiopulmonary bypass support. After the completion of rewarming from DHCA, 13-Carbon-labeled (13C) glucose as a metabolic tracer was infused. We used gas chromatography-mass spectrometry (GCMS) and nuclear magnetic resonance for metabolic analysis in the frontal cortex. Following 2.5 hours of cerebral reperfusion, we observed similar cerebral ATP levels, absolute levels of lactate and citric acid cycle intermediates, and 13C-enrichment. However, DHCA induced significant abnormalities in glutamate cycling resulting in reduced glutamate/glutamine and elevated γ-aminobutyric acid (GABA)/glutamate along with neuroapoptosis (TUNEL), which were all prevented by SCP. Conclusions: DHCA alone induces abnormalities in cycling of the major neurotransmitters in association with neuroapoptosis, but does not alter cerebral glucose utilization during reperfusion. The data suggest that SCP prevents these modifications in glutamate/glutamine/GABA cycling and protects the cerebral cortex from neuroapoptosis.

  8. Mantle dynamics and basalt petrogenesis

    Science.gov (United States)

    Ringwood, A. E.

    1985-03-01

    Differentiation at mid-ocean ridges generates a layered lithosphere consisting of a basaltic crust, immediately underlain by harzburgite and further underlain by pyrolite which has experienced depletion only of highly incompatible elements. The body forces driving subduction are concentrated mainly in the upper half of the lithosphere which is relatively cool and brittle. During subduction, the lower layer of relatively ductile, slightly depleted pyrolite is stripped off and resorbed into the upper mantle, thereby providing a future source region for MORB magmas. The slab which sinks to ~ 600 km is comprised mainly of differentiated former basalt and harzburgite which undergo a different series of phase transformations to those experienced by mantle pyrolite. In consequence, the former basaltic crust remains denser than surrounding mantle whereas former harzburgite becomes relatively buoyant below the 650 km seismic discontinuity. The resulting non-uniformity in stress distribution causes the slab to buckle at this depth and accrete to form a large, relatively cool ovoid "megalith" of mixed former harzburgite and basaltic crust. Heating of the megalith occurs over 1-2 b.y., leading to partial melting of the former basaltic crust. The resultant liquids contaminate regions of former harzburgite, rendering them fertile in the sense of future capacity to produce basaltic magmas. After thermal equilibration, the newly fertile, former harzburgite becomes buoyant, leading to the separation of diapirs which rise into the upper mantle. Such diapirs rising beneath sub-oceanic lithosphere experience small degrees of partial melting to produce ocean island basalts, mainly of the alkaline suite. Diapirs of fertile former harzburgite rising beneath continents become incorporated into the sub-continental lithosphere. This is a cumulative process and is ultimately responsible for the development of the chemical, physical and isotopic characteristics of the sub

  9. 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.

  10. Nitrogen evolution within the Earth's atmosphere-mantle system assessed by recycling in subduction zones

    Science.gov (United States)

    Mallik, Ananya; Li, Yuan; Wiedenbeck, Michael

    2018-01-01

    Understanding the evolution of nitrogen (N) across Earth's history requires a comprehensive understanding of N's behaviour in the Earth's mantle - a massive reservoir of this volatile element. Investigation of terrestrial N systematics also requires assessment of its evolution in the Earth's atmosphere, especially to constrain the N content of the Archaean atmosphere, which potentially impacted water retention on the post-accretion Earth, potentially causing enough warming of surface temperatures for liquid water to exist. We estimated the proportion of recycled N in the Earth's mantle today, the isotopic composition of the primitive mantle, and the N content of the Archaean atmosphere based on the recycling rates of N in modern-day subduction zones. We have constrained recycling rates in modern-day subduction zones by focusing on the mechanism and efficiency of N transfer from the subducting slab to the sub-arc mantle by both aqueous fluids and slab partial melts. We also address the transfer of N by aqueous fluids as per the model of Li and Keppler (2014). For slab partial melts, we constrained the transfer of N in two ways - firstly, by an experimental study of the solubility limit of N in melt (which provides an upper estimate of N uptake by slab partial melts) and, secondly, by the partitioning of N between the slab and its partial melt. Globally, 45-74% of N introduced into the mantle by subduction enters the deep mantle past the arc magmatism filter, after taking into account the loss of N from the mantle by degassing at mid-ocean ridges, ocean islands and back-arcs. Although the majority of the N in the present-day mantle remains of primordial origin, our results point to a significant, albeit minor proportion of mantle N that is of recycled origin (17 ± 8% or 12 ± 5% of N in the present-day mantle has undergone recycling assuming that modern-style subduction was initiated 4 or 3 billion years ago, respectively). This proportion of recycled N is enough to

  11. Inference of viscosity jump at 670 km depth and lower mantle viscosity structure from GIA observations

    Science.gov (United States)

    Nakada, Masao; Okuno, Jun'ichi; Irie, Yoshiya

    2018-03-01

    A viscosity model with an exponential profile described by temperature (T) and pressure (P) distributions and constant activation energy (E_{{{um}}}^{{*}} for the upper mantle and E_{{{lm}}}^* for the lower mantle) and volume (V_{{{um}}}^{{*}} and V_{{{lm}}}^*) is employed in inferring the viscosity structure of the Earth's mantle from observations of glacial isostatic adjustment (GIA). We first construct standard viscosity models with an average upper-mantle viscosity ({\\bar{η }_{{{um}}}}) of 2 × 1020 Pa s, a typical value for the oceanic upper-mantle viscosity, satisfying the observationally derived three GIA-related observables, GIA-induced rate of change of the degree-two zonal harmonic of the geopotential, {\\dot{J}_2}, and differential relative sea level (RSL) changes for the Last Glacial Maximum sea levels at Barbados and Bonaparte Gulf in Australia and for RSL changes at 6 kyr BP for Karumba and Halifax Bay in Australia. Standard viscosity models inferred from three GIA-related observables are characterized by a viscosity of ˜1023 Pa s in the deep mantle for an assumed viscosity at 670 km depth, ηlm(670), of (1 - 50) × 1021 Pa s. Postglacial RSL changes at Southport, Bermuda and Everglades in the intermediate region of the North American ice sheet, largely dependent on its gross melting history, have a crucial potential for inference of a viscosity jump at 670 km depth. The analyses of these RSL changes based on the viscosity models with {\\bar{η }_{{{um}}}} ≥ 2 × 1020 Pa s and lower-mantle viscosity structures for the standard models yield permissible {\\bar{η }_{{{um}}}} and ηlm (670) values, although there is a trade-off between the viscosity and ice history models. Our preferred {\\bar{η }_{{{um}}}} and ηlm (670) values are ˜(7 - 9) × 1020 and ˜1022 Pa s, respectively, and the {\\bar{η }_{{{um}}}} is higher than that for the typical value of oceanic upper mantle, which may reflect a moderate laterally heterogeneous upper-mantle

  12. Radiative conductivity and abundance of post-perovskite in the lowermost mantle

    Energy Technology Data Exchange (ETDEWEB)

    Lobanov, Sergey S.; Holtgrewe, Nicholas; Lin, Jung-Fu; Goncharov, Alexander F. (Texas); (CIW); (Howard)

    2017-12-01

    Thermal conductivity of the lowermost mantle governs the heat flow out of the core energizing planetary-scale geological processes. Yet, there are no direct experimental measurements of thermal conductivity at relevant pressure–temperature conditions of Earth's core–mantle boundary. Here we determine the radiative conductivity of post-perovskite at near core–mantle boundary conditions by optical absorption measurements in a laser-heated diamond anvil cell. Our results show that the radiative conductivity of Mg0.9Fe0.1SiO3 post-perovskite (~1.1 W/m/K) is almost two times smaller than that of bridgmanite (~2.0 W/m/K) at the base of the mantle. By combining this result with the present-day core–mantle heat flow and available estimations on the lattice thermal conductivity we conclude that post-perovskite is at least as abundant as bridgmanite in the lowermost mantle which has profound implications for the dynamics of the deep Earth.

  13. Radiative conductivity and abundance of post-perovskite in the lowermost mantle

    Science.gov (United States)

    Lobanov, Sergey S.; Holtgrewe, Nicholas; Lin, Jung-Fu; Goncharov, Alexander F.

    2017-12-01

    Thermal conductivity of the lowermost mantle governs the heat flow out of the core energizing planetary-scale geological processes. Yet, there are no direct experimental measurements of thermal conductivity at relevant pressure-temperature conditions of Earth's core-mantle boundary. Here we determine the radiative conductivity of post-perovskite at near core-mantle boundary conditions by optical absorption measurements in a laser-heated diamond anvil cell. Our results show that the radiative conductivity of Mg0.9Fe0.1SiO3 post-perovskite (∼1.1 W/m/K) is almost two times smaller than that of bridgmanite (∼2.0 W/m/K) at the base of the mantle. By combining this result with the present-day core-mantle heat flow and available estimations on the lattice thermal conductivity we conclude that post-perovskite is at least as abundant as bridgmanite in the lowermost mantle which has profound implications for the dynamics of the deep Earth.

  14. A Bayesian Method to Quantify Azimuthal Anisotropy Model Uncertainties: Application to Global Azimuthal Anisotropy in the Upper Mantle and Transition Zone

    Science.gov (United States)

    Yuan, K.; Beghein, C.

    2018-01-01

    Seismic anisotropy is a powerful tool to constrain mantle deformation, but its existence in the deep upper mantle and topmost lower mantle is still uncertain. Recent results from higher mode Rayleigh waves have, however, revealed the presence of 1 % azimuthal anisotropy between 300 km and 800 km depth, and changes in azimuthal anisotropy across the mantle transition zone boundaries. This has important consequences for our understanding of mantle convection patterns and deformation of deep mantle material. Here, we propose a Bayesian method to model depth variations in azimuthal anisotropy and to obtain quantitative uncertainties on the fast seismic direction and anisotropy amplitude from phase velocity dispersion maps. We applied this new method to existing global fundamental and higher mode Rayleigh wave phase velocity maps to assess the likelihood of azimuthal anisotropy in the deep upper mantle and to determine whether previously detected changes in anisotropy at the transition zone boundaries are robustly constrained by those data. Our results confirm that deep upper mantle azimuthal anisotropy is favored and well-constrained by the higher mode data employed. The fast seismic directions are in agreement with our previously published model. The data favor a model characterized, on average, by changes in azimuthal anisotropy at the top and bottom of the transition zone. However, this change in fast axes is not a global feature as there are regions of the model where the azimuthal anisotropy direction is unlikely to change across depths in the deep upper mantle. We were, however, unable to detect any clear pattern or connection with surface tectonics. Future studies will be needed to further improve the lateral resolution of this type of model at transition zone depths.

  15. Magma genesis by rifting of oceanic lithosphere above anomalous mantle: Terceira Rift, Azores

    Science.gov (United States)

    Beier, Christoph; Haase, Karsten M.; Abouchami, Wafa; Krienitz, Marc-S.; Hauff, Folkmar

    2008-12-01

    The Terceira Rift formed relatively recently (˜1 Ma ago) by rifting of the old oceanic lithosphere of the Azores Plateau and is currently spreading at a rate of 2-4mm/a. Together with the Mid-Atlantic Ridge, the Terceira Rift forms a triple junction that separates the Eurasian, African, and American Plates. Four volcanic systems (São Miguel, João de Castro, Terceira, Graciosa), three of which are islands, are distinguished along the axis and are separated by deep avolcanic basins similar to other ultraslow spreading centers. The major element, trace element and Sr-Nd-Pb isotope geochemistry of submarine and subaerial lavas display large along-axis variations. Major and trace element modeling suggests melting in the garnet stability field at smaller degrees of partial melting at the easternmost volcanic system (São Miguel) compared to the central and western volcanoes, which appear to be characterized by slightly higher melting degrees in the spinel/garnet transition zone. The degrees of partial melting at the Terceira Rift are slightly lower than at other ultraslow mid-ocean ridge spreading axes (Southwest Indian Ridge, Gakkel Ridge) and occur at greater depths as a result of the melting anomaly beneath the Azores. The combined interaction of a high obliquity, very slow spreading rates, and a thick preexisting lithosphere along the axis probably prevents the formation and eruption of larger amounts of melt along the Terceira Rift. However, the presence of ocean islands requires a relatively stable melting anomaly over relatively long periods of time. The trace element and Sr-Nd-Pb isotopes display individual binary mixing arrays for each volcanic system and thus provide additional evidence for focused magmatism with no (or very limited) melt or source interaction between the volcanic systems. The westernmost mantle sources beneath Graciosa and the most radiogenic lavas from the neighboring Mid-Atlantic Ridge suggest a mantle flow from Graciosa toward the Mid

  16. Mantle wedge exhumation beneath the Dora-Maira (U)HP dome unravelled by local earthquake tomography (Western Alps)

    Science.gov (United States)

    Solarino, Stefano; Malusà, Marco G.; Eva, Elena; Guillot, Stéphane; Paul, Anne; Schwartz, Stéphane; Zhao, Liang; Aubert, Coralie; Dumont, Thierry; Pondrelli, Silvia; Salimbeni, Simone; Wang, Qingchen; Xu, Xiaobing; Zheng, Tianyu; Zhu, Rixiang

    2018-01-01

    In continental subduction zones, the behaviour of the mantle wedge during exhumation of (ultra)high-pressure [(U)HP] rocks provides a key to distinguish among competing exhumation mechanisms. However, in spite of the relevant implications for understanding orogenic evolution, a high-resolution image of the mantle wedge beneath the Western Alps is still lacking. In order to fill this gap, we perform a detailed analysis of the velocity structure of the Alpine belt beneath the Dora-Maira (U)HP dome, based on local earthquake tomography independently validated by receiver function analysis. Our results point to a composite structure of the mantle wedge above the subducted European lithosphere. We found that the Dora-Maira (U)HP dome lays directly above partly serpentinized peridotites (Vp 7.5 km/s; Vp/Vs = 1.70-1.72), documented from 10 km depth down to the top of the eclogitized lower crust of the European plate. These serpentinized peridotites, possibly formed by fluid release from the subducting European slab to the Alpine mantle wedge, are juxtaposed against dry mantle peridotites of the Adriatic upper plate along an active fault rooted in the lithospheric mantle. We propose that serpentinized mantle-wedge peridotites were exhumed at shallow crustal levels during late Eocene transtensional tectonics, also triggering the rapid exhumation of (U)HP rocks, and were subsequently indented under the Alpine metamorphic wedge in the early Oligocene. Our findings suggest that mantle-wedge exhumation may represent a major feature of the deep structure of exhumed continental subduction zones. The deep orogenic levels here imaged by seismic tomography may be exposed today in older (U)HP belts, where mantle-wedge serpentinites are commonly associated with coesite-bearing continental metamorphic rocks.

  17. Towards modelling of water inflow into the mantle

    Science.gov (United States)

    Thielmann, M.; Eichheimer, P.; Golabek, G.

    2017-12-01

    The transport and storage of water in the mantle significantly affects various material properties of mantle rocks and thus water plays a key role in a variety of geodynamical processes (tectonics, magmatism etc.) Geological and seismological observations suggest different inflow mechanisms of water via the subducting slab like slab bending, thermal cracking and serpentinization (Faccenda et al., 2009; Korenaga, 2017). Most of the previous numerical models do not take different dip angles of the subduction slab and subduction velocities into account, while nature provides two different types of subduction regimes i.e. shallow and deep subduction (Li et al., 2011). To which extent both parameters influence the inflow and outflow of water in the mantle still remains unclear. For the investigation of the inflow and outflow of fluids e.g. water in the mantle, we use high resolution 2D finite element simulations, which allow us to resolve subducted sediments and crustal layers. For this purpose the finite element code MVEP2 (Kaus, 2010), is tested against benchmark results (van Keken et al., 2008). In a first step we reproduced the analytical cornerflow model (Batchelor, 1967) used in the benchmark of van Keken et al.(2008) as well as the steady state temperature field. Further steps consist of successively increasing model complexity, such as the incorporation of hydrogen diffusion, water transport and dehydration reactions. ReferencesBatchelor, G. K. An Introduction to Fluid Dynamics. Cambridge University Press, Cambridge, UK (1967) 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). Li, Z. H., Xu, Z. Q., and T.V. Gerya. Flat versus

  18. Thermal Stratification in Vertical Mantle Tanks

    DEFF Research Database (Denmark)

    Knudsen, Søren; Furbo, Simon

    2001-01-01

    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......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...

  19. Implications of Subduction Rehydration for Earth's Deep Water Cycle

    Science.gov (United States)

    Ruepke, L. H.; Phipps Morgan, J.; Dixon, J.

    2006-12-01

    The presence of liquid water is the principle difference between our Earth and other planets in the solar system. The global ocean is the obvious surface expression of this. The 'standard model' for the genesis of the oceans is that they are exhalations from Earth's deep interior continually rinsed through surface rocks by the global hydrologic cycle. The question of how much water resides within the Earth's deep interior remains unresolved and is a matter of vigorous ongoing scientific debate. We have addressed the question of water distribution between the exosphere and the mantle throughout Earth's history with simple mass balance considerations. In our model, water is outgassed from the mantle into the exosphere (atmosphere + continental crust) during pressure-release melting at mid-ocean ridges and hotspots. Plate subduction may transport water back from the surface into the deeper mantle thereby 'closing' the global geologic water cycle. In series of some 5000 model runs we have thoroughly explored the mutual effect of model parameters. All models correctly predict the formation of the present-day oceans but differ in their predicted sea-level changes through time and in the amount of water in the present-day mantle. To distinguish which model runs are the most realistic we use geochemical constraints and observed sealevel changes during the Phanerozoic. Recently Dixon et al. [2002] estimated water concentrations for some of the major mantle components and concluded that the most primitive (FOZO) are significantly wetter than the recycling associated EM or HIMU mantle components and the even drier depleted mantle source that melts to form MORB. Sealevel changes over hundreds of million of years are notoriously bad constrained. But a maximum drop in sealevel of 400-600m appears to be an upper bound. We find that only those model runs are consistent with these constraints in which deep water subduction is limited and in which the present-day mantle is

  20. Heating in the Solar Mantle

    Science.gov (United States)

    Chiuderi, C.

    1985-01-01

    In the case of the solar chromosphere and corona (the solar mantle) the primary energy source is the mechanical energy from photospheric motions. Plenty of energy is available; the problem is to transfer the needed amount of energy to the proper place to account for the observations. The global problem is reviewed from the point of view of the generation and transmission of energy, the intermediate storage of energy, and the release of energy in such a way that the observed features are generated.

  1. The effects of magmatic redistribution of heat producing elements on the lunar mantle evolution inferred from numerical models that start from various initial states

    Science.gov (United States)

    Ogawa, Masaki

    2018-02-01

    To discuss how redistribution of heat producing elements (HPEs) by magmatism affects the lunar mantle evolution depending on the initial condition, I present two-dimensional numerical models of magmatism in convecting mantle internally heated by incompatible HPEs. Mantle convection occurs beneath a stagnant lithosphere that inhibits recycling of the HPE-enriched crustal materials to the mantle. Magmatism is modeled by a permeable flow of magma generated by decompression melting through matrix. Migrating magma transports heat, mass, and HPEs. When the deep mantle is initially hot with the temperature TD around 1800 K at its base, magmatism starts from the beginning of the calculated history to extract HPEs from the mantle. The mantle is monotonously cooled, and magmatism ceases within 2 Gyr, accordingly. When the deep mantle is initially colder with TD around 1100 K, HPEs stay in the deep mantle for a longer time to let the planet be first heated up and then cooled only slightly. If, in addition, there is an HPE-enriched domain in the shallow mantle at the beginning of the calculation, magma continues ascending to the surface through the domain for more than 3 Gyr. The low TD models fit in with the thermal and magmatic history of the Moon inferred from spacecraft observations, although it is not clear if the models are consistent with the current understanding of the origin of the Moon and its magnetic field. Redistribution of HPEs by magmatism is a crucial factor that must be taken into account in future studies of the evolution of the Moon.

  2. Elasticity of superhydrous phase B at the mantle temperature and pressure: Implications for 800-km discontinuity and water flow into lower mantle

    Science.gov (United States)

    Yang, D.; Wang, W.; Wu, Z.

    2017-12-01

    Plate subduction can transport the water to the Earth's interior by forming hydrous phases and water can exert important effects on global dynamics and many processes within the deep Earth. Superhydrous phase B (ShyB), as an important candidate for transporting water into the mantle transition zone and lower mantle, is stable up to 31 GPa and will decompose into bridgmanite, periclase and water at a depth of 800 km [Komabayashi and Omori, 2006]. The decomposition of ShyB may be related to the seismic discontinuity at the depth of 800 km in Western-Pacific Subduction Zones [Liu et al., 2016; Porritt and Yoshioka, 2016]. The detail discussions on this topic require the elasticity of ShyB at the P-T conditions of the transition zone and lower mantle. In this contribution, we obtained the thermal elasticity of ShyB using first-principles calculations. ShyB shows a very low velocity and density compared to the bridgmanite and periclase, the major minerals in the lower mantle. The accumulation of ShyB will generate the low-velocity anomaly in the uppermost lower mantle. The dehydration of ShyB will cause the Vp, Vs, and density increase by 7.5%, 15.0% and 12%, respectively. It means that a slab with 10% ShyB could cause an impedance contrast of 2.7% at a depth of 800 km for shear wave. Furthermore, the released waters by the dehydration of ShyB probably migrate upward and promote the partial melt to reduce the sound velocity at shallower depth, which can further explain the low-velocity zones just above 800-km discontinuity in Western-Pacific Subduction Zones [Liu et al., 2016]. Komabayashi, T., and S. Omori (2006), Internally consistent thermodynamic data set for dense hydrous magnesium silicates up to 35GPa, 1600°C: Implications for water circulation in the Earth's deep mantle, Physics of the Earth and Planetary Interiors, 156(1-2), 89-107. Liu, Z., J. Park, and S. I. Karato (2016), Seismological detection of low-velocity anomalies surrounding the mantle transition

  3. Flow of mantle fluids through the ductile lower crust: Heliumisotope trends

    Energy Technology Data Exchange (ETDEWEB)

    Kennedy, B. Mack; van Soest, Matthijs C.

    2007-10-07

    Heat and mass are injected into the shallow crust when mantle fluids are able to flow through the ductile lower crust. Minimum 3He/4He ratios in surface fluids from the northern Basin and Range province, western North America increase systematically from low, crustal values in the east to high, mantle values in the west, a regional trend that correlates with the rates of active crustal deformation. The highest ratios occur where the extension and shear strain rates are greatest. The correspondence of helium isotope ratios and active trans-tensional deformation indicates a deformation enhanced permeability and that mantle fluids can penetrate the ductile lithosphere in regions even where there is no significant magmatism. Superimposed on the regional trend are local, high-{sup 3}He/{sup 4}He anomalies signifying hidden magmatic activity and/or deep fluid production with locally enhanced permeability, identifying zones with high resource potential, particularly for geothermal energy development.

  4. Seismic anisotropy; a window on how the Earth works: multiple mechanisms and sites, from shallow mantle to inner core

    Science.gov (United States)

    Osmaston, Miles

    2013-04-01

    , including generating internally a very strong push-apart force, the straightness of MOR segments is the automatic result of accretion controlled by lateral cooling [8]. Olivine crystal has grossly anisotropic thermal conductivity, high on the a-axis [9] so, contrasting with the much lower conductivity of melt, suitably oriented ones on the crack walls grow the fastest and build in the seismic anisotropy from the start. For ophiolites, I will illustrate a close relative of this thick-plate model, but geared to their specific near-continent genesis and emplacement, which provides for their very real shearing and anisotropy at the crust-tectonite junction and for the 25 - 50 km metamorphic pressures in their soles [10]. A remarkably fertile model for the genesis of intraplate volcanism, without plumes, is also provided by this thick-plate perspective of plate dynamics [11]. We now move to deeper in the mantle. Attachment of the LVZ material to the ocean plate and the low conductivity of its interstial melt renders it still buoyant when the bigger ridge push makes it subduct [12]. Seismological transects of subduction zones show that this heat re-emerges at depth to partially melt the interface former oceanic crust, the result (on experimental evidence) being stishovitic residue plus (because of its compressibility) very dense ultramafic melt [12]. Both will shower into the lower mantle and eventually form layers on D'', the melt being prevented from freezing because that would need the energy to increase its volume. Hence the seismic anisotropy of D''. Moving still deeper, to the outer-core flows from which the Inner Core has grown. I attribute its cigar shape to preferential addition to its polar regions, from a downwelling flow, not to deformation of the IC, except perhaps as weak isostatic adjustment to that polar addition. I speculate that polar-aligned columnar growth of iron crystals, although themselves not strongly anisotropic, would impound 'less pure' alloy between

  5. Episodic entrainment of primordial material in plumes from isolated lower mantle reservoirs

    Science.gov (United States)

    Williams, C. D.; McNamara, A. K.; Garnero, E. J.; Van Soest, M. C.

    2012-12-01

    The noble gas systematics observed in ocean island basalts (OIBs) relative to mid-ocean ridge basalts (MORBs), suggests OIBs preferentially sample a primordial reservoir located somewhere within Earth's mantle. The lower mantle has been favored as a candidate reservoir, either in its entirety or discrete reservoirs located within it. Thermal plumes originating from the lower mantle could potentially sample these reservoirs, which may have remained isolated from the MORB source region over much of Earth's history. Recently, seismic observations of two, nearly anti-podal large, low-shear velocity provinces (LLSVPs) in the lowermost mantle have been hypothesized as being chemically distinct, and thus, may be long-lived reservoirs that have retained primordial noble gas signatures from earlier in Earth's history. Geodynamic models predict that thermal plumes are likely to be associated with LLSVPs and could potentially entrain a small amount of these chemically distinct reservoirs, which may ultimately reach the surface of the Earth in the form of OIBs. However, isotopic variability within OIBs challenges the notion of multiple plumes tapping the same reservoir. Here, we perform geodynamic calculations that investigate the time-dependent rate of material entrained into thermal plumes from these primordial reservoirs. In particular, we examine how the rate of entrainment varies within a single, long-lived thermal plume with a relatively steady buoyancy flux. Using phase relations for mantle peridotite, the amount of entrained material comprising the melt is estimated. We find that time-dependent dynamical processes at the interface between a deep, primordial reservoir and the base of a mantle plume strongly influences the entrainment rate, causing the amount of entrainment to vary episodically with time. Thus, melts rising to the surface (e.g., OIBs) are predicted to contain variable proportions of material entrained from these primordial reservoirs. This time

  6. Imaging Lower Mantle Heterogeniety With Differential Dispersion and Attenuation of Core- Diffracted Waves

    Science.gov (United States)

    Euler, G. G.; Wysession, M. E.; Huhmann, B.

    2007-12-01

    We investigate global differential travel-time dispersion and attenuation of core-diffracted phases from large, deep earthquakes. This technique aids in constraining radial velocity structure at the core-mantle interface in a manner analogous to surface wave observables constraining upper mantle structure. We confirm that there is noticeable differential dispersion and attenuation caused by diffraction on a global basis for both Pdiff and Sdiff. Variations in differential dispersion and attenuation are observed with both geographic location and between Pdiff and Sdiff along the same azimuth suggesting lateral variations in Vp, Vs and Vp/Vs ratio in the lowermost mantle. We attempt to utilize dispersion and attenuation characteristics to put bounds on the magnitude and distribution of large-scale velocity perturbations in the lowermost mantle and draw comparisons to variations found in several 3D whole-mantle models. Our dataset consists of broadband records available from the IRIS DMC for deep (>180 km), large (>5.6 mb) teleseismic events. Preprocessing of the records includes deconvolution of the instrument response, rotation of horizontal components, filtering using a set of bandpass filters, and sample-rate decimation (5 sps). Relative arrival times and amplitudes are found by computing cross correlegrams in the frequency domain, detecting and removing poor recordings with cluster analysis, and iteratively converging on a stable low-variance solution with a weighted least-squares inversion while automatically remediating phase-skips utilizing a database of potential relative arrivals. Raypath-approximated corrections for reciever-side differences in ellipticity, mantle, and crust are applied for the derivation of phase velocites in the lowermost mantle as a function of azimuth and frequency. Following previous studies of diffracted signals, we limit our analysis to station pairs located in narrow azimuthal windows spread over a considerable distance while

  7. Constraining Lower Mantle Heterogeneity With Differential Dispersion of Core-Diffracted Waves

    Science.gov (United States)

    Euler, G. G.; Wysession, M. E.; Aleqabi, G. I.

    2006-12-01

    We investigate global differential travel-time dispersion of core-diffracted phases from large, deep earthquakes. This technique aids in constraining radial velocity structure at the core-mantle interface in a manner analogous to surface waves constraining upper mantle structure. We show that there is noticeable differential dispersion, that the cause is likely associated with the diffraction process and that the dispersion varies with geographic location. Variations in differential dispersion between Pdiff and Sdiff along the same azimuth are also observed. We attempt to utilize dispersion characteristics to put bounds on the magnitude and distribution of large-scale velocity perturbations in the lowermost mantle region and draw comparisons to variations found in several 3D whole-mantle models. We have included in our study all broadband recordings available from the IRIS DMC. Preprocessing of the records includes deconvolution of the instrument response, conversion to displacement, rotation of horizontals to the backazimuth, filtering using a set of bandpass filters, and sample-rate decimation (20 sps). Relative arrival times are found by computing cross correlegrams in the frequency domain, automatically detecting and removing poor recordings with cluster analysis, weighted least-squares inversion, and robust regression techniques to remedy misidentification in noisy signals. Raypath-approximated corrections for ellipticity, mantle, and crustal differences are applied to the relative times for the derivation of apparent slowness as a function of azimuth and frequency. Following previous studies of diffracted signals, we limit our analysis to stations located in narrow azimuthal windows spread over a considerable distance. This method has the advantage of removing source-side effects, averaging out minor timing errors, and, for our analysis, averaging out receiver-side upper mantle and crustal differential dispersion. Comparison with differential dispersion

  8. Thyroid dysfunction after mantle irradiation of Hodgkin's disease patients

    International Nuclear Information System (INIS)

    Khoo, V.S.; Liew, K.H.; Crennan, E.C.; D'Costa, I.M.; Quong, G.

    1998-01-01

    Thyroid dysfunction can develop in patients with Hodgkin's disease who are treated with mantle irradiation. During the period 1970-89, the records of 320 patients who received mantle irradiation and who had thyroid function tests (TFT) were retrospectively reviewed. The median age was 30 years (range, 7-69 years). The median mantle and thyroid dose was 36 Gy (range, 30-40 Gy) and 39.8 Gy (range, 32-65 Gy), respectively. Overall thyroid dysfunction was present in 39% of the patients. Clinical hypothyroidism was seen in 10% and biochemical hypothyroidism was noted in 25%. Hyperthyroidism was found in 4% of patients. Thyroid nodules had developed in six patients (2%), of which those in four patients were malignant. Age, sex, histological subtype, stage of disease, dose, Iymphangiogram and treatment with chemotherapy were not significant factors in the development of thyroid dysfunction. The narrow dose range prevented adequate analysis of dose effect. The results indicate that the incidence of thyroid abnormalities is high enough to warrant regular TFT assessment with pre-irradiation levels and follow-up testing for life because the development of abnormalities can occur many years later. Thyroid examination should form part of the routine follow-up examination and any abnormality should be promptly investigated. Copyright (1998) Blackwell Science Pty Ltd

  9. Mapping geomagnetic secular variation at the core-mantle boundary

    DEFF Research Database (Denmark)

    Holme, R.; Olsen, Nils; Bairstow, F. L.

    2011-01-01

    Data from recent satellite missions have vastly increased the resolution of models of the geomagnetic field, and its first and second time derivatives – secular variation (SV) and secular acceleration (SA). The spectra of both SV and SA are ‘blue’ at the core–mantle boundary, both well-fit by fun......Data from recent satellite missions have vastly increased the resolution of models of the geomagnetic field, and its first and second time derivatives – secular variation (SV) and secular acceleration (SA). The spectra of both SV and SA are ‘blue’ at the core–mantle boundary, both well......-fit by functions proportional to l(l + 1) where l is the spherical harmonic degree. The ratio of the two spectra defines a timescale for geomagnetic variations of approximately 10 yrs for all resolvable harmonic degrees. The blue spectra should prevent meaningful maps of the SV being generated; nevertheless...... core–mantle coupling than by electromagnetic screening. Comparison with maps from measurements prior to the recent satellites, using the ‘Comprehensive Model’, suggests that models back to at least 1970 are sufficiently good to enable direct comparison of the SV....

  10. Seismic structure of the central US crust and upper mantle: Uniqueness of the Reelfoot Rift

    Science.gov (United States)

    Pollitz, Fred; Mooney, Walter D.

    2014-01-01

    Using seismic surface waves recorded with Earthscope's Transportable Array, we apply surface wave imaging to determine 3D seismic velocity in the crust and uppermost mantle. Our images span several Proterozoic and early Cambrian rift zones (Mid-Continent Rift, Rough Creek Graben—Rome trough, Birmingham trough, Southern Oklahoma Aulacogen, and Reelfoot Rift). While ancient rifts are generally associated with low crustal velocity because of the presence of thick sedimentary sequences, the Reelfoot Rift is unique in its association with low mantle seismic velocity. Its mantle low-velocity zone (LVZ) is exceptionally pronounced and extends down to at least 200 km depth. This LVZ is of variable width, being relatively narrow (∼50km">∼50km wide) within the northern Reelfoot Rift, which hosts the New Madrid Seismic Zone (NMSZ). We hypothesize that this mantle volume is weaker than its surroundings and that the Reelfoot Rift consequently has relatively low elastic plate thickness, which would tend to concentrate tectonic stress within this zone. No other intraplate ancient rift zone is known to be associated with such a deep mantle low-velocity anomaly, which suggests that the NMSZ is more susceptible to external stress perturbations than other ancient rift zones.

  11. Mantle transition zone, stagnant slab and intraplate volcanism in Northeast Asia

    Science.gov (United States)

    Chen, Chuanxu; Zhao, Dapeng; Tian, You; Wu, Shiguo; Hasegawa, Akira; Lei, Jianshe; Park, Jung-Ho; Kang, Ik-Bum

    2017-04-01

    3-D P- and S-wave velocity structures of the mantle down to a depth of 800 km beneath NE Asia are investigated using ∼981 000 high-quality arrival-time data of local earthquakes and teleseismic events recorded at 2388 stations of permanent and portable seismic networks deployed in NE China, Japan and South Korea. Our results do not support the existence of a gap (or a hole) in the stagnant slab under the Changbai volcano, which was proposed by a previous study of teleseismic tomography. In this work we conducted joint inversions of both local-earthquake arrival times and teleseismic relative traveltime residuals, leading to a robust tomography of the upper mantle and the mantle transition zone (MTZ) beneath NE Asia. Our joint inversion results reveal clearly the subducting Pacific slab beneath the Japan Islands and the Japan Sea, as well as the stagnant slab in the MTZ beneath the Korean Peninsula and NE China. A big mantle wedge (BMW) has formed in the upper mantle and the upper part of the MTZ above the stagnant slab. Localized low-velocity anomalies are revealed clearly in the crust and the BMW directly beneath the active Changbai and Ulleung volcanoes, indicating that the intraplate volcanism is caused by hot and wet upwelling in the BMW associated with corner flows in the BMW and deep slab dehydration as well.

  12. Exotic crust formation on Mercury: Consequences of a shallow, FeO-poor mantle

    Science.gov (United States)

    Vander Kaaden, Kathleen E.; McCubbin, Francis M.

    2015-02-01

    The range in density and compressibility of Mercurian melt compositions was determined to better understand the products of a possible Mercurian magma ocean and subsequent volcanism. Our experiments indicate that the only mineral to remain buoyant with respect to melts of the Mercurian mantle is graphite; consequently, it is the only candidate mineral to have composed a primary floatation crust during a global magma ocean. This exotic result is further supported by Mercury's volatile-rich nature and inexplicably darkened surface. Additionally, our experiments illustrate that partial melts of the Mercurian mantle that compose the secondary crust were buoyant over the entire mantle depth and could have come from as deep as the core-mantle boundary. Furthermore, Mercury could have erupted higher percentages of its partial melts compared to other terrestrial planets because magmas would not have stalled during ascent due to gravitational forces. These findings stem from the FeO-poor composition and shallow depth of Mercury's mantle, which has resulted in both low-melt density and a very limited range in melt density responsible for Mercury's primary and secondary crusts. The enigmatically darkened, yet low-FeO surface, which is observed today, can be explained by secondary volcanism and impact processes that have since mixed the primary and secondary crustal materials.

  13. Fate of MgSiO3 melts at core-mantle boundary conditions.

    Science.gov (United States)

    Petitgirard, Sylvain; Malfait, Wim J; Sinmyo, Ryosuke; Kupenko, Ilya; Hennet, Louis; Harries, Dennis; Dane, Thomas; Burghammer, Manfred; Rubie, Dave C

    2015-11-17

    One key for understanding the stratification in the deep mantle lies in the determination of the density and structure of matter at high pressures, as well as the density contrast between solid and liquid silicate phases. Indeed, the density contrast is the main control on the entrainment or settlement of matter and is of fundamental importance for understanding the past and present dynamic behavior of the deepest part of the Earth's mantle. Here, we adapted the X-ray absorption method to the small dimensions of the diamond anvil cell, enabling density measurements of amorphous materials to unprecedented conditions of pressure. Our density data for MgSiO3 glass up to 127 GPa are considerably higher than those previously derived from Brillouin spectroscopy but validate recent ab initio molecular dynamics simulations. A fourth-order Birch-Murnaghan equation of state reproduces our experimental data over the entire pressure regime of the mantle. At the core-mantle boundary (CMB) pressure, the density of MgSiO3 glass is 5.48 ± 0.18 g/cm(3), which is only 1.6% lower than that of MgSiO3 bridgmanite at 5.57 g/cm(3), i.e., they are the same within the uncertainty. Taking into account the partitioning of iron into the melt, we conclude that melts are denser than the surrounding solid phases in the lowermost mantle and that melts will be trapped above the CMB.

  14. Rogue Mantle Helium and Neon

    Science.gov (United States)

    Albarede, F.

    2007-12-01

    The canonical view of He isotope geochemistry holds that high 3He/4He ratios in basalts fingerprints undegassed mantle sources. Hawaiian basalts with unradiogenic He with 3He/4He up to 30 RA are therefore seen as originating from parts of the mantle that is still primordial, at least much more so than MORB mantle (3He/4He ~ 8 RA). This view was strongly reinforced by the discovery of solar and even planetary Ne components in oceanic basalts and gas wells. The canonical view, however, conflicts with multiple observations on ocean islands, notably Hawaiian basalts: the correlation of {187}Os/{186}Os with δ 18O combined with the presence of unusually radiogenic Hf isotope compositions for a given Nd isotope composition and the correlation between Hf and Pb isotopes are all features strongly reminiscent of ancient subducted oceanic crust and pelagic sediments in the source of the Hawaiian plume. These conflicting observations beg the question of how Hawaiian basalts, which carry the embodiment of a primordial gas signature, at the same time can provide such strong evidence of surface material recycling. I here suggest and alternative model that uses the marble cake paradigm and Shuster et al.'s data on olivine. A solution to this conundrum lies in an analogy with oil genesis: 3He and Ne do not reside in the low-melting point peridotites in which they were originally hosted but rather migrated since early in Earth history into refractory 'reservoir' rocks. Since there can be no free gas phase percolating at pressures in excess of olivine carbonation at ~3 GPa, He must be largely redistributed by diffusion. The time scale of diffusion is the defining parameter: although over billions of years 3He diffuses across large distances, melting events are too short to efficiently strip residual refractory rocks from their high-3He/4He component. Assuming that melts begin forming over the uppermost 100 km with an upwelling rate of 10 m y-1 in plume conduits and 10 cm y-1 under

  15. Global P-wave tomography of mantle plumes and subducting slabs

    Science.gov (United States)

    Yamamoto, Y.; Zhao, D.

    2008-12-01

    zone. In Bering Sea, there are several intraplate volcanoes such as St. Paul island. Given the existence of the stagnant Pacific slab and very low-V mantle wedge above the slab, we think that the origin of the intraplate volcanoes in Bering Sea is most likely related to the deep subduction of the Pacific slab and its stagnancy in the mantle transition zone, similar to the Changbai and Wudalianchi volcanoes in Northeast Asia (Zhao, 2004). Zhao, D. (2001) Earth Planet. Sci. Lett. 192, 251-265. Zhao, D. (2004) Phys. Earth Planet. Inter. 146, 3-34.

  16. Low Abundances of Highly Siderophile Elements in the Lunar Mantle: Evidence for Prolonged Late Accretion

    Science.gov (United States)

    Walker, R. J.; Horan, M. F.; Shearer, C. K.; Papike, J. J.

    2004-01-01

    The highly siderophile elements (HSE: including Re, Au, Ir, Os, Ru, Pt, Pd, Rh) are strongly partitioned into metal relative to silicates. In the terrestrial planets these elements are concentrated in metallic cores. Earth s mantle has sufficiently high abundances of the HSE (0.008 times CI abundances) that it has been hypothesized approximately 0.1-0.5% of the mass of the Earth was added following the last major interaction between the core and mantle [e.g. 1]. The additional material added to the Earth and Moon has been termed a late veneer , and the process has often been termed late accretion [2]. The timing of the dominant late accretionary period of the Earth and Moon is still poorly known. The abundances of HSE in the lunar mantle could provide important constraints on when the late veneer was added. The material that ultimately became the silicate portion of the Moon was likely stripped of most of its HSE prior to and during coalescence of the Moon. Consequently the initial lunar mantle likely had very low concentrations of the HSE. Unlike Earth, the generation of permanent lunar crust by 4.4 Ga prevented subsequent additions of HSE to the lunar mantle via continued accretion. Thus, if a substantial portion of the late veneer was added after 4.4 Ga, the lunar mantle should have retained very low HSE concentrations. Conversely, if the late veneer was mostly added prior to 4.4 Ga, HSE abundances in the lunar mantle may be roughly similar to abundances in the terrestrial mantle.

  17. Structural Heterogeneities in Southeast Tibet: Implications for Regional Flow in the Lower Crust and Upper Mantle

    Directory of Open Access Journals (Sweden)

    Zhi Wang

    2012-01-01

    Full Text Available Our seismic study together with the MT analysis reveal a “R-shape” flow existing in both the lower crust and uppermost mantle, which suggests the crustal deformation along the deep, large sutures (such as the Longmen Shan fault and the Anninghe Fault under the southeastern Tibetan Plateau is maintained by dynamic pressure from the regional flow intermingled with the hot upwelling asthenosphere. The material in the lower crust and uppermost mantle flowing outward from the center of the plateau is buttressed by the old, strong lithosphere that underlies the Sichuan basin, pushing up on the crust above and maintaining steep orogenic belt through dynamic pressure. We therefore consider that the “R-shape” regional flow played a key role in the crustal deformation along the deep suture zones of the Bangong-Nujiang, the Longmen-Shan faults, and other local heavily faulted zones beneath the southeastern Tibetan Plateau.

  18. Deep Vein Thrombosis

    African Journals Online (AJOL)

    OWNER

    ABSTRACT. BACKGROUND: Deep vein thrombosis (DVT) is a cause of preventable morbidity and mortality in hospitalized surgical patients. The occurrence of the disease is related to presence of risk factors, which are related primarily to trauma, venous stasis and hyper-coagulability. DVT seems not to be taken seriously ...

  19. Application of deep geophysical data to the discussion on the relationship between deep faults, concealed over thrust napped structure and uranium metallogenesis in central-southern Jiangxi

    International Nuclear Information System (INIS)

    Jiang Jinyuan; Qi Liang

    1999-01-01

    Based on the comparative analysis and study on 10 profiles of telluric electromagnetic sounding (MT) and regional gravimetric, magnetic data and Moho surface, the deep geological-tectonic pattern of the central-southern Jiangxi is discussed. It is suggested that: the studied region belongs to the Soyth-China block; in the area along Pingxiang-Guangfeng, at the border with Yangzi block an approximately EW-trending mantle concave-mantle slope zone occurs; the NNE-NE trending mantle uplift-mantle slope-mantle concave structure is developed within the South-China block; deep fault zones are represented by variation sites of Moho surface. Then, a series of deep structures is inferred including the approximately EW-striking Pingxian-Guangfeng deep fault zone, the NNE-striking Fuzhou-Anyuan deep fault zone, the NNE-trending Fengcheng-Dayu deep fault zone, as well as the NE-striking Yudu-Ningdu over thrust napped and sliding thrust structural systems, the approximately E W-trending Le'an-Nancheng over thrust napped structural systems etc. According to the distribution of known uranium mineralizations it is confirmed that close time-space relation exists between the uranium metallogenesis and variations of Moho surface, and over thrust napped structures, providing clues for locating concealed uranium deposits

  20. The upper mantle low resistivity layer's relationship with endogenous metallic ore and petroleum reservoir

    Science.gov (United States)

    Qing, Z.; Hui, F.; Piyuan, Y.; Li, L.; Fagen, P.; Yongzhen, Y.

    2013-12-01

    Based on the 1°x1° depth map of the low resistivity layers in upper mantle in China(1996), with the addition of magnetotelluric data from 1995 to 2010, we created the new map of the upper mantle low resistivity layers in China. The distribution of upper mantle low resistivity layers in China appears north-south zonation and west-east block, overall performance for the shallow in the east, deep in the west, shallow in the north and deep in the south. The depth of the upper mantle low resistivity layers can vary widely in China, the shallowest place which located in the northeast of Songliao basin is about 50 ~ 60 km; The deepest place is located in Changsha -Guilin area at where the deepest depth can be 230 km and the average depth can be 100 ~ 120 km. According to the distribution form of the the upper mantle low resistivity layers in China, 27 uplift zones have been divided. The extensional faults generated by the uplift of the upper mantle low resistivity layers is the main passageway of earth interior material and energy migrating to the upper crust, not only produce the hydrothermal deposit in petroliferous basin surrounding orogenic belt , but also brought oil and gas to the basins. Comparing the distribution of metallic ore with oil and gas fields in China, we have found that there are good correlations between the distribution of Mesozoic endogenous metallic ore deposit and the upper mantle low resistivity layers uplift and depression pattern in China, by about 70% of the metallic ore deposit are located in the the upper mantle low resistivity layers uplift areas, 20% of the metallic ore deposit are located in the gradient areas. In eastern China, most of the petroliferous basins are located in the upper mantle low resistivity layers areas, and most of the oil and gas field are above the uplift area or on the transitional zones of the edge; In Western China, most of the petroliferous basins are located in the mantle depression areas, the main oil and gas

  1. Deep Value

    DEFF Research Database (Denmark)

    Asness, Clifford S.; Liew, John M.; Pedersen, Lasse Heje

    We define "deep value" as episodes where the valuation spread between cheap and expensive securities is wide relative to its history. Examining deep value across global individual equities, equity index futures, currencies, and global bonds provides new evidence on competing theories for the valu....... Lastly, we find that deep value episodes tend to cluster and a deep value trading strategy generates excess returns not explained by traditional risk factors.......We define "deep value" as episodes where the valuation spread between cheap and expensive securities is wide relative to its history. Examining deep value across global individual equities, equity index futures, currencies, and global bonds provides new evidence on competing theories for the value...... premium. Following these episodes, the value strategy has (1) high average returns; (2) low market betas, but high betas to a global value factor; (3) deteriorating fundamentals; (4) negative news sentiment; (5) selling pressure; (6) increased limits to arbitrage; and (7) increased arbitrage activity...

  2. Stability of a radiative mantle in ITER

    International Nuclear Information System (INIS)

    Mahdavi, M.A.; Staebler, G.M.; Wood, R.D.; Whyte, D.G.; West, W.P.

    1996-12-01

    We report results of a study to evaluate the efficacy of various impurities for heat dispersal by a radiative mantle and radiative divertor(including SOL). We have derived a stability criterion for the mantle radiation which favors low Z impurities and low ratios of edge to core thermal conductivities. Since on the other hand the relative strength of boundary line radiation to core bremsstrahlung favors high Z impurities, we find that for the ITER physics phase argon is the best gaseous impurity for mantle radiation. For the engineering phase of ITER, more detailed analysis is needed to select between krypton and argon

  3. Os-He Isotope Systematics of Iceland Picrites: Evidence for a Deep Origin of the Iceland Plume

    Science.gov (United States)

    Brandon, Alan D.; Graham, David W.; Waight, Tod; Gautason, Bjarni

    2007-01-01

    Recent work on the origin of the Iceland hotspot suggests that it may result from upwelling upper mantle material rather than a deep plume. To constrain the depths of origins of Iceland mantle sources, Os and He isotope systematics were obtained on a suite picrites that span the compositional range observed within the neovolcanic zones.

  4. Hydrate prevention during formation test of gas in deep water; Prevencao de formacao de hidratos durante teste de formacao de poco de gas em lamina d'agua profunda

    Energy Technology Data Exchange (ETDEWEB)

    Rodrigues, Renato Cunha [PETROBRAS, Rio de Janeiro, RJ (Brazil)

    2008-07-01

    This work shows a scenery of formation test in deep water, for a well of gas, for which, there were made simulations with objective of identifying possible pairs of points (Pressure x Temperature), favorable to the hydrates formation. Besides, they were made comparisons of the values obtained in the simulation with the values registered during the formation test for the well Alfa of the field Beta. Of ownership of those information, we made an evaluation of the real needs of injection of inhibitors with intention of preventing the hydrates formation in each phase of the test. In an including way, the work has as objective recommends the volumes of hydrates inhibitors to be injected in each phase of a test of formation of well of gas in deep water, in way to assure that the operations are made without there is risk of hydrates formation. (author)

  5. Hydrates prevention during deep-water formation gas well test; Prevencao de formacao de hidratos durante teste de formacao de poco de gas em lamina d'agua profunda

    Energy Technology Data Exchange (ETDEWEB)

    Rodrigues, Renato Cunha [Unidade de Operacoes de Exploracao e Producao do Espirito Santo. Engenharia de Producao. Gerencia de Engenharia de Poco, ES (Brazil)], e-mail: renatocr@petrobras.com.br; Freitas, Alexandre Mussumeci Valim de [Centro de Pesquisas da Petrobras (CENPES). Gerencia de Tecnologia de Elevacao e Escoamento da Producao (Brazil)], e-mail: amfreitas@petrobras.com.br; Nishimura, Nelson Satiro [E and P Engenharia de Producao. Reservas e Reservatorios. Gerencia de Avaliacao de Reservatorios (Brazil)], e-mail: nishimura@petrobras.com.br

    2010-06-15

    This study examines the situation of a deep water formation test for a gas well in which simulations were made to identify possible pairs of points (Pressure versus Temperature), favorable to hydrate formation. Furthermore, the values obtained in the simulation were compared with the values registered during the formation test for the Alfa well in the Beta Field. With this information, an evaluation was made of the necessity to inject inhibitors intended to prevent hydrate formation in each test phase. In a wider sense, the study's objective was to recommend the volumes of hydrate inhibitors to be injected in each phase of a deep water formation test of a gas well to assure the operation be done without the risk of hydrate formation. (author)

  6. Waveform inversion of mantle Love waves - The Born seismogram approach

    Science.gov (United States)

    Tanimoto, T.

    1984-01-01

    Normal mode theory, extended to the slightly laterally heterogeneous earth by the first-order Born approximation, is applied to the waveform inversion of mantle Love waves (200-500 sec) for the earth's lateral heterogeneity at l = 2 and a spherically symmetric anelasticity (Q sub mu) structure. The data are from the Global Digital Seismograph Network (GDSN). The l = 2 pattern is very similar to the results of other studies that used either different methods, such as phase velocity measurements and multiplet location measurements, or a different data set, such as mantle Rayleigh waves from different instruments. The results are carefully analyzed for variance reduction and are most naturally explained by heterogeneity in the upper 420 km. Because of the poor resolution of the data set for the deep interior, however, a fairly large heterogeneity in the transition zones, of the order of up to 3.5 percent in shear wave velocity, is allowed. It is noteworthy that Love waves of this period range can not constrain the structure below 420 km and thus any model presented by similar studies below this depth are likely to be constrained by Rayleigh waves (spheroidal modes) only.

  7. Waveform inversion of mantle Love waves: The born seismogram approach

    Science.gov (United States)

    Tanimoto, T.

    1983-01-01

    Normal mode theory, extended to the slightly laterally heterogeneous Earth by the first-order Born approximation, is applied to the waveform inversion of mantle Love waves (200-500 sec) for the Earth's lateral heterogeneity at l=2 and a spherically symmetric anelasticity (Q sub mu) structure. The data are from the Global Digital Seismograph Network (GDSN). The l=2 pattern is very similar to the results of other studies that used either different methods, such as phase velocity measurements and multiplet location measurements, or a different data set, such as mantle Rayleigh waves from different instruments. The results are carefully analyzed for variance reduction and are most naturally explained by heterogeneity in the upper 420 km. Because of the poor resolution of the data set for the deep interior, however, a fairly large heterogeneity in the transition zones, of the order of up to 3.5% in shear wave velocity, is allowed. It is noteworthy that Love waves of this period range can not constrain the structure below 420 km and thus any model presented by similar studies below this depth are likely to be constrained by Rayleigh waves (spheroidal modes) only.

  8. Teaching the Mantle Plumes Debate

    Science.gov (United States)

    Foulger, G. R.

    2010-12-01

    There is an ongoing debate regarding whether or not mantle plumes exist. This debate has highlighted a number of issues regarding how Earth science is currently practised, and how this feeds into approaches toward teaching students. The plume model is an hypothesis, not a proven fact. And yet many researchers assume a priori that plumes exist. This assumption feeds into teaching. That the plume model is unproven, and that many practising researchers are skeptical, may be at best only mentioned in passing to students, with most teachers assuming that plumes are proven to exist. There is typically little emphasis, in particular in undergraduate teaching, that the origin of melting anomalies is currently uncertain and that scientists do not know all the answers. Little encouragement is given to students to become involved in the debate and to consider the pros and cons for themselves. Typically teachers take the approach that “an answer” (or even “the answer”) must be taught to students. Such a pedagogic approach misses an excellent opportunity to allow students to participate in an important ongoing debate in Earth sciences. It also misses the opportunity to illustrate to students several critical aspects regarding correct application of the scientific method. The scientific method involves attempting to disprove hypotheses, not to prove them. A priori assumptions should be kept uppermost in mind and reconsidered at all stages. Multiple working hypotheses should be entertained. The predictions of a hypothesis should be tested, and unpredicted observations taken as weakening the original hypothesis. Hypotheses should not be endlessly adapted to fit unexpected observations. The difficulty with pedagogic treatment of the mantle plumes debate highlights a general uncertainty about how to teach issues in Earth science that are not yet resolved with certainty. It also represents a missed opportunity to let students experience how scientific theories evolve, warts

  9. 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

    - The flow structure in vertical mantle heat exchangers was investigated using a full-scale tank designed to facilitate flow visualisation. The flow structure and velocities in the mantle were measured using a particle Image Velocimetry (PIV) system. A CFD simulation model of vertical mantle heat...... 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...

  10. 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...

  11. 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.

  12. Big mantle wedge, anisotropy, slabs and earthquakes beneath the Japan Sea

    Science.gov (United States)

    Zhao, Dapeng

    2017-09-01

    The Japan Sea is a part of the western Pacific trench-arc-backarc system and has a complex bathymetry and intense seismic activities in the crust and upper mantle. Local seismic tomography revealed strong lateral heterogeneities in the crust and uppermost mantle beneath the eastern margin of the Japan Sea, which was determined using P and S wave arrival times of suboceanic earthquakes relocated precisely with sP depth phases. Ambient-noise tomography revealed a thin crust and a thin lithosphere beneath the Japan Sea and significant low-velocity (low-V) anomalies in the shallow mantle beneath the western and eastern margins of the Japan Sea. Observations with ocean-bottom seismometers and electromagnetometers revealed low-V and high-conductivity anomalies at depths of 200-300 km in the big mantle wedge (BMW) above the subducting Pacific slab, and the anomalies are connected with the low-V zone in the normal mantle wedge beneath NE Japan, suggesting that both shallow and deep slab dehydrations occur and contribute to the arc and back-arc magmatism. The Pacific slab has a simple geometry beneath the Japan Sea, and earthquakes occur actively in the slab down to a depth of ∼600 km beneath the NE Asian margin. Teleseismic P and S wave tomography has revealed that the Philippine Sea plate has subducted aseismically down to the mantle transition zone (MTZ, 410-660 km) depths beneath the southern Japan Sea and the Tsushima Strait, and a slab window is revealed within the aseismic Philippine Sea slab. Seismic anisotropy tomography revealed a NW-SE fast-velocity direction in the BMW, which reflects corner flows induced by the fast deep subduction of the Pacific slab. Large deep earthquakes (M > 7.0; depth > 500 km) occur frequently beneath the Japan Sea western margin, which may be related to the formation of the Changbai and Ulleung intraplate volcanoes. A metastable olivine wedge is revealed within the cold core of the Pacific slab at the MTZ depth, which may be related

  13. Mantle flow influence on subduction evolution

    Science.gov (United States)

    Chertova, Maria V.; Spakman, Wim; Steinberger, Bernhard

    2018-05-01

    The impact of remotely forced mantle flow on regional subduction evolution is largely unexplored. Here we investigate this by means of 3D thermo-mechanical numerical modeling using a regional modeling domain. We start with simplified models consisting of a 600 km (or 1400 km) wide subducting plate surrounded by other plates. Mantle inflow of ∼3 cm/yr is prescribed during 25 Myr of slab evolution on a subset of the domain boundaries while the other side boundaries are open. Our experiments show that the influence of imposed mantle flow on subduction evolution is the least for trench-perpendicular mantle inflow from either the back or front of the slab leading to 10-50 km changes in slab morphology and trench position while no strong slab dip changes were observed, as compared to a reference model with no imposed mantle inflow. In experiments with trench-oblique mantle inflow we notice larger effects of slab bending and slab translation of the order of 100-200 km. Lastly, we investigate how subduction in the western Mediterranean region is influenced by remotely excited mantle flow that is computed by back-advection of a temperature and density model scaled from a global seismic tomography model. After 35 Myr of subduction evolution we find 10-50 km changes in slab position and slab morphology and a slight change in overall slab tilt. Our study shows that remotely forced mantle flow leads to secondary effects on slab evolution as compared to slab buoyancy and plate motion. Still these secondary effects occur on scales, 10-50 km, typical for the large-scale deformation of the overlying crust and thus may still be of large importance for understanding geological evolution.

  14. Nanodiamond finding in the hyblean shallow mantle xenoliths.

    Science.gov (United States)

    Simakov, S K; Kouchi, A; Mel'nik, N N; Scribano, V; Kimura, Y; Hama, T; Suzuki, N; Saito, H; Yoshizawa, T

    2015-06-01

    Most of Earth's diamonds are connected with deep-seated mantle rocks; however, in recent years, μm-sized diamonds have been found in shallower metamorphic rocks, and the process of shallow-seated diamond formation has become a hotly debated topic. Nanodiamonds occur mainly in chondrite meteorites associated with organic matter and water. They can be synthesized in the stability field of graphite from organic compounds under hydrothermal conditions. Similar physicochemical conditions occur in serpentinite-hosted hydrothermal systems. Herein, we report the first finding of nanodiamonds, primarily of 6 and 10 nm, in Hyblean asphaltene-bearing serpentinite xenoliths (Sicily, Italy). The discovery was made by electron microscopy observations coupled with Raman spectroscopy analyses. The finding reveals new aspects of carbon speciation and diamond formation in shallow crustal settings. Nanodiamonds can grow during the hydrothermal alteration of ultramafic rocks, as well as during the lithogenesis of sediments bearing organic matter.

  15. Deep frying

    NARCIS (Netherlands)

    Koerten, van K.N.

    2016-01-01

    Deep frying is one of the most used methods in the food processing industry. Though practically any food can be fried, French fries are probably the most well-known deep fried products. The popularity of French fries stems from their unique taste and texture, a crispy outside with a mealy soft

  16. Deep learning

    CERN Document Server

    Goodfellow, Ian; Courville, Aaron

    2016-01-01

    Deep learning is a form of machine learning that enables computers to learn from experience and understand the world in terms of a hierarchy of concepts. Because the computer gathers knowledge from experience, there is no need for a human computer operator to formally specify all the knowledge that the computer needs. The hierarchy of concepts allows the computer to learn complicated concepts by building them out of simpler ones; a graph of these hierarchies would be many layers deep. This book introduces a broad range of topics in deep learning. The text offers mathematical and conceptual background, covering relevant concepts in linear algebra, probability theory and information theory, numerical computation, and machine learning. It describes deep learning techniques used by practitioners in industry, including deep feedforward networks, regularization, optimization algorithms, convolutional networks, sequence modeling, and practical methodology; and it surveys such applications as natural language proces...

  17. Influence of a West Antarctic mantle plume on ice sheet basal conditions

    Science.gov (United States)

    Seroussi, Helene; Ivins, Erik R.; Wiens, Douglas A.; Bondzio, Johannes

    2017-09-01

    The possibility that a deep mantle plume manifests Pliocene and Quaternary volcanism and potential elevated heat flux in West Antarctica has been studied for more than 30 years. Recent seismic images support the plume hypothesis as the cause of Marie Byrd Land (MBL) volcanism and geophysical structure. Mantle plumes may more than double the geothermal heat flux above nominal continental values. A dearth of in situ ice sheet basal data exists that samples the heat flux. Consequently, we examine a realistic distribution of heat flux associated with a possible late Cenozoic mantle plume in West Antarctica and explore its impact on thermal and melt conditions at the ice sheet base. We use a simple analytical mantle plume parameterization to produce geothermal heat flux at the base of the ice sheet. The three-dimensional ice flow model includes an enthalpy framework and full-Stokes stress balance. As both the putative plume location and extent are uncertain, we perform broadly scoped experiments to characterize the impact of the plume on geothermal heat flux and ice sheet basal conditions. The experiments show that mantle plumes have an important local impact on the ice sheet, with basal melting rates reaching several centimeters per year directly above the hotspot. In order to be consistent with observations of basal hydrology in MBL, the upper bound on the plume-derived geothermal heat flux is 150 mW/m2. In contrast, the active lake system of the lower part of Whillans Ice Stream suggests a widespread anomalous mantle heat flux, linked to a rift source.

  18. Teaching machines to find mantle composition

    Science.gov (United States)

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

    2017-04-01

    The composition of the mantle affects many geodynamical processes by altering factors such as the density, the location of phase changes, and melting temperature. The inferences we make about mantle composition also determine how we interpret the changes in velocity, reflections, attenuation and scattering seen by seismologists. However, the bulk composition of the mantle is very poorly constrained. Inferences are made from meteorite samples, rock samples from the Earth and inferences made from geophysical data. All of these approaches require significant assumptions and the inferences made are subject to large uncertainties. Here we present a new method for inferring mantle composition, based on pattern recognition machine learning, which uses large scale in situ observations of the mantle to make fully probabilistic inferences of composition for convection simulations. Our method has an advantage over other petrological approaches because we use large scale geophysical observations. This means that we average over much greater length scales and do not need to rely on extrapolating from localised samples of the mantle or planetary disk. Another major advantage of our method is that it is fully probabilistic. This allows us to include all of the uncertainties inherent in the inference process, giving us far more information about the reliability of the result than other methods. Finally our method includes the impact of composition on mantle convection. This allows us to make much more precise inferences from geophysical data than other geophysical approaches, which attempt to invert one observation with no consideration of the relationship between convection and composition. We use a sampling based inversion method, using hundreds of convection simulations run using StagYY with self consistent mineral physics properties calculated using the PerpleX package. The observations from these simulations are used to train a neural network to make a probabilistic inference

  19. Partial delamination of continental mantle lithosphere, uplift-related crust mantle decoupling, volcanism and basin formation: a new model for the Pliocene Quaternary evolution of the southern East-Carpathians, Romania

    Science.gov (United States)

    Chalot-Prat, F.; Girbacea, R.

    2000-11-01

    A geodynamic model is proposed for the Mid-Miocene to Quaternary evolution of the southern East-Carpathians in order to explain the relationships between shallow and deep geological phenomena that occurred synchronously during late-collision tectonics. In this area, an active volcanic zone cross-cuts since 2 My the suture between the overriding Tisza-Dacia and subducting European continental plates. Mafic calc-alkaline and alkaline magmas (south Harghita and Persani volcanoes) erupted contemporaneously. These magmas were supplied by partial melting of the mantle lithosphere of the subducting, and not of the overriding, plate. In an effort to decipher this geodynamically a-typical setting of magma generation, the spatial and temporal distribution of shallow and deep phenomena was successively examined in order to establish the degree of their interdependence. Our model indicates that intra-mantle delamination of the subducting European plate is the principal cause of a succession of events. It caused upwelling of the hot asthenosphere below a thinned continental lithosphere of the Carpathians, inducing the uplift of the lithosphere and its internal decoupling at the Moho level by isostatic and mostly thermal effects. During this uplift, the crust deformed flexurally whilst the mantle deformed in a ductile way. This triggered decompressional partial melting of the uppermost mantle lithosphere. Flexural deformation of the crust induced its fracturing, allowing for the rapid ascent of magmas to the surface, as well as reactivation of an older detachment horizon at the base of the Carpathian nappe stack above which the Brasov, Ciuc and Gheorghieni hinterland basins formed by extension and gravity spreading. The rapid subsidence of the Focsani foreland basin is controlled by the load exerted on the lithosphere by the delaminated mantle slab that is still attached to it. In this model, crust-mantle decoupling, magma genesis and volcanism, local near-surface hinterland

  20. Xe isotopic constraints on cycling of deep Earth volatiles

    Science.gov (United States)

    Parai, R.; Mukhopadhyay, S.

    2017-12-01

    The modern deep Earth volatile budget reflects primordial volatiles delivered during accretion, radiogenic ingrowth of volatile species (e.g., 40Ar produced by 40K decay), outgassing in association with mantle processing, and regassing via subduction. The noble gases are unique volatile tracers in that they are chemically inert, but are thought to be trapped within hydrous alteration phases in downwelling lithologies. Noble gases thus provide a tracer of volatile transport between the deep Earth and surface reservoirs. Constraints on the fluxes of noble gases between deep Earth and surface reservoirs over time can accordingly be used to provide insight into temperature conditions at subduction zones, limits on volatile cycling, and the evolving distribution of major volatile species in terrestrial reservoirs over time. Xe isotope systematics in mantle-derived rocks show that 80-90% of the mantle Xe budget is derived from recycling of atmospheric Xe, indicating that atmospheric Xe is retained in subducting slabs beyond depths of magma generation in subduction zones over Earth history. We present an integrated model of Xe cycling between the mantle and atmosphere in association with mantle processing over Earth history. We test a wide variety of outgassing and regassing rates and take the evolution of the atmospheric Xe isotopic composition [e.g., 1] into account. Models in which the deep Earth transitions from a net outgassing to net regassing regime best satisfy Xe isotopic constraints from mantle-derived rocks [2-6]. [1] Avice et al., 2017; Nature Communications, 8; [2] Mukhopadhyay, 2012, Nature 486, 101-104; [3] Parai et al., 2012, EPSL 359-360, 227-239; [4] Parai and Mukhopadhay, 2015, G-cubed 16, 719-735; [5] Peto et al., 2013, EPSL 369-370, 13-23; [6] Tucker et al., 2012, EPSL 355-356, 244-254.

  1. Deep Habits

    OpenAIRE

    Morten O. Ravn; Stephanie Schmitt-Grohe

    2004-01-01

    This paper generalizes the standard habit formation model to an environment in which agents form habits over individual varieties of goods as opposed to over a composite consumption good. We refer to this preference specification as ‘deep habit formation’. Under deep habits, the demand function faced by individual producers depends on past sales. This feature is typically assumed ad-hoc in customer market and brand switching cost models. A central result of the paper is that deep habits giv...

  2. Lithosphere erosion atop mantle plumes

    Science.gov (United States)

    Agrusta, R.; Arcay, D.; Tommasi, A.

    2012-12-01

    Mantle plumes are traditionally proposed to play an important role in lithosphere erosion. Seismic images beneath Hawaii and Cape Verde show a lithosphere-asthenosphere-boundary (LAB) up to 50 km shallower than the surroundings. However, numerical models show that unless the plate is stationary the thermo-mechanical erosion of the lithosphere does not exceed 30 km. We use 2D petrological-thermo-mechanical numerical models based on a finite-difference method on a staggered grid and marker in cell method to study the role of partial melting on the plume-lithosphere interaction. A homogeneous peridotite composition with a Newtonian temperature- and pressure-dependent viscosity is used to simulate both the plate and the convective mantle. A constant velocity, ranging from 5 to 12.5 cm/yr, is imposed at the top of the plate. Plumes are created by imposing a thermal anomaly of 150 to 350 K on a 50 km wide domain at the base of the model (700 km depth); the plate right above the thermal anomaly is 40 Myr old. Partial melting is modeled using batch-melting solidus and liquidus in anhydrous conditions. We model the progressive depletion of peridotite and its effect on partial melting by assuming that the melting degree only strictly increases through time. Melt is accumulated until a porosity threshold is reached and the melt in excess is then extracted. The rheology of the partially molten peridotite is determined using viscous constitutive relationship based on a contiguity model, which enables to take into account the effects of grain-scale melt distribution. Above a threshold of 1%, melt is instantaneously extracted. The density varies as a function of partial melting degree and extraction. Besides, we analyze the kinematics of the plume as it impacts a moving plate, the dynamics of time-dependent small-scale convection (SSC) instabilities developing in the low-viscosity layer formed by spreading of hot plume material at the lithosphere base, and the resulting thermal

  3. Mantle strength of the San Andreas fault system and the role of mantle-crust feedbacks

    NARCIS (Netherlands)

    Chatzaras, V.; Tikoff, B.; Newman, J.; Withers, A.C.; Drury, M.R.

    2015-01-01

    In lithospheric-scale strike-slip fault zones, upper crustal strength is well constrained from borehole observations and fault rock deformation experiments, but mantle strength is less well known. Using peridotite xenoliths, we show that the upper mantle below the San Andreas fault system

  4. Nature of the uppermost mantle below the Porcupine Basin, offshore Ireland: new insights from seismic refraction and gravity data modeling

    Science.gov (United States)

    Prada, M.; Watremez, L.; Chen, C.; O'Reilly, B.; Minshull, T. A.; Reston, T. J.; Wagner, G.; Gaw, V.; Klaeschen, D.; Shannon, P.

    2015-12-01

    The Porcupine Basin is a tongue-shaped basin SW of Ireland formed during the opening of the North Atlantic Ocean. Its history of sedimentation reveals several rifting and subsidence phases during the Late Paleozoic and Cenozoic, with a particular major rift phase occurring in Late Jurassic-Early Cretaceous times. Previous work, focused on seismic and gravity data, suggest the presence of major crustal faulting and uppermost mantle serpentinization in the basin. Serpentinization is a key factor in lithospheric extension since it reduces the strength of mantle rocks, and hence, influences the tectonics of the lithosphere. Besides reducing the seismic velocity of the rock, serpentinization decreases mantle rock density favoring isostatic rebound and basin uplift, thus affecting the tectonic and thermal evolution of the basin. Here we characterize the deep structure of the Porcupine Basin from wide-angle seismic (WAS) and gravity data, with especial emphasis on the nature of the underlying mantle. The WAS data used were acquired along a 300 km long transect across the northern region of the basin. We used a travel time inversion method to model the data and obtain a P-wave velocity (Vp) model of the crust and uppermost mantle, together with the geometry of the main geological interfaces. The crustal structure along the model reveals a maximum stretching factor of ~5-6. These values are well within the range of crustal extension at which the crust becomes entirely brittle allowing the formation of major crustal faulting and serpentinization of the mantle. To further constrain the seismic structure and hence the nature of the mantle we assess the Vp uncertainty of the model by means of a Monte Carlo analysis and perform gravity modeling to test different interpretations regarding mantle rock nature. This project is funded by the Irish Shelf Petroleum Studies Group (ISPSG) of the Irish Petroleum Infrastructure Programme Group 4.

  5. Global Cycling of Carbon Constrained by Partial Melting Experiments of Carbonated Mantle Peridotite and Eclogite

    Science.gov (United States)

    Dasgupta, R.; Hirschmann, M. M.; Withers, A. C.

    2005-12-01

    The mass of carbon stored in the mantle exceeds that in all other Earth's reservoirs combined1 and large fluxes of carbon are cycled into and out of the mantle via subduction and volcanic emission. Outgassing of CO2 from the mantle has a critical influence on Earth's climate for time scales of 108-109 yr1. The residence time for carbon in the mantle is thought to exceed the age of the Earth1,2, but it could be significantly less owing to pervasive deep melting beneath oceanic ridges. The chief flux of subducted carbon is via carbonate in altered ocean-floor basalts, which survives dehydration during subduction. Because solidi of carbonated eclogite remain hotter than average subduction geotherms at least up to transition zone3, significant subducted C is delivered to the deep Earth. In upwelling mantle, however, partial melting of carbonated eclogite releases calcio-dolomitic carbonatite melt at depths near ~400 km and metasomatically implants carbonate to surrounding peridotite. Thus, volcanic release of CO2 to basalt source regions is controlled by the solidus of carbonated peridotite. We conducted experiments with nominally anhydrous, carbonated garnet lherzolite (PERC: MixKLB-1+2.5 wt.% CO2) using Pt/C capsules in piston cylinder (3 GPa) and Walker-style multi-anvil presses (4 to 10 GPa) and between 1075-1500 °C. The stable near-solidus crystalline carbonate is dolomitess at 3 GPa and magnesitess from 4 to 10 GPa. Carbonate melt is stabilized at the solidus and crystalline carbonate disappears within 20-60°. The solidus increases from ≥1075 °C at 3 GPa to 1110-1140 °C at 4.1 GPa as the stable carbonate transforms from dolomitess to magnesitess. From 4.1 GPa, the solidus of PERC magnesite lherzolite increases to ~1500 °C at 10 GPa. In upwelling mantle the solidus of carbonated lherzolite is ~100-200 km shallower than that of eclogite+CO2, but beneath oceanic ridges, initial melting occurs as deep as 300-330 km. For peridotite with ~120-1200 ppm CO2, this

  6. The hottest lavas of the Phanerozoic and the survival of deep Archaean reservoirs

    Science.gov (United States)

    Trela, Jarek; Gazel, Esteban; Sobolev, Alexander V.; Moore, Lowell; Bizimis, Michael; Jicha, Brian; Batanova, Valentina G.

    2017-06-01

    Large igneous provinces and some hotspot volcanoes are thought to form above thermochemical anomalies known as mantle plumes. Petrologic investigations that support this model suggest that plume-derived melts originated at high mantle temperatures (greater than 1,500 °C) relative to those generated at ambient mid-ocean ridge conditions (about 1,350 °C). Earth's mantle has also cooled appreciably during its history and the temperatures of modern mantle derived melts are substantially lower than those produced during the Archaean (2.5 to 4.0 billion years ago), as recorded by komatiites (greater than 1,700 °C). Here we use geochemical analyses of the Tortugal lava suite to show that these Galapagos-Plume-related lavas, which formed 89 million years ago, record mantle temperatures as high as Archaean komatiites and about 400 °C hotter than the modern ambient mantle. These results are also supported by highly magnesian olivine phenocrysts and Al-in-olivine crystallization temperatures of 1,570 +/- 20 °C. As mantle plumes are chemically and thermally heterogeneous, we interpret these rocks as the result of melting the hot core of the plume head that produced the Caribbean large igneous province. Our results imply that a mantle reservoir as hot as those responsible for some Archaean lavas has survived eons of convection in the deep Earth and is still being tapped by mantle plumes.

  7. The mantle cells lymphoma: a proposed treatment

    International Nuclear Information System (INIS)

    Chavez Martinez, Marlene Elizabeth

    2012-01-01

    A literature review was performed on mantle cells lymphoma in the therapeutic schemes. The literature that has been used is published in journals of medicine specializing in hematology, oncology, radiation therapy, molecular biology and internal medicine. The literature review was performed to propose a scheme of treatment according to Costa Rica. Epigenetic alterations have been revealed in patients with mantle lymphoma on current researches. The mantle lymphoma pathology has been described in various forms of clinical and histological presentation, stressing the importance of detailing the different methods and diagnostic reports. Working groups have proposed and developed various chemotherapy regimens and concluded that CHOP alone is without effect in mantle cell lymphoma unlike R-hyper-CVAD, CHOP / DHAP, high-dose Ara-C. Researchers have tried to develop new treatments based vaccines, use of modified viruses, specific monoclonal antibodies. The classic treatment has been triple intrathecal therapy. The central nervous system has been one of the most momentous sites of mantle cell lymphoma infiltration because poorer patient prognosis [es

  8. Radiation doses from radioactivity in incandescent mantles

    International Nuclear Information System (INIS)

    1985-01-01

    Thorium nitrate is used in the production of incandescent mantles for gas lanterns. In this report dose estimates are given for internal and external exposure that result from the use of the incandescent mantles for gas lanterns. The collective, effective dose equivalent for all users of gas mantles is estimated to be about 100 Sv per annum in the Netherlands. For the population involved (ca. 700,000 persons) this is roughly equivalent to 5% to 10% of the collective dose equivalent associated with exposure to radiation from natural sources. The major contribution to dose estimates comes from inhalation of radium during burning of the mantles. A pessimistic approach results in individual dose estimates for inhalation of up to 0.2 mSv. Consideration of dose consequences in case of a fire in a storage department learns that it is necessary for emergency personnel to wear respirators. It is concluded that the uncontrolled removal of used gas mantles to the environment (soil) does not result in a significant contribution to environmental radiation exposure. (Auth.)

  9. Driving forces: Slab subduction and mantle convection

    Science.gov (United States)

    Hager, Bradford H.

    1988-01-01

    Mantle convection is the mechanism ultimately responsible for most geological activity at Earth's surface. To zeroth order, the lithosphere is the cold outer thermal boundary layer of the convecting mantle. Subduction of cold dense lithosphere provides tha major source of negative buoyancy driving mantle convection and, hence, surface tectonics. There are, however, importnat differences between plate tectonics and the more familiar convecting systems observed in the laboratory. Most important, the temperature dependence of the effective viscosity of mantle rocks makes the thermal boundary layer mechanically strong, leading to nearly rigid plates. This strength stabilizes the cold boundary layer against small amplitude perturbations and allows it to store substantial gravitational potential energy. Paradoxically, through going faults at subduction zones make the lithosphere there locally weak, allowing rapid convergence, unlike what is observed in laboratory experiments using fluids with temperature dependent viscosities. This bimodal strength distribution of the lithosphere distinguishes plate tectonics from simple convection experiments. In addition, Earth has a buoyant, relatively weak layer (the crust) occupying the upper part of the thermal boundary layer. Phase changes lead to extra sources of heat and bouyancy. These phenomena lead to observed richness of behavior of the plate tectonic style of mantle convection.

  10. Electromagnetic core-mantle coupling associated with changes in the geomagnetic dipole field

    International Nuclear Information System (INIS)

    Watanabe, Hidehumi; Yukutake, Takesi.

    1975-01-01

    On a shelluar earth model electromagnetic coupling between the mantle and the core is investigated when the geomagnetic dipole field changes its intensity. Besides electromagnetic interaction between the dipole change and the relative slip of the mantle to the core, coupling of the dipole change with shear motions within the core is considered. If, in the core, the dipole change is limited within a surface layer shallower than a few hundred kilometers, the electromagnetic interaction gives the same order of magnitudes and phases of mantle oscillation as suggested from observation for three different periods, 8000, 400 and 65 years, provided that the electrical conductivity of the bottom part of the mantle is 10 -9 to 10 -8 emu. It is shown that mean motion of the surface shells of the core thus calculated is compatible with the observed variations in the drift velocity of the geomagnetic secular change. Except for surface shells, those in the deep interior is confirmed to oscillate almost with the same angular velocity, like a rigid rotation, for all the periods. (auth.)

  11. Mantle plumes on Venus revisited

    Science.gov (United States)

    Kiefer, Walter S.

    1992-01-01

    The Equatorial Highlands of Venus consist of a series of quasicircular regions of high topography, rising up to about 5 km above the mean planetary radius. These highlands are strongly correlated with positive geoid anomalies, with a peak amplitude of 120 m at Atla Regio. Shield volcanism is observed at Beta, Eistla, Bell, and Atla Regiones and in the Hathor Mons-Innini Mons-Ushas Mons region of the southern hemisphere. Volcanos have also been mapped in Phoebe Regio and flood volcanism is observed in Ovda and Thetis Regiones. Extensional tectonism is also observed in Ovda and Thetis Regiones. Extensional tectonism is also observed in many of these regions. It is now widely accepted that at least Beta, Atla, Eistla, and Bell Regiones are the surface expressions of hot, rising mantel plumes. Upwelling plumes are consistent with both the volcanism and the extensional tectonism observed in these regions. The geoid anomalies and topography of these four regions show considerable variation. Peak geoid anomalies exceed 90 m at Beta and Atla, but are only 40 m at Eistla and 24 m at Bell. Similarly, the peak topography is greater at Beta and Atla than at Eistla and Bell. Such a range of values is not surprising because terrestrial hotspot swells also have a side range of geoid anomalies and topographic uplifts. Kiefer and Hager used cylindrical axisymmetric, steady-state convection calculations to show that mantle plumes can quantitatively account for both the amplitude and the shape of the long-wavelength geoid and topography at Beta and Atla. In these models, most of the topography of these highlands is due to uplift by the vertical normal stress associated with the rising plume. Additional topography may also be present due to crustal thickening by volcanism and crustal thinning by rifting. Smrekar and Phillips have also considered the geoid and topography of plumes on Venus, but they restricted themselves to considering only the geoid-topography ratio and did not

  12. Thermal Conductivity of Lower Mantle Minerals and Heat Flux Across the Core-Mantle Boundary

    Science.gov (United States)

    Bennett, C.; Rainey, E.; Kavner, A.

    2014-12-01

    The thermal conductivity properties of the minerals comprising the Earth's lowermost mantle control the core-mantle boundary heat flux, and are therefore critical properties for determining the thermal state and evolution of the Earth's interior. Here we present measurements of the thermal conductivity of lower mantle oxides and silicates as a function of pressure, temperature, and iron content determined in the laser-heated diamond anvil cell using a combination of measurements and 3-D modeling. Our models and measurements demonstrate that the measured steady-state temperature and its increase with increasing laser power depend on the sample thermal conductivity as well as the experimental geometry, enabling measurements of the pressure- and temperature- dependence of lattice thermal conductivity in the laser-heated diamond anvil cell. We applied this technique to iron-bearing silicate perovskites and MgO at lower mantle pressure and temperature conditions. For MgO, we determine the increase in thermal conductivity k with density ρ to be ∂lnk/∂lnρ=4.7±0.6, which is in agreement with results obtained using other experimental and computational techniques. For (Mg0.8,Fe0.2)SiO3 perovskite, we find ∂lnk/∂lnρ=2.9±0.6. We use these values in combination with independent computational and experimental results to determine thermal conductivity of lower mantle minerals up to core-mantle boundary conditions. We combine the mineralogical thermal conductivity estimates in a composite model and include an estimate for the radiative contribution to thermal conductivity. Our new value of the thermal conductivity of the lowermost mantle is ~5-6 W/m/K and is sensitive to the details of the lower mantle assemblage, but is relatively insensitive to pressure and temperature. We combine our mantle thermal conductivity with models for the lower mantle boundary layer to generate a series of two-dimensional maps of core-mantle boundary heat flux, which emphasize the

  13. Conjecture with water and rheological control for subducting slab in the mantle transition zone

    Directory of Open Access Journals (Sweden)

    Fumiko Tajima

    2015-01-01

    Full Text Available Seismic observations have shown structural variation near the base of the mantle transition zone (MTZ where subducted cold slabs, as visualized with high seismic speed anomalies (HSSAs, flatten to form stagnant slabs or sink further into the lower mantle. The different slab behaviors were also accompanied by variation of the “660 km” discontinuity depths and low viscosity layers (LVLs beneath the MTZ that are suggested by geoid inversion studies. We address that deep water transport by subducted slabs and dehydration from hydrous slabs could affect the physical properties of mantle minerals and govern slab dynamics. A systematic series of three-dimensional numerical simulation has been conducted to examine the effects of viscosity reduction or contrast between slab materials on slab behaviors near the base of the MTZ. We found that the viscosity reduction of subducted crustal material leads to a separation of crustal material from the slab main body and its transient stagnation in the MTZ. The once trapped crustal materials in the MTZ eventually sink into the lower mantle within 20–30 My from the start of the plate subduction. The results suggest crustal material recycle in the whole mantle that is consistent with evidence from mantle geochemistry as opposed to a two-layer mantle convection model. Because of the smaller capacity of water content in lower mantle minerals than in MTZ minerals, dehydration should occur at the phase transformation depth, ∼660 km. The variation of the discontinuity depths and highly localized low seismic speed anomaly (LSSA zones observed from seismic P waveforms in a relatively high frequency band (∼1 Hz support the hypothesis of dehydration from hydrous slabs at the phase boundary. The LSSAs which correspond to dehydration induced fluids are likely to be very local, given very small hydrogen (H+ diffusivity associated with subducted slabs. The image of such local LSSA zones embedded in HSSAs may not

  14. Mantle to surface degassing of alkalic magmas at Erebus volcano, Antarctica

    Science.gov (United States)

    Oppenheimer, C.; Moretti, R.; Kyle, P.R.; Eschenbacher, A.; Lowenstern, J. B.; Hervig, R.L.; Dunbar, N.W.

    2011-01-01

    Continental intraplate volcanoes, such as Erebus volcano, Antarctica, are associated with extensional tectonics, mantle upwelling and high heat flow. Typically, erupted magmas are alkaline and rich in volatiles (especially CO2), inherited from low degrees of partial melting of mantle sources. We examine the degassing of the magmatic system at Erebus volcano using melt inclusion data and high temporal resolution open-path Fourier transform infrared (FTIR) spectroscopic measurements of gas emissions from the active lava lake. Remarkably different gas signatures are associated with passive and explosive gas emissions, representative of volatile contents and redox conditions that reveal contrasting shallow and deep degassing sources. We show that this unexpected degassing signature provides a unique probe for magma differentiation and transfer of CO2-rich oxidised fluids from the mantle to the surface, and evaluate how these processes operate in time and space. Extensive crystallisation driven by CO2 fluxing is responsible for isobaric fractionation of parental basanite magmas close to their source depth. Magma deeper than 4kbar equilibrates under vapour-buffered conditions. At shallower depths, CO2-rich fluids accumulate and are then released either via convection-driven, open-system gas loss or as closed-system slugs that ascend and result in Strombolian eruptions in the lava lake. The open-system gases have a reduced state (below the QFM buffer) whereas the closed-system gases preserve their deep oxidised signatures (close to the NNO buffer). ?? 2011 Elsevier B.V.

  15. Geothermal constraints on Emeishan mantle plume magmatism: paleotemperature reconstruction of the Sichuan Basin, SW China

    Science.gov (United States)

    Zhu, Chuanqing; Hu, Shengbiao; Qiu, Nansheng; Jiang, Qiang; Rao, Song; Liu, Shuai

    2018-01-01

    The Middle-Late Permian Emeishan Large Igneous Province (ELIP) in southwestern China represents a classic example of a mantle plume origin. To constrain the thermal regime of the ELIP and contemporaneous magmatic activity in the northeastern Sichuan Basin, maximum paleotemperature profiles of deep boreholes were reconstructed using vitrinite reflectance (Ro) and apatite fission track data. Two heating patterns were identified: (1) heating of the overlying lithosphere by magma storage regions and/or magmatic activity related to the mantle plume, which resulted in a relatively strong geothermal field and (2) direct heating of country rock by stock or basalt. Borehole Ro data and reconstructed maximum paleotemperature profiles near the ELIP exhibit abrupt tectonothermal unconformities between the Middle and Late Permian. The profiles in the lower subsections (i.e., pre-Middle Permian) exhibited significantly higher gradients than those in the upper subsections. Distal to the basalt province, high paleo-geotemperatures (hereafter, paleotemperatures) were inferred, despite deformation of the paleogeothermal curve due to deep faults and igneous rocks within the boreholes. In contrast, Ro profiles from boreholes without igneous rocks (i.e., Late Permian) contained no break at the unconformity. Paleotemperature gradients of the upper and the lower subsections and erosion at the Middle/Late Permian unconformity revealed variations in the thermal regime. The inferred spatial distribution of the paleothermal regime and the erosion magnitudes record the magmatic and tectonic-thermal response to the Emeishan mantle plume.

  16. Variable Azimuthal Anisotropy in Earth's Lowermost Mantle

    Science.gov (United States)

    Garnero, Edward J.; Maupin, Valérie; Lay, Thorne; Fouch, Matthew J.

    2004-10-01

    A persistent reversal in the expected polarity of the initiation of vertically polarized shear waves that graze the D'' layer (the layer at the boundary between the outer core and the lower mantle of Earth) in some regions starts at the arrival time of horizontally polarized shear waves. Full waveform modeling of the split shear waves for paths beneath the Caribbean requires azimuthal anisotropy at the base of the mantle. Models with laterally coherent patterns of transverse isotropy with the hexagonal symmetry axis of the mineral phases tilted from the vertical by as much as 20° are consistent with the data. Small-scale convection cells within the mantle above the D'' layer may cause the observed variations by inducing laterally variable crystallographic or shape-preferred orientation in minerals in the D'' layer.

  17. Deep sole burns in several participants in a traditional festival of the firewalking ceremony in Kee-lung, Taiwan--clinical experiences and prevention strategies.

    Science.gov (United States)

    Chang, Shun-Cheng; Hsu, Chih-Kang; Tzeng, Yuan-Sheng; Teng, Shou-Cheng; Fu, Ju-Peng; Dai, Niann-Tzyy; Chen, Shyi-Gen; Chen, Tim-Mo; Feng, Chun-Che

    2012-11-01

    Firewalking is a common Taoist cleansing ceremony in Taiwan, but burns associated with the practice have rarely been reported. We analyzed the patients with plantar burns from one firewalking ceremony. In one firewalking ceremony, 12 Taoist disciples suffered from contact burns to the soles of their feet while walking over burning coals. Eight of them had at least second-degree burns over areas larger than 1% of their total body surface areas (TBSAs). The age, sex, medical history, date of injury, time taken to traverse the fire pit, depth and TBSA of the burns, treatment, length of stay, and outcome were recorded and analyzed. Deep, disseminated second- to third-degree burns were noted and healing took as long as three weeks in some patients. Because disseminated hypertrophic scars form after burns, the soles involved regain much of their tensile strength while walking. The patients experienced only a few difficulties in their daily lives three months after injury. From our experience treating patients with deep disseminated second- to third-degree plantar burns caused by firewalking, we conclude that they should be treated conservatively, with secondary healing rather than a skin graft. Copyright © 2011 Elsevier Ltd and ISBI. All rights reserved.

  18. Plume Generation Zones (PGZs) at the Core-Mantle Boundary (CMB)

    Science.gov (United States)

    Burke, K. C.; Torsvik, T. H.; Smethurst, M. A.; Steinberger, B. M.

    2006-12-01

    We find (Torsvik et al., Geophys. J. Int., in press) that Large Igneous Province (LIP) eruption sites of the past 200 My when (1) rotated (using any one of five alternative reference frames) to the places that they occupied at their time of eruption and (2) being then projected vertically downward to the CMB come to lie close to the 1 % slow δ V_s margins of either the African or the Pacific Large Low Velocity Provinces (LLVPs of Lay 2005). More than 20 active hot spot volcanoes project down to the same narrowly defined regions. During the past 200 My plumes of deep mantle origin that have generated LIPs and major hotspot volcanoes at the Earth's surface appear to have come only from the margins at the CMB of either one or the other LLVP. The 1 % slow δ V_s contours at the CMB define Plume Generation Zones (PGZs). On present spatial resolution the Earth's two deep PGZs together occupy about 10 % of the surface area of the CMB. LIP and major hotspot sources correspondingly occur in two newly identified episodically and sporadically active "Rings of Fire", beneath about 10 % of the lithosphere. Our work confirms Morgan's (1971) suggestion that a population of plumes originates at the CMB. We here show that population to be sourced in the PGZs where three distinct volumes of the Earth's interior meet: (i) the outer core (ii) one or other of the two LLVPs and (iii) the seismically faster part of the deep mantle. The core, the LLVPs and the faster part of the deep mantle all appear to have played a part in one of more of: (i) generating plume material (ii) concentrating that material to form localized plumes within the PGZs and (iii) stimulating the sporadic, episodic, rapid and vertical rise of the plumes from the PGZs to the base of the lithosphere.

  19. Mixing properties of thermal convection in the earth's mantle

    NARCIS (Netherlands)

    Schmalzl, J.T.

    1996-01-01

    The structure of mantle convection will greatly influence the generation and the survival of compositional heterogeneities. Conversely, geochemical observations can be used to obtain information about heterogeneities in the mantle and then, with certain model assumptions, information about the

  20. OPTIMISATION OF MANTLE TANKS FOR LOW FLOW SOLAR HEATING SYSTEMS

    DEFF Research Database (Denmark)

    Shah, Louise Jivan; Furbo, Simon

    1996-01-01

    A model, describing the heat transfer coefficients in the mantle of a mantle tank has been developed. The model is validated by means of measurements with varying operational conditions for different designed mantle tanks. The model has been implemented in an existing detailed mathematical...... programme that simulates the thermal behaviour of low flow SDHW systems. The yearly thermal performance of low flow SDHW systems with different designed mantle tanks has been calculated. The influence of the mantle tank design on the thermal performance is investigated by means of the calculations...... with the programme and by means of tests of three SDHW systems with different designed mantle tanks. Based on the investigations design rules for mantle tanks are proposed. The model, describing the heat transfer coefficients in the mantle is approximate. In addition, the measurements have revealed...

  1. Formation of ridges in a stable lithosphere in mantle convection models with a viscoplastic rheology.

    Science.gov (United States)

    Rozel, A; Golabek, G J; Näf, R; Tackley, P J

    2015-06-28

    Numerical simulations of mantle convection with a viscoplastic rheology usually display mobile, episodic or stagnant lid regimes. In this study, we report a new convective regime in which a ridge can form without destabilizing the surrounding lithosphere or forming subduction zones. Using simulations in 2-D spherical annulus geometry, we show that a depth-dependent yield stress is sufficient to reach this ridge only regime. This regime occurs when the friction coefficient is close to the critical value between mobile lid and stagnant lid regimes. Maps of convective regime as a function of the parameters friction coefficients and depth dependence of viscosity are provided for both basal heating and mixed heating situations. The ridge only regime appears for both pure basal heating and mixed heating mode. For basal heating, this regime can occur for all vertical viscosity contrasts, while for mixed heating, a highly viscous deep mantle is required.

  2. Anisotropy in the deep Earth

    Science.gov (United States)

    Romanowicz, Barbara; Wenk, Hans-Rudolf

    2017-08-01

    Seismic anisotropy has been found in many regions of the Earth's interior. Its presence in the Earth's crust has been known since the 19th century, and is due in part to the alignment of anisotropic crystals in rocks, and in part to patterns in the distribution of fractures and pores. In the upper mantle, seismic anisotropy was discovered 50 years ago, and can be attributed for the most part, to the alignment of intrinsically anisotropic olivine crystals during large scale deformation associated with convection. There is some indication for anisotropy in the transition zone, particularly in the vicinity of subducted slabs. Here we focus on the deep Earth - the lower mantle and core, where anisotropy is not yet mapped in detail, nor is there consensus on its origin. Most of the lower mantle appears largely isotropic, except in the last 200-300 km, in the D″ region, where evidence for seismic anisotropy has been accumulating since the late 1980s, mostly from shear wave splitting measurements. Recently, a picture has been emerging, where strong anisotropy is associated with high shear velocities at the edges of the large low shear velocity provinces (LLSVPs) in the central Pacific and under Africa. These observations are consistent with being due to the presence of highly anisotropic MgSiO3 post-perovskite crystals, aligned during the deformation of slabs impinging on the core-mantle boundary, and upwelling flow within the LLSVPs. We also discuss mineral physics aspects such as ultrahigh pressure deformation experiments, first principles calculations to obtain information about elastic properties, and derivation of dislocation activity based on bonding characteristics. Polycrystal plasticity simulations can predict anisotropy but models are still highly idealized and neglect the complex microstructure of polyphase aggregates with strong and weak components. A promising direction for future progress in understanding the origin of seismic anisotropy in the deep mantle

  3. Rationale, design, and baseline findings from a pilot randomized trial of an IVR-Supported physical activity intervention for cancer prevention in the Deep South: The DIAL study

    Directory of Open Access Journals (Sweden)

    Dori Pekmezi

    2017-12-01

    Full Text Available Telephone-delivered interventions do not require frequent clinic visits, literacy, or costly technology and thus may represent promising approaches to promoting physical activity in the Deep South, a largely rural U.S. region, with generally lower physical activity, income, and education levels. Building on past Interactive Voice Response (IVR system-based HIV studies and extensive formative research (11 focus groups on physical activity intervention needs/preferences in the Deep South, the resulting IVR-supported physical activity intervention is now being tested in a randomized controlled trial with a waitlist control. The sample (n = 63 includes mostly obese (Mean BMI = 30.1 adults (Mean age = 43 years in Birmingham, AL. Both genders (55.6% male and African Americans (58.7% are well-represented. Most participants reported at least some college (92%, full time employment (63.5%, and household income <$50,000 per year (61.9%. Baseline physical activity (Mean = 39.6 min/week, SD = 56.4, self-efficacy, self-regulation, and social support were low. However, high physical activity enjoyment and outcome expectations bode well. Self-report physical activity was associated with physical activity enjoyment (r = 0.36 and social support (friends r = 0.25, p's < 0.05 at baseline. Consequently, these may be important variables to emphasize in our program. Depression and anxiety were negatively correlated with some early indicators of behavior change (e.g., physical activity self-regulation; r's = -0.43 and −0.46, respectively, p's < 0.01 and thus may require additional attention. Such technology-supported strategies have great potential to reach underserved populations and address physical activity-related health disparities in this region.

  4. Deep seismic profiling of the continents and their margins

    DEFF Research Database (Denmark)

    Ito, T.; Iwasaki, T.; Thybo, Hans

    2009-01-01

    Application of deep seismic methods to studies of the crust and lithospheric mantle receives considerable interest and the methods are constantly refined and new methods are developed, which allows the extension of studies to new subjects and regions. Deep seismic methods are applied to a long......, in many applications, the methods are used up-to their limits at the present technological state. Therefore, development of methods has high priority in the seismic community. This volume provides an overview of recent development of deep seismic techniques and their application to the imaging and probing...

  5. 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

    - The flow structure in vertical mantle heat exchangers was investigated using a full-scale tank designed to facilitate flow visualisation. The flow structure and velocities in the mantle were measured using a particle Image Velocimetry (PIV) system. A CFD simulation model of vertical mantle heat...

  6. The tungsten isotopic composition of the Earth's mantle before the terminal bombardment.

    Science.gov (United States)

    Willbold, Matthias; Elliott, Tim; Moorbath, Stephen

    2011-09-07

    Many precious, 'iron-loving' metals, such as gold, are surprisingly abundant in the accessible parts of the Earth, given the efficiency with which core formation should have removed them to the planet's deep interior. One explanation of their over-abundance is a 'late veneer'--a flux of meteorites added to the Earth after core formation as a 'terminal' bombardment that culminated in the cratering of the Moon. Some 3.8 billion-year-old rocks from Isua, Greenland, are derived from sources that retain an isotopic memory of events pre-dating this cataclysmic meteorite shower. These Isua samples thus provide a window on the composition of the Earth before such a late veneer and allow a direct test of its importance in modifying the composition of the planet. Using high-precision (less than 6 parts per million, 2 standard deviations) tungsten isotope analyses of these rocks, here we show that they have a isotopic tungsten ratio (182)W/(184)W that is significantly higher (about 13 parts per million) than modern terrestrial samples. This finding is in good agreement with the expected influence of a late veneer. We also show that alternative interpretations, such as partial remixing of a deep-mantle reservoir formed in the Hadean eon (more than four billion years ago) or core-mantle interaction, do not explain the W isotope data well. The decrease in mantle (182)W/(184)W occurs during the Archean eon (about four to three billion years ago), potentially on the same timescale as a notable decrease in (142)Nd/(144)Nd (refs 3 and 6). We speculate that both observations can be explained if late meteorite bombardment triggered the onset of the current style of mantle convection.

  7. The tungsten isotopic composition of the Earth's mantle before the terminal bombardment

    Science.gov (United States)

    Willbold, Matthias; Elliott, Tim; Moorbath, Stephen

    2011-09-01

    Many precious, `iron-loving' metals, such as gold, are surprisingly abundant in the accessible parts of the Earth, given the efficiency with which core formation should have removed them to the planet's deep interior. One explanation of their over-abundance is a `late veneer'--a flux of meteorites added to the Earth after core formation as a `terminal' bombardment that culminated in the cratering of the Moon. Some 3.8 billion-year-old rocks from Isua, Greenland, are derived from sources that retain an isotopic memory of events pre-dating this cataclysmic meteorite shower. These Isua samples thus provide a window on the composition of the Earth before such a late veneer and allow a direct test of its importance in modifying the composition of the planet. Using high-precision (less than 6 parts per million, 2 standard deviations) tungsten isotope analyses of these rocks, here we show that they have a isotopic tungsten ratio 182W/184W that is significantly higher (about 13 parts per million) than modern terrestrial samples. This finding is in good agreement with the expected influence of a late veneer. We also show that alternative interpretations, such as partial remixing of a deep-mantle reservoir formed in the Hadean eon (more than four billion years ago) or core-mantle interaction, do not explain the W isotope data well. The decrease in mantle 182W/184W occurs during the Archean eon (about four to three billion years ago), potentially on the same timescale as a notable decrease in 142Nd/144Nd (refs 3 and 6). We speculate that both observations can be explained if late meteorite bombardment triggered the onset of the current style of mantle convection.

  8. Hydrogen self-diffusion in single crystal olivine and electrical conductivity of the Earth's mantle.

    Science.gov (United States)

    Novella, Davide; Jacobsen, Benjamin; Weber, Peter K; Tyburczy, James A; Ryerson, Frederick J; Du Frane, Wyatt L

    2017-07-13

    Nominally anhydrous minerals formed deep in the mantle and transported to the Earth's surface contain tens to hundreds of ppm wt H 2 O, providing evidence for the presence of dissolved water in the Earth's interior. Even at these low concentrations, H 2 O greatly affects the physico-chemical properties of mantle materials, governing planetary dynamics and evolution. The diffusion of hydrogen (H) controls the transport of H 2 O in the Earth's upper mantle, but is not fully understood for olivine ((Mg, Fe) 2 SiO 4 ) the most abundant mineral in this region. Here we present new hydrogen self-diffusion coefficients in natural olivine single crystals that were determined at upper mantle conditions (2 GPa and 750-900 °C). Hydrogen self-diffusion is highly anisotropic, with values at 900 °C of 10 -10.9 , 10 -12.8 and 10 -11.9 m 2 /s along [100], [010] and [001] directions, respectively. Combined with the Nernst-Einstein relation, these diffusion results constrain the contribution of H to the electrical conductivity of olivine to be σ H  = 10 2.12 S/m·C H2O ·exp -187kJ/mol/(RT) . Comparisons between the model presented in this study and magnetotelluric measurements suggest that plausible H 2 O concentrations in the upper mantle (≤250 ppm wt) can account for high electrical conductivity values (10 -2 -10 -1  S/m) observed in the asthenosphere.

  9. Negative dynamic topography of the East European Craton: metasomatised cratonic lithosphere or mantle downwelling?

    Science.gov (United States)

    Artemieva, I. M.

    2010-12-01

    While most of the East European Craton lacks surface topography, the topography of its basement exceeds 20 km, the amplitude of topography undulations at the crustal base reaches almost 30 km with an amazing amplitude of ca. 50 km in variation in the thickness of the consolidated crust, and the amplitude of topography variations at the lithosphere-asthenosphere boundary exceeds 200 km. This paper examines the relative roles of the crust, the subcrustal lithosphere, and the dynamic support of the sublithospheric mantle in maintaining surface topography, using regional seismic data on the structure of the consolidated crust and the sedimentary cover, and thermal and large-scale seismic tomography data on the structure of the lithospheric mantle. The isostatic contribution of the crust to the surface topography of the East European Craton is almost independent of age (ca. 4.5 km) due to an interplay of age-dependent crustal and sedimentary thicknesses and lithospheric temperatures. On the contrary, the contribution of the subcrustal lithosphere to the topography strongly depends on the age, being slightly positive (+0.3+0.7 km) for the regions older than 1.6 Ga and negative (-0.5-1 km) for younger structures. This leads to age-dependent variations in the contribution of the sublithospheric mantle to the topography (residual, or dynamic topography). Positive dynamic topography at the cratonic margins, which exceeds 2 km in the Norwegian Caledonides and in the Urals, clearly links their on-going uplift with deep mantle processes. Negative residual topography beneath the Archean-Paleoproterozoic cratons (-1-2 km) indicates either smaller density deficit (ca. 0.9 per cent) in their subcrustal lithosphere than predicted by petrologic data or the presence of a strong downwelling in the mantle. Dynamic topography in the southern parts of the craton may be associated with the Peri-Tethys collisional tectonics. (Artemieva I.M., Global and Planetary Change, 2007, 58, 411-434).

  10. Global rates of mantle serpentinization and H2 release at oceanic transform faults

    Science.gov (United States)

    Ruepke, Lars; Hasenclever, Joerg

    2017-04-01

    The cycling of seawater through the ocean floor is the dominant mechanism of biogeochemical exchange between the solid earth and the global ocean. Crustal fluid flow appears to be typically associated with major seafloor structures, and oceanic transform faults (OTF) are one of the most striking yet poorly understood features of the global mid-ocean ridge systems. Fracture zones and transform faults have long been hypothesized to be sites of substantial biogeochemical exchange between the solid Earth and the global ocean. This is particularly interesting with regard to the ocean biome. Deep ocean ecosystems constitute 60% of it but their role in global ocean biogeochemical cycles is much overlooked. There is growing evidence that life is supported by chemosynthesis at hydrothermal vents but also in the crust, and therefore this may be a more abundant process than previously thought. In this context, the serpentine forming interaction between seawater and cold lithospheric mantle rocks is particularly interesting as it is also a mechanism of abiotic hydrogen and methane formation. Interestingly, a quantitative global assessment of mantle serpentinization at oceanic transform faults in the context of the biogeochemical exchange between the seafloor and the global ocean is still largely missing. Here we present the results of a set of 3-D thermo-mechanical model calculations that investigate mantle serpentinization at OTFs for the entire range of globally observed slip rates and fault lengths. These visco-plastic models predict the OTF thermal structure and the location of crustal-scale brittle deformation, which is a prerequisite for mantle serpentinization to occur. The results of these simulations are integrated with information on the global distribution of OTF lengths and slip rates yielding global estimates on mantle serpentinization and associated H2 release. We find that OTFs are potentially sites of intense crustal fluid flow and are in terms of H2 release

  11. Linking erosion history and mantle processes in southern Africa

    Science.gov (United States)

    Stanley, J. R.; Braun, J.; Flowers, R. M.; Baby, G.; Wildman, M.; Guillocheau, F.; Robin, C.; Beucher, R.; Brown, R. W.

    2017-12-01

    The large, low relief, high elevation plateau of southern Africa has been the focus of many studies, but there is still considerable debate about how it formed. Lack of tectonic convergence and crustal thickening suggests mantle dynamics play an important role in the evolution of topography there, but the time and specific mechanisms of topographic development are still contested. Many mantle mechanisms of topographic support have been suggested including dynamic topography associated with either deep or shallow mantle thermal anomalies, thermochemical modification of the lithosphere, and plume tails related to Mesozoic magmatic activity. These mechanisms predict different timing and patterns of surface uplift such that better constraints on the uplift history have the potential to constrain the nature of the source of topographic support. Here we test several of these geodynamic hypotheses using a landscape evolution model that is used to predict the erosional response to surface uplift. Several recent studies have provided a clearer picture of the erosion history of the plateau surface and margins using low temperature thermochronology and the geometries of the surrounding offshore depositional systems. Model results are directly compared with these data. We use an inversion method (the Neighborhood Algorithm) to constrain the range in erosional and uplift parameters that can best reproduce the observed data. The combination of different types of geologic information including sedimentary flux, landscape shape, and thermochronolology is valuable for constraining many of these parameters. We show that both the characteristics of the geodynamic forcing as well as the physical characteristics of the eroding plateau have significant control on the plateau erosion patterns. Models that match the erosion history data well suggest uplift of the eastern margin in the Cretaceous ( 100 Ma) followed by uplift of the western margin 20 Myr later. The amplitude of this uplift

  12. Early-stage mantle cell lymphoma

    DEFF Research Database (Denmark)

    Dabaja, B S; Zelenetz, A D; Ng, A K

    2017-01-01

    Background: Mantle cell lymphoma (MCL) rarely presents as early-stage disease, but clinical observations suggest that patients who present with early-stage disease may have better outcomes than those with advanced-stage disease. Patients and methods: In this 13-institution study, we examined...

  13. Deep Fish.

    Science.gov (United States)

    Ishaq, Omer; Sadanandan, Sajith Kecheril; Wählby, Carolina

    2017-01-01

    Zebrafish ( Danio rerio) is an important vertebrate model organism in biomedical research, especially suitable for morphological screening due to its transparent body during early development. Deep learning has emerged as a dominant paradigm for data analysis and found a number of applications in computer vision and image analysis. Here we demonstrate the potential of a deep learning approach for accurate high-throughput classification of whole-body zebrafish deformations in multifish microwell plates. Deep learning uses the raw image data as an input, without the need of expert knowledge for feature design or optimization of the segmentation parameters. We trained the deep learning classifier on as few as 84 images (before data augmentation) and achieved a classification accuracy of 92.8% on an unseen test data set that is comparable to the previous state of the art (95%) based on user-specified segmentation and deformation metrics. Ablation studies by digitally removing whole fish or parts of the fish from the images revealed that the classifier learned discriminative features from the image foreground, and we observed that the deformations of the head region, rather than the visually apparent bent tail, were more important for good classification performance.

  14. New Constraints on Upper Mantle Structure Underlying the Diamondiferous Central Slave Craton, Canada, from Teleseismic Body Wave Tomography

    Science.gov (United States)

    Esteve, C.; Schaeffer, A. J.; Audet, P.

    2017-12-01

    Over the past number of decades, the Slave Craton (Canada) has been extensively studied for its diamondiferous kimberlites. Not only are diamonds a valuable resource, but their kimberlitic host rocks provide an otherwise unique direct source of information on the deep upper mantle (and potentially transition zone). Many of the Canadian Diamond mines are located within the Slave Craton. As a result of the propensity for diamondiferous kimberlites, it is imperative to probe the deep mantle structure beneath the Slave Craton. This work is further motivated by the increase in high-quality broadband seismic data across the Northern Canadian Cordillera over the past decade. To this end we have generated a P and S body wave tomography model of the Slave Craton and its surroundings. Furthermore, tomographic inversion techniques are growing ever more capable of producing high resolution Earth models which capture detailed structure and dynamics across a range of scale lengths. Here, we present preliminary results on the structure of the upper mantle underlying the Slave Craton. These results are generated using data from eight different seismic networks such as the Canadian National Seismic Network (CNSN), Yukon Northwest Seismic Network (YNSN), older Portable Observatories for Lithospheric Analysis and Reseach Investigating Seismicity (POLARIS), Regional Alberta Observatory for Earthquake Studies Network (RV), USArray Transportable Array (TA), older Canadian Northwest Experiment (CANOE), Batholith Broadband (XY) and the Yukon Observatory (YO). This regional model brings new insights about the upper mantle structure beneath the Slave Craton, Canada.

  15. Intracratonic asthenosphere upwelling and lithosphere rejuvenation beneath the Hoggar swell (Algeria): Evidence from HIMU metasomatised lherzolite mantle xenoliths

    Science.gov (United States)

    Beccaluva, L.; Azzouni-Sekkal, A.; Benhallou, A.; Bianchini, G.; Ellam, R. M.; Marzola, M.; Siena, F.; Stuart, F. M.

    2007-08-01

    The mantle xenoliths included in Quaternary alkaline volcanics from the Manzaz-district (Central Hoggar) are proto-granular, anhydrous spinel lherzolites. Major and trace element analyses on bulk rocks and constituent mineral phases show that the primary compositions are widely overprinted by metasomatic processes. Trace element modelling of the metasomatised clinopyroxenes allows the inference that the metasomatic agents that enriched the lithospheric mantle were highly alkaline carbonate-rich melts such as nephelinites/melilitites (or as extreme silico-carbonatites). These metasomatic agents were characterized by a clear HIMU Sr-Nd-Pb isotopic signature, whereas there is no evidence of EM1 components recorded by the Hoggar Oligocene tholeiitic basalts. This can be interpreted as being due to replacement of the older cratonic lithospheric mantle, from which tholeiites generated, by asthenospheric upwelling dominated by the presence of an HIMU signature. Accordingly, this rejuvenated lithosphere (accreted asthenosphere without any EM influence), may represent an appropriate mantle section from which deep alkaline basic melts could have been generated and shallower mantle xenoliths sampled, respectively. The available data on lherzolite xenoliths and alkaline lavas (including He isotopes, Ra Pan-African basement. This can be considered a far-field foreland reaction of the Africa-Europe collisional system since the Eocene.

  16. Reconstructing mantle flow and long-wavelength dynamic topography since the Jurassic Period (GD Division Outstanding ECS Award Lecture)

    Science.gov (United States)

    Flament, Nicolas

    2017-04-01

    Global tectonic reconstructions can be used as boundary conditions of forward mantle convection models to simulate past mantle flow and long-wavelength dynamic topography. The predictions of such models can be compared to seismic tomography, to estimates of residual topography and to geological indicators of past vertical motions. Here we present models that reproduce the present-day structure of the lower mantle, including two large structures that resemble the Pacific and African Large Low Shear Velocity Provinces (LLSVPs, ˜15,000 km in diameter) and a smaller structure that resembles the recently discovered Perm Anomaly (˜1,000 km in diameter). The match between predicted and seismically inferred lower mantle structure is quantified across a series of mantle flow and tomography models. In the models, the Perm-like anomaly forms in isolation within a closed and long-lived subduction network (East Asia, Northern Tethys and Mongol-Okhotsk) ˜22,000 km in circumference before migrating ˜1,500 km westward at an average rate of 1 cm yr-1 since 150 million years ago. These results indicate a greater mobility of deep mantle structures than previously recognized, and illustrate that the predictive power of mantle flow models has significantly increased over the last thirty years. We suggest that the mobile Perm Anomaly could be linked to the ˜258 Ma Emeishan volcanics, in contrast to the previously proposed ˜251 Ma Siberian Traps. We also compare the present-day dynamic topography predicted by forward mantle flow models to residual topography models, and show that radial and lateral viscosity variations significantly influence the distribution of power of predicted dynamic topography as a function of spherical harmonic degree. We finally show how past vertical motions preserved in the geological record and the present-day position of slabs in the mantle inferred from seismic tomography may be used to constrain tectonic reconstructions and mantle rheology, including

  17. Heat transport in the high-pressure ice mantle of large icy moons

    Science.gov (United States)

    Choblet, Gael; Tobie, Gabriel; Sotin, Christophe; Kalousova, Klara; Grasset, Olivier

    2017-04-01

    While the existence of a buried ocean sandwiched between surface ice and high-pressure (HP) polymorphs of ice emerges as the most plausible structure for the hundreds-of-kilometers thick hydrospheres within large icy moons of the Solar System (Ganymede, Callisto, Titan), little is known about the thermal structure of the deep HP ice mantle and its dynamics, possibly involving melt production and extraction. This has major implications for the thermal history of these objects as well as on the habitability of their ocean as the HP ice mantle is presumed to limit chemical transport from the rock component to the ocean. Here, we describe 3D spherical simulations of subsolidus thermal convection tailored to the specific structure of the HP ice mantle of large icy moons. Melt production is monitored and melt transport is simplified by assuming instantaneous extraction to the ocean above. The two controlling parameters for these models are the rheology of ice VI and the heat flux from the rock core. Reasonable end-members are considered for both parameters as disagreement remains on the former (especially the pressure effect on viscosity) and as the latter is expected to vary significantly during the moon's history. We show that the heat power produced by radioactive decay within the rock core is mainly transported through the HP ice mantle by melt extraction to the ocean, with most of the melt produced directly above the rock/water interface. While the average temperature in the bulk of the HP ice mantle is always relatively cool when compared to the value at the interface with the rock core (˜ 5 K above the value at the surface of the HP ice mantle), maximum temperatures at all depths are close to the melting point, often leading to the interconnection of a melt path via hot convective plume conduits throughout the HP ice mantle. Overall, we predict long periods of time during these moons' history where water generated in contact with the rock core is transported to

  18. Using geoneutrinos to constrain the radiogenic power in the Earth's mantle

    Science.gov (United States)

    Šrámek, Ondřej; Roskovec, Bedřich; Wipperfurth, Scott A.; Xi, Yufei; McDonough, William F.

    2017-04-01

    The Earth's engine is driven by unknown proportions of primordial energy and heat produced in radioactive decay. Unfortunately, competing models of Earth's composition reveal an order of magnitude uncertainty in the amount of radiogenic power driving mantle dynamics. Together with established geoscientific disciplines (seismology, geodynamics, petrology, mineral physics), experimental particle physics now brings additional constraints to our understanding of mantle energetics. Measurements of the Earth's flux of geoneutrinos, electron antineutrinos emitted in β- decays of naturally occurring radionuclides, reveal the amount of uranium and thorium in the Earth and set limits on the amount of radiogenic power in the planet. Comparison of the flux measured at large underground neutrino experiments with geologically informed predictions of geoneutrino emission from the crust provide the critical test needed to define the mantle's radiogenic power. Measuring geoneutrinos at oceanic locations, distant from nuclear reactors and continental crust, would best reveal the mantle flux and by performing a coarse scale geoneutrino tomography could even test the hypothesis of large heterogeneous structures in deep mantle enriched in heat-producing elements. The current geoneutrino detecting experiments, KamLAND in Japan and Borexino in Italy, will by year ˜ 2020 be supplemented with three more experiments: SNO+ in Canada, and JUNO and Jinping in China. We predict the geoneutrino flux at all experimental sites. Within ˜ 8 years from today, the combination of data from all experiments will exclude end-member compositional models of the silicate Earth at the 1σ level, reveal the radiogenic contribution to the global surface heat loss, and provide tight limits on radiogenic power in the Earth's mantle. Additionally, we discuss how the geoneutrino measurements at the three relatively near-lying (≤ 3000 km) detectors KamLAND, JUNO, and Jinping may be harnessed to improve the

  19. Mantle Serpentinization near the Central Mariana Trench Constrained by Ocean Bottom Surface Wave Observations

    Science.gov (United States)

    Cai, C.; Wiens, D. A.; Lizarralde, D.; Eimer, M. O.; Shen, W.

    2017-12-01

    . Assuming the velocity anomaly remaining in the subducting plate mantle is caused by serpentinization, calculations suggest the top 20 km of the slab mantle retains 10-15% serpentinization beyond the outer forearc. The amount of water carried into the deep mantle by this layer ( 54 Tg/Myr/m) is two to three times greater than previous estimates for the entire slab.

  20. Efficacy in Deep Vein Thrombosis Prevention With Extended Mechanical Compression Device Therapy and Prophylactic Aspirin Following Total Knee Arthroplasty: A Randomized Control Trial.

    Science.gov (United States)

    Snyder, Mark A; Sympson, Alexandra N; Scheuerman, Christina M; Gregg, Justin L; Hussain, Lala R

    2017-05-01

    Aspirin at 325 mg twice daily is now included as a nationally approved venous thromboembolism (VTE) prophylaxis protocol for low-risk total knee arthroplasty (TKA) patients. The purpose of this study is to examine whether there is a difference in deep vein thrombosis (DVT) occurrence after a limited tourniquet TKA using aspirin-based prophylaxis with or without extended use of mechanical compression device (MCD) therapy. One hundred limited tourniquet TKA patients, whose DVT risk was managed with aspirin 325 mg twice daily for 3 weeks, were randomized to either using an MCD during hospitalization only or extended use at home up to 6 weeks postoperatively. Lower extremity duplex venous ultrasonography (LEDVU) was completed on the second postoperative day, 14 days postoperatively, and at 3 months postoperatively to confirm the absence of DVT after treatment. The DVT rate for the postdischarge MCD therapy group was 0% and 23.1% for the inpatient MCD group (P aspirin for 3 weeks postoperatively, and on MCD therapy for up to 6 weeks postoperatively experienced superior DVT prophylaxis than patients receiving MCD therapy only as an inpatient (P aspirin and extended-use MCD further validates this type of prophylaxis in low DVT risk TKA patients. Copyright © 2016 Elsevier Inc. All rights reserved.

  1. Cosmochemical Estimates of Mantle Composition

    Science.gov (United States)

    Palme, H.; O'Neill, H. St. C.

    2003-12-01

    In 1794 the German physicist Chladni published a small book in which he suggested the extraterrestrial origin of meteorites. The response was skepticism and disbelief. Only after additional witnessed falls of meteorites did scientists begin to consider Chladni's hypothesis seriously. The first chemical analyses of meteorites were published by the English chemist Howard in 1802, and shortly afterwards by Klaproth, a professor of chemistry in Berlin. These early investigations led to the important conclusion that meteorites contained the same elements that were known from analyses of terrestrial rocks. By the year 1850, 18 elements had been identified in meteorites: carbon, oxygen, sodium, magnesium, aluminum, silicon, phosphorous, sulfur, potassium, calcium, titanium, chromium, manganese, iron, cobalt, nickel, copper, and tin (Burke, 1986). A popular hypothesis, which arose after the discovery of the first asteroid Ceres on January 1, 1801 by Piazzi, held that meteorites came from a single disrupted planet between Mars and Jupiter. In 1847 the French geologist Boisse (1810-1896) proposed an elaborate model that attempted to account for all known types of meteorites from a single planet. He envisioned a planet with layers in sequence of decreasing densities from the center to the surface. The core of the planet consisted of metallic iron surrounded by a mixed iron-olivine zone. The region overlying the core contained material similar to stony meteorites with ferromagnesian silicates and disseminated grains of metal gradually extending into shallower layers with aluminous silicates and less iron. The uppermost layer consisted of metal-free stony meteorites, i.e., eucrites or meteoritic basalts. About 20 years later, Daubrée (1814-1896) carried out experiments by melting and cooling meteorites. On the basis of his results, he came to similar conclusions as Boisse, namely that meteorites come from a single, differentiated planet with a metal core, a silicate mantle

  2. Deep neuromuscular blockade and low insufflation pressure during laparoscopic hysterectomy

    DEFF Research Database (Denmark)

    Madsen, Matias Vested; Istre, Olav; Springborg, Henrik Halvor

    2017-01-01

    INTRODUCTION: Establishment of sufficient muscle relaxation is essential in laparoscopic surgery. During laparoscopy, surgeons can experience abdominal contractions in their patients. Deep neuromuscular block (NMB) has the potential to prevent such episodes. In this study, we explored if deep NMB...

  3. Volcanism on Mercury (dikes, lava flows, pyroclastics): Crust/mantle density contrasts, the evolution of compressive stress and the presence of mantle volatiles

    Science.gov (United States)

    Wilson, L.; Head, J. W., III

    2008-09-01

    Background. There is great uncertainty about the internal structure of Mercury and the composition of the mantle [e.g., 1, 2]. The high mean density of the body suggests that it may have lost parts of its crust and mantle in a giant impact at some stage after most of its initial accretion was sufficiently complete that at least partial separation of a core had occurred. It is the uncertainty about the timing of the giant impact, and hence the physico-chemical state of proto-Mercury at the time that it occurred, that leads to difficulties in predicting the interior structure and mantle composition. However, it seems reasonable to assume that the Mercury we see today has some combination of a relatively low-density crust and a relatively highdensity mantle; uncertainty remains about the presence and types of volatiles [2]. The second uncertainty is the nature of the surface plains units, specifically, are these lava flows and pyroclastics erupted from the interior, or impact-reworked earlier crust [3-5] (Figs. 1-2)? The detection of candidate pyroclastic deposits [4] has very important implications for mantle volatiles. Furthermore, whatever the surface composition, the presence of planet-wide systems of wrinkle ridges and thrust faults implies that a compressive crustal stress regime became dominant at some stage in the planet's history [3, 6]. If the plains units are indeed lava flows, then the fact that the products of the compressive regime deform many plains units suggests that the development of the compressive stresses may have played a vital role in determining when and if surface eruptions of mantle-derived magmas could occur. This would be analogous to the way in which the change with time from extensional to compressive global stresses in the lithosphere of the Moon influenced the viability of erupting magmas from deep mantle sources [7-9]. Analysis: To investigate the relationship between lithospheric stresses and magma eruption conditions [e.g., 9-11] we

  4. Preliminary three-dimensional model of mantle convection with deformable, mobile continental lithosphere

    Science.gov (United States)

    Yoshida, Masaki

    2010-06-01

    Characteristic tectonic structures such as young orogenic belts and suture zones in a continent are expected to be mechanically weaker than the stable part of the continental lithosphere with the cratonic root (or cratonic lithosphere) and yield lateral viscosity variations in the continental lithosphere. In the present-day Earth's lithosphere, the pre-existing, mechanically weak zones emerge as a diffuse plate boundary. However, the dynamic role of a weak (low-viscosity) continental margin (WCM) in the stability of continental lithosphere has not been understood in terms of geophysics. Here, a new numerical simulation model of mantle convection with a compositionally and rheologically heterogeneous, deformable, mobile continental lithosphere is presented for the first time by using three-dimensional regional spherical-shell geometry. A compositionally buoyant and highly viscous continental assemblage with pre-existing WCMs, analogous to the past supercontinent, is modeled and imposed on well-developed mantle convection whose vigor of convection, internal heating rate, and rheological parameters are appropriate for the Earth's mantle. The visco-plastic oceanic lithosphere and the associated subduction of oceanic plates are incorporated. The time integration of the advection of continental materials with zero chemical diffusion is performed by a tracer particle method. The time evolution of mantle convection after setting the model supercontinent is followed over 800 Myr. Earth-like continental drift is successfully reproduced, and the characteristic thermal interaction between the mantle and the continent/supercontinent is observed in my new numerical model. Results reveal that the WCM protects the cratonic lithosphere from being stretched by the convecting mantle and may play a significant role in the stability of the cratonic lithosphere during the geological timescale because it acts as a buffer that prevents the cratonic lithosphere from undergoing global

  5. USArray Enables Improved Resolution Studies of Earth's Upper and Lower Mantle

    Science.gov (United States)

    Garnero, E. J.; Lay, T.

    2007-12-01

    The first full deployment of EarthScope's USArray has now been completed, with over 400 high-quality broadband stations distributed over a 70-km grid covering the western U.S. The openly-available USArray data can be obtained in near real-time using convenient IRIS-hosted data retrieval tools (e.g., SOD, JWeed). The dramatic increase in number of seismograms for each event, along with the unusual combination of large aperture and dense wave field sampling, are enabling improved resolution of deep Earth structure in diverse applications. Automation is now important for most initial data processing steps, in order to handle the large numbers of records that quickly accumulate. We highlight several applications of USArray data to Earth structure investigations in locations remote from North American lithosphere where the bulk of applications are focused. Earthquake source distributions relative to the USArray define several target study regions. For example, deep focus South American and Fiji-Tonga earthquakes allow high-resolution analyses of lower mantle structure beneath the Cocos Plate and the central Pacific, respectively. The increasingly detailed models that are inferred have many thermal, compositional and dynamical implications. Fiji-Tonga events recorded by USArray are enabling detailed mapping of upper mantle discontinuity structures in the vicinity of the Tonga slab. Images of upper mantle discontinuities beneath South America and Hawaii are brought into sharper focus using teleseismic data recorded by USArray. Various data processing approaches, such as stacking, migration, and source wavelet deconvolution are now stabilized by the dense USArray data sets. The increasingly detailed characterization of deep structure is motivating both advances in 3D wave propagation methods and collaborative interdisciplinary efforts to provide viable interpretations.

  6. Continuous eclogite melting and variable refertilisation in upwelling heterogeneous mantle.

    Science.gov (United States)

    Rosenthal, Anja; Yaxley, Gregory M; Green, David H; Hermann, Joerg; Kovács, István; Spandler, Carl

    2014-08-18

    Large-scale tectonic processes introduce a range of crustal lithologies into the Earth's mantle. These lithologies have been implicated as sources of compositional heterogeneity in mantle-derived magmas. The model being explored here assumes the presence of widely dispersed fragments of residual eclogite (derived from recycled oceanic crust), stretched and stirred by convection in the mantle. Here we show with an experimental study that these residual eclogites continuously melt during upwelling of such heterogeneous mantle and we characterize the melting reactions and compositional changes in the residue minerals. The chemical exchange between these partial melts and more refractory peridotite leads to a variably metasomatised mantle. Re-melting of these metasomatised peridotite lithologies at given pressures and temperatures results in diverse melt compositions, which may contribute to the observed heterogeneity of oceanic basalt suites. We also show that heterogeneous upwelling mantle is subject to diverse local freezing, hybridization and carbonate-carbon-silicate redox reactions along a mantle adiabat.

  7. Deep geothermics

    International Nuclear Information System (INIS)

    Anon.

    1995-01-01

    The hot-dry-rocks located at 3-4 km of depth correspond to low permeable rocks carrying a large amount of heat. The extraction of this heat usually requires artificial hydraulic fracturing of the rock to increase its permeability before water injection. Hot-dry-rocks geothermics or deep geothermics is not today a commercial channel but only a scientific and technological research field. The Soultz-sous-Forets site (Northern Alsace, France) is characterized by a 6 degrees per meter geothermal gradient and is used as a natural laboratory for deep geothermal and geological studies in the framework of a European research program. Two boreholes have been drilled up to 3600 m of depth in the highly-fractured granite massif beneath the site. The aim is to create a deep heat exchanger using only the natural fracturing for water transfer. A consortium of german, french and italian industrial companies (Pfalzwerke, Badenwerk, EdF and Enel) has been created for a more active participation to the pilot phase. (J.S.). 1 fig., 2 photos

  8. Pb evolution in the Martian mantle

    Science.gov (United States)

    Bellucci, J. J.; Nemchin, A. A.; Whitehouse, M. J.; Snape, J. F.; Bland, P.; Benedix, G. K.; Roszjar, J.

    2018-03-01

    The initial Pb compositions of one enriched shergottite, one intermediate shergottite, two depleted shergottites, and Nakhla have been measured by Secondary Ion Mass Spectrometry (SIMS). These values, in addition to data from previous studies using an identical analytical method performed on three enriched shergottites, ALH 84001, and Chassigny, are used to construct a unified and internally consistent model for the differentiation history of the Martian mantle and crystallization ages for Martian meteorites. The differentiation history of the shergottites and Nakhla/Chassigny are fundamentally different, which is in agreement with short-lived radiogenic isotope systematics. The initial Pb compositions of Nakhla/Chassigny are best explained by the late addition of a Pb-enriched component with a primitive, non-radiogenic composition. In contrast, the Pb isotopic compositions of the shergottite group indicate a relatively simple evolutionary history of the Martian mantle that can be modeled based on recent results from the Sm-Nd system. The shergottites have been linked to a single mantle differentiation event at 4504 Ma. Thus, the shergottite Pb isotopic model here reflects a two-stage history 1) pre-silicate differentiation (4504 Ma) and 2) post-silicate differentiation to the age of eruption (as determined by concordant radiogenic isochron ages). The μ-values (238U/204Pb) obtained for these two different stages of Pb growth are μ1 of 1.8 and a range of μ2 from 1.4-4.7, respectively. The μ1-value of 1.8 is in broad agreement with enstatite and ordinary chondrites and that proposed for proto Earth, suggesting this is the initial μ-value for inner Solar System bodies. When plotted against other source radiogenic isotopic variables (Sri, γ187Os, ε143Nd, and ε176Hf), the second stage mantle evolution range in observed mantle μ-values display excellent linear correlations (r2 > 0.85) and represent a spectrum of Martian mantle mixing-end members (depleted

  9. Utility of Deep Inspiration Breath Hold for Left-Sided Breast Radiation Therapy in Preventing Early Cardiac Perfusion Defects: A Prospective Study

    Energy Technology Data Exchange (ETDEWEB)

    Zagar, Timothy M., E-mail: zagar@med.unc.edu [Department of Radiation Oncology, University of North Carolina, Chapel Hill, North Carolina (United States); Kaidar-Person, Orit [Department of Radiation Oncology, University of North Carolina, Chapel Hill, North Carolina (United States); Tang, Xiaoli [Memorial Sloan Kettering Cancer Center, West Harrison, New York (United States); Jones, Ellen E.; Matney, Jason; Das, Shiva K.; Green, Rebecca L. [Department of Radiation Oncology, University of North Carolina, Chapel Hill, North Carolina (United States); Sheikh, Arif [Department of Radiology, Columbia University, New York, New York (United States); Khandani, Amir H.; McCartney, William H.; Oldan, Jorge Daniel; Wong, Terence Z. [Department of Radiology, University of North Carolina, Chapel Hill, North Carolina (United States); Marks, Lawrence B. [Department of Radiation Oncology, University of North Carolina, Chapel Hill, North Carolina (United States)

    2017-04-01

    Purpose: To evaluate early cardiac single photon computed tomography (SPECT) findings after left breast/chest wall postoperative radiation therapy (RT) in the setting of deep inspiration breath hold (DIBH). Methods and Materials: We performed a prospective single-institution single-arm study of patients who were planned for tangential RT with DIBH to the left breast/chest wall (± internal mammary nodes). The DIBH was done by use of a controlled surface monitoring technique (AlignRT, Vision RT Ltd, London, UK). The RT was given with tangential fields and a heart block. Radiation-induced cardiac perfusion and wall motion changes were assessed by pre-RT and 6-month post-RT SPECT scans. A cumulative SPECT summed-rest score was used to quantify perfusion in predefined left ventricle segments. The incidence of wall motion abnormalities was assessed in each of these same segments. Results: A total of 20 patients with normal pre-RT scans were studied; their median age was 56 years (range, 39-72 years). Seven (35%) patients also received irradiation to the left internal mammary chain, and 5 (25%) received an additional RT field to supraclavicular nodes. The median heart dose was 94 cGy (range, 56-200 cGy), and the median V25{sub Gy} was zero (range, 0-0.1). None of the patients had post-RT perfusion or wall motion abnormalities. Conclusions: Our results suggest that DIBH and conformal cardiac blocking for patients receiving tangential RT for left-sided breast cancer is an effective means to avoid early RT-associated cardiac perfusion defects.

  10. Combination of deep sea water andSesamum indicumleaf extract prevents high-fat diet-induced obesity through AMPK activation in visceral adipose tissue.

    Science.gov (United States)

    Yuan, Haidan; Chung, Sunghyun; Ma, Qianqian; Ye, L I; Piao, Guangchun

    2016-01-01

    The aim of the present study was to evaluate the protective effects of a combination of deep sea water (DSW) and Sesamum indicum leaf extract (SIE) against high-fat diet (HFD)-induced obesity and investigate its molecular mechanisms in adipose tissue. ICR mice were randomly divided into three groups: HFD control (HFC), DSW and DSW + 125 mg/kg SIE (DSS) groups. The mice in the HFC group had free access to drinking water while those in the DSW and DSS groups had free access to DSW. The mice in the DSS group were treated with SIE once per day for 8 weeks. The mice in all three groups were allowed to freely access a HFD. Compared with the HFC group, the DSS group showed lower body weight gain and serum levels of glucose, triglycerides and leptin. Histological analyses of the epididymal white, retroperitoneal white and scapular brown adipose tissue of mice in the DSS group revealed that the adipocytes were markedly decreased in size compared with those in the HFC group. Moreover, DSS significantly increased the levels of phosphorylated adenosine monophosphate-activated protein kinase (AMPK) and its substrate, acetyl-CoA carboxylase (ACC) in mice epididymal adipose tissues. Furthermore, DSS upregulated the expression levels of lipolysis-associated mRNA, specifically peroxisome proliferator-activated receptor-α (PPAR-α) and cluster of differentiation 36 (CD36), and energy expenditure-associated mRNA, namely uncoupling protein 2 (UCP2) and carnitine palmitoyltransferase-1 (CPT1) in the epididymal adipose tissues. By contrast, DSS suppressed the expression of the lipogenesis-related gene sterol regulatory element-binding protein-1 (SREBP1) at the mRNA level. These results suggest that DSS is effective for suppressing body weight gain and enhancing the lipid profile.

  11. Combination of deep sea water and Sesamum indicum leaf extract prevents high-fat diet-induced obesity through AMPK activation in visceral adipose tissue

    Science.gov (United States)

    YUAN, HAIDAN; CHUNG, SUNGHYUN; MA, QIANQIAN; YE, LI; PIAO, GUANGCHUN

    2016-01-01

    The aim of the present study was to evaluate the protective effects of a combination of deep sea water (DSW) and Sesamum indicum leaf extract (SIE) against high-fat diet (HFD)-induced obesity and investigate its molecular mechanisms in adipose tissue. ICR mice were randomly divided into three groups: HFD control (HFC), DSW and DSW + 125 mg/kg SIE (DSS) groups. The mice in the HFC group had free access to drinking water while those in the DSW and DSS groups had free access to DSW. The mice in the DSS group were treated with SIE once per day for 8 weeks. The mice in all three groups were allowed to freely access a HFD. Compared with the HFC group, the DSS group showed lower body weight gain and serum levels of glucose, triglycerides and leptin. Histological analyses of the epididymal white, retroperitoneal white and scapular brown adipose tissue of mice in the DSS group revealed that the adipocytes were markedly decreased in size compared with those in the HFC group. Moreover, DSS significantly increased the levels of phosphorylated adenosine monophosphate-activated protein kinase (AMPK) and its substrate, acetyl-CoA carboxylase (ACC) in mice epididymal adipose tissues. Furthermore, DSS upregulated the expression levels of lipolysis-associated mRNA, specifically peroxisome proliferator-activated receptor-α (PPAR-α) and cluster of differentiation 36 (CD36), and energy expenditure-associated mRNA, namely uncoupling protein 2 (UCP2) and carnitine palmitoyltransferase-1 (CPT1) in the epididymal adipose tissues. By contrast, DSS suppressed the expression of the lipogenesis-related gene sterol regulatory element-binding protein-1 (SREBP1) at the mRNA level. These results suggest that DSS is effective for suppressing body weight gain and enhancing the lipid profile. PMID:26889265

  12. Deep Vein Thrombosis

    Science.gov (United States)

    Deep vein thrombosis, or DVT, is a blood clot that forms in a vein deep in the body. Most deep vein ... the condition is called thrombophlebitis. A deep vein thrombosis can break loose and cause a serious problem ...

  13. Deep Seismic Reflection Profiling in Africa

    Science.gov (United States)

    Attoh, K.; Brown, L. D.

    2006-05-01

    Africa represents one of the true frontiers for systematic deep seismic reflection profiling of the type pioneered by COCORP, LITHOPROBE, BIRPS, DEKORP, and ECORS in the northern hemisphere. However, there have been a number of notable individual surveys that have sampled key components of the African lithosphere, and several systematic regional geophysical initiatives which suggest African is fertile ground for future efforts. Among the latter are the KRISP refraction/wide-angle program to probe the East African Rift system in the 1990's, the Kaapvaal Experiment to image the deep lithosphere with passive techniques and most recently the EAGLE active/passive experiments in the Afar. Examples of true multichannel deep reflection surveys to delineate crustal structure include the transects of the Limpopo Belt, a Neoarchean mobile zone that sutures the Kaapval and Zimbabwe cratons, deep oil prospecting surveys in the Nosop basin of southern Botswana that reveal dramatic basement reflectors off the NW margin of the Kaapvaal craton, and most recently deep vibroseis surveys within the Kaapvaal craton that indicate a crustal stack of tectonic slivers as well as tectonic shingling of the upper mantle. The passive margin of western Africa, with its strategic oil resources, has been a target of several deep studies using marine seismic surveys, including the PROBE initiative of the late 1980's and more recent deep surveys offshore Angola. Reprocessing of lines from oil exploration grids reveal Proterozoic mid-lower crustal features offshore of Ghana. Among the potentially rich targets for future surveys in Africa are the West African and Congo cratons and their suturing Pan-African (Neoproterozoic) mobile belts. This suite of cratonic lithosphere elements is largely largely untouched by modern high resolution seismic methodologies. New initiatives such as LEGENDS ( targeting the East African Orogen) and exploitation of existing oil industry seismic data for deep information

  14. The lithospheric mantle below southern West Greenland

    DEFF Research Database (Denmark)

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

    2009-01-01

    Geothermobarometry of primarily garnet lherzolitic xenoliths from several localities in southern West Greenland is applied to address the diamond potential, pressure and temperature distribution and the stratigraphy of the subcontinental lithospheric mantle ~600 Ma ago. The samples are from...... kimberlitic and ultramafic lamprophyre (senso lato) dikes and sills emplaced into three tectonically distinct crustal areas in the North Atlantic Craton. Several geothermobarometry formulations have been applied and a thorough assessment of which P-T combinations are most applicable to this sample suite has...... and the Kirkland Lake locality within the Superior craton. In supporting previous studies we find that the continental lithospheric mantle is layered and increases in fertility with depth. Twenty-five of 32 investigated samples are estimated to be derived from the diamond stability field that extends...

  15. Upper mantle flow in the western Mediterranean

    International Nuclear Information System (INIS)

    Panza, G.F.; Raykova, R.; Carminati, E.; Doglioni, C.

    2006-07-01

    Two cross-sections of the western Mediterranean Neogene-to-present backarc basin are presented, in which geological and geophysical data of the Transmed project are tied to a new shear-wave tomography. Major results are i) the presence of a well stratified upper mantle beneath the older African continent, with a marked low-velocity layer between 130-200 km of depth; ii) the dilution of this layer within the younger western Mediterranean backarc basin to the north, and iii) the easterly raising of a shallower low-velocity layer from about 140 km to about 30 km in the Tyrrhenian active part of the backarc basin. These findings suggest upper mantle circulation in the western Mediterranean backarc basin, mostly easterly-directed and affecting the boundary between upper asthenosphere (LVZ) and lower asthenosphere, which undulates between about 180 km and 280 km. (author)

  16. Five years of the Normal Oceanic Mantle (NOMan) Project

    Science.gov (United States)

    Utada, Hisashi; Kawakatsu, Hitoshi; Shiobara, Hajime; Baba, Kiyoshi; Isse, Takehi; Suetsugu, Daisuke; NOMan Project Team

    2016-04-01

    conducted in 2014, we have recovered instruments from all sites except only one site (NM03) where a few EM instruments were left and are to be retrieved in September, 2015. The seafloor age difference between study areas A and B is only about 10 Ma, which was thought small enough for the temperature difference between two areas to be ignored at the first order approximation. So we originally expected that corresponding results in area B show close similarity to those in are A. However, a result of 1-D array analysis of the surface waves indicated substantial difference in the lithosphere-asthenosphere structure between areas A and B. 1-D inversion results of multi-station seafloor magnetotelluric (MT) data also show a certain difference between these two areas. Furthermore, MT results in surrounding areas obtained by previous projects imply the presence of further significant heterogeneity in the old oceanic mantle in the northwestern Pacific toward the subduction zone. For the moment, we are trying to invert each of NOMan geophysical dataset as accurately as possible so as to characterize the mantle structure and its lateral variation. Later we try to clarify the cause for these lateral variabilities, as it can be one of the key issues to understand the lithosphere-asthenosphere system in the old oceanic mantle. For the key question (b), high-quality data obtained by the long-term seafloor observations are used to investigate the MTZ structure. In particular, electric field data obtained by EFOS (with 2 km electrode separation) provide longer period MT responses sensitive to the MTZ. Resulting MT and GDS (Geomagnetic Deep sounding) responses are almost consistent with the NW Pacific semi-global 1-D model (Shimizu et al., 2010). This indicates that the MTZ conductivity below the study region has weak lateral variation (well approximated by a 1-D model) and is also consistent with the conductivity of MTZ minerals containing at most 0.1-0.5 wt.% water.

  17. Mantle fluid metallogeny of granite-type uranium deposits in northern Guangdong

    International Nuclear Information System (INIS)

    Shen Weihou; Ling Hongfei; Sun Tao; Deng Ping; Zhu Ba; Huang Guolong' Tan Zhengzhong

    2010-01-01

    form mantle fluids which finally flew into crust through deep extensional tectonic activities (or intrusion of mafic dike magmas). During moving up process, the mantle fluids which were enriched in alkali and ΣCO 2 interacted with the crustal rocks (especially uranium-rich rocks), resulting in alkaline alteration of crustal rocks and mobilizing uranium and other metals in the rocks. As a result, the mantle-derived fluids gradually became uranium-rich fluids. Deposition of pitchblende during late evolution stages of the mantle fluids was related with following factors: 1) mixing of the ore-forming fluids with fluids of meteoric-water origin so as to change the physicochemical conditions of the fluids, 2) boiling of the fluids when they entering low pressure environment and thus escaping of CO 2 to lead to decomposition of the uranyl-carbonate ions in the fluids, 3) interaction between uranyl-ion bearing fluids and reducer bearing mafic dikes.. (authors)

  18. Core formation and mantle differentiation on Mars

    OpenAIRE

    Mezger Klaus; Debaille Vinciane; Kleine Thorsten

    2012-01-01

    Geochemical investigation of Martian meteorites (SNC meteorites) yields important constraints on the chemical and geodynamical evolution of Mars. These samples may not be representative of the whole of Mars; however they provide constraints on the early differentiation processes on Mars. The bulk composition of Martian samples implies the presence of a metallic core that formed concurrently as the planet accreted. The strong depletion of highly siderophile elements in the Martian mantle is on...

  19. Water in Earth's mantle: Hydrogen analysis of mantle olivine, pyroxenes and garnet using the SIMS

    Science.gov (United States)

    Kurosawa, Masanori; Yurimoto, Hisayoshi; Sueno, Shigeho

    1993-01-01

    Hydrogen (or water) in the Earth's interior plays a key role in the evolution and dynamics of the planet. However, the abundance and the existence form of the hydrogen have scarcely been clear in practice. Hydrogen in the mantle was incorporated in the interior during the formation of the Earth. The incorporated hydrogen was hardly possible to concentrate locally inside the Earth considering its high mobility and high reactivity. The hydrogen, preferably, could be distributed homogeneously over the mantle and the core by the subsequent physical and chemical processes. Therefore, hydrogen in the mantle could be present in the form of trace hydrogen in nominally anhydrous mantle minerals. The hydrogen and the other trace elements in mantle olivines, orthopyroxenes, clinopyroxenes, and garnets were determined using secondary ion mass spectrometry (SIMS) for elucidating (1) the exact hydrogen contents, (2) the correlation between the hydrogen and the other trace elements, (3) the dependence of the hydrogen contents on the depth, and (4) the dependence of the whole rock water contents on the depth.

  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. Mantle updrafts and mechanisms of oceanic volcanism.

    Science.gov (United States)

    Anderson, Don L; Natland, James H

    2014-10-14

    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.

  2. Deep smarts.

    Science.gov (United States)

    Leonard, Dorothy; Swap, Walter

    2004-09-01

    When a person sizes up a complex situation and rapidly comes to a decision that proves to be not just good but brilliant, you think, "That was smart." After you watch him do this a few times, you realize you're in the presence of something special. It's not raw brainpower, though that helps. It's not emotional intelligence, either, though that, too, is often involved. It's deep smarts. Deep smarts are not philosophical--they're not"wisdom" in that sense, but they're as close to wisdom as business gets. You see them in the manager who understands when and how to move into a new international market, in the executive who knows just what kind of talk to give when her organization is in crisis, in the technician who can track a product failure back to an interaction between independently produced elements. These are people whose knowledge would be hard to purchase on the open market. Their insight is based on know-how more than on know-what; it comprises a system view as well as expertise in individual areas. Because deep smarts are experienced based and often context specific, they can't be produced overnight or readily imported into an organization. It takes years for an individual to develop them--and no time at all for an organization to lose them when a valued veteran walks out the door. They can be taught, however, with the right techniques. Drawing on their forthcoming book Deep Smarts, Dorothy Leonard and Walter Swap say the best way to transfer such expertise to novices--and, on a larger scale, to make individual knowledge institutional--isn't through PowerPoint slides, a Web site of best practices, online training, project reports, or lectures. Rather, the sage needs to teach the neophyte individually how to draw wisdom from experience. Companies have to be willing to dedicate time and effort to such extensive training, but the investment more than pays for itself.

  3. Apparent splitting of S waves propagating through an isotropic lowermost mantle

    KAUST Repository

    Parisi, Laura

    2018-03-24

    Observations of shear‐wave anisotropy are key for understanding the mineralogical structure and flow in the mantle. Several researchers have reported the presence of seismic anisotropy in the lowermost 150–250 km of the mantle (i.e., D” layer), based on differences in the arrival times of vertically (SV) and horizontally (SH) polarized shear waves. By computing waveforms at period > 6 s for a wide range of 1‐D and 3‐D Earth structures we illustrate that a time shift (i.e., apparent splitting) between SV and SH may appear in purely isotropic simulations. This may be misinterpreted as shear wave anisotropy. For near‐surface earthquakes, apparent shear wave splitting can result from the interference of S with the surface reflection sS. For deep earthquakes, apparent splitting can be due to the S‐wave triplication in D”, reflections off discontinuities in the upper mantle and 3‐D heterogeneity. The wave effects due to anomalous isotropic structure may not be easily distinguished from purely anisotropic effects if the analysis does not involve full waveform simulations.

  4. Water in the Cratonic Mantle: Insights from FTIR Data on Lac De Gras Xenoliths (Slave Craton, Canada)

    Science.gov (United States)

    Peslier, Anne H.; Brandon, Alan D.; Schaffer, Lillian Aurora; O'Reilly, Suzanne Yvette; Griffin, William L.; Morris, Richard V.; Graff, Trevor G.; Agresti, David G.

    2014-01-01

    The mantle lithosphere beneath the cratonic part of continents is the deepest (> 200 km) and oldest (>2-3 Ga) on Earth, remaining a conundrum as to how these cratonic roots could have resisted delamination by asthenospheric convection over time. Water, or trace H incorporated in mineral defects, could be a key player in the evolution of continental lithosphere because it influences melting and rheology of the mantle. Mantle xenoliths from the Lac de Gras kimberlite in the Slave craton were analyzed by FTIR. The cratonic mantle beneath Lac de Gras is stratified with shallow (<145 km) oxidized ultradepleted peridotites and pyroxenites with evidence for carbonatitic metasomatism, underlain by reduced and less depleted peridotites metasomatized by kimberlite melts. Peridotites analyzed so far have H O contents in ppm weight of 7-100 in their olivines, 58 to 255 in their orthopyroxenes (opx), 11 to 84 in their garnet, and 139 in one clinopyroxene. A pyroxenite contains 58 ppm H2O in opx and 5 ppm H2O in its olivine and garnet. Olivine and garnet from the deep peridotites have a range of water contents extending to higher values than those from the shallow ones. The FTIR spectra of olivines from the shallow samples have more prominent Group II OH bands compared to the olivines from the deep samples, consistent with a more oxidized mantle environment. The range of olivine water content is similar to that observed in Kaapvaal craton peridotites at the same depths (129-184 km) but does not extend to as high values as those from Udachnaya (Siberian craton). The Slave, Kaapvaal and Siberian cratons will be compared in terms of water content distribution, controls and role in cratonic root longevity.

  5. Complex seismic anisotropy and mantle dynamics beneath Turkey

    Science.gov (United States)

    Lemnifi, Awad A.; Elshaafi, Abdelsalam; Karaoğlu, Özgür; Salah, Mohamed K.; Aouad, Nassib; Reed, Cory A.; Yu, Youqiang

    2017-12-01

    Seismic anisotropy is an unambiguous property of the deep Earth that is often detected through shear wave splitting (SWS) and anisotropic receiver function (RF) techniques, which are then used to infer the lithospheric and asthenospheric deformational structure. The Anatolian plate and its associated Mediterranean, Eurasian, and Arabian plate boundaries represent the consequences of a variety of convergent and transform tectonic regimes; these boundaries are thus well-suited for studying seismic anisotropy related to subduction, orogenic, and strike-slip processes. We apply a joint SWS and RF analysis to identify the magnitude and orientation of deformation associated with lithosphere-asthenosphere coupling beneath the Anatolian plate system as well as intra-plate fossil fabrics resulting from ancient and ongoing collision. SWS analysis reveals the existence of complex anisotropic fabrics beneath the Anatolian region, where the upper-layer fast orientations are either parallel to strike-slip faults or orthogonal to reverse faults. Strongly oriented NE-SW lower-layer fast orientations suggest that they originate from slab-modulated flow in the mantle wedge overlying the northward-subducting African plate. The results of the RF analysis show that the fast orientations are spatially variable but are generally consistent with crustal fabrics developed mostly through intensive faulting and are possibly associated with sub-vertical lower crustal shear zones.

  6. Deep-Earth Equilibration between Molten Iron and Solid Silicates

    Science.gov (United States)

    Brennan, M.; Zurkowski, C. C.; Chidester, B.; Campbell, A.

    2017-12-01

    Elemental partitioning between iron-rich metals and silicate minerals influences the properties of Earth's deep interior, and is ultimately responsible for the nature of the core-mantle boundary. These interactions between molten iron and solid silicates were influential during planetary accretion, and persist today between the mantle and liquid outer core. Here we report the results of diamond anvil cell experiments at lower mantle conditions (40 GPa, >2500 K) aimed at examining systems containing a mixture of metals (iron or Fe-16Si alloy) and silicates (peridotite). The experiments were conducted at pressure-temperature conditions above the metallic liquidus but below the silicate solidus, and the recovered samples were analyzed by FIB/SEM with EDS to record the compositions of the coexisting phases. Each sample formed a three-phase equilibrium between bridgmanite, Fe-rich metallic melt, and an oxide. In one experiment, using pure Fe, the quenched metal contained 6 weight percent O, and the coexisting oxide was ferropericlase. The second experiment, using Fe-Si alloy, was highly reducing; its metal contained 10 wt% Si, and the coexisting mineral was stishovite. The distinct mineralogies of the two experiments derived from their different starting metals. These results imply that metallic composition is an important factor in determining the products of mixed phase iron-silicate reactions. The properties of deep-Earth interfaces such as the core-mantle boundary could be strongly affected by their metallic components.

  7. Mineralogy and composition of the oceanic mantle

    Science.gov (United States)

    Putirka, Keith; Ryerson, F.J.; Perfit, Michael; Ridley, W. Ian

    2011-01-01

    The mineralogy of the oceanic basalt source region is examined by testing whether a peridotite mineralogy can yield observed whole-rock and olivine compositions from (1) the Hawaiian Islands, our type example of a mantle plume, and (2) the Siqueiros Transform, which provides primitive samples of normal mid-ocean ridge basalt. New olivine compositional data from phase 2 of the Hawaii Scientific Drilling Project (HSDP2) show that higher Ni-in-olivine at the Hawaiian Islands is due to higher temperatures (T) of melt generation and processing (by c. 300°C) related to the Hawaiian mantle plume. DNi is low at high T, so parental Hawaiian basalts are enriched in NiO. When Hawaiian (picritic) parental magmas are transported to shallow depths, olivine precipitation occurs at lower temperatures, where DNi is high, leading to high Ni-in-olivine. Similarly, variations in Mn and Fe/Mn ratios in olivines are explained by contrasts in the temperatures of magma processing. Using the most mafic rocks to delimit Siqueiros and Hawaiian Co and Ni contents in parental magmas and mantle source compositions also shows that both suites can be derived from natural peridotites, but are inconsistent with partial melting of natural pyroxenites. Whole-rock compositions at Hawaii and Siqueiros are also matched by partial melting experiments conducted on peridotite bulk compositions. Hawaiian whole-rocks have elevated FeO contents compared with Siqueiros, which can be explained if Hawaiian parental magmas are generated from peridotite at 4-5 GPa, in contrast to pressures of slightly greater than 1 GPa for melt generation at Siqueiros; these pressures are consistent with olivine thermometry, as described in an earlier paper. SiO2-enriched Koolau compositions are reproduced if high-Fe Hawaiian parental magmas re-equilibrate at 1-1·5 GPa. Peridotite partial melts from experimental studies also reproduce the CaO and Al2O3 contents of Hawaiian (and Siqueiros) whole-rocks. Hawaiian magmas have TiO2

  8. Porous Flow and Diffusion of Water in the Mantle Wedge: Melting and Hydration Patterns

    Science.gov (United States)

    Conder, J. A.

    2005-12-01

    It is widely accepted that melting at volcanic arcs is primarily triggered by fluxing the mantle wedge from the dehydrating subducting slab. However, there is less concensus regarding how water moves into and within the mantle wedge. There are at least four possible mechanisms for water migration in the wedge: buoyant porous flow, diffusion through mineral crystals, advection of hydrated minerals, and compositionally buoyant diapers. The latter two mechanisms require at least one of the first two to occur to get water from the slab into the wedge before they can function. Using geodynamic models of mantle flow in a simplified subduction setting, we explore the implications of diffusion and porous flow of water in the wedge, particularly as they would affect the time for recycling water through the subduction factory and the predicted pattern of basalt hydration across the arc. The slab is assumed to dehydrate in a continuous fashion as the solubility of water in subducted oceanic crust decreases with temperature and pressure and the water then enters the wedge via one of the two transport mechanisms. Diffusion is controlled by temperature and by which minerals are present. Although olivine dominates the mantle mineral fraction, pyroxenes may control the diffusion of water in the wedge as the diffusivity of pyroxene is one or more orders of magnitude greater than olivine. Even assuming the faster diffusion rate of orthopyroxene in the models, diffusion can only be an important transport mechanism when subduction rates are slower than ~3 cm/yr. Flux melting occurs in the wedge above where the slab is ~100-160 km deep with the maximum above where the slab is ~120 km deep. Models including porous flow can result in melting at higher subduction rates provided the permeability of the mantle is greater than 10-17 m2. The true magnitude of the permeability likely varies with the corresponding porosity created by the free phase. With porous flow, melting occurs 20-30 km

  9. The Lowermost Mantle Beneath Central America Imaged by Kirchhoff Migration of Scatterers and Reflectors

    Science.gov (United States)

    Hutko, A.; Lay, T.; Revenaugh, J.

    2007-05-01

    We use tens of thousands of seismograms from South and Central American earthquakes recorded by western North American seismic networks to image the lowermost mantle beneath Central America using a 3D Kirchhoff migration method. P wave studies of the deep mantle often rely on some form of stacking of many records in order to enhance the signal-to-noise ratio of weak phases generated by deep structure, such as reflections off of the D" discontinuity. These methods, however, often assume one-dimensional structure, which is at odds with the evidence for significant heterogeneity. Kirchhoff migration is a three-dimensional stacking method that allows interactions with structure outside of the source-receiver plane, thus illuminating a much larger volume. The D" discontinuity beneath Central America has been readily observed in S wave studies and may be the result of the shear wave velocity increase associated with the recently discovered perovskite to post-perovskite phase transition. This phase transition is expected to have weaker effects on P wave velocities than on S wave velocities and the sharpness of this transition is unknown. Using data at post-critical distances, we observe structures consistent with a P velocity discontinuity about 200 km above the core-mantle boundary (CMB). Observing this using short period data suggests that the boundary must be less than a few 10s of km thick, while observation with lower frequency broadband data exclude the possibility of it being a thin layer. Whether this discontinuity is co-located for both P and S waves is difficult to resolve. Both the broadband and the short period P wave data sets also reveal a sharp out-of-plane scatterer, which may be located close to the CMB. The short period data also indicate reflectivity about 400 km above the CMB, well above the D" discontinuity, and similar reflectivity is observed under the Central Pacific. This feature appears to be more consistent with a discontinuity than a scatterer

  10. Dynamics of mantle rock metasomatic transformation in permeable lithospheric zones beneath Siberian craton

    Science.gov (United States)

    Sharapov, Victor; Sorokin, Konstantin; Perepechko, Yury

    2015-04-01

    inevitably causes the formation of the faults in ultrabasic lithospheric mantle and creation of zonal metasomatic columns, 2) input of the major silicate components to the depleted ultrabasic lithospheric mantle transform them to substrates, which can be attributed to deep seated analogs rodingites, or developing of granatites within the original matrix 3) input of any carbon bearing combinations of fluid follows to the deep carbonation of metasomatic substrate 4 above the marked zones the regenerated pyroxenite zone appears, followed by phlogopitzation and amphibolization, 5) evaluation of heat-mass transfer according to the two-velocity hydrodynamics showed that Darcy approximation Apparently brings to the overestimation of the the rate of thermal wave development during the convective warming up underestimation of the pressure in the fluid stream. It is shown that grospidity, previously considered to be eclogites are the legitimate metasomatic rock associations appearing in permeable zones of lithospheric mantle above the magmatic chambers

  11. The longevity of Archean mantle residues in the convecting upper mantle and their role in young continent formation

    Science.gov (United States)

    Liu, Jingao; Scott, James M.; Martin, Candace E.; Pearson, D. Graham

    2015-08-01

    The role played by ancient melt-depleted lithospheric mantle in preserving continental crust through time is critical in understanding how continents are built, disrupted and recycled. While it has become clear that much of the extant Archean crust is underpinned by Archean mantle roots, reports of Proterozoic melt depletion ages for peridotites erupted through Phanerozoic terranes raise the possibility that ancient buoyant lithospheric mantle acts as a "life-raft" for much of the Earth's continental crust. Here we report the largest crust-lithospheric mantle age decoupling (∼2.4 Ga) so far observed on Earth and examine the potential cause for such extreme age decoupling. The Phanerozoic (Zealandia continent explains the decoupled age relationship that we observe today. Hence, the newly formed lithospheric root incorporates a mixture of ancient and modern mantle derived from the convecting mantle, cooled and accreted in recent times. We argue that in this case, the ancient components played no earlier role in continent stabilization, but their highly depleted nature along with that of their younger counterparts now represents a highly viscous, stable continental keel. This model could account for the large spectrum of ages observed in fertile to moderately depleted peridotites sampled from lithospheric mantle beneath SE Australia, W Antarctica and other locations in Zealandia, as well as the oceanic mantle. Our data confirm the longevity and dispersal of ancient depleted mantle domains in the convecting mantle and their re-appearance beneath young continents.

  12. Modelling the possible interaction between edge-driven convection and the Canary Islands mantle plume

    Science.gov (United States)

    Negredo, A. M.; Rodríguez-González, J.; Fullea, J.; Van Hunen, J.

    2017-12-01

    The close location between many hotspots and the edges of cratonic lithosphere has led to the hypothesis that these hotspots could be explained by small-scale mantle convection at the edge of cratons (Edge Driven Convection, EDC). The Canary Volcanic Province hotspot represents a paradigmatic example of this situation due to its close location to the NW edge of the African Craton. Geochemical evidence, prominent low seismic velocity anomalies in the upper and lower mantle, and the rough NE-SW age-progression of volcanic centers consistently point out to a deep-seated mantle plume as the origin of the Canary Volcanic Province. It has been hypothesized that the plume material could be affected by upper mantle convection caused by the thermal contrast between thin oceanic lithosphere and thick (cold) African craton. Deflection of upwelling blobs due to convection currents would be responsible for the broader and more irregular pattern of volcanism in the Canary Province compared to the Madeira Province. In this study we design a model setup inspired on this scenario to investigate the consequences of possible interaction between ascending mantle plumes and EDC. The Finite Element code ASPECT is used to solve convection in a 2D box. The compositional field and melt fraction distribution are also computed. Free slip along all boundaries and constant temperature at top and bottom boundaries are assumed. The initial temperature distribution assumes a small long-wavelength perturbation. The viscosity structure is based on a thick cratonic lithosphere progressively varying to a thin, or initially inexistent, oceanic lithosphere. The effects of assuming different rheologies, as well as steep or gradual changes in lithospheric thickness are tested. Modelling results show that a very thin oceanic lithosphere (< 30 km) is needed to generate partial melting by EDC. In this case partial melting can occur as far as 700 km away from the edge of the craton. The size of EDC cells is

  13. Mantle-derived trace element variability in olivines and their melt inclusions

    Science.gov (United States)

    Neave, David A.; Shorttle, Oliver; Oeser, Martin; Weyer, Stefan; Kobayashi, Katsura

    2018-02-01

    Trace element variability in oceanic basalts is commonly used to constrain the physics of mantle melting and the chemistry of Earth's deep interior. However, the geochemical properties of mantle melts are often overprinted by mixing and crystallisation processes during ascent and storage. Studying primitive melt inclusions offers one solution to this problem, but the fidelity of the melt-inclusion archive to bulk magma chemistry has been repeatedly questioned. To provide a novel check of the melt inclusion record, we present new major and trace element analyses from olivine macrocrysts in the products of two geographically proximal, yet compositionally distinct, primitive eruptions from the Reykjanes Peninsula of Iceland. By combining these macrocryst analyses with new and published melt inclusion analyses we demonstrate that olivines have similar patterns of incompatible trace element (ITE) variability to the inclusions they host, capturing chemical systematics on intra- and inter-eruption scales. ITE variability (element concentrations, ratios, variances and variance ratios) in olivines from the ITE-enriched Stapafell eruption is best accounted for by olivine-dominated fractional crystallisation. In contrast, ITE variability in olivines and inclusions from the ITE-depleted Háleyjabunga eruption cannot be explained by crystallisation alone, and must have originated in the mantle. Compatible trace element (CTE) variability is best described by crystallisation processes in both eruptions. Modest correlations between host and inclusion ITE contents in samples from Háleyjabunga suggest that melt inclusions can be faithful archives of melting and magmatic processes. It also indicates that degrees of ITE enrichment can be estimated from olivines directly when melt inclusion and matrix glass records of geochemical variability are poor or absent. Inter-eruption differences in olivine ITE systematics between Stapafell and Háleyjabunga mirror differences in melt

  14. The Sensitivity of Joint Inversions of Seismic and Geodynamic Data to Mantle Viscosity

    Science.gov (United States)

    Lu, C.; Grand, S. P.; Forte, A. M.; Simmons, N. A.

    2017-12-01

    Seismic tomography has mapped the existence of large scale mantle heterogeneities in recent years. However, the origin of these velocity anomalies in terms of chemical and thermal variations is still under debate due to the limitations of tomography. Joint inversion of seismic, geodynamic, and mineral physics observations has proven to be a powerful tool to decouple thermal and chemical effects in the deep mantle (Simmons et al. 2010). The approach initially attempts to find a model that can be explained assuming temperature controls lateral variations in mantle properties and then to consider more complicated lateral variations that account for the presence of chemical heterogeneity to further fit data. The geodynamic observations include Earth's free air gravity field, tectonic plate motions, dynamic topography and the excess ellipticity of the core. The sensitivity of the geodynamic observables to density anomalies, however, depends on an assumed radial mantle viscosity profile. Here we perform joint inversions of seismic and geodynamic data using a number of published viscosity profiles. The goal is to test the sensitivity of joint inversion results to mantle viscosity. For each viscosity model, geodynamic sensitivity kernels are calculated and used to jointly invert the geodynamic observations as well as a new shear wave data set for a model of density and seismic velocity. Also, compared with previous joint inversion studies, two major improvements have been made in our inversion. First, we use a nonlinear inversion to account for anelastic effects. Applying the very fast simulate annealing (VFSA) method, we let the elastic scaling factor and anelastic parameters from mineral physics measurements vary within their possible ranges and find the best fitting model assuming thermal variations are the cause of the heterogeneity. We also include an a priori subducting slab model into the starting model. Thus the geodynamic and seismic signatures of short wavelength

  15. Mantle hydration and Cl-rich fluids in the subduction forearc

    Science.gov (United States)

    Reynard, Bruno

    2016-12-01

    a given thermal state through variations of fluid salinity. High-Cl fluids produced by serpentinization can mix with the source rocks of the volcanic arc and explain geochemical signatures of primitive magma inclusions. Signature of deep high-Cl fluids was also identified in forearc hot springs. These observations suggest the existence of fluid circulations between the forearc mantle and the hot spring hydrothermal system or the volcanic arc. Such circulations are also evidenced by recent magnetotelluric profiles.

  16. Crust and Upper Mantle Structure of Antarctica from Rayleigh Wave Tomography

    Science.gov (United States)

    Wiens, D. A.; Heeszel, D. S.; Sun, X.; Chaput, J. A.; Aster, R. C.; Nyblade, A.; Anandakrishnan, S.; Wilson, T. J.; Huerta, A. D.

    2012-12-01

    We combine data from three temporary arrays of seismometers (AGAP/GAMSEIS 2007-2010, ANET/POLENET 2007-2012, TAMSEIS 2001-2003) deployed across Antarctica, along with permanent stations in the region, to produce a large scale shear velocity model of the continent extending from the Gamburtsev Subglacial Mountains (GSM) in East Antarctica, across the Transantarctic Mountains (TAM) and West Antarctic Rift System (WARS) to Marie Byrd Land (MBL) in West Antarctica. Our combined dataset consists of Rayleigh wave phase and amplitude measurements from 112 stations across the study region. We first invert for 2-D Rayleigh wave phase velocities using the two-plane wave method. These results are then inverted for shear velocity structure using crustal thicknesses derived from ambient noise tomography and teleseismic receiver functions. We refine our shear velocity model by performing a Monte Carlo simulation that explores the tradeoff between crustal thickness and upper mantle seismic velocities. The resulting model is higher resolution than previous studies (~150 km resolution length) and highlights significant differences in crustal and uppermost mantle structure between East and West Antarctica in greater detail than previously possible. East Antarctica is underlain by thick crust (reaching ~55 km beneath the GSM) and fast, cratonic lithosphere. West Antarctica is defined by thinner crust and slow upper mantle velocities indicative of its more recent tectonic activity. The observed boundary in crustal thickness closely follows the TAM front. MBL is underlain by a thicker lithosphere than that observed beneath the WARS, but slow mantle velocities persist to depths greater than 200 km, indicating a 'deep seated' (i.e. deeper than the deepest resolvable features of our model) thermal source for volcanism in the region. The slowest seismic velocities at shallow depths are observed in the Terror Rift region of the Ross Sea along an arc following the TAM front, where the most

  17. Seismic scatterers in the mid-lower mantle beneath Tonga-Fiji

    Science.gov (United States)

    Kaneshima, Satoshi

    2018-01-01

    We analyze deep and intermediate-depth earthquakes at the Tonga-Fiji region in order to reveal the distribution of scattering objects in the mid-lower mantle. By array processing waveform data recorded at regional seismograph stations in the US, Alaska, and Japan, we investigate S-to-P scattering waves in the P coda, which arise from kilometer-scale chemically distinct objects in the mid-lower mantle beneath Tonga-Fiji. With ten scatterers previously reported by the author included, twenty-three mid-lower mantle scatterers have been detected below 900 km depth, while scatterers deeper than 1900 km have not been identified. Strong mid-lower mantle S-to-P scattering most frequently occurs at the scatterers located within a depth range between 1400 km and 1600 km. The number of scatterers decreases below 1600 km depth, and the deeper objects tend to be weaker. The scatterer distribution may reflect diminishing elastic anomalies of basaltic rocks with depth relative to the surrounding mantle rocks, which mineral physics has predicted to occur. The predominant occurrence of strong S-to-P scattering waves within a narrow depth range may reflect significant reduction of rigidity due to the ferro-elastic transformation of stishovite in basaltic rocks. Very large signals associated with mid-mantle scatterers are observed only for a small portion of the entire earthquake-array pairs. Such infrequent observations of large scattering signals, combined with quite large event-to-event differences in the scattering intensity for each scatterer, suggest both that the strong arrivals approximately represent ray theoretical S-to-P converted waves at objects with a plane geometry. The plane portions of the strong scatterers may often dip steeply, with the size exceeding 100 km. For a few strong scatterers, the range of receivers showing clear scattered waves varies substantially from earthquake-array pair to pair. Some of the scatterers are also observed at different arrays that have

  18. Structure of Lithospheric and Upper Mantle Discontinuities beneath Central Mongolia from Receiver Functions

    Science.gov (United States)

    Cui, Z.; Meltzer, A.; Fischer, K. M.; Stachnik, J. C.; Munkhuu, U.; Tsagaan, B.; Russo, R. M.

    2017-12-01

    The origin and preservation of high-elevation low-relief surfaces in continental interiors remains an open questions. Central Mongolia constitutes a major portion of the Mongolian Plateau and is an excellent place to link deep earth and surface processes. The lithosphere of Mongolia was constructed through accretionary orogenesis associated with the Central Asian Orogenic Belt (CAOB) from the late Paleozoic to the early Triassic. Alkaline volcanic basalt derived from sublithospheric sources has erupted sporadically in Mongolia since 30 Ma. Constraining the depth variation of lithospheric and upper mantle discontinuities is crucial for understanding the interaction between upper mantle structure and surface topography. We conducted receiver functions (RF) analyses suitable data recorded at112 seismic broadband stations in central Mongolia to image the LAB and mantle transition zone beneath Central Mongolia. A modified H-κ stacking was performed to determine crustal average thickness (H) and Vp/Vs ratio (κ). Central Mongolia is characterized by thick crust (43-57 km) enabling use of both P wave RF and to S wave RF to image the LAB. The PRF traces in the depth domain are stacked based on piercing point locations for the 410 and 660 discontinuities using 0.6 ° × 0.6 ° bins in a grid. From south to north, the average lithospheric thickness is 85km in Gobi Altai gradually thinning northeastward to 78km in the southern Hangay Dome, 72 km in the northern Hangay Dome then increases to 75km in Hovsgol area. While there is overall thinning of the lithosphere from SW to NE, beneath the Hangay, there is a slight increase beneath the highest topography. The thickness of the mantle transition zone (MTZ) beneath central Mongolia is similar to global averages. This evidence argues against the hypothesis that a mantle plume exists beneath Central Mongolia causing low velocity anomalies in the upper mantle. To the east of the Hovsgol area in northern Mongolia, the MTZ thickens

  19. Present mantle flow in North China Craton constrained by seismic anisotropy and numerical modelling

    Science.gov (United States)

    Qu, W.; Guo, Z.; Zhang, H.; Chen, Y. J.

    2017-12-01

    North China Carton (NCC) has undergone complicated geodynamic processes during the Cenozoic, including the westward subduction of the Pacific plate to its east and the collision of the India-Eurasia plates to its southwest. Shear wave splitting measurements in NCC reveal distinct seismic anisotropy patterns at different tectonic blocks, that is, the predominantly NW-SE trending alignment of fast directions in the western NCC and eastern NCC, weak anisotropy within the Ordos block, and N-S fast polarization beneath the Trans-North China Orogen (TNCO). To better understand the origin of seismic anisotropy from SKS splitting in NCC, we obtain a high-resolution dynamic model that absorbs multi-geophysical observations and state-of-the-art numerical methods. We calculate the mantle flow using a most updated version of software ASPECT (Kronbichler et al., 2012) with high-resolution temperature and density structures from a recent 3-D thermal-chemical model by Guo et al. (2016). The thermal-chemical model is obtained by multi-observable probabilistic inversion using high-quality surface wave measurements, potential fields, topography, and surface heat flow (Guo et al., 2016). The viscosity is then estimated by combining the dislocation creep, diffusion creep, and plasticity, which is depended on temperature, pressure, and chemical composition. Then we calculate the seismic anisotropy from the shear deformation of mantle flow by DREX, and predict the fast direction and delay time of SKS splitting. We find that when complex boundary conditions are applied, including the far field effects of the deep subduction of Pacific plate and eastward escaping of Tibetan Plateau, our model can successfully predict the observed shear wave splitting patterns. Our model indicates that seismic anisotropy revealed by SKS is primarily resulting from the LPO of olivine due to the shear deformation from asthenospheric flow. We suggest that two branches of mantle flow may contribute to the

  20. Combined micro and macro geodynamic modelling of mantle flow: methods, potentialities and limits.

    Science.gov (United States)

    Faccenda, M.

    2015-12-01

    Over the last few years, geodynamic simulations aiming at reconstructing the Earth's internal dynamics have increasingly attempted to link processes occurring at the micro (i.e., strain-induced lattice preferred orientation (LPO) of crystal aggregates) and macro scale (2D/3D mantle convection). As a major outcome, such a combined approach results in the prediction of the modelled region's elastic properties that, in turn, can be used to perform seismological synthetic experiments. By comparison with observables, the geodynamic simulations can then be considered as a good numerical analogue of specific tectonic settings, constraining their deep structure and recent tectonic evolution. In this contribution, I will discuss the recent methodologies, potentialities and current limits of combined micro- and macro-flow simulations, with particular attention to convergent margins whose dynamics and deep structure is still the object of extensive studies.

  1. Iron isotope fractionation and the oxygen fugacity of the mantle.

    Science.gov (United States)

    Williams, Helen M; McCammon, Catherine A; Peslier, Anne H; Halliday, Alex N; Teutsch, Nadya; Levasseur, Sylvain; Burg, Jean-Pierre

    2004-06-11

    The oxygen fugacity of the mantle exerts a fundamental influence on mantle melting, volatile speciation, and the development of the atmosphere. However, its evolution through time is poorly understood. Changes in mantle oxidation state should be reflected in the Fe3+/Fe2+ of mantle minerals, and hence in stable iron isotope fractionation. Here it is shown that there are substantial (1.7 per mil) systematic variations in the iron isotope compositions (delta57/54Fe) of mantle spinels. Spinel delta57/54Fe values correlate with relative oxygen fugacity, Fe3+/sigmaFe, and chromium number, and provide a proxy of changes in mantle oxidation state, melting, and volatile recycling.

  2. Constraining subducted slab properties with deep earthquakes

    Science.gov (United States)

    Zhan, Z.; Yang, T.; Gurnis, M.; Shen, Z.; Wu, F.

    2017-12-01

    The discovery of deep earthquakes and Wadati-Benioff zone was a critical piece in the early history of plate tectonics. Today, deep earthquakes continue to serve as important markers/probes of subducted slab geometry, structure, and stress state. Here we discuss three examples in which we have recently used deep earthquakes to provide new insights to subducted slab properties. In the first application, we investigate the slab morphology and stress regimes under different trench motion histories with geodynamic models. We find that the isolation of the 2015 Mw 7.9 Bonin Islands deep earthquake from the background Wadati-Benioff zone may be explained as a result of Pacific slab buckling in response to the slow trench retreat. Additionally, subducted slab is inherently heterogeneous due to non-linear viscosity, contributing to the occurrences of isolated deep earthquakes. In the second application, we quantify the coda waveform differences from nearby deep earthquakes to image fine-scale slab structures. We find that large metastable olivine wedge suggested by several previous studies can not fit our observations. Therefore, the effects of metastable olivine on slab dynamics should be re-assessed. In the third application, we take advantage of P and S differential travel times from deep earthquake clusters to isolate signatures of Vp/Vs ratios within slabs from ambient mantle. We observe substantial deviations of slab Vp/Vs from that in 1D reference Earth models, and even possible lateral variations. This sheds light on potential difference in slab temperature or water content. All three applications underscore that deep earthquakes are still incredibly useful in informing us more about subducted slabs.

  3. Past plate and mantle motion from new ages for the Hawaiian-Emperor Seamount Chain

    Science.gov (United States)

    O'Connor, John; Steinberger, Bernhard; Regelous, Marcel; Koppers, Anthony; Wijbrans, Jan; Haase, Karsten; Stoffers, Peter; Jokat, Wilfried; Garbe-Schoenberg, C.-Dieter

    2014-05-01

    Estimates of the relative motion between the Hawaiian and Louisville hotspots have consequences for understanding the role and character of deep Pacific-mantle return flow. The relative motion between these primary hotspots can be inferred by comparing the age records for their seamount trails. Our new 40Ar/39Ar ages for 18 lavas from 10 seamounts along the Hawaiian-Emperor Seamount Chain (HESC) show that volcanism started in the sharp portion of the Hawaiian-Emperor Bend (HEB) at ≥47.5 Ma and continued for ≥5 Myr (O'Connor et al., 2013). The slope of the along-track distance from the currently active Hawaiian hotspot plotted versus age is remarkably linear between ~57 and 25 Ma in the central ˜1900 km of the seamount chain, including the HEB. This model predicts an age for the oldest Emperor Seamounts that matches published ages, implying that a linear age-distance relationship might extend back to at least 82 Ma. In contrast, Hawaiian age progression was much faster since at least ~15 Ma and possibly as early as ~27 Ma. Linear age-distance relations for the Hawaii-Emperor and Louisville seamount chains predict ~300 km overall hotspot relative motion between 80 and 47.5 Ma, in broad agreement with numerical models of plumes in a convecting mantle, and paleomagnetic data. We show that a change in hotspot relative motion may also have occurred between ~55 Ma and ~50 Ma. We interpret this change in hotspot motion as evidence that the HEB reflects a combination of hotspot and plate motion changes driven by the same plate/mantle reorganization. O'Connor et al. (2013), Constraints on past plate and mantle motion from new ages for the Hawaiian-Emperor Seamount Chain, Geochem. Geophys. Geosyst., 14, 4564-4584, doi:10.1002/ggge.20267.

  4. Climatic Evolution and Habitability of Terrestrial Planets: Perspectives from Coupled Atmosphere-Mantle Systems

    Science.gov (United States)

    Basu Sarkar, D.; Moore, W. B.

    2016-12-01

    A multitude of factors including the distance from the host star and the stage of planetary evolution affect planetary climate and habitability. The complex interactions between the atmosphere and dynamics of the deep interior of the planets along with stellar fluxes present a formidable challenge. This work employs simplified approaches to address these complex issues in a systematic way. To be specific, we are investigating the coupled evolution of atmosphere and mantle dynamics. The overarching goal here is to simulate the evolutionary history of the terrestrial planets, for example Venus, Earth and Mars. This research also aims at deciphering the history of Venus-like runaway greenhouse and thus explore the possibility of cataclysmic shifts in climate of Earth-like planets. We focus on volatile cycling within the solid planets to understand the role of carbon/water in climatic and tectonic outcomes of such planets. In doing so, we are considering the feedbacks in the coupled mantle-atmosphere system. The primary feedback between the atmosphere and mantle is the surface temperature established by the greenhouse effect, which regulates the temperature gradient that drives the mantle convection and controls the rate at which volatiles are exchanged through weathering. We start our models with different initial assumptions to determine the final climate outcomes within a reasonable parameter space. Currently, there are very few planetary examples, to sample the climate outcomes, however this will soon change as exoplanets are discovered and examined. Therefore, we will be able to work with a significant number of potential candidates to answer questions like this one: For every Earth is there one Venus? ten? a thousand?

  5. Abnormal high surface heat flow caused by the Emeishan mantle plume

    Science.gov (United States)

    Jiang, Qiang; Qiu, Nansheng; Zhu, Chuanqing

    2016-04-01

    It is commonly believed that increase of heat flow caused by a mantle plume is small and transient. Seafloor heat flow data near the Hawaiian hotspot and the Iceland are comparable to that for oceanic lithosphere elsewhere. Numerical modeling of the thermal effect of the Parana large igneous province shows that the added heat flow at the surface caused by the magmatic underplating is less than 5mW/m2. However, the thermal effect of Emeishan mantle plume (EMP) may cause the surface hear-flow abnormally high. The Middle-Late Emeishan mantle plume is located in the western Yangtze Craton. The Sichuan basin, to the northeast of the EMP, is a superimposed basin composed of Paleozoic marine carbonate rocks and Mesozoic-Cenozoic terrestrial clastic rocks. The vitrinite reflectance (Ro) data as a paleogeothermal indicator records an apparent change of thermal regime of the Sichuan basin. The Ro profiles from boreholes and outcrops which are close to the center of the basalt province exhibit a 'dog-leg' style at the unconformity between the Middle and Upper Permian, and they show significantly higher gradients in the lower subsection (pre-Middle Permian) than the Upper subsection (Upper Permian to Mesozoic). Thermal history inversion based on these Ro data shows that the lower subsection experienced a heat flow peak much higher than that of the upper subsection. The abnormal heat flow in the Sichuan basin is consistent with the EMP in temporal and spatial distribution. The high-temperature magmas from deep mantle brought heat to the base of the lithosphere, and then large amount of heat was conducted upwards, resulting in the abnormal high surface heat flow.

  6. Mix or un-mix? Trace element segregation from a heterogeneous mantle, simulated.

    Science.gov (United States)

    Katz, R. F.; Keller, T.; Warren, J. M.; Manley, G.

    2016-12-01

    Incompatible trace-element concentrations vary in mid-ocean ridge lavas and melt inclusions by an order of magnitude or more, even in samples from the same location. This variability has been attributed to channelised melt flow [Spiegelman & Kelemen, 2003], which brings enriched, low-degree melts to the surface in relative isolation from depleted inter-channel melts. We re-examine this hypothesis using a new melting-column model that incorporates mantle volatiles [Keller & Katz 2016]. Volatiles cause a deeper onset of channelisation: their corrosivity is maximum at the base of the silicate melting regime. We consider how source heterogeneity and melt transport shape trace-element concentrations in basaltic lavas. We use both equilibrium and non-equilibrium formulations [Spiegelman 1996]. In particular, we evaluate the effect of melt transport on probability distributions of trace element concentration, comparing the inflow distribution in the mantle with the outflow distribution in the magma. Which features of melt transport preserve, erase or overprint input correlations between elements? To address this we consider various hypotheses about mantle heterogeneity, allowing for spatial structure in major components, volatiles and trace elements. Of interest are the roles of wavelength, amplitude, and correlation of heterogeneity fields. To investigate how different modes of melt transport affect input distributions, we compare melting models that produce either shallow or deep channelisation, or none at all.References:Keller & Katz (2016). The Role of Volatiles in Reactive Melt Transport in the Asthenosphere. Journal of Petrology, http://doi.org/10.1093/petrology/egw030. Spiegelman (1996). Geochemical consequences of melt transport in 2-D: The sensitivity of trace elements to mantle dynamics. Earth and Planetary Science Letters, 139, 115-132. Spiegelman & Kelemen (2003). Extreme chemical variability as a consequence of channelized melt transport. Geochemistry

  7. Postaragonite phases of CaCO3 at lower mantle pressures

    Science.gov (United States)

    Smith, Dean; Lawler, Keith V.; Martinez-Canales, Miguel; Daykin, Austin W.; Fussell, Zachary; Smith, G. Alexander; Childs, Christian; Smith, Jesse S.; Pickard, Chris J.; Salamat, Ashkan

    2018-01-01

    The stability, structure, and properties of carbonate minerals at lower mantle conditions have significant impact on our understanding of the global carbon cycle and the composition of the interior of the Earth. In recent years there has been significant interest in the behavior of carbonates at lower mantle conditions, specifically in their carbon hybridization, which has relevance for the storage of carbon within the deep mantle. Using high-pressure synchrotron x-ray diffraction in a diamond anvil cell coupled with direct laser heating of CaCO3 using a CO2 laser, we identify a crystalline phase of the material above 40 GPa—corresponding to a lower mantle depth of around 1000 km—which has first been predicted by ab initio structure predictions. The observed s p2 carbon hybridized species at 40 GPa is monoclinic with P 21/c symmetry and is stable up to 50 GPa, above which it transforms into a structure which cannot be indexed by existing known phases. A combination of ab initio random structure search (AIRSS) and quasiharmonic approximation (QHA) calculations are used to re-explore the relative phase stabilities of the rich phase diagram of CaCO3. Nudged elastic band (NEB) calculations are used to investigate the reaction mechanisms between relevant crystal phases of CaCO3 and we postulate that the mineral is capable of undergoing s p2-s p3 hybridization change purely in the P 21/c structure—forgoing the accepted postaragonite P m m n structure.

  8. The latest geodynamics in Asia: Synthesis of data on volcanic evolution, lithosphere motion, and mantle velocities in the Baikal-Mongolian region

    Directory of Open Access Journals (Sweden)

    Sergei Rasskazov

    2017-07-01

    Full Text Available From a synthesis of data on volcanic evolution, movement of the lithosphere, and mantle velocities in the Baikal-Mongolian region, we propose a comprehensive model for deep dynamics of Asia that assumes an important role of the Gobi, Baikal, and North Transbaikal transition-layer melting anomalies. This layer was distorted by lower-mantle fluxes at the beginning of the latest geodynamic stage (i.e. in the early late Cretaceous due to avalanches of slab material that were stagnated beneath the closed fragments of the Solonker, Ural-Mongolian paleoceans and Mongol-Okhotsk Gulf of Paleo-Pacific. At the latest geodynamic stage, Asia was involved in east–southeast movement, and the Pacific plate moved in the opposite direction with subduction under Asia. The weakened upper mantle region of the Gobi melting anomaly provided a counterflow connected with rollback in the Japan Sea area. These dynamics resulted in the formation of the Honshu-Korea flexure of the Pacific slab. A similar weakened upper mantle region of the North Transbaikal melting anomaly was associated with the formation of the Hokkaido-Amur flexure of the Pacific slab, formed due to progressive pull-down of the slab material into the transition layer in the direction of the Pacific plate and Asia convergence. The early–middle Miocene structural reorganization of the mantle processes in Asia resulted in the development of upper mantle low-velocity domains associated with the development of rifts and orogens. We propose that extension at the Baikal Rift was caused by deviator flowing mantle material, initiated under the moving lithosphere in the Baikal melting anomaly. Contraction at the Hangay orogen was created by facilitation of the tectonic stress transfer from the Indo-Asian interaction zone due to the low-viscosity mantle in the Gobi melting anomaly.

  9. 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...

  10. Chemical equilibration of the Earth's core and upper mantle

    Science.gov (United States)

    Brett, R.

    1984-01-01

    The oxygen fugacity (fO2) of the Earth's upper mantle appears to lie somewhat above that of the iron-wu??stite buffer, its fO2 is assumed to have been similar to the present value at the time of core formation. In the upper mantle, the Fe-rich liquid protocore that would form under such conditions of fO2 at elevated temperatures would lie predominantly in the system Fe-S-O. Distribution coefficients for Co, Cu, Ni, Ir, Au, Ir, W, Re, Mo, Ag and Ga between such liquids and basalt are known and minimum values are known for Ge. From these coefficients, upper mantle abundances for the above elements can be calculated by assuming cosmic abundances for the whole Earth and equilibrium between the Fe-S-O protocore and upper mantle. These calculated abundances are surprisingly close to presently known upper mantle abundances; agreements are within a factor of 5, except for Cu, W, and Mo. Therefore, siderophile element abundances in the upper mantle based on known distribution coefficients do not demand a late-stage meteoritic bombardment, and a protocore formed from the upper mantle containing S and O seems likely. As upper mantle abundances fit a local equilibrium model, then either the upper mantle has not been mixed with the rest of the mantle since core formation, or else partition coefficients between protocore and mantle were similar for the whole mantle regardless of P, T, and fO2. The latter possibility seems unlikely over such a P-T range. ?? 1984.

  11. The boron and lithium isotopic composition of mid-ocean ridge basalts and the mantle

    Science.gov (United States)

    Marschall, Horst R.; Wanless, V. Dorsey; Shimizu, Nobumichi; Pogge von Strandmann, Philip A. E.; Elliott, Tim; Monteleone, Brian D.

    2017-06-01

    variation is unrelated to differentiation, assimilation or mantle source indicators, such as radiogenic isotopes or trace elements. It, therefore, seems likely that kinetic fractionation of Li isotopes during magma extraction, transport and storage may generate δ7 Li excursions in MORB. No mantle heterogeneities, such as those generated by deeply recycled subducted materials, are invoked in the interpretation of the Li and B isotope data presented here, in contrast to previous work on smaller data sets. Lithium and boron budgets for the silicate Earth are presented that are based on isotope and element mass balance. A refined estimate for the B isotopic composition of the bulk continental crust is given as δ11 B = - 9.1 ± 2.4 ‰ . Mass balance allows the existence of recycled B reservoirs in the deep mantle, but these are not required. However, mass balance among the crust, sediments and seawater shows enrichment of 6 Li in the surface reservoirs, which requires the existence of 7 Li -enriched material in the mantle. This may have formed by the subduction of altered oceanic crust since the Archaean.

  12. Water distribution in the lower mantle: Implications for hydrolytic weakening

    Science.gov (United States)

    Muir, Joshua M. R.; Brodholt, John P.

    2018-02-01

    The presence of water in lower mantle minerals is thought to have substantial effects on the rheological properties of the Earth's lower mantle in what is generally known as "hydrolytic weakening". This weakening will have profound effects on global convection, but hydrolytic weakening in lower mantle minerals has not been observed experimentally and thus the effect of water on global dynamics remains speculative. In order to constrain the likelihood of hydrolytic weakening being important in the lower mantle, we use first principles methods to calculate the partitioning of water (strictly protons) between mineral phases of the lower mantle under lower mantle conditions. We show that throughout the lower mantle water is primarily found either in the minor Ca-perovskite phase or in bridgmanite as an Al3+-H+ pair. Ferropericlase remains dry. However, neither of these methods of water absorption creates additional vacancies in bridgmanite and thus the effect of hydrolytic weakening is likely to be small. We find that water creates significant number of vacancies in bridgmanite only at the deepest part of the lower mantle and only for very high water contents (>1000 ppm). We conclude that water is thus likely to have only a limited effect on the rheological properties of the lower mantle.

  13. Melting and reactive flow of a volatilized mantle beneath mid-ocean ridges: theory and numerical models

    Science.gov (United States)

    Keller, Tobias; Katz, Richard F.

    2015-04-01

    Laboratory experiments indicate that even small concentrations volatiles (H2O or CO2) in the upper mantle significantly affect the silicate melting behavior [HK96,DH06]. The presence of volatiles stabilizes volatile-rich melt at high pressure, thus vastly increasing the volume of the upper mantle expected to be partially molten [H10,DH10]. These small-degree melts have important consequences for chemical differentiation and could affect the dynamics of mantle flow. We have developed theory and numerical implementation to simulate thermo-chemically coupled magma/mantle dynamics in terms of a two-phase (rock+melt), three component (dunite+MORB+volatilized MORB) physical model. The fluid dynamics is based on McKenzie's equations [McK84], while the thermo-chemical formulation of the system is represented by a novel disequilibrium multi-component melting model based on thermo-dynamic theory [RBS11]. This physical model is implemented as a parallel, two-dimensional, finite-volume code that leverages tools from the PETSc toolkit. Application of this simulation code to a mid-ocean ridge system suggests that the methodology captures the leading-order features of both hydrated and carbonated mantle melting, including deep, low-degree, volatile-rich melt formation. Melt segregation leads to continuous dynamic thermo-chemical dis-equilibration, while phenomenological reaction rates are applied to continually move the system towards re-equilibration. The simulations will be used first to characterize volatile extraction from the MOR system assuming a chemically homogeneous mantle. Subsequently, simulations will be extended to investigate the consequences of heterogeneity in lithology [KW12] and volatile content. These studies will advance our understanding of the role of volatiles in the dynamic and chemical evolution of the upper mantle. Moreover, they will help to gauge the significance of the coupling between the deep carbon cycle and the ocean/atmosphere system. REFERENCES

  14. Constitution and structure of earth's mantle

    DEFF Research Database (Denmark)

    Zunino, Andrea; Khan, Amir; Cupillard, Paul

    2016-01-01

    This chapter describes a quantitative approach that integrates data and results from mineral physics, petrological analyses, and geophysical inverse calculations to map geophysical data directly for mantle composition and thermal state. Seismic tomography has proved an important tool to image...... seismic data. There is a growing consensus that the cause of the imaged wavespeed anomalies not only relates to variations in temperature, but also bears a strong compositional component. However, separation of thermal and chemical effects from seismic wave speeds alone is difficult and is further...

  15. MicroRNAs in mantle cell lymphoma

    DEFF Research Database (Denmark)

    Husby, Simon; Geisler, Christian; Grønbæk, Kirsten

    2013-01-01

    Mantle cell lymphoma (MCL) is a rare and aggressive subtype of non-Hodgkin lymphoma. New treatment modalities, including intensive induction regimens with immunochemotherapy and autologous stem cell transplant, have improved survival. However, many patients still relapse, and there is a need...... for novel therapeutic strategies. Recent progress has been made in the understanding of the role of microRNAs (miRNAs) in MCL. Comparisons of tumor samples from patients with MCL with their normal counterparts (naive B-cells) have identified differentially expressed miRNAs with roles in cellular growth...

  16. P and SH velocity structure in the upper mantle beneath Northeast China: Evidence for a stagnant slab in hydrous mantle transition zone

    Science.gov (United States)

    Li, Juan; Wang, Xin; Wang, Xiujiao; Yuen, David A.

    2013-04-01

    Using high-dense regional body waves for three deep earthquakes that occurred around Russia-China border, we investigate both S and P wave velocity structures in the mantle transition zone beneath Northeast China and northern part of North China Craton, where the northwestern Pacific plate is imaged to subhorizontally lie above the 660-km discontinuity. We observe an increasing trend of S-P travel time residuals along the epicentral distance within a distance range of 11-16.5°, indicating a velocity anomaly in MTZ. We seek the simplest model that explains the observed broadband waveforms and relative travel times of triplication for a confined azimuth sector. Both SH and P data suggest a ˜140±20 km high velocity layer lying above a slightly depressed and broad 660-km discontinuity. Shear velocity reduction of ˜2.5% in the deeper part of the transition zone is required to compensate for the significantly large relative time between AB and CD triplicate branches and the increased trending of S-P travel time residuals as well. The MTZ, as a whole, is featured by low shear velocity and high Vp/Vs ratio. A water-rich mantle transition zone with 0.2-0.4 wt% of H2O may account for the discrepancy between the observed Vp and Vs velocity structures. Our result supports the scenario of a viscosity-dominated stagnant slab with an increased thickness of ˜140 km, which was caused by the large viscosity contrast between the lower and upper mantles. The addition of water and eastward trench retreat might facilitate stagnation of the subducting Pacific slab beneath Northeast China.

  17. Os-186 and Os-187 Enrichments and High-He-3/He-4 sources in the Earth's Mantle: Evidence from Icelandic Picrites

    Science.gov (United States)

    Brandon, Alan D.; Graham, David W.; Waight, Tod; Gautason, Bjarni

    2007-01-01

    Picrites from the neovolcanic zones in Iceland display a range in Os-187/Os-188O from 0.1297 to 0.1381 ((gamma)Os = 0.0 to 6.5) and uniform Os-186/Os-188 of 0.1198375+/-32 (2 (sigma)). The value for Os-186/Os-188 is within uncertainty of the present-day value for the primitive upper mantle of 0.1198398+/-16. These Os isotope systematics are best explained by ancient recycled crust or melt enrichment in the mantle source region. If so, then the coupled enrichments displayed in Os-186/Os-188 and Os-187/Os-188 from lavas of other plume systems must result from an independent process, the most viable candidate at present remains core-mantle interaction. While some plumes with high He-3/He-4, such as Hawaii, appear to have been subjected to detectable addition of Os (and possibly He) from the outer core, others such as Iceland do not. A positive correlation between Os-187/Os-188 and He-3/He-4 from 9.6 to 19 RA in Iceland picrites is best modeled as mixtures of 500 Ma or older ancient recycled crust mixed with primitive mantle, creating a hybrid source region that subsequently mixes with the convecting MORB mantle during ascent and melting. This multistage mechanism to explain these isotope systematics is consistent with ancient recycled crust juxtaposed with more primitive, relatively He-rich mantle, in convective isolation from the upper mantle, most likely in the lowermost mantle. This is inconsistent with models that propose random mixing between heterogeneities in the convecting upper mantle as a mechanism to explain the observed isotopic variation in oceanic lavas or models that produce a high He-3/He-4 signature in melt depleted and strongly outgassed, He-poor mantle. Instead these systematics require a deep mantle source to explain the 3He/4He signature in Iceland lavas. The He-3/He-4 of lavas derived from the Iceland plume changed over time, from a maximum of 50 RA at 60 Ma, to approximately 25-27 RA at present. The changes are coupled with distinct

  18. An experimental study of Fe-Ni exchange between sulfide melt and olivine at upper mantle conditions: implications for mantle sulfide compositions and phase equilibria

    Science.gov (United States)

    Zhang, Zhou; von der Handt, Anette; Hirschmann, Marc M.

    2018-03-01

    attributable to differences in temperature and pressure between experimental studies. It may be related in part to the effects of metal/sulfur ratio in sulfide melt. Application of these results to the composition of molten sulfide in peridotite indicates that compositions are intermediate in composition (X_{{{Ni}}}^{{{sulfide}}} 0.4-0.6) in the shallow mantle at 50 km, becomes more Ni rich with depth as the O content of the melt diminishes, reaching a maximum (0.6-0.7) at depths near 80-120 km, and then becomes more Fe rich in the deeper mantle where conditions are more reduced, approaching (X_{{{Ni}}}^{{{sulfide}}} 0.28) > 140 km depth. Because Ni-rich sulfide in the shallow upper mantle melts at lower temperature than more Fe-rich compositions, mantle sulfide is likely molten in much of the deep continental lithosphere, including regions of diamond formation.

  19. 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

  20. Mantle transition zone beneath the central Tien Shan: Lithospheric delamination and mantle plumes

    Science.gov (United States)

    Kosarev, Grigoriy; Oreshin, Sergey; Vinnik, Lev; Makeyeva, Larissa

    2018-01-01

    We investigate structure of the mantle transition zone (MTZ) under the central Tien Shan in central Asia by using recordings of seismograph stations in Kyrgyzstan, Kazakhstan and adjacent northern China. We apply P-wave receiver functions techniques and evaluate the differential time between the arrivals of seismic phases that are formed by P to SV mode conversion at the 410-km and 660-km seismic boundaries. The differential time is sensitive to the thickness of the MTZ and insensitive to volumetric velocity anomalies above the 410-km boundary. Under part of the southern central Tien Shan with the lowest S wave velocity in the uppermost mantle and the largest thickness of the crust, the thickness of the MTZ increases by 15-20 km relative to the ambient mantle and the reference model IASP91. The increased thickness is a likely effect of low (about - 150 K) temperature. This anomaly is indicative of delamination and sinking of the mantle lithosphere. The low temperature in the MTZ might also be a relic of subduction of the oceanic lithosphere in the Paleozoic, but this scenario requires strong coupling and coherence between structures in the MTZ and in the lithosphere during plate motions in the last 300 Myr. Our data reveal a reduction of thickness of the MTZ of 10-15 km under the Fergana basin, in the neighborhood of the region of small-scale basaltic volcanism at the time near the Cretaceous-Paleogene boundary. The reduced thickness of the MTZ is the effect of a depressed 410-km discontinuity, similar to that found in many hotspots. This depression suggests a positive temperature anomaly of about 100-150 K, consistent with the presence of a thermal mantle plume. A similar depression on the 410-km discontinuity is found underneath the Tarim basin.

  1. Spatial relationships between crustal structures and mantle seismicity in the Vrancea Seismogenic Zone of Romania: Implications for geodynamic evolution

    Science.gov (United States)

    Enciu, Dana-Mihaela

    Integration of active and passive-source seismic data is employed to study the relationships between crustal structures and seismicity in the SE Carpathian foreland of Romania, and the connection with the Vrancea Seismogenic Zone. Relocated crustal epicenters and focal mechanisms are correlated with industry seismic profiles Comanesti, Ramnicu Sarat, Braila and Buzau, the reprocessed DACIA PLAN profile and the DRACULA (Deep Reflection Acquisition Constraining Unusual Lithospheric Activity) II and III profiles in order to understand the link between neo-tectonic foreland deformation and Vrancea mantle seismicity. Projection of crustal foreland hypocenters onto deep seismic profiles identified active crustal faults suggesting a mechanical coupling between sedimentary, crustal and upper mantle structures on the Trotus, Sinaia and newly observed Ialomita Faults. Seismic reflection imaging revealed the absence of west dipping reflectors in the crust and an east dipping to horizontal Moho in the proximity of the Vrancea area. These findings argue against both 'subduction-in-place' and 'slab break-off' as viable mechanisms for generating Vrancea mantle seismicity.

  2. Electromagnetic exploration of the oceanic mantle.

    Science.gov (United States)

    Utada, Hisashi

    2015-01-01

    Electromagnetic exploration is a geophysical method for examining the Earth's interior through observations of natural or artificial electromagnetic field fluctuations. The method has been in practice for more than 70 years, and 40 years ago it was first applied to ocean areas. During the past few decades, there has been noticeable progress in the methods of instrumentation, data acquisition (observation), data processing and inversion. Due to this progress, applications of this method to oceanic regions have revealed electrical features of the oceanic upper mantle down to depths of several hundred kilometers for different geologic and tectonic environments such as areas around mid-oceanic ridges, areas around hot-spot volcanoes, subduction zones, and normal ocean areas between mid-oceanic ridges and subduction zones. All these results estimate the distribution of the electrical conductivity in the oceanic mantle, which is key for understanding the dynamics and evolution of the Earth together with different physical properties obtained through other geophysical methods such as seismological techniques.

  3. Deep breathing after surgery

    Science.gov (United States)

    ... page: //medlineplus.gov/ency/patientinstructions/000440.htm Deep breathing after surgery To use the sharing features on ... way to do so is by doing deep breathing exercises. Deep breathing keeps your lungs well-inflated ...

  4. Fe-bearing carbonates in the lower mantle: an experimental approach

    Science.gov (United States)

    Cerantola, Valerio; Kupenko, Ilya; McCammon, Catherine; Dubrovinsky, Leonid; Kantor, Innokenty; Marini, Carlo; Solopova, Natalia; Ismailova, Leyla; Chumakov, Alexander; Pascarelli, Sakura

    2014-05-01

    Carbon, a constituent element of life, is continuously exchanged between the surface and the deep Earth's interior. During subduction, this element is brought inside the Earth mainly by means of carbonate, and Fe-bearing carbonates are potential carbon carriers down to the deep lower mantle. Indeed, the presence of iron influences the stability of these phases at high pressures and high temperatures (HPHT), partly due to the spin-pairing of Fe-d electrons. Our study is focused on identifying and characterizing the dominant carbon phases in the deep mantle at the relevant conditions of fO2, P and T, and investigating their thermoelastic properties. To achieve this goal, we performed experiments in a laser-heated diamond anvil cell (DAC) to generate the HPHT conditions prevailing in the Earth's lower mantle. We used a variety of in situ analysis methods, including X-ray diffraction, Mössbauer, Raman and XANES spectroscopies and nuclear inelastic scattering (NIS). All samples were enriched in 57Fe to ensure a strong signal for Mössbauer spectroscopy and NIS. We determined the spin crossover pressure of Fe in single-crystal FeCO3 and Mg0.74Fe0.26CO3 at room temperature using Mössbauer and Raman spectroscopies to be 41(1)-45(1) and 45(1)-48(1) GPa, respectively, showing a slight effect of composition on the transition pressure. We observed that spin crossover of both compositions shifts to higher pressures at T > 650 K based on HPHT Raman experiments. We discovered that new C-rich phases formed from breakdown of these compositions in laser-heated DAC experiments using in situ XANES and synchrotron Mössbauer source (SMS) measurements, which was confirmed by ex situ XRD patterns after quenching. The new C-rich phases contain Fe3+ as observed using SMS spectroscopy, both in situ and after quenching, which implies that redox reactions took place. For comparison, our experiments have also included room temperature measurements of NiCO3 using Raman and XANES

  5. Physical mineralogy of (Ca,Al)-rich silicate phases of the Earth's mantle. Geodynamic implications

    International Nuclear Information System (INIS)

    Gautron, Laurent

    2008-01-01

    Mineral physics could provide answers to many questions we asked about mineral phases present in the Earth's mantle, their characteristics, their crystal structure, their phase transitions. In the second part of the twentieth century, high pressure and high temperature experiments could give essential data about materials from the deep Earth: these data could then be combined to those obtained by seismology measurements, geochemistry analyses, experimental and theoretical geodynamics, for a better understanding of the deep parts of our planet. Many former studies revealed that silicate phases bearing calcium and/or aluminium could display very interesting characteristics and properties, with important geodynamics implications. The combination of calcium and aluminium is know to be very useful for mineral phases: indeed, calcium is able to be substituted by atoms which display large cations, while aluminium when replacing silicon atoms could allow the eventual charge compensation required by the substitution of calcium. Moreover, there is an increasing amount of data which reveal the existence of many new (Ca,Al)-rich silicate phases at (P,T) conditions of the Earth's mantle: these phase are found to display very original structure and properties. In this thesis manuscript, we report the main results obtained about the aluminous calcium perovskite, Al-CaSiO 3 , which is one of the three main mineral phases present in the lower mantle. We show that this phase is able to incorporate huge amount of natural actinides uranium and thorium which provide the main part of the heat produced in our planet, by radioactive decay. Then the Al-rich Ca-perovskite bearing U and Th could be the thermal engine of the Earth's lower mantle. These results obtained by mineral physics experiments and methodology are presented with the objective to better constrain the recent geodynamics models. Here, we propose that the (U,Th)-Al-CaSiO 3 perovskite alone is able to provide the entire

  6. Coupled Deep Earth and surface processes and their impact on geohazards

    NARCIS (Netherlands)

    Cloetingh, S.; Tibaldi, A.; Burov, E.

    2012-01-01

    Better understanding of coupled Deep Earth and surface processes is the key for resolving the evolution of the continental lithosphere and its surface topography. The thermo-mechanical structure of the lithosphere exerts a prime control on the interaction of mantle instabilities and tectonic forces

  7. DeepPy: Pythonic deep learning

    DEFF Research Database (Denmark)

    Larsen, Anders Boesen Lindbo

    This technical report introduces DeepPy – a deep learning framework built on top of NumPy with GPU acceleration. DeepPy bridges the gap between highperformance neural networks and the ease of development from Python/NumPy. Users with a background in scientific computing in Python will quickly...

  8. Continental smokers couple mantle degassing and distinctive microbiology within continents

    Science.gov (United States)

    Crossey, Laura J.; Karlstrom, Karl E.; Schmandt, Brandon; Crow, Ryan R.; Colman, Daniel R.; Cron, Brandi; Takacs-Vesbach, Cristina D.; Dahm, Clifford N.; Northup, Diana E.; Hilton, David R.; Ricketts, Jason W.; Lowry, Anthony R.

    2016-02-01

    The discovery of oceanic black (and white) smokers revolutionized our understanding of mid-ocean ridges and led to the recognition of new organisms and ecosystems. Continental smokers, defined here to include a broad range of carbonic springs, hot springs, and fumaroles that vent mantle-derived fluids in continental settings, exhibit many of the same processes of heat and mass transfer and ecosystem niche differentiation. Helium isotope (3He/4He) analyses indicate that widespread mantle degassing is taking place in the western U.S.A., and that variations in mantle helium values correlate best with low seismic-velocity domains in the mantle and lateral contrasts in mantle velocity rather than crustal parameters such as GPS, proximity to volcanoes, crustal velocity, or composition. Microbial community analyses indicate that these springs can host novel microorganisms. A targeted analysis of four springs in New Mexico yield the first published occurrence of chemolithoautotrophic Zetaproteobacteria in a continental setting. These observations lead to two linked hypotheses: that mantle-derived volatiles transit through conduits in extending continental lithosphere preferentially above and at the edges of mantle low velocity domains. High CO2 and other constituents ultimately derived from mantle volatiles drive water-rock interactions and heterogeneous fluid mixing that help structure diverse and distinctive microbial communities.

  9. Geophysical evidence for chemical variations in the Australian Continental Mantle

    NARCIS (Netherlands)

    Gerven, Luuk van; Deschamps, Frédéric; Hilst, R.D. van der

    2004-01-01

    The relative density-to-shear velocity scaling (ζ) provides a diagnostic for the presence of compositional variations in the mantle. We invert shear-wave velocity from a recent 3-D model and gravity anomalies for radial profiles of ζ of the uppermost mantle beneath Australia. We performed

  10. Geophysical evidence for chemical variations in the Australian continental mantle

    NARCIS (Netherlands)

    Gerven, van L.P.A.; Deschamps, F.; Hilst, R.D.

    2004-01-01

    The relative density-to-shear velocity scaling (¿) provides a diagnostic for the presence of compositional variations in the mantle. We invert shear-wave velocity from a recent 3-D model and gravity anomalies for radial profiles of ¿ of the uppermost mantle beneath Australia. We performed

  11. Hf isotope evidence for a hidden mantle reservoir

    DEFF Research Database (Denmark)

    Bizzarro, Martin; Simonetti, A.; Stevenson, R.K.

    2002-01-01

    High-precision Hf isotopic analyses and U-Pb ages of carbonatites and kimberlites from Greenland and eastern North America, including Earth's oldest known carbonatite (3 Ga), indicate derivation from an enriched mantle source. This previously unidentified mantle reservoir-marked by an unradiogenic...

  12. Influencing parameters on performance of a mantle heat exchanger ...

    African Journals Online (AJOL)

    The experiments arte simulated and validated by using CFD tool ANSYS-CFX and a good agreement is obtained between experiments and simulations. The objective of this paper is to investigate the influence of location of hot fluid inlet, mass flow rate of mantle fluid and type of hot fluid on the performance of the mantle ...

  13. The hottest lavas of the Phanerozoic and the survival of deep Archean reservoirs

    Science.gov (United States)

    Gazel, Esteban; Trela, Jarek; More, Lowell; Alex, Sobolev; Bizimis, Michael; Jicha, Brian

    2017-04-01

    The mantle plume hypothesis is widely accepted for the formation of large igneous provinces and many modern day hotspot volcanoes. Petrologic models suggest that plume-derived melts originate at high mantle temperatures (>1500 °C) relative to those generated at ambient mid-ocean ridge conditions ( 1350 °C). Earth's mantle has also cooled during its history due to heat loss and decrease in radioactive heat production, thus the temperatures of modern day basalts are substantially lower than those produced during the Archean (>2.5 Ga), as recorded by komatiites (>1700 °C). We discovered that the 90 Ma Galapagos-related Tortugal Suite accreted in Costa Rica not only record mantle potential temperatures as high as ancient Archean komatiites ( 1800 °C), but we also collected the highest olivine-spinel crystallization temperatures ever reported in the literature (1600 °C). Therefore, to the best of our knowledge, this suite represents the record of the hottest lavas of the Phanerozoic. These type of magmas occurred more frequently during the Archean due to overall higher ambient mantle temperatures, yet our data suggest that anomalously hot, isolated domains still exist in the deep portions of the planet that have survived billions of years of mantle convection and cooling. This finding is in line with the recent results that showed that early-formed 182W/184W mantle heterogeneities, produced during the first 50 million years of planetary accretion, survived to present time and has been sampled by mantle plumes. Our finding supports the existence of primitive Archean reservoirs, although in most plumes cooler ambient mantle entrainment probably dilutes its temperature signature.

  14. How to fully exploit frequency-dependent S-wave travel times for refining the Earth's mantle imaging?

    Science.gov (United States)

    Zaroli, C.; Nolet, G.; Charlety, J.; Debayle, E.; Sambridge, M.

    2011-12-01

    To better constrain the structure of the Earth's interior, new theoretical developments on seismic wave propagation have emerged in recent years, and received increasing attention in global tomography. A recent focus has been to take into account the "Finite-Frequency" (FF) behaviour of seismic waves (e.g. wavefront-healing). We have chosen to use the FF approach by Dahlen et al. (2000) in multiple frequency bands, based on a ray-Born approximation, also known as Multiple-Frequency Tomography (MFT). The principle of MFT is to invert delay times measured in several frequency bands, using 3-D FF sensitivity kernels for modeling single-scattering phenomena undergone by seismic waves. Such FF effects are intrinsically always present in delay times measured by waveform cross-correlation (as opposed to onset measurements in ray theory). In this study, we pose the question how much MFT really contributes to improving the 3-D imaging of the deep Earth structure? We investigate the role of the model parameterization and regularization when using MFT, in our ability/unability to map the structural dispersion present in the data into a tomographic model. Our data consist of 274 066 globally distributed S, ScS and SS time residuals measured at 10, 15, 22 and 34 s period (Zaroli et al., 2010). Two ways of parameterizing the Earth's mantle, and their implications on the model obtained using MFT, are presented. One is based on irregularly spaced spherical triangular prisms, with nodes spacing ranging from 200 to 900 km, i.e. a "coarse" parameterization. The other is based on a "cubed Earth", that consists of cubic cells of 70 km size near the top, down to 35 km near the base of the mantle, i.e. a "fine" parameterization. We also investigate how the model regularization (i.e. choice of the damping parameter in the inversion) may prevent us from fully exploiting the extra information, on the 3-D structure, present in our multi-band dataset. We present a comparison of a multi

  15. Carbon isotope heterogeneities in deep Earth: Recycling of surface carbon or from core?

    Science.gov (United States)

    Satish-Kumar, Madhusoodhan

    2017-04-01

    Subduction of crustal materials, mantle melting and upwelling of deep mantle, in addition to a potential source from the core, largely controls the Earth's deep carbon cycle. Large variations in carbon isotopic composition between different reservoirs have been used widely to differentiate the source of carbon and to understand the carbon inventories and its recycling processes. However, how far high-temperature and hign-pressure conditions can affect the carbon isotope distribution, is a question still unanswered to clearly address the deep carbon cycle. I present here a review on carbon isotope fractionation processes in deep Earth and critically evaluate whether we can easily differentiate between surface carbon and deep carbon based on isotope characteristics. Recent experimental carbon isotope fractionation studies in the Fe-C system suggests that light carbon is selectively partition into metallic core during early magma ocean environment (Satish-Kumar et al., 2011). Furthermore, carbonate melts can be a medium for efficient crystallisation of diamonds in Earth's mantle (Palyanov et al., 2013). Rayleigh fractionation modelling based on fractionation suggests that core can be a reservoir of 12C enriched carbon and can itself form a reservoir which can cause heterogeneity in mantle carbon (Wood et al., 2013). In addition, high pressure experiments in the carbon-saturated model harzburgite system (Enstatite-Magnesite-Olivine-Graphite), carbonated silicate melting resulted in 13C enrichment in the carbon dissolved in the silicate melt relative to elemental graphite (Mizutani et al., 2014). 13C enrichment in carbonate melt were further confirmed in experiments where redox melting between olivine and graphite produced a carbonate melt as well as carbonate reduction experiments to form graphite. A third factor, still unconquered is the effect of pressure on isotope fractionation process. Theoretical studies as well as preliminary experimental studies have suggested

  16. Fluorine and chlorine in mantle minerals and the halogen budget of the Earth's mantle

    Science.gov (United States)

    Urann, B. M.; Le Roux, V.; Hammond, K.; Marschall, H. R.; Lee, C.-T. A.; Monteleone, B. D.

    2017-07-01

    The fluorine (F) and chlorine (Cl) contents of arc magmas have been used to track the composition of subducted components, and the F and Cl contents of MORB have been used to estimate the halogen content of depleted MORB mantle (DMM). Yet, the F and Cl budget of the Earth's upper mantle and their distribution in peridotite minerals remain to be constrained. Here, we developed a method to measure low concentrations of halogens (≥0.4 µg/g F and ≥0.3 µg/g Cl) in minerals by secondary ion mass spectroscopy. We present a comprehensive study of F and Cl in co-existing natural olivine, orthopyroxene, clinopyroxene, and amphibole in seventeen samples from different tectonic settings. We support the hypothesis that F in olivine is controlled by melt polymerization, and that F in pyroxene is controlled by their Na and Al contents, with some effect of melt polymerization. We infer that Cl compatibility ranks as follows: amphibole > clinopyroxene > olivine orthopyroxene, while F compatibility ranks as follows: amphibole > clinopyroxene > orthopyroxene ≥ olivine, depending on the tectonic context. In addition, we show that F, Cl, Be and B are correlated in pyroxenes and amphibole. F and Cl variations suggest that interaction with slab melts and fluids can significantly alter the halogen content of mantle minerals. In particular, F in oceanic peridotites is mostly hosted in pyroxenes, and proportionally increases in olivine in subduction-related peridotites. The mantle wedge is likely enriched in F compared to un-metasomatized mantle, while Cl is always low (<1 µg/g) in all tectonic settings studied here. The bulk anhydrous peridotite mantle contains 1.4-31 µg/g F and 0.14-0.38 µg/g Cl. The bulk F content of oceanic-like peridotites (2.1-9.4 µg/g) is lower than DMM estimates, consistent with F-rich eclogite in the source of MORB. Furthermore, the bulk Cl budget of all anhydrous peridotites studied here is lower than previous DMM estimates. Our results indicate that

  17. Viscosity of MgSiO3 liquid at Earth's mantle conditions: implications for an early magma ocean.

    Science.gov (United States)

    Karki, Bijaya B; Stixrude, Lars P

    2010-05-07

    Understanding the chemical and thermal evolution of Earth requires knowledge of transport properties of silicate melts at high pressure and high temperature. Here, first-principles molecular dynamics simulations show that the viscosity of MgSiO3 liquid varies by two orders of magnitude over the mantle pressure regime. Addition of water systematically lowers the viscosity, consistent with enhanced structural depolymerization. The combined effects of pressure and temperature along model geotherms lead to a 10-fold increase in viscosity with depth from the surface to the base of the mantle. Based on these calculations, efficient heat flux from a deep magma ocean may have exceeded the incoming solar flux early in Earth's history.

  18. Molybdenum isotope fractionation in the mantle

    Science.gov (United States)

    Liang, Yu-Hsuan; Halliday, Alex N.; Siebert, Chris; Fitton, J. Godfrey; Burton, Kevin W.; Wang, Kuo-Lung; Harvey, Jason

    2017-02-01

    We report double-spike molybdenum (Mo) isotope data for forty-two mafic and fifteen ultramafic rocks from diverse locations and compare these with results for five chondrites. The δ98/95Mo values (normalized to NIST SRM 3134) range from -0.59 ± 0.04 to +0.10 ± 0.08‰. The compositions of one carbonaceous (CI) and four ordinary chondrites are relatively uniform (-0.14 ± 0.01‰, 95% ci (confidence interval)) in excellent agreement with previous data. These values are just resolvable from the mean of 10 mid-ocean ridge basalts (MORBs) (0.00 ± 0.02‰, 95% ci). The compositions of 13 mantle-derived ultramafic xenoliths from Kilbourne Hole, Tariat and Vitim are more diverse (-0.39 to -0.07‰) with a mean of -0.22 ± 0.06‰ (95% ci). On this basis, the isotopic composition of the bulk silicate Earth (BSE or Primitive Mantle) is within error identical to chondrites. The mean Mo concentration of the ultramafic xenoliths (0.19 ± 0.07 ppm, 95% ci) is similar in magnitude to that of MORB (0.48 ± 0.13 ppm, 95% ci), providing evidence, either for a more compatible behaviour than previously thought or for selective Mo enrichment of the subcontinental lithospheric mantle. Intraplate and ocean island basalts (OIBs) display significant isotopic variability within a single locality from MORB-like to strongly negative (-0.59 ± 0.04‰). The most extreme values measured are for nephelinites from the Cameroon Line and Trinidade, which also have anomalously high Ce/Pb and low Mo/Ce relative to normal oceanic basalts. δ98/95Mo correlates negatively with Ce/Pb and U/Pb, and positively with Mo/Ce, explicable if a phase such as an oxide or a sulphide liquid selectively retains isotopically heavy Mo in the mantle and fractionates its isotopic composition in low degree partial melts. If residual phases retain Mo during partial melting, it is possible that the [Mo] for the BSE may be misrepresented by values estimated from basalts. This would be consistent with the high Mo

  19. DeepPy: Pythonic deep learning

    OpenAIRE

    Larsen, Anders Boesen Lindbo

    2016-01-01

    This technical report introduces DeepPy – a deep learning framework built on top of NumPy with GPU acceleration. DeepPy bridges the gap between highperformance neural networks and the ease of development from Python/NumPy. Users with a background in scientific computing in Python will quickly be able to understand and change the DeepPy codebase as it is mainly implemented using high-level NumPy primitives. Moreover, DeepPy supports complex network architectures by letting the user compose mat...

  20. Asymmetric three-dimensional topography over mantle plumes.

    Science.gov (United States)

    Burov, Evgueni; Gerya, Taras

    2014-09-04

    The role of mantle-lithosphere interactions in shaping surface topography has long been debated. In general, it is supposed that mantle plumes and vertical mantle flows result in axisymmetric, long-wavelength topography, which strongly differs from the generally asymmetric short-wavelength topography created by intraplate tectonic forces. However, identification of mantle-induced topography is difficult, especially in the continents. It can be argued therefore that complex brittle-ductile rheology and stratification of the continental lithosphere result in short-wavelength modulation and localization of deformation induced by mantle flow. This deformation should also be affected by far-field stresses and, hence, interplay with the 'tectonic' topography (for example, in the 'active/passive' rifting scenario). Testing these ideas requires fully coupled three-dimensional numerical modelling of mantle-lithosphere interactions, which so far has not been possible owing to the conceptual and technical limitations of earlier approaches. Here we present new, ultra-high-resolution, three-dimensional numerical experiments on topography over mantle plumes, incorporating a weakly pre-stressed (ultra-slow spreading), rheologically realistic lithosphere. The results show complex surface evolution, which is very different from the smooth, radially symmetric patterns usually assumed as the canonical surface signature of mantle upwellings. In particular, the topography exhibits strongly asymmetric, small-scale, three-dimensional features, which include narrow and wide rifts, flexural flank uplifts and fault structures. This suggests a dominant role for continental rheological structure and intra-plate stresses in controlling dynamic topography, mantle-lithosphere interactions, and continental break-up processes above mantle plumes.

  1. Scattering beneath Western Pacific subduction zones: evidence for oceanic crust in the mid-mantle

    Science.gov (United States)

    Bentham, H. L. M.; Rost, S.

    2014-06-01

    Small-scale heterogeneities in the mantle can give important insight into the dynamics and composition of the Earth's interior. Here, we analyse seismic energy found as precursors to PP, which is scattered off small-scale heterogeneities related to subduction zones in the upper and mid-mantle. We use data from shallow earthquakes (less than 100 km depth) in the epicentral distance range of 90°-110° and use array methods to study a 100 s window prior to the PP arrival. Our analysis focuses on energy arriving off the great circle path between source and receiver. We select coherent arrivals automatically, based on a semblance weighted beampower spectrum, maximizing the selection of weak amplitude arrivals. Assuming single P-to-P scattering and using the directivity information from array processing, we locate the scattering origin by ray tracing through a 1-D velocity model. Using data from the small-aperture Eielson Array (ILAR) in Alaska, we are able to image structure related to heterogeneities in western Pacific subduction zones. We find evidence for ˜300 small-scale heterogeneities in the region around the present-day Japan, Izu-Bonin, Mariana and West Philippine subduction zones. Most of the detected heterogeneities are located in the crust and upper mantle, but 6 per cent of scatterers are located deeper than 600 km. Scatterers in the transition zone correlate well with edges of fast features in tomographic images and subducted slab contours derived from slab seismicity. We locate deeper scatterers beneath the Izu-Bonin/Mariana subduction zones, which outline a steeply dipping pseudo-planar feature to 1480 km depth, and beneath the ancient (84-144 Ma) Indonesian subduction trench down to 1880 km depth. We image the remnants of subducted crustal material, likely the underside reflection of the subducted Moho. The presence of deep scatterers related to past and present subduction provides evidence that the subducted crust does descend into the lower mantle at

  2. Stability of Carbonated Eclogite in the Upper Mantle: Experimental Solidus from 2 to 9 GPa

    Science.gov (United States)

    Dasgupta, R.; Withers, A. C.; Hirschmann, M. M.

    2003-12-01

    intersects the oceanic geotherm deeper than 400 km. Thus, eclogite cannot host carbonates in the asthenosphere. Carbonated eclogite bodies entering the convecting upper mantle would release carbonate melt in the mantle transition zone. Upon release, this small volume, highly reactive melt could be an effective agent of deep mantle metasomatism. Comparison of our eclogite-CO2 solidus with that of peridotite-CO2 shows a shallower solidus-geotherm intersection for the latter. This implies that carbonated peridotite is a more likely proximal source of magmatic carbon in oceanic provinces. However, carbonated eclogite is a potential source of continental carbonatites, as its solidus crosses the continental shield geotherm at ca. 4 GPa.

  3. Combined teleseismic surface wave and receiver function analysis of the crust and upper mantle of Madagascar

    Science.gov (United States)

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

    2014-12-01

    probe the transition zone and determine whether or not these low-velocity zones extend into the deep mantle.

  4. 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.

  5. Modeling the Crust and Upper Mantle in Northern Beata Ridge (CARIBE NORTE Project)

    Science.gov (United States)

    Núñez, Diana; Córdoba, Diego; Cotilla, Mario Octavio; Pazos, Antonio

    2016-05-01

    The complex tectonic region of NE Caribbean, where Hispaniola and Puerto Rico are located, is bordered by subduction zone with oblique convergence in the north and by incipient subduction zone associated to Muertos Trough in the south. Central Caribbean basin is characterized by the presence of a prominent topographic structure known as Beata Ridge, whose oceanic crustal thickness is unusual. The northern part of Beata Ridge is colliding with the central part of Hispaniola along a transverse NE alignment, which constitutes a morphostructural limit, thus producing the interruption of the Cibao Valley and the divergence of the rivers and basins in opposite directions. The direction of this alignment coincides with the discontinuity that could explain the extreme difference between west and east seismicity of the island. Different studies have provided information about Beata Ridge, mainly about the shallow structure from MCS data. In this work, CARIBE NORTE (2009) wide-angle seismic data are analyzed along a WNW-ESE trending line in the northern flank of Beata Ridge, providing a complete tectonic view about shallow, middle and deep structures. The results show clear tectonic differences between west and east separated by Beata Island. In the Haiti Basin area, sedimentary cover is strongly influenced by the bathymetry and its thickness decreases toward to the island. In this area, the Upper Mantle reaches 20 km deep increasing up to 24 km below the island where the sedimentary cover disappears. To the east, the three seamounts of Beata Ridge provoke the appearance of a structure completely different where sedimentary cover reaches thicknesses of 4 km between seamounts and Moho rises up to 13 km deep. This study has allowed to determine the Moho topography and to characterize seismically the first upper mantle layers along the northern Beata Ridge, which had not been possible with previous MCS data.

  6. NoMelt Experiment: High-resolution constraints on Pacific upper mantle fabric inferred from radial and azimuthal anisotropy

    Science.gov (United States)

    Russell, J. B.; Gaherty, J. B.; Lin, P. P.; Lizarralde, D.; Collins, J. A.; Hirth, G.; Evans, R. L.

    2017-12-01

    Observations of seismic anisotropy in the ocean basins are important for constraining deformation and melting processes in the upper mantle. The NoMelt OBS array was deployed on relatively pristine, 70 Ma seafloor in the central Pacific with the aim of constraining upper mantle circulation and the evolution of the lithosphere-asthenosphere system. Surface-waves traversing the array provide a unique opportunity to estimate a comprehensive set of anisotropic parameters. Azimuthal variations in Rayleigh-wave velocity over a period band of 15-180 s suggest strong anisotropic fabric both in the lithosphere and deep in the asthenosphere. High-frequency ambient noise (4-10 s) provides constraints on average VSV and VSH as well as azimuthal variations in both VS and VP in the upper ˜10 km of the mantle. Our best fitting models require radial anisotropy in the uppermost mantle with VSH > VSV by 3 - 7% and as much as 2% radial anisotropy in the crust. Additionally, we find a strong azimuthal dependence for Rayleigh- and Love-wave velocities, with Rayleigh 2θ fast direction parallel to the fossil spreading direction (FSD) and Love 2θ and 4θ fast directions shifted 90º and 45º from the FSD, respectively. These are some of the first direct observations of the Love 2θ and 4θ azimuthal signal, which allows us to directly invert for anisotropic terms G, B, and E in the uppermost Pacific lithosphere, for the first time. Together, these observations of radial and azimuthal anisotropy provide a comprehensive picture of oceanic mantle fabric and are consistent with horizontal alignment of olivine with the a-axis parallel to fossil spreading and having an orthorhombic or hexagonal symmetry.

  7. A large mantle water source for the northern San Andreas Fault System: A ghost of subduction past

    Science.gov (United States)

    Kirby, Stephen H.; Wang, Kelin; Brocher, Thomas M.

    2014-01-01

    Recent research indicates that the shallow mantle of the Cascadia subduction margin under near-coastal Pacific Northwest U.S. is cold and partially serpentinized, storing large quantities of water in this wedge-shaped region. Such a wedge probably formed to the south in California during an earlier period of subduction. We show by numerical modeling that after subduction ceased with the creation of the San Andreas Fault System (SAFS), the mantle wedge warmed, slowly releasing its water over a period of more than 25 Ma by serpentine dehydration into the crust above. This deep, long-term water source could facilitate fault slip in San Andreas System at low shear stresses by raising pore pressures in a broad region above the wedge. Moreover, the location and breadth of the water release from this model gives insights into the position and breadth of the SAFS. Such a mantle source of water also likely plays a role in the occurrence of Non-Volcanic Tremor (NVT) that has been reported along the SAFS in central California. This process of water release from mantle depths could also mobilize mantle serpentinite from the wedge above the dehydration front, permitting upward emplacement of serpentinite bodies by faulting or by diapiric ascent. Specimens of serpentinite collected from tectonically emplaced serpentinite blocks along the SAFS show mineralogical and structural evidence of high fluid pressures during ascent from depth. Serpentinite dehydration may also lead to tectonic mobility along other plate boundaries that succeed subduction, such as other continental transforms, collision zones, or along present-day subduction zones where spreading centers are subducting.

  8. Calcium isotopic composition of mantle peridotites

    Science.gov (United States)

    Huang, F.; Kang, J.; Zhang, Z.

    2015-12-01

    Ca isotopes are useful to decipher mantle evolution and the genetic relationship between the Earth and chondrites. It has been observed that Ca isotopes can be fractionated at high temperature [1-2]. However, Ca isotopic composition of the mantle peridotites and fractionation mechanism are still poorly constrained. Here, we report Ca isotope composition of 12 co-existing pyroxene pairs in 10 lherzolites, 1 harzburgite, and 1 wehrlite xenoliths collected from Hainan Island (South Eastern China). Ca isotope data were measured on a Triton-TIMS using the double spike method at the Guangzhou Institute of Geochemistry, CAS. The long-term external error is 0.12‰ (2SD) based on repeated analyses of NIST SRM 915a and geostandards. δ44Ca of clinopyroxenes except that from the wehrlite ranges from 0.85‰ to 1.14‰, while opx yields a wide range from 0.98‰ up to 2.16‰. Co-existing pyroxene pairs show large Δ44Caopx-cpx (defined as δ44Caopx-δ44Cacpx) ranging from 0 to 1.23‰, reflecting equilibrium fractionation controlled by variable Ca contents in the opx. Notably, clinopyroxene of wehrlite shows extremely high δ44Ca (3.22‰). δ44Ca of the bulk lherzolites and harzburgites range from 0.86‰ to 1.14‰. This can be explained by extracting melts with slightly light Ca isotopic compositions. Finally, the high δ44Ca of the wehrlite (3.22‰) may reflect metasomatism by melt which has preferentially lost light Ca isotopes due to chemical diffusion during upwelling through the melt channel. [1] Amini et al (2009) GGR 33; [2] Huang et al (2010) EPSL 292.

  9. Lithospheric mantle evolution in the Afro-Arabian domain: Insights from Bir Ali mantle xenoliths (Yemen)

    Science.gov (United States)

    Sgualdo, P.; Aviado, K.; Beccaluva, L.; Bianchini, G.; Blichert-Toft, J.; Bryce, J. G.; Graham, D. W.; Natali, C.; Siena, F.

    2015-05-01

    Detailed petrological and geochemical investigations of an extensive sampling of mantle xenoliths from the Neogene-Quaternary Bir Ali diatreme (southern Yemen) indicate that the underlying lithospheric mantle consists predominantly of medium- to fine-grained (often foliated) spinel-peridotites (85-90%) and spinel-pyroxenites (10-15%) showing thermobarometric estimates in the P-T range of 0.9-2.0 GPa and 900-1150 °C. Peridotites, including lherzolites, harzburgites and dunites delineate continuous chemical, modal and mineralogical variations compatible with large extractions of basic melts occurring since the late Proterozoic (~ 2 Ga, according to Lu-Hf model ages). Pyroxenites may represent intrusions of subalkaline basic melts interacting and equilibrated with the host peridotite. Subsequent metasomatism has led to modal changes, with evidence of reaction patches and clinopyroxene and spinel destabilization, as well as formation of new phases (glass, amphibole and feldspar). These changes are accompanied by enrichment of the most incompatible elements and isotopic compositions. 143Nd/144Nd ranges from 0.51419 to 0.51209 (εNd from + 30.3 to - 10.5), 176Hf/177Hf from 0.28459 to 0.28239 (εHf from + 64.4 to - 13.6), and 208Pb/204Pb from 36.85 to 41.56, thus extending from the depleted mantle (DM) towards the enriched OIB mantle (EM and HIMU) components. 3He/4He (R/RA) ratios vary from 7.2 to 7.9 with He concentrations co-varying with the most incompatible element enrichment, in parallel with metasomatic effects. These metasomatic events, particularly effective in harzburgites and dunites, are attributable to the variable interaction with alkaline basic melts related to the general extensional and rifting regime affecting the East Africa-Arabian domain during the Cenozoic. In this respect, Bir Ali mantle xenoliths resemble those occurring along the Arabian margins and the East Africa Rift system, similarly affected by alkaline metasomatism, whereas they are

  10. Greedy Deep Dictionary Learning

    OpenAIRE

    Tariyal, Snigdha; Majumdar, Angshul; Singh, Richa; Vatsa, Mayank

    2016-01-01

    In this work we propose a new deep learning tool called deep dictionary learning. Multi-level dictionaries are learnt in a greedy fashion, one layer at a time. This requires solving a simple (shallow) dictionary learning problem, the solution to this is well known. We apply the proposed technique on some benchmark deep learning datasets. We compare our results with other deep learning tools like stacked autoencoder and deep belief network; and state of the art supervised dictionary learning t...

  11. The ruthenium isotopic composition of the oceanic mantle

    Science.gov (United States)

    Bermingham, K. R.; Walker, R. J.

    2017-09-01

    The approximately chondritic relative, and comparatively high absolute mantle abundances of the highly siderophile elements (HSE), suggest that their concentrations in the bulk silicate Earth were primarily established during a final ∼0.5 to 1% of ;late accretion; to the mantle, following the cessation of core segregation. Consequently, the isotopic composition of the HSE Ru in the mantle reflects an amalgamation of the isotopic compositions of late accretionary contributions to the silicate portion of the Earth. Among cosmochemical materials, Ru is characterized by considerable mass-independent isotopic variability, making it a powerful genetic tracer of Earth's late accretionary building blocks. To define the Ru isotopic composition of the oceanic mantle, the largest portion of the accessible mantle, we report Ru isotopic data for materials from one Archean and seven Phanerozoic oceanic mantle domains. A sample from a continental lithospheric mantle domain is also examined. All samples have identical Ru isotopic compositions, within analytical uncertainties, indicating that Ru isotopes are well mixed in the oceanic mantle, defining a μ100Ru value of 1.2 ± 7.2 (2SD). The only known meteorites with the same Ru isotopic composition are enstatite chondrites and, when corrected for the effects of cosmic ray exposure, members of the Main Group and sLL subgroup of the IAB iron meteorite complex which have a collective CRE corrected μ100Ru value of 0.9 ± 3.0. This suggests that materials from the region(s) of the solar nebula sampled by these meteorites likely contributed the dominant portion of late accreted materials to Earth's mantle.

  12. Drilling the Oceanic Lower Crust and Mantle

    Science.gov (United States)

    1989-11-01

    tests (in Puget Sound) scheduled for late summer or fall of 1989, and full scale, deep-ocean (>-000 m) tests on the Washington margin and Gorda Ridge...Klamath Mountains and Sierra Nevada and suggests a spreading geometry where short spreading segments are separated by long arc-parallel transforms

  13. Solar combi system based on a mantle tank

    DEFF Research Database (Denmark)

    Yazdanshenas, Eshagh; Furbo, Simon

    2007-01-01

    A solar combisystem based on a mantle tank is investigated numerically and experimentally. Three different houses with four different radiator systems are considered for the simulations. The needed temperature for the auxiliary heater is determined for different houses and radiator systems....... The thermal performance of the solar combisystem is compared to the thermal performance of a solar domestic hot water system based on a mantle tank. In the experimental study, tank temperatures and the heat transfer coefficient for the top mantle for a discharge test is determined. The investigations showed...

  14. A numerical model of mantle convection with deformable, mobile continental lithosphere within three-dimensional spherical geometry

    Science.gov (United States)

    Yoshida, M.

    2010-12-01

    stretched by the convecting mantle and may play a significant role in the stability of the cratonic lithosphere during the geological timescale because it acts as a buffer that prevents the cratonic lithosphere from undergoing global deformation. From geological evidence that a cratonic root survives at the surface for billions of years, the WCM may have existed in the past supercontinent throughout the Earth's geologic history. The preliminary model presented here should represent an important step toward realizing a more realistic model that could be used to address many outstanding geodynamic problems about the thermal and mechanical feedbacks between the mantle and continents and the temporal evolution of the Earth's mantle structure.

  15. Simultaneous Inversion of Mantle Mode Splitting Coefficients for Vs, Vp and ρ Using the Neighbourhood Algorithm.

    Science.gov (United States)

    Rousset, S. C.; Romanowicz, B.

    2003-12-01

    Unlike travel times or waveform data, normal mode data are directly sensitive to the density of the Earth. However, the sensitivity kernels for density are much smaller than those for velocities, so the controversy about the possibility of resolution of the mantle's density is vivid, especially since the publication of model SPRD6 (Ishii and Tromp, 1999) whose high density structures corresponding with the "plumes" under Pacific and Africa would have important consequences on deep mantle dynamics. Using least squares inversion, several authors (e.g. Resovsky and Ritzwoller, 1999, Kuo and Romanowicz, 2002) pointed out significant trade-offs between velocity and density structure. Using a stochastic method may end the controversy about the resolution of density by estimating the posterior probability density of the parameter space. Such an approach was used by Resovsky and Ritzwoller (2002) who concluded in the non resolution of the density but did not investigate further. Here we investigate the effect of other parameterizations and of an extended dataset (Widmer, 2002). In particular, we look at the possibility of resolving a spline-based shear velocity model and the scaling relations d(ln Vp)/d(ln Vs) and d(ln ρ )/d(ln Vs). We search for 3 scaling parameters (lowermost, middle and upper mantle) and allow spatial variations of these parameters as each degree 2 spherical harmonic coefficient is considered separately. We present the results of the sampling of the parameter space and of the appraising of the ensemble generated in the form of marginal probabilities for the different parameters.

  16. Mapping the mantle transition zone beneath the central Mid-Atlantic Ridge using Ps receiver functions.

    Science.gov (United States)

    Agius, M. R.; Rychert, C.; Harmon, N.; Kendall, J. M.

    2017-12-01

    Determining the mechanisms taking place beneath ridges is important in order to understand how tectonic plates form and interact. Of particular interest is establishing the depth at which these processes originate. Anomalies such as higher temperature within the mantle transition zone may be inferred seismically if present. However, most ridges are found in remote locations beneath the oceans restricting seismologists to use far away land-based seismometers, which in turn limits the imaging resolution. In 2016, 39 broadband ocean-bottom seismometers were deployed across the Mid-Atlantic Ridge, along the Romanche and Chain fracture zones as part of the PI-LAB research project (Passive Imaging of the Lithosphere and Asthenosphere Boundary). The one-year long seismic data is now retrieved and analysed to image the mantle transition zone beneath the ridge. We determine P-to-s (Ps) receiver functions to illuminate the 410- and 660-km depth mantle discontinuities using the extended multitaper deconvolution. The data from ocean-bottom seismometers have tilt and compliance noise corrections and is filtered between 0.05-0.2 Hz to enhance the signal. 51 teleseismic earthquakes generated hundreds of good quality waveforms, which are then migrated to depth in 3-D. The topography at the d410 deepens towards the west of the Romanche and Chain fracture zone by 15 km, whereas the topography of d660 shallows beneath the ridge between the two zones. Transition zone thickness thins from 5 to 20 km. Thermal anomalies determined from temperature relationships with transition zone thickness and depth variations of the d410 and d660 suggests hotter temperatures of about 200 K. Overall, the result suggests mid-ocean ridges may have associated thermal signatures as deep as the transition zone.

  17. Mantle structure beneath the western United States and its implications for convection processes

    Science.gov (United States)

    Xue, Mei; Allen, Richard M.

    2010-07-01

    We present tomographic images of the mantle structure beneath the western United States. Our Dynamic North America Models of P and S velocity structure (DNA07-P and DNA07-S) use teleseismic body waves recorded at ˜600 seismic stations provided by the Earthscope Transportable Array and regional networks. DNA07-P and -S benefit from the unprecedented aperture of the network while maintaining a dense station distribution providing high-resolution body wave imaging of features through the transition zone and into the lower mantle. The main features imaged include (1) the Juan de Fuca subduction system that bottoms at ˜400 km beneath Oregon, implying interaction with the Yellowstone anomaly; (2) a low-velocity conduit beneath Yellowstone National Park that bottoms at 500 km and dips toward the northwest; (3) shallow low-velocity anomalies (upper 200 km) beneath the eastern Snake River Plain (ESRP) and the High Lava Plains, and a deep low-velocity anomaly (>600 km) beneath the ESRP but not Newberry; (4) a low-velocity "slab gap" to ˜400 km depth immediately south of the Mendocino Triple Junction and south of the Gorda slab; and (5) high-velocity "drips" beneath the Transverse Ranges, the southern Central Valley/Sierra Nevada, and central Nevada. These observations reveal extremely heterogeneous mantle structure for the western United States and suggest that we are only just beginning to image the complex interactions between geologic objects. The transportable array allows for analysis of the relationships between these anomalies in an internally consistent single tomographic model. The DNA velocity models are available for download and slicing at http://dna.berkeley.edu.

  18. Multiple-frequency tomography of the upper mantle beneath the African/Iberian collision zone

    Science.gov (United States)

    Bonnin, Mickaël; Nolet, Guust; Villaseñor, Antonio; Gallart, Josep; Thomas, Christine

    2014-09-01

    During the Cenozoic, the geodynamics of the western Mediterranean domain has been characterized by a complex history of subduction of Mesozoic oceanic lithosphere. The final stage of these processes is proposed to have led to the development of the Calabria and Gibraltar arcs, whose formation is still under debate. In this study, we take advantage of the dense broad-band station networks now available in the Alborán Sea region, to develop a high-resolution 3-D tomographic P velocity model of the upper mantle beneath the African/Iberian collision zone that will better constraint the past dynamics of this zone. The model is based on 13200 teleseismic arrival times recorded between 2008 and 2012 at 279 stations for which cross-correlation delays are measured with a new technique in different frequency bands centred between 0.03 and 1.0 Hz, and for the first time interpreted using multiple frequency tomography. Our model shows, beneath the Alborán Sea, a strong (4 per cent) fast vertically dipping anomaly observed to at least 650 km depth. The arched shape of this anomaly, and its extent at depth, are coherent with a lithospheric slab, thus favouring the hypothesis of a westward consumption of the Ligurian ocean slab by roll-back during Cenozoic. In addition to this fast anomaly in the deep upper mantle, high intensity slow anomalies are widespread in the lithosphere and asthenosphere beneath Morocco and southern Spain. These anomalies are correlated at the surface with the position of the Rif and Atlas orogens and with Cenozoic volcanic fields. We thus confirm the presence, beneath Morocco, of an anomalous (hot?) upper mantle, but without clear indication for a lateral spreading of the Canary plume to the east.

  19. Tomography of the upper mantle beneath the African/Iberian collision zone

    Science.gov (United States)

    Mickael, B.; Nolet, G.; Villasenor, A.; Josep, G.; Thomas, C.

    2013-12-01

    During Cenozoic, geodynamics of the western Mediterranean domain has been characterized by a complex history of subduction of Mesozoic oceanic lithosphere. The final stage of these processes is proposed to have led to the development of the Calabria and Gibraltar arcs, whose formation is still under debate. In this study we take advantage of the dense broadband-station networks now available in Alborán Sea region, to develop a high-resolution 3D tomographic P velocity model of the upper mantle beneath the African/Iberian collision zone that will bring new constraints on the past dynamics of this zone. The model is based on 13200 teleseismic arrival times recorded between 2008 and 2012 at 279 stations for which cross-correlation delays are measured with a new technique in different frequency bands centered between 0.03 and 1.0 Hz, and interpreted using multiple frequency tomography. Our model shows, beneath Alborán Sea, a strong (~ 4%) fast vertically dipping anomaly observed to at least 650 km depth. The arched shape of this anomaly and its extent at depth are coherent with a lithospheric slab, thus favoring the hypothesis of a westward consumption of the Ligurian ocean slab by roll-back during Cenozoic. In addition to this fast anomaly in the deep upper-mantle, several high intensity slow anomalies are widely observed in the lithosphere and asthenosphere beneath Morocco and southern Spain. These anomalies are correlated at surface with the position of the orogens (Rif and Atlas) and with Cenozoic volcanic fields. We thus confirm the presence, beneath Morocco, of an anomalous (hot) upper mantle, with piece of evidence for a lateral connection with the Canary volcanic islands, likely indicating a lateral spreading of the Canary plume to the east.

  20. THE STRUCTURE OF THE LITHOSPHERIC MANTLE OF THE SIBERAIN CRATON AND SEISMODYNAMICS OF DEFORMATION WAVES IN THE BAIKAL SEISMIC ZONE

    Directory of Open Access Journals (Sweden)

    A. A. Stepashko

    2013-01-01

    Full Text Available  The evolution and specific features of seismogynamics of the Baikal zones are reviewed in the context of interactions between deep deformation waves and the regional structure of the lithospheric mantle. The study is based on a model of the mantle structure with reference to chemical compositions of mantle peridotites from ophiolotic series located in the south-western framing of the Siberian craton (Fig. 1. The chemical zonation of the lithospheric mantle at the regional scale is determined from results of analyses of the heterogeneity of compositions of peridotites (Fig. 2, Table 1 and variations of contents of whole rock major components, such as iron, magnesium and silica (Fig. 3. According to spatial variations of the compositions of peridotites, the mantle has the concentric zonal structure, and the content of SiO2 is regularly decreasing, while concentrations of FeO∑ and MgO are increasing towards the centre of such structure (Fig. 4. This structure belongs to the mantle of the Siberian craton, which deep edge extends beyond the surface contour of the craton and underlies the north-western segment of the Central Asian orogenic belt.Results of the studies of peridotites of the Baikal region are consistent with modern concepts [Snyder, 2002; O’Reilly, Griffin, 2006; Chen et al., 2009] that suggest that large mantle lenses underlie the Archaean cratons (Fig. 5. The lenses are distinguished by high-density ultrabasic rocks and compose high-velocity roots of cratons which have remained isolated from technic processes. Edges of the mantle lenses may extend a few hundred kilometers beyond the limits of the cratons and underlie orogenic belts that frame the cratons, and this takes place in the south-western segment of the Siberian craton.The revealed structure of the lithospheric mantle is consistent with independent results of seismic and magmatectonical studies of the region. The Angara geoblock is located above the central part of the

  1. Airway support using a pediatric intubation tube in adult patients with atrial fibrillation: A simple and unique method to prevent heart movement during catheter ablation under continuous deep sedation

    Directory of Open Access Journals (Sweden)

    Masateru Takigawa, MD

    2017-08-01

    Conclusion: This unique airway management technique using a pediatric intubation tube for CA procedures performed in adult patients with AF under continuous deep sedation was easy, safe, and effective.

  2. Numerical experiments on thermal convection of highly compressible fluids with variable viscosity and thermal conductivity: Implications for mantle convection of super-Earths

    Science.gov (United States)

    Kameyama, Masanori; Yamamoto, Mayumi

    2018-01-01

    We conduct a series of numerical experiments of thermal convection of highly compressible fluids in a two-dimensional rectangular box, in order to study the mantle convection on super-Earths. The thermal conductivity and viscosity are assumed to exponentially depend on depth and temperature, respectively, while the variations in thermodynamic properties (thermal expansivity and reference density) with depth are taken to be relevant for the super-Earths with 10 times the Earth's. From our experiments we identified a distinct regime of convecting flow patterns induced by the interplay between the adiabatic temperature change and the spatial variations in viscosity and thermal conductivity. That is, for the cases with strong temperature-dependent viscosity and depth-dependent thermal conductivity, a "deep stratosphere" of stable thermal stratification is formed at the base of the mantle, in addition to thick stagnant lids at their top surfaces. In the "deep stratosphere", the fluid motion is insignificant particularly in the vertical direction in spite of smallest viscosity owing to its strong dependence on temperature. Our finding may further imply that some of super-Earths which are lacking in mobile tectonic plates on their top surfaces may have "deep stratospheres" at the base of their mantles.

  3. Thermokarst, mantling and Late Amazonian Epoch periglacial-revisions in the Argyre region, Mars

    Science.gov (United States)

    Soare, R. J.; Baoini, D.; Conway, S. J.; Dohm, J. M.; Kargel, J. S.

    2015-10-01

    Thermokarst, mantling and Late Amazonian Epoch periglacial-revisions in the Argyre region, Mars R.J. Soare(1), D. Baioni(2), S.J. Conway (3), J.M. Dohm(4)and J.S. Kargel (5)(1) Geography Department, Dawson College, Montreal, Canada H3Z 1A4 rsoare@dawsoncollege.qc.ca.(2) Dipartimento di Scienze della Terra,della Vita e Ambiente, Università di Urbino "Carlo Bo", Campus SOGESTA, 61029 Urbino (PU) Italy. (3) Department of Physical Sciences, Open University, Milton Keynes, United Kingdom, MK7 6AA. (4) The University Museum, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-, Japan.(5) Department of Hydrology & Water Resources, University of Arizona, Tucson, Arizona, USA 85719.1.Introduction Metre to decametre-deep depressions that are rimless, relatively flat-floored, polygonised and scallop-shaped have been widely observed in Utopia Planitia (UP) [e.g. 1-5] and Malea Planum (MP) [6-8]. Although there is some debate about whether the depressions formed by means of sublimation or evaporation, it is commonly believed that the terrain in which the depressions occur is ice-rich.Moreover, most workers assume that this "ice-richness" is derived of a bi-hemispheric, latitudinally-dependent and atmospherically-precipitated mantle that is metres thick [2,4,6-10].

  4. Evidence for a spike in mantle carbon outgassing during the Ediacaran period

    Science.gov (United States)

    Paulsen, Timothy; Deering, Chad; Sliwinski, Jakub; Bachmann, Olivier; Guillong, Marcel

    2017-12-01

    Long-term cycles in Earth's climate are thought to be primarily controlled by changes in atmospheric CO2 concentrations. Changes in carbon emissions from volcanic activity can create an imbalance in the carbon cycle. Large-scale changes in volcanic activity have been inferred from proxies such as the age abundance of detrital zircons, but the magnitude of carbon emissions depends on the style of volcanism as well as the amount. Here we analyse U-Pb age and trace element data of detrital zircons from Antarctica and compare the results with the global rock record. We identify a spike in CO2-rich carbonatite and alkaline magmatism during the Ediacaran period. Before the Ediacaran, secular cooling of the mantle and the advent of cooler subduction regimes promoted the sequestration of carbon derived from decarbonation of subducting oceanic slabs in the mantle. We infer that subsequent magmatism led to the extensive release of carbon that may at least in part be recorded in the Shuram-Wonoka carbon isotope excursion. We therefore suggest that this pulse of alkaline volcanism reflects a profound reorganization of the Neoproterozoic deep and surface carbon cycles and promoted planetary warming before the Cambrian radiation.

  5. European upper mantle tomography: adaptively parameterized models

    Science.gov (United States)

    Schäfer, J.; Boschi, L.

    2009-04-01

    We have devised a new algorithm for upper-mantle surface-wave tomography based on adaptive parameterization: i.e. the size of each parameterization pixel depends on the local density of seismic data coverage. The advantage in using this kind of parameterization is that a high resolution can be achieved in regions with dense data coverage while a lower (and cheaper) resolution is kept in regions with low coverage. This way, parameterization is everywhere optimal, both in terms of its computational cost, and of model resolution. This is especially important for data sets with inhomogenous data coverage, as it is usually the case for global seismic databases. The data set we use has an especially good coverage around Switzerland and over central Europe. We focus on periods from 35s to 150s. The final goal of the project is to determine a new model of seismic velocities for the upper mantle underlying Europe and the Mediterranean Basin, of resolution higher than what is currently found in the literature. Our inversions involve regularization via norm and roughness minimization, and this in turn requires that discrete norm and roughness operators associated with our adaptive grid be precisely defined. The discretization of the roughness damping operator in the case of adaptive parameterizations is not as trivial as it is for the uniform ones; important complications arise from the significant lateral variations in the size of pixels. We chose to first define the roughness operator in a spherical harmonic framework, and subsequently translate it to discrete pixels via a linear transformation. Since the smallest pixels we allow in our parameterization have a size of 0.625 °, the spherical-harmonic roughness operator has to be defined up to harmonic degree 899, corresponding to 810.000 harmonic coefficients. This results in considerable computational costs: we conduct the harmonic-pixel transformations on a small Beowulf cluster. We validate our implementation of adaptive

  6. Magnitude corrections for attenuation in the upper mantle

    International Nuclear Information System (INIS)

    Anon.

    1978-01-01

    Since 1969, a consistent discrepancy in seismic magnitudes of nuclear detonations at NTS compared with magnitudes of detonations elsewhere in the world has been observed. This discrepancy can be explained in terms of a relatively high seismic attenuation for compressional waves in the upper mantle beneath the NTS and in certain other locations. A correction has been developed for this attenuation based on a relationship between the velocity of compressional waves at the top of the earth's mantle (just beneath the Mohorovicic discontinuity) and the seismic attenuation further down in the upper mantle. Our new definition of body-wave magnitude includes corrections for attenuation in the upper mantle at both ends of the teleseismic body-wave path. These corrections bring the NTS oservations into line with measurements of foreign events, and enable one to make more reliable estimates of yields of underground nuclear explosions, wherever the explosion occurs

  7. Density structure of the cratonic mantle in southern Africa

    DEFF Research Database (Denmark)

    Artemieva, Irina; Vinnik, Lev P.

    2016-01-01

    . An unusually high topography may be caused by a low density (high depletion) of the cratonic lithospheric mantle and/or by the dynamic support of the mantle with origin below the depth of isostatic compensation (assumed here to be at the lithosphere base). We use free-board constraints to examine the relative...... contributions of the both factors to surface topography in the cratons of southern Africa. Our analysis takes advantage of the SASE seismic experiment which provided high resolution regional models of the crustal thickness.We calculate the model of density structure of the lithospheric mantle in southern Africa...... and show that it has an overall agreement with xenolith-based data for lithospheric terranes of different ages. Density of lithospheric mantle has significant short-wavelength variations in all tectonic blocks of southern Africa and has typical SPT values of ca. 3.37-3.41g/cm3 in the Cape Fold and Namaqua...

  8. Structure of the Crust and the Lithosperic Mantle in Siberia

    DEFF Research Database (Denmark)

    Cherepanova, Yulia

    the development of a new regional crustal model, SibCrust, that is a digital crustal model for both the Siberian Craton and the West Siberian Basin. The SibCrust model, constrained by digitizing of all available seismic profiles and crustal velocity models across the Siberia, also includes a critical quality...... assessment of regional seismic data and crustal regionalization based on seismic structure of the crust. The second part of the study included the development of the SibDensity model that is the density model of the lithospheric mantle calculated by the mass balance method. Mantle density modeling involved...... in the lithospheric mantle density, are interpreted in terms of regional tectonic evolution, namely the mechanism by which the Paleozoic intracontinental basin has been formed and the tectono-magmatic processes by which the Archean-Proterozoic craton has been modified as reflected in the composition of its mantle....

  9. Thermochemical structure of the Earth's mantle and continental crust

    DEFF Research Database (Denmark)

    Guerri, Mattia

    in determining crustal seismic discontinuities. In the second chapter, I deal about the possibility to disentangle the dynamic and isostatic contribution in shaping the Earth's surface topography. Dynamic topography is directly linked to mantle convection driven by mantle thermo-chemical anomalies, and can......A detailed knowledge of the Earth's thermal structure and chemical composition is fundamental in order to understand the processes driving the planet ormation and evolution. The inaccessibility of most of the Earth's interior makes the determination of its thermo-chemical conditions a challenging...... argue therefore that our understandings of the lithosphere density structure, needed to determine the isostatic topography, and of the mantle density and viscosity, required to compute the dynamic topography, are still too limited to allow a robust determination of mantle convection effects on the Earth...

  10. Mantle properties and the MOR process: a new and versatile model for mid-ocean ridges

    Science.gov (United States)

    Osmaston, Miles

    2014-05-01

    overlooked by mantle modellers is the presence of two phase-changes (PCs) in the uppermost mantle - (a) garnet peridotite-to-spinel peridotite at say 90km depth; (b) spinel peridotite-to-plagioclase peridotite at say 10km depth. The total density change across the (a) boundary can approximate that of 800K change by pure thermal expansivity, so should never be ignored by modellers [4]. Primary features of the new model. This has a deep, narrow subaxial crack between walls of now-stiff LVZ mantle, to which thermal accretion from the magma ascending the crack offsets the separation rate. This crack (20 cm nominal) offers special properties:- (i) Cooling-controlled differential accretion to the opposite walls of a non-straight crack will make the MOR segment become straight and orthogonally segmented [8]; (ii) Columnar growth of olivine at the crack walls, due to its high a-axis thermal conductivity [9], emphasized by the low thermal conductivity of surrounding melt [10] will, by crystallization, build in seismic anisotropy at the start. Olivine crystals that chance to have their a-axis perpendicular to the wall will extract latent heat and grow fastest, giving columnar structure [8, 11]. Crystals with other orientation get crowded out. Also seen at margins of exhumed magma chambers (CH Donaldson pers comm 1997). Magma segregation - Log-jam segregation of magma rising in the crack. Upward-decreasing wall temperature increases cooling of the flow; the solids grow again by cumulate intergrowth until they form a jam in the crack through which the melt is forced diapirically [12, 13]. PT at the jam depth defines the major-element composition. Accreting crack walls are very hot, so the jam forms at shallow depth and tholeiite is the result. Ridge-push mechanism - Solid-state phase-change (PC) push-apart of the walls. A fresh eruption up the crack will heat the walls. Thermodynamic calculations show that these PCs cause >50 times more volume increase/joule than thermal expansivity, so

  11. Execution of mantle field with multileaf collimator: A simple approach

    Directory of Open Access Journals (Sweden)

    Prabhakar Ramachandran

    2008-01-01

    Full Text Available Background: Until very recently mantle field radiotherapy remained the gold standard for the treatment of favorable early-stage Hodgkin′s lymphoma. The classic mantle includes all the major lymph nodes above the diaphragm and extends from the inferior portion of the mandible to the level of the insertion of the diaphragm. Aims: To describe a simple technique that has been devised to treat the mantle field with the help of multileaf collimator and using computed tomography (CT-based treatment planning. Materials and Methods: CT scan was performed with the patient in the supine position and the datasets were transferred to the Eclipse™ treatment planning system. Elekta Precise™ linear accelerator equipped with 40 pairs of multileaf collimator (MLC was used for the execution of the mantle field. The MLC′s shapes were designed to take the shape of the conventional customized blocks used for treatment of mantle field. The anterior mantle field was divided into three separate MLC segments with the collimator kept at 0°. The first MLC segment was shaped to cover the neck, clavicular regions, and mediastinum. The second and the third MLC segments covered the right and left axilla, respectively. The posterior fields were opposed to the anterior subfields in a similar fashion. The dose was prescribed at the midplane, using reference points. Results and Conclusion: The technique described in this study is very simple, easy to implement, and avoids unnecessary delay in the execution of the mantle field. The mantle field can be easily shaped with the multileaf collimators, without any collimator rotation.

  12. Early mantle differentiation: constraint from 146Sm-142Nd systematics

    International Nuclear Information System (INIS)

    Caro, G.

    2005-07-01

    We present new ultra-high precision 142 Nd/ 144 Nd measurements of early Archaean rocks using the new generation thermal ionization mass spectrometer TRITON. Repeated measurements of the Ames Nd standard demonstrate that the 142 Nd/ 144 Nd ratio can be determined with external precision of 2 ppm (2s), allowing confident resolution of anomalies as small as 5 ppm. A major analytical improvement lies in the elimination of the double normalization procedure required to correct our former measurements from a secondary mass fractionation effect. Our new results indicate that metasediments, meta-basalts and orthogneisses from the 3.6 - 3.8 Ga West Greenland craton display positive 142 Nd anomalies ranging from 8 to 15 ppm. Using a simple two-stage model with initial e 143 Nd value of 1.9 ± 0.6 e-units, coupled 147 Sm- 143 Nd and 146 Sm- 142 Nd chronometry constrains mantle differentiation to 50 to 200 Ma after formation of the solar system. This chronological constraint is consistent with differentiation of the Earth's mantle during the late stage of crystallization of a magma ocean. We have developed a two-box model describing 142 Nd and 143 Nd isotopic evolution of depleted mantle during the subsequent evolution of the crust-mantle system. Our results indicate that early terrestrial proto-crust had a lifetime of ca. 500 Ma in order to produce the observed Nd isotope signature of Archaean rocks. In the context of this two box mantle-crust system, we model the evolution of isotopic and chemical heterogeneity of depleted mantle as a function of the mantle stirring time. Using the dispersion of 142 Nd/ 144 Nd and 143 Nd/ 144 Nd ratios observed in early Archaean rocks, we constrain the stirring time of early Earth's mantle to 100 - 150 Ma, a factor of 5 to 10 shorter than stirring time inferred from modern oceanic basalts. (author)

  13. Radiological safety assessment of gas mantle industries in India

    International Nuclear Information System (INIS)

    Sadagopan, G.; Venkataraman, G.

    1994-01-01

    Thorium, a radioactive element of actinide family was discovered by Berzelius in 1828 and named by him in honor of the Scandinavian God open-quote Thor close-quote. Following its discovery the earliest known use of thorium was in the making of gas mantles. The other use as an X-ray contrast medium open-quote Thorotrast close-quote has since long been discontinued, where as even today its use in gas mantles is continued. Gas lights have been used as a source of light since 1800's. In India, although electric bulbs have replaced most of the gas lights, even today in villages and in urban areas where there is no continuous power supply and in outdoor lightings gas lamps are used. The mantle which is used in these lamps is called the Welsbach mantle and is a netted hose that is impregnated with thorium nitrate and other metals. The function of a gas mantle is to produce a bright light during operation of the lighting device (gas or kerosene lamp) in which the mantle is placed. When placed in a lighting device and heated to 1300-1800 degree Celcius thorium in the mantle incandesces and gives off bright light. In India presently there are about 70 manufacturing units handling 150 metric tons of thorium nitrate annually. There are about four hundred persons involved in manufacturing 200 million mantles per year. Thorium is chosen because of its property of incadescence, however since it is radioactive, radiation safety of the workplace, handling personnel and safe environmental condition for members of public have to be maintained

  14. 3-D electromagnetic induction studies using the Swarm constellation: Mapping conductivity anomalies in the Earth's mantle

    DEFF Research Database (Denmark)

    Kuvshinov, A.; Sabaka, T.; Olsen, Nils

    2006-01-01

    . For validation of the approach, 3 years of realistic synthetic data at Simulated orbits of the forthcoming Swarm constellation of 3 satellites have been used. To obtain the synthetic data for a given 3-D conductivity Earth's model a time-domain scheme has been applied which relies oil a Fourier transformation...... coefficients of the magnetic potential. From the coefficients, time series of the magnetic vertical component and of the horizontal divergence of the horizontal components are synthesized oil the grid and the C-responses are determined by means of signal processing of the corresponding time series...... of the inducing field, and oil a frequency domain forward modelling. The conductivity model consists of a thin Surface layer of realistic conductance and a 3-D mantle that incorporates a hypothetic deep regional anomaly beneath the Pacific Ocean plate. To establish the ability of the approach to capture...

  15. Sr-Nd evidence of paleoproterozoic mantle metasomatism in the lithospheric mantle beneath northeastern Brazil

    International Nuclear Information System (INIS)

    Hollanda, M.H.B.M.; Pimentel, M.M.; Jardim de Sa, E.F

    2001-01-01

    discuss about mantle metasomatism against crustal contamination. The difficulty in commenting about this question taking into consideration Proterozoic mantle-derived plutonic rocks is related to non-uniqueness in interpreting the common enriched signatures, since that are similar to geochemical signature of crustal rocks. In this study, the data were carefully treated for filtering out the effects of crustal contamination to recognise the nature of their mantle source and obtain a picture of the lithospheric mantle chemical at Proterozoic time (au)

  16. Late-orogenic mantle garnet pyroxenites evidence mantle refertilization during exhumation of orogenic belt

    Science.gov (United States)

    Chazot, G.; France, L.; Kornprobst, J.; Dallai, L.; Vannucci, R.

    2008-12-01

    The petrological and geochemical study of garnet bearing pyroxenites from four localities (FMC, Morocco, Jordan, Cameroon) demonstrates that these rocks are cumulates crystallised in the lithospheric mantle domain. Metamorphic reactions, exsolutions and trace elements WR analysis demonstrate that their crystallisation pressure ranges between 1 and 2GPa (30 to 60km). The elaboration of the PTt paths for the studied samples attests of important movements in the respective lithospheres. Replaced in the geodynamical contexts, the samples are interpreted to represent the crystallisation of melts formed during exhumation of orogenic domains. Radiogenic isotopes (Sr-Nd) show that in a very same region, the samples are isotopicaly heterogeneous but are similar to the respective regional lithosphere. Initial isotopic ratios lead to propose that the FMC samples have crystallised at the end of the Hercynian orogen and that the samples from the other localities (Morocco, Jordan and Cameroon) have crystallised at the end of the Pan-African orogen. After recalculation at the crystallisation time, the isotopic compositions are in good agreement with the respective regional lithosphere ones and so samples of this study could represent the product of the melting of these lithospheres. The analyses of oxygen stable isotopes allow to precise the model; they show that twelve of the samples come from the melting of a lherzolitic mantle and that the four others come from the melting of a heterogeneous mantle formed of lherzolites and eclogites. The presence of some hydrous minerals such as amphiboles and micas and the trace elements WR analyses show that some of the samples were affected by a late metasomatic event. Results of our study show that thermal relaxation following orogenic events lead to the crystallisation of pyroxenites in the lithosphere. The presence of lage amounts of mantle pyroxenites in old orogenic regions confers physical and chemical particularities to these

  17. [Cytostructure of the mantle zone in lymphatic tissue].

    Science.gov (United States)

    Bednár, B

    1993-04-01

    Four cellular layers of the follicular mantle zone in palatine tonsil lymphatic tissue were studied by electron microscopy after simultaneous immunophenotypical investigation. The first layer of the mantle zone consisting of small blastic cells was analogous to the small (centrocytoid) blastic layer of germinal centres. The second B monocytoid layer was lacking analogy in basic series of lymphocytes and seemed to be an independent morphological and probably functional unit. Plasmacytoid and clarocellular elements in outer layers of follicular mantle zone were in a way similar to T plasmacytoid and clarocellular components of Sézary syndrome infiltrates but considering transitional forms they had a local origin from incompletely transformed elements of B monocytoid layer. Inner follicular mantle zone was discussed as a source of incompletely transformed B lymphocytes for further mantle layers where their immunophenotypical modulation is taking place according to actual need. Outer mantle layers are aggressive against damaged epithelial and litoral structures and may be instrumental in a common reaction of B and T components.

  18. Seismic anisotropy and mantle flow below subducting slabs

    Science.gov (United States)

    Walpole, Jack; Wookey, James; Kendall, J.-Michael; Masters, T.-Guy

    2017-05-01

    Subduction is integral to mantle convection and plate tectonics, yet the role of the subslab mantle in this process is poorly understood. Some propose that decoupling from the slab permits widespread trench parallel flow in the subslab mantle, although the geodynamical feasibility of this has been questioned. Here, we use the source-side shear wave splitting technique to probe anisotropy beneath subducting slabs, enabling us to test petrofabric models and constrain the geometry of mantle fow. Our global dataset contains 6369 high quality measurements - spanning ∼ 40 , 000 km of subduction zone trenches - over the complete range of available source depths (4 to 687 km) - and a large range of angles in the slab reference frame. We find that anisotropy in the subslab mantle is well characterised by tilted transverse isotropy with a slow-symmetry-axis pointing normal to the plane of the slab. This appears incompatible with purely trench-parallel flow models. On the other hand it is compatible with the idea that the asthenosphere is tilted and entrained during subduction. Trench parallel measurements are most commonly associated with shallow events (source depth slab. This may correspond to the shape preferred orientation of cracks, fractures, and faults opened by slab bending. Meanwhile the deepest events probe the upper lower mantle where splitting is found to be consistent with deformed bridgmanite.

  19. Pervasive seismic low-velocity zones within stagnant plates in the mantle transition zone: Thermal or compositional origin?

    Science.gov (United States)

    Tauzin, B.; Kim, S.; Kennett, B. L. N.

    2017-11-01

    We exploit conversions between P and S waves for large-scale, high-resolution imaging of the mantle transition zone beneath Northwest Pacific and the margin of Eastern Asia. We find pervasive reflectivity concentrated in two bands with apparent wave-speed reduction of -2% to -4% about 50 km thick at the top of the transition zone and 100 km thick at the bottom. This negative reflectivity associated with the scattered-waves at depth is interpreted jointly with larger-scale mantle tomographic images, and is shown to delineate the stagnant portions of the subducted Pacific plate in the transition zone, with largely positive shear-wave velocity contrasts. The upper reflectivity zone connects to broad low-velocity regions below major intra-plate volcanoes, whereas the lower zone coincides locally with the occurrence of deep-focus earthquakes along the East Asia margin. Similar reflectivity is found in Pacific Northwest of the USA. We demonstrate that the thermal signature of plates alone is not sufficient to explain such features. Alternative explanations for these reflective zones include kinetic effects on olivine phase transitions (meta-stability), compositional heterogeneities within and above stagnant plates, complex wave-propagation effects in the heterogeneous slab structure, or a combination of such factors. We speculate that part of the negative reflectivity is the signature of compositional heterogeneities, as revealed by numerous other studies of seismic scattering throughout the mantle, and that such features could be widespread across the globe.

  20. Platinum Concentrations and Tungsten Isotope Ratios of Earth's Mantle as Tracers for Late Veneer Mixing into the Early Mantle

    Science.gov (United States)

    Zeng, L.; Jacobsen, S. B.; Sasselov, D. D.

    2014-12-01

    Platinum (Pt) and tungsten (W) are both depleted in Earth's mantle. Due to their siderophile nature, they were both strongly partitioned into the Earth's core during its formation. However, in particular the Pt concentration in the Earth's mantle is much higher than expected from experimental data on metal-silicate partitioning appropriate for the conditions of core formation. A plausible explanation for this high Pt concentration is the late veneer hypothesis, where volatile-rich chondritic type material was delivered to Earth's surface after core formation. This can in principle explain both the volatiles in the Earth's ocean-atmosphere as well as the high Pt concentrations in the Earth's mantle. There are tungsten isotopic heterogeneities (182W/183W variations) in the early Earth that have been explained as being due to late veneer addition, as this material would have lower 182W/183W than the post-core formation mantle. There is also the gradual increase of Pt abundance through history in mantle as measured in mantle-derived rocks of various old ages. Both observations are thought to be caused by gradual mixing of late veneer material into Earth's mantle through plate subduction and mantle convection through geologic time. This would increase the Pt concentration and decrease the 182W/183W ratio in the mantle with time, as observed. Here we model the late veneer material as a thin sheet which is subducted into the mantle, and get stretched and mixed with the mantle material gradually. The stretching is assumed to follow a simple exponential law of decrease of the characteristic size of heterogeneity regions. The melting events that produce the rock samples of various ages measured on the surface are modeled as random geometric sampling of a sampling box with a certain length-scale. We are testing various scenarios of this mathematical model to see if both the variations in W isotopic ratio and the Pt concentration in Earth's history can be made consistent with

  1. Crustal and uppermost mantle structure and deformation in east-central China

    Science.gov (United States)

    Li, H.; Yang, X.; Ouyang, L.; Li, J.

    2017-12-01

    We conduct a non-linear joint inversion of receiver functions and Rayleigh wave dispersions to obtain the crustal and upper mantle velocity structure in east-central China. In the meanwhile, the lithosphere and upper mantle deformation beneath east-central China is also evaluated with teleseismic shear wave splitting measurements. The resulting velocity model reveals that to the east of the North-South Gravity Lineament, the crust and the lithosphere are significantly thinned. Furthermore, three extensive crustal/lithospheric thinning sub-regions are clearly identified within the study area. This indicates that the modification of the crust and lithosphere in central-eastern China is non-uniform due to the heterogeneity of the lithospheric strength. Extensive crustal and lithospheric thinning could occur in some weak zones such as the basin-range junction belts and large faults. The structure beneath the Dabie orogenic belt is complex due to the collision between the North and South China Blocks during the Late Paleozoic-Triassic. The Dabie orogenic belt is generally delineated by a thick crust with a mid-crust low-velocity zone and a two-directional convergence in the lithospheric scale. Obvious velocity contrast exhibits in the crust and upper mantle at both sides of the Tanlu fault, which suggests the deep penetration of this lithospheric-scale fault. Most of our splitting measurements show nearly E-W trending fast polarization direction which is slightly deviating from the direction of plate motion. The similar present-day lithosphere structure and upper mantle deformation may imply that the eastern NCC and the eastern SCB were dominated by a common dynamic process after late Mesozoic, i.e., the westward subduction of Pacific plate and the retreat of the subduction plate. The westward subduction of the Philippine plate and the long-range effects of the collision between the Indian plate and Eurasia plate during Cenozoic may have also contributed to the present

  2. Full seismic waveform inversion of the African crust and Mantle - Initial Results

    Science.gov (United States)

    Afanasiev, Michael; Ermert, Laura; Staring, Myrna; Trampert, Jeannot; Fichtner, Andreas

    2016-04-01

    We report on the progress of a continental-scale full-waveform inversion (FWI) of Africa. From a geodynamic perspective, Africa presents an especially interesting case. This interest stems from the presence of several anomalous features such as a triple junction in the Afar region, a broad region of high topography to the south, and several smaller surface expressions such as the Cameroon Volcanic Line and Congo Basin. The mechanisms behind these anomalies are not fully clear, and debate on their origin spans causative mechanisms from isostatic forcing, to the influence of localized asthenospheric upwelling, to the presence of deep mantle plumes. As well, the connection of these features to the African LLSVP is uncertain. Tomographic images of Africa present unique challenges due to uneven station coverage: while tectonically active areas such as the Afar rift are well sampled, much of the continent exhibits a severe dearth of seismic stations. As well, while mostly surrounded by tectonically active spreading plate boundaries (a fact which contributes to the difficulties in explaining the South's high topography), sizeable seismic events (M > 5) in the continent's interior are relatively rare. To deal with these issues, we present a combined earthquake and ambient noise full-waveform inversion of Africa. The noise component serves to boost near-surface sensitivity, and aids in mitigating issues related to the sparse source / station coverage. The earthquake component, which includes local and teleseismic sources, aims to better resolve deeper structure. This component also has the added benefit of being especially useful in the search for mantle plumes: synthetic tests have shown that the subtle scattering of elastic waves off mantle plumes makes the plumes an ideal target for FWI [1]. We hope that this new model presents a fresh high-resolution image of sub-African geodynamic structure, and helps advance the debate regarding the causative mechanisms of its surface

  3. Memories of Earth Formation in the Modern Mantle: W Isotopic Composition of Flood Basalt Lavas

    Science.gov (United States)

    Rizo Garza, H. L.; Walker, R. J.; Carlson, R.; Horan, M. F.; Mukhopadhyay, S.; Francis, D.; Jackson, M. G.

    2015-12-01

    Four and a half billion years of geologic activity has overprinted much of the direct evidence for processes involved in Earth's formation and its initial chemical differentiation. Xenon isotopic ratios [1] and 3He/22Ne ratios [2] suggest that heterogeneities formed during Earth's accretion have been preserved to the present time. New opportunities to learn about early Earth history have opened up with the development of analytical techniques that allow high precision analysis of short-lived isotopic systems. The Hf-W system (t½ = 8.9 Ma) is particularly valuable for studying events that occurred during the first ~50 Ma of Solar System history. Here we report new data for ~ 60 Ma Baffin Bay and ~ 120 Ma Ontong Java Plateau lava samples. Both are large igneous provinces that may have sampled a primitive, less degassed deep mantle reservoir that has remained isolated since shortly after Earth formation [3,4]. Three samples analyzed have 182W/184W ratios that are 10 to 48 ppm higher than our terrestrial standard. These excesses in 182W are the highest ever measured in terrestrial rocks, and may reflect 182W ingrowth in an early-formed high Hf/W mantle domain that was produced by magma ocean differentiation [5]. Long and short-lived Sm-Nd systematics in these samples, however, are inconsistent with this hypothesis. The 182W excessses could rather reflect the derivation of these lavas from a mantle reservoir that was isolated from late accretionary additions [6]. The chondritic initial Os isotopic compositions and highly siderophile element abundances of these samples, however, are inconsistent with this interpretation. Tungsten concentrations for the Baffin Bay and Ontong Java Plateau samples range from 23 ppb to 62 ppb, and are negatively correlated with their 182W/184W ratios. We propose that the source reservoirs for these flood basalts likely formed through Hf/W fractionation caused by core-forming events occuring over a protacted time interval during Earth

  4. Geochemistry of oceanic carbonatites compared with continental carbonatites: mantle recycling of oceanic crustal carbonate

    Science.gov (United States)

    Hoernle, Kaj; Tilton, George; Le Bas, Mike; Duggen, Svend; Garbe-Schönberg, Dieter

    .g. limestone) recycled through shallow, subcontinental-lithospheric-mantle and deep, lower-mantle sources.

  5. 3-D S-velocity structure in the lowermost mantle beneath the Northern Pacific

    Science.gov (United States)

    Suzuki, Y.; Kawai, K.; Geller, R. J.; Borgeaud, A. F. E.; Konishi, K.

    2017-12-01

    We previously (Suzuki et al., EPS, 2016) reported the results of waveform inversion to infer the three-dimensional (3-D) S-velocity structure in the lowermost 400 km of the mantle (the Dʺ region) beneath the Northern Pacific region. Our dataset consists of about 20,000 transverse component broadband body-wave seismograms observed at North American stations (mainly USArray) for 131 intermediate and deep earthquakes which occurred beneath the western Pacific subduction region. Synthetic resolution tests indicate that our methods and dataset can resolve the velocity structure in the target region with a horizontal scale of about 150 km and a vertical scale of about 50 km. The 3-D S-velocity model obtained in that study shows three prominent features: (i) horizontal high-velocity anomalies up to about 3 per cent faster than the Preliminary Reference Earth Model (PREM) with a thickness of a few hundred km and a lower boundary which is at most about 150 km above the core-mantle boundary (CMB), (ii) low-velocity anomalies about 2.5 per cent slower than PREM beneath the high-velocity anomalies at the base of the lower mantle, (iii) a thin (about 150 km) low-velocity structure continuous from the base of the low-velocity zone to at least 400 km above the CMB. We interpret these features respectively as: (i) remnants of slab material where the Mg-perovskite to Mg-post-perovskite phase transition could have occurred within the slab, (ii, iii) large amounts of hot and less dense materials beneath the cold Kula or Pacific slab remnants immediately above the CMB which ascend and form a passive plume upwelling at the edge of the slab remnants. Since our initial work we subsequently conducted waveform inversion using both the transverse- and radial-component horizontal waveform data to infer the isotropic shear velocity structure in the lowermost mantle beneath the Northern Pacific in more detail. We also compute partial derivatives with respect to the 5 independent elastic

  6. Deep Incremental Boosting

    OpenAIRE

    Mosca, Alan; Magoulas, George D

    2017-01-01

    This paper introduces Deep Incremental Boosting, a new technique derived from AdaBoost, specifically adapted to work with Deep Learning methods, that reduces the required training time and improves generalisation. We draw inspiration from Transfer of Learning approaches to reduce the start-up time to training each incremental Ensemble member. We show a set of experiments that outlines some preliminary results on some common Deep Learning datasets and discuss the potential improvements Deep In...

  7. Liquid state physics of the magnesium oxide-silicon dioxide system at deep mantle pressures

    Science.gov (United States)

    de Koker, Nico Pieter Jan

    As the primary medium through which planetary differentiation occurs, silicate liquids have a central role in the study of the thermal and chemical evolution of Earth. First principles molecular dynamics simulations were used to study the liquid state physics of the MgO-SiO2 join. We find the structure of liquids to vary continuously upon compression, and to differ markedly from that of the respective isochemical crystalline polymorphs. Liquid structure also depends strongly on composition, with a further notable difference between the structure of magnesio-silicate liquids and that of pure silica. Liquid structure is expressed in the liquid state thermodynamic properties. A density crossover along the forsterite melting curve is found within the stability field of the mineral, a feature which a melting curve computed through the Lindemann criterion from the mean squared atomic displacements in forsterite is unable to reproduce. Composition dependent structural differences within the liquid are expressed as a liquid immiscibility field at low pressure in high silica compositions. We develop a self-consistent thermodynamic description of liquid state thermodynamics relevant to silicate liquids over a large range of pressures and temperatures. To constrain the description, we use simulation results for liquid MgO, MgSiO3, Mg2SiO4 and SiO2, including the thermal electronic contribution to the free energy. With liquid state thermodynamics constrained self-consistently, we investigate the high pressure melting of MgO periclase and MgSiO3 perovskite, with special focus on the changes in density and sound velocity which would be expected during shock melting of periclase and enstatite. We further apply the thermodynamic description to the thermodynamics of mixing along the full extent of the binary. At low pressure the enthalpy of mixing is notably pressure dependent, primarily due to the disappearance of a maximum at high silica compositions with pressure. The assumption of pressure independence in the enthalpy of mixing, with the implication of ideal mixing of liquid volumes, commonly applied in experimental thermodynamic studies is thus found not to hold at low pressures for liquids in the MgO-SiO 2 system. Liquid immiscibility, and its disappearance with pressure, is found to result from significant differences between SiO2 and intermediate composition liquids in liquid structure and its response to compression.

  8. Chemical interaction of Fe and Al(2)O3 as a source of heterogeneity at the Earth's core-mantle boundary.

    Science.gov (United States)

    Dubrovinsky, L; Annersten, H; Dubrovinskaia, N; Westman, F; Harryson, H; Fabrichnaya, O; Carlson, S

    2001-08-02

    Seismological studies have revealed that a complex texture or heterogeneity exists in the Earth's inner core and at the boundary between core and mantle. These studies highlight the importance of understanding the properties of iron when modelling the composition and dynamics of the core and the interaction of the core with the lowermost mantle. One of the main problems in inferring the composition of the lowermost mantle is our lack of knowledge of the high-pressure and high-temperature chemical reactions that occur between iron and the complex Mg-Fe-Si-Al-oxides which are thought to form the bulk of the Earth's lower mantle. A number of studies have demonstrated that iron can react with MgSiO3-perovskite at high pressures and high temperatures, and it was proposed that the chemical nature of this process involves the reduction of silicon by the more electropositive iron. Here we present a study of the interaction between iron and corundum (Al(2)O3) in electrically- and laser-heated diamond anvil cells at 2,000-2,200 K and pressures up to 70 GPa, simulating conditions in the Earth's deep interior. We found that at pressures above 60 GPa and temperatures of 2,200 K, iron and corundum react to form iron oxide and an iron-aluminium alloy. Our results demonstrate that iron is able to reduce aluminium out of oxides at core-mantle boundary conditions, which could provide an additional source of light elements in the Earth's core and produce significant heterogeneity at the core-mantle boundary.

  9. Deep Space Telecommunications

    Science.gov (United States)

    Kuiper, T. B. H.; Resch, G. M.

    2000-01-01

    The increasing load on NASA's deep Space Network, the new capabilities for deep space missions inherent in a next-generation radio telescope, and the potential of new telescope technology for reducing construction and operation costs suggest a natural marriage between radio astronomy and deep space telecommunications in developing advanced radio telescope concepts.

  10. The European Continent : Surface Expression of Upper Mantle Dynamics

    Science.gov (United States)

    Tondi, M. R.; Schivardi, R.; Molinari, I.; Morelli, A.

    2012-12-01

    The surface topography of Europe shows important variations, most of which are relatively well explained by isostatic compensation of density contrasts within the crust and lithosphere. However, not all of the density contrasts leading to topography reside within the lithosphere. The crucial problem is how to detect the extra topography signal, in addition to that associated with both crustal and lithospheric anomalies. Forte and Perry, 2000 estimate the amplitude of the dynamic topography by removal of the crustal isostatic topography signal from the surface of the Earth. Faccenna and Becker, 2010 infer the equivalent dynamic topography from the normal stress generated at the surface by mantle viscous flow driven by thermal anomalies. Here we consider the correlation between residual topography and mantle residual gravity anomalies. As shown by Pekeris, 1935 and Hager et al., 1985, the viscous mantle flow that is driven by the thermal density contrasts is responsible for the long-wavelength gravity anomalies observed at the surface. They have demonstrated that the gravitational effects of surface deformation caused by the flow is opposite in sign and comparable in magnitude to that of the driving density contrast. The 1°x1° recently assembled European crustal model, EPCrust (Molinari and Morelli, 2011) is used to estimate the effects of the isostatic crust and the mantle residual gravity anomalies. We calculate the correlation matrix between the residual topography and the mantle residual gravity anomalies and we define the regions where the sublithospheric mantle density, below the European continent, contributes to surface topography. To recover the residual topography, the effects of the isostatic crust is estimated with the Panasyuk and Hager (2000) algorithm and subtracted from the observed elevation (ETOPO-1). The mantle residual gravity anomalies are estimated as the differences between the produced gravity field of EPCrust and the observations. 3-D

  11. Lenalidomide-bendamustine-rituximab in untreated mantle cell lymphoma > 65 years with untreated mantle cell lymphoma

    DEFF Research Database (Denmark)

    Albertsson-Lindblad, Alexandra; Kolstad, Arne; Laurell, Anna

    2016-01-01

    For elderly patients with mantle cell lymphoma (MCL), there is no defined standard therapy. In this multicenter open-label phase I/II trial we evaluated the addition of lenalidomide (LEN) to rituximab-bendamustine (R-B) as first-line treatment to elderly MCL patients. Patients >65 years with untr......For elderly patients with mantle cell lymphoma (MCL), there is no defined standard therapy. In this multicenter open-label phase I/II trial we evaluated the addition of lenalidomide (LEN) to rituximab-bendamustine (R-B) as first-line treatment to elderly MCL patients. Patients >65 years...... patients (median age 71 years) were enrolled 2009-2013. In phase I, the MTD of LEN was defined as 10 mg in cycles 2-6, and omitted in cycle 1. After six cycles, the complete remission rate (CRR) was 64% and 36% were MRD negative. At a median follow-up time of 31 months, median PFS was 42 months and 3 year...

  12. Deep Vein Thrombosis (DVT) / Pulmonary Embolism (PE) - Blood Clot Forming in a Vein

    Science.gov (United States)

    ... Recommend on Facebook Tweet Share Compartir Deep Vein Thrombosis and Pulmonary Embolism (DVT/PE) are often underdiagnosed and serious, but preventable medical conditions. Deep vein thrombosis (DVT) is a medical condition that occurs when ...

  13. Surfactant in the gas mantle of the snail Helix aspersa.

    Science.gov (United States)

    Daniels, C B; Wood, P G; Loptako, O V; Codd, J R; Johnston, S D; Orgeig, S

    1999-01-01

    Surfactant occurs in cyclically inflating and deflating, gas-holding structures of vertebrates to reduce the surface tension of the inner fluid lining, thereby preventing collapse and decreasing the work of inflation. Here we determined the presence of surfactant in material lavaged from the airspace in the gas mantle of the pulmonate snail Helix aspersa. Surfactant is characterized by the presence of disaturated phospholipid (DSP), especially disaturated phosphatidylcholine (PC), lavaged from the airspace, by the presence of lamellated osmiophilic bodies (LBs) in the airspaces and epithelial tissue, and by the ability of the lavage to reduce surface tension of fluid in a surface balance. Lavage had a DSP/phospholipid (PL) ratio of 0.085, compared to 0.011 in membranes, with the major PL being PC (45.3%). Cholesterol, the primary fluidizer for pulmonary surfactant, was similar in lavage and in lipids extracted from cell homogenates (cholesterol/PL: 0.04 and 0. 03, respectively). LBs were found in the tissues and airspaces. The surface activity of the lavage material is defined as the ability to reduce surface tension under compression to values much lower than that of water. In addition, surface-active lipids will vary surface tension, increasing it upon inspiration as the surface area expands. By these criteria, the surface activity of lavaged material was poor and most similar to that shown by pulmonary lavage of fish and toads. Snail surfactant displays structures, a biochemical PL profile, and biophysical properties similar to surfactant obtained from primitive fish, teleost swim bladders, the lung of the Dipnoan Neoceratodus forsteri, and the amphibian Bufo marinus. However, the cholesterol/PL and cholesterol/DSP ratios are more similar to the amphibian B. marinus than to the fish, and this similarity may indicate a crucial physicochemical relationship for these lipids.

  14. The deep structure of the Scandes and its relation to tectonic history and present-day topography

    NARCIS (Netherlands)

    Maupin, V.; Agostini, A.; Artemieva, I.; Balling, N.; Beekman, F.; Ebbing, J.; England, R.W.; Frassetto, A.; Gradmann, S.; Jacobsen, B.H.; Köhler, A.; Kvarven, T.; Medhus, A.B.; Mjelde, R.; Ritter, J.; Sokoutis, D.; Stratford, W.; Thybo, H.; Wawerzinek, B.; Weidle, C.

    2013-01-01

    We review the results of the TopoScandiaDeep project, a component of the TOPOEUROPE project, in which we have studied the crustal and upper mantle structures of southern Norway in relation to its high topography. The Scandinavian Mountain Chain (the Scandes) is an intracontinental mountain chain at

  15. Joint Inversion Of Local And Teleseismic Data For The Crust And Mantle Structure Of The Chinese Capital Region

    Science.gov (United States)

    Huang, J.; Zhao, D.

    2004-12-01

    . Our tomographic images of the deep crust and upper mantle layers also show different velocity features under different tectonic units. In the Yanshan uplift, a high-V patch is visible from the crust to about 300 km depth, which may reflect that the Yanshan uplift is a stable block without strong earthquakes. In the North China Basin, especially around Beijing, Tianjin and Tangshan,broad low-V anomalies are visible in the lower crust and at depths of 50¡«100 km. Beneath the Bohai Bay, low-V anomalies exist and extend down to about 120 km depth. These results suggest that the lithosphere becomes thinner in this region. From the Taihangshan uplift to the Shanxi rift low-V anomalies exist from the uppermost mantle to about 300 km depth. In this region, lava rocks are distributed broadly and the Datong volcano is located. In addition, most of the large earthquakes, such as the 1976 Tangshan earthquake and the 1679 Sanhe earthquake (M 8.0), generally occurred in high-V areas in the upper to middle crust. However, in the lower crust and uppermost mantle under the source zones of the large earthquakes, low-V and high-conductivity anomalies exist. This result suggests the occurrence of strong earthquakes is related to the deep structure and processes in the deep crust and upper mantle.

  16. Rheological structure of a lithosphere-asthenosphere boundary zone, decoded from EBSD analysis of mantle xenoliths from Ichinomegata, NE Japan

    Science.gov (United States)

    Sato, Y.; Ozawa, K.

    2017-12-01

    Mantle xenoliths are fragments of mantle materials entrapped in alkali basalts or kimberlites and transported to the surface (Nixon, 1987). They provide information on rheological, thermal, chemical, petrological structures of the upper mantle (e.g. Green et al., 2010; McKenzie and Bickle, 1988; O'Reilly and Griffin, 1996). They potentially represent materials from a boundary zone of lithosphere and asthenosphere (LABZ), where the heat transportation mechanism changes from convection to conduction (Sleep, 2005, 2006). However, difficulties in geobarometry for spinel peridotite (e.g. O'Reilly et al., 1997) have hampered our understanding of shallow LABZ. Ichinomegata located in the back-arc side of NE Japan is a latest Pleistocene andesitic-dacitic volcano yielding spinel peridotite xenoliths (Katsui et al., 1979). Through our works (Sato and Ozawa, 2016, 2017a, 2017b), we have overcome difficulties in geobarometry of spinel peridotites and gained accurate thermal structure (0.74-1.60 GPa, 832-1084 °C) from eight of the nine examined xenoliths. The rheological and chemical features suggest drastic changes: undeformed (granular), depleted, subsolidus mantle representing lithospheric mantle (ca. 28-35 km) and deformed (porphyroclastic), fertile, hydrous supersolidus mantle representing rheological LABZ (ca. 35-54 km). We investigate depth dependent variation of crystallographic preferred orientation (CPO) of constituent minerals of the xenoliths by electron back-scattered diffraction analysis (using JSM-7000F with a CCD detector and the CHANNEL5 software at the University of Tokyo). A shallower (ca. 32 km) sample with tabulargranular texture and coarse olivine size (0.92 mm) has A-type olivine CPO with [100] maximum as reported by Satsukawa and Michibayashi (2014) (hereafter SM14), whereas a deep (ca. 51 km) sample with porphyroclastic texture and finer olivine size (0.46 mm) has CPO with weaker fabric intensity characterized by a [100] girdle similar to AG-type and

  17. The effect of the Caloris impact on the mantle dynamics and volcanism of Mercury

    Science.gov (United States)

    Roberts, J. H.; Barnouin, O. S.

    2011-12-01

    MESSENGER has now imaged over 95% of the surface of Mercury, including the entirety of Caloris, the largest impact basin on Mercury [1]. These images reveal evidence for volcanic plains within and exterior to the basin that appear to be younger than the basin rim [2-4], and might be associated with the long-term aftermath of Caloris' formation. The broad influence of Caloris on the surface indicates that it might also affect heating of the deep mantle and therby, the core dynamics. Here we investigate possible links between the Caloris impact on Mercury and volcanism within and surrounding the basin. While the apparent age difference between the rim and plains [3-4] indicates that the plains materials cannot be impact melts, the thermal impulse from such an impact can alter the underlying mantle dynamics, producing volcanism late on. We use standard methods of impact scalings [5-8] and a finite element model of thermochemical convection in a spherical shell [9-11] to explore the melt production, and geodynamic evolution in the Mercurian mantle as a result of the Caloris impact. We find that a single impact may produce multiple episodes of volcanism. The shock heating distribution from larger projectiles penetrates into convective upwellings up to 800 km away; beyond the basin rim. This promotes melt production in these upwellings, beneath a relatively thick stagnant lid. The associated melt is thus produced at depth and may be erupted to the surface much later than the direct impact melts. This is consistent with the relatively young age of the exterior plains [2-4]. We also find that impacts may sample different regions of the mantle. Direct impact melts are primarily in the near surface, while exterior melting is located in deeper mantle plume heads. Volcanic plains may therefore reveal pre-existing compositional stratification of the crust and mantle [2,12]. We further find that an impact capable of forming Caloris cannot significantly heat the core and should

  18. Quantitative assessments of mantle flow models against seismic observations: Influence of uncertainties in mineralogical parameters

    Science.gov (United States)

    Schuberth, Bernhard S. A.

    2017-04-01

    One of the major challenges in studies of Earth's deep mantle is to bridge the gap between geophysical hypotheses and observations. The biggest dataset available to investigate the nature of mantle flow are recordings of seismic waveforms. On the other hand, numerical models of mantle convection can be simulated on a routine basis nowadays for earth-like parameters, and modern thermodynamic mineralogical models allow us to translate the predicted temperature field to seismic structures. The great benefit of the mineralogical models is that they provide the full non-linear relation between temperature and seismic velocities and thus ensure a consistent conversion in terms of magnitudes. This opens the possibility for quantitative assessments of the theoretical predictions. The often-adopted comparison between geodynamic and seismic models is unsuitable in this respect owing to the effects of damping, limited resolving power and non-uniqueness inherent to tomographic inversions. The most relevant issue, however, is related to wavefield effects that reduce the magnitude of seismic signals (e.g., traveltimes of waves), a phenomenon called wavefront healing. Over the past couple of years, we have developed an approach that takes the next step towards a quantitative assessment of geodynamic models and that enables us to test the underlying geophysical hypotheses directly against seismic observations. It is based solely on forward modelling and warrants a physically correct treatment of the seismic wave equation without theoretical approximations. Fully synthetic 3-D seismic wavefields are computed using a spectral element method for 3-D seismic structures derived from mantle flow models. This way, synthetic seismograms are generated independent of any seismic observations. Furthermore, through the wavefield simulations, it is possible to relate the magnitude of lateral temperature variations in the dynamic flow simulations directly to body-wave traveltime residuals. The

  19. Mantle to surface degassing of carbon- and sulphur-rich alkaline magma at El Hierro, Canary Islands

    Science.gov (United States)

    Longpré, Marc-Antoine; Stix, John; Klügel, Andreas; Shimizu, Nobumichi

    2017-02-01

    Basaltic volcanoes transfer volatiles from the mantle to the surface of the Earth. The quantification of deep volatile fluxes relies heavily on estimates of the volatile content of primitive magmas, the best archive of which is provided by melt inclusions. Available data from volcanoes producing mafic alkaline lavas in a range of tectonic settings suggest high volatile fluxes, but information remains sparse, particularly for intraplate ocean islands. Here we present measurements of volatile and trace element concentrations, as well as sulphur speciation, in olivine-hosted melt inclusions and matrix glasses from quenched basanite lava balloon samples from the 2011-2012 submarine eruption at El Hierro, Canary Islands. The results reveal remarkably high concentrations of dissolved volatiles and incompatible trace elements in this magma, with ∼80 ppm Nb and up to 3420 ppm CO2, 3.0 wt.% H2O and 5080 ppm S. Reconstructed primitive CO2 contents, considering CO2/Nb systematics and possible CO2 sequestration in shrinkage bubbles, reach weight percent levels, indicating that carbon is a major constituent of Canary Island magmas at depth and that exsolution of a CO2-rich fluid begins in the mantle at pressures in excess of 1 GPa. Correlations between sulphur concentration, sulphur speciation and water content suggest strong reduction of an initially oxidised mantle magma, likely controlled by coupled H2O and S degassing. This late-stage redox change may have triggered sulphide saturation, recorded by globular sulphide inclusions in clinopyroxene and ulvöspinel. The El Hierro basanite thus had a particularly high volatile-carrying capacity and released a minimum of 1.3-2.1 Tg CO2 and 1.8-2.9 Tg S to the environment, causing substantial stress on the local submarine ecosystem. These results highlight the important contribution of alkaline ocean island volcanoes, such as the Canary Islands, to volatile fluxes from the mantle.

  20. Constraints on Past Plate and Mantle Motion from New Ages for the Hawaiian-Emperor Seamount Chain

    Science.gov (United States)

    O'Connor, J. M.; Steinberger, B. M.; Regelous, M.; Koppers, A. A.; Wijbrans, J. R.; Haase, K. M.; Stoffers, P.; Jokat, W.; Garbe-Schoenberg, C.

    2013-12-01

    Estimates of the relative motion between the Hawaiian and Louisville hotspots have consequences for understanding the role and character of deep Pacific-mantle return flow. The relative motion between these primary hotspots can be inferred by comparing the age records for their seamount trails. Our new 40Ar/39Ar ages for 18 lavas from 10 seamounts along the Hawaiian-Emperor Seamount Chain (HESC) show that volcanism started in the sharp portion of the Hawaiian-Emperor Bend (HEB) at ≥47.5 Ma and continued for ≥5 Myr (O'Connor et al., 2013). The slope of the along-track distance from the currently active Hawaiian hotspot plotted versus age is remarkably linear between ~57 and 25 Ma in the central ˜1900 km of the seamount chain, including the HEB. This model predicts an age for the oldest Emperor Seamounts that matches published ages, implying that a linear age-distance relationship might extend back to at least 82 Ma. In contrast, Hawaiian age progression was much faster since at least ~15 Ma and possibly as early as ~27 Ma. Linear age-distance relations for the Hawaii-Emperor and Louisville seamount chains predict ~300 km overall hotspot relative motion between 80 and 47.5 Ma, in broad agreement with numerical models of plumes in a convecting mantle, and paleomagnetic data. We show that a change in hotspot relative motion may also have occurred between ~55 Ma and ~50 Ma. We interpret this change in hotspot motion as evidence that the HEB reflects a combination of hotspot and plate motion changes driven by the same plate/mantle reorganization. O'Connor et al. (2013), Constraints on past plate and mantle motion from new ages for the Hawaiian-Emperor Seamount Chain. Geochem. Geophys. Geosyst., in press.

  1. Interaction between Edge-Driven Convection and Mantle Plumes

    Science.gov (United States)

    Manjón-Cabeza Córdoba, A.; Ballmer, M.

    2017-12-01

    Intraplate volcanism can occur in a variety of geodynamic settings. Its characteristics can inform about the underlying mantle dynamics. A non-negligible number of intraplate oceanic volcanoes are located close to continental shelves (e.g. Bermuda, Canary Islands, Cape Verde…). In these regions, any putative plumes would interact with Edge-Driven Convection (EDC), a mode of Small-Scale Convection that is triggered along steps of lithospheric thickness. We have systematically explored 2-D geodynamic models of EDC, varying e.g. the viscosity of the mantle, geometry of the edge, potential temperature, etc. In addition, we study the influence of a mantle plume with variable excess temperature and buoyancy flux at a given distance to the edge. The mantle-convection code is coupled with a new melting parameterization that considers the depletion effect on productivity. We apply this parameterization not only to predict the extent of melting for a given lithology, but also the major-element composition of extracted melts for comparison with geochemical data. Results show that the first EDC upwellings are always localized in the oceanic domain at a distance from the continental margin that depends on mantle viscosity. The initial geometry of the edge does not have a significant influence on the "steady-state" shape of EDC. Depending on the distance of the plume from the edge and plume vigor, the plume is either deflected or enhanced by EDC. The mix of materials that melts in the mantle, as well as the amount of melting, is controlled by the interaction of the plume with EDC (e.g., with melting restricted to fertile heterogeneities in the end-member EDC case). Because several model parameters affect this interaction and related melting, a joint analysis of major-element and trace-element composition of hotspot lavas is required to constrain mantle processes.

  2. Sulfur in Earth's Mantle and Its Behavior During Core Formation

    Science.gov (United States)

    Chabot, Nancy L.; Righter,Kevin

    2006-01-01

    The density of Earth's outer core requires that about 5-10% of the outer core be composed of elements lighter than Fe-Ni; proposed choices for the "light element" component of Earth's core include H, C, O, Si, S, and combinations of these elements [e.g. 1]. Though samples of Earth's core are not available, mantle samples contain elemental signatures left behind from the formation of Earth's core. The abundances of siderophile (metal-loving) elements in Earth's mantle have been used to gain insight into the early accretion and differentiation history of Earth, the process by which the core and mantle formed, and the composition of the core [e.g. 2-4]. Similarly, the abundance of potential light elements in Earth's mantle could also provide constraints on Earth's evolution and core composition. The S abundance in Earth's mantle is 250 ( 50) ppm [5]. It has been suggested that 250 ppm S is too high to be due to equilibrium core formation in a high pressure, high temperature magma ocean on early Earth and that the addition of S to the mantle from the subsequent accretion of a late veneer is consequently required [6]. However, this earlier work of Li and Agee [6] did not parameterize the metalsilicate partitioning behavior of S as a function of thermodynamic variables, limiting the different pressure and temperature conditions during core formation that could be explored. Here, the question of explaining the mantle abundance of S is revisited, through parameterizing existing metal-silicate partitioning data for S and applying the parameterization to core formation in Earth.

  3. Improved design of mantle tanks for small low flow SDHW systems

    DEFF Research Database (Denmark)

    Furbo, Simon; Knudsen, Søren

    2006-01-01

    of the mantle and the other mantle tank has the mantle inlet port moved 0.175 m down from the top of the mantle. The thermal performance is almost the same for the two systems in the measuring period of 252 days. The solar fractions were 0.66 and 0.68 for the two systems. The tests showed also that the system...... with the low mantle inlet perform better than the system with the high mantle inlet in periods with low solar fractions, that is in less sunny periods. Further, calculations with a simulation model for low flow SDHW systems based on mantle tanks showed that mantle tanks currently marketed can be greatly...... improved by relatively simple design changes: increasing the height/diameter ratio, reducing the mantle height and increasing the insulation thickness on the sides of t he tank....

  4. Analysis of the flow structure and heat transfer in a vertical mantle heat exchanger

    DEFF Research Database (Denmark)

    Knudsen, Søren; Morrison, GL; Behnia, M

    2005-01-01

    Velocimetry (PIV) system. A Computational Fluid Dynamics (CFD) model of the vertical mantle heat exchanger was also developed for a detailed evaluation of the heat flux at the mantle wall and at the tank wall. The flow structure was evaluated for both high and low temperature incoming flows and for both......The flow structure inside the inner tank and inside the mantle of a vertical mantle heat exchanger was investigated using a full-scale tank designed to facilitate flow visualisation. The flow structure and velocities in the inner tank and in the mantle were measured using a Particle Image...... initially mixed and initially stratified inner tank and mantle. The analysis of the heat transfer showed that the flow in the mantle near the inlet is mixed convection flow and that the heat transfer is dependent on the mantle inlet temperature relative to the core tank temperature at the mantle level. (C...

  5. What Is Deep Vein Thrombosis?

    Science.gov (United States)

    ... To Health Topics / Deep Vein Thrombosis Deep Vein Thrombosis Leer en español What Is Deep vein thrombosis ( ... life-threatening problems if not treated. Deep Vein Thrombosis Only about half of the people who have ...

  6. Deep learning with Python

    CERN Document Server

    Chollet, Francois

    2018-01-01

    DESCRIPTION Deep learning is applicable to a widening range of artificial intelligence problems, such as image classification, speech recognition, text classification, question answering, text-to-speech, and optical character recognition. Deep Learning with Python is structured around a series of practical code examples that illustrate each new concept introduced and demonstrate best practices. By the time you reach the end of this book, you will have become a Keras expert and will be able to apply deep learning in your own projects. KEY FEATURES • Practical code examples • In-depth introduction to Keras • Teaches the difference between Deep Learning and AI ABOUT THE TECHNOLOGY Deep learning is the technology behind photo tagging systems at Facebook and Google, self-driving cars, speech recognition systems on your smartphone, and much more. AUTHOR BIO Francois Chollet is the author of Keras, one of the most widely used libraries for deep learning in Python. He has been working with deep neural ...

  7. Heterogeneously hydrated mantle beneath the late Archean Yilgarn Craton

    Science.gov (United States)

    Ivanic, T. J.; Nebel, O.; Jourdan, F.; Faure, K.; Kirkland, C. L.; Belousova, E. A.

    2015-12-01

    Archean mafic-ultramafic melts, crystallized as layered intrusions in the upper crust and extruded as komatiitic flows, are primary probes of upper mantle chemistry. However, the message from their primary chemical composition can be compromised by different modes of contamination. Contaminants are typically cryptic in terms of their geochemical and isotopic signals but may be related to metasomatised mantle sources, ambient crustal assimilation or subduction-related inputs. In this work we present critical evidence for both dry and wet Archean mantle sources for two juxtaposed layered intrusions in the Australian Yilgarn Craton. The ca. 2813 Ma Windimurra and ca. 2800 Ma Narndee Igneous Complexes in Western Australia are two adjacent layered intrusions and would be expected to derive via similar mantle sections. A key difference in their chemistry is the presence of crystal-bound water in the Narndee Igneous Complex, represented primarily by abundant hornblende. Such a primary hydrous phase is notably absent in the Windimurra Igneous Complex. New 40Ar/39Ar plateau ages for fresh Narndee hornblende (weighted mean: 2805 ± 14 Ma, MSWD = 1.8, probability = 0.18) agrees with the published U-Pb age of 2800 ± 6 Ma for the complex and is consistent with a magmatic origin for this phase. Zircon Hf and whole-rock Hf and Nd isotopes for the Narndee Igneous Complex indicate only minor crustal contamination, in agreement with H and O isotope values in amphibole and O isotope values in rare zircon crystals, plagioclase and pyroxene within both complexes. These findings illustrate a fast temporal transition, in proximal bodies, from anhydrous to hydrous mantle sources with very minor crustal contamination. These large layered mafic-ultramafic intrusions are igneous bodies with a primitive chemical bulk composition that requires large degrees of mantle melting. This has been attributed by many workers to mantle plume activity, yet not without dispute, as subduction-related flux

  8. Volatile element content of the heterogeneous upper mantle

    Science.gov (United States)

    Shimizu, K.; Saal, A. E.; Hauri, E. H.; Forsyth, D. W.; Kamenetsky, V. S.; Niu, Y.

    2014-12-01

    The physical properties of the asthenosphere (e.g., seismic velocity, viscosity, electrical conductivity) have been attributed to either mineral properties at relevant temperature, pressure, and water content or to the presence of a low melt fraction. We resort to the geochemical studies of MORB to unravel the composition of the asthenosphere. It is important to determine to what extent the geochemical variations in axial MORB do represent a homogeneous mantle composition and variations in the physical conditions of magma generation and transport; or alternatively, they represent mixing of melts from a heterogeneous upper mantle. Lavas from intra-transform faults and off-axis seamounts share a common mantle source with axial MORB, but experience less differentiation and homogenization. Therefore they provide better estimates for the end-member volatile budget of the heterogeneous upper mantle. We present major, trace, and volatile element data (H2O, CO2, Cl, F, S) as well as Sr, Nd, and Pb isotopic compositions [1, 2] of basaltic glasses (MgO > 6.0 wt%) from the NEPR seamounts, Quebrada-Discovery-Gofar transform fault system, and Macquarie Island. The samples range from incompatible trace element (ITE) depleted (DMORB: Th/La0.07) spanning the entire range of EPR MORB. The isotopic composition of the samples correlates with the degree of trace element enrichment indicating long-lived mantle heterogeneity. Once shallow-level processes (degassing, crystallization, and crustal assimilation) have been considered, we conducted a two-component (DMORB- and EMORB-) mantle melting-mixing model. Our model reproduces the major, trace and volatile element contents and isotopic composition of our samples and suggests that (1) 90% of the upper mantle is highly depleted in ITE (DMORB source) with only 10% of an enriched component (EMORB source), (2) the EMORB source is peridotitic rather than pyroxenitic, and (3) NMORB do not represent an actual mantle source, but the product of

  9. Plume Generation Zones On The Core Mantle Boundary: their origin and what they tell about how the Earth works - and how it has worked (Arthur Holmes Medal Lecture)

    Science.gov (United States)

    Burke, Kevin

    2014-05-01

    It is more than 50 years since Wilson (1963) suggested that a fixed plume of deep origin from the convecting mantle is generating the Hotspots of the Hawaiian chain on the overlying moving rigid lithosphere and nearly 45 years since Morgan (1972) followed by suggesting that the plumes which generate Hotspots rise only from the Core/Mantle Boundary (CMB). During the past ~ 15 years testing has begun of a refinement of Morgan's idea based on the observation that Plumes responsible for Hotspots, Large Igneous Provinces (LIPs) and a significant fraction of other igneous rocks (including kimberlites) originate only in Plume Generation Zones (PGZs) at the edges on the CMB of one or other of TUZO and JASON the 2 antipodal, equatorial, Large Low Shear Wave Velocity Provinces (LLSVPs) of the deep mantle (Garnero et al. 2007) or from similar PGZs at the edges on the CMB of ~8 smaller Low Shear Wave Velocity Provinces. Today I will: (i) demonstrate using dated Hotspot, Large Igneous Province and Kimberlite occurrence history and paleomagnetic rotations (e.g. Torsvik et al. 2010, Burke et al.2008) the stability throughout the past 0.55 Ga of the LLSVPs and LSVPs (ii) show from the history of the Earth and Mars how the LLSVPs and LSVPs are likely to have formed early in Earth history and to have been stable since ~ 4.4 Ga (Burke et al. 2012) (iii) show, following an analogy suggested by Jack Whitehead of similarity to atmospheric fronts, why plumes are generated only from PGZs on the CMB at the margins of LLSVPs and LSVPs. (iv) show from results of recent seismological studies of Iceland, Jan Mayen, Hawaii, Yellowstone, the Afar and Ontong Java, that although plumes rise vertically in the deep mantle from the CMB their fate in the top ~ 1, 000 km of the mantle is proving to be varied and to depend largely, as Wilson suggested, on how they interact with the plates above them. Properties of the Plume Generation Zones (PGZs) on the CMB and of the plumes that rise from them are

  10. Nd-isotopes in selected mantle-derived rocks and minerals and their implications for mantle evolution

    Science.gov (United States)

    Basu, A.R.; Tatsumoto, M.

    1980-01-01

    The Sm-Nd systematics in a variety of mantle-derived samples including kimberlites, alnoite, carbonatite, pyroxene and amphibole inclusions in alkali basalts and xenolithic eclogites, granulites and a pyroxene megacryst in kimberlites are reported. The additional data on kimberlites strengthen our earlier conclusion that kimberlites are derived from a relatively undifferentiated chondritic mantle source. This conclusion is based on the observation that the e{open}Nd values of most of the kimberlites are near zero. In contrast with the kimberlites, their garnet lherzolite inclusions show both time-averaged Nd enrichment and depletion with respect to Sm. Separated clinopyroxenes in eclogite xenoliths from the Roberts Victor kimberlite pipe show both positive and negative e{open}Nd values suggesting different genetic history. A whole rock lower crustal scapolite granulite xenolith from the Matsoku kimberlite pipe shows a negative e{open}Nd value of -4.2, possibly representative of the base of the crust in Lesotho. It appears that all inclusions, mafic and ultramafic, in kimberlites are unrelated to their kimberlite host. The above data and additional Sm-Nd data on xenoliths in alkali basalts, alpine peridotite and alnoite-carbonatites are used to construct a model for the upper 200 km of the earth's mantle - both oceanic and continental. The essential feature of this model is the increasing degree of fertility of the mantle with depth. The kimberlite's source at depths below 200 km in the subcontinental mantle is the most primitive in this model, and this primitive layer is also extended to the suboceanic mantle. However, it is clear from the Nd-isotopic data in the xenoliths of the continental kimberlites that above 200 km the continental mantle is distinctly different from their suboceanic counterpart. ?? 1980 Springer-Verlag.

  11. Blending geological observations and convection models to reconstruct mantle dynamics

    Science.gov (United States)

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

    2015-04-01

    Knowledge of the state of the Earth mantle and its temporal evolution is fundamental to a variety of disciplines in Earth Sciences, from the internal dynamics to its many expressions in the geological record (postglacial rebound, sea level change, ore deposit, tectonics or geomagnetic reversals). Mantle convection theory is the centerpiece to unravel the present and past state of the mantle. For the past 40 years considerable efforts have been made to improve the quality of numerical models of mantle convection. However, they are still sparsely used to estimate the convective history of the solid Earth, in comparison to ocean or atmospheric models for weather and climate prediction. The main shortcoming is their inability to successfully produce Earth-like seafloor spreading and continental drift self-consistently. Recent convection models have begun to successfully predict these processes. Such breakthrough opens the opportunity to retrieve the recent dynamics of the Earth's mantle by blending convection models together with advanced geological datasets. A proof of concept will be presented, consisting in a synthetic test based on a sequential data assimilation methodology.

  12. [The mantle zone in lymphatic follicles and its stratification].

    Science.gov (United States)

    Bednár, B

    1993-04-01

    Ten inguinal lymph nodes and spleens from autopsies were chosen according to age decades in order to get an idea about usual appearance of follicular structures. The group was complemented by 4 palatine tonsils from routine biopsies. Phenotype was ascertained by using about 30 standard markers and results were compared with a basic histocytological picture. The appearance of lymphatic tissue was quite different according to location and age categories, nevertheless, there were common immunophenotypic and structural features of follicular mantle in younger persons. It mostly comprised four cellular layers, more conspicuous at the upper pole of the follicle. An innermost layer was small-celled blastic, MB 2 and IgD positive, the next B monocytoid layer had medium sized cells of a similar phenotype but more alc, phosphatase positive. An inconstant plasmacytoid layer and a clarocellular layer used to be incomplete. It was cytostructurally characteristic but immunohistologically non-standard (faint CD 19 et CD 20 positivity). T 4 lymphocytes and perhaps some other elements leaving germinal centres were admixed into the inner mantle layer. Various small lymphoid cells, especially T 8 lymphocytes and sometimes litoral cells, were admixed into mantle periphery. Mutual exchange of lymphatic cells between the germinal and mantle zones was very scant. The mantle zone is presumed therefore to be independent from the structural and functional point of view as well.

  13. Ancient, highly heterogeneous mantle beneath Gakkel ridge, Arctic Ocean.

    Science.gov (United States)

    Liu, Chuan-Zhou; Snow, Jonathan E; Hellebrand, Eric; Brügmann, Gerhard; von der Handt, Anette; Büchl, Anette; Hofmann, Albrecht W

    2008-03-20

    The Earth's mantle beneath ocean ridges is widely thought to be depleted by previous melt extraction, but well homogenized by convective stirring. This inference of homogeneity has been complicated by the occurrence of portions enriched in incompatible elements. Here we show that some refractory abyssal peridotites from the ultraslow-spreading Gakkel ridge (Arctic Ocean) have very depleted 187Os/188Os ratios with model ages up to 2 billion years, implying the long-term preservation of refractory domains in the asthenospheric mantle rather than their erasure by mantle convection. The refractory domains would not be sampled by mid-ocean-ridge basalts because they contribute little to the genesis of magmas. We thus suggest that the upwelling mantle beneath mid-ocean ridges is highly heterogeneous, which makes it difficult to constrain its composition by mid-ocean-ridge basalts alone. Furthermore, the existence of ancient domains in oceanic mantle suggests that using osmium model ages to constrain the evolution of continental lithosphere should be approached with caution.

  14. Centrifugal librations due to lunar core-mantle couplings

    Science.gov (United States)

    Bois, Eric

    2005-01-01

    We present a study of the dynamical behavior of a molten core inside the Moon related to the mantle by inertial coupling. In order to integrate the lunar core-mantle interaction in a realistic model of the Moon's rotation we have used our SONYR (acronym of Spin-Orbit N-bodY Relativistic) model of the solar System including the Moon's spin-orbit motion. This model was previously built in accordance with the requirements of the Lunar Laser Ranging observational accuracy. We have extended this model to the spin-orbit couplings of the terrestrial planets in order to compare different dynamical behaviors of core-mantle interactions in these planets (Mercury Venus Earth and Mars). Our core-mantle mechanism prove to be adequate to excite the two resonant frequencies of the lunar physical librations namely 2.9 and 80.1 years. Signature of such a core with for instance a 1/10 homothetic ratio appears clearly on the proper rotation angle; the amplitude is then around 12 milliarcseconds and its period 2.9 years. Besides we present the results obtained for various lunar nucleus radii and various initial nutations of the core relatively to the mantle. Other computations and comparisons are in progress involving Mercury the Earth and Mars.

  15. Convective upwelling in the mantle beneath the Gulf of California.

    Science.gov (United States)

    Wang, Yun; Forsyth, Donald W; Savage, Brian

    2009-11-26

    In the past six million years, Baja California has rifted obliquely apart from North America, opening up the Gulf of California. Between transform faults, seafloor spreading and rifting is well established in several basins. Other than hotspot-dominated Iceland, the Gulf of California is the only part of the world's seafloor-spreading system that has been surrounded by enough seismometers to provide horizontal resolution of upper-mantle structure at a scale of 100 kilometres over a distance great enough to include several spreading segments. Such resolution is needed to address the long-standing debate about the relative importance of dynamic and passive upwelling in the shallow mantle beneath spreading centres. Here we use Rayleigh-wave tomography to image the shear velocity in the upper 200 kilometres or so of the mantle. Low shear velocities similar to those beneath the East Pacific Rise oceanic spreading centre underlie the entire length of the Gulf, but there are three concentrated locations of anomalously low velocities spaced about 250 kilometres apart. These anomalies are 40 to 90 kilometres beneath the surface, at which depths petrological studies indicate that extensive melting of passively upwelling mantle should begin. We interpret these seismic velocity anomalies as indicating that partial melting triggers dynamic upwelling driven by either the buoyancy of retained melt or by the reduced density of depleted mantle.

  16. Intraplate mantle oxidation by volatile-rich silicic magmas

    Energy Technology Data Exchange (ETDEWEB)

    Martin, Audrey M.; Médard, Etienne; Righter, Kevin; Lanzirotti, Antonio

    2017-11-01

    The upper subcontinental lithospheric mantle below the French Massif Central is more oxidized than the average continental lithosphere, although the origin of this anomaly remains unknown. Using iron oxidation analysis in clinopyroxene, oxybarometry, and melt inclusions in mantle xenoliths, we show that widespread infiltration of volatile (HCSO)-rich silicic melts played a major role in this oxidation. We propose the first comprehensive model of magmatism and mantle oxidation at an intraplate setting. Two oxidizing events occurred: (1) a 365–286 Ma old magmatic episode that produced alkaline vaugnerites, potassic lamprophyres, and K-rich calc-alkaline granitoids, related to the N–S Rhenohercynian subduction, and (2) < 30 Ma old magmatism related to W–E extension, producing carbonatites and hydrous potassic trachytes. These melts were capable of locally increasing the subcontinental lithospheric mantle fO2 to FMQ + 2.4. Both events originate from the melting of a metasomatized lithosphere containing carbonate + phlogopite ± amphibole. The persistence of this volatile-rich lithospheric source implies the potential for new episodes of volatile-rich magmatism. Similarities with worldwide magmatism also show that the importance of volatiles and the oxidation of the mantle in intraplate regions is underestimated.

  17. Thermally-Driven Mantle Plumes Reconcile Hot-spot Observations

    Science.gov (United States)

    Davies, D.; Davies, J.

    2008-12-01

    Hot-spots are anomalous regions of magmatism that cannot be directly associated with plate tectonic processes (e.g. Morgan, 1972). They are widely regarded as the surface expression of upwelling mantle plumes. Hot-spots exhibit variable life-spans, magmatic productivity and fixity (e.g. Ito and van Keken, 2007). This suggests that a wide-range of upwelling structures coexist within Earth's mantle, a view supported by geochemical and seismic evidence, but, thus far, not reproduced by numerical models. Here, results from a new, global, 3-D spherical, mantle convection model are presented, which better reconcile hot-spot observations, the key modification from previous models being increased convective vigor. Model upwellings show broad-ranging dynamics; some drift slowly, while others are more mobile, displaying variable life-spans, intensities and migration velocities. Such behavior is consistent with hot-spot observations, indicating that the mantle must be simulated at the correct vigor and in the appropriate geometry to reproduce Earth-like dynamics. Thermally-driven mantle plumes can explain the principal features of hot-spot volcanism on Earth.

  18. The Oxidation State of Komatiites and the Redox History of the Mantle

    Science.gov (United States)

    Nicklas, R. W.; Puchtel, I. S.; Ash, R. D.

    2015-12-01

    Oxygen fugacity (fO2) is an important intensive variable in magmatic systems. Previous studies argued that, at the level of resolution of ca. 1.0 ΔNNO log units, the mantle has been at a near-constant oxidation state since core formation [1,3]. Here, we revisit this hypothesis using the V partitioning between olivine or chromite and komatiite liquid as oxybarometers [1,2] by obtaining high-precision V abundance data for komatiite lava flows. Whole-rock samples collected across each lava flow were analyzed for V and other transition metal abundances using Standard Addition ICP-MS (SA ICP-MS); liquidus olivines and chromites were analyzed using Laser Ablation ICP-MS. Our external precision for V concentrations is 5% (2SD) for SA-ICP-MS, based on replicate analysis of standard reference materials. The V data, when plotted against wt.% MgO, define regression lines consistent with olivine control for V. Linear regressions through the V vs. MgO data for samples for each flow were used to determine V content of the emplaced lavas using known MgO contents. Calculated partition coefficients for V were used to determine the oxygen fugacity of each komatiite system using experimental calibrations of [1,2] with a precision of 0.10 - 0.05 ΔNNO log units (2SE). The calculated oxygen fugacities show a well-defined trend of increasing fO2 (>0.5 ΔNNO log units) over ~1.0 Ga of Earth's history, approaching that of modern mantle at 2.4 Ga, immediately before the Great Oxidation Event (GOE). An exception is the 3.55 Ga Schapenburg komatiite, which plots 0.5 log units above the trend, likely reflecting primordial mantle heterogeneity. Our data suggest that the mantle was becoming increasingly oxidized leading up to the GOE. A change in deep Earth buffering capacity could change the oxidation state of volcanic gases, triggering the rise in atmospheric O2 at 2.4 Ga. [1] Canil (1997) Nature 389. [2] Canil, 1999; [3] Li et al. (2004) EPSL 228. Oxygen fugacity (fO2) is an important

  19. Long-term cycling of mantle Pb: A trace element study of the major mantle mineral phases in abyssal peridotites

    Science.gov (United States)

    D'Errico, M. E.; Warren, J. M.; Godard, M.; Ildefonse, B.

    2012-12-01

    Peridotites from ultraslow-spreading ridges preserve signatures of the depleted mantle, while also reflecting the fine scale compositional variability present in the mantle. Traditional analyses of these depleted rocks have focused on clinopyroxene, the main trace element host in spinel peridotites. However, key isotopic systems, such as lead and osmium, are hosted in other phases at low but significant concentration levels. The amount of lead contained within mantle mineral phases is of critical importance to understanding the long-term evolution of the Earth, because the radiogenic isotopes of lead are sensitive to past material cycling and melt-rock interaction. Sulfides have long been suggested as the main host for lead (Pb) in the mantle, but recent studies have demonstrated that Pb is not exclusively hosted in this trace phase. Therefore, the Pb contents of the major peridotite mineral phases (olivine, orthopyroxene, and clinopyroxene) need to be reassessed. Lead concentration data is available for orogenic and xenolith peridotite samples, which are typically more enriched than abyssal peridotites, but these do not provide direct information on the oceanic upper mantle. Direct measurement of Pb in abyssal peridotites has so far been limited because of its extremely low concentration (often spreading Gakkel and Southwest Indian Ridges (SWIR), with samples coming from segments with full spreading rates Gakkel and SWIR samples are relatively unaltered (Gakkel. A total of five Gakkel and six SWIR peridotites were analyzed by LA-ICP-MS, with a subset of samples also analyzed for bulk rock trace elements by solution ICP-MS. Combined with mineral modal data, this study provides a direct comparison of measured and calculated bulk rock Pb concentrations to determine a comprehensive assessment of the distribution of Pb among upper mantle phases Results indicate that all three of the main mantle mineral phases have similar Pb concentrations, ranging from 2-20 ppb, which

  20. High seismic attenuation at a mid-ocean ridge reveals the distribution of deep melt.

    Science.gov (United States)

    Eilon, Zachary C; Abers, Geoffrey A

    2017-05-01

    At most mid-ocean ridges, a wide region of decompression melting must be reconciled with a narrow neovolcanic zone and the establishment of full oceanic crustal thickness close to the rift axis. Two competing paradigms have been proposed to explain melt focusing: narrow mantle upwelling due to dynamic effects related to in situ melt or wide mantle upwelling with lateral melt transport in inclined channels. Measurements of seismic attenuation provide a tool for identifying and characterizing the presence of melt and thermal heterogeneity in the upper mantle. We use a unique data set of teleseismic body waves recorded on the Cascadia Initiative's Amphibious Array to simultaneously measure seismic attenuation and velocity across an entire oceanic microplate. We observe maximal differential attenuation and the largest delays ([Formula: see text] s and δ T S ~ 2 s) in a narrow zone seismic quality factor ( Q s ≤ 25) is among the lowest observed worldwide. Models harnessing experimentally derived anelastic scaling relationships require a 150-km-deep subridge region containing up to 2% in situ melt. The low viscosity and low density associated with this deep, narrow melt column provide the conditions for dynamic mantle upwelling, explaining a suite of geophysical observations at ridges, including electrical conductivity and shear velocity anomalies.

  1. Synchronous adenocarcinoma and mantle cell lymphoma of the colon.

    Science.gov (United States)

    Padmanabhan, Vijayalakshmi; Trainer, Thomas D

    2003-02-01

    Synchronous occurrence of malignant lymphoma and carcinoma, both located in the intestinal tract, is unusual. We report a unique case of an adenocarcinoma of the cecum and a simultaneous mantle cell lymphoma of the colon, terminal ileum, and regional lymph nodes in an 85-year-old man. Grossly, the adenocarcinoma was identified as a cecal mass. Lymphomatous involvement of the gastrointestinal tract was evident only on microscopic examination. The terminal ileum and colon showed microscopic disseminated multiple mucosal nodules, with involvement of the regional lymph nodes. There was no involvement of distant organs, suggesting that the mantle cell lymphoma was early in its evolution without formation of polyps or a mass lesion. To our knowledge, this is the fourth reported case with this association and the second case that showed early involvement of the gastrointestinal tract with mantle cell lymphoma without polyp formation.

  2. Mantle Melting as a Function of Water Content in Arcs

    Science.gov (United States)

    Kelley, K. A.; Plank, T.; Newman, S.; Stolper, E.; Grove, T. L.; Parman, S.; Hauri, E.

    2003-12-01

    Subduction zone magmas are characterized by high concentrations of dissolved H2O, presumably derived from the subducted plate and ultimately responsible for melt generation in this tectonic setting. Almost ten years ago, Stolper and Newman (EPSL, 1994) illustrated a linear relationship between the concentration of water (H2Oo) and the fraction of melting (F) in the mantle beneath the Mariana back-arc. Here we report new major element and volatile data for olivine-hosted melt inclusions from the Mariana Islands to test this relationship for melting beneath an arc. Basaltic melt inclusions from the Mariana arc have water contents (2.3-6.1 wt% H2O) significantly higher than all basaltic glasses or melt inclusions from the Mariana back-arc (0.2-2.2 wt% H2O). We use TiO2 as a proxy for F, after correcting for crystal fractionation, and evaluate the Ti source composition with a model based on Ti/Y variations in mid-ocean ridge basalts (MORBs). Each calculated F thus represents the amount of mantle melting for a single melting episode. Even after accounting for mantle depletion, the TiO2 concentrations in Mariana arc magmas record higher extents of mantle melting (F = 10-30%) than recorded in back-arc magmas (F = 5-24%). As a whole, the Mariana arc broadly extends the linear H2Oo-F array defined by the back-arc, although in detail the islands show important differences. Two islands from the Mariana arc (Guguan and Pagan) define a H2Oo-F slope similar to the Mariana back-arc, suggesting similar mantle potential temperature beneath the arc and back-arc ( ˜1360 +/- 20° C). Melts from Agrigan island, however, indicate a steeper slope suggestive both of cooler mantle beneath Agrigan and of along-strike thermal variations beneath the Mariana Islands. Both the arc and back-arc arrays project to finite F at zero water in the mantle, providing evidence for decompression melting in both settings. These relationships may be extended globally to other back-arc and arc systems

  3. Gastric and colonic mantle cell lymphoma - incidental discovery.

    Science.gov (United States)

    Pitigoi, Dan; Stoica, Victor; Stoia, Razvan; Dobrea, Camelia; Becheanu, Gabriel; Diculescu, Mircea

    2009-03-01

    A 65-year old patient, with no medical history, was admitted for lower gastrointestinal bleeding. On clinical examination the patient seemed to be in good health. However the examination was completed with a rectosigmoidoscopy revealing the presence of mucosal erosions, ulcerations, multiple papulae. The histopathological examination raised the suspicion of a colonic lymphoma. Gastric biopsies suggested a gastric MALT type lymphoma associated to the colonic lymphoma, but the immunohistochemical profile corresponded to a mantle cell lymphoma. In spite of the general poor prognosis of mantle cell lymphoma, our patient had a good clinical and endoscopic response to the standard cyclophosphamide, vincristine, prednisone (CVP) therapy. The cases of gastric and colonic mantle lymphoma are rare, the response to therapy is poor; fortunately, our patient had a complete resolution after completion of the six cycles of chemotherapy.

  4. Improved design of mantle tanks for small low flow SDHW systems

    DEFF Research Database (Denmark)

    Furbo, Simon; Knudsen, Søren

    2006-01-01

    Side-by-side tests of two small low flow SDHW systems based on mantle tanks have been carried out under the same test conditions in a laboratory test facility. The systems are identical with exception of the mantle tanks. One of the mantle tanks has the mantle inlet port located at the top of the...... improved by relatively simple design changes: increasing the height/diameter ratio, reducing the mantle height and increasing the insulation thickness on the sides of t he tank.......Side-by-side tests of two small low flow SDHW systems based on mantle tanks have been carried out under the same test conditions in a laboratory test facility. The systems are identical with exception of the mantle tanks. One of the mantle tanks has the mantle inlet port located at the top...... of the mantle and the other mantle tank has the mantle inlet port moved 0.175 m down from the top of the mantle. The thermal performance is almost the same for the two systems in the measuring period of 252 days. The solar fractions were 0.66 and 0.68 for the two systems. The tests showed also that the system...

  5. Evidence for chemically heterogeneous Arctic mantle beneath the Gakkel Ridge

    Science.gov (United States)

    D'Errico, Megan E.; Warren, Jessica M.; Godard, Marguerite

    2016-02-01

    Ultraslow spreading at mid-ocean ridges limits melting due to on-axis conductive cooling, leading to the prediction that peridotites from these ridges are relatively fertile. To test this, we examined abyssal peridotites from the Gakkel Ridge, the slowest spreading ridge in the global ocean ridge system. Major and trace element concentrations in pyroxene and olivine minerals are reported for 14 dredged abyssal peridotite samples from the Sparsely Magmatic (SMZ) and Eastern Volcanic (EVZ) Zones. We observe large compositional variations among peridotites from the same dredge and among dredges in close proximity to each other. Modeling of lherzolite trace element compositions indicates varying degrees of non-modal fractional mantle melting, whereas most harzburgite samples require open-system melting involving interaction with a percolating melt. All peridotite chemistry suggests significant melting that would generate a thick crust, which is inconsistent with geophysical observations at Gakkel Ridge. The refractory harzburgites and thin overlying oceanic crust are best explained by low present-day melting of a previously melted heterogeneous mantle. Observed peridotite compositional variations and evidence for melt infiltration demonstrates that fertile mantle components are present and co-existing with infertile mantle components. Melt generated in the Gakkel mantle becomes trapped on short length-scales, which produces selective enrichments in very incompatible rare earth elements. Melt migration and extraction may be significantly controlled by the thick lithosphere induced by cooling at such slow spreading rates. We propose the heterogeneous mantle that exists beneath Gakkel Ridge is the consequence of ancient melting, combined with subsequent melt percolation and entrapment.

  6. Is composition a critical dynamical element of mantle convection?

    Science.gov (United States)

    Davies, J. H.; Davies, D. R.; Wolstencroft, M. W.

    2009-04-01

    It is clear from observations of differentiation producing oceanic crust and depleted residue, and its ultimate subduction that compositional heterogeneity does exist in the mantle. An important question for mantle dynamics however, is how important is this composition? Compositional variations have been attributed to be critical for explaining many dynamical aspects of mantle upwellings as evidenced in hot-spots, such as their relative fixity (Jellinek and Manga, 2004) and non-steady upwelling velocity (Lin and van Keken, 2005). They have also been attributed to causing peaks in magma production. Our modeling work in spherical geometry shows that a wide variety of upwelling behaviour can be produced in models that have NO compositional variations and are only driven by thermal anomalies. The critical component of this family of models is a high, Earth-like Rayleigh number. Our models have also reproduced time varying magma production on a long time-scale in thermal convection models. The critical element is again a very high Rayleigh number, but this time combined with a realistic Clapeyron slope at the 660km discontinuity. Schuberth et al., 2009, have also shown that composition is not required to explain some of the seismic signatures of mantle convection models either, including at the base of the mantle. While, as stated initially, composition must play a role, we would argue that given that much of the supposedly ‘non-thermal' behaviour can be explained by thermal models that the simplest current paradigm is to assume thermally driven convection. A further advantage of this class of model is that there are fewer degrees of freedom in comparing the geodynamics models with seismology, and therefore tighter tests will be possible. While there are other arguments for compositional variations close to the core-mantle boundary and in the upper boundary / lithosphere; tests from simpler models could help to refine and bound the degree of compositional variation

  7. Deep Learning the Universe

    Science.gov (United States)

    Singh, Shiwangi; Bard, Deborah

    2017-01-01

    Weak gravitational lensing is an effective tool to map the structure of matter in the universe, and has been used for more than ten years as a probe of the nature of dark energy. Beyond the well-established two-point summary statistics, attention is now turning to methods that use the full statistical information available in the lensing observables, through analysis of the reconstructed shear field. This offers an opportunity to take advantage of powerful deep learning methods for image analysis. We present two early studies that demonstrate that deep learning can be used to characterise features in weak lensing convergence maps, and to identify the underlying cosmological model that produced them.We developed an unsupervised Denoising Convolutional Autoencoder model in order to learn an abstract representation directly from our data. This model uses a convolution-deconvolution architecture, which is fed with input data (corrupted with binomial noise to prevent over-fitting). Our model effectively trains itself to minimize the mean-squared error between the input and the output using gradient descent, resulting in a model which, theoretically, is broad enough to tackle other similarly structured problems. Using this model we were able to successfully reconstruct simulated convergence maps and identify the structures in them. We also determined which structures had the highest “importance” - i.e. which structures were most typical of the data. We note that the structures that had the highest importance in our reconstruction were around high mass concentrations, but were highly non-Gaussian.We also developed a supervised Convolutional Neural Network (CNN) for classification of weak lensing convergence maps from two different simulated theoretical models. The CNN uses a softmax classifier which minimizes a binary cross-entropy loss between the estimated distribution and true distribution. In other words, given an unseen convergence map the trained CNN determines

  8. IBM Deep Learning Service

    OpenAIRE

    Bhattacharjee, Bishwaranjan; Boag, Scott; Doshi, Chandani; Dube, Parijat; Herta, Ben; Ishakian, Vatche; Jayaram, K. R.; Khalaf, Rania; Krishna, Avesh; Li, Yu Bo; Muthusamy, Vinod; Puri, Ruchir; Ren, Yufei; Rosenberg, Florian; Seelam, Seetharami R.

    2017-01-01

    Deep learning driven by large neural network models is overtaking traditional machine learning methods for understanding unstructured and perceptual data domains such as speech, text, and vision. At the same time, the "as-a-Service"-based business model on the cloud is fundamentally transforming the information technology industry. These two trends: deep learning, and "as-a-service" are colliding to give rise to a new business model for cognitive application delivery: deep learning as a servi...

  9. Deep cascade learning

    OpenAIRE

    Marquez, Enrique, Salvador; Hare, Jonathon; Niranjan, Mahesan

    2018-01-01

    In this paper, we propose a novel approach for efficient training of deep neural networks in a bottom-up fashion using a layered structure. Our algorithm, which we refer to as Deep Cascade Learning, is motivated by the Cascade Correlation approach of Fahlman who introduced it in the context of perceptrons. We demonstrate our algorithm on networks of convolutional layers, though its applicability is more general. Such training of deep networks in a cascade, directly circumvents the well-know...

  10. Cutaneous lesions as presentation form of mantle cell lymphoma

    Directory of Open Access Journals (Sweden)

    Nayra Merino de Paz

    2011-12-01

    Full Text Available Mantle cell lymphoma is a type of no-Hodgkin lymphoma that affects extranodal areas, especially, bone narrow, digestive tract and Waldeyer ring. Here we report a case of mantle cell lymphoma IV Ann Arbor stage with cutaneous lesions on nasal dorsum and gland as the first manifestations. Skin involvement is a very rare manifestation and less than 20 cases have been reported in the literature. The importance of stablishing multidisciplinary relationships for a global approach has been shown by this clinical case.

  11. Connectivity-Based Parcellation of the Cortical Mantle Using q-Ball Diffusion Imaging

    Directory of Open Access Journals (Sweden)

    Muriel Perrin

    2008-01-01

    Full Text Available This paper exploits the idea that each individual brain region has a specific connection profile to create parcellations of the cortical mantle using MR diffusion imaging. The parcellation is performed in two steps. First, the cortical mantle is split at a macroscopic level into 36 large gyri using a sulcus recognition system. Then, for each voxel of the cortex, a connection profile is computed using a probabilistic tractography framework. The tractography is performed from q-ball fields using regularized particle trajectories. Fiber ODF are inferred from the q-balls using a sharpening process focusing the weight around the q-ball local maxima. A sophisticated mask of propagation computed from a T1-weighted image perfectly aligned with the diffusion data prevents the particles from crossing the cortical folds. During propagation, the particles father child particles in order to improve the sampling of the long fascicles. For each voxel, intersection of the particle trajectories with the gyri lead to a connectivity profile made up of only 36 connection strengths. These profiles are clustered on a gyrus by gyrus basis using a K-means approach including spatial regularization. The reproducibility of the results is studied for three subjects using spatial normalization.

  12. Effect of Mantle Rheology on Viscous Heating induced during Ice Sheet Cycles

    Science.gov (United States)

    Huang, Pingping; Wu, Patrick; van der Wal, Wouter

    2017-04-01

    Hanyk et al. (2005) studied the viscous shear heating in the mantle induced by the surface loading and unloading of a parabolic-shaped Laurentide-size ice sheet. They found that for linear rheology, viscous heating is mainly concentrated below the ice sheet. The depth extent of the heating in the mantle is determined by the viscosity distribution. Also, the magnitude of viscous heating is significantly affected by the rate of ice thickness change. However, only one ice sheet has been considered in their work and the interactions between ice sheets and ocean loading have been neglected. Furthermore, only linear rheology has been considered, although they suggested that non-Newtonian rheology may have a stronger effect. Here we follow Hanyk et al. (2005) and computed the viscous dissipation for viscoelastic models using the finite element methodology of Wu (2004) and van der Wal et al. (2010). However, the global ICE6G model (Peltier et al. 2015) with realistic oceans is used here to provide the surface loading. In addition, viscous heating in non-linear rheology, composite rheology, in addition to linear rheology with uniform or VM5a profile are computed and compared. Our results for linear rheology mainly confirm the findings of Hanyk et al. (2005). For both non-linear and composite rheologies, viscous heating is also mainly distributed near and under the ice sheets, but, more concentrated; depending on the horizontal dimension of the ice sheet, it can extend into the lower mantle, but for some of the time, not as deep as that for linear rheology. For composite rheology, the viscous heating is dominated by the effect of non-linear re