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Sample records for mantle transition zone

  1. Water-induced convection in the Earth's mantle transition zone

    Richard, Guillaume C.; Bercovici, David

    2009-01-01

    Water enters the Earth's mantle by subduction of oceanic lithosphere. Most of this water immediately returns to the atmosphere through arc volcanism, but a part of it is expected as deep as the mantle transition zone (410-660 km depth). There, slabs can be deflected and linger before sinking into the lower mantle. Because it lowers the density and viscosity of the transition zone minerals (i.e., wadsleyite and ringwoodite), water is likely to affect the dynamics of the transition zone mantle overlying stagnant slabs. The consequences of water exchange between a floating slab and the transition zone are investigated. In particular, we focus on the possible onset of small-scale convection despite the adverse thermal gradient (i.e., mantle is cooled from below by the slab). The competition between thermal and hydrous effects on the density and thus on the convective stability of the top layer of the slab is examined numerically, including water-dependent density and viscosity and temperature-dependent water solubility. For plausible initial water content in a slab (≥0.5 wt %), an episode of convection is likely to occur after a relatively short time delay (5-20 Ma) after the slab enters the transition zone. However, water induced rheological weakening is seen to be a controlling parameter for the onset time of convection. Moreover, small-scale convection above a stagnant slab greatly enhances the rate of slab dehydration. Small-scale convection also facilitates heating of the slab, which in itself may prolong the residence time of the slab in the transition zone.

  2. Mantle transition zone structure beneath the Canadian Shield

    Thompson, D. A.; Helffrich, G. R.; Bastow, I. D.; Kendall, J. M.; Wookey, J.; Eaton, D. W.; Snyder, D. B.

    2010-12-01

    The Canadian Shield is underlain by one of the deepest and most laterally extensive continental roots on the planet. Seismological constraints on the mantle structure beneath the region are presently lacking due to the paucity of stations in this remote area. Presented here is a receiver function study on transition zone structure using data from recently deployed seismic networks from the Hudson Bay region. High resolution images based on high signal-to-noise ratio data show clear arrivals from the 410 km and 660 km discontinuities, revealing remarkably little variation in transition zone structure. Transition zone thickness is close to the global average (averaging 245 km across the study area), and any deviations in Pds arrival time from reference Earth models can be readily explained by upper-mantle velocity structure. The 520 km discontinuity is not a ubiquitous feature, and is only weakly observed in localised areas. These results imply that the Laurentian root is likely confined to the upper-mantle and if any mantle downwelling exists, possibly explaining the existence of Hudson Bay, it is also confined to the upper 400 km. Any thermal perturbations at transition zone depths associated with the existence of the root, whether they be cold downwellings or elevated temperatures due to the insulating effect of the root, are thus either non-existent or below the resolution of the study.

  3. Response of mantle transition zone thickness to plume buoyancy flux

    Das Sharma, S.; Ramesh, D. S.; Li, X.; Yuan, X.; Sreenivas, B.; Kind, R.

    2010-01-01

    The debate concerning thermal plumes in the Earth's mantle, their geophysical detection and depth characterization remains contentious. Available geophysical, petrological and geochemical evidence is at variance regarding the very existence of mantle plumes. Utilizing P-to-S converted seismic waves (P receiver functions) from the 410 and 660 km discontinuities, we investigate disposition of these boundaries beneath a number of prominent hotspot regions. The thickness of the mantle transition zone (MTZ), measured as P660s-P410s differential times (tMTZ), is determined. Our analyses suggest that the MTZ thickness beneath some hotspots correlates with the plume strength. The relationship between tMTZ, in response to the thermal perturbation, and the strength of plumes, as buoyancy flux B, follows a power law. This B-tMTZ behavior provides unprecedented insights into the relation of buoyancy flux and excess temperature at 410-660 km depth below hotspots. We find that the strongest hotspots, which are located in the Pacific, are indeed plumes originating at the MTZ or deeper. According to the detected power law, even the strongest plumes may not shrink the transition zone by significantly more than ~40 km (corresponding to a maximum of 300-400° excess temperature).

  4. Tracing the influence of the Trans-European Suture Zone into the mantle transition zone

    Knapmeyer-Endrun, B.; Krüger, F.; Legendre, C. P.; Geissler, W.H.; Plomerová, Jaroslava; Babuška, Vladislav; Gaždová, Renata; Jedlička, Petr; Kolínský, Petr; Málek, Jiří; Novotný, Oldřich; Růžek, Bohuslav

    2013-01-01

    Roč. 363, FEB 1 (2013), s. 73-87 ISSN 0012-821X Institutional support: RVO:67985530 ; RVO:67985891 Keywords : mantle transition zone * Trans-European Suture Zone * East European Craton Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 4.724, year: 2013

  5. The upper-mantle transition zone beneath the Chile-Argentina flat subduction zone

    Bagdo, Paula; Bonatto, Luciana; Badi, Gabriela; Piromallo, Claudia

    2016-04-01

    The main objective of the present work is the study of the upper mantle structure of the western margin of South America (between 26°S and 36°S) within an area known as the Chile-Argentina flat subduction zone. For this purpose, we use teleseismic records from temporary broad band seismic stations that resulted from different seismic experiments carried out in South America. This area is characterized by on-going orogenic processes and complex subduction history that have profoundly affected the underlying mantle structure. The detection and characterization of the upper mantle seismic discontinuities are useful to understand subduction processes and the dynamics of mantle convection; this is due to the fact that they mark changes in mantle composition or phase changes in mantle minerals that respond differently to the disturbances caused by mantle convection. The discontinuities at a depth of 410 km and 660 km, generally associated to phase changes in olivine, vary in width and depth as a result of compositional and temperature anomalies. As a consequence, these discontinuities are an essential tool to study the thermal and compositional structure of the mantle. Here, we analyze the upper-mantle transition zone discontinuities at a depth of 410 km and 660 km as seen from Pds seismic phases beneath the Argentina-Chile flat subduction.

  6. Receiver Function Imaging of Mantle Transition Zone Discontinuities Beneath Alaska

    Dahm, Haider Hassan Faraj

    Subduction of tectonic plates is one of the most important tectonic processes, yet many aspects of subduction zone geodynamics remain unsolved and poorly understood, such as the depth extent of the subducted slab and its geometry. The Alaska subduction zone, which is associated with the subduction of the Pacific Plate beneath the North America plate, has a complex tectonic setting and carries a series of subduction episodes, and represents an excellent target to study such plate tectonic processes. Previous seismological studies in Alaska have proposed different depth estimations and geometry for the subducted slab. The Mantle transition zone discontinuities of the 410km and the 660 km provide independent constraints on the depth extent of the subducted slabs. We conducted a receiver function study to map the topography of the 410 km and the 660 km discontinuities beneath Alaska and its adjacent areas by taking advantage of the teleseismic data from the new USArray deployment in Alaska and northwestern Canada. Stacking over 75,000 high-quality radial receiver functions recorded in Alaska with more than 40 years of recording period, the topographies of the 410 km and 660 km are mapped. The depths of both d410 and d660 show systematic spatial variations, the mean depth of d410 and d660 are within 6 km and 6 km from the global average, respectively. The mean MTZ thickness of the entire study area is within -2 km from the global average of 250 km, suggesting normal MTZ conditions on average. Central and south-central Alaska are characterized by a larger than normal MTZ thickness, suggesting that the subducting Pacific slab is thermally interacted with the MTZ. This study shows that lateral upper mantle velocity variations contribute the bulk of the observed apparent undulations of the MTZ discontinuities.

  7. Ps mantle transition zone imaging beneath the Colorado Rocky Mountains: Evidence for an upwelling hydrous mantle

    Zhang, Zhu; Dueker, Kenneth G.; Huang, Hsin-Hua

    2018-06-01

    We analyze teleseismic P-to-S conversions for high-resolution imaging of the mantle transition zone beneath the Colorado Rocky Mountains using data from a dense PASSCAL seismic broadband deployment. A total of 6,021 P-to-S converted receiver functions are constructed using a multi-channel minimum-phase deconvolution method and migrated using the common converted point technique with the 3-D teleseismic P- and S-wave tomography models of Schmandt and Humphreys (2010). The image finds that the average depths of the 410-km discontinuity (the 410) and 660-km discontinuity (the 660) at 408 ± 1.9 km and 649 ± 1.6 km respectively. The peak-to-peak topography of both discontinuities is 33 km and 27 km respectively. Additionally, prominent negative polarity phases are imaged both above and below the 410. To quantify the mean properties of the low-velocity layers about 410 km, we utilize double gradient layer models parameterization to fit the mean receiver function waveform. This waveform fitting is accomplished as a grid-search using anelastic synthetic seismograms. The best-fitting model reveals that the olivine-wadsleyite phase transformation width is 21 km, which is significantly larger than anhydrous mineral physics prediction (4-10 km) (Smyth and Frost, 2002). The findings of a wide olivine-wadsleyite phase transformation and the negative polarity phases above and below the 410, suggest that the mantle, at least in the 350-450 km depth range, is significantly hydrated. Furthermore, a conspicuous negative polarity phase below the 660 is imaged in high velocity region, we speculate the low velocity layer is due to dehydration flux melting in an area of convective downwelling. Our interpretation of these results, in tandem with the tomographic image of a Farallon slab segment at 800 km beneath the region (Schmandt and Humphreys, 2010), is that hydrous and upwelling mantle contributes to the high-standing Colorado Rocky Mountains.

  8. Heterogeneous distribution of water in the mantle transition zone beneath United States inferred from seismic observations

    Wang, Y.; Pavlis, G. L.; Li, M.

    2017-12-01

    The amount of water in the Earth's deep mantle is critical for the evolution of the solid Earth and the atmosphere. Mineral physics studies have revealed that Wadsleyite and Ringwoodite in the mantle transition zone could store several times the volume of water in the ocean. However, the water content and its distribution in the transition zone remain enigmatic due to lack of direct observations. Here we use seismic data from the full deployment of the Earthscope Transportable Array to produce 3D image of P to S scattering of the mantle transition zone beneath the United States. We compute the image volume from 141,080 pairs of high quality receiver functions defined by the Earthscope Automated Receiver Survey, reprocessed by the generalized iterative deconvolution method and imaged by the plane wave migration method. We find that the transition zone is filled with previously unrecognized small-scale heterogeneities that produce pervasive, negative polarity P to S conversions. Seismic synthetic modeling using a point source simulation method suggests two possible structures for these objects: 1) a set of randomly distributed blobs of slight difference in size, and 2) near vertical diapir structures from small scale convections. Combining with geodynamic simulations, we interpret the observation as compositional heterogeneity from small-scale, low-velocity bodies that are water enriched. Our results indicate there is a heterogeneous distribution of water through the entire mantle transition zone beneath the contiguous United States.

  9. Interaction of the Cyprus/Tethys Slab With the Mantle Transition Zone Beneath Anatolia

    Thompson, D. A.; Rost, S.; Taylor, G.; Cornwell, D. G.

    2017-12-01

    The geodynamics of the eastern Mediterranean are dominated by northward motion of the Arabian/African continents and subduction of the oldest oceanic crust on the planet along the Aegean and Cyprean trenches. These slabs have previously been imaged using seismic tomography on a continental scale, but detailed information regarding their descent from upper to lower mantle and how they interact with the mantle transition zone have been severely lacking. The Dense Array for North Anatolia (DANA) was a 73 station passive seismic deployment active between 2012-2013 with the primary aim of imaging shallow structure beneath the North Anatolian Fault. However, we exploit the exceptional dataset recorded by DANA to characterise a region where the Cyprus Slab impinges upon the mantle transition zone beneath northern Turkey, providing arguably the most detailed view of a slab as it transits from the upper to lower mantle. We map varying depths and amplitudes of the transition zone seismic discontinuities (`410', `520' and `660') in 3D using over 1500 high quality receiver functions over an area of approximately 200km x 300km. The `410' is observed close to its predicted depth, but the `660' is depressed to >670 km across the entirety of the study region. This is consistent with an accumulation of cold subducted material at the base of the upper mantle, and the presence of a `520' discontinuity in the vicinity of the slab surface also suggests that the slab is present deep within the transition zone. Anomalous low velocity layers above and within the transition zone are constrained and may indicate hydration and ongoing mass/fluid flux between upper and lower mantle in the presence of subduction. The results of the study have implications not only for the regional geodynamics of Anatolia, but also for slab dynamics globally.

  10. Global Transition Zone Anisotropy and Consequences for Mantle Flow and Earth's Deep Water Cycle

    Beghein, C.; Yuan, K.

    2011-12-01

    The transition zone has long been at the center of the debate between multi- and single-layered convection models that directly relate to heat transport and chemical mixing throughout the mantle. It has also been suggested that the transition zone is a reservoir that collects water transported by subduction of the lithosphere into the mantle. Since water lowers mantle minerals density and viscosity, thereby modifying their rheology and melting behavior, it likely affects global mantle dynamics and the history of plate tectonics. Constraining mantle flow is therefore important for our understanding of Earth's thermochemical evolution and deep water cycle. Because it can result from deformation by dislocation creep during convection, seismic anisotropy can help us model mantle flow. It is relatively well constrained in the uppermost mantle, but its presence in the transition zone is still debated. Its detection below 250 km depth has been challenging to date because of the poor vertical resolution of commonly used datasets. In this study, we used global Love wave overtone phase velocity maps, which are sensitive to structure down to much larger depths than fundamental modes alone, and have greater depth resolution than shear wave-splitting data. This enabled us to obtain a first 3-D model of azimuthal anisotropy for the upper 800km of the mantle. We inverted the 2Ψ terms of anisotropic phase velocity maps [Visser, et al., 2008] for the first five Love wave overtones between 35s and 174s period. The resulting model shows that the average anisotropy amplitude for vertically polarized shear waves displays two main stable peaks: one in the uppermost mantle and, most remarkably, one in the lower transition zone. F-tests showed that the presence of 2Ψ anisotropy in the transition zone is required to improve the third, fourth, and fifth overtones fit. Because of parameter trade-offs, however, we cannot exclude that the anisotropy is located in the upper transition zone as

  11. Supercritical fluid in the mantle transition zone deduced from H-D interdiffusion of wadsleyite

    Sun, Wei; Yoshino, Takashi; Sakamoto, Naoya; Yurimoto, Hisayoshi

    2018-02-01

    Knowledge of the distribution of water in the Earth's mantle is key to understanding the mantle convection and geochemical evolution of the Earth. As wadsleyite and ringwoodite can incorporate large amounts of water in their crystal structures, proton conduction has been invoked to account for the widespread conductive anomalies observed in the mantle wedge, where descending slab stagnates at the transition zone. However, there is a lot of controversy on whether proton conduction by itself is able to explain such anomalies, because of large discrepancy in the extent of the water effect deduced from previous electrical conductivity measurements on hydrous polycrystalline wadsleyite and ringwoodite. Here we report the hydrogen self-diffusion coefficient obtained from H-D interdiffusion experiments in wadsleyite single-crystal couples. Our results demonstrate that the effect of water on the electrical conductivity of wadsleyite is limited and hydrous wadsleyite by itself is unable to explain conductive anomalies in the transition zone. In contrast, the expected hydrogen effective diffusion does not allow the wide propagation of water between the stagnant slab and surrounding mantle, probably leading to persistence of local water saturation and continuous release of supercritical fluids at the stagnant slab roof on geological time scales. This phenomenon provides an alternative explanation for both the high-conductivity and seismic-velocity anomalies observed in the mantle wedge at the transition-zone depth.

  12. Global Discontinuity Structure of the Mantle Transition Zone from Finite-Frequency Tomography of SS Precursors

    Guo, Z.; Zhou, Y.

    2017-12-01

    We report global structure of the 410-km and 660-km discontinuities from finite-frequency tomography using frequency-dependent traveltime measurements of SS precursors recorded at the Global Seismological Network (GSN). Finite-frequency sensitivity kernels for discontinuity depth perturbations are calculated in the framework of traveling-wave mode coupling. We parametrize the global discontinuities using a set of spherical triangular grid points and solve the tomographic inverse problem based on singular value decomposition. Our global 410-km and 660-km discontinuity models reveal distinctly different characteristics beneath the oceans and subduction zones. In general, oceanic regions are associated with a thinner mantle transition zone and depth perturbations of the 410-km and 660-km discontinuities are anti-correlated, in agreement with a thermal origin and an overall warm and dry mantle beneath the oceans. The perturbations are not uniform throughout the oceans but show strong small-scale variations, indicating complex processes in the mantle transition zone. In major subduction zones (except for South America where data coverage is sparse), depth perturbations of the 410-km and 660-km discontinuities are correlated, with both the 410-km and the 660-km discontinuities occurring at greater depths. The distributions of the anomalies are consistent with cold stagnant slabs just above the 660-km discontinuity and ascending return flows in a superadiabatic upper mantle.

  13. Mapping the mantle transition zone beneath the central Mid-Atlantic Ridge using Ps receiver functions.

    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.

  14. Seismic Structure of Mantle Transition Zone beneath Northwest Pacific Subduction Zone and its Dynamic Implication

    Li, J.; Guo, G.; WANG, X.; Chen, Q.

    2017-12-01

    The northwest Pacific subduction region is an ideal location to study the interaction between the subducting slab and upper mantle discontinuities. Various and complex geometry of the Pacific subducting slab can be well traced downward from the Kuril, Japan and Izu-Bonin trench using seismicity and tomography images (Fukao and Obayashi, 2013). Due to the sparse distribution of seismic stations in the sea, investigation of the deep mantle structure beneath the broad sea regions is very limited. In this study, we applied the well- developed multiple-ScS reverberations method (Wang et al., 2017) to analyze waveforms recorded by the Chinese Regional Seismic Network, the densely distributed temporary seismic array stations installed in east Asia. A map of the topography of the upper mantle discontinuities beneath the broad oceanic regions in northwest Pacific subduction zone is imaged. We also applied the receiver function analysis to waveforms recorded by stations in northeast China and obtain the detailed topography map beneath east Asia continental regions. We then combine the two kinds of topography of upper mantle discontinuities beneath oceanic and continental regions respectively, which are obtained from totally different methods. A careful image matching and spatial correlation is made in the overlapping study regions to calibrate results with different resolution. This is the first time to show systematically a complete view of the topography of the 410-km and 660-km discontinuities beneath the east Asia "Big mantle wedge" (Zhao and Ohtani, 2009) covering the broad oceanic and continental regions in the Northwestern Pacific Subduction zone. Topography pattern of the 660 and 410 is obtained and discussed. Especially we discovered a broad depression of the 410-km discontinuity covering more than 1000 km in lateral, which seems abnormal in the cold subducting tectonic environment. Based on plate tectonic reconstruction studies and HTHP mineral experiments, we

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

    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

  16. Garnet Yield Strength at High Pressures and Implications for Upper Mantle and Transition Zone Rheology

    Kavner, A.

    2008-01-01

    Garnet helps control the mechanical behavior of the Earth's crust, mantle, and transition zone. Here, measurements are presented suggesting that garnet, long considered to be a high-viscosity phase, is actually weaker than the other dominant components in the transition zone. The mechanical behavior of garnet at high pressures was examined using radial diffraction techniques in the diamond anvil cell. The yield strength of grossular garnet was inferred from synchrotron X-ray measurements of differential lattice strains. The differential stress was found to increase from 1.3 (±0.6) GPa at a hydrostatic pressure 5.8 (±1.1) GPa to 4.1 (±0.4) GPa at 15.7 (±1.0) GPa, where it was level to 19 GPa. The strength results are consistent with inferred strength values for majorite garnet from measurements in the diamond cell normal geometry, bolstering the idea that garnet-structured materials may all have similar strengths. In this low-temperature, high differential stress regime, garnet is shown to be significantly weaker than anhydrous ringwoodite and to have a strength similar to hydrous ringwoodite. This result suggests that the presence of water in the transition zone may not be required to explain a weak rheology, and therefore models of transition zone behavior built assuming that garnet is the high-strength phase may need to be revised.

  17. Heterogeneous seismic anisotropy in the transition zone and uppermost lower mantle: evidence from South America, Izu-Bonin and Japan

    Lynner, Colton; Long, Maureen D.

    2015-06-01

    Measurements of seismic anisotropy are commonly used to constrain deformation in the upper mantle. Observations of anisotropy at mid-mantle depths are, however, relatively sparse. In this study we probe the anisotropic structure of the mid-mantle (transition zone and uppermost lower mantle) beneath the Japan, Izu-Bonin, and South America subduction systems. We present source-side shear wave splitting measurements for direct teleseismic S phases from earthquakes deeper than 300 km that have been corrected for the effects of upper mantle anisotropy beneath the receiver. In each region, we observe consistent splitting with delay times as large as 1 s, indicating the presence of anisotropy at mid-mantle depths. Clear splitting of phases originating from depths as great as ˜600 km argues for a contribution from anisotropy in the uppermost lower mantle as well as the transition zone. Beneath Japan, fast splitting directions are perpendicular or oblique to the slab strike and do not appear to depend on the propagation direction of the waves. Beneath South America and Izu-Bonin, splitting directions vary from trench-parallel to trench-perpendicular and have an azimuthal dependence, indicating lateral heterogeneity. Our results provide evidence for the presence of laterally variable anisotropy and are indicative of variable deformation and dynamics at mid-mantle depths in the vicinity of subducting slabs.

  18. Sulfide enrichment at an oceanic crust-mantle transition zone: Kane Megamullion (23°N, MAR)

    Ciazela, Jakub; Koepke, Juergen; Dick, Henry J. B.; Botcharnikov, Roman; Muszynski, Andrzej; Lazarov, Marina; Schuth, Stephan; Pieterek, Bartosz; Kuhn, Thomas

    2018-06-01

    The Kane Megamullion oceanic core complex located along the Mid-Atlantic Ridge (23°30‧N, 45°20‧W) exposes lower crust and upper mantle directly on the ocean floor. We studied chalcophile elements and sulfides in the ultramafic and mafic rocks of the crust-mantle transition and the mantle underneath. We determined mineralogical and elemental composition and the Cu isotope composition of the respective sulfides along with the mineralogical and elemental composition of the respective serpentines. The rocks of the crust-mantle transition zone (i.e., plagioclase harzburgite, peridotite-gabbro contacts, and dunite) overlaid by troctolites are by one order of magnitude enriched in several chalcophile elements with respect to the spinel harzburgites of the mantle beneath. Whereas the range of Cu concentrations in spinel harzburgites is 7-69 ppm, the Cu concentrations are highly elevated in plagioclase harzburgites with a range of 90-209 ppm. The zones of the peridotite-gabbro contacts are even more enriched, exhibiting up to 305 ppm Cu and highly elevated concentrations of As, Zn, Ga, Sb and Tl. High Cu concentrations show pronounced correlation with bulk S concentrations at the crust-mantle transition zone implying an enrichment process in this horizon of the oceanic lithosphere. We interpret this enrichment as related to melt-mantle reaction, which is extensive in crust-mantle transition zones. In spite of the ubiquitous serpentinization of primary rocks, we found magmatic chalcopyrites [CuFeS2] as inclusions in plagioclase as well as associated with pentlandite [(Fe,Ni)9S8] and pyrrhotite [Fe1-xS] in polysulfide grains. These chalcopyrites show a primary magmatic δ65Cu signature ranging from -0.04 to +0.29 ‰. Other chalcopyrites have been dissolved during serpentinization. Due to the low temperature (enrichment, increased sulfide modes, and potentially formation of small sulfide deposits could be expected globally along the petrological Moho.

  19. Investigating the relationship between the mantle transition zone and the fate of subducted slabs: an adaptative-mesh numerical approach

    Garel, F.; Davies, R.; Goes, S. D.; Davies, J.; Lithgow-Bertelloni, C. R.; Stixrude, L. P.

    2012-12-01

    Seismic observations show a wide range of slab morphologies within the mantle transition zone. This zone is likely to have been critical in Earth's thermal and chemical evolution, acting as a 'valve' that controls material transfer between the upper and lower mantle. However, the interaction between slabs and this complex region remains poorly understood. The complexity arises from non-linear and multi-scale interactions between several aspects of the mantle system, including mineral phase changes and material rheology. In this study, we will utilize new, multi-scale geodynamic models to determine what controls the seismically observed variability in slab behavior within the mantle transition zone and, hence, the down-going branch of the mantle 'valve'. Our models incorporate the newest mineral physics and theoretical constraints on density, phase proportions and rheology. In addition we exploit novel and unique adaptive grid methodologies to provide the resolution necessary to capture rapid changes in material properties in and around the transition zone. Our early results, which will be presented, illustrate the advantages of the new modelling technique for studying subduction including the effects of changes in material properties and mineral phases.

  20. 2-dimensional triplicated waveform modeling of the mantle transition zone beneath Northeast Asia

    Lai, Y.; Chen, L.; Wang, T.

    2017-12-01

    The Mantle Transition Zone (MTZ) of Northeast Asia has long been investigated by geoscientists for its critical importance where the subducted Pacific slab is stagnant above the 660km discontinuity, accompanied by complicated mantle processes. Taking advantages of the frequent occurrent deep earthquakes in subduction zone and dense seismic arrays in Northeast China, we successfully constructed the fine-scale P and SH velocity structure of a narrow azimuthal fan area based on 2-Dimensional (2D) triplicated waveform modeling for three deep close earthquakes, in which the triplicated waveforms are very sensitive to MTZ velocity structure in general, particularly the morphology of the stagnant slab in Northeast Asia. In our 2D triplication study, for the first time, we show a quite consistent feature of a high velocity layer for both Vp and Vs with the thickness of 140km and the length of 1200km just atop the 660km discontinuity, the western edge of the stagnant slab intersect with the North-South Gravity Lineament in China and has the subducting age of 30 Ma. Compared with a quite normal Vp, the Shear wave velocity reduction of -0.5% in the slab and -2.5% in the upper MTZ is required to reconcile the SH waves featured by the broad BOD. The high Vp/Vs ratio beneath Northeast Asia may imply a water-rich MTZ with the H2O content of 0.1-0.3 wt%. Particularly, a low velocity anomaly of about 150km wide was detected in the overall high-velocity stagnant slab by both P and SH triplicated waveform modeling, with the velocity anomaly value of -1% and -3%, respectively. The gap/window in the stagnant slab may provide a passage for hot deeper mantle materials to penetrate through the thick slab and feed the surface Changbaishan volcano. We also speculate that the existence of such a gap can be the manifestation of the original heterogeneity in the subducted slab and will further exacerbatethe impending gravitational instability and speed up mantle avalanche.

  1. Triplicated P-wave measurements for waveform tomography of the mantle transition zone

    S. C. Stähler

    2012-11-01

    Full Text Available Triplicated body waves sample the mantle transition zone more extensively than any other wave type, and interact strongly with the discontinuities at 410 km and 660 km. Since the seismograms bear a strong imprint of these geodynamically interesting features, it is highly desirable to invert them for structure of the transition zone. This has rarely been attempted, due to a mismatch between the complex and band-limited data and the (ray-theoretical modelling methods. Here we present a data processing and modelling strategy to harness such broadband seismograms for finite-frequency tomography. We include triplicated P-waves (epicentral distance range between 14 and 30° across their entire broadband frequency range, for both deep and shallow sources. We show that is it possible to predict the complex sequence of arrivals in these seismograms, but only after a careful effort to estimate source time functions and other source parameters from data, variables that strongly influence the waveforms. Modelled and observed waveforms then yield decent cross-correlation fits, from which we measure finite-frequency traveltime anomalies. We discuss two such data sets, for North America and Europe, and conclude that their signal quality and azimuthal coverage should be adequate for tomographic inversion. In order to compute sensitivity kernels at the pertinent high body wave frequencies, we use fully numerical forward modelling of the seismic wavefield through a spherically symmetric Earth.

  2. Synthetic receiver function profiles through the upper mantle and the transition zone for upwelling scenarios

    Nagel, Thorsten; Düsterhöft, Erik; Schiffer, Christian

    2017-04-01

    We investigate the signature relevant mantle lithologies leave in the receiver function record for different adiabatic thermal gradients down to 800 kilometers depth. The parameter space is chosen to target the visibility of upwelling mantle (a plume). Seismic velocities for depleted mantle, primitive mantle, and three pyroxenites are extracted from thermodynamically calculated phases diagrams, which also provide the adiabatic decompression paths. Results suggest that compositional variations, i.e. the presence or absence of considerable amounts of pyroxenites in primitive mantle should produce a clear footprint while horizontal differences in thermal gradients for similar compositions might be more subtle. Peridotites best record the classic discontinuities at around 410 and 650 kilometers depth, which are associated with the olivin-wadsleyite and ringwoodite-perovskite transitions, respectively. Pyroxenites, instead, show the garnet-perovskite transition below 700 kilometers depth and SiO2-supersaturated compositions like MORB display the coesite-stishovite transition between 300 and 340 kilometers depth. The latter shows the strongest temperature-depth dependency of all significant transitions potentially allowing to infer information about the thermal state if the mantle contains a sufficient fraction of MORB-like compositions. For primitive and depleted mantle compositions, the olivin-wadsleyite transition shows a certain temperature-depth dependency reflected in slightly larger delay times for higher thermal gradients. The lower-upper-mantle discontinuity, however, is predicted to display larger delay times for higher thermal gradients although the associated assemblage transition occurs at shallower depths thus requiring a very careful depth migration if a thermal anomaly should be recognized. This counterintuitive behavior results from the downward replacement of the assemblage wadsleyite+garnet with the assemblage garnet+periclase at high temperatures

  3. Global shear speed structure of the upper mantle and transition zone

    Schaeffer, A. J.; Lebedev, S.

    2013-07-01

    resolution of the imaging. Our new shear speed model is parametrized on a triangular grid with a ˜280 km spacing. In well-sampled continental domains, lateral resolution approaches or exceeds that of regional-scale studies. The close match of known surface expressions of deep structure with the distribution of anomalies in the model provides a useful benchmark. In oceanic regions, spreading ridges are very well resolved, with narrow anomalies in the shallow mantle closely confined near the ridge axis, and those deeper, down to 100-120 km, showing variability in their width and location with respect to the ridge. Major subduction zones worldwide are well captured, extending from shallow depths down to the transition zone. The large size of our waveform fit data set also provides a strong statistical foundation to re-examine the validity field of the JWKB approximation and surface wave ray theory. Our analysis shows that the approximations are likely to be valid within certain time-frequency portions of most seismograms with high signal-to-noise ratios, and these portions can be identified using a set of consistent criteria that we apply in the course of waveform fitting.

  4. A Bayesian method to quantify azimuthal anisotropy model uncertainties: application to global azimuthal anisotropy in the upper mantle and transition zone

    Yuan, K.; Beghein, C.

    2018-04-01

    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 per cent azimuthal anisotropy between 300 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 favoured and well constrained by the higher mode data employed. The fast seismic directions are in agreement with our previously published model. The data favour 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.

  5. Layered crust-mantle transition zone below a large crustal intrusion in the Norwegian-Danish basin

    Sandrin, Alessandro; Nielsen, Lars; Thybo, Hans

    2009-01-01

    the lowermost crust (7.7 km/s) and the uppermost mantle (7.9-8.0 km/s). The seismic data show a "ringing" Moho below the western part of the intrusion. The coda trailing the main PmP reflection is about 1.0 s long and is composed of 4-5 wavelets. We demonstrate that this feature may be explained by a layered......The crust and uppermost mantle below the large positive gravity anomaly in the central part of the Norwegian-Danish Basin, the Silkeborg Gravity High (SGH), is investigated using controlled source seismic data. A more than 80 km long and ~ 20 km thick intrusion is interpreted. The seismic velocity...... transition zone between 30 and 35 km depth, where high-velocity layers of mantle affinity (7.9-8.05 km/s) alternate with layers of typical lower crustal velocity (6.7-7.3 km/s). The characteristics of this layering, which causes thePmP coda, are modelled by matching synthetic seismograms to the observed data...

  6. Mantle transition zone beneath northeast China from P-receiver function

    Zhang, R.; Wu, Q.

    2015-12-01

    We used receiver functions to examine lateral topographical variations on the 410- and 660-km beneath northeast China and particularly the Kuril-Japan arc junctions. Compared to other receiver functions studies, our analysis was based on greater station coverage of higher density by combining all recent seismic arrays so far deployed in northeast China. Our image shows that the 410-km is featured by a ~10-20 km uplift extending in the NNE direction beneath some areas of the Quaternary basaltic rocks distributed at Abaga and at Wudalianchi. The Clapeyron slope of the olivine phase transiton at 410-km suggests that the uplift is compatible with a negative thermal anomaly. We also confirm a significant depression of the 660 from the Changbai volcanism in the north to Korea in the south along the NW-SE direction. The depression is also accompanied by an uplift of the 660 to the west. The shallow 660-km discontinuity is also particularly detected beneath the Kuril-Japan arc junctions, while it was not detected before. The thermal anomaly at 410 km depth is most likely a remnant of a detached mantle lithosphere that recently sank to depth, thus providing robust evidence for the source and evolution of these basalts. The depression of the 660-km discontinuity may support that the subducting Pacific slab bends sharply and becomes stagnant when it meets strong resistance at a depth of about 670 km. After accumulation to a great extent the stagnant slab finally penetrates into the lower mantle. Combined with the previous triplicated studies, the shallow 660-km may suggest that descending Pacific slab at its leading and junction edges might be accommodated by a tearing near a depth of 660 km. Acknowledgements. Two liner seismic arrays were deployed by the Institute of Geophysics, China Earthquake Administration. The data of the permanent stations were provided by the Data Management Centre of China, National Seismic Network at the Institute of Geophysics, China Earthquake

  7. Crustal Structure and Mantle Transition Zone Thickness beneath the Central Mongolia from Teleseismic Receiver Functions

    He, J.; Wu, Q.; Gao, M.; Munkhuu, U.; Demberel, S. G.

    2013-12-01

    The Mongolian Plateau (northern Asia) is situated between the Gobi-Altai range and the Siberian craton. In order to understand the crustal and mantle structure environmental characteristics, we use the teleseismic data recorded by 69 broadband stations located in the Central Mongolia(103.5°-111.5°E, 42°-50°N). The teleseismic events are selected from the global earthquakes between Aug. 2011 and Dec. 2013 with magnitude >5.5and the epicentral distance range from 30° to 95° to the center of the network. Lateral variations of the crustal thicknesses H and Vp/Vs ratios are obtained by using receiver function method. The crust thins gradually from northwest to southeast in the studying field. We found that the thinnest crust is ~37.5km in the southeast which is Gobi. The distribution of Vp/Vs ratios are between 1.68 and 1.84, which shows the heterogeneity. There are three high-anomaly areas: the Gobi range which is the Later Paleozoic Orogeny; the Khentei Mountains which is in the Jurassic-Cretaceous Reactive Continental Margin; the northwest area which is granite. Our research not only reveals the powerful evident of the crustal formation and evolution mechanism, but also provides some constraints on the mechanism of uplift of the Mongolian Plateau.This study was supported by the international cooperation project of the Ministry of Science and Technology of China (2011DFB20120).

  8. Lateral Variations of the Mantle Transition Zone Structure beneath the Southeastern Tibetan Plateau Revealed by P-wave Receiver Functions

    Bai, Y.; Ai, Y.; Jiang, M.; He, Y.; Chen, Q.

    2017-12-01

    The deep structure of the southeastern Tibetan plateau is of great scientific importance to a better understanding of the India-Eurasia collision as well as the evolution of the magnificent Tibetan plateau. In this study, we collected 566 permanent and temporary seismic stations deployed in SE Tibet, with a total of 77853 high quality P-wave receiver functions been extracted by maximum entropy deconvolution method. On the basis of the Common Conversion Point (CCP) stacking technique, we mapped the topography of the 410km and 660km discontinuities (hereinafter called the `410' and the `660'), and further investigated the lateral variation of the mantle transition zone (MTZ) thickness beneath this region. The background velocity model deduced from H-κ stacking results and a previous body-wave tomographic research was applied for the correction of the crustal and upper mantle heterogeneities beneath SE Tibet for CCP stacking. Our results reveal two significantly thickened MTZ anomalies aligned nearly in the south-north direction. The magnitude of both anomalies are 30km above the global average of 250km. The southern anomaly located beneath the Dianzhong sub-block and the Indo-China block is characterized by a slightly deeper `410' and a greater-than-normal `660', while the northern anomaly beneath western Sichuan has an uplifted `410' and a depressed `660'. Combining with previous studies in the adjacent region, we suggest that slab break-off may occurred during the eastward subduction of the Burma plate, with the lower part of the cold slab penetrated into the MTZ and stagnated at the bottom of the `660' which may cause the southern anomaly in our receiver function images. The origin of the Tengchong volcano is probably connected to the upwelling of the asthenospheric material caused by the slab break-off or to the ascending of the hot and wet material triggered by the dehydration of stagnant slab in the MTZ. The anomaly in the north, on the other hand, might be

  9. Seismic images of the transition zone: is Hawaiian volcanism produced by a secondary plume from the top of the lower mantle?

    Cao, Q.; van der Hilst, R. D.; Shim, S.; De Hoop, M. V.

    2011-12-01

    The Hawaiian hotspot is often attributed to hot material rising from depth in the mantle, but efforts to detect a thermal plume seismically have been inconclusive. Most tomographic models reveal anomalously low wavespeeds beneath Hawaii, but the depth extent of this structure is not well known. S or P data used in traveltime inversions are associated with steep rays to distant sources, which degrades depth resolution, and surface wave dispersion does not have sufficient sensitivity at the depths of interest. To investigate pertinent thermal anomalies we mapped depth variations of upper mantle discontinuities using precursors of the surface-reflected SS wave. Instead of stacking the data over geographical bins, which leads to averaging of topography and hence loss of spatial resolution, we used a generalized Radon transform (GRT) to detect and map localized elasticity contrasts in the transition zone (Cao et al., PEPI, 2010). We apply the GRT to produce 3D image volumes beneath a large area of the Pacific Ocean, including Hawaii and the Hawaii-Emperor seamount chain (Cao et al., Science, 2011). The 3D image volumes reveal laterally continuous interfaces near 410 and 660 km depths, that is, the traditional boundaries of the transition zone, but also suggest (perhaps intermittent) scatter horizons near 300-350, 520-550, and 800-1000 km depth. The upper mantle appears generally hot beneath Hawaii, but the most conspicuous topographic (and probably thermal) anomalies are found west of Hawaii. The GRT images reveal a 800 km wide uplift of the 660 discontinuity just west of Hawaii, but there is no evidence for a corresponding localized depression of the 410 discontinuity. This expression of the 410 and 660 km topographies is consistent with some existed geodynamical modeling results, in which a deep-rooted mantle plume impinging on the transition zone, creating a broad pond of hot material underneath endothermic phase change at 660 km depth, and with secondary plumes

  10. Ringwoodite growth rates from olivine with ~75 ppmw H2O: Metastable olivine must be nearly anhydrous to exist in the mantle transition zone

    Du Frane, Wyatt L. [Arizona State Univ., Tempe, AZ (United States). School of Earth and Space Exploration; Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Atmospheric, Earth and Energy Division; Sharp, Thomas G. [Arizona State Univ., Tempe, AZ (United States). School of Earth and Space Exploration; Mosenfelder, Jed L. [California Inst. of Technology (CalTech), Pasadena, CA (United States). Division of Geological and Planetary Sciences; Leinenweber, Kurt [Arizona State Univ., Tempe, AZ (United States). School of Earth and Space Exploration

    2013-04-15

    It has been previously demonstrated that as little as 300 ppmw H2O increases wadsleyite and ringwoodite growth rates to magnitudes that are inconsistent with the metastable olivine hypothesis. To further test this hypothesis, we present new ringwoodite growth rate measurements from olivine with ~75 ppmw H2O at 18 GPa and 700, 900, and 1100 °C. These growth rates are nearly identical to those from olivine with ~300 ppmw H2O, and significantly higher than those from nominally anhydrous olivine. We infer that transformation of olivine with 75-300 ppmw H2O is primarily enhanced by hydrolytic weakening of reaction rims, which reduces the elastic strain-energy barrier to growth. We present a new method for fitting nonlinear nominally anhydrous data, to demonstrate that reduction of growth rates by elastic strain energy is an additional requirement for metastable olivine. In conclusion, based on previous thermokinetic modeling, these enhanced growth rates are inconsistent with the persistence of metastable olivine wedges into the mantle transition zone. Metastable persistence of olivine into the mantle transition-zone would therefore require < 75 ppmw H2O.

  11. [Cytostructure of the mantle zone in lymphatic tissue].

    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.

  12. The role of upper mantle mineral phase transitions on the current structure of large-scale Earth's mantle convection.

    Thoraval, C.

    2017-12-01

    Describing the large-scale structures of mantle convection and quantifying the mass transfer between upper and lower mantle request to account for the role played by mineral phase transitions in the transition zone. We build a density distribution within the Earth mantle from velocity anomalies described by global seismic tomographic models. The density distribution includes thermal anomalies and topographies of the phase transitions at depths of 410 and 660 km. We compute the flow driven by this density distribution using a 3D spherical circulation model, which account for depth-dependent viscosity. The dynamic topographies at the surface and at the CMB and the geoid are calculated as well. Within the range of viscosity profiles allowing for a satisfying restitution of the long wavelength geoid, we perform a parametric study to decipher the role of the characteristics of phase diagrams - mainly the Clapeyron's slopes - and of the kinetics of phase transitions, which may modify phase transition topographies. Indeed, when a phase transition is delayed, the boundary between two mineral phases is both dragged by the flow and interfere with it. The results are compared to recent estimations of surface dynamic topography and to the phase transition topographies as revealed by seismic studies. The consequences are then discussed in terms of structure of mantle flow. Comparisons between various tomographic models allow us to enlighten the most robust features. At last, the role played by the phase transitions on the lateral variations of mass transfer between upper and lower mantle are quantified by comparison to cases with no phase transitions and confronted to regional tomographic models, which reflect the variability of the behaviors of the descending slabs in the transition zone.

  13. Crustal structure and mantle transition zone thickness beneath a hydrothermal vent at the ultra-slow spreading Southwest Indian Ridge (49°39'E): a supplementary study based on passive seismic receiver functions

    Ruan, Aiguo; Hu, Hao; Li, Jiabiao; Niu, Xiongwei; Wei, Xiaodong; Zhang, Jie; Wang, Aoxing

    2017-06-01

    As a supplementary study, we used passive seismic data recorded by one ocean bottom seismometer (OBS) station (49°41.8'E) close to a hydrothermal vent (49°39'E) at the Southwest Indian Ridge to invert the crustal structure and mantle transition zone (MTZ) thickness by P-to-S receiver functions to investigate previous active seismic tomographic crustal models and determine the influence of the deep mantle thermal anomaly on seafloor hydrothermal venting at an ultra-slow spreading ridge. The new passive seismic S-wave model shows that the crust has a low velocity layer (2.6 km/s) from 4.0 to 6.0 km below the sea floor, which is interpreted as partial melting. We suggest that the Moho discontinuity at 9.0 km is the bottom of a layer (2-3 km thick); the Moho (at depth of 6-7 km), defined by active seismic P-wave models, is interpreted as a serpentinized front. The velocity spectrum stacking plot made from passive seismic data shows that the 410 discontinuity is depressed by 15 km, the 660 discontinuity is elevated by 18 km, and a positive thermal anomaly between 182 and 237 K is inferred.

  14. Deep mantle seismic heterogeneities in Western Pacific subduction zones

    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

  15. Joint inversion of satellite-detected tidal and magnetospheric signals constrains electrical conductivity and water content of the upper mantle and transition zone

    Grayver, Alexander V.; Munch, F. D.; Kuvshinov, Alexey V.

    2017-01-01

    and ocean tidal magnetic signals from the most recent Swarm and CHAMP data. The challenging task of properly accounting for the ocean effect in the data was addressed through full three-dimensional solution of Maxwell's equations. We show that simultaneous inversion of magnetospheric and tidal magnetic......We present a new global electrical conductivity model of Earth's mantle. The model was derived by using a novel methodology, which is based on inverting satellite magnetic field measurements from different sources simultaneously. Specifically, we estimated responses of magnetospheric origin...

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

    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

  17. [The mantle zone in lymphatic follicles and its stratification].

    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.

  18. Upper-mantle P- and S- wave velocities across the Northern Tornquist Zone from traveltime tomography

    Hejrani, Babak; Balling, N.; Jacobsen, B. H.

    2015-01-01

    This study presents P- and S-wave velocity variations for the upper mantle in southern Scandinavia and northern Germany based on teleseismic traveltime tomography. Tectonically, this region includes the entire northern part of the prominent Tornquist Zone which follows along the transition from old...... delineated between shield areas (with high seismic mantle velocity) and basins (with lower velocity). It continues northwards into southern Norway near the Oslo Graben area and further north across the Southern Scandes Mountains. This main boundary, extending to a depth of at least 300 km, is even more...

  19. Noble gases recycled into the mantle through cold subduction zones

    Smye, Andrew J.; Jackson, Colin R. M.; Konrad-Schmolke, Matthias; Hesse, Marc A.; Parman, Steve W.; Shuster, David L.; Ballentine, Chris J.

    2017-08-01

    Subduction of hydrous and carbonated oceanic lithosphere replenishes the mantle volatile inventory. Substantial uncertainties exist on the magnitudes of the recycled volatile fluxes and it is unclear whether Earth surface reservoirs are undergoing net-loss or net-gain of H2O and CO2. Here, we use noble gases as tracers for deep volatile cycling. Specifically, we construct and apply a kinetic model to estimate the effect of subduction zone metamorphism on the elemental composition of noble gases in amphibole - a common constituent of altered oceanic crust. We show that progressive dehydration of the slab leads to the extraction of noble gases, linking noble gas recycling to H2O. Noble gases are strongly fractionated within hot subduction zones, whereas minimal fractionation occurs along colder subduction geotherms. In the context of our modelling, this implies that the mantle heavy noble gas inventory is dominated by the injection of noble gases through cold subduction zones. For cold subduction zones, we estimate a present-day bulk recycling efficiency, past the depth of amphibole breakdown, of 5-35% and 60-80% for 36Ar and H2O bound within oceanic crust, respectively. Given that hotter subduction dominates over geologic history, this result highlights the importance of cooler subduction zones in regassing the mantle and in affecting the modern volatile budget of Earth's interior.

  20. Scattering beneath Western Pacific subduction zones: evidence for oceanic crust in the mid-mantle

    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

  1. The role of solid-solid phase transitions in mantle convection

    Faccenda, Manuele; Dal Zilio, Luca

    2017-01-01

    With changing pressure and temperature conditions, downwelling and upwelling crustal and mantle rocks experience several solid-solid phase transitions that affect the mineral physical properties owing to structural changes in the crystal lattice and to the absorption or release of latent heat. Variations in density, together with phase boundary deflections related to the non-null reaction slope, generate important buoyancy forces that add to those induced by thermal perturbations. These buoyancy forces are proportional to the density contrast between reactant and product phases, their volume fraction, the slope and the sharpness of the reaction, and affect the style of mantle convection depending on the system composition. In a homogeneous pyrolitic mantle there is little tendency for layered convection, with slabs that may stagnate in the transition zone because of the positive buoyancy caused by post-spinel and post-ilmenite reactions, and hot plumes that are accelerated by phase transformations in the 600-800 km depth range. By adding chemical and mineralogical heterogeneities as on Earth, phase transitions introduce bulk rock and volatiles filtering effects that generate a compositional gradient throughout the entire mantle, with levels that are enriched or depleted in one or more of these components. Phase transitions often lead to mechanical softening or hardening that can be related to a different intrinsic mechanical behaviour and volatile solubility of the product phases, the heating or cooling associated with latent heat, and the transient grain size reduction in downwelling cold material. Strong variations in viscosity would enhance layered mantle convection, causing slab stagnation and plume ponding. At low temperatures and relatively dry conditions, reactions are delayed due to the sluggish kinetics, so that non-equilibrium phase aggregates can persist metastably beyond the equilibrium phase boundary. Survival of low-density metastable olivine

  2. Coupled Hf-Nd-Pb isotope co-variations of HIMU oceanic island basalts from Mangaia, Cook-Austral islands, suggest an Archean source component in the mantle transition zone

    Nebel, Oliver; Arculus, Richard J.; van Westrenen, Wim; Woodhead, Jon D.; Jenner, Frances E.; Nebel-Jacobsen, Yona J.; Wille, Martin; Eggins, Stephen M.

    2013-07-01

    Although it is widely accepted that oceanic island basalts (OIB) sample geochemically distinct mantle reservoirs including recycled oceanic crust, the composition, age, and locus of these reservoirs remain uncertain. OIB with highly radiogenic Pb isotope signatures are grouped as HIMU (high-μ, with μ = 238U/204Pb), and exhibit unique Hf-Nd isotopic characteristics, defined as ΔɛHf, deviant from a terrestrial igneous rock array that includes all other OIB types. Here we combine new Hf isotope data with previous Nd-Pb isotope measurements to assess the coupled, time-integrated Hf-Nd-Pb isotope evolution of the most extreme HIMU location (Mangaia, French Polynesia). In comparison with global MORB and other OIB types, Mangaia samples define a unique trend in coupled Hf-Nd-Pb isotope co-variations (expressed in 207Pb/206Pb vs. ΔɛHf). In a model employing subducted, dehydrated oceanic crust, mixing between present-day depleted MORB mantle (DMM) and small proportions (˜5%) of a HIMU mantle endmember can re-produce the Hf-Nd-Pb isotope systematics of global HIMU basalts (sensu stricto; i.e., without EM-1/EM-2/FOZO components). An age range of 3.5 to 3 Gyr and implies that OIB chemistry can be used to test geodynamic models.

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

    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

  4. Mantle helium along the Newport-Inglewood fault zone, Los Angeles basin, California: A leaking paleo-subduction zone

    Boles, J. R.; Garven, G.; Camacho, H.; Lupton, J. E.

    2015-07-01

    Mantle helium is a significant component of the helium gas from deep oil wells along the Newport-Inglewood fault zone (NIFZ) in the Los Angeles (LA) basin. Helium isotope ratios are as high as 5.3 Ra (Ra = 3He/4He ratio of air) indicating 66% mantle contribution (assuming R/Ra = 8 for mantle), and most values are higher than 1.0 Ra. Other samples from basin margin faults and from within the basin have much lower values (R/Ra geothermal gradients, and is modeled as truncated by a proposed major, potentially seismically active, décollement beneath the LA basin. Our results demonstrate that the NIFZ is a deep-seated fault directly or indirectly connected with the mantle. Based on a 1-D model, we calculate a maximum Darcy flow rate q ˜ 2.2 cm/yr and a fault permeability k ˜ 6 × 10-17 m2 (60 microdarcys), but the flow rates are too low to create a geothermal anomaly. The mantle leakage may be a result of the NIFZ being a former Mesozoic subduction zone in spite of being located 70 km west of the current plate boundary at the San Andreas fault.

  5. Transformations of humus and soil mantle in the urbanized areas of the Chernobyl NPP exclusion zone

    Tyutyunnik, Yu.G.; Bednaya, S.M.

    1998-01-01

    Presented are investigations into the demutation processes of the towns plant community in the Chernobyl NPP exclusion zone (Pripyat, Chernobyl, Chernobyl-2). Demonstrated is the specific nature of the reduction of humus and soil mantle in the abandoned towns under the impact of the natural factors. 21 refs., 5 tab., 7 figs

  6. Molecular differences in transition zone and peripheral zone prostate tumors

    Sinnott, Jennifer A.; Rider, Jennifer R.; Carlsson, Jessica; Gerke, Travis; Tyekucheva, Svitlana; Penney, Kathryn L.; Sesso, Howard D.; Loda, Massimo; Fall, Katja; Stampfer, Meir J.; Mucci, Lorelei A.; Pawitan, Yudi; Andersson, Sven-Olof; Andrén, Ove

    2015-01-01

    Prostate tumors arise primarily in the peripheral zone (PZ) of the prostate, but 20–30% arise in the transition zone (TZ). Zone of origin may have prognostic value or reflect distinct molecular subtypes; however, it can be difficult to determine in practice. Using whole-genome gene expression, we built a signature of zone using normal tissue from five individuals and found that it successfully classified nine tumors of known zone. Hypothesizing that this signature captures tumor zone of origin, we assessed its relationship with clinical factors among 369 tumors of unknown zone from radical prostatectomies (RPs) and found that tumors that molecularly resembled TZ tumors showed lower mortality (P = 0.09) that was explained by lower Gleason scores (P = 0.009). We further applied the signature to an earlier study of 88 RP and 333 transurethral resection of the prostate (TURP) tumor samples, also of unknown zone, with gene expression on ~6000 genes. We had observed previously substantial expression differences between RP and TURP specimens, and hypothesized that this might be because RPs capture primarily PZ tumors, whereas TURPs capture more TZ tumors. Our signature distinguished these two groups, with an area under the receiver operating characteristic curve of 87% (P zones. Zone of origin may be important to consider in prostate tumor biomarker research. PMID:25870172

  7. High-Resolution P'P' Precursor Imaging of Nazca-South America Plate Boundary Zones and Inferences for Transition Zone Temperature and Composition

    Gu, Y. J.; Schultz, R.

    2013-12-01

    Knowledge of upper mantle transition zone stratification and composition is highly dependent on our ability to efficiently extract and properly interpret small seismic arrivals. A promising high-frequency seismic phase group particularly suitable for a global analysis is P'P' precursors, which are capable of resolving mantle structures at vertical and lateral resolution of approximately 5 and 200 km, respectively, owing to their shallow incidence angle and small, quasi-symmetric Fresnel zones. This study presents a simultaneous analysis of SS and P'P' precursors based on deconvolution, Radon transform and depth migration. Our multi-resolution survey of the mantle near Nazca-South America subduction zone reveals both olivine and garnet related transitions at depth below 400 km. We attribute a depressed 660 to thermal variations, whereas compositional variations atop the upper-mantle transition zone are needed to explain the diminished or highly complex reflected/scattered signals from the 410 km discontinuity. We also observe prominent P'P' reflections within the transition zone, especially near the plate boundary zone where anomalously high reflection amplitudes result from a sharp (~10 km thick) mineral phase change resonant with the dominant frequency of the P'P' precursors. Near the base of the upper mantle, the migration of SS precursors shows no evidence of split reflections near the 660-km discontinuity, but potential majorite-ilmenite (590-640 km) and ilmenite-perovskite transitions (740-750 km) are identified based on similarly processed high-frequency P'P' precursors. At nominal mantle temperatures these two phase changes may be seismically indistinguishable, but colder mantle conditions from the descending Nazca plate, the presence of water and variable Fe contents may cause sufficient separation for a reliable analysis. In addition, our preliminary results provide compelling evidence for multiple shallow lower-mantle reflections (at ~800 km) along the

  8. A possible mechanism for earthquakes found in the mantle wedge of the Nazca subduction zone

    Warren, L. M.; Chang, Y.; Prieto, G. A.

    2017-12-01

    Beneath Colombia, the Cauca cluster of intermediate-depth earthquakes extends for 200 km along the trench (3.5°N-5.5°N, 77.0°W-75.3°W) and, with 58 earthquakes per year with local magnitude ML >= 2.5, has a higher rate of seismicity than the subduction zone immediately to the north or south. By precisely locating 433 cluster earthquakes from 1/2010-3/2014 with data from the Colombian National Seismic Network, we found that the earthquakes are located both in a continuous Nazca plate subducting at an angle of 33°-43° and in the overlying mantle wedge. The mantle wedge earthquakes (12% of the earthquakes) form two isolated 40-km-tall columns extending perpendicular to the subducting slab. Using waveform inversion, we computed focal mechanisms for 69 of the larger earthquakes. The focal mechanisms are variable, but the intraslab earthquakes are generally consistent with an in-slab extensional stress axis oriented 25° counterclockwise from the down-dip direction. We suggest that the observed mantle wedge earthquakes are the result of hydrofracture in a relatively cool mantle wedge. This segment of the Nazca Plate is currently subducting at a normal angle, but Wagner et al. (2017) suggested that a flat slab slowly developed in the region between 9-5.9 Ma and persisted until 4 Ma. During flat slab subduction, the overlying mantle wedge typically cools because it is cut off from mantle corner flow. After hydrous minerals in the slab dehydrate, the dehydrated fluid is expelled from the slab and migrates through the mantle wedge. If a cool mantle wedge remains today, fluid dehydrated from the slab may generate earthquakes by hydrofracture, with the mantle wedge earthquakes representing fluid migration pathways. Dahm's (2000) model of water-filled fracture propagation in the mantle wedge shows hydrofractures propagating normal to the subducting slab and extending tens of km into the mantle wedge, as we observe.

  9. Stress relief of transition zones

    Woodward, J.; van Rooyen, D.

    1984-01-01

    This paper considers the problem of intergranular stress corrosion cracking, initiated on the primary side, in the expansion transition region of roller expanded Alloy 600 tubing. In general it is believed that residual stresses, arising from the expansion process, are the cause of the problem. The work reported here concentrated on the identification of an optimal, in-situ stress relief treatment

  10. Dynamics of the solar transition zone

    Bruner, E. C., Jr.

    1978-01-01

    Time-resolved profiles of the 1548-A C IV line arising from the solar transition region are analyzed in order to determine whether the 300-sec oscillations characteristic of the photosphere and chromosphere penetrate into the transition zone and to measure the rms amplitude of transition-zone disturbances as well as their dependence on solar activity. The rms velocity amplitude is used to set limits on the mechanical energy flux available for solar heating. A power-spectrum analysis indicates that acoustic waves appear to have been detected in the transition zone, that at least one case of a strong 200- to 300-sec oscillation was observed, but that strong periodicities are not found on the average in either the intensity or the velocity field. It is suggested that the rms velocity that may be attributed to directly observable wave motion is between 3 and 7 km/s, depending on whether the individual emission elements seen in rocket spectra are coherent or independent in phase.

  11. Effect of Spin Transition onComposition and Seismic Structure of the Lower Mantle

    Wu, Z.

    2015-12-01

    Spin transition of iron in ferropericlase (Fp) causes a significant softening in bulk modulus [e.g.,1,2], which leads to unusual dVP/dT>0. Because dVP/dT>0 in Fp cancels out with dVP/dTMao, Z., Marquardt, H., 2013. . Rev Geophys 51, 244-275 (2013). [3] Wu, Z.Q., Wentzcovitch, R.M., 2014. Spin crossover in ferropericlase and velocity heterogeneities in the lower mantle. Proc. Natl. Acad. Sci. U. S. A. 111, 10468-10472. [4] Zhao, D.P., 2007. Seismic images under 60 hotspots: Search for mantle plumes. Gondwana Res 12, 335-355. [5] van der Hilst, R.D., Karason, H., 1999. Science 283, 1885-1888. [6] Huang,C., Leng, W., Wu, Z. Q., 2015. Iron-spin transition controls structure and stability of LLSVPs in the lower mantle, Earth Planet. Sci. Lett. 423, 173-181.

  12. Simulating the Seismic Signal of Phase Transitions in the Deepest Mantle (Invited)

    Walker, A.; Dobson, D. P.; Nowacki, A.; Wookey, J. M.; Forte, A. M.; Kendall, J. M.

    2013-12-01

    The discovery of the perovskite to post-perovskite phase transition in (Mg,Fe)SiO3 explains many of the seismic observations of the lowermost mantle including the presence of multiple seismic discontinuities and significant seismic anisotropy. However, the explanations of many detailed features remain elusive. The recent discovery of a topotactic relationship between the orientation of perovskite and post-perovskite crystals in a partially transformed analogue opens the possibility of texture inheritance through the phase transition [1]. This must be captured in simulations designed to explain the anisotropy of the lowermost mantle, especially those which link mantle dynamics with seismic observations. We have extended our previous work linking models of flow in the lowermost mantle with simulations of texture development and predictions of seismic anisotropy [2] to account for the topotaxy between perovskite and post-perovskite. In particular, we compare four cases: (1) As in [2], anisotropy is only generated in post-perovskite by dislocation mediated deformation dominated by one of a number of slip systems, phase transitions destroy texture and ferropericlase and perovskite dominated rocks are isotropic. (2) Although phase transitions destroy texture, ferropericlase and/or perovskite deform by dislocation motion permitting the generation of seismic anisotropy in warmer regions of the mantle where post-perovskite is unstable. We account for the possibility of the inversion of slip-system activities in ferropericlase at high pressure as suggested by models of dislocation motion based on atomic scale simulations [3]. (3) Allow texture development by dislocation motion in perovskite and post-perovskite and texture inheritance through phase transitions by the mechanism described in [1]. However, we assume that the bulk of the lower mantle deforms by a mechanism that does not lead to the development of texture and so begin the simulation from a random distribution of

  13. Ultra-low velocity zone heterogeneities at the core-mantle boundary from diffracted PKKPab waves

    Ma, Xiaolong; Sun, Xinlei

    2017-08-01

    Diffracted waves around Earth's core could provide important information of the lowermost mantle that other seismic waves may not. We examined PKKPab diffraction waves from 52 earthquakes occurring at the western Pacific region and recorded by USArray to probe the velocity structure along the core-mantle boundary (CMB). These diffracted waves emerge at distances up to 10° past the theoretical cutoff epicentral distance and show comparable amplitudes. We measured the ray parameters of PKKPab diffraction waves by Radon transform analysis that is suitable for large-aperture arrays. These ray parameters show a wide range of values from 4.250 to 4.840 s/deg, suggesting strong lateral heterogeneities in sampling regions at the base of the mantle. We further estimated the P-wave velocity variations by converting these ray parameters and found the CMB regions beneath the northwestern edge of African Anomaly (Ritsma et al. in Science 286:1925-1928, 1999) and southern Sumatra Islands exhibit velocity reductions up to 8.5% relative to PREM. We suggest that these low velocity regions are Ultra-low velocity zones, which may be related to partial melt or iron-enriched solids.[Figure not available: see fulltext.

  14. Multiple-frequency tomography of the upper mantle beneath the African/Iberian collision zone

    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.

  15. Tomography of the upper mantle beneath the African/Iberian collision zone

    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.

  16. The transition zone above a lumbosacral fusion.

    Hambly, M F; Wiltse, L L; Raghavan, N; Schneiderman, G; Koenig, C

    1998-08-15

    The clinical and radiographic effect of a lumbar or lumbosacral fusion was studied in 42 patients who had undergone a posterolateral fusion with an average follow-up of 22.6 years. To examine the long-term effects of posterolateral lumbar or lumbosacral fusion on the cephalad two motion segments (transition zone). It is commonly held that accelerated degeneration occurs in the motion segments adjacent to a fusion. Most studies are of short-term, anecdotal, uncontrolled reports that pay particular attention only to the first motion segment immediately cephalad to the fusion. Forty-two patients who had previously undergone a posterolateral lumbar or lumbosacral fusion underwent radiographic and clinical evaluation. Rate of fusion, range of motion, osteophytes, degenerative spondylolisthesis, retrolisthesis, facet arthrosis, disc ossification, dynamic instability, and disc space height were all studied and statistically compared with an age- and gender-matched control group. The patient's self-reported clinical outcome was also recorded. Degenerative changes occurred at the second level above the fused levels with a frequency equal to those occurring in the first level. There was no statistical difference between the study group and the cohort group in the presence of radiographic changes within the transition zone. In those patients undergoing fusion for degenerative processes, 75% reported a good to excellent outcome, whereas 84% of those undergoing fusion for spondylolysis or spondylolisthesis reported a good to excellent outcome. Radiographic changes occur within the transition zone cephalad to a lumbar or lumbosacral fusion. However, these changes are also seen in control subjects who have had no surgery.

  17. Enrichments of the mantle sources beneath the Southern Volcanic Zone (Andes) by fluids and melts derived from abraded upper continental crust

    Holm, Paul Martin; Søager, Nina; Dyhr, Charlotte Thorup

    2014-01-01

    Mafic basaltic-andesitic volcanic rocks from the Andean Southern Volcanic Zone (SVZ) exhibit a northward increase in crustal components in primitive arc magmas from the Central through the Transitional and Northern SVZ segments. New elemental and Sr–Nd-high-precision Pb isotope data from the Quat......Mafic basaltic-andesitic volcanic rocks from the Andean Southern Volcanic Zone (SVZ) exhibit a northward increase in crustal components in primitive arc magmas from the Central through the Transitional and Northern SVZ segments. New elemental and Sr–Nd-high-precision Pb isotope data from...... mantle by means of subduction erosion in response to the northward increasingly strong coupling of the converging plates. Both types of enrichment had the same Pb isotope composition in the TSVZ with no significant component derived from the subducting oceanic crust. Pb–Sr–Nd isotopes indicate a major...

  18. Radial and Azimuthal Anisotropy Tomography of the NE Japan Subduction Zone: Implications for the Pacific Slab and Mantle Wedge Dynamics

    Ishise, Motoko; Kawakatsu, Hitoshi; Morishige, Manabu; Shiomi, Katsuhiko

    2018-05-01

    We investigate slab and mantle structure of the NE Japan subduction zone from P wave azimuthal and radial anisotropy using travel time tomography. Trench normal E-W-trending azimuthal anisotropy (AA) and radial anisotropy (RA) with VPV > VPH are found in the mantle wedge, which supports the existence of small-scale convection in the mantle wedge with flow-induced LPO of mantle minerals. In the subducting Pacific slab, trench parallel N-S-trending AA and RA with VPH > VPV are obtained. Considering the effect of dip of the subducting slab on apparent anisotropy, we suggest that both characteristics can be explained by the presence of laminar structure, in addition to AA frozen-in in the subducting plate prior to subduction.

  19. Crystal preferred orientations of minerals from mantle xenoliths in alkali basaltic rocks form the Catalan Volcanic Zone (NE Spain)

    Fernández-Roig, Mercè; Galán, Gumer; Mariani, Elisabetta

    2015-04-01

    there is good correlation between the [100] olivine axis and the [001] pyroxene axis in most protogranular peridotites. However, the [001] axes of the three silicates are parallel in equigranular and some porphyroclastic lherzolites. CPOs and misorientation axes indicate deformation by dislocation creep accommodated mainly by the [100](010) slip system for olivine and the [001](100), [001](010) for orthopyroxene. Also, subsidiary slip systems for olivine are [100]{0kl}, [001](100), [100](001) in porphyroclastic and equigranular lherzolites. The fabric strength of the three main silicates are consistent, all of them decreasing with grain size reduction. These results indicate that the lithospheric mantle in this area was affected by several deformation stages that took place at decreasing temperature and pressure. An earlier stage is preserved in protogranular peridotites and a pyroxenite, with olivine [010]-fiber patterns and consistent deformation of pyroxenes. It could be related to axial shortening, transpression and/or subsequent recovery and annealing. Later deformation stages would be recorded by most porphyroclastic and equigranular lherzolites characterized by orthorhombic and [100]-fiber patterns for olivine, and transitions between them and with the [010]-fiber one. These samples would come most likely from an active shear zone at shallower upper mantle depth, where deformation at higher strain rates would explain the olivine [100]-fiber symmetry. Transient deformation patterns for olivine, grain size reduction along with weakening of the fabric strength could be due to dynamic recrystallization through grain boundary migration and subgrain rotation mechanisms.

  20. Grain growth kinetics of ringwoodite and majorite garnet mixtures and implications for the rheology of the transition zone

    Ezad, I.; Dobson, D. P.; Brodholt, J. P.; Thomson, A.; Hunt, S.

    2017-12-01

    The grain size of the transition zone is a poorly known but important geophysical parameter. Among others, the grain size may control the rheology, seismic attenuation and radiative thermal conductivity of the mantle. However, the grain size of the transition zone minerals ringwoodite (Mg,Fe)2SiO4 and majorite garnet MgSiO3 under appropriate zone conditions is currently unknown and there are very few experiments with which to constrain it. In order to determine the grain size of the transition zone, the grain growth kinetics must be determined for a range of mantle compositions. We have, therefore, experimentally determined the grain growth kinetics of the lowermost transition zone minerals through multi anvil experiments at University College London (UCL). This is achieved through a comprehensive set of time series experiments at pressures of 21 GPa and temperatures relevant to the transition zone. We have also determined the effect of varying water content, oxygen fugacity, iron content and aluminium content also discussed by Dobson and Mariani., (2014). Our initial grain growth experiments conducted at 1200°C and 1400°C at 18 GPa show extremely slow grain growth kinetics; time series experiments extended to 105.8 seconds are unable to produce grains larger than 100 nm. This suggests that fine-grained material at the base of the transition zone will persist on geological timescales. Such small grains size suggests that diffusion creep might be the dominant deformation mechanism in this region. Reference: Dobson, D.P., Mariani, E., 2014. The kinetics of the reaction of majorite plus ferropericlase to ringwoodite: Implications for mantle upwellings crossing the 660 km discontinuity. Earth Planet. Sci. Lett. 408, 110-118. doi:10.1016/j.epsl.2014.10.009

  1. Small Effect of Hydration on Elastic Wave Velocities of Ringwoodite in Earth's Transition Zone

    Schulze, K.; Marquardt, H.; Boffa Ballaran, T.; Kurnosov, A.; Kawazoe, T.; Koch-Müller, M.

    2017-12-01

    Ringwoodite can incorporate significant amounts of hydrogen as OH-defects into its crystal structure. The measurement of 1.4 wt.% H20 in a natural ringwoodite diamond inclusion (Pearson et al. 2014) showed that hydrous ringwoodite can exist in the Earth's mantle. Since ringwoodite is considered to be the major phase in the mantle between 520 and 660 km depth it likely plays an important role for Earth's deep water cycle and the mantle water budget. Previous experimental work has shown that hydration reduces seismic wave velocities in ringwoodite, motivating attempts to map the hydration state of the mantle using seismic wave speed variations as depicted by seismic tomography. However, large uncertainties on the actual effects at transition zone pressures and temperatures remain. A major difficulty is the comparability of studies with different experimental setups and pressure- and temperature conditions. Here, we present results from a comparative elasticity study designed to quantify the effects of hydration on the seismic wave velocities of ringwoodite in Earth's transition zone. Focused ion beam cut single-crystals of four samples of either Fo90 or Fo100 ringwoodite with hydration states between 0.21 - 1.71 wt.% H2O were loaded in the pressure chamber of one diamond-anvil cell to ensure identical experimental conditions. Single-crystal Brillouin Spectroscopy and X-ray diffraction measurements were performed at room temperature to a pressure of 22 GPa. Additional experiments at high pressure and temperatures up to 500 K were performed. Our data collected at low pressures show a significant reduction of elastic wave velocities with hydration, consistent with previous work. However, in contrast to previous inferences, our results indicate that pressure significantly reduces the effect of hydration. Based on the outcome of our work, the redution in aggregate velocities caused by 1 wt.% H2O becomes smaller than 1% in ringwoodite at pressures equivalent to the Earth

  2. Dynamics of the solar transition zone

    Bruner, E.C. Jr.

    1978-01-01

    This paper reports on the analysis of time-resolved C IV line profiles arising from the solar transition zone. Objectives were twofold: to determine whether the 300 s photospheric oscillations penetrate to the transition zone, and to measure the rms velocity disturbance amplitude and its dependence upon solar activity. The data set consisted of 44 times sequences of 50 min average duration and included samples from study experiments of both active and quiet regions of the disk. Power-spectrum analysis of the time series of intensity and line position measurements showed at least one example of a well-developed 300 s oscillation. There was no evidence, however, for 300 s peaks in the average power spectra either in the quiet network or in active regions.The rms velocities were found to be about 2.3 km s - 1 in active regions and 5.7 km s -1 in quiet regions. The suggested average value, allowing for the substantial statistical noise contribution to the quiet Sun data, is about 3 km s -1 . The inferred energy flux, assuming energy transport by acoustic waves, is at most 1.6 x 10 4 ergs cm -2 s -1 for spatial scales greater than 15,000 km and periods in the range 100--1800 s. The acoustic-wave hypothesis apparently fails by at least one order of magnitude to provide the 2--6 x 10 5 ergs cm -2 s -1 thought to be required to replace coronal energy losses. The data are, however, consistent with heating mechanisms based on energy transport by magnetohydrodynamic waves

  3. Teleseismic P and S wave attenuation constraints on temperature and melt of the upper mantle in the Alaska Subduction Zone.

    Soto Castaneda, R. A.; Abers, G. A.; Eilon, Z.; Christensen, D. H.

    2017-12-01

    Recent broadband deployments in Alaska provide an excellent opportunity to advance our understanding of the Alaska-Aleutians subduction system, with implications for subduction processes worldwide. Seismic attenuation, measured from teleseismic body waves, provides a strong constraint on thermal structure as well as an indirect indication of ground shaking expected from large intermediate-depth earthquakes. We measure P and S wave attenuation from pairwise amplitude and phase spectral ratios for teleseisms recorded at 204 Transportable Array, Alaska Regional, and Alaska Volcano Observatory, SALMON (Southern Alaska Lithosphere & Mantle Observation Network) and WVLF (Wrangell Volcanics & subducting Lithosphere Fate) stations in central Alaska. The spectral ratios are inverted in a least squares sense for differential t* (path-averaged attenuation operator) and travel time anomalies at every station. Our preliminary results indicate a zone of low attenuation across the forearc and strong attenuation beneath arc and backarc in the Cook Inlet-Kenai region where the Aleutian-Yakutat slab subducts, similar to other subduction zones. This attenuation differential is observed in both the volcanic Cook Inlet segment and amagmatic Denali segments of the Aleutian subduction zone. By comparison, preliminary results for the Wrangell-St. Elias region past the eastern edge of the Aleutian slab show strong attenuation beneath the Wrangell Volcanic Field, as well as much further south than in the Cook Inlet-Kenai region. This pattern of attenuation seems to indicate a short slab fragment in the east of the subduction zone, though the picture is complex. Results also suggest the slab may focus or transmit energy with minimal attenuation, adding to the complexity. To image the critical transition between the Alaska-Aleutian slab and the region to its east, we plan to incorporate new broadband data from the WVLF array, an ongoing deployment of 37 PASSCAL instruments installed in 2016

  4. Complex plume dynamics in the transition zone underneath the Hawaii hotspot: seismic imaging results

    Cao, Q.; van der Hilst, R. D.; de Hoop, M. V.; Shim, S.

    2010-12-01

    In recent years, progress has been made in seismology to constrain the depth variations of the transition zone discontinuities, e.g. 410 km and 660 km discontinuities, which can be used to constrain the local temperature and chemistry profiles, and hence to infer the existences and morphology of mantle plumes. Taking advantage of the abundance of natural earthquake sources in western Pacific subduction zones and the many seismograph stations in the Americas, we used a generalized Radon transform (GRT), a high resolution inverse-scattering technique, of SS precursors to form 3-D images of the transition zone structures of a 30 degree by 40 degree area underneath Hawaii and the Hawaii-Emperor seamount chain. Rather than a simple mushroom-shape plume, our seismic images suggest complex plume dynamics interacting with the transition zone phase transitions, especially at the 660’ discontinuity. A conspicuous uplift of the 660 discontinuity in a region of 800km in diameter is observed to the west of Hawaii. No correspondent localized depression of the 410 discontinuity is found. This lack of correlation between and differences in lateral length scale of the topographies of the 410 and 660 km discontinuities are consistent with many geodynamical modeling results, in which a deep-mantle plume impinging on the transition zone, creating a pond of hot material underneath endothermic phase change at 660 km depth, and with secondary plumes connecting to the present-day hotspot at Earth’s surface. This more complex plume dynamics suggests that the complicated mass transport process across the transition zone should be taken into account when we try to link the geochemical observations of Hawaiian basalt geochemistry at the Earth’s surface to deep mantle domains. In addition to clear signals at 410km, 520km and 660km depth, the data also reveals rich structures near 350km depth and between 800 - 1000km depth, which may be regional, laterally intermittent scatter interfaces

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

    Arredondo, K.; Billen, M. I.

    2013-12-01

    While slab pull is considered the dominant force controlling plate motion and speed, its magnitude is controlled by slab behavior in the mantle, where tomographic studies show a wide range of possibilities from direct penetration to folding, or stagnation directly above the lower mantle (e.g. Fukao et al., 2009). Geodynamic studies have investigated various parameters, such as plate age and two phase transitions, to recreate observed behavior (e.g. Běhounková and Cízková, 2008). However, past geodynamic models have left out known slab characteristics that may have a large impact on slab behavior and our understanding of subduction processes. Mineral experiments and seismic observations have indicated the existence of additional phase transitions in the mantle transition zone that may produce buoyancy forces large enough to affect the descent of a subducting slab (e.g. Ricard et al., 2005). The current study systematically tests different common assumptions used in geodynamic models: kinematic versus free-slip boundary conditions, the effects of adiabatic heating, viscous dissipation and latent heat, compositional layering and a more complete suite of phase transitions. Final models have a complete energy equation, with eclogite, harzburgite and pyrolite lithosphere compositional layers, and seven composition-dependent phase transitions within the olivine, pyroxene and garnet polymorph minerals. Results show important feedback loops between different assumptions and new behavior from the most complete models. Kinematic models show slab weakening or breaking above the 660 km boundary and between compositional layers. The behavior in dynamic models with a free-moving trench and overriding plate is compared to the more commonly found kinematic models. The new behavior may have important implications for the depth distribution of deep earthquakes within the slab. Though the thermodynamic parameters of certain phase transitions may be uncertain, their presence and

  6. Deformation of "stable" continental interiors by mantle convection: Implications for intraplate stress in the New Madrid Seismic Zone

    Forte, A. M.; Moucha, R.; Simmons, N. A.; Grand, S. P.; Mitrovica, J. X.

    2011-12-01

    The enigmatic origin of large-magnitude earthquakes far from active plate boundaries, especially those occurring in so-called "stable" continental interiors, is a source of continuing controversy that has eluded a satisfactory explanation using past geophysical models of intraplate deformation and faulting. One outstanding case of such major intraplate earthquakes is the 1811-1812 series of events in the New Madrid Seismic Zone (NMSZ). We contend that the origin of some of these enigmatic intraplate events is due to regional variations in the pattern of tectonic stress generated by mantle convective flow acting on the overlying lithosphere and crust. Mantle convection affects the entire surface of the planet, irrespective of the current configuration of surface plate boundaries. In addition, it must be appreciated that plate tectonics is not a 2-D process, because the convective flow that drives the observed horizontal motions of the tectonic plates also drives vertical displacements of the crust across distances as great as 2 to 3 km. This dynamic topography is directly correlated with convection-driven stress field variations in the crust and lithosphere and these stresses can be locally focussed if the mantle rheology below the lithosphere is characterised by sufficiently low viscosities. We have developed global models of convection-driven mantle flow [Forte et al. 2009,2010] that are based on recent high-resolution 3-D tomography models derived from joint inversions of seismic, geodynamic and mineral physics data [Simmons et al. 2007,2008,2010]. These tomography-based mantle convection models also include a full suite of surface geodynamic (postglacial rebound and convection) constraints on the depth-dependent average viscosity of the mantle [Mitrovica & Forte 2004]. Our latest tomography-based and geodynamically-constrained convection calculations reveal that mantle flow under the central US are driven by density anomalies within the lower mantle associated

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

    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 ...

  8. Long Term Seismic Observation in Mariana by OBSs : Double Seismic Zone and Upper Mantle Structure

    Shiobara, H.; Sugioka, H.; Mochizuki, K.; Oki, S.; Kanazawa, T.; Fukao, Y.; Suyehiro, K.

    2005-12-01

    In order to obtain the deep arc structural image of Mariana, a large-scale seismic observation by using 58 long-term ocean bottom seismometers (LTOBS) had been performed from June 2003 until April 2004, which is a part of the MARGINS program funded by the NSF. Prior to this observation, a pilot long-term seismic array observation was conducted in the same area by using 10 LTOBSs from Oct. 2001 until Feb. 2003. At that time, 8 LTOBSs were recovered but one had no data. Recently, 2 LTOBSs, had troubles in the releasing, were recovered by the manned submersible (Shinkai 6500, Jamstec) for the research of the malfunction in July 2005. By using all 9 LTOBS's data, those are about 11 months long, hypocenter determination was performed and more than 3000 local events were found. Even with the 1D velocity structure based on the iasp91 model, double seismic zones and a systematic shift of epicenters between the PDE and this study were observed. To investigate the detail of hypocenter distribution and the 3D velocity structure, the DD inversion (tomoDD: Zhang and Thurber, 2003) was applied for this data set with the 1D structure initial model except for the crust, which has been surveyed by using a dense airgun-OBS system (Takahashi et al., 2003). The result of relocated hypocenters shows clear double seismic zones until about 200 km depth, a high activity area around the fore-arc serpentine sea-mount, the Big Blue, and a lined focuses along the current ridge axis in the back-arc basin, and the result of the tomography shows a image of subducting slab and a low-Vs region below the same sea-mount mentioned. The wedge mantle structure was not clearly resolved due to the inadequate source-receiver coverage, which will be done in the recent experiment.

  9. Dynamics of Mantle Plume Controlled by both Post-spinel and Post-garnet Phase Transitions

    Liu, H.; Leng, W.

    2017-12-01

    Mineralogical studies indicate that two major phase transitions occur near 660 km depth in the Earth's pyrolitic mantle: the ringwoodite (Rw) to perovskite (Pv) + magnesiowüstite (Mw) and majorite (Mj) to perovskite (Pv) phase transitions. Seismological results also show a complicated phase boundary structure for plume regions at this depth, including broad pulse, double reflections and depressed 660 km discontinuity beneath hot regions etc… These observations have been attributed to the co-existence of these two phase transformations. However, previous geodynamical modeling mainly focused on the effects of Rw-Pv+Mw phase transition on the plume dynamics and largely neglected the effects of Mj-Pv phase transition. Here we develop a 3-D regional spherical geodynamic model to study the influence of the combination of Rw - Pv+Mw and Mj - Pv phase transitions on plume dynamics, including the topography fluctuation of 660 km discontinuity, plume shape and penetration capability of plume. Our results show that (1) a double phase boundary occurs at the hot center area of plume while for other regions with relatively lower temperature the phase boundary is single and flat, which respectively corresponds to the double reflections in the seismic observations and a high velocity prism-like structure at the top of 660 km discontinuity; (2) a large amount of low temperature plume materials could be trapped to form a complex trapezoid overlying the 660 km depth; (3) Mj - Pv phase change strongly enhances the plume penetration capability at 660 km depth, which significantly increases the plume mass flux due to the increased plume radius, but significantly reduces plume heat flux due to the decreased plume temperature in the upper mantle. Our model results provide new enlightenments for better constraining seismic structure and mineral reactions at 660 km phase boundaries.

  10. Effect of H2O on Upper Mantle Phase Transitions in MgSiO3: is the Seismic X-discontinuity an Indicator of Mantle Water Content

    S Jacobsen; Z Liu; T Boffa Ballaran; E Littlefield; L Ehm; R Hemley

    2011-12-31

    The mantle X-discontinuity, usually assigned to positive seismic velocity reflectors in the 260-330 km depth range, has proved difficult to explain in terms of a single mineralogical phase transformation in part because of its depth variability. The coesite to stishovite transition of SiO{sub 2} matches deeper X-discontinuity depths but requires 5-10% free silica in the mantle to match observed impedance contrast. The orthoenstatite (OEn) to high-pressure clinoenstatite (HPCen) transformation of MgSiO{sub 3} also broadly coincides with depths of the X but requires chemically depleted and orthoenstatite-rich lithology at 300 km depth in order to match observed seismic impedance contrast. On the basis of high-pressure infrared spectroscopy, X-ray diffraction, and Raman spectroscopy, we show that 1300 ppm variation of H{sub 2}O content in MgSiO{sub 3} can displace the transition of low-pressure clinoenstatite (LPCen) to HPCen by up to 2 GPa, similar to previous quench experiments on the OEn to HPCen phase transition, where about 30-45 km (1.0-1.5 GPa) of deflection could occur per 0.1 wt% H{sub 2}O. If the mantle X-discontinuity results from pyroxene transitions in a depleted harzburgite layer, because of the strong influence of minor amounts of water on the transformation boundary, the depth of the mantle X-discontinuity could serve as a potentially sensitive indicator of water content in the uppermantle.

  11. High Resolution Seismic Images of Transition Zone Discontinuities beneath the Hawaii-Emperor Seamount Chain

    Cao, Q.; Wang, P.; van der Hilst, R. D.; Shim, S.

    2009-12-01

    Taking advantage of the abundance of natural sources (earthquakes) in western Pacific subduction zones and the many seismograph stations in the Americas, we use inverse scattering - a generalized Radon transform - of SS precursors to image the transition zone discontinuities underneath Hawaii and the Hawaii-Emperor seamount chain. The GRT makes use of scattering theory and extracts structural information from broad band data windows that include precursors to SS (which are the specular reflections at the discontinuities that form the main arrivals) as well as non-specular scattered energy (which is often discarded as noise). More than 150,000 seismograms (from the IRIS Data Management Center) are used to form a 3-D image of the transition zone discontinuities beneath the central Pacific. In addition to clear signals near 410, 520, and 660 km depth, the data also reveal scatter interfaces near 370 km dept and between 800-1000 km depth, which may be regional, laterally intermittent scatter horizons. Our images reveal a conspicuous uplift of the 660 discontinuity in a region of 800km in diameter to the west of the active volcanoes of Hawaii. No correspondent localized depression of the 410 discontinuity is found. Instead, we find a smaller scale anomaly suggesting that the 410 discontinuity is locally elevated in the same region. This may indicate the presence of melt or minor chemical constitutes. The lack of correlation between and differences in lateral length scale of the topographies of the 410 and 660 km discontinuities are also consistent with a deep-mantle plume impinging on the transition zone, creating a pond of hot material underneath 660 discontinuity, and with secondary plumes connecting to the present-day hotspot at Earth’s surface. Our observations suggest that more complicated plume morphology and plume dynamics within the Earth's mantle should be taken into account to describe the plumes and, in particular, mass transport across the transition zone

  12. Microstructural evolution and seismic anisotropy of upper mantle rocks in rift zones. Geologica Ultraiectina (300)

    Palasse, L.N.

    2008-01-01

    This thesis investigates field-scale fragments of subcontinental upper mantle rocks from the ancient Mesozoic North Pyrenean rift and Plio-Pleistocene xenoliths from the active Baja California rift, in order to constrain the deformation history of the uppermost mantle. The main focus of the study is

  13. Mantle to Surface Dynamics Across Subduction-Collision Transitions in Space and Time: Results from the CD-CAT Project in Anatolia

    Whitney, D. L.; Abgarmi, B.; Beck, S. L.; Brocard, G. Y.; Cosca, M. A.; Darin, M. H.; Delph, J. R.; Hui, H.; Kahraman, M.; Kaymakci, N.; Kuscu, G.; Meijers, M. J.; Mulch, A.; Özacar, A.; Portner, D. E.; Reid, M. R.; Rey, P. F.; Rojay, B.; Schlieffarth, W. K.; Sandvol, E. A.; Schoenbohm, L. M.; Tank, B.; Teoman, U.; Teyssier, C. P.; Thomson, S. N.; Turkelli, N.; Umhoefer, P. J.; Uslular, G.; Willenbring, J. K.

    2017-12-01

    From west to east, the southern plate boundary of Anatolia varies from subduction to continental collision; plate dynamics are influenced by the interaction of back-arc extension in the west (Aegean) and convergence in the east (Arabia-Eurasia). Prior to 40 Ma, the entire margin was a subduction zone. The NSF project "Continental Dynamics-Central Anatolian Tectonics (CD-CAT)" has contributed to understanding how the mantle, crust, and surface evolve in subduction-to-collision transitions in time and space. Differences are seen in changes in deformation style as collision proceeded; e.g. from distributed across a broad zone to highly localized on a series of oblique-slip faults, and from transpression to transtension (W of the Central Anatolian fault zone, CAFZ) or strike-slip (E of the CAFZ); age, composition, and sources of magmatism, including a magmatic lull from 40-20 Ma, followed by expansion of magmatism SE-ward in central Anatolia; properties and architecture of the lithosphere and sub-lithospheric mantle (e.g. significant and locally abrupt crustal thickness variations, including thick crust under the Tauride Mts; thin to absent lithospheric mantle; and a torn and disaggregating slab that varies from shallow to steep below central Anatolia); and a topographic gradient from a high eastern plateau (> 2 km) to a central plateau (1-1.5 km) bounded to the N and S by mountain ranges that rose > 2 km from the sea between 11-5 Ma, producing a rain shadow in the Anatolian interior. Thermochronologic and structural studies of exhumed mid-crust and associated basins and fault zones as well as geophysical data for Anatolia today show the extent to which inherited features (suture zones, faults) have affected the tectonic evolution of Anatolia, particularly in the vicinity of the CAFZ/East Anatolian Fault, and mantle properties. Results also show that the Miocene was a dynamic time in the thermal and mechanical evolution of the region, as early Miocene rollback

  14. Deformation associated to exhumation of serpentinized mantle rocks in a fossil Ocean Continent Transition: The Totalp unit in SE Switzerland

    Picazo, S.; Manatschal, G.; Cannat, M.; Andréani, M.

    2013-08-01

    Although the exhumation of ultramafic rocks in slow and ultraslow spreading Mid-Ocean Ridges and Ocean Continent Transitions (OCTs) has been extensively investigated, the deformation processes related to mantle exhumation are poorly constrained. In this paper we present a new geological map and a section across the exhumed serpentinized peridotites of the Totalp unit near Davos (SE Switzerland), and we propose that the Totalp unit is formed by two Alpine thrust sheets. Geological mapping indicates local exposure of a paleo-seafloor that is formed by an exhumed detachment surface and serpentinized peridotites. The top of the exhumed mantle rocks is made of ophicalcites that resulted from the carbonation of serpentine under static conditions at the seafloor. The ophicalcites preserve depositional contacts with Upper Jurassic to Lower Cretaceous pelagic sediments (Bernoulli and Weissert, 1985). These sequences did not exceed prehnite-pumpellyite metamorphic facies conditions, and locally escaped Alpine deformation. Thin mylonitic shear zones as well as foliated amphibole-bearing ultramafic rocks have been mapped. The age of these rocks and the link with the final exhumation history are yet unknown but since amphibole-bearing ultramafic rocks can be found as clasts in cataclasites related to the detachment fault, they pre-date detachment faulting. Our petrostructural study of the exhumed serpentinized rocks also reveals a deformation gradient from cataclasis to gouge formation within 150 m in the footwall of the proposed paleo-detachment fault. This deformation postdates serpentinization. It involves a component of plastic deformation of serpentine in the most highly strained intervals that has suffered pronounced grain-size reduction and a polyphase cataclastic overprint.

  15. Water and Slabs in the Transition Zone - Hydrous Ringwoodite in Diamond

    Pearson, D. G.; Brenker, F. E.; Nestola, F.; McNeill, J.; Nasdala, L.; Hutchison, M.; Matveev, S.; Mather, K.; Vincze, L.; Schmitz, S.; Vekemens, B.

    2014-12-01

    Theory and experiments have shown that the Earth's Transition Zone (TZ) could be a major repository for water, due to the ability of the higher-pressure polymorphs of olivine - wadsleyite and ringwoodite - to host up to ~2.5wt. % H2O. Despite experimental demonstration of the water-bearing capacity of these phases, geophysical probes such as electrical conductivity have provided conflicting results, and the issue of whether the TZ contains abundant water remains highly controversial. We report X-ray diffraction, Raman and infra-red spectroscopic evidence for the first terrestrial occurrence of any higher pressure polymorph of olivine: ringwoodite, included in a diamond from Juína, Brazil. The ringwoodite occurs with a Ca-walstromite phase that we interpret to be retrogressed Ca-silicate perovskite. The most likely interpretation of this two-phase assemblage is that it represents a partially retrogressed portion of a somewhat Fe-rich peridotitic mantle, in which hydrous ringwoodite, and former CaSiO3- perovskite co-existed above 15GPa. The ringwoodite has a Mg# of ~ 75, suggesting that it may be mantle hybrised with a more fertile component such as subducted oceanic crust. The water-rich nature of this inclusion (~1.5 wt%), along with the preservation of ringwoodite, is the first direct evidence that, at least locally, the TZ is hydrous, to about 1 wt%. As well as being in agreement with recent magnetotelluric estimates of the TZ water content, this amount of water helps to reconcile measured TZ seismic velocities with those predicted from lab experiments. The finding also indicates that some kimberlites must have their primary sources in this deep mantle region. The high water content of the ringwoodite suggests that it was not close to the mantle geotherm when trapped in the diamond. This may be an indication that the the assemblage was part of a water-rich subducted slab out of thermal equilibrium, within the transition zone. The water-rich nature of the

  16. Spin crossover and Mott—Hubbard transition under high pressure and high temperature in the low mantle of the Earth

    Ovchinnikov, S. G.; Ovchinnikova, T. M.; Plotkin, V. V.; Dyad'kov, P. G.

    2015-11-01

    Effect of high pressure induced spin crossover on the magnetic, electronic and structural properties of the minerals forming the Earth's low mantle is discussed. The low temperature P, T phase diagram of ferropericlase has the quantum phase transition point Pc = 56 GPa at T = 0 confirmed recently by the synchrotron Mössbauer spectroscopy. The LDA+GTB calculated phase diagram describes the experimental data. Its extension to the high temperature resulted earlier in prediction of the metallic properties of the Earth's mantle at the depth 1400 km insulator transition and compare them with the experimental seismic and geomagnetic field data.

  17. Abnormal Elasticity of Single-Crystal Magnesiosiderite across the Spin Transition in Earth's Lower Mantle

    Fu, Suyu; Yang, Jing; Lin, Jung-Fu

    2017-01-01

    Brillouin light scattering and impulsive stimulated light scattering have been used to determine the full elastic constants of magnesiosiderite [(Mg0.35Fe0.65)CO3 ] up to 70 GPa at room temperature in a diamond-anvil cell. Drastic softening in C11 , C33 , C12 , and C13 elastic moduli associated with the compressive stress component and stiffening in C44 and C14 moduli associated with the shear stress component are observed to occur within the spin transition between ˜42.4 and ˜46.5 GPa . Negative values of C12 and C13 are also observed within the spin transition region. The Born criteria constants for the crystal remain positive within the spin transition, indicating that the mixed-spin state remains mechanically stable. Significant auxeticity can be related to the electronic spin transition-induced elastic anomalies based on the analysis of Poisson's ratio. These elastic anomalies are explained using a thermoelastic model for the rhombohedral system. Finally, we conclude that mixed-spin state ferromagnesite, which is potentially a major deep-carbon carrier, is expected to exhibit abnormal elasticity, including a negative Poisson's ratio of -0.6 and drastically reduced VP by 10%, in Earth's midlower mantle.

  18. THE STRUCTURE OF THE LITHOSPHERIC MANTLE OF THE SIBERAIN CRATON AND SEISMODYNAMICS OF DEFORMATION WAVES IN THE BAIKAL SEISMIC ZONE

    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

  19. Birch's Mantle

    Anderson, D. L.

    2002-12-01

    Francis Birch's 1952 paper started the sciences of mineral physics and physics of the Earth's interior. Birch stressed the importance of pressure, compressive strain and volume in mantle physics. Although this may seem to be an obvious lesson many modern paradoxes in the internal constitution of the Earth and mantle dynamics can be traced to a lack of appreciation for the role of compression. The effect of pressure on thermal properties such as expansivity can gravitational stratify the Earth irreversibly during accretion and can keep it chemically stratified. The widespread use of the Boussinesq approximation in mantle geodynamics is the antithesis of Birchian physics. Birch pointed out that eclogite was likely to be an important component of the upper mantle. Plate tectonic recycling and the bouyancy of oceanic crust at midmantle depths gives credence to this suggestion. Although peridotite dominates the upper mantle, variations in eclogite-content may be responsible for melting- or fertility-spots. Birch called attention to the Repetti Discontinuity near 900 km depth as an important geodynamic boundary. This may be the chemical interface between the upper and lower mantles. Recent work in geodynamics and seismology has confirmed the importance of this region of the mantle as a possible barrier. Birch regarded the transition region (TR ; 400 to 1000 km ) as the key to many problems in Earth sciences. The TR contains two major discontinuities ( near 410 and 650 km ) and their depths are a good mantle thermometer which is now being exploited to suggest that much of plate tectonics is confined to the upper mantle ( in Birch's terminology, the mantle above 1000 km depth ). The lower mantle is homogeneous and different from the upper mantle. Density and seismic velocity are very insensitive to temperature there, consistent with tomography. A final key to the operation of the mantle is Birch's suggestion that radioactivities were stripped out of the deeper parts of

  20. Transit Traffic Analysis Zone Delineating Method Based on Thiessen Polygon

    Shuwei Wang

    2014-04-01

    Full Text Available A green transportation system composed of transit, busses and bicycles could be a significant in alleviating traffic congestion. However, the inaccuracy of current transit ridership forecasting methods is imposing a negative impact on the development of urban transit systems. Traffic Analysis Zone (TAZ delineating is a fundamental and essential step in ridership forecasting, existing delineating method in four-step models have some problems in reflecting the travel characteristics of urban transit. This paper aims to come up with a Transit Traffic Analysis Zone delineation method as supplement of traditional TAZs in transit service analysis. The deficiencies of current TAZ delineating methods were analyzed, and the requirements of Transit Traffic Analysis Zone (TTAZ were summarized. Considering these requirements, Thiessen Polygon was introduced into TTAZ delineating. In order to validate its feasibility, Beijing was then taken as an example to delineate TTAZs, followed by a spatial analysis of office buildings within a TTAZ and transit station departure passengers. Analysis result shows that the TTAZs based on Thiessen polygon could reflect the transit travel characteristic and is of in-depth research value.

  1. Spatial Relationship Between Crustal Structure and Mantle Seismicity in the Vrancea Seismogenic Zone of Romania

    Knapp, C. C.; Enciu, D. M.; Knapp, J. H.

    2007-12-01

    Active crustal deformation and subsidence in the Southeast Carpathian foreland has previously been attributed to active foundering of thickened continental lithosphere beneath the Carpathian bend region (Knapp et al, 2005). The present study involves integration of active and passive-source seismic data in order to place constraints on the duration, timing, and scale of crustal deformation in the Carpathian foreland, and in particular to assess the genetic relationship with the Vrancea intermediate-depth seismogenic zone (VSZ). Relocated crustal earthquakes and focal mechanisms were correlated with four deep industry seismic profiles, the reprocessed DACIA PLAN deep seismic profile, and the DRACULA (Deep Reflection Acquisition Constraining Unusual Lithospheric Activity) II and III profiles. Projection of foreland crustal hypocenters onto the deep seismic lines correlates well with previously identified crustal faults such as the Trotus and Sinaia, as well as the newly identified Ialomita Fault. Specifically, results of this study (1) image the full crustal and uppermost mantle structure of the Focsani Basin in the close proximity of the VSZ, (2) show evidence for a sub-horizontal, slightly east-dipping Moho in the vicinity of the VSZ and thinning of the crust towards the Carpathian orogen, (3) illustrate the conspicuous absence of west-dipping fabrics or structures in the crust and across the Moho, (4) present evidence that the Trotus Fault is a crustal-scale active fault with a dextral sense of motion, (5) suggest that the Paleozoic age Peceneaga-Camena and Capidava-Ovidiu Faults have not been active in post-Paleozoic time, and (6) show evidence for a new active crustal scale sinistral fault, named the Ialomita fault. Both the seismogenic Vrancea body and deformation in the Focsani Basin appear to be concentrically bound by the Trotus Fault in the north and east and the Sinaia-Ialomita Fault in the south, suggesting a coupled deformation between the VSZ and the

  2. St Paul fracture zone intratransform ridge basalts (Equatorial Atlantic): Insight within the mantle source diversity

    Hemond, C.; Brunelli, D.; Maia, M.; Prigent, S.; Sichel, S. E.

    2017-12-01

    The St Paul Transform System offsets by 630 km the Equatorial Mid Atlantic Ridge at 1° N. It consists of four Major faults separating three intra transform ridge axes. Volcanic glassy samples were collected inside two intratransform ridge (ITR) segments during the COLMEIA cruise (Maia et al ; 2016) and samples from the third ITR available from a previous cruise ST PAUL (Hékinian et al. 2000). Major, trace elements and Hf, Pb, Sr and Nd isotopes were determined on selected hand picked glass chips. Few glassy samples recovered and analysed from abyssal hill samples open a time window of about 4.5 million years in the chemistry of the northern ITR. Results show that all samples are basaltic in composition but trace elements display contrasting images for the three ITR. The northern ITR samples are all light REE and highly incompatible enriched and are E-MORB; the central ITR samples display rather flat REE pattern with a level on enrichment of the HREE higher than the other two ITR and are T-MORB. Southern ITR samples are more heterogeneous N-MORB to T-MORB with a lower level of HREE. Isotopes reveal that the ITRs sample distinct mantle sources. In various isotope plans, the northern ITR samples plot together with published results from the MAR directly north of the St Paul F.Z. Therefore they exhibit some flavor of the Sierra Leone hotspot interacting with the MAR at 1.7°N. Central and southern ITR samples have very distinct composition from the northern ITR but resemble each other. However, for identical 206Pb/204Pb ratios, central ITR has slightly but significantly higher 207Pb/204Pb and 208Pb/204Pb, also higher 143Nd/144Nd for a given 87Sr/86Sr. Southern ITR is in chemical continuity of the MAR southward. So that central ITR samples display a rather specific composition. Off axis samples corresponding to the activity of the northern ITR up to 4.6 m.y. show that the hotspot contribution was even bigger on the spreading axis than today and might be fading with

  3. Petrography and mineral chemistry of wehrlites in contact zone of gabbro intrusions and mantle peridotites of the Naein ophiolite

    Farhad Ghaseminejad

    2014-10-01

    , banded meta-chert, and succession of schist and marble (Davoudzadeh, 1972; Jabbari, 1997; Pirnia Naeini, 2006; Torabi, 2012; Shirdashtzadeh, 2006. In this ophiolite, the leucogabbro intrusions crosscut all other rock units. Materials and Methods Mineralogical analyses were conducted by wavelength-dispersive EPMA (JEOL JXA-8800R at the Cooperative Centre of Kanazawa University (Japan. The analyses were performed under an accelerating voltage of 15 kV and a beam current of 15 nA. JEOL software using ZAF corrections was employed for data reduction. Natural and synthetic minerals of known composition are used as standards. The Fe3+ content in minerals was estimated by assuming mineral stoichiometry. Results In the contact zone of leucogabbros and mantle peridotites of the Naein ophiolite, wehrlite and olivine clinopyroxenite are formed. Rock-forming minerals of these wehrlites are olivine (chrysolite, clinopyroxene (diopside, Cr-spinel, serpentine, amphibole (tremolite and tremolitic hornblende, epidote and magnetite. Comparison of mineral chemistry of olivine, clinopyroxene and chromian spinel in wehrlites and mantle peridotites indicate that chemical composition of clinopyroxene and olivine in these rocks are different, but chemistry of Cr-spinels in harzburgite and wehrlite are nearly same. Discussion According to the resistance of Cr-spinel against the metamorphism and alteration, it can be concluded that the wehrlites in contact zone of gabbros and mantle peridotites are formed at the expense of harzburgite. Olivine and clinopyroxene of wehrlites are formed by serpentine metamorphism and interaction of serpentine and calcium of gabbro, respectively. Field study of the research area shows that the leucogabbro intrudes the harzburgite. This research shows that after the serpentinization of mantle harzburgite, the gabbro intrusions crosscut the serpentinized peridotites, and wehrlite and olivine clinopyroxenite formed in the contact zone. Acknowledgements The authors thank

  4. Monitoring of transition zones in railways

    Coelho, B.; Priest, J.; Holscher, P.; Powrie, W.

    2009-01-01

    Transitions between railway track on embankments or natural ground and fixed structures such as bridges and culverts often require substantial additional maintenance to preserve line, level and ride quality. This extra maintenance not only increases costs but also causes delays. Despite its

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

    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.

  6. Rheological structure of a lithosphere-asthenosphere boundary zone, decoded from EBSD analysis of mantle xenoliths from Ichinomegata, NE Japan

    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

  7. Fluid circulations in response to mantle exhumation at the passive margin setting in the north Pyrenean zone, France

    Corre, B.; Boulvais, P.; Boiron, M. C.; Lagabrielle, Y.; Marasi, L.; Clerc, C.

    2018-02-01

    Sub-continental lithospheric mantle rocks are exhumed in the distal part of magma-poor passive margins. Remnants of the North Iberian paleo-passive margin are now exposed in the North-Pyrenean Zone (NPZ) and offers a field analogue to study the processes of continental crust thinning, subcontinental mantle exhumation and associated fluid circulations. The Saraillé Massif which belongs to the `Chaînons Béarnais' range (Western Pyrenees), displays field, petrographic and stable isotopic evidence of syn-kinematic fluid circulations. Using electron probe micro-analyses on minerals, O, C, Sr isotopes compositions and micro thermometry/Raman spectrometry of fluid inclusions, we investigate the history of fluid circulations along and in the surroundings of the Saraillé detachment fault. The tectonic interface between the pre-rift Mesozoic sedimentary cover and the mantle rocks is marked by a metasomatic talc-chlorite layer. This layer formed through the infiltration of a fluid enriched in chemical elements like Cr leached from the exhuming serpentinized mantle rocks. In the overlying sediments (dolomitic and calcitic marbles of Jurassic to Aptian age), a network of calcitic veins, locally with quartz, formed as a consequence of the infiltration of aqueous saline fluids (salinities up to 34 wt% NaCl are recorded in quartz-hosted fluid inclusions) at moderate temperatures ( 220 °C). These brines likely derived from the dissolution of the local Triassic evaporites. In the upper part of the metasomatic system, upward movement of fluids is limited by the Albian metasediments, which likely acted as an impermeable layer. The model of fluid circulation in the Saraillé Massif sheds light onto other synchronous metasomatic systems in the Pyrenean realm.

  8. Metasomatic Reaction Zones as Monitors of Trace Element Transfer at the Slab-Mantle Interface: the Case of the Hochwart Peridotite (Ulten Zone, Italy)

    Marocchi, M.; Hermann, J.; Bargossi, G. M.; Mair, V.; Morten, L.

    2006-12-01

    phases (phlogopite and amphibole) in different metasomatic zones indicate mobility of many elements, including elements such as Ta which are considered to have scarce mobility in fluids. Trace element composition of accessory minerals in the phlogopite-rich zone suggests that the trace element signature of subduction zone fluids may be fractionated in this zone. The progressive depletion in some trace elements (LREE) and enrichment in LILE and Li from the peridotite towards the gneiss suggests a strong influence of bulk composition on the trace element budget of hydrous minerals. Since the ultramafic blocks can be representative of metasomatic processes occurring at the slab-mantle interface, we can infer that metasomatic reactions between slab-derived fluids and ultramafic mantle wedge will follow a specific series of reactions, creating mineral zonation similar to those observed in this study. Our results further favour the evidence that the primary composition of subduction zone fluids is modified substantially by metasomatic reactions occurring in the mantle wedge.

  9. Significance and clinical value of the transitional zone volume (TZV ...

    M. El Ghoneimy

    2017-01-12

    Jan 12, 2017 ... Objective: The aim of this work was to evaluate the significance and clinical value of the TZI, which has been a point of ... Conclusion: Estimating the transition zone volume during TRUS is a reasonable way to obtain the required ... Besides the IPSS score, a complete medical and surgical history was also.

  10. Dilution in Transition Zone between Rising Plumes and Surface Plumes

    Larsen, Torben

    2004-01-01

    The papers presents some physical experiments with the dilution of sea outfall plumes with emphasize on the transition zone where the relative fast flowing vertical plume turns to a horizontal surface plume following the slow sea surface currents. The experiments show that a considerable dilution...

  11. Experimental analysis of railway track settlement in transition zones

    Wang, H.; Markine, V.L.; Liu, X.

    2017-01-01

    Transition zones in railway tracks are the locations with considerable changes in the vertical support structures. Due to the differential stiffness and settlement in the open track and the engineering structure resulting in the dynamic amplification of the wheel forces, track settlement is usually

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

    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.

  13. The Late Jurassic Panjeh submarine volcano in the northern Sanandaj-Sirjan Zone, northwest Iran: Mantle plume or active margin?

    Azizi, Hossein; Lucci, Federico; Stern, Robert J.; Hasannejad, Shima; Asahara, Yoshihiro

    2018-05-01

    The tectonic setting in which Jurassic igneous rocks of the Sanandaj-Sirjan Zone (SaSZ) of Iran formed is controversial. SaSZ igneous rocks are mainly intrusive granodiorite to gabbroic bodies, which intrude Early to Middle Jurassic metamorphic basement; Jurassic volcanic rocks are rare. Here, we report the age and petrology of volcanic rocks from the Panjeh basaltic-andesitic rocks complex in the northern SaSZ, southwest of Ghorveh city. The Panjeh magmatic complex consists of pillowed and massive basalts, andesites and microdioritic dykes and is associated with intrusive gabbros; the overall sequence and relations with surrounding sediments indicate that this is an unusually well preserved submarine volcanic complex. Igneous rocks belong to a metaluminous sub-alkaline, medium-K to high-K calc-alkaline mafic suite characterized by moderate Al2O3 (13.7-17.6 wt%) and variable Fe2O3 (6.0-12.6 wt%) and MgO (0.9-11.1 wt%) contents. Zircon U-Pb ages (145-149 Ma) define a Late Jurassic (Tithonian) age for magma crystallization and emplacement. Whole rock compositions are enriched in Th, U and light rare earth elements (LREEs) and are slightly depleted in Nb, Ta and Ti. The initial ratios of 87Sr/86Sr (0.7039-0.7076) and εNd(t) values (-1.8 to +4.3) lie along the mantle array in the field of ocean island basalts and subcontinental metasomatized mantle. Immobile trace element (Ti, V, Zr, Y, Nb, Yb, Th and Co) behavior suggests that the mantle source was enriched by fluids released from a subducting slab (i.e. deep-crustal recycling) with some contribution from continental crust for andesitic rocks. Based the chemical composition of Panjeh mafic and intermediate rocks in combination with data for other gabbroic to dioritic bodies in the Ghorveh area we offer two interpretations for these (and other Jurassic igneous rocks of the SaSZ) as reflecting melts from a) subduction-modified OIB-type source above a Neo-Tethys subduction zone or b) plume or rift tectonics involving

  14. Using thermodynamic data to reproduce main seismic features of transition zone

    Fomin, Ilya; Saukko, Anna; Edwards, Paul; Schiffer, Christian

    2016-04-01

    Most of the seismic tomography studies nowadays are based on comprehensive models with optimization of lots of parameters. These models are able to resolve very subtle features of the Earth's mantle, but the influence of each specific parameter is not seen directly. In our research we try to minimize the number of processed parameters to produce simple synthetic cases. The main goals of our model are to see how water content influences the depth of the transition zone, and if melting at the transition zone is plausible. We also attempt to see how water content and the presence of melts influence the signal strength of the transition zone in receiver functions. Our MATLAB-code calculates phase assemblage according to specific temperature and pressure within 2D numerical domain (e.g. 300x700 km). Phase properties are calculated with database of Stixrude and Lithgow-Bertelloni [2011], with corrections for water impact on elastic constants according to Liu et al., [2012]. We use the mantle phase composition 55% garnet and 45% olivine-polymorph, soliduses by Ohtani et al. [2004] and melt properties by Sakamaki et al. [2006]. These data are used to calculate seismic velocities and, furthermore, receiver functions with standard routines (e.g.[Schiffer et al., 2012]). Model predicts Vs within 5 to 5.5 km/s and Vp around 9.5-10 km/s within transition zone (Vp/Vs = 1.84-1.87), which is close to standard values. The presence of water enlarges the wadsleyite region, but also dampens the peak of receiver functions down to background level. Increase in water content causes melting at much shallower depths. Using a normal thermal gradient, we can get up to 10% of melt at depths around 390 km with 80% of water saturation, shown by a negative anomaly on receiver functions. This result is similar to data obtained for Afar Plateau [Thompson et al., 2015]. With cratonic thermal gradient, the olivine-wadsleyite transition and corresponding melt layer appear at depths around 350 km

  15. Critical Transition in Critical Zone of Intensively Managed Landscapes

    Kumar, P.

    2017-12-01

    Intensification of industrial agriculture has resulted in severe unintended global impacts, including degradation of arable land and eutrophication of receiving water bodies. Modern agricultural practices rely on significant direct and indirect human energy inputs, which have created imbalances between increased rates of biogeochemical processes related to production and background rates of natural processes. These imbalances have cascaded through the deep inter-dependencies between carbon, soil, water, nutrient and ecological processes, resulting in a critical transition of the Critical Zone and creating emergent dynamics and evolutionary trajectories. Understanding of these novel organization and function of the Critical Zone is vital for developing sustainable agricultural practices.

  16. Hirschsprung's disease: problems with transition-zone pull-through.

    Ghose, S I; Squire, B R; Stringer, M D; Batcup, G; Crabbe, D C

    2000-12-01

    It is generally accepted that if surgery for Hirschsprung's disease is to be successful, ganglionic bowel must be anastomosed to the lower rectum or anal canal. Above the aganglionic distal bowel lies a transition zone (TZ) where more subtle abnormalities of innervation are apparent. The significance of this transition zone in respect to the functional outcome of surgery has received little attention. The aim of this study was to identify the incidence of transition zone pull-through (TZPT) in a cohort of children who underwent surgery for Hirschsprung's disease, to identify the reasons why TZPTs occurred, and to identify the functional consequences. The authors report the long-term outcome of these children with emphasis on bowel function and the results of subsequent surgery. A Retrospective study was conducted of children treated at a single institution from 1979 through 1994. TZPT patients were subject to detailed review of surgical records and histopathologic material. Thirteen children were identified with a TZPT. In 12 cases, histopathologic errors contributed to the TZPT: in 5 cases this was caused by single point biopsies missing an asymmetrical TZ, whereas in 7 cases the histopathologic features of the TZ were not recognized. In 1 case the TZPT was caused by surgical error. As a consequence of the TZPT 7 children underwent repeat pull-through. One child is fully continent, one has daytime fecal continence, and 2 others are incontinent. Two children have permanent stomas. One child is clean with antegrade colonic washouts. Repeat pull-throughs were not attempted in 6 children. Two children have achieved full continence, 2 have permanent stomas, 1 is clean with antegrade colonic washouts, and 1 child receives regular suppositories. Transition zone pull-throughs occurred because of a combination of surgical and histopathologic errors. The transition zone may follow an asymmetric course around the circumference of the bowel and may be missed if single

  17. Coexistence and transition between shear zones in slow granular flows.

    Moosavi, Robabeh; Shaebani, M Reza; Maleki, Maniya; Török, János; Wolf, Dietrich E; Losert, Wolfgang

    2013-10-04

    We report experiments on slow granular flows in a split-bottom Couette cell that show novel strain localization features. Nontrivial flow profiles have been observed which are shown to be the consequence of simultaneous formation of shear zones in the bulk and at the boundaries. The fluctuating band model based on a minimization principle can be fitted to the experiments over a large variation of morphology and filling height with one single fit parameter, the relative friction coefficient μ(rel) between wall and bulk. The possibility of multiple shear zone formation is controlled by μ(rel). Moreover, we observe that the symmetry of an initial state, with coexisting shear zones at both side walls, breaks spontaneously below a threshold value of the shear velocity. A dynamical transition between two asymmetric flow states happens over a characteristic time scale which depends on the shear strength.

  18. "Textural analysis of multiparametric MRI detects transition zone prostate cancer".

    Sidhu, Harbir S; Benigno, Salvatore; Ganeshan, Balaji; Dikaios, Nikos; Johnston, Edward W; Allen, Clare; Kirkham, Alex; Groves, Ashley M; Ahmed, Hashim U; Emberton, Mark; Taylor, Stuart A; Halligan, Steve; Punwani, Shonit

    2017-06-01

    To evaluate multiparametric-MRI (mpMRI) derived histogram textural-analysis parameters for detection of transition zone (TZ) prostatic tumour. Sixty-seven consecutive men with suspected prostate cancer underwent 1.5T mpMRI prior to template-mapping-biopsy (TPM). Twenty-six men had 'significant' TZ tumour. Two radiologists in consensus matched TPM to the single axial slice best depicting tumour, or largest TZ diameter for those with benign histology, to define single-slice whole TZ-regions-of-interest (ROIs). Textural-parameter differences between single-slice whole TZ-ROI containing significant tumour versus benign/insignificant tumour were analysed using Mann Whitney U test. Diagnostic accuracy was assessed by receiver operating characteristic area under curve (ROC-AUC) analysis cross-validated with leave-one-out (LOO) analysis. ADC kurtosis was significantly lower (p Textural features of the whole prostate TZ can discriminate significant prostatic cancer through reduced kurtosis of the ADC-histogram where significant tumour is included in TZ-ROI and reduced T1 entropy independent of tumour inclusion. • MR textural features of prostate transition zone may discriminate significant prostatic cancer. • Transition zone (TZ) containing significant tumour demonstrates a less peaked ADC histogram. • TZ containing significant tumour reveals higher post-contrast T1-weighted homogeneity. • The utility of MR texture analysis in prostate cancer merits further investigation.

  19. “Ductile to brittle” transition in thermally stable antigorite gouge at mantle pressures

    Proctor, Brooks; Hirth, Greg

    2016-01-01

    General shear experiments on antigorite-rich serpentinite show a transition from ductile (distributed) to brittle (localized) deformation with increasing temperature from 300°C to 500°C at confining pressures from 1 to 2 GPa. The coefficient of friction associated with slip along fractures decreases from 0.23 to 0.07 with an increase in temperature from 300°C to 500°C. Velocity stepping experiments exhibit a positive rate dependence, as parameterized by a-b values, that decrease modestly with increasing temperature from ~0.015 at 300°C to ~0.01 at 500°C. Fractures contain fine-grained foliated antigorite, and there is no evidence of dehydration. All samples have a moderate foliation and show microstructural evidence for both plastic and brittle deformation mechanisms. Under certain conditions the transition to brittle deformation, at high pressures and temperatures in antigorite, might generate earthquakes, which could explain the occurrence of some intermediate-depth seismicity within subduction zones in serpentinized regions that are too cold to induce dehydration.

  20. Structure of the mantle lithosphere in continental collision zones of Europe, North America and China from S-receiver functions

    Kind, R.; Shen, X.

    2017-12-01

    Seismic tomography and receiver functions are the most common methods to study the structure of the mantle lithosphere. We use S-receiver functions to study continent-continent collision zones in Europe, North America and China. In order to avoid possible numerical problems caused by filtering effects (side lobes) we process the data practically without filtering (also excluding deconvolution). Side lobes are still a fundamental question to check the reality of the Mid-Lithospheric Discontinuity (MLD). We use openly available data of mostly permanent seismic broadband stations from the European portal EIDA, from IRIS and from the Chinese Seismic Network. We obtained several ten thousands of useful records in each region by visual and fully automatic processing. We observed the MLD in all cratonic regions near 100 km depth and the Lithosphere-Asthenosphere Boundary (LAB) partly in cratonic regions near 200 km depth. The observation of the cratonic LAB with converted waves requires a relatively sharp discontinuity which excludes temperature as only cause of the LAB. In younger tectonic active regions we observed the LAB near 100 km depth. TheLAB and MLD are in collision zones significantly structured. In central Europe we observed the deep cratonic LAB reaching far to the west of the Tornquist-Teisseyre Zone below Phanerozoic cover. Below the northern edge of the Bohemian Massif seems to be a tear in the LAB leading to a jump in its depth of about 100 km. In North America we see north of Yellowstone a smooth deepening of the western LAB from about 100 km depth to 200 km depth at the Mid-Continental Rift System. Similarly to the LAB jump below the Bohemian Massif in Europe, we see below the Sevier Thrust Belt also a jump of about 100 km in the LAB depth. In China we see the cratonic LAB deepening to the south-west far below eastern Tibet. Below the craton in north-east China is only the shallow LAB/MLD visible. These observations in three continents show that the

  1. Inversion for Double-Layer Anisotropy in the Mantle Beneath the Middle America and Izu-Bonin Subduction Zones

    Kuo, B. Y.

    2017-12-01

    We measured shear wave splitting for the intraslab events in the Middle America and Izu-Bonin subduction zones recorded at Pacific stations to infer the anisotropic structure in the subslab mantle. The receiver-side anisotropy is accounted for by considering both azimuthal anisotropy determined by SKS splitting and radial anisotropy given in global tomographic model, although the latter does not change the overall pattern of subslab anisotropy. By removing the anisotropy effects from both receiver and source sides, the initial polarization directions (p) of the shear waves used were recovered, most of which are in reasonable agreement with that predicted form the CMT solutions. For both subduction zones, the polarization-splitting plots strongly suggest the presence of two layers of anisotropy. To constrain the two-layer model, we perform inversions which minimize the misfit in both the splitting parameters and p. In the MASZ, the best model contains an upper layer with the fast direction in parallel with the absolute plate motion of the Cocos plate and a lower layer 40-60 degree clockwise from the APM. The delay times are 1.5 and 1.9 s respectively. The interference of the double layer produced dts in excess of 3 s at a certain range of p. The SKS splitting were also inverted for a two-layer model, yielding similar splitting characters and the clockwise rotation. We are investigating why this rotation takes place and how this observation is related to the dynamics of the asthenosphere.

  2. Mantle roots of the Emeishan plume: an evaluation based on teleseismic P-wave tomography

    C. He

    2017-11-01

    Full Text Available The voluminous magmatism associated with large igneous provinces (LIPs is commonly correlated to upwelling plumes from the core–mantle boundary (CMB. Here we analyse seismic tomographic data from the Emeishan LIP in southwestern China. Our results reveal vestiges of delaminated crustal and/or lithospheric mantle, with an upwelling in the upper mantle beneath the Emeishan LIP rather than a plume rooted in the CMB. We suggest that the magmatism and the Emeishan LIP formation might be connected with the melting of delaminated lower crustal and/or lithospheric components which resulted in plume-like upwelling from the upper mantle or from the mantle transition zone.

  3. Seismic Imaging of Mantle Plumes

    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.

  4. A Bayesian approach to infer the radial distribution of temperature and anisotropy in the transition zone from seismic data

    Drilleau, M.; Beucler, E.; Mocquet, A.; Verhoeven, O.; Moebs, G.; Burgos, G.; Montagner, J.

    2013-12-01

    Mineralogical transformations and matter transfers within the Earth's mantle make the 350-1000 km depth range (considered here as the mantle transition zone) highly heterogeneous and anisotropic. Most of the 3-D global tomographic models are anchored on small perturbations from 1-D models such as PREM, and are secondly interpreted in terms of temperature and composition distributions. However, the degree of heterogeneity in the transition zone can be strong enough so that the concept of a 1-D reference seismic model may be addressed. To avoid the use of any seismic reference model, we developed a Markov chain Monte Carlo algorithm to directly interpret surface wave dispersion curves in terms of temperature and radial anisotropy distributions, considering a given composition of the mantle. These interpretations are based on laboratory measurements of elastic moduli and Birch-Murnaghan equation of state. An originality of the algorithm is its ability to explore both smoothly varying models and first-order discontinuities, using C1-Bézier curves, which interpolate the randomly chosen values for depth, temperature and radial anisotropy. This parameterization is able to generate a self-adapting parameter space exploration while reducing the computing time. Using a Bayesian exploration, the probability distributions on temperature and anisotropy are governed by uncertainties on the data set. The method was successfully applied to both synthetic data and real dispersion curves. Surface wave measurements along the Vanuatu- California path suggest a strong anisotropy above 400 km depth which decreases below, and a monotonous temperature distribution between 350 and 1000 km depth. On the contrary, a negative shear wave anisotropy of about 2 % is found at the top of the transition zone below Eurasia. Considering compositions ranging from piclogite to pyrolite, the overall temperature profile and temperature gradient are higher for the continental path than for the oceanic

  5. The Interfacial Transition Zone in Alkali-Activated Slag Mortars

    Rackel eSan Nicolas

    2015-12-01

    Full Text Available The interfacial transition zone (ITZ is known to strongly influence the mechanical and transport properties of mortars and concretes. This paper studies the ITZ between siliceous (quartz aggregates and alkali activated slag binders in the context of mortar specimens. Backscattered electron images (BSE generated in an environmental scanning electron microscope (ESEM are used to identify unreacted binder components, reaction products and porosity in the zone surrounding aggregate particles, by composition and density contrast. X-ray mapping is used to exclude the regions corresponding to the aggregates from the BSE image of the ITZ, thus enabling analysis of only the binder phases, which are segmented into binary images by grey level discrimination. A distinct yet dense ITZ region is present in the alkali-activated slag mortars, containing a reduced content of unreacted slag particles compared to the bulk binder. The elemental analysis of this region shows that it contains a (C,N-A-S-H gel which seems to have a higher content of Na (potentially deposited through desiccation of the pore solution and a lower content of Ca than the bulk inner and outer products forming in the main binding region. These differences are potentially important in terms of long-term concrete performance, as the absence of a highly porous interfacial transition zone region is expected to provide a positive influence on the mechanical and transport properties of alkali-activated slag concretes.

  6. 33 CFR 165.103 - Safety and Security Zones; LPG Vessel Transits in Portland, Maine, Captain of the Port Zone...

    2010-07-01

    ... within a 500-yard radius of any Liquefied Petroleum Gas (LPG) vessel while it is moored at the LPG... 33 Navigation and Navigable Waters 2 2010-07-01 2010-07-01 false Safety and Security Zones; LPG... and Security Zones; LPG Vessel Transits in Portland, Maine, Captain of the Port Zone, Portsmouth...

  7. Large-scale compositional heterogeneity in the Earth's mantle

    Ballmer, M.

    2017-12-01

    Seismic imaging of subducted Farallon and Tethys lithosphere in the lower mantle has been taken as evidence for whole-mantle convection, and efficient mantle mixing. However, cosmochemical constraints point to a lower-mantle composition that has a lower Mg/Si compared to upper-mantle pyrolite. Moreover, geochemical signatures of magmatic rocks indicate the long-term persistence of primordial reservoirs somewhere in the mantle. In this presentation, I establish geodynamic mechanisms for sustaining large-scale (primordial) heterogeneity in the Earth's mantle using numerical models. Mantle flow is controlled by rock density and viscosity. Variations in intrinsic rock density, such as due to heterogeneity in basalt or iron content, can induce layering or partial layering in the mantle. Layering can be sustained in the presence of persistent whole mantle convection due to active "unmixing" of heterogeneity in low-viscosity domains, e.g. in the transition zone or near the core-mantle boundary [1]. On the other hand, lateral variations in intrinsic rock viscosity, such as due to heterogeneity in Mg/Si, can strongly affect the mixing timescales of the mantle. In the extreme case, intrinsically strong rocks may remain unmixed through the age of the Earth, and persist as large-scale domains in the mid-mantle due to focusing of deformation along weak conveyor belts [2]. That large-scale lateral heterogeneity and/or layering can persist in the presence of whole-mantle convection can explain the stagnation of some slabs, as well as the deflection of some plumes, in the mid-mantle. These findings indeed motivate new seismic studies for rigorous testing of model predictions. [1] Ballmer, M. D., N. C. Schmerr, T. Nakagawa, and J. Ritsema (2015), Science Advances, doi:10.1126/sciadv.1500815. [2] Ballmer, M. D., C. Houser, J. W. Hernlund, R. Wentzcovitch, and K. Hirose (2017), Nature Geoscience, doi:10.1038/ngeo2898.

  8. Influence of the Ringwoodite-Perovskite transition on mantle convection in spherical geometry as a function of Clapeyron slope and Rayleigh number

    M. Wolstencroft

    2011-12-01

    Full Text Available We investigate the influence on mantle convection of the negative Clapeyron slope ringwoodite to perovskite and ferro-periclase mantle phase transition, which is correlated with the seismic discontinuity at 660 km depth. In particular, we focus on understanding the influence of the magnitude of the Clapeyron slope (as measured by the Phase Buoyancy parameter, P and the vigour of convection (as measured by the Rayleigh number, Ra on mantle convection. We have undertaken 76 simulations of isoviscous mantle convection in spherical geometry, varying Ra and P. Three domains of behaviour were found: layered convection for high Ra and more negative P, whole mantle convection for low Ra and less negative P, and transitional behaviour in an intervening domain. The boundary between the layered and transitional domain was fit by a curve P = α Raβ where α = −1.05, and β = −0.1, and the fit for the boundary between the transitional and whole mantle convection domain was α = −4.8, and β = −0.25. These two curves converge at Ra ≈ 2.5 × 104 (well below Earth mantle vigour and P ≈ −0.38. Extrapolating to high Ra, which is likely earlier in Earth history, this work suggests a large transitional domain. It is therefore likely that convection in the Archean would have been influenced by this phase change, with Earth being at least in the transitional domain, if not the layered domain.

  9. POROUS MICROSTRUCTURE OF THE INTERFACIAL TRANSITION ZONE IN GEOPOLYMER COMPOSITES

    Steinerová M.

    2013-12-01

    Full Text Available The study deals with a comparison of the differences in the structure, composition and micromechanical properties of a metakaolinite geopolymer composite matrix, inside and outside of the interfacial transition zone (ITZ with quartz grains of added silica sand. The microstructure is investigated by a measurement of the mercury porosimetry, microscopy and by a measurement in SEM and AFM, completed by Raman spectroscopy. Weaker mechanical properties, micropores in the ITZ, a higher concentration of Al atoms and hydroxyl groups than in the ambient matrix were detected. The water transport is probably the reason for the micropore formation, caused by disequilibrium in the course of solid-phase building from geopolymer dispersion.

  10. The Root Transition Zone: A Hot Spot for Signal Crosstalk.

    Kong, Xiangpei; Liu, Guangchao; Liu, Jiajia; Ding, Zhaojun

    2018-05-01

    The root transition zone (TZ), located between the apical meristem and basal elongation region, has a unique role in root growth and development. The root TZ is not only the active site for hormone crosstalk, but also the perception site for various environmental cues, such as aluminum (Al) stress and low phosphate (Pi) stress. We propose that the root TZ is a hot spot for the integration of diverse inputs from endogenous (hormonal) and exogenous (sensorial) stimuli to control root growth. Copyright © 2018 Elsevier Ltd. All rights reserved.

  11. Subduction and volcanism in the Iberia-North Africa collision zone from tomographic images of the upper mantle

    Villaseñor, Antonio; Chevrot, Sébastien; Harnafi, Mimoun; Gallart, Josep; Pazos, Antonio; Serrano, Inmaculada; Córdoba, Diego; Pulgar, Javier A.; Ibarra, Pedro

    2015-11-01

    New tomographic images of the upper mantle beneath the westernmost Mediterranean suggest that the evolution of the region experienced two subduction-related episodes. First subduction of oceanic and/or extended continental lithosphere, now located mainly beneath the Betics at depths greater than 400 km, took place on a NW-SE oriented subduction zone. This was followed by a slab-tear process that initiated in the east and propagated to the west, leading to westward slab rollback and possibly lower crustal delamination. The current position of the slab tear is located approximately at 4°W, and to the west of this location the subducted lithosphere is still attached to the surface along the Gibraltar Arc. Our new P-wave velocity model is able to image the attached subducted lithosphere as a narrow high-velocity body extending to shallow depths, coinciding with the region of maximum curvature of the Gibraltar Arc, the occurrence of intermediate-depth earthquakes, and anomalously thick crust. This thick crust has a large influence in the measured teleseismic travel time residuals and therefore in the obtained P-wave tomographic model. We show that removing the effects of the thick crust significantly improves the shallow images of the slab and therefore the interpretations based on the seismic structure.

  12. Complex Morphology of Subducted Lithosphere in the Mantle below the Molucca Collision Zone from Non-linear Seismic Tomography

    Sri Widiyantoro

    2003-05-01

    Full Text Available Results of seismic studies presented in previous publications depict two opposing subducted oceanic lithospheric slabs under the Molucca region. This unique structure is related to the arc-arc collision between the Halmahera and Sangihe arcs. Recently, we have revisited the complex subduction zone structure by employing a non-linear tomographic imaging technique in which 3-D ray tracing has been implemented. We have used P- as well as S-wave arrival times from carefully reprocessed global data set. The results provide some improvements in the positioning of wave-speed anomalies. Consistent with earlier results, the new P-wave model depicts the two opposing subducted slabs of the Molucca Sea plate. The intriguing new observation is that the westward dipping slab appears to penetrate into the lower mantle by taking the form of folded slab. We envisage that the folding behavior may have been caused by the shift of the whole subduction system in the Molucca region toward the Eurasian continent due to the westward thrust of the Pacific plate combined with the large left-lateral movement of the Sorong fault. The inversion of travel-time residuals of direct S phases strongly confirms the new observation.

  13. Deformation associated to exhumation by detachment faulting of upper mantle rocks in a fossil Ocean Continent Transition: The example of the Totalp unit in SE Switzerland

    Picazo, S.; Manatschal, G.; Cannat, M.

    2013-12-01

    The exhumation of upper mantle rocks along detachment faults is widespread at Mid-Ocean Ridges and at the Ocean-Continent Transition (OCT) of rifted continental margins. Thermo-mechanical models indicate that significant strain softening of the fault rocks in the footwall is required in order to produce such large fault offsets. Our work focuses on deformation textures, and the associated mineralogy in ultramafic rocks sampled in the upper levels of the footwall next to the exhumation fault. We present two OCT examples, the Totalp relict of a paleo-Tethys OCT exposed in SE Switzerland, and the Iberian distal margin (ODP Leg 173 Site 1070). We built a new geological map and a section of the Totalp unit near Davos (SE Switzerland) and interpreted this area as a local exposure of a paleo-seafloor that is formed by an exhumed detachment surface and serpentinized peridotites. The top of the exhumed mantle rocks is made of ophicalcites that resulted from the carbonation of serpentine under static conditions at the seafloor. The ophicalcites preserve depositional contacts with Upper Jurassic to Lower Cretaceous pelagic sediments. These sequences did not exceed prehnite-pumpellyite metamorphic facies conditions, and locally escaped Alpine deformation. Thin mylonitic shear zones as well as foliated amphibole-bearing ultramafic rocks have been mapped. The age of these rocks and the link with the final exhumation history are yet unknown but since amphibole-bearing ultramafic rocks can be found as clasts in cataclasites related to the detachment fault, they pre-date detachment faulting. Our petrostructural study of the exhumed serpentinized rocks also reveals a deformation gradient from cataclasis to gouge formation within 150m in the footwall of the proposed paleo-detachment fault. This deformation postdates serpentinization. It involves a component of plastic deformation of serpentine in the most highly strained intervals that has suffered pronounced grain-size reduction and

  14. Deformation and seismic anisotropy of the subcontinental lithospheric mantle in NE Spain: EBSD data on xenoliths from the Catalan Volcanic Zone

    Fernández-Roig, Mercè; Galán, Gumer; Mariani, Elisabetta

    2017-02-01

    Mantle xenoliths in Neogene-Quaternary basaltic rocks related to the European Cenozoic Rift System serve to assess the evolution of the subcontinental lithospheric mantle beneath the Catalan Volcanic Zone in NE Spain. Crystallographic preferred orientations, major element composition of minerals, and temperature and pressure estimates have been used to this end. The mantle consists of spinel lherzolites, harzburgites and subordinate websterites. Protogranular microstructures are found in all peridotites and websterites, but lherzolites also display finer-grained porphyroclastic and equigranular microstructures. The dominant olivine deformation fabric is [010] fiber, but subordinate orthorhombic and [100]-fiber types are also present, especially in porphyroclastic and equigranular lherzolites. The fabric strength (J index = 10.12-1.91), equilibrium temperature and pressure are higher in xenoliths with [010]-fiber fabric and decrease in those with orthorhombic and [100]-fiber type. Incoherence between olivine and pyroxene deformation fabric is mostly found in porphyroclastic and equigranular lherzolites. Seismic anisotropy, estimated from the crystal preferred orientations, also decreases (AVp = 10.2-2.60%; AVs max = 7.95-2.19%) in porphyroclastic and equigranular lherzolites. The olivine [010]-fiber fabric points to deformation by simple shear or transpression which is likely to have occured during the development of late-Hercynian strike-slip shear zones, and to subsequent annealing during late Hercynian decompression, Permian and Cretaceous rifting. Also, it cannot be excluded that the percolation of mafic magmas during these extensional events provoked the refertilization of the lithospheric mantle. However, no clear relationship has been observed between fabric strength and mineral mode and composition. Later transtensional deformation during late Alpine orogenesis, at higher stress and decreasing temperature and pressure, transformed the earlier fabric into

  15. Measurements of traveling transition zone along a superconductor

    Lottin, J.C.; Miller, J.R.; Lue, J.W.; Dresner, L.

    1978-01-01

    The spatial variation of the temperature in a traveling superconducting-normal transition zone can provide valuable information on transient heat transfer in realistic coil conditions. In this paper, temperature wave curves are presented for several transport currents corresponding to propagation and recovery in a high magnetic field. The temperature profiles have been constructed in the form T = T (x + vt) by measuring the wave velocity and the temperature at one point as a function of time. The temperature is measured directly with differential thermocouples; simultaneous voltage measurements provide a continuous temperature reference in the current sharing region. Information is given about thermocouple calibration in the high magnetic field and about the temperature and magnetic field dependence of the thermal conductivity of the sample

  16. Analytical Determination of the Boundaries of Transition Natural Zones (Ecotones

    Rulev Aleksandr Sergeevich

    2015-04-01

    Full Text Available The morphological units that are part of the catena, are recognized in accordance with the response to the geomorphological and soil processes. The spatial relationship is the main unit between them. In this regard, the landscape patterns acquire a cascade type, and their main link becomes the zonal catena, which has specific stable features, reflecting the dependence of the complex of natural conditions and processes of latitude. However, clear-cut boundaries do not exist – they have spatial and temporal displacement, associated with the cyclical nature of the global climatic processes. The landscapes in these transition zones (ecotones a priori can be considered unstable. The detection of ecotones boundaries provides the opportunity to divide natural zones to potentially stable and potentially unstable parts for planning measures on preventing the degradation of landscapes localized in them. The latitude of the ecotones localization can be determined through the connection of the radiation heat flux on land (R with the normalized geographical latitude of the subboreal belt (x, which is described by the equation of the energy balance, expressed in the logistic function R = А / [1 + 0,72 exp(4,25 – Bx] + C.

  17. Mantle and crustal contribution in the genesis of Recent basalts from off-rift zones in Iceland: Constraints from Th, Sr and O isotopes

    Sigmarsson, Olgeir; Condomines, Michel; Fourcade, Serge

    1992-05-01

    Along the two volcanic off-rift zones in Iceland, the Sn˦fellsnes volcanic zone (SNVZ) and the South Iceland volcanic zone (SIVZ), geochemical parameters vary regularly along the strike towards the centre of the island. Recent basalts from the SNVZ change from alkali basalts to tholeiites where the volcanic zone reaches the active rift axis, and their 87Sr/ 86Sr and Th/U ratios decrease in the same direction. These variations are interpreted as the result of mixing between mantle melts from two distinct reservoirs below Sn˦fellsnes. The mantle melt would be more depleted in incompatible elements, but with a higher 3He/ 4He ratio ( R/Ra≈ 20) beneath the centre of Iceland than at the tip of the Sn˦fellsnes volcanic zone ( R/Ra≈ 7.5). From southwest to northeast along the SIVZ, the basalts change from alkali basalts to FeTi basalts and quartz-normative tholeiites. The Th/U ratio of the Recent basalts increases and both ( 230Th/ 232Th ) and δ 18O values decrease in the same direction. This reflects an important crustal contamination of the FeTi-rich basalts and the quartz tholeiites. The two types of basalts could be produced through assimilation and fractional crystallization in which primary alkali basaltic and olivine tholeiitic melts 'erode' and assimilate the base of the crust. The increasingly tholeiitic character of the basalts towards the centre of Iceland, which reflects a higher degree of partial melting, is qualitatively consistent with increasing geothermal gradient and negative gravity anomaly. The highest Sr isotope ratio in Recent basalts from Iceland is observed inÖr˦fajökull volcano, which has a 3He/ 4He ratio ( R/Ra≈ 7.8) close to the MORB value, and this might represent a mantle source similar to that of Mauna Loa in Hawaii.

  18. Earthquake rupture below the brittle-ductile transition in continental lithospheric mantle.

    Prieto, Germán A; Froment, Bérénice; Yu, Chunquan; Poli, Piero; Abercrombie, Rachel

    2017-03-01

    Earthquakes deep in the continental lithosphere are rare and hard to interpret in our current understanding of temperature control on brittle failure. The recent lithospheric mantle earthquake with a moment magnitude of 4.8 at a depth of ~75 km in the Wyoming Craton was exceptionally well recorded and thus enabled us to probe the cause of these unusual earthquakes. On the basis of complete earthquake energy balance estimates using broadband waveforms and temperature estimates using surface heat flow and shear wave velocities, we argue that this earthquake occurred in response to ductile deformation at temperatures above 750°C. The high stress drop, low rupture velocity, and low radiation efficiency are all consistent with a dissipative mechanism. Our results imply that earthquake nucleation in the lithospheric mantle is not exclusively limited to the brittle regime; weakening mechanisms in the ductile regime can allow earthquakes to initiate and propagate. This finding has significant implications for understanding deep earthquake rupture mechanics and rheology of the continental lithosphere.

  19. STEM tomography analysis of the trypanosome transition zone.

    Trépout, Sylvain; Tassin, Anne-Marie; Marco, Sergio; Bastin, Philippe

    2018-04-01

    The protist Trypanosoma brucei is an emerging model for the study of cilia and flagella. Here, we used scanning transmission electron microscopy (STEM) tomography to describe the structure of the trypanosome transition zone (TZ). At the base of the TZ, nine transition fibres irradiate from the B microtubule of each doublet towards the membrane. The TZ adopts a 9 + 0 structure throughout its length of ∼300 nm and its lumen contains an electron-dense structure. The proximal portion of the TZ has an invariant length of 150 nm and is characterised by a collarette surrounding the membrane and the presence of electron-dense material between the membrane and the doublets. The distal portion exhibits more length variation (from 55 to 235 nm) and contains typical Y-links. STEM analysis revealed a more complex organisation of the Y-links compared to what was reported by conventional transmission electron microscopy. Observation of the very early phase of flagellum assembly demonstrated that the proximal portion and the collarette are assembled early during construction. The presence of the flagella connector that maintains the tip of the new flagellum to the side of the old was confirmed and additional filamentous structures making contact with the membrane of the flagellar pocket were also detected. The structure and potential functions of the TZ in trypanosomes are discussed, as well as its mode of assembly. Copyright © 2017 Elsevier Inc. All rights reserved.

  20. Transition zone cells reach G2 phase before initiating elongation in maize root apex

    M. Victoria Alarcón

    2017-06-01

    Full Text Available Root elongation requires cell divisions in the meristematic zone and cell elongation in the elongation zone. The boundary between dividing and elongating cells is called the transition zone. In the meristem zone, initial cells are continuously dividing, but on the basal side of the meristem cells exit the meristem through the transition zone and enter in the elongation zone, where they stop division and rapidly elongate. Throughout this journey cells are accompanied by changes in cell cycle progression. Flow cytometry analysis showed that meristematic cells are in cycle, but exit when they enter the elongation zone. In addition, the percentage of cells in G2 phase (4C strongly increased from the meristem to the elongation zone. However, we did not observe remarkable changes in the percentage of cells in cell cycle phases along the entire elongation zone. These results suggest that meristematic cells in maize root apex stop the cell cycle in G2 phase after leaving the meristem.

  1. Importance of ecotone type to landscape dynamics at biome transition zones

    Landscapes in biome transition zones consist of a mosaic of patches dominated or codominated by species from adjacent biomes. Shifts in the vegetation composition and dynamics of a biome transition zone depend upon the underlying patch dynamics of the ecotones between these dominant species. Landsc...

  2. Analysis of Bridge Transition Zones in Railways Considering the Moisture Condition of the Ballast and Subballast

    Wang, Haoyu; Silvast, Mika; Markine, V.L.; Wiljanen, Bruce

    2017-01-01

    Transition zones in railway tracks are the locations with considerable changes in vertical support structures, e.g., near bridges. Due to possible water flow constrictions in transition zone structures, there is frequently an increased moisture level in the ballast/subballast layers, which is a

  3. Tradeoffs in Chemical and Thermal Variations in the Post-perovskite Phase Transition: Mixed Phase Regions in the Deep Lower Mantle?

    Giles, G. F.; Spera, F. J.; Yuen, D. A.

    2005-12-01

    The recent discovery of a phase-transition in Mg-rich perovskite (Pv) to a post-perovskite (pPv) phase at lower mantle depths and its relationship to D", lower mantle heterogeneity and iron content prompted an investigation of the relative importance of lower mantle (LM) compositional and temperature fluctuations in creating topographic undulations on mixed phase regions. Above the transition, Mg-rich Pv makes up ~70 percent by mass of the LM. Using results from experimental phase equilibria, first-principles computations and thermodynamic relations for Fe2+-Mg mixing in silicates, a preliminary thermodynamic model for the perovskite to post-perovskite phase transition in the divariant system MgSiO3-FeSiO3 is developed. Complexities associated with components Fe2O3 and Al2O3 and other phases (Ca-Pv, magnesiowustite) are neglected. The model predicts phase transition pressures are sensitive to the FeSiO3 content of perovskite (~-1.5 GPa per one mole percent FeSiO3). This leads to considerable topography along the top boundary of the mixed phase region. The Clapeyron slope for the Pv to pPv transition at XFeSiO3=0.1 is +11 MPa/K about 20% higher than for pure Mg-Pv. Increasing bulk concentration of iron elevates the mixed (two-phase) layer above the core-mantle boundary (CMB); increasing temperature acts to push the mixed layer deeper into the LM into the D" thermal boundary layer resting upon the (CMB). For various LM geotherms and CMB temperatures, a single mixed layer of thickness ~300 km lies within the bottom 40% of the lower mantle. For low iron contents (XFeSiO3 ~5 mole percent or less), two perched layers are found. This is the divariant analog to the univariant double-crosser. The hotter the mantle, the deeper the mixed phase layer; the more iron-rich the LM, the higher the mixed phase layer. In a hotter Hadean Earth with interior temperatures everywhere 200-500 K warmer pPv is not stable unless the LM bulk composition is Fe-enriched compared to the present

  4. Flow in the Deep Mantle from Seisimc Anisotropy: Progress and Prospects

    Long, M. D.

    2017-12-01

    Observations of seismic anisotropy, or the directional dependence of seismic wavespeeds, provide one some of the most direct constraints on the pattern of flow in the Earth's mantle. In particular, as our understanding of crystallographic preferred orientation (CPO) of olivine aggregates under a range of deformation conditions has improved, our ability to exploit observations of upper mantle anisotropy has led to fundamental discoveries about the patterns of flow in the upper mantle and the drivers of that flow. It has been a challenge, however, to develop a similar framework for understanding flow in the deep mantle (transition zone, uppermost lower mantle, and lowermost mantle), even though there is convincing observational evidence for seismic anisotropy at these depths. Recent progress on the observational front has allowed for an increasingly detailed view of mid-mantle anisotropy (transition zone and uppermost lower mantle), particularly in subduction systems, which may eventually lead to a better understanding of mid-mantle deformation and the dynamics of slab interaction with the surrounding mid-mantle. New approaches to the observation and modeling of lowermost mantle anisotropy, in combination with constraints from mineral physics, are progressing towards interpretive frameworks that allow for the discrimination of different mantle flow geometries in different regions of D". In particular, observational strategies that involve the use of multiple types of body wave phases sampled over a range of propagation azimuths enable detailed forward modeling approaches that can discriminate between different mechanisms for D" anisotropy (e.g., CPO of post-perovskite, bridgmanite, or ferropericlase, or shape preferred orientation of partial melt) and identify plausible anisotropic orientations. We have recently begun to move towards a full waveform modeling approach in this work, which allows for a more accurate simulation for seismic wave propagation. Ongoing

  5. Impact of spectral transition zone in reference ENIGMA configuration

    Aliberti, G.; Palmiotti, G.; Taiwo, T. A.; Tommasi, J.

    2005-01-01

    Investigation of Gas-cooled reactor at Masurca) is being planned for Cadarache. This new experiment would provide better understanding of GFR neutronic features and will be the basis for the extension of current neutronics code validation domain (particularly, the ERANOS code system in France) to the analysis of GFRs. Experimental planning and decisions are ongoing for ENIGMA. One of the items that have been evaluated is the feasibility of obtaining different flux spectra in the ENIGMA reference configuration, giving the flexibility of simulating a large series of proposed gas-cooled fast systems with harder or softer spectra. In order to achieve this goal it was proposed to use a spectral transition zone in the center region of the ENIGMA core configuration. Another goal of the study is to evaluate the impact of the graphite cross-sections on the performance characteristics of the MASURCA configurations. The work was supported by ANL, through the residence of one of the authors at CEA-Cadarache in 2005. In this report, the impacts of the transition zone on the core physics parameters of the reference ENIGMA configuration are summarized

  6. Microbial Mineral Colonization Across a Subsurface Redox Transition Zone

    Brandon eConverse

    2015-08-01

    Full Text Available This study employed 16S rRNA gene amplicon pyrosequencing to examine the hypothesis that chemolithotrophic Fe(II-oxidizing bacteria (FeOB would preferentially colonize the Fe(II-bearing mineral biotite compared to quartz sand when the minerals were incubated in situ within a subsurface redox transition zone (RTZ at the Hanford 300 Area site in Richland, WA, USA. The work was motivated by the recently documented presence of neutral-pH chemolithotrophic FeOB capable of oxidizing structural Fe(II in primary silicate and secondary phyllosilicate minerals in 300 Area sediments and groundwater (Benzine et al., 2013. Sterilized portions of sand+biotite or sand alone were incubated in situ for five months within a multilevel sampling (MLS apparatus that spanned a ca. 2-m interval across the RTZ in two separate groundwater wells. Parallel MLS measurements of aqueous geochemical species were performed prior to deployment of the minerals. Contrary to expectations, the 16S rRNA gene libraries showed no significant difference in microbial communities that colonized the sand+biotite versus sand-only deployments. Both mineral-associated and groundwater communities were dominated by heterotrophic taxa, with organisms from the Pseudomonaceae accounting for up to 70% of all reads from the colonized minerals. These results are consistent with previous results indicating the capacity for heterotrophic metabolism (including anaerobic metabolism below the RTZ as well as the predominance of heterotrophic taxa within 300 Area sediments and groundwater. Although heterotrophic organisms clearly dominated the colonized minerals, several putative lithotrophic (NH4+, H2, Fe(II, and HS- oxidizing taxa were detected in significant abundance above and within the RTZ. Such organisms may play a role in the coupling of anaerobic microbial metabolism to oxidative pathways with attendant impacts on elemental cycling and redox-sensitive contaminant behavior in the vicinity of the

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

    Brandt, Frederik Ejvang

    The thesis is a contribution towards the understanding of the generation of the source mantle for magmas related to the subduction of the Nazca plate under South America with an emphasis on the geochemistry of the volatiles Cl, F, S, H2O and CO2. The study presents analytical data for tephra, min...

  8. Re-Os isotope and platinum group elements of a FOcal ZOne mantle source, Louisville Seamounts Chain, Pacific ocean

    Tejada, Maria Luisa G.; Hanyu, Takeshi; Ishikawa, Akira; Senda, Ryoko; Suzuki, Katsuhiko; Fitton, Godfrey; Williams, Rebecca

    2015-02-01

    The Louisville Seamount Chain (LSC) is, besides the Hawaiian-Emperor Chain, one of the longest-lived hotspot traces. We report here the first Re-Os isotope and platinum group element (PGE) data for Canopus, Rigil, and Burton Guyots along the chain, which were drilled during IODP Expedition 330. The LSC basalts possess (187Os/188Os)i = 0.1245-0.1314 that are remarkably homogeneous and do not vary with age. A Re-Os isochron age of 64.9 ± 3.2 Ma was obtained for Burton seamount (the youngest of the three seamounts drilled), consistent with 40Ar-39Ar data. Isochron-derived initial 187Os/188Os ratio of 0.1272 ± 0.0008, together with data for olivines (0.1271-0.1275), are within the estimated primitive mantle values. This (187Os/188Os)i range is similar to those of Rarotonga (0.124-0.139) and Samoan shield (0.1276-0.1313) basalts and lower than those of Cook-Austral (0.136-0.155) and Hawaiian shield (0.1283-0.1578) basalts, suggesting little or no recycled component in the LSC mantle source. The PGE data of LSC basalts are distinct from those of oceanic lower crust. Variation in PGE patterns can be largely explained by different low degrees of melting under sulfide-saturated conditions of the same relatively fertile mantle source, consistent with their primitive mantle-like Os and primordial Ne isotope signatures. The PGE patterns and the low 187Os/188Os composition of LSC basalts contrast with those of Ontong Java Plateau (OJP) tholeiites. We conclude that the Re-Os isotope and PGE composition of LSC basalts reflect a relatively pure deep-sourced common mantle sampled by some ocean island basalts but is not discernible in the composition of OJP tholeiites.

  9. Discordant lymphoma consisting of splenic mantle cell lymphoma and marginal zone lymphoma involving the bone marrow and peripheral blood: a case report

    Caracciolo Francesco

    2011-09-01

    Full Text Available Abstract Introduction Discordant lymphomas are rare entities characterized by the simultaneous presence of two distinct types of lymphomas in different anatomic sites. We describe a very rare case of simultaneous occurrence of splenic mantle cell lymphoma and marginal zone lymphoma involving the bone marrow and peripheral blood. Case presentation We report the case of a 60-year-old asymptomatic Caucasian woman in whom discordant lymphomas were discovered when a slight lymphocytosis and a conspicuous splenomegaly were observed. The different morphological, immunophenotypical and immunohistochemical features found in the different pathologic samples obtained from peripheral blood, bone marrow and spleen sections made it possible to differentiate two types of non-Hodgkin B-cell lymphomas: a mantle cell lymphoma infiltrating the spleen and a marginal zone lymphoma involving both the bone marrow and peripheral blood. Since a similar IgH gene rearrangement was found both in the bone marrow and in the spleen, the hypothesis of a common origin, followed by a different clonal selection of the neoplastic lymphocytes may be taken into consideration. Conclusion Our case emphasizes the usefulness of investigating simultaneous specimens from different anatomic sites from the same patient and the relevant diagnostic role of splenectomy.

  10. Reconciling laboratory and observational models of mantle rheology in geodynamic modelling

    King, Scott D.

    2016-10-01

    Experimental and geophysical observations constraining mantle rheology are reviewed with an emphasis on their impact on mantle geodynamic modelling. For olivine, the most studied and best-constrained mantle mineral, the tradeoffs associated with the uncertainties in the activation energy, activation volume, grain-size and water content allow the construction of upper mantle rheology models ranging from nearly uniform with depth to linearly increasing from the base of the lithosphere to the top of the transition zone. Radial rheology models derived from geophysical observations allow for either a weak upper mantle or a weak transition zone. Experimental constraints show that wadsleyite and ringwoodite are stronger than olivine at the top of the transition zone; however the uncertainty in the concentration of water in the transition zone precludes ruling out a weak transition zone. Both observational and experimental constraints allow for strong or weak slabs and the most promising constraints on slab rheology may come from comparing inferred slab geometry from seismic tomography with systematic studies of slab morphology from dynamic models. Experimental constraints on perovskite and ferropericlase strength are consistent with general feature of rheology models derived from geophysical observations and suggest that the increase in viscosity through the top of the upper mantle could be due to the increase in the strength of ferropericlase from 20-65 GPa. The decrease in viscosity in the bottom half of the lower mantle could be the result of approaching the melting temperature of perovskite. Both lines of research are consistent with a high-viscosity lithosphere, a low viscosity either in the upper mantle or transition zone, and high viscosity in the lower mantle, increasing through the upper half of the lower mantle and decreasing in the bottom half of the lower mantle, with a low viscosity above the core. Significant regions of the mantle, including high

  11. Water in geodynamical models of mantle convection and plate tectonics

    Rodríguez-González, J.; Van Hunen, J.; Chotalia, K.; Lithgow-Bertelloni, C. R.; Rozel, A.; Tackley, P. J.; Nakagawa, T.

    2017-12-01

    The presence of water in the the mantle has a significant effect in the dynamical and thermal evolution of Earth, which partially explains the differences with other planets and is a key factor for the presence of life on Earth. First, a small amount of water can decrease the mantle viscosity by a several orders of magnitude, thereby changing the convection regime and affecting the thermal evolution. Second, the presence of water significantly changes the solidus curve, with crucial implications for melting. Third, water in the mantle can change the Clapeyron slope of mantle materials, which changes the depth at which phase transitions take place. The thermal and dynamical evolution of Earth under the presence of water in the mantle has been the focus of recent studies, but many questions remain unanswered. In this project we intend to investigate how the maximum water capacity of different mantle regions affects water transport and Earth's convective regime. We will study the effect phase transitions under the presence of water, which can change the buoyancy of slabs in the transition zone. We present preliminary results numerical models of global mantle convection for the whole history of earth using the numerical geodynamics software tool StagYY. We will use a new parametrisation of dehydration processes, obtained from high-resolution numerical simulations, to implement a more accurate description of the water released from the slab as it travels through the mantle. We have integrated recent experimental results of the water capacity of deep mantle minerals to study the water circulation and the total water budget. We use data from the most recent experiments and ab-inito calculations to implement a realistic rheology.

  12. The thermal effects of steady-state slab-driven mantle flow above a subducting plate: the Cascadia subduction zone and backarc

    Currie, C. A.; Wang, K.; Hyndman, Roy D.; He, Jiangheng

    2004-06-01

    At subduction zones, geophysical and geochemical observations indicate that the arc and backarc regions are hot, in spite of the cooling effects of a subducting plate. At the well-studied Cascadia subduction zone, high mantle temperatures persist for over 500 km into the backarc, with little lateral variation. These high temperatures are even more surprising due to the juxtaposition of the hot Cascadia backarc against the thick, cold North America craton lithosphere. Given that local heat sources appear to be negligible, mantle flow is required to transport heat into the wedge and backarc. We have examined the thermal effects of mantle flow induced by traction along the top of the subducting plate. Through systematic tests of the backarc model boundary, we have shown that the model thermal structure of the wedge is primarily determined by the assumed temperatures along this boundary. To get high temperatures in the wedge, it is necessary for flow to mine heat from depth, either by using a temperature-dependent rheology, or by introducing a deep cold boundary through a thick adjacent lithosphere, consistent with the presence of a craton. Regardless of the thermal conditions along the backarc boundary, flow within an isoviscous wedge is too slow to transport a significant amount of heat into the wedge corner. With a more realistic stress- and temperature-dependent wedge rheology, flow is focused into the wedge corner, resulting in rapid flow upward toward the corner and enhanced temperatures below the arc, compatible with temperatures required for arc magma generation. However, this strong flow focusing produces a nearly stagnant region further landward in the shallow backarc mantle, where model temperatures and heat flow are much lower than observed. Observations of high backarc temperatures, particularly in areas that have not undergone recent extension, provide an important constraint on wedge dynamics. None of the models of simple traction-driven flow were able

  13. Structural Health Monitoring of Railway Transition Zones Using Satellite Radar Data.

    Wang, Haoyu; Chang, Ling; Markine, Valeri

    2018-01-31

    Transition zones in railway tracks are locations with considerable changes in the rail-supporting structure. Typically, they are located near engineering structures, such as bridges, culverts and tunnels. In such locations, severe differential settlements often occur due to the different material properties and structure behavior. Without timely maintenance, the differential settlement may lead to the damage of track components and loss of passenger's comfort. To ensure the safety of railway operations and reduce the maintenance costs, it is necessary to consecutively monitor the structural health condition of the transition zones in an economical manner and detect the changes at an early stage. However, using the current in situ monitoring of transition zones is hard to achieve this goal, because most in situ techniques (e.g., track-measuring coaches) are labor-consuming and usually not frequently performed (approximately twice a year in the Netherlands). To tackle the limitations of the in situ techniques, a Satellite Synthetic Aperture Radar (InSAR) system is presented in this paper, which provides a potential solution for a consecutive structural health monitoring of transition zones with bi-/tri-weekly data update and mm-level precision. To demonstrate the feasibility of the InSAR system for monitoring transition zones, a transition zone is tested. The results show that the differential settlement in the transition zone and the settlement rate can be observed and detected by the InSAR measurements. Moreover, the InSAR results are cross-validated against measurements obtained using a measuring coach and a Digital Image Correlation (DIC) device. The results of the three measuring techniques show a good correlation, which proves the applicability of InSAR for the structural health monitoring of transition zones in railway track.

  14. Structural Health Monitoring of Railway Transition Zones Using Satellite Radar Data

    Haoyu Wang

    2018-01-01

    Full Text Available Transition zones in railway tracks are locations with considerable changes in the rail-supporting structure. Typically, they are located near engineering structures, such as bridges, culverts and tunnels. In such locations, severe differential settlements often occur due to the different material properties and structure behavior. Without timely maintenance, the differential settlement may lead to the damage of track components and loss of passenger’s comfort. To ensure the safety of railway operations and reduce the maintenance costs, it is necessary to consecutively monitor the structural health condition of the transition zones in an economical manner and detect the changes at an early stage. However, using the current in situ monitoring of transition zones is hard to achieve this goal, because most in situ techniques (e.g., track-measuring coaches are labor-consuming and usually not frequently performed (approximately twice a year in the Netherlands. To tackle the limitations of the in situ techniques, a Satellite Synthetic Aperture Radar (InSAR system is presented in this paper, which provides a potential solution for a consecutive structural health monitoring of transition zones with bi-/tri-weekly data update and mm-level precision. To demonstrate the feasibility of the InSAR system for monitoring transition zones, a transition zone is tested. The results show that the differential settlement in the transition zone and the settlement rate can be observed and detected by the InSAR measurements. Moreover, the InSAR results are cross-validated against measurements obtained using a measuring coach and a Digital Image Correlation (DIC device. The results of the three measuring techniques show a good correlation, which proves the applicability of InSAR for the structural health monitoring of transition zones in railway track.

  15. Articular Cartilage Increases Transition Zone Regeneration in Bone-tendon Junction Healing

    Qin, Ling; Lee, Kwong Man; Leung, Kwok Sui

    2008-01-01

    The fibrocartilage transition zone in the direct bone-tendon junction reduces stress concentration and protects the junction from failure. Unfortunately, bone-tendon junctions often heal without fibrocartilage transition zone regeneration. We hypothesized articular cartilage grafts could increase fibrocartilage transition zone regeneration. Using a goat partial patellectomy repair model, autologous articular cartilage was harvested from the excised distal third patella and interposed between the residual proximal two-thirds bone fragment and tendon during repair in 36 knees. We evaluated fibrocartilage transition zone regeneration, bone formation, and mechanical strength after repair at 6, 12, and 24 weeks and compared them with direct repair. Autologous articular cartilage interposition resulted in more fibrocartilage transition zone regeneration (69.10% ± 14.11% [mean ± standard deviation] versus 8.67% ± 7.01% at 24 weeks) than direct repair at all times. There was no difference in the amount of bone formation and mechanical strength achieved. Autologous articular cartilage interposition increases fibrocartilage transition zone regeneration in bone-tendon junction healing, but additional research is required to ascertain the mechanism of stimulation and to establish the clinical applicability. PMID:18987921

  16. Multiple magmatism in an evolving suprasubduction zone mantle wedge: The case of the composite mafic-ultramafic complex of Gaositai, North China Craton

    Yang, Fan; Santosh, M.; Tsunogae, T.; Tang, Li; Teng, Xueming

    2017-07-01

    The suprasubduction zone mantle wedge of active convergent margins is impregnated by melts and fluids leading to the formation of a variety of magmatic and metasomatic rock suites. Here we investigate a composite mafic-ultramafic intrusion at Gaositai, in the northern margin of the North China Craton (NCC). The hornblende gabbro-serpentinite-dunite-pyroxenite-gabbro-diorite suite surrounded by hornblendites of this complex has long been considered to represent an "Alaskan-type" zoned pluton. We present petrologic, mineral chemical, geochemical and zircon U-Pb and Lu-Hf data from the various rock types from Gaositai including hornblende gabbro, serpentinite, dunite, pyroxenite, diorite and the basement hornblendite which reveal the case of multiple melt generation and melt-peridotite interaction. Our new mineral chemical data from the mafic-ultramafic suite exclude an "Alaskan-type" affinity, and the bulk geochemical features are consistent with subduction-related magmatism with enrichment of LILE (K, Rb, and Ba) and LREE (La and Ce), and depletion of HFSE (Nb, Ta, Zr, and Hf) and HREE. Zircon U-Pb geochronology reveals that the hornblendites surrounding the Gaositai complex are nearly 2 billion years older than the intrusive complex and yield early Paleoproterozoic emplacement ages (2433-2460 Ma), followed by late Paleoproterozoic metamorphism (1897 Ma). The serpentinites trace the history of a long-lived and replenished ancient sub-continental lithospheric mantle with the oldest zircon population dated as 2479 Ma and 1896 Ma, closely corresponding with the ages obtained from the basement rock, followed by Neoproterozoic and Phanerozoic zircon growth. The oldest member in the Gaositai composite intrusion is the dunite that yields emplacement age of 755 Ma, followed by pyroxenite formed through the interaction of slab melt and wedge mantle peridotite at 401 Ma. All the rock suites also carry multiple population of younger zircons ranging in age from Paleozoic to

  17. Fatigue Resistance of the Grain Size Transition Zone in a Dual Microstructure Superalloy Disk

    Gabb, T. P.; Kantzos, P. T.; Telesman, J.; Gayda, J.; Sudbrack, C. K.; Palsa, B. S.

    2010-01-01

    Mechanical property requirements vary with location in nickel-based superalloy disks. To maximize the associated mechanical properties, heat treatment methods have been developed for producing tailored microstructures. In this study, a specialized heat treatment method was applied to produce varying grain microstructures from the bore to the rim portions of a powder metallurgy processed nickel-based superalloy disk. The bore of the contoured disk consisted of fine grains to maximize strength and fatigue resistance at lower temperatures. The rim microstructure of the disk consisted of coarse grains for maximum resistance to creep and dwell crack growth at high temperatures up to 704 C. However, the fatigue resistance of the grain size transition zone was unclear, and needed to be evaluated. This zone was located as a band in the disk web between the bore and rim. Specimens were extracted parallel and transverse to the transition zone, and multiple fatigue tests were performed at 427 and 704 C. Mean fatigue lives were lower at 427 C than for 704 C. Specimen failures often initiated at relatively large grains, which failed on crystallographic facets. Grain size distributions were characterized in the specimens, and related to the grains initiating failures as well as location within the transition zone. Fatigue life decreased with increasing maximum grain size. Correspondingly, mean fatigue resistance of the transition zone was slightly higher than that of the rim, but lower than that of the bore. The scatter in limited tests of replicates was comparable for all transition zone locations examined.

  18. Buckling instabilities of subducted lithosphere beneath the transition zone

    Ribe, N.M.; Stutzmann, E.; Ren, Y.; Hilst, R.D. van der

    2007-01-01

    A sheet of viscous fluid poured onto a surface buckles periodically to generate a pile of regular folds. Recent tomographic images beneath subduction zones, together with quantitative fluid mechanical scaling laws, suggest that a similar instability can occur when slabs of subducted oceanic

  19. From mantle to critical zone: A review of large and giant sized deposits of the rare earth elements

    M.P. Smith

    2016-05-01

    Full Text Available The rare earth elements are unusual when defining giant-sized ore deposits, as resources are often quoted as total rare earth oxide, but the importance of a deposit may be related to the grade for individual, or a limited group of the elements. Taking the total REE resource, only one currently known deposit (Bayan Obo would class as giant (>1.7 × 107 tonnes contained metal, but a range of others classify as large (>1.7 × 106 tonnes. With the exception of unclassified resource estimates from the Olympic Dam IOCG deposit, all of these deposits are related to alkaline igneous activity – either carbonatites or agpaitic nepheline syenites. The total resource in these deposits must relate to the scale of the primary igneous source, but the grade is a complex function of igneous source, magmatic crystallisation, hydrothermal modification and supergene enrichment during weathering. Isotopic data suggest that the sources conducive to the formation of large REE deposits are developed in subcontinental lithospheric mantle, enriched in trace elements either by plume activity, or by previous subduction. The reactivation of such enriched mantle domains in relatively restricted geographical areas may have played a role in the formation of some of the largest deposits (e.g. Bayan Obo. Hydrothermal activity involving fluids from magmatic to meteoric sources may result in the redistribution of the REE and increases in grade, depending on primary mineralogy and the availability of ligands. Weathering and supergene enrichment of carbonatite has played a role in the formation of the highest grade deposits at Mount Weld (Australia and Tomtor (Russia. For the individual REE with the current highest economic value (Nd and the HREE, the boundaries for the large and giant size classes are two orders of magnitude lower, and deposits enriched in these metals (agpaitic systems, ion absorption deposits may have significant economic impact in the near future.

  20. Risk Assessment of Maize Drought Disaster in Agro-Pastoral Transitional Zone in North China

    Jia, H.; Pan, D.

    2017-12-01

    Agricultural drought is one of the focuses of global concern and one of the natural disasters that affect the agriculture production mostly in China. Farming-pastoral zones in China are located in the monsoon fringe area, precipitation of which is extremely unstable, and drought occurs frequently. The agro-pastoral transitional zone in North China is one of the main producing areas of northern spring maize in northern China, and maize is the second largest grain crop in the region. An assessment of the risk of drought disaster in this region is therefore important in ensuring a reduction in such disasters and an increase in food security. A risk assessment model, EPIC (Environmental Policy Integrated Climate) model, for maize drought disasters based on the Erosion Productivity Impact Calculator crop model is proposed for areas with the topographic characteristics of agro-pastoral transitional zone in North China. The results showed that the hazard risk level for the maize zone of agro-pastoral transitional zone in North China is generally high. Most hazard index values were between 0.4 and 0.5, accounting for 48.77% of total study area. The high-risk areas were mainly distributed in Ordos Plateau (South of Inner Mongolia Autonomous region), South of Ningxia Hui Autonomous Region and Center of Gansu Province. These results provide a scientific basis and support for the reduction of agricultural drought disasters and an increase in food security in the agro-pastoral transitional zone in North China.

  1. Fatigue Failure Modes of the Grain Size Transition Zone in a Dual Microstructure Disk

    Gabb, Timothy P.; Kantzos, Pete T.; Palsa, Bonnie; Telesman, Jack; Gayda, John; Sudbrack, Chantal K.

    2012-01-01

    Mechanical property requirements vary with location in nickel-based superalloy disks. In order to maximize the associated mechanical properties, heat treatment methods have been developed for producing tailored grain microstructures. In this study, fatigue failure modes of a grain size transition zone in a dual microstructure disk were evaluated. A specialized heat treatment method was applied to produce varying grain microstructure in the bore to rim portions of a powder metallurgy processed nickel-based superalloy disk. The transition in grain size was concentrated in a zone of the disk web, between the bore and rim. Specimens were extracted parallel and transversely across this transition zone, and multiple fatigue tests were performed at 427 C and 704 C. Grain size distributions were characterized in the specimens, and related to operative failure initiation modes. Mean fatigue life decreased with increasing maximum grain size, going out through the transition zone. The scatter in limited tests of replicates was comparable for failures of uniform gage specimens in all transition zone locations examined.

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

    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. Slab Penetration vs. Slab Stagnation: Mantle Reflectors as an Indicator

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

    2011-12-01

    Subducting oceanic lithosphere along convergent margins may stagnate near the base of the upper mantle or penetrate into the lower mantle. These dynamic processes cause extensive thermal and compositional variations, which can be observed in terms of impedance contrast (reflectivity) and topography of mantle transition zone (MTZ) discontinuities, i.e., 410- and 660-km discontinuities. In this study, we utilize ~ 15000 surface-reflected shear waves (SS) and their precursory arrivals (S410S and S660S) to analyze subduction related deformations on mantle reflectivity structure. We apply pre-stack, time-to-depth migration technique to SS precursors, and move weak underside reflections using PREM-predicted travel-time curves. Common Mid-point gathers are formed to investigate structure under the western Pacific, south America, and Mediterranean convergent boundaries. In general, mantle reflectivity structures are consistent with previous seismic tomography models. In regions of slab penetration (e.g., southern Kurile arc, Aegean Sea), our results show 1) a substantial decrease in S660S amplitude, and 2) strong lower mantle reflector(s) at ~ 900 km depth. These reflective structures are supported by zones of high P and S velocities extending into the lower mantle. Our 1-D synthetic simulations suggest that the decreasing S660S amplitudes are, at least partially, associated with shear wave defocusing due to changes in reflector depth (by ±20 km) within averaging bin. Assuming a ~500 km wide averaging area, a dipping reflector with 6-8 % slope can reduce the amplitude of a SS precursor by ~50%. On the other hand, broad depressions with strong impedance contrast at the base of the MTZ characterize the regions of slab stagnation, such as beneath the Tyrrhenian Sea and northeastern China. For the latter region, substantial topography on the 660-km discontinuity west of the Wadati-Benioff zone suggests that the stagnant part of the Pacific plate across Honshu arc is not

  4. Phase transition and thermal equations of state of (Fe,Al)-bridgmanite and post-perovskite: Implication for the chemical heterogeneity at the lowermost mantle

    Sun, Ningyu; Wei, Wei; Han, Shunjie; Song, Junhao; Li, Xinyang; Duan, Yunfei; Prakapenka, Vitali B.; Mao, Zhu

    2018-05-01

    In this study, we have determined the phase boundary between Mg0.735Fe0.21Al0.07Si0.965O3-Bm and PPv and the thermal equations of state of both phases up to 202 GPa and 2600 K using synchrotron X-ray diffraction in laser heated diamond anvil cells. Our experimental results have shown that the combined effect of Fe and Al produces a wide two-phase coexistence region with a thickness of 26 GPa (410 km) at 2200 K, and addition of Fe lowers the onset transition pressure to 98 GPa at 2000 K, consistent with previous experimental results. Furthermore, addition of Fe was noted to reduce the density (ρ) and bulk sound velocity (VΦ) contrasts across the Bm-PPv phase transition, which is in contrast to the effect of Al. Using the obtained phase diagram and thermal equations of state of Bm and PPv, we have also examined the effect of composition variations on the ρ and VΦ profiles of the lowermost mantle. Our modeling results have shown that the pyrolitic lowermost mantle should be highly heterogeneous in composition and temperature laterally to match the observed variations in the depth and seismic signatures of the D″ discontinuity. Normal mantle in a pyrolitic composition with ∼10% Fe and Al in Bm and PPv will lack clear seismic signature of the D″ discontinuity because the broad phase boundary could smooth the velocity contrast between Bm and PPv. On the other hand, Fe-enriched regions close to the cold slabs may show a seismic signature with a change in the velocity slope of the D″ discontinuity, consistent with recent seismic observations beneath the eastern Alaska. Only regions depleted in Fe and Al near the cold slabs would show a sharp change in velocity. Fe in such regions could be removed to the outer core by strong core-mantle interactions or partitions together with Al to the high-pressure phases in the subduction mid ocean ridge basalts. Our results thus have profound implication for the composition of the lowermost mantle.

  5. Transit and radial velocity survey efficiency comparison for a habitable zone Earth

    Burke, Christopher J.; McCullough, P. R.

    2014-01-01

    Transit and radial velocity searches are two techniques for identifying nearby extrasolar planets to Earth that transit bright stars. Identifying a robust sample of these exoplanets around bright stars for detailed atmospheric characterization is a major observational undertaking. In this study we describe a framework that answers the question of whether a transit or radial velocity survey is more efficient at finding transiting exoplanets given the same amount of observing time. Within the framework we show that a transit survey's window function can be approximated using the hypergeometric probability distribution. We estimate the observing time required for a transit survey to find a transiting Earth-sized exoplanet in the habitable zone (HZ) with an emphasis on late-type stars. We also estimate the radial velocity precision necessary to detect the equivalent HZ Earth-mass exoplanet that also transits when using an equal amount of observing time as the transit survey. We find that a radial velocity survey with σ rv ∼ 0.6 m s –1 precision has comparable efficiency in terms of observing time to a transit survey with the requisite photometric precision σ phot ∼ 300 ppm to find a transiting Earth-sized exoplanet in the HZ of late M dwarfs. For super-Earths, a σ rv ∼ 2.0 m s –1 precision radial velocity survey has comparable efficiency to a transit survey with σ phot ∼ 2300 ppm.

  6. Perception of the Transition Zones from Urban to Suburban Area Using Mobile Eye

    Paolo Magris

    2014-12-01

    Full Text Available Road users adjust their driving behavior based on the perception of the route and the surrounding environment. The eye-tracking technology allows interpreting the driver behavior, analyzing aspects otherwise not considered in the design stage. This technology has been used for transition zone analysis at town entrances along the SP 610 “Selice Montanara”, to verify the efficiency of gateway created to reduce the input speed in urban areas. Results show that the installation of traffic calming measures at transition zones leads to a change of the environment perception by drivers, and consequently safety increase.

  7. Childhood obesity in transition zones: an analysis using structuration theory.

    Chan, Christine; Deave, Toity; Greenhalgh, Trisha

    2010-07-01

    Childhood obesity is particularly prevalent in areas that have seen rapid economic growth, urbanisation, cultural transition, and commodification of food systems. Structuration theory may illuminate the interaction between population and individual-level causes of obesity. We conducted in-depth ethnographies of six overweight/obese and four non-overweight preschool children in Hong Kong, each followed for 12-18 months. Analysis was informed by Stones' strong structuration theory. Risk factors played out differently for different children as social structures were enacted at the level of family and preschool. The network of caregiving roles and relationships around the overweight/obese child was typically weak and disjointed, and the primary caregiver appeared confused by mixed messages about what is normal, expected and legitimate behaviour. In particular, external social structures created pressure to shift childcare routines from the logic of nurturing to the logic of consumption. Our findings suggest that threats to what Giddens called ontological security in the primary caregiver may underpin the poor parenting, family stress and weak mealtime routines that mediate the relationship between an obesogenic environment and the development of obesity in a particular child. This preliminary study offers a potentially transferable approach for studying emerging epidemics of diseases of modernity in transition societies.

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

    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.

  9. Analysis of the Dynamic Wheel Loads in Railway Transition Zones Considering the Moisture Condition of the Ballast and Subballast

    Haoyu Wang

    2017-11-01

    Full Text Available Transition zones in railway tracks are the locations with considerable changes in vertical support structures, e.g., near bridges. Due to possible water flow constrictions in transition zone structures, there is frequently an increased moisture level in the ballast/subballast layers, which is a potential source of track degradation. This paper presents results of the moisture condition measured in three transition zones using ground penetrating radar, where the ballast/subballast are analyzed. The relationship between the moisture condition and track degradation in the transition zones is studied by comparing it to the longitudinal track level that is measured by the track inspection coaches. A strong connection is found between the high moisture condition and track degradation in the transition zones. The dynamic behavior of the transition zones with high moisture condition is analyzed using the Finite Element method. Differential stiffness and settlement are taken into consideration in the transition zone model, which is also coupled with a vehicle. The ballast/subballast layers are modelled as solid elements. Increased moisture conditions are considered as a reduction of elastic modulus, according to laboratory findings. Results show that high moisture leads to an increase of dynamic wheel loads in the transition zone, which explains the connection and confirms that the high moisture condition is a source of transition zone problems.

  10. The Sorgenfrei-Tornquist Zone as the mantle edge of Baltica lithosphere: new evidence from three-dimensional seismic anisotropy

    Babuška, Vladislav; Plomerová, Jaroslava

    2004-01-01

    Roč. 16, č. 5 (2004), s. 243-249 ISSN 0954-4879 R&D Projects: GA AV ČR KSK3012103; GA ČR GA205/04/0748; GA AV ČR IAA3012405 Keywords : seismic experiment TOR * Trans-European Suture Zone * seismic anisotropy Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.059, year: 2004

  11. The influence of train running direction and track supports position on the behaviour of transition zones

    Sañudo Ortega, R.; Miranda Manzanares, M.; Markine, V.; Dell' Olio, L.

    2016-07-01

    Different types of track infrastructure can be found along railway lines. Separation zones between these different types of structures are the source of a lot of problems. Transition zones on a railway line represent a gradual solution for the problems between conventional railway structure and singular structures located at different points along the line. The different nature, positioning and geometry used with the materials generate changes in the stiffness on both sides of these singular zones leading to an increase in wear and a loss of geometry, with the associated maintenance costs. This article describes the use of mathematical modelling to represent the behaviour of these zones as a function of train running direction and track supports. Available research into transition zones has not studied these separation points where high increases in load are generated for very short periods of time. Finite elements are used to model two types of track (conventional ballasted track and slab track), using a vehicle to dynamically simulate the behaviour in these zones as a function of train running direction and the position of track supports. The magnitudes analysed were the vertical stresses and the vertical displacements under the sleepers and the supports in both types of structure. The results show increased stresses at the separation zone between both structures which varied in magnitude and position depending most of track supports’ location than the train running direction. (Author)

  12. Mantle Upwellings Below the Ibero-Maghrebian Region with a Common Deep Source from P Travel-time Tomography

    Civiero, C.; Custodio, S.; Silveira, G. M.; Rawlinson, N.; Arroucau, P.

    2017-12-01

    The processes responsible for the geodynamical evolution of the Ibero-Maghrebian domain are still enigmatic. Several geophysical studies have improved our understanding of the region, but no single model has been accepted yet. This study takes advantage of the dense station networks deployed from France in the north to Canary Islands and Morocco in the south to provide a new high-resolution P-wave velocity model of the structure of the upper-mantle and top of the lower mantle. These images show subvertical small-scale upwellings below Atlas Range, Canary Islands and Central Iberia that seem to cross the transition zone. The results, together with geochemical evidence and a comparison with previous global tomographic models, reveal the ponding or flow of deep-plume material beneath the transition zone, which seems to feed upper-mantle "secondary" pulses. In the upper mantle the plumes, in conjunction with the subduction-related upwellings, allow the hot mantle to rise in the surrounding zones. During its rising, the mantle interacts with horizontal SW slab-driven flow which skirts the Alboran slab and connects with the mantle upwelling below Massif Central through the Valencia Trough rift.

  13. Formation and modification of chromitites in the mantle

    Arai, Shoji; Miura, Makoto

    2016-11-01

    Podiform chromitites have long supplied us with unrivaled information on various mantle processes, including the peridotite-magma reaction, deep-seated magmatic evolution, and mantle dynamics. The recent discovery of ultrahigh-pressure (UHP) chromitites not only sheds light on a different aspect of podiform chromitites, but also changes our understanding of the whole picture of podiform chromitite genesis. In addition, new evidence was recently presented for hydrothermal modification/formation chromite/chromitite in the mantle, which is a classical but innovative issue. In this context, we present here an urgently needed comprehensive review of podiform chromitites in the upper mantle. Wall-rock control on podiform chromitite genesis demonstrates that the peridotite-magma reaction at the upper mantle condition is an indispensable process. We may need a large system in the mantle, far larger than the size of outcrops or mining areas, to fulfill the Cr budget requirement for podiform chromitite genesis. The peridotite-magma reaction over a large area may form a melt enriched with Na and other incompatible elements, which mixes with a less evolved magma supplied from the depth to create chromite-oversaturated magma. The incompatible-element-rich magma trapped by the chromite mainly precipitates pargasite and aspidolite (Na analogue of phlogopite), which are stable under upper mantle conditions. Moderately depleted harzburgites, which contain chromite with a moderate Cr# (0.4-0.6) and a small amount of clinopyroxene, are the best reactants for the chromitite-forming reaction, and are the best hosts for podiform chromitites. Arc-type chromitites are dominant in ophiolites, but some are of the mid-ocean ridge type; chromitites may be common beneath the ocean floor, although it has not yet been explored for chromitite. The low-pressure (upper mantle) igneous chromitites were conveyed through mantle convection or subduction down to the mantle transition zone to form

  14. Study on microstructure of transition zone and its strong contrast of single T700 carbon fibers

    Guo, Xinshuang; Zhang, Kexiang [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Fan, Zhen; Feng, Zhihai [National Key Laboratory of Advanced Functional Composite Materials, Aerospace Research Institute of Materials and Processing Technology, Beijing 100076 (China); He, LianLong, E-mail: llhe@imr.ac.cn [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China)

    2017-06-01

    Highlights: • The transition zone of T700 carbon fiber was first identified with higher density in addition to higher orientation. • The higher sample density still existed while the higher orientation disappeared after heat treatment at 2800 °C. • The strong contrast of the transition zone mainly results from its higher density. • The transition zone with higher density and orientation may exist not only in the T700 but other PAN-based carbon fibers. - Abstract: The transition zone (TZ) between the skin and core of Toray T700 carbon fiber was investigated by transmission electron microscopy. The higher basal-plane orientation was identified in the TZ compared with the skin and core, but it disappeared after heat treatment at 2800 °C. Plasmon peak energy in the TZ was higher than that in the skin and core about 0.7–0.8 eV, indicating the TZ with higher density. No element concentration existed in the TZ. The TZ with strong contrast manifests itself before and after heat treatment, and formation mechanism of its strong contrast was proposed.

  15. Cilium transition zone proteome reveals compartmentalization and differential dynamics of ciliopathy complexes

    Dean, S.; Moreira-Leite, F.; Varga, Vladimír; Gull, K.

    2016-01-01

    Roč. 113, č. 35 (2016), E5135-E5143 ISSN 0027-8424 Institutional support: RVO:68378050 Keywords : transition zone * cilium/flagellum * BBSome * MKS/B9 complex * trypanosome Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 9.661, year: 2016

  16. Structural health monitoring of railway transition zones using satellite radar data

    Wang, Haoyu; Chang, L.; Markine, V.L.

    2018-01-01

    Transition zones in railway tracks are locationswith considerable changes in the rail-supporting structure. Typically, they are located near engineering structures, such as bridges, culverts and tunnels. In such locations, severe differential settlements often occur due to the different material

  17. Select transition zone prostate cancers may be radiocurable despite markedly elevated prostate-specific antigen levels

    D'Amico, Anthony V.; Kaplan, Irving

    1996-01-01

    In 1993, three men with transition zone prostate cancers were described (Stamey et al., J. Urol. 149: 510-515, 1993) who despite high prostate-specific antigen (PSA) levels remained PSA failure-free at 22 months postoperatively. This report illustrates that prolonged PSA failure free survival may be achieved when external beam radiation therapy is used to treat similar patients

  18. Household vulnerability and small ruminant benefits in transitional zone of Ghana

    Duku, S.; Zijpp, van der A.J.; Udo, H.M.J.

    2012-01-01

    This study investigated household vulnerability and small ruminant benefits in the transitional zone of Ghana. The dimensions of vulnerability considered were the sex and socio-economic status of the household head, and household morbidity and mortality. Data was collected from 11 key informants,

  19. Improvement of train-track interaction in transition zones via reduction of ballast damage

    Wang, H.; Markine, V.L.; Dollevoet, R.P.B.J.; Shevtsov, I.Y.

    2015-01-01

    Transition zones in railway tracks are locations with considerable changes in the vertical stiffness of the rail support. Typically they are located near engineering structures, such as bridges, culverts, tunnels and level crossings. In such locations, the differential settlement always exists and

  20. Long-rod penetration: the transition zone between rigid and hydrodynamic penetration modes

    Jian-feng Lou

    2014-06-01

    Full Text Available Long-rod penetration in a wide range of velocity means that the initial impact velocity varies in a range from tens of meters per second to several kilometers per second. The long rods maintain rigid state when the impact velocity is low, the nose of rod deforms and even is blunted when the velocity gets higher, and the nose erodes and fails to lead to the consumption of long projectile when the velocity is very high due to instantaneous high pressure. That is, from low velocity to high velocity, the projectile undergoes rigid rods, deforming non-erosive rods, and erosive rods. Because of the complicated changes of the projectile, no well-established theoretical model and numerical simulation have been used to study the transition zone. Based on the analysis of penetration behavior in the transition zone, a phenomenological model to describe target resistance and a formula to calculate penetration depth in transition zone are proposed, and a method to obtain the boundary velocity of transition zone is determined. A combined theoretical analysis model for three response regions is built by analyzing the characteristics in these regions. The penetration depth predicted by this combined model is in good agreement with experimental result.

  1. 210Pb sediment dating in coastal transition zones: tropical saltmarshes.

    Ruiz-Fernandez, A. C.; Sanchez-Cabeza, J. A.; Carnero-Bravo, V.; Perez-Bernal, L. H.

    2016-12-01

    Sea level rise (SLR) is one of the climate change effects expected to have the largest impact on coastal environments. SLR rates are not uniform around the planet and, therefore, local and regional data and trends are needed for proper adaptation plans. As long term monitoring stations of SLR are very scarce in most of the world, SLR trends obtained from 210Pb-dated sediment cores from tropical saltmarshes have become a practical alternative to obtain SLR trends within the past century, under the assumption that these ecosystems accrete at a similar rate to SLR. However, tropical saltmarshes are challenging environments for 210Pb dating: they are regularly dry, intermittently covered by seawater only during the highest tides, and sedimentary records often reflect the transition between terrestrial and marine environments (e.g. changes in grain size distribution, organic matter content and elemental composition) with all these factors contributing for atypical 210Pb depth profiles. In addition, 137Cs, the chronostratigraphic marker most commonly used to corroborate 210Pb dating, fails to be preserved in the sedimentary record in tropical areas, owing to its solubility in marine waters, if at all detectable. The present study describes the challenges and proposed solutions for 210Pb dating saltmarsh sediment cores from two saltmarsh areas (southern Gulf of California and Yucatan Peninsula) including the use of plutonium isotopes for corroboration purposes. Acknowledgements: projects CONACYT CB2010/153492 and PDCPN201301/214349; UNAM PAPIIT-IN203313 and the PRODEP network "Aquatic contamination: levels and effects" (year 3).

  2. Density structure of the cratonic mantle in southern Africa

    Artemieva, Irina; Vinnik, Lev P.

    2016-01-01

    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...... that mantle residual (dynamic) topography may be associated with the low-density region below the depth of isostatic compensation. A possible candidate is the low velocity layer between the lithospheric base and the mantle transition zone, where a temperature anomaly of 100-200. °C in a ca. 100-150. km thick...... layer may explain the observed reduction in Vs velocity and may produce ca. 0.5-1.0. km to the regional topographic uplift....

  3. Diffusion-weighted magnetic resonance imaging in the prostate transition zone: histopathological validation using magnetic resonance-guided biopsy specimens

    Hoeks, C.M.A.; Vos, E.K.; Bomers, J.G.R.; Barentsz, J.O.; Kaa, C.A. van de; Scheenen, T.W.J.

    2013-01-01

    OBJECTIVES: The objective of this study was to evaluate the apparent diffusion coefficient (ADC) of diffusion-weighted magnetic resonance (MR) imaging for the differentiation of transition zone cancer from non-cancerous transition zone with and without prostatitis and for the differentiation of

  4. Mantle-cell lymphoma.

    Barista, I; Romaguera, J E; Cabanillas, F

    2001-03-01

    During the past decade, mantle-cell lymphoma has been established as a new disease entity. The normal counterparts of the cells forming this malignant lymphoma are found in the mantle zone of the lymph node, a thin layer surrounding the germinal follicles. These cells have small to medium-sized nuclei, are commonly indented or cleaved, and stain positively with CD5, CD20, cyclin D1, and FMC7 antibodies. Because of its morphological appearance and a resemblance to other low-grade lymphomas, many of which grow slowly, this lymphoma was initially thought to be an indolent tumour, but its natural course was not thoroughly investigated until the 1990s, when the BCL1 oncogene was identified as a marker for this disease. Mantle-cell lymphoma is a discrete entity, unrelated to small lymphocytic or small-cleaved-cell lymphomas.

  5. Seismic investigation of an ocean-continent transition zone in the northern South China Sea

    Zhu, J.; Qiu, X.; Xu, H.; Zhan, W.; Sun, Z.

    2011-12-01

    Rifted continental margins and basins are mainly formed by the lithospheric extension. Thined lithosphere of passive continental margins results in decompression melt of magma and created oceanic crust and thined ocean-continent transition (OCT) zone. Two refraction profiles used ocean bottom seismometers deployed in the broad continental shelf and three multi-channel seismic reflection lines in the northern South China Sea, acquired by the ship "Shiyan 2" of the South China Sea Institute of Oceanology, Chinese Academy of Sciences in 2010, are processed and interpreted in this study. Seismic reflection lines cut through the Dongsha rise, Zhu-1 and Zhu-2 depression within a Tertiary basin, Pear River Mouth basin (called as Zhujiangkou basin). These tectonic features are clear imaged in the seismic reflection records. Numerous normal faults, cutted through the basement and related to the stretch of the northern South China Sea margin, are imaged and interpreted. Reflection characteristics of the ocean-continent transition (OCT) zone are summaried and outlined. The COT zone is mainly divided into the northern syn-rift subsidence zone, central volcano or buried volcano uplift zone and tilt faulted block near the South Chia Sea basin. Compared to the previous seismic reflection data and refraction velocity models, the segmentation range of the OCT zone is outlined, from width of about 225 km in the northeastern South China Sea , of 160 km in the central to of 110 km in the north-central South China Sea. Based on the epicenter distribution of sporadic and large than 6 magnitude earthquakes, it suggests the OCT zone in the northern South China Sea at present is still an active seismic zone.

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

    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

  7. Three-dimensional Seismic Survey of the Continental-Ocean Transition Zone of the Northern South China Sea

    Zhao, M.; Wang, Q.; Sibuet, J. C.; Sun, L.; Sun, Z.; Qiu, X.

    2017-12-01

    91428204, 41576070 and 41176053). Key words: Continental-ocean transition zone (COT); 3D refraction survey; IODP Expeditions 367/368; nature of crust.

  8. Diverse, discrete, mantle-derived batches of basalt erupted along a short normal fault zone: The Poison Lake chain, southernmost Cascades

    Muffler, L.J.P.; Clynne, M.A.; Calvert, A.T.; Champion, D.E.

    2011-01-01

    The Poison Lake chain consists of small, monogenetic, calc-alkaline basaltic volcanoes located east of the Cascade arc axis, 30 km ENE of Lassen Peak in northeastern California. This chain consists of 39 distinguishable units in a 14-km-long and 2-kmwide zone trending NNW, parallel to nearby Quaternary normal faults. The 39 units fall into nine coherent groups based on stratigraphy, field characteristics, petrography, and major-element compositions. Petrographic differences among groups are expressed by different amounts and proportions of phenocrysts. MgO-SiO 2, K 2O-SiO 2, and TiO 2-SiO 2 variation diagrams illustrate clear differences in compatible and incompatible elements among the groups. Variation of K 2O/ TiO 2 and K 2O/P 2O 5 with MgO indicates that most of the basalts of the Poison Lake chain cannot be related by crystal fractionation at different pressures and that compositions have not been affected significantly by incorporation of low-degree silicic crustal melt or interaction with sialic crust. Limited traceelement and whole-rock isotopic data also suggest little if any incorporation of uppercrustal material, and that compositional variation among groups primarily reflects source compositional differences. Precise 40Ar/ 39Ar determinations show that the lavas were erupted between 100 and 110 ka. The migration of paleomagnetic remanent directions over 30?? suggests that the entire Poison Lake chain could represent three short-lived episodes of volcanism within a period as brief as 500 yr. The diverse geologic, petrographic, chemical, paleomagnetic, and age data indicate that each of the nine groups represents a small, discrete magma batch generated in the mantle and stored briefly in the lower crust. A NNW normal fault zone provided episodic conduits that allowed rapid ascent of these batches to the surface, where they erupted as distinct volcanic groups, each aligned along a segment of the Poison Lake chain. Compositional diversity of these primitive

  9. Dynamics of baroclinic wave pattern in transition zones between different flow regimes

    Larcher, Thomas von; Egbers, Christoph

    2005-01-01

    Baroclinic waves, both steady and time-dependent, are studied experimentally in a differentially heated rotating cylindrical gap with a free surface, cooled from within. Water is used as working fluid. We focus especially on transition zones between different flow regimes, where complex flow pattern like mixed-mode states are found. The transition from steady wave regime to irregular flow is also of particular interest. The surface flow is observed with visualisation techniques. Velocity time series are measured with the optical laser-Doppler-velocimetry technique. Thermographic measurements are applied for temperature field visualisations

  10. Upper Mantle Discontinuities Underneath Central and Southern Mexico

    Perez-Campos, X.; Clayton, R. W.

    2011-12-01

    Central and southern Mexico are affected by the subduction of Cocos plate beneath North American plate. The MesoAmerican Subduction Experiment (MASE) and the Veracruz-Oaxaca (VEOX) project have mapped the geometry of the Cocos slab. It is characterized in central Mexico by a shallow horizontal geometry up to ~300 km from the trench, then it dives steeply (70°) into the mantle, to its apparent end at 500 km depth. In contrast, some 400 km to the south, the slab subducts smoothly, with a dip angle of ~26° to a depth of 150 km. We use receiver functions from teleseismic events, recorded at stations from MASE, VEOX, and the Servicio Sismológico Nacional (SSN, Mexican National Seismological Service) to map the upper mantle discontinuities and properties of the transition zone in central and southern Mexico. We also use data from the Mapping the Rivera Subduction Zone (MARS) Experiment to get a complete picture of the subduction regime in central Mexico and compare the mantle transition zone in a slab tear regime. The 410 discontinuity shows significant variation in topography in central Mexico, particularly where the slab is expected to reach such depth. The 660 discontinuity shows a smoother topography, indicating that the slab does not penetrate this far down. The results will be compared with a ridge regime in the Gulf of California.

  11. Observations of solar flare transition zone plasmas from the Solar Maximum Mission

    Cheng, C.-C.; Bruner, E. C.; Tandberg-Hanssen, E.; Woodgate, B. E.; Shine, R. A.; Kenny, P. J.; Henze, W.; Poletto, G.

    1982-01-01

    The spatial and temporal evolution of the Si IV and O IV intensity, density and mass motions in preflare and flare transition zone plasmas are studied for the case of the April 8, 1980 flare. It is found that: (1) the UV flare observed in the Si IV and O IV lines is unambiguously identified as occurring in a low-lying, preexisting transition zone loop which spanned the magnetic neutral line separating a larger leader spot and a newly emerged, isolated spot of opposite polarity; (2) at the onset of the flare, the easternmost footpoint, which was anchored in an isolated spot region of high longitudinal magnetic field gradient, showed sudden, impulsive brightening with large intensity increases; and (3) the release flare energy was transported by way of large-scale connecting field lines to other parts of the active region, producing the hot plasma and H-alpha kernels observed near the trailing spot.

  12. Changes in melatonin secretion in tourists after rapid movement to another lighting zone without transition of time zone.

    Wieczorek, Joanna; Blazejczyk, Krzysztof; Morita, Takeshi

    2016-01-01

    Most of the research in the field of Chronobiology is focused on the problem of the circadian rhythms (CR) desynchronization. In travelers, it results mostly from the changes of surrounding: photoperiod, local climate conditions (radiation and thermal load) and behavior (e.g. type and place of tourism and activity level). Until now, it was not documented whether the changes in melatonin (MLT) secretion occur in effect of mid-distance transparallel travels (TpT), without complications arising due to time-zone transitions (e.g. jet-lag syndrome). To cope with this problem, a special field experiment was carried out. In the experiment, MLT characteristics were examined twice a year in real conditions through a group of young tourists (23-26 years old) at their place of habitual residence (Warsaw, Poland), and at their tourist destination (Tromso, Norway). Transition to circumpolar zone in summer has resulted in insignificant reduction in melatonin peak value (MPV) compared to preflight control (2 days before travel) and the melatonin peak time (MPT) was delayed. However, after traveling southward on the returning flight, MPV was lower compared to control and MPT was advanced. In winter, MPV was insignificantly higher in comparison to preflight control and MPT was almost unchanged. While changes in MPV do not depend on season, flight direction and day of stay after flight than MPT was differentiated seasonally and due to direction of flight. MPV and MPT were significantly modified by characteristics of individual light exposure during daytime and evening. The experiment showed also that in real conditions activity level is an important factor affected melatonin peak in tourists. In winter, greater daytime activity significantly influenced earlier MPT occurrence, both after northward and southward flights.

  13. Deep Subducction in a Compressible Mantle: Observations and Theory

    King, S. D.

    2017-12-01

    Our understanding of slab dynamics is primarily based on the results of numerical models of subduction. In such models coherent, cold slabs are clearly visible from the surface of the Earth to the core mantle boundary. In contrast, fast seismic anomalies associated with cold subducted slabs are difficult to identify below 1500-2000 km in tomographic models of Earth's mantle. One explanation for this has been the resolution, or lack thereof, of seismic tomography in the mid-mantle region; however in this work I will explore the impact of compressibility on the dynamics of subducting slabs, specifically shear heating of the slab and latent heat of phase transformations. Most geodynamic models of subduction have used an incompressible formulation, thus because subducted slabs are assumed to be cold and stiff, the primary means of thermal equilibration is conduction. With an assumed sinking velocity of approximately 0.1 m/yr, a subducted slab reaches the core-mantle boundary in approximately 30 Myrs—too fast for significant conductive cooling of the downgoing slab. In this work I consider a whole-mantle geometry and include both phase transformations with associated latent heat and density changes from the olivine-wadsleyite-ringwoodite-bridgmanite system and the pyroxene-garnet system. The goal of this work is to understand both the eventual fate and thermal evolution of slabs beneath the transition zone.

  14. Mineralogy of the Hydrous Lower Mantle

    Shim, S. H.; Chen, H.; Leinenweber, K. D.; Kunz, M.; Prakapenka, V.; Bechtel, H.; Liu, Z.

    2017-12-01

    The hydrous ringwoodite inclusions found in diamonds suggest water storage in the mantle transition zone. However, water storage in the lower mantle remains unclear. Bridgmanite and magnesiowustite appear to have very little storage capacity for water. Here, we report experimental results indicating significant changes in the lower-mantle mineralogy under the presence of water. We have synthesized Mg2SiO4 ringwoodite with 2 wt% water in multi-anvil press at 20 GPa and 1573 K at ASU. The hydrous ringwoodite sample was then loaded to diamond anvil cells with Ar or Ne as a pressure medium. We heated the pure hydrous ringwoodite samples at lower-mantle pressure using a CO2 laser heating system at ASU. We measured X-ray diffraction patterns at the GSECARS sector of the Advanced Photon Source (APS) and 12.2.2 sector of the Advanced Light Source (ALS). For the separate Pt-mixed samples, we have conducted in situ heating at the beamlines using near IR laser heating systems. We measured the infrared spectra of the heated samples at high pressure and after pressure quench at 1.4.4 sector of ALS. In the in situ experiments with hydrous ringwoodite + Pt mixture as a starting material, we found formation of stishovite together with bridgmanite and periclase during heating with a near IR laser beams at 1300-2500 K and 35-66 GPa. However, some hydrous ringwoodite still remains even after a total of 45 min of heating. In contrast, the hydrous ringwoodite samples heated without Pt by CO2 laser beams are transformed completely to bridgmanite, periclase and stishovite at 31-55 GPa and 1600-1900 K. We have detected IR active OH mode of stishovite from the samples heated at lower-mantle pressures. The unit-cell volume of stishovite measured after pressure quench is greater than that of dry stishovite by 0.3-0.6%, supporting 0.5-1 wt% of H2O in stishovite in these samples. Stishovite is a thermodynamically forbidden phase in the dry lower mantle because of the existence of periclase and

  15. Dynamics of the transition zone in coastal zone color scanner-sensed ocean color in the North Pacific during oceanographic spring

    Glover, David M.; Wroblewski, J. S.; Mcclain, Charles R.

    1994-01-01

    A transition zone in phytoplankton concentration running across the North Pacific basin at 30 deg to 40 deg north latitude corresponds to a basin-wide front in surface chlorophyll observed in a composite of coastal zone color scanner (CZCS) images for May, June, and July 1979-1986. This transition zone with low chlorophyll to the south and higher chlorophyll to the north can be simulated by a simple model of the concentration of phytoplankton, zooplankton, and dissolved nutrient (nitrate) in the surface mixed layer of the ocean applied to the North Pacific basin for the climatological conditions during oceanographic springtime (May, June, and July). The model is initialized with a 1 deg x 1 deg gridded estimate of wintertime (February, March, and April) mixed layer nitrate concentrations calculated from an extensive nutrient database and a similarly gridded mixed layer depth data set. Comparison of model predictions with CZCS data provides a means of evaluating the dynamics of the transition zone. We conclude that in the North Pacific, away from major boundary currents and coastal upwelling zones, wintertime vertical mixing determines the total nutrient available to the plankton ecosystem in the spring. The transition zone seen in basin-scale CZCS images is a reflection of the geographic variation in the wintertime mixed layer depth and the nitracline, leading to a latitudinal gradient in phytoplankton chlorophyll.

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

    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.

  17. Small-scale spatial variability of phenoxy acid mineralization potentials in transition zones with a multidisciplinary approach

    Pazarbasi, Meric Batioglu

    The phenoxy acid group of herbicides is widely used to control broadleaf weeds, and it contaminates groundwater and surface water by leaching from agricultural soil or landfills. Due to the distinct vertical and horizontal gradients in nutrients and hydrologic exchange in transition zones...... in two transition zones, (1) the interfaces of unsaturated and saturated zones and (2) groundwater and surface water. Small-scale spatial variability of phenoxy acids was previously shown in topsoil; however, such small-scale studies are scarce in subsurface environments. We therefore studied the factors...... classes in the different mineralization potentials of discharge zones. Understanding of the natural attenuation potential of groundwater-surface water transition zones is important for stream water protection. In landfill-impacted groundwater-surface water interface, we further analyzed bacterial...

  18. Steady flows in the chromosphere and transition-zone above active regions as observed by OSO-8

    Lites, B. W.

    1980-01-01

    Two years of data from the University of Colorado ultraviolet spectrometer aboard OSO-8 were searched for steady line-of-sight flows in the chromosphere and transition-zone above active regions. The most conspicuous pattern that emerges from this data set is that many sunspots show persistent blueshifts of transition-zone lines indicating velocities of about 20 km/s with respect to the surrounding plage areas. The data show much smaller shifts in ultraviolet emission lines arising from the chromosphere: the shifts are frequently to the blue, but sometimes redshifts do occur. Plage areas often show a redshift of the transition-zone lines relative to the surrounding quiet areas, and a strong gradient of the vertical component of the velocity is evident in many plages. One area of persistent blueshift was observed in the transition-zone above an active region filament. The energy requirement of these steady flows over sunspots is discussed.

  19. Does the "mantle" helium signature provide useful information about lithospheric architecture of Tibet/Himalaya?

    Klemperer, S. L.; Liu, T.; Hilton, D. R.; Karlstrom, K. E.; Crossey, L. J.; Zhao, P.

    2015-12-01

    Measurements of 3He/4He > 0.1*Ra (where Ra = 3He/4He in Earth's atmosphere) in geothermal fluids are conventionally taken to represent derivation from a mantle source. 3He/4He values 0.1*Ra may still be argued to result from mantle-derived 3He previously stored in the crust. However, our growing regional database of widely spaced observations of 3He/4He > 0.1*Ra, from the Karakoram Fault in the west to the Sangri-Cona rift and Yalaxiangbo Dome in the east, and from south of the Yarlung-Zangbo suture (YZS) to north of the Banggong-Nujiang suture, makes such special pleading increasingly implausible. The observation of 3He/4He > 0.1*Ra at the YZS and even within the Tethyan Himalaya south of the YZS cannot represent melting of Indian mantle close to the Moho unless existing thermal models are grossly in error. The source of 3He close to the YZS is likely either asthenosphere accessed by faults and shear zones that cut through subducting Indian lithospheric mantle; or incipient melt of Asian lithospheric mantle at the Moho north of the northern edge of underthrust India (the "mantle suture") which must therefore lie close to the YZS. Thus far we have barely tapped the rich potential that helium-isotope data offer for understanding transit of mantle volatiles through some of Earth's thickest (and ductilely flowing) crust.

  20. An anisotropic shear velocity model of the Earth's mantle using normal modes, body waves, surface waves and long-period waveforms

    Moulik, P.; Ekström, G.

    2014-12-01

    We use normal-mode splitting functions in addition to surface wave phase anomalies, body wave traveltimes and long-period waveforms to construct a 3-D model of anisotropic shear wave velocity in the Earth's mantle. Our modelling approach inverts for mantle velocity and anisotropy as well as transition-zone discontinuity topographies, and incorporates new crustal corrections for the splitting functions that are consistent with the non-linear corrections we employ for the waveforms. Our preferred anisotropic model, S362ANI+M, is an update to the earlier model S362ANI, which did not include normal-mode splitting functions in its derivation. The new model has stronger isotropic velocity anomalies in the transition zone and slightly smaller anomalies in the lowermost mantle, as compared with S362ANI. The differences in the mid- to lowermost mantle are primarily restricted to features in the Southern Hemisphere. We compare the isotropic part of S362ANI+M with other recent global tomographic models and show that the level of agreement is higher now than in the earlier generation of models, especially in the transition zone and the lower mantle. The anisotropic part of S362ANI+M is restricted to the upper 300 km in the mantle and is similar to S362ANI. When radial anisotropy is allowed throughout the mantle, large-scale anisotropic patterns are observed in the lowermost mantle with vSV > vSH beneath Africa and South Pacific and vSH > vSV beneath several circum-Pacific regions. The transition zone exhibits localized anisotropic anomalies of ˜3 per cent vSH > vSV beneath North America and the Northwest Pacific and ˜2 per cent vSV > vSH beneath South America. However, small improvements in fits to the data on adding anisotropy at depth leave the question open on whether large-scale radial anisotropy is required in the transition zone and in the lower mantle. We demonstrate the potential of mode-splitting data in reducing the trade-offs between isotropic velocity and

  1. Hydration-reduced lattice thermal conductivity of olivine in Earth's upper mantle.

    Chang, Yun-Yuan; Hsieh, Wen-Pin; Tan, Eh; Chen, Jiuhua

    2017-04-18

    Earth's water cycle enables the incorporation of water (hydration) in mantle minerals that can influence the physical properties of the mantle. Lattice thermal conductivity of mantle minerals is critical for controlling the temperature profile and dynamics of the mantle and subducting slabs. However, the effect of hydration on lattice thermal conductivity remains poorly understood and has often been assumed to be negligible. Here we have precisely measured the lattice thermal conductivity of hydrous San Carlos olivine (Mg 0.9 Fe 0.1 ) 2 SiO 4 (Fo90) up to 15 gigapascals using an ultrafast optical pump-probe technique. The thermal conductivity of hydrous Fo90 with ∼7,000 wt ppm water is significantly suppressed at pressures above ∼5 gigapascals, and is approximately 2 times smaller than the nominally anhydrous Fo90 at mantle transition zone pressures, demonstrating the critical influence of hydration on the lattice thermal conductivity of olivine in this region. Modeling the thermal structure of a subducting slab with our results shows that the hydration-reduced thermal conductivity in hydrated oceanic crust further decreases the temperature at the cold, dry center of the subducting slab. Therefore, the olivine-wadsleyite transformation rate in the slab with hydrated oceanic crust is much slower than that with dry oceanic crust after the slab sinks into the transition zone, extending the metastable olivine to a greater depth. The hydration-reduced thermal conductivity could enable hydrous minerals to survive in deeper mantle and enhance water transportation to the transition zone.

  2. Hydrometer in the mantle: dln(Vs)/dln(Vp)

    Li, L.; Weidner, D. J.

    2010-12-01

    The absorption of water into nominally non-hydrous phases is the probable storage mechanism of hydrogen throughout most of the mantle. Thus the water capacity in the mantle is greatest in the transition zone owing to the large water-solubility of ringwoodite and wadsleyite. However, the actual amount of water that is stored there is highly uncertain. Since water is probably brought down by subduction activity, it’s abundance is probably laterally variable. Thus, a metric that is sensitive to variations of water content are good candidates for hydrometers. Here we evaluate the parameter, dln(Vs)/dln(Vp), as such a parameter. It is useful to detect lateral variations of water if the effects of hydration on the parameter are different than those of temperature or composition. We compare the value of dln(Vs)/dln(Vp) due to the temperature with that due to the water content as a function of depth for the upper mantle. We have calculated dln(Vs)/dln(Vp) due to both water and temperature using a density functional theory approach, and available experimental data. Our results indicate that dln(Vs)/dln(Vp) due to water is distinguishable from dln(Vs)/dln(Vp) due to temperature or variations in iron content, particularly in ringwoodite. The difference increases with depth and making the lower part of the transition zone most identifiable as a water reservoir.

  3. Identifying the transition to the maturation zone in three ecotypes of Arabidopsis thaliana roots.

    Cajero Sánchez, Wendy; García-Ponce, Berenice; Sánchez, María de la Paz; Álvarez-Buylla, Elena R; Garay-Arroyo, Adriana

    2018-01-01

    The Arabidopsis thaliana (hereafter Arabidopsis) root has become a useful model for studying how organ morphogenesis emerge from the coordination and balance of cell proliferation and differentiation, as both processes may be observed and quantified in the root at different stages of development. Hence, being able to objectively identify and delimit the different stages of root development has been very important. Up to now, three different zones along the longitudinal axis of the primary root of Arabidopsis, have been identified: the root apical meristematic zone (RAM) with two domains [the proliferative (PD) and the transition domain (TD)], the elongation zone (EZ) and the maturation zone (MZ). We previously reported a method to quantify the length of the cells of the meristematic and the elongation zone, as well as the boundaries or transitions between the root domains along the growing part of the Arabidopsis root. In this study, we provide a more accurate criterion to identify the MZ. Traditionally, the transition between the EZ to the MZ has been established by the emergence of the first root-hair bulge in the epidermis, because this emergence coincides with cell maturation in this cell type. But we have found here that after the emergence of the first root-hair bulge some cells continue to elongate and we have confirmed this in three different Arabidopsis ecotypes. We established the limit between the EZ and the MZ by looking for the closest cortical cell with a longer length than the average cell length of 10 cells after the cortical cell closest to the epidermal cell with the first root-hair bulge in these three ecotypes. In Col-0 and Ws this cell is four cells above the one with the root hair bulge and, in the Ler ecotype, this cell is five cells above. To unambiguously identifying the site at which cells stop elongating and attain their final length and fate at the MZ, we propose to calculate the length of completely elongated cortical cells counting 10

  4. Mantle contribution and tectonic transition in the Aqishan-Yamansu Belt, Eastern Tianshan, NW China: Insights from geochronology and geochemistry of Early Carboniferous to Early Permian felsic intrusions

    Du, Long; Long, Xiaoping; Yuan, Chao; Zhang, Yunying; Huang, Zongying; Wang, Xinyu; Yang, Yueheng

    2018-04-01

    very low P2O5, indicating characteristics of I-type granites. They also have positive εNd(t) values (+2.22 to +2.34) and juvenile TDM2 ages (868-878 Ma), suggesting this pluton was also produced by partial melting of relatively young crustal source. Based on an isotopic mixing simulation, significant mantle contributions were added to the magma source of both the Early Carboniferous and the Early Permian felsic rocks. The mantle contribution changes from 60% in the Early Carboniferous to 75% in the Early Permian. The remarkably increasing of mantle materials in the magma source of the felsic rocks in the Aqishan-Yamansu belt was most likely induced by the tectonic transition from an Early Carboniferous continental arc to an Early Permian post-collisional extension environment.

  5. Abyssal and hydrated mantle wedge serpentinised peridotites: a comparison of the 15°20'N fracture zone and New Caledonia serpentinites

    Mothersole, Fiona Elizabeth; Evans, Katy; Frost, B. Ronald

    2017-08-01

    Subduction of serpentinised mantle transfers oxidised and hydrated mantle lithosphere into the Earth, with consequences for the oxidation state of sub-arc mantle and the genesis of arc-related ore deposits. The role of subducted serpentinised mantle lithosphere in earth system processes is uncertain because subduction fluxes are poorly constrained. Most subducted serpentinised mantle is serpentinised on the ocean floor settings. Yet this material is poorly represented in the literature because it is difficult to access. Large volumes of accessible serpentinite are available in ophiolite complexes, and most interpretations of subduction fluxes associated with ultramafic rocks are based on ophiolite studies. Seafloor and ophiolite serpentinisation can occur under different conditions, so it is necessary to assess if ophiolite serpentinites are a good proxy for seafloor serpentinites. Serpentinites sampled during ODP cruise 209 were compared with serpentinites from New Caledonia. The ODP209 serpentinites were serpentinised by modified seawater in a shallow hydrothermal seafloor setting. The New Caledonia serpentinites were serpentinised in a mantle wedge setting by slab-derived fluids, with possible contributions from oceanic serpentinisation and post-obduction serpentinisation. Petrological, whole rock and mineralogical analyses were combined to compare the two sample sets. Petrologically, the evolution of serpentinisation was close to identical in the two environments. However, more oxidised iron, Cl, S and C is present in serpentine from the ODP209 serpentinites relative to the New Caledonia serpentinites. Given these observations, the use of serpentinites from different geodynamic settings as a proxy for abyssal serpentinites from spreading settings must be undertaken with caution.

  6. The constructed catchment Chicken Creek as Critical Zone Observatory under transition

    Gerwin, Werner; Schaaf, Wolfgang; Elmer, Michael; Hinz, Christoph

    2014-05-01

    The constructed catchment Chicken Creek was established in 2005 as an experimental landscape laboratory for ecosystem research. The 6 ha area with clearly defined horizontal as well as vertical boundary conditions was left for an unrestricted primary succession. All Critical Zone elements are represented at this site, which allows the study of most processes occurring at the interface of bio-, pedo-, geo- and hydrosphere. It provides outstanding opportunities for investigating interactions and feedbacks between different evolving compartments during ecosystem development. The catchment is extensively instrumented since 2005 in order to detect transition stages of the ecosystem. Data recorded with a high spatial and temporal resolution include hydrological, geomorphological, pedological, limnological as well as biological parameters. In contrast to other Critical Zone Observatories, this site offers the unique situation of an early stage ecosystem with highly dynamic system properties. The first years of development were characterized by a fast formation of geomorphological structures due to massive erosion processes at the initially non-vegetated surface. Hydrological processes led to the establishment of a local groundwater body within 5 years. In the following years the influence of biological structures like vegetation patterns gained an increasing importance. Feedbacks between developing vegetation and e.g. hydrological features became more and more dominant. As a result, different phases of ecosystem development could be distinguished until now. This observatory offers manifold possibilities to identify and disentangle complex interactions between Critical Zone processes in situ under natural conditions. The originally low complexity of the system is growing with time facilitating the identification of influences of newly developing structures on system functions. Thus, it is possible to study effects of small-scale processes on the whole system at the

  7. Geology of the Terra Cimmeria-Utopia Planitia Highland Lowland Transitional Zone: Final Technical Approach and Scientific Results

    Skinner, J. A., Jr.; Tanaka, K. L.

    2010-01-01

    The southern Utopia highland-lowland transitional zone extends from northern Terra Cimmeria to southern Utopia Planitia and contains broad, bench-like platforms with depressions, pitted cones, tholi, and lobate flows. The locally occurring geologic units and landforms contrast other transitional regions and record a spatially partitioned geologic history. We systematically delineated and described the geologic units and landforms of the southern Utopia-Cimmeria highland-lowland transitional zone for the production of a 1:1,000,000-scale geologic map (MTMs 10237, 15237, 20237, 10242, 15242, 20242, 10247, 15247, and 20247). Herein, we present technical and scientific results of this mapping project.

  8. C2 Domains as Protein-Protein Interaction Modules in the Ciliary Transition Zone

    Kim Remans

    2014-07-01

    Full Text Available RPGR-interacting protein 1 (RPGRIP1 is mutated in the eye disease Leber congenital amaurosis (LCA and its structural homolog, RPGRIP1-like (RPGRIP1L, is mutated in many different ciliopathies. Both are multidomain proteins that are predicted to interact with retinitis pigmentosa G-protein regulator (RPGR. RPGR is mutated in X-linked retinitis pigmentosa and is located in photoreceptors and primary cilia. We solved the crystal structure of the complex between the RPGR-interacting domain (RID of RPGRIP1 and RPGR and demonstrate that RPGRIP1L binds to RPGR similarly. RPGRIP1 binding to RPGR affects the interaction with PDEδ, the cargo shuttling factor for prenylated ciliary proteins. RPGRIP1-RID is a C2 domain with a canonical β sandwich structure that does not bind Ca2+ and/or phospholipids and thus constitutes a unique type of protein-protein interaction module. Judging from the large number of C2 domains in most of the ciliary transition zone proteins identified thus far, the structure presented here seems to constitute a cilia-specific module that is present in multiprotein transition zone complexes.

  9. [Plant communities in the terrestrial-aquatic transition zone in the paramo of Chingaza, Colombia].

    Schmidt-Mumm, Udo; Vargas Ríos, Orlando

    2012-03-01

    Plant communities in the terrestrial-aquatic transition zone in the paramo of Chingaza, Colombia. High Andean paramo ecosystems are an important water resource for many towns, and major cities in this region. The aquatic and wetland vegetation of different paramo lakes, pond, swamps and bogs was studied according to the classical phytosociological approach, which is based on homogenous stands, but excludes any border phenomena or transitional zone. The present research aimed at determining the aquatic and wetland vegetation along different moisture gradients. A total of 89 species in 30 transects were reported, of which Crassula venezuelensis, Carex honplandii, Callitriche nubigena, Eleocharis macrostachya, Ranunculus flagelliformis, R. nubigenus, Eleocharis stenocarpa, Galium ascendens y Alopecurus aequalis were present in more than one third of the transects. Numerical classification and indicator species analysis resulted in the definition of the next 18 communities: 1) Calamagrostis effusa, 2) Sphagnum cuspidatum, 3) Cyperus rufus, 4) Eleocharis stenocarpa, 5) Carex acutata, 6) Poa annua,7) Valeriana sp., 8) Ranunculus flagelliformis, 9) Carex bonplandii, 10) Festuca andicola. 11) Muhlenbergia fustigiata, 12) Elatine paramoana, 13) Isoëtes palmeri, 14) Crassula venezuelensis, 15) Lilaeopsis macloviana, 16) Callitriche nubigena, 17) Potamogeton paramoanus and 18) Potamogeton illinoensis. The ordination of communities reveals the presence of three different aquatic-terrestrial gradients which are related to the life form structure of species that characterized the various communities. We concluded that patchiness and heterogeneity of the vegetation is mainly the result of alterations caused by human activities (burning, cattle raise and material extraction for road and dam construction).

  10. Functional Connectivity of Precipitation Networks in the Brazilian Rainforest-Savanna Transition Zone

    Adera, S.; Larsen, L.; Levy, M. C.; Thompson, S. E.

    2016-12-01

    In the Brazilian rainforest-savanna transition zone, vegetation change has the potential to significantly affect precipitation patterns. Deforestation, in particular, can affect precipitation patterns by increasing land surface albedo, increasing aerosol loading to the atmosphere, changing land surface roughness, and reducing transpiration. Understanding land surface-precipitation couplings in this region is important not only for sustaining Amazon and Cerrado ecosystems, but also for cattle ranching and agriculture, hydropower generation, and drinking water management. Simulations suggest complex, scale-dependent interactions between precipitation and land cover. For example, the size and distribution of deforested patches has been found to affect precipitation patterns. We take an empirical approach to ask: (1) what are the dominant spatial and temporal length scales of precipitation coupling in the Brazilian rainforest-savanna transition zone? (2) How do these length scales change over time? (3) How does the connectivity of precipitation change over time? The answers to these questions will help address fundamental questions about the impacts of deforestation on precipitation. We use rain gauge data from 1100 rain gauges intermittently covering the period 1980 - 2013, a period of intensive land cover change in the region. The dominant spatial and temporal length scales of precipitation coupling are resolved using transfer entropy, a metric from information theory. Connectivity of the emergent network of couplings is quantified using network statistics. Analyses using transfer entropy and network statistics reveal the spatial and temporal interdependencies of rainfall events occurring in different parts of the study domain.

  11. Hybridization between mouse lemurs in an ecological transition zone in southern Madagascar.

    Gligor, M; Ganzhorn, J U; Rakotondravony, D; Ramilijaona, O R; Razafimahatratra, E; Zischler, H; Hapke, A

    2009-02-01

    Hybrid zones in ecotones can be useful model systems for the study of evolutionary processes that shape the distribution and discreteness of species. Such studies could be important for an improved understanding of the complex biogeography of Madagascar, which is renowned for its outstanding degree of small-scale endemism. Certain forest remnants in central Madagascar indicate that transitional corridors across the island could have connected microendemics in different forest types in the past. Evolutionary processes in such corridors are difficult to study because most of these corridors have disappeared due to deforestation in central Madagascar. We studied a hybrid zone in one of the few remaining ecotonal corridors between dry and humid forests in Madagascar, which connects two species of mouse lemurs, Microcebus griseorufus in dry spiny forest and Microcebus murinus in humid littoral forest. We sampled 162 mouse lemurs at nine sites across this boundary. Morphometric analyses revealed intermediate morphotypes of many individuals in transitional habitat. Bayesian clustering of microsatellite genotypes and assignment tests yielded evidence for a mixed ancestry of mouse lemurs in the ecotone, where we also observed significant linkage disequilibria and heterozygote deficiency. In contrast to these observations, mitochondrial haplotypes displayed a sharply delimited boundary at the eastern edge of spiny forest, which was noncoincident with the signals from microsatellite data. Among several alternative scenarios, we propose asymmetric nuclear introgression due to male-biased dispersal, divergent environmental selection, and an expansion of dry spiny forest in the course of aridification as a probable explanation of our observations.

  12. An Equation Governing Ultralow-Velocity Zones: Implications for Holes in the ULVZ, Lateral Chemical Reactions at the Core-Mantle Boundary, and Damping of Heat Flux Variations in the Core

    Hernlund, J. W.; Matsui, H.

    2017-12-01

    Ultralow-velocity zones (ULVZ) are increasingly illuminated by seismology, revealing surprising diversity in size, shape, and physical characteristics. The only viable hypotheses are that ULVZs are a compositionally distinct FeO-enriched dense material, which could have formed by fractional crystallization of a basal magma ocean, segregation of subducted banded iron formations, precipitation of solids from the outer core, partial melting and segregation of iron-rich melts from subducted basalts, or most likely a combination of many different processes. But many questions remain: Are ULVZ partially molten in some places, and not in others? Are ULVZ simply the thicker portions of an otherwise global thin layer, covering the entire CMB and thus blocking or moderating chemical interactions between the core and overlying mantle? Is such a layer inter-connected and able to conduct electrical currents that allow electro-magnetic coupling of core and mantle angular momentum? Are they being eroded and shrinking in size due to viscous entrainment, or is more material being added to ULVZ over time? Here we derive an advection-diffusion-like equation that governs the dynamical evolution of a chemically distinct ULVZ. Analysis of this equation shows that ULVZ should become readily swept aside by viscous mantle flows at the CMB, exposing "ordinary mantle" to the top of the core, thus inducing chemical heterogeneity that drives lateral CMB chemical reactions. These reactions are correlated with heat flux, thus maintaining large-scale pressure variations atop the core that induce cyclone-like flows centered around ULVZ and ponded subducted slabs. We suggest that turbulent diffusion across adjacent cyclone streams inside a stratified region atop the core readily accommodates lateral transport and re-distribution of components such as O and Si, in addition to heat. Our model implies that the deeper core is at least partly shielded from the influence of strong heat flux variations at

  13. Dynamical geochemistry of the mantle

    G. F. Davies

    2011-09-01

    Full Text Available The reconciliation of mantle chemistry with the structure of the mantle inferred from geophysics and dynamical modelling has been a long-standing problem. This paper reviews three main aspects. First, extensions and refinements of dynamical modelling and theory of mantle processing over the past decade. Second, a recent reconsideration of the implications of mantle heterogeneity for melting, melt migration, mantle differentiation and mantle segregation. Third, a recent proposed shift in the primitive chemical baseline of the mantle inferred from observations of non-chondritic 142Nd in the Earth. It seems most issues can now be resolved, except the level of heating required to maintain the mantle's thermal evolution.

    A reconciliation of refractory trace elements and their isotopes with the dynamical mantle, proposed and given preliminary quantification by Hofmann, White and Christensen, has been strengthened by work over the past decade. The apparent age of lead isotopes and the broad refractory-element differences among and between ocean island basalts (OIBs and mid-ocean ridge basalts (MORBs can now be quantitatively accounted for with some assurance.

    The association of the least radiogenic helium with relatively depleted sources and their location in the mantle have been enigmatic. The least radiogenic helium samples have recently been recognised as matching the proposed non-chondritic primitive mantle. It has also been proposed recently that noble gases reside in a so-called hybrid pyroxenite assemblage that is the result of melt from fusible pods reacting with surrounding refractory peridotite and refreezing. Hybrid pyroxenite that is off-axis may not remelt and erupt at MORs, so its volatile constituents would recirculate within the mantle. Hybrid pyroxenite is likely to be denser than average mantle, and thus some would tend to settle in the D" zone at the base of the mantle, along with some old subducted

  14. Interpreting Brightness Asymmetries in Transition Disks: Vortex at Dead Zone or Planet-carved Gap Edges?

    Regály, Zs.; Juhász, A.; Nehéz, D.

    2017-12-01

    Recent submillimeter observations show nonaxisymmetric brightness distributions with a horseshoe-like morphology for more than a dozen transition disks. The most-accepted explanation for the observed asymmetries is the accumulation of dust in large-scale vortices. Protoplanetary disks’ vortices can form by the excitation of Rossby wave instability in the vicinity of a steep pressure gradient, which can develop at the edges of a giant planet–carved gap or at the edges of an accretionally inactive zone. We studied the formation and evolution of vortices formed in these two distinct scenarios by means of two-dimensional locally isothermal hydrodynamic simulations. We found that the vortex formed at the edge of a planetary gap is short-lived, unless the disk is nearly inviscid. In contrast, the vortex formed at the outer edge of a dead zone is long-lived. The vortex morphology can be significantly different in the two scenarios: the vortex radial and azimuthal extensions are ∼1.5 and ∼3.5 times larger for the dead-zone edge compared to gap models. In some particular cases, the vortex aspect ratios can be similar in the two scenarios; however, the vortex azimuthal extensions can be used to distinguish the vortex formation mechanisms. We calculated predictions for vortex observability in the submillimeter continuum with ALMA. We found that the azimuthal and radial extent of the brightness asymmetry correlates with the vortex formation process within the limitations of α-viscosity prescription.

  15. Thermal structure and geodynamics of subduction zones

    Wada, Ikuko

    The thermal structure of subduction zones depends on the age-controlled thermal state of the subducting slab and mantle wedge flow. Observations indicate that the shallow part of the forearc mantle wedge is stagnant and the slab-mantle interface is weakened. In this dissertation, the role of the interface strength in controlling mantle wedge flow, thermal structure, and a wide range of subduction zone processes is investigated through two-dimensional finite-element modelling and a global synthesis of geological and geophysical observations. The model reveals that the strong temperature-dependence of the mantle strength always results in full slab-mantle decoupling along the weakened part of the interface and hence complete stagnation of the overlying mantle. The interface immediately downdip of the zone of decoupling is fully coupled, and the overlying mantle is driven to flow at a rate compatible with the subduction rate. The sharpness of the transition from decoupling to coupling depends on the rheology assumed and increases with the nonlinearity of the flow system. This bimodal behaviour of the wedge flow gives rise to a strong thermal contrast between the cold stagnant and hot flowing parts of the mantle wedge. The maximum depth of decoupling (MDD) thus dictates the thermal regime of the forearc. Observed surface heat flow patterns and petrologically and geochemically estimated mantle wedge temperatures beneath the volcanic arc require an MDD of 70--80 km in most, if not all, subduction zones regardless of their thermal regime of the slab. The common MDD of 70--80 km explains the observed systematic variations of the petrologic, seismological, and volcanic processes with the thermal state of the slab and thus explains the rich diversity of subduction zones in a unified fashion. Models for warm-slab subduction zones such as Cascadia and Nankai predict shallow dehydration of the slab beneath the cold stagnant part of the mantle wedge, which provides ample fluid

  16. Afferent and Efferent Connections of the Cortex-Amygdala Transition Zone in Mice.

    Cádiz-Moretti, Bernardita; Abellán-Álvaro, María; Pardo-Bellver, Cecília; Martínez-García, Fernando; Lanuza, Enrique

    2016-01-01

    The transitional zone between the ventral part of the piriform cortex and the anterior cortical nucleus of the amygdala, named the cortex-amygdala transition zone (CxA), shows two differential features that allow its identification as a particular structure. First, it receives dense cholinergic and dopaminergic innervations as compared to the adjacent piriform cortex and amygdala, and second, it receives projections from the main and accessory olfactory bulbs. In this work we have studied the pattern of afferent and efferent projections of the CxA, which are mainly unknown, by using the retrograde tracer Fluorogold and the anterograde tracer biotinylated dextranamine. The results show that the CxA receives a relatively restricted set of intratelencephalic connections, originated mainly by the olfactory system and basal forebrain, with minor afferents from the amygdala. The only relevant extratelencephalic afference originates in the ventral tegmental area (VTA). The efferent projections of the CxA reciprocate the inputs from the piriform cortex and olfactory amygdala. In addition, the CxA projects densely to the basolateral amygdaloid nucleus and the olfactory tubercle. The extratelencephalic projections of the CxA are very scarce, and target mainly hypothalamic structures. The pattern of connections of the CxA suggests that it is indeed a transitional area between the piriform cortex and the cortical amygdala. Double labeling with choline acetyltransferase indicates that the afferent projection from the basal forebrain is the origin of its distinctive cholinergic innervation, and double labeling with dopamine transporter shows that the projection from the VTA is the source of dopaminergic innervation. These connectivity and neurochemical features, together with the fact that it receives vomeronasal in addition to olfactory information, suggest that the CxA may be involved in processing olfactory information endowed with relevant biological meaning, such as odors

  17. High Resolution Global Electrical Conductivity Variations in the Earth's Mantle

    Kelbert, A.; Sun, J.; Egbert, G. D.

    2013-12-01

    Electrical conductivity of the Earth's mantle is a valuable constraint on the water content and melting processes. In Kelbert et al. (2009), we obtained the first global inverse model of electrical conductivity in the mantle capable of providing constraints on the lateral variations in mantle water content. However, in doing so we had to compromise on the problem complexity by using the historically very primitive ionospheric and magnetospheric source assumptions. In particular, possible model contamination by the auroral current systems had greatly restricted our use of available data. We have now addressed this problem by inverting for the external sources along with the electrical conductivity variations. In this study, we still focus primarily on long period data that are dominated by quasi-zonal source fields. The improved understanding of the ionospheric sources allows us to invert the magnetic fields directly, without a correction for the source and/or the use of transfer functions. It allows us to extend the period range of available data to 1.2 days - 102 days, achieving better sensitivity to the upper mantle and transition zone structures. Finally, once the source effects in the data are accounted for, a much larger subset of observatories may be used in the electrical conductivity inversion. Here, we use full magnetic fields at 207 geomagnetic observatories, which include mid-latitude, equatorial and high latitude data. Observatory hourly means from the years 1958-2010 are employed. The improved quality and spatial distribution of the data set, as well as the high resolution modeling and inversion using degree and order 40 spherical harmonics mapped to a 2x2 degree lateral grid, all contribute to the much improved resolution of our models, representing a conceptual step forward in global electromagnetic sounding. We present a fully three-dimensional, global electrical conductivity model of the Earth's mantle as inferred from ground geomagnetic

  18. Mantle dynamics following supercontinent formation

    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. Seismic structure of the crust and upper mantle in central-eastern Greenland

    Kraft, Helene Anja

    Geophysical and geological knowledge of the interior of Greenland is very limited. The lack of knowledge arises mainly due to the logistical challenges related to conducting geophysical fieldwork on the up to 3400 m thick ice sheet, which covers around 80% of the land area. This PhD thesis is based...... on the very first regional passive seismic study in central-Eastern Greenland, focusing on the area between Scoresby Sund and Summit. The study aims to image the structure of subsurface Greenland starting from the crust and down to the mantle transition zone. Furthermore, the thesis links these observations....... The receiver functions were jointly inverted for the velocity structure of the crust and delay times, and shapes of signals originating at the mantle transition zone discontinuities, P410s and P660s, were analysed. The crustal models show a deepening of the Moho from east to west from less than 20 km depth...

  20. Effects of Atlantic warm pool variability over climate of South America tropical transition zone

    Ricaurte Villota, Constanza; Romero-Rodríguez, Deisy; Andrés Ordoñez-Zuñiga, Silvio; Murcia-Riaño, Magnolia; Coca-Domínguez, Oswaldo

    2016-04-01

    Colombia is located in the northwestern corner of South America in a climatically complex region due to the influence processes modulators of climate both the Pacific and Atlantic region, becoming in a transition zone between phenomena of northern and southern hemisphere. Variations in the climatic conditions of this region, especially rainfall, have been attributed to the influence of the El Nino Southern Oscillation (ENSO), but little is known about the interaction within Atlantic Ocean and specifically Caribbean Sea with the environmental conditions of this region. In this work We studied the influence of the Atlantic Warm Pool (AWP) on the Colombian Caribbean (CC) climate using data of Sea Surface Temperature (SST) between 1900 - 2014 from ERSST V4, compared with in situ data SIMAC (National System for Coral Reef Monitoring in Colombia - INVEMAR), rainfall between 1953-2013 of meteorological stations located at main airports in the Colombian Caribbean zone, administered by IDEAM, and winds data between 2003 - 2014 from WindSat sensor. The parameters analyzed showed spatial differences throughout the study area. SST anomalies, representing the variability of the AWP, showed to be associated with Multidecadal Atlantic Oscillation (AMO) and with the index of sea surface temperature of the North-tropical Atlantic (NTA), the variations was on 3 to 5 years on the ENSO scale and of approximately 11 years possibly related to solar cycles. Rainfall anomalies in the central and northern CC respond to changes in SST, while in the south zone these are not fully engage and show a high relationship with the ENSO. Finally, the winds also respond to changes in SST and showed a signal approximately 90 days possibly related to the Madden-Julian Oscillation, whose intensity depends on the CC region being analyzed. The results confirm that region is a transition zone in which operate several forcing, the variability of climate conditions is difficult to attribute only one, as ENSO

  1. Rifting-to-drifting transition of the South China Sea: Moho reflection characteristics in continental-ocean transition zone

    Wen, Y.; Li, C.

    2017-12-01

    Dispute remains on the process of continental rifting to subsequent seafloor spreading in the South China Sea (SCS). Several crust-scale multi-channel seismic reflection profiles acquired in the continent-ocean transition zone (COT) of the SCS provide a detailed overview of Moho and deep crustal reflectors and give key information on rifting-to-drifting transition of the area. Moho has strong but discontinuous seismic reflection in COT. These discontinuities are mainly located in the landward side of continent-ocean boundary (COB), and may own to upwelling of lower crustal materials during initial continental extension, leading to numerous volcanic edifices and volcanic ridges. The continental crust in COT shows discontinuous Moho reflections at 11-8.5 s in two-way travel time (twtt), and thins from 18-20.5 km under the uppermost slope to 6-7 km under the lower slope, assuming an average crustal velocity of 6.0 km/s. The oceanic crust has Moho reflections of moderate to high continuity mostly at 1.8-2.2 s twtt below the top of the igneous basement, which means that the crustal thickness excluding sediment layer in COT is 5.4-6.6 km. Subhorizontal Moho reflections are often abruptly interrupted by large seaward dipping normal faults in southern COT but are more continuous compared with the fluctuant and very discontinuous Moho reflections in northern COT. The thickness of thinned continental crust (4.2-4.8 km) is smaller than that of oceanic crust (5.4-6.0 km) near southern COB, indicating that the continental crust has experienced a long period of rifting before seafloor spreading started. The smaller width of northern COT (0-40 km) than in southern COT (0-60 km), and thinner continental crust in southern COT, all indicate that the continental margin rifting and extension was asymmetric. The COT width in the SCS is narrower than that found in other magma-poor continental margins, indicating a swift transition from the final stage of rifting to the inception of

  2. Prostate-specific membrane antigen PET/MRI validation of MR textural analysis for detection of transition zone prostate cancer.

    Bates, Anthony; Miles, Kenneth

    2017-12-01

    To validate MR textural analysis (MRTA) for detection of transition zone (TZ) prostate cancer through comparison with co-registered prostate-specific membrane antigen (PSMA) PET-MR. Retrospective analysis was performed for 30 men who underwent simultaneous PSMA PET-MR imaging for staging of prostate cancer. Thirty texture features were derived from each manually contoured T2-weighted, transaxial, prostatic TZ using texture analysis software that applies a spatial band-pass filter and quantifies texture through histogram analysis. Texture features of the TZ were compared to PSMA expression on the corresponding PET images. The Benjamini-Hochberg correction controlled the false discovery rate at prostate cancer. • Prostate transition zone (TZ) MR texture analysis may assist in prostate cancer detection. • Abnormal transition zone PSMA expression correlates with altered texture on T2-weighted MR. • TZ with abnormal PSMA expression demonstrates significantly reduced MI, SD and MPP.

  3. Repeating Deep Very Low Frequency Earthquakes: An Evidence of Transition Zone between Brittle and Ductile Zone along Plate Boundary

    Ishihara, Y.; Yamamoto, Y.; Arai, R.

    2017-12-01

    Recently slow or low frequency seismic and geodetic events are focused under recognition of important role in tectonic process. The most western region of Ryukyu trench, Yaeyama Islands, is very active area of these type events. It has semiannual-like slow slip (Heki et.al., 2008; Nishimura et.al.,2014) and very frequent shallow very low frequency earthquakes near trench zone (Ando et.al.,2012; Nakamura et.al.,2014). Arai et.al.(2016) identified clear reverse phase discontinuity along plate boundary by air-gun survey, suggesting existence of low velocity layer including fluid. The subducting fluid layer is considered to control slip characteristics. On the other hand, deep low frequency earthquake and tremor observed at south-western Honshu and Shikoku of Japan are not identified well due to lack of high-quality seismic network. A broadband seismic station(ISG/PS) of Pacific21 network is operating in last 20 years that locates on occurrence potential area of low frequency earthquake. We tried to review continuous broadband record, searching low frequency earthquakes. In pilot survey, we found three very low frequency seismic events which are dominant in less than 0.1Hz component and are not listed in earthquake catalogue. Source locates about 50km depth and at transition area between slow slip event and active area of general earthquake along plate boundary. To detect small and/or hidden very low frequency earthquake, we applied matched filter analysis to continuous three components waveform data using pre-reviewed seismogram as template signal. 12 events with high correlation are picked up in last 10 years. Most events have very similar waveform, which means characteristics of repeating deep very low frequency earthquake. The event history of very low frequency earthquake is not related with one of slow slip event in this region. In Yaeyama region, low frequency earthquake, general earthquake and slow slip event occur dividing in space and have apparent

  4. Compositionally heterogeneous podiform chromitite in the Shetland Ophiolite Complex (Scotland): Implications for chromitite petrogenesis and late-stage alteration in the upper mantle portion of a supra-subduction zone ophiolite

    Derbyshire, E. J.; O'Driscoll, B.; Lenaz, D.; Gertisser, R.; Kronz, A.

    2013-03-01

    The mantle sequence of the ~ 492 Ma Shetland Ophiolite Complex (SOC; Scotland) contains abundant compositionally heterogeneous podiform chromitite bodies enclosed in elongate dunite lenses in the vicinity of the petrological Moho. Chromitite petrogenesis and late-stage alteration events recorded in these seams are examined here using petrography, mineral chemistry and crystal structural data. The resistant nature of Cr-spinel to serpentinisation and other late-stage alteration means that primary igneous compositions are preserved in unaltered crystal cores. Chromitite mineralogy and texture from five sampled localities at The Viels, Hagdale, Harold's Grave, Nikka Vord and Cliff reveal significant inter-pod chemical heterogeneity. The Cr-spinel mineral chemistry is consistent with supra-subduction zone melt extraction from the SOC peridotites. The occurrence of chromitite seams in the centres of the dunite lenses combined with variable Cr-spinel compositions at different chromitite seam localities supports a model of chromitite formation from spatially (and temporally?) fluctuating amounts of melt-rock interaction through channelised and/or porous melt flow. Pervasive serpentinisation of the SOC has led to the almost complete replacement of the primary (mantle) silicate mineral assemblages with serpentine (lizardite with minor chrysotile and antigorite). Magmatic sulphide (e.g., pentlandite) in dunite and chromitite is locally converted to reduced Ni-sulphide varieties (e.g., heazlewoodite and millerite). A post-serpentinisation (prograde) oxidisation event is recorded in the extensively altered Cliff chromitite seams in the west of the studied area, where chromitite Cr-spinel is extensively altered to ferritchromit. The ferritchromit may comprise > 50% of the volume of the Cliff Cr-spinels and contain appreciable quantities of 1-2 μm inclusions of sperrylite (PtAs2) and Ni-arsenide, signifying the coeval formation of these minerals with ferritchromit at

  5. Zone 1 retinopathy of prematurity in a transitional economy: a cautionary note.

    Carden, Susan M; Lan, Luu Ngoc; Huynh, Tess

    2006-06-01

    To describe three low risk infants in whom severe retinopathy of prematurity developed. A prospective, observational case series. setting: National Hospital of Pediatrics, Hanoi, Vietnam. study population: Premature infants in the neonatal ward. observation procedure: Eye examinations. Severe retinopathy of prematurity occurred in three infants. All had zone 1 disease and other unusually severe findings, such as neovascularization of the disk. These infants would not be at risk for the development of such severe retinopathy of prematurity in countries with a developed economy. Unusual characteristics of retinopathy of prematurity may be occurring in countries with transitional economies. Screening programs should be implemented and should take into consideration the possibility that retinopathy of prematurity may occur in infants who fall outside the screening guidelines that are used in the developed world.

  6. Influence of compaction on the interfacial transition zone and the permeability of concrete

    Leemann, Andreas; Muench, Beat; Gasser, Philippe; Holzer, Lorenz

    2006-01-01

    The interfacial transition zone (ITZ) is regarded as a key feature for the transport properties and the durability of concrete. In this study one self-compacting concrete (SCC) mixture and two conventionally vibrated concrete (CVC) mixtures are studied in order to determine the influence of compaction on the porosity of the ITZ. Additionally oxygen permeability and water conductivity were measured in vertical and horizontal direction. The quantitative analysis of images made with an optical microscope and an environmental scanning electron microscope shows a significantly increased porosity and width of the ITZ in CVC compared to SCC. At the same time oxygen permeability and water conductivity of CVC are increased in comparison to SCC. Moreover, considerable differences in the porosity of the lower, lateral and upper ITZ are observed in both types of concrete. The anisotropic distribution of pores in the ITZ does not necessarily cause anisotropy in oxygen permeability and water conductivity though

  7. Micromechanical performance of interfacial transition zone in fiber-reinforced cement matrix

    Zacharda, V.; Němeček, J.; Štemberk, P.

    2017-09-01

    The paper investigates microstructure, chemical composition and micromechanical behavior of an interfacial transition zone (ITZ) in steel fiber reinforced cement matrix. For this goal, a combination of scanning electron microscopy (SEM), nanoindentation and elastic homogenization theory are used. The investigated sample of cement paste with dispersed reinforcement consists of cement CEM I 42,5R and a steel fiber TriTreg 50 mm. The microscopy revealed smaller portion of clinkers and larger porosity in the ITZ. Nanoindentation delivered decreased elastic modulus in comparison with cement bulk (67%) and the width of ITZ (∼ 40 μm). The measured properties served as input parameters for a simple two-scale model for elastic properties of the composite. Although, no major influence of ITZ properties on the composite elastic behavior was found, the findings about the ITZ reduced properties and its size can serve as input to other microstructural fracture based models.

  8. PWR steam generators tube integrity: plugging criteria for PWSCC in roll transition zone

    Mattar Neto, Miguel; Cruz, Julio R.B.

    1999-01-01

    One of the most important causes for tube plugging in PWR (Pressurized Water Reactor) steam generators is the degradation mechanism called Primary Water Stress Corrosion Cracking (PWSCC) in roll transition zone (RTZ) near the tubesheet, mainly for Alloy 600 tubes. To avoid an excessive tube plugging, alternative criteria have been developed based on an approach that consists in withdrawing from service any tube containing a defect for which there is a high probability of a critical size under accident conditions to be reached during next operation cycle. Predictions of the number of tubes to be plugged can be done aiming at preventive maintenance and tube repair, and even a steam generator replacement, without a large and non-planned plant outage. This work presents important aspects related to tube plugging criteria for PWSCC in RTZ based on the risk of break after a leak detection. Calculations of allowable crack length and allowable leak rate for a particular situation are also shown. (author)

  9. Transition-zone observations of rapid flare events as observed by OSO-8

    Lites, B. W.

    1981-01-01

    The rapid dissipation of flare energy has been observed in the transition-zone line of C IV at 1548.2 A using the University of Colorado spectrometer aboard OSO-8. Impulsive brightenings have been resolved with characteristic rise times as low as 3.5s. One event is analyzed in detail, and it is inferred that the electron density is greater than 2 x 10 to the 11th/cu cm at a temperature of 60,000 K, and that the flare energy is deposited at a rate of 2 ergs/cu cm per sec or greater. The temporal behavior of the intensity at the center of the C IV line is consistent with a nonequilibrium ionization of C III through C V. If this event is a result of the multiple tearing mode instability as the primary energy release mechanism, then the observations indicate a preflare magnetic field of about 175 G.

  10. Performance Analysis of a Recycled Concrete Interfacial Transition Zone in a Rapid Carbonization Environment

    Gongbing Yue

    2018-01-01

    Full Text Available Based on the characteristics of recycled concrete interface structures, a multi-interface reconstruction model was established. To study the microstructure evolution of the interfacial transition zone (ITZ during the carbonization process of recycled concrete, the microstructure characteristics of the ITZ of C30, C40, and C50 grade recycled concrete and the mortar matrix before and after carbonization were studied through the microhardness tester and SEM. The results show that the microhardness values of the ITZ and the mortar matrix are obviously increased and that the width of the ITZ decreases, while the ITZ performance of the C50 grade recycled concrete is not significantly changed. The ITZ exhibits a large amount of granular CaCO3 after carbonization, the pores are refined, and microcracks are generated. Overall, there are significant differences in the microstructures between the ITZ and the mortar matrix before and after carbonization.

  11. DEEP STRUCTURE OF THE SIBERIAN PLATFORM – CENTRAL ASIAN MOBILE BELT TRANSITION ZONE FROM TELESEISMIC DATA

    V. V. Mordvinova

    2016-01-01

    Full Text Available Deep velocity sections of the transition zone from the Siberian platform to the Central Asian mobile belt are constructed by teleseismic tomography and P-receiver function techniques. An array of the dense ancient Siberian craton is identified in the velocity sections with areas of high seismic velocity. In the SSW section MOBAL_2003, the surface boundary of the craton corresponds to the southern margin of the Siberian platform and is nearly vertical to a depth of 120 km. At larger depths, the craton slides almost horizontally underneath the Tunka rift area. At depths from 150 to 250 km, it is in contact with the area under the Khamar-Daban mountain range. In the southeast, according to the SE velocity section PASSCAL_1992 across the South Baikal basin and the Khamar-Daban mountain range, the Siberian craton thickness is reduced from 270 to 150 km at the contact of the Siberian platform with the Baikal folded area. In this contact zone, the upper part of the craton is wedge-shaped and has an angle of about 45° with the ground surface; it completely tapers off at a depth of 150 km to the east of Lake Baikal. The vertical configuration of the southern segment of the Siberian craton, which evolved with time, may determine the nature of the Baikal rifting in the Cenozoic. 

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

    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

  13. Mantle wedge serpentinization effects on slab dips

    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.

  14. Observed Spectral Invariant Behavior of Zenith Radiance in the Transition Zone Between Cloud-Free and Cloudy Regions

    Marshak, A.; Knyazikhin, Y.; Chiu, C.; Wiscombe, W.

    2010-01-01

    The Atmospheric Radiation Measurement Program's (ARM) new Shortwave Spectrometer (SWS) looks straight up and measures zenith radiance at 418 wavelengths between 350 and 2200 nm. Because of its 1-sec sampling resolution, the SWS provides a unique capability to study the transition zone between cloudy and clear sky areas. A surprising spectral invariant behavior is found between ratios of zenith radiance spectra during the transition from cloudy to cloud-free atmosphere. This behavior suggests that the spectral signature of the transition zone is a linear mixture between the two extremes (definitely cloudy and definitely clear). The weighting function of the linear mixture is found to be a wavelength-independent characteristic of the transition zone. It is shown that the transition zone spectrum is fully determined by this function and zenith radiance spectra of clear and cloudy regions. This new finding may help us to better understand and quantify such physical phenomena as humidification of aerosols in the relatively moist cloud environment and evaporation and activation of cloud droplets.

  15. How Models Simulate the Radiative Effect in the Transition Zone of the Aerosol-Cloud Continuum

    Calbo Angrill, J.; González, J. A.; Long, C. N.; McComiskey, A. C.

    2017-12-01

    Several studies have pointed towards dealing with clouds and aerosols as two manifestations of what is essentially the same physical phenomenon: a suspension of tiny particles in the air. Although the two extreme cases (i.e., pure aerosol and well-defined cloud) are easily distinguished, and obviously produce different radiative effects, there are many situations in the transition (or "twilight") zone. In a recent paper [Calbó et al., Atmos. Res. 2017, j.atmosres.2017.06.010], the authors of the current communication estimated that about 10% of time there might be a suspension of particles in the air that is difficult to distinguish as either cloud or aerosol. Radiative transfer models, however, simulate the effect of clouds and aerosols with different modules, routines, or parameterizations. In this study, we apply a sensitivity analysis approach to assess the ability of two radiative transfer models (SBDART and RRTM) in simulating the radiative effect of a suspension of particles with characteristics in the boundary between cloud and aerosol. We simulate this kind of suspension either in "cloud mode" or in "aerosol mode" and setting different values of optical depth, droplet size, water path, aerosol type, cloud height, etc. Irradiances both for solar and infrared bands are studied, both at ground level and at the top of the atmosphere, and all analyses are repeated for different solar zenith angles. We obtain that (a) water clouds and ice clouds have similar radiative effects if they have the same optical depth; (b) the spread of effects regarding different aerosol type/aerosol characteristics is remarkable; (c) radiative effects of an aerosol layer and of a cloud layer are different, even if they have similar optical depth; (d) for a given effect on the diffuse component, the effect on the direct component is usually greater (more extinction of direct beam) by aerosols than by clouds; (e) radiative transfer models are somewhat limited when simulating the

  16. Dynamic recrystallization mechanisms and their transition in the Daling Thrust (DT) zone, Darjeeling-Sikkim Himalaya

    Ghosh, Subhajit; Bose, Santanu; Mandal, Nibir; Dasgupta, Sujoy

    2016-04-01

    The Daling Thrust (DT) delineates a zone of intense shear localization in the Lesser Himalayan Sequence (LHS) of the Darjeeling-Sikkim Himalaya. From microstructural studies of deformed quartzite samples, we show a transition in the dynamic recrystallization mechanism with increasing distance from the DT, dominated by grain boundary bulging (BLG) recrystallization closest to the DT, and progressively replaced by sub-grain rotation (SGR) recrystallization away from the thrust. The transition is marked by a characteristic variation in the fractal dimension (D) of grain boundaries, estimated from the area-perimeter method. For the BLG regime, D ≈ 1.046, which decreases significantly to a value as low as 1.025 for the SGR regime. Using the available thermal data for BLG and SGR recrystallization, we infer increasing deformation temperatures away from the DT in the hanging wall. Based on the quartz piezometer our estimates reveal strong variations in the flow stress (59.00 MPa to 16.00 MPa) over a distance of 1.2 km from the DT. Deformation mechanism maps constructed for different temperatures indicate that the strain rates (10- 12 S- 1 to 10- 14 S- 1) comply with the geologically possible range. Finally, we present a mechanical model to provide a possible explanation for the cause of stress intensification along the DT.

  17. CATCHING QUENCHING GALAXIES: THE NATURE OF THE WISE INFRARED TRANSITION ZONE

    Alatalo, Katherine; Appleton, Philip N.; Rich, Jeffrey A. [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States); Cales, Sabrina L. [Department of Astronomy, Faculty of Physical and Mathematical Sciences, Universidad de Concepción, Casilla 160-C, Concepción (Chile); Kewley, Lisa J. [Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston, ACT 2611 (Australia); Lacy, Mark [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Lisenfeld, Ute [Departamento de Física Teórica y del Cosmos, Universidad de Granada, Granada (Spain); Nyland, Kristina, E-mail: kalatalo@caltech.edu [Physics Department, New Mexico Tech, Socorro, NM 87801 (United States)

    2014-10-10

    We present the discovery of a prominent bifurcation between early-type galaxies and late-type galaxies, in [4.6]-[12] μm colors from the Wide Field Infrared Survey Explorer (WISE). We then use an emission-line diagnostic comparison sample to explore the nature of objects found both within and near the edges of this WISE infrared transition zone (IRTZ). We hypothesize that this bifurcation might be due to the presence of hot dust and polyaromatic hydrocarbon (PAH) emission features in late-type galaxies. Using a sample of galaxies selected through the Shocked Poststarburst Galaxy Survey (SPOGS), we are able to identify galaxies with strong Balmer absorption (EW(Hδ) > 5 Å) as well as emission lines inconsistent with star formation (deemed SPOG candidates, or SPOGs*) that lie within the optical green valley. Seyferts and low-ionization nuclear emission line regions, whose u – r colors tend to be red, are strongly represented within IRTZ, whereas SPOGs* tend to sit near the star-forming edge. Although active galactic nuclei are well represented in the IRTZ, we argue that the dominant IRTZ population is composed of galaxies that are in late stages of transitioning across the optical green valley, shedding the last of their remnant interstellar media.

  18. A deterministic and stochastic velocity model for the Salton Trough/Basin and Range transition zone and constraints on magmatism during rifting

    Larkin, Steven P.; Levander, Alan; Okaya, David; Goff, John A.

    1996-12-01

    As a high resolution addition to the 1992 Pacific to Arizona Crustal Experiment (PACE), a 45-km-long deep crustal seismic reflection profile was acquired across the Chocolate Mountains in southeastern California to illuminate crustal structure in the transition between the Salton Trough and the Basin and Range province. The complex seismic data are analyzed for both large-scale (deterministic) and fine-scale (stochastic) crustal features. A low-fold near-offset common-midpoint (CMP) stacked section shows the northeastward lateral extent of a high-velocity lower crustal body which is centered beneath the Salton Trough. Off-end shots record a high-amplitude diffraction from the point where the high velocity lower crust pinches out at the Moho. Above the high-velocity lower crust, moderate-amplitude reflections occur at midcrustal levels. These reflections display the coherency and frequency characteristics of reflections backscattered from a heterogeneous velocity field, which we model as horizontal intrusions with a von Kármán (fractal) distribution. The effects of upper crustal scattering are included by combining the mapped surface geology and laboratory measurements of exposed rocks within the Chocolate Mountains to reproduce the upper crustal velocity heterogeneity in our crustal velocity model. Viscoelastic finite difference simulations indicate that the volume of mafic material within the reflective zone necessary to produce the observed backscatter is about 5%. The presence of wavelength-scale heterogeneity within the near-surface, upper, and middle crust also produces a 0.5-s-thick zone of discontinuous reflections from a crust-mantle interface which is actually a first-order discontinuity.

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

    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

  20. Magnetic Data Interpretation for the Source-Edge Locations in Parts of the Tectonically Active Transition Zone of the Narmada-Son Lineament in Central India

    Ghosh, G. K.

    2016-02-01

    The study has been carried out in the transition zone of the Narmada-Son lineament (NSL) which is seismically active with various geological complexities, upwarp movement of the mantle material into the crust through fault, fractures lamination and upwelling. NSL is one of the most prominent lineaments in central India after the Himalaya in the Indian geology. The area of investigation extends from longitude 80.25°E to 81.50°E and latitude 23.50°N to 24.37°N in the central part of the Indian continent. Different types of subsurface geological formations viz. alluvial, Gondwana, Deccan traps, Vindhyan, Mahakoshal, Granite and Gneisses groups exist in this area with varying geological ages. In this study area tectonic movement and crustal variation have been taken place during the past time and which might be reason for the variation of magnetic field. Magnetic anomaly suggests that the area has been highly disturbed which causes the Narmada-Son lineament trending in the ENE-WSW direction. Magnetic anomaly variation has been taken place due to the lithological variations subject to the changes in the geological contacts like thrusts and faults in this area. Shallow and deeper sources have been distinguished using frequency domain analysis by applying different filters. To enhance the magnetic data, various types of derivatives to identify the source-edge locations of the causative source bodies. The present study carried out the interpretation using total horizontal derivative, tilt angle derivative, horizontal tilt angle derivative and Cos (θ) derivative map to get source-edge locations. The results derived from various derivatives of magnetic data have been compared with the basement depth solutions calculated from 3D Euler deconvolution. It is suggested that total horizontal derivative, tilt angle derivative and Cos (θ) derivative are the most useful tools for identifying the multiple source edge locations of the causative bodies in this tectonically active

  1. Deformation processes and weakening mechanisms within the frictional viscous transition zone of major crustal-scale faults: insights from the Great Glen Fault Zone, Scotland

    Stewart, M.; Holdsworth, R. E.; Strachan, R. A.

    2000-05-01

    The Great Glen Fault Zone (GGFZ), Scotland, is a typical example of a crustal-scale, reactivated strike-slip fault within the continental crust. Analysis of intensely strained fault rocks from the core of the GGFZ near Fort William provides a unique insight into the nature of deformation associated with the main phase of (sinistral) movements along the fault zone. In this region, an exhumed sequence of complex mid-crustal deformation textures that developed in the region of the frictional-viscous transition (ca. 8-15 km depth) is preserved. Fault rock fabrics vary from mylonitic in quartzites to cataclastic in micaceous shear zones and feldspathic psammites. Protolith mineralogy exerted a strong control on the initial textural development and distribution of the fault rocks. At lower strains, crystal-plastic deformation occurred in quartz-dominated lithologies to produce mylonites simultaneously with widespread fracturing and cataclasis in feldspar- and mica-dominated rocks. At higher strains, shearing appears to increasingly localise into interconnected networks of cataclastic shear zones, many of which are strongly foliated. Textures indicative of fluid-assisted diffusive mass transfer mechanisms are widespread in such regions and suggest that a hydrous fluid-assisted, grainsize-controlled switch in deformation behaviour followed the brittle comminution of grains. The fault zone textural evolution implies that a strain-induced, fluid-assisted shallowing and narrowing of the frictional-viscous transition occurred with increasing strain. It is proposed that this led to an overall weakening of the fault zone and that equivalent processes may occur along many other long-lived, crustal-scale dislocations.

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

    Schellart, W. P.; Spakman, W.

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

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

    Schellart, W.P.; Spakman, W.

    2012-01-01

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

  4. Seismic Discontinuities within the Crust and Mantle Beneath Indonesia as Inferred from P Receiver Functions

    Woelbern, I.; Rumpker, G.

    2015-12-01

    Indonesia is situated at the southern margin of SE Asia, which comprises an assemblage of Gondwana-derived continental terranes, suture zones and volcanic arcs. The formation of SE Asia is believed to have started in Early Devonian. Its complex history involves the opening and closure of three distinct Tethys oceans, each accompanied by the rifting of continental fragments. We apply the receiver function technique to data of the temporary MERAMEX network operated in Central Java from May to October 2004 by the GeoForschungsZentrum Potsdam. The network consisted of 112 mobile stations with a spacing of about 10 km covering the full width of the island between the southern and northern coast lines. The tectonic history is reflected in a complex crustal structure of Central Java exhibiting strong topography of the Moho discontinuity related to different tectonic units. A discontinuity of negative impedance contrast is observed throughout the mid-crust interpreted as the top of a low-velocity layer which shows no depth correlation with the Moho interface. Converted phases generated at greater depth beneath Indonesia indicate the existence of multiple seismic discontinuities within the upper mantle and even below. The strongest signal originates from the base of the mantle transition zone, i.e. the 660 km discontinuity. The phase related to the 410 km discontinuity is less pronounced, but clearly identifiable as well. The derived thickness of the mantle-transition zone is in good agreement with the IASP91 velocity model. Additional phases are observed at roughly 33 s and 90 s relative to the P onset, corresponding to about 300 km and 920 km, respectively. A signal of reversed polarity indicates the top of a low velocity layer at about 370 km depth overlying the mantle transition zone.

  5. Exploring the Cross-sectional Association between Transit-Oriented Development Zoning and Active Travel and Transit Usage in the United States, 2010-2014

    Emily eThrun

    2016-06-01

    Full Text Available Background: In response to traditional zoning codes that contribute to car-dependent, sprawling, and disconnected neighborhoods, communities are reforming their land use laws to create pedestrian-friendly areas that promote physical activity. One such reform is the adoption of transit-oriented developments or districts (TODs. TODs are higher-density, compact, mixed use areas located around transit stops that are designed to encourage walking.Purpose: To identify the characteristics of communities that have adopted TODs in their land use laws and examine if communities that have included TODs in their zoning codes are more likely to have adults that commute by any form of active transportation (i.e., walking, biking, or public transportation or by using public transportation specifically.Methods: Zoning codes effective as of 2010 were obtained for a purposeful sample of the largest 3,914 municipal jurisdictions located in 473 of the most populous US counties and consolidated cities within 48 states and the District of Columbia. They were evaluated to determine whether they included TOD districts or regulations using a coding tool developed by the study team. Descriptive statistics together with t-tests and Pearson’s chi-squared independence test were used to compare characteristics of jurisdictions with and without TOD zoning. Multivariate linear regressions were used to compute the adjusted association between TOD zoning and taking public or active transportation to work.Results: Jurisdictions with TOD zoning were located more in the South and West than non-TOD jurisdictions and were more populous, higher income, more racially diverse, and younger. Jurisdictions with TOD zoning had significantly higher percentages of occupied housing with no vehicle than those without TOD zoning. TOD zoning was associated with significantly higher rates of public transportation to work (β=2.10, 95% CI=0.88, 3.32 and active transportation to work (β=2.48, 95

  6. Aggregate-cement paste transition zone properties affecting the salt-frost damage of high-performance concretes

    Cwirzen, Andrzej; Penttala, Vesa

    2005-01-01

    The influence of the cement paste-aggregate interfacial transition zone (ITZ) on the frost durability of high-performance silica fume concrete (HPSFC) has been studied. Investigation was carried out on eight non-air-entrained concretes having water-to-binder (W/B) ratios of 0.3, 0.35 and 0.42 and different additions of condensed silica fume. Studies on the microstructure and composition of the cement paste have been made by means of environmental scanning electron microscope (ESEM)-BSE, ESEM-EDX and mercury intrusion porosimetry (MIP) analysis. The results showed that the transition zone initiates and accelerates damaging mechanisms by enhancing movement of the pore solution within the concrete during freezing and thawing cycles. Cracks filled with ettringite were primarily formed in the ITZ. The test concretes having good frost-deicing salt durability featured a narrow transition zone and a decreased Ca/Si atomic ratio in the transition zone compared to the bulk cement paste. Moderate additions of silica fume seemed to densify the microstructure of the ITZ

  7. Earthworm activities in cassava and egusi melon fields in the transitional zone of Benin: linking farmers' perceptions with field studies

    Saïdou, A.; Kossou, D.; Brussaard, L.; Richards, P.; Kuyper, T.W.

    2008-01-01

    Farmers' perceptions of earthworm activities were studied in the transitional zone of Benin and linked to scientific explanations of earthworm casting activities. Earthworm activity was assessed in farmers' fields with three different cassava cultivars and in a field experiment with three different

  8. Migration agricole et usages durables de la terre dans la zone de transition forêt-savane (Ghana)

    van der Geest, K.

    2010-01-01

    Au Ghana, d’après des images satellites, la zone de transition entre la forêt et la savane a subi en trente ans une profonde dégradation environnementale. La forte immigration de cultivateurs du Haut Ghana occidental, accentuant une rapide croissance démographique, a accru la pression sur les

  9. Microphysical characteristics of squall-line stratiform precipitation and transition zones inferred using an ice particle property-evolving model

    Jensen, A. A.; Harrington, J. Y.; Morrison, H.

    2017-12-01

    A quasi-idealized 3D squall line (based on a June 2007 Oklahoma case) is simulated using a novel bulk microphysics scheme called the Ice-Spheroids Habit Model with Aspect-ratio Evolution (ISHMAEL). In ISHMAEL, the evolution of ice particle properties, such as mass, shape, maximum diameter, density, and fall speed, are tracked as these properties evolve from vapor growth, sublimation, riming, and melting. Thus, ice properties evolve from various microphysical processes without needing separate unrimed and rimed ice categories. Simulation results show that ISHMAEL produces both a squall-line transition zone and an enhanced stratiform precipitation region. The ice particle properties produced in this simulation are analyzed and compared to observations to determine the characteristics of ice that lead to the development of these squall-line features. It is shown that rimed particles advected rearward from the convective region produce the enhanced stratiform precipitation region. The development of the transition zone results from hydrometer sorting: the evolution of ice particle properties in the convective region produces specific fall speeds that favor significant ice advecting rearward of the transition zone before reaching the melting level, causing a local minimum in precipitation rate and reflectivity there. Microphysical sensitivity studies, for example turning rime splintering off, that lead to changes in ice particle properties reveal that the fall speed of ice particles largely determines both the location of the enhanced stratiform precipitation region and whether or not a transition zone forms.

  10. Seismic structure of the lithosphere beneath NW Namibia: Impact of the Tristan da Cunha mantle plume

    Yuan, Xiaohui; Heit, Benjamin; Brune, Sascha; Steinberger, Bernhard; Geissler, Wolfram H.; Jokat, Wilfried; Weber, Michael

    2017-01-01

    Northwestern Namibia, at the landfall of the Walvis Ridge, was affected by the Tristan da Cunha mantle plume during continental rupture between Africa and South America, as evidenced by the presence of the Etendeka continental flood basalts. Here we use data from a passive-source seismological network to investigate the upper mantle structure and to elucidate the Cretaceous mantle plume-lithosphere interaction. Receiver functions reveal an interface associated with a negative velocity contrast within the lithosphere at an average depth of 80 km. We interpret this interface as the relic of the lithosphere-asthenosphere boundary (LAB) formed during the Mesozoic by interaction of the Tristan da Cunha plume head with the pre-existing lithosphere. The velocity contrast might be explained by stagnated and "frozen" melts beneath an intensively depleted and dehydrated peridotitic mantle. The present-day LAB is poorly visible with converted waves, indicating a gradual impedance contrast. Beneath much of the study area, converted phases of the 410 and 660 km mantle transition zone discontinuities arrive 1.5 s earlier than in the landward plume-unaffected continental interior, suggesting high velocities in the upper mantle caused by a thick lithosphere. This indicates that after lithospheric thinning during continental breakup, the lithosphere has increased in thickness during the last 132 Myr. Thermal cooling of the continental lithosphere alone cannot produce the lithospheric thickness required here. We propose that the remnant plume material, which has a higher seismic velocity than the ambient mantle due to melt depletion and dehydration, significantly contributed to the thickening of the mantle lithosphere.

  11. Mantle superplumes induce geomagnetic superchrons

    Peter eOlson

    2015-07-01

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

  12. Determinants of Transitional Zone Area and Porosity of the Proximal Femur Quantified In Vivo in Postmenopausal Women.

    Shigdel, Rajesh; Osima, Marit; Lukic, Marko; Ahmed, Luai A; Joakimsen, Ragnar M; Eriksen, Erik F; Bjørnerem, Åshild

    2016-04-01

    Bone architecture as well as size and shape is important for bone strength and risk of fracture. Most bone loss is cortical and occurs by trabecularization of the inner part of the cortex. We therefore wanted to identify determinants of the bone architecture, especially the area and porosity of the transitional zone, an inner cortical region with a large surface/matrix volume available for intracortical remodeling. In 211 postmenopausal women aged 54 to 94 years with nonvertebral fractures and 232 controls from the Tromsø Study, Norway, we quantified femoral subtrochanteric architecture in CT images using StrAx1.0 software, and serum levels of bone turnover markers (BTM, procollagen type I N-terminal propeptide and C-terminal cross-linking telopeptide of type I collagen). Multivariable linear and logistic regression analyses were used to quantify associations of age, weight, height, and bone size with bone architecture and BTM, and odds ratio (OR) for fracture. Increasing age, height, and larger total cross-sectional area (TCSA) were associated with larger transitional zone CSA and transitional zone CSA/TCSA (standardized coefficients [STB] = 0.11 to 0.80, p ≤ 0.05). Increasing weight was associated with larger TCSA, but smaller transitional zone CSA/TCSA and thicker cortices (STB = 0.15 to 0.22, p zone (STB = 0.12 to 0.46, p zone CSA/TCSA, and higher porosity of each of the cortical compartments (p zone CSA and higher porosity than controls (p zone, OR for fracture was 1.71 (95% CI, 1.37 to 2.14) and 1.51 (95% CI, 1.23 to 1.85), respectively. Cortical bone architecture is determined mainly by bone size as built during growth and is modified by lifestyle factors throughout life through bone turnover. Fracture cases exhibited larger transitional zone area and porosity, highlighting the importance of cortical bone architecture for fracture propensity. © 2015 American Society for Bone and Mineral Research.

  13. Magnetotelluric Imaging of Lower Crustal Melt and Lithospheric Hydration in the Rocky Mountain Front Transition Zone, Colorado, USA

    Feucht, D. W.; Sheehan, A. F.; Bedrosian, P. A.

    2017-12-01

    We present an electrical resistivity model of the crust and upper mantle from two-dimensional (2-D) anisotropic inversion of magnetotelluric data collected along a 450 km transect of the Rio Grande rift, southern Rocky Mountains, and High Plains in Colorado, USA. Our model provides a window into the modern-day lithosphere beneath the Rocky Mountain Front to depths in excess of 150 km. Two key features of the 2-D resistivity model are (1) a broad zone ( 200 km wide) of enhanced electrical conductivity (minerals, with maximum hydration occurring beneath the Rocky Mountain Front. This lithospheric "hydration front" has implications for the tectonic evolution of the continental interior and the mechanisms by which water infiltrates the lithosphere.

  14. Differentiation of prostate cancer lesions in the Transition Zone by diffusion-weighted MRI

    Jie Bao

    Full Text Available Objective: To differentiate prostate cancer lesions in transition zone by diffusion-weighted-MRI (DW-MRI. Methods: Data from a total of 63 patients who underwent preoperative DWI (b of 0–1000 s/mm2 were prospectively collected and processed by a monoexponential (DWI model and compared with a biexponential (IVIM model for quantitation of apparent diffusion coefficients (ADCs, perfusion fraction f, diffusivity D and pseudo-diffusivity D*. Histogram analyses were performed by outlining entire-tumor regions of interest (ROIs. These parameters (separately and combined in a logistic regression model were used to differentiate lesions depending on histopathological analysis of Magnetic Resonance/transrectal Ultrasound (MR/TRUS fusion-guided biopsy. The diagnostic ability of differentiate the PCa from BHP in TZ was analyzed by ROC regression. Histogram analysis of quantitative parameters and Gleason score were assessed with Spearman correlation. Results: Thirty (30 foci cases of PCa in PZ and 33 (36 foci cases of BPH were confirmed by pathology. Mean ADC, median ADC, 10th percentile ADC, 90th percentile ADC, kurtosis and skewness of ADC and mean D values, median D and 90th percentile D differed significantly between PCa and BHP in TZ. The highest classification accuracy was achieved by the mean ADC (0.841 and mean D (0.809. A logistic regression model based on mean ADC and mean D led to an AUC of 0.873, however, the difference is not significant. There were 7 Gleason 6 areas, 9 Gleason 7 areas, 8 Gleason 8 areas, 5 Gleason 9 areas and 2 Gleason 10 areas detected from the 31 prostate cancer areas, the mean Gleason value was(7.5 ± 1.2. The mean ADC and mean D had correlation with Gleason score(r = −0.522 and r = −0.407 respectively, P < 0.05. Conclusion: The diagnosis efficiency of IVIM parameters was not superior to ADC in the diagnosis of PCa in TZ. Moreover, the combination of mean ADC and mean D did not

  15. Stress Drops for Oceanic Crust and Mantle Intraplate Earthquakes in the Subduction Zone of Northeastern Japan Inferred from the Spectral Inversion Analysis

    Si, H.; Ishikawa, K.; Arai, T.; Ibrahim, R.

    2017-12-01

    Understanding stress drop related to intraplate earthquakes in the subducting plate is very important for seismic hazard mitigation. In previous studies, Kita et al. (2015) analyzed stress drops for intraplate earthquakes under Hokkaido, Northern Japan, using S-coda wave spectral ratio analysis methods, and found that the stress drop for events occurring more than 10 km beneath the upper surface of the subducting plate (within the oceanic mantle) was larger than the stress drop for events occurring within 10 km of the upper surface of the subducting plate (in the oceanic crust). In this study, we focus on intraplate earthquakes that occur under Tohoku, Northeastern Japan, to determine whether similar stress drop differences may exist between earthquakes occurring within the upper 10 km of the subducting plate (within the oceanic crust) and those occurring deeper than 10 km (within the oceanic mantle), based on spectral inversion analysis of seismic waveforms recorded during the earthquakes. We selected 64 earthquakes with focal depths between 49-76 km and Mw 3.5-5.0 that occurred in the source area of the 2003 Miyagi-ken-oki earthquake (Mw 7.0) (region 1), and 82 earthquakes with focal depths between 49-67 km and Mw 3.5-5.5 in the source area of the 2011 Miyagi- ken-oki earthquake (Mw 7.1) (region 2). Records from the target earthquakes at 24 stations in region 1 and 21 stations in region 2 were used in the analysis. A 5-sec time window following S-wave onset was used for each station record. Borehole records of KiK-net station (MYGH04) was used as a reference station for both regions 1 and 2. We applied the spectral inversion analysis method of Matsunami et al. (2003) separately to regions 1 and 2. Our results show that stress drop generally increases with focal depth and that the stress drop for events occurring deeper than 10 km in the plate (within the oceanic mantle) were larger than the stress drop for events occurring within 10 km of the upper surface of the

  16. Forging the Link: Using a Conservative Mixing Framework to Characterize Connections between Rivers and Great Lakes in River-lake Transition Zones

    River-to-Great Lake transition zones are hydrologically, biogeochemically and biologically dynamic areas that regulate nutrient and energy fluxes between rivers and Great Lakes. Our goal is to characterize the biogeochemical properties of the river-lake transition zones and under...

  17. Numerical simulations of the mantle lithosphere delamination

    Morency, C.; Doin, M.-P.

    2004-03-01

    Sudden uplift, extension, and increased igneous activity are often explained by rapid mechanical thinning of the lithospheric mantle. Two main thinning mechanisms have been proposed, convective removal of a thickened lithospheric root and delamination of the mantle lithosphere along the Moho. In the latter case, the whole mantle lithosphere peels away from the crust by the propagation of a localized shear zone and sinks into the mantle. To study this mechanism, we perform two-dimensional (2-D) numerical simulations of convection using a viscoplastic rheology with an effective viscosity depending strongly on temperature, depth, composition (crust/mantle), and stress. The simulations develop in four steps. (1) We first obtain "classical" sublithospheric convection for a long time period (˜300 Myr), yielding a slightly heterogeneous lithospheric temperature structure. (2) At some time, in some simulations, a strong thinning of the mantle occurs progressively in a small area (˜100 km wide). This process puts the asthenosphere in direct contact with the lower crust. (3) Large pieces of mantle lithosphere then quickly sink into the mantle by the horizontal propagation of a detachment level away from the "asthenospheric conduit" or by progressive erosion on the flanks of the delaminated area. (4) Delamination pauses or stops when the lithospheric mantle part detaches or when small-scale convection on the flanks of the delaminated area is counterbalanced by heat diffusion. We determine the parameters (crustal thicknesses, activation energies, and friction coefficients) leading to delamination initiation (step 2). We find that delamination initiates where the Moho temperature is the highest, as soon as the crust and mantle viscosities are sufficiently low. Delamination should occur on Earth when the Moho temperature exceeds ˜800°C. This condition can be reached by thermal relaxation in a thickened crust in orogenic setting or by corner flow lithospheric erosion in the

  18. TRANSIT SURVEYS FOR EARTHS IN THE HABITABLE ZONES OF WHITE DWARFS

    Agol, Eric

    2011-01-01

    To date the search for habitable Earth-like planets has primarily focused on nuclear burning stars. I propose that this search should be expanded to cool white dwarf stars that have expended their nuclear fuel. I define the continuously habitable zone of white dwarfs and show that it extends from ∼0.005 to 0.02 AU for white dwarfs with masses from 0.4 to 0.9 M sun , temperatures less than ∼10 4 K, and habitable durations of at least 3 Gyr. As they are similar in size to Earth, white dwarfs may be deeply eclipsed by terrestrial planets that orbit edge-on, which can easily be detected with ground-based telescopes. If planets can migrate inward or reform near white dwarfs, I show that a global robotic telescope network could carry out a transit survey of nearby white dwarfs placing interesting constraints on the presence of habitable Earths. If planets were detected, I show that the survey would favor detection of planets similar to Earth: similar size, temperature, and rotation period, and host star temperatures similar to the Sun. The Large Synoptic Survey Telescope could place even tighter constraints on the frequency of habitable Earths around white dwarfs. The confirmation and characterization of these planets might be carried out with large ground and space telescopes.

  19. Distribution of Neuroendocrine Cells in the Transition Zone of the Prostate

    Yuki Kyoda

    2017-01-01

    Full Text Available Objectives. To evaluate the distribution of neuroendocrine (NE cells which may influence the development of benign prostatic hyperplasia (BPH in the transition zone (TZ. Methods. We reviewed specimens from 80 patients who underwent radical prostatectomy in our institution and evaluated the density of NE cells in the TZ. They were histologically classified into 3 groups: those with no adenomatous nodule in the TZ (group A, those with small nodules with normal epithelium and stroma around them in the TZ (group B, and those with large nodules occupying the TZ (group C. In the patients of group B, intra-adenoma (adenomatous nodules and extra-adenoma (normal tissue NE cells in the TZ were separately counted. Results. There were 22, 23, and 35 patients in groups A, B, and C, respectively. The median density of NE cells in the TZ of group B patients, 2.80/mm2, was significantly higher than that of NE cells in group A, 1.43/mm2, and group C, 0.61/mm2 (p<0.001. In group B, the median density of extra-adenoma NE cells was significantly higher than that of intra-adenoma. Conclusions. Many NE cells exist around small adenoma in the TZ. NE cells may influence the initial growth of BPH in a paracrine fashion. Trial Registration. This study approved by our institutional review board was retrospectively registered (#272-14.

  20. Large and giant hydrocarbon accumulations in the transitional continent-ocean zone

    Khain, V. E.; Polyakova, I. D.

    2008-05-01

    The petroleum resource potential is considered for the Atlantic, West Pacific, and East Pacific types of deepwater continental margins. The most considerable energy resources are concentrated at the Atlantic-type passive margins in the zone transitional to the ocean. The less studied continental slope of backarc seas of the generally active margins of the West Pacific type is currently not so rich in discoveries as the Atlantic-type margin, but is not devoid of certain expectations. In some of their parameters, the margins bounded by continental slopes may be regarded as analogs of classical passive margins. At the margins of the East Pacific type, the petroleum potential is solely confined to transform segments. In the shelf-continental-slope basins of the rift and pull-apart nature, petroleum fields occur largely in the upper fan complex, and to a lesser extent in the lower graben (rift) complex. In light of world experience, the shelf-continental-slope basins of the Arctic and Pacific margins of Russia are evaluated as highly promising.

  1. Soil Structure Evaluation Across Geologic Transition Zones Using 2D Electrical Resistivity Imaging Technique

    Geraldine C Anukwu

    2017-06-01

    Full Text Available This study utilizes the electrical resistivity values obtained using 2-D Electrical resistivity imaging (ERI technique to evaluate the subsurface lithology across different geological units. The primary objective was to determine the effect of subsurface lithology on the integrity of a road pavement, which had developed cracks and potholes at various locations. The dipole-dipole configuration was utilized and a total of nine traverses were established in the study area, whose geology cuts across both the basement and sedimentary complexes. The inverted resistivity section obtained showed significant variation in resistivity along established traverses and also across the different rock units, with the resistivity value ranging from about 4 ohm-m to greater than 7000 ohm- m. The lithology as interpreted from the resistivity section revealed the presence topsoil, clay, sandy clay, sand, sand stones/basement rocks, with varying vertical and horizontal arrangements to a depth of 40m. Results suggest that the geologic sequence and structure might have contributed to the observed pavement failure. The capability of the 2D ERI as an imaging tool is observed, especially across the transition zones as depicted in this study. The study further stressed the ability of this technique if properly designed and implemented, to be capable of providing a wealth of information that could complement other traditional geotechnical and geologic techniques.

  2. Role of Transition Zone Index in the Prediction of Clinical Benign Prostatic Hyperplasia

    Muhammet Güzelsoy

    2016-12-01

    Full Text Available Objective The objective of this study was to determine the role of the transition zone (TZ index (TZI in the prediction of clinical benign prostatic hyperplasia (BPH in patients who underwent transurethral prostatectomy (TUR-P and to analyze the correlation between the amount of resected tissue and TZ volume (TZV. Materials and Methods Twenty-six male clinical BPH patients with obstructive complaints and 17 male benign prostate enlargement (BPE patients without any complaints were included in the study. Both the groups were over the age of 50. Clinical BPH patients underwent complete TUR-P. Statistical analysis was done with SPSS. Sensitivity, specificity, positive and negative predictive values of TZI-as a method of assessing clinical BPH-were measured. Results There was a statistically significant difference in prostate volume, uroflowmetry patterns, prostate-specific antigen (PSA, International prostate symptom score (IPSS, TZV and TZI between the two groups. There was a correlation between TZV and the amount of resected tissue (r=0.97; p0.40 has a high level of sensitivity and specificity in the prediction of clinical BPH among patients who undergo TUR-P due to obstructive symptoms and reported as BPH. There is a strong correlation between the amount of resected tissue and TZV. TZI is a valuable tool in diagnosis, and TZV gives valuable information about the patient to the surgeon.

  3. STEEL-SLAG AS SUBSTITUTE TO NATURAL AGGREGATES, PROPERTIES AND THE INTERFACIAL TRANSITION ZONE

    Han Ay Lie

    2012-02-01

    Full Text Available Steel-slag is a residual product of the steel industry that has potential ability to pollute the ground water and soil containing heavy metals. To overcome this problem, attempts have been made for using the slag as substitute for both coarse and fine aggregates in concrete. The solidification process will prevent the metal components from polluting the water and soil. Test results on the mechanical properties of slag-concrete showed that while the compression strength of slag-concrete increased significantly as a function of slag-to-natural aggregate’s use, the tensile strength dropped accordingly. The substitution of fine-slag to Muntilan sand was even more negative, the compression strength decreased as a function of slag use. Research into the influences of the Interfacial Transition Zone was conducted, since the ITZ itself forms a weak link within the concrete matrix. The SEM tests were performed at the Quarter Laboratory, Department of Geology in Bandung using a Scanning Electron Microscope type JEOL.

  4. Finite Element Method Analysis of An Out Flow With Free Surface In Transition Zones

    Saoula, R. Iddir S.; Mokhtar, K. Ait

    The object of this work is to present this part of the fluid mechanics that relates to out-flows of the fluid to big speeds in transitions. Results usually gotten by the classic processes can only have a qualitative aspect. The method fluently used for the count of these out-flows to big speeds is the one of characteristics, this approach remains interesting so much that doesn't appear within the out-flow of intersections of shock waves, as well as of reflections of these. In the simple geometry case, the method of finite differences satisfying result, But when the complexity of this geometry imposes itself, it is the method of finite elements that is proposed to solve this type of prob- lem, in particular for problems Trans critic. The goal of our work is to analyse free surface flows in channels no prismatic has oblong transverse section in zone of tran- sition. (Convergent, divergent). The basic mathematical model of this study is Saint Venant derivatives partial equations. To solve these equations we use the finite ele- ment method, the element of reference is the triangular element with 6 nodes which are quadratic in speed and linear in height (pressure). Our results and their obtains by others are very close to experimental results.

  5. Upper Mantle Responses to India-Eurasia Collision in Indochina, Malaysia, and the South China Sea

    Hongsresawat, S.; Russo, R. M.

    2016-12-01

    parallel the strike of the now-inoperative spreading center in the South China Sea. This transition appears to occur in the central portion of Peninsular Malaysia and may mark the boundary between Tethyan upper mantle extruded from the India-Asia collision zone and supra-subduction upper mantle of the Indonesian arc.

  6. Fine-scale structure of the mid-mantle characterised by global stacks of PP precursors

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

    2017-08-01

    Subduction zones are likely a major source of compositional heterogeneities in the mantle, which may preserve a record of the subduction history and mantle convection processes. The fine-scale structure associated with mantle heterogeneities can be studied using the scattered seismic wavefield that arrives as coda to or as energy preceding many body wave arrivals. In this study we analyse precursors to PP by creating stacks recorded at globally distributed stations. We create stacks aligned on the PP arrival in 5° distance bins (with range 70-120°) from 600 earthquakes recorded at 193 stations stacking a total of 7320 seismic records. As the energy trailing the direct P arrival, the P coda, interferes with the PP precursors, we suppress the P coda by subtracting a best fitting exponential curve to this energy. The resultant stacks show that PP precursors related to scattering from heterogeneities in the mantle are present for all distances. Lateral variations are explored by producing two regional stacks across the Atlantic and Pacific hemispheres, but we find only negligible differences in the precursory signature between these two regions. The similarity of these two regions suggests that well mixed subducted material can survive at upper and mid-mantle depth. To describe the scattered wavefield in the mantle, we compare the global stacks to synthetic seismograms generated using a Monte Carlo phonon scattering technique. We propose a best-fitting layered heterogeneity model, BRT2017, characterised by a three layer mantle with a background heterogeneity strength (ɛ = 0.8%) and a depth-interval of increased heterogeneity strength (ɛ = 1%) between 1000 km and 1800 km. The scalelength of heterogeneity is found to be 8 km throughout the mantle. Since mantle heterogeneity of 8 km scale may be linked to subducted oceanic crust, the detection of increased heterogeneity at mid-mantle depths could be associated with stalled slabs due to increases in viscosity

  7. Testosterone and dihydrotestosterone levels in the transition zone correlate with prostate volume.

    Pejčić, Tomislav; Tosti, Tomislav; Tešić, Živoslav; Milković, Borivoj; Dragičević, Dejan; Kozomara, Milutin; Čekerevac, Milica; Džamić, Zoran

    2017-07-01

    There is still no consensus regarding intraprostatic androgen levels and the accumulation of androgens in the hyperplastic prostatic tissue. The current opinion is that intraprostatic dihydrotestosterone (DHT) concentrations are maintained but not elevated in benign prostatic hyperplasia (BPH), while there is no similar data concerning intraprostatic testosterone (T). Tissue T (tT) and tissue DHT (tDHT) concentration were determined in 93 patients scheduled for initial prostate biopsy. The criteria for biopsy were abnormal DRE and/or PSA > 4 ng/mL. Total prostate volume (TPV) was determined by transrectal ultrasound (TRUS). During TRUS- guided prostate biopsy, 10-12 samples were collected from the peripheral zone (PZ) and two additional samples were collected from the transition zone (TZ). The samples from the TZ were immediately frozen in liquid nitrogen at -70°C, and transported for tissue androgen determination, using liquid chromatography mass spectrometry (LC-MS). Pathological analysis revealed that prostate cancer (PCa) was present in 45 and absent in 48 patients. In the whole group, there were 42 men with small prostate (TPV prostate (TPV ≥ 31 mL). The overall average tT level was 0.79 ± 0.66 ng/g, while the average tDHT level was 10.27 ± 7.15 ng/g. There were no differences in tT and tDHT level in prostates with and without PCa. However, tT and tDHT levels were significantly higher in larger, than in smaller prostates (tT: 1.05 ± 0.75 and 0.46 ± 0.29 ng/g, and tDHT: 15.0 ± 6.09 and 4.51 ± 2.75 ng/g, respectively). There were strong correlations between tT and TPV (r = 0.71), and tDHT and TPV (r = 0.74). The present study confirmed that both T and DHT accumulated in the stroma of enlarged prostates; the degree of accumulation correlated with prostate volume. © 2017 Wiley Periodicals, Inc.

  8. Low incidence of prostate cancer identified in the transition and anterior zones with transperineal biopsy

    Danforth TL

    2012-12-01

    Full Text Available Teresa L Danforth,1 K Kent Chevli,1,2 Louis Baumann,1,2 Michael Duff1,21The State University of New York (SUNY, Buffalo, NY, 2Cancer Care of Western New York, Cheektowaga, NY, USAPurpose: Determine the incidence of anterior (AZ and transition (TZ zone prostate cancers using a transperineal mapping approach.Methods: A retrospective review of 137 patients with history of previous negative biopsy undergoing transperineal saturation biopsy for an elevated prostate-specific antigen (PSA, high-grade prostate intraepithelial neoplasia, atypical small acinar proliferation history, or abnormal digital rectal exam. The number of biopsy cores was determined by prostate volume and obtained using a predefined template. The electronic medical records were reviewed for patients' clinical and pathological characteristics.Results: Forty-one of 137 patients (31.4% had positive biopsy for prostate adenocarcinoma; 11 were from 24-core, 19 from 36-core, and 11 from 48-core sampling. Glands > 45 mL had a mean of 1.7 previous biopsies and a PSA of 9.1 ng/mL. Glands < 30 mL were 1.3 and 6.3 ng/mL and glands 30–45 mL were 1.4 and 6.5 ng/mL. Glands < 45 mL had a higher number of positive biopsies per total cores. Seven patients chose active surveillance while 34 chose treatment. Of the 36- and 48-cores biopsies, 2.2% and 1.5%, respectively, were positive in the TZ. One patient was AZ-positive, 1 was TZ-positive, and 18 were peripheral zone (PZ-positive alone. Twelve patients had cancer detected in PZ and TZ. Two patients developed urinary retention and one had a urine infection.Conclusion: Transperineal saturation biopsy is a safe and efficacious method of prostate cancer detection in patients with previous negative biopsy and high suspicion for cancer. Few cancers were found to originate in the TZ or AZ alone. We recommend that initial biopsy templates should sample PZ with less focus on the TZ.Keywords: carcinoma, prostate, biopsy, transperineal

  9. Stochastic Inversion of Geomagnetic Observatory Data Including Rigorous Treatment of the Ocean Induction Effect With Implications for Transition Zone Water Content and Thermal Structure

    Munch, F. D.; Grayver, A. V.; Kuvshinov, A.; Khan, A.

    2018-01-01

    In this paper we estimate and invert local electromagnetic (EM) sounding data for 1-D conductivity profiles in the presence of nonuniform oceans and continents to most rigorously account for the ocean induction effect that is known to strongly influence coastal observatories. We consider a new set of high-quality time series of geomagnetic observatory data, including hitherto unused data from island observatories installed over the last decade. The EM sounding data are inverted in the period range 3-85 days using stochastic optimization and model exploration techniques to provide estimates of model range and uncertainty. The inverted conductivity profiles are best constrained in the depth range 400-1,400 km and reveal significant lateral variations between 400 km and 1,000 km depth. To interpret the inverted conductivity anomalies in terms of water content and temperature, we combine laboratory-measured electrical conductivity of mantle minerals with phase equilibrium computations. Based on this procedure, relatively low temperatures (1200-1350°C) are observed in the transition zone (TZ) underneath stations located in Southern Australia, Southern Europe, Northern Africa, and North America. In contrast, higher temperatures (1400-1500°C) are inferred beneath observatories on islands, Northeast Asia, and central Australia. TZ water content beneath European and African stations is ˜0.05-0.1 wt %, whereas higher water contents (˜0.5-1 wt %) are inferred underneath North America, Asia, and Southern Australia. Comparison of the inverted water contents with laboratory-constrained water storage capacities suggests the presence of melt in or around the TZ underneath four geomagnetic observatories in North America and Northeast Asia.

  10. Molecular landscape of modified histones in Drosophila heterochromatic genes and euchromatin-heterochromatin transition zones.

    Jiro C Yasuhara

    2008-01-01

    Full Text Available Constitutive heterochromatin is enriched in repetitive sequences and histone H3-methylated-at-lysine 9. Both components contribute to heterochromatin's ability to silence euchromatic genes. However, heterochromatin also harbors hundreds of expressed genes in organisms such as Drosophila. Recent studies have provided a detailed picture of sequence organization of D. melanogaster heterochromatin, but how histone modifications are associated with heterochromatic sequences at high resolution has not been described. Here, distributions of modified histones in the vicinity of heterochromatic genes of normal embryos and embryos homozygous for a chromosome rearrangement were characterized using chromatin immunoprecipitation and genome tiling arrays. We found that H3-di-methylated-at-lysine 9 (H3K9me2 was depleted at the 5' ends but enriched throughout transcribed regions of heterochromatic genes. The profile was distinct from that of euchromatic genes and suggests that heterochromatic genes are integrated into, rather than insulated from, the H3K9me2-enriched domain. Moreover, the profile was only subtly affected by a Su(var3-9 null mutation, implicating a histone methyltransferase other than SU(VAR3-9 as responsible for most H3K9me2 associated with heterochromatic genes in embryos. On a chromosomal scale, we observed a sharp transition to the H3K9me2 domain, which coincided with increased retrotransposon density in the euchromatin-heterochromatin (eu-het transition zones on the long chromosome arms. Thus, a certain density of retrotransposons, rather than specific boundary elements, may demarcate Drosophila pericentric heterochromatin. We also demonstrate that a chromosome rearrangement that created a new eu-het junction altered H3K9me2 distribution and induced new euchromatic sites of enrichment as far as several megabases away from the breakpoint. Taken together, the findings argue against simple classification of H3K9me as the definitive signature

  11. Differences in microRNA expression during tumor development in the transition and peripheral zones of the prostate

    Carlsson, Jessica; Helenius, Gisela; Karlsson, Mats G; Andrén, Ove; Klinga-Levan, Karin; Olsson, Björn

    2013-01-01

    The prostate is divided into three glandular zones, the peripheral zone (PZ), the transition zone (TZ), and the central zone. Most prostate tumors arise in the peripheral zone (70-75%) and in the transition zone (20-25%) while only 10% arise in the central zone. The aim of this study was to investigate if differences in miRNA expression could be a possible explanation for the difference in propensity of tumors in the zones of the prostate. Patients with prostate cancer were included in the study if they had a tumor with Gleason grade 3 in the PZ, the TZ, or both (n=16). Normal prostate tissue was collected from men undergoing cystoprostatectomy (n=20). The expression of 667 unique miRNAs was investigated using TaqMan low density arrays for miRNAs. Student’s t-test was used in order to identify differentially expressed miRNAs, followed by hierarchical clustering and principal component analysis (PCA) to study the separation of the tissues. The ADtree algorithm was used to identify markers for classification of tissues and a cross-validation procedure was used to test the generality of the identified miRNA-based classifiers. The t-tests revealed that the major differences in miRNA expression are found between normal and malignant tissues. Hierarchical clustering and PCA based on differentially expressed miRNAs between normal and malignant tissues showed perfect separation between samples, while the corresponding analyses based on differentially expressed miRNAs between the two zones showed several misplaced samples. A classification and cross-validation procedure confirmed these results and several potential miRNA markers were identified. The results of this study indicate that the major differences in the transcription program are those arising during tumor development, rather than during normal tissue development. In addition, tumors arising in the TZ have more unique differentially expressed miRNAs compared to the PZ. The results also indicate that separate mi

  12. Validation of Small Kepler Transiting Planet Candidates in or near the Habitable Zone

    Torres, Guillermo; Kane, Stephen R.; Rowe, Jason F.; Batalha, Natalie M.; Henze, Christopher E.; Ciardi, David R.; Barclay, Thomas; Borucki, William J.; Buchhave, Lars A.; Crepp, Justin R.; Everett, Mark E.; Horch, Elliott P.; Howard, Andrew W.; Howell, Steve B.; Isaacson, Howard T.; Jenkins, Jon M.; Latham, David W.; Petigura, Erik A.; Quintana, Elisa V.

    2017-12-01

    A main goal of NASA’s Kepler Mission is to establish the frequency of potentially habitable Earth-size planets ({η }\\oplus ). Relatively few such candidates identified by the mission can be confirmed to be rocky via dynamical measurement of their mass. Here we report an effort to validate 18 of them statistically using the BLENDER technique, by showing that the likelihood they are true planets is far greater than that of a false positive. Our analysis incorporates follow-up observations including high-resolution optical and near-infrared spectroscopy, high-resolution imaging, and information from the analysis of the flux centroids of the Kepler observations themselves. Although many of these candidates have been previously validated by others, the confidence levels reported typically ignore the possibility that the planet may transit a star different from the target along the same line of sight. If that were the case, a planet that appears small enough to be rocky may actually be considerably larger and therefore less interesting from the point of view of habitability. We take this into consideration here and are able to validate 15 of our candidates at a 99.73% (3σ) significance level or higher, and the other three at a slightly lower confidence. We characterize the GKM host stars using available ground-based observations and provide updated parameters for the planets, with sizes between 0.8 and 2.9 R ⊕. Seven of them (KOI-0438.02, 0463.01, 2418.01, 2626.01, 3282.01, 4036.01, and 5856.01) have a better than 50% chance of being smaller than 2 R ⊕ and being in the habitable zone of their host stars.

  13. Decomposition of Phragmites australis rhizomes in artificial land-water transitional zones (ALWTZs) and management implications

    Han, Zhen; Cui, Baoshan; Zhang, Yongtao

    2015-09-01

    Rhizomes are essential organs for growth and expansion of Phragmites australis. They function as an important source of organic matter and as a nutrient source, especially in the artificial land-water transitional zones (ALWTZs) of shallow lakes. In this study, decomposition experiments on 1- to 6-year-old P. australis rhizomes were conducted in the ALWTZ of Lake Baiyangdian to evaluate the contribution of the rhizomes to organic matter accumulation and nutrient release. Mass loss and changes in nutrient content were measured after 3, 7, 15, 30, 60, 90, 120, and 180 days. The decomposition process was modeled with a composite exponential model. The Pearson correlation analysis was used to analyze the relationships between mass loss and litter quality factors. A multiple stepwise regression model was utilized to determine the dominant factors that affect mass loss. Results showed that the decomposition rates in water were significantly higher than those in soil for 1- to 6-year-old rhizomes. However, the sequence of decomposition rates was identical in both water and soil. Significant relationships between mass loss and litter quality factors were observed at a later stage, and P-related factors proved to have a more significant impact than N-related factors on mass loss. According to multiple stepwise models, the C/P ratio was found to be the dominant factor affecting the mass loss in water, and the C/N and C/P ratios were the main factors affecting the mass loss in soil. The combined effects of harvesting, ditch broadening, and control of water depth should be considered for lake administrators.

  14. Transitions in Land Use Architecture under Multiple Human Driving Forces in a Semi-Arid Zone

    Issa Ouedraogo

    2015-07-01

    Full Text Available The present study aimed to detect the main shifts in land-use architecture and assess the factors behind the changes in typical tropical semi-arid land in Burkina Faso. Three sets of time-series LANDSAT data over a 23-year period were used to detect land use changes and their underpinning drivers in multifunctional but vulnerable ecologies. Group discussions in selected villages were organized for mapping output interpretation and collection of essential drivers of change as perceived by local populations. Results revealed profound changes and transitions during the study period. During the last decade, shrub and wood savannahs exhibited high net changes (39% and −37% respectively with a weak net positive change for cropland (only 2%, while cropland and shrub savannah exhibited high swap (8% and 16%. This suggests that the area of cropland remained almost unchanged but was subject to relocation, wood savannah decreased drastically, and shrub savannah increased exponentially. Cropland exhibited a null net persistence while shrub and wood savannahs exhibited positive and negative net persistence (1.91 and −10.24, respectively, indicating that there is movement toward agricultural intensification and wood savannah tended to disappear to the benefit of shrub savannah. Local people are aware of the changes that have occurred and support the idea that illegal wood cutting and farming are inappropriate farming practices associated with immigration; absence of alternative cash generation sources, overgrazing and increasing demand for wood energy are driving the changes in their ecosystems. Policies that integrate restoration and conservation of natural ecosystems and promote sustainable agroforestry practices in the study zone are highly recommended.

  15. Logistic regression model for diagnosis of transition zone prostate cancer on multi-parametric MRI

    Dikaios, Nikolaos; Halligan, Steve; Taylor, Stuart; Atkinson, David; Punwani, Shonit [University College London, Centre for Medical Imaging, London (United Kingdom); University College London Hospital, Departments of Radiology, London (United Kingdom); Alkalbani, Jokha; Sidhu, Harbir Singh; Fujiwara, Taiki [University College London, Centre for Medical Imaging, London (United Kingdom); Abd-Alazeez, Mohamed; Ahmed, Hashim; Emberton, Mark [University College London, Research Department of Urology, London (United Kingdom); Kirkham, Alex; Allen, Clare [University College London Hospital, Departments of Radiology, London (United Kingdom); Freeman, Alex [University College London Hospital, Department of Histopathology, London (United Kingdom)

    2014-09-17

    We aimed to develop logistic regression (LR) models for classifying prostate cancer within the transition zone on multi-parametric magnetic resonance imaging (mp-MRI). One hundred and fifty-five patients (training cohort, 70 patients; temporal validation cohort, 85 patients) underwent mp-MRI and transperineal-template-prostate-mapping (TPM) biopsy. Positive cores were classified by cancer definitions: (1) any-cancer; (2) definition-1 [≥Gleason 4 + 3 or ≥ 6 mm cancer core length (CCL)] [high risk significant]; and (3) definition-2 (≥Gleason 3 + 4 or ≥ 4 mm CCL) cancer [intermediate-high risk significant]. For each, logistic-regression mp-MRI models were derived from the training cohort and validated internally and with the temporal cohort. Sensitivity/specificity and the area under the receiver operating characteristic (ROC-AUC) curve were calculated. LR model performance was compared to radiologists' performance. Twenty-eight of 70 patients from the training cohort, and 25/85 patients from the temporal validation cohort had significant cancer on TPM. The ROC-AUC of the LR model for classification of cancer was 0.73/0.67 at internal/temporal validation. The radiologist A/B ROC-AUC was 0.65/0.74 (temporal cohort). For patients scored by radiologists as Prostate Imaging Reporting and Data System (Pi-RADS) score 3, sensitivity/specificity of radiologist A 'best guess' and LR model was 0.14/0.54 and 0.71/0.61, respectively; and radiologist B 'best guess' and LR model was 0.40/0.34 and 0.50/0.76, respectively. LR models can improve classification of Pi-RADS score 3 lesions similar to experienced radiologists. (orig.)

  16. The ichthyoplankton assemblage of the Canaries-African Coastal Transition Zone: A review

    Rodriguez, J. M.; Moyano, M.; Hernandez-Leon, S.

    2009-12-01

    In this paper we review information on the ichthyoplankton assemblage of the Canaries-African Coastal Transition Zone (C-ACTZ). This CTZ shows the singularity that the Canary Archipelago interrupts the main flow of the Canary Current and Trade Winds, introducing large mesoscale variability, in the form of island warm wakes and cyclonic and anticyclonic eddies downstream of the islands. Besides, upwelling filaments stretch towards the archipelago from the African coastal upwelling, transporting phytoplankton, zooplankton and fish larvae. They also interact with eddies shed from the islands to exchange water properties and biogenic material. All these mesoscale features influence the composition, structure, abundance and distribution of the larval fish community (LFC) of the region. The Canary Current (CC) and eddies shed from the islands drag larvae of island neritic fish species into the oceanic region and contribute, along warm wakes, to the horizontal distribution of fish larvae. Upwelling and upwelling filaments transport larvae of African neritic species into the oceanic region. These larvae dominate the LFC and account for the relatively high average larval fish abundance found in the C-ACTZ during the summer upwelling season. Filaments originated in the region of Cape Juby-Cape Bojador are entrained around a quasi-permanent cyclonic eddy, trapped between Gran Canaria Island and the African coast, forming a system through which most of the African neritic larvae may return to the African shelf. However, some larvae reach the eastern islands of the Canary archipelago and they may be spread all over the neritic region of the archipelago by eddies shed from the islands. Also in summer, the distribution of the LFC of the C-ACTZ is vertically stratified and fish larvae seem to carry out little or not diel vertical migration. Overall, this study highlights the strong relationship between mesoscale oceanographic processes and the LFC in the C-ACTZ.

  17. Logistic regression model for diagnosis of transition zone prostate cancer on multi-parametric MRI

    Dikaios, Nikolaos; Halligan, Steve; Taylor, Stuart; Atkinson, David; Punwani, Shonit; Alkalbani, Jokha; Sidhu, Harbir Singh; Fujiwara, Taiki; Abd-Alazeez, Mohamed; Ahmed, Hashim; Emberton, Mark; Kirkham, Alex; Allen, Clare; Freeman, Alex

    2015-01-01

    We aimed to develop logistic regression (LR) models for classifying prostate cancer within the transition zone on multi-parametric magnetic resonance imaging (mp-MRI). One hundred and fifty-five patients (training cohort, 70 patients; temporal validation cohort, 85 patients) underwent mp-MRI and transperineal-template-prostate-mapping (TPM) biopsy. Positive cores were classified by cancer definitions: (1) any-cancer; (2) definition-1 [≥Gleason 4 + 3 or ≥ 6 mm cancer core length (CCL)] [high risk significant]; and (3) definition-2 (≥Gleason 3 + 4 or ≥ 4 mm CCL) cancer [intermediate-high risk significant]. For each, logistic-regression mp-MRI models were derived from the training cohort and validated internally and with the temporal cohort. Sensitivity/specificity and the area under the receiver operating characteristic (ROC-AUC) curve were calculated. LR model performance was compared to radiologists' performance. Twenty-eight of 70 patients from the training cohort, and 25/85 patients from the temporal validation cohort had significant cancer on TPM. The ROC-AUC of the LR model for classification of cancer was 0.73/0.67 at internal/temporal validation. The radiologist A/B ROC-AUC was 0.65/0.74 (temporal cohort). For patients scored by radiologists as Prostate Imaging Reporting and Data System (Pi-RADS) score 3, sensitivity/specificity of radiologist A 'best guess' and LR model was 0.14/0.54 and 0.71/0.61, respectively; and radiologist B 'best guess' and LR model was 0.40/0.34 and 0.50/0.76, respectively. LR models can improve classification of Pi-RADS score 3 lesions similar to experienced radiologists. (orig.)

  18. ''Textural analysis of multiparametric MRI detects transition zone prostate cancer''

    Sidhu, Harbir S.; Johnston, Edward W.; Taylor, Stuart A.; Halligan, Steve [Centre for Medical Imaging, University College London, London (United Kingdom); University College London Hospitals NHS Foundation Trust, London (United Kingdom); Benigno, Salvatore; Dikaios, Nikos [Centre for Medical Imaging, University College London, London (United Kingdom); Ganeshan, Balaji [Institute of Nuclear Medicine, University College London, University College Hospital, London (United Kingdom); Allen, Clare; Kirkham, Alex [University College London Hospitals NHS Foundation Trust, London (United Kingdom); Groves, Ashley M. [University College London Hospitals NHS Foundation Trust, London (United Kingdom); Institute of Nuclear Medicine, University College London, University College Hospital, London (United Kingdom); Ahmed, Hashim U.; Emberton, Mark [University College London Hospitals NHS Foundation Trust, London (United Kingdom); University College London, Research Department of Urology, London (United Kingdom); Punwani, Shonit [Centre for Medical Imaging, University College London, London (United Kingdom); University College London Hospitals NHS Foundation Trust, London (United Kingdom); Centre for Medical Imaging, University College London and University College London Hospitals NIHR Biomedical Research Centre, London (United Kingdom)

    2017-06-15

    To evaluate multiparametric-MRI (mpMRI) derived histogram textural-analysis parameters for detection of transition zone (TZ) prostatic tumour. Sixty-seven consecutive men with suspected prostate cancer underwent 1.5T mpMRI prior to template-mapping-biopsy (TPM). Twenty-six men had 'significant' TZ tumour. Two radiologists in consensus matched TPM to the single axial slice best depicting tumour, or largest TZ diameter for those with benign histology, to define single-slice whole TZ-regions-of-interest (ROIs). Textural-parameter differences between single-slice whole TZ-ROI containing significant tumour versus benign/insignificant tumour were analysed using Mann Whitney U test. Diagnostic accuracy was assessed by receiver operating characteristic area under curve (ROC-AUC) analysis cross-validated with leave-one-out (LOO) analysis. ADC kurtosis was significantly lower (p < 0.001) in TZ containing significant tumour with ROC-AUC 0.80 (LOO-AUC 0.78); the difference became non-significant following exclusion of significant tumour from single-slice whole TZ-ROI (p = 0.23). T1-entropy was significantly lower (p = 0.004) in TZ containing significant tumour with ROC-AUC 0.70 (LOO-AUC 0.66) and was unaffected by excluding significant tumour from TZ-ROI (p = 0.004). Combining these parameters yielded ROC-AUC 0.86 (LOO-AUC 0.83). Textural features of the whole prostate TZ can discriminate significant prostatic cancer through reduced kurtosis of the ADC-histogram where significant tumour is included in TZ-ROI and reduced T1 entropy independent of tumour inclusion. (orig.)

  19. VALIDATION OF 12 SMALL KEPLER TRANSITING PLANETS IN THE HABITABLE ZONE

    Torres, Guillermo; Kipping, David M.; Fressin, Francois; Newton, Elisabeth R. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Caldwell, Douglas A.; Twicken, Joseph D. [SETI Institute/NASA Ames Research Center, Moffett Field, CA 94035 (United States); Ballard, Sarah [University of Washington, Seattle, WA 98195 (United States); Batalha, Natalie M.; Bryson, Stephen T.; Henze, Christopher E.; Howell, Steve B.; Jenkins, Jon M.; Barclay, Thomas; Borucki, William J. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Ciardi, David R. [NASA Exoplanet Science Institute/Caltech, Pasadena, CA 91125 (United States); Isaacson, Howard T.; Petigura, Erik A. [Astronomy Department, University of California, Berkeley, CA 94720 (United States); Muirhead, Philip S. [Department of Astronomy, Boston University, Boston, MA 02215 (United States); Crepp, Justin R. [University of Notre Dame, Notre Dame, IN 46556 (United States); Everett, Mark E., E-mail: gtorres@cfa.harvard.edu [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States); and others

    2015-02-20

    We present an investigation of 12 candidate transiting planets from Kepler with orbital periods ranging from 34 to 207 days, selected from initial indications that they are small and potentially in the habitable zone (HZ) of their parent stars. Few of these objects are known. The expected Doppler signals are too small to confirm them by demonstrating that their masses are in the planetary regime. Here we verify their planetary nature by validating them statistically using the BLENDER technique, which simulates large numbers of false positives and compares the resulting light curves with the Kepler photometry. This analysis was supplemented with new follow-up observations (high-resolution optical and near-infrared spectroscopy, adaptive optics imaging, and speckle interferometry), as well as an analysis of the flux centroids. For 11 of them (KOI-0571.05, 1422.04, 1422.05, 2529.02, 3255.01, 3284.01, 4005.01, 4087.01, 4622.01, 4742.01, and 4745.01) we show that the likelihood they are true planets is far greater than that of a false positive, to a confidence level of 99.73% (3σ) or higher. For KOI-4427.01 the confidence level is about 99.2% (2.6σ). With our accurate characterization of the GKM host stars, the derived planetary radii range from 1.1 to 2.7 R {sub ⊕}. All 12 objects are confirmed to be in the HZ, and nine are small enough to be rocky. Excluding three of them that have been previously validated by others, our study doubles the number of known rocky planets in the HZ. KOI-3284.01 (Kepler-438b) and KOI-4742.01 (Kepler-442b) are the planets most similar to the Earth discovered to date when considering their size and incident flux jointly.

  20. Fe-phyllosilicate redox cycling organisms from a redox transition zone in Hanford 300 Area sediments

    Jason eBenzine

    2013-12-01

    Full Text Available Microorganisms capable of reducing or oxidizing structural iron (Fe in Fe-bearing phyllosilicate minerals were enriched and isolated from a subsurface redox transition zone at the Hanford 300 Area site in eastern Washington, USA. Both conventional and in situ i-chip enrichment strategies were employed. One Fe(III-reducing Geobacter (G. bremensis strain R1, Deltaproteobacteria and six Fe(II phyllosilicate-oxidizing isolates from the Alphaproteobacteria (Bradyrhizobium japonicum strains 22, is5, and in8p8, Betaproteobacteria (Cupriavidus necator strain A5-1, Dechloromonas agitata strain is5, and Actinobacteria (Nocardioides sp. strain in31 were recovered. The G. bremensis isolate grew by oxidizing acetate with the oxidized form of NAu-2 smectite as the electron acceptor. The Fe(II-oxidizers grew by oxidation of chemically reduced smectite as the energy source with nitrate as the electron acceptor. The Bradyrhizobium isolates could also carry out aerobic oxidation of biotite. This is the first report of the recovery of a Fe(II-oxidizing Nocardioides, and to date only one other Fe(II-oxidizing Bradyrhizobium is known. The 16S rRNA gene sequences of the isolates were similar to ones found in clone libraries from Hanford 300 sediments and groundwater, suggesting that such organisms may be present and active in situ. Whole genome sequencing of the isolates is underway, the results of which will enable comparative genomic analysis of mechanisms of extracellular phyllosilicate Fe redox metabolism, and facilitate development of techniques to detect the presence and expression of genes associated with microbial phyllosilicate Fe redox cycling in sediments.

  1. Modelling of interfacial transition zone effect on resistance to crack propagation in fine-grained cement-based composites

    Šimonová, H.; Vyhlídal, M.; Kucharczyková, B.; Bayer, P.; Keršner, Z.; Malíková, Lucie; Klusák, Jan

    2017-01-01

    Roč. 11, č. 41 (2017), s. 211-219 ISSN 1971-8993 R&D Projects: GA ČR(CZ) GA16-18702S Institutional support: RVO:68081723 Keywords : Effective fracture toughness * Fine-grained concrete * Interfacial transition zone * Three-point bending fracture test * Scanning electron microscopy Subject RIV: JL - Materials Fatigue, Friction Mechanics OBOR OECD: Audio engineering, reliability analysis

  2. Global Scale Exploration Seismics: Mapping Mantle Discontinuities with Inverse Scattering Methods and Millions of Seismograms

    van der Hilst, R. D.; de Hoop, M. V.; Shim, S. H.; Shang, X.; Wang, P.; Cao, Q.

    2012-04-01

    Over the past three decades, tremendous progress has been made with the mapping of mantle heterogeneity and with the understanding of these structures in terms of, for instance, the evolution of Earth's crust, continental lithosphere, and thermo-chemical mantle convection. Converted wave imaging (e.g., receiver functions) and reflection seismology (e.g. SS stacks) have helped constrain interfaces in crust and mantle; surface wave dispersion (from earthquake or ambient noise signals) characterizes wavespeed variations in continental and oceanic lithosphere, and body wave and multi-mode surface wave data have been used to map trajectories of mantle convection and delineate mantle regions of anomalous elastic properties. Collectively, these studies have revealed substantial ocean-continent differences and suggest that convective flow is strongly influenced by but permitted to cross the upper mantle transition zone. Many questions have remained unanswered, however, and further advances in understanding require more accurate depictions of Earth's heterogeneity at a wider range of length scales. To meet this challenge we need new observations—more, better, and different types of data—and methods that help us extract and interpret more information from the rapidly growing volumes of broadband data. The huge data volumes and the desire to extract more signal from them means that we have to go beyond 'business as usual' (that is, simplified theory, manual inspection of seismograms, …). Indeed, it inspires the development of automated full wave methods, both for tomographic delineation of smooth wavespeed variations and the imaging (for instance through inverse scattering) of medium contrasts. Adjoint tomography and reverse time migration, which are closely related wave equation methods, have begun to revolutionize seismic inversion of global and regional waveform data. In this presentation we will illustrate this development - and its promise - drawing from our work

  3. Observation of the Spectrally Invariant Properties of Clouds in Cloudy-to-Clear Transition Zones During the MAGIC Field Campaign

    Yang, Weidong; Marshak, Alexander; McBride, Patrick; Chiu, J. Christine; Knyazikhin, Yuri; Schmidt, K. Sebastian; Flynn, Connor; Lewis, Ernie R.; Eloranta, Edwin W.

    2016-01-01

    We use the spectrally invariant method to study the variability of cloud optical thickness tau and droplet effective radius r(sub eff) in transition zones (between the cloudy and clear sky columns) observed from Solar Spectral Flux Radiometer (SSFR) and Shortwave Array Spectroradiometer-Zenith (SASZe) during the Marine ARM GPCI Investigation of Clouds (MAGIC) field campaign. The measurements from the SSFR and the SASZe are different, however inter-instrument differences of self-normalized measurements (divided by their own spectra at a fixed time) are small. The spectrally invariant method approximates the spectra in the cloud transition zone as a linear combination of definitely clear and cloudy spectra, where the coefficients, slope and intercept, characterize the spectrally invariant properties of the transition zone. Simulation results from the SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer) model demonstrate that (1) the slope of the visible band is positively correlated with the cloud optical thickness t while the intercept of the near-infrared band has high negative correlation with the cloud drop effective radius r(sub eff)even without the exact knowledge of tau; (2) the above relations hold for all Solar Zenith Angle (SZA) and for cloud-contaminated skies. In observations using redundant measurements from SSFR and SASZe, we find that during cloudy-to-clear transitions, (a) the slopes of the visible band decrease, and (b) the intercepts of the near-infrared band remain almost constant near cloud edges. The findings in simulations and observations suggest that, while the optical thickness decreases during the cloudy-to-clear transition, the cloud drop effective radius does not change when cloud edges are approached. These results support the hypothesis that inhomogeneous mixing dominates near cloud edges in the studied cases.

  4. Three dimensional proton MR spectroscopic imaging in transition zone prostate cancer

    Yang Yi; Zhao Wenlu; Shen Junkang

    2012-01-01

    Objective: To discuss the clinical value of three dimensional proton MR spectroscopic imaging (3D 1 HMRSI) in the detection of transition zone (TZ) prorate cancer and evaluate the feasibility of 3D 1 HMRSI for determining the aggressiveness of TZ cancer by analyzing its metabolic characteristics. Methods: The 3D 1 HMRSI data of sixty patients suspected TZ cancer in conventional MR examinations were retrospectively analyzed. The values of (Cho + Cre)/Cit of TZ cancer and benign prostatic hyperplasia (BPH) voxels were recorded and compared using independent sample t' test, and the area under the ROC curve was used to evaluate the diagnostic accuracy. Based on Gleason scores, TZ cancer voxels were divided into three groups,including low-risk (Gleason score <7), intermediate-risk (Gleason score =7) and high-risk (Gleason score >7). The values of (Cho + Cre)/Cit were compared among the three groups using Kruskal-Wallis test. The correlation of the value of (Cho + Cre)/Cit and Gleason score was analyzed using rank correlation analysis. Results: Among the 60 patients, histopathology confirmed TZ cancer in 25 patients and BPH in 35 patients. The inversion of Cho and Cit peak value with increased (Cho + Cre)/Cit was detected in 160 out of 177 TZ cancer voxels. Most spectral curves of the 517 BPH voxels were similar with that of normal peripheral zone on 1 HMRSI. The mean values of (Cho + Cre)/Cit of TZ cancer and BPH voxels were 2.17 ± 1.29 and 0.77 ± 0.20, respectively, with significant difference between them (t'=14.38, P<0.01). Using (Cho + Cre)/Cit for distinguishing TZ cancer, the area under ROC curve was 0.985 (P<0.01).With the cut-off point 1.08, the sensitivity, specificity and accuracy of TZ cancer diagnosis was 92.7%, 94.2% and 93.8%, respectively. The number of low-risk, intermediate-risk and high-risk TZ cancer voxels were 57, 64 and 56 respectively, and the mean values of (Cho + Cre)/Cit of the three groups were 1.43 (1.16-1.87), 1.66 (1

  5. Environmental Risk of Metal Mining Contaminated River Bank Sediment at Redox-Transitional Zones

    Sarah F. L. Lynch

    2014-01-01

    Full Text Available Diffuse metal pollution from mining impacted sediment is widely recognised as a potential source of contamination to river systems and may significantly hinder the achievement of European Union Water Framework Directive objectives. Redox-transitional zones that form along metal contaminated river banks as a result of flood and drought cycles could cause biogeochemical changes that alter the behaviour of polyvalent metals iron and manganese and anions such as sulphur. Trace metals are often partitioned with iron, manganese and sulphur minerals in mining-contaminated sediment, therefore the dissolution and precipitation of these minerals may influence the mobility of potentially toxic trace metals. Research indicates that freshly precipitated metal oxides and sulphides may be more “reactive” (more adsorbent and prone to dissolution when conditions change than older crystalline forms. Fluctuations at the oxic-anoxic interface brought about through changes in the frequency and duration of flood and drought episodes may therefore influence the reactivity of secondary minerals that form in the sediment and the flux of dissolved trace metal release. UK climate change models predict longer dry periods for some regions, interspersed with higher magnitude flood events. If we are to fully comprehend the future environmental risk these climate change events pose to mining impacted river systems it is recommended that research efforts focus on identifying the primary controls on trace metal release at the oxic-anoxic interface for flood and drought cycles of different duration and frequency. This paper critically reviews the literature regarding biogeochemical processes that occur at different temporal scales during oxic, reducing and dry periods and focuses on how iron and sulphur based minerals may alter in form and reactivity and influence the mobility of trace metal contaminants. It is clear that changes in redox potential can alter the composition

  6. Logistic regression model for diagnosis of transition zone prostate cancer on multi-parametric MRI.

    Dikaios, Nikolaos; Alkalbani, Jokha; Sidhu, Harbir Singh; Fujiwara, Taiki; Abd-Alazeez, Mohamed; Kirkham, Alex; Allen, Clare; Ahmed, Hashim; Emberton, Mark; Freeman, Alex; Halligan, Steve; Taylor, Stuart; Atkinson, David; Punwani, Shonit

    2015-02-01

    We aimed to develop logistic regression (LR) models for classifying prostate cancer within the transition zone on multi-parametric magnetic resonance imaging (mp-MRI). One hundred and fifty-five patients (training cohort, 70 patients; temporal validation cohort, 85 patients) underwent mp-MRI and transperineal-template-prostate-mapping (TPM) biopsy. Positive cores were classified by cancer definitions: (1) any-cancer; (2) definition-1 [≥Gleason 4 + 3 or ≥ 6 mm cancer core length (CCL)] [high risk significant]; and (3) definition-2 (≥Gleason 3 + 4 or ≥ 4 mm CCL) cancer [intermediate-high risk significant]. For each, logistic-regression mp-MRI models were derived from the training cohort and validated internally and with the temporal cohort. Sensitivity/specificity and the area under the receiver operating characteristic (ROC-AUC) curve were calculated. LR model performance was compared to radiologists' performance. Twenty-eight of 70 patients from the training cohort, and 25/85 patients from the temporal validation cohort had significant cancer on TPM. The ROC-AUC of the LR model for classification of cancer was 0.73/0.67 at internal/temporal validation. The radiologist A/B ROC-AUC was 0.65/0.74 (temporal cohort). For patients scored by radiologists as Prostate Imaging Reporting and Data System (Pi-RADS) score 3, sensitivity/specificity of radiologist A 'best guess' and LR model was 0.14/0.54 and 0.71/0.61, respectively; and radiologist B 'best guess' and LR model was 0.40/0.34 and 0.50/0.76, respectively. LR models can improve classification of Pi-RADS score 3 lesions similar to experienced radiologists. • MRI helps find prostate cancer in the anterior of the gland • Logistic regression models based on mp-MRI can classify prostate cancer • Computers can help confirm cancer in areas doctors are uncertain about.

  7. Actin Cytoskeleton-Based Plant Synapse as Gravitransducer in the Transition Zone of the Root Apex

    Baluska, Frantisek; Barlow, Peter; Volkmann, Dieter; Mancuso, Stefano

    The actin cytoskeleton was originally proposed to act as the signal transducer in the plant gravity sensory-motoric circuit. Surprisingly, however, several studies have documented that roots perfom gravisensing and gravitropism more effectively if exposed to diverse anti-F-actin drugs. Our study, using decapped maize root apices, has revealed that depolymerization of F-actin stimulates gravity perception in cells of the transition zone where root gravitropism is initiated (Mancuso et al. 2006). It has been proposed (Balǔka et al. 2005, 2009a) that s the non-growing adhesive end-poles, enriched with F-actin and myosin VIII, and active in endocytic recycling of both PIN transporters and cell wall pectins cross-linked with calcium and boron, act as the gravisensing domains, and that these impinge directly upon the root motoric responses via control of polar auxin transport. This model suggests that mechanical asymmetry at these plant synapses determines vectorial gravity-controlled auxin transport. Due to the gravity-imposed mechanical load upon the protoplast, a tensional stress is also imposed upon the plasma membrane of the physically lower synaptic cell pole. This stress is then relieved by shifting the endocytosis-exocytosis balance towards exocytosis (Balǔka et al. s 2005, 2009a,b). This `Synaptic Auxin Secretion' hypothesis does not conflict with the `Starch Statolith' hypothesis, which is based on amyloplast sedimentation. In fact, the `Synaptic Auxin Secretion' hypothesis has many elements which allow its unification with the Starch-Statolith model (Balǔka et al. 2005, 2009a,b). s References Balǔka F, Volkmann D, Menzel D (2005) Plant synapses: actin-based adhesion s domains for cell-to-cell communication. Trends Plant Sci 10: 106-111 Balǔka F, Schlicht M, s Wan Y-L, Burbach C, Volkmann D (2009a) Intracellular domains and polarity in root apices: from synaptic domains to plant neurobiology. Nova Acta Leopoldina 96: 103-122 Balǔka s F, Mancuso S

  8. Novel Pelagic Iron-Oxidizing Zetaproteobacteria from the Chesapeake Bay Oxic–Anoxic Transition Zone

    Chiu, Beverly K.; Kato, Shingo; McAllister, Sean M.; Field, Erin K.; Chan, Clara S.

    2017-01-01

    Chemolithotrophic iron-oxidizing bacteria (FeOB) could theoretically inhabit any environment where Fe(II) and O2 (or nitrate) coexist. Until recently, marine Fe-oxidizing Zetaproteobacteria had primarily been observed in benthic and subsurface settings, but not redox-stratified water columns. This may be due to the challenges that a pelagic lifestyle would pose for Zetaproteobacteria, given low Fe(II) concentrations in modern marine waters and the possibility that Fe oxyhydroxide biominerals could cause cells to sink. However, we recently cultivated Zetaproteobacteria from the Chesapeake Bay oxic–anoxic transition zone, suggesting that they can survive and contribute to biogeochemical cycling in a stratified estuary. Here we describe the isolation, characterization, and genomes of two new species, Mariprofundus aestuarium CP-5 and Mariprofundus ferrinatatus CP-8, which are the first Zetaproteobacteria isolates from a pelagic environment. We looked for adaptations enabling strains CP-5 and CP-8 to overcome the challenges of living in a low Fe redoxcline with frequent O2 fluctuations due to tidal mixing. We found that the CP strains produce distinctive dreadlock-like Fe oxyhydroxide structures that are easily shed, which would help cells maintain suspension in the water column. These oxides are by-products of Fe(II) oxidation, likely catalyzed by the putative Fe(II) oxidase encoded by the cyc2 gene, present in both CP-5 and CP-8 genomes; the consistent presence of cyc2 in all microaerophilic FeOB and other FeOB genomes supports its putative role in Fe(II) oxidation. The CP strains also have two gene clusters associated with biofilm formation (Wsp system and the Widespread Colonization Island) that are absent or rare in other Zetaproteobacteria. We propose that biofilm formation enables the CP strains to attach to FeS particles and form flocs, an advantageous strategy for scavenging Fe(II) and developing low [O2] microenvironments within more oxygenated waters

  9. Temperature Profile of the Upper Mantle

    Anderson, O.L.

    1980-01-01

    Following the procedure outlined by Magnitsky [1971], thermal profiles of the upper mantle are computed by deriving the thermal gradient from the seismic data given as dv/sub s//drho used along with the values of (dv/sub s//dT9/sub p/ and (dv/sub s//dP)/sub T/ of selected minerals, measured at high temperature. The resulting values of dT/dZ are integrated from 380 km upward toward the surface, where the integrating constant is taken from Akagi and Akimoto's work, T=1400 0 C at 380 km. The resulting geotherms for minerals are used to derive geotherms for an eclogite mantle and a lherzolite mantle, with and without partial melting in the low-velocity zone. The geotherms are all subadiabatic, and some are virtually isothermal in the upper mantle. Some are characterized by a large thermal hump at the lithosphere boundary

  10. Isosymmetric pressure-induced bonding increase changes compression behavior of clinopyroxenes across jadeite-aegirine solid solution in subduction zones: ISOSYMMETRIC PHASE TRANSITION

    Xu, Jingui [Key Laboratory of High Temperature and High Pressure Study of the Earth' s Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang China; Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai' i at Mānoa, Honolulu Hawaii USA; University of Chinese Academy of Sciences, Beijing China; Zhang, Dongzhou [Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai' i at Mānoa, Honolulu Hawaii USA; Fan, Dawei [Key Laboratory of High Temperature and High Pressure Study of the Earth' s Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang China; Downs, Robert T. [Department of Geosciences, University of Arizona, Tucson Arizona USA; Hu, Yi [Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai' i at Mānoa, Honolulu Hawaii USA; Dera, Przemyslaw K. [Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai' i at Mānoa, Honolulu Hawaii USA

    2017-01-01

    Pyroxenes are among the most important minerals of Earth's crust and upper mantle and play significant role in controlling subduction at convergent margins. In this study, synchrotron-based single-crystal X-ray diffraction experiments were carried out on a natural aegirine [NaFe3+Si2O6] sample at ambient temperature and high pressures to 60 GPa, simulating conditions within the coldest part of a subduction zone consisting of old lithosphere. The diffraction data reveal no obvious sign of structural phase transition in aegirine within this pressure range; however, several relevant structural parameter trends change noticeably at approximately 24 GPa, indicating the presence of the previously predicted isosymmetric bonding change, related to increase of coordination number of Na+ at M2 site. The pressure-volume data, fit with third-order Birch-Murnaghan (BM3) equation of state over the whole pressure range, yields KT0 = 126(2) GPa and K'T0 = 3.3(1), while separate BM3 fits performed for the 0–24.0 GPa and 29.9–60.4 GPa pressure ranges give KT0 = 118(3) GPa, K'T0 = 4.2(3) and KT0 = 133(2) GPa, K'T0 = 3.0(1), suggesting that the structure stiffens as a result of the new bond formation. Aegirine exhibits strong anisotropic compression with unit strain axial ratios ε1:ε2:ε3 = 1.00:2.44:1.64. Structural refinements reveal that NaO8 polyhedron is the most compressible and SiO4 tetrahedron has the lowest compressibility. The consequence of bonding transition is that the compressional behavior of aegirine below ~24 GPa and above that pressure is quite different, with likely consequences for relevant thermodynamic parameters and ion diffusion coefficients.

  11. Tracing the Paleo sulfate-methane transition zones and H2S seepage events in marine sediments: An application of C-S-Mo systematics

    Peketi, A; Mazumdar, A; Joshi, R.K.; Patil, D.J.; Srinivas, P.L.; Dayal, A

    Microbially mediated anaerobic oxidation of methane (AOM) coupled with sulfate consumption within the sulfate methane transition zone (SMTZ) in marine sediments is a widely recorded biogeochemical reaction and has profound influence...

  12. Can Lower Mantle Slab-like Seismic Anomalies be Explained by Thermal Coupling Between the Upper and Lower Mantles?

    Cízková, H. (Hana); Cadek, O.; Berg, A.P. van den; Vlaar, N.J.

    1999-01-01

    Below subduction zones, high resolution seismic tomographic models resolve fast anomalies that often extend into the deep lower mantle. These anomalies are generally interpreted as slabs penetrating through the 660-km seismic discontinuity, evidence in support of whole-mantle convection. However,

  13. Effect of In-Vehicle Audio Warning System on Driver’s Speed Control Performance in Transition Zones from Rural Areas to Urban Areas

    Xuedong Yan

    2016-06-01

    Full Text Available Speeding is a major contributing factor to traffic crashes and frequently happens in areas where there is a mutation in speed limits, such as the transition zones that connect urban areas from rural areas. The purpose of this study is to investigate the effects of an in-vehicle audio warning system and lit speed limit sign on preventing drivers’ speeding behavior in transition zones. A high-fidelity driving simulator was used to establish a roadway network with the transition zone. A total of 41 participants were recruited for this experiment, and the driving speed performance data were collected from the simulator. The experimental results display that the implementation of the audio warning system could significantly reduce drivers’ operating speed before they entered the urban area, while the lit speed limit sign had a minimal effect on improving the drivers’ speed control performance. Without consideration of different types of speed limit signs, it is found that male drivers generally had a higher operating speed both upstream and in the transition zones and have a larger maximum deceleration for speed reduction than female drivers. Moreover, the drivers who had medium-level driving experience had the higher operating speed and were more likely to have speeding behaviors in the transition zones than those who had low-level and high-level driving experience in the transition zones.

  14. Transition to University Life: Insights from High School and University Female Students in Wolaita Zone, Ethiopia

    Thuo, Mary; Edda, Medhanit

    2017-01-01

    The purpose of this study was to get an insight about how high school female students perceive the transition to university life, and to understand the transition experience of university female students in the first semester. An exploratory study design was used where 166 high school female students and 88 first year university female students…

  15. Mantle convection patterns reveal the enigma of the Red Sea rifting

    Petrunin, Alexey; Kaban, Mikhail; El Khrepy, Sami; Al-Arifi, Nassir

    2017-04-01

    Initiation and further development of the Red Sea rift (RSR) is usually associated with the Afar plume at the Oligocene-Miocene separating the Arabian plate from the rest of the continent. Usually, the RSR is divided into three parts with different geological, tectonic and geophysical characteristics, but the nature of this partitioning is still debatable. To understand origin and driving forces responsible for the tectonic partitioning of the RSR, we have developed a global mantle convection model based on the refined density model and viscosity distribution derived from tectonic, rheological and seismic data. The global density model of the upper mantle is refined for the Middle East based on the high-resolution 3D model (Kaban et al., 2016). This model based on a joint inversion of the residual gravity and residual topography provides much better constraints on the 3D density structure compared to the global model based on seismic tomography. The refined density model and the viscosity distribution based on a homologous temperature approach provide an initial setup for further numerical calculations. The present-day snapshot of the mantle convection is calculated by using the code ProSpher 3D that allows for strong lateral variations of viscosity (Petrunin et al., 2013). The setup includes weak plate boundaries, while the measured GPS velocities are used to constrain the solution. The resulting mantle flow patterns show clear distinctions among the mantle flow patterns below the three parts of the RSR. According to the modeling results, tectonics of the southern part of the Red Sea is mainly determined by the Afar plume and the Ethiopian rift opening. It is characterized by a divergent mantle flow, which is connected to the East African Rift activity. The rising mantle flow is traced down to the transition zone and continues in the lower mantle for a few thousand kilometers south-west of Afar. The hot mantle anomaly below the central part of the RSR can be

  16. Genetic diversity and biogeographical patterns of Caulerpa prolifera across the Mediterranean and Mediterranean/Atlantic transition zone

    Varela-Á lvarez, Elena; Balau, Ana C.; Marbà , Nú rià N.; Afonso-Carrillo, Julio; Duarte, Carlos M.; Serrã o, Ester Á lvares

    2015-01-01

    Knowledge of spatial patterns of genetic differentiation between populations is key to understanding processes in evolutionary history of biological species. Caulerpa is a genus of marine green algae, which has attracted much public attention, mainly because of the impacts of invasive species in the Mediterranean. However, very little is known about the ecological and evolutionary history of the Mediterranean native Caulerpa prolifera, a species which is currently found at sites distributed worldwide. C. prolifera provides a good model to explore the patterns of genetic diversity at different scales across the Mediterranean and Atlantic area. This study aims to investigate the biogeographical patterns of diversity and differentiation of C. prolifera in the Mediterranean, with special focus on the Mediterranean/Atlantic transition zone. We used two nuclear (ITS rDNA and the hypervariable microsatellite locus CaPr_J2) and one chloroplast (tufA) DNA markers on samples of C. prolifera from its entire range. Analyses of 51 sequences of the cpDNA tufA of C. prolifera, 87 ITS2 sequences and genotypes of 788 ramets of C. prolifera for the locus CaPr_J2 revealed three different biogeographical areas: West Atlantic, East Atlantic and a larger area representing the Mediterranean, the Mediterranean/Atlantic transition zone and a Pacific site (Bali). It was found out that the Mediterranean/Atlantic transition zone is a biogeographical boundary for C. prolifera. A lack of connectivity was revealed between Atlantic and Mediterranean types, and identical sequences found in the Mediterranean and Indo-Pacific suggest either recent gene flow along the Red Sea connection or a possible ancient Indo-Pacific origin.

  17. Genetic diversity and biogeographical patterns of Caulerpa prolifera across the Mediterranean and Mediterranean/Atlantic transition zone

    Varela-Álvarez, Elena

    2015-01-11

    Knowledge of spatial patterns of genetic differentiation between populations is key to understanding processes in evolutionary history of biological species. Caulerpa is a genus of marine green algae, which has attracted much public attention, mainly because of the impacts of invasive species in the Mediterranean. However, very little is known about the ecological and evolutionary history of the Mediterranean native Caulerpa prolifera, a species which is currently found at sites distributed worldwide. C. prolifera provides a good model to explore the patterns of genetic diversity at different scales across the Mediterranean and Atlantic area. This study aims to investigate the biogeographical patterns of diversity and differentiation of C. prolifera in the Mediterranean, with special focus on the Mediterranean/Atlantic transition zone. We used two nuclear (ITS rDNA and the hypervariable microsatellite locus CaPr_J2) and one chloroplast (tufA) DNA markers on samples of C. prolifera from its entire range. Analyses of 51 sequences of the cpDNA tufA of C. prolifera, 87 ITS2 sequences and genotypes of 788 ramets of C. prolifera for the locus CaPr_J2 revealed three different biogeographical areas: West Atlantic, East Atlantic and a larger area representing the Mediterranean, the Mediterranean/Atlantic transition zone and a Pacific site (Bali). It was found out that the Mediterranean/Atlantic transition zone is a biogeographical boundary for C. prolifera. A lack of connectivity was revealed between Atlantic and Mediterranean types, and identical sequences found in the Mediterranean and Indo-Pacific suggest either recent gene flow along the Red Sea connection or a possible ancient Indo-Pacific origin.

  18. Mapping and quantifying geodiversity in land-water transition zones using MBES and topobathymetric LiDAR

    Brandbyge Ernstsen, Verner; Skovgaard Andersen, Mikkel; Gergely, Aron; Schulze Tenberge, Yvonne; Al-Hamdani, Zyad; Steinbacher, Frank; Rolighed Larsen, Laurids; Winter, Christian; Bartholomä, Alexander

    2016-04-01

    Land-water transition zones, like e.g. coastal and fluvial environments, are valuable ecosystems which are often characterised by high biodiversity and geodiversity. However, often these land-water transition zones are difficult or even impossible to map and investigate in high spatial resolution due to the challenging environmental conditions. Combining vessel borne shallow water multibeam echosounder (MBES) surveys ,to cover the subtidal coastal areas and the river channel areas, with airborne topobathymetric light detection and ranging (LiDAR) surveys, to cover the intertidal and supratidal coastal areas and the river floodplain areas, potentially enables full-coverage and high-resolution mapping in these challenging environments. We have carried out MBES and topobathymetric LiDAR surveys in the Knudedyb tidal inlet system, a coastal environment in the Danish Wadden Sea which is part of the Wadden Sea National Park and UNESCO World Heritage, and in the Ribe Vesterå, a fluvial environment in the Ribe Å river catchment discharging into the Knudedyb tidal basin. Detailed digital elevation models (DEMs) with a grid cell size of 0.5 m x 0.5 m were generated from the MBES and the LiDAR point clouds, which both have point densities in the order of 20 points/m2. Morphometric analyses of the DEMs enabled the identification and mapping of the different landforms within the coastal and fluvial environments. Hereby, we demonstrate that vessel borne MBES and airborne topobathymetric LiDAR, here in combination, are promising tools for seamless mapping across land-water transition zones as well as for the quantification of a range of landforms at landscape scale in different land-water transition zone environments. Hence, we demonstrate the potential for mapping and quantifying geomorphological diversity, which is one of the main components of geodiversity and a prerequisite for assessing geoheritage. Acknowledgements This work was funded by the Danish Council for

  19. Patterns of forest composition and their long term environmental drivers in the tropical dry forest transition zone of southern Africa

    Vera De Cauwer

    2016-09-01

    Full Text Available Background Tropical dry forests cover less than 13 % of the world’s tropical forests and their area and biodiversity are declining. In southern Africa, the major threat is increasing population pressure, while drought caused by climate change is a potential threat in the drier transition zones to shrub land. Monitoring climate change impacts in these transition zones is difficult as there is inadequate information on forest composition to allow disentanglement from other environmental drivers. Methods This study combined historical and modern forest inventories covering an area of 21,000 km2 in a transition zone in Namibia and Angola to distinguish late succession tree communities, to understand their dependence on site factors, and to detect trends in the forest composition over the last 40 years. Results The woodlands were dominated by six tree species that represented 84 % of the total basal area and can be referred to as Baikiaea - Pterocarpus woodlands. A boosted regression tree analysis revealed that late succession tree communities are primarily determined by climate and topography. The Schinziophyton rautanenii and Baikiaea plurijuga communities are common on slightly inclined dune or valley slopes and had the highest basal area (5.5 – 6.2 m2 ha−1. The Burkea africana - Guibourtia coleosperma and Pterocarpus angolensis – Dialium englerianum communities are typical for the sandy plateaux and have a higher proportion of smaller stems caused by a higher fire frequency. A decrease in overall basal area or a trend of increasing domination by the more drought and cold resilient B. africana community was not confirmed by the historical data, but there were significant decreases in basal area for Ochna pulchra and the valuable fruit tree D. englerianum. Conclusions The slope communities are more sheltered from fire, frost and drought but are more susceptible to human expansion. The community with the important timber tree P

  20. Data set: A modeling dataset that spans the rain - snow transition zone: Johnston Draw catchment, Reynolds Creek Experimental Watershed, Idaho, USA

    Hydrometeorological data from the rain-to-snow transition zone in mountain basins are limited. As the climate warms, the transition from rain to snow in mountain regions is moving to higher elevations, and these changes are altering the timing of water delivery to the downstream streams, lakes and w...

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

    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.

  2. Petrology and geochemistry at the Lower zone-Middle zone transition of the Panzhihua intrusion, SW China: Implications for differentiation and oxide ore genesis

    Kwan-Nang Pang

    2013-09-01

    Full Text Available A sequence of gabbros showing isotropic, layered and fine-grained textures is exposed in the Nalaqing mine at the southern tip of the ∼260 Ma Panzhihua intrusion, SW China. The field relations, structure, texture and mineralogy of the rocks indicate that the sequence represents the transition between the Lower zone and Middle zone of the intrusion. Isotropic gabbros characteristic of the Lower zone pass upward to layered gabbros of the Middle zone through a ∼5 m-thick microgabbro sheet, within and close to which small-scaled, concordant Fe-Ti oxide ore horizons are identified. Strong fractionation between HFSE and REE in a subset of samples is ascribed to cumulus titanomagnetite into which HFSE are preferentially incorporated over REE, as reflected in the parallel relations between Nb/La, Hf/Sm and Ti/Ti*. Both the isotropic and layered gabbros display cumulate textures and have similar mineral compositions (Mg# of clinopyroxene = ∼76–79 and An59–61, isotopic compositions [(87Sr/86Sri = 0.7044–0.7045 and εNd(t = +2.4 to +3.9] and trapped liquid contents inferred from Zr abundance (∼17–34 ppm. However, there are substantial variations in elemental abundances (V, Cr and PGE and ratios (Ti/V, La/Yb, Ba/Y and Cu/Pd between the two types of gabbros, features that cannot be explained by cumulate formation from a common magma in a closed system. The microgabbros generally resemble high-Ti Emeishan basalts in major element compositions, but their low trace element abundances indicate some lost of residual liquid is inevitable despite rapid nucleation and cooling. Combined with available data and observations, we propose a model involving in-situ crystallization, followed by magma recharge and closed-system fractionation to explain the formation of texturally distinctive gabbros at Nalaqing and the evolution of the lower part of the Panzhihua intrusion.

  3. A discrete transition zone organizes the topological and regulatory autonomy of the adjacent tfap2c and bmp7 genes.

    Taro Tsujimura

    2015-01-01

    Full Text Available Despite the well-documented role of remote enhancers in controlling developmental gene expression, the mechanisms that allocate enhancers to genes are poorly characterized. Here, we investigate the cis-regulatory organization of the locus containing the Tfap2c and Bmp7 genes in vivo, using a series of engineered chromosomal rearrangements. While these genes lie adjacent to one another, we demonstrate that they are independently regulated by distinct sets of enhancers, which in turn define non-overlapping regulatory domains. Chromosome conformation capture experiments reveal a corresponding partition of the locus in two distinct structural entities, demarcated by a discrete transition zone. The impact of engineered chromosomal rearrangements on the topology of the locus and the resultant gene expression changes indicate that this transition zone functionally organizes the structural partition of the locus, thereby defining enhancer-target gene allocation. This partition is, however, not absolute: we show that it allows competing interactions across it that may be non-productive for the competing gene, but modulate expression of the competed one. Altogether, these data highlight the prime role of the topological organization of the genome in long-distance regulation of gene expression.

  4. OSO-8 observations of the impulsive phase of solar flares in the transition-zone and corona

    Lites, B.W.

    1981-01-01

    Several solar flares have been observed from their onset in C IV lambda 1548.2 and 1-8 Angstroem X-rays using instruments aboard OSO-8. In addition, microwave and Hα flare patrol data have been obtained for this study. The impulsive brightening in C IV is frequently accompanied by redshifts, interpreted as downflows, of the order of 80 km s -1 . The maximum soft X-ray intensity usually arrives several minutes after the maximum C IV intensity. The most energetic C IV event studied shows a small blueshift just before reaching maximum intensity, and estimates of the mass flux associated with this upflow through the transition-zone are consistent with the increase of mass in the coronal loops as observed in soft X-rays. This event had no observable microwave burst, suggesting that electron beams did not play a major role in the chromospheric and transition-zone excitation. Lastly, our observations suggest that the frequent occurrence of violent dynamical processes at the onset of the flare are associated with the initial energy release mechanism. (orig.)

  5. Effect of the roughening transition on the vicinal surface in the step droplet zone

    Akutsu, Noriko

    2017-06-01

    For vicinal surfaces around the (001) surface inclined towards the 〈 111 〉 direction, the influence of roughening transitions on the surface tension and on step droplets is studied numerically. The surface tension is calculated using a restricted solid-on-solid model with a point-contact type step-step attraction (p-RSOS model) on a square lattice. To ensure the reliability of the calculations, the density matrix renormalization group method is used. The growth rate of the vicinal surface near equilibrium is also calculated by the Monte Carlo method. It is found that the roughening transition changes the morphology around the (001) surface, and the roughening transition affects the size of locally merged steps (step droplets).

  6. Uranium in mantle processes

    Cortini, M.

    1984-01-01

    (1) Metasomatism is an effective process in the mantle. It controls the distribution of U, Th and Pb in the mantle before the onset of magma formation. (2) Radioactive disequilibria demonstrate that magma formation is an open-system very fast process in which Ra, U and Th are extracted in large amounts from a mantle source that is geochemically distinct from the mantle fraction from which the melt is formed. (3) Because the enrichment of U, Th and Ra in the magma is so fast, the concept of mineral-melt partition coefficient is not valid for these elements during magma formation. (4) Metasomatism seems to generally produce an increase in μ and a decrease in K of the metasomatized mantle region. (5) Magma formation at oceanic ridges and islands seems to generally produce a decrease in K, in its mantle source region. (6) The major source of U, Th, Ra and Pb in a magma probably is the metasomatic mantle component. Instead, the major source of Sr and Nd in a magma is the non-metasomatic, more 'refractory' mantle component. (7) This proposed model is testable. It predicts isotopic disequilibrium of Pb between coexisting minerals and whole rocks, and a correlation of Pb with Th isotopes. (author)

  7. ACUTE ZONAL OCCULT OUTER RETINOPATHY: Structural and Functional Analysis Across the Transition Zone Between Healthy and Diseased Retina.

    Duncker, Tobias; Lee, Winston; Jiang, Fan; Ramachandran, Rithambara; Hood, Donald C; Tsang, Stephen H; Sparrow, Janet R; Greenstein, Vivienne C

    2018-01-01

    To assess structure and function across the transition zone (TZ) between relatively healthy and diseased retina in acute zonal occult outer retinopathy. Six patients (6 eyes; age 22-71 years) with acute zonal occult outer retinopathy were studied. Spectral-domain optical coherence tomography, fundus autofluorescence, near-infrared reflectance, color fundus photography, and fundus perimetry were performed and images were registered to each other. The retinal layers of the spectral-domain optical coherence tomography scans were segmented and the thicknesses of two outer retinal layers, that is, the total receptor and outer segment plus layers, and the retinal nerve fiber layer were measured. All eyes showed a TZ on multimodal imaging. On spectral-domain optical coherence tomography, the TZ was in the nasal retina at varying distances from the fovea. For all eyes, it was associated with loss of the ellipsoid zone band, significant thinning of the two outer retinal layers, and in three eyes with thickening of the retinal nerve fiber layer. On fundus autofluorescence, all eyes had a clearly demarcated peripapillary area of abnormal fundus autofluorescence delimited by a border of high autofluorescence; the latter was associated with loss of the ellipsoid zone band and with a change from relatively normal to markedly decreased or nonrecordable visual sensitivity on fundus perimetry. The results of multimodal imaging clarified the TZ in acute zonal occult outer retinopathy. The TZ was outlined by a distinct high autofluorescence border that correlated with loss of the ellipsoid zone band on spectral-domain optical coherence tomography. However, in fundus areas that seemed healthy on fundus autofluorescence, thinning of the outer retinal layers and thickening of the retinal nerve fiber layer were observed near the TZ. The TZ was also characterized by a decrease in visual sensitivity.

  8. Counterclockwise and Clockwise Rotation of QRS Transitional Zone: Prospective Correlates of Change and Time-Varying Associations With Cardiovascular Outcomes.

    Patel, Siddharth; Kwak, Lucia; Agarwal, Sunil K; Tereshchenko, Larisa G; Coresh, Josef; Soliman, Elsayed Z; Matsushita, Kunihiro

    2017-11-03

    A few studies have recently reported clockwise and counterclockwise rotations of QRS transition zone as predictors of mortality. However, their prospective correlates and associations with individual cardiovascular disease (CVD) outcomes are yet to be investigated. Among 13 567 ARIC (Atherosclerosis Risk in Communities) study participants aged 45 to 64 years, we studied key correlates of changes in the status of clockwise and counterclockwise rotation over time as well as the association of rotation status with incidence of coronary heart disease (2408 events), heart failure (2196 events), stroke (991 events), composite CVD (4124 events), 898 CVD deaths, and 3469 non-CVD deaths over 23 years of follow-up. At baseline, counterclockwise rotation was most prevalent (52.9%), followed by no (40.5%) and clockwise (6.6%) rotation. Of patients with no rotation, 57.9% experienced counterclockwise or clockwise rotation during follow-up, with diabetes mellitus and black race significantly predicting clockwise and counterclockwise conversion, respectively. Clockwise rotation was significantly associated with higher risk of heart failure (hazard ratio, 1.20; 95% confidence interval [CI], 1.02-1.41) and non-CVD death (hazard ratio, 1.28; 95% CI, 1.12-1.46) after adjusting for potential confounders including other ECG parameters. On the contrary, counterclockwise rotation was significantly related to lower risk of composite CVD (hazard ratio, 0.93; 95% CI, 0.87-0.99]), CVD mortality (hazard ratio, 0.76; 95% CI, 0.65-0.88), and non-CVD deaths (hazard ratio, 0.92; 95% CI, 0.85-0.99 [borderline significance with heart failure]). Counterclockwise rotation, the most prevalent QRS transition zone pattern, demonstrated the lowest risk of CVD and mortality, whereas clockwise rotation was associated with the highest risk of heart failure and non-CVD mortality. These results have implications on how to interpret QRS transition zone rotation when ECG was recorded. © 2017 The Authors

  9. A mantle plume model for the Equatorial Highlands of Venus

    Kiefer, Walter S.; Hager, Bradford H.

    1991-01-01

    The possibility that the Equatorial Highlands are the surface expressions of hot upwelling mantle plumes is considered via a series of mantle plume models developed using a cylindrical axisymmetric finite element code and depth-dependent Newtonian rheology. The results are scaled by assuming whole mantle convection and that Venus and the earth have similar mantle heat flows. The best model fits are for Beta and Atla. The common feature of the allowed viscosity models is that they lack a pronounced low-viscosity zone in the upper mantle. The shape of Venus's long-wavelength admittance spectrum and the slope of its geoid spectrum are also consistent with the lack of a low-viscosity zone. It is argued that the lack of an asthenosphere on Venus is due to the mantle of Venus being drier than the earth's mantle. Mantle plumes may also have contributed to the formation of some smaller highland swells, such as the Bell and Eistla regions and the Hathor/Innini/Ushas region.

  10. Temporary streams in temperate zones: recognizing, monitoring and restoring transitional aquatic-terrestrial ecosystems

    Stubbington, Rachel; England, Judy; Wood, Paul J.; Sefton, Catherine E.M.

    2017-01-01

    Temporary streams are defined by periodic flow cessation, and may experience partial or complete loss of surface water. The ecology and hydrology of these transitional aquatic-terrestrial ecosystems have received unprecedented attention in recent years. Research has focussed on the arid, semi-arid, and Mediterranean regions in which temporary systems are the dominant stream type, and those in cooler, wetter temperate regions with an oceanic climate influence are also receiving increasing atte...

  11. Mutations in DZIP1L, which encodes a ciliary transition zone protein, cause autosomal recessive polycystic kidney disease

    Lu, Hao; Galeano, Maria C. Rondón; Ott, Elisabeth; Kaeslin, Geraldine; Kausalya, P. Jaya; Kramer, Carina; Ortiz-Brüchle, Nadina; Hilger, Nadescha; Metzis, Vicki; Hiersche, Milan; Tay, Shang Yew; Tunningley, Robert; Vij, Shubha; Courtney, Andrew D.; Whittle, Belinda; Wühl, Elke; Vester, Udo; Hartleben, Björn; Neuber, Steffen; Frank, Valeska; Little, Melissa H.; Epting, Daniel; Papathanasiou, Peter; Perkins, Andrew C.; Wright, Graham D.; Hunziker, Walter; Gee, Heon Yung; Otto, Edgar A.; Zerres, Klaus; Hildebrandt, Friedhelm; Roy, Sudipto; Wicking, Carol; Bergmann, Carsten

    2017-01-01

    Autosomal recessive polycystic kidney disease (ARPKD), usually considered to be a genetically homogeneous disease caused by mutations in PKHD1, has been associated with ciliary dysfunction. Here, we describe mutations in the DAZ interacting protein 1-like (DZIP1L) gene in patients with ARPKD, findings we have further validated by loss-of-function studies in mice and zebrafish. DZIP1L localizes to centrioles and at the distal end of basal bodies, and interacts with septin2, a protein implicated in maintenance of the periciliary diffusion barrier at the ciliary transition zone. Consistent with a defect in the diffusion barrier, we found that the ciliary membrane translocation of the PKD proteins, polycystin-1 and −2, is compromised in DZIP1L mutant cells. Together, these data provide the first conclusive evidence that ARPKD is not a homogeneous disorder, and establishes DZIP1L as a second gene involved in its pathogenesis. PMID:28530676

  12. Mutations in DZIP1L, which encodes a ciliary-transition-zone protein, cause autosomal recessive polycystic kidney disease.

    Lu, Hao; Galeano, Maria C Rondón; Ott, Elisabeth; Kaeslin, Geraldine; Kausalya, P Jaya; Kramer, Carina; Ortiz-Brüchle, Nadina; Hilger, Nadescha; Metzis, Vicki; Hiersche, Milan; Tay, Shang Yew; Tunningley, Robert; Vij, Shubha; Courtney, Andrew D; Whittle, Belinda; Wühl, Elke; Vester, Udo; Hartleben, Björn; Neuber, Steffen; Frank, Valeska; Little, Melissa H; Epting, Daniel; Papathanasiou, Peter; Perkins, Andrew C; Wright, Graham D; Hunziker, Walter; Gee, Heon Yung; Otto, Edgar A; Zerres, Klaus; Hildebrandt, Friedhelm; Roy, Sudipto; Wicking, Carol; Bergmann, Carsten

    2017-07-01

    Autosomal recessive polycystic kidney disease (ARPKD), usually considered to be a genetically homogeneous disease caused by mutations in PKHD1, has been associated with ciliary dysfunction. Here, we describe mutations in DZIP1L, which encodes DAZ interacting protein 1-like, in patients with ARPKD. We further validated these findings through loss-of-function studies in mice and zebrafish. DZIP1L localizes to centrioles and to the distal ends of basal bodies, and interacts with septin2, a protein implicated in maintenance of the periciliary diffusion barrier at the ciliary transition zone. In agreement with a defect in the diffusion barrier, we found that the ciliary-membrane translocation of the PKD proteins polycystin-1 and polycystin-2 is compromised in DZIP1L-mutant cells. Together, these data provide what is, to our knowledge, the first conclusive evidence that ARPKD is not a homogeneous disorder and further establish DZIP1L as a second gene involved in ARPKD pathogenesis.

  13. Variability and Dynamics of Dissolved Oxygen in the Transition Zone of the North Sea and the Baltic Sea

    Jonasson, Lars

    information about the seasonal to decadal oxygen variations in the bottom water of the Kattegat, the Danish Straits, the Sound and the Western Baltic Sea and investigates the relative importance of physical and biogeochemical processes, climate change and nutrient load reductions on the oxygen variability......The bottom water in the transition zone of the North Sea and Baltic Sea suffers from seasonal hypoxia, usually during late summer and autumn. Hypoxia is a natural phenomenon in this region because of the strong vertical stratification which prevents the bottom water to be ventilated by atmospheric...... concentrations by 15-30 μmol O2 l−1 yr−1 while the reduced nutrient concentration has increased the oxygen concentration with approximately the same amount. Thus, the positive effect on oxygen conditions from reduced nutrient concentrations have been counteracted by increased water temperatures. This has made...

  14. OSO-8 observations of the impulsive phase of solar flares in the transition-zone and corona

    Lites, B. W.; Bruner, E. C., Jr.; Wolfson, C. J.

    1981-01-01

    Several solar flares were observed from their onset in C IV 1548.2 A and 1-8 A X-rays using instruments on OSO-8. It is found that impulsive brightening in C IV is often accompanied by redshifts, interpreted as downflows, of the order of 80 km/s. The maximum soft X-ray intensity usually arrives several minutes after the maximum C IV intensity. The most energetic C IV event observed shows a small blueshift just before reaching maximum intensity; estimates of the mass flux associated with this upflow through the transition zone are consistent with the increase of mass in the coronal loops as observed in soft X-rays. Finally, it is suggested that the frequent occurrence of violent dynamical processes at the onset of the flare is associated with the initial energy release mechanism.

  15. Simulation of groundwater flow pathlines and freshwater/saltwater transition zone movement, Manhasset Neck, Nassau County, New York

    Misut, Paul; Aphale, Omkar

    2014-01-01

    A density-dependent groundwater flow and solute transport model of Manhasset Neck, Long Island, New York, was used to analyze (1) the effects of seasonal stress on the position of the freshwater/saltwater transition zone and (2) groundwater flowpaths. The following were used in the simulation: 182 transient stress periods, representing the historical record from 1920 to 2011, and 44 transient stress periods, representing future hypothetical conditions from 2011 to 2030. Simulated water-level and salinity (chloride concentration) values are compared with values from a previously developed two-stress-period (1905–1944 and 1945–2005) model. The 182-stress-period model produced salinity (chloride concentration) values that more accurately matched the observed salinity (chloride concentration) values in response to hydrologic stress than did the two-stress-period model, and salinity ranged from zero to about 3 parts per thousand (equivalent to zero to 1,660 milligrams per liter chloride). The 182-stress-period model produced improved calibration statistics of water-level measurements made throughout the study area than did the two-stress-period model, reducing the Lloyd aquifer root mean square error from 7.0 to 5.2 feet. Decreasing horizontal and vertical hydraulic conductivities (fixed anisotropy ratio) of the Lloyd and North Shore aquifers by 20 percent resulted in nearly doubling the simulated salinity(chloride concentration) increase at Port Washington observation well N12508. Groundwater flowpath analysis was completed for 24 production wells to delineate water source areas. The freshwater/saltwater transition zone moved toward and(or) away from wells during future hypothetical scenarios.

  16. Could the peristaltic transition zone be caused by non-uniform esophageal muscle fiber architecture? A simulation study.

    Kou, W; Pandolfino, J E; Kahrilas, P J; Patankar, N A

    2017-06-01

    Based on a fully coupled computational model of esophageal transport, we analyzed how varied esophageal muscle fiber architecture and/or dual contraction waves (CWs) affect bolus transport. Specifically, we studied the luminal pressure profile in those cases to better understand possible origins of the peristaltic transition zone. Two groups of studies were conducted using a computational model. The first studied esophageal transport with circumferential-longitudinal fiber architecture, helical fiber architecture and various combinations of the two. In the second group, cases with dual CWs and varied muscle fiber architecture were simulated. Overall transport characteristics were examined and the space-time profiles of luminal pressure were plotted and compared. Helical muscle fiber architecture featured reduced circumferential wall stress, greater esophageal distensibility, and greater axial shortening. Non-uniform fiber architecture featured a peristaltic pressure trough between two high-pressure segments. The distal pressure segment showed greater amplitude than the proximal segment, consistent with experimental data. Dual CWs also featured a pressure trough between two high-pressure segments. However, the minimum pressure in the region of overlap was much lower, and the amplitudes of the two high-pressure segments were similar. The efficacy of esophageal transport is greatly affected by muscle fiber architecture. The peristaltic transition zone may be attributable to non-uniform architecture of muscle fibers along the length of the esophagus and/or dual CWs. The difference in amplitude between the proximal and distal pressure segments may be attributable to non-uniform muscle fiber architecture. © 2017 John Wiley & Sons Ltd.

  17. Comprehensive understanding of a deep transition zone from an unstable- to stable-slip regime of the megathrust interplate earthquake

    Kato, A.; Iidaka, T.; Ikuta, R.; Yoshida, Y.; Katsumata, K.; Iwasaki, T.; Sakai, S.; Yamaoka, K.; Watanabe, T.; Kunitomo, T.; Yamazaki, F.; Tsumura, N.; Nozaki, K.; Okubo, M.; Suzuki, S.; Hirata, N.; Zhang, H.; Thurber, C. H.

    2009-12-01

    Most slow slips have occurred in the deep transition zone from an unstable- to stable-slip regime. Detailed knowledge about a deep transition zone is essentially important to understand the mechanism of the slow slips, and the stress concentration process to the source region of the megathrust interplate earthquake. We have conducted a very dense seismic observation in the Tokai-region from the April to the August in 2008 through a linear deployment of 75 portable stations, in Japan. The array extended from the bottom part of the source region of the Tokai earthquake to deep low-frequency earthquakes (LFE, ~ 35 km depth) including the long-term slow-slip region (~ 25 km depth). Here we present a high-resolution tomographic imaging of seismic velocities and highly-accurate hypocenters including LFEs, using first arrival data from the dense seismograph deployment. We manually picked the first arrivals of P- and S- waves from each waveform for about 700 earthquakes including about 20 LFEs observed by the dense array. Then, we applied the TomoDD-code [Zhang and Thurber, 2003] to the arrival data set, adding an accurate double-difference data estimated by a waveform cross-correlation technique. A low velocity (Vp, Vs) layer with high Poisson’s ratio is clearly imaged, and tilts to the northwestward with a low dip angle, which corresponds to the subducting oceanic crust of the Philippine Sea Slab. Although seismicity within the oceanic crust is significantly low, few earthquakes occur within the oceanic crust. The LFEs are linearly aligned along the top surface of the subducting oceanic crust at depths from 30 to 40 km. The Poisson’s ratio within the oceanic crust does not show significant depth-dependent increase beneath the linear alignment of LFEs. This result argues against a depth section of Poisson’s ratio obtained in the SW Japan [Shelly et al., 2006]. Beneath the LFEs, active cluster of slab earthquakes are horizontally distributed. At the depths greater

  18. Isotopic evidence for the spatial heterogeneity of the planktonic food webs in the transition zone between river and lake ecosystems

    Hideyuki Doi

    2013-12-01

    Full Text Available Resources and organisms in food webs are distributed patchily. The spatial structure of food webs is important and critical to understanding their overall structure. However, there is little available information about the small-scale spatial structure of food webs. We investigated the spatial structure of food webs in a lake ecosystem at the littoral transition zone between an inflowing river and a lake. We measured the carbon isotope ratios of zooplankton and particulate organic matter (POM; predominantly phytoplankton in the littoral zone of a saline lake. Parallel changes in the δ 13C values of zooplankton and their respective POMs indicated that there is spatial heterogeneity of the food web in this study area. Lake ecosystems are usually classified at the landscape level as either pelagic or littoral habitats. However, we showed small-scale spatial heterogeneity among planktonic food webs along an environmental gradient. Stable isotope data is useful for detecting spatial heterogeneity of habitats, populations, communities, and ecosystems.

  19. A phylogeographic study of the endemic rodent Eliurus carletoni (Rodentia: Nesomyinae) in an ecological transition zone of Northern Madagascar.

    Rakotoarisoa, Jean-Eric; Raheriarisena, Martin; Goodman, Steven M

    2013-01-01

    We conducted a mitochondrial phylogeographic study of the endemic dry forest rodent Eliurus carletoni (Rodentia: Nesomyinae) in an ecological transition zone of northern Madagascar (Loky-Manambato) and 2 surrounding regions (Ankarana and Analamerana). The main goal was to assess the evolutionary consequences on this taxon of the complex landscape features and Quaternary ecological vicissitudes. Three haplogroups were identified from the 215 specimens obtained from 15 populations. High levels of genetic diversity and significant genetic differentiation among populations were observed. The different geographical subdivisions of the study area by regions, by river catchment zones, and the physical distance between populations are not correlated with genetic patterns. In contrast, population structure is mostly explained by the geographic distribution of the samples among existing forest blocks. E. carletoni experienced a genetic bottleneck between 18 750 and 7500 years BP, which correlates with periods when moister climates existed on the island. Overall, our data suggest that the complex genetic patterns of E. carletoni can be explained by Quaternary climatic vicissitudes that resulted in habitat fluctuations between dry and humid forests, as well as subsequent human-induced fragmentation of forest habitat.

  20. Imprints from genetic drift and mutation imply relative divergence times across marine transition zones in a Pan European small pelagic fish (Sprattus sprattus)

    Limborg, Morten; Hanel, R.; Debes, P.

    2012-01-01

    .) by combining inference from both mtDNA and microsatellite genetic markers throughout the species’ distribution. We compared effects from genetic drift and mutation for both genetic markers in shaping genetic differentiation across four transition zones. Microsatellite markers revealed significant isolation...... by distance and a complex population structure across the species0 distribution (overall yST¼0.038, Po0.01). Across transition zones markers indicated larger effects of genetic drift over mutations in the northern distribution of sprat contrasting a stronger relative impact of mutation in the species...

  1. Probability density functions for radial anisotropy: implications for the upper 1200 km of the mantle

    Beghein, Caroline; Trampert, Jeannot

    2004-01-01

    The presence of radial anisotropy in the upper mantle, transition zone and top of the lower mantle is investigated by applying a model space search technique to Rayleigh and Love wave phase velocity models. Probability density functions are obtained independently for S-wave anisotropy, P-wave anisotropy, intermediate parameter η, Vp, Vs and density anomalies. The likelihoods for P-wave and S-wave anisotropy beneath continents cannot be explained by a dry olivine-rich upper mantle at depths larger than 220 km. Indeed, while shear-wave anisotropy tends to disappear below 220 km depth in continental areas, P-wave anisotropy is still present but its sign changes compared to the uppermost mantle. This could be due to an increase with depth of the amount of pyroxene relative to olivine in these regions, although the presence of water, partial melt or a change in the deformation mechanism cannot be ruled out as yet. A similar observation is made for old oceans, but not for young ones where VSH> VSV appears likely down to 670 km depth and VPH> VPV down to 400 km depth. The change of sign in P-wave anisotropy seems to be qualitatively correlated with the presence of the Lehmann discontinuity, generally observed beneath continents and some oceans but not beneath ridges. Parameter η shows a similar age-related depth pattern as shear-wave anisotropy in the uppermost mantle and it undergoes the same change of sign as P-wave anisotropy at 220 km depth. The ratio between dln Vs and dln Vp suggests that a chemical component is needed to explain the anomalies in most places at depths greater than 220 km. More tests are needed to infer the robustness of the results for density, but they do not affect the results for anisotropy.

  2. Sedimentology and geochemistry of early Proterozoic storm-dominated deposits in the transition zone from microbanded Kuruman to granular Griquatown iron-formation, Griqualand West

    Beukes, N.J.; Klein, C.

    1990-01-01

    A transition from microbanded Kuruman to granular Griquatown iron-formation is described in terms of sedimentological, petrographic, and geochemical characteristics, as well as whole rock carbon and oxygen isotopic compositions. Five major lithofacies are present in the Kuruman-Griquatown transition zone. The lithofacies are arranged in an upward coarsening sequence. It is concluded that the coarsening upward microbanded-granular iron-formation units in the Kuruman-Griquatown sequence represent shallowing upward storm-dominated deposits. 2 refs

  3. Validation of small Kepler transiting planet candidates in or near the habitable zone

    Torres, Guillermo; Kane, Stephen R.; Rowe, Jason F.

    2017-01-01

    A main goal of NASA's Kepler Mission is to establish the frequency of potentially habitable Earth-size planets (). Relatively few such candidates identified by the mission can be confirmed to be rocky via dynamical measurement of their mass. Here we report an effort to validate 18 of them...... statistically using the BLENDER technique, by showing that the likelihood they are true planets is far greater than that of a false positive. Our analysis incorporates follow-up observations including high-resolution optical and near-infrared spectroscopy, high-resolution imaging, and information from...... the analysis of the flux centroids of the Kepler observations themselves. Although many of these candidates have been previously validated by others, the confidence levels reported typically ignore the possibility that the planet may transit a star different from the target along the same line of sight...

  4. Contribution to the study of velocity fields of chromosphere and solar transition zone

    Artzner, C.

    1982-06-01

    The LPSP (Laboratoire de Physique Stellaire et Planetaire) experiment on board 0508 is described. The properties of the instrument are discussed together with their evolution with time. The chromospheric oscillations and transients were studied (sunspost and active regions, prominences, oscillations in the chromosphere, chromosphere-corona transition lines). Simultaneous time-resolved observations of the H Lα, Mg k 2795A, and Ca, K solar lines were made. They indicate that the temporal variations of wavelength of the reversal of the solar H Lα and Mg k lines are correlated. A narrow absorption on the red part of the solar H Lα profile was observed and attributed to atomic hydrogen of the nearby interplanetary gas [fr

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

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

    2018-04-01

    The solubility of nitrogen in the major minerals of the Earth's transition zone and lower mantle (wadsleyite, ringwoodite, bridgmanite, and Ca-silicate perovskite) coexisting with a reduced, nitrogen-rich fluid phase was measured. Experiments were carried out in multi-anvil presses at 14 to 24 GPa and 1100 to 1800 °C close to the Fe-FeO buffer. Starting materials were enriched in 15N and the nitrogen concentrations in run products were measured by secondary ion mass spectrometry. Observed nitrogen (15N) solubilities in wadsleyite and ringwoodite typically range from 10 to 250 μg/g and strongly increase with temperature. Nitrogen solubility in bridgmanite is about 20 μg/g, while Ca-silicate perovskite incorporates about 30 μg/g under comparable conditions. Partition coefficients of nitrogen derived from coexisting phases are DNwadsleyite/olivine = 5.1 ± 2.1, DNringwoodite/wadsleyite = 0.49 ± 0.29, and DNbridgmanite/ringwoodite = 0.24 (+ 0.30 / - 0.19). Nitrogen solubility in the solid, iron-rich metal phase coexisting with the silicates was also measured and reached a maximum of nearly 1 wt.% 15N at 23 GPa and 1400 °C. These data yield a partition coefficient of nitrogen between iron metal and bridgmanite of DNmetal/bridgmanite ∼ 98, implying that in a lower mantle containing about 1% of iron metal, about half of the nitrogen still resides in the silicates. The high nitrogen solubility in wadsleyite and ringwoodite may be responsible for the low nitrogen concentrations often observed in ultradeep diamonds from the transition zone. Overall, the solubility data suggest that the transition zone and the lower mantle have the capacity to store at least 33 times the mass of nitrogen presently residing in the atmosphere. By combining the nitrogen solubility data in minerals with data on nitrogen solubility in silicate melts, mineral/melt partition coefficients of nitrogen can be estimated, from which the behavior of nitrogen during magma ocean crystallization can

  6. TEM Microstructure and Chemical Composition of Transition Zone Between Steel Tube and An Inconel 625 Weld Overlay Coating Produced by CMT Method

    Rozmus-Górnikowska M.

    2017-06-01

    Full Text Available The aim of this work was to investigate the microstructure and chemical composition of the transition zone between 16Mo3 steel and Inconel 625 weld overlay coating produced by the Cold Metal Transfer (CMT method. Investigations were primarily carried out through transmission electron microscopy (TEM on thin foils prepared by FIB (Focus Ion Beam.

  7. Small ruminant feed systems: perceptions and practices in the transitional zone of Ghana

    van der Zijpp Akke J

    2010-03-01

    and agronomic investigations into major feeds, the creation of non-cropping zones around village fringes and studies on labour demands of different feed systems are proposed. The insight gained in this study on farmers' perceptions and practices relating to small ruminant feeds could guide in the selection and introduction of feed innovations that fit into current feed systems to enhance adoption.

  8. Executive Summary: “Mantle Frontier” Workshop

    Workshop Report Writing Group

    2011-03-01

    Full Text Available The workshop on “Reaching the Mantle Frontier: Moho and Beyond” was held at the Broad Branch Road Campus of the Carnegie Institution of Washington on 9–11 September 2010. The workshop attracted seventy-four scientists and engineers from academia and industry in North America, Asia, and Europe.Reaching and sampling the mantle through penetration of the entire oceanic crust and the Mohorovičić discontinuity (Moho has been a longstanding goal of the Earth science community. The Moho is a seismic transition, often sharp, from a region with compressional wave velocities (Vp less than 7.5 km s-1 to velocities ~8 km s-1. It is interpreted in many tectonic settings, and particularly in tectonic exposures of oceanic lower crust, as the transition from igneous crust to mantle rocks that are the residues of melt extraction. Revealing the in situ geological meaning of the Moho is the heart of the Mohole project. Documenting ocean-crust exchanges and the nature and extent of the subseafloor biosphere have also become integral components of the endeavor. The purpose of the “Mantle Frontier” workshop was to identify key scientific objectives associated with innovative technology solutions along with associated timelines and costs for developments and implementation of this grandchallenge.

  9. Organization of the Zone of Transition between the Pretectum and the Thalamus, with Emphasis on the Pretectothalamic Lamina

    Emmanuel Márquez-Legorreta

    2016-08-01

    Full Text Available The zone of transition between the pretectum, derived from prosomere 1, and the thalamus, derived from prosomere 2, is structurally complex and its understanding has been hampered by cytoarchitectural and terminological confusion. Herein, using a battery of complementary morphological approaches, including cytoarchitecture, myeloarchitecture and the expression of molecular markers, we pinpoint the features or combination of features that best characterize each nucleus of the pretectothalamic transitional zone of the rat. Our results reveal useful morphological criteria to identify and delineate, with unprecedented precision, several [mostly auditory] nuclei of the posterior group of the thalamus, namely the pretectothalamic lamina (PTL; formerly known as the posterior limitans nucleus, the medial division of the medial geniculate body (MGBm, the suprageniculate nucleus (SG, and the ethmoid, posterior triangular and posterior nuclei of the thalamus. The PTL is a sparsely-celled and fiber rich flattened nucleus apposed to the lateral surface of the anterior pretectal nucleus that marks the border between the pretectum and the thalamus; this structure stains selectively with the Wisteria floribunda agglutinin (WFA, and is essentially immunonegative for the calcium binding protein parvalbumin. The MGBm, located medial to the ventral division of the medial geniculate body, can be unequivocally identified by the large size of many of its neurons, its dark immunostaining for parvalbumin, and its rather selective staining for WFA. The SG, which extends for a considerable caudorostral distance and deviates progressively from the MGB, is characterized by its peculiar cytoarchitecture, the paucity of myelinated fibers, and the conspicuous absence of staining for calretinin; indeed, in many calretinin-stained sections, the SG stands out as a blank spot. Because most of these nuclei are small and show unique anatomical relationships, the information provided

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

    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.

  11. Light Stable Isotopic Compositions of Enriched Mantle Sources: Resolving the Dehydration Paradox

    Dixon, J. E.; Bindeman, I. N.; Kingsley, R. H.

    2017-12-01

    An outstanding puzzle in mantle geochemistry has been the origin and evolution of Earth's volatile components. The "dehydration paradox" refers to the following conundrum. Mantle compositions for some enriched mid-ocean ridge (MORB) and ocean island (OIB) basalts basalts require involvement of a mostly dehydrated slab component to explain the trace element ratios and radiogenic isotopic compositions, but a fully hydrated slab component to explain the stable isotopic compositions. Volatile and stable isotopic data on enriched MORB show a diversity of enriched components. Pacific PREMA-type basalts (H2O/Ce = 215 ± 30, δDSMOW = -45 ± 5 ‰) are similar to those in the north Atlantic (H2O/Ce = 220 ± 30; δDSMOW = -30 to -40 ‰). Basalts with EM-type signatures have regionally variable volatile compositions. North Atlantic EM-type basalts are wetter (H2O/Ce = 330 ± 30) and have isotopically heavier hydrogen (δDSMOW = -57 ± 5 ‰) than north Atlantic MORB. South Atlantic EM-type basalts are damp (H2O/Ce = 120 ± 10) with intermediate δDSMOW (-68 ± 2 ‰), similar to dDSMOW for Pacific MORB. North EPR EM-type basalts are dry (H2O/Ce = 110 ± 20) and isotopically light (δDSMOW = -94 ± 3 ‰). Boron and lithium isotopic ratios parallel the trends observed for dDSMOW. A multi-stage metasomatic and melting model accounts for the origin of the enriched components by extending the subduction factory concept down through the mantle transition zone, with slab temperature a key variable. The dehydration paradox is resolved by decoupling of volatiles from lithophile elements, reflecting primary dehydration of the slab followed by secondary rehydration and re-equilibration by fluids derived from subcrustal hydrous phases (e.g., antigorite) in cooler, deeper parts of the slab. The "expanded subduction factory" model includes melting at several key depths, including 1) 180 to 280 km, where EM-type mantle compositions are generated above slabs with average to hot thermal

  12. The uniquely high-temperature character of Cullinan diamonds: A signature of the Bushveld mantle plume?

    Korolev, N. M.; Kopylova, M.; Bussweiler, Y.; Pearson, D. G.; Gurney, J.; Davidson, J.

    2018-04-01

    The mantle beneath the Cullinan kimberlite (formerly known as "Premier") is a unique occurrence of diamondiferous cratonic mantle where diamonds were generated contemporaneously and shortly following a mantle upwelling that led to the formation of a Large Igneous Province that produced the world's largest igneous intrusion - the 2056 Ma Bushveld Igneous Complex (BIC). We studied 332 diamond inclusions from 202 Cullinan diamonds to investigate mantle thermal effects imposed by the formation of the BIC. The overwhelming majority of diamonds come from three parageneses: (1) lithospheric eclogitic (69%), (2) lithospheric peridotitic (21%), and (3) sublithospheric mafic (9%). The lithospheric eclogitic paragenesis is represented by clinopyroxene, garnet, coesite and kyanite. Main minerals of the lithospheric peridotitic paragenesis are forsterite, enstatite, Cr-pyrope, Cr-augite and spinel; the sublithospheric mafic association includes majorite, CaSiO3 phases and omphacite. Diamond formation conditions were calculated using an Al-in-olivine thermometer, a garnet-clinopyroxene thermometer, as well as majorite and Raman barometers. The Cullinan diamonds may be unique on the global stage in recording a cold geotherm of 40 mW/m2 in cratonic lithosphere that was in contact with underlying convecting mantle at temperatures of 1450-1550 °C. The studied Cullinan diamonds contain a high proportion of inclusions equilibrated at temperatures exceeding the ambient 1327 °C adiabat, i.e. 54% of eclogitic diamonds and 41% of peridotitic diamonds. By contrast, ≤ 1% of peridotitic diamond inclusions globally yield equally high temperatures. We propose that the Cullinan diamond inclusions recorded transient, slow-dissipating thermal perturbations associated with the plume-related formation of the 2 Ga Bushveld igneous province. The presence of inclusions in diamond from the mantle transition zone at 300-650 km supports this view. Cullinan xenoliths indicative of the thermal state of

  13. The Mantle and Basalt-Crust Interaction Below the Mount Taylor Volcanic Field, New Mexico

    Schrader, Christian M.; Crumpler, Larry S.; Schmidt, Marick E.

    2010-01-01

    The Mount Taylor Volcanic Field (MTVF) lies on the Jemez Lineament on the southeastern margin of the Colorado Plateau. The field is centered on the Mt. Taylor composite volcano and includes Mesa Chivato to the NE and Grants Ridge to the WSW. MTVF magmatism spans approximately 3.8-1.5 Ma (K-Ar). Magmas are dominantly alkaline with mafic compositions ranging from basanite to hy-basalt and felsic compositions ranging from ne-trachyte to rhyolite. We are investigating the state of the mantle and the spatial and temporal variation in basalt-crustal interaction below the MTVF by examining mantle xenoliths and basalts in the context of new mapping and future Ar-Ar dating. The earliest dated magmatism in the field is a basanite flow south of Mt. Taylor. Mantle xenolith-bearing alkali basalts and basanites occur on Mesa Chivato and in the region of Mt. Taylor, though most basalts are peripheral to the main cone. Xenolith-bearing magmatism persists at least into the early stages of conebuilding. Preliminary examination of the mantle xenolith suite suggests it is dominantly lherzolitic but contains likely examples of both melt-depleted (harzburgitic) and melt-enriched (clinopyroxenitic) mantle. There are aphyric and crystal-poor hawaiites, some of which are hy-normative, on and near Mt. Taylor, but many of the more evolved MTVF basalts show evidence of complex histories. Mt. Taylor basalts higher in the cone-building sequence contain >40% zoned plagioclase pheno- and megacrysts. Other basalts peripheral to Mt. Taylor and at Grants Ridge contain clinopyroxene and plagioclase megacrysts and cumulate-textured xenoliths, suggesting they interacted with lower crustal cumulates. Among the questions we are addressing: What was the chemical and thermal state of the mantle recorded by the basaltic suites and xenoliths and how did it change with time? Are multiple parental basalts (Si-saturated vs. undersaturated) represented and, if so, what changes in the mantle or in the tectonic

  14. Tomography and Dynamics of Western-Pacific Subduction Zones

    Zhao, D.

    2012-01-01

    the Japan Sea and the East Asia margin may be related to a metastable olivine wedge in the subducting Pacific slab. The Pacific slab becomes stagnant in the mantle transition zone under East Asia, and a big mantle wedge (BMW) has formed above the stagnant slab. Convective circulations and fluid and magmatic processes in the BMW may have caused intraplate volcanism (e.g., Changbai and Wudalianchi), reactivation of the North China craton, large earthquakes, and other active tectonics in East Asia. Deep subduction and dehydration of continental plates (such as the Eurasian plate, Indian plate and Burma microplate) are also found, which have caused intraplate magmatism (e.g., Tengchong) and geothermal anomalies above the subducted continental plates. Under Kamchatka, the subducting Pacific slab shortens toward the north and terminates near the Aleutian-Kamchatka junction. The slab loss was induced by friction with the surrounding asthenosphere, as the Pacific plate rotated clockwise 30 Ma ago, and then it was enlarged by the slab-edge pinch-off by the asthenospheric flow. The stagnant slab finally collapses down to the bottom of the mantle, which may trigger upwelling of hot mantle materials from the lower mantle to the shallow mantle. Suggestions are also made for future directions of the seismological research of subduction zones.

  15. A Transition Zone Showing Highly Discontinuous or Alternating Levels of Stem Cell and Proliferation Markers Characterizes the Development of PTEN-Haploinsufficient Colorectal Cancer.

    Arvai, Kevin J; Hsu, Ya-Hsuan; Lee, Lobin A; Jones, Dan

    2015-01-01

    Stepwise acquisition of oncogene mutations and deletion/inactivation of tumor suppressor genes characterize the development of colorectal cancer (CRC). These genetic events interact with discrete morphologic transitions from hyperplastic mucosa to adenomatous areas, followed by in situ malignant transformation and finally invasive carcinoma. The goal of this study was to identify tissue markers of the adenoma-carcinoma morphogenetic transitions in CRC. We analyzed the patterns of expression of growth regulatory and stem cell markers across these distinct morphologic transition zones in 735 primary CRC tumors. In 202 cases with preserved adenoma-adenocarcinoma transition, we identified, in 37.1% of cases, a zone of adenomatous epithelium, located immediately adjacent to the invasive component, that showed rapidly alternating intraglandular stretches of PTEN+ and PTEN- epithelium. This zone exactly overlapped with similar alternating expression of Ki-67 and inversely with the transforming growth factor-beta (TGF-β) growth regulator SMAD4. These zones also show parallel alternating levels and/or subcellular localization of multiple cancer stem/progenitor cell (CSC) markers, including β-catenin/CTNNB1, ALDH1, and CD44. PTEN was always re-expressed in the invasive tumor in these cases, unlike those with complete loss of PTEN expression. Genomic microarray analysis of CRC with prominent CSC-like expansions demonstrated a high frequency of PTEN genomic deletion/haploinsufficiency in tumors with CSC-like transition zones (62.5%) but not in tumors with downregulated but non-alternating PTEN expression (14.3%). There were no significant differences in the levels of KRAS mutation or CTNNB1 mutation in CSC-like tumors as compared to unselected CRC cases. In conclusion, we have identified a distinctive CSC-like pre-invasive transition zone in PTEN-haploinsufficient CRC that shows convergent on-off regulation of the PTEN/AKT, TGF-β/SMAD and Wnt/β-catenin pathways. This

  16. A Transition Zone Showing Highly Discontinuous or Alternating Levels of Stem Cell and Proliferation Markers Characterizes the Development of PTEN-Haploinsufficient Colorectal Cancer.

    Kevin J Arvai

    Full Text Available Stepwise acquisition of oncogene mutations and deletion/inactivation of tumor suppressor genes characterize the development of colorectal cancer (CRC. These genetic events interact with discrete morphologic transitions from hyperplastic mucosa to adenomatous areas, followed by in situ malignant transformation and finally invasive carcinoma. The goal of this study was to identify tissue markers of the adenoma-carcinoma morphogenetic transitions in CRC.We analyzed the patterns of expression of growth regulatory and stem cell markers across these distinct morphologic transition zones in 735 primary CRC tumors. In 202 cases with preserved adenoma-adenocarcinoma transition, we identified, in 37.1% of cases, a zone of adenomatous epithelium, located immediately adjacent to the invasive component, that showed rapidly alternating intraglandular stretches of PTEN+ and PTEN- epithelium. This zone exactly overlapped with similar alternating expression of Ki-67 and inversely with the transforming growth factor-beta (TGF-β growth regulator SMAD4. These zones also show parallel alternating levels and/or subcellular localization of multiple cancer stem/progenitor cell (CSC markers, including β-catenin/CTNNB1, ALDH1, and CD44. PTEN was always re-expressed in the invasive tumor in these cases, unlike those with complete loss of PTEN expression. Genomic microarray analysis of CRC with prominent CSC-like expansions demonstrated a high frequency of PTEN genomic deletion/haploinsufficiency in tumors with CSC-like transition zones (62.5% but not in tumors with downregulated but non-alternating PTEN expression (14.3%. There were no significant differences in the levels of KRAS mutation or CTNNB1 mutation in CSC-like tumors as compared to unselected CRC cases.In conclusion, we have identified a distinctive CSC-like pre-invasive transition zone in PTEN-haploinsufficient CRC that shows convergent on-off regulation of the PTEN/AKT, TGF-β/SMAD and Wnt

  17. Polymineralic inclusions in mantle chromitites from the Oman ophiolite indicate a highly magnesian parental melt

    Rollinson, Hugh; Mameri, Lucan; Barry, Tiffany

    2018-06-01

    Polymineralic inclusions interpreted as melt inclusions in chromite from the dunitic Moho Transition Zone in the Maqsad area of the Oman ophiolite have been analysed and compositions integrated using a rastering technique on the scanning electron microscope. The inclusions now comprise a range of inter-grown hydrous phases including pargasite, aspidolite, phlogopite and chlorite, indicating that the parental melts were hydrous. Average inclusion compositions for seven samples contain between 23.1 and 26.8 wt% MgO and 1.7-3.6 wt% FeO. Compositions were corrected to allow for the low FeO concentrations using coexisting olivine compositions. These suggest that the primary melt has between 20 and 22 wt% MgO and 7-9.7 wt% FeO and has an affinity with boninitic melts, although the melts have a higher Ti content than most boninites. Average rare earth element concentrations suggest that the melts were derived from a REE depleted mantle source although fluid-mobile trace elements indicate a more enriched source. Given the hydrous nature of the inclusions this enrichment could be fluid driven. An estimate of the melt temperature can be made from the results of homogenisation experiments on these inclusions and suggests 1300 °C, which implies for a harzburgite solidus, relatively shallow melting at depths of <50 km and is consistent with a boninitic origin. The current "basaltic" nature of the chromite host to highly magnesian melt inclusions suggests that the dunitic Moho Transition Zone operated as a reaction filter in which magnesian melts were transformed into basalts by the removal of high magnesian olivines, particularly in areas where the Moho Transition Zone is unusually thick. We propose therefore that podiform mantle chromitites, even those with an apparent MORB-like chemical signature, have crystallised from a highly magnesian parental melt. The data presented here strongly support the view that this took place in a subduction initiation setting.

  18. Seismic structure of the European upper mantle based on adjoint tomography

    Zhu, Hejun; Bozdağ, Ebru; Tromp, Jeroen

    2015-04-01

    . Furthermore, enhanced attenuation is observed within the mantle transition zone beneath the North Atlantic Ocean. Consistent with typical radial anisotropy in 1-D reference models, the European continent is dominated by features with a radially anisotropic parameter ξ > 1, indicating predominantly horizontal flow within the upper mantle. In addition, subduction zones, such as the Apennines and Hellenic arcs, are characterized by vertical flow with ξ region. Averaged radial peak-to-peak anisotropic strength profiles identify distinct brittle-ductile deformation in lithospheric strength beneath oceans and continents. Finally, we use the `point-spread function' to assess image quality and analyse trade-offs between different model parameters.

  19. Munroa argentina, a Grass of the South American Transition Zone, Survived the Andean Uplift, Aridification and Glaciations of the Quaternary

    Amarilla, Leonardo D.; Anton, Ana M.; Chiapella, Jorge O.; Manifesto, María M.; Angulo, Diego F.; Sosa, Victoria

    2015-01-01

    The South American Transition Zone (SATZ) is a biogeographic area in which not only orogeny (Andes uplift) and climate events (aridification) since the mid-Miocene, but also Quaternary glaciation cycles had an important impact on the evolutionary history of the local flora. To study this effect, we selected Munroa argentina, an annual grass distributed in the biogeographic provinces of Puna, Prepuna and Monte. We collected 152 individuals from 20 localities throughout the species’ range, ran genetic and demographic analyses, and applied ecological niche modeling. Phylogenetic and population genetic analyses based on cpDNA and AFLP data identified three phylogroups that correspond to the previously identified subregions within the SATZ. Molecular dating suggests that M. argentina has inhabited the SATZ since approximately 3.4 (4.2–1.2) Ma and paleomodels predict suitable climate in these areas during the Interglacial period and the Last Glacial Maximum. We conclude that the current distribution of M. argentina resulted from the fragmentation of its once continuous range and that climate oscillations promoted ecological differences that favored isolation by creating habitat discontinuity. PMID:26110533

  20. Munroa argentina, a Grass of the South American Transition Zone, Survived the Andean Uplift, Aridification and Glaciations of the Quaternary.

    Leonardo D Amarilla

    Full Text Available The South American Transition Zone (SATZ is a biogeographic area in which not only orogeny (Andes uplift and climate events (aridification since the mid-Miocene, but also Quaternary glaciation cycles had an important impact on the evolutionary history of the local flora. To study this effect, we selected Munroa argentina, an annual grass distributed in the biogeographic provinces of Puna, Prepuna and Monte. We collected 152 individuals from 20 localities throughout the species' range, ran genetic and demographic analyses, and applied ecological niche modeling. Phylogenetic and population genetic analyses based on cpDNA and AFLP data identified three phylogroups that correspond to the previously identified subregions within the SATZ. Molecular dating suggests that M. argentina has inhabited the SATZ since approximately 3.4 (4.2-1.2 Ma and paleomodels predict suitable climate in these areas during the Interglacial period and the Last Glacial Maximum. We conclude that the current distribution of M. argentina resulted from the fragmentation of its once continuous range and that climate oscillations promoted ecological differences that favored isolation by creating habitat discontinuity.

  1. Design and Development of Maize Dehusker cum Sheller: A Technology for Northern Transition Zone of Karnataka, India

    Chilur, Rudragouda; Kumar, Sushilendra

    2018-06-01

    The Maize ( Zea mays L.) crop is one of the most important cereal in agricultural production systems of Northern Transition Zone (Hyderabad-Karnataka region) in India. These Hyderabad Karnataka farmers (small-medium) are lack of economic technologies with maize dehusking and shelling, which fulfils the two major needs as crops and as livestock in farming. The portable medium size (600 kg/h capacity) electric motor (2.23 kW) operated Maize Dehusker cum Sheller (MDS) was designed to resolve the issue by considering engineering properties of maize. The developed trapezium shaped MDS machine having overall dimensions (length × (top and bottom) × height) of 1200 × (500 and 610) × 810 mm. The selected operational parameters viz, cylinder peripheral speed (7.1 m/s), concave clearance (25 mm) and feed rate (600 kg/h) were studied for machine-performance and seed-quality parameters. The performance of machine under these parameters showed the dehusking efficiency of 99.56%, shelling efficiency of 98.01%, cleaning efficiency of 99.11%, total loss of 3.63% machine capacity of 527.11 kg/kW-h and germination percentage of 98.93%. Overall machine performance was found satisfactory for maize dehusking cum shelling operation as well as to produce the maize grains for seeding purpose.

  2. Influence of aggregate size, water cement ratio and age on the microstructure of the interfacial transition zone

    Elsharief, Amir; Cohen, Menashi D.; Olek, Jan

    2003-01-01

    This paper presents the results of an investigation on the effect of water-cement ratio (w/c), aggregate size, and age on the microstructure of the interfacial transition zone (ITZ) between normal weight aggregate and the bulk cement paste. Backscattered electron images (BSE) obtained by scanning electron microscope were used to characterize the ITZ microstructure. The results suggest that the w/c plays an important role in controlling the microstructure of the ITZ and its thickness. Reducing w/c from 0.55 to 0.40 resulted in an ITZ with characteristics that are not distinguishable from those of the bulk paste as demonstrated by BSE images. Aggregate size appears to have an important influence on the ITZ characteristics. Reducing the aggregate size tends to reduce the ITZ porosity. The evolution of the ITZ microstructure relative to that of the bulk paste appears to depend on the initial content of the unhydrated cement grains (UH). The results suggest that the presence of a relatively low amount of UH in the ITZ at early age may cause the porosity of the ITZ, relative to that of the bulk paste, to increase with time. The presence of relatively large amount of UH in the ITZ at early ages may cause its porosity, relative to that of the bulk paste, to decrease with time

  3. Munroa argentina, a Grass of the South American Transition Zone, Survived the Andean Uplift, Aridification and Glaciations of the Quaternary.

    Amarilla, Leonardo D; Anton, Ana M; Chiapella, Jorge O; Manifesto, María M; Angulo, Diego F; Sosa, Victoria

    2015-01-01

    The South American Transition Zone (SATZ) is a biogeographic area in which not only orogeny (Andes uplift) and climate events (aridification) since the mid-Miocene, but also Quaternary glaciation cycles had an important impact on the evolutionary history of the local flora. To study this effect, we selected Munroa argentina, an annual grass distributed in the biogeographic provinces of Puna, Prepuna and Monte. We collected 152 individuals from 20 localities throughout the species' range, ran genetic and demographic analyses, and applied ecological niche modeling. Phylogenetic and population genetic analyses based on cpDNA and AFLP data identified three phylogroups that correspond to the previously identified subregions within the SATZ. Molecular dating suggests that M. argentina has inhabited the SATZ since approximately 3.4 (4.2-1.2) Ma and paleomodels predict suitable climate in these areas during the Interglacial period and the Last Glacial Maximum. We conclude that the current distribution of M. argentina resulted from the fragmentation of its once continuous range and that climate oscillations promoted ecological differences that favored isolation by creating habitat discontinuity.

  4. Prostate-specific membrane antigen PET/MRI validation of MR textural analysis for detection of transition zone prostate cancer

    Bates, Anthony; Miles, Kenneth

    2017-01-01

    To validate MR textural analysis (MRTA) for detection of transition zone (TZ) prostate cancer through comparison with co-registered prostate-specific membrane antigen (PSMA) PET-MR. Retrospective analysis was performed for 30 men who underwent simultaneous PSMA PET-MR imaging for staging of prostate cancer. Thirty texture features were derived from each manually contoured T2-weighted, transaxial, prostatic TZ using texture analysis software that applies a spatial band-pass filter and quantifies texture through histogram analysis. Texture features of the TZ were compared to PSMA expression on the corresponding PET images. The Benjamini-Hochberg correction controlled the false discovery rate at <5%. Eighty-eight T2-weighted images in 18 patients demonstrated abnormal PSMA expression within the TZ on PET-MR. 123 images were PSMA negative. Based on the corrected p-value of 0.005, significant differences between PSMA positive and negative slices were found for 16 texture parameters: Standard deviation and mean of positive pixels for all spatial filters (p = <0.0001 for both at all spatial scaling factor (SSF) values) and mean intensity following filtration for SSF 3-6 mm (p = 0.0002-0.0018). Abnormal expression of PSMA within the TZ is associated with altered texture on T2-weighted MR, providing validation of MRTA for the detection of TZ prostate cancer. (orig.)

  5. Prostate-specific membrane antigen PET/MRI validation of MR textural analysis for detection of transition zone prostate cancer

    Bates, Anthony [Princess Alexandra Hospital, Brisbane (Australia); Miles, Kenneth [Princess Alexandra Hospital, Department of Diagnostic Radiology, Brisbane, QLD (Australia); University College London, Institute of Nuclear Medicine, London (United Kingdom)

    2017-12-15

    To validate MR textural analysis (MRTA) for detection of transition zone (TZ) prostate cancer through comparison with co-registered prostate-specific membrane antigen (PSMA) PET-MR. Retrospective analysis was performed for 30 men who underwent simultaneous PSMA PET-MR imaging for staging of prostate cancer. Thirty texture features were derived from each manually contoured T2-weighted, transaxial, prostatic TZ using texture analysis software that applies a spatial band-pass filter and quantifies texture through histogram analysis. Texture features of the TZ were compared to PSMA expression on the corresponding PET images. The Benjamini-Hochberg correction controlled the false discovery rate at <5%. Eighty-eight T2-weighted images in 18 patients demonstrated abnormal PSMA expression within the TZ on PET-MR. 123 images were PSMA negative. Based on the corrected p-value of 0.005, significant differences between PSMA positive and negative slices were found for 16 texture parameters: Standard deviation and mean of positive pixels for all spatial filters (p = <0.0001 for both at all spatial scaling factor (SSF) values) and mean intensity following filtration for SSF 3-6 mm (p = 0.0002-0.0018). Abnormal expression of PSMA within the TZ is associated with altered texture on T2-weighted MR, providing validation of MRTA for the detection of TZ prostate cancer. (orig.)

  6. Feeding habit of the Brazilian tapir, Tapirus terrestris (Perissodactyla: Tapiridae in a vegetation transition zone in south-eastern Brazil

    Sônia A. Talamoni

    2009-06-01

    Full Text Available Tapirs are considered generalist herbivores and the differences in the proportions of dietary items are often attributed to differences in the habitats where individuals live. This study characterized the feeding habit of Tapirus terrestris (Linnaeus, 1758 in a nature reserve in south-eastern Brazil, located in a region considered a transition zone between the Cerrado (Brazilian savanna and the Atlantic Forest biomes. Fecal samples from T. terrestris individuals were collected monthly at six sampling areas that encompassed a total of 242.22 ha. There were 147 fresh samples found (77 during the dry season and 70 during the wet season. The diet of the tapirs in this reserve was characterized by the prevalent browsing on leaves and stems. There was a low frequency of fruit seeds in the diet of the tapirs during both the wet and dry seasons. However, in the dry season a higher percentage of samples containing seeds was observed. Fruits of Rubiaceae, Solanaceae, and Annonaceae were most consumed during the dry season. Most of the fruit seeds found presented small mean diameter (3.7-8.4 mm and most of the fruits were capsules and dry fruits. The characteristics of the fruits consumed by the tapirs indicate that they forage in the lower forest stratum and upon species from Cerrado. Additionally, Psidium myrtoides O. Berg. clusters found in the study site suggest that the tapirs may be acting as dispersal agents of this species.

  7. Design and Development of Maize Dehusker cum Sheller: A Technology for Northern Transition Zone of Karnataka, India

    Chilur, Rudragouda; Kumar, Sushilendra

    2018-02-01

    The Maize (Zea mays L.) crop is one of the most important cereal in agricultural production systems of Northern Transition Zone (Hyderabad-Karnataka region) in India. These Hyderabad Karnataka farmers (small-medium) are lack of economic technologies with maize dehusking and shelling, which fulfils the two major needs as crops and as livestock in farming. The portable medium size (600 kg/h capacity) electric motor (2.23 kW) operated Maize Dehusker cum Sheller (MDS) was designed to resolve the issue by considering engineering properties of maize. The developed trapezium shaped MDS machine having overall dimensions (length × (top and bottom) × height) of 1200 × (500 and 610) × 810 mm. The selected operational parameters viz, cylinder peripheral speed (7.1 m/s), concave clearance (25 mm) and feed rate (600 kg/h) were studied for machine-performance and seed-quality parameters. The performance of machine under these parameters showed the dehusking efficiency of 99.56%, shelling efficiency of 98.01%, cleaning efficiency of 99.11%, total loss of 3.63% machine capacity of 527.11 kg/kW-h and germination percentage of 98.93%. Overall machine performance was found satisfactory for maize dehusking cum shelling operation as well as to produce the maize grains for seeding purpose.

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

    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. Electrical conductivity imaging in the western Pacific subduction zone

    Utada, Hisashi; Baba, Kiyoshi; Shimizu, Hisayoshi

    2010-05-01

    Oceanic plate subduction is an important process for the dynamics and evolution of the Earth's interior, as it is regarded as a typical downward flow of the mantle convection that transports materials from the near surface to the deep mantle. Recent seismological study showed evidence suggesting the transportation of a certain amount of water by subduction of old oceanic plate such as the Pacific plate down to 150-200 km depth into the back arc mantle. However it is not well clarified how deep into the mantle the water can be transported. The electromagnetic induction method to image electrical conductivity distribution is a possible tool to answer this question as it is known to be sensitive to the presence of water. Here we show recent result of observational study from the western Pacific subduction zone to examine the electrical conductivity distribution in the upper mantle and in the mantle transition zone (MTZ), which will provide implications how water distributes in the mantle. We take two kinds of approach for imaging the mantle conductivity, (a) semi-global and (b) regional induction approaches. Result may be summarized as follows: (a) Long (5-30 years) time series records from 8 submarine cables and 13 geomagnetic observatories in the north Pacific region were analyzed and long period magnetotelluric (MT) and geomagnetic deep sounding (GDS) responses were estimated in the period range from 1.7 to 35 days. These frequency dependent response functions were inverted to 3-dimensional conductivity distribution in the depth range between 350 and 850 km. Three major features are suggested in the MTZ depth such as, (1) a high conductivity anomaly beneath the Philippine Sea, (2) a high conductivity anomaly beneath the Hawaiian Islands, and (3) a low conductivity anomaly beneath and in the vicinity of northern Japan. (b) A three-year long deployment of ocean bottom electro-magnetometers (OBEM's) was conducted in the Philippine Sea and west Pacific Ocean from 2005

  10. Clustering of arc volcanoes caused by temperature perturbations in the back-arc mantle.

    Lee, Changyeol; Wada, Ikuko

    2017-06-29

    Clustering of arc volcanoes in subduction zones indicates along-arc variation in the physical condition of the underlying mantle where majority of arc magmas are generated. The sub-arc mantle is brought in from the back-arc largely by slab-driven mantle wedge flow. Dynamic processes in the back-arc, such as small-scale mantle convection, are likely to cause lateral variations in the back-arc mantle temperature. Here we use a simple three-dimensional numerical model to quantify the effects of back-arc temperature perturbations on the mantle wedge flow pattern and sub-arc mantle temperature. Our model calculations show that relatively small temperature perturbations in the back-arc result in vigorous inflow of hotter mantle and subdued inflow of colder mantle beneath the arc due to the temperature dependence of the mantle viscosity. This causes a three-dimensional mantle flow pattern that amplifies the along-arc variations in the sub-arc mantle temperature, providing a simple mechanism for volcano clustering.

  11. Depth-Dependent Earthquake Properties Beneath Long-Beach, CA: Implications for the Rheology at the Brittle-Ductile Transition Zone

    Inbal, A.; Clayton, R. W.; Ampuero, J. P.

    2015-12-01

    Except for a few localities, seismicity along faults in southern California is generally confined to depths shallower than 15 km. Among faults hosting deep seismicity, the Newport-Inglewood Fault (NIF), which traverses the Los-Angeles basin, has an exceptionally mild surface expression and low deformation rates. Moreover, the NIF structure is not as well resolved as other, less well instrumented faults because of poor signal-to-noise ratio. Here we use data from three temporary dense seismic arrays, which were deployed for exploration purposes and contain up to several thousands of vertical geophones, to investigate the properties of deep seismicity beneath Long-Beach (LB), Compton and Santa-Fe Springs (SFS). The latter is located 15 km northeast of the NIF, presumably above a major detachment fault underthrusting the basin.Event detection is carried out using a new approach for microseismic multi-channel picking, in which downward-continued data are back-projected onto the volume beneath the arrays, and locations are derived from statistical analysis of back-projection images. Our technique reveals numerous, previously undetected events along the NIF, and confirms the presence of an active shallow structure gently dipping to the north beneath SFS. Seismicity characteristics vary along the NIF strike and dip. While LB seismicity is uncorrelated with the mapped trace of the NIF, Compton seismicity illuminates a sub-vertical fault that extends down to about 20 km. This result, along with the reported high flux of mantle Helium along the NIF (Boles et al., 2015), suggests that the NIF is deeply rooted and acts as a major conduit for mantle fluids. We find that the LB size distribution obeys the typical power-law at shallow depths, but falls off exponentially for events occurring below 20 km. Because deep seismicity occurs uniformly beneath LB, this transition is attributed to a reduction in seismic asperity density with increasing depth, consistent with a transition

  12. Plate-Tectonic Circulation is Driven by Cooling From the Top and is Closed Within the Upper Mantle

    Hamilton, W. B.

    2001-12-01

    . Plate motions are driven by subduction, the passive falling away of oceanic lithosphere which is negatively buoyant because of top-down cooling. Slabs have top and bottom rolling hinges and sink subvertically (inclinations of slabs mark their positions, not trajectories) into the transition zone, where they are laid down on, and depress, the 660-km discontinuity. Rollback of upper hinges into subducting plates is required by plate behavior at all scales. That fronts of overriding plates advance at rollback velocity is required by common preservation atop their thin leading edges of little-deformed fore-arc basins. Convergence velocity also commonly equals rollback but is faster in some arcs. Steeply-sinking inclined slabs push sublithospheric upper mantle forward into the shrinking ocean from which they came, forcing seafloor spreading therein, and pull overriding plates behind them. Continental plates pass over sunken slabs like tanks above their basal treads, and material from, and displaced rearward by, sunken slabs is cycled into pull-apart oceans opening behind the continents, thus transferring mantle from shrinking to enlarging oceans. Hot mantle displaced above slabs enables backarc spreading. Spreading ridges, in both shrinking and enlarging oceans, are passive byproducts of subduction, and migrate because it is more energy efficient to process new asthenosphere than to get partial melt from increasingly distant sources. A plate-motion framework wherein hinges roll back, ridges migrate, Antarctica is approximately fixed, and intraplate deformation is integrated may approximate an absolute reference to sluggish lower mantle, whereas the hotspot frame is invalid, and the no-net-rotation frame minimizes trench and ridge motions.

  13. Migration Imaging of the Java Subduction Zones

    Dokht, Ramin M. H.; Gu, Yu Jeffrey; Sacchi, Mauricio D.

    2018-02-01

    Imaging of tectonically complex regions can greatly benefit from dense network data and resolution enhancement techniques. Conventional methods in the analysis of SS precursors stack the waveforms to obtain an average discontinuity depth, but smearing due to large Fresnel zones can degrade the fine-scale topography on the discontinuity. To provide a partial solution, we introduce a depth migration algorithm based on the common scattering point method while considering nonspecular diffractions from mantle transition zone discontinuities. Our analysis indicates that, beneath the Sunda arc, the depth of the 410 km discontinuity (the 410) is elevated by 30 km and the 660 km discontinuity (the 660) is depressed by 20-40 km; the region of the strongest anticorrelation is correlated with the morphology of the subducting Indo-Australian slab. In eastern Java, a "flat" 410 coincides with a documented slab gap, showing length scales greater than 400 km laterally and 200 km vertically. This observation could be explained by the arrival of a buoyant oceanic plateau at the Java trench at approximately 8 Ma ago, which may have caused a temporary cessation of subduction and formed a tear in the subducting slab. Our results highlight contrasting depths of the 410 and 660 along the shallow-dipping slab below the Banda trench. The 660, however, becomes significantly uplifted beneath the Banda Sea, which is accompanied by enhanced reflection amplitudes. We interpret these observations as evidence for a subslab low-velocity zone, possibly related to the lower mantle upwelling beneath the subducting slab.

  14. Iron-carbonate interaction at Earth's core-mantle boundary

    Dorfman, S. M.; Badro, J.; Nabiei, F.; Prakapenka, V.; Gillet, P.

    2015-12-01

    Carbon storage and flux in the deep Earth are moderated by oxygen fugacity and interactions with iron-bearing phases. The amount of carbon stored in Earth's mantle versus the core depends on carbon-iron chemistry at the core-mantle boundary. Oxidized carbonates subducted from Earth's surface to the lowermost mantle may encounter reduced Fe0 metal from disproportionation of Fe2+ in lower mantle silicates or mixing with the core. To understand the fate of carbonates in the lowermost mantle, we have performed experiments on sandwiches of single-crystal (Ca0.6Mg0.4)CO3 dolomite and Fe foil in the laser-heated diamond anvil cell at lower mantle conditions of 49-110 GPa and 1800-2500 K. Syntheses were conducted with in situ synchrotron X-ray diffraction to identify phase assemblages. After quench to ambient conditions, samples were sectioned with a focused Ga+ ion beam for composition analysis with transmission electron microscopy. At the centers of the heated spots, iron melted and reacted completely with the carbonate to form magnesiowüstite, iron carbide, diamond, magnesium-rich carbonate and calcium carbonate. In samples heated at 49 and 64 GPa, the two carbonates exhibit a eutectoid texture. In the sample heated at 110 GPa, the carbonates form rounded ~150-nm-diameter grains with a higher modal proportion of interspersed diamonds. The presence of reduced iron in the deep lower mantle and core-mantle boundary region will promote the formation of diamonds in carbonate-bearing subducted slabs. The complete reaction of metallic iron to oxides and carbides in the presence of mantle carbonate supports the formation of these phases at the Earth's core-mantle boundary and in ultra-low velocity zones.

  15. 33 CFR 165.110 - Safety and Security Zone; Liquefied Natural Gas Carrier Transits and Anchorage Operations, Boston...

    2010-07-01

    ... 33 Navigation and Navigable Waters 2 2010-07-01 2010-07-01 false Safety and Security Zone... Limited Access Areas First Coast Guard District § 165.110 Safety and Security Zone; Liquefied Natural Gas.... The following areas are safety and security zones: (1) Vessels underway. All navigable waters of the...

  16. Upper mantle beneath foothills of the western Himalaya: subducted lithospheric slab or a keel of the Indian shield?

    Vinnik, L.; Singh, A.; Kiselev, S.; Kumar, M. Ravi

    2007-12-01

    The fate of the mantle lithosphere of the Indian Plate in the India-Eurasia collision zone is not well understood. Tomographic studies reveal high P velocity in the uppermost mantle to the south of the western Himalaya, and these high velocities are sometimes interpreted as an image of subducting Indian lithosphere. We suggest that these high velocities are unrelated to the ongoing subduction but correspond to a near-horizontal mantle keel of the Indian shield. In the south of the Indian shield upper-mantle velocities are anomalously low, and relatively high velocities may signify a recovery of the normal shield structure in the north. Our analysis is based on the recordings of seismograph station NIL in the foothills of the western Himalaya. The T component of the P receiver functions is weak relative to the Q component, which is indicative of a subhorizontally layered structure. Joint inversion of the P and S receiver functions favours high uppermost mantle velocities, typical of the lithosphere of Archean cratons. The arrival of the Ps converted phase from 410 km discontinuity at NIL is 2.2 s earlier than in IASP91 global model. This can be an effect of remnants of Tethys subduction in the mantle transition zone and of high velocities in the keel of the Indian shield. Joint inversion of SKS particle motions and P receiver functions reveals a change in the fast direction of seismic azimuthal anisotropy from 60° at 80-160 km depths to 150° at 160-220 km. The fast direction in the lower layer is parallel to the trend of the Himalaya. The change of deformation regimes at a depth of 160 km suggests that this is the base of the lithosphere of the Indian shield. A similar boundary was found with similar techniques in central Europe and the Tien Shan region, but the base of the lithosphere in these regions is relatively shallow, in agreement with the higher upper-mantle temperatures. The ongoing continental collision is expressed in crustal structure: the crust

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

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

    2015-04-24

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

  18. Diverse effects of crop distribution and climate change on crop production in the agro-pastoral transitional zone of China

    Qiao, Jianmin; Yu, Deyong; Wang, Qianfeng; Liu, Yupeng

    2018-06-01

    Both crop distribution and climate change are important drivers for crop production and can affect food security, which is an important requirement for sustainable development. However, their effects on crop production are confounded and warrant detailed investigation. As a key area for food production that is sensitive to climate change, the agro-pastoral transitional zone (APTZ) plays a significant role in regional food security. To investigate the respective effects of crop distribution and climate change on crop production, the well-established GIS-based Environmental Policy Integrated Climate (EPIC) model was adopted with different scenario designs in this study. From 1980 to 2010, the crop distribution for wheat, maize, and rice witnessed a dramatic change due to agricultural policy adjustments and ecological engineering-related construction in the APTZ. At the same time, notable climate change was observed. The simulation results indicated that the climate change had a positive impact on the crop production of wheat, maize, and rice, while the crop distribution change led to an increase in the production of maize and rice, but a decrease in the wheat production. Comparatively, crop distribution change had a larger impact on wheat (-1.71 × 106 t) and maize (8.53 × 106 t) production, whereas climate change exerted a greater effect on rice production (0.58 × 106 t), during the period from 1980 to 2010 in the APTZ. This study is helpful to understand the mechanism of the effects of crop distribution and climate change on crop production, and aid policy makers in reducing the threat of future food insecurity.

  19. Diverse effects of crop distribution and climate change on crop production in the agro-pastoral transitional zone of China

    Qiao, Jianmin; Yu, Deyong; Wang, Qianfeng; Liu, Yupeng

    2017-07-01

    Both crop distribution and climate change are important drivers for crop production and can affect food security, which is an important requirement for sustainable development. However, their effects on crop production are confounded and warrant detailed investigation. As a key area for food production that is sensitive to climate change, the agro-pastoral transitional zone (APTZ) plays a significant role in regional food security. To investigate the respective effects of crop distribution and climate change on crop production, the well-established GIS-based Environmental Policy Integrated Climate (EPIC) model was adopted with different scenario designs in this study. From 1980 to 2010, the crop distribution for wheat, maize, and rice witnessed a dramatic change due to agricultural policy adjustments and ecological engineering-related construction in the APTZ. At the same time, notable climate change was observed. The simulation results indicated that the climate change had a positive impact on the crop production of wheat, maize, and rice, while the crop distribution change led to an increase in the production of maize and rice, but a decrease in the wheat production. Comparatively, crop distribution change had a larger impact on wheat (-1.71 × 106 t) and maize (8.53 × 106 t) production, whereas climate change exerted a greater effect on rice production (0.58 × 106 t), during the period from 1980 to 2010 in the APTZ. This study is helpful to understand the mechanism of the effects of crop distribution and climate change on crop production, and aid policy makers in reducing the threat of future food insecurity.

  20. Tc(VII) and Cr(VI) Interaction with Naturally Reduced Ferruginous Smectite from a Redox Transition Zone.

    Qafoku, Odeta; Pearce, Carolyn I; Neumann, Anke; Kovarik, Libor; Zhu, Mengqiang; Ilton, Eugene S; Bowden, Mark E; Resch, Charles T; Arey, Bruce W; Arenholz, Elke; Felmy, Andrew R; Rosso, Kevin M

    2017-08-15

    Fe(II)-rich clay minerals found in subsurface redox transition zones (RTZs) can serve as important sources of electron equivalents limiting the transport of redox-active contaminants. While most laboratory reactivity studies are based on reduced model clays, the reactivity of naturally reduced field samples remains poorly explored. Characterization of the clay size fraction of a fine-grained unit from the RTZ interface at the Hanford site, Washington, including mineralogy, crystal chemistry, and Fe(II)/(III) content, indicates that ferruginous montmorillonite is the dominant mineralogical component. Oxic and anoxic fractions differ significantly in Fe(II) natural content, but Fe TOTAL remains constant, demonstrating no Fe loss during its reduction-oxidation cyclings. At native pH of 8.6, the anoxic fraction, despite its significant Fe(II), ∼23% of Fe TOTAL , exhibits minimal reactivity with TcO 4 - and CrO 4 2- and much slower reaction kinetics than those measured in studies with biologically/chemically reduced model clays. Reduction capacity is enhanced by added/sorbed Fe(II) (if Fe(II) SORBED > 8% clay Fe(II) LABILE ); however, the kinetics of this conceptually surface-mediated reaction remain sluggish. Surface-sensitive Fe L-edge X-ray absorption spectroscopy shows that Fe(II) SORBED and the resulting reducing equivalents are not available in the outermost few nanometers of clay surfaces. Slow kinetics thus appear related to diffusion-limited access to electron equivalents retained within the clay mineral structure.

  1. Biogeochemical cycles at the sulfate-methane transition zone (SMTZ) and geochemical characteristics of the pore fluids offshore southwestern Taiwan

    Hu, Ching-Yi; Frank Yang, Tsanyao; Burr, George S.; Chuang, Pei-Chuan; Chen, Hsuan-Wen; Walia, Monika; Chen, Nai-Chen; Huang, Yu-Chun; Lin, Saulwood; Wang, Yunshuen; Chung, San-Hsiung; Huang, Chin-Da; Chen, Cheng-Hong

    2017-11-01

    In this study, we used pore water dissolved inorganic carbon (DIC), SO42-, Ca2+ and Mg2+ gradients at the sulfate-methane transition zone (SMTZ) to estimate biogeochemical fluxes for cored sediments collected offshore SW Taiwan. Net DIC flux changes (ΔDIC-Prod) were applied to determine the proportion of sulfate consumption by organic matter oxidation (heterotrophic sulfate reduction) and anaerobic oxidation of methane (AOM), and to determine reliable CH4 fluxes at the SMTZ. Our results show that SO42- profiles are mainly controlled by AOM rather than heterotrophic sulfate reduction. Refinement of CH4 flux estimates enhance our understanding of methane abundance from deep carbon reservoirs to the SMTZ. Concentrations of chloride (Cl-), bromide (Br-) and iodide (I-) dissolved in pore water were used to identify potential sources that control fluid compositions and the behavior of dissolved ions. Constant Cl- concentrations throughout ∼30 m sediment suggest no influence of gas hydrates for the compositions within the core. Bromide (Br-) and Iodine (I-) concentrations increase with sediment depth. The I-/Br- ratio appears to reflect organic matter degradation. SO42- concentrations decrease with sediment depth at a constant rate, and sediment depth profiles of Br- and I- concentrations suggests diffusion as the main transport mechanism. Therefore diffusive flux calculations are reasonable. Coring sites with high CH4 fluxes are more common in the accretionary wedge, amongst thrust faults and fractures, than in the passive continental margin offshore southwestern Taiwan. AOM reactions are a major sink for CH4 passing upward through the SMTZ and prevent high methane fluxes in the water column and to the atmosphere.

  2. Is transition zone index useful in assessing bladder outflow obstruction due to benign prostatic hyperplasia?: A prospective study

    S L Sailo

    2006-01-01

    Full Text Available BACKGROUND: Benign prostatic enlargement (BPE is the commonest cause of bladder outlet obstruction in men above 50 years of age. Though pressure-flow study is the gold standard in establishing outlet obstruction, it is associated with definite morbidity. Several noninvasive parameters are described to diagnose outlet obstruction due to BPE and evaluate treatment efficacy. AIM: We studied the role of transitional zone index (TZI in assessing bladder outlet obstruction (BOO due to BPE. SETTING AND DESIGN: Prospective hospital-based cross-sectional diagnostic study. MATERIALS AND METHODS: Thirty-five men aged between 50 and 77 years with untreated lower urinary tract symptoms due to BPE were studied. Patients with prostate cancer, prostatitis, active UTI urethral stricture, neurovesical dysfunction and diabetes mellitus were excluded. All patients underwent a standard assessment using the American Urological Association (AUA symptom score, uroflow, pressure-flow (PF study and transrectal ultrasound (TRUS estimation of TZI. Investigators undertaking PF studies and TRUS were blinded to the investigation of others. From the PF studies, Abrams Griffith (AG number was calculated. Based on this, patients were grouped into obstructed (AG>40 and unobstructed (AG< 40 groups. STATISTICAL ANALYSIS: TZI was calculated and compared with PF studies using Mann-Whitney U test, logistic regression analysis and receiver operator characteristic curve (ROC. RESULTS: The mean age was 63.2 years (SD. The mean AUA scores and peak flow rate were 16.7 and 7.5 ml/sec, respectively. Of the 35 men, 21 were obstructed and 14 were unobstructed. TZI was not significantly different between the two groups, while the differences in age, AUA symptom score, prostate volume and TZ volume were statistically significant. Logistic regression model did not show any independent effect of TZI in predicting obstruction. ROC curve showed a poor overall accuracy in diagnosing obstruction due

  3. Geodynamic Modeling of the Subduction Zone around the Japanese Islands

    Honda, S.

    2017-06-01

    the Aleutian arc and the Kurile arc is generally weak and we have suggested the possible contribution of a hot anomaly in the sub-slab mantle as the origin of possible trench-parallel flow there. A 3D mantle flow model of the back-arc around the junction between the northeast Japan arc and the Kurile arc shows a trench-normal flow at a shallow depth. As a result, the expected seismic anisotropy shows the fast direction normal to the arc, even in the region of oblique subduction. This result is generally consistent with observations there. The existence of a hot anomaly in the sub-slab mantle under the Pacific plate was proposed from an analysis of the seismic tomography, and we have studied its possible origins. The origin of a hot anomaly adjacent to the cold downgoing flow, typically observed in internally heated convection, is preferable to that of a hot anomaly, such as a plume head, carried far from the subduction zone. The nature of the western edge of the stagnant slab under northeast China has been investigated with modeling studies, which take into account the subduction history and the phase changes in the mantle. It is likely to be a ridge-type plate boundary between the extinct Izanagi plate and the Pacific plate. Thus, we have concluded that the slab gap under northeast China is not a breakage of the stagnant slab. Further studies have suggested that the existence of the rheological weakening of the slab in the transition zone, and the additional effects of a hot anomaly in the sub-slab mantle under the Pacific plate, may explain the differences in slab morphology under the northern Okhotsk arc and the northeast Japan arc.

  4. Dynamics of upper mantle rocks decompression melting above hot spots under continental plates

    Perepechko, Yury; Sorokin, Konstantin; Sharapov, Victor

    2014-05-01

    Numeric 2D simulation of the decompression melting above the hot spots (HS) was accomplished under the following conditions: initial temperature within crust mantle section was postulated; thickness of the metasomatized lithospheric mantle is determined by the mantle rheology and position of upper asthenosphere boundary; upper and lower boundaries were postulated to be not permeable and the condition for adhesion and the distribution of temperature (1400-2050°C); lateral boundaries imitated infinity of layer. Sizes and distribution of lateral points, their symmetry, and maximum temperature varied between the thermodynamic condition for existences of perovskite - majorite transition and its excess above transition temperature. Problem was solved numerically a cell-vertex finite volume method for thermo hydrodynamic problems. For increasing convergence of iterative process the method of lower relaxation with different value of relaxation parameter for each equation was used. The method of through calculation was used for the increase in the computing rate for the two-layered upper mantle - lithosphere system. Calculated region was selected as 700 x (2100-4900) km. The time step for the study of the asthenosphere dynamics composed 0.15-0.65 Ma. The following factors controlling the sizes and melting degree of the convective upper mantle, are shown: a) the initial temperature distribution along the section of upper mantleb) sizes and the symmetry of HS, c) temperature excess within the HS above the temperature on the upper and lower mantle border TB=1500-2000oC with 5-15% deviation but not exceed 2350oC. It is found, that appearance of decompression melting with HS presence initiate primitive mantle melting at TB > of 1600oC. Initial upper mantle heating influence on asthenolens dimensions with a constant HS size is controlled mainly by decompression melting degree. Thus, with lateral sizes of HS = 400 km the decompression melting appears at TB > 1600oC and HS

  5. On predicting mantle mushroom plumes

    Ka-Kheng Tan

    2011-04-01

    Top cooling may produce plunging plumes of diameter of 585 km and at least 195 Myr old. The number of cold plumes is estimated to be 569, which has not been observed by seismic tomography or as cold spots. The cold plunging plumes may overwhelm and entrap some of the hot rising plumes from CMB, so that together they may settle in the transition zone.

  6. Sub-Moho Reflectors, Mantle Faults and Lithospheric Rheology

    Brown, L. D.

    2013-12-01

    One of the most unexpected and dramatic observations from the early years of deep reflection profiling of the continents using multichannel CMP techniques was the existing of prominent reflections from the upper mantle. The first of these, the Flannan thrust/fault/feature, was traced by marine profiling of the continental margin offshore Britain by the BIRPS program, which soon found them to be but one of several clear sub-crustal discontinuities in that area. Subsequently, similar mantle reflectors have been observed in many areas around the world, most commonly beneath Precambrian cratonic areas. Many, but not all, of these mantle reflections appear to arise from near the overlying Moho or within the lower crust before dipping well into the mantle. Others occur as subhorizontal events at various depths with the mantle, with one suite seeming to cluster at a depth of about 75 km. The dipping events have been variously interpreted as mantle roots of crustal normal faults or the deep extension of crustal thrust faults. The most common interpretation, however, is that these dipping events are the relicts of ancient subduction zones, the stumps of now detached Benioff zones long since reclaimed by the deeper mantle. In addition to the BIRPS reflectors, the best known examples include those beneath Fennoscandia in northern Europe, the Abitibi-Grenville of eastern Canada, and the Slave Province of northwestern Canada (e.g. on the SNORCLE profile). The most recently reported example is from beneath the Sichuan Basin of central China. The preservation of these coherent, and relatively delicate appearing, features beneath older continental crust and presumably within equally old (of not older) mantle lithosphere, has profound implications for the history and rheology of the lithosphere in these areas. If they represent, as widely believe, some form of faulting with the lithosphere, they provide corollary constraints on the nature of faulting in both the lower crust and

  7. The Mineral Character and Geomechanical Properties of the Transitional Rocks from the Mesozoic-Neogene Contact Zone in the Bełchatów Lignite Deposit

    Agnieszka Pękala

    2014-01-01

    Originality/value: Against the background of a number of published papers on the rocks accompanying lignite seams there is a lack of the "Bełchatów" mineralogical-petrographic studies of the transitional sediments in the Mesozoic-Neogene contact zone in the "Bełchatów" lignite deposit taking into account the aspect of raw materials. This paper has been produced to fill the void in this area.

  8. TRANSIT

    First page Back Continue Last page Overview Graphics. TRANSIT. SYSTEM: DETERMINE 2D-POSITION GLOBALLY BUT INTERMITTENT (POST-FACTO). IMPROVED ACCURACY. PRINCIPLE: POLAR SATELLITES WITH INNOVATIONS OF: GRAVITY-GRADIENT ATTITUDE CONTROL; DRAG COMPENSATION. WORKS ...

  9. Ancient melt depletion overprinted by young carbonatitic metasomatism in the New Zealand lithospheric mantle

    Scott, James M.; Hodgkinson, A.; Palin, J.M.

    2014-01-01

    radiogenic than, the HIMU mantle reservoir. Metasomatism appears to pre-date ubiquitous pyroxene core to rim Al diffusion zoning, which may have resulted from cooling of the lithospheric mantle following cessation of Late Cretaceous-Eocene rifting of Zealandia from Gondwana. Nd isotope data, however, suggest...

  10. The durability of mortar: consideration of interfacial transition zones to characterize and to model the physicals and chemicals mechanisms involved in mortar corrosion

    Bourdette, B.

    1994-01-01

    In the framework of a study program aiming at anticipating the lifetime of concrete containers used for radioactive waste surface storage, the aim of this work is to model the physical and chemical processes of leaching of the mortars (cement paste + sand) by low ionized water at pH=8.5. This step is indispensable before the predicting of concrete durability (cement paste + sand + gravels) in which it can exist an initial microcrack. The mortar can be described as a three-phase system: the aggregates, the transition aureoles (aggregates-cement paste interfaces) and the cement matrix. The evolution of the very particular characteristics of the transition aureoles in terms of the degradation have been studied. The study has shown that the thickness of the degraded zone in the transition aureole is identical to those of the cement matrix. It has been shown too that the diffusion coefficient in the degraded transition aureole is similar to the diffusion coefficient in the degraded cement matrix. These observations can eventually be explained by a recombination of the texture and of the structure of the transition aureole during the degradation. This reorganization could lead to a decrease of the textural and structural differences which exist between the transition aureole and the cement matrix. As it has been supposed that the characteristics of the degraded zone govern the degradation kinetics, the thickness degraded in the transition aureole is then similar to those of the cement matrix. Mortar can then be considered as a two-phase system towards the degradation: the cement paste is assimilated to a pure paste but with different characteristics due to the presence of transition aureoles. In order to model the degradation of the mortar, the model used has been developed and validated by Adenot for pure cement pastes. At 300 years, the model anticipates that the thickness of the degraded zone in the mortar is of 2.9 cm, which is lightly higher than for the pure paste

  11. Intrinsic Mechanisms of Ductile-brittle Transition for F460 Steel Welding Coarse Grained Heat Affected Zones with Different Heat Inputs

    LI Jing

    2016-08-01

    Full Text Available Coarse grain heat affected zone (HAZ of F460 steel was simulated by a Gleeble 3800 thermo-mechanical simulator. The microstructure, critical event of the HAZ formed at various heat inputs (E were characterized and determined by optical microscopy (OM and scanning electronic microscopy (SEM, and cleavage fracture stress σf was also calculated by ABAQUS software. Based on above systematic analysis, the intrinsic mechanism of ductile-brittle transition for F460 steel heat affected zones with different heat inputs were revealed. The results indicate that:with the improvement of heat input, the microstructures in sequence are a minority of lath martensite and massive fine lath bainite, more lath bainite with less granular bainite, more granular bainite with less lath bainite, bulky of granular bainite; and the maximum size of the original austenite grain and bainite packet becomes bigger with the improvement of heat input. The size of bainite packet is critical event of the cleavage fracture for coarse grain heat affected zone specimens with various heat inputs by comparing the relationships among residual crack length, original austenite grain size and bainite packet size. With the decreasing of the bainitic packet, the ductile to brittle transition temperature decreases. In addition, cleavage fracture stress σf is also calculated by ABAQUS software, σf gradually decreases with the increase of the heat input, which can explain the intrinsic mechanism of ductile to brittle transition temperature Tk with the change of the heat input.

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

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

    2008-10-08

    the product of melting of deeply recycled (subducted) Archean-age metasediments in the mantle transition zone [Murphy, D.T., Collerson, K.D., Kamber, B.S., 2002. Lamproites from Gaussberg, Antartica: possible transition zone melts of Archaean subducted sediments. J. Petrol. 43, 981-1001]. Here we report the results of phase equilibria experiments on two different natural sedimentary compositions (a high-grade metapelite with < 1 wt.% H{sub 2}O, and a marine 'mud' with 8 wt.% H{sub O}) at 16-23 GPa. In both materials, the high-pressure mineral assemblages contain {approx} 15-30 wt.% K-hollandite (KAlSi{sub 3}O{sub 8}), in addition to stishovite, garnet, an Al-silicate phase (kyanite or phase egg), and a Fe-Ti spinel (corundum). Ion microprobe analyses of K-hollandite for a range of trace elements reveal that this phase controls a significant proportion of the whole-rock budget of incompatible, large-ion lithophile elements (LILEs, e.g., Rb, Ba, Sr, K, Pb, La, Ce and Th). Comparisons between the abundances and ratios of these elements in K-hollandite with those in EM-I type ocean-island basalts from Pitcairn Island and related seamounts, and with the Gaussberg lamproites, indicate the presence of deeply recycled, continent-derived sediments in these lavas sources. Our results suggest that the incompatible trace-element signature of EM-I OIB reservoirs in general and of the Gaussberg lamproites in particular can be attributed to recycling of K-hollandite-bearing continental sediments to transition zone depths.

  13. Future of mantle tomography and interface imaging: old questions, new challenges and opportunities

    van der Hilst, R. D.

    2011-12-01

    Over the past three decades, tremendous progress has been made with the mapping of mantle heterogeneity and with the understanding of these structures in terms of, for instance, the evolution of Earth's crust, continental lithosphere, and thermo-chemical mantle convection. Converted wave imaging (e.g., receiver functions) and reflection seismology (e.g. SS stacks) have helped constrain interfaces in crust and mantle; surface wave dispersion (from earthquake or ambient noise signals) characterizes wavespeed variations in continental and oceanic lithosphere, and body wave and multi-mode surface wave data have been used to map trajectories of mantle convection and delineate mantle regions of anomalous elastic properties. Collectively, these studies have revealed substantial ocean-continent differences and suggest that convective flow is strongly influenced by but permitted to cross the upper mantle transition zone. Many questions have remained unanswered, however, and further advances in understanding require more accurate depictions of Earth's heterogeneity at a wider range of length scales. To meet this challenge we need new observations: more, better, and different types of data. Even without technological innovation, the use of new data will continue to produce spectacular results. Good examples are the positive impact on image quality of the seismograph arrays of the Australian Skippy project and USArray. At the same time, the huge volumes of (array) data and the desire to extract and interpret more signal from these data means that we have to abandon 'business as usual' (that is, simplified theory, manual inspection of seismograms, ...). Indeed, it inspires the development of automated full wave methods, both for tomographic delineation of smooth wavespeed variations and the imaging (for instance through inverse scattering) of medium contrasts. Adjoint tomography and reverse time migration, closely related wave equation methods, have begun to revolutionize

  14. Louisiana Speaks Transportation Option B Transit Corridors, UTM Zone 15N NAD 83, Louisiana Recovery Authority (2007), [louisiana_speaks_transportation_option_b_transit_corridors

    Louisiana Geographic Information Center — This GIS shapefile data illustrates the regional, subregional, and local transit corridors included in the Louisiana Speaks Regional Plan community growth option of...

  15. Louisiana Speaks Transportation Option C Transit Corridors, UTM Zone 15N NAD 83, Louisiana Recovery Authority (2007), [louisiana_speaks_transportation_option_c_transit_corridors

    Louisiana Geographic Information Center — This GIS shapefile data illustrates the regional, subregional, and local transit corridors included in the Louisiana Speaks Regional Plan community growth option of...

  16. Louisiana Speaks Transportation Option C Transit Stations, UTM Zone 15N NAD 83, Louisiana Recovery Authority (2007), [louisiana_speaks_transportation_option_c_transit_stations

    Louisiana Geographic Information Center — This GIS shapefile data illustrates potential fixed-transit stations included in the Louisiana Speaks Regional Plan community growth option of compact development...

  17. Louisiana Speaks Regional Vision Transit Corridors, UTM Zone 15N NAD 83, Louisiana Recovery Authority (2007), [louisiana_speaks_vision_transit_corridors

    Louisiana Geographic Information Center — This GIS shapefile data illustrates the primary and secondary transit corridors included in the Louisiana Speaks Regional Plan Vision. This network accommodates a...

  18. Length-scales of Slab-induced Asthenospheric Deformation from Geodynamic Modeling, Mantle Deformation Fabric, and Synthetic Shear Wave Splitting

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

    2017-12-01

    The viscosity structure of the Earth's interior is critically important, because it places a first order constraint on plate motion and mantle flow rates. Geodynamic models using a composite viscosity based on experimentally derived flow laws for olivine aggregates show that lateral viscosity variations emerge in the upper mantle due to the subduction dynamics. However, the length-scale of this transition is still not well understood. Two-dimensional numerical models of subduction are presented that investigate the effect of initial slab dip, maximum yield stress (slab strength), and viscosity formulation (Newtonian versus composite) on the emergent lateral viscosity variations in the upper-mantle and magnitude of slab-driven mantle flow velocity. Significant viscosity reductions occur in regions of large flow velocity gradients due to the weakening effect of the dislocation creep deformation mechanism. The dynamic reductions in asthenospheric viscosity (less than 1018 Pa s) occur within approximately 500 km from driving force of the slab, with peak flow velocities occurring in models with a lower yield stress (weaker slab) and higher stress exponent. This leads to a sharper definition of the rheological base of the lithosphere and implies lateral variability in tractions along the base of the lithosphere. As the dislocation creep mechanism also leads to mantle deformation fabric, we then examine the spatial variation in the LPO development in the asthenosphere and calculate synthetic shear wave splitting. The models show that olivine LPO fabric in the asthenosphere generally increases in alignment strength with increased proximity to the slab, but can be transient and spatially variable on small length scales. The vertical flow fields surrounding the slab tip can produce shear-wave splitting variations with back-azimuth that deviate from the predictions of uniform trench-normal anisotropy, a result that bears on the interpretation of complexity in shear

  19. 33 CFR 165.1709 - Security Zones: Liquefied Natural Gas Tanker Transits and Operations at Phillips Petroleum LNG...

    2010-07-01

    ... Gas Tanker Transits and Operations at Phillips Petroleum LNG Pier, Cook Inlet, AK. 165.1709 Section...: Liquefied Natural Gas Tanker Transits and Operations at Phillips Petroleum LNG Pier, Cook Inlet, AK. (a... and outbound transits through Cook Inlet, Alaska between the Phillips Petroleum LNG Pier, 60°40′43″ N...

  20. Pillars of the Mantle

    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.

  1. A detailed map of the 660-kilometer discontinuity beneath the izu-bonin subduction zone.

    Wicks, C W; Richards, M A

    1993-09-10

    Dynamical processes in the Earth's mantle, such as cold downwelling at subduction zones, cause deformations of the solid-state phase change that produces a seismic discontinuity near a depth of 660 kilometers. Observations of short-period, shear-to-compressional wave conversions produced at the discontinuity yield a detailed map of deformation beneath the Izu-Bonin subduction zone. The discontinuity is depressed by about 60 kilometers beneath the coldest part of the subducted slab, with a deformation profile consistent with the expected thermal signature of the slab, the experimentally determined Clapeyron slope of the phase transition, and the regional tectonic history.

  2. Characteristics of Conducting the Multi-Component Seismic Prospecting in the Transition Zone in Conditions of Very Shallow Water of Arctic Seas

    I. A. Matveev

    2017-12-01

    Full Text Available Transition zones of transition from land to sea are the areas where it is extremely difficult to conduct geophysical works with conventional methods. In the Arctic seas of Russia, there are additional difficulties associated with the short field season, unfavorable hydrometeorological conditions, and severe restrictions imposed on the methodology and acquisition techniques by requirements of the environmental nature protection legislation. To obtain high-quality seismic data it is extremely important to select the most suitable equipment for data acquisition, optimal shooting geometry and data acquisition methodology, and the most advanced data processing and quality control software. The purpose of this article is to show developed at JSC MAGE 4-component 2D seismic technology based on use of the autonomous bottom stations. It allows conducting the seismic regional 2D survey in the transit area with registration of converted (PS waves at higher efficiency level.

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

    Jean H. Bédard

    2018-01-01

    Full Text Available The lower plate is the dominant agent in modern convergent margins characterized by active subduction, as negatively buoyant oceanic lithosphere sinks into the asthenosphere under its own weight. This is a strong plate-driving force because the slab-pull force is transmitted through the stiff sub-oceanic lithospheric mantle. As geological and geochemical data seem inconsistent with the existence of modern-style ridges and arcs in the Archaean, a periodically-destabilized stagnant-lid crust system is proposed instead. Stagnant-lid intervals may correspond to periods of layered mantle convection where efficient cooling was restricted to the upper mantle, perturbing Earth's heat generation/loss balance, eventually triggering mantle overturns. Archaean basalts were derived from fertile mantle in overturn upwelling zones (OUZOs, which were larger and longer-lived than post-Archaean plumes. Early cratons/continents probably formed above OUZOs as large volumes of basalt and komatiite were delivered for protracted periods, allowing basal crustal cannibalism, garnetiferous crustal restite delamination, and coupled development of continental crust and sub-continental lithospheric mantle. Periodic mixing and rehomogenization during overturns retarded development of isotopically depleted MORB (mid-ocean ridge basalt mantle. Only after the start of true subduction did sequestration of subducted slabs at the core-mantle boundary lead to the development of the depleted MORB mantle source. During Archaean mantle overturns, pre-existing continents located above OUZOs would be strongly reworked; whereas OUZO-distal continents would drift in response to mantle currents. The leading edge of drifting Archaean continents would be convergent margins characterized by terrane accretion, imbrication, subcretion and anatexis of unsubductable oceanic lithosphere. As Earth cooled and the background oceanic lithosphere became denser and stiffer, there would be an increasing

  4. Sudden disintegration of ice in the glacial-proglacial transition zone of the largest glacier in Austria

    Kellerer-Pirklbauer, Andreas; Avian, Michael; Hirschmann, Simon; Lieb, Gerhard Karl; Seier, Gernot; Sulzer, Wolfgang; Wakonigg, Herwig

    2017-04-01

    Rapid deglaciation does not only reveal a landscape which is prone to rapid geomorphic changes and sediment reworking but also the glacier ice itself might be in a state of disintegration by ice melting, pressure relief, crevasse formation, ice collapse or changes in the glacier's hydrology. In this study we considered the sudden disintegration of glacier ice in the glacial-proglacial transition zone of Pasterze Glacier. Pasterze Glacier is a typical alpine valley glacier and covers currently some 16.5 km2 making it to the largest glacier in Austria. This glacier is an important site for alpine mass tourism in Austria related to a public high alpine road and a cable car which enable access to the glacier rather easily also for unexperienced mountaineers. Spatial focus in our research is given on two particular study areas where several ice-mass movement events occurred during the 2015- and 2016-melting seasons. The first study area is a crevasse field at the lower third of the glacier tongue. This lateral crevasse field has been substantially modified during the last two melting seasons particularly because of thermo-erosional effects of a glacial stream which changed at this site from subglacial (until 2015) to glacier-lateral revealing a several tens of meters high unstable ice cliff prone to ice falls of different magnitudes. The second study area is located at the proglacial area. At Pasterze Glacier the proglacial area is widely influenced by dead-ice bodies of various dimensions making this area prone to slow to sudden geomorphic changes caused by ice mass changes. A particular ice-mass movement event took place on 20.09.2016. Within less than one hour the surface of the proglacial area changed substantially by tilting, lateral shifting, and subsidence of the ground accompanied by complete ice disintegration of once-debris covered ice. To understand acting processes at both areas of interest and to quantify mass changes we used field observations, terrain

  5. Frozen Martian lahars? Evaluation of morphology, degradation and geologic development in the Utopia-Elysium transition zone

    Pedersen, G. B. M.

    2013-09-01

    Regional coverage of high-resolution data from the CTX camera has permitted new, detailed morphologic analysis of the enigmatic Utopia-Elysium flows which dominate the transition zone between Elysium volcanic province and Utopia Planitia. Based on topographic and morphologic analysis of the Galaxias region, this study supports the lahar hypothesis put forth by previous works and suggests that the center and the margins of the outflow deposits have very diverse morphologies that can be explained by varying degrees of water drainage and freezing. Regular channel and flood plain deposits are found in the central part of the outflow deposits, whereas the marginal deposits are interpreted to contain significant amount of ice because of their distinct morphological properties (smooth, lobate flow-fronts with upward convex snouts, unusual crater morphologies, raised rim fractures and localized flow fronts indicating rheomorphism). Thus, this study suggest that, unlike terrestrial lahars, lahar emplacement under Martian conditions only drain in the central parts, whereas the water in the margins of the outflow deposit (∼75% of the total outflow deposit in the Galaxias region) freezes up resulting in a double-layered deposit consisting of ice-rich core with an ice-poor surface layer. It is here furthermore suggested that continued intrusive volcanic activity was highly affected by the presence of the ice-rich lahar deposits, generating ground-ice-volcano interactions resulting in a secondary suite of morphologies. These morphologies include seventeen ridges that are interpreted to be möberg ridges (due to their NW-SE orientation, distinct ridge-crests and association with fractures and linear ridges) and depressions with nested faults interpreted to be similar to terrestrial ice-cauldrons, which form by enhanced subglacial geothermal activity including subglacial volcanic eruptions. These sub-lahar intrusions caused significant volatile loss in the ice-rich core of the

  6. Involvement of trigeminal transition zone and laminated subnucleus caudalis in masseter muscle hypersensitivity associated with tooth inflammation.

    Kohei Shimizu

    Full Text Available A rat model of pulpitis/periapical periodontitis was used to study mechanisms underlying extraterritorial enhancement of masseter response associated with tooth inflammation. Periapical bone loss gradually increased and peaked at 6 weeks after complete Freund's adjuvant (CFA application to the upper molar tooth pulp (M1. On day 3, the number of Fos-immunoreactive (IR cells was significantly larger in M1 CFA rats compared with M1 vehicle (veh rats in the trigeminal subnucleus interpolaris/caudalis transition zone (Vi/Vc. The number of Fos-IR cells was significantly larger in M1 CFA and masseter (Mass capsaicin applied (M1 CFA/Mass cap rats compared with M1 veh/Mass veh rats in the contralateral Vc and Vi/Vc. The number of phosphorylated extracellular signal-regulated kinase (pERK-IR cells was significantly larger in M1 CFA/Mass cap and M1 veh/Mass cap rats compared to Mass-vehicle applied rats with M1 vehicle or CFA in the Vi/Vc. Pulpal CFA application caused significant increase in the number of Fos-IR cells in the Vi/Vc but not Vc on week 6. The number of pERK-IR cells was significantly lager in the rats with capsaicin application to the Mass compared to Mass-vehicle treated rats after pulpal CFA- or vehicle-application. However, capsaicin application to the Mass did not further affect the number of Fos-IR cells in the Vi/Vc in pulpal CFA-applied rats. The digastric electromyographic (d-EMG activity after Mass-capsaicin application was significantly increased on day 3 and lasted longer at 6 weeks after pulpal CFA application, and these increase and duration were significantly attenuated by i.t. PD98059, a MEK1 inhibitor. These findings suggest that Vi/Vc and Vc neuronal excitation is involved in the facilitation of extraterritorial hyperalgesia for Mass primed with periapical periodontitis or acute pulpal-inflammation. Furthermore, phosphorylation of ERK in the Vi/Vc and Vc play pivotal roles in masseter hyperalgesia after pulpitis or

  7. Sedimentary fabrics of the macrotidal, mud-dominated, inner estuary to fluvio-tidal transition zone, Petitcodiac River estuary, New Brunswick, Canada

    Shchepetkina, Alina; Gingras, Murray K.; Zonneveld, John-Paul; Pemberton, S. George

    2016-03-01

    The study provides a detailed description of mud-dominated sedimentary fabrics and their application for the rock record within the inner estuary to the fluvial zone of the Petitcodiac River estuary, New Brunswick, Canada. Sedimentological characteristics and facies distributions of the clay- and silt-rich deposits are reported. The inner estuary is characterized by thick accumulations of interbedded silt and silty clay on intertidal banks that flank the tidally influenced channel. The most common sedimentary structures observed are parallel and wavy lamination, small-scale soft-sediment deformation with microfaults, and clay and silt current ripples. The tidal channel contains sandy silt and clayey silt with planar lamination, massive and convolute bedding. The fluvio-tidal transition zone is represented by interbedded trough cross-stratified sand and gravel beds with planar laminated to massive silty mud. The riverine, non-tidal reach of the estuary is characterized by massive, planar tabular and trough cross-stratified gravel-bed deposits. The absence of bioturbation within the inner estuary to the fluvio-tidal transition zone can be explained by the following factors: low water salinities (0-5 ppt), amplified tide and current speeds, and high concentrations of flocculated material in the water body. Notably, downstream in the middle and outer estuary, bioturbation is seasonally pervasive: in those locales the sedimentary conditions are similar, but salinity is higher. In this study, the sedimentological (i.e., grain size, bedding characters, sedimentary structures) differences between the tidal estuary and the fluvial setting are substantial, and those changes occur over only a few hundred meters. This suggests that the widely used concept of an extensive fluvio-tidal transition zone and its depositional character may not be a geographically significant component of fluvial or estuary deposits, which can go unnoticed in the study of the ancient rocks.

  8. Genetic population structure of turbot ( Scophthalmus maximus L.) supports the presence of multiple hybrid zones for marine fishes in the transition zone between the Baltic Sea and the North Sea

    Eg Nielsen, Einar; Nielsen, P.H.; Meldrup, Dorte

    2004-01-01

    Sea, suggesting high gene flow among populations in these areas. In contrast, there was a sharp cline in genetic differentiation going from the low saline Baltic Sea to the high saline North Sea. The data were explained best by two divergent populations connected by a hybrid zone; however......, a mechanical mixing model could not be ruled out. A significant part of the genetic variance could be ascribed to variation among years within locality. Nevertheless, the population structure was relatively stable over time, suggesting that the observed pattern of genetic differentiation is biologically...... significant. This study suggests that hybrid zones are a common phenomenon for marine fishes in the transition area between the North Sea and the Baltic Sea and highlights the importance of using interspecific comparisons for inferring population structure in high gene flow species such as most marine fishes....

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

    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. Upper mantle structure under western Saudi Arabia from Rayleigh wave tomography and the origin of Cenozoic uplift and volcanism on the Arabian Shield

    Park, Y; Nyblade, A; Rodgers, A; Al-Amri, A

    2007-11-09

    The shear velocity structure of the shallow upper mantle beneath the Arabian Shield has been modeled by inverting new Rayleigh wave phase velocity measurements between 45 and 140 s together with previously published Rayleigh wave group velocity measurement between 10 and 45 s. For measuring phase velocities, we applied a modified array method that minimizes the distortion of raypaths by lateral heterogeneity. The new shear velocity model shows a broad low velocity region in the lithospheric mantle across the Shield and a low velocity region at depths {ge} 150 km localized along the Red Sea coast and Makkah-Madinah-Nafud (MMN) volcanic line. The velocity reduction in the upper mantle corresponds to a temperature anomaly of {approx}250-330 K. These finding, in particular the region of continuous low velocities along the Red Sea and MMN volcanic line, do not support interpretations for the origin of the Cenozoic plateau uplift and volcanism on the Shield invoking two separate plumes. When combined with images of the 410 and 660 km discontinuities beneath the southern part of the Arabian Shield, body wave tomographic models, a S-wave polarization analysis, and SKS splitting results, our new model supports an interpretation invoking a thermal upwelling of warm mantle rock originating in the lower mantle under Africa that crosses through the transition zone beneath Ethiopia and moves to the north and northwest under the eastern margin of the Red Sea and the Arabian Shield. In this interpretation, the difference in mean elevation between the Platform and Shield can be attributed to isostatic uplift caused by heating of the lithospheric mantle under the Shield, with significantly higher region along the Red Sea possibly resulting from a combination of lithosphere thinning and dynamic uplift.

  11. Deep and persistent melt layer in the Archaean mantle

    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.

  12. Mantle structure and tectonic history of SE Asia

    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

  13. Louisiana Speaks Transportation Option B Transit Stations, UTM Zone 15N NAD 83, Louisiana Recovery Authority (2007), [louisiana_speaks_transportation_option_b_transit_stations

    Louisiana Geographic Information Center — This GIS shapefile data illustrates potential fixed-transit stations included in the Louisiana Speaks Regional Plan community growth option of compact and dispersed...

  14. An inverted continental Moho and serpentinization of the forearc mantle.

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

    2002-05-30

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

  15. C-O-H-N fluids circulations and graphite precipitation in reactivated Hudsonian shear zones during basement uplift of the Wollaston-Mudjatik Transition Zone: Example of the Cigar Lake U deposit

    Martz, Pierre; Cathelineau, Michel; Mercadier, Julien; Boiron, Marie-Christine; Jaguin, Justine; Tarantola, Alexandre; Demacon, Mickael; Gerbeaud, Olivier; Quirt, David; Doney, Amber; Ledru, Patrick

    2017-12-01

    Graphitic shear zones are spatially associated with unconformity-related uranium deposits that are located around the unconformity between the strata of the Paleo- to Mesoproterozoic Athabasca Basin (Saskatchewan, Canada) and its underlying Archean to Paleoproterozoic basement. The present study focuses on basement-hosted ductile-brittle graphitic shear zones near the Cigar Lake U deposit, one of the largest unconformity-related U deposits. The goal of the study is to decipher the pre-Athabasca Basin fluid migration history recorded within such structures and its potential role on the formation of such exceptional deposit. Dominantly C-O-H(-N) metamorphic fluids have been trapped in Fluid Inclusion Planes (FIPs) in magmatic quartz within ductile-brittle graphitic shear zones active during retrograde metamorphism associated with the formation of the Wollaston-Mudjatik Transition Zone (WMTZ) between ca. 1805 and 1720 Ma. Such fluids show a compositional evolution along the retrograde path, from a dense and pure CO2 fluid during the earliest stages, through a lower density CO2 ± CH4-N2 (± H2O) fluid and, finally, to a very low density CH4-N2 fluid. Statistical study of the orientation, distribution, proportion, and chemical characterization of the FIPs shows that: i) CO2 (δ13CCO2 around - 9‰ PDB) from decarbonation reactions and/or partial water-metamorphic graphite equilibrium initially migrated regionally and pervasively under lithostatic conditions at about 500 to 800 °C and 150 to 300 MPa. Such P-T conditions attest to a high geothermal gradient of around 60 to 90 °C/km, probably related to rapid exhumation of the basement or a large-scale heat source. ii) Later brittle reactivation of the shear zone at around 450 °C and 25-50 MPa favored circulation of CO2-CH4-N2(± H2O) fluids in equilibrium with metamorphic graphite (δ13CCO2 around - 14‰) under hydrostatic conditions and only within the shear zones. Cooling of these fluids and the water uptake linked

  16. Tectonic predictions with mantle convection models

    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

  17. Ice-VII inclusions in diamonds: Evidence for aqueous fluid in Earth’s deep mantle

    Tschauner, O.; Huang, S.; Greenberg, E.; Prakapenka, V. B.; Ma, C.; Rossman, G. R.; Shen, A. H.; Zhang, D.; Newville, M.; Lanzirotti, A.; Tait, K.

    2018-03-01

    Water-rich regions in Earth’s deeper mantle are suspected to play a key role in the global water budget and the mobility of heat-generating elements. We show that ice-VII occurs as inclusions in natural diamond and serves as an indicator for such water-rich regions. Ice-VII, the residue of aqueous fluid present during growth of diamond, crystallizes upon ascent of the host diamonds but remains at pressures as high as 24 gigapascals; it is now recognized as a mineral by the International Mineralogical Association. In particular, ice-VII in diamonds points toward fluid-rich locations in the upper transition zone and around the 660-kilometer boundary.

  18. Comparative Study on the Electrical Properties of the Oceanic Mantle Beneath the Northwest Pacific Ocean

    Toh, H.

    2013-12-01

    We have been conducting long-term seafloor electromagnetic (EM) observations at two sites in the northwest Pacific since 2001. The older site was established at the deep seafloor (~5600m) on the northwest Pacific basin (Site NWP), while the new one was installed on the west Philippine basin (Site WPB) in 2006 at the slightly deeper (~5700m) seafloor. The ages of the oceanic basins at those sites are approximately 129 Ma for Site NWP (Shipboard Scientific Party of ODP Leg 191, 2000) and 49 Ma for Site WPB (Salisbury et al., 2006), respectively. The EM instruments deployed at those sites are seafloor EM stations (SFEMS; Toh et al., 2004 and 2006) and capable of measuring vector EM fields at the seafloor for as long as one year or more with other physical quantities such as the instruments' attitude, orientation and temperature. One of the objectives of the seafloor long-term EM observations by SFEMSs is to make a comparative study of the oceanic mantle with and without influence of the so-called 'stagnant slabs' in terms of their electrical conductivity. It is anticipated that the mantle transition zone under the influence of the stagnant slab has a higher electrical conductivity because the transition zone there could be wetter than that in the absence of the stagnant slab. In this context, the mantle transition zone beneath Site WPB can be said to have influence by the stagnant slab, while that beneath Site NWP does not. It, therefore, is basically possible to estimate how much water is present in each transition zone by comparison of the electrical conductivity profiles of the two. The one-dimensional electrical profile beneath Site NWP has been derived so far using the magnetotelluric (MT) and geomagnetic depth sounding (GDS) methods with significant jumps in the electrical property at 410 and 660km discontinuities. The jumps are approximately factors of 10 and 2, respectively (Ichiki et al., 2009). Here we show a profile beneath Site WPB using both MT and GDS

  19. Effect of sediment composition on methane concentration and production in the transition zone of a mangrove (Sepetiba Bay, Rio de Janeiro, Brazil)

    Marinho,CC.; Campos,EA.; Guimarães,JRD.; Esteves,FA.

    2012-01-01

    The aim of this research was to evaluate the effect of sediment composition on methane (CH4) dynamics in sediments of different areas in the transition zone between a mangrove and the sea. This research was conducted in a mangrove at Coroa Grande, on the southern coast of Rio de Janeiro. Samples were collected at three stations: (1) region colonised by Rhizophora mangle L. on the edge of the mangrove, (2) region colonised by seagrasses and (3) infra-littoral region without vegetation. Samples...

  20. Elastic Wave Velocity Measurements on Mantle Peridotite at High Pressure and Temperature

    Mistler, G. W.; Ishikawa, M.; Li, B.

    2002-12-01

    With the success of conducting ultrasonic measurements at high pressure and high temperature in large volume high pressure apparatus with in-situ measurement of the sample length by X-ray imaging, it is now possible to measure elastic wave velocities on aggregate samples with candidate compositions of the mantle to the conditions of the Earth's transition zone in the laboratory. These data can be directly compared with seismic data to distinguish the compositional models in debate. In this work, we carried out velocity measurements on natural peridotite KLB-1 at the conditions of the Earth's upper mantle. Fine powered sample of natural KLB-1 was used as starting material. Specimens for ultrasonic measurements were hot-pressed and equilibrated at various pressure and temperature conditions along geotherm up to the transition zone. The recovered samples were characterized with density measurement, X-ray diffraction and microprobe analysis. Bench top P and S wave velocities of KLB-1 sample sintered at 3-4 GPa and 1400 degree centigrade showed a very good agreement with the VRH average of pyrolite. High pressure and high temperature measurements was conducted up to 7 GPa and 800 degree centigrade using ultrasonic interferometric method in a DIA-type high pressure apparatus in conjunction with X-ray diffraction and X-ray imaging. The utilization of X-ray imaging technique provides direct measurements of sample lengths at high pressure and high temperature, ensuring a precise determination of velocities. The results of P and S wave velocities at high pressure and high temperature as well as their comparison with calculated pyrolite model will be presented.

  1. The basal part of the Oman ophiolitic mantle: a fossil Mantle Wedge?

    Prigent, Cécile; Guillot, Stéphane; Agard, Philippe; Godard, Marguerite; Chauvet, Alain; Dubacq, Benoit; Monié, Patrick; Yamato, Philippe

    2014-05-01

    Although the Oman ophiolite is classically regarded as being the direct analog of oceanic lithosphere created at fast spreading ridges, the geodynamic context of its formation is still highly debated. The other alternative end-member model suggests that this ophiolite entirely formed in a supra-subduction zone setting. Fluids involved in the hydration of the oceanic lithosphere and in the presence of a secondary boninitic and andesitic volcanism may provide a way to discriminate between these two interpretations: are they descending near-axis hydrothermal fluxes (first model) or ascending from a subducting slab (second model)? We herein focus on the base of the ophiolitic mantle in order to characterize the origin of fluids and decipher hydration processes. Samples were taken along hecto- to kilometre-long sections across the basal banded unit directly overlying the amphibolitic/granulitic metamorphic sole. We carried out a petrological, structural and geochemical study on these rocks and their constitutive minerals. Our results show that, unlike the generally refractory character of Oman harzburgites, all the basal mantle rocks display secondary crystallization of clinopyroxene and amphibole through metasomatic processes. The microstructures and the chronology of these secondary mineralizations (clinopyroxene, pargasitic amphibole, antigorite and then lizardite/chrysotile) suggest that these basal rocks have been affected by cooling from mantle temperatures (serpentines (B, Sr, Rb, Ba, As), are consistent with amphibolite-derived fluids (Ishikawa et al., 2005) and cannot be easily explained by other sources. Based on these observations, we propose a geodynamic model in which intense and continuous metasomatism of the cooling base of the ophiolitic mantle is due to the release of fluids coming from the progressive dehydration of underlying amphibolitic rocks. This process is compatible with the progressive subduction of the Arabian margin during the Upper

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

    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

  3. Electromagnetic exploration of the oceanic mantle.

    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.

  4. The Earth's mantle and geoneutrinos

    Fiorentini, Giovanni; Fogli, Gian Luigi; Lisi, Eligio; Mantovani, Fabio; Rotunno, Anna Maria; Xhixha, Gerti

    2013-01-01

    The KamLAND and Borexino experiments have observed, each at ∼4σ level, signals of electron antineutrinos produced in the decay chains of thorium and uranium in the Earth's crust and mantle (Th and U geoneutrinos). Various pieces of geochemical and geophysical information allow an estimation of the crustal geoneutrino flux components with relatively small uncertainties. The mantle component may then be inferred by subtracting the estimated crustal flux from the measured total flux. We find that crust-subtracted signals show hints of a residual mantle component, emerging at ∼2.4σ level by combining the KamLAND and Borexino data. The inferred mantle flux, slightly favoring scenarios with relatively high Th and U abundances, within ∼1σ uncertainties is comparable to the predictions from recent mantle models

  5. Numerical modelling of volatiles in the deep mantle

    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).

  6. Radiomic features for prostate cancer detection on MRI differ between the transition and peripheral zones: Preliminary findings from a multi-institutional study.

    Ginsburg, Shoshana B; Algohary, Ahmad; Pahwa, Shivani; Gulani, Vikas; Ponsky, Lee; Aronen, Hannu J; Boström, Peter J; Böhm, Maret; Haynes, Anne-Maree; Brenner, Phillip; Delprado, Warick; Thompson, James; Pulbrock, Marley; Taimen, Pekka; Villani, Robert; Stricker, Phillip; Rastinehad, Ardeshir R; Jambor, Ivan; Madabhushi, Anant

    2017-07-01

    To evaluate in a multi-institutional study whether radiomic features useful for prostate cancer (PCa) detection from 3 Tesla (T) multi-parametric MRI (mpMRI) in the transition zone (TZ) differ from those in the peripheral zone (PZ). 3T mpMRI, including T2-weighted (T2w), apparent diffusion coefficient (ADC) maps, and dynamic contrast-enhanced MRI (DCE-MRI), were retrospectively obtained from 80 patients at three institutions. This study was approved by the institutional review board of each participating institution. First-order statistical, co-occurrence, and wavelet features were extracted from T2w MRI and ADC maps, and contrast kinetic features were extracted from DCE-MRI. Feature selection was performed to identify 10 features for PCa detection in the TZ and PZ, respectively. Two logistic regression classifiers used these features to detect PCa and were evaluated by area under the receiver-operating characteristic curve (AUC). Classifier performance was compared with a zone-ignorant classifier. Radiomic features that were identified as useful for PCa detection differed between TZ and PZ. When classification was performed on a per-voxel basis, a PZ-specific classifier detected PZ tumors on an independent test set with significantly higher accuracy (AUC = 0.61-0.71) than a zone-ignorant classifier trained to detect cancer throughout the entire prostate (P  0.14) were obtained for all institutions. A zone-aware classifier significantly improves the accuracy of cancer detection in the PZ. 3 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:184-193. © 2016 International Society for Magnetic Resonance in Medicine.

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

    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.

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

    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.

  9. Laparoscopy-assisted versus transabdominal reoperation in Hirschprung's disease for residual aganglionosis and transition zone pathology after transanal pull-through.

    Xia, Xue; Li, Ning; Wei, Jia; Zhang, Wen; Yu, Donghai; Zhu, Tianqi; Feng, Jiexiong

    2016-04-01

    This study aims to describe laparoscopic reoperation (LSR) and compare its outcomes with transabdominal reoperation (TAR) for treating Hirschsprung's disease (HD). Eighteen patients with HD underwent reoperation for recurring constipation due to residual aganglionosis and transition zone pathology after an initial transanal procedure (LSR, n=10; TAR, n=8). Preoperative, operative and postoperative data were collected through patient follow-ups ranging from 13 to 75months to compare operative characteristics and postoperative outcomes between the two groups. Ten patients underwent laparoscopic reoperation in our institution without major complications. On average, blood loss was significantly lower in the LSR group (mean±standard deviation, 83±32.7mL) than in the TAR group (185±69mL) (P=0.001). The LSR group had a shorter hospitalization time (12±2days) than the TAR group (15±2.1days) (P=0.02). There was no statistically significant difference in incidence of postoperative complications between the two groups. LSR is safe and technically feasible in HD for recurring constipation due to residual aganglionosis and transition zone pathology, when initial transanal procedure fails. Although RA and TZP can be cured by reoperation, great efforts should be made to diminish the necessity of reoperation. Copyright © 2015 Elsevier Inc. All rights reserved.

  10. The role of strain hardening in the transition from dislocation-mediated to frictional deformation of marbles within the Karakoram Fault Zone, NW India

    Wallis, David; Lloyd, Geoffrey E.; Hansen, Lars N.

    2018-02-01

    The onset of frictional failure and potentially seismogenic deformation in carbonate rocks undergoing exhumation within fault zones depends on hardening processes that reduce the efficiency of aseismic dislocation-mediated deformation as temperature decreases. However, few techniques are available for quantitative analysis of dislocation slip system activity and hardening in natural tectonites. Electron backscatter diffraction maps of crystal orientations offer one such approach via determination of Schmid factors, if the palaeostress conditions can be inferred and the critical resolved shear stresses of slip systems are constrained. We analyse calcite marbles deformed in simple shear within the Karakoram Fault Zone, NW India, to quantify changes in slip system activity as the rocks cooled during exhumation. Microstructural evidence demonstrates that between ∼300 °C and 200-250 °C the dominant deformation mechanisms transitioned from dislocation-mediated flow to twinning and frictional failure. However, Schmid factor analysis, considering critical resolved shear stresses for yield of undeformed single crystals, indicates that the fraction of grains with sufficient resolved shear stress for glide apparently increased with decreasing temperature. Misorientation analysis and previous experimental data indicate that strain-dependent work hardening is responsible for this apparent inconsistency and promoted the transition from dislocation-mediated flow to frictional, and potentially seismogenic, deformation.

  11. The role of sexual vs. asexual recruitment of Artemisia wudanica in transition zone habitats between inter-dune lowlands and active dunes in Inner Mongolia, China

    Wang, Yongcui; Alberto, Busso Carlos; Jiang, Deming; Ala, Musa; Li, Xuehua; Zhou, Quanlai; Lin, Jixiang; Ren, Guohua; Jia, Lian

    2016-04-01

    Artemisia wudanica is an endemic, perennial, pioneering psammophyte species in the sand dune ecosystems of western Horqin Sand Land in northern China. However, no studies have addressed how sexual and asexual reproduction modes of A. wudanica perform at the transitional zones between active dune inter-dune lowlands and active dunes. In early spring, quadrats were randomly set up in the study area to monitor surviving seedling and/or ramet density and frequency coming from sexual/asexual reproduction of A. wudanica. Iron sticks were inserted near each quadrat to determine wind erosion intensity (WE). Additionally, soil samples were collected nearby each quadrat to test for soil moisture (SM), organic matter (OM) and pH. Surviving seedlings of A. wudanica showed an inverse response in comparison with ramets to SM, OM and WE. Soil moisture showed the most positive effect, and WE the negative effect, on surviving, sexual reproduction seedlings. Contrarily, WE had the most positive effect, and SM the negative effect, on asexual reproduction ramets. This suggests that increases in SM and decreases in WE should benefit recruitment of A. wudanica seedlings. On the contrary, ramets coming from asexual reproduction showed a different response to environmental factors in transition zone habitats. While SM was not a key constraint for the survival of seedlings, they showed a better, positive response to wind erosion environments. Overall, various study environmental parameters could be improved to foster A. wudanica invasion and settlement in the plant community through different reproductive modes, thereby promoting vegetation restoration and rehabilitation.

  12. Li Isotope Studies of Olivine in Mantle Xenoliths by SIMS

    Bell, D. R.; Hervig, R. L.; Buseck, P. R.

    2005-01-01

    Variations in the ratio of the stable isotopes of Li are a potentially powerful tracer of processes in planetary and nebular environments [1]. Large differences in the 7Li/6Li ratio between the terrestrial upper mantle and various crustal materials make Li isotope composition a potentially powerful tracer of crustal recycling processes on Earth [2]. Recent SIMS studies of terrestrial mantle and Martian meteorite samples report intra-mineral Li isotope zoning [3-5]. Substantial Li isotope heterogeneity also exists within and between the components of chondritic meteorites [6,7]. Experimental studies of Li diffusion suggest the potential for rapid isotope exchange at elevated temperatures [8]. Large variations in 7Li, exceeding the range of unaltered basalts, occur in terrestrial mantle-derived xenoliths from individual localities [9]. The origins of these variations are not fully understood.

  13. A new conceptual model for whole mantle convection and the origin of hotspot plumes

    Yoshida, Masaki

    2014-08-01

    A new conceptual model of mantle convection is constructed for consideration of the origin of hotspot plumes, using recent evidence from seismology, high-pressure experiments, geodynamic modeling, geoid inversion studies, and post-glacial rebound analyses. This conceptual model delivers several key points. Firstly, some of the small-scale mantle upwellings observed as hotspots on the Earth's surface originate at the base of the mantle transition zone (MTZ), in which the Archean granitic continental material crust (TTG; tonalite-trondhjemite-granodiorite) with abundant radiogenic elements is accumulated. Secondly, the TTG crust and the subducted oceanic crust that have accumulated at the base of MTZ could act as thermal or mechanical insulators, leading to the formation of a hot and less viscous layer just beneath the MTZ; which may enhance the instability of plume generation at the base of the MTZ. Thirdly, the origin of some hotspot plumes is isolated from the large low shear-wave velocity provinces (LLSVPs) under Africa and the South Pacific. I consider that the conceptual model explains why almost all the hotspots around Africa are located above the margins of the African LLSVP. Because a planetary-scale trench system surrounding a “Pangean cell” has been spatially stable throughout the Phanerozoic, a large amount of the oceanic crustal layer is likely to be trapped in the MTZ under the Pangean cell. Therefore, under Africa, almost all of the hotspot plumes originate from the base of the MTZ, where a large amount of TTG and/or oceanic crusts has accumulated. This conceptual model may explain the fact that almost all the hotspots around Africa are located on margins above the African LLSVP. It is also considered that some of the hotspot plumes under the South Pacific thread through the TTG/oceanic crusts accumulated around the bottom of the MTZ, and some have their roots in the South Pacific LLSVP while others originate from the MTZ. The numerical simulations

  14. UV filters, ethylhexyl methoxycinnamate, octocrylene and ethylhexyl dimethyl PABA from untreated wastewater in sediment from eastern Mediterranean river transition and coastal zones.

    Amine, Helmieh; Gomez, Elena; Halwani, Jalal; Casellas, Claude; Fenet, Hélène

    2012-11-01

    UVF may occur in the aquatic environment through two principal sources: direct inputs from recreational activities and indirect wastewater- and river-borne inputs. The aim of this study was to obtain a first overview of levels of three UVF (EHMC, OC and OD-PABA) in coastal areas subjected to river inputs, untreated wastewater discharges and dumpsite leachates. We selected three eastern Mediterranean rivers that have been impacted for decades by untreated wastewater release and collected sediment in the coastal zone during the hot and humid seasons. Western Mediterranean sites receiving treated wastewaters were analyzed for comparison. The results gave an overview of sediment contamination under these two contrasted situations representative of Mediterranean coastal areas without bathing activities. The analysis of the three UVF revealed the ubiquity and high point source contamination by EHMC and OC in transition and coastal zones, with levels as high as 128 ng g(-1)d.w. OD-PABA was also frequently detected, but at lower concentrations (zones. Copyright © 2012. Published by Elsevier Ltd.

  15. Mantle Convection on Modern Supercomputers

    Weismüller, J.; Gmeiner, B.; Huber, M.; John, L.; Mohr, M.; Rüde, U.; Wohlmuth, B.; Bunge, H. P.

    2015-12-01

    Mantle convection is the cause for plate tectonics, the formation of mountains and oceans, and the main driving mechanism behind earthquakes. The convection process is modeled by a system of partial differential equations describing the conservation of mass, momentum and energy. Characteristic to mantle flow is the vast disparity of length scales from global to microscopic, turning mantle convection simulations into a challenging application for high-performance computing. As system size and technical complexity of the simulations continue to increase, design and implementation of simulation models for next generation large-scale architectures is handled successfully only in an interdisciplinary context. A new priority program - named SPPEXA - by the German Research Foundation (DFG) addresses this issue, and brings together computer scientists, mathematicians and application scientists around grand challenges in HPC. Here we report from the TERRA-NEO project, which is part of the high visibility SPPEXA program, and a joint effort of four research groups. TERRA-NEO develops algorithms for future HPC infrastructures, focusing on high computational efficiency and resilience in next generation mantle convection models. We present software that can resolve the Earth's mantle with up to 1012 grid points and scales efficiently to massively parallel hardware with more than 50,000 processors. We use our simulations to explore the dynamic regime of mantle convection and assess the impact of small scale processes on global mantle flow.

  16. Modulation of flagellum attachment zone protein FLAM3 and regulation of the cell shape in Trypanosoma brucei life cycle transitions

    Sunter, J.C.; Benz, C.; Andre, L.; Whipple, S.; McKean, P.G.; Gull, K.; Ginger, M. L.; Lukeš, Julius

    2015-01-01

    Roč. 128, č. 16 (2015), s. 3117-3130 ISSN 0021-9533 R&D Projects: GA MŠk(CZ) EE2.3.30.0032; GA MŠk LH12104 EU Projects: European Commission(XE) 316304 Institutional support: RVO:60077344 Keywords : Trypanosomes * Morphogenesis * Flagellum attachment zone Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 4.706, year: 2015

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

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

    2012-04-01

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

  18. ANALYSIS OF DEFORMED STATE STRUCTURES OF THE KYIV METRO RUNNING TUNNELS ON A TRANSITION ZONE FROM SPONDYLOV’S CLAY TO BUCHATSKIY SANDS

    V. D. Petrenko

    2014-07-01

    Full Text Available Purpose. In the section of changes geotechnical conditions of spondylov’s clay to buchatskiy sands may have significant structural deformation of running tunnels. It is necessary to identify the cause of deformities develop ways to minimize and based modeling and calculations to prove the effectiveness of measures to reduce deformation.Methodology. To solve the analysis problem of the stress-strain state (SSS of the system «structure array» it was conducted the numerical simulation using the finite element method (FEM. On the basis of the obtained results the graphs were constructed and the dependencies were determined. Findings. The presence of weak water-saturated soils in tray of the tunnel on an area of transition from spondylov’s clay to buchatskiy sand causes significant increasing in strain construction of tunnels and general vibration liquefaction in soil basis. Also change the physical and mechanical characteristics of soils within the frames of tunnels influences on the level of strain state of most frames. Improved strain state settings of tunnels in areas of change soil characteristics of the array (especially at the bottom of casing can be achieved by chemical consolidation of weak soils. Composition of solutions for fixing the weak soils should be determined based on the study of grain size, porosity, and other parameters of physical and mechanical and physical and chemical characteristics of soils.Originality.The basic cause significant strain on transition zone from spondylov’s clay to buchatskiy sands is found, that is explained by saturated phenomenon vibration liquefaction basis under the tunnel.Practical value.The approaches to reduce the strain in the construction of running tunnels in the transition zone from spondylov’s clay to buchatskiy sands are developed, as well as in the area ofthe station «Glybochytska»the Kyiv Metro.

  19. Diagnostic sedimentary structures of the fluvial-tidal transition zone – Evidence from deposits of the Rhine and Meuse

    Berg, J.H. van den; Boersma, J.R.; Gelder, A. van

    2007-01-01

    n mesotidal settings the transition of a coastal plain estuary to the river is marked by the change of a multiple ebb and flood channel configurationto a single channel system. At high river discharge fluvial processes operate, whereas in periods of low discharge the flow is complicated by a

  20. Teleseismic Investigations of the Malawi and Luangwa Rift Zones: Ongoing Observations From the SAFARI Experiment

    Reed, C. A.; Gao, S. S.; Liu, K. H.; Yu, Y.; Chindandali, P. R. N.; Massinque, B.; Mdala, H. S.; Mutamina, D. M.

    2015-12-01

    In order to evaluate the influence of crustal and mantle heterogeneities upon the initiation of the Malawi rift zone (MRZ) and reactivation of the Zambian Luangwa rift zone (LRZ) subject to Cenozoic plate boundary stress fields and mantle buoyancy forces, we installed and operated 33 Seismic Arrays For African Rift Initiation (SAFARI) three-component broadband seismic stations in Malawi, Mozambique, and Zambia from 2012 to 2014. During the twenty-four month acquisition period, nearly 6200 radial receiver functions (RFs) were recorded. Stations situated within the MRZ, either along the coastal plains or within the Shire Graben toward the south, report an average crustal thickness of 42 km relative to approximately 46 km observed at stations located along the rift flanks. This implies the juvenile MRZ is characterized by a stretching factor not exceeding 1.1. Meanwhile, P-to-S velocity ratios within the MRZ increase from 1.71 to 1.82 in southernmost Malawi, indicating a substantial modification of the crust during Recent rifting. Time-series stacking of approximately 5500 RFs recorded by the SAFARI and 44 neighboring network stations reveals an apparent uplift of 10 to 15 km along both the 410- and 660-km mantle transition zone (MTZ) discontinuities beneath the MRZ and LRZ which, coupled with an apparently normal 250-km MTZ thickness, implies a first-order high-velocity contribution from thickened lithosphere. Preliminary manual checking of SAFARI shear-wave splitting (SWS) measurements provides roughly 650 high-quality XKS phases following a component re-orientation to correct station misalignments. Regional azimuthal variations in SWS fast orientations are observed, from rift-parallel in the vicinity of the LRZ to rift-oblique in the MRZ. A major 60° rotation in the fast orientation occurs at approximately 31°E, possibly resulting from the modulation of mantle flow around a relatively thick lithospheric keel situated between the two rift zones.

  1. Tracing halogen and B cycling in subduction zones based on obducted, subducted and forearc serpentinites of the Dominican Republic.

    Pagé, Lilianne; Hattori, Keiko

    2017-12-19

    Serpentinites are important reservoirs of fluid-mobile elements in subduction zones, contributing to volatiles in arc magmas and their transport into the Earth's mantle. This paper reports halogen (F, Cl, Br, I) and B abundances of serpentinites from the Dominican Republic, including obducted and subducted abyssal serpentinites and forearc mantle serpentinites. Abyssal serpentinite compositions indicate the incorporation of these elements from seawater and sediments during serpentinization on the seafloor and at slab bending. During their subduction and subsequent lizardite-antigorite transition, F and B are retained in serpentinites, whilst Cl, Br and I are expelled. Forearc mantle serpentinite compositions suggest their hydration by fluids released from subducting altered oceanic crust and abyssal serpentinites, with only minor sediment contribution. This finding is consistent with the minimal subduction of sediments in the Dominican Republic. Forearc mantle serpentinites have F/Cl and B/Cl ratios similar to arc magmas, suggesting the importance of serpentinite dehydration in the generation of arc magmatism in the mantle wedge.

  2. Ancient mantle in a modern arc: osmium isotopes in izu-bonin-mariana forearc peridotites

    Parkinson; Hawkesworth; Cohen

    1998-09-25

    Mantle peridotites drilled from the Izu-Bonin-Mariana forearc have unradiogenic 187Os/188Os ratios (0.1193 to 0.1273), which give Proterozoic model ages of 820 to 1230 million years ago. If these peridotites are residues from magmatism during the initiation of subduction 40 to 48 million years ago, then the mantle that melted was much more depleted in incompatible elements than the source of mid-ocean ridge basalts (MORB). This result indicates that osmium isotopes record information about ancient melting events in the convecting upper mantle not recorded by incompatible lithophile isotope tracers. Subduction zones may be a graveyard for ancient depleted mantle material, and portions of the convecting upper mantle may be less radiogenic in osmium isotopes than previously recognized.

  3. Probing Mantle Heterogeneity Across Spatial Scales

    Hariharan, A.; Moulik, P.; Lekic, V.

    2017-12-01

    Inferences of mantle heterogeneity in terms of temperature, composition, grain size, melt and crystal structure may vary across local, regional and global scales. Probing these scale-dependent effects require quantitative comparisons and reconciliation of tomographic models that vary in their regional scope, parameterization, regularization and observational constraints. While a range of techniques like radial correlation functions and spherical harmonic analyses have revealed global features like the dominance of long-wavelength variations in mantle heterogeneity, they have limited applicability for specific regions of interest like subduction zones and continental cratons. Moreover, issues like discrepant 1-D reference Earth models and related baseline corrections have impeded the reconciliation of heterogeneity between various regional and global models. We implement a new wavelet-based approach that allows for structure to be filtered simultaneously in both the spectral and spatial domain, allowing us to characterize heterogeneity on a range of scales and in different geographical regions. Our algorithm extends a recent method that expanded lateral variations into the wavelet domain constructed on a cubed sphere. The isolation of reference velocities in the wavelet scaling function facilitates comparisons between models constructed with arbitrary 1-D reference Earth models. The wavelet transformation allows us to quantify the scale-dependent consistency between tomographic models in a region of interest and investigate the fits to data afforded by heterogeneity at various dominant wavelengths. We find substantial and spatially varying differences in the spectrum of heterogeneity between two representative global Vp models constructed using different data and methodologies. Applying the orthonormality of the wavelet expansion, we isolate detailed variations in velocity from models and evaluate additional fits to data afforded by adding such complexities to long

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

    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...

  5. Effect of sediment composition on methane concentration and production in the transition zone of a mangrove (Sepetiba Bay, Rio de Janeiro, Brazil).

    Marinho, C C; Campos, E A; Guimarães, J R D; Esteves, F A

    2012-08-01

    The aim of this research was to evaluate the effect of sediment composition on methane (CH4) dynamics in sediments of different areas in the transition zone between a mangrove and the sea. This research was conducted in a mangrove at Coroa Grande, on the southern coast of Rio de Janeiro. Samples were collected at three stations: (1) region colonised by Rhizophora mangle L. on the edge of the mangrove, (2) region colonised by seagrasses and (3) infra-littoral region without vegetation. Samples were collected from the surface layer of the sediment to determine the concentrations of nutrients (C, N and P) and CH4 concentration and production. We observed that concentrations of CH4 and carbon (C) were significantly higher (p Mangrove Coroa Grande is a function of available OM suggesting a possible inhibition of methanotrophy by intense oxygen consumption in the soil surface covered by detritus of Rhizophora mangle vegetation.

  6. Diachronism in the late Neoproterozoic-Cambrian arc-rift transition of North Gondwana: A comparison of Morocco and the Iberian Ossa-Morena Zone

    Álvaro, J. Javier; Bellido, Félix; Gasquet, Dominique; Pereira, M. Francisco; Quesada, Cecilio; Sánchez-García, Teresa

    2014-10-01

    In the northwestern border of the West African craton (North Gondwana), a transition from late Neoproterozoic subduction/collision to Cambrian rift processes was recorded in the Anti-Atlas (Morocco) and in the Ossa-Morena Zone (Iberia). Cambrian rifting affected both Pan-African and Cadomian basements in a stepwise and diachronous way. Subsequently, both areas evolved into a syn-rift margin episodically punctuated by uplift and tilting that precluded Furongian sedimentation. A comparison of sedimentary, volcanic and geodynamic evolution is made in the late Neoproterozoic (Pan-African and Cadomian) belts and Cambrian rifts trying to solve the apparent diachronous (SW-NE-trending) propagation of an early Palaeozoic rifting regime that finally led to the opening of the Rheic Ocean.

  7. The first report of a microdiverse anammox bacteria community in waters of Colombian Pacific, a transition area between prominent oxygen minimum zones of the eastern tropical Pacific.

    Castro-González, M; Molina, V; Rodríguez-Rubio, E; Ulloa, O

    2014-12-01

    Anaerobic ammonium oxidizers contribute to the removal of fixed nitrogen in oxygen-deficient marine ecosystems such as oxygen minimum zones (OMZ). Here we surveyed for the first time the occurrence and diversity of anammox bacteria in the Colombian Pacific, a transition area between the prominent South and North Pacific OMZs. Anammox bacteria were detected in the coastal and oceanic areas of the Colombian Pacific in low oxygen (Chile and Arabian Sea) within Candidatus ‘Scalindua spp’. Moreover, some anammox bacteria OTUs shared a low similarity with environmental phylotypes (86–94%). Our results indicated that a microdiverse anammox community inhabits the Colombian Pacific, generating new questions about the ecological and biogeochemical differences influencing its community structure.

  8. [Carbon balance of household production system in the transition zone from the Loess Plateau to the Qinghai-Tibet Plateau, China].

    Wu, Chao Chao; Gao, Xiao Ye; Hou, Fu Jiang

    2017-10-01

    The transition zone from the Loess Plateau to the Qinghai-Tibet Plateau is one of the regions with most dramatic changes in agricultural production mode and most sensitive response to the carbon balance effect. This paper analyzed the carbon balance of the agriculture system along the altitude gradient in Tongwei, Weiyuan and Xiahe counties. The results showed that with the increase of altitude, the carbon emission, carbon fixation and carbon sink capacity of crops per unit area decreased accordingly, while the average carbon emission, carbon fixation and carbon source capacity of each household in livestock system increased. The integrated crop-livestock production system changed from carbon sink to carbon source. The average carbon emission of each household rose with altitude, but the carbon fixation was the opposite. The change of percentage ofhousehold in the transition zone from the Loess Plateau to the Qinghai-Tibet Plateau with carbon balance could be fitted with Logistic equation. In the crop system of Tongwei, Weiyuan and Xiahe with the altitude increase, carbon emission at the inflection point where the household percentage accounted for 50.0% was 1491, 857 and 376 kg CE·household -1 , and carbon fixation was 6187, 3872 and 778 kg CE·household -1 , respectively. For the livestock system, carbon emission was 2218, 3725 and 49511 kg CE·household -1 , and carbon fixation was 138, 230 and 2706 kg CE·household -1 , respectively. For the integrated crop-livestock system, carbon emission was 3615, 4583 and 49918 kg CE·household -1 , and carbon fixation was 6289, 4113 and 3819 kg CE·household -1 , respectively, which could be the key point for the regulation of regional carbon balance.

  9. Vema-TRANSIT - An interdisciplinary study on the bathymetry of the Vema-Fracture Zone and Puerto Rico Trench as well as abyssal Atlantic biodiversity

    Riehl, Torben; Kaiser, Stefanie; Brandt, Angelika

    2018-02-01

    The seafloor below 3500 m remains largely unexplored. The paucity of knowledge of abyssal and hadal environments encompasses a wide spectrum of geological and biological patterns and processes as well as their interactions. Historically most marine research has been conducted in the North Atlantic. However, the high proportion of undescribed taxa frequently discovered at greater depth there underline the need to fill in these knowledge gaps. The Vema-TRANSIT campaign in northern winter 2014-2015 surveyed and sampled along almost the entire extent of one of the major offsets of the Mid-Atlantic Ridge (MAR), the Vema Fracture Zone (VFZ), as well as the deepest trench in the Atlantic, the Puerto Rico Trench (PRT). The discoveries that were made include new data on deep-sea habitats showing geologically complex features across all crust ages from 110 Ma until present. Moreover, some new species and genera of the abyssal and hadal benthos were described herein. Not only the taxa themselves, but also their distributions and genetic structure were elucidated. In this context, significant differences in abundances, community composition, and species distribution were detected that were affected by the MAR as well as by the depth transition between hadal PRT and the adjacent abyss. Despite significant differences between eastern and western communities, the MAR does not represent an absolute barrier. Instead, the VFZ, and especially the VTF may serve as a connecting feature between east and west and this may be exemplary for fracture zones across the whole Atlantic. Nevertheless, the MAR as well as the 3000-m-depth gradient between abyss and hadal appear to restrict gene flow for poor dispersers and thus contribute to speciation processes in the deep sea.

  10. Assessing the hydrological response from an ensemble of CMIP5 climate projections in the transition zone of the Atlantic region (Bay of Biscay)

    Meaurio, Maite; Zabaleta, Ane; Boithias, Laurie; Epelde, Ane Miren; Sauvage, Sabine; Sánchez-Pérez, Jose-Miguel; Srinivasan, Raghavan; Antiguedad, Iñaki

    2017-05-01

    The climate changes projected for the 21st century will have consequences on the hydrological response of catchments. These changes, and their consequences, are most uncertain in the transition zones. The study area, in the Bay of Biscay, is located in the transition zone of the European Atlantic region, where hydrological impact of climate change was scarcely studied. In order to address this scarcity, the hydrological impacts of climate change on river discharge were assessed. To do so, a hydrological modelling was carried out considering 16 climate scenarios that include 5 General Circulation Models (GCM) from the 5th report of the Coupled Model Intercomparison Project (CMIP5), 2 statistical downscaling methods and 2 Representative Concentration Pathways. Projections for future discharge (2011-2100) were divided into three 30-year horizons (2030s, 2060s and 2090s) and a comparison was made between these time horizons and the baseline (1961-2000). The results show that the downscaling method used resulted in a higher source of uncertainty than GCM itself. In addition, the uncertainties inherent to the methods used at all the levels do not affect the results equally along the year. In spite of those uncertainties, general trends for the 2090s predict seasonal discharge decreases by around -17% in autumn, -16% in spring, -11% in winter and -7% in summer. These results are in line with those predicted for the Atlantic region (France and the Iberian Peninsula). Trends for extreme flows were also analysed: the most significant show an increase in the duration (days) of low flows. From an environmental point of view, and considering the need to meet the objectives established by the Water Framework Directive (WFD), this will be a major challenge for the future planning on water management.

  11. Impacts of extensive driftnet fishery and late 1990s climate regime shift on dominant epipelagic nekton in the Transition Region and Subtropical Frontal Zone: Implications for fishery management

    Ichii, T.; Nishikawa, H.; Igarashi, H.; Okamura, H.; Mahapatra, K.; Sakai, M.; Wakabayashi, T.; Inagake, D.; Okada, Y.

    2017-01-01

    We investigated the impacts of extensive anthropogenic (high seas driftnet squid fishery) and natural (late 1990s major climate regime shift) events on dominant epipelagic fish, squid, and shark in the central North Pacific Transition Region based on a driftnet survey covering the years 1979-2006. Fishing was conducted by Japan, Korea and Taiwan to target neon flying squid in the period 1979-1992, resulting in a decline in stocks of the target species and non-target species (Pacific pomfret and juvenile blue shark), which were by-catch of this fishery. The catch was found to be at the maximum sustainable yield (MSY) level for neon flying squid, the underfished level for juvenile blue shark, but the overfished level for Pacific pomfret. The MSY of Pacific pomfret indicated that this species is more susceptible to exploitation than previously considered. In response to the late 1990s regime shift, neon flying squid and Pacific saury showed low stock levels in 1999-2002 and 1998-2002, respectively, as a result of reduced productivity in their nursery grounds (the Subtropical Frontal Zone and Kuroshio Extension Bifurcation Region, respectively). On the other hand, Pacific pomfret showed no decreasing trend in stock during the low- and intermediate-productivity regimes because of the high productivity of their main spawning/nursery ground (Transition Zone Chlorophyll Front), which was independent of the regime shifts. Thus, squid and saury appear to be more susceptible to the regime shift than pomfret. We discuss the implications for stock management of the species-specific responses to the fishery and the regime shift.

  12. Amount of Asian lithospheric mantle subducted during the India/Asia collision

    Replumaz, A.; Guillot, S.; Villaseñor, Antonio; Negredo, A. M.

    2013-01-01

    Body wave seismic tomography is a successful technique for mapping lithospheric material sinking into the mantle. Focusing on the India/Asia collision zone, we postulate the existence of several Asian continental slabs, based on seismic global tomography. We observe a lower mantle positive anomaly between 1100 and 900 km depths, that we interpret as the signature of a past subduction process of Asian lithosphere, based on the anomaly position relative to positive anomalies related to Indian c...

  13. Broad plumes rooted at the base of the Earth's mantle beneath major hotspots.

    French, Scott W; Romanowicz, Barbara

    2015-09-03

    Plumes of hot upwelling rock rooted in the deep mantle have been proposed as a possible origin of hotspot volcanoes, but this idea is the subject of vigorous debate. On the basis of geodynamic computations, plumes of purely thermal origin should comprise thin tails, only several hundred kilometres wide, and be difficult to detect using standard seismic tomography techniques. Here we describe the use of a whole-mantle seismic imaging technique--combining accurate wavefield computations with information contained in whole seismic waveforms--that reveals the presence of broad (not thin), quasi-vertical conduits beneath many prominent hotspots. These conduits extend from the core-mantle boundary to about 1,000 kilometres below Earth's surface, where some are deflected horizontally, as though entrained into more vigorous upper-mantle circulation. At the base of the mantle, these conduits are rooted in patches of greatly reduced shear velocity that, in the case of Hawaii, Iceland and Samoa, correspond to the locations of known large ultralow-velocity zones. This correspondence clearly establishes a continuous connection between such zones and mantle plumes. We also show that the imaged conduits are robustly broader than classical thermal plume tails, suggesting that they are long-lived, and may have a thermochemical origin. Their vertical orientation suggests very sluggish background circulation below depths of 1,000 kilometres. Our results should provide constraints on studies of viscosity layering of Earth's mantle and guide further research into thermochemical convection.

  14. Sulfate reduction and methane oxidation activity below the sulfate-methane transition zone in Alaskan Beaufort Sea continental margin sediments: Implications for deep sulfur cycling

    Treude, Tina; Krause, Stefan; Maltby, Johanna; Dale, Andrew W.; Coffin, Richard; Hamdan, Leila J.

    2014-11-01

    Two ∼6 m long sediment cores were collected along the ∼300 m isobath on the Alaskan Beaufort Sea continental margin. Both cores showed distinct sulfate-methane transition zones (SMTZ) at 105 and 120 cm below seafloor (cmbsf). Sulfate was not completely depleted below the SMTZ but remained between 30 and 500 μM. Sulfate reduction and anaerobic oxidation of methane (AOM) determined by radiotracer incubations were active throughout the methanogenic zone. Although a mass balance could not explain the source of sulfate below the SMTZ, geochemical profiles and correlation network analyses of biotic and abiotic data suggest a cryptic sulfur cycle involving iron, manganese and barite. Inhibition experiments with molybdate and 2-bromoethanesulfonate (BES) indicated decoupling of sulfate reduction and AOM and competition between sulfate reducers and methanogens for substrates. While correlation network analyses predicted coupling of AOM to iron reduction, the addition of manganese or iron did not stimulate AOM. Since none of the classical archaeal anaerobic methanotrophs (ANME) were abundant, the involvement of unknown or unconventional phylotypes in AOM is conceivable. The resistance of AOM activity to inhibitors implies deviation from conventional enzymatic pathways. This work suggests that the classical redox cascade of electron acceptor utilization based on Gibbs energy yields does not always hold in diffusion-dominated systems, and instead biotic processes may be more strongly coupled to mineralogy.

  15. Determination of Mantle Discontinuity Depths beneath the South Pacific Superswell As Inferred Using Data From Broadband OBS Array

    Suetsugu, D.; Shiobara, H.; Sugioka, H.; Kanazawa, T.; Fukao, Y.

    2005-12-01

    discontinuity depths were estimated to be 403-431 km over the Superswell region, which are not substantially different from the global average considering the estimation error of 10 km. The 660-km discontinuity depths were also determined to be 654-674 km, close to the global average, at most of the stations. Data from a station near the Society hot spot, however, provide an anomalously shallow depth of 623 km, indicating a presence of a local hot anomaly at the bottom of the mantle transition zone beneath near the Society hot spot. Taking into consideration a possible effect of velocity anomalies on the depth estimation, the shallow anomaly is significant. The present result suggests that the thermal anomalies are not obvious in the Superswell-scale, but present locally beneath the Society hot spot.

  16. Zircon and allanite U-Pb ID-TIMS ages of vaugnerites from the Calzadilla pluton, Salamanca (Spain): dating mantle-derived magmatism and post-magmatic subsolidus overprint

    López-Moro, F.J.; Romer, R. L.; López-Plaza, M.; González Sánchez, M.

    2017-01-01

    Basic to intermediate high-K, high-Mg mantle-derived rocks occur throughout the Iberian Massif and are particularly important in the Tormes Dome, where vaugnerites form several stocks and small plutons. One of the largest and geochemically most variable among these plutons is the Calzadilla pluton in the Tormes Dome that crystallized at 318 ± 1.4Ma (Bashkirian; U-Pb TIMS zircon). This age reveals that the vaugnerite pluton was emplaced during the transition from late D2 extensional deformation to early D3 contractional deformation (319 to 317Ma). Large-scale extension in the area resulted, on one hand, in extensive anatexis in the crust due to quasiisothermal decompression and mica-dehydration melting and, on the other hand, in the upwelling of the mantle, which induced partial melting of the enriched domains in the lithospheric mantle. The driving reason why crustal and mantle melts were coeval is extension. The U-Pb ID-TIMS age of allanite is not related to the emplacement nor cooling of the Calzadilla vaugnerite, but it seems to be related to a younger subsolidus overprint ca. 275Ma that, in the scale of the Central Iberian Zone, corresponds to a period of hydrothermal alteration, including episyenite formation and tungsten mineralization.

  17. Zircon and allanite U-Pb ID-TIMS ages of vaugnerites from the Calzadilla pluton, Salamanca (Spain): dating mantle-derived magmatism and post-magmatic subsolidus overprint

    López-Moro, F.J.; Romer, R. L.; López-Plaza, M.; González Sánchez, M.

    2017-07-01

    Basic to intermediate high-K, high-Mg mantle-derived rocks occur throughout the Iberian Massif and are particularly important in the Tormes Dome, where vaugnerites form several stocks and small plutons. One of the largest and geochemically most variable among these plutons is the Calzadilla pluton in the Tormes Dome that crystallized at 318 ± 1.4Ma (Bashkirian; U-Pb TIMS zircon). This age reveals that the vaugnerite pluton was emplaced during the transition from late D2 extensional deformation to early D3 contractional deformation (319 to 317Ma). Large-scale extension in the area resulted, on one hand, in extensive anatexis in the crust due to quasiisothermal decompression and mica-dehydration melting and, on the other hand, in the upwelling of the mantle, which induced partial melting of the enriched domains in the lithospheric mantle. The driving reason why crustal and mantle melts were coeval is extension. The U-Pb ID-TIMS age of allanite is not related to the emplacement nor cooling of the Calzadilla vaugnerite, but it seems to be related to a younger subsolidus overprint ca. 275Ma that, in the scale of the Central Iberian Zone, corresponds to a period of hydrothermal alteration, including episyenite formation and tungsten mineralization.

  18. Sublithospheric flows in the mantle

    Trifonov, V. G.; Sokolov, S. Yu.

    2017-11-01

    The estimated rates of upper mantle sublithospheric flows in the Hawaii-Emperor Range and Ethiopia-Arabia-Caucasus systems are reported. In the Hawaii-Emperor Range system, calculation is based on motion of the asthenospheric flow and the plate moved by it over the branch of the Central Pacific plume. The travel rate has been determined based on the position of variably aged volcanoes (up to 76 Ma) with respect to the active Kilauea Volcano. As for the Ethiopia-Arabia-Caucasus system, the age of volcanic eruptions (55-2.8 Ma) has been used to estimate the asthenospheric flow from the Ethiopian-Afar superplume in the northern bearing lines. Both systems are characterized by variations in a rate of the upper mantle flows in different epochs from 4 to 12 cm/yr, about 8 cm/yr on average. Analysis of the global seismic tomographic data has made it possible to reveal rock volumes with higher seismic wave velocities under ancient cratons; rocks reach a depth of more than 2000 km and are interpreted as detached fragments of the thickened continental lithosphere. Such volumes on both sides of the Atlantic Ocean were submerged at an average velocity of 0.9-1.0 cm/yr along with its opening. The estimated rates of the mantle flows clarify the deformation properties of the mantle and regulate the numerical models of mantle convection.

  19. Structural, physiognomic and above-ground biomass variation in savanna–forest transition zones on three continents – how different are co-occurring savanna and forest formations?

    E. M. Veenendaal

    2015-05-01

    Full Text Available Through interpretations of remote-sensing data and/or theoretical propositions, the idea that forest and savanna represent "alternative stable states" is gaining increasing acceptance. Filling an observational gap, we present detailed stratified floristic and structural analyses for forest and savanna stands located mostly within zones of transition (where both vegetation types occur in close proximity in Africa, South America and Australia. Woody plant leaf area index variation was related to tree canopy cover in a similar way for both savanna and forest with substantial overlap between the two vegetation types. As total woody plant canopy cover increased, so did the relative contribution of middle and lower strata of woody vegetation. Herbaceous layer cover declined as woody cover increased. This pattern of understorey grasses and herbs progressively replaced by shrubs as the canopy closes over was found for both savanna and forests and on all continents. Thus, once subordinate woody canopy layers are taken into account, a less marked transition in woody plant cover across the savanna–forest-species discontinuum is observed compared to that inferred when trees of a basal diameter > 0.1 m are considered in isolation. This is especially the case for shrub-dominated savannas and in taller savannas approaching canopy closure. An increased contribution of forest species to the total subordinate cover is also observed as savanna stand canopy closure occurs. Despite similarities in canopy-cover characteristics, woody vegetation in Africa and Australia attained greater heights and stored a greater amount of above-ground biomass than in South America. Up to three times as much above-ground biomass is stored in forests compared to savannas under equivalent climatic conditions. Savanna–forest transition zones were also found to typically occur at higher precipitation regimes for South America than for Africa. Nevertheless, consistent across all three

  20. Seismic attenuation structure beneath Nazca Plate subduction zone in southern Peru

    Jang, H.; Kim, Y.; Clayton, R. W.

    2017-12-01

    We estimate seismic attenuation in terms of quality factors, QP and QS using P and S phases, respectively, beneath Nazca Plate subduction zone between 10°S and 18.5°S latitude in southern Peru. We first relocate 298 earthquakes with magnitude ranges of 4.0-6.5 and depth ranges of 20-280 km. We measure t*, which is an integrated attenuation through the seismic raypath between the regional earthquakes and stations. The measured t* are inverted to construct three-dimensional attenuation structures of southern Peru. Checkerboard test results for both QP and QS structures ensure good resolution in the slab-dip transition zone between flat and normal slab subduction down to a depth of 200 km. Both QP and QS results show higher attenuation continued down to a depth of 50 km beneath volcanic arc and also beneath the Quimsachata volcano, the northernmost young volcano, located far east of the main volcanic front. We also observe high attenuation in mantle wedge especially beneath the normal subduction region in both QP and QS (100-130 in QP and 100-125 in QS) and slightly higher QP and QS beneath the flat-subduction and slab-dip transition regions. We plan to relate measured attenuation in the mantle wedge to material properties such as viscosity to understand the subduction zone dynamics.

  1. Compressive strength and interfacial transition zone of sugar cane bagasse ash concrete: A comparison to the established pozzolans

    Hussein, Asma Abd Elhameed; Shafiq, Nasir; Nuruddin, Muhd Fadhil

    2015-05-01

    Agricultural and industrial by-products are commonly used in concrete production as cement replacement materials (CRMs) or as admixtures to enhance both fresh and hardened properties of concrete as well as to save the environment from the negative effects caused by their disposal. Sugar Cane Bagasse Ash (SCBA) is one of the promising CRMs, it is used as a partial replacement of cement for producing concrete; properties of such concrete depend on the chemical composition, fineness, and burning temperature of SCBA. Approximately 1500 Million tons of sugarcane are annually produced over all the world which leave about 40-45% bagasse after juice crushing for sugar industry giving an average annual production of about 600 Million tons of bagasse as a waste material. This paper presents some findings on the effect of SCBA on workability, compressive strength and microstructure of interfacial zone of concrete and its performance is compared to some of the established CRMs namely Densified Silica Fume, Fly Ash and Microwave Incinerated Rice Husk Ash.

  2. Upper Mantle Structure beneath Afar: inferences from surface waves.

    Sicilia, D.; Montagner, J.; Debayle, E.; Lepine, J.; Leveque, J.; Cara, M.; Ataley, A.; Sholan, J.

    2001-12-01

    The Afar hotspot is related to one of the most important plume from a geodynamic point of view. It has been advocated to be the surface expression of the South-West African Superswell. Below the lithosphere, the Afar plume might feed other hotspots in central Africa (Hadiouche et al., 1989; Ebinger & Sleep, 1998). The processes of interaction between crust, lithosphere and plume are not well understood. In order to gain insight into the scientific issue, we have performed a surface-wave tomography covering the Horn of Africa. A data set of 1404 paths for Rayleigh waves and 473 paths for Love waves was selected in the period range 45-200s. They were collected from the permanent IRIS and GEOSCOPE networks and from the PASSCAL experiment, in Tanzania and Saudi Arabia. Other data come from the broadband stations deployed in Ethiopia and Yemen in the framework of the French INSU program ``Horn of Africa''. The results presented here come from a path average phase velocities obtained with a method based on a least-squares minimization (Beucler et al., 2000). The local phase velocity distribution and the azimuthal anisotropy were simultaneously retrieved by using the tomographic technique of Montagner (1986). A correction of the data is applied according to the crustal structure of the 3SMAC model (Nataf & Ricard, 1996). We find low velocities down to 200 km depth beneath the Red Sea, the Gulf of Aden, Afars, the Ethiopian Plateau and southern Arabia. High velocities are present in the eastern Arabia and the Tanzania Craton. The anisotropy beneath Afar seems to be complex, but enables to map the flow pattern at the interface lithosphere-asthenosphere. The results presented here are complementary to those obtained by Debayle et al. (2001) at upper-mantle transition zone depths using waveform inversion of higher Rayle igh modes.

  3. Unraveling the channel–lobe transition zone with high-resolution AUV bathymetry: Navy Fan, offshore Baja California, Mexico

    Carvajal, Cristian; Paull, Charles K.; Caress, David W.; Fildani, Andrea; Lundsten, Eve M.; Anderson, Krystle; Maier, Katherine L.; McGann, Mary; Gwiazda, Roberto; Herguera, Juan Carlos

    2017-01-01

    Ultra-high-resolution (1 m * 1 m * 0.25 m) bathymetry was acquired with an autonomous underwater vehicle (AUV) over a sector of the Navy Fan offshore Baja California. The survey specifically targeted an area where the former interpretation of the fan showed a channel–lobe transition; however, the lobe and the transition were not recognized. Instead, the newly acquired bathymetry shows that the previously identified channel continues basinward changing its overall morphology and stratigraphic architecture, becoming gradually but significantly wider (650–1000 m) and of lower relief (3–4 m). Cores from the channel thalweg recovered mud-poor (< 5%) well-sorted sands, interpreted as deposited by fully turbulent flows. The cores also show several mud-rich (9–18%) poorly sorted sands, probably indicating deposition from more cohesive flows.The high-resolution bathymetry shows large sectors of the seafloor sculpted by elaborate bedforms and scours. The overbank area north of the channel exhibits the most numerous and prominent scours, interpreted to have been largely generated by flow stripping at a bend in the channel. Along high-gradient sectors (more than approximately 1¯) of this area, the scours are largest and deepest. Some of these scours show an erosional headwall and a distal upflow-dipping depositional bulge, forming repetitive bedforms interpreted as erosional cyclic steps associated with locked-in-place trains of hydraulic jumps. The scours seem to coalesce to form an incipient channel, which would likely drive the avulsion of the main channel. Further basinward, average gradients decrease (< 0.6¯ ) and scours become smaller and less deep suggesting a gradient control on erosion. The southern channel margin and adjacent overbank area exhibit a trend of scours that are elongated transverse to flow, that successively repeat themselves basinwards, and that at times merge with sediment waves. Probably these scours are genetically linked to sediment waves

  4. Sr-Nd evidence of paleoproterozoic mantle metasomatism in the lithospheric mantle beneath northeastern Brazil

    Hollanda, M.H.B.M.; Pimentel, M.M.; Jardim de Sa, E.F

    2001-01-01

    In the Borborema Province (Northeastern Brazil), the Brasiliano/Pan-African Cycle is expressed by two prominent and penecontemporaneous features: a regional network of transcurrent shear zones and associated large granitoid magmatism. The Rio Grande do Norte Domain (RGND) is an orogenic domain located in the northeastern part of the Borborema Province, and its tectonic evolution is largely related to the Brasiliano orogeny (ca. 600 Ma). This domain includes four major tectonic terranes, which are represented by two metavolcanosedimentary sequences Jaguaribe-Oeste Potiguar and Serido belts, and its gneiss-migmatite Paleoproterozoic basement the Rio Piranhas and Sao Jose de Campestre massifs (Brito Neves et al., 2000). The rocks have been metamorphosed up to the amphibolite facies. Its deformational fabrics are dominated by extensive Brasiliano ductile shear zones displaying predominantly dextral transcurrent kinematic regime. These structures control the emplacement of several Neoproterozoic granitoid intrusions which are made up mainly by porphyritic granitoid suites with subalkaline monzonitic affinity. These occur as isolated plutons of various sizes or as composite intrusions, associated with basic-tointermediate suites. In the latter case, magma mingling and mixing attest that these are contemporaneous igneous suites. Several features suggest coeval relationships with granitic magmas, possibly implying processes such as assimilation or magma mixing. Field evidence of magma mixing include (i) extensive capture of feldspar phenocrysts of the acid mushes by the basic magmas, (ii) common presence of globular to ellipsoidal basic enclaves in the granitic suites, (iii) stockwork-type features consisting of felsic material veining through a diorite host and (iv) syn-plutonic basic dykes intruded into the porphyritic granites (Jardim de S 1994). In this work, Rb-Sr and Sm-Nd isotopic compositions from six distinct basic-to-intermediate suites were investigated to

  5. Topography of upper mantle seismic discontinuities beneath the North Atlantic: the Azores, Canary and Cape Verde plumes

    Saki, Morvarid; Thomas, Christine; Nippress, Stuart E. J.; Lessing, Stephan

    2015-04-01

    We are mapping the topography of upper mantle seismic discontinuities beneath the North Atlantic and surrounding regions by using precursor arrivals to PP and SS seismic waves that reflect off the seismic discontinuities. Many source-receiver combinations have been used in order to collect a large dataset of reflection points beneath our investigating area. We analyzed over 1700 seismograms from MW>5.8 events using array seismic methods to enhance the signal to noise ratio. The measured time lag between PP (SS) arrivals and their corresponding precursors on robust stacks are used to measure the depth of the transition zone boundaries. The reflectors' depths show a correlation between the location of hotspots and a significantly depressed 410 km discontinuity indicating a temperature increase of 200-300 K compared to the surrounding mantle. For the 660 km discontinuity three distinct behaviours are visible: i) normal depths beneath Greenland and at a distance of a few hundred kilometres away from the hotspots and ii) shallower 660 km discontinuity compared with the global average value near hotspots closer to the Mid-Atlantic Ridge and iii) very few observations of a 660 km discontinuity at the hotspot locations. We interpret our observations as a large upwelling beneath the southern parts of our study region, possibly due to the South Atlantic convection cell. The thermal anomaly may be blocked by endothermic phase transformation and likely does not extend through the top of the transition zone as whole except for those branches which appear as the Azores, Canaries and Cape Verde hotspots at the surface.

  6. Diagnosis of lesions of the acetabular labrum, of the labral-chondral transition zone, and of the cartilage in femoroacetabular impingement: Correlation between direct magnetic resonance arthrography and hip arthroscopy.

    Crespo Rodríguez, A M; de Lucas Villarrubia, J C; Pastrana Ledesma, M A; Millán Santos, I; Padrón, M

    2015-01-01

    To determine the sensitivity and accuracy of direct MR arthrography in the diagnosis of intra-articular lesions associated with femoroacetabular impingement. We used direct MR arthrography to study 51 patients with femoroacetabular impingement who underwent arthroscopic hip surgery. Surgery demonstrated 37 labral tears, 44 lesions in the labral-chondral transitional zone, and 40 lesions of the articular cartilage. We correlated the findings at preoperative direct MR arthrography with those of hip arthroscopy and calculated the sensitivity, specificity, positive predictive value, negative predictive value, and validity index for direct MR arthrography. The sensitivity and specificity of MR arthrography were 94.5% and 100%, respectively, for diagnosing labral tears, 100% and 87.5%, respectively, for diagnosing lesions of the labral-chondral transition zone, and 92.5% and 54.5%, respectively, for diagnosing lesions of the articular cartilage. The negative predictive value of MR arthrography for lesions of the labral-chondral transitional zone was 100%. MR arthrography accurately defined extensive lesions of the cartilage and the secondary osseous changes (the main factor in poor prognosis), although its diagnostic performance was not so good in small chondral lesions. In patients with femoroacetabular impingement, direct MR arthrography can adequately detect and characterize lesions of the acetabular labrum and of the labral-chondral transitional zone as well as extensive lesions of the articular cartilage and secondary osseous changes. Copyright © 2013 SERAM. Published by Elsevier España, S.L.U. All rights reserved.

  7. Magnetic field reversals, polar wander, and core-mantle coupling.

    Courtillot, V; Besse, J

    1987-09-04

    True polar wander, the shifting of the entire mantle relative to the earth's spin axis, has been reanalyzed. Over the last 200 million years, true polar wander has been fast (approximately 5 centimeters per year) most of the time, except for a remarkable standstill from 170 to 110 million years ago. This standstill correlates with a decrease in the reversal frequency of the geomagnetic field and episodes of continental breakup. Conversely, true polar wander is high when reversal frequency increases. It is proposed that intermittent convection modulates the thickness of a thermal boundary layer at the base of the mantle and consequently the core-to-mantle heat flux. Emission of hot thermals from the boundary layer leads to increases in mantle convection and true polar wander. In conjunction, cold thermals released from a boundary layer at the top of the liquid core eventually lead to reversals. Changes in the locations of subduction zones may also affect true polar wander. Exceptional volcanism and mass extinctions at the Cretaceous-Tertiary and Permo-Triassic boundaries may be related to thermals released after two unusually long periods with no magnetic reversals. These environmental catastrophes may therefore be a consequence of thermal and chemical couplings in the earth's multilayer heat engine rather than have an extraterrestrial cause.

  8. Water contents of clinopyroxenes from sub-arc mantle peridotites

    Turner, Michael; Turner, Simon; Blatter, Dawnika; Maury, Rene; Perfit, Michael; Yogodzinski, Gene

    2017-01-01

    One poorly constrained reservoir of the Earth's water budget is that of clinopyroxene in metasomatised, mantle peridotites. This study presents reconnaissance Sensitive High-Resolution, Ion Microprobe–Stable Isotope (SHRIMP–SI) determinations of the H2O contents of (dominantly) clinopyroxenes in rare mantle xenoliths from four different subduction zones, i.e. Mexico, Kamchatka, Philippines, and New Britain (Tabar-Feni island chain) as well as one intra-plate setting (western Victoria). All of the sub-arc xenoliths have been metasomatised and carry strong arc trace element signatures. Average measured H2O contents of the pyroxenes range from 70 ppm to 510 ppm whereas calculated bulk H2O contents range from 88 ppm to 3 737 ppm if the variable presence of amphibole is taken into account. In contrast, the intra-plate, continental mantle xenolith from western Victoria has higher water contents (3 447 ppm) but was metasomatised by alkali and/or carbonatitic melts and does not carry a subduction-related signature. Material similar to the sub-arc peridotites can either be accreted to the base of the lithosphere or potentially be transported by convection deeper into the mantle where it will lose water due to amphibole breakdown.

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

    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

  10. Slabs and plumes crossing a broad density/viscosity discontinuity in the mid lower mantle (Invited)

    Morra, G.; Yuen, D. A.; Cammarano, F.

    2010-12-01

    The depth-dependence of the viscosity is not well constrained by observations alone. Non-monotonic viscosity profiles have been often proposed in the past and are in the range of possible solutions. Such viscosity structures find new vigor on the light of recent discoveries of iron-spin transition in mantle minerals and their consequences on seismic interpretation [1] and dynamical evolution of the mantle. Using the recently introduced Multipole-Accelerated Boundary Element Method, we study the entire space of possible models of plumes and slabs crossing a broad region where mantle viscosity and/or density are non-monotonic [2]. The viscosity peak considered are 1, to 100 times then the rest of the mantle, while the density step considered is 0 to 2% different from the adiabatic profile. We identify the critical viscosity and density profiles that produce stalling or penetration of slabs and the continuous or intermittent penetration of plumes through the mid lower mantle. Based on our results, we envisage possible dynamic scenarios that would separate the mantle in two regions,suggesting a long term bifurcation originating, probably, from the spin transition itself. References: [1] Cammarano, F.; Marquardt, H.; Speziale, S.; Tackley, P. J., 2010, Role of iron-spin transition in ferropericlase on seismic interpretation: A broad thermochemical transition in the mid mantle? Geophysical Research Letters, Volume 37, Issue 3, CiteID L03308 [2] G. Morra, D. A. Yuen, L. Boschi, P. Chatelain, P. Koumoutzakos and P. Tackley, 2010, The fate of the slabs interacting with a smooth viscosity discontinuity in the mid lower mantle, Physics of the Earth and Planetary Interiors, Volume 180, Issues 3-4, 271-282, doi:10.1016/j.pepi.2010.04.001

  11. Insights from 3D numerical simulations on the dynamics of the India-Asia collision zone

    Pusok, A. E.; Kaus, B.; Popov, A.

    2013-12-01

    The dynamics of the India-Asia collision zone remains one of the most remarkable topics of the current research interest: the transition from subduction to collision and uplift, followed by the rise of the abnormally thick Tibetan plateau, and the deformation at its Eastern and Western syntaxes, are processes still not fully understood. Models that have addressed this topic include wholescale underthrusting of Indian lithospheric mantle under Tibet, distributed homogeneous shortening or the thin-sheet model, slip-line field model for lateral extrusion or lower crustal flow models for the exhumation of the Himalayan units and lateral spreading of the Tibetan plateau. Of these, the thin-sheet model has successfully illustrated some of the basic physics of continental collision and has the advantage of a 3D model being reduced to 2D, but one of its major shortcomings is that it cannot simultaneously represent channel flow and gravitational collapse of the mantle lithosphere, since these mechanisms require the lithosphere to interact with the underlying mantle, or to have a vertically non-homogeneous rheology. As a consequence, 3D models are emerging as powerful tools to understand the dynamics of coupled systems. However, because of yet recent developments and various complexities, the current 3D models simulating the dynamics of continent collision zones have relied on certain explicit assumptions, such as replacing part of the asthenosphere with various types of boundary conditions that mimic the effect of mantle flow, in order to focus on the lithospheric/crustal deformation. Here, we employ the parallel 3D code LaMEM (Lithosphere and Mantle Evolution Model), with a finite difference staggered grid solver, which is capable of simulating lithospheric deformation while simultaneously taking mantle flow and a free surface into account. We present qualitative results on lithospheric and upper-mantle scale simulations in which the Indian lithosphere is subducted and

  12. Dehydration of δ-AlOOH in the lower mantle

    Piet, H.; Shim, S. H.; Tappan, J.; Leinenweber, K. D.; Greenberg, E.; Prakapenka, V. B.

    2017-12-01

    Hydrous phase δ-AlOOH is an important candidate for water transport and storage in the Earth's deep mantle [1]. Knowing the conditions, under which it is stable and dehydrated, is therefore important for understanding the water transportation to the deep mantle or even to the core. A few experimental studies [1, 2] have shown that δ-AlOOH may be stable in cold descending slabs while it is dehydrated into a mixture of corundum and water under normal mantle conditions, up to 25 GPa. A subsequent study [3] reported the stability of δ-AlOOH in cold descending slabs to the core-mantle boundary conditions (2300 K at 135 GPa). However, the dehydration of δ-AlOOH has not bee directly observed in the experiments conducted at pressures above 25 GPa. We have synthesized δ-AlOOH from diaspore and Al(OH)3 in multi-anvil press at ASU. The sample was mixed with Au for coupling with near IR laser beams and loaded in diamond-anvil cells. We performed the laser-heated diamond anvil cell experiments at the 13IDD beamline of the Advanced Photon Source and ASU. At APS, we measured X-ray diffraction patterns at in situ high pressure and temperature. We observed the appearance of the corundum diffraction lines at 1700-2000 K and 55-90 GPa, indicating the dehydration of δ-AlOOH to Al2O3+ H2O. We found that the transition occurs over a broad range of temperature (500 K). We also observed that the dehydration of δ-AlOOH was accompanied by sudden change in laser coupling, most likely due to the release of fluids. The property change also helps us to determine the dehydration at ASU without in situ XRD. Our new experimental results indicate that δ-AlOOH would be stable in most subducting slabs in the deep mantle. However, because the dehydration occurs very close to the temperatures expected for the lower mantle, its stability is uncertain in the normal mantle. [1] Ohtani et al. 2001, Stability field of new hydrous phase, delta-AlOOH, Geophysical Research Letters 28, 3991-3993. [2

  13. Evolution of the Oxidation State of the Earth's Mantle

    Danielson, L. R.; Righter, K.; Keller, L.; Christoffersen, E.; Rahman, Z.

    2015-01-01

    The oxidation state of the Earth's mantle during formation remains an unresolved question, whether it was constant throughout planetary accretion, transitioned from reduced to oxidized, or from oxidized to reduced. We investigate the stability of Fe3(+) at depth, in order to constrain processes (water, late accretion, dissociation of FeO) which may reduce or oxidize the Earth's mantle. In our previous experiments on shergottite compositions, variable fO2, T, and P less than 4 GPa, Fe3(+)/sigma Fe decreased slightly with increasing P, similar to terrestrial basalt. For oxidizing experiments less than 7GPa, Fe3(+)/sigma Fe decreased as well, but it's unclear from previous modelling whether the deeper mantle could retain significant Fe3(+). Our current experiments expand our pressure range deeper into the Earth's mantle and focus on compositions and conditions relevant to the early Earth. Preliminary multi-anvil experiments with Knippa basalt as the starting composition were conducted at 5-7 GPa and 1800 C, using a molybdenum capsule to set the fO2 near IW, by buffering with Mo-MoO3. TEM and EELS analyses revealed the run products quenched to polycrystalline phases, with the major phase pyroxene containing approximately equal to Fe3(+)/2(+). Experiments are underway to produce glassy samples that can be measured by EELS and XANES, and are conducted at higher pressures.

  14. Crust-mantle contribution to Andean magmatism

    Ruiz, J; Hildreth, W; Chesley, J

    2001-01-01

    There has long been great interest in quantifying the contributions of the continental crust to continental arc magmas, such as those of the Andes using osmium isotopes (Alves et al., 1999; Borg et al., 2000; Brandon et al., 1996; McInnes et al., 1999). In general, Andean volcanic rocks of all compositions show relatively low Sr-isotope ratios and positive to mildly negative epsilon Nd values. Nonetheless, in the Southern Volcanic Zone of central Chile, basalt-andesite-dacite volcanoes along the Quaternary volcanic front were shown (by Hildreth and Moorbath, 1988) to have latitudinally systematic chemical variations, as well as a monotonic increase in 87Sr/Sr86 from ca. 0.7035 to 0.7055 and a decrease in epsilon Nd values from ca. +3 to -1. The isotopic variations correlate with basement elevation of the volcanic edifices and with Bouguer gravity anomalies, both of which are thought to reflect along-arc variations in thickness and average age of the underlying crust. Volcanoes with the most evolved isotopic signatures were fed through the thickest crust. Correlation of chemical and isotopic variations with crustal thickness was interpreted to be caused by Melting (of deep-crustal host rocks), Assimilation, Storage, and Homogenization (MASH) of mantle-derived magmas in long-lived lower-crustal reservoirs beneath each center prior to eruption. We have now determined Os-isotope ratios for a sample suite from these volcanoes (33-36 S lat.), representing a range of crustal thickness from ca. 60-35 km. The samples range in MgO from ca. 8-4% and in SiO2 from 51-57%. The most evolved eruptive products occur above the thickest crust and have 87Sr/86Sr ratios of 0.7054 and epsilon Nd values of -1.5. The 187Os/188Os ratios correlate with the other isotopic systems and with crustal thickness. Volcanoes on the thinnest crust have 187Os/188Os ratios of 0.18-0.21. Those on the thickest crust have 187Os/188Os ratios as high as 0.64. All the Os values are much too radiogenic to

  15. Erosion Potential of a Burn Site in the Mojave-Great Basin Transition Zone: Interim Summary of One Year of Measurements

    Etyemezian, V.; Shafer, D.; Miller, J.; Kavouras, I.; Campbell, S.; DuBois, D.; King, J.; Nikolich, G.; Zitzer, S.

    2010-05-18

    A historic return interval of 100 years for large fires in deserts in the Southwest U.S. is being replaced by one where fires may reoccur as frequently as every 20 to 30 years. This increase in fires has implications for management of Soil Sub-Project Corrective Action Units (CAUs) for which the Department of Energy, National Nuclear Security Administration Nevada Site office (NNSA/NSO) has responsibility. A series of studies has been initiated at uncontaminated analog sites to better understand the possible impacts of erosion and transport by wind and water should contaminated soil sites burn over to understand technical and perceived risk they might pose to site workers and public receptors in communities around the NTS, TTR, and NTTR; and to develop recommendations for stabilization and restoration after a fire. The first of these studies was undertaken at the Jacob fire, a lightning-caused fire approximately 12 kilometers north of Hiko, Nevada, that burned approximately 200 ha between August 6-8, 2008, and is representative of a transition zone on the NTS between the Mojave and Great Basin Deserts, where the largest number of Soil Sub-Project CAUs/CASs are located.

  16. Rapid change of chromomeric and pairing patterns of polytene chromosome tips in D. melanogaster: migration of polytene-nonpolytene transition zone?

    Roberts, P A

    1979-07-01

    The high variability of chromomeric patterns in near-terminal regions of polytene chromosome arms has been explored in a number of races, strains and hybrids of Drosophila melanogaster. Traditional explanations for tip differences between strains (differential compaction of chromatin, somatic or germinal deletion) are examined and, in the light of the reported observations, rejected. The range of polytene tip variability and rates of change in wild races are greater than has been supposed: strains formerly considered to be terminally deleted appear to gain terminal bands; others, formerly considered normal, appear to have lost them. Strains with high cell-to-cell tip variability are also described. Cell-to-cell variations, as well as much of the observed rapid changes in tip appearance, are probably due to heritable differences in the location of an abrupt transition zone between polytene and nonpolytene chromatin. A quantitative relationship between the amount of certain subterminal bands present and the frequency of tip association of nonhomologous chromosomes is shown and its possible significance for chromosome is shown and its possible for chromosome pairing discussed.

  17. Optical measurements in the North Sea-Baltic Sea transition zone. I. On the origin of the deep water in the Kattegat

    Højerslev, N. K.; Holt, N.; Aarup, T.

    1996-08-01

    In the North Sea-Baltic Sea region, several studies have shown that yellow substance can be treated as a quasi-conservative parameter that is negatively correlated with salinity. A review of more than 5000 historic and recently gathered yellow substance absorption and salinity measurements from the transition zone between the North Sea and the Baltic Sea have been analyzed for the purpose of water mass identification. Salinity-yellow substance scatter plots show that three water masses can be identified in the area: (1) North Sea water (high salinity, low yellow substance content); (2) Baltic Sea water (low salinity, intermediate-high yellow substance content); and (3) German Bight/Southern North Sea water (intermediate-high salinity, high yellow substance content). Based on the volume flow estimates used in a two-layer box-model of the Kattegat (Jørgensen, Continental Shelf Research, 12, 103-114, 1992) and conservation of yellow substance, it is argued that the long-term average composition of the bottom layer inflow to the Kattegat from the Skagerrak consists of about 90% North Sea/Atlantic water and 10% German Bight/Southern North Sea water. The German Bight content estimate is substantially lower than the ones given in earlier studies (50-67%) and implies that the Jutland Coastal Current only has a small impact on the water quality of the Kattegat.

  18. Development and validation of a logistic regression model to distinguish transition zone cancers from benign prostatic hyperplasia on multi-parametric prostate MRI

    Iyama, Yuji [Kumamoto Chuo Hospital, Department of Diagnostic Radiology, Kumamoto, Kumamoto (Japan); Kumamoto University, Department of Diagnostic Radiology, Graduate School of Medical Sciences, Kumamoto, Kumamoto (Japan); Nakaura, Takeshi; Nagayama, Yasunori; Utsunomiya, Daisuke; Yamashita, Yasuyuki [Kumamoto University, Department of Diagnostic Radiology, Graduate School of Medical Sciences, Kumamoto, Kumamoto (Japan); Katahira, Kazuhiro; Oda, Seitaro [Kumamoto Chuo Hospital, Department of Diagnostic Radiology, Kumamoto, Kumamoto (Japan); Iyama, Ayumi [National Hospital Organization Kumamoto Medical Center, Department of Diagnostic Radiology, Kumamoto, Kumamoto (Japan)

    2017-09-15

    To develop a prediction model to distinguish between transition zone (TZ) cancers and benign prostatic hyperplasia (BPH) on multi-parametric prostate magnetic resonance imaging (mp-MRI). This retrospective study enrolled 60 patients with either BPH or TZ cancer, who had undergone 3 T-MRI. We generated ten parameters for T2-weighted images (T2WI), diffusion-weighted images (DWI) and dynamic MRI. Using a t-test and multivariate logistic regression (LR) analysis to evaluate the parameters' accuracy, we developed LR models. We calculated the area under the receiver operating characteristic curve (ROC) of LR models by a leave-one-out cross-validation procedure, and the LR model's performance was compared with radiologists' performance with their opinion and with the Prostate Imaging Reporting and Data System (Pi-RADS v2) score. Multivariate LR analysis showed that only standardized T2WI signal and mean apparent diffusion coefficient (ADC) maintained their independent values (P < 0.001). The validation analysis showed that the AUC of the final LR model was comparable to that of board-certified radiologists, and superior to that of Pi-RADS scores. A standardized T2WI and mean ADC were independent factors for distinguishing between BPH and TZ cancer. The performance of the LR model was comparable to that of experienced radiologists. (orig.)

  19. Influence of the micro- and nanoscale local mechanical properties of the interfacial transition zone on impact behavior of concrete made with different aggregates

    Erdem, Savaş; Dawson, Andrew Robert; Thom, Nicholas Howard

    2012-01-01

    The influence of the microscale local mechanical properties of the interfacial transition zone (ITZ) on macro-level mechanical response and impact behavior is studied for concretes made with copper slag and gravel aggregates. 3D nanotech vertical scanning interferometry, scanning electron microscopy coupled with energy dispersive X-ray micro-analysis, digital image analysis, and 3D X-ray computed tomography were used to characterize the microstructures and the ITZs. It was deduced that a stronger and denser ITZ in the copper slag specimen would reduce its vulnerability to stiffness loss and contribute to its elastic and more ductile response under impact loading. The analysis also indicated that a significant degeneration in the pore structure of the gravel specimen associated with a relatively weaker and non-homogeneous ITZ occurred under impact. Finally, it was also concluded that increased roughness of ITZ may contribute to the load-carrying capacity of concrete under impact by improving contact point interactions and energy dissipation.

  20. Pilot study of a novel tool for input-free automated identification of transition zone prostate tumors using T2- and diffusion-weighted signal and textural features.

    Stember, Joseph N; Deng, Fang-Ming; Taneja, Samir S; Rosenkrantz, Andrew B

    2014-08-01

    To present results of a pilot study to develop software that identifies regions suspicious for prostate transition zone (TZ) tumor, free of user input. Eight patients with TZ tumors were used to develop the model by training a Naïve Bayes classifier to detect tumors based on selection of most accurate predictors among various signal and textural features on T2-weighted imaging (T2WI) and apparent diffusion coefficient (ADC) maps. Features tested as inputs were: average signal, signal standard deviation, energy, contrast, correlation, homogeneity and entropy (all defined on T2WI); and average ADC. A forward selection scheme was used on the remaining 20% of training set supervoxels to identify important inputs. The trained model was tested on a different set of ten patients, half with TZ tumors. In training cases, the software tiled the TZ with 4 × 4-voxel "supervoxels," 80% of which were used to train the classifier. Each of 100 iterations selected T2WI energy and average ADC, which therefore were deemed the optimal model input. The two-feature model was applied blindly to the separate set of test patients, again without operator input of suspicious foci. The software correctly predicted presence or absence of TZ tumor in all test patients. Furthermore, locations of predicted tumors corresponded spatially with locations of biopsies that had confirmed their presence. Preliminary findings suggest that this tool has potential to accurately predict TZ tumor presence and location, without operator input. © 2013 Wiley Periodicals, Inc.

  1. Factors influencing smallholder farmers' behavioural intention towards adaptation to climate change in transitional climatic zones: A case study of Hwedza District in Zimbabwe.

    Zamasiya, Byron; Nyikahadzoi, Kefasi; Mukamuri, Billy Billiard

    2017-08-01

    This paper examines factors influencing behavioural change among smallholder farmers towards adaptation to climate change in transitional climatic zones of Africa, specifically, Hwedza District in Zimbabwe. Data for this study were collected from 400 randomly-selected smallholder farmers, using a structured questionnaire, focus group discussions and key informant interviews. The study used an ordered logit model to examine the factors that influence smallholder farmers' behavioural intention towards adaptation to climate change. Results from the study show that the gender of the household head, access to extension services on crop and livestock production, access to climate information, membership to social groups and experiencing a drought have a positive influence on farmers' attitude towards adaptation to climate change and variability. The study concluded that although the majority of smallholder farmers perceive that the climate is changing, they continue to habour negative attitudes towards prescribed climate change adaptation techniques. This study recommends more education on climate change, as well as adaptation strategies for both agricultural extension workers and farmers. This can be complemented by disseminating timely climate information through extension officers and farmers' groups. Copyright © 2017 Elsevier Ltd. All rights reserved.

  2. Palaeoenvironmental implications of a Holocene sequence of lacustrine-peat sediments from the desert-loess transitional zone in Northern China

    Jia, Feifei; Lu, Ruijie; Liu, Xiaokang; Zhao, Chao; Lv, Zhiqiang; Gao, Shangyu

    2018-05-01

    A high-resolution lacustrine-peat record from the desert-loess transitional zone in Northern China was obtained to reconstruct Holocene environmental change in the region. AMS 14C dates are used to provide a chronology. The results indicate that the site was a desert environment before 12.2 cal kyr BP, and was then occupied by a paleolake which started to shrink, with a wetland occurring from 6.2 to 3.0 cal kyr BP. Subsequently, the site became a seasonally water-filled depression. Based on the lithology and measurements of grain size and total organic carbon content, the climate changed from arid to humid at 12.2 cal kyr BP, and became more humid after 8.3 cal kyr BP. From 6.2 to 3.0 cal kyr BP, precipitation decreased but the climate remained at an optimum. After 3.0 cal kyr BP, the climate was dry overall but with several humid intervals. A comparison of paleoclimatic records from lacustrine and aeolian deposits from the region reveals a discrepancy about the nature of the early Holocene climate, and we conclude that this is because lacustrine sediments responded more sensitively to precipitation than aeolian deposits when the temperature was low. The environmental evolution of the region was synchronous with changes in the Asian summer monsoon (ASM), but temperature also played a key role in the early Holocene.

  3. Deformation, Fluid Flow and Mantle Serpentinization at Oceanic Transform Faults

    Rupke, L.; Hasenclever, J.

    2017-12-01

    Oceanic transform faults (OTF) and fracture zones have long been hypothesized to be sites of enhanced fluid flow and biogeochemical exchange. In this context, the serpentine forming interaction between seawater and cold lithospheric mantle rocks is particularly interesting. The transformation of peridotite to serpentinite not only leads to hydration of oceanic plates and is thereby an important agent of the geological water cycle, it is also a mechanism of abiotic hydrogen and methane formation, which can support archeal and bacterial communities at the seafloor. Inferring the likely amount of mantle undergoing serpentinization reactions therefore allows estimating the amount of biomass that may be autotrophically produced at and around oceanic transform faults and mid-ocean ridges Here we present results of 3-D geodynamic model simulations that explore the interrelations between deformation, fluid flow, and mantle serpentinization at oceanic transform faults. We investigate how slip rate and fault offset affect the predicted patterns of mantle serpentinization around oceanic transform faults. Global rates of mantle serpentinization and associated H2 production are calculated by integrating the modeling results with plate boundary data. The global additional OTF-related production of H2 is found to be between 6.1 and 10.7 x 1011 mol per year, which is comparable to the predicted background mid-ocean ridge rate of 4.1 - 15.0 x 1011 mol H2/yr. This points to oceanic transform faults as potential sites of intense fluid-rock interaction, where chemosynthetic life could be sustained by serpentinization reactions.

  4. Cascading ecohydrological transitions: Multiple changes in vegetation and hydrology over the past 500 years for a semiarid forest/woodland boundary zone in New Mexico, USA

    Allen, Craig D.

    2010-05-01

    On decadal and centennial time scales, multiple drivers can cause substantial changes in vegetation cover, which can trigger associated changes in runoff and erosion patterns and processes, with consequent feedbacks to the vegetation - cumulatively this can lead to a cascading series of non-equilibrial ecosystem changes through time. The work reported here provides a relatively detailed 500-year perspective of such changes on the mesas the eastern Jemez Mountains in northern New Mexico (USA), which today exhibit vegetation transitions along an elevational gradient between semiarid ponderosa pine (Pinus ponderosa) forests, mixed woodlands dominated by piñon (Pinus edulis) and one-seed juniper (Juniperus monosperma), and juniper savannas. Using multiple lines of evidence, a history of major ecosystem changes since ca. 1500 A.D. is reconstructed for a dynamic transition zone on one such mesa (Frijolito Mesa). Evidence includes intensive archaeological surveys, dendrochronological reconstructions of the demographic and spatial patterns of establishment and mortality for these three main tree species, dendrochronological reconstructions of fire regimes and climate patterns, broad-scale mapping of vegetation changes from historic aerial photographs since 1935, monitoring of vegetation from permanent transects since 1991, detailed soil maps and interpretations, intensive ecohydrological studies since 1993 on portions of this mesa, and research on the ecosystem effects of an experimental tree-thinning experiment conducted in 1997. Frijolito Mesa was fully occupied by large numbers of Native American farmers from the A.D. 1200's until the late 1500's, when they left these mesas for settlements in the adjoining Rio Grande Valley. Archaeological evidence and tree ages indicate that the mesa was likely quite deforested when abandoned, followed by episodic tree establishment dominated by ponderosa pine during the Little Ice Age. By the late 1700's Frijolito Mesa included

  5. Heat transfer correlations in mantle tanks

    Furbo, Simon; Knudsen, Søren

    2005-01-01

    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...... 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......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...

  6. Chemical provinces and dynamic melting of the NE Atlantic mantle

    Tronnes, R. G.

    2009-12-01

    Low-degree melting of fertile parts of the NE Atlantic mantle yields primitive alkaline basalts in the Icelandic off-rift zones and at Jan Mayen. Olivine tholeiites in the Icelandic rift zones and oceanic spreading ridges are formed by protracted decompressional melting. The V-shaped ridges SW and NE of Iceland indicate that rising, hot material is supplied by a pulsating plume and deflected laterally for distances of about 1000 km from Iceland (Jones et al. GGG 2002; Breivik et al. JGR 2006). Plume material deflected along the rift zones and spreading ridges undergoes mixing with the ambient asthenosphere and extensive melting at shallow level, whereas material deflected in other directions may flow laterally at deeper levels and remain largely unmelted and fertile. A recent investigation of a suite of primitive off-rift basalts from Iceland and Jan Mayen (Debaille et al., 2009, GCA) demonstrated an important source contribution from subcontinental lithospheric mantle (SCLM). Available data on the primitive off-rift basalts and tholeiitic basalts from Iceland and the NE Atlantic ridges indicates the existence of three main composite mantle components, characterized by the following relative isotope ratios (H: high, I: intermediate and L: low ratio) for 87/86Sr, 143/144Nd, 206/204Pb, 187/188Os and 3/4He, respectively: 1. Iceland plume with depleted lower mantle mixed with recycled oceanic crust: I, I, H, H, H 2. Strongly depleted and later re-enriched SCLM: H, L, I, L, L 3. Depleted asthenosphere: L, H, L, I, L The two first composite components contain enriched and depleted subcomponents with distinct isotope signatures. The isotope ratio variations between the fertile components are larger than between the refractory components. The 3/4He ratio, however, is much higher in the depleted plume component than in the depleted SCLM and asthenospheric components. The old SCLM material could in principle be recycled and embedded in the lower mantle and supplied to the

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

    Plomerova, Jaroslava; Babuska, Vladislav

    2017-04-01

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

  8. Linking Serpentinite Geochemistry with Possible Alteration and Evolution of Supra-Subduction Wedge Mantle

    Scambelluri, M.; Cannaò, E.; Agostini, S.; Gilio, M.

    2016-12-01

    Serpentinites are able to transport and release volatiles and fluid-mobile elements (FME) found in arc magmas. Constraining the trace element compositions of these rocks and of fluids released by de-serpentinization improves our knowledge of mass transfer from subduction zones to volcanic arcs, and of the role of slab and wedge mantle in this global process. Studies of high-pressure ultramafic rocks exhumed from plate interface settings reveal the fluid/rock interactions atop the slab and the processes that can affect the mantle wedge. Alpine eclogite-facies antigorite serpentinite (Voltri Massif) and fully de-serpentinized meta-peridotite (Cima di Gagnone) are enriched in sediment-derived As, Sb, U, Pb before peak dehydration. Their Sr, Pb and B isotopic compositions are reset during prograde (forearc) interaction with slab fluids. The eclogitic garnet and olivine from the Cima di Gagnone metaperidotite trap primary inclusions of the fluid released during breakdown of antigorite and chlorite. The inclusions display FME enrichments (high Cl, S; variable Cs, Rb, Ba, B, Pb, As, Sb) indicating element release from rock