Sample records for subducted sediment composition

  1. Velocities of Subducted Sediments and Continents (United States)

    Hacker, B. R.; van Keken, P. E.; Abers, G. A.; Seward, G.


    The growing capability to measure seismic velocities in subduction zones has led to unusual observations. For example, although most minerals have VP/ VS ratios around 1.77, ratios 1.8 have been observed. Here we explore the velocities of subducted sediments and continental crust from trench to sub-arc depths using two methods. (1) Mineralogy was calculated as a function of P & T for a range of subducted sediment compositions using Perple_X, and rock velocities were calculated using the methodology of Hacker & Abers [2004]. Calculated slab-top temperatures have 3 distinct depth intervals with different dP/dT gradients that are determined by how coupling between the slab and mantle wedge is modeled. These three depth intervals show concomitant changes in VP and VS: velocities initially increase with depth, then decrease beyond the modeled decoupling depth where induced flow in the wedge causes rapid heating, and increase again at depth. Subducted limestones, composed chiefly of aragonite, show monotonic increases in VP/ VS from 1.63 to 1.72. Cherts show large jumps in VP/ VS from 1.55-1.65 to 1.75 associated with the quartz-coesite transition. Terrigenous sediments dominated by quartz and mica show similar, but more-subdued, transitions from ~1.67 to 1.78. Pelagic sediments dominated by mica and clinopyroxene show near-monotonic increases in VP/ VS from 1.74 to 1.80. Subducted continental crust that is too dry to transform to high-pressure minerals has a VP/ VS ratio of 1.68-1.70. (2) Velocity anisotropy calculations were made for the same P-T dependent mineralogies using the Christoffel equation and crystal preferred orientations measured via electron-backscatter diffraction for typical constituent phases. The calculated velocity anisotropies range from 5-30%. For quartz-rich rocks, the calculated velocities show a distinct depth dependence because crystal slip systems and CPOs change with temperature. In such rocks, the fast VP direction varies from slab-normal at

  2. Mass/age distribution and composition of sediments on the ocean floor and the global rate of sediment subduction


    Hay, William W.; Sloan, J. L.; Wold, C. N.


    The total mass of sediments on the ocean floor is estimated to be 262 × 1021 g. The overall mass/age distribution is approximated by an exponential decay curve: (11.02 × 1021 g)e−0.0355t Ma. The mass/age distribution is a function of the area/age distribution of ocean crust, the supply of sediment to the deep sea, and submarine erosion and redeposition. About 140 × 1021 g of the sediment on the ocean floor is pelagic sediment, consisting of about 74% CaCO3, with the remainder opaline silica a...

  3. Frictional behavior of carbonate-rich sediments in subduction zones (United States)

    Rabinowitz, H. S.; Savage, H. M.; Carpenter, B. M.; Collettini, C.


    preliminary results indicate that carbonate/clay compositions could have a significant impact on the frictional behavior of subducting sediments.

  4. Recycling Revisited: Where did all the Subducted Sediments go? (United States)

    Hofmann, A. W.; Chauvel, C.; Lewin, E.; Kelemen, P. B.; Hacker, B. R.


    Several lines of reasoning have revived the idea [1] that subduction has recycled continent-derived sediments into the mantle on a massive scale. For example, well-known peaks in zircon ages have been reinterpreted as reflecting variable rates of crust destruction via erosion and sediment subduction [2]. In addition, assessment of the trace element budgets of subducted sediments and arc volcanics, as well as geological and geophysical studies of accretionary wedges have led to estimates that about one mass of present-day continental crust has been returned to the mantle [3]. If these ideas are correct, then recycled sedimentary components should be present in MORB and OIB sources. As previously established, Nb/U and 87Sr/86Sr are negatively correlated in all EM2-type OIBs, clearly indicating continental/sedimentary input. However, the MORB source reservoir, being depleted in incompatible elements, is particularly susceptible to "pollution" by subducted sediments. Chauvel et al. [4] modeled the Hf-Nd isotopic array of MORBs+OIBs and concluded that it requires the addition of up to 6 % subducted sediment. We revisit this issue and show that global MORBs show no decrease in Nb/U with increasing 87Sr/86Sr, ruling out extensive addition of recycled sediment into global MORB sources. Instead, the Hf-Nd array can be obtained by recycled alkali basalts derived from subducted seamounts and ocean islands, rather than sediments. Moreover, mantle plumes with clearly identifiable sediment input contribute less than 20% of the total plume flux. We conclude that most of the subducted sediment flux is not returned to the convecting mantle. Instead, its most plausible fate is to be underplated beneath existing continental crust via "relamination" [5]. These results imply that continental recycling is subordinate and the growth of the continental crust has been largely irreversible. [1] Armstrong, 1968, Rev. Geophys. 6, 175. [2] Hawkesworth et al., 2009, Science 323, 49. [3] Porter

  5. Sediment-derived fluids in subduction zones: Isotopic evidence from veins in blueschist and eclogite of the Franciscan Complex, California

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    Nelson, B.K. (Univ. of Washington, Seattle (United States))


    Isotopic analyses of minerals from veins that cut high-grade blueschist and eclogite blocks in the central belt of the Franciscan Complex provide constraints on the chronology of metamorphic events and on the origin and movement of fluids within the subduction zone. A Rb-Sr age of 153 {plus minus}1 Ma obtained for minerals from veins and open cavities that formed contemporaneously with retrograde blueschist facies metamorphism is a minimum age for the prograde metamorphism. The veining precedes the last episode of sedimentary-matrix melange formation by a minimum 15 to 20 Ma, during which time the blocks must have been stored within the subduction complex at low temperatures and without undergoing penetrative deformation. Initial Nd-isotope compositions ({epsilon}{sub Nd}) of the vein minerals range from +10.8 to {minus}2.4, indicating that some fluids were derived predominantly from dehydration of subducted mid-ocean ridge basalt, but that other fluids had a component derived from subducted sediment. The provenance of the subducted sediment was within old continental crust, thus associating the Franciscan paleo-subduction complex with a continental craton by the time of vein formation.

  6. Tracing subducted sediment inputs to the Ryukyu arc-Okinawa Trough system: Evidence from thallium isotopes (United States)

    Shu, Yunchao; Nielsen, Sune G.; Zeng, Zhigang; Shinjo, Ryuichi; Blusztajn, Jerzy; Wang, Xiaoyuan; Chen, Shuai


    Sediments are actively subducted in virtually every arc worldwide. However, quantifying their contributions to arc lavas and thereby establishing budgets of how sediments participate in slab-mantle interaction is challenging. In this contribution we use thallium (Tl) abundances and isotopic compositions of lavas from the Ryukyu arc (including south Kyushu) and its back-arc basin, Okinawa Trough, to investigate the influence of sediments from arc to back-arc. We also present extensive geochemical data for sediments and altered oceanic crust (AOC) outboard of the northern (DSDP Sites 296, 442B, 443 and 444) and central (DSDP Sites 294 and 295) part of the Ryukyu arc. The Tl isotopic compositions of sediments change systematically from lighter outboard of northern Ryukyu arc to heavier outboard of central Ryukyu arc. The feature reflects the dominance of terrigenous material and pelagic sedimentation outboard of the northern and central Ryukyu arc, respectively. Central and northern sections of Ryukyu arc and Okinawa Trough display larger range of Tl isotopic variation than southern section, which is consistent with more pelagic provenance for sediments outboard of central and northern Ryukyu arcs than that of expected sediments outboard of southern Ryukyu arc. Identical Tl, Sr, Nd and Pb isotope variations are found when comparing arc and back arc lavas, which indicates that sediments fluxes also account for the Tl isotopic variations in the Okinawa Trough lavas. Two-end-member mixing models of Tl with Pb, Sr and Nd isotopes require sediment inputs ofsediment end members predict very similar sediment fluxes when using Tl, Sr, Nd and Pb isotopes, which indicates that fractionation of these elements must have happened after mixing between mantle and sediments. This conclusion is corroborated by model calculations of mixing between sediment melts with fractionated Sr/Nd ratios and mantle wedge, which show that no arc lava plot on such mixing lines. Thus bulk sediment

  7. Oblique subduction modelling indicates along-trench tectonic transport of sediments. (United States)

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


    Convergent plate margins are currently distinguished as 'accretional' or 'erosional', depending on the tendency to accumulate sediments, or not, at the trench. Accretion and erosion can coexist along the same margin and we have noticed that this mostly occurs where subduction is oblique. Here we show that at oblique subduction zones, sediments that enter the trench are first buried, and later migrate laterally parallel to the trench and at various depths. Lateral migration of sediments continues until they reach a physical barrier where they begin to accumulate. The accretionary wedge size decreases along the trench moving away from the barrier. We therefore suggest that the gradual variation of the accretionary wedge size and sediment amount at the trench along one single subduction zone, as observed in many active plate margins worldwide, can be explained by the lateral tectonic migration of sediments driven by obliquity of subduction as well.

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

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


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

  9. Partial Melting of Subducted Sediments Produced Early Mesozoic Calc-alkaline Lamprophyres from Northern Guangxi Province, South China. (United States)

    Su, Hui-Min; Jiang, Shao-Yong; Zhang, Dong-Yang; Wu, Xiang-Ke


    There is growing agreement that subducted sediments recycled into the deep mantle could make a significant contribution to the generation of various mantle-derived rocks. However, solid evidence and examples to support this view are few, and whether or not the subducted sediments can act as the dominating material source for the magma is unclear. Here, we report a comprehensive geochemical study that demonstrates that the newly identified Early Mesozoic calc-alkaline lamprophyres in the northern Guangxi Province, southeastern Yangtze Block in South China were likely derived in large part from the partial melting of the subducted terrigenous sediments in the deep mantle. The investigated lamprophyres are SiO2-rich minettes, characterized by moderate TFeO and MgO and high Mg# (>70). The multi-element pattern shows a typical crustal-like signature, such as enrichments in large-ion lithophile elements (LILE) and light rare earth elements (LREE) with troughs in Nb-Ta, Ti and Eu and peaks in Th-U and Pb. These rocks also show sediment-like ratios of Nb/U, Nb/Th and Ce/Pb, together with extremely radiogenic 87Sr/86Sr (0.71499-0.71919), unradiogenic 143Nd/144Nd (0.51188-0.51195) and radiogenic 207Pb/204Pb (15.701-15.718) isotopic compositions.

  10. Contrasting sediment melt and fluid signatures for magma components in the Aeolian Arc: Implications for numerical modeling of subduction systems (United States)

    Zamboni, Denis; Gazel, Esteban; Ryan, Jeffrey G.; Cannatelli, Claudia; Lucchi, Federico; Atlas, Zachary D.; Trela, Jarek; Mazza, Sarah E.; De Vivo, Benedetto


    The complex geodynamic evolution of Aeolian Arc in the southern Tyrrhenian Sea resulted in melts with some of the most pronounced along the arc geochemical variation in incompatible trace elements and radiogenic isotopes worldwide, likely reflecting variations in arc magma source components. Here we elucidate the effects of subducted components on magma sources along different sections of the Aeolian Arc by evaluating systematics of elements depleted in the upper mantle but enriched in the subducting slab, focusing on a new set of B, Be, As, and Li measurements. Based on our new results, we suggest that both hydrous fluids and silicate melts were involved in element transport from the subducting slab to the mantle wedge. Hydrous fluids strongly influence the chemical composition of lavas in the central arc (Salina) while a melt component from subducted sediments probably plays a key role in metasomatic reactions in the mantle wedge below the peripheral islands (Stromboli). We also noted similarities in subducting components between the Aeolian Archipelago, the Phlegrean Fields, and other volcanic arcs/arc segments around the world (e.g., Sunda, Cascades, Mexican Volcanic Belt). We suggest that the presence of melt components in all these locations resulted from an increase in the mantle wedge temperature by inflow of hot asthenospheric material from tears/windows in the slab or from around the edges of the sinking slab.

  11. Seawater subduction controls the heavy noble gas composition of the mantle. (United States)

    Holland, Greg; Ballentine, Chris J


    The relationship between solar volatiles and those now in the Earth's atmosphere and mantle reservoirs provides insight into the processes controlling the acquisition of volatiles during planetary accretion and their subsequent evolution. Whereas the light noble gases (helium and neon) in the Earth's mantle preserve a solar-like isotopic composition, heavy noble gases (argon, krypton and xenon) have an isotopic composition very similar to that of the modern atmosphere, with radiogenic and (in the case of xenon) solar contributions. Mantle noble gases in a magmatic CO2 natural gas field have been previously corrected for shallow atmosphere/groundwater and crustal additions. Here we analyse new data from this field and show that the elemental composition of non-radiogenic heavy noble gases in the mantle is remarkably similar to that of sea water. We challenge the popular concept of a noble gas 'subduction barrier'--the convecting mantle noble gas isotopic and elemental composition is explained by subduction of sediment and seawater-dominated pore fluids. This accounts for approximately 100% of the non-radiogenic argon and krypton and 80% of the xenon. Approximately 50% of the convecting mantle water concentration can then be explained by this mechanism. Enhanced recycling of subducted material to the mantle plume source region then accounts for the lower ratio of radiogenic to non-radiogenic heavy noble gas isotopes and higher water content of plume-derived basalts.

  12. Subduction factory in an ampoule: Experiments on sediment-peridotite interaction under temperature gradient conditions (United States)

    Woodland, A. B.; Bulatov, V. K.; Brey, G. P.; Girnis, A. V.; Höfer, H. E.; Gerdes, A.


    To better understand processes above subducted oceanic slabs, we have undertaken experiments with juxtaposed sediment and peridotite layers at pressures of 7.5 and 10.5 GPa at a controlled temperature gradient from ∼100 to ∼500 °C per a sample length of ∼3 mm. The sediment starting material contains H2O (6.9 wt%) and CO2 (5.9 wt%) and has a major-element composition similar to GLOSS (Plank and Langmuir, 1998) doped with trace elements at 10-100 ppm levels. Several experiments were conducted with ∼0.5 wt% Cl or F. The peridotite layer is composed of natural olivine (66 wt%), orthopyroxene (27 wt%) and garnet (7 wt%) mixed with ∼15 wt% graphite. Several experimental configurations were investigated, but the "basic" setup has the sediment layer at the bottom in the cold zone (400-1200 °C) overlain by peridotite at 900-1500 °C. The temperature distribution was determined by two thermocouples and orthopyroxene-garnet thermometry. Features common to many experiments are (1) the development of multiple layers of various lithologies and a pool of hydrous silicate or carbonate-silicate melt in the hottest part of the capsule; (2) replacement of olivine by orthopyroxene in the metaperidotite; (3) preservation and growth of garnet and local development of magnesite in the metaperidotite layer; (4) enrichment in garnet within the metasediment layer at the contact with the metaperidotite; (5) formation of a clinopyroxene-garnet assemblage at the bottom (the coldest part); (6) presence of K-bearing phases (phlogopite or phengite) and carbonates in the metasediment layer only at temperatures <700 °C; and (7) occurrence of accessory zircon, rutile and phosphates in the coldest regions. In terms of element redistribution, the peridotite becomes strongly enriched in SiO2 compared to the starting composition, and the sediment gains MgO, FeO and Cr2O3. Potassium is fully extracted into the melt, while Na and Ca are largely retained in the coldest part of the metasediment

  13. Sharp Permeability Transitions due to Shallow Diagenesis of Subduction Zone Sediments (United States)

    James, S.; Screaton, E.


    The permeability of hemipelagic sediments is an important factor in fluid flow in subduction zones and can be affected by porosity changes and cementation-dissolution processes acting during diagenesis. Anomalously high porosities have been observed in cores from the Shikoku Basin sediments approaching the Nankai Trough subduction zone. These high porosities have been attributed to the presence of minor amounts of amorphous silica cement that strengthen the sediment and inhibit consolidation. The porosity rapidly drops from 66-68% to 54-56% at a diagenetic boundary where the amorphous silica cement dissolves. Although the anomalous porosity profiles at Nankai have received attention, the magnitude of the corresponding permeability change has not been addressed. In this study, permeability profiles were constructed using permeability-porosity relationships from previous studies, to estimate the magnitude and rate of permeability changes with depth. The predicted permeability profiles for the Nankai Trough sediment cores indicate that permeability drops by almost one order of magnitude across the diagenetic boundary. This abrupt drop in permeability has the potential to facilitate significant changes in pore fluid pressures and thus to influence the deformation of the sediment onto the accretionary prism. At the Costa Rica subduction zone, results vary with location. Site U1414 offshore the Osa Peninsula shows porosities stable at 69% above 145 mbsf and then decrease to 54% over a 40 m interval. A porosity drop of that magnitude is predicted to correlate to an order of magnitude permeability decrease. In contrast, porosity profiles from Site 1039 offshore the Nicoya Peninsula and Site U1381 offshore the Osa Peninsula show anomalously high porosities but no sharp drop. It is likely that sediments do not cross the diagenetic boundary due to the extremely low (<10°C/km) thermal gradient at Site 1039 and the thin (<100 m) sediment cover at Site U1381. At these locations

  14. Organic matter cracking: A source of fluid overpressure in subducting sediments (United States)

    Raimbourg, Hugues; Thiéry, Régis; Vacelet, Maxime; Famin, Vincent; Ramboz, Claire; Boussafir, Mohammed; Disnar, Jean-Robert; Yamaguchi, Asuka


    The pressure of deep fluids in subduction zones is a major control on plate boundary strength and earthquake genesis. The record, by methane-rich fluid inclusions, of large ( 50-100 MPa) and instantaneous pressure variations in the Shimanto Belt (Japan) points to the presence of large fluid overpressure at depth (300-500 MPa, 250 °C). To further analyze the connection between methane and fluid overpressure, we determined with Rock-Eval the potential for a worldwide selection of deep seafloor sediments to produce methane as a result of organic matter (OM) cracking due to temperature increase during subduction. The principal factor controlling the methanogenesis potential of sediments is OM proportion, while OM nature is only a subordinate factor. In turn, OM proportion is mainly controlled by the organic terrigenous input. Considering a typical sediment from ocean-continent subduction zones, containing 0.5 wt% of type III OM, cracking of OM has two major consequences: (1) Methane is produced in sufficient concentration as to oversaturate the pore-filling water. The deep fluid in accretionary prisms is therefore a mechanical mixture of water-rich and methane-rich phases; (2) CH4 production can generate large fluid overpressure, of the order of several tens of MPa, The conditions for these large overpressure are a low permeability of the upper plate (z > 10 km) where OM thermal cracking occurs. At these depths, OM thermal cracking appears as a source of overpressure larger than the last increments of smectite-to-illite reaction. Such large overpressures play potentially a role in facilitating slip along the plate interface. Conversely, the scarcity of earthquakes in ocean-ocean subduction zones such as Marianna or Barbados may be related to the low influx of detrital OM and the limited methane/overpressure generation at depth.

  15. Distribution of dehalogenation activity in subseafloor sediments of the Nankai Trough subduction zone. (United States)

    Futagami, Taiki; Morono, Yuki; Terada, Takeshi; Kaksonen, Anna H; Inagaki, Fumio


    Halogenated organic matter buried in marine subsurface sediment may serve as a source of electron acceptors for anaerobic respiration of subseafloor microbes. Detection of a diverse array of reductive dehalogenase-homologous (rdhA) genes suggests that subseafloor organohalide-respiring microbial communities may play significant ecological roles in the biogeochemical carbon and halogen cycle in the subseafloor biosphere. We report here the spatial distribution of dehalogenation activity in the Nankai Trough plate-subduction zone of the northwest Pacific off the Kii Peninsula of Japan. Incubation experiments with slurries of sediment collected at various depths and locations showed that degradation of several organohalides tested only occurred in the shallow sedimentary basin, down to 4.7 metres below the seafloor, despite detection of rdhA in the deeper sediments. We studied the phylogenetic diversity of the metabolically active microbes in positive enrichment cultures by extracting RNA, and found that Desulfuromonadales bacteria predominate. In addition, for the isolation of genes involved in the dehalogenation reaction, we performed a substrate-induced gene expression screening on DNA extracted from the enrichment cultures. Diverse DNA fragments were obtained and some of them showed best BLAST hit to known organohalide respirers such as Dehalococcoides, whereas no functionally known dehalogenation-related genes such as rdhA were found, indicating the need to improve the molecular approach to assess functional genes for organohalide respiration.

  16. Postglacial (after 18 ka) deep-sea sedimentation along the Hikurangi subduction margin (New Zealand): Characterisation, timing and origin of turbidites


    Pouderoux, Hugo; Proust, Jean-Noël; Lamarche, Geoffroy; Orpin, Alan; Neil, Helen


    International audience; Recent sedimentation along the Hikurangi subduction margin off northeastern New Zealand is investigated using a series of piston cores collected between 2003 and 2008. The active Hikurangi Margin lies along the Pacific-Australia subduction plate boundary and contains a diverse range of geomorphologic settings. Slope basin stratigraphy is thick and complex, resulting from sustained high rates of sedimentation from adjacent muddy rivers throughout the Quaternary. Turbidi...

  17. Hafnium at subduction zones: isotopic budget of input and output fluxes; L'hafnium dans les zones de subduction: bilan isotopique des flux entrant et sortant

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    Marini, J.Ch


    Subduction zones are the primary regions of mass exchanges between continental crust and mantle of Earth through sediment subduction toward the earth's mantle and by supply of mantellic magmas to volcanic arcs. We analyze these mass exchanges using Hafnium and Neodymium isotopes. At the Izu-Mariana subduction zone, subducting sediments have Hf and Nd isotopes equivalent to Pacific seawater. Altered oceanic crust has Hf and Nd isotopic compositions equivalent to the isotopic budget of unaltered Pacific oceanic crust. At Luzon and Java subduction zones, arc lavas present Hf isotopic ratios highly radiogenic in comparison to their Nd isotopic ratios. Such compositions of the Luzon and Java arc lavas are controlled by a contamination of their sources by the subducted oceanic sediments. (author)

  18. The impact of rapid sediment accumulation on pore pressure development and dehydration reactions during shallow subduction in the Gulf of Alaska (United States)

    Meridth, Lanie N.; Screaton, Elizabeth J.; Jaeger, John M.; James, Stephanie R.; Villaseñor, Tania


    In the Gulf of Alaska region, sediment has rapidly accumulated (>1 km/my) in the trench sourced from intensified glaciation in the past ˜1.2 million years. This rapid sediment accumulation increases overburden and should accelerate dehydration of hydrous minerals by insulating the underlying sediment column. These processes have the potential to generate fluid overpressures in the low permeability sediments entering the subduction zone. A 1-D model was developed to simulate dehydration reaction progress and investigate excess pore pressures as sediments approach the trench and are subducted. At the deformation front, simulated temperatures increase by ˜30°C due to the insulating effect of trench sediments. As a result, opal-A begins to react to form quartz while smectite remains mostly unreacted. Loading due to the trench sediments elevates excess pore pressures to ˜30% of lithostatic pressure at the deformation front; however, deformation front excess pore pressures are sensitive to assumptions about the permeability of outer wedge sediments. If the outer wedge sediments are coarse-grained and high-permeability rather than mud-dominated, excess pore pressures are lower but still have an insulating effect. During early subduction, simulated pore pressures continue to rise and reach ˜70% of lithostatic by 60 km landward. The 1-D modeling results suggest that the elevated pore pressures are primarily due to loading and that dehydration reactions are not a significant component of excess pore pressure generation at this margin.

  19. Great (≥Mw8.0) megathrust earthquakes and the subduction of excess sediment and bathymetrically smooth seafloor (United States)

    Scholl, David W.; Kirby, Stephe H.; von Huene, Roland; Ryan, Holly F.; Wells, Ray E.; Geist, Eric L.


    Using older and in part flawed data, Ruff (1989) suggested that thick sediment entering the subduction zone (SZ) smooths and strengthens the trench-parallel distribution of interplate coupling. This circumstance was conjectured to favor rupture continuation and the generation of high-magnitude (≥Mw8.0) interplate thrust (IPT) earthquakes. Using larger and more accurate compilations of sediment thickness and instrumental (1899 to January 2013) and pre-instrumental era (1700–1898) IPTs (n = 176 and 12, respectively), we tested if a compelling relation existed between where IPT earthquakes ≥Mw7.5 occurred and where thick (≥1.0 km) versus thin (≤1.0 km) sedimentary sections entered the SZ.

  20. Sulphide-sulphate stability and melting in subducted sediment and its role in arc mantle redox and chalcophile cycling in space and time (United States)

    Canil, Dante; Fellows, Steven A.


    The redox budget during subduction is tied to the evolution of oxygen and biogeochemical cycles on Earth's surface over time. The sulphide-sulphate couple in subducted crust has significant potential for redox and control on extraction of chalcophile metals from the arc mantle. We derive oxygen buffers for sulphide-sulphate stability ('SSO buffers') using mineral assemblages in subducted crust within the eclogite facies, and examine their disposition relative to the fO2 in the arc mantle along various P-T trajectories for subduction. The fO2 required for sulphide stability in subducted crust passing beneath an arc is shifted by variations in the bulk Ca/(Ca + Mg + Fe) of the subducting crust alone. Hotter slabs and more Fe-rich sediments stabilize sulphide and favour chalcophile sequestration deep into the mantle, whereas colder slabs and calcic sediment will stabilize anhydrite, in some cases at depths of melt generation in the arc mantle (earth history. Oxidation of arc mantle and the proliferation of porphyry Cu deposits may be latter-day advents in earth history partly due to the rise of planktic calcifiers in the oceans in only the past 250 million years.

  1. Loss of solar He and Ne from IDPS in subducting sediment: Diffusion and the effect of phase changes (United States)

    Hiyagon, H.


    The results of the diffusion experiment for solar He and Ne in IDP's in a magnetic separate from Pacific Ocean sediment suggest that solar He and Ne would be easily released from IDP grains and hence lost from subducting slabs at shallow depths. However, since the diffusion experiments was conducted under high vacuum, there may be a possibility that magnetite grains, which are supposedly the main constituent of the magnetic fraction, might be partly reduced to form a metal phase due to low oxygen fugacity in the experimental condition. If this is the case, such a phase change might affect the gas release and hence the results of the diffusion coefficients. In order to examine whether or not such a phase change really occurred in the condition of the diffusion experiment, I conducted a heating experiment for a magnetic separate from Pacific Ocean sediment. In the same condition as in the diffusion experiment, and the run products were examined with an x ray diffraction method. Three samples were prepared: they were wrapped with platinum foil, put in a vacuum line, and heated in a molybdenum crucible for two hours at 500 C, 800 C,and 950 C, respectively. After cooling the furnace, the samples were taken out from the crucible and analyzed with an x ray diffraction method.

  2. Isotopic compositions of boron in sediments and their implications

    Digital Repository Service at National Institute of Oceanography (India)

    Shirodkar, P.V.; Yingkai, X.

    The abundance and isotopic compositions of boron in sediments from the salt lakes of Qaidam Basin, China have been determined by thermal ionization mass spectrometry of cesium borate. The results show large variations in the isotopic compositions...

  3. Sediment distribution and composition on the shallow water ...

    African Journals Online (AJOL)

    Sediments of the shallow water carbonate basin in Zanzibar channel were investigated for composition and grain size distribution. The surface sediment composition was dominated by carbonate sands (with CaCO3 > 30%), except in the area adjacent to mainland coastline and a thin lobe which projects from Ruvu River to ...

  4. Subduction Controls of Hf and Nd Isotopes in Lavas of the Aleutian Island Arc

    Energy Technology Data Exchange (ETDEWEB)

    Yogodzinski, Gene; Vervoort, Jeffery; Brown, Shaun Tyler; Gerseny, Megan


    The Hf and Nd isotopic compositions of 71 Quaternary lavas collected from locations along the full length of the Aleutian island arc are used to constrain the sources of Aleutian magmas and to provide insight into the geochemical behavior of Nd and Hf and related elements in the Aleutian subduction-magmatic system. Isotopic compositions of Aleutian lavas fall approximately at the center of, and form a trend parallel to, the terrestrial Hf-Nd isotopic array with {var_epsilon}{sub Hf} of +12.0 to +15.5 and {var_epsilon}{sub Nd} of +6.5 to +10.5. Basalts, andesites, and dacites within volcanic centers or in nearby volcanoes generally all have similar isotopic compositions, indicating that there is little measurable effect of crustal or other lithospheric assimilation within the volcanic plumbing systems of Aleutian volcanoes. Hafnium isotopic compositions have a clear pattern of along-arc increase that is continuous from the eastern-most locations near Cold Bay to Piip Seamount in the western-most part of the arc. This pattern is interpreted to reflect a westward decrease in the subducted sediment component present in Aleutian lavas, reflecting progressively lower rates of subduction westward as well as decreasing availability of trench sediment. Binary bulk mixing models (sediment + peridotite) demonstrate that 1-2% of the Hf in Aleutian lavas is derived from subducted sediment, indicating that Hf is mobilized out of the subducted sediment with an efficiency that is similar to that of Sr, Pb and Nd. Low published solubility for Hf and Nd in aqueous subduction fluids lead us to conclude that these elements are mobilized out of the subducted component and transferred to the mantle wedge as bulk sediment or as a silicate melt. Neodymium isotopes also generally increase from east to west, but the pattern is absent in the eastern third of the arc, where the sediment flux is high and increases from east to west, due to the presence of abundant terrigenous sediment in the

  5. Influence of subduction zone conditions and gouge composition on frictional slip stability of megathrust faults

    NARCIS (Netherlands)

    den Hartog, S.A.M.; Spiers, C.J.


    To understand the temperature/depth distribution of destructive earthquakes in subduction megathrusts, and the mechanisms of nucleation of these events, data on the frictional behaviour of phyllosilicate/quartz-rich megathrust fault gouges under in-situ conditions are needed. We performed rotary

  6. Controls on the barium isotope compositions of marine sediments (United States)

    Bridgestock, Luke; Hsieh, Yu-Te; Porcelli, Donald; Homoky, William B.; Bryan, Allison; Henderson, Gideon M.


    The accumulation of barium (Ba) in marine sediments is considered to be a robust proxy for export production, although this application can be limited by uncertainty in BaSO4 preservation and sediment mass accumulation rates. The Ba isotope compositions of marine sediments could potentially record insights into past changes in the marine Ba cycle, which should be insensitive to these limitations, enabling more robust interpretation of sedimentary Ba as a proxy. To investigate the controls on the Ba isotope compositions of marine sediments and their potential for paleo-oceanographic applications, we present the first Ba isotope compositions results for sediments, as well as overlying seawater depth profiles collected in the South Atlantic. Variations in Ba isotope compositions of the sediments predominantly reflect changes in the relative contributions of detrital and authigenic Ba sources, with open-ocean sediments constraining the isotope composition of authigenic Ba to be δ138/134Ba ≈ + 0.1 ‰. This value is consistent with the average isotope composition inferred for sinking particulate Ba using simple mass balance models of Ba in the overlying water column and is hypothesized to reflect the removal of Ba from the upper water column with an associated isotopic fractionation of Δdiss-part 138/134Ba ≈ + 0.4 to +0.5. Perturbations to upper ocean Ba cycling, due to changes in export production and the supply of Ba via upwelling, should therefore be recorded by the isotope compositions of sedimentary authigenic Ba. Such insights will help to improve the reliable application of Ba accumulation rates in marine sediments as a proxy for past changes in export production.

  7. The Compositions And Sources Of Fluids Through Time In A 1.8 Gya UHP Subduction Complex (United States)

    Glassley, W. E.; Korstgård, J.; Sorensen, K.


    The HP and UHP history of a 1.8 Gya terrain in West Greenland (Glassley et al., 2014) is only preserved in pods, lenses and tectonic slices that escaped hydration during transit to lower P-T conditions from the UHP environment. The terrain consists of a tectonic assemblage of metasomatically altered pillow basalts, ultramafic bodies, exhalative and chemical oceanic metasediments, pelites, and quartzo-feldspathic gneisses, that are the preserved remnants of a subduction channel. Only those rocks that escaped significant hydration during decompression preserve evidence of the sequence of recrystallization episodes under evolving fluid conditions. The highest-pressure mineral assemblages exhibit no evidence of fluid presence, implying very low activities of potential fluid components. During ascent from UHP conditions, recrystallization involved a sequence of fluid-sensitive mineral assemblages (graphite precipitation > carbonate precipitation > OH-bearing mineral growth) as well as exsolution features involving oxides. Buffering mineral assemblages, e.g., QFM, developed as decompression progressed. Carbon isotope measurements on graphite document a biogenic origin (∂C13 = -24.6) for the C in the precipitated graphite. The results, when placed in a time sequence correlating with P-T trajectory suggest that the subduction channel may have been zoned with respect to the dominant fluid components. The results demonstrate that: 1) The extent of recrystallization during decompression is mainly a reflection of local rock chemistry/mineralogy and fluid activity; 2) Preservation of the prograde P-T-t path during subduction is a very sensitive function of the fluid composition and activity during decompression.

  8. Chemical composition of Lake Orta sediments

    Directory of Open Access Journals (Sweden)

    Monica BELTRAMI


    Full Text Available Lake Orta (18.2 km2, 1.3 km3, 143 m max. depth has been severely polluted since industrialisation of its watershed began in 1926, at which time the lake began to receive industrial effluents containing high concentrations of copper and ammonia. Chromium-, nickel-, and zinc-rich effluents from plating factories have also contributed to pollution levels, and pH -levels dropped below 4.0 as a result of the oxidation of ammonia to nitrates. More than 60 papers have documented the evolution of the chemical characteristics of both water and sediment, and the sudden decline of plankton, as well as benthos and fish. As a remedial action the lake was limed from May 1989 to June 1990 with 10,900 tons of CaCO3. The treatment was immediately effective in raising the pH and decreasing the metal concentrations in the water column, and plankton and fish communities quickly rebounded. However, the chemical characteristics of sediments were influenced by the liming to a much lesser extent. Since 900 tons of copper and the same amount of chromium were contained in the top 10 cm of sediment, it appears likely that the sediment could potentially act as a current and future source of these metals to the water column. This observation has resulted in the implementation of a vigorous monitoring regime to track the post-liming recovery of Lake Orta.

  9. Nitrogen recycling at the Costa Rican subduction zone: The role of incoming plate structure. (United States)

    Lee, Hyunwoo; Fischer, Tobias P; de Moor, J Maarten; Sharp, Zachary D; Takahata, Naoto; Sano, Yuji


    Efficient recycling of subducted sedimentary nitrogen (N) back to the atmosphere through arc volcanism has been advocated for the Central America margin while at other locations mass balance considerations and N contents of high pressure metamorphic rocks imply massive addition of subducted N to the mantle and past the zones of arc magma generation. Here, we report new results of N isotope compositions with gas chemistry and noble gas compositions of forearc and arc front springs in Costa Rica to show that the structure of the incoming plate has a profound effect on the extent of N subduction into the mantle. N isotope compositions of emitted arc gases (9-11 N°) imply less subducted pelagic sediment contribution compared to farther north. The N isotope compositions (δ(15)N = -4.4 to 1.6‰) of forearc springs at 9-11 N° are consistent with previously reported values in volcanic centers (δ(15)N = -3.0 to 1.9‰). We advocate that subduction erosion enhanced by abundant seamount subduction at 9-11 N° introduces overlying forearc crustal materials into the Costa Rican subduction zone, releasing fluids with lighter N isotope signatures. This process supports the recycling of heavier N into the deep mantle in this section of the Central America margin.

  10. Subduction and volatile recycling in Earth's mantle (United States)

    King, S. D.; Ita, J. J.; Staudigel, H.


    The subduction of water and other volatiles into the mantle from oceanic sediments and altered oceanic crust is the major source of volatile recycling in the mantle. Until now, the geotherms that have been used to estimate the amount of volatiles that are recycled at subduction zones have been produced using the hypothesis that the slab is rigid and undergoes no internal deformation. On the other hand, most fluid dynamical mantle flow calculations assume that the slab has no greater strength than the surrounding mantle. Both of these views are inconsistent with laboratory work on the deformation of mantle minerals at high pressures. We consider the effects of the strength of the slab using two-dimensional calculations of a slab-like thermal downwelling with an endothermic phase change. Because the rheology and composition of subducting slabs are uncertain, we consider a range of Clapeyron slopes which bound current laboratory estimates of the spinel to perovskite plus magnesiowustite phase transition and simple temperature-dependent rheologies based on an Arrhenius law diffusion mechanism. In uniform viscosity convection models, subducted material piles up above the phase change until the pile becomes gravitationally unstable and sinks into the lower mantle (the avalanche). Strong slabs moderate the 'catastrophic' effects of the instabilities seen in many constant-viscosity convection calculations; however, even in the strongest slabs we consider, there is some retardation of the slab descent due to the presence of the phase change.

  11. The system controlling the composition of clastic sediments (United States)

    Johnsson, Mark J.


    The composition of clastic sediments and rocks is controlled by a complex suite of parameters operating during pedogenesis, erosion, transport, deposition, and burial. The principal first-order parameters include source rock composition, modification by chemical weathering, mechanical disaggregation and abrasion, authigenic inputs, hydrodynamic sorting, and diagenesis. Each of these first-order parameters is influenced to varying degrees by such factors as the tectonic settings of the source region, transportational system and depositional environment, climate, vegetation, relief, slope, and the nature and energy of transportational and depositional systems. These factors are not independent; rather a complicated web of interrelationships and feedback mechanisms causes many factors to be modulated by others. Accordingly, processes controlling the composition of clastic sediments are best viewed as constituting a system, and in evaluating compositional information the dynamics of the system must be considered as whole.

  12. Preliminary results of high resolution subbottom survey and surface sediment sampling by ROV "NSS" in the Nankai subduction zone off Kumano (United States)

    Ashi, J.; Kh-10-3 Science Party


    The Nankai subduction zone off Kumano has been extensively investigated for site surveys of IODP Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) by bathymetirc survey, 2D and 3D seismic reflection survey, dive observation and sidescan sonar survey. However, subbottom profiling and surface sediment sampling were limited due to steep and complex topography under strong Kuroshio Current. We carried out deep-tow subbottom survey and pinpoint core sampling by ROV "NSS (Navigable Sampling System)" of Atmosphere and Ocean Research Institute, the Univ. Tokyo during Hakuho-maru KH-10-3 cruise. A pilot vehicle of NSS is equipped with four thrusters, observation cameras and a hock for a heavy payload. Depth capability of the pilot vehicle is 4000 m and maximum payload weight is 1.5 tons. We introduced a chirp subbottom profiling system of EdgeTech DW-106 for high resolution mapping of shallow structures and determination of a sampling point on this year's survey. Three survey lines crossed the splay fault area around IODP drilling sites. Subbottom profiles show that seafloor is completely covered by stratified sediments and any fault displacement cannot be identified although maximum penetration of chirp signal is only 15 meters in prism slope regions. In contrast, landward progressive tilting of slope basin sediments and talus deposits on it are well imaged along the steep scarp 30 km southwest of the drilling sites. Dense chemosynthetic biological community revealed by camera observations also suggests existence of active fault in this area. The scarp more gentle slope than the above is located 4 kilometers trenchward of it. Subbottom profiles show well-stratified sediment cover without fault deformation. Seismic reflection profiles and existence of dense traces of bivalves, however, suggest existence of a splay fault beneath it. A long-term heat flow meter of ERI, Univ. Tokyo was installed at each fault scarp for monitoring of cold seep activity. We also present

  13. Seasonal variation of surface sediments composition in Mondego River estuary. (United States)

    Pereira, Patrícia; Vale, Carlos; Ferreira, Ana Maria; Pereira, Eduarda; Pardal, Miguel Angelo; Marques, João Carlos


    Concentrations of major (Al, Si, Ca, Mg, Fe), minor (Mn), and trace elements (Zn, Pb, Cr, Cu, Ag, Cd, Hg) and organochlorine compounds (PCB congeners, pp'DDT, and metabolites) were determined in 24 samples of surface sediments (0-5 cm) collected along the Mondego River estuary in two periods: February and August 2003. All sediment samples showed low levels of contamination reflecting the weak industrialization of the region. Higher incorporation of elements (Mg, Fe, Zn, Cr, Cu, Cd, Hg) and DDT was registered in muds deposited in the inner part of the south channel. Sediments of the rest of the estuary are coarser (mean Si/Al ratio around 11) and showed much lower Me/Al ratios. Concentrations of Mn, Pb, Ag, and PCB showed no geographical distribution tendency. However, Pb, Cu, Ag, Zn, Cd ratios to Al and PCB concentrations were higher in coarser sediments collected in February than in August. In addition, the lower chlorinated CBs (tri + tetra-CB) showed a higher proportion in sediments collected in February, due to its higher mobility and low contamination in the area. The results obtained in this river-dominated estuarine system, with weak local contamination sources, indicate that chemical composition of surface sediments reflects the diffuse source of contaminants associated with the rainy season.

  14. A discussion of numerical subduction initiation (United States)

    Buiter, Susanne; Ellis, Susan


    In nature, subduction can initiate in various ways: Shortening can localise at oceanic transform faults, extinct spreading centres, or inherited passive margin faults; or, alternatively, subduction can be triggered from existing subduction systems by along-strike trench propagation, polarity reversals, or trench jumps. Numerical studies that specifically address subduction initiation have highlighted the roles of sediment loading, rheological strength contrasts, strain softening, and continental topographic gradients, among others. Usually, however, numerical models that aim to investigate subduction dynamics prefer to bypass the subduction initiation phase and its complexities, and focus instead on the stages during which the slab is descending into the mantle. However, even in these models, subduction still needs to begin. It is disturbingly easy to define initial model geometries that do not result in subduction. The specific combination of initial model geometries and values for rheological parameters that successfully initiates subduction has even been referred to as 'the sweet spot' in model space. One cause of subduction initiation failure is when the subducting and overriding plates lock, resulting in either indentation or severe dragging downwards of the overriding plate. This may point to a difficulty in maintaining a weak subduction interface during model evolution. A second factor that may cause difficulties is that initial model geometry and stresses need to balance, as otherwise the first model stages may show spurious deformation associated with reaching equilibrium. A third requirement that may cause problems is that the surface needs to have sufficient displacement freedom to allow the overriding plate to overthrust the subducting plate. That also implies an exclusion of sharp corners in the subduction interface near the surface. It is the interplay of subduction interface geometry, interface strength and subducting plate rheology that determines

  15. Metallogeny of subduction zones

    Directory of Open Access Journals (Sweden)

    Sorokhtin N. O.


    Full Text Available The paper deals with the multistage mechanism of the Earth's crust enrichment in ore elements in underthrust zones. The processes of metamorphism and the formation of hydrothermal solutions at pulling of the watered oceanic lithospheric plate into the subduction zone have been described. Some physical and chemical transformation regularities of structural-material complexes in these areas and mechanisms of the formation of ore deposits have been discussed. Spatio-temporal patterns of the localization of a number of endogenetic and exogenetic deposits have been described using metallogeny of the Ural and the Verkhoyansk-Kolyma Fold Belts as an example. It has been shown that in nature there are several effective mechanisms of the enrichment of the crust in ore minerals. One of them is the process of pulling into subduction zone of metalliferous sediments and ferromanganese crusts as well as seabed nodules, their metamorphic transformation, partial melting and transition of ore components into magmatic melts and mineralized fluids. In the future this leads to the release of ore material by magmas and hydrothermal solutions into the folded formations of island-arc and Andean types and the formation of igneous, metasomatic and hydrothermal deposits. Another, yet no less powerful natural mechanism of a conveyor enrichment of the crust in ore elements is the process of destruction and sedimentation of mineral deposits formed in the folded areas as well as the formation of placers and their transfer to the marginal parts of the continent. Later, during the collision of active and passive margins of two lithospheric plates, such as the collision of the Kolyma Massif with the eastern part of the Siberian craton in the middle of the Mesozoic there was a thrusting of a younger lithospheric plate over a more ancient one. As a result, the sedimentary sequences of the passive margin of the Siberian plate were submerged and partially melted by the basic magmas

  16. Chemical composition of sediments from White Sea, Russian Arctic (United States)

    Gamza, Olga; Shevchenko, Vladimir; Novigatsky, Aleksandr


    The White Sea, the only Russian inland sea, is located on the north of outlying districts of the European part of Russia, belongs to Arctic Ocean. Area of water of sea occupies about 90 tousend square kilometers. The sea can be divided into some general parts: neck, funnel, basin and 4 Bays: Dvina Bay, Kandalaksha Bay, Mezen Bay and Onega Bay. The purpose of this work was geochemical mapping of the surface sediments of this area. The main tasks were: compilation data base of element composition of the surface sediments, geochemical mapping of each element, research of the anormal concentration of elements on the surface. To detect the content of chemical elements several methods were used: atomic absorption spectrometry (P.P. Shirshov Institute of Oceanology); neutron activation analysis (Vernadsky Institute of Geochemistry and Analytical Chemistry), total and organic carbon analysis, photometric method to detection Si, Al, P (P.P. Shirshov Institute of Oceanology). Bulk composition is one of the fundamental characteristics of sediments and bottom deposites of modern basins. Coarse-grained sediments with portion of pelitic component 80%). Character of elements distribution correlates with facial distribution of sediments from White Sea. According to litologic description, bottom surface of Dvina Bay is practically everywhere covered by layer of fine-grained sand. In the border area between Dvina Bay and White Sea basin on terraced subwater slope aleurite politic silts are abundant. They tend to exhange down the slope to clay silts. In Onega Bay fractions of non-deposition are observed. They are characterized by wide spread of thin blanket poorgraded sediments, which are likely to be relic. Relief of Kandalakscha Bay bottom is presented as alternation of abyssal fosses (near 300 m) with silles and elevations (depressions and in central part of the sea, which is quite wide from both places of original sedimentation and run off sources [2]. Thus, the interrelation

  17. Chemical composition of the sediment from Lake 20 (Antarctica

    Directory of Open Access Journals (Sweden)

    Daria ROSSI


    Full Text Available Lake 20 (19,000 m2 is located on the coast of the Ross Sea, in the North-Central part of Victoria Land, and its surface is ice-free between the end of December and early February. Within the framework of the Italian National Research Programme in Antarctica, a study was made of the chemical composition of sediments from the lake, with the intention of using this information to contribute to a better understanding of the processes involved in the long range transport of pollutants and their role in global changes. A sediment core from Lake 20 (Antarctica, 18 cm long, was collected in 1994, sliced into 2 cm sections and analysed using X Ray fluorescence spectrometry for 17 elements (Si, Al, Ca, K, Fe, Mg, Ti, S, P, Pb, Zn, Cu, Ni, Mn, Cr, Na, Cl, by CHN Elemental Analyser for C and N, by Flameless Atomic Absorption Spectrometry for As, and by Cold Vapour Atomic Absorption Spectrometry for Hg. The chemical composition of the sediments is consistent with the known geochemical characteristics of the drainage basin. While the chemical analyses reveal that sedimentation in Lake 20 has changed through time, the variations along the core are most probably related to the climatic evolution of the area, to the consequent changes in weathering processes, and possibly to an increase in the primary productivity of the lake, rather than to anthropogenic influences on the biogeochemical cycles of the elements.

  18. Subduction of continental material in the Banda Arc, Eastern Indonesia : Sr-Nd-Pb isotope and trace-element evidence from volcanics and sediments

    NARCIS (Netherlands)

    Vroon, P.Z.


    This thesis presents the results of a geochemical study of the Banda Arc (East Indonesia) where magma genesis is influenced by subducted source components that are controlled by an active arc-continent collision. The main objective of this study is to investigate the role of subducted continental

  19. NOAA ESRI Shapefile - sediment composition class predictions in New York offshore planning area from Biogeography Branch (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This dataset represents sediment composition class predictions from a sediment spatial model developed for the New York offshore spatial planning area. The...

  20. Boron cycling in subduction zones


    Palmer, Martin R.


    Subduction zones are geologically dramatic features, with much of the drama being driven by the movement of water. The “light and lively” nature of boron, coupled with its wide variations in isotopic composition shown by the different geo-players in this drama, make it an ideal tracer for the role and movement of water during subduction. The utility of boron ranges from monitoring how the fluids that are expelled from the accretionary prism influence seawater chemistry, to the subduction of c...

  1. Grain-size composition of Quaternary South Atlantic sediments and its paleoceanographic significance.


    Frenz, M


    The grain-size composition is an fundamental property of sediments. The grain-size signature contains information about the history of a deposit such as sediment source, input mechanism, accumulation, redistribution, modification or alteration of sediment compounds. In previous studies mainly downcore results of grain-size distributions were used to infer climate variability from the changes of sediment input or current intensity. The spatial aspect of sediment input and distribution is often...

  2. Using multiple composite fingerprints to quantify fine sediment source contributions: A new direction (United States)

    Sediment source fingerprinting provides a vital means for estimating sediment source contributions, which are needed not only for soil conservation planning but also for erosion model evaluation. A single optimum composite fingerprint has been widely used in the literature to estimate sediment prov...

  3. Trace element composition of rutile in eclogite from the Karakaya Complex, NW Anatolia: Implications for rutile growth during subduction zone metamorphism (United States)

    Şengün, Fırat


    High-pressure/low-temperature (HP/LT) eclogite-facies terranes are widely regarded to represent exhumed fragments of subducted slabs. Therefore, the metamorphic studies of eclogites and associated high-pressure rocks yield crucial information about their P-T evolution and associated tectonometamorphic processes at depth in subduction zones. Especially rutile in eclogites record chemical history of subduction zones and also constrain metamorphic temperatures of subduction zone processes. Eclogites occur as a tectonic slice within metabasite-phyllite-marble intercalation of the Karakaya Complex. In this study, trace element geochemistry of rutiles and Zr-in-rutile thermometry have been investigated. The main mineralogical composition eclogites are composed of omphacite, garnet, glaucophane, epidote and quartz. Core-rim analyses through rutile grains yield remarkable trace element zoning with lower contents of Nb, Ta and Zr in the core than in the rim. The variations in Nb, Ta and Zr can be ascribed to the growth zoning rather than diffusion effect. The Nb/Ta and Zr/Hf ratios increase with a decrease in Ta and Hf contents, which could be ascribed to the effect of metamorphic dehydration at subduction zones on rutile Nb/Ta differentiation. The rutile grains from eclogites in the Karakaya Complex are characterized by subchondritic Nb/Ta and Zr/Hf ratios. It can be noted that the subchondritic Nb/Ta ratios may record rutile growth from local sinks of aqueous fluids from metamorphic dehydration. The Zr contents of the all rutile grains vary between 81 and 160 ppm with the average of 123 ppm. The Zr-in-rutile thermometer yielded the metamorphic temperature of 559-604 oC (average 585 oC) for eclogites occurring in the Karakaya Complex. This average temperature suggests the peak growth temperature of rutile. Moreover, Zr contents and calculated temperatures in both inclusion rutile and matrix rutile from eclogites are identical to each other, which suggests that rutiles in

  4. Origin and dynamics of depositionary subduction margins (United States)

    Vannucchi, Paola; Morgan, Jason P.; Silver, Eli; Kluesner, Jared W.


    Here we propose a new framework for forearc evolution that focuses on the potential feedbacks between subduction tectonics, sedimentation, and geomorphology that take place during an extreme event of subduction erosion. These feedbacks can lead to the creation of a “depositionary forearc,” a forearc structure that extends the traditional division of forearcs into accretionary or erosive subduction margins by demonstrating a mode of rapid basin accretion during an erosive event at a subduction margin. A depositionary mode of forearc evolution occurs when terrigenous sediments are deposited directly on the forearc while it is being removed from below by subduction erosion. In the most extreme case, an entire forearc can be removed by a single subduction erosion event followed by depositionary replacement without involving transfer of sediments from the incoming plate. We need to further recognize that subduction forearcs are often shaped by interactions between slow, long-term processes, and sudden extreme events reflecting the sudden influences of large-scale morphological variations in the incoming plate. Both types of processes contribute to the large-scale architecture of the forearc, with extreme events associated with a replacive depositionary mode that rapidly creates sections of a typical forearc margin. The persistent upward diversion of the megathrust is likely to affect its geometry, frictional nature, and hydrogeology. Therefore, the stresses along the fault and individual earthquake rupture characteristics are also expected to be more variable in these erosive systems than in systems with long-lived megathrust surfaces.

  5. Origin and dynamics of depositionary subduction margins (United States)

    Vannucchi, Paola; Morgan, Jason P.; Silver, Eli A.; Kluesner, Jared W.


    Here we propose a new framework for forearc evolution that focuses on the potential feedbacks between subduction tectonics, sedimentation, and geomorphology that take place during an extreme event of subduction erosion. These feedbacks can lead to the creation of a "depositionary forearc," a forearc structure that extends the traditional division of forearcs into accretionary or erosive subduction margins by demonstrating a mode of rapid basin accretion during an erosive event at a subduction margin. A depositionary mode of forearc evolution occurs when terrigenous sediments are deposited directly on the forearc while it is being removed from below by subduction erosion. In the most extreme case, an entire forearc can be removed by a single subduction erosion event followed by depositionary replacement without involving transfer of sediments from the incoming plate. We need to further recognize that subduction forearcs are often shaped by interactions between slow, long-term processes, and sudden extreme events reflecting the sudden influences of large-scale morphological variations in the incoming plate. Both types of processes contribute to the large-scale architecture of the forearc, with extreme events associated with a replacive depositionary mode that rapidly creates sections of a typical forearc margin. The persistent upward diversion of the megathrust is likely to affect its geometry, frictional nature, and hydrogeology. Therefore, the stresses along the fault and individual earthquake rupture characteristics are also expected to be more variable in these erosive systems than in systems with long-lived megathrust surfaces.

  6. Evolving metasomatic agent in the North Andean subduction, deduced from magma composition of the long-lived Pichincha volcanic complex (Ecuador) (United States)

    Samaniego, P.; Robin, C.; Chazot, G.; Bourdon, E. P.; Jo, C.


    Geochemical studies of long-lived volcanic complexes are crucial for the understanding of the nature and composition of the subduction component of arc magmatism. The Pichincha Volcanic Complex (Northern Andean Volcanic Zone) consists of: (1) an older, highly eroded edifice, the Rucu Pichincha, whose lavas are mostly andesites, erupted from 1100 to 150 ka; and (2) a younger, essentially dacitic, Guagua Pichincha composite edifice, with three main construction phases (Basal Guagua Pichincha, Toaza and Cristal) which formed over the last 60 ka. This structural evolution was accompanied by a progressive increase of most incompatible trace element abundances and ratios, as well as by a sharp decrease of fluid-mobile to fluid-immobile element ratios. Geochemical data indicate that fractional crystallization of an amphibole-rich cumulate could account for the evolution from the Guagua Pichincha andesites to dacites. However, in order to explain the passage from the Rucu Pichincha andesites to Guagua Pichincha dacites, the mineralogical and geochemical data indicate the predominance of magma mixing processes between a mafic, trace-element depleted, mantle-derived end-member, and a siliceous, trace-element enriched, adakitic end-member. The systematic variation of trace element abundances and ratios in primitive samples of this volcanic complex leads us to propose that the Rucu Pichincha magmas came from a hydrous-fluid metasomatized mantle wedge, whereas Guagua Pichincha magmas are related to partial melting of a siliceous-melt metasomatized mantle. This temporal evolution implies a change from dehydration to partial melting of the slab, which may be associated with an increase in the geothermal gradient along the slab due to the presence of the subducted Carnegie Ridge at the subduction system. This work emphasizes the importance of studying arc-magma systems over long periods of time (of at least 1 million of years), in order to evaluate the potential variations of the

  7. Evolving metasomatic agent in the Northern Andean subduction zone, deduced from magma composition of the long-lived Pichincha volcanic complex (Ecuador) (United States)

    Samaniego, Pablo; Robin, Claude; Chazot, Gilles; Bourdon, Erwan; Cotten, Joseph


    Geochemical studies of long-lived volcanic complexes are crucial for the understanding of the nature and composition of the subduction component of arc magmatism. The Pichincha Volcanic Complex (Northern Andean Volcanic Zone) consists of: (1) an old, highly eroded edifice, the Rucu Pichincha, whose lavas are mostly andesites, erupted from 1,100 to 150 ka; and (2) a younger, essentially dacitic, Guagua Pichincha composite edifice, with three main construction phases (Basal Guagua Pichincha, Toaza, and Cristal) which developed over the last 60 ka. This structural evolution was accompanied by a progressive increase of most incompatible trace element abundances and ratios, as well as by a sharp decrease of fluid-mobile to fluid-immobile element ratios. Geochemical data indicate that fractional crystallization of an amphibole-rich cumulate may account for the evolution from the Guagua Pichincha andesites to dacites. However, in order to explain the transition between the Rucu Pichincha andesites and Guagua Pichincha dacites, the mineralogical and geochemical data indicate the predominance of magma mixing processes between a mafic, trace-element depleted, mantle-derived end-member, and a siliceous, trace-element enriched, adakitic end-member. The systematic variation of trace element abundances and ratios in primitive samples leads us to propose that the Rucu Pichincha magmas came from a hydrous-fluid metasomatized mantle wedge, whereas Guagua Pichincha magmas are related to partial melting of a siliceous-melt metasomatized mantle. This temporal evolution implies a change from dehydration to partial melting of the slab, which may be associated with an increase in the geothermal gradient along the slab due to the presence of the subducted Carnegie Ridge at the subduction system. This work emphasizes the importance of studying arc-magma systems over long periods of time (of at least 1 million of years), in order to evaluate the potential variations of the slab contribution

  8. Influence of suspended kelp culture on seabed sediment composition in Heini Bay, China (United States)

    Liu, Yanxia; Huang, Haijun; Yan, Liwen; Liu, Xiao; Zhang, Zehua


    Kelp aquaculture activities occupy large nearshore areas with significant effects on sediment properties, primarily caused by the influence of the suspended kelp on local hydrodynamics. Changes in sediment composition and grain-size distributions were investigated prior to and following the commencement of kelp aquaculture activities in Heini Bay in eastern China. Seabed sediment types and the particulate matter in suspension during the kelp seeding and harvesting periods, and in sediment cores, were analyzed. While suspended sediment in the kelp aquaculture area was up to 20% organic material, sediment organic content on the seabed remained at similar levels as areas lacking aquaculture. The composition of the seabed sediment in the kelp aquaculture area became finer-grained by the capture of fine particles. Within the kelp aquaculture area, the sediments are poorly sorted and positively skewed, whereas at the shoreward and seaward of the aquaculture area the sediments are relatively coarse-grained, well-sorted and nearly symmetrically distributed. Therefore, the kelp aquaculture activities not only increase the fine particulate fraction in the sediments within the aquaculture area, but also result in similar deposits seaward of it, indicating that seabed erosion and accretion is also controlled by the sediment source and the hydrodynamic conditions. The analysis of sediment cores showed that kelp culturing refines the sediment by preferentially capturing particles in the 38-40 μm size class, while having no effect on the kelp aquaculture area. The same effect was observed in the seabed sediments seaward of the aquaculture area.

  9. H2O and CO2 devolatilization in subduction zones: implications for the global water and carbon cycles (Invited) (United States)

    van Keken, P. E.; Hacker, B. R.; Syracuse, E. M.; Abers, G. A.


    Subduction of sediments and altered oceanic crust functions as a major carbon sink. Upon subduction the carbon may be released by progressive metamorphic reactions, which can be strongly enhanced by free fluids. Quantification of the CO2 release from subducting slabs is important to determine the provenance of CO2 that is released by the volcanic arc and to constrain the flux of carbon to the deeper mantle. In recent work we used a global set of high resolution thermal models of subduction zones to predict the flux of H2O from the subducting slab (van Keken, Hacker, Syracuse, Abers, Subduction factory 4: Depth-dependent flux of H2O from subducting slabs worldwide, J. Geophys. Res., under review) which provides a new estimate of the dehydration efficiency of the global subducting system. It was found that mineralogically bound water can pass efficiently through old and fast subduction zones (such as in the western Pacific) but that warm subduction zones (such as Cascadia) see nearly complete dehydration of the subducting slab. The top of the slab is sufficiently hot in all subduction zones that the upper crust dehydrates significantly. The degree and depth of dehydration is highly diverse and strongly depends on (p,T) and bulk rock composition. On average about one third of subducted H2O reaches 240 km depth, carried principally and roughly equally in the gabbro and peridotite sections. The present-day global flux of H2O to the deep mantle translates to an addition of about one ocean mass over the age of the Earth. We extend the slab devolatilization work to carbon by providing an update to Gorman et al. (Geochem. Geophys. Geosyst, 2006), who quantified the effects of free fluids on CO2 release. The thermal conditions were based on three end-member subduction zones with linear interpolation to provide a global CO2 flux. We use the new high resolution and global set of models to provide higher resolution predictions for the provenance and pathways of CO2 release to

  10. Modelling the joint variability of grain size and chemical composition in sediments

    NARCIS (Netherlands)

    Bloemsma, M.R.; Zabel, M.; Stuut, J.B.W.; Tjallingii, R.; Collins, J.A.; Weltje, G.J.


    The geochemical composition of siliciclastic sediments correlates strongly with grain size. Hence, geochemical composition may serve as a grain-size proxy. In the absence of grain-size variations, geochemical data of siliciclastic sediments may be used to characterise size-independent processes,

  11. Extensive decarbonation of continuously hydrated subducting slabs (United States)

    Arzilli, Fabio; Burton, Mike; La Spina, Giuseppe; Macpherson, Colin G.


    CO2 release from subducting slabs is a key element of Earth's carbon cycle, consigning slab carbon either to mantle burial or recycling to the surface through arc volcanism, however, what controls subducted carbon's fate is poorly understood. Fluids mobilized by devolatilization of subducting slabs play a fundamental role in the melting of mantle wedges and in global geochemical cycles [1]. The effect of such fluids on decarbonation in subducting lithologies has been investigated recently [2-5], but several thermodynamic models [2-3], and experimental studies [6] suggest that carbon-bearing phases are stable at sub-arc depths (80-140 km; 2.6-4.5 GPa), implying that this carbon can be carried to mantle depths of >140 km. This is inconsistent with observations of voluminous CO2 release from arc volcanoes [7-10], located above slabs that are at 2.6-4.5 GPa pressure. The aim of this study is to re-evaluate the role of metamorphic decarbonation, showing if decarbonation reactions could be feasible at sub-arc depths combined with a continuous hydration scenario. We used the PerpleX software combined with a custom-designed algorithm to simulate a pervasive fluid infiltration characterized by "continuous hydration" combined with a distillation model, in which is possible to remove CO2 when decarbonation occurs, to obtain an open-system scenario. This is performed by repeatedly flushing the sediment with pure H2O at 0.5, 1.0 or 5 wt.% until no further decarbonation occurs. Here we show that continuous hydrated of sediment veneers on subducting slabs by H2O released from oceanic crust and serpentinised mantle lithosphere [11-13], produces extensive slab decarbonation over a narrow, sub-arc pressure range, even for low temperature subduction pathways. This explains the location of CO2-rich volcanism, quantitatively links the sedimentary composition of slab material to the degree of decarbonation and greatly increases estimates for the magnitude of carbon flux through the arc

  12. Microbial communities within saltmarsh sediments: Composition, abundance and pollution constraints (United States)

    Machado, Ana; Magalhães, Catarina; Mucha, Ana P.; Almeida, C. Marisa R.; Bordalo, Adriano A.


    The influence of the saltmarsh plant Halimione portucaloides and the level of sediment metal contamination on the distribution of microbial communities were investigated in two Portuguese estuarine systems with different degrees of metal contamination: the Cavado (41.5 N; 8.7 W) and Sado estuaries. In the Sado, two saltmarshes were studied: Lisnave (38.4 N; 8.7 W) and Comporta (38.4 N; 8.8 W). A PCR rDNA-DGGE approach and direct microscopic counts of DAPI-stained cells were applied to study the biodiversity and abundance of prokaryotic communities. Sediment characteristics and metal concentrations (Cd, Cr, Cu, Fe, Pb, Mn, Ni and Zn) were also evaluated to identify possible environmental pollution constraints on spatial and temporal microbial dynamics. Redundancy analysis (RDA) revealed that the Lisnave saltmarsh microbial community was usually associated with a higher degree of metal contamination, especially the metal Pb. In clear contrast, the Cavado estuary microbial assemblage composition was associated with low metal concentrations but higher organic matter content. The Comporta saltmarsh bacterial community clustered in a separate branch, and was associated with higher levels of different metals, such as Ni, Cr and Zn. Additionally, the microbial community structure of the Lisnave and Cavado showed a seasonal pattern. Moreover, microbial abundance correlated negatively with metal concentrations, being higher at the Cavado estuarine site and with general higher counts in the rhizosediment. These findings suggest that increased metal concentrations negatively affect the abundance of prokaryotic cells and that saltmarsh plants may have a pivotal role in shaping the microbial community structure.

  13. Separation of supercritical slab-fluids to form aqueous fluid and melt components in subduction zone magmatism. (United States)

    Kawamoto, Tatsuhiko; Kanzaki, Masami; Mibe, Kenji; Matsukage, Kyoko N; Ono, Shigeaki


    Subduction-zone magmatism is triggered by the addition of H(2)O-rich slab-derived components: aqueous fluid, hydrous partial melts, or supercritical fluids from the subducting slab. Geochemical analyses of island arc basalts suggest two slab-derived signatures of a melt and a fluid. These two liquids unite to a supercritical fluid under pressure and temperature conditions beyond a critical endpoint. We ascertain critical endpoints between aqueous fluids and sediment or high-Mg andesite (HMA) melts located, respectively, at 83-km and 92-km depths by using an in situ observation technique. These depths are within the mantle wedge underlying volcanic fronts, which are formed 90 to 200 km above subducting slabs. These data suggest that sediment-derived supercritical fluids, which are fed to the mantle wedge from the subducting slab, react with mantle peridotite to form HMA supercritical fluids. Such HMA supercritical fluids separate into aqueous fluids and HMA melts at 92 km depth during ascent. The aqueous fluids are fluxed into the asthenospheric mantle to form arc basalts, which are locally associated with HMAs in hot subduction zones. The separated HMA melts retain their composition in limited equilibrium with the surrounding mantle. Alternatively, they equilibrate with the surrounding mantle and change the major element chemistry to basaltic composition. However, trace element signatures of sediment-derived supercritical fluids remain more in the melt-derived magma than in the fluid-induced magma, which inherits only fluid-mobile elements from the sediment-derived supercritical fluids. Separation of slab-derived supercritical fluids into melts and aqueous fluids can elucidate the two slab-derived components observed in subduction zone magma chemistry.

  14. Chemistry, isotopic composition, and origin of a methane-hydrogen sulfide hydrate at the Cascadia subduction zone (United States)

    Kastner, M.; Kvenvolden, K.A.; Lorenson, T.D.


    Although the presence of extensive gas hydrate on the Cascadia margin, offshore from the western U.S. and Canada, has been inferred from marine seismic records and pore water chemistry, solid gas hydrate has only been found at one location. At Ocean Drilling Program (ODP) Site 892, offshore from central Oregon, gas hydrate was recovered close to the sediment - water interface at 2-19 m below the seafloor, (mbsf) at 670 m water depth. The gas hydrate occurs as elongated platy crystals or crystal aggregates, mostly disseminated irregularly, with higher concentrations occurring in discrete zones, thin layers, and/or veinlets parallel or oblique to the bedding. A 2-to 3-cm thick massive gas hydrate layer, parallel to bedding, was recovered at ???17 mbsf. Gas from a sample of this layer was composed of both CH4 and H2S. This sample is the first mixed-gas hydrate of CH4-H2S documented in ODP; it also contains ethane and minor amounts of CO2. Measured temperature of the recovered core ranged from 2 to - 18??C and are 6 to 8 degrees lower than in-situ temperatures. These temperature anomalies were caused by the partial dissociation of the CH4-H2S hydrate during recovery without a pressure core sampler. During this dissociation, toxic levels of H2S (??34S, +27.4???) were released. The ??13C values of the CH4 in the gas hydrate, -64.5 to -67.5???(PDB), together with ??D values of - 197 to - 199???(SMOW) indicate a primarily microbial source for the CH4. The ??18O value of the hydrate H2O is +2.9???(SMOW), comparable with the experimental fractionation factor for sea-ice. The unusual composition (CH4-H2S) and depth distribution (2-19 mbsf) of this gas hydrate indicate mixing between a methane-rich fluid with a pore fluid enriched in sulfide; at this site the former is advecting along an inclined fault into the active sulfate reduction zone. The facts that the CH4-H2S hydrate is primarily confined to the present day active sulfate reduction zone (2-19 mbsf), and that from here

  15. Microphytobenthos and benthic macroalgae determine sediment organic matter composition in shallow photic sediments

    Directory of Open Access Journals (Sweden)

    A. K. Hardison


    Full Text Available Microphytobenthos and benthic macroalgae play an important role in system metabolism within shallow coastal bays. However, their independent and interactive influences on sediment organic matter (SOM are not well understood. We investigated the influence of macroalgae and microphytobenthos on SOM quantity and quality in an experimental mesocosm system using bulk and molecular level (total hydrolyzable amino acids, THAA; phospholipid linked fatty acids, PLFA; pigment analyses. Our experiment used an incomplete factorial design made up of two factors, each with two levels: (1 light (ambient vs. dark and (2 macroalgae (presence vs. absence of live macroalgae. Over the course of the 42-day experiment, total organic carbon (TOC and total nitrogen (TN increased under ambient light by 173 ± 14 and 141 ± 7%, respectively, compared to in the dark (78 ± 29 and 39 ± 22%. THAA comprised a substantial fraction of SOM (~ 16% of TOC, 35% of TN and followed TOC and TN accumulation patterns. Mole percent composition of the THAA pool indicated that SOM was composed of more labile organic material (e.g., L-glutamic acid, phenylalanine under ambient light conditions while SOM in dark treatments was more degraded, with higher proportions of glycine and D-alanine. PLFA content, which represents viable biomass, made up ~ 1% of TOC and contained high levels of algal fatty acids in the light, particularly PLFA derived from diatoms. In the presence of microphytobenthos (i.e., light and macroalgae treatments, SOM lability increased, resulting in the observed increases in bacterial PLFA concentrations. Macroalgae, which were added to half of the light treatments, decreased SOM accumulation compared to light treatments without macroalgae, with TOC and TN increasing by only 130 ± 32 and 94 ± 24%, respectively. This decrease likely resulted from shading by macroalgae, which reduced production of microphytobenthos. The presence of macroalgae decreased SOM lability as

  16. Microphytobenthos and benthic macroalgae determine sediment organic matter composition in shallow photic sediments (United States)

    Hardison, A. K.; Canuel, E. A.; Anderson, I. C.; Tobias, C. R.; Veuger, B.; Waters, M. N.


    Microphytobenthos and benthic macroalgae play an important role in system metabolism within shallow coastal bays. However, their independent and interactive influences on sediment organic matter (SOM) are not well understood. We investigated the influence of macroalgae and microphytobenthos on SOM quantity and quality in an experimental mesocosm system using bulk and molecular level (total hydrolyzable amino acids, THAA; phospholipid linked fatty acids, PLFA; pigment) analyses. Our experiment used an incomplete factorial design made up of two factors, each with two levels: (1) light (ambient vs. dark) and (2) macroalgae (presence vs. absence of live macroalgae). Over the course of the 42-day experiment, total organic carbon (TOC) and total nitrogen (TN) increased under ambient light by 173 ± 14 and 141 ± 7%, respectively, compared to in the dark (78 ± 29 and 39 ± 22%). THAA comprised a substantial fraction of SOM (~ 16% of TOC, 35% of TN) and followed TOC and TN accumulation patterns. Mole percent composition of the THAA pool indicated that SOM was composed of more labile organic material (e.g., L-glutamic acid, phenylalanine) under ambient light conditions while SOM in dark treatments was more degraded, with higher proportions of glycine and D-alanine. PLFA content, which represents viable biomass, made up ~ 1% of TOC and contained high levels of algal fatty acids in the light, particularly PLFA derived from diatoms. In the presence of microphytobenthos (i.e., light and macroalgae treatments), SOM lability increased, resulting in the observed increases in bacterial PLFA concentrations. Macroalgae, which were added to half of the light treatments, decreased SOM accumulation compared to light treatments without macroalgae, with TOC and TN increasing by only 130 ± 32 and 94 ± 24%, respectively. This decrease likely resulted from shading by macroalgae, which reduced production of microphytobenthos. The presence of macroalgae decreased SOM lability as well, which

  17. Backreef and beach carbonate sediments of the Red Sea, Saudi Arabia: impacts of reef geometry and currents on sediment composition

    KAUST Repository

    Missimer, T. M.


    Three sites in the Red Sea were investigated to assess the variability of composition in Holocene sediments of the backreef environment within 0–2 m of water depth. This is important because composition of the sediment is commonly used to estimate water depth in ancient carbonate rocks. The site located at the King Abdullah Economic City (Saudi Arabia) contains a fringing reef with the reef tract located very close to the beach at the north end, flaring to the south to produce a narrower backreef area compared to the other two sites. This geometry produces a north to south current with a velocity of up to 15 cm s−1, particularly during high onshore winds. The sediments contain predominantly non-skeletal grains, including peloids, coated grains, ooids, and grapestones that form on the bottom. The percentage of coralgal grains in the sediment was significantly lower than at the other two sites studied. Om Al Misk Island and Shoaiba have a much lower-velocity current within the backreef zone and contain predominantly coralgal sediments from the beach to the landward edge of the reef tract. The two locations containing the predominantly coralgal microfacies were statistically similar, but the King Abdullah Economic City site was statistically different despite having a similar water depth profile. Slight differences in reef configuration, including reef orientation and distance from the shore, can produce considerable differences in sediment thickness and composition within the backreef environment, which should induce caution in the interpretation of water depth in ancient carbonate rocks using composition.

  18. Backreef and beach carbonate sediments of the Red Sea, Saudi Arabia: impacts of reef geometry and currents on sediment composition (United States)

    Missimer, T. M.; Al-Mashharawi, S.; Dehwah, A. H. A.; Coulibaly, K.


    Three sites in the Red Sea were investigated to assess the variability of composition in Holocene sediments of the backreef environment within 0-2 m of water depth. This is important because composition of the sediment is commonly used to estimate water depth in ancient carbonate rocks. The site located at the King Abdullah Economic City (Saudi Arabia) contains a fringing reef with the reef tract located very close to the beach at the north end, flaring to the south to produce a narrower backreef area compared to the other two sites. This geometry produces a north to south current with a velocity of up to 15 cm s-1, particularly during high onshore winds. The sediments contain predominantly non-skeletal grains, including peloids, coated grains, ooids, and grapestones that form on the bottom. The percentage of coralgal grains in the sediment was significantly lower than at the other two sites studied. Om Al Misk Island and Shoaiba have a much lower-velocity current within the backreef zone and contain predominantly coralgal sediments from the beach to the landward edge of the reef tract. The two locations containing the predominantly coralgal microfacies were statistically similar, but the King Abdullah Economic City site was statistically different despite having a similar water depth profile. Slight differences in reef configuration, including reef orientation and distance from the shore, can produce considerable differences in sediment thickness and composition within the backreef environment, which should induce caution in the interpretation of water depth in ancient carbonate rocks using composition.

  19. Sediment accretion rates and sediment composition in Prairie Pothole wetlands under varying land use practices, Montana, United States (United States)

    Preston, T.M.; Sojda, R.S.; Gleason, R.A.


    Increased sedimentation and nutrient cycle changes in Prairie Pothole Region wetlands associated with agriculture threaten the permanence and ecological functionality of these important resources. To determine the effects of land use on sedimentation and nutrient cycling, soil cores were analyzed for cesium-137 (137Cs), lead-210 (210Pb), and potassium-40 (40K) activities; textural composition; organic and inorganic carbon (C); and total nitrogen (N) from twelve wetlands surrounded by cropland, Conservation Reserve Program (CRP) lands, or native prairie uplands. Separate soil cores from nine of these wetlands were also analyzed for phosphorus (P), nitrate (NO3), and ammonium (NH4) concentrations. Wetlands surrounded by cropland had significantly greater linear sediment accretion rates than wetlands surrounded by CRP or native prairie. Linear sediment accretion rates from wetlands surrounded by cropland were 2.7 and 6 times greater than wetlands surrounded by native prairie when calculated from the initial and peak occurrence of 137Cs, respectively, and 0.15 cm y−1 (0.06 in yr−1) greater when calculated from 210Pb. Relative to wetlands surrounded by CRP, linear sediment accretion rates for wetlands surrounded by cropland were 4.4 times greater when calculated from the peak occurrence of 137Cs. No significant differences existed between the linear sediment accretion rates between wetlands surrounded by native prairie or CRP uplands. Wetlands surrounded by cropland had increased clay, P, NO3, and NH4, and decreased total C and N concentrations compared to wetlands surrounded by native prairie. Wetlands surrounded by CRP had the lowest P and NO3 concentrations and had clay, NH4, C, and N concentrations between those of cropland and native prairie wetlands. We documented increased linear sediment accretion rates and changes in the textural and chemical properties of sediments in wetlands with cultivated uplands relative to wetlands with native prairie uplands. These

  20. UV radiation and organic matter composition shape bacterial functional diversity in sediments

    Directory of Open Access Journals (Sweden)

    Ellard Roy Hunting


    Full Text Available AbstractUV radiation and organic matter (OM composition are known to influence the speciescomposition of bacterioplankton communities. Potential effects of UV radiation onbacterial communities residing in sediments remain completely unexplored to date.However, it has been demonstrated that UV radiation can reach the bottom of shallowwaters and wetlands and alter the OM composition of the sediment, suggesting thatUV radiation may be more important for sediment bacteria than previously anticipated.It is hypothesized here that exposure of shallow OMcontaining sediments to UVradiation induces OMsource dependant shifts in the functional composition ofsediment bacterial communities. This study therefore investigated the combinedinfluence of both UV radiation and OM composition on bacterial functional diversity inlaboratory sediments. Two different organic matter sources, labile and recalcitrantorganic matter (OM, were used and metabolic diversity was measured with BiologGN. Radiation exerted strong negative effects on the metabolic diversity in thetreatments containing recalcitrant OM, more than in treatments containing labile OM.The functional composition of the bacterial community also differed significantlybetween the treatments. Our findings demonstrate that a combined effect of UVradiation and OM composition shapes the functional composition of microbialcommunities developing in sediments, hinting that UV radiation may act as animportant sorting mechanism for bacterial communities and driver for bacterialfunctioning in shallow lakes and wetlands.

  1. The effects of subtidal mussel seed fisheries in the Dutch Wadden Sea on sediment composition

    NARCIS (Netherlands)

    Bemmelen, van R.S.A.; Brinkman, A.G.; Holthuyzen, S.; Jansen, J.


    In this report, the effect of seed mussel fishery activities on sediment composition is analysed. The hypothesis is that dredging for mussels brings fine silt in suspension. Tidal currents move silt away from the fishing site and a more course sediment is left behind. For PRODUS experimental plots

  2. A new approach of using multiple composite fingerprints to apportion sediment sources (United States)

    Sediment source fingerprinting provides an essential means for estimating sediment source contributions, which are needed not only for soil conservation planning but also for erosion model evaluation and refinement. A single optimum composite fingerprint has been widely used in the literature to es...

  3. Mapping subduction interface coupling using magnetotellurics: Hikurangi margin, New Zealand (United States)

    Heise, W.; Caldwell, T. G.; Bannister, S.; Bertrand, E. A.; Ogawa, Y.; Bennie, S. L.; Ichihara, H.


    The observation of slow-slip, seismic tremor, and low-frequency earthquakes at subduction margins has provided new insight into the mechanisms by which stress accumulates between large subduction (megathrust) earthquakes. However, the relationship between the physical properties of the subduction interface and the nature of the controls on interplate seismic coupling is not fully understood. Using magnetotelluric data, we show in situ that an electrically resistive patch on the Hikurangi subduction interface corresponds with an area of increased coupling inferred from geodetic data. This resistive patch must reflect a decrease in the fluid or sediment content of the interface shear zone. Together, the magnetotelluric and geodetic data suggest that the frictional coupling of this part on the Hikurangi margin may be controlled by the interface fluid and sediment content: the resistive patch marking a fluid- and sediment-starved area with an increased density of small, seismogenic-asperities, and therefore a greater likelihood of subduction earthquake nucleation.

  4. Sediment composition and provenance of the Pab Formation, Kirthar Fold Belt, Pakistan

    DEFF Research Database (Denmark)

    Umar, Muhammad; Friis, Henrik; Khan, Abdul Salem


    late Maastrichtian times. Moreover, geochemical indicators demonstrate that the ultimate composition of Pab sediments has been strongly influenced by intense chemical weathering, associated with warm/humid climatic conditions in the source areas, accompanied by significant diagenetic effects....

  5. Microphytobenthos and benthic macroalgae determine sediment organic matter composition in shallow photic sediments

    NARCIS (Netherlands)

    Hardison, A.K.; Canuel, E.A/; Anderson, I.C.; Tobias, C.R.; Veuger, B.; Waters, M.N.


    Microphytobenthos and benthic macroalgae play an important role in system metabolism within shallow coastal bays. However, their independent and interactive influences on sediment organic matter (SOM) are not well understood. We investigated the influence of macroalgae and microphytobenthos on SOM

  6. Defining Incipient Subduction by Detecting Serpentenised Mantle in the Regional Magnetic Field (United States)

    Pires, Rui; Clark, Stuart; Reis, Rui


    Keywords: Subduction initiation, Incipient Subduction, Active Margins, Southeast Asia, Mantle wedge The mechanisms of subduction initiation are poorly understood. One idea is to look for incipient subduction zones in the present day and see what features are common in these zones. However, incipient subduction zones are very difficult to detect and debate surrounds particular cases as to whether they qualify as incipient or not. In the analysis conducted in this work, we use the signal of the presence of a mantle wedge in the magnetic anomaly field as an indicator of incipient subduction. Each subduction zone exhibits variations in the particular responses of the system, such as slab-dip angle, maximum earthquake depths and volcanism to various parameters. So far, attempts to reduce the system to a dominate controlling parameter have failed, probably as a result of the limited number of cases and the large variety of controlling parameters. Parameters such as down-going and overriding plate morphology and velocity, mantle flow, the presence of plumes or not, sediment transport into the trench are a few of the parameters that have been studied in the literature. However, one of the characteristics associated with a subduction zones is the presence of a mantelic wedge as a result of the partial melt of the subducting plate and the development of a mantle wedge between the subducting plate and the overriding plate. The wedge is characterised by the presence of water (coming from sediments in the down-going plate) as well as lower temperatures (because the wedge is between two relatively cold lithospheres). As a results a serpentinized mantle wedge is formed that contains hydrous minerals, of which magnetite is an example, that alter the composition and properties of this region. According to Blakely (2005), this region exhibits both higher magnetic susceptibility and lower densities than the surrounding medium. We analysed five active margin boundaries located

  7. Organic matter composition, metazoan meiofauna and nematode biodiversity in Mediterranean deep-sea sediments (United States)

    Pusceddu, Antonio; Gambi, Cristina; Zeppilli, Daniela; Bianchelli, Silvia; Danovaro, Roberto


    To identify the relationships between the abundance and biodiversity of deep-sea meiofauna and their food resources in the Tyrrhenian Sea (Mediterranean Sea), we have investigated the quantity and biochemical composition of sediment organic matter, the metazoan meiofauna abundance and biomass, and the nematode biodiversity at meso- (>50 km) and/or local (sea sites (from 3430 to 3581 m in depth), two of which were close to two seamounts. The analysis of variance revealed significant differences at both the meso- and local scales (i.e. between sites and between stations at each site), and showed that the variability at the mesoscale was much higher than that at the local scale. The values of all of the investigated variables were generally lowest in sediments surrounding the seamounts, suggesting a role for these submersed structures in the abundance of the metazoan meiofauna and their resources. The nematode assemblage composition changed significantly across the four sites. Among the 96 identified nematode species, 14 were exclusively seen in sediments around the two seamounts, and only three species were present at all sampling stations. Differences in the trophic structures of the nematode assemblages were also linked with differences in the biochemical composition of sediment organic matter. These results indicate that high β-diversity in soft sediments around deep seamounts is associated with diversification of the benthic food webs, and suggest that while making the sediments poorer for food availability for benthic consumers, the presence of seamounts enhances the biodiversity in neighbouring sediments.

  8. Boron desorption and fractionation in Subduction Zone Fore Arcs: Implications for the sources and transport of deep fluids (United States)

    Saffer, Demian M.; Kopf, Achim J.


    At many subduction zones, pore water geochemical anomalies at seafloor seeps and in shallow boreholes indicate fluid flow and chemical transport from depths of several kilometers. Identifying the source regions for these fluids is essential toward quantifying flow pathways and volatile fluxes through fore arcs, and in understanding their connection to the loci of excess pore pressure at depth. Here we develop a model to track the coupled effects of boron desorption, smectite dehydration, and progressive consolidation within sediment at the top of the subducting slab, where such deep fluid signals likely originate. Our analysis demonstrates that the relative timing of heating and consolidation is a dominant control on pore water composition. For cold slabs, pore water freshening is maximized because dehydration releases bound water into low porosity sediment, whereas boron concentrations and isotopic signatures are modest because desorption is strongly sensitive to temperature and is only partially complete. For warmer slabs, freshening is smaller, because dehydration occurs earlier and into larger porosities, but the boron signatures are larger. The former scenario is typical of nonaccretionary margins where insulating sediment on the subducting plate is commonly thin. This result provides a quantitative explanation for the global observation that signatures of deeply sourced fluids are generally strongest at nonaccretionary margins. Application of our multitracer approach to the Costa Rica, N. Japan, N. Barbados, and Mediterranean Ridge subduction zones illustrates that desorption and dehydration are viable explanations for observed geochemical signals, and suggest updip fluid migration from these source regions over tens of km.

  9. Compositional Data for Bengal Delta Sediment Collected from a Borehole at Rajoir, Bangladesh (United States)

    Breit, George N.; Yount, James C.; Uddin, Md. Nehal; Muneem, Ad. Atual; Lowers, Heather; Berry, Cyrus J.; Whitney, John W.


    Processes active within sediment of the Bengal basin have attracted world concern because of the locally high content of arsenic dissolved in ground water drawn from that sediment. Sediment samples were collected from a borehole in the town of Rajoir, Rajoir upazila, Madaripur district, Bangladesh, to investigate the processes contributing to arsenic contamination. The samples were mineralogically and chemically analyzed to determine compositional variations related to the arsenic content of the sediment. Mineralogy of the sediment was determined using powder X-ray diffraction. Bulk chemical composition was measured by Combustion; Inductively Coupled Plasma Atomic Emission Spectroscopy; Energy Dispersive X-ray Fluorescence; and Hydride Generation Atomic Absorption Spectrophotometry. Sediment was treated with 0.5 N HCl and resulting solutions were analyzed, primarily to evaluate the abundance and oxidation state of acid-soluble iron. Acid-volatile sulfide, acid-soluble sulfate, and reducible sulfide were also measured on a few samples. Sediment sampled at Rajoir is typically unlithified, gray, micaceous, feldspathic arenaceous sand with a few silt and clay layers. Arsenic content of the sediment ranges from 0.6 to 21 ppm with a median of 1.2 ppm.

  10. Earthquake nucleation in weak subducted carbonates

    NARCIS (Netherlands)

    Kurzawski, Robert M.; Stipp, Michael; Niemeijer, André R.; Spiers, Chirstopher J.; Behrmann, Jan H.

    Ocean-floor carbonate- and clay-rich sediments form major inputs to subduction zones, especially at low-latitude convergent plate margins. Therefore, knowledge of their frictional behaviour is fundamental for understanding plate-boundary earthquakes. Here we report results of mechanical tests

  11. Bulk Sediment and Diatom Silica Carbon Isotope Composition from Coastal Marine Sediments off East Antarctica

    NARCIS (Netherlands)

    Berg, S.; Leng, M.J.; Kendrick, C.P.; Cremer, H.; Wagner, B.


    Organic carbon occluded in diatom silica is assumed to be protected from degradation in the sediment. δ13C from diatom carbon (δ13C(diatom)) therefore potentially provides a signal of conditions during diatom growth. However, there have been few studies based on δ13C(diatom). Numerous variables can

  12. Magnetic susceptibility and element composition mangrove sediments in Malang, East Java (United States)

    Azzahro, Rosyida; Zulaikah, Siti; Diantoro, Markus; Budi, Pranitha Septiana


    Mangrove sediment has a unique environmental absorption characteristics, as it has two sources of sediment which are from allocthonous sediment and authochtonous sediment. In this research, the mangrove sediment samples are taken from Clungup Mangrove Conservation in Malang, East Java, Indonesia. The samples are taken from four spots around the mouth of the river, and four spots around mangrove conservation. Those samples are analyzed based on the magnetic characteristics and the element composition to reveal the magnetic properties and element composition so in the future they can be used as indicators to trace the source of magnetic minerals that are precipitated in the mangrove ecosystem. The magnetic susceptibility value based on mass for mangrove sediment around the river area h as the range of (38,8-2130)×10-8m3kg-1, while for the conservation area has the range of (0,97-122,5)×10-8m3kg-1. Based on XRF analysis, the mangrove sediment both from the river area and mangrove conservation area has a non-metallic element S, Br, metallic element Ca, Si, Al, K, Ti, Sr, and heavy metallic element Fe, Ni, Cu, Cr, Zn, Zr, Mn, and V, with the highest concentration of Fe element followed by Ca, Al, Si, and Ti.

  13. Compositional changes of surface sediments and variability of manganese nodules in the Peru Basin (United States)

    Marchig, Vesna; von Stackelberg, Ulrich; Hufnagel, Heinz; Durn, Goran

    Two types of manganese nodules were observed in the Peru Basin: large botryoidal nodules in basins and small ellipsoidal nodules on slope positions. The sediment in areas with large botryoidal nodules contains a thinner and weaker oxidation zone than the sediment under small ellipsoidal nodules, indicating that diagenetic processes in the sediment, which supply manganese nodules with metals for their growth, are stronger in sediments on which large botryoidal nodules grow. Organic matter, which activates remobilization of metals, occurs mostly in the form of refractory lipidic compounds in the inner capsule of radiolaria. This material needs bacterial degradation to act as a reducing agent. Easily oxidizable organic components could not be found in the sediments. Other changes in sediment composition do not have a link to manganese nodule growth. Biogenous components (radiolarians, organogenic barite and apatite) increase towards the equatorial high-productivity zone. Authigenous clay minerals (nontronite as well as montmorillonite with high Fe +3 incorporation on positions of ochtaedral Al) increase with distance from the continent. The assessment of environmental impacts will have to take into account the regional differences in sediment composition and the small-scale variability of manganese nodules.

  14. Application of zeolite/hydrous zirconia composite as a novel sediment capping material to immobilize phosphorus. (United States)

    Fan, Yi; Li, Yiwen; Wu, Deyi; Li, Chunjie; Kong, Hainan


    A unique sediment-capping agent consisting of a zeolite/hydrous zirconia composite (ZHZ) was developed and tested for P-immobilization in the overlying water and sediment cores from a freshwater pond. In the ZHZ, NaP1 zeolite was covered with hydrous zirconia, which existed as an amorphous phase. Experimental results in pond water indicated that ZHZ could efficiently remove soluble reactive phosphorus. The 28-day sediment incubation experiments showed that capping sediment with ZHZ resulted in a more efficient, rapid and sustained decrease in P concentration when compared with the traditional alum treatment method. Furthermore, ZHZ increased the sediment stability, resulting in the lowest turbidity, total phosphorus and soluble reactive phosphorus concentrations in overlying water following artificially induced resuspension of sediment. Phosphorus fractionation of sediment showed that the dominant P form transferred from HCl-extractable P to residual P, and the most release-sensitive P (labile P and reductant reactive P) was decreased after ZHZ application. Overall, ZHZ is a highly effective P-immobilization material. ZHZ has high potential as a sediment capping material to control internal P loading in eutrophic water bodies. Copyright © 2017 Elsevier Ltd. All rights reserved.

  15. Multi-scale factors affecting composition, diversity, and abundance of sediment denitrifying microorganisms in Yangtze lakes. (United States)

    Jiang, Xiaoliang; Yao, Lu; Guo, Laodong; Liu, Guihua; Liu, Wenzhi


    Sediment denitrification is the dominant nitrogen removal pathway in many aquatic habitats and can be regulated by local-, landscape-, and regional-scale factors. However, the mechanisms for how these multiple scale factors and their interactions affect the sediment denitrifying communities remain poorly understood. In this study, we investigated the community composition, diversity, and abundance of nitrite reductase genes (nirK and nirS)-encoding denitrifiers in 74 sediment samples from 22 Yangtze lakes using clone library and quantitative PCR techniques. Information of location, climate, catchment land use, water quality, sediment properties, and plant communities at each sampling site was analyzed to elucidate the effects of regional, landscape, and local factors on the characteristics of sediment denitrifying communities. Results of canonical correspondence analysis indicated that local factors were the key determinants of denitrifying community composition, accounting for over 20% of the total variation. Additionally, certain regional and landscape factors, including elevation and catchment built-up land, were also significantly related to the composition of denitrifying communities. Variance partitioning analyses revealed that diversity and abundance in the nirK denitrifier community were largely influenced by local factors, while those in the nirS community were controlled by both local and regional factors. Our findings highlight the importance of using different scale factors to explain adequately the composition and structure of denitrifying communities in aquatic environments.

  16. Plume-induced subduction (United States)

    Gerya, T.; Stern, R. J.; Baes, M.; Sobolev, S. V.; Whattam, S. A.


    Dominant present-day subduction initiation mechanisms require acting plate forces and/or pre-existing zones of lithospheric weakness, which are themselves consequences of plate tectonics. In contrast, recently discovered plume-induced subduction initiation could have started the first subduction zone without pre-existing plate tectonics. Here, we investigate this new mechanism with high-resolution 3D numerical thermomechanical modeling experiments. We show that typical plume-induced subduction dynamics is subdivided into five different stages: (1) oceanic plateau formation by arrival of a mantle plume head; (2) formation of an incipient trench and a descending nearly-circular slab at the plateau margins; (3) tearing of the circular slab; (4) formation of several self-sustained retreating subduction zones and (5) cooling and spreading of the new lithosphere formed between the retreating subduction zones. At the final stage of plume-induced subduction initiation, a mosaic of independently moving, growing and cooling small oceanic plates heading toward individual retreating subduction zones forms. The plates are separated by spreading centers, triple junctions and transform faults and thus the newly formed multi-slab subduction system operates as an embryonic plate tectonic cell. We demonstrate that three key physical factors combine to trigger self-sustained plume-induced subduction: (1) old negatively buoyant oceanic lithosphere; (2) intense weakening of the lithosphere by plume-derived magmas; and (3) lubrication of the forming subduction interface by hydrated oceanic crust. We furthermore discuss that plume-induced subduction, which is rare at present day conditions, may have been common in the Precambrian time and likely started global plate tectonics on Earth.

  17. Composition and exchange capacity of deep sea sediments

    NARCIS (Netherlands)

    Eisma, D.


    The cores discussed in this report present a wide variety of types, ranging from coarse-grained to fine-grained and from predominantly organogene carbonate composition to predominantly mineral composition, while two cores contain a relatively large amount of amorphous (organogene) silica. Also, the

  18. Biochemical composition and sediment temperature in relation to the reproductive cycle in the Lugworm arenicola marina (United States)

    Mayes, E.; Howie, D. I. D.

    Sediment temperature, and the biochemical composition of lugworm tissues, have been studied in relation to the reproductive cycle. Frequency distributions of oocyte diameter were used as an index of reproductive maturity. There is some evidence that the annual cycle of sediment temperature has a role in controlling events in the reproductive cycle. Fluctuations in biochemical composition are due chiefly to the storage and utilisation of reserve materials in the reproductive process. Protein and lipid in the gut tissue are the main reserves used in gametogenesis.

  19. Differences in the composition of archaeal communities in sediments from contrasting zones of Lake Taihu

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    Xianfang Fan


    Full Text Available In shallow lakes, different primary producers might impact the physiochemical characteristics of the sediment and the associated microbial communities. Until now, little was known about the features of sediment Archaea and their variation across different primary producer-dominated ecosystems. Lake Taihu provides a suitable study area with cyanobacteria- and macrophyte-dominated zones co-occurring in one ecosystem. The composition of the sediment archaeal community was assessed using 16S rRNA gene amplicon sequencing technology, based on which the potential variation with respect to the physiochemical characteristics of the sediment was analyzed. Euryarchaeota (30.19% of total archaeal sequences and Bathyarchaeota (28.00% were the two most abundant phyla, followed by Crenarchaeota (11.37%, Aigarchaeota (10.24% and Thaumarchaeota (5.98%. The differences found in the composition of the archaeal communities between the two zones was significant (p = 0.005. Sediment from macrophyte-dominated zones had high TOC and TN content and an abundance of archaeal lineages potentially involved in the degradation of complex organic compounds, such as the order Thermoplasmatales. In the area dominated by cyanobacteria, archaeal lineages related to sulfur metabolism, for example, Sulfolobales and Desulfurococcales, were significantly enriched. Among Bathyarchaeota, subgroups MCG-6 and MCG-15 were significantly accumulated in the sediment of areas dominated by macrophytes whereas MCG-4 was consistently dominant in both type of sediments. The present study contributes to the knowledge of sediment archaeal communities with different primary producers and their possible biogeochemical functions in sediment habitats.

  20. Towards a Quantitative Framework for Modelling the Composition of Clastic Sediments (United States)

    von Eynatten, H.


    The composition of clastic sediments is controlled by a range of processes beginning with initial weathering and erosion of rocks in the source area, followed by abrasion, mixing, and sorting during sediment transport and deposition, and, finally, compaction, authigenesis and intrastratal solution in the course of diagenesis. All of these processes cause specific changes in sediment composition (petrography, chemistry, grain size). Thus, any sediment may be described by summing the incremental changes caused by individual processes, each of it acting at varying intensity depending on the regional geological conditions (e.g., climate, topography, fluid flow). The aim of this contribution is to outline a quantitative model to describe sediment composition. Data on sediment composition are usually compositional data that means each component is non-negative and all components sum to a constant (usually 100%). The sample space for such compositional data is not the real space but the open simplex. Special techniques are necessary to analyse compositional data with statistical rigour. In this contribution an attempt is made to model compositional changes using mathematical operations in the simplex like perturbation, power transformation, and non-centered principal component analysis. This modelling approach can be applied to a wide range of processes and combinations of processes causing compositional changes of soils, sediments, or rocks. To demonstrate the potential of the approach we have chosen two examples from the literature dealing with the initial part of the sedimentary cycle: (i) chemical weathering of granitoid source rocks, both on a local and on a global scale, and (ii) mechanical weathering of high-grade metamorphic and granitoid source rocks leading to comminution and sorting of chemically unaltered detritus. The two examples, based on chemical major element data, demonstrate the usefulness of the approach for quantifying the degree of weathering. In a

  1. Depositionary Margins: The Destruction and Renovation of Subduction Forearcs (United States)

    Vannucchi, P.; Morgan, J. P.; Silver, E. A.; Kluesner, J.


    A depositionary margin is a new framework for forearc evolution that focuses on the potential feedbacks between subduction tectonics, sedimentation, and geomorphology that take place during an extreme event of subduction erosion. These feedbacks can lead to the creation of a forearc structure that extends the traditional division of forearcs into accretionary or erosive subduction margins by demonstrating a mode of rapid basin accretion during an erosive event at a subduction margin. A depositionary mode of forearc evolution occurs when terrigenous sediments are deposited directly on the forearc while it is being removed from below by subduction erosion. In the most extreme case, an entire forearc can be removed by a single subduction erosion event followed by depositionary replacement without involving transfer of sediments from the incoming plate. We need to further recognize that subduction forearcs are often shaped by interactions between slow, long-term processes and sudden extreme events reflecting the sudden influences of large-scale morphological variations in the incoming plate. Both types of processes contribute to the large-scale architecture of the forearc, with extreme events associated with a replacive depositionary mode that rapidly creates sections of a typical forearc margin. The persistent upward diversion of the megathrust is likely to affect its geometry, frictional nature, and hydrogeology. Therefore, the stresses along the fault and individual earthquake rupture characteristics are also expected to be more variable in these erosive systems than in systems with long-lived megathrust surfaces.

  2. Sandstone provenance and U-Pb ages of detrital zircons from Permian-Triassic forearc sediments within the Sukhothai Arc, northern Thailand: Record of volcanic-arc evolution in response to Paleo-Tethys subduction (United States)

    Hara, Hidetoshi; Kunii, Miyuki; Miyake, Yoshihiro; Hisada, Ken-ichiro; Kamata, Yoshihito; Ueno, Katsumi; Kon, Yoshiaki; Kurihara, Toshiyuki; Ueda, Hayato; Assavapatchara, San; Treerotchananon, Anuwat; Charoentitirat, Thasinee; Charusiri, Punya


    Provenance analysis and U-Pb dating of detrital zircons in Permian-Triassic forearc sediments from the Sukhothai Arc in northern Thailand clarify the evolution of a missing arc system associated with Paleo-Tethys subduction. The turbidite-dominant formations within the forearc sediments include the Permian Ngao Group (Kiu Lom, Pha Huat, and Huai Thak formations), the Early to earliest Late Triassic Lampang Group (Phra That and Hong Hoi formations), and the Late Triassic Song Group (Pha Daeng and Wang Chin formations). The sandstones are quartzose in the Pha Huat, Huai Thak, and Wang Chin formations, and lithic wacke in the Kiu Lom, Phra That, Hong Hoi and Pha Daeng formations. The quartzose sandstones contain abundant quartz, felsic volcanic and plutonic fragments, whereas the lithic sandstones contain mainly basaltic to felsic volcanic fragments. The youngest single-grain (YSG) zircon U-Pb age generally approximates the depositional age in the study area, but in the case of the limestone-dominant Pha Huat Formation the YSG age is clearly older. On the other hand, the youngest cluster U-Pb age (YC1σ) represents the peak of igneous activity in the source area. Geological evidence, geochemical signatures, and the YC1σ ages of the sandstones have allowed us to reconstruct the Sukhothai arc evolution. The initial Sukhothai Arc (Late Carboniferous-Early Permian) developed as a continental island arc. Subsequently, there was general magmatic quiescence with minor I-type granitic activity during the Middle to early Late Permian. In the latest Permian to early Late Triassic, the Sukhothai Arc developed in tandem with Early to Middle Triassic I-type granitic activity, Middle to Late Triassic volcanism, evolution of an accretionary complex, and an abundant supply of sediments from the volcanic rocks to the trench through a forearc basin. Subsequently, the Sukhothai Arc became quiescent as the Paleo-Tethys closed after the Late Triassic. In addition, parts of sediments of

  3. Elemental composition of a deep sediment core from Lake Stocksjoen in the Forsmark area

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    Stroemgren, Maarten [Umeaa Univ. (Sweden). Dept. of Ecology and Environmental Sciences; Brunberg, Anna-Kristina [Uppsala Univ. (Sweden). Dept. of Ecology and Evolution/Limnology


    A deep sediment core was taken from Lake Stocksjoen, situated within the Forsmark site investigation area. The 55 cm long sediment core, representing the entire history of the lake (approx 430 years) was sliced in 5 cm portions and analysed for various chemical elements, using ICP-MS technique. In total, 54 different elements - classified as main elements, heavy metals and trace elements - were analysed. In general terms, three different patterns of stratigraphy were derived from all the analysed elements. Calcium, manganese, lead and mercury occurred in highest concentrations in the upper sediments (<30 cm depth). Phosphorus, zinc, cadmium, antimony, tin and strontium occurred in more even proportions throughout the sediment core. All the other elements were substantially reduced in the upper parts (<30 cm) compared to the deeper parts of the sediment core. Metals that are considered as airborne pollutants were found in low or moderate concentrations. This is in concert with other investigations of pollutants that have been performed in the Forsmark area. The sediment of Lake Stocksjoen is highly organic, and has been so during the entire history of the lake. Much of the organic Material seems to be refractory and less susceptible for mineralisation and respiration during the prevailing environmental conditions. This corresponds well with the characteristic gelatinous cyanophycee gyttja found in the lower parts of the sediment core. Although speculative, the pronounced changes in elemental composition of the sediment at 30 cm depth may correspond to the final isolation of the lake from the Baltic Sea, which occurred approximately 230 years ago. The deeper parts (below 30 cm depth) thus may represent the time period with regular intrusions of brackish water into the lake basin. One important factor governing the environmental conditions and the resulting elemental composition of the sediment is the unusually thick 'microbial mat', which is characteristic

  4. Mineralogy of subducted clay and clay restite in the lower mantle (United States)

    Armstrong, L.; Skora, S. E.; Walter, M. J.


    Seismic tomography indicates that subducting oceanic lithosphere often penetrates the transition zone and eventually the lower mantle [e.g. 1, 2]. While mineralogical changes in the mafic and ultramafic portions of slabs have been well documented experimentally, the phase relations of overlying sediments at pressures above 25 GPa remain poorly studied. This is in part because sediments are expected to partially melt at sub-arc depth (P~2.5-4.5 GPa), and contribute to the genesis of arc magmas. Sediment restites left behind after the extraction of low pressure melts undergo major chemical changes, according to the melting reaction: Coe+Phen+Cpx+H2O = Grt+Ky+Melt [3]. However, sediments may not always melt depending on the thermal regime and volatile availability and composition [3]. Hence, chemically unmodified sediments as well as restites may be entrained to greater depths and contribute to compositional heterogeneity in the deep mantle. Indeed, mineral inclusions with compositions indicative of subducted sedimentary protoliths (CAS-phase; K-hollandite; stishovite) have been reported in 'ultradeep' diamonds and suggest that deep subduction and survival of sediments occurs to at least transition zone depths [4]. With this in mind, we have performed laser heated diamond anvil cell experiments at pressures of 8-80 GPa on two anhydrous glass starting materials: a marine clay and the restite that is left after 50% melt extraction of this clay at 3 GPa and 800 °C [3]. We chose to work with an anhydrous version of the marine clay given that the investigated pressure range exceeds that of phengite stability [5], and phengite is the only hydrous phase in subducted sediments at UHP conditions. The clay was heated along a P-T path representative of a cold subduction geotherm, whereas the clay restite was heated along a hotter subduction geotherm consistent with low pressure melting. Phases were identified by synchrotron X-ray micro-diffraction at beamline I15 of the Diamond

  5. Assessment of Water and Sediment Physical-Chemical Composition in the West Coast of Maracaibo Lake

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    Jorge Moronta-Riera


    Full Text Available The objective of this investigation was to determine the physical and chemical composition of the water streams and sediments of the Maracaibo Lake in three sampling areas located in Tía Juana, Lagunillas and Ceuta in order to know the level of contamination and assess water quality based on permissible values established by the 883 Decree. The results indicate that the overall hydrocarbon concentrations in the water and sediments are above permissible levels. It is concluded that petroleum prospection is the root cause of the lake contamination.

  6. Release of mineral-bound water prior to subduction tied to shallow seismogenic slip off Sumatra. (United States)

    Hüpers, Andre; Torres, Marta E; Owari, Satoko; McNeill, Lisa C; Dugan, Brandon; Henstock, Timothy J; Milliken, Kitty L; Petronotis, Katerina E; Backman, Jan; Bourlange, Sylvain; Chemale, Farid; Chen, Wenhuang; Colson, Tobias A; Frederik, Marina C G; Guèrin, Gilles; Hamahashi, Mari; House, Brian M; Jeppson, Tamara N; Kachovich, Sarah; Kenigsberg, Abby R; Kuranaga, Mebae; Kutterolf, Steffen; Mitchison, Freya L; Mukoyoshi, Hideki; Nair, Nisha; Pickering, Kevin T; Pouderoux, Hugo F A; Shan, Yehua; Song, Insun; Vannucchi, Paola; Vrolijk, Peter J; Yang, Tao; Zhao, Xixi


    Plate-boundary fault rupture during the 2004 Sumatra-Andaman subduction earthquake extended closer to the trench than expected, increasing earthquake and tsunami size. International Ocean Discovery Program Expedition 362 sampled incoming sediments offshore northern Sumatra, revealing recent release of fresh water within the deep sediments. Thermal modeling links this freshening to amorphous silica dehydration driven by rapid burial-induced temperature increases in the past 9 million years. Complete dehydration of silicates is expected before plate subduction, contrasting with prevailing models for subduction seismogenesis calling for fluid production during subduction. Shallow slip offshore Sumatra appears driven by diagenetic strengthening of deeply buried fault-forming sediments, contrasting with weakening proposed for the shallow Tohoku-Oki 2011 rupture, but our results are applicable to other thickly sedimented subduction zones including those with limited earthquake records. Copyright © 2017, American Association for the Advancement of Science.

  7. An Alternative Mechanism for Producing Global Changes in the Carbon Isotopic Composition of Platform Derived Sediments (United States)

    Swart, P. K.


    The stable carbon isotopic composition of the skeletons of carbonate organisms and sediments has been widely used not only in order to derive information upon the burial of organic material throughout the geological record, but also for correlative purposes. While the preferred type of material for analysis in sediments younger than ~ 200 Ma are microfossils derived from oceanic sediments, in older deposits one is forced to use the δ13C of bulk sediments deposited on and surrounding carbonate platforms. Such sediments are often problematic as a result of diagenesis and the fact that they are derived from a variety of different sources which have differing δ13C values. This can lead to the correlation of the δ13C in age equivalent strata prograding from a carbonate platform. A notable example of this is shown in the Bahamas which show good correlations between individual sequences, but little correlation to global carbon curves derived from planktonic and benthonic foraminifera. In order to assess whether similar phenomenon are present surrounding other carbonate edifices over the same time period, the δ13C was measured in Holocene to Miocene aged material from cores taken off the Maldives (Ocean Drilling Program Site 716), the Queensland Plateau (Site 817), the Great Barrier Reef (Sites 821 and 822), and the Great Australian Bight (Site 1126). All these sites showed similar patterns in the δ13C values of the bulk sediments compared to the Bahamas between the present day and the middle Miocene and no correlation with the global δ13C curve. It is suggested that the synchronous variations in the δ13C values in sediments of equivalent age are related to variations in sea level which flood the platform, allowing the production of carbonate sediments with positive δ13C values. These sediments become admixed into pelagic sediments producing an apparent global signal. These results have obvious implications on the use of δ13C records in carbonate derived sediments

  8. Bacterial community composition and extracellular enzyme activity in temperate streambed sediment during drying and rewetting.

    Directory of Open Access Journals (Sweden)

    Elisabeth Pohlon

    Full Text Available Droughts are among the most important disturbance events for stream ecosystems; they not only affect stream hydrology but also the stream biota. Although desiccation of streams is common in Mediterranean regions, phases of dryness in headwaters have been observed more often and for longer periods in extended temperate regions, including Central Europe, reflecting global climate change and enhanced water withdrawal. The effects of desiccation and rewetting on the bacterial community composition and extracellular enzyme activity, a key process in the carbon flow of streams and rivers, were investigated in a typical Central European stream, the Breitenbach (Hesse, Germany. Wet streambed sediment is an important habitat in streams. It was sampled and exposed in the laboratory to different drying scenarios (fast, intermediate, slow for 13 weeks, followed by rewetting of the sediment from the fast drying scenario via a sediment core perfusion technique for 2 weeks. Bacterial community structure was analyzed using CARD-FISH and TGGE, and extracellular enzyme activity was assessed using fluorogenic model substrates. During desiccation the bacterial community composition shifted toward composition in soil, exhibiting increasing proportions of Actinobacteria and Alphaproteobacteria and decreasing proportions of Bacteroidetes and Betaproteobacteria. Simultaneously the activities of extracellular enzymes decreased, most pronounced with aminopeptidases and less pronounced with enzymes involved in the degradation of polymeric carbohydrates. After rewetting, the general ecosystem functioning, with respect to extracellular enzyme activity, recovered after 10 to 14 days. However, the bacterial community composition had not yet achieved its original composition as in unaffected sediments within this time. Thus, whether the bacterial community eventually recovers completely after these events remains unknown. Perhaps this community undergoes permanent changes

  9. Intrinsic and Extrinsic Factors in Subduction Dynamics (United States)

    Billen, Magali; Arredondo, Katrina


    Since the realization that tectonic plates sink into the mantle, in a process we now call subduction, our understanding of this process has improved dramatically through the combined application of observations, theory and modeling. During that time independent research groups focusing on different aspects of subduction have identified factors with a significant impact on subduction, such as three-dimensionality, slab rollback, rheology of the slab and mantle and magnitude of phase changes. However, as each group makes progress we often wonder how these different factors interact as we all strive to understand the real world subduction system. These factors can be divided in two groups: intrinsic factors, including the age of the slab, its thermal structure, composition, and rheology, and extrinsic factors including others forces on plates, overall mantle flow, structure of the overriding plate, rheology of the mantle and phase changes. In addition, while modeling has been a powerful tool for understanding subduction, all models make important (but often necessary) approximations, such as using two dimensions, imposed boundary conditions, and approximations of the conservation equations and material properties. Here we present results of a study in which the "training wheels" are systematically removed from 2D models of subduction to build a more realistic model of subduction and to better understand how combined effects of intrinsic and extrinsic factors contribute to the dynamics. We find that a change from the Boussinesq to the extended Boussinesq form of the conservation equations has a dramatic effect on slab evolution in particular when phase changes are included. Allowing for free (dynamically-driven) subduction and trench motion is numerically challenging, but also an important factor that allows for more direct comparison to observations of plate kinematics. Finally, compositional layering of the slab and compositionally-controlled phase changes also have

  10. MinSORTING: an Excel macro for modelling sediment composition and grain-size distribution (United States)

    Resentini, Alberto; Malusà, Marco G.; Garzanti, Eduardo


    Detrital mineral analyses are gaining increasing attention in the geosciences as new single-grain analytical techniques are constantly improving their resolution, and consequently widening their range of application, including sedimentary petrology, tectonic geomorphology and archaeology (Mange and Wright, 2007; von Eynatten and Dunkl, 2012). We present here MinSORTING, a new tool to quickly predict the size distribution of various minerals and rock fragments in detrital sediments, based on the physical laws that control sedimentation by tractive wind or water currents (Garzanti et al., 2008). The input values requested by the software are the sediment mean size, sorting, fluid type (seawater, freshwater, air) and standard sediment composition chosen from a given array including nine diverse tectonic settings. MinSORTING calculates the bulk sediment density and the settling velocity. The mean size of each single detrital component, assumed as lognormally-distributed, is calculated from its characteristic size-shift with respect to bulk sediment mean size, dependent in turn on its density and shape. The final output of MinSORTING is the distribution of each single detrital mineral in each size classes (at the chosen 0.25, 0.5 or 1 phi intervals). This allows geochronolgists to select the most suitable grain size of sediment to be sampled in the field, as well as the most representative size-window for analysis. Also, MinSORTING provides an estimate of the volume/weight of the fractions not considered in both sizes finer and coarser than the selected size-window. A beta version of the software is available upon request from: Mange, M., and Wright, D. (eds), 2007. Heavy minerals in use. Developments in Sedimentology Series, 58. Elsevier, Amsterdam. Garzanti, E., Andò, S., Vezzoli, G., 2008. Settling-equivalence of detrital minerals and grain-size dependence of sediment composition. Earth and Planetary Science Letters 273, 138-151. von

  11. Diatom-derived carbohydrates as factors affecting bacterial community composition in estuarine sediments. (United States)

    Haynes, Kelly; Hofmann, Tanja A; Smith, Cindy J; Ball, Andrew S; Underwood, Graham J C; Osborn, A Mark


    Microphytobenthic biofilms in estuaries, dominated by epipelic diatoms, are sites of high primary productivity. These diatoms exude large quantities of extracellular polymeric substances (EPS) comprising polysaccharides and glycoproteins, providing a substantial pool of organic carbon available to heterotrophs within the sediment. In this study, sediment slurry microcosms were enriched with either colloidal carbohydrates or colloidal EPS (cEPS) or left unamended. Over 10 days, the fate of these carbohydrates and changes in beta-glucosidase activity were monitored. Terminal restriction fragment length polymorphism (T-RFLP), DNA sequencing, and quantitative PCR (Q-PCR) analysis of 16S rRNA sequences were used to determine whether sediment bacterial communities exhibited compositional shifts in response to the different available carbon sources. Initial heterotrophic activity led to reductions in carbohydrate concentrations in all three microcosms from day 0 to day 2, with some increases in beta-glucosidase activity. During this period, treatment-specific shifts in bacterial community composition were not observed. However, by days 4 and 10, the bacterial community in the cEPS-enriched sediment diverged from those in colloid-enriched and unamended sediments, with Q-PCR analysis showing elevated bacterial numbers in the cEPS-enriched sediment at day 4. Community shifts were attributed to changes in cEPS concentrations and increased beta-glucosidase activity. T-RFLP and sequencing analyses suggested that this shift was not due to a total community response but rather to large increases in the relative abundance of members of the gamma-proteobacteria, particularly Acinetobacter-related bacteria. These experiments suggest that taxon- and substrate-specific responses within the bacterial community are involved in the degradation of diatom-derived extracellular carbohydrates.

  12. Influence of mineralogical and heavy metal composition on natural radionuclide concentrations in the river sediments. (United States)

    Suresh, G; Ramasamy, V; Meenakshisundaram, V; Venkatachalapathy, R; Ponnusamy, V


    The natural radiation level has been determined for the sediment samples of the Ponnaiyar River with an aim of evaluating the radiation hazard. The mineralogical characterizations of the sediments have been carried out using the Fourier Transform Infrared (FTIR) spectroscopic technique. The relative distribution of major minerals is determined by calculating extinction coefficient. The concentration and spatial distribution of heavy metals (Pb, Cr, Cu, Zn and Ni) have been studied to understand the heavy metal contamination and its level of toxicity. To evaluate the potential toxicity, heavy metal concentrations are compared with different toxicological and geological reference values. The comparison results suggest that the present metals create an adverse effect on the aquatic ecosystems associated with this river. To assess the sediment contamination due to the studied heavy metals, the Pollution Load Index (PLI) is calculated. Multivariate Statistical analyses (Pearson Correlation, Cluster and Factor analysis) were carried out between the parameters obtained from radioactivity, mineralogical and geochemical analysis to know the existing relations. Obtained results showed that the effect of mineralogy on level of radioactivity should be significant. However, mineralogy effect on heavy metal composition in the sediments should be limited, indicating that other factors such as vicinity of the pollution sources are more important. Also, the influence of mineralogical characterization on level of radioactivity is significant, whereas the influence of the heavy metal composition on level of radioactivity should be limited. Copyright © 2011 Elsevier Ltd. All rights reserved.

  13. Bioassay of Lake Onego bottom sediments toxicity based on their chemical composition and deepwater macrozoobenthos state

    Directory of Open Access Journals (Sweden)

    Kalinkina Nataliya Michailovna


    Full Text Available The bioassay of the toxicity of bottom sediments sampled in different areas of Lake Onega was carried out by crustaceans biotesting (Ceriodaphnia affinis Lillijeborg. It was shown that in the most areas of Lake Onega there are non-toxic bottom sediments. Toxic bottom sediments were found in Kondopogskaya Bay, intensively polluted with pulp-and-paper mill wastewaters. For the first time in the deep central part of Lake Onega the area was revealed where the toxic bottom sediments contain a high content of iron, manganese and other trace elements typical for the central areas of the lake. The mapping of the bottom of Lake Onega was accomplished, and three zones were identified based on the analysis of the data concerning the chemical composition of bottom sediments, bioassay toxicity data and the results of the deepwater macrozoobenthos assessment. For each zone the parameters of the main groups of benthos (Amphipoda, Oligochaeta, Chironomidae were defined. The first zone is located in the area of intensive anthropogenic influence (Kondopogskaya Bay, Petrozavodskaya Bay, Povenets Bay, Kizhi Skerries. The second zone is located mostly in the deep part of Petrozavodskaya Bay, where the most intensive development of amphipods is observed. The third area is identified for the first time: it is located in the central deep part of Lake Onega, where the communities of macrozoobenthos are limited by a natural toxic factor.

  14. Composition and source of butyltins in sediments of Kaohsiung Harbor, Taiwan (United States)

    Dong, Cheng-Di; Chen, Chih-Feng; Chen, Chiu-Wen


    Fifty-eight sediment samples were collected from the Kaohsiung Harbor (Taiwan) for analyses of monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT), using gas chromatography/flame photometric detector (GC/FPD). The concentration of total butyltins (ΣBTs), sum of MBT, DBT, and TBT, varied from 3.9 to 158.5 ng Sn/g dw in sediment samples with TBT being the major component of the sediment samples, except for the vicinity of the Love River mouth where MBT was the most abundant BT compound (a proportion of over 57%). Based on the BTs concentration, distribution, composition and correlations, the sources of BTs found in harbor sediments are shipping activities, and TBT is the main pollutant; the estuary (i.e. Love River) has been the anthropogenic source of MBT from upstream inputs. Influences of TBT on aquatic organisms are evaluated using the toxicity guidelines proposed by the US EPA (US Environmental Protection Agency) and the ACCI (assessment class criterion for imposex) proposed by OSPAR (Oslo and Paris Commission). The evaluation shows that the TBT contained in the sediment at Kaohsiung Harbor is likely to have a negative influence at ACCI class C because gastropods present imposex and TBT levels are above ecotoxicological assessment criteria (EAC) limits.

  15. Factors that control the stable carbon isotopic composition of methane produced in an anoxic marine sediment (United States)

    Alperin, M. J.; Blair, Neal E.; Albert, D. B.; Hoehler, T. M.; Martens, C. S.


    The carbon isotopic composition of methane produced in anoxic marine sediment is controlled by four factors: (1) the pathway of methane formation, (2) the isotopic composition of the methanogenic precursors, (3) the isotope fractionation factors for methane production, and (4) the isotope fractionation associated with methane oxidation. The importance of each factor was evaluated by monitoring stable carbon isotope ratios in methane produced by a sediment microcosm. Methane did not accumulate during the initial 42-day period when sediment contained sulfate, indicating little methane production from 'noncompetitive' substrates. Following sulfate depletion, methane accumulation proceeded in three distinct phases. First, CO2 reduction was the dominant methanogenic pathway and the isotopic composition of the methane produced ranged from -80 to -94 per thousand. The acetate concentration increased during this phase, suggesting that acetoclastic methanogenic bacteria were unable to keep pace with acetate production. Second, acetate fermentation became the dominant methanogenic pathway as bacteria responded to elevated acetate concentrations. The methane produced during this phase was progressively enriched in C-13, reaching a maximum delta(C-13) value of -42 per thousand. Third, the acetate pool experienced a precipitous decline from greater than 5 mM to less than 20 micro-M and methane production was again dominated by CO2 reduction. The delta(C-13) of methane produced during this final phase ranged from -46 to -58 per thousand. Methane oxidation concurrent with methane production was detected throughout the period of methane accumulation, at rates equivalent to 1 to 8 percent of the gross methane production rate. Thus methane oxidation was too slow to have significantly modified the isotopic signature of methane. A comparison of microcosm and field data suggests that similar microbial interactions may control seasonal variability in the isotopic composition of methane

  16. Sapropelic, diatomaceous and coccolith sediments (units Ib, Ia) of the Black Sea bottom genesis, composition and properties


    Dimitrov, D.


    Holocene Black Sea basin sediments were formed in our opinion in happened geocatastrofic event on the border Pleistocene-Holocene (8-9 thousand years ago). As a result on the Upper Pleistocene lake sediments occur organogenicmineral (sapropel diatoms and coccolith) marine sediments. The characteristic features of happened catastrophe is the occurrence of hydrogen sulfide charging that conserved the organic matter and protect it from decomposition. Chemical composition and properties of deep w...

  17. Sediment composition influences spatial variation in the abundance of human pathogen indicator bacteria within an estuarine environment.

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    Tracy L Perkins

    Full Text Available Faecal contamination of estuarine and coastal waters can pose a risk to human health, particularly in areas used for shellfish production or recreation. Routine microbiological water quality testing highlights areas of faecal indicator bacteria (FIB contamination within the water column, but fails to consider the abundance of FIB in sediments, which under certain hydrodynamic conditions can become resuspended. Sediments can enhance the survival of FIB in estuarine environments, but the influence of sediment composition on the ecology and abundance of FIB is poorly understood. To determine the relationship between sediment composition (grain size and organic matter and the abundance of pathogen indicator bacteria (PIB, sediments were collected from four transverse transects of the Conwy estuary, UK. The abundance of culturable Escherichia coli, total coliforms, enterococci, Campylobacter, Salmonella and Vibrio spp. in sediments was determined in relation to sediment grain size, organic matter content, salinity, depth and temperature. Sediments that contained higher proportions of silt and/or clay and associated organic matter content showed significant positive correlations with the abundance of PIB. Furthermore, the abundance of each bacterial group was positively correlated with the presence of all other groups enumerated. Campylobacter spp. were not isolated from estuarine sediments. Comparisons of the number of culturable E. coli, total coliforms and Vibrio spp. in sediments and the water column revealed that their abundance was 281, 433 and 58-fold greater in sediments (colony forming units (CFU/100g when compared with the water column (CFU/100ml, respectively. These data provide important insights into sediment compositions that promote the abundance of PIB in estuarine environments, with important implications for the modelling and prediction of public health risk based on sediment resuspension and transport.

  18. Sediment composition influences spatial variation in the abundance of human pathogen indicator bacteria within an estuarine environment. (United States)

    Perkins, Tracy L; Clements, Katie; Baas, Jaco H; Jago, Colin F; Jones, Davey L; Malham, Shelagh K; McDonald, James E


    Faecal contamination of estuarine and coastal waters can pose a risk to human health, particularly in areas used for shellfish production or recreation. Routine microbiological water quality testing highlights areas of faecal indicator bacteria (FIB) contamination within the water column, but fails to consider the abundance of FIB in sediments, which under certain hydrodynamic conditions can become resuspended. Sediments can enhance the survival of FIB in estuarine environments, but the influence of sediment composition on the ecology and abundance of FIB is poorly understood. To determine the relationship between sediment composition (grain size and organic matter) and the abundance of pathogen indicator bacteria (PIB), sediments were collected from four transverse transects of the Conwy estuary, UK. The abundance of culturable Escherichia coli, total coliforms, enterococci, Campylobacter, Salmonella and Vibrio spp. in sediments was determined in relation to sediment grain size, organic matter content, salinity, depth and temperature. Sediments that contained higher proportions of silt and/or clay and associated organic matter content showed significant positive correlations with the abundance of PIB. Furthermore, the abundance of each bacterial group was positively correlated with the presence of all other groups enumerated. Campylobacter spp. were not isolated from estuarine sediments. Comparisons of the number of culturable E. coli, total coliforms and Vibrio spp. in sediments and the water column revealed that their abundance was 281, 433 and 58-fold greater in sediments (colony forming units (CFU)/100g) when compared with the water column (CFU/100ml), respectively. These data provide important insights into sediment compositions that promote the abundance of PIB in estuarine environments, with important implications for the modelling and prediction of public health risk based on sediment resuspension and transport.

  19. Nitrate distribution and isotopic composition in vadose-zone sediments underlying large dairy operations (United States)

    Esser, B. K.; Singleton, M. J.; Moran, J. E.; Roberts, S. K.; Barton, C. G.; Watanabe, N.; Harter, T.


    Understanding the transport and cycling of nitrate in the vadose zone is essential to 1) linking agronomic models of nitrate flux out of the root zone to groundwater models of nitrate loading at the water table, 2) quantifying the impact of vadose-zone biogeochemical processes on nitrate isotopic composition for the purpose of source attribution, and 3) constraining transport time scales through the vadose zone in order to assess the impact of changes in agricultural nutrient management on underlying groundwater quality. In this study, we have investigated the isotopic composition of water-leachable nitrate extracted from sediment cores underlying three dairy operations in the southern San Joaquin Valley of California. One of the dairy operations is new (less than ten years old) and is sited on former range land; the other two operations are older (with one having been continuously operated for over a century). All use dairy wastewater for irrigation, and have vadose zones of 25-60 meters thickness developed in sedimentary sequences dominated by alluvial fan deposits. Sediment core samples from a UC-Davis monitor well drilling program were extracted with an equal amount of ultrapure water, and analyzed for nitrate isotopic composition using the denitrifying bacteria method at LLNL. The range in nitrate isotopic composition (δ15N,air = 4.8 to 26.6 permil, δ18O,VSMOW = -0.3 to 16.2 permil) is large, comparable to isotopic compositions observed in dairy wastewater-impacted groundwaters (Singleton et al., 2007, ES&T 41:759-765), and varies from site to site. The range is the largest on the oldest operation (δ15N = 5.2 to 26.6), and most tightly clustered on the youngest operation (δ15N = 4.8 to 7.8). Leachable nitrate-δ18O correlates with nitrate-δ15N along a characteristic denitrification trend for individual cores. Leachable nitrate-δ15N is not simply correlated with leachable nitrate concentration (which is generally high in shallow sediments and decreases

  20. Thermal impact of magmatism in subduction zones (United States)

    Rees Jones, David W.; Katz, Richard F.; Tian, Meng; Rudge, John F.


    Magmatism in subduction zones builds continental crust and causes most of Earth's subaerial volcanism. The production rate and composition of magmas are controlled by the thermal structure of subduction zones. A range of geochemical and heat flow evidence has recently converged to indicate that subduction zones are hotter at lithospheric depths beneath the arc than predicted by canonical thermomechanical models, which neglect magmatism. We show that this discrepancy can be resolved by consideration of the heat transported by magma. In our one- and two-dimensional numerical models and scaling analysis, magmatic transport of sensible and latent heat locally alters the thermal structure of canonical models by ∼300 K, increasing predicted surface heat flow and mid-lithospheric temperatures to observed values. We find the advection of sensible heat to be larger than the deposition of latent heat. Based on these results we conclude that thermal transport by magma migration affects the chemistry and the location of arc volcanoes.

  1. A Transformational Journey: Compositional Changes in Organic Matter during Desorption from Sediments (United States)

    Matiasek, S. J.; Pellerin, B. A.; Spencer, R.; Bergamaschi, B. A.; Hernes, P.


    The release of organic matter (OM) from suspended particles via desorption is a critical component of OM cycling since dissolved OM (DOM) fuels aquatic ecosystems and is a precursor for disinfection by-products formation. This study assessed the elemental and molecular composition of DOM desorbed abiotically from sediments and soils of an irrigated agricultural watershed of northern California. Relative to mineral-bound OM, the released DOM was nitrogen-poor (lower carbon:nitrogen ratios) and depleted in amino acids and lignin phenols (lower carbon-normalized yields). Water-extracted DOM appeared substantially more degraded than its parent particulate OM with increased molar contributions of acidic amino acids, non-protein amino acids, and acidic lignin phenols, all molecular indicators of a more extensively processed OM pool. Desorption processes also significantly altered lignin compositional ratios which help distinguish vascular-plant sources of DOM. Specific optical parameters, including spectral slope, specific UV absorbance at 254 nm (SUVA254), and fluorescence index (FI), did not constitute useful proxies for the desorbed DOM pool, while absorption coefficients and fluorescence peak intensities were strongly correlated with extracted DOM concentrations and composition. This study highlights the profound impact of desorption on DOM composition which, if unaccounted for, could lead to misinterpretations of common biomarkers and optical proxies used to predict DOM sources and reactivity. Our findings suggest that sediments contribute a biogeochemically distinct source of DOM to surface waters, with potential impacts on aquatic health and drinking water quality.

  2. Composition And Characteristic Of The Surficial Sediments In The Southern Corniche Of Jeddah, Red Sea Coast

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    Talha A Al-Dubai


    Full Text Available This work discusses the composition and characteristic of the surficial sediments in the southern corniche of Jeddah, Saudi Red Sea coast, in an attempt to infer the surficial distribution pattern of minerals and provenance of sediments. Twenty-six superficial sediments samples were collected from backreef and forereef areas and were analyzed for grain size, CaCO3 content, and mineralogy. The textural of grain size range from gravel to mud fraction. The mud-dominated substrates (<63 µm occur generally in the back-reef area near the shoreline (sheltered area and in the lagoon. Gravel rich-sediments are mostly found in forereef regions. The highest content of aragonite and Mg-calcite occur in the forereef area, probably because to suitability the forereef region for chemical and biochemical precipitation of these minerals. High Mg-calcite and Dolomite are low in both the regions. The pyrite occurs in lagoon; this indicates the reductive conditions in this part. However, on the contrary the percentage of carbonate minerals were low in the backreef-flat area, which could be attributed to the supply of non-carbonate terrigenous materials. The terrigenous material contains quartz, k-feldspar, plagioclase and amphibole minerals and are dominant in backreef-flat area with averages of 12.7%, 7.13%, 2.93% and 0.65%, respectively. Their abundance could be attributed to the supply of terrigenous materials by Aeolian deposits and intermittent Wadis.

  3. Community Composition of Nitrous Oxide-Related Genes in Salt Marsh Sediments Exposed to Nitrogen Enrichment

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    John H. Angell


    Full Text Available Salt marshes provide many key ecosystem services that have tremendous ecological and economic value. One critical service is the removal of fixed nitrogen from coastal waters, which limits the negative effects of eutrophication resulting from increased nutrient supply. Nutrient enrichment of salt marsh sediments results in higher rates of nitrogen cycling and, commonly, a concurrent increase in the flux of nitrous oxide, an important greenhouse gas. Little is known, however, regarding controls on the microbial communities that contribute to nitrous oxide fluxes in marsh sediments. To address this disconnect, we generated profiles of microbial communities and communities of micro-organisms containing specific nitrogen cycling genes that encode several enzymes (amoA, norB, nosZ related to nitrous oxide flux from salt marsh sediments. We hypothesized that communities of microbes responsible for nitrogen transformations will be structured by nitrogen availability. Taxa that respond positively to high nitrogen inputs may be responsible for the elevated rates of nitrogen cycling processes measured in fertilized sediments. Our data show that, with the exception of ammonia-oxidizing archaea, the community composition of organisms involved in the production and consumption of nitrous oxide was altered under nutrient enrichment. These results suggest that previously measured rates of nitrous oxide production and consumption are likely the result of changes in community structure, not simply changes in microbial activity.

  4. Subduction of shallowly formed arc cumulates: Evidence from clinopyroxene compositions of garnet peridotites in the Rio San Juan Complex, northern Dominican Republic (United States)

    Hattori, K.; Tubrett, M.; Saumur, B.-M.; Guillot, S.


    Garnet peridotites are very rare in oceanic subduction complexes, with only two reported occurrences. One is in the Sambagawa metamorphic belt in Shikoku, Japan, and the other example is in the southern part of the Rio Juan Complex, northern Dominican Republic. In both locations, garnet peridotite occurs in close association with eclogites in high metamorphic grade of the terranes. The Rio Juan Complex represents rocks formed during the southwestern subduction of the Proto-Caribbean oceanic plate below the Carribean Plate during late Cretaceous to early Eocene. Garnet peridotites (clinopyroxene[Cpx]-bearing dunite, wehrlite, olivine clinopyroxenite) occur as large (The rocks are all low in Ir-group PGE (Ir, Ru, Os), indicating that they are cumulates of a melt, since these remain in the residue during partial melting. A cumulate origin of the ultramafic rocks is consistent with relatively low Mg contents of olivine (Fo 74-83) compared to olivine in mantle peridotites. Extended trace element plots of the bulk rocks show a so-called "arc geochemical signature" with high fluid-mobile element concentrations, such as Sr, U, and Pb, and low HFSE, such as Nb and Zr, indicating that formation of the parental magmas were related to subduction. Two representative garnet-bearing samples (wehrlite and clinopyroxenite) were selected for trace element analysis of Cpx grains using a LA HR ICP-MS. The data show a negatively sloped normalized pattern of REE; low contents of light REE (0.1-0.3 of the primitive mantle values) and similar concentrations of middle to heavy REE (1-2 of the primitive mantle values). Extended trace element patterns of Cpx are similar between two samples and also to that of the bulk rocks, with low Nb and Zr and high fluid-mobile elements. The Y and heavy REE patterns of Cpx do not show anomalies between the samples. As these elements would be preferentially incorporated into garnet, the lack of anomalies indicates early crystallization of Cpx and later

  5. Composition of Archaea in seawater, sediment, and sponges in the Kepulauan Seribu reef system, Indonesia. (United States)

    Polónia, Ana R M; Cleary, Daniel F R; Duarte, Leticia N; de Voogd, Nicole J; Gomes, Newton C M


    Coral reefs are among the most diverse and productive ecosystems in the world. Most research has, however, focused on eukaryotes such as corals and fishes. Recently, there has been increasing interest in the composition of prokaryotes, particularly those inhabiting corals and sponges, but these have mainly focused on bacteria. There have been very few studies of coral reef Archaea, despite the fact that Archaea have been shown to play crucial roles in nutrient dynamics, including nitrification and methanogenesis, of oligotrophic environments such as coral reefs. Here, we present the first study to assess Archaea in four different coral reef biotopes (seawater, sediment, and two sponge species, Stylissa massa and Xestospongia testudinaria). The archaeal community of both sponge species and sediment was dominated by Crenarchaeota, while the seawater community was dominated by Euryarchaeota. The biotope explained more than 72% of the variation in archaeal composition. The number of operational taxonomic units (OTUs) was highest in sediment and seawater biotopes and substantially lower in both sponge hosts. No "sponge-specific" archaeal OTUs were found, i.e., OTUs found in both sponge species but absent from nonhost biotopes. Despite both sponge species hosting phylogenetically distinct microbial assemblages, there were only minor differences in Kyoto Encyclopedia of Genes and Genomes (KEGG) functional pathways. In contrast, most functional pathways differed significantly between microbiomes from sponges and nonhost biotopes including all energy metabolic pathways. With the exception of the methane and nitrogen metabolic pathway, all energy metabolic pathways were enriched in sponges when compared to nonhost biotopes.

  6. Source, composition, and environmental implication of neutral carbohydrates in sediment cores of subtropical reservoirs, South China (United States)

    Duan, Dandan; Zhang, Dainan; Yang, Yu; Wang, Jingfu; Chen, Jing'an; Ran, Yong


    Neutral monosaccharides, algal organic matter (AOM), and carbon stable isotope ratios in three sediment cores of various trophic reservoirs in South China were determined by high-performance anion-exchange chromatography, Rock-Eval pyrolysis, and Finnigan Delta Plus XL mass spectrometry, respectively. The carbon isotopic compositions were corrected for the Suess effect. The concentrations of total neutral carbohydrates (TCHO) range from 0.51 to 6.4 mg g-1 at mesotrophic reservoirs, and from 0.83 to 2.56 mg g-1 at an oligotrophic reservoir. Monosaccharide compositions and diagnostic parameters indicate a predominant contribution of phytoplankton in each of the three cores, which is consistent with the results inferred from the corrected carbon isotopic data and C/N ratios. The sedimentary neutral carbohydrates are likely to be structural polysaccharides and/or preserved in sediment minerals, which are resistant to degradation in the sediments. Moreover, the monosaccharide contents are highly related to the carbon isotopic data, algal productivity estimated from the hydrogen index, and increasing mean air temperature during the past 60 years. The nutrient input, however, is not a key factor affecting the primary productivity in the three reservoirs. The above evidence demonstrates that some of the resistant monosaccharides have been significantly elevated by climate change, even in low-latitude regions.

  7. Shifts in coastal sediment oxygenation cause pronounced changes in microbial community composition and associated metabolism. (United States)

    Broman, Elias; Sjöstedt, Johanna; Pinhassi, Jarone; Dopson, Mark


    A key characteristic of eutrophication in coastal seas is the expansion of hypoxic bottom waters, often referred to as 'dead zones'. One proposed remediation strategy for coastal dead zones in the Baltic Sea is to mix the water column using pump stations, circulating oxygenated water to the sea bottom. Although microbial metabolism in the sediment surface is recognized as key in regulating bulk chemical fluxes, it remains unknown how the microbial community and its metabolic processes are influenced by shifts in oxygen availability. Here, coastal Baltic Sea sediments sampled from oxic and anoxic sites, plus an intermediate area subjected to episodic oxygenation, were experimentally exposed to oxygen shifts. Chemical, 16S rRNA gene, metagenomic, and metatranscriptomic analyses were conducted to investigate changes in chemistry fluxes, microbial community structure, and metabolic functions in the sediment surface. Compared to anoxic controls, oxygenation of anoxic sediment resulted in a proliferation of bacterial populations in the facultative anaerobic genus Sulfurovum that are capable of oxidizing toxic sulfide. Furthermore, the oxygenated sediment had higher amounts of RNA transcripts annotated as sqr, fccB, and dsrA involved in sulfide oxidation. In addition, the importance of cryptic sulfur cycling was highlighted by the oxidative genes listed above as well as dsvA, ttrB, dmsA, and ddhAB that encode reductive processes being identified in anoxic and intermediate sediments turned oxic. In particular, the intermediate site sediments responded differently upon oxygenation compared to the anoxic and oxic site sediments. This included a microbial community composition with more habitat generalists, lower amounts of RNA transcripts attributed to methane oxidation, and a reduced rate of organic matter degradation. These novel data emphasize that genetic expression analyses has the power to identify key molecular mechanisms that regulate microbial community responses

  8. The composition of Alpine marine sediments (Bündnerschiefer Formation, W Alps) and the mobility of their chemical components during orogenic metamorphism (United States)

    Garofalo, Paolo S.


    The Bündnerschiefer of the Swiss-Italian Alps is a large sedimentary complex deposited on the Piemonte-Liguria and Valais oceans and associated continental margins from the upper Jurassic to Eocene. It is made of a large variety of sequences associated or not with an ophiolitic basement. The Bündnerschiefer makes an accretionary prism that developed syn-tectonically from the onset of alpine subduction, and it records orogenic metamorphism following episodes of HP metamorphism. The Bündnerschiefer shares important similarities with the Otago schists of New Zealand and with the Wepawaug schists of Connecticut, both of which form accretionary prisms and have an orogenic metamorphic imprint. With the aim of testing the hypothesis of mobility of chemical components as a function of metamorphic grade, in this work I present fifty-five bulk chemical analyses of various lithological facies of the Bündnerschiefer collected along the well-studied field gradient of the Lepontine dome of Central Switzerland, in the Prättigau half window of East Switzerland, and in the Tsaté Nappe of Valle d'Aosta (Italy). The dataset includes the concentration of major components, large ion lithophile elements (Rb, Sr, Ba, Cs), high field strength elements (Zr, Ti, Nb, Th, U, Ta, Hf), fluid-mobile light elements (B, Li), volatiles (CO 2, S), REEs, and Y, V, Cr, Co, Sn, Pb, Cu, Zn, Tl, Sb, Be, and Au. These data are compared against the compositions of the global marine sediment reservoir, typical crustal reservoirs, and against the previously measured compositions of Otago and Wepawaug schists. Results reveal that, irrespective of their metamorphic evolution, the bulk chemical compositions of orogenic metasediments are characterized by mostly constant compositional ratios ( e.g., K 2O/Al 2O 3, Ba/Al 2O 3, Sr/CaO, etc.), whose values in most cases are undistinguishable from those of actual marine sediments and other crustal reservoirs. For these rocks, only volatile concentrations

  9. Setting limits for acceptable change in sediment particle size composition: testing a new approach to managing marine aggregate dredging. (United States)

    Cooper, Keith M


    A baseline dataset from 2005 was used to identify the spatial distribution of macrofaunal assemblages across the eastern English Channel. The range of sediment composition found in association with each assemblage was used to define limits for acceptable change at ten licensed marine aggregate extraction areas. Sediment data acquired in 2010, 4 years after the onset of dredging, were used to assess whether conditions remained within the acceptable limits. Despite the observed changes in sediment composition, the composition of sediments in and around nine extraction areas remained within pre-defined acceptable limits. At the tenth site, some of the observed changes within the licence area were judged to have gone beyond the acceptable limits. Implications of the changes are discussed, and appropriate management measures identified. The approach taken in this study offers a simple, objective and cost-effective method for assessing the significance of change, and could simplify the existing monitoring regime. Copyright © 2013 Elsevier Ltd. All rights reserved.

  10. Metamorphic zirconology of continental subduction zones (United States)

    Chen, Ren-Xu; Zheng, Yong-Fei


    Zircon is widely used to date geological events and trace geochemical sources in high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic rocks of continental subduction zones. However, protolith zircons may be modified by three different types of metamorphic recrystallization via mechanisms of solid-state transformation, metasomatic alteration and dissolution reprecipitation; new zircon growth may be induced by dehydration reactions below the wet solidus of crustal rocks (metamorphic zircon) or peritectic reactions above the wet solidus (peritectic zircon). As a consequence, there are different origins of zircon domains in high-grade metamorphic rocks from collisional orogens. Thus, determining the nature of individual zircon domains is substantial to correct interpretation of their origin in studies of isotopic geochronology and geochemical tracing. We advocate an integrated study of zircon mineragraphy (internal structure and external morphology), U-Pb ages, mineral inclusions, trace elements, and Lu-Hf and O isotope compositions. Only in this way we are in a position to advance the simple zircon applications to metamorphic zirconology, enabling discrimination between the different origins of zircon and providing constraints on the property of fluid activity at subduction-zone conditions. The metamorphic recrystallization of protolith zircons and the new growth of metamorphic and peritectic zircons are prominent in HP to UHP metamorphic rocks of collisional orogens. These different types of recrystallized and grown zircons can be distinguished by their differences in element and isotope compositions. While the protolith nature of metamorphosed rocks dictates water availability, the P-T conditions of subduction zones dictate the property of subduction-zone fluids. The fluids of different properties may be produced at different positions of subducting and exhuming crustal slices, and they may physically and chemically mix with each other in continental

  11. Noble gases recycled into the mantle through cold subduction zones (United States)

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


    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.

  12. Methodical Features of the Field Researches of the Anapa Bay-Bar Sediment Composition (United States)

    Krylenko, Marina; Krylenko, Viacheslav; Gusakova, Anastasiya; Kosyan, Alisa


    Resort Anapa (Black Sea coast, Russia) holds leading positions in the Russian market of sanatorium-resort and children's recreation. The 50-200 m sandy beaches of Anapa bay-bar are the main value of the resort. Anapa bay-bar is an extensive accumulative sandy body having the length about 47 km. Obvious attributes of the beaches degradation demanding immediate measures on their protection and restoration are observed in last years. The main reason of degradation is beach material deficiency. To organize researches of the sediments of this extensive natural object is a difficult challenge. It is necessary to reduce number of tests to minimum. It is important to record differences of separate bay-bar sites and to receive comparable data for different seasons and years. Our researches showed that the grain-size sediment composition significantly depends of position on local relief. Consequently, researching of the alongshore change of the sediment size is effectual to realize at this morphological elements. Shelly detritus makes to 30% of total amount of beach sediments. It is necessary to consider that quantitative shell distribution along the coast significantly depends on a configuration of the coastline and an underwater relief. Quantity of the shells for cross-shore profile is maximal near coastline. For identification of the sediment sources and researching of their fluxes to use minerals markers (heavy minerals) is optimum. The maximum of heavy minerals concentration is characteristic for fraction 0.1-0.05mm at depth more 5 m. The maintenance of this fraction within other morphological zones isn't enough for the analysis or is excessively changeable. Use of the revealed features allowed to conduct the representative field researches of grain-size and mineral sediment composition for all morphological zones of underwater and coast part of the Anapa bay-bar. This methodic recommendations are workable for researches on others coast accumulative body. The work is

  13. Diverse melanges of an ancient subduction complex

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    Lash, G.G.


    Three lithologically and structurally diverse melanges occur within an early Paleozoic (Early-Middle Ordovician) subduction complex in the central Appalachian orogen. Type I melange, characterized by horizons of variably deformed sandstone and scaly mudstone that alternate with coherent sandstone-rich sequences, is interpreted to reflect accretion-related deformation of water-saturated trench deposits. Type II melange, composed of exotic radiolaria-bearing mudstone clasts in a scaly mudstone matrix, can be explained by remobilization and mixing of inner-trench slope sediments. Type III melange is a poorly sorted polymict assemblage of native lithology clasts in a scaly mudstone matrix. Evidence of forceful injection of matrix mud into clasts and inferred discordant contacts between melange and surrounding bedded deposits suggest that the type III melange formed from mud diapirism. The close association of these melanges points out the diversity of tectonic and sedimentary processes previously documented from modern convergent margins that may be reflected in older subduction complexes.

  14. Decarbonation of subducting slabs: insight from thermomechanical-petrological numerical modelling (United States)

    Gonzalez, Christopher M.; Gorczyk, Weronika; Gerya, Taras


    This work extends a numerical geodynamic modelling code (I2VIS) to simulate subduction of carbonated lithologies (altered basalts and carbonated sediments) into the mantle. Code modifications now consider devolatilisation of H2O-CO2 fluids, a CO2-melt solubility parameterisation for molten sediments, and allows for carbonation of mantle peridotites. The purpose is to better understand slab generated CO2 fluxes and consequent subduction of carbonates into the deep mantle via numerical simulation. Specifically, we vary two key model parameters: 1) slab convergence rate (1,2,3,4,5 cm y-1) and 2) converging oceanic slab age (20,40,60,80 Ma) based on a half-space cooling model. The aim is to elucidate the role subduction dynamics has (i.e., spontaneous sedimentary diapirism, slab roll-back, and shear heating) with respect to slab decarbonation trends not entirely captured in previous experimental and thermodynamic investigations. This is accomplished within a fully coupled petrological-thermomechanical modelling framework utilising a characteristics-based marker-in-cell technique capable of solving visco-plastic rheologies. The thermodynamic database is modified from its original state to reflect the addition of carbonate as CO2 added to the rock's overall bulk composition. Modifications to original lithological units and volatile bulk compositions are as follows: GLOSS average sediments (H2O: 7.29 wt% & CO2: 3.01 wt%), altered basalts (H2O: 2.63 wt% & CO2: 2.90 wt%), and metasomatised peridotite (H2O: 1.98 wt% & CO2: 1.5 wt%). We resolve stable mineralogy and extract rock properties via PerpleX at a resolution of 5K and 25 MPa. Devolatilisation/consumption and stability of H2O-CO2 fluid is determined by accessing the thermodynamic database. When fluid is released due to unstable conditions, it is tracked via markers that freely advect within the velocity field until consumed. 56 numerical models were completed and our results show excellent agreement in dynamics with

  15. The dynamics of the cellular composition of urine sediment in conditions of an artificial bladder


    Savchuk, R. V.; Kostyev, F. I.; Dekhtiar, Y. M.; Zhukovsky, D. A.; Nasibulin, B. A.; Kuznietsov, D. А.


    Savchuk R. V., Kostyev F. I., Dekhtiar Y. M., Zhukovsky D. A., Nasibulin B. A., Kuznietsov D. А. The dynamics of the cellular composition of urine sediment in conditions of an artificial bladder. Journal of Education, Health and Sport. 2017;7(10):154-161. eISSN 2391-8306. DOI The journal has had 7 points in Ministry of Science and Higher Education parametric evaluati...

  16. The role of frictional strength on plate coupling at the subduction interface

    KAUST Repository

    Tan, Eh


    At a subduction zone the amount of friction between the incoming plate and the forearc is an important factor in controlling the dip angle of subduction and the structure of the forearc. In this paper, we investigate the role of the frictional strength of sediments and of the serpentinized peridotite on the evolution of convergent margins. In numerical models, we vary thickness of a serpentinized layer in the mantle wedge (15 to 25km) and the frictional strength of both the sediments and serpentinized mantle (friction angle 1 to 15, or static friction coefficient 0.017 to 0.27) to control the amount of frictional coupling between the plates. With plastic strain weakening in the lithosphere, our numerical models can attain stable subduction geometry over millions of years. We find that the frictional strength of the sediments and serpentinized peridotite exerts the largest control on the dip angle of the subduction interface at seismogenic depths. In the case of low sediment and serpentinite friction, the subduction interface has a shallow dip, while the subduction zone develops an accretionary prism, a broad forearc high, a deep forearc basin, and a shallow trench. In the high friction case, the subduction interface is steep, the trench is deeper, and the accretionary prism, forearc high and basin are all absent. The resultant free-air gravity and topographic signature of these subduction zone models are consistent with observations. We believe that the low-friction model produces a geometry and forearc structure similar to that of accretionary margins. Conversely, models with high friction angles in sediments and serpentinite develop characteristics of an erosional convergent margin. We find that the strength of the subduction interface is critical in controlling the amount of coupling at the seismogenic zone and perhaps ultimately the size of the largest earthquakes at subduction zones. © 2012. American Geophysical Union. All Rights Reserved.

  17. Subducted oceanic relief locks the shallow megathrust in central Ecuador (United States)

    Collot, Jean-Yves; Sanclemente, Eddy; Nocquet, Jean-Mathieu; Leprêtre, Angélique; Ribodetti, Alessandra; Jarrin, Paul; Chlieh, Mohamed; Graindorge, David; Charvis, Philippe


    Whether subducted oceanic reliefs such as seamounts promote seismic rupture or aseismic slip remains controversial. Here we use swath bathymetry, prestack depth-migrated multichannel seismic reflection lines, and wide-angle seismic data collected across the central Ecuador subduction segment to reveal a broad 55 km × 50 km, 1.5-2.0 km high, low height-to-width ratio, multipeaked, sediment-bare, shallow subducted oceanic relief. Owing to La Plata Island and the coastline being located, respectively, 35 km and 50-60 km from the trench, GPS measurements allow us to demonstrate that the subducted oceanic relief spatially correlates to a shallow, 80 km × 55 km locked interplate asperity within a dominantly creeping subduction segment. The oceanic relief geometrical anomaly together with its highly jagged topography, the absence of a subduction channel, and a stiff erosive oceanic margin are found to be long-term geological characteristics associated with the shallow locking of the megathrust. Although the size and level of locking observed at the subducted relief scale could produce an Mw >7+ event, no large earthquakes are known to have happened for several centuries. On the contrary, frequent slow slip events have been recorded since 2010 within the locked patch, and regular seismic swarms have occurred in this area during the last 40 years. These transient processes, together with the rough subducted oceanic topography, suggest that interplate friction might actually be heterogeneous within the locked patch. Additionally, we find that the subducted relief undergoes internal shearing and produces a permanent flexural bulge of the margin, which uplifted La Plata Island.

  18. On the initiation of subduction (United States)

    Mueller, Steve; Phillips, Roger J.


    Estimates of shear resistance associated with lithospheric thrusting and convergence represent lower bounds on the force necessary to promote trench formation. Three environments proposed as preferential sites of incipient subduction are investigated: passive continental margins, transform faults/fracture zones, and extinct ridges. None of these are predicted to convert into subduction zones simply by the accumulation of local gravitational stresses. Subduction cannot initiate through the foundering of dense oceanic lithosphere immediately adjacent to passive continental margins. The attempted subduction of buoyant material at a mature trench can result in large compressional forces in both subducting and overriding plates. This is the only tectonic force sufficient to trigger the nucleation of a new subduction zone. The ubiquitous distribution of transform faults and fracture zones, combined with the common proximity of these features to mature subduction complexes, suggests that they may represent the most likely sites of trench formation if they are even marginally weaker than normal oceanic lithosphere.

  19. Great earthquakes hazard in slow subduction zones (United States)

    Marcaillou, B.; Gutscher, M.; Westbrook, G. K.


    Research on the Sumatra-Andaman earthquake of 2004 has challenged two popular paradigms; that the strongest subduction earthquakes strike in regions of rapid plate convergence and that rupture occurs primarily along the contact between the basement of the overriding plate and the downgoing plate. Subduction zones presenting similar structural and geodynamic characteristics (slow convergence and thick wedges of accreted sediment) may be capable of generating great megathrust earthquakes (M>8.5) despite an absence of thrust type earthquakes over the past 40 years. Existing deep seismic sounding data and hypocenters are used to constrain the geometry of several key slow subduction zones (Antilles, Hellenic, Sumatra). This geometry forms the basis for numerical modelling of fore-arc thermal structure, which is applied to calculate the estimated width of the seismogenic portion of the subduction fault plane. The margins with the thickest accretionary wedges are commonly found to have the widest (predicted) seismogenic zone. Furthermore, for these margins there exists a substantial (20-60 km wide) region above the up-dip limit for which the contribution to tsunami generation is poorly understood. As the rigidity (mu) of these high-porosity sediments is low, co-seismic slip here can be expected to be slow. Accordingly, the contribution to seismic moment will be low, but the contribution to tsunami generation may be very high. Indeed, recent seismological data from Nankai indicate very low frequency shallow-thrust earthquakes beneath this portion of the accretionary wedge, long-considered to be "aseismic". We propose that thick accumulations of sediment on the downgoing plate and the presence of a thick accretionary wedge can increase the maximum size of the potential rupture fault plane in two ways; 1) by thermally insulating the downgoing plate and thereby increasing the total downdip length of the fault which can rupture seismically and 2) by "smoothing out" the

  20. Transparent heavy minerals and magnetite geochemical composition of the Yangtze River sediments: Implication for provenance evolution of the Yangtze Delta (United States)

    Yue, Wei; Jin, Bingfu; Zhao, Baocheng


    Heavy mineral and detrital magnetite geochemistry were analyzed to extract sediment provenance indexes from different reaches of the modern Yangtze River which were used to trace sediment source of the Yangtze Delta and to speculate its geomorphology change since the Pliocene. Our results show that diagnostic heavy minerals of the upper Yangtze sediment are characterized by clinopyroxene (12% on average) and magnetite (7% on average); the middle reaches by ilmenite, zircon and tourmaline; and the local small rivers by fluorite. Detrital magnetite composition of Ti, Mg, V and Cr is high in the upper Yangtze from the underlying basalt. These diagnostic indexes are then used in the Pliocene sediment core to extract provenance signal of different Yangtze reaches. Analysis of core sediment of the Yangtze Delta reveals that sediment provenance of the Pliocene was from local small rivers. Since the beginning of the Pleistocene, core sediments provenance was similar to that of the middle Yangtze tributaries. After 1.2 Ma, high content of pyroxene and magnetite grains that are rich in Ti, Mg, V, Cr imply sediment provenance signals from the upper Yangtze. Sediment provenance shift from short-distance sources to more distant sources indicates that the geomorphology of the Yangtze Delta region has undergone a great transformation since the Pliocene. This dramatic landform change is likely in response to continuous uplift of the Tibetan plateau and accelerated subsidence of the east China coast since the Pliocene.

  1. Characteristics of heavy metals and Pb isotopic composition in sediments collected from the tributaries in three Gorges Reservoir, China. (United States)

    Gao, Bo; Zhou, Huaidong; Huang, Yong; Wang, Yuchun; Gao, Jijun; Liu, Xiaobo


    The concentrations, distribution, accumulation, and potential ecological risk of heavy metals (Cr, Cu, Zn, Ni, As, Pb, Cd, and Hg) in sediments from the Three Gorges Reservoir (TGR) tributaries were determined and studied. Pb isotopic compositions in sediments were also measured to effectively identify the potential Pb sources. The results showed that the average concentrations of heavy metals in sediment of TGR tributaries were higher than the local background values of soils and sediments in China. The assessment by Geoaccumulation Index indicated that Cu, Ni, and Hg were at the "slightly polluted" level and Cd was ranked as the "moderately polluted" level in tributary sediments of TGR. The assessment by Potential Ecological Risk Index showed that Hg and Cd were the predominant elements in tributary sediments in TGR. The Pb isotopic ratios in sediments varied from 1.171 to 1.202 for (206)Pb/(207)Pb and from 2.459 to 2.482 for (208)Pb/(207)Pb in TGR. All Pb isotopic ratios in sediments were similar to those from coal combustion, lead ores (the mining activities and smelting process), and cement material, indicating that these anthropogenic inputs may be the main sources for Pb pollution in sediments of TGR tributaries.

  2. Biodiversity and community composition of sediment macrofauna associated with deep-sea Lophelia pertusa habitats in the Gulf of Mexico (United States)

    Demopoulos, Amanda W.J.; Bourque, Jill R.; Frometa, Janessy


    Scleractinian corals create three-dimensional reefs that provide sheltered refuges, facilitate sediment accumulation, and enhance colonization of encrusting fauna. While heterogeneous coral habitats can harbor high levels of biodiversity, their effect on the community composition within nearby sediments remains unclear, particularly in the deep sea. Sediment macrofauna from deep-sea coral habitats (Lophelia pertusa) and non-coral, background sediments were examined at three sites in the northern Gulf of Mexico (VK826, VK906, MC751, 350–500 m depth) to determine whether macrofaunal abundance, diversity, and community composition near corals differed from background soft-sediments. Macrofaunal densities ranged from 26 to 125 individuals 32 cm−2 and were significantly greater near coral versus background sediments only at VK826. Of the 86 benthic invertebrate taxa identified, 16 were exclusive to near-coral habitats, while 14 were found only in background sediments. Diversity (Fisher’s α) and evenness were significantly higher within near-coral sediments only at MC751 while taxon richness was similar among all habitats. Community composition was significantly different both between near-coral and background sediments and among the three primary sites. Polychaetes numerically dominated all samples, accounting for up to 70% of the total individuals near coral, whereas peracarid crustaceans were proportionally more abundant in background sediments (18%) than in those near coral (10%). The reef effect differed among sites, with community patterns potentially influenced by the size of reef habitat. Taxon turnover occurred with distance from the reef, suggesting that reef extent may represent an important factor in structuring sediment communities near L. pertusa. Polychaete communities in both habitats differed from other Gulf of Mexico (GOM) soft sediments based on data from previous studies, and we hypothesize that local environmental conditions found near L

  3. Land use-related chemical composition of street sediments in Beijing. (United States)

    Kuang, Cen; Neumann, Thomas; Norra, Stefan; Stüben, Doris


    More than 10 million people are currently living in Beijing. This city faces severe anthropogenic air pollution caused by an intense vehicle increase (11% per year in China), coal combusting power plants, heavy industry, huge numbers of household and restaurant cookers, and domestic heating stoves. Additionally, each year dust storms are carrying particulate matter from the deserts of Gobi and Takla Makan towards Beijing, especially in spring. Other geogenic sources of particulate matter which contribute to the air pollution are bare soils, coal heaps and construction sites occurring in and around Beijing. Streets function as receptor surfaces for atmospheric dusts. Thus, street sediments consist of particles of different chemical compositions from many different sources, such as traffic, road side soils and industry. Distributions and concentrations of various chemical elements in street sediments were investigated along a rural-urban transect in Beijing, China. Chemical elements were determined with X-ray fluorescence analysis. Factor analysis was used to extract most important element sources contributing to particulate pollution along a main arterial route of the Chinese capital. The statistical evaluation of the data by factor analysis identifies three main anthropogenic sources responsible for the contamination of Beijing street sediments. The first source is a steel factory in the western part of Beijing. From this source, Mn, Fe, and Ti were emitted into the atmosphere through chimneys and by wind from coal heaps used as the primary energy source for the factory. The second source is a combination of traffic, domestic heating and some small factories in the center of Beijing discharging Cu, Pb, Zn and Sn. Calcium and Cr characterize a third anthropogenic element source of construction materials such as concrete and mortar. Beside the anthropogenic contamination, some elements like Y, Zr, Nb, Ce, and Rb are mainly derived from natural soils and from the

  4. Sediment Composition and Facies of Coral Reef Islands in the Spermonde Archipelago, Indonesia

    Directory of Open Access Journals (Sweden)

    Alexander Janßen


    Full Text Available Sedimentological and geomorphological characteristics of coral reef islands are strongly related to past and recent boundary conditions such as the hydrodynamic regime, wind directions, sea-level fluctuations, and the ecological footprint of the surrounding reef complexes. Alterations in the physical, chemical, and biological boundary controls may affect the stability of reef islands. Additionally, these factors are of importance in the context of future climate change. Such alterations through time may well be documented within the sedimentary record of reef islands and a better knowledge on its effects could help to improve our understanding of island responses to future changes of the status quo. However, detailed studies on the sedimentology and geomorphology of reef islands from southwest Sulawesi, Indonesia, are still rare. Here we report on the sedimentary composition and related facies zonation of four uninhabited coral reef islands in the Spermonde Archipelago. Sediment samples from onshore- and reef-flat environments were analyzed in regard to their grain size, component assemblages and facies distribution. Our results show that the analyzed island sediments are characterized by medium- to coarse-grained sand fractions and are well to poorly sorted. Across all islands examined, the surface sediment is predominately composed of materials identified as scleractinian coral and coralline red algae fragments, with minor additions from bivalves, gastropods and foraminifers. Importantly, statistical analyses of the variations in the percentage of these components allow for a clear sedimentary distinction of the four study sites into three outer shelf islands, situated closer to the open marine Makassar Strait, and one inner shelf island. On the inner shelf island, additional subsurface sedimentological analyses indicate a potential shift in major sediment contributors through time, preserved as coral-dominated accumulations within the

  5. Isotopic Characteristics of Thermal Fluids from Mexican Subduction Zone (United States)

    Taran, Y.; Inguaggiato, S.


    Chemical (major and trace elements) and isotopic (H,O,N,C,He) composition of waters and gases from thermal springs and geothermal wells of Mexican subduction zone have been measured. Three main geochemical profiles have been realized: (1) along the frontal Trans-Mexican Volcanic Belt (TMVB) zone through high- temperature Acoculco, Los Humeros, Los Azufres and La Primavera hydrothermal systems, Colima and Ceboruco volcanoes; (2) along the for-arc region of Pacific coast (12 groups of hot springs); (3) across the zone, from Pacific coast to TMVB, through the Jalisco Block. Fluids from El Chichon volcano in Chiapanecan arc system and Tacana volcano from the Central America Volcanic Arc have also been sampled. The frontal zone of TMVB is characterized by high 3He/4He ratios, from 7.2Ra in Ceboruco fumaroles to 7.6Ra in gases from Acoculco and Los Humeros calderas (Ra is atmospheric value of 1.4x10-6). These values are significantly higher than those published earlier in 80-s (up to 6.8Ra). Gases from coastal springs are low in 3He, usually < 1Ra with a minimum value of 0.2Ra in the northernmost submarine Punta Mita hot springs and a maximum value of 2.4Ra in La Tuna springs at the southern board of the Colima graben. An important feature of the TMVB thermal fluids is the absence of excess nitrogen in gases and, as a consequence, close to zero d15N values. In contrast, some coastal for-arc gases and gases from the Jalisco Block have high N2/Ar ratios and d15N up to +5 permil. Isotopic composition of carbon of CO2 along TMVB is close to typical "magmatic" values from -3 permil to -5 permil, but d13C of methane varies significantly indicating multiple sources of CH4 in geothermal fluids and a partial temperature control. High 3He/4He ratios and pure atmospheric nitrogen may indicate a low contribution of subducted sediments into the TMVB magmas and magmatic fluids. In contrast, El Chichon and Tacana fluids show some excess nitrogen (N2/Ar up to 500) and variable d15N, but

  6. Occurrence, compositional distribution, and toxicity assessment of pyrethroid insecticides in sediments from the fluvial systems of Chaohu Lake, Eastern China. (United States)

    Wang, Ji-Zhong; Bai, Ya-Shu; Wu, Yakton; Zhang, Shuo; Chen, Tian-Hu; Peng, Shu-Chuan; Xie, Yu-Wei; Zhang, Xiao-Wei


    Surface sediment-associated synthetic pyrethroid insecticides (SPs) are known to pose high risks to the benthic organisms in Chaohu Lake, a shallow lake of Eastern China. However, the pollution status of the lake's tributaries and estuaries is still unknown. The present study was conducted to investigate the occurrence, compositional distribution, and toxicity of 12 currently used SPs in the surface sediments from four important tributaries, as well as in the sediment cores at their estuaries, using GC-MS for quantification. All SPs selected were detectable, with cypermethrin, es/fenvalerate, and permethrin dominant in both surface and core sediments, suggesting that these compounds were extensively applied. Urban samples contained the highest summed concentrations of the 12 SPs analyzed (Σ12SP) in both surface and core sediments compared with rural samples, suggesting that urban areas near aquatic environments posed high risks for SPs. The mean concentration of Σ12SP in surface sediments of each river was generally higher than that found in core sediments from its corresponding estuary, perhaps implying recent increases in SP usage. Surface sediments were significantly dominated by cypermethrin and permethrin, whereas core sediments were dominated by permethrin and es/fenvalerate. The compositional distributions demonstrated a spatial variation for surface sediments because urban sediments generally contained greater percentages of permethrin and cypermethrin, but rural sediments had significant levels of es/fenvalerate and cypermethrin. In all sediment cores, the percentage of permethrin gradually increased, whereas es/fenvalerate tended to decrease, from the bottom sediments to the top, indicating that the former represented fresh input, whereas the latter represented historical residue. Most urban samples would be expected to be highly toxic to benthic organisms due to the residue of SPs based on a calculation of toxic units (TUs) using toxicity data of the

  7. Nitrogen cycling processes and microbial community composition in bed sediments in the Yukon River at Pilot Station (United States)

    Repert, Deborah A.; Underwood, Jennifer C.; Smith, Richard L.; Song, Bongkeun


    Information on the contribution of nitrogen (N)-cycling processes in bed sediments to river nutrient fluxes in large northern latitude river systems is limited. This study examined the relationship between N-cycling processes in bed sediments and N speciation and loading in the Yukon River near its mouth at the Bering Sea. We conducted laboratory bioassays to measure N-cycling processes in sediment samples collected over distinct water cycle seasons. In conjunction, the microbial community composition in the bed sediments using genes involved in N-cycling (narG, napA, nosZ, and amoA) and 16S rRNA gene pyrosequences was examined. Temporal variation was observed in net N mineralization, nitrate uptake, and denitrification rate potentials and correlated strongly with sediment carbon (C) and extractable N content and microbial community composition rather than with river water nutrient concentrations. The C content of the bed sediment was notably impacted by the spring flood, ranging from 1.1% in the midst of an ice-jam to 0.1% immediately after ice-out, suggesting a buildup of organic material (OM) prior to scouring of the bed sediments during ice break up. The dominant members of the microbial community that explained differences in N-processing rates belonged to the genera Crenothrix,Flavobacterium, and the family of Comamonadaceae. Our results suggest that biogeochemical processing rates in the bed sediments appear to be more coupled to hydrology, nutrient availability in the sediments, and microbial community composition rather than river nutrient concentrations at Pilot Station.

  8. Earth's oldest mantle fabrics indicate Eoarchaean subduction. (United States)

    Kaczmarek, Mary-Alix; Reddy, Steven M; Nutman, Allen P; Friend, Clark R L; Bennett, Vickie C


    The extension of subduction processes into the Eoarchaean era (4.0-3.6 Ga) is controversial. The oldest reported terrestrial olivine, from two dunite lenses within the ∼3,720 Ma Isua supracrustal belt in Greenland, record a shape-preferred orientation of olivine crystals defining a weak foliation and a well-defined lattice-preferred orientation (LPO). [001] parallel to the maximum finite elongation direction and (010) perpendicular to the foliation plane define a B-type LPO. In the modern Earth such fabrics are associated with deformation of mantle rocks in the hanging wall of subduction systems; an interpretation supported by experiments. Here we show that the presence of B-type fabrics in the studied Isua dunites is consistent with a mantle origin and a supra-subduction mantle wedge setting, the latter supported by compositional data from nearby mafic rocks. Our results provide independent microstructural data consistent with the operation of Eoarchaean subduction and indicate that microstructural analyses of ancient ultramafic rocks provide a valuable record of Archaean geodynamics.

  9. Accessory minerals and subduction zone metasomatism: a geochemical comparison of two mélanges (Washington and California, U.S.A.) (United States)

    Sorensen, Sorena S.; Grossman, Jeffrey N.


    The ability of a subducted slab or subducted sediment to contribute many incompatible trace elements to arc source regions may depend on the stabilities of accessory minerals within these rocks, which can only be studied indirectly. In contrast, the role of accessory minerals in lower-T and -P metasomatic processes within paleo-subduction zones can be studied directly in subduction-zone metamorphic terranes.

  10. Continental basalts record the crust-mantle interaction in oceanic subduction channel: A geochemical case study from eastern China (United States)

    Xu, Zheng; Zheng, Yong-Fei


    Continental basalts, erupted in either flood or rift mode, usually show oceanic island basalts (OIB)-like geochemical compositions. Although their depletion in Sr-Nd isotope compositions is normally ascribed to contributions from the asthenospheric mantle, their enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE) is generally associated with variable enrichments in the Sr-Nd isotope compositions. This indicates significant contributions from crustal components such as igneous oceanic crust, lower continental crust and seafloor sediment. Nevertheless, these crustal components were not incorporated into the mantle sources of continental basalts in the form of solidus rocks. Instead they were processed into metasomatic agents through low-degree partial melting in order to have the geochemical fractionation of the largest extent to achieve the enrichment of LILE and LREE in the metasomatic agents. Therefore, the mantle sources of continental basalts were generated by metasomatic reaction of the depleted mid-ocean ridge basalts (MORB) mantle with hydrous felsic melts. Nevertheless, mass balance considerations indicate differential contributions from the mantle and crustal components to the basalts. While the depleted MORB mantle predominates the budget of major elements, the crustal components predominate the budget of melt-mobile incompatible trace elements and their pertinent radiogenic isotopes. These considerations are verified by model calculations that are composed of four steps in an ancient oceanic subduction channel: (1) dehydration of the subducting crustal rocks at subarc depths, (2) anataxis of the dehydrated rocks at postarc depths, (3) metasomatic reaction of the depleted MORB mantle peridotite with the felsic melts to generate ultramafic metasomatites in the lower part of the mantle wedge, and (4) partial melting of the metasomatites for basaltic magmatism. The composition of metasomatites is quantitatively dictated by

  11. Variations of Bacterial Community Structure and Composition in Mangrove Sediment at Different Depths in Southeastern Brazil

    Directory of Open Access Journals (Sweden)

    Lucas William Mendes


    Full Text Available Tropical mangroves are considered one of the most productive ecosystems of the world, being characterized as nurseries and food sources for fish and other animals. Microorganisms play important roles in these environments, and the study of bacterial communities is of paramount importance for a better comprehension of mangrove dynamics. This study focused on the structure and composition of bacterial communities in mangrove sediments at different depths and points, located in Southeastern Brazil. Terminal Restriction Fragment Length Polymorphism (T-RFLP was used to determine the community structure, and 16S rRNA gene pyrosequencing was used to characterize the community composition. Redundancy analysis of T-RFLP patterns revealed differences in bacterial community structure according to soil attributes and depth. The parameters K and depth presented significant correlation with general community structure. Most sequences were classified into the phylum Proteobacteria (88%, which presented differences according to the depth, where the classes Betaproteobacteria (21% and Deltaproteobacteria (16% were abundant at 10 cm and Epsilonproteobacteria (35% was abundant at 40 cm depth. Clear differences were observed in community composition as shown by the differential distribution of the phyla Firmicutes (1.13% and 3.8%, for 10 cm and 40 cm respectively, Chloroflexi (2.8% and 0.75%, and Acidobacteria (2.75% and 0.57% according to the depth. Bacterial diversity measurements indicated higher diversity in shallow samples. Taken together, our findings indicate that mangrove holds a diverse bacterial community, which is shaped by the variations found in the ecosystem, such as sediment properties and depth.

  12. Including granulometric sediment coastal data composition into the Black Sea GIS (United States)

    Zhuk, Elena; Khaliulin, Alexey; Krylenko, Marina; Krylenko, Viacheslav; Zodiatis, George; Nikolaidis, Marios; Nikolaidis, Andreas


    The module structure of the Black Sea GIS allows the increasing of its functionality, including new data types and defining new procedures accessing them, their visualization and integration with existing data by their conjoint processing and representation. The Black Sea GIS is released as free software; Mapserver is used as a mapping service; MySQL DBMS works with relational data. A new additional feature provided, is the ability of including coastal data obtained in SB SIO RAS. The data represent granulometric composition of the Anapa bay-bar sediments. The Anapa bay-bar is an accumulative sand form (about 50 km long) located on the northwest Russian Black Sea coast. The entire bay-bar and especially its southern part with sand beaches 50-200 m wide is intensively used in recreation. This work is based on the results of field studies of 2010-2014 in the southern part of the Anapa bay-bar researched by scientists of the Shirshov Institute of Oceanology RAS. Since the shore under consideration has no clearly pronounced reference points, "virtual" points located within 1 km distance from each other were selected. Transversal profiles cross these points. The granulometric composition was studied along with 45 profiles. The samples taken in every profile were from the most characteristic morphological parts of the beach. In this study we used shoreline zone samples. Twenty one granule fractions (mm) were separated in the laboratory. The module which processes coastal data allows to select coastal data based on territory/region and granulometric sediment composition. Also, it allows to visualize coastal maps with user-selected features combined with other GIS data.

  13. Characteristic of quaternary sedimentation on a shelf of the Laptev Sea according to the molecular composition of n-alkanes (United States)

    Ulyantsev, A. S.; Romankevich, E. A.; Bratskaya, S. Yu.; Prokuda, N. A.; Sukhoverkhov, S. V.; Semiletov, I. P.; Sergienko, V. I.


    The molecular composition and distribution of the concentration of n-alkanes are considered for sediments of boreholes drilled in the shallow part of the Laptev Sea, in the area of Buor Khaya Gulf. The diverse molecular composition of n-alkanes is dominated by long-chain odd homologs, which indicate terrigenous organic matter (OM). Heterogeneous distribution and burial of OM are shown under conditions of pulsating contribution of river and thermoabrasive material and multiple changes in them up to hiatuses in sedimentation.

  14. Prokaryotic Community Composition in Arctic Kongsfjorden and Sub-Arctic Northern Bering Sea Sediments As Revealed by 454 Pyrosequencing

    Directory of Open Access Journals (Sweden)

    Yin-Xin Zeng


    Full Text Available Fjords and continental shelves represent distinct marine ecosystems in the pan-arctic region. Kongsfjorden is a glacial fjord that is located on the west coast of Svalbard, and is influenced by both Atlantic and Arctic water masses. The Bering Sea consists of a huge continental shelf in the northeast and a deep ocean basin in the southwest, and is influenced by Pacific water. Microbial community compositions of Arctic sediment samples BJ4 from outer basin and BJ36 from inner basin of Kongsfjorden and sub-Arctic samples NEC5 from shallow shelf and DBS1 from deep basin region of the northern Bering Sea were investigated using 454 pyrosequencing of archaeal and bacterial 16S rRNA genes. Most archaeal sequences in the sediments were related to Thaumarchaeota, though Euryarchaeota were more abundant in the Arctic glacier-influencing inner basin sediment BJ36. Thaumarchaeota Group C3 was the dominant archaeal population in all samples. Proteobacteria and Bacteroidetes dominated the sediment bacterial communities. Acidobacteria and Actinobacteria were also dominant in the northern Bering Sea samples. Alphaproteobacteria and Epsilonproteobacteria were the two main classes in Kongsfjorden sediment bacterial communities while Deltaproteobacteria and Gammaproteobacteria were dominant in the northern Bering Sea sediments. Differences in the presence and abundance of other dominant archaeal and bacterial populations were observed among sediment samples. In contrast to archaeal community differences that the Arctic BJ36 archaeal community was distinct from the sub-Arctic sediments and the Arctic outer basin sediment BJ4, cluster analysis based on bacterial OTU (operational taxonomic unit distributions indicated that the Arctic and sub-Arctic bacterial communities segregated from one another. These results suggest that the sediment archaeal and bacterial community compositions can be driven by different environmental factors. Differences in the presence and

  15. Rare earth, major and trace element composition of Leg 127 sediments (United States)

    Murray, R.W.; Buchholtz ten Brink, Marilyn R.; Brumsack, Hans-Juergen; Gerlach, David C.; Russ III, G. Price


    The relative effects of paleoceanographic and paleogeographic variations, sediment lithology, and diagenetic processes on the final preserved chemistry of Japan Sea sediments are evaluated by investigating the rare earth element (REE), major element, and trace element concentrations in 59 squeeze-cake whole-round and 27 physical-property sample residues from Sites 794, 795, and 797, cored during ODP Leg 127. The most important variation in sedimentary chemical composition is the increase in SiO2 concentration through the Pliocene diatomaceous sequences, which dilutes most other major and trace element components by various degrees. This biogenic input is largest at Site 794 (Yamato Basin), moderately developed at Site 797 (Yamato Basin), and of only minor importance at Site 795 (Japan Basin), potentially reflecting basinal contrasts in productivity with the Yamato Basin recording greater biogenic input than the Japan Basin and with the easternmost sequence of Site 794 lying beneath the most productive waters. There are few systematic changes in solid-phase chemistry resulting from the opal-A/opal-CT or opal-CT/quartz silica phase transformations. Most major and trace element concentrations are controlled by the aluminosilicate fraction of the sediment, although the effects of diagenetic silica phases and manganese carbonates are of localized importance. REE total abundances (IREE) in the Japan Sea are strongly dependent upon the paleoceanographic position of a given site with respect to terrigenous and biogenic sources. REE concentrations at Site 794 overall correspond well to aluminosilicate chemical indices and are strongly diluted by SiO2 within the upper Miocene-Pliocene diatomaceous sequence. Eu/Eu* values at Site 794 reach a maximum through the diatomaceous interval as well, most likely suggesting an association of Eu/Eu* with the siliceous component, or reflecting slight incorporation of a detrital feldspar phase. XREE at Site 795 also is affiliated strongly

  16. Characterization of Vadose Zone Sediment: Uncontaminated RCRA Borehole Core Samples and Composite Samples

    Energy Technology Data Exchange (ETDEWEB)

    Serne, R. Jeffrey; Bjornstad, Bruce N.; Schaef, Herbert T.; Williams, Bruce A.; Lanigan, David C.; Horton, Duane G.; Clayton, Ray E.; Mitroshkov, Alexandre V.; Legore, Virginia L.; O' Hara, Matthew J.; Brown, Christopher F.; Parker, Kent E.; Kutnyakov, Igor V.; Serne, Jennifer N.; Last, George V.; Smith, Steven C.; Lindenmeier, Clark W.; Zachara, John M.; Burke, Deborah S.


    This report was revised in September 2008 to remove acid-extractable sodium data from Tables 4.14, 4.16, 5.20, 5.22, 5.43, and 5.45. The sodium data was removed due to potential contamination introduced during the acid extraction process. The rest of the text remains unchanged from the original report issued in February 2002. The overall goal of the of the Tank Farm Vadose Zone Project, led by CH2M HILL Hanford Group, Inc., is to define risks from past and future single-shell tank farm activities. To meet this goal, CH2M HILL Hanford Group, Inc. asked scientists from Pacific Northwest National Laboratory to perform detailed analyses on vadose zone sediment from within the S-SX Waste Management Area. This report is one in a series of four reports to present the results of these analyses. Specifically, this report contains all the geologic, geochemical, and selected physical characterization data collected on vadose zone sediment recovered from Resource Conservation and Recovery Act (RCRA) borehole bore samples and composite samples.

  17. Shift in the microbial community composition of surface water and sediment along an urban river. (United States)

    Wang, Lan; Zhang, Jing; Li, Huilin; Yang, Hong; Peng, Chao; Peng, Zhengsong; Lu, Lu


    Urban rivers represent a unique ecosystem in which pollution occurs regularly, leading to significantly altered of chemical and biological characteristics of the surface water and sediments. However, the impact of urbanization on the diversity and structure of the river microbial community has not been well documented. As a major tributary of the Yangtze River, the Jialing River flows through many cities. Here, a comprehensive analysis of the spatial microbial distribution in the surface water and sediments in the Nanchong section of Jialing River and its two urban branches was conducted using 16S rRNA gene-based Illumina MiSeq sequencing. The results revealed distinct differences in surface water bacterial composition along the river with a differential distribution of Proteobacteria, Cyanobacteria, Actinobacteria, Bacteroidetes and Acidobacteria (P urban water. PICRUSt metabolic inference analysis revealed a growing number of genes associated with xenobiotic metabolism and nitrogen metabolism in the urban water, indicating that urban discharges might act as the dominant selective force to alter the microbial communities. Redundancy analysis suggested that the microbial community structure was influenced by several environmental factors. TP (P urban river. These results highlight that river microbial communities exhibit spatial variation in urban areas due to the joint influence of chemical variables associated with sewage discharging and construction of hydropower stations. Copyright © 2018 Elsevier B.V. All rights reserved.

  18. The Role of Alkalinity Inputs in the Composition of Sediments in AN Acid Mine Drainage Remediated Stream: Hewett Fork, Ohio (United States)

    Lopez, D. L.; Korenowsky, R. K.; Kruse, N.; Bowman, J.


    Hewett Fork, a tributary of Raccoon Creek in SE Ohio, is severely impacted by acid mine drainage. This stream is being actively treated using a calcium oxide doser. In this work, we report the results of our investigations into the chemical effect of remediation in the stream throughout an evaluation of the chemical composition of its sediments. Results show that the grain size of the sediments is finer in the areas where high alkalinity loads enter the stream, at the output from the doser and downstream of the confluence with alkaline tributaries. The composition of heavy metals (magnesium, aluminum, calcium, nickel, zinc, manganese, potassium, lead, chromium, copper, cobalt and arsenic) is higher in concentration in the fine-grained sediments where alkalinity enters the stream, forming two peaks of high sediment concentration along the stream, one at the doser and the second after the confluence with alkaline tributaries. Iron has a different behavior with a higher sediment concentration downstream from the doser at the areas where the grain size is larger, due to the kinetics of the oxidation process for the formation of iron (III) minerals. These results suggest that in remediation of acid-mine-drainage impacted streams, alkalinity inputs along and oxidation processes are important for the storage of heavy metals in the sediments.

  19. Mineral composition of soils and bottom sediments in bays of Novaya Zemlya (United States)

    Krupskaya, V. V.; Miroshnikov, A. Yu.; Dorzhieva, O. V.; Zakusin, S. V.; Semenkov, I. N.; Usacheva, A. A.


    We have analyzed the specific features of the mineralogical composition of bottom sediments of Blagopoluchiya, Tsivol'ki, and Abrosimov bays and soils on Cape Zhelaniya and the coasts of Abrosimov and Stepovoi bays. The data were obtained during two scientific expeditions of the R/V Professor Shtokman in 2014 (cruise 128) and R/V Akademik Mstislav Keldysh in 2015 (cruise 63). These investigations revealed patterns in the transportation of terrigenous material in the coastal zone of the bays: a decrease in the share of nonclay minerals and an increase in that of clay minerals with distance from shore. The increase in kaolinite and smectite content in soil horizons is related to biochemical weathering, while illite is mainly formed as a result of physical weathering.

  20. Correlation between magnetic parameters and chemical composition of lake sediments from northern Bohemia?Preliminary study (United States)

    Petrovsky, E.; Kapička, A.; Zapletal, K.; Šebestova, E.; Spanilá, T.; Dekkers, M. J.; Rochette, P.

    Recently, magnetic measurements have been used to outline areas with increased loading of toxic metals due to industrial activity. It is supposed that magnetic minerals, which are easily detectable, can carry toxic metals of anthropic origin. However, physical background of this relationship is not comprehended yet. In this study, we present our first results on statistical correlation of various magnetic parameters on one side and chemical composition on the other, obtained on sediments from the bottom of lake Nechranice, located in northern Bohemia; the captive area being typical for intensive industrial and mining activity (brown-coal basins, uranium mines, coal-burning power plants). Our results suggest, that magnetic susceptibility, which has been used in other studies as indicator of increase pollution levels due to local sources, does not actually link to any of the toxic elements in concern. This finding can be explained in terms of complex inlet due to different types of pollution sources.

  1. Tracking along-arc sediment inputs to the Aleutian arc using thallium isotopes (United States)

    Nielsen, Sune G.; Yogodzinski, Gene; Prytulak, Julie; Plank, Terry; Kay, Suzanne M.; Kay, Robert W.; Blusztajn, Jerzy; Owens, Jeremy D.; Auro, Maureen; Kading, Tristan


    Sediment transport from the subducted slab to the mantle wedge is an important process in understanding the chemical and physical conditions of arc magma generation. The Aleutian arc offers an excellent opportunity to study sediment transport processes because the subducted sediment flux varies systematically along strike (Kelemen et al., 2003) and many lavas exhibit unambiguous signatures of sediment addition to the sub-arc mantle (Morris et al., 1990). However, the exact sediment contribution to Aleutian lavas and how these sediments are transported from the slab to the surface are still debated. Thallium (Tl) isotope ratios have great potential to distinguish sediment fluxes in subduction zones because pelagic sediments and low-temperature altered oceanic crust are highly enriched in Tl and display heavy and light Tl isotope compositions, respectively, compared with the upper mantle and continental crust. Here, we investigate the Tl isotope composition of lavas covering almost the entire Aleutian arc a well as sediments outboard of both the eastern (DSDP Sites 178 and 183) and central (ODP Hole 886C) portions of the arc. Sediment Tl isotope compositions change systematically from lighter in the Eastern to heavier in the Central Aleutians reflecting a larger proportion of pelagic sediments when distal from the North American continent. Lavas in the Eastern and Central Aleutians mirror this systematic change to heavier Tl isotope compositions to the west, which shows that the subducted sediment composition is directly translated to the arc east of Kanaga Island. Moreover, quantitative mixing models of Tl and Pb, Sr and Nd isotopes reveal that bulk sediment transfer of ∼0.6-1.0% by weight in the Eastern Aleutians and ∼0.2-0.6% by weight in the Central Aleutians can account for all four isotope systems. Bulk mixing models, however, require that fractionation of trace element ratios like Ce/Pb, Cs/Tl, and Sr/Nd in the Central and Eastern Aleutians occurs after

  2. Effects of pesticides on community composition and activity of sediment microbes--responses at various levels of microbial community organization. (United States)

    Widenfalk, Anneli; Bertilsson, Stefan; Sundh, Ingvar; Goedkoop, Willem


    A freshwater sediment was exposed to the pesticides captan, glyphosate, isoproturon, and pirimicarb at environmentally relevant and high concentrations. Effects on sediment microorganisms were studied by measuring bacterial activity, fungal and total microbial biomass as community-level endpoints. At the sub-community level, microbial community structure was analysed (PLFA composition and bacterial 16S rRNA genotyping, T-RFLP). Community-level endpoints were not affected by pesticide exposure. At lower levels of microbial community organization, however, molecular methods revealed treatment-induced changes in community composition. Captan and glyphosate exposure caused significant shifts in bacterial community composition (as T-RFLP) at environmentally relevant concentrations. Furthermore, differences in microbial community composition among pesticide treatments were found, indicating that test compounds and exposure concentrations induced multidirectional shifts. Our study showed that community-level end points failed to detect these changes, underpinning the need for application of molecular techniques in aquatic ecotoxicology.

  3. Sediment phosphate composition in relation to emergent macrophytes in the Doñana Marshes (SW Spain). (United States)

    Reina, M; Espinar, J L; Serrano, L


    We have studied the effect of the presence of emergent macrophytes on the sediment phosphate composition of a eutrophic shallow marsh on the NE margin of Doñana (SW Spain). Top sediment and water samples were collected from both the open-water and the vegetated sites at three areas covered by different plant species: Scirpus maritimus, Juncus subulatus and Phragmites australis. The concentration of organic matter was significantly higher in the top sediment of sites covered by vegetation than in their adjacent open-water sites at the three vegetation areas. The P-fractional composition showed that the sediment was dominated by the inorganic P-fractions in all cases, reaching the highest concentration in the Ca-bound P-fraction (281-372 microg g(-1) d.w.). The sum of all P-fractions was significantly higher in the top sediment of the sites covered by J. subulatus and S. maritimus than in their adjacent open-water sites, and so were the org-P fraction extracted by hot NaOH and the concentration of phytate within this fraction. Deposition of plant material on the top sediment of areas vegetated by J. subulatus and S. maritimus explains these differences. The P-fractional composition of the seeds from J. subulatus showed that they contained a large proportion of organic P-fractions, particularly of the fraction extracted by hot NaOH (1868 microg g(-1) d.w., 85% of which was phytate). The presence of emergent macrophytes, therefore, influenced the distribution of P-fractions in the sediment depending on plant species. The P-bioavailability of shallow aquatic systems must be fully understood if wetlands are to be protected from further eutrophication.

  4. Buoyant subduction on Venus: Implications for subduction around coronae (United States)

    Burt, J. D.; Head, J. W.


    Potentially low lithospheric densities, caused by high Venus surface and perhaps mantle temperatures, could inhibit the development of negative buoyancy-driven subduction and a global system of plate tectonics/crustal recycling on that planet. No evidence for a global plate tectonic system was found so far, however, specific features strongly resembling terrestrial subduction zones in planform and topographic cross-section were described, including trenches around large coronae and chasmata in eastern Aphrodite Terra. The cause for the absence, or an altered expression, of plate tectonics on Venus remains to be found. Slab buoyancy may play a role in this difference, with higher lithospheric temperatures and a tendency toward positive buoyancy acting to oppose the descent of slabs and favoring under thrusting instead. The effect of slab buoyancy on subduction was explored and the conditions which would lead to under thrusting versus those allowing the formation of trenches and self-perpetuating subduction were defined. Applying a finite element code to assess the effects of buoyant forces on slabs subducting into a viscous mantle, it was found that mantle flow induced by horizontal motion of the convergent lithosphere greatly influences subduction angle, while buoyancy forces produce a lesser effect. Induced mantle flow tends to decrease subduction angle to near an under thrusting position when the subducting lithosphere converges on a stationary overriding lithosphere. When the overriding lithosphere is in motion, as in the case of an expanding corona, subduction angles are expected to increase. An initial stage involved estimating the changes in slab buoyancy due to slab healing and pressurization over the course of subduction. Modeling a slab, descending at a fixed angle and heated by conduction, radioactivity, and the heat released in phase changes, slab material density changes due to changing temperature, phase, and pressure were derived.

  5. Chemical composition of sediments, suspended matter, river water and ground water of the Nile (Aswan-Sohag traverse). (United States)

    Dekov, V M; Komy, Z; Araújo, F; Van Put, A; Van Grieken, R


    Sediment, suspended matter, river water and ground water samples were collected at twelve sites in the drainage valley of the Nile River, around Sohag (Central Egypt) and close to the Aswan High Dam. Elemental composition of the river water (27 elements), ground water (eight elements), suspended matter (12 elements) and sediments (12 elements) was studied. Aswan High Dam construction, agricultural and industrial human activities have led to dramatic changes in the Nile River chemistry. Nowadays, the Nile River has the highest dissolved salt content among the major African rivers. Dissolved transport is a major process for Ca, K, Sr, Zn, Cu, Ni and V. Manganese, Fe and Cr are mainly carried by suspended matter. The Nile suspended matter is exhausted in almost all elements studied (except for Mn) compared to the world average river suspended matter. Along the course of the river, the distribution of elements in the suspended matter and sediments is generally controlled by natural processes: the relative importance of elemental transport phases; and the oxidation, precipitation and sedimentation of mineral species through the varying physico-chemical conditions of the environment. Pollution input in the Nile particulate load is not major, as compared to the natural inputs. Eight genetic particle types describe the composition of the Nile suspended matter and sediments: (1) biogenous-aeolian (or silica); (2) terrigenous (Fe-aluminosilicate); (3) authigenic (calcium carbonate); (4) biogenous (apatite); (5) authigenous-terrigenous (Fe-oxyhydroxide-montmorillonite); (6) diagenetic (iron-sulfide); (7) terrigenous (titanium oxide); (8) authigenous (Mn-Fe-oxyhydroxide).

  6. Improved prediction of vegetation composition in NW European softwater lakes by combining location, water and sediment chemistry

    DEFF Research Database (Denmark)

    Pulido Pérez, Cristina; Jensen, Kaj Sand; Lucassen, Esther C.H.E.T.


    with environmental variables for surface water, porewater and sediment significantly improved prediction of vegetation composition. Specifically, the combination of latitude, surface water alkalinity, porewater phosphate and redox potential offered the highest correlation (BIO ENV correlation 0.66) to vegetation......Isoetids, as indicators of near-pristine softwater lakes, have a high priority in national and international (European Water Directive Framework) assessments of ecological lake quality. Our main goal was to identify the most important environmental factors that influence the composition of plant...... communities and specifically determine the presence and abundance of the isoetid Lobelia dortmanna in NW European softwater lakes. Geographical position and composition of surface water, porewater, sediment and plant communities were examined in 39 lakes in four regions (The Netherlands, Denmark, West Norway...

  7. Minor impact of ocean acidification to the composition of the active microbial community in an Arctic sediment. (United States)

    Tait, Karen; Laverock, Bonnie; Shaw, Jennifer; Somerfield, Paul J; Widdicombe, Steve


    Effects of ocean acidification on the composition of the active bacterial and archaeal community within Arctic surface sediment was analysed in detail using 16S rRNA 454 pyrosequencing. Intact sediment cores were collected and exposed to one of five different pCO(2) concentrations [380 (present day), 540, 750, 1120 and 3000 μatm] and RNA extracted after a period of 14 days exposure. Measurements of diversity and multivariate similarity indicated very little difference between pCO(2) treatments. Only when the highest and lowest pCO(2) treatments were compared were significant differences evident, namely increases in the abundance of operational taxonomic units most closely related to the Halobacteria and differences to the presence/absence structure of the Planctomycetes. The relative abundance of members of the classes Planctomycetacia and Nitrospira increased with increasing pCO(2) concentration, indicating that these groups may be able to take advantage of changing pH or pCO(2) conditions. The modest response of the active microbial communities associated with these sediments may be due to the low and fluctuating pore-water pH already experienced by sediment microbes, a result of the pH buffering capacity of marine sediments, or due to currently unknown factors. Further research is required to fully understand the impact of elevated CO(2) on sediment physicochemical parameters, biogeochemistry and microbial community dynamics. © 2013 John Wiley & Sons Ltd and Society for Applied Microbiology.

  8. Composite cement mortars based on marine sediments and oyster shell powder

    Directory of Open Access Journals (Sweden)

    Ez-zaki, H.


    Full Text Available Additions of dredged marine sediments and oyster shell powder (OS as cement substitute materials in mortars are examined by several techniques. The sediments have high water and chloride contents and calcite, quartz, illite and kaolinite as principal minerals. The OS powders are entirely composed of calcium carbonate and traces of other impurities. Four mixtures of treated sediments and OS powders at 650 °C and 850 °C are added to Portland cement at 8%, 16% and 33% by weight. The hydration of composite pastes is followed by calorimetric tests, the porosity accessible to water, the bulk density, the permeability to gas, the compressive strength and the accelerated carbonation resistance are measured. In general, the increase of addition amounts reduced the performance of mortars. However, a reduction of gas permeability was observed when the addition was up to 33%. Around 16% of addition, the compressive strength and carbonation resistance were improved.En este trabajo se ha valorado la sustitución de cemento en morteros por sedimentos marinos dragados y polvo de concha de ostra (OS. Los sedimentos tienen altos contenidos de agua, cloruros, calcita, cuarzo, illita y caolinita como minerales principales. Los polvos OS están compuestos de carbonato cálcico y trazas de otras impurezas. Se añadieron a un cemento Portland, cuatro mezclas de los sedimentos y polvos de OS tratados a 650 °C y 850 °C en proporciones del 8%, 16% y 33% en peso. La hidratación de pastas se estudió a través de calorimetría. Se estudió además la porosidad accesible al agua, densidad aparente, permeabilidad al gas, resistencia a compresión y carbonatación acelerada. En general, un aumento en la adición produjo una reducción del rendimiento de los morteros. Se observó, sin embargo, una reducción de la permeabilidad a los gases con porcentajes de adición de hasta el 33%. Con valores del 16% de sustitución, mejoraron las resistencias mecánicas y la

  9. Evolution of the Archaean crust by delamination and shallow subduction. (United States)

    Foley, Stephen F; Buhre, Stephan; Jacob, Dorrit E


    The Archaean oceanic crust was probably thicker than present-day oceanic crust owing to higher heat flow and thus higher degrees of melting at mid-ocean ridges. These conditions would also have led to a different bulk composition of oceanic crust in the early Archaean, that would probably have consisted of magnesium-rich picrite (with variably differentiated portions made up of basalt, gabbro, ultramafic cumulates and picrite). It is unclear whether these differences would have influenced crustal subduction and recycling processes, as experiments that have investigated the metamorphic reactions that take place during subduction have to date considered only modern mid-ocean-ridge basalts. Here we present data from high-pressure experiments that show that metamorphism of ultramafic cumulates and picrites produces pyroxenites, which we infer would have delaminated and melted to produce basaltic rocks, rather than continental crust as has previously been thought. Instead, the formation of continental crust requires subduction and melting of garnet-amphibolite--formed only in the upper regions of oceanic crust--which is thought to have first occurred on a large scale during subduction in the late Archaean. We deduce from this that shallow subduction and recycling of oceanic crust took place in the early Archaean, and that this would have resulted in strong depletion of only a thin layer of the uppermost mantle. The misfit between geochemical depletion models and geophysical models for mantle convection (which include deep subduction) might therefore be explained by continuous deepening of this depleted layer through geological time.

  10. Spatial variability of organic matter molecular composition and elemental geochemistry in surface sediments of a small boreal Swedish lake (United States)

    Tolu, Julie; Rydberg, Johan; Meyer-Jacob, Carsten; Gerber, Lorenz; Bindler, Richard


    The composition of sediment organic matter (OM) exerts a strong control on biogeochemical processes in lakes, such as those involved in the fate of carbon, nutrients and trace metals. While between-lake spatial variability of OM quality is increasingly investigated, we explored in this study how the molecular composition of sediment OM varies spatially within a single lake and related this variability to physical parameters and elemental geochemistry. Surface sediment samples (0-10 cm) from 42 locations in Härsvatten - a small boreal forest lake with a complex basin morphometry - were analyzed for OM molecular composition using pyrolysis gas chromatography mass spectrometry for the contents of 23 major and trace elements and biogenic silica. We identified 162 organic compounds belonging to different biochemical classes of OM (e.g., carbohydrates, lignin and lipids). Close relationships were found between the spatial patterns of sediment OM molecular composition and elemental geochemistry. Differences in the source types of OM (i.e., terrestrial, aquatic plant and algal) were linked to the individual basin morphometries and chemical status of the lake. The variability in OM molecular composition was further driven by the degradation status of these different source pools, which appeared to be related to sedimentary physicochemical parameters (e.g., redox conditions) and to the molecular structure of the organic compounds. Given the high spatial variation in OM molecular composition within Härsvatten and its close relationship with elemental geochemistry, the potential for large spatial variability across lakes should be considered when studying biogeochemical processes involved in the cycling of carbon, nutrients and trace elements or when assessing lake budgets.

  11. Louisville seamount subduction and its implication on mantle flow beneath the central Tonga-Kermadec arc. (United States)

    Timm, Christian; Bassett, Daniel; Graham, Ian J; Leybourne, Matthew I; de Ronde, Cornel E J; Woodhead, Jon; Layton-Matthews, Daniel; Watts, Anthony B


    Subduction of intraplate seamounts beneath a geochemically depleted mantle wedge provides a seldom opportunity to trace element recycling and mantle flow in subduction zones. Here we present trace element and Sr, Nd and Pb isotopic compositions of lavas from the central Tonga-Kermadec arc, west of the contemporary Louisville-Tonga trench intersection, to provide new insights into the effects of Louisville seamount subduction. Elevated (206)Pb/(204)Pb, (208)Pb/(204)Pb, (86)Sr/(87)Sr in lavas from the central Tonga-Kermadec arc front are consistent with localized input of subducted alkaline Louisville material (lavas and volcaniclastics) into sub-arc partial melts. Furthermore, absolute Pacific Plate motion models indicate an anticlockwise rotation in the subducted Louisville seamount chain that, combined with estimates of the timing of fluid release from the subducting slab, suggests primarily trench-normal mantle flow beneath the central Tonga-Kermadec arc system.

  12. A two-way interaction between the Hainan plume and the Manila subduction zone

    NARCIS (Netherlands)

    Mériaux, Catherine A.; Duarte, João C.; Schellart, Wouter P.; Mériaux, Anne Sophie


    The interaction between mantle plumes and subducting slabs is well accepted, but the influence of slabs on plumes has more often been portrayed than the reverse. Here we present three-dimensional upper mantle laboratory models in which a compositional plume rises underneath a subducting plate.

  13. Thallium-isotopic compositions of euxinic sediments as a proxy for global manganese-oxide burial (United States)

    Owens, Jeremy D.; Nielsen, Sune G.; Horner, Tristan J.; Ostrander, Chadlin M.; Peterson, Larry C.


    Thallium (Tl) isotopes are a new and potentially powerful paleoredox proxy that may track bottom water oxygen conditions based on the global burial flux of manganese oxides. Thallium has a residence time of ∼20 thousand years, which is longer than the ocean mixing time, and it has been inferred that modern oxic seawater is conservative with respect to both concentration and isotopes. Marine sources of Tl have nearly identical isotopic values. Therefore, the Tl sinks, adsorption onto manganese oxides and low temperature oceanic crust alteration (the dominant seawater output), are the primary controls of the seawater isotopic composition. For relatively short-term, ∼million years, redox events it is reasonable to assume that the dominant mechanism that alters the Tl isotopic composition of seawater is associated with manganese oxide burial because large variability in low temperature ocean crust alteration is controlled by long-term, multi-million years, average ocean crust production rates. This study presents new Tl isotope data for an open ocean transect in the South Atlantic, and depth transects for two euxinic basins (anoxic and free sulfide in the water column), the Cariaco Basin and Black Sea. The Tl isotopic signature of open ocean seawater in the South Atlantic was found to be homogeneous with ε205Tl = -6.0 ± 0.3 (±2 SD, n = 41) while oxic waters from Cariaco and the Black Sea are -5.6 and -2.2, respectively. Combined with existing data from the Pacific and Arctic Oceans, our Atlantic data establish the conservatism of Tl isotopes in the global ocean. In contrast, partially- and predominantly-restricted basins reveal Tl isotope differences that vary between open-ocean (-6) and continental material (-2) ε205Tl, scaling with the degree of restriction. Regardless of the differences between basins, Tl is quantitatively removed from their euxinic waters below the chemocline. The burial of Tl in euxinic sediments is estimated to be an order of magnitude

  14. Subduction-stage P-T path of eclogite from the Sambagawa belt: Prophetic record for oceanic-ridge subduction (United States)

    Aoya, M.; Uehara, S.; Wallis, S. R.; Enami, M.


    The Sambagawa belt in SW Japan is a subduction-type high-P/T metamorphic belt. Subduction-stage P-T paths of its constituent rocks are important because they directly constrain physical conditions of the EarthOs interior at the time exhumation of high-P/T metamorphic rocks became feasible. Although a few examples of subduction-stage P-T paths for the Sambagawa rocks have been recognized, these are limited to relatively low-pressure regions (~10 kbar). To augment these data the subduction-stage P-T path of the Kotsu glaucophane (Gln) eclogite is derived. The tectonic significance of the derived and previously determined P-T paths is further examined using a new thermal model. By using compositions of matrix minerals and rims of porphyroblastic garnet (Grt), the peak-T conditions of the Kotsu Gln eclogite have been estimated as ~20 kbar/ 600° C. However, the dP/dT of the P-T path leading to the peak-T conditions is unknown. Petrological studies focusing on inclusion minerals in Grt show: (1) albite is absent as inclusions within Grt; (2) acmite (Acm) component of cpx decreased during growth of Grt; (3) Tschermakite (Ts) component of amphibole decreased and Gln component increased during growth of Grt; and (4) Grt-Cpx thermometry shows a temperature increase during growth of Grt. Along with mineral textures observed in the matrix, the Gln-formation reaction can be determined as: 4Acm + 2Ts + 2quartz + H2O (R) 2Gln + 2epidote + hematite. P-T curve of this reaction always has a large positive dP/dT (>7.1 kbar/100 ?C) with the Gln stability field on the high-P/T side. To cross this reaction curve into the Gln stability field during a rise in temperature, the Kotsu eclogite must trace a very steep subduction-type P-T path. Compilation of previously obtained subduction-stage P-T paths for the Sambagawa rocks along with the P-T path of the Kotsu Gln eclogite shows that the series of subduction-stage P-T paths are not distributed on a straight line starting from the origin

  15. Sources of organic matter affect depth-related microbial community composition in sediments of Lake Erhai, Southwest China

    Directory of Open Access Journals (Sweden)

    Wei Xiong


    Full Text Available Sediment cores taken from different areas of the mesotrophic Lake Erhai were analysed to investigate the vertical distribution of bacterial community composition (BCC, as well as physicochemical parameters. PCR-denaturing gradient gel electrophoresis (DGGE, stable carbon isotope (δ13C, C/N atomic ratio and canonical correspondence analysis (CCA were used to explore the relationships between the succession of bacterial communities and environmental variables, emphasising changes in the sources of organic matter (OM. The BCC in natural environments was characterised by DGGE of the 16S rRNA gene with subsequent sequencing of bands of interest. The CCA revealed that the depth-related variation in sediment bacterial communities in different areas of the lake was significantly influenced by varying environmental factors. The OM source, however, played an important role in structuring BCC at all sites. The DGGE banding patterns revealed that the abundance of Deltaproteobacteria decreased with accompanying elevated levels of C4 plant-derived organic carbon. The sequencing of DGGE bands suggested that the majority of the sequences were affiliated with common phylogenetic groups in lake sediments: Chloroflexi, Deltaproteobacteria and Firmicutes. Betaproteobacteria detected in our study appeared as a prominent phylotype in the upper sediment. The Shannon-Wiener diversity index of bacterial communities was directly affected by the OM source. Constant OM sources resulted in a stable higher diversity of bacterial communities and broader enzymatic capabilities to access OM. We conclude that the differences in the diversity of bacterial communities in sediments differing in their sources of OM were related to environmental variables (e.g. water level, river runoff and terrestrial vegetation composition. Our study provided insights into the relationships between natural BCC and OM sources, facilitating a better understanding of microbial community structure in

  16. Synoptic patterns of meiofaunal and macrofaunal abundances and specific composition in littoral sediments (United States)

    Armonies, Werner; Hellwig-Armonies, Monika


    During recent years, many investigations on small zoobenthos have been performed at the island of Sylt. As these studies were carried out sporadically over many years and as different extraction methods were used, comparisons of the results have been hampered. Therefore, in August/September 1986, 24 sites were sampled and evaluated using one quantitative method throughout. Sites range from mud to exposed sand and from the sublittoral to the supralittoral. Macrofauna and the taxa Plathelminthes, Polychaeta, and Oligochaeta are determined to species level. Macrofaunal (>0.5 mm) abundance is highest in mud and continuously decreases with increasing exposure to wave action. Meiofaunal (taxa only intermittently. Related to surface area, no correlation between macro-and meiofaunal abundance is apparent. Plathelminthes and Copepoda reach highest abundance per surface area in sand but their per volume density is higher in mud and muddy sand. Related to sediment volume instead of surface area, the meiofaunal abundance pattern is very similar to the macrofaunal pattern. The faunal composition changes gradually along the tidal gradient without general faunal boundaries. On an averange, the faunal similarity of neighbouring sites is highest in Oligochaeta and lowest in Plathelminthes. Presumably, Oligochaeta tolerate wider ranges of environmental factors. This may explain the low number of oligochaete species. On the other hand, Plathelminthes seem to adapt to relatively narrow ranges of factors and their species richness is highest. Because of macrofaunameiofauna interaction it is suggested that the meiofaunal assemblage will be least stable in mud and muddy sand, and most stable in exposed sand.

  17. The melting of subducted banded iron formations (United States)

    Kang, Nathan; Schmidt, Max W.


    Banded iron formations (BIF) were common shelf and ocean basin sediments 3.5-1.8 Ga ago. To understand the fate of these dense rocks upon subduction, the melting relations of carbonated BIF were determined in Fe-Ca-(Mg)-Si-C-O2 at 950-1400 °C, 6 and 10 GPa, oxidizing (fO2 = hematite-magnetite, HM) and moderately reducing (fO2 ∼CO2-graphite/diamond, CCO) conditions. Solidus temperatures under oxidizing conditions are 950-1025 °C with H2O, and 1050-1150 °C anhydrous, but 250-175 °C higher at graphite saturation (values at 6-10 GPa). The combination of Fe3+ and carbonate leads to a strong melting depression. Solidus curves are steep with 17-20 °C/GPa. Near-solidus melts are ferro-carbonatites with ∼22 wt.% FeOtot, ∼48 wt% CO2 and 1-5 wt.% SiO2 at fO2 ∼ HM and ∼49 wt.% FeOtot, ∼20 wt% CO2 and 19-25 wt.% SiO2 at fO2 ∼ CCO . At elevated subduction geotherms, as likely for the Archean, C-bearing BIF could melt out all carbonate around 6 GPa. Fe-rich carbonatites would rise but stagnate gravitationally near the slab/mantle interface until they react with the mantle through Fe-Mg exchange and partial reduction. The latter would precipitate diamond and yield Fe- and C-rich mantle domains, yet, Fe-Mg is expected to diffusively re-equilibrate over Ga time scales. We propose that the oldest subduction derived diamonds stem from BIF derived melts.

  18. Annual 18O/16O composition of authigenic calcite in varved lake sediments reflects regional air temperature (United States)

    Wirth, Stefanie; Gilli, Adrian


    The oxygen isotopic composition (18O/16O) of authigenic calcite in lake sediments reflects the temperature and the isotopic composition of the lake water from which the calcite is precipitated and thus contains information about the climatic conditions at the time of calcite formation. Varved lake sediments containing laminae of authigenically precipitated calcite provide the possibility to analyze the 18O/16O composition at an annual resolution, thus yielding high-resolution climatic information. Yet, despite this high potential the number of studies having used this approach is relatively low. Reasons for this are probably sampling challenges, the scarceness of suitable varved sediments, missing instrumental records to compare with, as well as uncertainties regarding the factors influencing the calcite isotopic composition (water/air temperature, precipitation, lake-internal factors). Still, annually resolved data of the 18O/16O composition of calcite seems a promising climate proxy and we therefore investigated the 18O/16O pattern of the authigenic calcite in the varved sediments of Lake Zurich. Lake Zurich is a pre-alpine lake with a surface area of 88 km2, a maximal water depth of 137 m and a theoretical water residence time of 1.4 years. Sediments are varved since the late 19th century due to anthropogenic lake eutrophication. For this calibration study, we analyzed the 18O/16O composition of the authigenic calcite for the time period 1960-2010 at annual resolution. The δ18O values range from -10.8 to -13.4 o; and the pattern is dominated by a conspicuous shift to more enriched values between 1985 and 1987. The same shift has been observed for local to large-scale climatic parameters such as lake, river, and groundwater temperatures throughout Switzerland, the mean air temperature for Switzerland, and the NAO index. The consistency of the instrumental temperature data sets with the 18O/16O composition of the authigenic calcite emphasizes the high potential

  19. Subduction related fluids fractionate Nb/Ta (United States)

    Salters, V. J.; Bizimis, M.; Sachi-Kocher, A.; Taylor, R.; Savov, I. P.; Stern, C. R.


    Key differences between the chemical composition of terrestrial materials and those of meteorites have led to the suggestion that a `hidden’ high Nb/Ta reservoir exists in the Earth’s mantle. In order to test this hypothesis we must identify the processes that can create such a reservoir. It has been suggested that during subduction Nb is more refractory then Ta resulting in low Nb/Ta in the subducted slab, which then serves as a reservoir for the high Nb/Ta. Here we report high precision HFSE data on products of the subduction processes thought to fractionate Nb from Ta: boninites (hydrous melting), adakites (slab melting), oceanic island arc basalts and supra subduction zone peridotites. We developed a new method for the high precision determination of Nb, Ta, Zr, Hf concentrations based on a modified version of standard addition. All analyses were performed on a single collector ICPMS (ELEMENT 1), using Y and Yb as internal standards to correct for instrumental drift during the unspiked -spiked sample sequence. Concentrations are calculated using a York- type regression that accounts for all measured and propagated errors. Long-term reproducibility (multiple dissolutions and multiple spike solutions) for the standards BHVO-1, BIR-1 AGV-1 and BCR-1 are better than 0.8% (1s) for Nb/Ta and Zr/Hf ratios. The advantages of this method compared to previous methods are fast throughput, no column chemistry and low blanks. While the Zr/Hf ratios in subduction-related volcanics and ocean island basalts vary by less than a factor of two, the Nb/Ta ratio varies by a factor of four. Most of the Nb/Ta variation is observed in subduction related rocks. Samples with the highest Nb/Ta ratio (up to 19.5) are adakites from the Austral Volcanic Zone (Andes) which are thought to represent eclogitic melts from subducted oceanic crust which was most likely dehydrated. The lowest Nb/Ta (5) was found in boninites from Chichi-Jima, Bonin Island. Samples from Chichi-Jima and from the

  20. Mercury in litterfall and sediment using elemental and isotopic composition of carbon and nitrogen in the mangrove of Southeastern Brazil (United States)

    Fragoso, Cynara Pedrosa; Bernini, Elaine; Araújo, Beatriz Ferreira; Almeida, Marcelo Gomes de; Rezende, Carlos Eduardo de


    Mercury and elemental and isotopic compositions of carbon and nitrogen were determined in litterfall and sediments from the mangrove of the Paraíba do Sul River, Rio de Janeiro, Brazil. Total mercury (THg) and monomethylmercury (MMHg) concentrations in sediment ranged from 33 to 123 ng g-1 and 0.20-1.38 ng g-1, respectively. The δ13C in sediment varied from -29.4 to -26.5‰ and from 2.4 to 5.8‰ in δ15N. The THg concentration in litterfall and its annual input to the mangrove was 21 ± 2 ng g-1 and 16 ± 4 μg m-2 for the species Laguncularia racemosa, 18 ± 1 ng g-1 and 17 ± 3 μg m-2 for Rhizophora mangle, and 53 ± 4 ng g-1 and 33 ± 4 μg m-2 for Avicennia germinans, respectively. The isotopic composition of leaf litter ranged from -28.6 to -26.9‰ for δ13C and 4.5-7.2‰ for δ15N. Both the highest annual Hg input via litterfall and highest sediment Hg concentration were observed in areas dominated by A. germinans. These results suggest that the rate of litterfall of plant species and the atmospheric deposition have played an important role in the Hg biogeochemical cycle in the mangrove ecosystem.

  1. Seismicity and the subduction process (United States)

    Ruff, L.; Kanamori, H.


    There is considerable variation between subduction zones in the largest characteristic earthquake within each zone. Assuming that coupling between downgoing and upper plates is directly related to characteristic earthquake size, tests for correlations between variation in coupling and other physical features of subduction zones are conducted: the lateral extent and penetration depth of Benioff zones, age of subducting lithosphere, convergence rate, and back-arc spreading. Using linear multivariate regression, coupling is correlated with two variables: convergence rate and lithosphere age. Secondary correlations within the data set are penetration depth versus lithosphere age, and lateral extent versus convergence rate. Taken together, the observed correlations suggest a simple qualitative model where convergence rate and lithosphere age determine the horizontal and sinking rates, respectively, of slabs: these parameters influence the seismic coupling in the subduction zone. In the limit of a fast sinking rate and slow convergence rate, back-arc spreading occurs and thereby appears to be a passive process.

  2. Quantitative model of carbon and nitrogen isotope composition to highlight phosphorus cycling and sources in coastal sediments (Toulon Bay, France). (United States)

    Dang, Duc Huy; Evans, R Douglas; Durrieu, Gael; Layglon, Nicolas; El Houssainy, Amonda; Mullot, Jean-Ulrich; Lenoble, Véronique; Mounier, Stéphane; Garnier, Cédric


    Nutrient loadings from either point or non-point sources to the environment are related to the growing global population. Subsequent negative impacts of nutrient loading to aquatic environments requires a better understanding of the biogeochemical cycling and better tools to track their sources. This study examines the carbon (C), nitrogen (N) and phosphorus (P) discharge and cycling in a Mediterranean coastal area from rivers to marine sediments and assesses the anthropogenic contributions. Carbon and N concentrations and isotope compositions in rivers particles, surface sediments, and sediment cores were investigated to build up a quantitative multiple-end-member mixing model for C and N isotopes. This model predicts the contribution of four natural and one anthropogenic sources to the sediments and highlighted the anthropogenic fraction of P based on the relationship with anthropogenic δ15N. Although P is a monoisotopic element and total P concentration has been the sole index to study P loading, this study suggests an alternative approach to differentiate anthropogenic and non-anthropogenic (diagenetic) P, revealed point and non-point sources of P, and the corresponding P loading. Also, the diagenetic P background has been calculated for the 50-cm sediment layer of the whole Bay. Copyright © 2017 Elsevier Ltd. All rights reserved.

  3. Mineralogical, chemical composition and distribution of rare earth elements in clay-rich sediments from Southeastern Nigeria (United States)

    Odoma, A. N.; Obaje, N. G.; Omada, J. I.; Idakwo, S. O.; Erbacher, J.


    Cretaceous claystone sediments from Enugu, Southeastern, Nigeria were analyzed for their mineralogy and chemistry. Major minerals are quartz and kaolinite while montmorillonite is in minor quantity. The sediments are silica-rich, but showed low values of Al, Fe, Sc and Cr. The values of the chemical index of alteration (CIA) ranged from 89.9 to 94.5 and the values of chemical index of weathering (CIW) ranged from 95.1 to 98.9. Low contents of the alkali and alkali earth elements (Na, K, Mg, Al, Ca) of the clay-rich sediments suggest a relatively more intense weathering of source area. Depleted Ba, Rb, Ca, and Mg suggest that they were probably flushed out by water during sedimentation. The mineralogical composition, REE contents, and elemental ratios in the sediments suggest a provenance from mainly felsic rocks, with only minor contributions from basic sources. Despite intense weathering the REE, Th, and Sc remained in the clays suggesting that they were immobile.

  4. Dry Juan de Fuca slab revealed by quantification of water entering Cascadia subduction zone (United States)

    Canales, J. P.; Carbotte, S. M.; Nedimović, M. R.; Carton, H.


    Water is carried by subducting slabs as a pore fluid and in structurally bound minerals, yet no comprehensive quantification of water content and how it is stored and distributed at depth within incoming plates exists for any segment of the global subduction system. Here we use seismic data to quantify the amount of pore and structurally bound water in the Juan de Fuca plate entering the Cascadia subduction zone. Specifically, we analyse these water reservoirs in the sediments, crust and lithospheric mantle, and their variations along the central Cascadia margin. We find that the Juan de Fuca lower crust and mantle are drier than at any other subducting plate, with most of the water stored in the sediments and upper crust. Variable but limited bend faulting along the margin limits slab access to water, and a warm thermal structure resulting from a thick sediment cover and young plate age prevents significant serpentinization of the mantle. The dryness of the lower crust and mantle indicates that fluids that facilitate episodic tremor and slip must be sourced from the subducted upper crust, and that decompression rather than hydrous melting must dominate arc magmatism in central Cascadia. Additionally, dry subducted lower crust and mantle can explain the low levels of intermediate-depth seismicity in the Juan de Fuca slab.

  5. Combined studies of chemical composition of urine sediments and kidney stones by means of infrared microspectroscopy (United States)

    Tamošaitytė, Sandra; Hendrixson, Vaiva; Želvys, Arūnas; Tyla, Ramūnas; Kučinskienė, Zita A.; Jankevičius, Feliksas; Pučetaitė, Milda; Jablonskienė, Valerija; Šablinskas, Valdas


    Results of the structural analysis of urinary sediments by means of infrared spectral microscopy are presented. The results are in good agreement with the results of standard optical microscopy in the case of single-component and crystalline urinary sediments. It is found that for noncrystalline or multicomponent sediments, the suggested spectroscopic method is superior to optical microscopy. The chemical structure of sediments of any molecular origin can be elucidated by this spectroscopic method. The method is sensitive enough to identify solid particles of drugs present in urine. Sulfamethoxazole and traces of other medicines are revealed in this study among the other sediments. We also show that a rather good correlation exists between the type of urinary sediments and the renal stones removed from the same patient. Spectroscopic studies of urinary stones and corresponding sediments from 76 patients suffering from renal stone disease reveal that in 73% of cases such correlation exists. This finding is a strong argument for the use of infrared spectral microscopy to prevent kidney stone disease because stones can be found in an early stage of formation by using the nonintrusive spectroscopic investigation of urinary sediments. Some medical recommendations concerning the overdosing of certain pharmaceuticals can also be derived from the spectroscopic studies of urinary sediments.

  6. Some consequences of the subduction of young slabs

    NARCIS (Netherlands)

    England, P.; Wortel, R.

    The negative buoyancy force exerted by a subducting oceanic slab depends on its descent velocity, and strongly on its age. For lithosphere close to thermal equilibrium, this force dominates by a large margin the resisting forces arising from friction on the plate boundary and compositional buoyancy.

  7. Dynamic evolution in a Cretaceous high-P/T subduction channel evidenced by the juxtaposition of amphibolite blocks with different P-T paths: an example from the Kamuikotan belt, northern Japan (United States)

    Okamoto, A.; Takeshita, T.


    A subduction channel developed at the boundary between a subducting oceanic plate and an overlying plate could be geologically defined as the place, where accretionary sediments were dragged down to great depth with an oceanic plate to suffer a high-P/T type metamorphism, and transformed to high-P/T metamorphic rocks (e.g. blueschist and eclogite). In the study area, while typical high-P/T metamorphic rocks (blueschist), which originated from Cretaceous accretionary sediments, amphibolites and metacherts also occur as tectonic blocks in mélange surrounded by either serpentinite or pelitic matrix, which originally suffered intermediate-P/T type metamorphism, but later the same high-P/T type metamorphism as the sediments did. In this research, we have analyzed mineral assemblages in these amphibolites and metacherts, and conducted micro-chemical analyses of compositional zoning in amphibole and garnet from these rocks with an EPMA. As a result, compositional zoning in some constituent amphibole can be divided into 3 types. Type I is a dominant type, where actinolite is overgrown by glaucophane, indicating pressure increase. Type II, which has been found in only one sample, is defined as the compositional zoning in amphibole consisting of magnesiohornblende, actinolite and glaucophane from core to rim. The compositional zoning shows a change of the temperature gradient from low-P/T (or intermediate-P/T) type to high-P/T type, which could reflect a cooling of the subduction channel with time from the onset of subduction to a steady state. Type III is characterized by the compositional zoning in amphibole from tschermakite to glaucophane-magnesioriebeckite. This also shows a cooling of the subduction channel with time. In this sample, garnet also shows a compositional zoning from a Mn-rich and Ca-poor inner core to a Mn-poor and Ca-rich outer core, which is surrounded by a Mn-rich rim, showing a compositional discontinuity across the core-rim boundary. The

  8. Porosity and Salt Content Determine if Subduction Can Occur in Europa's Ice Shell (United States)

    Johnson, Brandon C.; Sheppard, Rachel Y.; Pascuzzo, Alyssa C.; Fisher, Elizabeth A.; Wiggins, Sean E.


    Motivated by recent evidence for subduction in Europa's ice shell, we explore the geophysical feasibility of this process. Here we construct a simple model to track the evolution of porosity and temperature within a slab that is forced to subduct. We also vary the initial salt content in Europa's ice shell and determine the buoyancy of our simulated subducting slab. We find that porosity and salt content play a dominant role in determining whether the slab is nonbuoyant and subduction in Europa's ice shell is actually possible. Generally, we find that initially low porosities and high salt contents within the conductive lid are more conducive to subduction. If salt contents are laterally homogenous, and Europa has a reasonable surface porosity of ϕ0 = 0.1, the conductive portion of Europa's shell must have salt contents exceeding 22% for subduction to occur. However, if salt contents are laterally heterogeneous, with salt contents varying by a few percent, subduction may occur for a surface porosity of ϕ0 = 0.1 and overall salt contents of 5%. Thus, we argue that under plausible conditions, subduction in Europa's ice shell is possible. Moreover, assuming that subduction is actively occurring or has occurred in Europa's recent past provides important constraints on the structure and composition of the ice shell.

  9. Rare Earth Element Compositions of Chlorite-rich Hydrothermal Sediments in the middle Okinawa Trough, East China Sea (United States)

    Shao, H.; Yang, S.; Humphris, S. E.; Cai, D.; Wang, Q.


    Rare earth elements (REEs) have been used as powerful tracers in the study of hot fluid-rock reaction in hydrothermal system. However, the behavior of the REEs during interaction of hydrothermal solution with rocks remains to be clarified more quantitatively. The Okinawa Trough (OT), located in the East Asian continental margin, is characterized by thick terrigenous sediment and ubiquitous volcanic-hydrothermal activities. In this study, the sediments collected during IODP Expedition 331 to the mid-OT were determined for mineralogical and REEs as well as Nd isotopic compositions, aiming to investigate the geochemical behavior of REEs during hydrothermal processes. All samples were separated into bulk and clay-size (˂ 2 μm) fractions and pretreated by 1N HCl to remove carbonate and other unstable components. The hydrothermal sediments in the mid-OT is dominated by Mg-rich chlorite based on the XRD analysis, especially the clay-size fraction comprising pure chlorite. The clay-size samples bear different mineralogical and geochemical compositions between the upper and lower parts in this hydrothermal area. All hydrothermal samples are relatively enriched in HREEs in the residues. The upper clays have higher values of δEu and (La/Yb)N as well as LREEs concentration than the lower part, while the bulk samples have weak REE differentiation. In the 1N HCl leachates, the concentrations of REEs in the bulk samples are higher than in the clays in the lower part but LREEs are obviously enriched in the upper clays. We infer that the grain size may be an important factor controlling the behavior of REEs in the mid-OT hydrothermal system. Both bulk and clay samples show negative Eu anomalies relative to chondrite, similar as the detrital sediments and volcanic rocks. This study confirms the hypothesis that HREEs patterns are constant throughout the system compatible with higher LREEs mobility as chlorine ion complexes in acidic solutions (Mills and Elderfield 1995; Douville

  10. Friction and stress coupling on the subduction interfaces (United States)

    Tan, E.; Lavier, L.; van Avendonk, H.


    At a subduction zone, the down-going oceanic plate slides underneath the overriding plate. The frictional resistance to the relative motion between the plates generates great earthquakes along the subduction interface, which can cause tremendous damage in the civil life and property. There is a strong incentive to understand the frictional strength of the subduction interface. One fundamental question of mechanics of subuction is the degree of coupling between the plates, which is linked to the size of earthquakes. It has been noted that the trench-parallel (along-strike) gravity variation correlates positively with the trench-parallel topography anomaly and negatively with the activity of great earthquake (Song and Simons, 2003). Regions with a negative trench-parallel gravity anomaly are more likely to have great earthquakes. The interpretation of such correlation is that strong coupling along subduction interface will drag down the for-arc region of the overriding plate, which generates the gravity and topography anomalies, and could store more strain energy to be released during a great earthquake. We developed a 2D numerical thermo-mechanical code for modeling subduction. The numerical method is based on an explicit finite element method similar to the Fast Lagrangian Analysis of Continua (FLAC) technique. The constitutive law is visco-elasti-plastic with strain weakening. The cohesion and friction angle are reduced with increasing plastic strain after yielding. To track different petrologic phases, Lagrangian particles are distributed in the domain. Basalt-eclogite, sediment-schist and peridotite-serpentinite phase changes are included in the model. Our numerical models show that the degree of coupling negatively correlates with the coefficient of friction. In the low friction case, the subduction interface has very shallow dipping angle, which helps to elastically couple the downing plate with the overriding plate. The topography and gravity anomalies of the

  11. Quantifying sediment provenance using multiple composite fingerprints in a small watershed in Oklahoma (United States)

    Quantitative information on sediment provenance is badly needed for calibration and validation of process-based soil erosion models. However, sediment source data are rather limited due to difficulties in direct measurement of various source contributions at a watershed scale. The objectives are t...

  12. Chromium isotope signature during continental crust subduction recorded in metamorphic rocks

    National Research Council Canada - National Science Library

    Shen, Ji; Liu, Jia; Qin, Liping; Wang, Shui‐Jiong; Li, Shuguang; Xia, Jiuxing; Ke, Shan; Yang, Jingsui


    The chromium isotope compositions of 27 metamorphic mafic rocks with varying metamorphic degrees from eastern China were systematically measured to investigate the Cr isotope behavior during continental crust subduction...

  13. Effect of particle size and composition of suspended sediment on denitrification in river water

    Energy Technology Data Exchange (ETDEWEB)

    Jia, Zhimei; Liu, Ting; Xia, Xinghui, E-mail:; Xia, Na


    Rivers with high suspended sediment (SPS) concentration are common worldwide, and previous studies reported the occurrence of denitrification on SPS. In this work, effect of particle size and composition of SPS on denitrification in river water was studied in laboratory. The {sup 15}N isotope tracer technique was used to investigate the denitrification in water containing 8 g L{sup −1} SPS with different particle sizes, including < 20 μm, 20–50 μm, 50–100 μm, and 100–200 μm. The results showed that the denitrification rate was negatively related to particle size, and the SPS with particle size below 20 μm had the highest {sup 15}N{sub 2} emission rate of 0.27 mg-N/m{sup 3}·d, which was twice that of 100–200 μm. The denitrifying bacteria population in the system decreased with the increase of particle size, which was positively correlated with denitrification rate (p < 0.05). There was a positive correlation between organic carbon content of SPS and denitrifying bacteria population (p < 0.01), indicating that organic carbon is a key factor influencing denitrifying bacteria. Different from the {sup 15}N{sub 2} production, {sup 15}N{sub 2}O emission rate reached the highest of 1.02 μg-N/m{sup 3}·d in the system containing SPS of 20–50 μm, which was 14.8 times that of 100–200 μm. This was due to the difference in denitrifying bacteria species in different systems due to different oxic/anoxic conditions around SPS. This study suggests that not only the SPS concentration but also the SPS size and composition should be considered in studying the nitrogen cycle in river systems, especially for the production of N{sub 2}O. - Highlights: • Denitrification rate was negatively related to particle size of SPS. • Denitrification in the < 20 μm SPS had the highest N{sub 2} emission rate of 0.27 mg-N/m{sup 3} d. • {sup 15}N{sub 2}O production in the system with SPS of 20–50 μm was 14.8 times that of 100–200 μm. • The denitrifying bacteria

  14. Boron desorption in subduction forearcs: Systematics and implications for the origin and transport of deeply-sourced fluids (United States)

    Saffer, D. M.; Kopf, A.


    At many subduction zones, pore water geochemical anomalies at seafloor seeps and in shallow boreholes indicate upward fluid flow and chemical transport from depths of several km. Identifying the source regions and flow pathways of these fluids is a key step toward quantifying volatile fluxes through forearcs, and in understanding their potential connection to loci of excess pore pressure along the plate boundary. Here, we focus on observations of pore water freshening (reported in terms of [Cl]), elevated [B], and light δ11B. Pore water freshening is generally thought to result from clay dehydration, whereas the B and δ11B signatures are interpreted to reflect desorption of isotopically light B from pelitic sediments with increasing temperature. We develop a model to track the coupled effects of B desorption, smectite dehydration, and progressive consolidation within the underthrusting sediment section. Our model incorporates established kinetic models of clay dehydration, and experimental data that define the temperature-dependent distribution coefficient (Kd) and fractionation of B in marine sediments. A generic sensitivity analysis demonstrates that the relative timing of heating and consolidation is a dominant control on pore water composition. For cold slabs, freshening is maximized because dehydration releases bound water into low porosity sediment, whereas B concentrations and isotopic signatures are modest because desorption is only partially complete. For warmer slabs, [B] and [Cl] signals are smaller, because heating and desorption occur shallower and into larger porosities, but the predicted δ11B signal is larger. The former scenario is typical of non-accretionary margins where the insulating sediment layer on the subducting plate is commonly <1 km thick. This result provides a quantitative explanation for the global observation that [Cl] depletion and [B] enrichment signals are generally strongest at non-accretionary margins. Application of our multi

  15. Subduction and vertical coastal motions in the eastern Mediterranean (United States)

    Howell, Andy; Jackson, James; Copley, Alex; McKenzie, Dan; Nissen, Ed


    Convergence in the eastern Mediterranean of oceanic Nubia with Anatolia and the Aegean is complex and poorly understood. Large volumes of sediment obscure the shallow structure of the subduction zone, and since much of the convergence is accommodated aseismically, there are limited earthquake data to constrain its kinematics. We present new source models for recent earthquakes, combining these with field observations, published GPS velocities and reflection-seismic data to investigate faulting in three areas: the Florence Rise, SW Turkey and the Pliny and Strabo Trenches. The depths and locations of earthquakes reveal the geometry of the subducting Nubian plate NE of the Florence Rise, a bathymetric high that is probably formed by deformation of sediment at the surface projection of the Anatolia-Nubia subduction interface. In SW Turkey, the presence of a strike-slip shear zone has often been inferred despite an absence of strike-slip earthquakes. We show that the GPS-derived strain-rate field is consistent with extension on the orthogonal systems of normal faults observed in the region and that strike-slip faulting is not required to explain observed GPS velocities. Further SW, the Pliny and Strabo Trenches are also often interpreted as strike-slip shear zones, but almost all nearby earthquakes have either reverse-faulting or normal-faulting focal mechanisms. Oblique convergence across the trenches may be accommodated either by a partitioned system of strike-slip and reverse faults or by oblique slip on the Aegean-Nubia subduction interface. The observed late-Quaternary vertical motions of coastlines close to the subduction zone are influenced by the interplay between: (1) thickening of the material overriding the subduction interface associated with convergence, which promotes coastal uplift; and (2) subsidence due to extension and associated crustal thinning. Long-wavelength gravity data suggest that some of the observed topographic contrasts in the eastern

  16. (210)Pb and compositional data of sediments from Rondonian lakes, Madeira River basin, Brazil. (United States)

    Bonotto, Daniel Marcos; Vergotti, Marcelo


    Gold exploration has been intensive in Brazilian Amazon over the last 40 years, where the use of mercury as an amalgam has caused abnormal Hg concentrations in water bodies. Special attention has been directed to Madeira River due to fact it is a major tributary of Amazon River and that since 1986, gold exploration has been officially permitted along a 350km sector of the river. The (21)(0)Pb method has been used to date sediments taken from nine lakes situated in Madeira River basin, Rondônia State, and to verify where anthropogenic Hg might exist due to gold exploitation in Madeira River. Activity profiles of excess (21)(0)Pb determined in the sediment cores provided a means to evaluate the sedimentation rates using a Constant Flux: Constant Sedimentation (CF:CS) and Constant Rate of Supply (CRS) of unsupported/excess (21)(0)Pb models. A significant relationship was found between the CF:CS sedimentation rates and the mean values of the CRS sedimentation rates (Pearson correlation coefficient r=0.59). Chemical data were also determined in the sediments for identifying possible relationships with Hg occurring in the area. Significant values were found in statistical correlation tests realized among the Hg, major oxides and Total Organic Carbon (TOC) content in the sediments. The TOC increased in the sediment cores accompanied by a loss on ignition (LOI) increment, whereas silica decreased following a specific surface area raising associated to the TOC increase. The CRS model always provided ages within the permitted range of the (21)(0)Pb-method in the studied lakes, whereas the CF:CS model predicted two values above 140 years. Copyright © 2015 Elsevier Ltd. All rights reserved.

  17. Effects of pesticides on community composition and activity of sediment microbes - responses at various levels of microbial community organization

    Energy Technology Data Exchange (ETDEWEB)

    Widenfalk, Anneli [Department of Environmental Assessment, Swedish University of Agricultural Sciences, P.O. Box 7050, SE-750 07 Uppsala (Sweden)], E-mail:; Bertilsson, Stefan [Limnology/Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Norbyvaegen 20, SE-752 36 Uppsala (Sweden); Sundh, Ingvar [Department of Microbiology, Swedish University of Agricultural Sciences, P.O. Box 7025, SE-750 07 Uppsala (Sweden); Goedkoop, Willem [Department of Environmental Assessment, Swedish University of Agricultural Sciences, P.O. Box 7050, SE-750 07 Uppsala (Sweden)


    A freshwater sediment was exposed to the pesticides captan, glyphosate, isoproturon, and pirimicarb at environmentally relevant and high concentrations. Effects on sediment microorganisms were studied by measuring bacterial activity, fungal and total microbial biomass as community-level endpoints. At the sub-community level, microbial community structure was analysed (PLFA composition and bacterial 16S rRNA genotyping, T-RFLP). Community-level endpoints were not affected by pesticide exposure. At lower levels of microbial community organization, however, molecular methods revealed treatment-induced changes in community composition. Captan and glyphosate exposure caused significant shifts in bacterial community composition (as T-RFLP) at environmentally relevant concentrations. Furthermore, differences in microbial community composition among pesticide treatments were found, indicating that test compounds and exposure concentrations induced multidirectional shifts. Our study showed that community-level end points failed to detect these changes, underpinning the need for application of molecular techniques in aquatic ecotoxicology. - Molecular techniques revealed pesticide-induced changes at lower levels of microbial community organization that were not detected by community-level end points.

  18. Molybdenum mobility and isotopic fractionation during subduction at the Mariana arc (United States)

    Freymuth, Heye; Vils, Flurin; Willbold, Matthias; Taylor, Rex N.; Elliott, Tim


    The fate of crustal material recycled into the convecting mantle by plate tectonics is important for understanding the chemical and physical evolution of the planet. Marked isotopic variability of Mo at the Earth's surface offers the promise of providing distinctive signatures of such recycled material. However, characterisation of the behaviour of Mo during subduction is needed to assess the potential of Mo isotope ratios as tracers for global geochemical cycles. Here we present Mo isotope data for input and output components of the archetypical Mariana arc: Mariana arc lavas, sediments from ODP Sites 800, 801 and 802 near the Mariana trench and the altered mafic, oceanic crust (AOC), from ODP Site 801, together with samples of the deeper oceanic crust from ODP Site 1256. We also report new high precision Pb isotope data for the Mariana arc lavas and a dataset of Pb isotope ratios from sediments from ODP Sites 800, 801 and 802. The Mariana arc lavas are enriched in Mo compared to elements of similar incompatibility during upper mantle melting, and have distinct, isotopically heavy Mo (high 98Mo/95Mo) relative to the upper mantle, by up to 0.3 parts per thousand. In contrast, the various subducting sediment lithologies dominantly host isotopically light Mo. Coupled Pb and Mo enrichment in the Mariana arc lavas suggests a common source for these elements and we further use Pb isotopes to identify the origin of the isotopically heavy Mo. We infer that an aqueous fluid component with elevated [Mo], [Pb], high 98Mo/95Mo and unradiogenic Pb is derived from the subducting, mafic oceanic crust. Although the top few hundred metres of the subducting, mafic crust have a high 98Mo/95Mo, as a result of seawater alteration, tightly defined Pb isotope arrays of the Mariana arc lavas extrapolate to a fluid component akin to fresh Pacific mid-ocean ridge basalts. This argues against a flux dominantly derived from the highly altered, uppermost mafic crust or indeed from an Indian

  19. Bacterial community composition of South China Sea sediments through pyrosequencing-based analysis of 16S rRNA genes. (United States)

    Zhu, Daochen; Tanabe, Shoko-Hosoi; Yang, Chong; Zhang, Weimin; Sun, Jianzhong


    Subseafloor sediments accumulate large amounts of organic and inorganic materials that contain a highly diverse microbial ecosystem. The aim of this study was to survey the bacterial community of subseafloor sediments from the South China Sea. Pyrosequencing of over 265,000 amplicons of the V3 hypervariable region of the 16S ribosomal RNA gene was performed on 16 sediment samples collected from multiple locations in the northern region of the South China Sea from depths ranging from 35 to 4000 m. A total of 9,726 operational taxonomic units (OTUs; between 695 and 2819 unique OTUs per sample) at 97% sequence similarity level were generated. In total, 40 bacterial phyla including 22 formally described phyla and 18 candidate phyla, with Proteobacteria, Firmicutes, Planctomycetes, Actinobacteria and Chloroflexi being most diverse, were identified. The most abundant phylotype, accounting for 42.6% of all sequences, belonged to Gammaproteobacteria, which possessed absolute predominance in the samples analyzed. Among the 18 candidate phyla, 12 were found for the first time in the South China Sea. This study provided a novel insight into the composition of bacterial communities of the South China Sea subseafloor. Furthermore, abundances and community similarity analysis showed that the compositions of the bacterial communities are very similar at phylum level at different depths from 35-4000 m.

  20. Subduction zone processes and continental crust formation in the southern Central Andes: insights from geochemistry and geochronology


    Jones, Rosemary Ellen


    Subduction zones, such as the Andean convergent margin, are the sites at which new continental crust is generated, and where subducting material is either recycled to the crust via arc magmatism or transferred to the deep mantle. The composition of arc magmas and associated new continental crust reflects variable contributions from mantle, crustal and subducted reservoirs. Insights into crustal growth and recycling processes in the southern Central Andes, specifically in the ...

  1. Identification of contamination in a lake sediment core using Hg and Pb isotopic compositions, Lake Ballinger, Washington, USA (United States)

    Gray, John E.; Pribil, Michael J.; Van Metre, Peter C.; Borrok, David M.; Thapalia, Anita


    Concentrations and isotopic compositions of Hg and Pb were measured in a sediment core collected from Lake Ballinger, near Seattle, Washington, USA. Lake Ballinger has been affected by input of metal contaminants emitted from the Tacoma smelter, which operated from 1887 to 1986 and was located about 53 km south of the lake. Concentrations and loadings of Hg and Pb in Lake Ballinger increased by as much as three orders of magnitude during the period of smelting as compared to the pre-smelting period. Concentrations and loadings of Hg and Pb then decreased by about 55% and 75%, respectively, after smelting ended. Isotopic compositions of Hg changed considerably during the period of smelting (δ202Hg = −2.29‰ to −0.38‰, mean −1.23‰, n = 9) compared to the pre-smelting period (δ202Hg = −2.91‰ to −2.50‰, mean −2.75‰, n = 4). Variations were also observed in 206Pb/207Pb and 208Pb/207Pb isotopic compositions during these periods. Data for Δ199Hg and Δ201Hg indicate mass independent fractionation (MIF) of Hg isotopes in Lake Ballinger sediment during the smelting and post-smelting period and suggest MIF in the ore smelted, during the smelting process, or chemical modification at some point in the past. Negative values for Δ199Hg and Δ201Hg for the pre-smelting period are similar to those previously reported for soil, peat, and lichen, likely suggesting some component of atmospheric Hg. Variations in the concentrations and isotopic compositions of Hg and Pb were useful in tracing contaminant sources and the understanding of the depositional history of sedimentation in Lake Ballinger.

  2. Climatology of sediment flux and composition in the subarctic Northeast Pacific Ocean with biogeochemical implications (United States)

    Timothy, D. A.; Wong, C. S.; Barwell-Clarke, J. E.; Page, J. S.; White, L. A.; Macdonald, R. W.


    Sequentially sampling conical sediment traps were maintained at Ocean Station Papa (OSP; 50°N, 145°W) in the Alaska Gyre from September 1982 to June 2006. The time series began with a single trap at 3800 m and traps were added at 1000 m and 200 m in March 1983 and May 1989, respectively. A trap at 3500-3700 m also was moored 5° north of OSP from May 1990 to August 1992. Total mass, biogenic silica (BSi), calcium carbonate (CaCO3), particulate organic carbon (POC) and particulate nitrogen (PN) were routinely measured. In this paper, we develop climatologies of sediment flux and composition at OSP, describing the characteristic features for comparison to sedimentary conditions globally. We then expand our use of the climatologies to arrive at four main conclusions regarding ecology and geochemistry at OSP. Fluxes of BSi and CaCO3 at 200 m and 1000 m lag by one month the annual cycle of irradiance and arrive at 3800 m ∼16 d later, with maximum export occurring several months later for POC. Next, the annual cycle of BSi flux shows that diatom production in late winter and spring is higher than indicated by spring decline of surface nutrients. We then show that the annual cycle of POC flux implies a net community production of organic carbon (NCPOC) of 3.6-5.3 mol m-2 y-1, double estimates based on mixed layer tracers but similar to estimates unaffected by mixing. NCPOC, combined with a CaCO3:POC production ratio of 0.18 determined from trap fluxes, gives a net community production of CaCO3 (NCPIC) of 0.65-0.95 mol m-2 y-1, in agreement with CaCO3 dissolution in the water column plus abyssal CaCO3 flux. Lastly, the flux climatologies at 1000 m and 3800 m are used to infer particle transformations in the bathypelagic zone including disaggregation and remineralization. Fluxes at 3800 m are best described as the sum of a primary flux sinking rapidly and a slowly-sinking secondary flux. Disaggregation of the primary flux is the likely source of secondary fluxes, with a

  3. Relationships between Cd and Zn partitioning and geochemical composition in sediments from Chinese rivers. (United States)

    Peng, Shu-Heng; Wang, Wen-xiong; Chen, Jingsheng


    Adsorption isotherm experiments were conducted to determine the distribution coefficients (Kd) for Cd and Zn between water and sediments from twelve rivers in eastern China. The low metal concentration (sediment-water system enabled the direct measurements of linear adsorption isotherms. When other solution parameters, such as ionic strength, were controlled, sediment geochemical characteristics were the major factors affecting metal distribution. The Kd was highly dependent on the total organic carbon contents and Fe-Mn oxide at pH = 7.0, and was affected significantly by the carbonate content in the sediments due to its control of pH. The Kd of the Huanghe sediments, which had the highest carbonate concentration (13.1%), increased sharply for both Cd and Zn when the pH increased. A quantitative model using the experimentally obtained phase distribution coefficients (Kd)i was applied to study the effects of different geochemical phases in the sediment on metal distributions. The (Kd)i of carbonate was correlated significantly with the carbonate content in the sediment, whereas the (Kd)i of total organic carbon (TOC) and Fe-Mn oxide phases were highly pH dependent. Using the (Kd)i for each geochemical phase, the calculation showed that about 91% and 85% of sorbed Cd and Zn, respectively, added to the batch reactors were distributed among the three major geochemical phases: TOC, Fe-Mn oxide, and carbonate. Total organic carbon was the most important binding phase for Cd, and Fe-Mn oxide for Zn. Furthermore, adsorption experiments with simulated sediments show the importance of interactions between different geochemical phases on metal partitioning.

  4. Longitudinal changes on grain size and sediments composition in the Baghi River (Northwest of Neyshabur

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    حسام کاویان


    Full Text Available Marusk Catchment with an area of 131.87 square kilometers is located in the Northwest of Neyshabur. Baghi River as one of the main tributary of this catchment has been studied with a length of about20.1km.For sedimentological studies a total of 32 sediment samples taken from the active mid-channel of the river that after drying, the granulometry has been analyzed by dry sieving method. After the sample sieving, statistical parameters (median, mean, sorting, skewness and kurtosis were calculated.3 sedimentary discontinuities have been detected in the sediments of the river. First and second discontinuity is due to input of sediments from the alluvial fan and tributary into the main channel, respectively, and third discontinuity is due to changes in lithology. To determine the percentage of erosion in the formations in this region and determine the amount of sediment yield in each of formations, Abrasion Los Angeles Test is done. Based on this method, Dalichai Formation with according to its lithology and also a great expansion in the region is main formation for sediment yield in this area. In the study area, coarse-grained sedimentary facies (Gmg, Gci, medium-grained sedimentary facies (Sm and fine-grained sedimentary facies (Fl were identified. According to sedimentary facies, the architectural elements of SG and FF have been identified. Sedimentary models proposed for this river are including braided gravelly river with sediment gravity flow and shallow braided river with gravel-bed load.

  5. Early Diagenesis Records and Pore Water Composition of Methane-Seep Sediments from the Southeast Hainan Basin, South China Sea

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    Daidai Wu


    Full Text Available Several authigenic minerals were identified by XRD and SEM analyses in shallow sediments from the Southeast Hainan Basin, on the northern slope of South China Sea. These minerals include miscellaneous carbonates, sulphates, and framboidal pyrite, and this mineral assemblage indicates the existence of gas hydrates and a methane seep. The assemblage and fabric features of the minerals are similar to those identified in cold-seep sediments, which are thought to be related to microorganisms fostered by dissolved methane. Chemical composition of pore water shows that the concentrations of SO42-, Ca2+, Mg2+, and Sr2+ decrease clearly, and the ratios of Mg2+ to Ca2+ and Sr2+ to Ca2+ increase sharply with depth. These geochemical properties are similar to those where gas hydrates occur in the world. All results seem to indicate clearly the presence of gas hydrates or deep water oil (gas reservoirs underneath the seafloor.

  6. Microbial communities and organic matter composition in surface and subsurface sediments of the Helgoland mud area, North Sea

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    Oluwatobi Emmanuel Oni


    Full Text Available The role of microorganisms in the cycling of sedimentary organic carbon is a crucial one. To better understand relationships between molecular composition of a potentially bioavailable fraction of organic matter and microbial populations, bacterial and archaeal communities were characterized using pyrosequencing-based 16S rRNA gene analysis in surface (top 30 cm and subsurface sediments (30-530 cm of the Helgoland mud area, North Sea. Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS was used to characterize a potentially bioavailable organic matter fraction (hot-water extractable organic matter, WE-OM. Algal polymer-associated microbial populations such as members of the Gammaproteobacteria, Bacteroidetes and Verrucomicrobia were dominant in surface sediments while members of the Chloroflexi (Dehalococcoidales and candidate order GIF9 and Miscellaneous Crenarchaeota Groups (MCG, both of which are linked to degradation of more recalcitrant, aromatic compounds and detrital proteins, were dominant in subsurface sediments. Microbial populations dominant in subsurface sediments (Chloroflexi, members of MCG, and Thermoplasmata showed strong correlations to total organic carbon content. Changes of WE-OM with sediment depth reveal molecular transformations from oxygen-rich (high Oxygen to Carbon (O/C, low Hydrogen to Carbon (H/C ratios aromatic compounds and highly unsaturated compounds towards compounds with lower O/C and higher H/C ratios. The observed molecular changes were most pronounced in organic compounds containing only CHO atoms. Our data thus, highlights classes of sedimentary organic compounds that may serve as microbial energy sources in methanic marine subsurface environments.

  7. Ecological effects and chemical composition of fine sediments in Upper Austrian streams and resulting implications for river management (United States)

    Höfler, Sarah; Pichler-Scheder, Christian; Gumpinger, Clemens


    In the current scientific discussion high loads of fine sediments are considered one of the most important causes of river ecosystem degradation worldwide. Especially in intensively used catchment areas changes in the sediment household must be regarded as a reason, which prevents the achievement of the objectives of the European Water Framework Directive (WFD). Therefore, the Upper Austrian Water Authorities have launched two comprehensive studies on the topic. The first one was a survey on the current siltation status of river courses in Upper Austria. The second study deals with two selected catchments in detail, in order to get a clear picture of the impacts of the fines on the aquatic fauna (trout eggs, benthic invertebrates), the chemical composition of these fractions, the crucial hydrogeological processes and to develop possible role models for measures both in the catchments and in the streams. At eight sites within the two catchments sediment and water samples were collected at two dates for detailed chemical analysis. On one date additionally the benthic invertebrate fauna was investigated on the microhabitat level. Thereby it was possible to enhance the understanding of the range of ecological impacts caused by silting-up in different hydro-morphological circumstances and with different fine sediment loads. The water samples as well as the sediment fraction samples elements were analysed. Furthermore, a GIS-based analysis was carried out for the two examined catchments. The model included data gained from a digital elevation model, land use data and digital soil classification maps. This led to findings concerning the main sources and processes, which are responsible for anthropogenically induced high fine sediment loads in the streams. According to these results a GIS-based risk assessment tool for all Upper Austrian watercourses is developed, which will be used as instrument for the planning and measure implementation of the water management

  8. Effects of artificial disturbance on quantity and biochemical composition of organic matter in sediments of a coastal lagoon

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    Lenzi M.


    Full Text Available The eutrophication of the coastal lagoon of Burano (Tuscany, Italy produces periodic toxic-anoxic events. The possibility of mitigating eutrophication of a lagoon by resuspension of sediment was tested in a three-year field experiment conducted in 2008–2009. An unreplicated before-after control-impact (BACI study design was used to ascertain variations in the quantity and biochemical composition of organic matter in sediment artificially disturbed by a specially equipped boat. In October 2008, before beginning disturbance, January 2009, half way through the disturbance period, and May 2009, at the end of disturbance, sediment was sampled in a disturbed area and an undisturbed control area to determine chlorophyll-a (Chl-a, phaeopigments (PHAE, proteins (PRT, carbohydrates (CHO, lipids (LIP, labile organic matter (LOM, refractory organic matter (ROM, total organic carbon (TOC and total nitrogen (TN. The disturbed area, measuring 44 ha, was divided into nine subareas, eight of which were subjected to four different frequencies of disturbance (from 2 to 5 in the period October 2008 – April 2009. Sediment was sampled in each sub-area in the three months mentioned above to determine labile and total organic matter. The results were processed by univariate and multivariate analysis using Primer 6.0, Permanova  +  and Prism 5.0 software. The findings were as follows: (1 a large proportion of the biopolymeric carbon consisted of labile matter throughout the lagoon; (2 higher abatement of labile organic matter was recorded in the disturbed area; (3 a lower protein:carbohydrate ratio was found in the disturbed than in the undisturbed area; (4 the C:N ratio of sediment was much lower in the undisturbed area than in the disturbed area at the end of the study period; (5 sediment and macroalgal C:N ratios did not significantly change in response to disturbance; (6 initial accumulation of organic matter from phytoplankton was greater in the disturbed

  9. The Molybdenum Isotope System as a Tracer of Slab Input in Subduction Zones: An Example From Martinique, Lesser Antilles Arc (United States)

    Gaschnig, Richard M.; Reinhard, Christopher T.; Planavsky, Noah J.; Wang, Xiangli; Asael, Dan; Chauvel, Catherine


    Molybdenum isotopes are fractionated by Earth-surface processes and may provide a tracer for the recycling of crustal material into the mantle. Here, we examined the Mo isotope composition of arc lavas from Martinique in the Lesser Antilles arc, along with Cretaceous and Cenozoic Deep Sea Drilling Project sediments representing potential sedimentary inputs into the subduction zone. Mo stable isotope composition (defined as δ98Mo in ‰ deviation from the NIST 3134 standard) in lavas older than ˜7 million years (Ma) exhibits a narrow range similar to and slightly higher than MORB, whereas those younger than ˜7 Ma show a much greater range and extend to unusually low δ98Mo values. Sediments from DSDP Leg 78A, Site 543 have uniformly low δ98Mo values whereas Leg 14, Site 144 contains both sediments with isotopically light Mo and Mo-enriched black shales with isotopically heavy Mo. When coupled with published radiogenic isotope data, Mo isotope systematics of the lavas can be explained through binary mixing between a MORB-like end-member and different sedimentary compositions identified in the DSDP cores. The lavas older than ˜7 Ma were influenced by incorporation of isotopically heavy black shales into the mantle wedge. The younger lavas are the product of mixing isotopically light sedimentary material into the mantle wedge. The change in Mo isotope composition of the lavas at ˜7 Ma is interpreted to reflect the removal of the Cretaceous black shale component due to the arrival of younger ocean crust where the age-equivalent Cretaceous sediments were deposited in shallower oxic waters. Isotopic fractionation of Mo during its removal from the slab is not required to explain the observed systematics in this system.

  10. The course of water in Archean subduction systems (United States)

    Bouilhol, P.; Magni, V.; Van Hunen, J.; Kaislaniemi, L.


    The andesitic nature of the bulk continental crust, as well as its characteristic trace element ratios, have a close resemblance to the differentiated crust of volcanic arcs, thus leading to models for formation of continental crust in subduction zone settings. If the modern processes leading to continental crust formation at convergent margins are well constrained, the extrapolation to early Earth conditions is hazardous, because the composition of Earth's early crust can be achieved through several processes. We study the different scenarios that may have operated during early Earth subduction to form differentiated crust. Each scenario (e.g. arc crust melting, slab melting, mantle melting followed by differentiation…) has a common denominator that is the fate of water, because it reflects slab devolatilization and controls the melting process and the stability of minerals such as garnet, amphibole and plagioclase, which are major players in the final melt composition. To this end, we present thermomechanical numerical models that incorporate internally consistent thermodynamic data in order to simulate slab dehydration. Our goal is to track the fate of subducted water in an Archean style subduction regime to better comprehend its modus operandi.

  11. Processes and consequences of deep subduction

    NARCIS (Netherlands)

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


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

  12. Boron isotope variations in Tonga-Kermadec-New Zealand arc lavas: Implications for the origin of subduction components and mantle influences (United States)

    Leeman, William P.; Tonarini, Sonia; Turner, Simon


    The Tonga-Kermadec-New Zealand volcanic arc is an end-member of arc systems with fast subduction suggesting that the Tonga sector should have the coolest modern slab thermal structure on Earth. New data for boron concentration and isotopic composition are used to evaluate the contrasting roles of postulated subduction components (sediments and oceanic slab lithologies) in magma genesis. Major observations include: (a) Tonga-Kermadec volcanic front lavas are enriched in B (as recorded by B/Nb and similar ratios) and most have relatively high δ11B (>+4‰), whereas basaltic lavas from New Zealand have relatively low B/Nb and δ11B (back-arc, as observed elsewhere; and (d) low δ11B is observed in volcanic front samples from Ata, an anomalous sector where the back-arc Valu Fa Spreading Center impinges on the arc and the Louisville Seamount Chain is presently subducting. Otherwise, volcanic front lavas exhibit positive correlations for both B/Nb and δ11B with other plausible indicators of slab-derived fluid contributions (e.g., Ba/Nb, U/Th, (230Th/232Th) and 10Be/9Be), and with estimated degree of melting to produce the mafic lavas. Inferred B-enrichments in the arc magma sources are likely dominated by serpentinite domains deeper within the subducting slab (±altered oceanic crust), and B systematics are consistent with dominant transport by slab-derived aqueous fluids. Effects of this process are amplified by mantle wedge source depletion due to prior melt extraction.Plain Language SummaryBoron isotope and other geochemical data are used to evaluate contributions from subducted materials to magma sources for volcanoes of the Tonga-Kermadec-New Zealand volcanic arc. The data are used to estimate the composition of modified mantle sources for the arc magmas as well as the extent of melting to produce them. It is shown that the mantle was previously depleted in melt components, and then overprinted by B and other components from the subducting slab, predominantly by

  13. Influence of Initial Geometry and Boundary Conditions on Flat Subduction Models and Resulting Topography (United States)

    Nelson, P.; Moucha, R.


    Numerical investigations of surface deformation in response to flat slab subduction began with seminal papers by Bird (1988) and Mitrovica et al. (1989). Recently, a number of numerical studies have begun to explore the complexity in the dynamics of flat-slab subduction initiation and continuation, but did not address the corresponding surface deformation (English et al., 2003; Pérez-Campos et al., 2008; Liu et al., 2010; Jones et al., 2011; Arrial and Billen, 2013; Vogt and Gerya, 2014). Herein, we explore the conditions that lead to flat-slab subduction and characterize the resulting surface deformation using a 2D finite-difference marker-in-cell method. We specifically explore how initial model geometry and boundary conditions affect the evolution of the angle at which a slab subducts in the presence/absence of a buoyant oceanic plateau and the resulting surface topography. In our simulations, the surface is tracked through time as an internal erosion/sedimentation surface. The top boundary of the crust is overlaid by a "sticky" (viscous 10^17 Pa.s) water/air layer with correspondingly stratified densities. We apply a coupled surface processes model that solves the sediment transport/diffusion erosion equation at each time step to account for the corresponding crustal mass flux and its effect on crustal deformation. Model results show the initial angle of subduction has a substantial impact on the subduction angle of the slab and hence the evolution of topography. The results also indicate plate velocity and the presence of an oceanic plateau in a forced subduction only have a moderate effect on the angle of subduction.

  14. Building a Subduction Zone Observatory (United States)

    Gomberg, Joan S.; Bodin, Paul; Bourgeois, Jody; Cashman, Susan; Cowan, Darrel; Creager, Kenneth C.; Crowell, Brendan; Duvall, Alison; Frankel, Arthur; Gonzalez, Frank; Houston, Heidi; Johnson, Paul; Kelsey, Harvey; Miller, Una; Roland, Emily C.; Schmidt, David; Staisch, Lydia; Vidale, John; Wilcock, William; Wirth, Erin


    Subduction zones contain many of Earth’s most remarkable geologic structures, from the deepest oceanic trenches to glacier-covered mountains and steaming volcanoes. These environments formed through spectacular events: Nature’s largest earthquakes, tsunamis, and volcanic eruptions are born here.

  15. The influence of a subduction component on magmatism in the Okinawa Trough: Evidence from thorium and related trace element ratios (United States)

    Guo, Kun; Zeng, Zhi-Gang; Chen, Shuai; Zhang, Yu-Xiang; Qi, Hai-Yan; Ma, Yao


    The Okinawa Trough (OT) is a back-arc, initial continental marginal sea basin located behind the Ryukyu Arc-Trench System. Formation and evolution of the OT have been intimately related to subduction of the Philippine Sea Plate (PSP) since the late Miocene; thus, the magma source of the trough has been affected by subduction components, as in the case of other active back-arc basins, including the Lau Basin (LB) and Mariana Trough (MT). We review all the available geochemical data relating to basaltic lavas from the OT and the middle Ryukyu Arc (RA) in this paper in order to determine the influence of the subduction components on the formation of arc and back-arc magmas within this subduction system. The results of this study reveal that the abundances of Th in OT basalts (OTBs) are higher than that in LB (LBBs) and MT basalts (MTBs) due to the mixing of subducted sediments and EMI-like enriched materials. The geochemical characteristics of Th and other trace element ratios indicate that the OTB originated from a more enriched mantle source (compared to N-mid-ocean ridge basalt, N-MORB) and was augmented by subducted sediments. Data show that the magma sources of the south OT (SOT) and middle Ryukyu Arc (MRA) basalts were principally influenced by subducted aqueous fluids and bulk sediments, which were potentially added into magma sources by accretion and underplating. At the same time, the magma sources of the middle OT (MOT) and Kobi-syo and Sekibi-Syo (KBS+SBS) basalts were impacted by subducted aqueous fluids from both altered oceanic crust (AOC) and sediment. The variable geochemical characteristics of these basalts are due to different Wadati-Benioff depths and tectonic environments of formation, while the addition of subducted bulk sediment to SOT and MRA basalts may be due to accretion and underplating, and subsequent to form mélange formation, which would occur partial melting after aqueous fluids are added. The addition of AOC and sediment aqueous fluid

  16. Chemical composition of cave sediment in Potočka zijalka, Mt.Olševa, North Slovenia

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    Polona Kralj


    Full Text Available Potočka zijalka was a station of Aurignatien hunters and the site of rich fossil remains of Pleistocene large mammals. Clastic sediments were deposited in Würm and are an intimate mixture of gravel, sand, silt and clay occurring in various proportions. Thefractions form distinct populations, which were transported by different agents, like rockfall, flowing water, ephemeral torrent flows and cryoturbation. The sediment constituents are petrologically rather diverse and indicate that they were derived from different parent rocks - Mesozoic limestone, Permian-Carboniferous shales, Tertiary fine-grained sediments and fluvial pebbly deposits.Bulk chemical composition is strongly influenced by the limestone component, but the majority of trace elements, like Ti, Li, V, Fe, Co, Zn, Ga, Y, REE, Zr, Nb, Cs, Hf and Th originates from clay and fine silt, and Mn, Pb, Ni, Cu and Sn mainly from the heavyminerals in the sand fraction. Ca, Mg, Br, Rb, Sr and U show strong correlation with the amount of carbonate component. Rare earth elements, normalised to PAAS are not appreciable fractionated and show light positive europium anomalies.

  17. Major factors influencing the elemental composition of surface estuarine sediments: the case of 15 estuaries in Portugal. (United States)

    Mil-Homens, M; Vale, C; Raimundo, J; Pereira, P; Brito, P; Caetano, M


    Upper sediments (0-5 cm) were sampled in 94 sites of water bodies of the fifteen Portuguese estuaries characterized by distinct settings of climate, topography and lithology, and marked by diverse anthropogenic pressures. Confined areas recognized as highly anthropogenic impacted, as well as areas dominated by erosion or frequently dredged were not sampled. Grain size, organic carbon (Corg), Al and trace elements (As, Cd, Co, Cr, Cu, Hg, Ni, Pb and Zn) were determined. Normalisation of trace element concentrations to Al and Corg, correlations between elements and Principal Component Analysis (PCA) allowed identifying elemental associations and the relevance of grain-size, lithology and anthropogenic inputs on sediment chemical composition. Whereas grain-size is the dominant effect for the majority of the studied estuaries, the southern estuaries Mira, Arade and Guadiana are dominated by specific lithologies of their river basins, and anthropogenic effects are identified in Ave, Leça, Tagus and Sado. This study emphasizes how baseline values of trace elements in sediments may vary within and among estuarine systems. Copyright © 2014 Elsevier Ltd. All rights reserved.

  18. Thermal buoyancy on Venus - Underthrusting vs subduction (United States)

    Burt, Jeffrey D.; Head, James W.


    The thermal and buoyancy consequences of the subduction endmember are modeled in an attempt to evaluate the conditions distinguishing underthrusting and subduction. Thermal changes in slabs subducting into the Venusian mantle with a range of initial geotherms are used to predict density changes and, thus, slab buoyancy. Based on a model for subduction-induced mantle flow, it is then argued that the angle of the slab dip helps differentiate between underthrusting and subduction. Mantle flow applies torques to the slab which, in combination with torques due to slab buoyancy, act to change the angle of slab dip.

  19. Assessment of Available Phosphorus in the Lake Sediments Using an Innovative Composite Membrane (United States)

    Huang, Qinghui; Wang, Zijian; Wang, Donghong


    An innovative iron oxide embedded cellulose acetate membrane (FeO/CAM) was synthesized and used to study available phosphorus in Chinese lake sediments. The kinetics of available P release was investigated by FeO/CAM for different types of sediments ranging in Olsen-P from 19.1 to 170.6 mg/kg. The results showed that the average kd values (0.094 h-1) of the Taihu sediments were comparable to those of the soils with similar texture estimated by iron oxide impregnated filter paper (FeO paper) though they were generally lower than those of sandy soils. It is indicated that the FeO/CAM can be used as an infinite P sink to estimate available P (FeO-P). The concentrations of FeO-P were significantly correlated with those of extractable P forms, e.g. Olsen-P (R2 = 0.962, pCAM is useful to assess phosphorus bioavailability of the sediments.

  20. Archaeal and bacterial communities of Xestospongia testudinaria and sediment differ in diversity, composition and predicted function in an Indonesian coral reef environment (United States)

    Polónia, Ana Rita Moura; Cleary, Daniel Francis Richard; Freitas, Rossana; Gomes, Newton Carlos Marcial; de Voogd, Nicole Joy


    Little is known about the microbial diversity, composition and predicted functional similarities and dissimilarities between prokaryotic kingdoms and among coral reef biotopes located in close spatial proximity to one other. In this study, we compared communities of Archaea and Bacteria in two distinct biotopes, namely, the sponge Xestospongia testudinaria and sediment of the Berau reef system, Indonesia. Using a 16S rRNA gene barcoded pyrosequencing approach and a recently developed predictive metagenomic approach (PICRUSt), we tested to what extent sediment and X. testudinaria host compositionally and functionally distinct communities of Archaea and Bacteria. Although Crenarchaeota (Archaea) and Proteobacteria (Bacteria) were the dominant phyla in the microbial communities of both sediment and sponge, there were significant differences in composition between them. Biotope proved to be the main identifiable factor affecting composition. In line with the compositional differences between sediment and sponge prokaryote communities, there were also differences in predicted functions. The archaeal and bacterial communities of sediment were enriched for functions associated with the Metabolism and Environmental Information Processing categories; those of X. testudinaria were enriched for functions associated with the Genetic Information Processing category. The significant levels of concordance between archaeal and bacterial communities and the similar enrichment of these communities in the same functional categories suggests a certain degree of functional redundancy between Archaea and Bacteria in the studied biotopes, which for the sponge may result in an increased resilience to environmental perturbations.

  1. Mineral composition and heavy metal contamination of sediments originating from radium rich formation water. (United States)

    Bzowski, Zbigniew; Michalik, Bogusław


    Radium rich formation water is often associated with fossil fuels as crude oil, natural gas and hard coal. As a result of fossil fuels exploitation high amount of such water is released into environment. In spite of the high radium content such waters create a serious radiation risk neither to humans nor biota directly. First and foremost due to very high mineralization they are not drinkable at all. But after discharge chemical and physical conditions are substantially changed and sediments which additionally concentrated radium are arising. Due to features of technological processes such phenomenon is very intensive in underground coal mining where huge volume of such water must be pumped into surface in order to keep underground galleries dry. Slightly different situation occurs in oil rigs, but finally also huge volume of so called process water is pumped into environment. Regardless their origin arising sediments often contain activity concentration of radium isotopes exceeding the clearance levels set for naturally occurring radioactive materials (NORM) (Council Directive, 2013). The analysis of metals and minerals content showed that besides radioactivity such sediments contain high amount of metals geochemically similar to radium as barium, strontium and lead. Correlation analysis proved that main mechanism leading to sediment creation is co-precipitation radium with these metals as a sulfate. The absorption on clay minerals is negligible even when barium is not present in significant quantities. Owing to very low solubility of sulfates radium accumulated in this way should not migrate into environment in the neighborhood of a site where such sediment were deposited. Copyright © 2014 Elsevier Ltd. All rights reserved.

  2. Upper Plate Response to Varying Subduction Styles in the Forearc Cook Inlet Basin in South Central Alaska (United States)

    Sanchez-Lohff, S. K.; Enkelmann, E.; Finzel, E.; Reid, M. M.


    The Cook Inlet forearc basin strata record the upper plate response to changes in subduction since 170 Ma. Subduction of normal oceanic crust during the Jurassic and Cretaceous was followed by spreading ridge subduction in the Paleocene, which initiated near trench magmatism and a shallow subduction angle. This was followed by a period of normal subduction until the Oligocene when subduction of an oceanic plateau commenced causing flat-slab subduction. We study the sedimentary record of the Cook Inlet Basin and analyze the sediment provenance, magmatic sources, paleotopography, and rock exhumation of southern Alaska, and their changes through time. We use a double dating technique on single detrital zircon grains from 25 samples combining fission track and U-Pb dating. We collected Jurassic to Pliocene sandstone, and modern fluvial deposits. Eight Mesozoic samples were taken from the eastern inverted section of the Cook Inlet Basin. Seven Cenozoic samples were taken from outcrops on the northern and southern margin of the basin, and four from northern offshore cores. Six modern river sands were sampled from four rivers to analyze what is currently draining into the basin from the north, east, and south. Zircon fission track data reveal that the Jurassic samples have been fully reset, while Cretaceous and Eocene samples have been partially reset. Subduction of the spreading ridge probably increased the geothermal gradient in the upper plate and caused thermal resetting of the underlying strata. Oligocene to Pliocene sediments contain the youngest age populations with lag times ranging 13-25 Myr. Samples from the northern margin (arc side) yield generally shorter lag times than samples from the south side (prism side). This pattern is consistent with modern sediments that show the youngest ages are sourced from the Alaska Range, revealed by a 14 Ma age peak in the Susitna River. In contrast, the youngest age populations found in the sediments of rivers draining the

  3. Rational Selection of Tailored Amendment Mixtures and Composites for In Situ Remediation of Contaminated Sediments (United States)


    persistent organic pollutants and natural minerals such as apatites, zeolites , or bauxite for the binding of toxic metals in sediments. This research...the addition of such amendments as activated carbon for persistent organic pollutants; natural minerals such as apatite, zeolites , or bauxite contaminants. Recent work by Ghosh (the Principle Investigator [PI] of this proposal) and others proposes that hydrophobic organic contaminants

  4. Geologic signature of early Tertiary ridge subduction in Alaska (United States)

    Bradley, Dwight C.; Kusky, Timothy M.; Haeussler, Peter J.; Goldfarb, Richard J.; Miller, Marti L.; Dumoulin, Julie A.; Nelson, Steven W.; Karl, Susan M.


    A mid-Paleocene to early Eocene encounter between an oceanic spreading center and a subduction zone produced a wide range of geologic features in Alaska. The most striking effects are seen in the accretionary prism (Chugach–Prince William terrane), where 61 to 50 Ma near-trench granitic to gabbroic plutons were intruded into accreted trench sediments that had been deposited only a few million years earlier. This short time interval also saw the genesis of ophiolites, some of which contain syngenetic massive sulfide deposits; the rapid burial of these ophiolites beneath trench turbidites, followed immediately by obduction; anomalous high-T, low-P, near-trench metamorphism; intense ductile deformation; motion on transverse strike-slip and normal faults; gold mineralization; and uplift of the accretionary prism above sea level. The magmatic arc experienced a brief flare-up followed by quiescence. In the Alaskan interior, 100 to 600 km landward of the paleotrench, several Paleocene to Eocene sedimentary basins underwent episodes of extensional subsidence, accompanied by bimodal volcanism. Even as far as 1000 km inboard of the paleotrench, the ancestral Brooks Range and its foreland basin experienced a pulse of uplift that followed about 40 million years of quiescence.All of these events - but most especially those in the accretionary prism - can be attributed with varying degrees of confidence to the subduction of an oceanic spreading center. In this model, the ophiolites and allied ore deposits were produced at the soon-to-be subducted ridge. Near-trench magmatism, metamorphism, deformation, and gold mineralization took place in the accretionary prism above a slab window, where hot asthenosphere welled up into the gap between the two subducted, but still diverging, plates. Deformation took place as the critically tapered accretionary prism adjusted its shape to changes in the bathymetry of the incoming plate, changes in the convergence direction before and after

  5. Implications for metal and volatile cycles from the pH of subduction zone fluids. (United States)

    Galvez, Matthieu E; Connolly, James A D; Manning, Craig E


    The chemistry of aqueous fluids controls the transport and exchange-the cycles-of metals and volatile elements on Earth. Subduction zones, where oceanic plates sink into the Earth's interior, are the most important geodynamic setting for this fluid-mediated chemical exchange. Characterizing the ionic speciation and pH of fluids equilibrated with rocks at subduction zone conditions has long been a major challenge in Earth science. Here we report thermodynamic predictions of fluid-rock equilibria that tie together models of the thermal structure, mineralogy and fluid speciation of subduction zones. We find that the pH of fluids in subducted crustal lithologies is confined to a mildly alkaline range, modulated by rock volatile and chlorine contents. Cold subduction typical of the Phanerozoic eon favours the preservation of oxidized carbon in subducting slabs. In contrast, the pH of mantle wedge fluids is very sensitive to minor variations in rock composition. These variations may be caused by intramantle differentiation, or by infiltration of fluids enriched in alkali components extracted from the subducted crust. The sensitivity of pH to soluble elements in low abundance in the host rocks, such as carbon, alkali metals and halogens, illustrates a feedback between the chemistry of the Earth's atmosphere-ocean system and the speciation of subduction zone fluids via the composition of the seawater-altered oceanic lithosphere. Our findings provide a perspective on the controlling reactions that have coupled metal and volatile cycles in subduction zones for more than 3 billion years(7).

  6. Electrical Resistivity Correlation to Vadose Zone Sediment and Pore-Water Composition for the BC Cribs and Trenches Area

    Energy Technology Data Exchange (ETDEWEB)

    Serne, R. Jeffrey; Ward, Anderson L.; Um, Wooyong; Bjornstad, Bruce N.; Rucker, Dale F.; Lanigan, David C.; Benecke, Mark W.


    This technical report documents the results of geochemical and soil resistivity characterization of sediment obtained from four boreholes drilled in the BC Cribs and Trench area. Vadose zone sediment samples were obtained at a frequency of about every 2.5 ft from approximately 5 ft bgs to borehole total depth. In total, 505 grab samples and 39 six-inch long cores were obtained for characterization. The pore-water chemical composition data, laboratory-scale soil resistivity and other ancillary physical and hydrologic measurements and analyses described in this report are designed to provide a crucial link between direct measurements on sediments and the surface-based electrical-resistivity information obtained via field surveys. A second goal of the sediment characterization was to measure the total and water-leachable concentrations of key contaminants of concern as a function of depth and distance from the footprints of inactive disposal facilities. The total and water-leachable concentrations of key contaminants will be used to update contaminant distribution conceptual models and to provide more data for improving base-line risk predictions and remedial alternative selections. The ERC “ground truthing” exercise for the individual boreholes showed mixed results. In general, the high concentrations of dissolved salts in the pore waters of sediments from C5923, C5924 and C4191 produced a low resistivity “target” in the processed resistivity field surveys, and variability could be seen in the resistivity data that could relate to the variability in pore- water concentrations but the correlations (regression R2 were mediocre ranging from 0.2 to 0.7 at best; where perfect correlation is 1.0). The field-based geophysical data also seemed to suffer from a sort of vertigo, where looking down from the ground surface, the target (e.g., maximum pore-water salt concentration) depth was difficult to resolve. The best correlations between the field electrical

  7. Horizontal mantle flow controls subduction dynamics. (United States)

    Ficini, E; Dal Zilio, L; Doglioni, C; Gerya, T V


    It is generally accepted that subduction is driven by downgoing-plate negative buoyancy. Yet plate age -the main control on buoyancy- exhibits little correlation with most of the present-day subduction velocities and slab dips. "West"-directed subduction zones are on average steeper (~65°) than "East"-directed (~27°). Also, a "westerly"-directed net rotation of the lithosphere relative to the mantle has been detected in the hotspot reference frame. Thus, the existence of an "easterly"-directed horizontal mantle wind could explain this subduction asymmetry, favouring steepening or lifting of slab dip angles. Here we test this hypothesis using high-resolution two-dimensional numerical thermomechanical models of oceanic plate subduction interacting with a mantle flow. Results show that when subduction polarity is opposite to that of the mantle flow, the descending slab dips subvertically and the hinge retreats, thus leading to the development of a back-arc basin. In contrast, concordance between mantle flow and subduction polarity results in shallow dipping subduction, hinge advance and pronounced topography of the overriding plate, regardless of their age-dependent negative buoyancy. Our results are consistent with seismicity data and tomographic images of subduction zones. Thus, our models may explain why subduction asymmetry is a common feature of convergent margins on Earth.

  8. The arc arises: The links between volcanic output, arc evolution and melt composition (United States)

    Brandl, Philipp A.; Hamada, Morihisa; Arculus, Richard J.; Johnson, Kyle; Marsaglia, Kathleen M.; Savov, Ivan P.; Ishizuka, Osamu; Li, He


    Subduction initiation is a key process for global plate tectonics. Individual lithologies developed during subduction initiation and arc inception have been identified in the trench wall of the Izu-Bonin-Mariana (IBM) island arc but a continuous record of this process has not previously been described. Here, we present results from International Ocean Discovery Program Expedition 351 that drilled a single site west of the Kyushu-Palau Ridge (KPR), a chain of extinct stratovolcanoes that represents the proto-IBM island arc, active for ∼25 Ma following subduction initiation. Site U1438 recovered 150 m of oceanic igneous basement and ∼1450 m of overlying sediments. The lower 1300 m of these sediments comprise volcaniclastic gravity-flow deposits shed from the evolving KPR arc front. We separated fresh magmatic minerals from Site U1438 sediments, and analyzed 304 glass (formerly melt) inclusions, hosted by clinopyroxene and plagioclase. Compositions of glass inclusions preserve a temporal magmatic record of the juvenile island arc, complementary to the predominant mid-Miocene to recent activity determined from tephra layers recovered by drilling in the IBM forearc. The glass inclusions record the progressive transition of melt compositions dominated by an early 'calc-alkalic', high-Mg andesitic stage to a younger tholeiitic stage over a time period of 11 Ma. High-precision trace element analytical data record a simultaneously increasing influence of a deep subduction component (e.g., increase in Th vs. Nb, light rare earth element enrichment) and a more fertile mantle source (reflected in increased high field strength element abundances). This compositional change is accompanied by increased deposition rates of volcaniclastic sediments reflecting magmatic output and maturity of the arc. We conclude the 'calc-alkalic' stage of arc evolution may endure as long as mantle wedge sources are not mostly advected away from the zones of arc magma generation, or the rate of

  9. Use of Composite Fingerprinting Technique to Determine Contribution of Paria River Sediments to Dam-Release Flood Deposits in Marble Canyon, Grand Canyon, Az (United States)

    Chapman, K.; Parnell, R. A.; Smith, M. E.; Grams, P. E.; Mueller, E. R.


    The 1963 closure of Glen Canyon Dam drastically reduced the downstream sediment supply and altered daily flow regimes of the Colorado River through Grand Canyon, resulting in significant sandbar erosion downstream of the dam. Dam-release floods, known as High Flow Experiments (HFEs), have occurred six times since 1996 and are intended to rebuild Grand Canyon sandbars using tributary-supplied sediment. In Marble Canyon (first 100 km of Grand Canyon) the targeted tributary is the Paria River which supplies approximately 90% of the annual suspended sediment flux through Marble Canyon; the same input contributed less than 6% prior to the dam. Annual topographic surveys have established that HFEs are effective at rebuilding sandbars. However, the long-term viability of using HFEs for sandbar maintenance is dependent on a sustainable source of sediments comprising HFE deposits. Significant use of non-tributary, main-stem sediments (i.e. pre-dam sand stored in eddies or the channel bed) in HFE deposits would indicate reliance on a limited resource, and diminishing returns in the ability of HFEs to rebuild sandbars. In this study, we sampled vertically throughout 12 bars in Marble Canyon to document temporal and downstream changes in the proportion of sediment sourced from the Paria River during the 2013 and 2014 HFEs. Preliminary data suggest that heavy mineral compositions and concentrations of Ti, S, Cr and Rb, all of which are influenced by grainsize, could be sufficiently capable of differentiating Paria-derived and main-stem sediments when combined into a composite fingerprint (CF). A multivariate mixing model using these CFs quantitatively determines the contribution of Paria-derived sediment in each HFE deposit sample. Mixing model endmembers for non-Paria sand include pre-dam flood deposits in Glen and Marble Canyons, and Marble Canyon dredge samples. These results elucidate the role of contemporary versus legacy sediment in long-term sandbar maintenance.

  10. Subduction of fracture zones controls mantle melting and geochemical signature above slabs. (United States)

    Manea, Vlad C; Leeman, William P; Gerya, Taras; Manea, Marina; Zhu, Guizhi


    For some volcanic arcs, the geochemistry of volcanic rocks erupting above subducted oceanic fracture zones is consistent with higher than normal fluid inputs to arc magma sources. Here we use enrichment of boron (B/Zr) in volcanic arc lavas as a proxy to evaluate relative along-strike inputs of slab-derived fluids in the Aleutian, Andean, Cascades and Trans-Mexican arcs. Significant B/Zr spikes coincide with subduction of prominent fracture zones in the relatively cool Aleutian and Andean subduction zones where fracture zone subduction locally enhances fluid introduction beneath volcanic arcs. Geodynamic models of subduction have not previously considered how fracture zones may influence the melt and fluid distribution above slabs. Using high-resolution three-dimensional coupled petrological-thermomechanical numerical simulations of subduction, we show that enhanced production of slab-derived fluids and mantle wedge melts concentrate in areas where fracture zones are subducted, resulting in significant along-arc variability in magma source compositions and processes.

  11. [Abundance and activity of microorganisms at the water-sediment interface and their effect on the carbon isotopic composition of suspended organic matter and sediments of the Kara Sea]. (United States)

    Ivanov, M V; Lein, A Iu; Savvichev, A S; Rusanov, I I; Veslopolova, E F; Zakharova, E E; Prusakova, T S


    At ten stations of the meridian profile in the eastern Kara Sea from the Yenisei estuary through the shallow shelf and further through the St. Anna trough, total microbial numbers (TMN) determined by direct counting, total activity of the microbial community determined by dark CO2 assimilation (DCA), and the carbon isotopic composition of organic matter in suspension and upper sediment horizons (δ13C, per thousand) were investigated. Three horizons were studied in detail: (1) the near-bottom water layer (20-30 cm above the sediment); (2) the uppermost, strongly hydrated sediment horizon, further termed warp (5-10 mm); and (3) the upper sediment horizon (1-5 cm). Due to decrease in the amount of isotopically light carbon of terrigenous origin with increasing distance from the Yenisei estuary, the TMN and DCA values decreased, and the δ13C changed gradually from -29.7 to -23.9 per thousand. At most stations, a noticeable decrease in TMN and DCA values with depth was observed in the water column, while the carbon isotopic composition of suspended organic matter did not change significantly. Considerable changes of all parameters were detected in the interface zone: TMN and DCA increased in the sediments compared to their values in near-bottom water, while the 13C content increased significantly, with δ13C of organic matter in the sediments being at some stations 3.5- 4.0 per thousand higher than in the near-bottom water. Due to insufficient illumination in the near-bottom zone, newly formed isotopically heavy organic matter (δ13C(-) -20 per thousand) could not be formed by photosynthesis, active growth of chemoautotrophic microorganisms in this zone is suggested, which may use reduced sulfur, nitrogen, and carbon compounds diffusing from anaerobic sediments. High DCA values for the interface zone samples confirm this hypothesis. Moreover, neutrophilic sulfur-oxidizing bacteria were retrieved from the samples of this zone.

  12. Importance of suspended sediment (SPS) composition and grain size in the bioavailability of SPS-associated pyrene to Daphnia magna. (United States)

    Xia, Xinghui; Zhang, Xiaotian; Zhou, Dong; Bao, Yimeng; Li, Husheng; Zhai, Yawei


    Hydrophobic organic compounds (HOCs) tend to associate with suspended sediment (SPS) in aquatic environments; the composition and grain size of SPS will affect the bioavailability of SPS-associated HOCs. However, the bioavailability of HOCs sorbed on SPS with different compositions and grain sizes is not well understood. In this work, passive dosing devices were made to control the freely dissolved concentration of pyrene, a typical HOC, in the exposure systems. The effect of pyrene associated with amorphous organic carbon (AOC), black carbon (BC), and minerals of SPS with grain sizes of 0-50 μm and 50-100 μm on the immobilization and enzymatic activities of Daphnia magna was investigated to quantify the bioavailability of pyrene sorbed on SPS with different grain sizes and compositions. The results showed that the contribution of AOC-, BC-, and mineral-associated pyrene to the total bioavailability of SPS-associated pyrene was approximately 50%-60%, 10%-29%, and 20%-30%, respectively. The bioavailable fraction of pyrene sorbed on the three components of SPS was ordered as AOC (22.4%-67.3%) > minerals (20.1%-46.0%) > BC (9.11%-16.8%), and the bioavailable fraction sorbed on SPS of 50-100 μm grain size was higher than those of 0-50 μm grain size. This is because the SPS grain size will affect the ingestion of SPS and the SPS composition will affect the desorption of SPS-associated pyrene in Daphnia magna. According to the results obtained in this study, a model has been developed to calculate the bioavailability of HOCs to aquatic organisms in natural waters considering both SPS grain size and composition. Copyright © 2016 Elsevier Ltd. All rights reserved.

  13. Geochemistry of jadeitites and jadeite-lawsonite rocks in a serpentinite mélange (Rio San Juan Complex, northern Dominican Republic): Constraints on fluid composition in a subduction channel environment (United States)

    Baese, Rauno; Maresch, Walter V.; Schenk, Volker; Schertl, Hans-Peter


    Jadeitites are excellent rock types for obtaining information on fluid composition in subduction zones. Recent studies indicate that many jadeitites appear to have formed by direct precipitation from a fluid [1]. In almost all localities worldwide (see e.g. Harlow and Sorensen, 2005) jadeitites are found either as allochthonous blocks or as veins and lenses directly within the serpentinite country rock of serpentinite mélanges. In the Rio San Juan Complex on the other hand jadeitite also frequently occurs as veins (cm to some dm in thickness) within lawsonite-blueschist blocks [2,3,4] entrained in the serpentinite mélange. The mélange of the Rio San Juan Complex also contains blocks (m to 10m scale) of different metamorphic grade and lithology (eclogites, blueschists, orthogneisses and very low grade rocks) showing contrasting but interrelated P-T-t paths. The consistency of such interrelated P-T-t paths with those obtained by numerical models led Krebs et al. [5] to interpret the mélange of the Rio San Juan Complex as a former subduction channel. So far, two types of jadeitite have been found in the blueschist blocks: either as discordant veins cutting the foliation, or as concordant layers. In some cases the jadeitites contain large amounts of lawsonite and should then better be called jadeite-lawsonite rocks. The latter rock type may form a network of thin (contact between vein and host rock is very sharp and petrographically no sign of a depletion zone near the vein can be recognized, indicating that the infiltrating fluid originated from an external source and was not released from the adjoining host rock. A mineralogical center-to-rim zonation has been identified in the jadeitite veins. Near the contact to the blueschist, lawsonite is the dominant mineral phase and towards the center the amount of jadeite increases. Major and trace element concentrations also change from centers to rims. Ca/Na varies from 0.75-0.77 in the center to 1.03-1.29 in the rim

  14. Chronicling a century of lead pollution in Mexico: stable lead isotopic composition analyses of dated sediment cores. (United States)

    Soto-Jimenez, Martin F; Hibdon, Sharon A; Rankin, Charley W; Aggarawl, Jugdeep; Ruiz-Fernandez, A Carolina; Paez-Osuna, Federico; Flegal, A Russell


    Analyses of lead isotopic compositions (204Pb, 206Pb, 207Pb, and 208Pb) of dated sediment cores from two coastal estuaries and two inland lakes chronicle the predominance of industrial lead emissions in Mexico over the past century. These isotopic ratios exhibit a shift in composition from the turn of the previous century (1900) that corresponds with measurable increases (from 2- to 10-fold) in lead concentrations in the cores above their baseline values (3-22 microg/g)--both changes are consistent with the development of Mexican lead production for export and the manufacture of tetraethyl lead additives for Mexican gasolines. While subsequent changes in lead concentrations in the cores correspond with calculated emissions from the combustion of leaded gasoline in Mexico, isotopic compositions of the cores remain relatively constant throughout most of the 1900s (e.g., 206Pb/207Pb = 1.200 +/- 0.003; 208Pb/207Pb = 2.463 +/- 0.004). That isotopic constancy is attributed to the widespread pollution from lead production in Mexico and the dispersion of some of that lead used as an additive in Mexican gasolines.

  15. What favors the occurrence of subduction mega-earthquakes? (United States)

    Brizzi, Silvia; Funiciello, Francesca; Corbi, Fabio; Sandri, Laura; van Zelst, Iris; Heuret, Arnauld; Piromallo, Claudia; van Dinther, Ylona


    Most of mega-earthquakes (MEqs; Mw > 8.5) occur at shallow depths along the subduction thrust fault (STF). The contribution of each subduction zone to the globally released seismic moment is not homogenous, as well as the maximum recorded magnitude MMax. Highlighting the ingredients likely responsible for MEqs nucleation has great implications for hazard assessment. In this work, we investigate the conditions favoring the occurrence of MEqs with a multi-disciplinary approach based on: i) multivariate statistics, ii) analogue- and iii) numerical modelling. Previous works have investigated the potential dependence between STF seismicity and various subduction zone parameters using simple regression models. Correlations are generally weak due to the limited instrumental seismic record and multi-parameter influence, which make the forecasting of the potential MMax rather difficult. To unravel the multi-parameter influence, we perform a multivariate statistical study (i.e., Pattern Recognition, PR) of the global database on convergent margins (Heuret et al., 2011), which includes seismological, geometrical, kinematic and physical parameters of 62 subduction segments. PR is based on the classification of objects (i.e., subduction segments) belonging to different classes through the identification of possible repetitive patterns. Tests have been performed using different MMax datasets and combination of inputs to indirectly test the stability of the identified patterns. Results show that the trench-parallel width of the subducting slab (Wtrench) and the sediment thickness at the trench (Tsed) are the most recurring parameters for MEqs occurrence. These features are mostly consistent, independently of the MMax dataset and combination of inputs used for the analysis. MEqs thus seem to be promoted for high Wtrench and Tsed, as their combination may potentially favor extreme (i.e., in the order of thousands of km) trench-parallel rupture propagation. To tackle the

  16. Long-term effects of dredging operations program. Effects of sediment organic-matter composition on bioaccumulation of sediment organic contaminants: Interim results. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Brannon, J.M.; Price, C.B.; Reilly, F.J.; Pennington, J.C.; McFarland, V.A.


    The relationship of sediment-bound polychlorinated biphenyl (PCB) 153 and fluoranthene to bioaccumulation by worms and clams and the relationship of sediment-bound PCB 153 and fluoranthene to concentrations in the interstitial water were examined. Bioaccumulation by both worms and clams was observed in all sediments. Apparent preference factor (APF) values showed that steady state was reached between sediment-bound contaminants and organism lipid pools. The APF values of organisms were close to the theoretical value for both contaminants in all sediments. These results showed that sediment total organic carbon (TOC) in conjunction with octanol water partition coefficients of nonpolar organic contaminants is a viable approach for predicting bioaccumulation of such compounds by infaunal organisms. Actual concentrations of contaminants in interstitial water were either overestimated or underestimated by the relationship between TOC and humic + fulvic acid organic matter fractions and sediment contaminant concentrations. Prediction of interstitial water concentrations was not as successful as use of APFs. The lack of agreement between predicted and actual interstitial water results was due to factors such as the presence of interstitial water contaminants bounds to microparticulates and dissolved organic material and the kind of organic material in the sediment.

  17. Retrograde lawsonite formation in the Franciscan subduction complex (United States)

    Myers, S.; Mulcahy, S. R.


    Lawsonite [CaAl2Si2O7(OH)2·H2O] is an index mineral of low-temperature subduction zones, contains a significant amount of water, and is an important host of rare-earth and trace elements in mafic protoliths. For these reasons, numerous studies have investigated the consequences of lawsonite breakdown during prograde subduction. In the Franciscan subduction complex, however, lawsonite in mafic blueschist largely formed along a retrograde path from pre-existing eclogite. In order to asses the conditions and significance of retrograde lawsonite formation we examined the petrology and geochemistry of lawsonite-bearing assemblages in Franciscan mafic rocks. All of the samples have the common assemblage: lawsonite, glaucophane, and sphene. Quartz is generally absent. Muscovite, chlorite, and relict epidote and rutile are variably present. Different index minerals calcite, aragonite, albite, and jadeitic pyroxene are present within lawsonite assemblages. Garnet occurs in equilibrium with lawsonite, as a relict mineral in lawsonite and the matrix, or is completely absent. Major element compositions vary from typical basalts and are strongly correlated with one another. Chondrite normalized REE compositions are variably LREE depleted or enriched, MREE are flat to enriched, and HREE are generally flat. Trace elements normalized to NMORB show variably enriched and depleted LILE. The petrology suggests lawsonite, glaucophane, and sphene formed from multiple retrograde reactions involving garnet, clinopyroxene, epidote, and rutile, together with significant hydration. Important index minerals imply lawsonite formed over a wide range of pressures within the subduction zone. The major, REE, and trace element compositions suggest lawsonite assemblages were derived from different protoliths or experienced variable amounts of metasomatism and interaction with crustally derived material and serpentinite.

  18. Benthic Bacterial Community Composition in the Oligohaline-Marine Transition of Surface Sediments in the Baltic Sea Based on rRNA Analysis

    Directory of Open Access Journals (Sweden)

    Julia Klier


    Full Text Available Salinity has a strong impact on bacterial community composition such that freshwater bacterial communities are very different from those in seawater. By contrast, little is known about the composition and diversity of the bacterial community in the sediments (bacteriobenthos at the freshwater-seawater transition (mesohaline conditions. In this study, partial 16S-rRNA sequences were used to investigate the bacterial community at five stations, representing almost freshwater (oligohaline to marine conditions, in the Baltic Sea. Samples were obtained from the silty, top-layer (0–2.5 cm sediments with mostly oxygenated conditions. The long water residence time characteristic of the Baltic Sea, was predicted to enable the development of autochthonous bacteriobenthos at mesohaline conditions. Our results showed that, similar to the water column, salinity is a major factor in structuring the bacteriobenthos and that there is no loss of bacterial richness at intermediate salinities. The bacterial communities of marine, mesohaline, and oligohaline sediments differed in terms of the relative rRNA abundances of the major bacterial phyla/classes. At mesohaline conditions typical marine and oligohaline operational taxonomic units (OTUs were abundant. Putative unique OTUs in mesohaline sediments were present only at low abundances, suggesting that the mesohaline environment consists mainly of marine and oligohaline bacteria with a broad salinity tolerance. Our study provides a first overview of the diversity patterns and composition of bacteria in the sediments along the Baltic Sea salinity gradient as well as new insights into the bacteriobenthos at mesohaline conditions.

  19. Effect of nutrient enrichment on the source and composition of sediment organic carbon in tropical seagrass beds in the South China Sea. (United States)

    Liu, Songlin; Jiang, Zhijian; Zhang, Jingping; Wu, Yunchao; Lian, Zhonglian; Huang, Xiaoping


    To assess the effect of nutrient enrichment on the source and composition of sediment organic carbon (SOC) beneath Thalassia hemprichii and Enhalus acoroides in tropical seagrass beds, Xincun Bay, South China Sea, intertidal sediment, primary producers, and seawater samples were collected. No significant differences on sediment δ(13)C, SOC, and microbial biomass carbon (MBC) were observed between T. hemprichii and E. acoroides. SOC was mainly of autochthonous origin, while the contribution of seagrass to SOC was less than that of suspended particulate organic matter, macroalgae and epiphytes. High nutrient concentrations contributed substantially to SOC of seagrass, macroalgae, and epiphytes. The SOC, MBC, and MBC/SOC ratio in the nearest transect to fish farming were the highest. This suggested a more labile composition of SOC and shorter turnover times in higher nutrient regions. Therefore, the research indicates that nutrient enrichment could enhance plant-derived contributions to SOC and microbial use efficiency. Copyright © 2016 Elsevier Ltd. All rights reserved.

  20. Multiple subduction imprints in the mantle below Italy detected in a single lava flow (United States)

    Nikogosian, Igor; Ersoy, Özlem; Whitehouse, Martin; Mason, Paul R. D.; de Hoog, Jan C. M.; Wortel, Rinus; van Bergen, Manfred J.


    Post-collisional magmatism reflects the regional subduction history prior to collision but the link between the two is complex and often poorly understood. The collision of continents along a convergent plate boundary commonly marks the onset of a variety of transitional geodynamic processes. Typical responses include delamination of subducting lithosphere, crustal thickening in the overriding plate, slab detachment and asthenospheric upwelling, or the complete termination of convergence. A prominent example is the Western-Central Mediterranean, where the ongoing slow convergence of Africa and Europe (Eurasia) has been accommodated by a variety of spreading and subduction systems that dispersed remnants of subducted lithosphere into the mantle, creating a compositionally wide spectrum of magmatism. Using lead isotope compositions of a set of melt inclusions in magmatic olivine crystals we detect exceptional heterogeneity in the mantle domain below Central Italy, which we attribute to the presence of continental material, introduced initially by Alpine and subsequently by Apennine subduction. We show that superimposed subduction imprints of a mantle source can be tapped during a melting episode millions of years later, and are recorded in a single lava flow.

  1. Sediment composition of big Chinese and Indochinese rivers reflects geology of their source, not tectonic setting of their sink. (United States)

    Garzanti, Eduardo; Andò, Sergio; Limonta, Mara; Nie, Junsheng; Resentini, Alberto; Vezzoli, Giovanni; Wang, Jiangang; Yang, Shouye


    There are several reasons why the tectonic setting of a sedimentary basin cannot be inferred from the composition of its sedimentary fill. One is that sediments can, and quite often are transported for thousands of kilometers from sources uplifted by certain tectonic processes to subsident basins created by totally different tectonic processes. A classical case is the Amazon River, carrying detritus from the Andean Cordillera to the Atlantic passive margin on the opposite side of South America (Franzinelli and Potter, 1983; Dickinson, 1988). Similar is the case of major rivers in China and Indochina, sourced in Tibetan orogenic highlands and reaching the Chinese passive margin or the back-arc/pull-apart Andaman Sea. The Huang He (Yellow River), the most sediment-laden river in the world, delivers annually to the Bohai Sea 1 billion tons of litho-feldspatho-quartzose sedimentaclastic/metamorphiclastic sediments with moderately rich, amphibole-epidote-garnet suites including apatite and zircon (Nie et al., 2015). The Changjiang (Yangtze) River, the fourth longest on Earth and the largest in Eurasia, carries to the East China Sea litho-feldspatho-quartzose sedimentaclastic/metamorphiclastic sand with moderately poor, amphibole-epidote suites including clinopyroxene and garnet (Vezzoli et al., 2016). The Ayeyarwadi (Irrawaddy) River, ranking among the five major rivers in the world for its annual load of 0.4 billion tons, carries to the Andaman Sea litho-feldspatho-quartzose metamorphiclastic/sedimentaclastic sand with moderately rich, amphibole-epidote suites including garnet and clinopyroxene (Garzanti et al., 2013). Detrital modes in these three very big river basins are thus similar, and would plot in the "Recycled Orogen" field of Dickinson (1985) rather than in the "Continental Block" or "Magmatic Arc" fields. The orogenic signature acquired in mountainous headwaters is carried all the way to the mouth, and even after long-distance transport across wide

  2. Isotopic compositions of tropical East African flora and their potential as source indicators of organic matter in coastal marine sediments (United States)

    Muzuka, Alfred N. N.


    The C and N stable isotope compositions of some flora of East Africa from coastal Tanzania and Amboseli National Park (Kenya) are used to assess if they can be used as a terrestrial end member during the estimation of terrestrial fraction in coastal marine sediments. The results of C isotope composition of various tree leaves, which average -29.3 ± 1.4%, indicate that these tropical higher land plant species follow a Calvin-Benson or non-Kranz (C 3) type of metabolism. The results for grass species, which average -13.2 ± 2.4%, indicate that most of them follow a Hatch-Slack or Kranz (C 4) type of metabolism. However, some of the succulent plants from the Amboseli National Park have δ13C values that average -14.7%, an indication that they follow a CAM (Crassulacean Acid Metabolism) type of metabolism. The N isotope values are relatively higher than expected for the terrestrial organic material. The average δ15N values for both tree and grass samples are higher than 5% and fall within the range normally considered to be marine. The high enrichment in 15N may be related to the environmental conditions in which plants thrive. Plants growing in sandy, dry and overgrazed environments are expected to be enriched in 15N owing to full utilisation of all available N species, regardless of their isotopic compositions. Other processes which may cause an enrichment in 15N include adsorption by various types of clay minerals, supply of 15N-enriched nitrate through sea-spray, and local denitrification, especially in swampy and lake margins where the input of organic matter may be higher than the rate of decomposition. The stable isotopic composition of organic C and N for surficial organic matter for the coastal marine sediments averages -17.0 ± 0.9% and 5.4 ± 1.1%, respectively. These values indicate a substantial contribution of C 4 plants and sea grasses. However, contribution of C 4 relative to that of sea grasses can not be evaluated owing to the fact that there is no

  3. Links between sediment consolidation and Cascadia megathrust slip behaviour (United States)

    Han, Shuoshuo; Bangs, Nathan L.; Carbotte, Suzanne M.; Saffer, Demian M.; Gibson, James C.


    At sediment-rich subduction zones, megathrust slip behaviour and forearc deformation are tightly linked to the physical properties and in situ stresses within underthrust and accreted sediments. Yet the role of sediment consolidation at the onset of subduction in controlling the downdip evolution and along-strike variation in megathrust fault properties and accretionary wedge structure is poorly known. Here we use controlled-source seismic data combined with ocean drilling data to constrain the sediment consolidation and in situ stress state near the deformation front of the Cascadia subduction zone. Offshore Washington where the megathrust is inferred to be strongly locked, we find over-consolidated sediments near the deformation front that are incorporated into a strong outer wedge, with little sediment subducted. These conditions are favourable for strain accumulation on the megathrust and potential earthquake rupture close to the trench. In contrast, offshore Central Oregon, a thick under-consolidated sediment sequence is subducting, and is probably associated with elevated pore fluid pressures on the megathrust in a region where reduced locking is inferred. Our results suggest that the consolidation state of the sediments near the deformation front is a key factor contributing to megathrust slip behaviour and its along-strike variation, and it may also have a significant role in the deformation style of the accretionary wedge.

  4. Composition, production, and loss of carbohydrates in subtropical shallow subtidal sandy sediments: Rapid processing and long-term retention revealed by 13C-labeling

    NARCIS (Netherlands)

    Oakes, J.M.; Eyre, B.D.; Middelburg, J.J.; Boschker, H.T.S.


    The composition and production of carbohydrates (mannose, rhamnose, fucose, galactose, glucose, and xylose) and their transfer among sediment compartments (microphytobenthos [MPB], bacteria, and detritus) was investigated through in situ labeling with 13C-bicarbonate. After 60 h, 13C was found in

  5. Variations in Organic Matter Burial and Composition in Sediments from the Indian Ocean Continental Margin Off SW Indonesia (Sumatra - Java - Flores) Since the Last Glacial Maximum (United States)

    Jennerjahn, T. C.; Gesierich, K.; Schefuß, E.; Mohtadi, M.


    Global climate change is a mosaic of regional changes to a large extent determined by region-specific feedbacks between climate and ecosystems. At present the ocean is forming a major sink in the global carbon cycle. Organic matter (OM) storage in sediments displays large regional variations and varied over time during the Quaternary. Upwelling regions are sites of high primary productivity and major depocenters of organic carbon (OC), the least understood of which is the Indian Ocean upwelling off Indonesia. In order to reconstruct the burial and composition of OM during the Late Quaternary, we analyzed five sediment cores from the Indian Ocean continental margin off the Indonesian islands Sumatra to Flores spanning the last 20,000 years (20 kyr). Sediments were analyzed for bulk composition, stable carbon and nitrogen isotopes of OM, amino acids and hexosamines and terrestrial plant wax n-alkanes and their stable carbon isotope composition. Sedimentation rates hardly varied over time in the western part of the transect. They were slightly lower in the East during the Last Glacial Maximum (LGM) and deglaciation, but increased strongly during the Holocene. The amount and composition of OM was similar along the transect with maximum values during the deglaciation and the late Holocene. High biogenic opal covarying with OM content indicates upwelling-induced primary productivity dominated by diatoms to be a major control of OM burial in sediments in the East during the past 20 kyr. The content of labile OM was low throughout the transect during the LGM and increased during the late Holocene. The increase was stronger and the OM less degraded in the East than in the West indicating that continental margin sediments off Java and Flores were the major depocenter of OC burial along the Indian Ocean margin off SW Indonesia. Temporal variations probably resulted from changes in upwelling intensity and terrestrial inputs driven by variations in monsoon strength.

  6. Seasonal variability in the composition of glycerol dialkyl glycerol tetraethers (GDGTs) associated with suspended sediment transported by the Mekong River, Cambodia (United States)

    Ellis, E. E.; Richey, J. E.; Truxal, L. T.; Keil, R. G.; Ingalls, A. E.


    The branched/isoprenoid tetraether (BIT) index has been proposed to be a proxy for the relative amounts of terrestrially verses marine-derived organic matter preserved in coastal sediments. To accurately interpret this index, it is first necessary to understand how this index and its constituents vary in non-marine environments, such as rivers and soils. As the composition of organic matter exported by tropical rivers can vary considerably between the dry and rainy seasons, we assessed the seasonal variability of the branched and isoprenoid GDGTs (glycerol dialkyl glycerol tetraethers) associated with suspended sediment exported by the Mekong River. Our results demonstrate that the concentration (in ng/L) of crenarchaeol (GDGT IV), and branched GDGTs (GDGTs I, II, and III) was positively correlated with discharge and suspended sediment. When normalized to organic carbon (OC) content, dry-season values were consistently lower than rainy-season values for crenarchaeol (1.0 ± 0.6 vs. 4.1 ± 2.1 ng GDGT/mg OC) and branched (3.8 ± 1.5 vs. 16.8 ± 10.6 ng GDGT/mg OC) GDGTs. Low dry-season values were likely due to the dilution of GDGTs by phytoplankton production. The BIT index of suspended sediments ranged from 0.56 to 0.93 throughout the year, with a mean of 0.77. No seasonal trends were observed in this variability, nor was it correlated with bulk suspended sediment concentration or composition. These values are considerably lower than the theoretical terrestrial end-member of 1 due to the presence of crenarchaeol. Between 47 to 59% of the crenarchaeol associated with riverine suspended sediments was derived from intact polar groups bound to core GDGTs, whereas 48 to 65% of the branched GDGTs were intact. To further understand additional sources of GDGTs within the Mekong River catchment, we analyzed soil and sediment samples from rainforests, pastures, wetlands, river beds, and river banks during the rainy season. Anaerobic environments, such as wetlands and river

  7. Investigating the Role of Dehydration Reactions in Subduction Zone Pore Pressures Using Newly-Developed Permeability-Porosity Relationships (United States)

    Screaton, E.; Daigle, H.; James, S.; Meridth, L.; Jaeger, J. M.; Villaseñor, T. G.


    Dehydration reactions are linked to shallow subduction zone deformation through excess pore pressures and their effect on mechanical properties. Two reactions, the transformation of smectite to illite and of opal-A to opal-CT and then to quartz, can occur relatively early in the subduction process and may affect the propagation of the plate boundary fault, the updip limit of velocity-weakening frictional paper, and tsunamigenesis. Due to large variations between subduction zones in heat flow, sedimentation rates, and geometries, dehydration location may peak prior to subduction to as much as 100 km landward of the deformation front. The location of the dehydration reaction peak relative to when compaction occurs, causes significant differences in pore pressure generation. As a result, a key element to modeling excess pore pressures due to dehydration reactions is the assumed relationship between permeability and porosity. Data from Integrated Ocean Drilling Program (IODP) drilling of subduction zone reference sites were combined with previously collected results to develop relationships for porosity-permeability behavior for various sediment types. Comparison with measurements of deeper analog data show that porosity-permeability trends are maintained through burial and diagenesis to porosities <10%, suggesting that behavior observed in shallow samples is informative for predicting behavior at depth following subduction. We integrate these permeability-porosity relationships, compaction behavior, predictions of temperature distribution, kinetic expressions for smectite and opal-A dehydration, into fluid flow models to examine the role of dehydration reactions in pore pressure generation.

  8. To what depth can continental crust be subducted: numerical predictions and critical observations (United States)

    Gerya, T.; Faccenda, M.


    We performed systematic two-dimensional numerical modeling of continental collision associated with subduction of the lithospheric mantle. Results of our experiments suggest that two contrasting modes of lithospheric subduction below an orogen can exist: one-sided and double-sided. One-sided subduction brings continental crust subducting atop the slab to the contact with hot asthenosperic mantle wedge below the overriding plate. This can result in strong heating, partial melting and rheological weakening of the crust triggering its delamination from subducting mantle lithosphere in form of compositionally buoyant structures (cold plumes) propagating away from subducting plate, passing through the hot mantle wedge, underplating the overriding lithosphere and producing large amount of relatively felsic syn-orogenic magmas at sub-lithospheric depths. One-sided subduction of the buoyant continental crust can also result in a transient "hot channel effect" triggering formation and exhumation of coesite- and diamond- bearing rocks metamorphosed at 700 to 900oC. Anomalously high temperature is caused by intense viscous and radiogenic heating in the channel composed of deeply subducted radiogenic upper-crustal rocks. Low effective viscosity of the channel subsequent to increased temperature and partial melting permits profound mixing of mantle and crustal rocks. The hot channel exists during few million years only but rapidly produces and exhumes large amounts of ultrahigh-pressure, high-temperature rocks within the orogen. Double-sided subduction can follow the one-sided mode at later stages of orogeny when significant rheological coupling between two plates occurs during the collision. In this case the orogen is characterized by double- verging structure, the layer of subducting continental crust is embedded between two negatively buoyant lithospheric slabs and delamination of the crust does not occur. This mode of subduction can bring crustal rocks from the bottom of an

  9. [Effects of Corbicula fluminea bioturbation on the community composition and abundance of ammonia-oxidizing archaea and bacteria in surface sediments]. (United States)

    Wang, Xue; Zhao, Da-Yong; Zeng, Jin; Yu, Duo-Wei; Wu, Qing-Long


    To better understand the effects of Corbicula fluminea bioturbation on the ammonia-oxidizing microorganisms in the surface sediment, sediment-water microcosms with different densities of Corbicula fluminea were constructed. Clone libraries and real-time qPCR were applied to analyze the community composition and abundance of ammonia-oxidizing archaea (AOA) and bacteria (AOB) in the surface sediments. The results obtained indicated that the bioturbation of Corbicula fluminea accelerated the release of nitrogen from the surface sediment. In the amoA gene clone libraries, the identified AOA amoA gene sequences affiliated with the two known clusters (marine and soil clusters). The identified AOB amoA gene sequences mostly belonged to the Nitrosomonas of beta-Proteobacteria. The abundance of the bacterial amoA gene was higher than that of the archaeal amoA gene in all treatments. With increasing density of Corbicula fluminea, decreased abundances of the bacterial amoA gene were observed. At the same time, the diversity of AOA and AOB reduced in the Corbicula fluminea containing microcosms. In conclusion, the bioturbation of Corbicula fluminea could affected the community composition and abundance of ammonia-oxidizing microorganisms in surface sediments.

  10. The influence of oxygen exposure time on the composition of macromolecular organic matter as revealed by surface sediments on the Murray Ridge (Arabian Sea) (United States)

    Nierop, Klaas G. J.; Reichart, Gert-Jan; Veld, Harry; Sinninghe Damsté, Jaap S.


    The Arabian Sea represents a prime example of an open ocean extended oxygen minimum zone (OMZ) with low oxygen concentrations (down to less than 2 μM) between 200 and 1000 m water depth. The OMZ impinges on the ocean floor, affecting organic matter (OM) mineralization. We investigated impact of oxygen depletion on the composition of macromolecular OM (MOM) along a transect through the OMZ on the slopes of the Murray Ridge. This sub-marine high in the northern Arabian Sea, with the top at approximately 500 m below sea surface (mbss), intersects the OMZ. We analyzed sediments deposited in the core of OMZ (suboxic conditions), directly below the OMZ (dysoxic conditions) and well below the OMZ (fully oxic conditions). The upper 18 cm of sediments from three stations recovered at different depths were studied. MOM was investigated by Rock Eval and flash pyrolysis techniques. The MOM was of a predominant marine origin and inferred from their pyrolysis products, most biomolecules (tetra-alkylpyrrole pigments, polysaccharides, proteins and their transformation products, and polyphenols including phlorotannins), showed a progressive relative degradation with increasing exposure to oxygen. Alkylbenzenes and, in particular, aliphatic macromolecules increased relatively. The observed differences in MOM composition between sediment deposited under various bottom water oxygen conditions (i.e. in terms of concentration and exposure time) was much larger than within sediment cores, implying that early diagenetic alteration of organic matter depends largely on bottom water oxygenation rather than subsequent anaerobic degradation within the sediments, even at longer time scales.

  11. Changes in Sediment Fatty Acid Composition during Passage through the Gut of Deposit Feeding Holothurians: Holothuria atra (Jaeger, 1883) and Holothuria leucospilota (Brandt, 1835). (United States)

    Mfilinge, Prosper L; Tsuchiya, Makoto


    Sea cucumbers Holothuria atra and Holothuria leucospilota play an important role in the bioturbation of sediment in coral reef and rocky intertidal ecosystems. This study investigated changes in sediment fatty acid (FA) composition during gut passage in H. atra and H. leucospilota. The FA composition did not differ significantly between species. Comparison of FA composition in ambient sediment (AS), foregut (FG), midgut (MG), hindgut (HG), and faecal pellets (FPs) indicated that marked changes in FA composition occurred during passage through the gut of H. atra and H. leucospilota. Saturated fatty acids (SAFAs), monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs), and branched fatty acids (BrFAs) were significantly higher in FG than in AS, suggesting that both species selectively ingested nutrient rich particles. Significant reduction of SAFAs, MUFAs, PUFAs, and BrFAs occurred in MD and HD, with complete elimination of most PUFAs in FPs. A decrease in PUFAs 20:5ω3, 18:4ω3, 22:5ω3, 22:6ω3, 18:2ω6, 18:3ω3, 18:3ω6, odd-numbered BrFAs, and MUFA 18:1ω7 indicated that algal detritus and bacteria were important part of diet. These results have implications for the fate of specific dietary FAs, especially ω3 and ω6, and the contribution holothurian FPs make to the FA composition of coral reef and rocky intertidal ecosystems.

  12. Subduction dynamics: Constraints from gravity field observations (United States)

    Mcadoo, D. C.


    Satellite systems do the best job of resolving the long wavelength components of the Earth's gravity field. Over the oceans, satellite-borne radar altimeters such as SEASAT provide the best resolution observations of the intermediate wavelength components. Satellite observations of gravity contributed to the understanding of the dynamics of subduction. Large, long wavelength geoidal highs generally occur over subduction zones. These highs are attributed to the superposition of two effects of subduction: (1) the positive mass anomalies of subducting slabs themselves; and (2) the surface deformations such as the trenches convectively inducted by these slabs as they sink into the mantle. Models of this subduction process suggest that the mantle behaves as a nonNewtonian fluid, its effective viscosity increases significantly with depth, and that large positive mass anomalies may occur beneath the seismically defined Benioff zones.

  13. Burrow distribution of three sandeel species relates to beam trawl fishing, sediment composition and water velocity, in Dutch coastal waters

    NARCIS (Netherlands)

    Tien, N.S.H.; Craeymeersch, J.; Damme, van C.; Couperus, A.S.; Adema, J.; Tulp, I.


    Sandeel partly spend their life buried in the sediment, without a permanent burrow opening or an inhalant opening in the sediment. We linked the presence of three sandeel species (Ammodytes tobianus, A. marinus and Hyperoplus lanceolatus) off the southern Dutch coast of the North Sea to sediment

  14. Ins and outs of a complex subduction zone: C cycling along the Sunda margin, Indonesia (United States)

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


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

  15. Reevaluating plate driving forces from 3-D models of subduction (United States)

    Stegman, D. R.; Freeman, J.; Schellart, W. P.; Moresi, L.; May, D.; Turnbull, R.


    , 2004), owing to the analog slab having a lateral extent smaller than the width of the box. These experiments clearly show subduction of a finite-width slab will generate a flow of material from behind the slab around both the side edges and under the nose of the slab into the mantle wedge. This rollback induced flow establishes a positive feedback with backward hinge migration on the surface, and has significant consequences for the composition and dynamics of the mantle wedge. Here we present results of 3-D numerical experiments aimed to quantify the partitioning between different forces acting on such a slab. These experiments include a high viscosity slab (relative to background mantle), a high viscosity lower mantle and a computational domain large enough so that the flow induced by subduction of a finite-width slab is not constrained by the side or bottom boundaries. We provide a self-consistent force balance and integrate the forces acting over the different portions of the slab, thereby partitioning such forces into specific components. We quantify the force due to rollback-induced flow, and signify its importance as a driving force relative to the other forces present: a net slab pull force, a force responsible for bending the slab at the subduction hinge, and a resistive force due to shear traction on the upper, lower, and nose (if present) surfaces of the subducted slab.

  16. Long-term fore-arc basin evolution in response to changing subduction styles in southern Alaska (United States)

    Finzel, Emily S.; Enkelmann, Eva; Falkowski, Sarah; Hedeen, Tyler


    Detrital zircon U-Pb and fission track double-dating and Hf isotopes from the Mesozoic and Cenozoic strata in the southern Alaska fore-arc basin system reveal the effects of two different modes of flat-slab subduction on the evolution of the overriding plate. The southern margin of Alaska has experienced subduction of a spreading-ridge ( 62-50 Ma) and an oceanic plateau ( 40-0 Ma). When a subducting spreading ridge drives slab flattening, our data suggest that after the ridge has moved along strike retro-arc sediment sources to the fore arc become more predominant over more proximal arc sources. Spreading-ridge subduction also results in thermal resetting of rocks in the upper plate that is revealed by thermochronologic data that record the presence of young age peaks found in subsequent, thin sedimentary strata in the fore-arc basin. When a subducting oceanic plateau drives slab flattening, our data suggest that basin catchments get smaller and local sediment sources become more predominant. Crustal thickening due to plateau subduction drives widespread surface uplift and significant vertical uplift in rheologically weak zones that, combined, create topography and increase rock exhumation rates. Consequently, the thermochronologic signature of plateau subduction has generally young age peaks that generate short lag times indicating rapid exhumation. The cessation of volcanism associated with plateau subduction limits the number of syndepositional volcanic grains that produce identical geochronologic and thermochronologic ages. This study demonstrates the merit of double-dating techniques integrated with stratigraphic studies to expose exhumational age signatures diagnostic of large-scale tectonic processes in magmatic regions.

  17. Subduction Zone Concepts and the 2010 Chile Earthqake (Arthur Holmes Medal Lecture) (United States)

    von Huene, Roland


    Knowledge of convergent margin systems evolved from hypothesis testing with marine geophysical technology that improved over decades. Wegener's drift hypothesis, Holmes mantle convection, and marine magnetic anomaly patterns were integrated into an ocean spreading concept that won wide acceptance after ocean drilling confirmed the crustal younging trend toward the Mid-Atlantic ridge. In contrast, the necessary disposal of oceanic and trench sediment at convergent margins remained largely hypothetical. Fresh interpretations of some coastal mountains as exposing ancient convergent margin rock assemblages and the seismologist's "Wadati-Benioff" zone were combined into a widely-accepted hypothesis. A convergent margin upper plate was pictured as an imbricate fan of ocean sediment thrust slices detached from the lower plate. During the 1980s ocean drilling to test the hypothesis revealed what then were counter-intuitive processes of sediment subduction and subduction erosion. Rather than the proposed seaward growth by accretion, many margins had lost material from erosion. In current concepts, individual margins are shaped by the net consequences of subduction accretion, sediment subduction, and subduction erosion. Similarly, recently acquired age data from ancient subduction complexes reveal periods dominated by accretion separated by periods dominated by tectonic erosion. Globally, the recycling of continental crustal material at subduction zones appears largely balanced by magmatic addition at volcanic arcs. The longevity of the original imbricate fan model in text books confirms its pictorial simplicity, because geophysical images and drill core evidence show that it commonly applies to only a relatively small frontal prism. A better understanding of convergent margin dynamics is of urgent societal importance as coastal populations increase rapidly and as recent disastrous earthquakes and tsunamis verify. The shift in convergent margin concepts has developed through

  18. Tectonics of the IndoBurma Oblique Subduction Zone (United States)

    Steckler, M. S.; Seeber, L.; Akhter, S. H.; Betka, P. M.; Cai, Y.; Grall, C.; Mondal, D. R.; Gahalaut, V. K.; Gaherty, J. B.; Maung Maung, P.; Ni, J.; Persaud, P.; Sandvol, E. A.; Tun, S. T.


    The Ganges-Brahmaputra Delta (GBD) is obliquely colliding with the IndoBurma subduction zone. Most of the 42 mm/y of arc-parallel motion is absorbed in a set of dextral to dextral-convergent faults, the Sagaing, Kabaw and Churachandpur-Mao Faults. The 13-17 mm/y of convergence with the delta has built a 250-km wide active accretionary prism. The upper part of the 19-km sediment thickness consists of a shallowing-up stack of prograding strata that has shifted the shelf edge 3-400 km since the Himalayan orogeny at 50 Ma. The upper 3-5 km sandy shelf to fluvial strata are deformed into a broad fold and thrust belt above an overpressured décollement. It forms a flat shallow roof thrust in the frontal accretionary prism. The structure of the deeper part of the accretionary prism, which must transfer the incoming sediments to the upper plate, is unknown. GPS indicates the downdip end of the megathrust locked zone is 25 km at 92.5°E. The deformation front, marked by nascent detachment folds above the shallow décollement reaches the megacity of Dhaka in the middle of the GBD. The seismogenic potential of this portion of the prism is unknown. Arc volcanism in Myanmar, 500 km east of the deformation front, is sparse. Limited geochemical data on the arc volcanics are consistent with hot slab conditions. One possibility is that the deep GBD slab and basement are metamorphosed and dewatered early in the subduction process whereby most of the fluids are transferred to the growing prism by buoyancy driven migration or accretion of fluid-rich strata. Since it is entirely subaerial this little-studied region crossing Bangladesh, India and Myanmar provides an opportunity for a detailed multidisciplinary geophysical and geological investigation. It has the potential to highlight the role of fluids in subduction zones, the tectonics of extreme accretion and their seismic hazards, and the interplay between driving and resistance forces of a subduction zone during a soft collision.

  19. Macromolecular composition of terrestrial and marine organic matter in sediments across the East Siberian Arctic Shelf

    Directory of Open Access Journals (Sweden)

    R. B. Sparkes


    Full Text Available Mobilisation of terrestrial organic carbon (terrOC from permafrost environments in eastern Siberia has the potential to deliver significant amounts of carbon to the Arctic Ocean, via both fluvial and coastal erosion. Eroded terrOC can be degraded during offshore transport or deposited across the wide East Siberian Arctic Shelf (ESAS. Most studies of terrOC on the ESAS have concentrated on solvent-extractable organic matter, but this represents only a small proportion of the total terrOC load. In this study we have used pyrolysis–gas chromatography–mass spectrometry (py-GCMS to study all major groups of macromolecular components of the terrOC; this is the first time that this technique has been applied to the ESAS. This has shown that there is a strong offshore trend from terrestrial phenols, aromatics and cyclopentenones to marine pyridines. There is good agreement between proportion phenols measured using py-GCMS and independent quantification of lignin phenol concentrations (r2 = 0.67, p < 0.01, n = 24. Furfurals, thought to represent carbohydrates, show no offshore trend and are likely found in both marine and terrestrial organic matter. We have also collected new radiocarbon data for bulk OC (14COC which, when coupled with previous measurements, allows us to produce the most comprehensive 14COC map of the ESAS to date. Combining the 14COC and py-GCMS data suggests that the aromatics group of compounds is likely sourced from old, aged terrOC, in contrast to the phenols group, which is likely sourced from modern woody material. We propose that an index of the relative proportions of phenols and pyridines can be used as a novel terrestrial vs. marine proxy measurement for macromolecular organic matter. Principal component analysis found that various terrestrial vs. marine proxies show different patterns across the ESAS, and it shows that multiple river–ocean transects of surface sediments transition from river-dominated to

  20. Silicate dissolution boosts the CO2 concentrations in subduction fluids. (United States)

    Tumiati, S; Tiraboschi, C; Sverjensky, D A; Pettke, T; Recchia, S; Ulmer, P; Miozzi, F; Poli, S


    Estimates of dissolved CO2 in subduction-zone fluids are based on thermodynamic models, relying on a very sparse experimental data base. Here, we present experimental data at 1-3 GPa, 800 °C, and ∆FMQ ≈ -0.5 for the volatiles and solute contents of graphite-saturated fluids in the systems COH, SiO2-COH ( + quartz/coesite) and MgO-SiO2-COH ( + forsterite and enstatite). The CO2 content of fluids interacting with silicates exceeds the amounts measured in the pure COH system by up to 30 mol%, as a consequence of a decrease in water activity probably associated with the formation of organic complexes containing Si-O-C and Si-O-Mg bonds. The interaction of deep aqueous fluids with silicates is a novel mechanism for controlling the composition of subduction COH fluids, promoting the deep CO2 transfer from the slab-mantle interface to the overlying mantle wedge, in particular where fluids are stable over melts.Current estimates of dissolved CO2 in subduction-zone fluids based on thermodynamic models rely on a very sparse experimental data base. Here, the authors show that experimental graphite-saturated COH fluids interacting with silicates at 1-3 GPa and 800 °C display unpredictably high CO2 contents.

  1. Effect of sediment composition on methane concentration and production in the transition zone of a mangrove (Sepetiba Bay, Rio de Janeiro, Brazil). (United States)

    Marinho, C C; Campos, E A; Guimarães, J R D; Esteves, F A


    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 ecotone at 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.

  2. Changes in the Circum-Alpine Climate as a Function of the Alpine Upliftment: Constraints from Isotopic Compositions of Fossils, Sediments, and Vein Quartz (United States)

    Vennemann, T. W.; Tutken, T.; Kocsis, L.; Mullis, J.


    The Tertiary circum-Alpine Molasse sediments were deposited during major periods of Alpine tectonism but also at a time of large global climatic change. They are well suited to study the effects of tectonic forcing on climate, because the sediments were deposited in marginal basins, partly to completely isolated from other major oceanic basins. Hence, a comparison of the past climatic and oceanographic evolution indicated by the sediments to those on a global scale, does allow for a qualitative evaluation of the relationship between tectonism and regional climate. Much is known about the geological-geochronological framework of alpine tectonism, including associated erosional rates and sediment volumes. Estimates of changes in paleoelevation and its direct influence on climate have, however, been less well constrained. Three independent lines of evidence indicate significant altitudes of the Alps during the Miocene: 1) H isotope compositions of clay minerals, formed as weathering products and subsequently deposited as part of the Alpine Molasse, have δD reaching values as low as -97‰. 2) O isotope compositions of retrograde metamorphic vein and fissure quartz and H isotope composition of its included fluids have δ18O values as low as -3.5‰ and δD values of -140‰, respectively. 3) ``Exotic" shark teeth from Swiss Upper Marine Molasse sediments that have δ18O values (VSMOW) around 11‰ (n=2), values unlike those from other teeth of the same locality (20.7 to 21.8‰; n=6), but for which the REE patterns support the same diagenetic history, hence supporting a freshwater formation of the low δ18O teeth (also supported by distinct Sr isotope compositions). Using these three approaches as a basis for estimating the isotopic composition of past precipitation and applying the present-day altitude effects on the compositions, it can be concluded that the Miocene Alps had mean altitudes of about 1500 to 2000 m, that is elevations similar to those of today

  3. Dynamics of intraoceanic subduction initiation: 2D thermomechanical modeling (United States)

    Zhou, X.; Gerya, T.; LI, Z.; Stern, R. J.


    Intraoceanic subduction initiation occurs in previous weak zones which could be transform faults or old fracture zones, and concurrents with the change of plate motions. It is an important process to understand the beginning of plate tectonics. However, the dynamic process during (after) subduction initiation remain obscure. The process of suducting slabs move from down to downdip is also not revealed clearly. In order to obtain better understanding of the transitional process of subducting slab motion, we use finite difference and marker-in-cell methods to establish a series of self-sustainable subduction initiation models and explore many visco-plastic parameters to qualify the dynamical process of subduction initiation. The following parameters are systematic tested: (1) the age of the subducting slab; (2) friction coefficient of the mantle material; (3) the mantle potential temperature; (4) the age of the overriding slab. We find out the critical age of the oceanic lithosphere which can produce subduction initiation. And the age of subducting slab plays important roles during subduction initiation. The young subducting slab induces fast trench retreat and then trench begin to advance. For the old subducting slab, it induces relative slower trench retreat and then stop moving. The age of overriding slabs impacts coupling with the subducting slab. The friction coefficient of lithosphere also impacts the backarc spreading and subduction velocity. Stronger subducted plate gives lower subduction velocity and faster trench retreat velocity. The mantle potential temperature changes the critical age of subducted slabs.

  4. Seismicity and sedimentation rate effects on submarine slope stability (United States)

    Ten Brink, U. S.; Andrews, B. D.; Miller, N. C.


    Large submarine mass-transport scars are commonly observed on continental margins, but are noticeably less abundant on margins that experience frequent earthquakes than on those that seldom experience them. This is a surprising observation, given that horizontal acceleration from earthquakes and associated strength loss from cyclic loading and liquefaction are commonly thought to provide the primary triggers for inducing failures and subsequent mass movements. Mapping submarine failure scars in ten margins worldwide, we find decreasing scar abundance with both increasing frequency of earthquakes and decreasing sedimentation rate. The decrease in scar abundance is interpreted to represent increasing slope stability. The increase in stability is non linear (power law with btectonic activity (salt diapirs, seamount subduction, etc.) leads to relatively rapid oversteepening of the slope, implying that the morphology of most margins is in fact, stable over many earthquake cycles. Note that the above correlation averages scar area and sedimentation rate over entire margin areas. Variations in sedimentation rate with time, such as over glacial-interglacial cycles, and intra-margin variations in seismic attenuation, sedimentation rate, composition, and pore pressure, have likely affected the abundance of slope failures in time and space.

  5. Source characterization of sedimentary organic matter using molecular and stable carbon isotopic composition of n-alkanes and fatty acids in sediment core from Lake Dianchi, China. (United States)

    Fang, Jidun; Wu, Fengchang; Xiong, Yongqiang; Li, Fasheng; Du, Xiaoming; An, Da; Wang, Lifang


    The distribution and compound-specific carbon isotope ratios of n-alkanes and fatty acids in a sediment core (63 cm) collected from Lake Dianchi were examined to investigate organic matter sources in the eutrophic lake. Fatty acids included free and bound fatty acids. The carbon isotope compositions of individual n-alkanes and fatty acids from Lake Dianchi sediments were determined using gas chromatography/isotope ratio mass spectrometry (GC-IRMS). The δ(13)C values of individual n-alkanes (C16-C31) varied between -24.1‰ and -35.6‰, suggesting a dominance of (13)C-depleted n-alkanes that originated from C3 plants and lacustrine algae. Fatty acids from the sediment extracts were analyzed for their abundances and carbon isotopic compositions. Molecular and isotopic evidence indicates that most of the short-chain fatty acids from Lake Dianchi sediment extracts are sourced from intense microbial recycling and resynthesis of organic matter. Long-chain free fatty acids are mainly derived from terrestrial sources. However, long-chain bound fatty acids are sourced from a combination of terrestrial organic matter, bacteria and algae, with the contribution from algal sources higher in the hypereutrophic stage. © 2013.

  6. Molecular and Isotopic Composition of Volatiles in Gas Hydrates and in Sediment from the Joetsu Basin, Eastern Margin of the Japan Sea

    Directory of Open Access Journals (Sweden)

    Akihiro Hachikubo


    Full Text Available Hydrate-bearing sediment cores were retrieved from the Joetsu Basin (off Joetsu city, Niigata Prefecture at the eastern margin of the Japan Sea during the MD179 gas hydrates cruise onboard R/V Marion Dufresne in June 2010. We measured molecular and stable isotope compositions of volatiles bound in the gas hydrates and headspace gases obtained from sediments to clarify how the minor components of hydrocarbons affects to gas hydrate crystals. The hydrate-bound hydrocarbons at Umitaka Spur (southwestern Joetsu Basin primarily consisted of thermogenic methane, whereas those at Joetsu Knoll (northwestern Joetsu Basin, about 15 km from Umitaka Spur contained both thermogenic methane and a mixture of thermogenic and microbial methane. The depth concentration profiles of methane, ethane, propane, CO2, and H2S in the sediments from the Joetsu Basin area showed shallow sulfate–methane interface (SMI and high microbial methane production beneath the SMI depth. Relatively high concentrations of propane and neopentane (2,2-dimethylpropane were detected in the headspace gases of the hydrate-bearing sediment cores obtained at Umitaka Spur and Joetsu Knoll. Propane and neopentane cannot be encaged in the structure I hydrate; therefore, they were probably excluded from the hydrate crystals during the structure I formation process and thus remained in the sediment and/or released from the small amounts of structure II hydrate that can host such large gas molecules. The lower concentrations of ethane and propane in the sediment, high δ13C of propane and isobutane, and below-detection normal butane and normal pentane at Umitaka Spur and Joetsu Knoll suggest biodegradation in the sediment layers.

  7. The impact of temperature change on the activity and community composition of sulfate-reducing bacteria in arctic versus temperate marine sediments

    DEFF Research Database (Denmark)

    Robador, Alberto; Brüchert, Volker; Jørgensen, Bo Barker


    -reducing bacteria (SRB). However, high rates at in situ temperatures compared with maximum rates showed the predominance of psychrophilic SRB even at high incubation temperatures. Changing apparent activation energies (Ea) showed that increasing temperatures had an initial negative impact on sulfate reduction...... that was weaker after prolonged incubations, which could imply an acclimatization response rather than a selection process of the SRB community. The microbial community composition was analysed by targeting the 16S ribosomal RNA using catalysed reporter deposition fluorescence in situ hybridization (CARD......-FISH). The results showed the decline of specific groups of SRB and confirmed a strong impact of increasing temperatures on the microbial community composition of arctic sediment. Conversely, in seasonally changing sediment sulfate reduction rates and sulfate-reducing bacterial abundance changed little in response...

  8. Cycling of sulfur in subduction zones: The geochemistry of sulfur in the Mariana Island Arc and back-arc trough (United States)

    Alt, J.C.; Shanks, Wayne C.; Jackson, M.C.


    The sulfur contents and sulfur isotopic compositions of 24 glassy submarine volcanics from the Mariana Island Arc and back-arc Mariana Trough were determined in order to investigate the hypothesis that subducted seawater sulfur (??34S = 21???) is recycled through arc volcanism. Our results for sulfur are similar to those for subaerial arc volcanics: Mariana Arc glasses are enriched in 34S (??34S = up to 10.3???, mean = 3.8???) and depleted in S (20-290 ppm, mean = 100 ppm) relative to MORB (850 ppm S, ??34S = 0.1 ?? 0.5???). The back-arc trough basalts contain 200-930 ppm S and have ??34S values of 1.1 ?? 0.5???, which overlap those for the arc and MORB. The low sulfur contents of the arc and some of the trough glasses are attributed to (1) early loss of small amounts of sulfur through separation of immiscible sulfide and (2) later vapor-melt equilibrium control of sulfur contents and loss of sulfur in a vapor phase from sulfide-undersaturated melts near the minimum in sulfur solubility at f{hook}O2 ??? NNO (nickel-nickel oxide). Although these processes removed sulfur from the melts their effects on the sulfur isotopic compositions of the melts were minimal. Positive trends of ??34S with 87Sr 86Sr, LILE and LREE contents of the arc volcanics are consistent with a metasomatic seawater sulfur component in the depleted sub-arc mantle source. The lack of a 34S-rich slab signature in the trough lavas may be attributed to equilibration of metasomatic fluid with mantle material along the longer pathway from the slab to the source of the trough volcanics. Sulfur is likely to have been transported into the mantle wedge by metasomatic fluid derived from subducted sediments and pore fluids. Gases extracted from vesicles in arc and back-arc samples are predominantly H2O, with minor CO2 and traces of H2S and SO2. CO2 in the arc and back-arc rocks has ??13C values of -2.1 to -13.1???, similar to MORB. These data suggest that degassing of CO2 could explain the slightly lower

  9. A subduction zone reference frame based on slab geometry and subduction partitioning of plate motion and trench migration

    NARCIS (Netherlands)

    Schellart, W. P.


    The geometry of subducted slabs that interact with the transition zone depends critically on the partitioning of the subduction velocity (v S⊥) at the surface into its subducting plate motion component (vSP⊥) and trench migration component (vT⊥). Geodynamic models of progressive subduction

  10. The earthquake cycle in subduction zones (United States)

    Melosh, H. J.; Fleitout, L.


    A simplified model of a subduction zone is presented, which incorporates the mechanical asymmetry induced by the subducted slab to anchor the subducting plate during post-seismic rebound and thus throw most of the coseismic stream release into the overthrust plate. The model predicts that the trench moves with respect to the deep mantle toward the subducting plate at a velocity equal to one-half of the convergence rate. A strong extensional pulse is propagated into the overthrust plate shortly after the earthquake, and although this extension changes into compression before the next earthquake in the cycle, the period of strong extension following the earthquake may be responsible for extensional tectonic features in the back-arc region.

  11. Seismic coupling and uncoupling at subduction zones (United States)

    Ruff, L.; Kanamori, H.


    Some of the correlations concerning the properties of subduction zones are reviewed. A quantitative global comparison of many subduction zones reveals that the largest earthquakes occur in zones with young lithosphere and fast convergence rates. Maximum earthquake size is directly related to the asperity distribution on the fault plane. This observation can be translated into a simple model of seismic coupling where the horizontal compressive stress between two plates is proportional to the ratio of the summed asperity area to the total area of the contact surface. Plate age and rate can control asperity distribution directly through the horizontal compressive stress associated with the vertical and horizontal velocities of subducting slabs. The basalt to eclogite phase change in the down-going oceanic crust may be largely responsible for the uncoupling of subduction zones below a depth of about 40 km.

  12. The “ophiolite rule”, chemostratigraphy of Teythan-type ophiolites and subduction initiation (United States)

    Whattam, S. A.; Stern, R. J.


    Characteristics of the classic late Jurassic and late Cretaceous Tethyan-type ophiolites of the Eastern Mediterranean - Persian Gulf region are consistent with formation in a supra-subduction zone (SSZ); the most robust model for their production entails formation upon subduction initiation in the forearc or proto-forearc region of a nascent intra-oceanic arc (IOA). The ‘ophiolite rule’ however, demonstrates that a co-existence of MOR-like (in addition to SSZ) lavas is the norm and not the exception. Specifically, the ‘normal’ chemostratigraphy of Tethyan-type ophiolites usually exhibits a thick, lower section of tholeiitic MOR-like lavas in addition to an upper section of dominantly calc-alkaline, HFSE-depleted, VAB-like lavas and intrusives and lesser boninites; latest stage dikes of boninitic affinity commonly cut both suites. This association testifies to changes in the ophiolitic melt source. To date, explanations for the near ubiquitous relationship of these two distinct tectonomagmatic suites usually infer that conventional MOR or marginal basin formation was followed by tectonic reorganization and consequent IOA construction above the (much older) first-formed MORB seafloor. While such ad hoc tectonic interpretations might apply to a few ophiolites, these explanations surely can’t explain what appears to be a global ophiolite phenomenon as this chemostratigraphy is now being recognized in other major ophiolitic belts (e.g., of the SW Pacific) and IOA forearcs (e.g., the Izu-Bonin-Mariana arc). A lack of hiatus between sequences is shown by boundaries between the two main ophiolitic units that are stratigraphic and not fault-bounded; there exists no significant temporal hiatus between formation of the lower tholeiitic and upper calc-alkaline suites (no sediment horizons or obvious unconformities); furthermore, lavas compositionally intermediate to MORB- and VAB-like occur stratigraphically between the sequences. We present a new model consistent

  13. Source contamination and tectonomagmatic signals of overlapping Early to Middle Miocene orogenic magmas associated with shallow continental subduction and asthenospheric mantle flows in Western Anatolia: A record from Simav (Kütahya) region (United States)

    Çoban, Hakan; Karacık, Zekiye; Ece, Ömer Işık


    The disappearances of mafic shoshonitic and ultrapotassic magma prior to Late Oligocene in Western Anatolia post-collisional tectonic settings, and the sudden appearance of Early-Middle Miocene potassic lavas with orogenic geochemical signatures, indicate a striking change of mantle sources during the Early-Middle Miocene period, and require a special explanation. In this regard, the Simav (Kütahya) region of Western Anatolia represents a critical area, where the Early-Middle Miocene mafic potassic (shoshonite, absarokite, ultrapotassic) and high-K calc-alkaline (andesite, dacite-rhyolite, granite) series rocks overlap in the extensional geotectonic setting in a back-arc position. The appraisal of petrological data obtained from Simav igneous complex indicates that there is a remarkable geochemical and isotopic similarity (e.g., negative Eu anomalies; Nb-Ta depletions; high Sr, low Nd and variable Pb isotope compositions) between coevally generated mafic potassic and high-K calc-alkaline magma series. The near primitive mafic potassic (MHKS) lavas with high Sr isotope compositions require a heterogeneous mantle source contaminated with crustal materials. Dragged and delaminated crustal components, caused by shallow continental subduction and the late arrived subducted terrigenous sediments from the Aegean trench are likely candidate sources of continental materials incorporated into the mantle source of the Simav mafic potassic (MHKS) magmas. The nature of these components also played a significant role in the compositional variations of Simav mafic series rocks. The Simav mafic potassic (MHKS) magmas were derived from a crust-contaminated, subduction-modified (metasomatized) EM-II type mantle source, interacting with influxed asthenosphere in a back-arc mantle wedge, whereas mixing of lower crustal silicic melts with underplated potassic mafic magmas resulted in coeval high-K calc-alkaline rocks, matched by the extent of crustal contamination observed in the more

  14. A numerical reference model for themomechanical subduction

    DEFF Research Database (Denmark)

    Quinquis, Matthieu; Chemia, Zurab; Tosi, Nicola


    response to systematic variations in input parameters, numerical studies often start from a 'reference' subduction model. However, the reference model often varies between different numerical studies, making it difficult to compare results directly. We aim therefore to define a numerical reference model......, and initial temperature distribution. We will show results of the evolution and dynamics of the subduction reference model using different numerical codes: a finite element code, SULEC, and two finite difference codes, YACC and FDcon....

  15. First direct evidence of sedimentary carbonate recycling in subduction-related xenoliths. (United States)

    Liu, Yongsheng; He, Detao; Gao, Changgui; Foley, Stephen; Gao, Shan; Hu, Zhaochu; Zong, Keqing; Chen, Haihong


    Carbon in rocks and its rate of exchange with the exosphere is the least understood part of the carbon cycle. The amount of carbonate subducted as sediments and ocean crust is poorly known, but essential to mass balance the cycle. We describe carbonatite melt pockets in mantle peridotite xenoliths from Dalihu (northern China), which provide firsthand evidence for the recycling of carbonate sediments within the subduction system. These pockets retain the low trace element contents and δ(18)OSMOW = 21.1 ± 0.3 of argillaceous carbonate sediments, representing wholesale melting of carbonates instead of filtered recycling of carbon by redox freezing and melting. They also contain microscopic diamonds, partly transformed to graphite, indicating that depths >120 km were reached, as well as a bizarre mixture of carbides and metal alloys indicative of extremely reducing conditions. Subducted carbonates form diapirs that move rapidly upwards through the mantle wedge, reacting with peridotite, assimilating silicate minerals and releasing CO2, thus promoting their rapid emplacement. The assimilation process produces very local disequilibrium and divergent redox conditions that result in carbides and metal alloys, which help to interpret other occurrences of rock exhumed from ultra-deep conditions.

  16. Petrogenesis of Eocene granitoids and microgranular enclaves in the western Tengchong Block: Constraints on eastward subduction of the Neo-Tethys (United States)

    Zhao, Shao-wei; Lai, Shao-cong; Qin, Jiang-feng; Zhu, Ren-Zhi


    Eocene granitic and related igneous rocks in the western Tengchong Block are considered to be the result of eastward subduction of Neo-Tethyan oceanic lithosphere beneath the Tengchong Block. In this paper we show that the granitic and mafic rocks in the western Tengchong Block exhibit a systematic compositional variation from west to east, with Na-rich granodiorites in the Nabang area (west) that differ from coeval high-K calc-alkaline granodiorites in the Bangwan area (east), and with tholeiitic mafic rocks in the Nabang area that differ from shoshonitic mafic microgranular enclaves (MMEs) in granodiorites of the Bangwan area. In addition, high-silica biotite granites were intruded into the granodiorites in the Bangwan area. The host granodiorites, MMEs, and biotite granites in the Bangwan area yield zircon U-Pb ages of ca. 50 Ma. The MMEs have relatively low SiO2 contents (53.1-64.95 wt%) and Mg# values (37-45), and high K2O (4.14-5.02 wt%) and ∑ REE contents (331-509 ppm); the MMEs contain acicular apatites that indicate quenching. The host granodiorites also have high K2O (4.48-5.95 wt%) and ∑ REE compositions (320-459 ppm), and together with the MMEs they are enriched in Th but depleted in Nb and Ti. The Sr-Nd-Pb isotopic compositions of the host granodiorites and the MMEs are similar, with εHf(t) values of - 1.0 to - 10.8 and 3.3 to - 11.1, respectively. The geochemical data and igneous textures suggest that the MMEs represent a mafic magma that was derived from the partial melting of mantle pyroxenite, with the melting induced by the influx of fluids/melts from the recycling of sediments in the subducted slab. The mafic melts then caused the partial melting of lower crustal tonalitic rocks to produce granodioritic magma that was subsequently mixed with mafic magma. The biotite granites have relatively high SiO2 contents and low Mg# values that indicate a purely crustal origin and derivation from the partial melting of upper crustal metagraywacke. The

  17. Responses in sediment phosphorus and lanthanum concentrations and composition across 10 lakes following applications of lanthanum modified bentonite

    NARCIS (Netherlands)

    Dithmer, Line; Nielsen, Ulla Gro; Lurling, Miguel; Spears, Bryan M.; Yasseri, Said; Lundberg, Daniel; Moore, Alanna; Jensen, Nicholai D.; Reitzel, Kasper


    A combined field and laboratory scale study of 10 European lakes treated between 2006 and 2013 with a lanthanum (La) modified bentonite (LMB) to control sediment phosphorus (P) release was conducted. The study followed the responses in sediment characteristics including La and P fractions and

  18. Spatio-temporal variations in the composition of organic matter in surface sediments of a mangrove receiving shrimp farm effluents (New Caledonia)

    Energy Technology Data Exchange (ETDEWEB)

    Aschenbroich, Adélaïde, E-mail: [UMR BOREA 7208 CNRS/MNHN/UPMC/IRD/UCBN, Muséum National d' Histoire Naturelle, CP 53, 61 rue Buffon, 75231 Paris cedex 5 (France); Marchand, Cyril [Institut de Recherche pour le Développement (IRD), UMR 7590, UR 206, BP A5, 98848 Nouméa, New Caledonia (France); Molnar, Nathalie [UMR BOREA 7208 CNRS/MNHN/UPMC/IRD/UCBN, Muséum National d' Histoire Naturelle, CP 53, 61 rue Buffon, 75231 Paris cedex 5 (France); Institut de Recherche pour le Développement (IRD), UMR 7590, UR 206, BP A5, 98848 Nouméa, New Caledonia (France); Deborde, Jonathan [Institut de Recherche pour le Développement (IRD), UMR 7590, UR 206, BP A5, 98848 Nouméa, New Caledonia (France); Hubas, Cédric; Rybarczyk, Hervé; Meziane, Tarik [UMR BOREA 7208 CNRS/MNHN/UPMC/IRD/UCBN, Muséum National d' Histoire Naturelle, CP 53, 61 rue Buffon, 75231 Paris cedex 5 (France)


    In order to investigate spatio-temporal variations in the composition and origin of the benthic organic matter (OM) at the sediment surface in mangrove receiving shrimp farm effluents, fatty acid (FA) biomarkers, natural stable isotopes (δ{sup 13}C and δ{sup 15}N), C:N ratios and chlorophyll-a (chl-a) concentrations were determined during the active and the non-active period of the farm. Fatty acid compositions in surface sediments within the mangrove forest indicated that organic matter inputs varied along the year as a result of farm activity. Effluents were the source of fresh particulate organic matter for the mangrove, as evidenced by the unsaturated fatty acid (UFA) distribution. The anthropogenic MUFA 18:1ω9 was not only accumulated at the sediment surface in some parts of the mangrove, but was also exported to the seafront. Direct release of bacteria and enhanced in situ production of fungi, as revealed by specific FAs, stimulated mangrove litter decomposition under effluent runoff condition. Also, microalgae released from ponds contributed to maintain high benthic chl-a concentrations in mangrove sediments in winter and to a shift in microphytobenthic community assemblage. Primary production was high whether the farm released effluent or not which questioned the temporary effect of shrimp farm effluent on benthic microalgae dynamic. This study outlined that mangrove benthic organic matter was qualitatively and quantitatively affected by shrimp farm effluent release and that responses to environmental condition changes likely depended on mangrove stand characteristics. - Highlights: • Fatty acid 18:1ω9 is a relevant marker to monitor effluent pathway in the mangrove. • OM nature and distribution at sediment surface varied in relation to farm activity. • Enhancement of litter-decomposer biomass and activity stimulates litter degradation. • Diatoms dominate the microalgae community under effluent runoff conditions. • Chl-a concentrations suggest

  19. Responses in sediment phosphorus and lanthanum concentrations and composition across 10 lakes following applications of lanthanum modified bentonite

    DEFF Research Database (Denmark)

    Dithmer, Line; Nielsen, Ulla Gro; Lürling, Miquel


    A combined field and laboratory scale study of 10 European lakes treated between 2006 and 2013 with a lanthanum (La) modified bentonite (LMB) to control sediment phosphorus (P) release was conducted. The study followed the responses in sediment characteristics including La and P fractions...... and binding forms, P adsorption capacity of discrete sediment layers, and pore water P concentrations. Lanthanum phosphate mineral phases were confirmed by solid state (31)P MAS NMR and LIII EXAFS spectroscopy. Rhabdophane (LaPO4 · nH2O) was the major phase although indications of monazite (LaPO4) formation...... were also reported, in the earliest treated lake. Molar ratios between La and P in the sediments were generally above 1, demonstrating excess La relative to P. Lanthanum was vertically mixed in the sediment down to a depth of 10 cm for eight of the ten lakes, and recovery of La in excess of 100...

  20. Environmental complexity of a port: Evidence from circulation of the water masses, and composition and contamination of bottom sediments. (United States)

    Cutroneo, L; Carbone, C; Consani, S; Vagge, G; Canepa, G; Capello, M


    Ports are complex environments due to their complicated geometry (quays, channels, and piers), the presence of human activities (vessel traffic, shipyards, industries, and discharges), and natural factors (stream and torrent inputs, sea action, and currents). Taking these factors into consideration, we have examined the marine environment of a port from the point of view of the circulation of the water masses, hydrological characteristics, distribution of the sediment grain-size, mineralogical characteristics, and metal concentrations of the bottom sediments. Our results show that, in the case of the Port of Genoa (north-western Italy), the impact of human activities (such as a coal power-plant, oil depots, shipyards, dredging of the bottom sediments, etc.), natural processes (such as currents, fresh water and sediment inputs from the torrents), and the morphology of the basin, are important factors in the sediment, water, and metal distributions that have given rise to a complex environment. Copyright © 2017 Elsevier Ltd. All rights reserved.

  1. A High-Level Fungal Diversity in the Intertidal Sediment of Chinese Seas Presents the Spatial Variation of Community Composition. (United States)

    Li, Wei; Wang, Mengmeng; Bian, Xiaomeng; Guo, Jiajia; Cai, Lei


    The intertidal region is one of the most dynamic environments in the biosphere, which potentially supports vast biodiversity. Fungi have been found to play important roles in marine ecosystems, e.g., as parasites or symbionts of plants and animals, and as decomposers of organic materials. The fungal diversity in intertidal region, however, remains poorly understood. In this study, sediment samples from various intertidal habitats of Chinese seas were collected and investigated for determination of fungal community and spatial distribution. Through ribosomal RNA internal transcribed spacer-2 (ITS2) metabarcoding, a high-level fungal diversity was revealed, as represented by 6,013 OTUs that spanned six phyla, 23 classes, 84 orders and 526 genera. The presence of typical decomposers (e.g., Corollospora in Ascomycota and Lepiota in Basidiomycota) and pathogens (e.g., Olpidium in Chytriomycota, Actinomucor in Zygomycota and unidentified Rozellomycota spp.), and even mycorrhizal fungi (e.g., Glomus in Glomeromycota) indicated a complicated origin of intertidal fungi. Interestingly, a small proportion of sequences were classified to obligate marine fungi (e.g., Corollospora, Lignincola, Remispora, Sigmoidea). Our data also showed that the East China Sea significantly differed from other regions in terms of species richness and community composition, indicating a profound effect of the huge discharge of the Yangtze River. No significant difference in fungal communities was detected, however, among habitat types (i.e., aquaculture, dock, plant, river mouth and tourism). These observations raise further questions on adaptation of these members to environments and the ecological functions they probably perform.

  2. A comparison of sedimentary DNA and pollen from lake sediments in recording vegetation composition at the Siberian treeline. (United States)

    Niemeyer, Bastian; Epp, Laura S; Stoof-Leichsenring, Kathleen R; Pestryakova, Luidmila A; Herzschuh, Ulrike


    Reliable information on past and present vegetation is important to project future changes, especially for rapidly transitioning areas such as the boreal treeline. To study past vegetation, pollen analysis is common, while current vegetation is usually assessed by field surveys. Application of detailed sedimentary DNA (sedDNA) records has the potential to enhance our understanding of vegetation changes, but studies systematically investigating the power of this proxy are rare to date. This study compares sedDNA metabarcoding and pollen records from surface sediments of 31 lakes along a north-south gradient of increasing forest cover in northern Siberia (Taymyr peninsula) with data from field surveys in the surroundings of the lakes. sedDNA metabarcoding recorded 114 plant taxa, about half of them to species level, while pollen analyses identified 43 taxa, both exceeding the 31 taxa found by vegetation field surveys. Increasing Larix percentages from north to south were consistently recorded by all three methods and principal component analyses based on percentage data of vegetation surveys and DNA sequences separated tundra from forested sites. Comparisons of the ordinations using procrustes and protest analyses show a significant fit among all compared pairs of records. Despite similarities of sedDNA and pollen records, certain idiosyncrasies, such as high percentages of Alnus and Betula in all pollen and high percentages of Salix in all sedDNA spectra, are observable. Our results from the tundra to single-tree tundra transition zone show that sedDNA analyses perform better than pollen in recording site-specific richness (i.e., presence/absence of taxa in the vicinity of the lake) and perform as well as pollen in tracing vegetation composition. © 2017 John Wiley & Sons Ltd.

  3. Marine Microbial Gene Abundance and Community Composition in Response to Ocean Acidification and Elevated Temperature in Two Contrasting Coastal Marine Sediments

    Directory of Open Access Journals (Sweden)

    Ashleigh R. Currie


    Full Text Available Marine ecosystems are exposed to a range of human-induced climate stressors, in particular changing carbonate chemistry and elevated sea surface temperatures as a consequence of climate change. More research effort is needed to reduce uncertainties about the effects of global-scale warming and acidification for benthic microbial communities, which drive sedimentary biogeochemical cycles. In this research, mesocosm experiments were set up using muddy and sandy coastal sediments to investigate the independent and interactive effects of elevated carbon dioxide concentrations (750 ppm CO2 and elevated temperature (ambient +4°C on the abundance of taxonomic and functional microbial genes. Specific quantitative PCR primers were used to target archaeal, bacterial, and cyanobacterial/chloroplast 16S rRNA in both sediment types. Nitrogen cycling genes archaeal and bacterial ammonia monooxygenase (amoA and bacterial nitrite reductase (nirS were specifically targeted to identify changes in microbial gene abundance and potential impacts on nitrogen cycling. In muddy sediment, microbial gene abundance, including amoA and nirS genes, increased under elevated temperature and reduced under elevated CO2 after 28 days, accompanied by shifts in community composition. In contrast, the combined stressor treatment showed a non-additive effect with lower microbial gene abundance throughout the experiment. The response of microbial communities in the sandy sediment was less pronounced, with the most noticeable response seen in the archaeal gene abundances in response to environmental stressors over time. 16S rRNA genes (amoA and nirS were lower in abundance in the combined stressor treatments in sandy sediments. Our results indicated that marine benthic microorganisms, especially in muddy sediments, are susceptible to changes in ocean carbonate chemistry and seawater temperature, which ultimately may have an impact upon key benthic biogeochemical cycles.

  4. Marine Microbial Gene Abundance and Community Composition in Response to Ocean Acidification and Elevated Temperature in Two Contrasting Coastal Marine Sediments. (United States)

    Currie, Ashleigh R; Tait, Karen; Parry, Helen; de Francisco-Mora, Beatriz; Hicks, Natalie; Osborn, A Mark; Widdicombe, Steve; Stahl, Henrik


    Marine ecosystems are exposed to a range of human-induced climate stressors, in particular changing carbonate chemistry and elevated sea surface temperatures as a consequence of climate change. More research effort is needed to reduce uncertainties about the effects of global-scale warming and acidification for benthic microbial communities, which drive sedimentary biogeochemical cycles. In this research, mesocosm experiments were set up using muddy and sandy coastal sediments to investigate the independent and interactive effects of elevated carbon dioxide concentrations (750 ppm CO2) and elevated temperature (ambient +4°C) on the abundance of taxonomic and functional microbial genes. Specific quantitative PCR primers were used to target archaeal, bacterial, and cyanobacterial/chloroplast 16S rRNA in both sediment types. Nitrogen cycling genes archaeal and bacterial ammonia monooxygenase (amoA) and bacterial nitrite reductase (nirS) were specifically targeted to identify changes in microbial gene abundance and potential impacts on nitrogen cycling. In muddy sediment, microbial gene abundance, including amoA and nirS genes, increased under elevated temperature and reduced under elevated CO2 after 28 days, accompanied by shifts in community composition. In contrast, the combined stressor treatment showed a non-additive effect with lower microbial gene abundance throughout the experiment. The response of microbial communities in the sandy sediment was less pronounced, with the most noticeable response seen in the archaeal gene abundances in response to environmental stressors over time. 16S rRNA genes (amoA and nirS) were lower in abundance in the combined stressor treatments in sandy sediments. Our results indicated that marine benthic microorganisms, especially in muddy sediments, are susceptible to changes in ocean carbonate chemistry and seawater temperature, which ultimately may have an impact upon key benthic biogeochemical cycles.

  5. Slab2 - Updated subduction zone geometries and modeling tools (United States)

    Portner, D. E.; Hayes, G. P.; Furtney, M.; Moore, G.; Flamme, H. E.; Hearne, M. G.


    The U.S. Geological Survey database of global subduction zone geometries (Slab1.0) combines a variety of geophysical data sets (earthquake hypocenters, moment tensors, active-source seismic survey images of the shallow subduction zone, bathymetry, trench locations, and sediment thickness information) to image the shape of subducting slabs in three dimensions, at approximately 85% of the world's convergent margins. The database is used extensively for a variety of purposes from earthquake source imaging to magnetotelluric modeling. Gaps in Slab1.0 exist where input data are sparse and/or where slabs are geometrically complex (and difficult to image with an automated approach). Slab1.0 also does not include information on the uncertainty in the modeled geometrical parameters, or the input data used to image them, and provides no means for others to reproduce the models it describes. Now near completion, Slab2 will update and replace Slab1.0 by: (1) extending modeled slab geometries to the full extent of all known global subduction zones; (2) incorporating regional data sets (e.g., tomography models) that may describe slab geometry more comprehensively than do previously used teleseismic data; (3) providing information on the uncertainties in each modeled slab surface; (4) modifying our modeling approach to a fully-three dimensional data interpolation, rather than following the 2-D to 3-D steps of Slab1.0; (5) adding further layers to the base geometry dataset, such as historic moment release, earthquake tectonic providence, and interface coupling; (6) migrating the slab modeling code base to a more universally distributable language, Python; and (7) providing the code base and input data we use to create our models, such that the community can both reproduce the slab geometries, and add their own data sets to ours to further improve upon those models in the future. In this presentation we will describe our progress made in creating Slab2, and provide information on

  6. Kinematics of subduction and subduction-induced flow in the upper mantle

    NARCIS (Netherlands)

    Schellart, W. P.


    Results of fluid dynamical experiments are presented to model the kinematics of lithospheric subduction in the upper mantle. The experiments model a dense highviscosity plate (subducting lithosphere) overlying a less dense low-viscosity layer (upper mantle). The overriding lithosphere is not

  7. Distribution and generic composition of culturable marine actinomycetes from the sediments of Indian continental slope of Bay of Bengal (United States)

    Das, Surajit; Lyla, P. S.; Ajmal Khan, S.


    Actinomycetes population from continental slope sediment of the Bay of Bengal was studied. Samples were collected during two voyages of FORV Sagar Sampada in 2004 (May-June) and 2005 (July) respectively from 11 transects (each transect had ca. 200 m, 500 m, and 1 000 m depth stations). The physicochemical parameters of overlying water, and sediment samples were also recorded. The actinomycete population ranged from 5.17 to 51.94 CFU/g dry sediment weight and 9.38 to 45.22 CFU/g dry sediment weight during the two cruises respectively. No actinomycete colony was isolated from stations in 1 000 m depth. Two-way analysis of variance showed significant variation among stations (ANOVA two-way, P0.05). Three actinomycetes genera were identified. Streptomyces was found to be the dominating one in both the cruises, followed by Micromonospora, and Actinomyces. The spore of Streptomyces isolates showed the abundance in spiral spore chain. Spore surface was smooth. Multiple regression analysis revealed that the influencing physico-chemical factors were sediment pH, sediment temperature, TOC, porosity, salinity, and pressure. The media used in the present study was prepared with seawater. Thus, they may represent an autochthonous marine flora and deny the theory of land runoff carriage into the sea for adaptation to the salinity of the seawater and sediments.

  8. Effects of composition of labile organic matter on biogenic production of methane in the coastal sediments of the Arabian Sea. (United States)

    Gonsalves, Maria-Judith; Fernandes, Christabelle E G; Fernandes, Sheryl Oliveira; Kirchman, David L; Bharathi, P A Loka


    Coastal regions are potential zones for production of methane which could be governed by ecological/environmental differences or even sediment properties of a niche. In order to test the hypothesis that methanogenesis in most marine sediments could be driven more by proteins than by carbohydrates and lipid content of labile organic matter (LOM), incubation experiments were carried out with sediments from different environmental niches to measure methane production. The methane production rates were examined in relationship to the sediment biochemistry, i.e., carbohydrates, proteins, and lipids. The gas production measured by head space method ranged from 216 ng g( -1) day( -1) in the mangrove sediments to 3.1 μg g( -1) day( -1) in the shallow Arabian Sea. LOM ranged from 1.56 to 2.85 mg g( -1) in the shallow Arabian Sea, from 3.35 to 5.43 mg g( -1) in the mangrove estuary, and from 0.66 to 0.70 mg g( -1) in the sandy sediments with proteins contributing maximum to the LOM pool. Proteins influenced methane production in the clayey sediments of shallow depths of the Arabian Sea (r = 0.933, p lability index. Thus, the lability index and protein content are important factors that determine methane production rates in these coastal ecosystems.

  9. Imprints of an "Arc" Signature onto Subduction Zone Eclogites from Central Guatemala (United States)

    Simons, K. K.; Sorensen, S. S.; Harlow, G. E.; Brueckner, H. K.; Goldstein, S. L.; Hemming, N. G.; Langmuir, C. H.


    High-pressure, low-temperature (HP-LT) rocks associated with the Motagua fault zone in central Guatemala occur as tectonic blocks in serpentinite mélange. Dismembered jadeitite and albitite veins within the melange are crystallization products of subduction fluids at glaucophane) in veins and overgrowths. The low temperatures recorded in these rocks indicate they have only seen an aqueous fluid, not a melt, and therefore, could provide a window into the acquisition of an arc signature at a cold margin. Trace-element patterns for both eclogite and jadeitite resemble arc lavas, with large enrichments in the most fluid mobile elements (e.g. Cs, Tl, Ba, Pb), moderate enrichments in U, Th, Be and LREE and generally little to no enrichment in HFSE and HREE, although enriched Nb in jadeitite indicates some HFSE mobility. Trace-element patterns also have similarities to average subducting sediment (GLOSS), with enrichments in Th, Be, Ba and Li that suggest a sediment contribution. Nd versus Sr isotopes lie to the right of the mantle array, indicating a hydrous fluid contribution from altered ocean crust or sediment. Overall, Guatemalan eclogites resemble counterparts from the Franciscan Complex (CA) and the Dominican Republic. Guatemalan and Franciscan eclogites are interpreted to have had a MORB protolith despite the arc trace element signature because of: 1) similarities in major elements to MORB; 2) HREE and HFSE abundances similar to MORB; and 3) high 143Nd/144Nd that overlap MORB values. The modifications that transformed these eclogites from a MORB trace element pattern to an arc one can be attributed to an aqueous subduction fluid at moderate depths (reactions, and an abundance of alkali-aluminosilicate components in subduction fluids. Together these may act to dissolve and transport trace elements (including elements considered insoluble like Nb) out of the slab and into the mantle wedge. The Guatemala data thus indicate that the arc geochemical fingerprint may be

  10. Some geophysical and geochemical consequences of slab serpentinization at subduction zones (United States)

    Phipps Morgan, J.; Ruepke, L. H.; Ranero, C.; Hort, M.


    Here we explore the potential impact of slab serpentinization and deserpentinization processes on arc-melting and on water, carbon-dioxide, U, Pb, and noble gas recycling into the deep mantle. We examine the consequences of a scenario in which bend-faulting between the outer rise and trench axis creates the conduits for seawater to reach and react with cold lithospheric mantle to serpentinize it. Water penetration to serpentinize the slab-lithosphere will be inhibited by thick sediments (e.g. Cascades) or thick oceanic crust (subducting oceanic plateaus), while subducting long-offset fracture zones will be especially serpentine-rich because they serpentinized at both the spreading center and subduction zone. If this process occurs, then the incoming lithosphere will typically contain ~500m of altered sediments, ~6 km of partially hydrated oceanic crust, and ~20-55km of partially serpentinized slab mantle. Possible regional geophysical consequences of this scenario are: (1) Fracture Zones preferentially become tears in subducting slabs because they are relatively serpentine rich, thus they deserpentinize more. (2) If so, then their greater deserpentinization should produce greater sub-arc water release which leads to greater arc melting above subducted fracture zones. (3) Regions of little serpentinization will be correlated with flat subduction, lower volumes of slab-water release, and relatively low rates of arc-volcanism. Our thermomechanical modelling implies, depending upon a slab's age and subduction rate, between 30-90% of the slab's chemically bound water is likely to survive sub-arc dehydration to transport its water into the deeper mantle. Possible global geochemical consequences of this scenario are: (1) At current subduction rates, 0.5-1.5 oceans of water would be recycled past the arc-melting region into the deeper mantle during the past Ga. (2) Since 0.3%, 1%, and 3% of the exosphere's Ne, Ar, and Xe are dissolved in the oceans, this implies that at

  11. Distribution and composition of verdine and glaucony facies from the sediments of the western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Thamban, M.; Rao, V.P.

    Investigations on green grains from sediments of the western continental margin of India, between Ratnagiri and Cape Comorin, (water depth 37-330 m) indicate the presence of verdine and glaucony facies. Verdine facies occurs over an area of about...

  12. Holocene variations in mineral and grain-size composition along the East Greenland glaciated margin (ca 67°–70°N): local versus long-distance sediment transport (United States)

    Andrews, John T.; Jennings, Anne E.; Coleman, George C.; Eberl, Dennis D.


    Quantitative X-Ray Diffraction (qXRD) analysis of the samples, and marine sediment cores that span the last 10-12 cal ka BP, are used to describe spatial and temporal variations in non-clay mineral compositions for an area between Kangerlussuaq Trough and Scoresby Sund (???67??-70??N), East Greenland. Bedrock consists primarily of an early Tertiary alkaline complex with high weight% of pyroxene and plagioclase. Farther inland and to the north, the bedrock is dominantly felsic with a high fraction of quartz and potassium feldspars. Principal Component (PC) analysis of the non-clay sediment compositions indicates the importance of quartz and pyroxene as compositional end members, with an abrupt shift from quartz and k-feldspar dominated sediments north of Scoresby Sund to sediments rich in pyroxene and plagioclase feldspars offshore from the early Tertiary basaltic outcrop. Coarse (<2 mm or <1 mm) ice-rafted sediments are largely absent from the trough sediments between ???8 and 5 cal ka BP, but then increase in the last 4 cal ka BP. Compositional unmixing of the sediments in Grivel Basin and Kangerlussuaq Trough indicate the dominance of local over long distance sediment sources, with pulses of sediment from tidewater glaciers in Kangerlussuaq and Nansen fjords reaching the inner shelf during the Neoglaciation. The change in IRD is more dramatic in the sediment grain-size proxies than in the quartz wt%. Forty to seventy percent of the variance in the quartz records from either side of Denmark Strait is explained by low frequency trends, but the data from the Grivel Basin, East Greenland, are distinctly different, with an approximate 2500 yr periodicity. ?? 2010 Elsevier Ltd.

  13. Chemical and oxygen isotope zonings in garnet from subducted continental crust record mineral replacement and metasomatism (United States)

    Vho, Alice; Rubatto, Daniela; Regis, Daniele; Baumgartner, Lukas; Bouvier, Anne-Sophie


    Garnet is a key mineral in metamorphic petrology for constraining pressure, temperature and time paths. Garnet can preserve multiple growth stages due to its wide P-T stability field and the relatively slow diffusivity for major and trace elements at sub-solidus temperatures. Pressure-temperature-time-fluid paths of the host rock may be reconstructed by combining metamorphic petrology with microscale trace element and oxygen isotope measurements in garnet. Subduction zones represent relevant geological settings for geochemical investigation of element exchanges during aqueous fluid-rock interactions. The Sesia Zone consists of a complex continental sequence containing a variety of mono-metamorphic and poly-metamorphic lithologies such as metagranitoids, sediments and mafic boudins. The precursor Varisican-Permian amphibolite-facies basement (6-9 kbar 650-850°C; Lardeaux and Spalla, 1991; Robyr et al., 2013) experienced high pressure metamorphism (15-22 kbar 500-550°C; Regis, et al. 2014; Robyr et al., 2013) during Alpine subduction. In different lithologies of the Internal Complex (Eclogitic Micaschist Complex), including metabasites from the Ivozio Complex, Ti-rich metasediments from Val Malone and pre-Alpine Mn-quartzites associated to metagabbros from Cima Bonze, garnet is abundant and shows a variety of complex textures that cannot be reconciled with typical growth zoning, but indicate resorption and replacement processes and possible metasomatism. In-situ, microscale oxygen isotopes analysis of garnet zones was performed by ion microprobe with the SwissSIMS Cameca IMS 1280-HR at University of Lausanne and SHRIMP-SI at the Australian National University. Each sample has a distinct δ18O composition, and the δ18O values show different degrees of variation between domains. Homogeneously low values of element geochemistry and P-T modelling allows reconstructing the major stages of metasomatism, as well as identifying the nature of the fluid interacting with the

  14. Ediacaran 2,500-km-long synchronous deep continental subduction in the West Gondwana Orogen. (United States)

    Ganade de Araujo, Carlos E; Rubatto, Daniela; Hermann, Joerg; Cordani, Umberto G; Caby, Renaud; Basei, Miguel A S


    The deeply eroded West Gondwana Orogen is a major continental collision zone that exposes numerous occurrences of deeply subducted rocks, such as eclogites. The position of these eclogites marks the suture zone between colliding cratons, and the age of metamorphism constrains the transition from subduction-dominated tectonics to continental collision and mountain building. Here we investigate the metamorphic conditions and age of high-pressure and ultrahigh-pressure eclogites from Mali, Togo and NE-Brazil and demonstrate that continental subduction occurred within 20 million years over at least a 2,500-km-long section of the orogen during the Ediacaran. We consider this to be the earliest evidence of large-scale deep-continental subduction and consequent appearance of Himalayan-scale mountains in the geological record. The rise and subsequent erosion of such mountains in the Late Ediacaran is perfectly timed to deliver sediments and nutrients that are thought to have been necessary for the subsequent evolution of sustainable life on Earth.

  15. Megathrust and accretionary wedge properties and behaviour in the Makran subduction zone (United States)

    Penney, Camilla; Tavakoli, Farokh; Saadat, Abdolreza; Nankali, Hamid Reza; Sedighi, Morteza; Khorrami, Fateme; Sobouti, Farhad; Rafi, Zahid; Copley, Alex; Jackson, James; Priestley, Keith


    We study the Makran subduction zone, along the southern coasts of Iran and Pakistan, to gain insights into the kinematics and dynamics of accretionary prism deformation. By combining techniques from seismology, geodesy and geomorphology, we are able to put constraints on the shape of the subduction interface and the style of strain across the prism. We also address the long-standing tectonic problem of how the right-lateral shear taken up by strike-slip faulting in the Sistan Suture Zone in eastern Iran is accommodated at the zone's southern end. We find that the subduction interface in the western Makran may be locked, accumulating elastic strain, and move in megathrust earthquakes. Such earthquakes, and associated tsunamis, present a significant hazard to populations around the Arabian Sea. The time-dependent strain within the accretionary prism, resulting from the megathrust earthquake cycle, may play an important role in the deformation of the Makran region. By considering the kinematics of the 2013 Balochistan and Minab earthquakes, we infer that the local gravitational and far-field compressive forces in the Makran accretionary prism are in balance. This force balance allows us to calculate the mean shear stress and effective coefficient of friction on the Makran megathrust, which we find to be 5-35 MPa and 0.01-0.03, respectively. These values are similar to those found in other subduction zones, showing that the abnormally high sediment thickness in the offshore Makran does not significantly reduce the shear stress on the megathrust.

  16. Investigating molecular changes in organic matter composition in two Holocene lake-sediment records from central Sweden using pyrolysis-GC/MS (United States)

    Ninnes, Sofia; Tolu, Julie; Meyer-Jacob, Carsten; Mighall, Tim M.; Bindler, Richard


    Organic matter (OM) is a key component of lake sediments, affecting carbon, nutrient, and trace metal cycling at local and global scales. Yet little is known about long-term (millennial) changes in OM composition due to the inherent chemical complexity arising from multiple OM sources and from secondary transformations. In this study we explore how the molecular composition of OM changes throughout the Holocene in two adjacent boreal lakes in central Sweden and compare molecular-level information with conventional OM variables, including total carbon, total nitrogen, C:N ratios, δ13C, and δ15N. To characterize the molecular OM composition, we employed a new method based on pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), which yields semiquantitative data on >100 organic compounds of different origin and degradation status. We identify large changes in OM composition after deglaciation (circa 8500 ± 500 B.C.), associated with early landscape development, and during the most recent 40-50 years, driven by degradation processes. With molecular-level information we can also distinguish between natural landscape development and human catchment disturbance during the last 1700 years. Our study demonstrates that characterization of the molecular OM composition by the high-throughput Py-GC/MS method is an efficient complement to conventional OM variables for identification and understanding of past OM dynamics in lake-sediment records. Holocene changes observed for pyrolytic compounds and compound classes known for having different reactivity indicate the need for further paleo-reconstruction of the molecular OM composition to better understand both past and future OM dynamics and associated environmental changes.

  17. Chemical data and lead isotopic compositions of geochemical baseline samples from streambed sediments and smelter slag, lead isotopic compositions in fluvial tailings, and dendrochronology results from the Boulder River watershed, Jefferson County, Montana (United States)

    Unruh, Daniel M.; Fey, David L.; Church, Stan E.


    and thirteen core samples. Sample localities are in table 1 and figures 1 and 2, and site and sample descriptions are in table 2.Geochemical data have been presented for cores through fluvial tailings on High Ore Creek, on upper Basin Creek, and on Jack Creek and Uncle Sam Gulch. Geochemical and lead isotopic data for modern streambed-sediment samples have been presented by Fey and others.Lead isotopic determinations in bed sediments have been shown to be an effective tool for evaluating the contributions from various sources to the metals in bed sediments. However, in order to make these calculations, the lead isotopic compositions of the contaminant sources must also be known. Consequently, we have determined the lead isotopic compositions of five streambed-sediment samples heavily contaminated with fluvial mine waste immediately downstream from large mines in the Boulder River watershed in order to determine the lead isotopic signatures of the contaminants. Summary geochemical data for the contaminants are presented here and geochemical data for the streambed-sediment samples are given by Fey and others.Downstream from the Katie mill site and Jib tailings, fluvial deposits of mill tailings are present on a 10-m by 50-m bar in the Boulder River below the confluence with Basin Creek. The source of these tailings is not known, but fluvial tailings are also present immediately downstream from the Katie mill site, which is immediately upstream from the confluence with Basin Creek. Nine cores of fluvial tailings from this bar were analyzed.Dendrochronology samples were taken at several stream terrace localities to provide age control on the stream terrace deposits. Trees growing on the surfaces of stream terraces provide a minimum age for the terrace deposits, although floods subsequent to the trees' growth could have deposited post-mining overbank deposits around the trees. Historical data were also used to provide estimates of minimum ages of cultural features and to

  18. Source characterization of sedimentary organic matter using molecular and stable carbon isotopic composition of n-alkanes and fatty acids in sediment core from Lake Dianchi, China

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Jidun [State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012 (China); Shandong Key Laboratory of Eco-Environmental Science for Yellow River Delta, Binzhou University, Binzhou, Shandong Province 256600 (China); Wu, Fengchang, E-mail: [State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012 (China); Xiong, Yongqiang [State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 (China); Li, Fasheng; Du, Xiaoming; An, Da [State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012 (China); Wang, Lifang [State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002 (China)


    The distribution and compound-specific carbon isotope ratios of n-alkanes and fatty acids in a sediment core (63 cm) collected from Lake Dianchi were examined to investigate organic matter sources in the eutrophic lake. Fatty acids included free and bound fatty acids. The carbon isotope compositions of individual n-alkanes and fatty acids from Lake Dianchi sediments were determined using gas chromatography/isotope ratio mass spectrometry (GC–IRMS). The δ{sup 13}C values of individual n-alkanes (C{sub 16}–C{sub 31}) varied between − 24.1‰ and − 35.6‰, suggesting a dominance of {sup 13}C-depleted n-alkanes that originated from C{sub 3} plants and lacustrine algae. Fatty acids from the sediment extracts were analyzed for their abundances and carbon isotopic compositions. Molecular and isotopic evidence indicates that most of the short-chain fatty acids from Lake Dianchi sediment extracts are sourced from intense microbial recycling and resynthesis of organic matter. Long-chain free fatty acids are mainly derived from terrestrial sources. However, long-chain bound fatty acids are sourced from a combination of terrestrial organic matter, bacteria and algae, with the contribution from algal sources higher in the hypereutrophic stage. - Highlights: • Long-chain n-alkanes and FFAs are mainly derived from terrestrial sources. • Short-chain n-alkanes and fatty acids are mainly derived from bacterial and/or algal sources. • Long-chain BFAs are mainly derived from algal sources in hypereutrophic lakes.

  19. Does subduction zone magmatism produce average continental crust (United States)

    Ellam, R. M.; Hawkesworth, C. J.


    The question of whether present day subduction zone magmatism produces material of average continental crust composition, which perhaps most would agree is andesitic, is addressed. It was argued that modern andesitic to dacitic rocks in Andean-type settings are produced by plagioclase fractionation of mantle derived basalts, leaving a complementary residue with low Rb/Sr and a positive Eu anomaly. This residue must be removed, for example by delamination, if the average crust produced in these settings is andesitic. The author argued against this, pointing out the absence of evidence for such a signature in the mantle. Either the average crust is not andesitic, a conclusion the author was not entirely comfortable with, or other crust forming processes must be sought. One possibility is that during the Archean, direct slab melting of basaltic or eclogitic oceanic crust produced felsic melts, which together with about 65 percent mafic material, yielded an average crust of andesitic composition.

  20. Evidence for retrograde lithospheric subduction on Venus (United States)

    Sandwell, David T.; Schubert, Gerald


    Annular moats and outer rises around large Venus coronas such as Artemis, Latona, and Eithinoha are similar in arcuate planform and topography to the trenches and outer rises of terrestrial subduction zones. On earth, trenches and outer rises are modeled as the flexural response of a thin elastic lithosphere to the bending moment of the subducted slab; this lithospheric flexure model also accounts for the trenches and outer rises outboard of the major coronas on Venus. Accordingly, it is proposed that retrograde lithospheric subduction may be occurring on the margins of the large Venus coronas while compensating back-arc extension is occurring in the expanding coronas interiors. Similar processes may be taking place at other deep arcuate trenches or chasmata on Venus such as those in the Dali-Diana chasmata area of aestern Aphrodite Terra.

  1. Seismic Structure of the Subducted Cocos Plate (United States)

    Clayton, R. W.; Davis, P. M.; Perez-Campos, X.


    The Meso-American Subduction Experiment (MASE) was designed to determine the critical parameters to necessary to simulate the subduction process in Central Mexico . A preliminary analysis of the data shows a 200km section of the slab that is subhorizontal and to within the resolution of the receiver functions it underplates the continental crust with no intervening asthenosphere. This is an interesting situation because the short-term (GPS) and long-term (geologic) strain measurements show almost no compressive strain in this region. This would imply that the crust is decoupled from the subducting slab. Near the coast, the receiver functions show that the slab cuts through the crust at an approximately a 15-degree angle, and under the Trans-Mexican Volcanic Belt the slab becomes detached from the crust, but its geometry at depth is not yet determined from the receiver functions, but a well-developed mantle wedge is apparent from the attenuation of regional earthquakes.

  2. Subduction zones seen by GOCE gravity gradients

    DEFF Research Database (Denmark)

    Švarc, Mario; Herceg, Matija; Cammarano, Fabio

    In this study, the GOCE (Gravity field and steady state Ocean Circulation Explorer) gradiometry data were used to study geologic structures and mass variations within the lithosphere in areas of known subduction zones. The advantage of gravity gradiometry over other gravity methods...... is that gradients are extremely sensitive to localized density contrasts within regional geological settings, which makes it ideally suited for detecting subduction zones. Second order gravity gradients of disturbing potential were extracted from global geopotential model, the fifth release GOCE model ‘EGM_TIM_RL05......’. In order to remove the signal which mainly corresponds to the gravity signal of the lower mantle, long wavelength part of the gravity signal was removed up to degree and order 60. Because the areas with notable topography differences coincide with subduction zones, topography correction was also performed...

  3. Seasonal flux and assemblage composition of planktic foraminifers from a sediment-trap study in the northern Gulf of Mexico (United States)

    Poore, Richard Z.; Spear, Jessica W.; Tedesco, Kathy A.


    Sediment-trap samples from the northern Gulf of Mexico reveal that Globorotalia truncatulinoides, Neogloboquadrina dutertrei, Pulleniatina spp. (includes P. obliquiloculata and P. finalis), and the Globorotalia menardii group (includes Gt. menardii, Gt. tumida, and Gt. ungulata) generally occur in cold months. Globigerinoides ruber (white and pink varieties) and Globigennoides sacculifer occur throughout the year. The seasonal occurrence of individual taxa of planktic foraminifers in the Gulf of Mexico have important differences with the seasonal occurrence of the same taxa observed in a 6-year sediment-trap dataset from the western Sargasso Sea. Thus information on the ecologic preferences of individual taxa determined in one region cannot necessarily be applied directly to another area. In the northern Gulf of Mexico 90% of the total flux of Globorotalia truncatulinoides tests to sediments occurs in January and February. Mg/Ca and d18Ο measurements indicate that nonencrusted forms of Gt. truncatulinoides calcify in the upper-surface-mixed zone. Thus, analyses of nonencrusted Gt. truncatulinoides in sediments of the northern Gulf of Mexico have potential for monitoring past conditions in the winter-surface-mixed layer. The relatively low overall abundance of Globigerinoides ruber (white) in sediment-trap samples is anomalous because Gs. ruber (white) is one of the most abundant foraminifers in>150 µm census data from northern Gulf of Mexico Holocene sediment core samples. Globigerinoides ruber (pink) is a relatively persistent and common component of the sediment-trap samples. Thus Gs. ruber (pink) has potential as a proxy for mean annual sea-surface temperature in the Gulf of Mexico

  4. Subduction trench migration since the Cretaceous (United States)

    Williams, S.; Flament, N. E.; Müller, D.; Butterworth, N. P.


    Much of our knowledge about subduction zone processes is derived from analyzing present-day Earth. Several studies of contemporary plate motions have investigated the balance between retreating and advancing trenches and shown that subduction zone kinematics are sensitive to the choice of Absolute Plate Motion (APM) model (or "reference frame"). For past times, the absolute motions of the lithospheric plates relative to the Earth's deep interior over tens of millions of years are commonly constrained using observations from paleomagnetism and age-progressive seamount trails. In contrast, a reference frame linking surface plate motions to subducted slab remnants mapped from seismic tomography has recently been proposed. APM models derived using different methodologies, different subsets of hotspots, or differing assumptions of hotspot motion, have contrasting implications for parameters that describe the long term state of the plate-mantle system, such as the balance between advance and retreat of subduction zones, plate velocities, and net lithospheric rotation. Here we quantitatively compare the subduction zone kinematics, net lithospheric rotation and fit to hotspot trails derived the last 130 Myr for a range of alternative reference frames and a single relative plate motion model. We find that hotspot and tomographic slab-remnant reference frames yield similar results for the last 70 Myr. For the period between 130 and 70 Ma, when hotspot trails become scarce, hotspot reference frames yield a much more dispersed distribution of slab advance and retreat velocities, which is considered geodynamically less plausible. By contrast, plate motions calculated using the slab-remnant reference frame, or using a reference frame designed to minimise net rotation, yield more consistent subduction zone kinematics for times older than 70 Ma. Introducing the global minimisation of trench migration rates as a key criterion in the construction of APM models forms the foundation

  5. Anthropogenic sediments and soils of tells of the Balkans and Anatolia: Composition, genesis, and relationships with the history of landscape and human occupation (United States)

    Sedov, S. N.; Aleksandrovskii, A. L.; Benz, M.; Balabina, V. I.; Mishina, T. N.; Shishkov, V. A.; Şahin, F.; Özkaya, V.


    Soils and sediments composing Tell Körtik Tepe (Epipaleolithic, Turkey) and Tell Yunatsite (Chalcolithic (Eneolithic), Bulgaria) have been studied with the aim to gain a better insight into their microfabrics, determine the composition of anthropogenic artifacts, and, on this basis, to analyze similarities and distinctions between these objects and the modern soils of urban areas. The methods of micromorphology, scanning electron microscopy with an energy dispersive X-ray microanalyzer, X-ray fluorometry, and other techniques to determine the chemical and physical properties of the soils and sediments have been applied. Two paleosols have been identified in Tell Yunatsite with a total thickness of 9 m: the paleosol buried under the tell and the paleosol in its middle part. Sediments of Tell Körtik Tepe have a total thickness of up to 5 m; their accumulation began at the end of Pleistocene over the surface of buried paleosol. The cultural layer of the tells consists of construction debris mainly represented by a mixture of clay and sand and of domestic wastes with the high content of phosphorus. The major source of phosphorus is calcium phosphate (apatite) of bone tissues. The abundance of various anthropogenic materials in the sediments is clearly seen in thin sections. Even in the paleosols developed within the cultural layer (the mid-profile paleosol in Tell Yunatsite), the amount of microinclusions of bone fragments, charcoal, and burnt clay (ceramics) is very high. Micromorphological data indicate that up to 50% of the layered material filling an Epipaleolithic construction in Tell Körtik Tepe consists of the anthropogenic inclusions: bone fragments, charcoal, etc. The features of pedogenic transformation are present in the sediments. Such sediments can be classified as synlithogenic soils similar to the modern Urbic Technosols. It is shown that the formation of paleosols and sediments of Tell Körtik Tepe took place under extreme environmental conditions

  6. Structural stability, microbial biomass and community composition of sediments affected by the hydric dynamics of an urban stormwater infiltration basin. Dynamics of physical and microbial characteristics of stormwater sediment. (United States)

    Badin, Anne Laure; Monier, Armelle; Volatier, Laurence; Geremia, Roberto A; Delolme, Cécile; Bedell, Jean-Philippe


    The sedimentary layer deposited at the surface of stormwater infiltration basins is highly organic and multicontaminated. It undergoes considerable moisture content fluctuations due to the drying and inundation cycles (called hydric dynamics) of these basins. Little is known about the microflora of the sediments and its dynamics; hence, the purpose of this study is to describe the physicochemical and biological characteristics of the sediments at different hydric statuses of the infiltration basin. Sediments were sampled at five time points following rain events and dry periods. They were characterized by physical (aggregation), chemical (nutrients and heavy metals), and biological (total, bacterial and fungal biomasses, and genotypic fingerprints of total bacterial and fungal communities) parameters. Data were processed using statistical analyses which indicated that heavy metal (1,841 μg/g dry weight (DW)) and organic matter (11%) remained stable through time. By contrast, aggregation, nutrient content (NH₄⁺, 53-717 μg/g DW), pH (6.9-7.4), and biological parameters were shown to vary with sediment water content and sediment biomass, and were higher consecutive to stormwater flows into the basin (up to 7 mg C/g DW) than during dry periods (0.6 mg C/g DW). Coinertia analysis revealed that the structure of the bacterial communities is driven by the hydric dynamics of the infiltration basin, although no such trend was found for fungal communities. Hydric dynamics more than rain events appear to be more relevant for explaining variations of aggregation, microbial biomass, and shift in the microbial community composition. We concluded that the hydric dynamics of stormwater infiltration basins greatly affects the structural stability of the sedimentary layer, the biomass of the microbial community living in it and its dynamics. The decrease in aggregation consecutive to rewetting probably enhances access to organic matter (OM), explaining the consecutive release

  7. Li isotopic constraints from the Erro-Tobbio serpentinites on Alpine subduction processes (United States)

    Chu, M.-F.; Scambelluri, M.; Griffin, W. L.; O'Reilly, S. Y.; Pearson, N. J.


    Subduction zones represent a unique feature of the dynamic Earth and provide important constraints on how plate tectonics works. Subduction of serpentinized oceanic lithosphere, characterized by releasing water into the mantle wedge via dehydration, i.e. breakdown of hydrous minerals, plays a critical role in not only the generation of continental crust but also the Earth's water cycle. To track the recycling of water or fluid released by subduction, the stable isotope system of Li, a lithophile and mobile element, shows its high potential because 7Li, relative to 6Li, preferentially moves into the fluid phase when fractionation occurs. Here we present new Li abundance and isotopic compositions of the Erro-Tobbio serpentinized peridotite complex, a remnant mantle slice of the Alpine subduction. Our data indicate that most of the serpentinized ultramafic rocks have uniform Li concentrations, around 1 ppm. These rocks, however, show variable Li isotopic compositions. Among them, the high-pressure antigorite-bearing metaperidotites, formed under a low-strain condition, have a limited range in Li isotopic values, with δ7Li = +1.5 to +4.0, similar to those of serpentinized peridotites. In contrast, apparently heavier Li isotopes, up to +10.0, are observed in the high-pressure serpentinite mylonites that also contain antigorite but formed in high-strain domains. We note that O-H isotope ratios of the high-pressure ultramafic rocks reported in previous study (Früh-Green et al., 2001, Contrib. Mineral Petrol. 141: 145-159) show insignificant variations between the low- and high-strain domains. This demonstrates the superiority of Li isotope than conventional stable isotope systems in offering critical information about fluid-releasing processes in subduction zones. Moreover, our new data unsupport the general assumption that fluid released from subducted slabs is in favor of extracting 7Li than 6Li, thus capable of forming the much lighter δ7Li values observed in

  8. Sequential extraction analysis of heavy metals in sediments of variable composition using nitrilotriacetic acid to counteract resorption. (United States)

    Howard, J L; Vandenbrink, W J


    Artificial sediments were made that contained variable amounts (up to 20% by weight) of feldspar, calcite, Fe-oxide or organic matter. Analysis of samples spiked with Pb and Zn in the presence and absence of nitrilotriacetic acid (NTA) showed that 400 mg l(-1) of chelating agent greatly reduced or eliminated sorption in each case. Further study showed that this NTA concentration did not cause significant mineral dissolution. Resorption during sequential extraction analysis of artificial sediments is indicated by the fact that with NTA, levels of metals are higher in the first step and lower during subsequent steps, compared with levels obtained without NTA. However, the addition of 400 mg l(-1) of NTA to each extracting solution in the sequence appears to be effective for counteracting resorption in feldspathic, calcareous, ferruginous and carbonaceous sediments.

  9. Influence of the subducting plate velocity on the geometry of the slab and migration of the subduction hinge

    NARCIS (Netherlands)

    Schellart, Wouter P.


    Geological observations indicate that along two active continental margins (East Asia and Mediterranean) major phases of overriding plate extension, resulting from subduction hinge-retreat, occurred synchronously with a reduction in subducting plate velocity. In this paper, results of fluid

  10. Slab melting as a barrier to deep carbon subduction. (United States)

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


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

  11. Deeper Subduction Zone Melting Explains Enrichment of Upper Mantle and Resolves Dehydration Paradox (United States)

    Dixon, Jacqueline; Bindeman, Ilya; Kingsley, Richard


    We present new volatile and stable isotope data on oceanic basaltic glasses with a range of enriched compositions. Basalt compositions studied here can be modeled by mixing between depleted mantle and various enriched (EM) and prevalent (PREMA) mantle components. We develop a multi-stage metasomatic and melting model for the origin of the enriched components, extending the subduction factory concept to involve melting of different components at different depths, down to the mantle transition zone (660 km), with slab temperature a key variable. EM components are heterogeneous, ranging from wet and heavy (Arctic Ridges) to dry and light (East Pacific Rise), and are derived from the subducted slab at depths of 150 to 250 km by addition of oceanic ridge and ocean island basalts requires involvement of a mostly dehydrated slab component to explain trace element ratios and radiogenic isotopic compositions, but a fully hydrated slab component to explain stable isotope compositions. In our model, thermal parameters of slabs control the timing and composition of subduction-derived components. This includes deep release of fluids from subcrustal hydrous phases that may rehydrate previously dehydrated slab, resolving the paradox.

  12. Stress orientations in subduction zones and the strength of subduction megathrust faults. (United States)

    Hardebeck, Jeanne L


    Subduction zone megathrust faults produce most of the world's largest earthquakes. Although the physical properties of these faults are difficult to observe directly, their frictional strength can be estimated indirectly by constraining the orientations of the stresses that act on them. A global investigation of stress orientations in subduction zones finds that the maximum compressive stress axis plunges systematically trenchward, consistently making an angle of 45° to 60° with respect to the subduction megathrust fault. These angles indicate that the megathrust fault is not substantially weaker than its surroundings. Together with several other lines of evidence, this implies that subduction zone megathrusts are weak faults in a low-stress environment. The deforming outer accretionary wedge may decouple the stress state along the megathrust from the constraints of the free surface. Copyright © 2015, American Association for the Advancement of Science.

  13. Stress orientations in subduction zones and the strength of subduction megathrust faults (United States)

    Hardebeck, Jeanne L.


    Subduction zone megathrust faults produce most of the world’s largest earthquakes. Although the physical properties of these faults are difficult to observe directly, their frictional strength can be estimated indirectly by constraining the orientations of the stresses that act on them. A global investigation of stress orientations in subduction zones finds that the maximum compressive stress axis plunges systematically trenchward, consistently making a 45°-60° angle to the subduction megathrust fault. These angles indicate that the megathrust fault is not substantially weaker than its surroundings. Together with several other lines of evidence, this implies that subduction zone megathrusts are weak faults in a low-stress environment. The deforming outer accretionary wedge may decouple the stress state along the megathrust from the constraints of the free surface.

  14. Probing the transition between seismically coupled and decoupled segments along an ancient subduction interface (United States)

    Angiboust, Samuel; Kirsch, Josephine; Oncken, Onno; Glodny, Johannes; Monié, Patrick; Rybacki, Erik


    The transition zone at the downdip end of seismic coupling along subduction interfaces is often the site of megathrust earthquake nucleation and concentrated postseismic afterslip, as well as the focus site of episodic tremor and slip features. Exhumed remnants of the former Alpine subduction zone found in the Swiss Alps allow analyzing fluid and deformation processes near the transition zone region (30-40 km paleodepth). The Dent Blanche Thrust (DBT) is a lower blueschist-facies shear zone interpreted as a fossilized subduction interface where granitic mylonites overlie a metamorphosed accretionary wedge. We report field observations from the DBT region where multiple, several tens of meters thick foliated cataclastic networks are interlayered within the basal DBT mylonites. Petrological results and microstructural observations indicate that the various cataclasis events took place at near-peak metamorphic conditions (400-500°C, 1.1-1.3 GPa) during subduction of the Tethyan seafloor in Eocene times (42-48 Ma). Some of these networks exhibit mutual crosscutting relationships between mylonites, foliated cataclasites, and vein systems indicating mutual overprinting between brittle deformation and ductile creep. Whole-rock chemical compositions, in situ 40Ar-39Ar age data of recrystallized phengite, and Sr isotopic signatures reveal that DBT rocks also underwent multiple hydrofracturing and metasomatic events via the infiltration of fluids mainly derived from the oceanic metasediments underneath the DBT. From the rock fabrics, we infer strain rate fluctuations of several orders of magnitude beyond subduction strain rates (˜10-12 s-1) accompanied by fluctuation of supralithostatic and quasi-lithostatic fluid pressures (1 ≥ λ > 0.95). DBT brittle-plastic deformation switches highlight the diversity of deformation processes and fluid-rock interactions in the transition zone region of the subduction interface.

  15. Melting carbonated epidote eclogites: carbonatites from subducting slabs (United States)

    Poli, Stefano


    Current knowledge on the solidus temperature for carbonated eclogites suggests that carbonatitic liquids should not form from a subducted oceanic lithosphere at sub-arc depth. However, the oceanic crust includes a range of gabbroic rocks, altered on rifts and transforms, with large amounts of anorthite-rich plagioclase forming epidote on metamorphism. Epidote disappearance with pressure depends on the normative anorthite content of the bulk composition; we therefore expect that altered gabbros might display a much wider pressure range where epidote persists, potentially affecting the solidus relationships. A set of experimental data up to 4.6 GPa, and 1000 °C, including new syntheses on mafic eclogites with 36.8 % normative anorthite, is discussed to unravel the effect of variable bulk and volatile compositions in model eclogites, enriched in the normative anorthite component ( An 37 and An 45). Experiments are performed in piston cylinder and multianvil machines. Garnet, clinopyroxene, and coesite form in all syntheses. Lawsonite was found to persist at 3.7 GPa, 750 °C, with both dolomite and magnesite; at 3.8 GPa, 775-800 °C, fluid-saturated conditions, epidote coexists with kyanite, dolomite, and magnesite. The anhydrous assemblage garnet, omphacite, aragonite, and kyanite is found at 4.2 GPa, 850 °C. At 900 °C, a silicate glass of granitoid composition, a carbonatitic precipitate, and Na-carbonate are observed. Precipitates are interpreted as evidence of hydrous carbonatitic liquids at run conditions; these liquids produced are richer in Ca compared to experimental carbonatites from anhydrous experiments, consistently with the dramatic role of H2O in depressing the solidus temperature for CaCO3. The fluid-absent melting of the assemblage epidote + dolomite, enlarged in its pressure stability for An-rich gabbros, is expected to promote the generation of carbonatitic liquids. The subsolidus breakdown of epidote in the presence of carbonates at depths

  16. Organic matter composition in the sediment of three Brazilian coastal lagoons: district of Macaé, Rio de Janeiro (Brazil

    Directory of Open Access Journals (Sweden)

    Zink Klaus-Gerhard


    Full Text Available Freshwater lagoons comprise important coastal ecosystems and natural buffers between urbanized land areas and open ocean in the Rio de Janeiro State, Brazil. Studies of sediment and water chemistry, zooplankton and bacterial communities to assess the extent of anthropogenic disturbance are available. Here we contribute with an organic-geochemical approach supplemented by some microbiological aspects to complete the characterization of these lagoonal ecosystems. Bulk organic matter and extractable lipids (aliphatic hydrocarbons, alcohols and fatty acids, sterols were investigated from two locations per lagoon: at the seaward site and landward ends - and at two depth intervals (0-3 and 3-6 cm per site. Urbanized Imboacica Lagoon received increased anthropogenic input over the most recent years represented by the topmost 3 cm of sediment, whereas deeper sediment layers are less affected by human influence. Eutrophication or nutrient availability favored enhanced algal/cyanobacterial growth. In remote Cabiúnas and Comprida Lagoons pristine conditions are preserved. Organic matter from vascular plants dominates (chain length of free lipids up to C36, which is exceptionally well preserved by acidic lagoonal waters. Differentiation between landward and seaward sites in these two lagoons is less well established due to much smaller surface/volume to catchment ratios. No anthropogenic influences are yet detectable in sediments of Cabiúnas and Comprida Lagoons.

  17. Effects of composition of labile organic matter on biogenic production of methane in the coastal sediments of the Arabian Sea

    Digital Repository Service at National Institute of Oceanography (India)

    Gonsalves, M.J.B.D.; Fernandes, C.E.G.; Fernandes, S.O.; Kirchman, D.L.; LokaBharathi, P.A.

    mixture of methane standards (concentration range of 1-5 g/L) from M/S Alchemie Gases Ltd. Biochemical parameters Protein analyses were carried out following extraction of 3 replicates of sediment sample with NaOH (0.5 M, 4 h) according to Hartree...

  18. Chemical data and lead isotopic compositions in stream-sediment samples from the Boulder River watershed, Jefferson County, Montana (United States)

    Fey, David L.; Unruh, Dan M.; Church, Stan E.


    Metal-mining related wastes in the Boulder River basin study area in northern Jefferson County, Montana, have been evaluated for their environmental effects as a part of the U.S. Geological Survey Abandoned Mine Lands Project. Many mine and prospect waste dumps, and mill wastes are located in the drainage basins of Basin Creek, Cataract Creek, and High Ore Creek, the three major tributaries to the Boulder River in the study area. Throughout the study area, mine-waste material has been transported into and down streams, where it mixes with and becomes incorporated into the bed sediments. In some locations, waste material was placed by mine operators directly in stream channels, and has been transported downstream forming fluvial tailings deposits along the stream banks. Water quality and aquatic habitat have been affected by acid generation and toxic-metal mobility during snowmelt and storm water runoff events. Colloids formed by the raising of pH downstream from these mine sites sorb metals contributing to the high concentrations observed in both bed and suspended sediments within the watershed. This report presents geochemical data for bed sediments from 67 sites and lead isotope data for 59 sites. Also included are geochemical data for seven suspended-sediment samples, and one smelter slag sample. 

  19. Identification and carbon isotope composition of a novel branched GDGT isomer in lake sediments: Evidence for lacustrine branched GDGT production

    NARCIS (Netherlands)

    Weber, Y.; De Jonge, C.; Rijpstra, W.I.C.; Hopmans, E.C.; Stadnitskaia, A.; Schubert, C.J.; Lehmann, M.F.; Sinninghe Damsté, J.S.; Niemann, H.


    Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial membrane lipids that occur ubiquitously in soils and lacustrine sediments and have great potential as proxy indicators for paleotemperature and pH reconstructions. Initially, brGDGTs in lakes were thought to originate from soils

  20. Global correlations between maximum magnitudes of subduction zone interface thrust earthquakes and physical parameters of subduction zones

    NARCIS (Netherlands)

    Schellart, W. P.; Rawlinson, N.


    The maximum earthquake magnitude recorded for subduction zone plate boundaries varies considerably on Earth, with some subduction zone segments producing giant subduction zone thrust earthquakes (e.g. Chile, Alaska, Sumatra-Andaman, Japan) and others producing relatively small earthquakes (e.g.

  1. Dynamics of intraoceanic subduction initiation : 1. Oceanic detachment fault inversion and the formation of supra-subduction zone ophiolites

    NARCIS (Netherlands)

    Maffione, Marco; Thieulot, Cedric|info:eu-repo/dai/nl/270177493; van Hinsbergen, Douwe J.J.|info:eu-repo/dai/nl/269263624; Morris, Antony; Plümper, Oliver|info:eu-repo/dai/nl/37155960X; Spakman, Wim|info:eu-repo/dai/nl/074103164

    Subduction initiation is a critical link in the plate tectonic cycle. Intraoceanic subduction zones can form along transform faults and fracture zones, but how subduction nucleates parallel to mid-ocean ridges, as in e.g., the Neotethys Ocean during the Jurassic, remains a matter of debate. In

  2. Oceanic-style Subduction Controls Late Cenozoic Deformation of the Northern Pamir and Alai (United States)

    Sobel, E. R.; Chen, J.; Schoenbohm, L. M.; Thiede, R. C.; Stockli, D. F.; Sudo, M.; Strecker, M. R.


    deformation and erosion within the Pamir, Alai - western Tarim Basins, and Tien Shan and prograde metamorphism in the Central Pamir domes to increased compression following the break-off of the north-dipping Indian slab; subsequent subduction (underthrusting) and rollback of the Alai slab released this stress, enabling rapid exhumation of the Central Pamir domes above excessively thickened Pamir crust and a hiatus of deformation farther north. Subduction erosion of the proximal hanging wall rather than vertical exhumation was dominant in the North Pamir during the middle Miocene. In the latest Miocene - Present, a pronounced influx of syn-tectonic sediments into the Alai and westernmost Tarim Basins and deformation within the downgoing slab thickened the crust, increased coupling and promoted subduction accretion, reflected by the thin-skinned propagation of the MPT and PFT. Consequently, the Pamir and Alai Basin are involved in a progressive, soft collision whose onset is difficult to date.

  3. Elemental (C/N ratios) and Isotope (δ13CTOC, δ15NTN) Compositions of Surface Sediments from the Barrier Islands in the Nakdong River Estuary, South Korea (United States)

    Lee, Jun-Ho; Woo, Han Jun; Jeong, Kap-Sik; Kang, Jeongwon; Choi, Jae Ung; Lee, Dong-Hun


    The Nakdong River Estuary (NRE) in South Korea is a typical, artificially-manipulated estuary and blocked by two large dam. The Noksan Dam, built in 1934, blocks the flow of the West Nakdong River, and the NRE Dam was completed between 1983 and 1987 to regulate the flow of the East Nakdong River (called the Eulsuk River locally). For the past half century, several huge industrial complexes have been developed in the reclaimed land near the NRE. In the estuary, the hydraulic circulation has been markedly modified caused by the changes in the river discharge and geomorphic configuration of such as the formation of a series of barrier islands, the two large dams resulting from the artificial control of the natural river flow and upstream intrusion of saltwater by the operation of the two large dams. Consequently, the saltwater wedge that once reached approximately 40 km upstream is now blocked at the dam, considerably reducing the tidal prism. The estuary is typified by barrier-lagoon system with various subenvironments and microtidal with a 1.5 m tidal range. We investigated the elemental (C/N ratios) and isotopic (δ13CTOC, δ15NTN) compositions of organic matters in various composition in the surface sediments in the NRE. In May 2015, 90 surface sediment samples were collected on and around three islands in the NRE. The mean grain size of the barrier island system in the NRE ranged from 1.1 to 8.9 Φ (average 3.9 Φ) in mean grain size, and they were composed of various sediment types, including muddy Sand (S), sandy Mud (sM), and Mud (M). A useful application of the C/N ratios is as a proxy for assessment of organic matter source change, related to the sediment origins terrestrial or marine. The C/N ratios (average, 5.88) imply that the organic matter in the study area was of marine origins, as indicated by the lower ratios between 4 and 10. The isotope composition of sedimentary organic matter (δ13CTOC, δ15NTN) indicated the deposition of algae-derived organic

  4. The effects of the 2010 flood on the composition and abundance of the terrestrial organic matter in sediments along the inner-shelf off the Changjiang Estuary, China (United States)

    Li, X.; Bianchi, T. S.; Allison, M. A.; Chapman, P.; Yang, G.


    Surface sediments were collected within the primary depositional pathway along the inner-shelf off the Changjiang Estuary in winter 2009 and fall 2010 - before and after the 2010 flood in the Changjiang River. Multiple proxies (stable isotopes, lignin-phenols, pigments, cutins) were analyzed to examine the influence of this flooding event on the composition and abundance of river-derived terrestrial organic matter in sediments off the Changjiang Estuary. Elemental and stable isotope analyses showed significantly higher molar C/N ratios and enriched δ13C signatures for 2010 samples, which likely reflected inputs of C4 vascular plant materials. Post-flood concentrations of lignin-phenols were significantly lower in concentration than pre-flood concentrations in 2009. Lignin-phenol acid/aldehyde (Ad/Al) ratios, the lignin degradation index, showed significantly more degraded lignin post-flood in 2010 than that in 2009, which suggests greater inputs of lignins that were likely associated more with degraded soils, due to enhanced erosion from the flood, than surface plant litter. This was also in good agreement with higher inputs of another lignin soil proxy, the 3,5-Bd (3,5-dihydroxybenzoic acid) /V. Lignin-phenol source plots showed no significant differences in pre-and post flood sources, with sources largely consisting of a mixture of woody and non-woody gymnosperm and angiosperm inputs. Short lived radionuclides such as 7Be, 234Th analysis showed no apparent short-term sediment accumulation. The lack of evidence for new sediments deposited to the inner shelf after the flood was likely influenced in part, by the effects of extensive upstream damming on the Changjiang, especially the more recently constructed Three Gorges Dam.

  5. Comment on 'Boron content and isotopic composition of oceanic basalts: Geochemical and cosmochemical implications' by M. Chaussidon and A. Jambon (United States)

    You, Chen-Feng


    Chaussidon and Jambon presented results of their ion microprobe study of boron concentrations and isotopic compositions in oceanic basaltic glasses. Although this study has extended the information on the geochemistry of B and delta B-11 in mid-ocean ridge basalts (E-MORB and N-MORB), back-arc basin basalts (BABB) and ocean island basalts (OIB), their calculation of the maximum amount of B recycled in subduction zones warrants special caution. They concluded that less than 2% of the B in subducted oceanic crust was added to the mantle source in order to explain the low delta B-11 values in the oceanic basalts (-7.4 - 0.6 per mil). Two comments regarding the calculation of Chaussidon and Jambon will be presented in this paper. First, sediments constitute one of the most important B reservoirs in subduction zones and should be considered in any budget calculation. Second, there is an important fractionation effect of both B and delta B-11 in the slab during subduction and this effect should be assessed.

  6. Mechanical and chemical properties of composite materials made of dredged sediments in a fly-ash based geopolymer. (United States)

    Lirer, S; Liguori, B; Capasso, I; Flora, A; Caputo, D


    Dredging activity in harbours and channels produces huge quantities of sediments, generally considered as waste soil (WS) to be disposed: the management of such sediments is a great environmental problem for many countries worldwide. Among the recycling possibilities, the use of dredged sediments for the manufacture of geopolymer-based materials seems to be an interesting alternative to disposal, due to their low cost and easy availability. In order to analyse the possibility to use these geopolymer materials as building materials - for instance as precast construction elements in maritime projects - a multi-disciplinary research activity has been developed at the Federico II University of Napoli (Italy). Some experimental tests have been carried out on different geopolymeric specimens made by mixing sediments from Napoli 'harbour and industrial fly ashes produced by a power plant in the South of Italy. A siliceous sand was used for comparison as an inert reference material. Chemical, morphological and mechanical properties of different specimens have been studied by X-ray diffraction, Scanning Electron Microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR) and finally unconfined compression tests. The experimental results highlight that the use of dredged sediments in combination with fly ash can lead to geopolymeric matrices with interesting mechanical performances. Some differences in the microstructure of the geocomposite built with the siliceous sand or the dredged materials were found. In terms of environmental impacts, on the basis of standard leaching tests and according to Italian thresholds, the adopted dredged mixtures satisfy the prescribed limit for inert or non hazardous waste. Copyright © 2017 Elsevier Ltd. All rights reserved.

  7. Polycyclic aromatic hydrocarbons (PAHs) in surface sediments from the intertidal zone of Bohai Bay, Northeast China: Spatial distribution, composition, sources and ecological risk assessment. (United States)

    Qian, Xiao; Liang, Baocui; Fu, Wenjun; Liu, Xinhui; Cui, Baoshan


    Polycyclic aromatic hydrocarbons (PAHs) can enter intertidal zones by various pathways and pose potential threats to intertidal ecosystem. We investigated distribution, composition, sources and risk assessment of PAHs in intertidal surface sediments of Bohai Bay. Total PAH concentrations ranged from 37.2ng·g-1 to 206.6ng·g-1, among which high values occurred near Nanpaishuihe River Estuary and Haihe River Estuary. The composition patterns of PAHs were characterized by the predominance of 3-ring and 4-ring PAHs, and acenaphthylene was the most dominant component. Diagnostic ratios and principal component analysis have confirmed that PAH contaminants originated from mixed sources, and the major was local combustion. The mean benzo(a)pyrene equivalent concentration of total PAHs in intertidal sediments was 15.67ng·g-1, which was mostly contributed by seven carcinogenic PAHs. According to ecological risk assessment, negative effects related to acenaphthylene would occur occasionally in partial survey regions of the study. Copyright © 2016 Elsevier Ltd. All rights reserved.

  8. Bacterial community composition and predicted functional ecology of sponges, sediment and seawater from the thousand islands reef complex, West Java, Indonesia. (United States)

    de Voogd, Nicole J; Cleary, Daniel F R; Polónia, Ana R M; Gomes, Newton C M


    In the present study, we assessed the composition of Bacteria in four biotopes namely sediment, seawater and two sponge species (Stylissa massa and Xestospongia testudinaria) at four different reef sites in a coral reef ecosystem in West Java, Indonesia. In addition to this, we used a predictive metagenomic approach to estimate to what extent nitrogen metabolic pathways differed among bacterial communities from different biotopes. We observed marked differences in bacterial composition of the most abundant bacterial phyla, classes and orders among sponge species, water and sediment. Proteobacteria were by far the most abundant phylum in terms of both sequences and Operational Taxonomic Units (OTUs). Predicted counts for genes associated with the nitrogen metabolism suggested that several genes involved in the nitrogen cycle were enriched in sponge samples, including nosZ, nifD, nirK, norB and nrfA genes. Our data show that a combined barcoded pyrosequencing and predictive metagenomic approach can provide novel insights into the potential ecological functions of the microbial communities. Not only is this approach useful for our understanding of the vast microbial diversity found in sponges but also to understand the potential response of microbial communities to environmental change. © FEMS 2015. All rights reserved. For permissions, please e-mail:

  9. Mantle Wedge formation during Subduction Initiation: evidence from the refertilized base of the Oman ophiolitic mantle (United States)

    Prigent, C.; Guillot, S.; Agard, P.; Godard, M.; Lemarchand, D.; Ulrich, M.


    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. The latter one is supported by studies on volcanic sequences whereas studies dealing on the mantle section do not involve a significant influence of subduction processes on its structure and composition. We herein focus on basal peridotites from all along the ophiolite strike in order to decipher and characterize potential fluid/melt transfers relate to subduction processes. Samples were taken across the basal banded unit directly overlying the amphibolitic/granulitic metamorphic sole which represents an accreted part of the lower plate. We carried out a petrological, structural and geochemical study on these rocks and their constitutive minerals. Our results show that basal peridotites range from lherzolites to highly depleted harzburgites in composition. Clinopyroxenes (cpx) display melt impregnation textures and co-crystallized with HT/HP amphiboles (amph), spinels and sulfurs. Major and trace elements of the constitutive minerals indicate that these minerals represent trapped incremental partial melt after hydrous melting. Different cpx-bearing lithologies then result from varying degrees of partial melting and melt extraction. Combined with Boron isotopic data, we demonstrate that fluids responsible for hydrous melting of these ophiolitic basal peridotites are subduction-related, most likely derived from dehydration of the metamorphic sole during its formation in subduction initiation. From these observations and thermal constraints, we interpret the occurrence of these basal lherzolites as representing a freezing front developed by thermal re-equilibration (cooling) during subduction processes: subduction-related hydrous partial melts were

  10. Tracking historical mobility behavior and sources of lead in the 59-year sediment core from the Huaihe River using lead isotopic compositions. (United States)

    Wang, Jie; Liu, Guijian; Liu, Houqi; Lam, Paul K S


    A historical perspective of past 59 years (1955-2014) for contamination and isotopic composition of Pb in sediment core system of the Huaihe River, Huainan City, Anhui Province of China is presented. Detailed investigation regarding changes in Pb sources, enrichment factor, sequential extraction and isotopic analysis revealed that high Pb concentrations were detected along the core, especially during the first two decades (1955-1974). Large variations in Pb isotopic compositions were observed, with 206Pb/207Pb and 208Pb/207Pb values ranging from 1.1504-1.1694, and 2.0817-2.1380, respectively. Diverse Pb sources were identified for sediment contamination over the time. Among anthropogenic sources, metallurgic dust and leaded petrol were on top during 1955-1974, especially when the Great Leap Forward Movement (1958-1960) was in progress in China, the time numerous small industries were established without wastewater treatment facility. However, coal and coal combustion were recognized as the primary sources of Pb emissions for the recent four decades (1974-2014) due to tremendous increase of coal consumption for power and heat generation. Unleaded vehicle exhaust, waste incineration and industrial emission were also sources of Pb during the years 1974-2014. Our estimates based on geochemical and lead isotopic approaches have shown that anthropogenic Pb contributions varied from 4.35 to 92.01%, and 13.28-99.06%, respectively. Assessment of lead speciation indicated an overwhelming presence of reducible fraction (Fe-Mn hydro-(oxides)) in the sediment core, except during 1995-1997, which was thought to be affected by water pollution accidents caused by heavy rainfall. Copyright © 2017 Elsevier Ltd. All rights reserved.

  11. Sedimentary ancient DNA and pollen reveal the composition of plant organic matter in Late Quaternary permafrost sediments of the Buor Khaya Peninsula (north-eastern Siberia) (United States)

    Hildegard Zimmermann, Heike; Raschke, Elena; Saskia Epp, Laura; Rosmarie Stoof-Leichsenring, Kathleen; Schwamborn, Georg; Schirrmeister, Lutz; Overduin, Pier Paul; Herzschuh, Ulrike


    Organic matter deposited in ancient, ice-rich permafrost sediments is vulnerable to climate change and may contribute to the future release of greenhouse gases; it is thus important to get a better characterization of the plant organic matter within such sediments. From a Late Quaternary permafrost sediment core from the Buor Khaya Peninsula, we analysed plant-derived sedimentary ancient DNA (sedaDNA) to identify the taxonomic composition of plant organic matter, and undertook palynological analysis to assess the environmental conditions during deposition. Using sedaDNA, we identified 154 taxa and from pollen and non-pollen palynomorphs we identified 83 taxa. In the deposits dated between 54 and 51 kyr BP, sedaDNA records a diverse low-centred polygon plant community including recurring aquatic pond vegetation while from the pollen record we infer terrestrial open-land vegetation with relatively dry environmental conditions at a regional scale. A fluctuating dominance of either terrestrial or swamp and aquatic taxa in both proxies allowed the local hydrological development of the polygon to be traced. In deposits dated between 11.4 and 9.7 kyr BP (13.4-11.1 cal kyr BP), sedaDNA shows a taxonomic turnover to moist shrub tundra and a lower taxonomic richness compared to the older samples. Pollen also records a shrub tundra community, mostly seen as changes in relative proportions of the most dominant taxa, while a decrease in taxonomic richness was less pronounced compared to sedaDNA. Our results show the advantages of using sedaDNA in combination with palynological analyses when macrofossils are rarely preserved. The high resolution of the sedaDNA record provides a detailed picture of the taxonomic composition of plant-derived organic matter throughout the core, and palynological analyses prove valuable by allowing for inferences of regional environmental conditions.

  12. Investigation on subduction erosion of the Central Costa Rica margin with seismic wide- angle data (United States)

    Zhu, J.; Flueh, E. R.; Kopp, H.; Klaeschen, D.


    Seismic wide-angle investigations along the Pacific margin off Central Costa Rica were carried out using closely spaced ocean bottom hydrophones and seismometers along two parallel strike and two parallel dip lines, intersecting at the mid slope. The structure and the P-wave velocities of the subducted oceanic Cocos Plate and overriding Carribean Plate were determined by modeling the wide-angle seismic data combined with the analysis of coincident reflection seismic data and the use of synthetic seismograms. Detailed velocity-depth distributions of two dip-lines and two strike-lines on the continental slope will be presented. Below the slope sediment, a wedge-shaped body, the margin wedge is defined by high velocities (4.3-6.1 km/s). This wedge shows a high velocity gradient zone in the uppermost one to two km, underlain by a low velocity gradient to the plate boundary. Between the subducted plate and overriding plate the low velocity zone including a lense-type structure is seen. This Megalens (4.0-4.3 km/s) and the subducted sediment comprise a low velocity zone (LVZ) all along the plate boundary. This LVZ is constrained by joint analysis of reflection seismic data and wide-angle data. The thickness of the wedge varies along the strike, this is associated with the subduction of the extension of Quepos Plateau, which also resulted in uplift of the margin. The extensional forearc environment is manifested by the normal faults indicated on the the multi-channel seismic (MCS) data. The Megalens is most probably comprised of material transferred from upper margin wedge at the tip of the wedge. The velocity structure within the Megalense resembles the velocities at the tip of the wedge, and is clearly lower than the oceanic crust, but higher thn subducted sediment. If this interpretation is valid, this material has been transported 16 km landward, which implies it was detached from the upper plate 0.2 Ma ago.

  13. Geoid anomalies in the vicinity of subduction zones (United States)

    Mcadoo, D. C.


    In the considered investigation, attention is given to the line source model, a surface source model, an application of the model, and a model of the thermal lithosphere associated with marginal basins. It is found that undulations in the altimetrically observed geoid of the southwest Pacific are strongly controlled by positive density anomalies in the subducting slabs of the region and the effects of elevation of the geotherm in behind arc lithosphere (corresponding to young marginal basins). Finer details of slab geometry do not obviously manifest themselves in the observed geoid. Such gravitational effects are quite attenuated at sea level and are apparently mixed with crustal effects, oceanographic noise, etc. It appears that slabs in global composite may contribute substantially to intermediate and long wavelength portions (down to spherical harmonic degree 3 or 4) of the earth's gravity field.

  14. Natural sulfurization of carbohydrates in marine sediments : consequences for the chemical and carbon isotopic composition of sedimentary organic matter


    Dongen, B.E. van


    Carbohydrates make up the largest part of the organic matter in the biosphere and are used by living organism for many different reasons. They serve, among others, as carbon and energy source as well as metabolic intermediates. Carbohydrates are generally thought to be remineralized during early diagenesis in the water column and in the sediment and thus not preserved in substantial amounts. However, earlier studies have suggested that preservation of carbohydrates through sulfurization could...

  15. Pantanal of Cáceres: granulometric composition of bottom sediments in the Paraguay River between the outfall of the Cabaçal River and the city of Cáceres, Mato Grosso, Brazil

    Directory of Open Access Journals (Sweden)

    Gustavo Roberto dos Santos Leandro


    Full Text Available The objective of the study was to verify the granulometric composition of bottom sediments along the longitudinal profile of the Paraguay River between the outfall of the Cabaçal River and the city of Cáceres, Mato Grosso, comprised by the geographic coordinates 15°58’00’’ and 16°50’00’’ South Latitude and 57°40’00’’ and 57°44’00’’ West Longitude. Work activity was conducted to characterize the sites and sediments collection with Van Veen sediment sampler (seven samples; textural analysis of the sediments by the pipetting and sieving method (the method uses a combination of sieving and sedimentation. The Paraguay River exhibits a meandering style with two distinct periods (periodic flooding regime and drought that associated with of bottom sediments alternate processes of erosion, transport and deposition from the discernible changes in the complex landscaping. Thus, the concentration of sand in the bed load transported in the channel (five samples is related to environmental elements and land use. The fine sediments are transferred to the features (bays and ponds and flood plain; the intense fluvial dynamics and the course (alluvial deposition areas contribute to changes in channel and morphologic features (capacity transport and sediment depositions.

  16. Erythrocyte sedimentation rate and fibrinogen concentration of whole blood influences the cellular composition of platelet-rich plasma obtained from centrifugation methods. (United States)

    Yin, Wenjing; Xu, Zhengliang; Sheng, Jiagen; Xie, Xuetao; Zhang, Changqing


    Erythrocyte sedimentation rate (ESR), which reflects the sedimentation rate of platelets, leukocytes and erythrocytes in response to centrifugal force, may influence the cellular composition of platelet-rich plasma (PRP) obtained via centrifugation methods. However, no relevant studies have substantiated this. In the present study, blood was collected from 40 healthy volunteers and used to prepare PRP with two plasma-based preparation systems [YinPRP and Plasma Rich in Growth Factor (PRGF) systems] and two buffy coat-based systems (RegenPRP and WEGOPRP systems) in a single-donor model. Volumes of PRP and platelet-poor plasma (PPP) that were removed in the preparation process were recorded. Analyses of ESR, haematocrit, C-reaction protein, coagulation, serum glucose and serum lipid of the whole blood used for PRP preparation were performed to evaluate the levels of ESR and the factors known to influence it. Whole blood analysis was performed to evaluate the cellular composition of PRP. Results demonstrated that there were marked positive correlations between the ESR of the whole blood used for PRP preparation and PPP removal efficiencies, platelet concentrations, platelet capture efficiencies and platelet enrichment factors of PRP formulations obtained from plasma-based systems, and PRP yield efficiency of RegenPRP and PPP removal efficiency of WEGOPRP. Furthermore, there were marked negative correlations between ESR and concentrations and enrichment factors of platelets, leukocytes and erythrocytes of RegenPRP. Fibrinogen concentration of the whole blood, which had a marked positive correlation with ESR, also influenced the cellular composition of PRP. These findings may increase the understanding of PRP preparation and provide substantial evidence for the individualised optimisation of PRP preparation systems used in clinical practice.

  17. Earth's first stable continents did not form by subduction. (United States)

    Johnson, Tim E; Brown, Michael; Gardiner, Nicholas J; Kirkland, Christopher L; Smithies, R Hugh


    The geodynamic environment in which Earth's first continents formed and were stabilized remains controversial. Most exposed continental crust that can be dated back to the Archaean eon (4 billion to 2.5 billion years ago) comprises tonalite-trondhjemite-granodiorite rocks (TTGs) that were formed through partial melting of hydrated low-magnesium basaltic rocks; notably, these TTGs have 'arc-like' signatures of trace elements and thus resemble the continental crust produced in modern subduction settings. In the East Pilbara Terrane, Western Australia, low-magnesium basalts of the Coucal Formation at the base of the Pilbara Supergroup have trace-element compositions that are consistent with these being source rocks for TTGs. These basalts may be the remnants of a thick (more than 35 kilometres thick), ancient (more than 3.5 billion years old) basaltic crust that is predicted to have existed if Archaean mantle temperatures were much hotter than today's. Here, using phase equilibria modelling of the Coucal basalts, we confirm their suitability as TTG 'parents', and suggest that TTGs were produced by around 20 per cent to 30 per cent melting of the Coucal basalts along high geothermal gradients (of more than 700 degrees Celsius per gigapascal). We also analyse the trace-element composition of the Coucal basalts, and propose that these rocks were themselves derived from an earlier generation of high-magnesium basaltic rocks, suggesting that the arc-like signature in Archaean TTGs was inherited from an ancestral source lineage. This protracted, multistage process for the production and stabilization of the first continents-coupled with the high geothermal gradients-is incompatible with modern-style plate tectonics, and favours instead the formation of TTGs near the base of thick, plateau-like basaltic crust. Thus subduction was not required to produce TTGs in the early Archaean eon.

  18. International Siberian Shelf Study 2008 (ISSS-08): towards establishing a geographically distributed picture of the bulk geochemical composition of surface sediments on the East Siberian Sea (United States)

    Vonk, J.; Dudarev, O.; Semiletov, I.; Charkin, A.; Andersson, P.; Sánchez-García, L.; Kruså, M.; van Dongen, B.; Porcelli, D.; Gustafsson, Ö.


    The Arctic Ocean has unusually large and shallow continental shelves, covering more than 50% of its total area. Large amounts of fluvially transported terrestrial organic carbon (terrOC) are delivered to the East Siberian Arctic Shelves (ESAS; Laptev, East Siberian and Chuckchi Seas), in addition to input of coastally eroded material that, based on very limited data, is estimated to be equally large. The fate of these large-scale releases of terrOC into the ESAS seas is still poorly understood. The urgency of this question is underscored by the fact that the East-Siberian Arctic landmass is expected to experience the strongest climate warming on Earth, with potential for various carbon-climate feedback links. Improving our understanding of terrOC processing on the Eurasian Arctic shelves was one of the main objectives of the International Siberian Shelf Study (ISSS-08), a 42-day ship-based research expedition onboard the Russian vessel Yakob Smirnitskiy in August/September 2008. The East Siberian Sea (ESS) was the main geographical focus as it is not only the largest Arctic shelf sea but also the least studied. The ISSS-08 campaign obtained surface sediments from over 60 locations and is here combined with results obtained from campaigns in 2003, 2004 and 2007 to facilitate a comprehensive investigation of the ESS sediment composition. The ISSS-08 sediments were obtained both from near coast, as were earlier samples, but also had coverage out to the mid-shelf region. Analyses of ESS surface sediments from 2003 and 2004 show sedimentary organic carbon contents between 0.5 and 1.5% with highest values, locally up to 2.5-3% near the Indigirka and Kolyma river mouths and in Long Strait. Stable carbon isotope values were mostly in the range of -27 to -25 per mille, with more depleted values close to the coast. A clear transition was observed east from 170° E towards Long Strait with more enriched values, signalling a regime shift with stronger influence of the Pacific

  19. Oxygen isotope constraints on the crustal contribution to the subduction-related magmatism of the Aeolian Islands, southern Italy (United States)

    Ellam, R. M.; Harmon, R. S.


    Oxygen isotope data are presented for 37 samples of subduction-related lavas from the Aeolian Islands, southern Italy, that were characterised for radiogenic isotopes (Sr, Nd, Pb) and major- and trace-element abundances in previous studies. The samples, which were all erupted within the past 500,000 years, span the full compositional range of Aeolian magmatism from the calc-alkaline basalt-dacite sequence of Salina to the shoshonites of Stromboli and the potassic leucite-bearing basalt to rhyolite series of Vulcano, Whole-rock δ 18O values range from +6.3‰ to +8.5‰, but in some cases (14 samples) 18O enrichment by post-crystallization hydration and low-temperature alteration is suspected, and an empirical correction for excess water yields a primary magmatic δ 18O range of +6.1‰ to +8.5‰ . Variations in δ 18O exhibit a compositional dependence, increased δ 18O values characterize the evolved samples of the various magmatic series, and δ 18O-SiO 2 trends are steeper than those predicted for closed system fractional crystallization. In general, O isotope variations are accompanied by only small shifts in radiogenic isotope ratios and, while weak correlations between δ 18O and 87Sr/ 86Sr etc., are observed within individual fractionation series, it is apparent that these radiogenic isotope variations are much smaller than the ranges for the whole data set. A two-stage model of magma genesis is proposed in which hybridization of the mantle by the introduction of subducted sediments gave rise to a range of radiogenic isotope ratios at fairly constant δ 18O. Subsequently, magmas derived from the heterogeneous mantle evolved within crustal magma chambers by AFC, involving assimilation of 18O-rich crust, and giving rise to evolved magmas with high δ 18O, decreased 206Pb/ 204Pb, but with only slightly higher 87Sr/ 86Sr and slightly lower 143Nd/ 144Nd.

  20. Thermal structure and intermediate-depth seismicity in the Tohoku-Hokkaido subduction zones

    Energy Technology Data Exchange (ETDEWEB)

    Van Keken, P.E. [Michigan Univ., Ann Arbor, MI (United States). Dept. of Earth and Environmental Sciences; Kita, S.; Nakajima, J. [Tohoku Univ., Sendai (Japan). Research Center for Prediction of Earthquakes and Volcanic Eruptions


    The cause of intermediate-depth (>40 km) seismicity in subduction zones is not well understood. The viability of proposed mechanisms, which include dehydration embrittlement, shear instabilities and the presence of fluids in general, depends significantly on local conditions, including pressure, temperature and composition. The wellinstrumented and well-studied subduction zone below Northern Japan (Tohoku and Hokkaido) provides an excellent testing ground to study the conditions under which intermediate-depth seismicity occurs. This study combines new finite element models that predict the dynamics and thermal structure of the Japan subduction system with a high-precision hypocenter data base. The upper plane of seismicity is principally contained in the crustal portion of the subducting slab and appears to thin and deepen within the crust at depths >80 km. The disappearance of seismicity overlaps in most of the region with the predicted phase change of blueschist to hydrous eclogite, which forms a major dehydration front in the crust. The correlation between the thermally predicted blueschist-out boundary and the disappearance of seismicity breaks down in the transition from the northern Japan to Kurile arc below western Hokkaido. Adjusted models that take into account the seismically imaged modified upper mantle structure in this region fail to adequately recover the correlation that is seen below Tohoku and eastern Hokkaido. We conclude that the thermal structure below Western Hokkaido is significantly affected by timedependent, 3-D dynamics of the slab. This study generally supports the role of fluids in the generation of intermediate-depth seismicity. (orig.)

  1. Subduction or obduction of continental crust in the northern Norwegian Caledonides? An example from the Nordmannvik Nappe (United States)

    Faber, Carly; Stünitz, Holger; Jeřábek, Petr; Gasser, Deta; Konopásek, Jiří; Kraus, Katrin


    The debate about how and why continental crust is subducted is ongoing (Ingalls et al., 2016). This work uses the tectonmetamorphic history of a the Nordmannvik nappe in the northern Scandinavian Caledonides to discuss mid- to lower-crustal processes involved in the subduction of continental crust during the Caledonian Orogeny. The Nordmannvik Nappe, together with the underlying Kåfjord and Vaddas nappes, constitutes the Reisa Nappe Complex (RNC). The RNC overlies continental rocks of the Kalak Nappe Complex (KNC), and a clear oceanic suture between Baltican basement, the KNC and the RNC is missing. The RNC consists mainly of paragneisses of mostly unknown depositional age. Rare fossils in the Vaddas Nappe indicate that it at least partly consists of Ordovician-Silurian (>460 Ma) metasediments (Binns and Gayer, 1980). Both the Nordmannvik and Vaddas Nappes were intruded by gabbroic melt around 439 Ma at 9 kbar (c. 30 km) (Getsinger et al., 2013). Therefore, the host and intrusive rocks were already buried to positions far deeper than oceanic crust prior to nappe stacking. Nordmannvik nappe rocks show at least two distinct metamorphic fabrics; 1) an early high-grade kyanite-present migmatitic fabric and 2) a pervasive mylonitic fabric. Based on microstructural observations and pseudosection modeling these two fabrics are estimated to have formed at 770-800 °C and 9.4-11 kbar and 580-630 °C and 8-9.8 kbar, respectively. The presence of sillimanite in garnet cores (confirmed by Raman spectra) and garnet core compositions also suggest that an earlier, less well constrained, history exists with metamorphism around 815 °C and 8.7 kbar, similar to that recognized in the KNC, where it is dated to be pre-Caledonian. The lack of ocean floor rocks between the Nordmannvik Nappe and the Baltica basement suggests that the Nordmannvik Nappe and nappe units below were fairly proximal to Baltica prior to the Caledonian Orogeny. Their position below the Lyngen Nappe (Iapetus

  2. Subduction zone earthquakes and stress in slabs (United States)

    Vassiliou, M. S.; Hager, B. H.


    Simple viscous fluid models of subducting slabs are used to explain observations of the distribution of earthquakes as a function of depth and the orientation of stress axes of deep (greater than 300 km) and intermediate (70-300 km) earthquakes. Results suggest the following features in the distribution of earthquakes with depth: (1) an exponential decrease from shallow depths down to 250 to 300 km, (2) a minimum near 250 to 300 km, and (3) a deep peak below 300 km. Many shallow subducting slabs show only the first characteristic, while deeper extending regions tend to show all three features, with the deep peak varying in position and intensity. These data, combined with the results on the stress orientations of various-depth earthquakes, are consistent with the existence of a barrier of some sort at 670-km depth and a uniform viscosity mantle above this barrier.

  3. The hidden simplicity of subduction megathrust earthquakes (United States)

    Meier, M.-A.; Ampuero, J. P.; Heaton, T. H.


    The largest observed earthquakes occur on subduction interfaces and frequently cause widespread damage and loss of life. Understanding the rupture behavior of megathrust events is crucial for earthquake rupture physics, as well as for earthquake early-warning systems. However, the large variability in behavior between individual events seemingly defies a description with a simple unifying model. Here we use three source time function (STF) data sets for subduction zone earthquakes, with moment magnitude Mw ≥ 7, and show that such large ruptures share a typical universal behavior. The median STF is scalable between events with different sizes, grows linearly, and is nearly triangular. The deviations from the median behavior are multiplicative and Gaussian—that is, they are proportionally larger for larger events. Our observations suggest that earthquake magnitudes cannot be predicted from the characteristics of rupture onsets.

  4. Experimental Determination of Chloritoid Stability in Subducting Oceanic Crust (United States)

    Forneris, J.; Holloway, J. R.


    Dehydration of subducting oceanic lithosphere is the key process for understanding arc magma generation and transport of H2O into the mantle. To establish when and how H2O may be released from the slab into the overlying mantle it is necessary to determine the stability of hydrous phases in the subducting lithosphere. In the past 10 years, experimental investigations of phase relationships in basaltic compositions representing the crustal component of the slab have led to controversial results. Results obtained by Schmidt and Poli (1998) and Pawley and Holloway (1993) on basaltic compositions under H2O saturated conditions showed the potential importance of hydrous phases other than amphibole (such as chloritoid, epidote and lawsonite) in the dehydration process. However, these results are in disagreement with the experiments of Liu et al. (1996), which showed that no hydrous phases are stable beyond the amphibole breakdown reaction at or above 650° C. In our study, piston-cylinder experiments were conducted between 2.2 GPa and 2.8 GPa at 650° C. The starting material consisted of a natural basaltic glass with blueschist/eclogite seeds and H2O. Samples were pressure-sealed in a thick-walled silver capsule with a gold lining designed to prevent hydrogen diffusion in long-duration experiments. The oxygen fugacity was fixed at or near Ni+NiO. These experiments have been focused on determining the stability field of chloritoid by running long-duration experiments (up to 1 month). Our results are in agreement with results by Liu et al. (1996): Chloritoid appears in short-duration runs (144 hours or less at 2.6 GPa and 650° C) but is not present in longer-duration experiments (696 hours or more under the same conditions). The amphiboles obtained in our run products have a glaucophane composition and seem to be stable up to higher pressures (at least 2.6 GPa) than the more calcic amphiboles obtained by the three other groups. Epidote/zoisite is present up to at least

  5. Volcanism and Subduction: The Kamchatka Region (United States)

    Eichelberger, John; Gordeev, Evgenii; Izbekov, Pavel; Kasahara, Minoru; Lees, Jonathan

    The Kamchatka Peninsula and contiguous North Pacific Rim is among the most active regions in the world. Kamchatka itself contains 29 active volcanoes, 4 now in a state of semi-continuous eruption, and I has experienced 14 magnitude 7 or greater earthquakes since accurate recording began in 1962. At its heart is the uniquely acute subduction cusp where the Kamchatka and Aleutian Arcs and Emperor Seamount Chain meet. Volcanism and Subduction covers coupled magmatism and tectonics in this spectacular region, where the torn North Pacific slab dives into hot mantle. Senior Russian and American authors grapple with the dynamics of the cusp with perspectives from the west and east of it, respectively, while careful tephrostratigraphy yields a remarkably precise record of behavior of storied volcanoes such as Kliuchevskoi and Shiveluch. Towards the south, Japanese researchers elucidate subduction earthquake processes with unprecedented geodetic resolution. Looking eastward, new insights on caldera formation, monitoring, and magma ascent are presented for the Aleutians. This is one of the first books of its kind printed in the English language. Students and scientists beginning research in the region will find in this book a useful context and introduction to the region's scientific leaders. Others who wish to apply lessons learned in the North Pacific to their areas of interest will find the volume a valuable reference.

  6. Regional differences in subduction ground motions

    CERN Document Server

    Beauval, Céline; Abrahamson, N; Theodulidis, N; Delavaud, E; Rodriguez, L; Scherbaum, F; Haendel, A


    A few ground-motion prediction models have been published in the last years, for predicting ground motions produced by interface and intraslab earthquakes. When one must carry out a probabilistic seismic hazard analysis in a region including a subduction zone, GMPEs must be selected to feed a logic tree. In the present study, the aim is to identify which models provide the best fit to the dataset M6+, global or local models. The subduction regions considered are Japan, Taiwan, Central and South America, and Greece. Most of the data comes from the database built to develop the new BCHydro subduction global GMPE (Abrahamson et al., submitted). We show that this model is among best-fitting models in all cases, followed closely by Zhao et al. (2006), whereas the local Lin and Lee (2008) is well predicting the data in Taiwan and also in Greece. The Scherbaum et al. (2009) LLH method prove to be efficient in providing one number quantifying the overall fit, but additional analysis on the between-event and within-ev...

  7. How depositional conditions control input, composition, and degradation of organic matter in sediments from the Chilean coastal upwelling region

    DEFF Research Database (Denmark)

    Niggemann, Jutta; Ferdelman, Timothy G.; Lomstein, Bente Aagaard


     m‑2 d‑1), which was partly due to the greater water depth of most of the sediments investigated in the northern region and consistent with a lower quality of the sedimentary OM at 23°S. Reaction rate constants for TOC degradation that were obtained from measured SRR (kSRR; 0.0004‑0.0022 yr‑1) showed...... of a small fraction of labile OM (represented by CI). Our study shows that although rates of organic carbon accumulation were similar in both investigated sites, the extent and kinetics of organic carbon degradation were closely linked to differing depositional conditions....

  8. Composition and Distribution Characteristics and Geochemical Significance of n-Alkanes in Core Sediments in the Northern Part of the South Yellow Sea

    Directory of Open Access Journals (Sweden)

    Jinxian He


    Full Text Available The South Yellow Sea is an important carbon sink and a significant research area of carbon cycle. After studying the composition and distribution of n-alkanes in a 250 cm long sediment core in the northern part of South Yellow Sea, it can be found that all n-alkanes of sediment samples in this research are distributed in three types, that is, double peak groups, predominance of long-chain n-alkanes, and predominance of short-chain n-alkanes. The average values of ∑C25−35/∑C15−21, ∑C27+29+31/∑C15+17+19, ∑C21-/∑C22+, and (C27+C29+C31+C33/∑C14–38 are 1.92, 4.22, 0.51, and 0.35, respectively; all above outcomes indicate significant predominance of terrigenous inputs. The average values of C31/C29 and ACL are 1.04 and 29.92, respectively; these results reflect that herbaceous plants and ligneous plants account for similar percentages in the sediment core samples. The average values of CPI1 of short-chain alkanes are 0.80, reflecting the apparent even predominance, which is the result of microbial degradation. The average values of CPI2 of long-chain alkanes of most samples are 2.77, reflecting the apparent odd predominance. The average values of CPI and Pr/Ph, as well as the Pr/nC17 and Ph/nC18 correlation diagram, reflect that the organic matter is immature and suggest reductive sedimentary environment.

  9. The effects of megafaunal burrows on radiotracer profiles and organic composition in deep-sea sediments: preliminary results from two sites in the bathyal north-east Atlantic (United States)

    Hughes, D. J.; Brown, L.; Cook, G. T.; Cowie, G.; Gage, J. D.; Good, E.; Kennedy, H.; MacKenzie, A. B.; Papadimitriou, S.; Shimmield, G. B.; Thomson, J.; Williams, M.


    Megafaunal burrows were detected in boxcores from two sites in the bathyal north-east Atlantic. Burrow contents were analysed to assess their significance to sediment radiotracer profiles and organic composition. At 1100 m depth, burrow openings up to 3 cm diameter occurred at a density of approximately 5 m -2. Burrows at 12-18 cm sediment depth extending horizontally for up to 35 cm and linked to the surface by vertical shafts were provisionally attributed to echiuran worms, although no occupants were found in situ. In one example the horizontal burrow section was filled with green slurry, for which scanning electron microscopy, 210Pb excess and organic content all indicated a phytodetrital origin. At 1920 m depth no large burrow openings were found in five boxcores examined, but large subsurface biogenic structures were present. Galleries at 15-26 cm depth were traced horizontally for up to 30 cm, but contained no occupants or filling. Extended linear bands of faecal pellets were found in three boxcores at 13-17 cm depth. Excess 210Pb content indicated that most of these structures resulted from surface deposit feeding. Faecal pellet bands may partially explain the occurrence of subsurface peaks detected in profiles of 210Pb excess at this site. Results suggest that 'caching' of phytodetritus and subsurface deposition of faeces are two mechanisms for the rapid, deep burial of relatively fresh organic matter, but the significance of these processes to sediment geochemistry cannot be quantified without much information on the distribution, identity and abundance of burrowing megafauna in the deep sea.

  10. Investigating Pu and U isotopic compositions in sediments: a case study in Lake Obuchi, Rokkasho Village, Japan using sector-field ICP-MS and ICP-QMS. (United States)

    Zheng, Jian; Yamada, Masatoshi


    The objectives of the present work were to study isotope ratios and the inventory of plutonium and uranium isotope compositions in sediments from Lake Obuchi, which is in the vicinity of several nuclear fuel facilities in Rokkasho, Japan. Pu and its isotopes were determined using sector-field ICP-MS and U and its isotopes were determined with ICP-QMS after separation and purification with a combination of ion-exchange and extraction chromatography. The observed (240)Pu/(239)Pu atom ratio (0.186 +/- 0.016) was similar to that of global fallout, indicating that the possible early tropospheric fallout Pu did not deliver Pu from the Pacific Proving Ground to areas above 40 degrees N. The previously reported higher Pu inventory in the deep water area of Lake Obuchi could be attributed to the lateral transportation of Pu deposited in the shallow area which resulted from the migration of deposited global fallout Pu from the land into the lake by river runoff and from the Pacific Ocean by tide movement and sea water scavenging, as well as from direct soil input by winds. The (235)U/(238)U atom ratios ranged from 0.00723 to 0.00732, indicating the natural origin of U in the sediments. The average (234)U/(238)U activity ratio of 1.11 in a sediment core indicated a significant sea water U contribution. No evidence was found for the release of U containing wastes from the nearby nuclear facilities. These results will serve as a reference baseline on the levels of Pu and U in the studied site so that any further contamination from the spent nuclear fuel reprocessing plants, the radioactive waste disposal and storage facilities, and the uranium enrichment plant can be identified, and the impact of future release can be rapidly assessed.

  11. Permian arc evolution associated with Panthalassa subduction along the eastern margin of the South China block, based on sandstone provenance and U-Pb detrital zircon ages of the Kurosegawa belt, Southwest Japan (United States)

    Hara, Hidetoshi; Hirano, Miho; Kurihara, Toshiyuki; Takahashi, Toshiro; Ueda, Hayato


    We have studied the petrography, geochemistry, and detrital zircon U-Pb ages of sandstones from shallow-marine forearc sediments, accretionary complexes (ACs), and metamorphosed accretionary complexes (Meta-ACs) within the Kurosegawa belt of Southwest Japan. Those rocks formed in a forearc region of a Permian island arc associated with subduction of the Panthalassa oceanic crust along the eastern margin of the South China block (Yangtze block). The provenance of the shallow-marine sediments was dominated by basaltic to andesitic volcanic rocks and minor granitic rocks during the late Middle to Late Permian. The ACs were derived from felsic to andesitic volcanic rocks during the Late Permian. The provenance of Meta-ACs was dominated by andesitic volcanic rocks in the Middle Permian. The provenance, source rock compositions, and zircon age distribution for the forearc sediments, ACs and Meta-ACs have allowed us to reconstruct the geological history of the Permian arc system of the Kurosegawa belt. During the Middle Permian, the ACs were accreted along the eastern margin of the South China block. The Middle Permian arc was an immature oceanic island arc consisting of andesitic volcanic rocks. During the Late Permian, the ACs formed in a mature arc, producing voluminous felsic to andesitic volcanic rocks. A forearc basin developed during the late Middle to Late Permian. Subsequently, the Middle Permian ACs and part of the Late Permian AC underwent low-grade metamorphism in the Late to Early Jurassic, presenting the Meta-ACs.

  12. Investigation of heavy metal (Cu, Pb, Cd, and Cr) stabilization in river sediment by nano-zero-valent iron/activated carbon composite. (United States)

    Chen, Wei-fang; Zhang, Jinghui; Zhang, Xiaomao; Wang, Weiya; Li, Yuxiang


    Nano-zero-valent iron/activated carbon (nZVI/AC) composite was evaluated for its effectiveness in the stabilization of Cu, Pb, Cd, and Cr in dredged river sediment. Synthetic precipitation leaching procedure (SPLP) and toxicity characteristic leaching procedure (TCLP) were adopted to compare the effects of nZVI/AC dosage, particle size, time duration, and temperature on heavy metal leachability. The results show that leachability dropped considerably with the addition of nZVI/AC and powdered particles in the size of 0.075-0.18 mm was more effective in stabilization than granular ones. Stabilization effect was stable in long-term and robust against changes in temperature. Tessier sequential extraction revealed that heavy metals were associated with solid particle, inorganic or organic matters in sediment. The addition of nZVI/AC was able to convert relatively weakly bound heavy metals into more strongly bound species and thus reduce the bioavailability and toxicity. Also, the standard potential of heavy metals may decide the mechanism of stabilization process.

  13. The U-Th isotopic composition of Australian aeolian deposits: implications for weathering and sediment transport timescales (United States)

    Handley, Heather; Turner, Simon; Hesse, Paul; Othayoth Suresh, Puthiyaveetil; Turner, Michael


    In order to quantify how fast a landscape responds to tectonic, climatic and human factors, accurate weathering rates and soil and/or sediment ages are required. The uranium-series (U-series) isotopes are a valuable tool for deriving the timescales of weathering and erosion processes. The impact of dust on calculated U-series isotope residence timescales of soil and fluvial sediment has received little attention to date, despite the fact that the typical grain size of aeolian material overlaps with that of interest in such studies, particularly for the comminution approach (Australia. We show that there is significant isotopic disequilibria in the samples, which are characterised by (230Th/238U) activity ratios > 1 and (234U/238U) activity ratios < 1. The finer-grained fractions (<5 microns) have higher (230Th/238U) but comparable (234U/238U) to the coarser-grained fractions (5-53 microns) of the same samples. This study shows that the aeolian component cannot be assumed to be in isotopic equilibrium and needs to be considered when calculating weathering and erosion timescales.

  14. Organic matter in surface sediments from the Gulf of Mexico and South China Sea: Compositions, distributions and sources. (United States)

    Wang, Cuiping; Jia, Weili; Wang, Dong; Song, Zhiguang


    Sediments from the Gulf of Mexico (GOM) and the South China Sea (SCS) were analyzed. The low δ 13 C values of pentamethylicosane (PMIs) and fatty acids (-81.3 to -85.2‰) were found in only the S-1 sample collected from the GOM, indicating that methanogenic archaea associated with gas hydrate formation contributed to the sediment organic matter. Principle component analysis of fatty acids suggested that similar microbial biomass was found in the S-1, S-9, O-3 and O-5 samples. However, a comparison of the alkanes, fatty acids, and alcohols indicated that the percentage of n-alkan-2-ols in the S-1 sample from the GOM was the highest, while n-alkanes and n-fatty acids were the highest percentages in other samples from the GOM and SCS. This finding suggests that microbial species or the oxidation/reduction environment of the sample site of S-1 were different from those of the other samples. The present study provides a basis for detecting gas hydrate sites on the seafloor of the SCS. Copyright © 2017. Published by Elsevier Ltd.

  15. Introduction to the structures and processes of subduction zones (United States)

    Zheng, Yong-Fei; Zhao, Zi-Fu


    Subduction zones have been the focus of many studies since the advent of plate tectonics in 1960s. Workings within subduction zones beneath volcanic arcs have been of particular interest because they prime the source of arc magmas. The results from magmatic products have been used to decipher the structures and processes of subduction zones. In doing so, many progresses have been made on modern oceanic subduction zones, but less progresses on ancient oceanic subduction zones. On the other hand, continental subduction zones have been studied since findings of coesite in metamorphic rocks of supracrustal origin in 1980s. It turns out that high-pressure to ultrahigh-pressure metamorphic rocks in collisional orogens provide a direct target to investigate the tectonism of subduction zones, whereas oceanic and continental arc volcanic rocks in accretionary orogens provide an indirect target to investigate the geochemistry of subduction zones. Nevertheless, metamorphic dehydration and partial melting at high-pressure to ultrahigh-pressure conditions are tectonically applicable to subduction zone processes at forearc to subarc depths, and crustal metasomatism is the physicochemical mechanism for geochemical transfer from the slab to the mantle in subduction channels. Taken together, these provide us with an excellent opportunity to find how the metamorphic, metasomatic and magmatic products are a function of the structures and processes in both oceanic and continental subduction zones. Because of the change in the thermal structures of subduction zones, different styles of metamorphism, metasomatism and magmatism are produced at convergent plate margins. In addition, juvenile and ancient crustal rocks have often suffered reworking in episodes independent of either accretionary or collisional orogeny, leading to continental rifting metamorphism and thus rifting orogeny for mountain building in intracontinental settings. This brings complexity to distinguish the syn-subduction

  16. Composition of dust deposited to snow cover in the Wasatch Range (Utah, USA): Controls on radiative properties of snow cover and comparison to some dust-source sediments (United States)

    Reynolds, Richard L.; Goldstein, Harland L.; Moskowitz, Bruce M.; Bryant, Ann C.; Skiles, S. McKenzie; Kokaly, Raymond F.; Flagg, Cody B.; Yauk, Kimberly; Berquó, Thelma; Breit, George; Ketterer, Michael; Fernandez, Daniel; Miller, Mark E.; Painter, Thomas H.


    Dust layers deposited to snow cover of the Wasatch Range (northern Utah) in 2009 and 2010 provide rare samples to determine the relations between their compositions and radiative properties. These studies are required to comprehend and model how such dust-on-snow (DOS) layers affect rates of snow melt through changes in the albedo of snow surfaces. We evaluated several constituents as potential contributors to the absorption of solar radiation indicated by values of absolute reflectance determined from bi-conical reflectance spectroscopy. Ferric oxide minerals and carbonaceous matter appear to be the primary influences on lowering snow-cover albedo. Techniques of reflectance and Mössbauer spectroscopy as well as rock magnetism provide information about the types, amounts, and grain sizes of ferric oxide minerals. Relatively high amounts of ferric oxide, indicated by hard isothermal remanent magnetization (HIRM), are associated with relatively low average reflectance (anthropogenic sources for at least some of the carbonaceous matter, such as emissions from transportation and industrial activities. The composition of the DOS samples can be compared with sediments in a likely dust-source setting at the Milford Flat Fire (MFF) area about 225 km southwest of Salt Lake City. The MFF area represents geologically and physiographically similar and widespread dust sources west-southwest of the Wasatch Range and heavily populated Wasatch Front. The DOS layers and MFF sediments are similar in some textural, chemical, and magnetic properties, as well as in the common presence of goethite, hematite, magnetite-bearing basalt fragments, quartz, plagioclase, illite, and kaolinite. Textural and some chemical differences among these deposits can be explained by atmospheric sorting as well as by inputs from other settings, such as salt-crusted playas and contaminant sources.

  17. Subduction of oceanic plate irregularities and seismicity distribution along the Mexican Subduction Zone (United States)

    Manea, Marina; Constantin Manea, Vlad; Gerya, Taras; Wong, Raul-Valenzuela; Radulian, Mircea


    It is known that oceanic plates morphology is not a simple one, but rather complicated by a series of irregularities as seamounts, fracture zones and mid-ocean ridges. These features present on the oceanic floor form part of the fabric of oceanic crust, and once formed they move together with the oceanic plates until eventually enter a subduction zone. Offshore Mexico the oceanic Cocos plate seafloor is littered with relatively small but numerous seamounts and seamount chains, and also large fracture zones. In this study we investigate the relationship between these oceanic irregularities located in the vicinity of the trench in Mexico and the distribution of subduction seismicity, including the rupture history of large subduction zone earthquakes. Since the interseismic locking degree is influenced by the rheological properties of crustal and mantle rocks, any variations along strike will result in significant changes in seismic behavior due to a change in frictional stability. Our preliminary study shows a direct relationship between the presence of seamounts chains on the incoming oceanic plate and the subduction seismicity distribution. We also found a clear relationship between the subduction of the Tehuantepec fracture zone (TFZ) and the low seismic activity in the region where this fracture zone intersects the trench. This region is also long term conspicuously quiet and considered a seismic gap where no significant large earthquake has occurred in more than 100 years. Using high-resolution three-dimensional coupled petrological-thermomechanical numerical simulations specifically tailored for the subduction of the Cocos plate in the region of TFZ we show that the weakened serpentinized fracture zone is partially scraped out in the forearc region because of its low strength and positive buoyancy. The presence of serpentinite in the fore arc apparently lowers the degree of interseismic locking, producing a seismic gap in southern Mexico.

  18. What's happening inside the subduction factory? (United States)

    Penniston-Dorland, S. C.; Bebout, G. E.; Gorman, J. K.; Piccoli, P. M.; Walker, R. J.


    Much research has focused on the inputs and outputs of the 'subduction factory,' however a variety of metamorphic processes occur within the subducting slab and at its interface with the mantle wedge that contribute to creating the mixed signals observed in arc magmas. Subduction-related metamorphic rocks from the Catalina Schist represent a range of metamorphic grades and provide a natural laboratory to investigate these processes. Hybrid rock types such as reaction zones or 'rinds' between mafic (crustal) and ultramafic (mantle) rocks have attracted recent interest since they have a different bulk chemistry and mineralogy compared to the original inputs to the subduction factory. Here we explore the mineralogical and geochemical differences between the metamorphic rocks, their reaction zones, and endmember subduction input lithologies over a range of metamorphic grades including lawsonite albite, lawsonite blueschist, and amphibolite facies (with peak T ranging from ~ 275 to ~ 750°C and peak P ranging up to ~1.1 GPa). The results shed light on chemical changes occurring within the subduction zone and the processes happening inside the 'subduction factory', including mass transfer of elements by both fluid infiltration and mechanical mixing. Elements commonly enriched in arc magmatic rocks, such as the LILE (e.g. Ba, K), are enriched in metamafic rocks at all metamorphic grades relative to likely MORB protoliths. These enrichments are interpreted as the product of metamorphic fluid infiltration. Many major- and trace-element concentrations in reaction rinds fall between those of metamafic blocks and surrounding ultramafic-rich mélange matrix (including TiO2, MgO, FeO, Al2O3, Zr, Ni and Cr). Spatial distributions of these elements within the rinds suggest that the intermediate concentrations may be due to mechanical mixing of crustal and mantle materials. Rind concentrations of the highly siderophile elements (HSE: including Os, Ir, Ru, Pt, Pd, Re) as well as

  19. Dehydration reactions in subducting oceanic crust: implications for arc volcanism (United States)

    Forneris, J. F.; Holloway, J. R.


    In subduction zones, oceanic lithosphere progressively dehydrates as it sinks deep into the underlying mantle. Fluids released from the subducting slab are thought to trigger partial melting in the overlying mantle wedge, leading to the formation of volcanic arcs. Experiments were conducted in the ranges of 2.2--3.4 GPa (70 to 100 km) and 625--750^oC to determine the dehydration reactions that control fluid release from the basaltic layer of the subducting slab. The experimental duration was typically one month, although some experiments were replicated with a shorter run duration (one to two weeks) in order to identify potentially metastable phases. A mixture of a natural mid-ocean ridge basalt glass and mineral seeds was used as the starting material. Oxygen fugacity was buffered within ±1.3 log units of nickel-bunsenite (NiNiO). The results obtained indicate that the transformation of a hydrated eclogite into a nominally dry eclogite occurs through the decomposition of three hydrous phases: amphibole, lawsonite, and zoisite. Chloritoid, a mineral described as an H_2O carrier in previous experimental studies, is found to be metastable in the examined pressure-temperature (P-T) range and therefore should not be involved in the global fluid release from the basaltic crust. A detailed chemical analysis reveals that amphiboles are sodic-calcic (barroisite) at low pressures (2.2 to 2.4 GPa), but become sodic (glaucophane) with increasing pressure. This observation is the first experimental confirmation of the high-pressure stability of glaucophane in metabasalt compositions. At pressures above the stability field of amphibole, zoisite/clinozoisite becomes the stable hydrous phase at temperatures above 645^oC, whereas lawsonite is stable at lower temperatures. H_2O contents of eclogitic assemblages have been estimated based on modal abundance of minerals calculated from electron microprobe analyses. These results indicate that a slab following an intermediate

  20. Slab-mantle interactions in simulations of self-consistent mantle convection with single-sided subduction (United States)

    Crameri, F.; Tackley, P. J.; Meilick, I.; Gerya, T. V.; Kaus, B. J. P.


    Subduction zones on present-day Earth are strongly asymmetric features (Zhao 2004) composed of an overriding plate above a subducting plate that sinks into the mantle. Our recent advances in numerical modelling allow global mantle convection models to produce single-sided subduction self-consistently by allowing for free surface topography on and lubrication between the converging plates (Crameri et al., 2012). Thereby, they are indicating important mantle-slab interactions. The increase of viscosity with depth is an important mantle property affecting the dynamics of subduction: a large viscosity increase on the one hand favours an immediate stagnant lid because the slab cannot sink fast enough, while a small increase on the other hand does not provide enough resistance for the sinking slab and therefore facilitates an immediate slab break-off. While in the mobile lid (plate tectonic like) regime, our model also shows that single-sided subduction in turn has strong implications on Earth's interior such as its rms. velocity or its stress distribution. The arcuate trench curvature is such a feature that is caused by single-sided subduction in 3-D geometry. The pressure difference between the mantle region below the inclined sinking slab and the region above it causes a toroidal mantle flow around the slab edges. This flow of mantle material is responsible for forming the slabs and subsequently also the subduction trenches above it towards an arcuate shape. For this study we perform experiments in 2-D and global spherical 3-D, fully dynamic mantle convection models with self-consistent plate tectonics. These are calculated using the finite volume multi-grid code StagYY (Tackley 2008) with strongly temperature and pressure-dependent viscosity, ductile and/or brittle plastic yielding, and non-diffusive tracers tracking compositional variations (the 'air' and the weak crustal layer in this case).

  1. Crustal and upper mantle structure of the Anatolian plate: Imaging the effects of subduction termination and continental collision with seismic techniques (United States)

    Delph, Jonathan R.

    The neotectonic evolution of the eastern Mediterranean is intimately tied to interactions between the underthrusting/subducting slab along the southern margin of Anatolia and the overriding plate. The lateral variations in the subduction zone can be viewed as a temporal analogue of the transition between continuous subduction and subduction termination by continent-continent collision. By investigating the lateral variations along this subduction zone in the overriding plate, we can gain insight into the processes that precede continent collision. This dissertation summarizes the results of three studies that focus on different parts of the subduction margin: 1) In the west, where the development of a slab tear represents the transition between continuous and enigmatic subduction, 2) In the east, where continent-continent collision between the Arabian and Eurasian Plate is leading to the development of the third largest orogenic plateau on earth after complete slab detachment, and 3) In central Anatolia, where the subducting slab is thought to be in the processes of breaking up, which is affecting the flow of mantle material leading to volcanism and uplift along the margin. In the first study, we interpret that variations in the composition of material in the downgoing plate (i.e. a change from the subduction of oceanic material to continental material) may have led to the development of a slab tear in the eastern Aegean. This underthrusting, buoyant continental fragment is controlling overriding plate deformation, separating the highly extensional strains of western Anatolia from the much lower extensional strains of central Anatolia. Based on intermediate depth seismicity, it appears that the oceanic portion of the slab is still attached to this underthrusting continental fragment. In the second study, we interpret that the introduction of continental lithosphere into the north-dipping subduction zone at the Arabian-Eurasian margin led to the rollback and

  2. Dynamic Linkages Between the Transition Zone & Surface Plate Motion in 2D Models of Subduction (United States)

    Arredondo, K.; Billen, M. I.


    Subduction zones exhibit a wide range of behavior, from slab stagnation at 660 km to direct penetration into the lower mantle. Due to uncertainties in the tectonic history of individual subduction zones, such as trench velocities, potential mechanisms for controlling slab behavior in the transition zone are explored using numerical models. Numerical simulations have utilized a range of assumptions to improve computational efficiency, such as ignoring latent heat, ignoring compositional effects or fixing the trench location: the net effect of these assumptions resulting modeled dynamics remains unclear. Additionally the eight major, composition-dependent, phase transitions for pyrolite, harzburgite and eclogite may be an important influence on subducting slab dynamics due to the additional forces that are dependent on depth and compositional layering within the slab (e.g., Ricard et al., 2005). With the goal of developing more complete, self-consistent, and less idealized simulations, we test the importance of various factors on slab behavior: the presence of shear, adiabatic and latent heating, compositional layering, composition-dependent phase transitions and explicit plate speeds versus dynamically evolving plate and trench velocities. Preliminary results indicate that individual components have a relatively minor effect, but produce large changes when combined together. The extent of slab folding and stagnation is overestimated by only modeling the 410 and 660 km phase transitions. Dynamic models with all seven composition-dependent phase transitions are very sensitive to the plate strength and weak zone viscosity, causing large changes in plate speed and slab detachment. Changes to the overriding plate buoyance and strength investigate the origin and influence of trench movement on slab deformation. These feedbacks and parameter-sensitive behavior indicate that the wide range of observed slab behavior may result from subtle differences in plate and plate

  3. Differential subsidence of the forearc wedge of the Ryukyu (Nansei-Shoto) Arc caused by subduction of ridges on the Philippine Sea Plate (United States)

    Okamura, Yukinobu; Nishizawa, Azusa; Oikawa, Mitsuhiro; Horiuchi, Daishi


    The Philippine Sea Plate (PSP) carrying several ridges has been sudbucting under the Ryukyu (Nansei-Shoto) Arc since middle Miocene. Because no extensive accretionary prism has been growing along the Ryukyu Trench, the arc provides an opportunity to examine effects of ridge subduction on structure of the forearc wedge and a clue to reconstruct ancient plate motion of the PSP that is inferred to have changed between NW and NNW. To examine this perspective, we clarified structure of the Ryukyu forearc wedge based on seismic profiles and bathymetric data and related them to ridge subduction. An erosional unconformity between pre-Neogen and Neogene rocks is widely recognized through the Ryukyu Arc, and we divided the forearc wedges into Zones I to IV from southwest to northeast by difference of depth of the erosional unconformity. We correlated these four zones to the locations of ridge subduction that have been shifting NE or SW along the Ryukyu Trench. Zone I is underlain by the largely subsided unconformity and we attributed the structure to tearing of the Eurasia plate due to subduction of the western margin of the PSP including the Luzon Arc. Zone II consists of a wide terrace on the shallow erosional unconformity, and no ridge that was subducting in this zone is known. Zone III is characterized by the seaward descending unconformity covered with a thick sequence of Neogene sediments and is related to subduction of the NW-SE trending Daito Ridge and the E-W trending Amami Plateau. Zone IV has the deeper unconformity and slope geometry and corresponds to subduction of the NNW-SSE trending Kyushu-Palau Ridge. The structure of the Ryukyu forearc is consistently related to subduction of ridges on the PSP, suggesting that the change of the plate motion of the PSP can be precisely reconstructed by further detailed survey.

  4. Deep structure and historical earthquakes in the Calabrian subduction zone (Southern Italy): preliminary results from multi-channel seismic reflection profiles (United States)

    Gallais, F.; Gutscher, M.; Torelli, L.; Polonia, A.; Riminucci, F.


    The Calabrian subduction zone is located in the complex Central Mediterranean area. This subduction is characterized by the presence of deep earthquakes under the Tyrrhenian Sea down to 500 km depth. The Tethyan remnant Ionian slab descends towards the NW at a dip of about 70° and is associated with an active volcanic arc (the Aeolian Islands). Recently reported GPS and seismicity studies suggest that the subduction of the Ionian lithosphere beneath the Calabrian Arc may be locally still active, though at very slow rates (thrust earthquakes, characteristic of active subduction zone, suggests that if subduction is active, the fault plane may be locked since the instrumental period. To seek evidence of continuous tectonic activity of the Calabrian system, we present preliminary results from reprocessed 96-channels seismic reflection profiles (French Archimede cruise, 1997) offshore Sicily. This analysis permits to recognize a well-defined stratigraphy in the Ionian Abyssal Plain, this stratigraphy becomes difficult to follow under the deformed Calabrian Prism. But the joint interpretation with the reprocessed PM01 profile (French PRISMED cruise, 1994) helps constrain this interpretation and to image some characteristic structures of an accretionary wedge (fore/back-thrusts, basal decollement...). This study also include interpretation of a more recent Italian seismic cruise (Calamare, 2008) and CROP profiles. This work will help to prepare a future cruise proposal (CIRCEE, to be submitted in January 2010) to study the Calabrian subduction with OBS, MCS seismic, heat-flow measurements and sediment coring. The goals are : 1/ to image the deep structure of this subduction zone, 2/ to characterize its thermal state to deduce a geometry of the seismogenic part of the plate interface and add new constraints on seismic risk linked with the Calabrian subduction.

  5. Constraining the hydration of the subducting Nazca plate beneath Northern Chile using subduction zone guided waves (United States)

    Garth, Tom; Rietbrock, Andreas


    Guided wave dispersion is observed from earthquakes at 180-280 km depth recorded at stations in the fore-arc of Northern Chile, where the 44 Ma Nazca plate subducts beneath South America. Characteristic P-wave dispersion is observed at several stations in the Chilean fore-arc with high frequency energy (>5 Hz) arriving up to 3 s after low frequency (first motion dispersion observed at multiple stations, or the extended P-wave coda observed in arrivals from intermediate depth events within the Nazca plate. These signals can however be accurately accounted for if dipping low velocity fault zones are included within the subducting lithospheric mantle. A grid search over possible LVL and faults zone parameters (width, velocity contrast and separation distance) was carried out to constrain the best fitting model parameters. Our results imply that fault zone structures of 0.5-1.0 km thickness, and 5-10 km spacing, consistent with observations at the outer rise are present within the subducted slab at intermediate depths. We propose that these low velocity fault zone structures represent the hydrated structure within the lithospheric mantle. They may be formed initially by normal faults at the outer rise, which act as a pathway for fluids to penetrate the deeper slab due to the bending and unbending stresses within the subducting plate. Our observations suggest that the lithospheric mantle is 5-15% serpentinised, and therefore may transport approximately 13-42 Tg/Myr of water per meter of arc. The guided wave observations also suggest that a thin LVL (∼1 km thick) interpreted as un-eclogitised subducted oceanic crust persists to depths of at least 220 km. Comparison of the inferred seismic velocities with those predicted for various MORB assemblages suggest that this thin LVL may be accounted for by low velocity lawsonite-bearing assemblages, suggesting that some mineral-bound water within the oceanic crust may be transported well beyond the volcanic arc. While older

  6. The weathering of oil after the Deepwater Horizon oil spill: insights from the chemical composition of the oil from the sea surface, salt marshes and sediments (United States)

    Liu, Zhanfei; Liu, Jiqing; Zhu, Qingzhi; Wu, Wei


    The oil released during the Deepwater Horizon (DWH) oil spill may have both short- and long-time impacts on the northern Gulf of Mexico ecosystems. An understanding of how the composition and concentration of the oil are altered by weathering, including chemical, physical and biological processes, is needed to evaluate the oil toxicity and impact on the ecosystem in the northern Gulf of Mexico. This study examined petroleum hydrocarbons in oil mousse collected from the sea surface and salt marshes, and in oil deposited in sediments adjacent to the wellhead after the DWH oil spill. Oil mousses were collected at two stations (OSS and CT, located 130 and 85 km away from the wellhead, respectively) in May 2010, and two sediment samples from stations SG and SC, within 6 km of the wellhead, in May 2011. We also collected oil mousse from salt marshes at Marsh Point (MP), Mississippi, 186 km away from the wellhead in July 2010. In these samples, n-alkanes, polycyclic aromatic hydrocarbons (PAHs), alkylated PAHs, BTEX (collective name of benzene, toluene, ethylbenzene and p-, m-, and o-xylenes), C3-benzenes and trace metals were measured to examine how the oil was altered chemically. The chemical analysis indicates that the oil mousses underwent different degrees of weathering with the pattern of OSS marshes. Also, the contents of trace metals Al, V, Cr, Fe, Mn, Ni, Co, Cu, As and Pb in the oil mousse generally increased along the way to the salt marshes, indicating that these trace metals were perhaps aggregated into the oil mousse during the transport. Petroleum hydrocarbon data reveal that the oil deposited in sediments underwent only light to moderate degradation one year after the DWH oil spill, as supported by the presence of short-chained n-alkanes (C10-C 15), BTEX and C 3-benzenes. The weathering of oil in sediment may result from biological degradation and dissolution, evidenced by the preferential loss of mid-chained n-alkanes C16-C 27, lower ratios of n-C 17/Pr

  7. Control of high oceanic features and subduction channel on earthquake ruptures along the Chile-Peru subduction zone (United States)

    Contreras-Reyes, Eduardo; Carrizo, Daniel


    We discuss the earthquake rupture behavior along the Chile-Peru subduction zone in terms of the buoyancy of the subducting high oceanic features (HOF's), and the effect of the interplay between HOF and subduction channel thickness on the degree of interplate coupling. We show a strong relation between subduction of HOF's and earthquake rupture segments along the Chile-Peru margin, elucidating how these subducting features play a key role in seismic segmentation. Within this context, the extra increase of normal stress at the subduction interface is strongly controlled by the buoyancy of HOF's which is likely caused by crustal thickening and mantle serpentinization beneath hotspot ridges and fracture zones, respectively. Buoyancy of HOF's provide an increase in normal stress estimated to be as high as 10-50 MPa. This significant increase of normal stress will enhance seismic coupling across the subduction interface and hence will affect the seismicity. In particular, several large earthquakes (Mw ≥ 7.5) have occurred in regions characterized by subduction of HOF's including fracture zones (e.g., Nazca, Challenger and Mocha), hotspot ridges (e.g., Nazca, Iquique, and Juan Fernández) and the active Nazca-Antarctic spreading center. For instance, the giant 1960 earthquake (Mw = 9.5) is coincident with the linear projections of the Mocha Fracture Zone and the buoyant Chile Rise, while the active seismic gap of north Chile spatially correlates with the subduction of the Iquique Ridge. Further comparison of rupture characteristics of large underthrusting earthquakes and the locations of subducting features provide evidence that HOF's control earthquake rupture acting as both asperities and barriers. This dual behavior can be partially controlled by the subduction channel thickness. A thick subduction channel smooths the degree of coupling caused by the subducted HOF which allows lateral earthquake rupture propagation. This may explain why the 1960 rupture propagates

  8. Influence of Peruvian flat-subduction dynamics on the evolution of western Amazonia (United States)

    Eakin, Caroline M.; Lithgow-Bertelloni, Carolina; Dávila, Federico M.


    Convection in the Earth's mantle is mainly driven by cold, dense subducting slabs, but relatively little is known about how 3D variations in slab morphology and buoyancy affect mantle flow or how the surface above deforms in response (i.e. dynamic topography). We investigate this problem by studying the dynamics of an active region of flat-slab subduction located in Peru in South America. Here the slab geometry is well known, based on the regional seismicity, and we have observations from the local geological record to validate our models. Of particular interest is the widespread subsidence and deposition of the Solimões Formation across western Amazonia that coincided with the development of the Peruvian flat-slab during the Mid-Late Miocene. This formation covers an extensive area from the foredeep to the Purus Arch located ∼ 2000km away from the trench. Close to the Andes the preservation of several kilometers of sedimentary thicknesses can be easily accounted for by flexure. Based on an estimate of the Andean loading we predict 2.8 to 3.6 km of accommodation space that spans 100 km. The spatial and temporal history of the Solimões Formation however, particularly the thick distal foreland accumulations up to 1.2 km deep, can only be matched with the addition of a longer-wavelength dynamic source of topography. Following the transition from normal to flat subduction, we predict over 1 km of dynamic subsidence (∼ 1500km wide) that propagates over 1000 km away from the trench, tracking the subduction leading edge. This is followed by a pulse of dynamic uplift over the flat segment behind it. We therefore propose that a combination of uplift, flexure and dynamic topography during slab flattening in Peru is responsible for the sedimentation history and landscape evolution of western Amazonia that eventually led to the configuration of the Amazon Drainage Basin we know today.

  9. Extending the global coverage of Slab1.0 3D subduction zone models (United States)

    Seidman, L.; Hayes, G. P.


    Slab1.0 is a three-dimensional model of subduction zone geometries that covers approximately 85% of global slabs by area. It is built from an automated interpolation of a combined dataset made up from subduction-related earthquakes, moment tensors, interpretations of active source seismic data, and models of bathymetry and sediment thickness. Those subduction zones that are missing from the model are difficult to characterize with this automated approach because of sparse teleseismically located, interplate seismicity (e.g., Cascadia, Hikurangi), complex geometry (e.g., Halmahera, southern Philippine Sea), or some combination of these issues (e.g., Caribbean). Here we attempt to solve this problem with a straightforward modification of the Slab1.0 approach. Instead of constructing a series of automated spline fits to our geophysical data in two-dimensional cross sections, we produce hand-contoured two-dimensional fits; under the assumption that where seismicity is sparse or geometry complex, a human guided by tectonic knowledge can produce a better fit to geometry than can a computer algorithm. These manual 2D sections are then interpolated into a 3D surface in the same way automated 2D fits are processed for Slab1.0. Following this approach, we produce models for slabs in the Caribbean, the Makran, the Manila Trench, the Halmahera Plate, and the Hellenic Arc. We also address regions of current models (e.g., Peru) that were poorly characterized by the original automated approach. These new models thus provide valuable information on subduction zone structure from the trench and into the mantle in regions previously missing from Slab1.0, and help to make existing models more accurate, and thus more useful, than was previously possible. In turn, the models can be used to better characterize associated seismic hazards.

  10. Diapiric flow at subduction zones: a recipe for rapid transport. (United States)

    Hall, P S; Kincaid, C


    Recent geochemical studies of uranium-thorium series disequilibrium in rocks from subduction zones require magmas to be transported through the mantle from just above the subducting slab to the surface in as little as approximately 30,000 years. We present a series of laboratory experiments that investigate the characteristic time scales and flow patterns of the diapiric upwelling model of subduction zone magmatism. Results indicate that the interaction between buoyantly upwelling diapirs and subduction-induced flow in the mantle creates a network of low-density, low-viscosity conduits through which buoyant flow is rapid, yielding transport times commensurate with those indicated by uranium-thorium studies.

  11. Rheological property of mafic schist and geological interpretation to the subduction dynamics (United States)

    Okazaki, K.; Hirth, G.


    To understand the spatial and temporal distribution of deformation (e.g., underplating and exhumation of metamorphic rocks) and earthquakes in subduction zones, it is important to constrain the rheological properties of metamorphic rocks (i.e., altered oceanic crust and sediments), and how they evolve during metamorphic reactions following hydration, carbonation and dehydration of the down-going slab. Metamorphism of oceanic crust has stimulated hypotheses on the relationship between intra-slab earthquakes and slab-wedge coupling along plate boundaries in subduction zone. While it is well known that metamorphisms have important effects on material circulation and arc volcanisms at subduction system, it remains unclear how the formation of metamorphic minerals followed by fluid release on the subduction dynamics influences rheology. Past experimental studies on mafic metamorphic rocks were mostly concentrated on phase equilibrium of mineral, thus there are very few reports on the mechanical data for these metamorphic rocks. We conducted triaxial deformation experiments on a mafic greenschist using Griggs-type solid pressure-medium apparatus installed in Brown University. Mafic schist (chlorite - amphibole - epidote - albite schist) containing calcite and quartz veins from Sambagawa metamorphic belt (Japan), which is metamorphosed at the condition of nearly the corner of mantle wedge in hot subduction (1 GPa of pressure and 520C of temperature), was used as experimental samples for typical metamorphic rocks composing oceanic crust in warm subduction zones. Constant strain rete experiments and strain rate step experiment were conducted at 1.0 GPa of confining pressure, 400 ~ 500C of temperature and 10-5 ~ 5×10-7 1/s of strain rate. At stable conditions of samples (1 GPa of confining pressure and 400 and 500C of temperature), differential stresses were higher than 1 GPa. Microstructure of recovered samples showed backing and several localized shear zones. Although

  12. Geochemical and geological constraints on the composition of marine sediment pore fluid: Possible link to gas hydrate deposits

    Digital Repository Service at National Institute of Oceanography (India)

    Mazumdar, A.; Joao, H.M.; Peketi, A.; Dewangan, P.; Kocherla, M.; Joshi, R.K.; Ramprasad, T.

    -sampling (Dickens et al., 1997; Paull and Ussler III, 2001). Highly depleted carbon isotopic compositions of methane below the SMTZ (-84.8 to -100.1‰VPDB), high C1/(C2+C3) ratios (1000-6000) and ��CO2-CH4 ranging from 59.8 to 80.4‰ indicate the microbial origin...

  13. Seamount subduction at the North-Ecuadorian convergent margin: Effects on structures, inter-seismic coupling and seismogenesis (United States)

    Marcaillou, Boris; Collot, Jean-Yves; Ribodetti, Alessandra; d'Acremont, Elia; Mahamat, Ammy-Adoum; Alvarado, Alexandra


    At the North-Ecuadorian convergent margin (1°S-1.5°N), the subduction of the rough Nazca oceanic plate leads to tectonic erosion of the upper plate and complex seismogenic behavior of the megathrust. We used three selected pre-stack depth migrated, multi-channel seismic reflection lines collected during the SISTEUR cruise to investigate the margin structure and decipher the impact of the subducted Atacames seamounts on tectonic erosion, interseismic coupling, and seismogenesis in the region of the 1942 Mw7.8 earthquake. This dataset highlights a subducted ∼ 30 × 40 km, double-peak seamount that belongs to the Atacames seamount chain and that is associated with a deep morphologic re-entrant containing mass transport deposits. The seamount subduction uplifted the margin basement by ∼1.6 km and pervasively broke the margin by deep and intense reverse faulting ahead of the seamount, a process that is likely to weaken considerably the margin. In the seamount wake, the basement reverse fault system rotated counter-clockwise. This faulted basement is overlain with slope sediment sliding along listric normal faults that sole out onto the BSR. This superposition of deep tectonic contraction within the basement and shallow gravitational extension deformation within the sediment highlights the key role of gas hydrate on outer slope erosion. In addition to long-term regional basal erosion, the margin basement has thinned locally by an extra 0.8-1 km in response to the subduction of the Atacames seamount chain and hydrofracturing by overpressured fluids at the margin toe. This pervasively and deeply fractured margin segment is associated with a seismically quiet and GPS-modeled low interseismic coupling corridor that terminates downdip near the 1942 epicenter and locked zone. We suggest that the deeply buried double-peak Atacames seamount triggered the 1942 earthquake ahead of its leading flank. This result supports previous studies proposing that subducted seamounts

  14. Coastal sedimentation (United States)

    Schubel, J. R.


    Several important coastal sedimentation problems are identified. Application of existing or anticipated remote sensing techniques to examine these problems is considered. Specifically, coastal fine particle sediment systems, floods and hy hurricanes and sedimentation f of coastal systems, routes and rates of sediment transport on continental shelves, and dredging and dredged material disposal are discussed.

  15. Deep nirS amplicon sequencing of San Francisco Bay sediments enables prediction of geography and environmental conditions from denitrifying community composition. (United States)

    Lee, Jessica A; Francis, Christopher A


    Denitrification is a dominant nitrogen loss process in the sediments of San Francisco Bay. In this study, we sought to understand the ecology of denitrifying bacteria by using next-generation sequencing (NGS) to survey the diversity of a denitrification functional gene, nirS (encoding cytchrome-cd 1 nitrite reductase), along the salinity gradient of San Francisco Bay over the course of a year. We compared our dataset to a library of nirS sequences obtained previously from the same samples by standard PCR cloning and Sanger sequencing, and showed that both methods similarly demonstrated geography, salinity and, to a lesser extent, nitrogen, to be strong determinants of community composition. Furthermore, the depth afforded by NGS enabled novel techniques for measuring the association between environment and community composition. We used Random Forests modelling to demonstrate that the site and salinity of a sample could be predicted from its nirS sequences, and to identify indicator taxa associated with those environmental characteristics. This work contributes significantly to our understanding of the distribution and dynamics of denitrifying communities in San Francisco Bay, and provides valuable tools for the further study of this key N-cycling guild in all estuarine systems. © 2017 Society for Applied Microbiology and John Wiley & Sons Ltd.

  16. Imaging of the subducted Kyushu-Palau Ridge in the Hyuga-nada region, western Nankai Trough subduction zone (United States)

    Yamamoto, Yojiro; Obana, Koichiro; Takahashi, Tsutomu; Nakanishi, Ayako; Kodaira, Shuichi; Kaneda, Yoshiyuki


    We performed 3D seismic tomography of the Hyuga-nada region, western Nankai subduction zone, to investigate the relationship of the subducted part of Kyushu-Palau Ridge (KPR) to coseismic rupture propagation, seismicity, and shallow very low frequency earthquakes. Combining active-source and passive-source data recorded both onshore and offshore, we imaged the deep slab from near the trough axis to the coastal area. Our results show the subducted KPR as a low-velocity belt oriented NW-SE extending down the plate boundary to around 30 km depth. At this depth, we suggest that the subducted KPR detaches from the slab and becomes underplated on the overriding continental plate. As the coseismic slip areas of past large earthquakes do not extend into the subducted KPR, we suggest that it may inhibit rupture propagation. The interior of the subducted KPR shows active intraslab seismicity with a wide depth distribution. Shallow very low frequency earthquakes are continuously active above the location of the subducted KPR, whereas they are intermittent to the northeast of the subducted KPR. Thus, the subducted KPR appears to be an important factor in coseismic rupture propagation and seismic phenomena in this region.

  17. Ablative subduction - A two-sided alternative to the conventional subduction model (United States)

    Tao, Winston C.; O'Connell, Richard J.


    The plausibility of a two-sided fluid-based model of lithospheric subduction that is based upon current views of lithospheric structure is examined. In this model the viscous lower lithosphere flows downward, and the brittle upper lithosphere deforms in passive response. This process is potentially double-sided, since it is found that even a buoyant plate can be dragged downward by a dense descending neighbor. Thus an apparent overriding plate may be worn away by a process of viscous ablation, with the rate of ablation a function of plate buoyancy. This process, called 'ablative subduction,' makes it possible to simply interpret observations concerning slab profiles, interplate seismicity, back arc tectonics, and complex processes such as double subduction and subduction polarity reversal. When experiments modeling the evolution of simple fluid 'slabs' are performed, slab profile is found to be strongly influenced by ablation in the overriding plate. When ablation is weak, as when a buoyant continent borders the trench, deformable slabs adopt shallow Andean-style profiles.

  18. Element composition of biota, water and sediment in the Forsmark area, Baltic Sea. Concentrations, bioconcentration factors and partitioning coefficients (K{sub d}) of 48 elements

    Energy Technology Data Exchange (ETDEWEB)

    Kumblad, Linda; Bradshaw, Clare (Dept. of Systems Ecology, Stockholm Univ. (Sweden))


    In this study the elemental composition of biota, water and sediment from a shallow bay in the Forsmark region have been determined. The report presents data for 48 different elements (Al, As, Ba, Br, C, Ca, Cd, Ce, Cl, Co, Cr, Cs, Cu, Dy, Er, Eu, F, Fe, Gd, Hg, Ho, I, K, Li, Lu, Mg, Mn, N, Na, Nd, Ni, P, Pb, Pr, Ra, Rb, S, Se, Si, Sm, Tb, Th, Ti, Tm, V, Yb, Zn, Zr) in all major functional groups of the coastal ecosystem (phytoplankton, zooplankton, benthic microalgae, macroalgae, macrophytes, benthic herbivores, benthic filter feeders, benthic detrivores, planktivorous fish, benthic omnivorous fish, carnivorous fish, dissolved and particulate matter in the water and the sediment) during spring 2005. The overall aim of the study is to contribute to a better understanding of ecological properties and processes that govern uptake and transfer of trace elements, heavy-metals, radionuclides and other non-essential elements/contaminants in coastal environments of the Baltic Sea. In addition, the data was collected to provide site-specific Bioconcentration Factors (BCF), Biomagnification Factors (BMF), partitioning coefficients (K{sub d}) and element ratios (relative to carbon) for use in ongoing SKB safety assessments. All these values, as well as the element concentration data from which they are derived, are presented here. As such, this is mainly a data report, although initial interpretations of the data also are presented and discussed. Reported data include element concentrations, CNP-stoichiometry, and multivariate data analysis. Elemental concentrations varied greatly between organisms and environmental components, depending on the function of the elements, and the habitat, ecosystem function, trophic level and morphology (taxonomy) of the organisms. The results show for instance that food intake and metabolism strongly influence the elemental composition of organisms. The three macrophytes had quite similar elemental composition (despite their taxonomic

  19. Lithium Isotopic Fractionation in Subduction Zones: Clues From Clays (United States)

    Williams, L. B.; Hervig, R. L.


    Lithium isotope ratios show such large variations in nature (>30 per mil), that many areas of geosciences are exploring the usefulness of this system in explaining the evolution of particular rocks. Here we show how the lithium isotope ratios change during the transformation of smectite clay minerals to illite during burial metamorphism. Such a transition may be a common feature in the shallow regions of subduction zones and may ultimately affect the Li isotope compositions of fluids contributing to arc magmatism. Lithium is a ubiquitous trace element in natural formation waters that, like B, shows large isotopic fractionation especially during interactions with clay minerals. Lithium is adsorbed in the interlayer region of expandable clay minerals but is easily exchanged. Lithium is also incorporated into the octahedral sites. The substitutions of Li in two crystallographic sites of clay minerals may complicate interpretations of bulk Li-isotope ratios. We suggest that the magnitude of the isotopic fractionation of Li between fluid and clay is different in the interlayer sites of clay minerals than in the octahedral sites of clay minerals. Examination of Li contents and isotope variations in experimental reactions of smectite to illite (300C, 100MPa) shows changes with structural re-arrangement of the clay layers. The Li-isotope trend declines (from ~+6 to -13 per mil, expressed as ratios of 7/6) throughout R1-ordering of the mixed-layered illite smectite (I/S). However, the equilibrium end products of the reaction have R3-ordering and show a heavier isotope ratio (~0 per mil). This observation is very similar to the trends we observed for B-isotopes, where the interlayer B initially overprinted the tetrahedral-layer B isotope composition, but as the interlayer sites were collapsed during illitization, the equilibrium isotope composition was approached. The significant Li and B isotopic changes that occur during ordering of I/S coincides with the temperatures

  20. Subducting Plate Breakup by Plume-Lithosphere Interaction (United States)

    Koptev, A.; Gerya, T.; Jolivet, L.; Leroy, S. D.


    We use a 3D high-resolution thermo-mechanical modeling to investigate the impact of active mantle plume on a subducting lithospheric plate. Initial model setup consists of an overriding continental lithosphere and subducting lithospheric plate including oceanic and continental lithosphere. A mantle plume thermal anomaly has been initially seeded at the bottom of the model box underneath the continental segment of subducting plate. Mantle plume impingement on lithospheric bottom leads to thinning of continental lithosphere and decompressional melting of both lithospheric and sublithospheric mantle along stretched trench-parallel zone. Further continental breakup is followed by opening of an oceanic basin separating a newly formed microcontinent from the main subducting continent. Despite continuous push applied at the boundary of subducting plate, plume-induced oceanic basin opens during several Myrs reaching several hundred kilometers wide. Cooling of the mantle plume and beginning of collision between the separated microcontinent and the overriding continental plate lead to gradual closure of newly formed oceanic basin that gets further involved into subduction and collision. The final stage sees continental subduction of main body of subducting plate and simultaneous tectonic exhumation of the upper crust of the subducted microcontinent. This scenario involving a plume-induced rifting of a microcontinent away from main body of subducted plate can be compared to the Mesozoic-Cenozoic development of the African plate characterized by the consecutive separation of the Apulian microcontinent and Arabian plate (in the Jurassic and the Neogene, respectively) during subduction of Neo-Tethys oceanic lithosphere beneath the Eurasian margin.

  1. Dynamics of interplate domain in subduction zones: influence of rheological parameters and subducting plate age

    Directory of Open Access Journals (Sweden)

    D. Arcay


    Full Text Available The properties of the subduction interplate domain are likely to affect not only the seismogenic potential of the subduction area but also the overall subduction process, as it influences its viability. Numerical simulations are performed to model the long-term equilibrium state of the subduction interplate when the diving lithosphere interacts with both the overriding plate and the surrounding convective mantle. The thermomechanical model combines a non-Newtonian viscous rheology and a pseudo-brittle rheology. Rock strength here depends on depth, temperature and stress, for both oceanic crust and mantle rocks. I study the evolution through time of, on one hand, the brittle-ductile transition (BDT depth, zBDT, and, on the other hand, of the kinematic decoupling depth, zdec, simulated along the subduction interplate. The results show that both a high friction and a low ductile strength at the asthenospheric wedge tip shallow zBDT. The influence of the weak material activation energy is of second order but not negligible. zBDT becomes dependent on the ductile strength increase with depth (activation volume if the BDT occurs at the interplate decoupling depth. Regarding the interplate decoupling depth, it is shallowed (1 significantly if mantle viscosity at asthenospheric wedge tip is low, (2 if the difference in mantle and interplate activation energy is weak, and (3 if the activation volume is increased. Very low friction coefficients and/or low asthenospheric viscosities promote zBDT = zdec. I then present how the subducting lithosphere age affects the brittle-ductile transition depth and the kinematic decoupling depth in this model. Simulations show that a rheological model in which the respective activation energies of mantle and interplate material are too close hinders the mechanical decoupling at the down-dip extent of the interplate

  2. Uplift of the Colorado Plateau due to lithosphere attenuation during Laramide low-angle subduction (United States)

    Spencer, J.E.


    The Colorado Plateau is blanketed by Phanerozoic marine and nonmarine strata as young as Cretaceous that are now exposed at elevations of about 2 km. Crustal thickening due to magmatism and horizontal crustal shortening was far less than necessary to cause this uplift, which is commonly attributed to the consequences of mantle lithosphere thinning and heating. The Colorado Plateau and the midcontinent region around Iowa consist of Precambrian bedrock overlain by a similar amount of Paleozoic platformal strata, and thus both regions once had similar lithospheric buoyancy. Mesozoic sedimentation increased the crustal thickness and lithospheric buoyancy of the Colorado Plateau relative to the midcontinent region. Backstripping calculations yield elevation without these sediments and lead to a calculated elevation difference between the two areas of about 1200 m, which represents unexplained plateau uplift. Review of constraints on uplift timing finds little support for a late Cenozoic uplift age and allows early to middle Cenozoic uplift, which is consistent with uplift mechanisms related to low-angle subduction that ended in the middle Cenozoic. Finite element heat flow calculations of low-angle subduction and lithosphere attenuation, using a range of initial lithosphere thicknesses and degree of attenuation, indicate that required uplift can result from tectonic removal of about 120 km of mantle lithosphere from an initially 200-km-thick lithosphere. This allows for partial preservation of North American mantle lithosphere with its distinctive isotopic signature in some late Cenozoic volcanic rocks and is consistent with normal Pn velocities in the uppermost mantle beneath the plateau.

  3. Mesoscale ocean fronts enhance carbon export due to gravitational sinking and subduction. (United States)

    Stukel, Michael R; Aluwihare, Lihini I; Barbeau, Katherine A; Chekalyuk, Alexander M; Goericke, Ralf; Miller, Arthur J; Ohman, Mark D; Ruacho, Angel; Song, Hajoon; Stephens, Brandon M; Landry, Michael R


    Enhanced vertical carbon transport (gravitational sinking and subduction) at mesoscale ocean fronts may explain the demonstrated imbalance of new production and sinking particle export in coastal upwelling ecosystems. Based on flux assessments from (238)U:(234)Th disequilibrium and sediment traps, we found 2 to 3 times higher rates of gravitational particle export near a deep-water front (305 mg C⋅m(-2)⋅d(-1)) compared with adjacent water or to mean (nonfrontal) regional conditions. Elevated particle flux at the front was mechanistically linked to Fe-stressed diatoms and high mesozooplankton fecal pellet production. Using a data assimilative regional ocean model fit to measured conditions, we estimate that an additional ∼225 mg C⋅m(-2)⋅d(-1) was exported as subduction of particle-rich water at the front, highlighting a transport mechanism that is not captured by sediment traps and is poorly quantified by most models and in situ measurements. Mesoscale fronts may be responsible for over a quarter of total organic carbon sequestration in the California Current and other coastal upwelling ecosystems.

  4. Zinc isotope evidence for sulfate-rich fluid transfer across subduction zones (United States)

    Pons, Marie-Laure; Debret, Baptiste; Bouilhol, Pierre; Delacour, Adélie; Williams, Helen


    Subduction zones modulate the chemical evolution of the Earth's mantle. Water and volatile elements in the slab are released as fluids into the mantle wedge and this process is widely considered to result in the oxidation of the sub-arc mantle. However, the chemical composition and speciation of these fluids, which is critical for the mobility of economically important elements, remain poorly constrained. Sulfur has the potential to act both as oxidizing agent and transport medium. Here we use zinc stable isotopes (δ66Zn) in subducted Alpine serpentinites to decipher the chemical properties of slab-derived fluids. We show that the progressive decrease in δ66Zn with metamorphic grade is correlated with a decrease in sulfur content. As existing theoretical work predicts that Zn-SO42- complexes preferentially incorporate heavy δ66Zn, our results provide strong evidence for the release of oxidized, sulfate-rich, slab serpentinite-derived fluids to the mantle wedge.

  5. Zinc isotope evidence for sulfate-rich fluid transfer across subduction zones. (United States)

    Pons, Marie-Laure; Debret, Baptiste; Bouilhol, Pierre; Delacour, Adélie; Williams, Helen


    Subduction zones modulate the chemical evolution of the Earth's mantle. Water and volatile elements in the slab are released as fluids into the mantle wedge and this process is widely considered to result in the oxidation of the sub-arc mantle. However, the chemical composition and speciation of these fluids, which is critical for the mobility of economically important elements, remain poorly constrained. Sulfur has the potential to act both as oxidizing agent and transport medium. Here we use zinc stable isotopes (δ(66)Zn) in subducted Alpine serpentinites to decipher the chemical properties of slab-derived fluids. We show that the progressive decrease in δ(66)Zn with metamorphic grade is correlated with a decrease in sulfur content. As existing theoretical work predicts that Zn-SO4(2-) complexes preferentially incorporate heavy δ(66)Zn, our results provide strong evidence for the release of oxidized, sulfate-rich, slab serpentinite-derived fluids to the mantle wedge.

  6. Subduction of hydrated basalt of the oceanic crust: Implications for recycling of water into the upper mantle and continental growth (United States)

    Rapp, R. P.


    Subduction zones are presently the dominant sites on Earth for recycling and mass transfer between the crust and mantle; they feed hydrated basaltic oceanic crust into the upper mantle, where dehydration reactions release aqueous fluids and/or hydrous melts. The loci for fluid and/or melt generation will be determined by the intersection of dehydration reaction boundaries of primary hydrous minerals within the subducted lithosphere with slab geotherms. For metabasalt of the oceanic crust, amphibole is the dominant hydrous mineral. The dehydration melting solidus, vapor-absent melting phase relationships; and amphibole-out phase boundary for a number of natural metabasalts have been determined experimentally, and the pressure-temperature conditions of each of these appear to be dependent on bulk composition. Whether or not the dehydration of amphibole is a fluid-generating or partial melting reaction depends on a number of factors specific to a given subduction zone, such as age and thickness of the subducting oceanic lithosphere, the rate of convergence, and the maturity of the subduction zone. In general, subduction of young, hot oceanic lithosphere will result in partial melting of metabasalt of the oceanic crust within the garnet stability field; these melts are characteristically high-Al2O3 trondhjemites, tonalites and dacites. The presence of residual garnet during partial melting imparts a distinctive trace element signature (e.g., high La/Yb, high Sr/Y and Cr/Y combined with low Cr and Y contents relative to demonstrably mantle-derived arc magmas). Water in eclogitized, subducted basalt of the oceanic crust is therefore strongly partitioned into melts generated below about 3.5 GPa in 'hot' subduction zones. Although phase equilibria experiments relevant to 'cold' subduction of hydrated natural basalts are underway in a number of high-pressure laboratories, little is known with respect to the stability of more exotic hydrous minerals (e.g., ellenbergite) and

  7. Composition and sediment dispersal pattern of the Upper Triassic flysch in the eastern Himalayas, China: significance to provenance and basin analysis (United States)

    Zhang, Chaokai; Li, Xianghui; Mattern, Frank; Zeng, Qinggao; Mao, Guozheng


    The paleogeography and basin type of Upper Triassic flysch (Langjiexue Group) in the eastern Himalayan Orogen are disputed. In order to shed new light on the flysch's origin, we applied different sedimentological methods. Assemblages of heavy minerals and clastic components of sandstones were utilized to determine the primary depositional composition. Heavy mineral indices, S/M ratios (thickness of sandstone + siltstone "S" versus slate/mudrock "M"), and paleocurrent data were combined to reveal the sediment dispersal pattern and the location of the source areas. In the analyzed sandstones, heavy minerals such as zircon, rutile, tourmaline, apatite, and anatase are most common, and zircon is predominant (most over 60 %). ZTR values range from 60 to 98 % and systematically increase southward. As a provenance-sensitive parameter, RuZi values vary in large magnitude and are significantly higher in both the east and west (>20 %) than in the center. The majority of S/M ratios decrease from north to south, suggesting an overall decrease in grain size to the south. Paleocurrent directions vary between 120° and 270° (main vector 205°, and 185° after 20° counterclockwise correction), displaying a radial-curved pattern. Variable heavy mineral assemblages indicate different sources, and the sandstones fall in the "recycled" and "mixed-arc orogeny" fields of Dickinson triplots, together supporting the view of multiple sources. Results of the ZTR values, S/M ratios, and paleocurrent directions illustrate a dispersal pattern, corresponding to a submarine fan system. The provenance and submarine fan dispersal pattern along with the basin configuration (deep basin with oceanic affinities) suggest that the Langjiexue Group accumulated in a remnant basin between Lhasa, Greater India, and Australia, where the sediments dispersed into the basin toward the developing orogen/suture zone and not away from the orogen, challenging the provenance direction for the traditional remnant

  8. Composition

    DEFF Research Database (Denmark)

    Bergstrøm-Nielsen, Carl


    Cue Rondo is an open composition to be realised by improvising musicians. See more about my composition practise in the entry "Composition - General Introduction". Caution: streaming the sound/video files will in some cases only provide a few minutes' sample, or the visuals will not appear at all...

  9. Composition

    DEFF Research Database (Denmark)

    Bergstrøm-Nielsen, Carl


    Strategies are open compositions to be realised by improvising musicians. See more about my composition practise in the entry "Composition - General Introduction". Caution: streaming the sound files will in some cases only provide a few minutes' sample. Please DOWNLOAD them to hear them in full...

  10. Composition

    DEFF Research Database (Denmark)

    Bergstrøm-Nielsen, Carl


    New Year is an open composition to be realised by improvising musicians. It is included in "From the Danish Seasons" (see under this title). See more about my composition practise in the entry "Composition - General Introduction". This work is licensed under a Creative Commons "by-nc" License. You...

  11. Composition

    DEFF Research Database (Denmark)


    Memory Pieces are open compositions to be realised solo by an improvising musicians. See more about my composition practise in the entry "Composition - General Introduction". Caution: streaming the sound files will in some cases only provide a few minutes' sample. Please DOWNLOAD them to hear them...

  12. Synoptic conditions of fine-particle transport to the last interglacial Red Sea-Dead Sea from Nd-Sr compositions of sediment cores (United States)

    Palchan, Daniel; Stein, Mordechai; Goldstein, Steven L.; Almogi-Labin, Ahuva; Tirosh, Ofir; Erel, Yigal


    The sediments deposited at the depocenter of the Dead Sea comprise high-resolution archive of hydrological changes in the lake's watershed and record the desert dust transport to the region. This paper reconstructs the dust transport to the region during the termination of glacial Marine Isotope Stage 6 (MIS 6; ∼135-129 ka) and the last interglacial peak period (MIS5e, ∼129-116 ka). We use chemical and Nd and Sr isotope compositions of fine detritus material recovered from sediment core drilled at the deepest floor of the Dead Sea. The data is integrated with data achieved from cores drilled at the floor of the Red Sea, thus, forming a Red Sea-Dead Sea transect extending from the desert belt to the Mediterranean climate zone. The Dead Sea accumulated flood sediments derived from three regional surface cover types: settled desert dust, mountain loess-soils and loess-soils filling valleys in the Dead Sea watershed termed here "Valley Loess". The Valley Loess shows a distinct 87Sr/86Sr ratio of 0.7081 ± 1, inherited from dissolved detrital calcites that originate from dried waterbodies in the Sahara and are transported with the dust to the entire transect. Our hydro-climate and synoptic conditions reconstruction illustrates the following history: During glacial period MIS6, Mediterranean cyclones governed the transport of Saharan dust and rains to the Dead Sea watershed, driving the development of both mountain soils and Valley Loess. Then, at Heinrich event 11, dry western winds blew Saharan dust over the entire Red Sea - Dead Sea transect marking latitudinal expansion of the desert belt. Later, when global sea-level rose, the Dead Sea watershed went through extreme aridity, the lake retreated, depositing salt and accumulating fine detritus of the Valley Loess. During peak interglacial MIS 5e, enhanced flooding activity flushed the mountain soils and fine detritus from all around the Dead Sea and Red Sea, marking a significant "contraction" of the desert belt

  13. GPS Monitoring of Subduction Zone Deformation in Costa Rica (United States)

    Lundgren, Paul


    The subduction of the Cocos plate beneath Costa Rica is among the highest convergence rates in the world. The high subduction rate and nearness of the Nicoya Peninsula, Costa Rica to the Middle America Trench (MAT) provide a unique opportunity to map variations in interseismic strain of the crust above the seismogenic zone in response to variations in seismic coupling.

  14. The subduction dichotomy of strong plates and weak slabs (United States)

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


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

  15. Slab detachment of subducted Indo-Australian plate beneath Sunda ...

    Indian Academy of Sciences (India)

    2007). We investigate the northward subduction of the. Indo-Australian plate along the eastern Sunda arc right from northwestern Sumatra, along Java to. Keywords. Slab detachment; subduction zone; Sunda arc; Indo-Australian slab; trench migration. J. Earth Syst. Sci. 120, No. 2, April 2011, pp. 193–204 c Indian Academy ...

  16. The Run-Up of Subduction Zones (United States)

    Riquelme, S.; Bravo, F. J.; Fuentes, M.; Matias, M.; Medina, M.


    Large earthquakes in subduction zones are liable to produce tsunamis that can cause destruction and fatalities. The Run-up is a geophysical parameter that quantifies damage and if critical facilities or population are exposed to. Here we use the coupling for certain subduction regions measured by different techniques (Potency and GPS observations) to define areas where large earthquakes can occur. Taking the slab 1.0 from the United States Geological Survey (USGS), we can define the geometry of the area including its tsunamigenic potential. By using stochastic earthquakes sources for each area with its maximum tsunamigenic potential, we calculate the numerical and analytical run-up for each case. Then, we perform a statistical analysis and calculate the envelope for both methods. Furthermore, we build an index of risk using: the closest slope to the shore in a piecewise linear approach (last slopecriteria) and the outputsfrom tsunami modeling. Results show that there are areas prone to produce higher run-up than others based on the size of the earthquake, geometrical constraints of the source, tectonic setting and the coast last slope. Based on these results, there are zones that have low risk index which can define escape routes or secure coastal areas for tsunami early warning, urban and planning purposes when detailed data is available.

  17. Sr–Nd isotope composition of the Bay of Bengal sediments: Impact of climate on erosion in the Himalaya

    Digital Repository Service at National Institute of Oceanography (India)

    Tripathy, G.R.; Singh, S.K.; Bhushan, R.; Ramaswamy, V.

    /Al and V/Al ratios) and Sr and Nd isotope compositions. 2. MATERIALS AND METHODS The samples for this study are from a 12.8 m long piston core (SK187/PC33) collected from the western BoB (16 º 16′ N, 84 º 30′ E; Fig. 1;) during the 187 th... carbonate samples were reanalyzed after treating them one more time with 0.6 N HCl. The decarbonated and washed samples were ashed at 600ºC to combust the organic matter. The residue (silicate phase), spiked with 84 Sr and 150 Nd, was digested with HF...

  18. Viscous Dissipation and Criticality of Subducting Slabs (United States)

    Riedel, Mike; Karato, Shun; Yuen, Dave


    Rheology of subducting lithosphere appears to be complicated. In the shallow part, deformation is largely accomodated by brittle failure, whereas at greater depth, at higher confining pressures, ductile creep is expected to control slab strength. The amount of viscous dissipation ΔQ during subduction at greater depth, as constrained by experimental rock mechanics, can be estimated on the basis of a simple bending moment equation [1,2] 2ɛ˙0(z) ∫ +h/2 2 M (z) = h ṡ -h/2 4μ(y,z)y dy , (1) for a complex multi-phase rheology in the mantle transition zone, including the effects of a metastable phase transition as well as the pressure, temperature, grain-size and stress dependency of the relevant creep mechanisms; μ is here the effective viscosity and ɛ˙0(z) is a (reference) strain rate. Numerical analysis shows that the maximum bending moment, Mcrit, that can be sustained by a slab is of the order of 1019 Nm per m according to Mcrit˜=σp ∗h2/4, where σp is the Peierl's stress limit of slab materials and h is the slab thickness. Near Mcrit, the amount of viscous dissipation grows strongly as a consequence of a lattice instability of mantle minerals (dislocation glide in olivine), suggesting that thermo-mechanical instabilities become prone to occur at places where a critical shear-heating rate is exceeded, see figure. This implies that the lithosphere behaves in such cases like a perfectly plastic solid [3]. Recently available detailed data related to deep seismicity [4,5] seems to provide support to our conclusion. It shows, e.g., that thermal shear instabilities, and not transformational faulting, is likely the dominating mechanism for deep-focus earthquakes at the bottom of the transition zone, in accordance with this suggested "deep criticality" model. These new findings are therefore briefly outlined and possible implications are discussed. References [1] Riedel, M. R., Karato, S., Yuen, D. A. Criticality of Subducting Slabs. University of Minnesota

  19. Nitrogen evolution within the Earth's atmosphere-mantle system assessed by recycling in subduction zones (United States)

    Mallik, Ananya; Li, Yuan; Wiedenbeck, Michael


    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

  20. Dynamic Linkages Between the Transition Zone & Surface Plate Motions in 2D Models of Subduction (United States)

    Arredondo, K.; Billen, M. I.


    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

  1. Multichannel Seismic Imaging of the Rivera Plate Subduction at the Seismogenic Jalisco Block Area (Western Mexican Margin) (United States)

    Bartolome, R.; Gorriz, E.; Danobeitia, J.; Barba, D. C., Sr.; Martí, D.; L Cameselle, A.; Nuñez-Cornu, F. J.; Bandy, W. L.; Mortera, C.; Nunez, D.; Alonso, J. L.; Castellon, A.; Prada, M.


    During the TSUJAL marine geophysical survey, conducted in February and March 2014 Spanish, Mexican and British scientists and technicians explored the western margin of Mexico, considered one of the most active seismic zones in America. This work aims to characterize the internal structure of the subduction zone of the Rivera plate beneath the North American plate in the offshore part of the Jalisco Block, to link the geodynamic and the recent tectonic deformation occurring there with the possible generation of tsunamis and earthquakes. For this purpose, it has been carried out acquisition, processing and geological interpretation of a multichannel seismic reflection profile running perpendicular to the margin. Crustal images show an oceanic domain, dominated by subduction-accretion along the lower slope of the margin with a subparallel sediment thickness of up to 1.6 s two way travel time (approx. 2 km) in the Middle American Trench. Further, from these data the region appears to be prone to giant earthquake production. The top of the oceanic crust (intraplate reflector) is very well imaged. It is almost continuous along the profile with a gentle dip (<10°); however, it is disrupted by normal faulting resulting from the bending of the plate during subduction. The continental crust presents a well-developed accretionary prism consisting of highly deformed sediments with prominent slumping towards the trench that may be the result of past tsunamis. Also, a Bottom Simulating Reflector (BSR) is identified in the first half a second (twtt) of the section. High amplitude reflections at around 7-8 s twtt clearly image a discontinuous Moho, defining a very gentle dipping subduction plane.

  2. Segmentation of plate coupling, fate of subduction fluids, and modes of arc magmatism in Cascadia, inferred from magnetotelluric resistivity (United States)

    Wannamaker, Philip E.; Evans, Rob L.; Bedrosian, Paul A.; Unsworth, Martyn J.; Maris, Virginie; McGary, R. Shane


    Five magnetotelluric (MT) profiles have been acquired across the Cascadia subduction system and transformed using 2-D and 3-D nonlinear inversion to yield electrical resistivity cross sections to depths of ∼200 km. Distinct changes in plate coupling, subduction fluid evolution, and modes of arc magmatism along the length of Cascadia are clearly expressed in the resistivity structure. Relatively high resistivities under the coasts of northern and southern Cascadia correlate with elevated degrees of inferred plate locking, and suggest fluid- and sediment-deficient conditions. In contrast, the north-central Oregon coastal structure is quite conductive from the plate interface to shallow depths offshore, correlating with poor plate locking and the possible presence of subducted sediments. Low-resistivity fluidized zones develop at slab depths of 35–40 km starting ∼100 km west of the arc on all profiles, and are interpreted to represent prograde metamorphic fluid release from the subducting slab. The fluids rise to forearc Moho levels, and sometimes shallower, as the arc is approached. The zones begin close to clusters of low-frequency earthquakes, suggesting fluid controls on the transition to steady sliding. Under the northern and southern Cascadia arc segments, low upper mantle resistivities are consistent with flux melting above the slab plus possible deep convective backarc upwelling toward the arc. In central Cascadia, extensional deformation is interpreted to segregate upper mantle melts leading to underplating and low resistivities at Moho to lower crustal levels below the arc and nearby backarc. The low- to high-temperature mantle wedge transition lies slightly trenchward of the arc.

  3. Sedimentation field-flow fractionation for characterization of citric acid-modified Hβ zeolite particles: Effect of particle dispersion and carrier composition. (United States)

    Dou, Haiyang; Bai, Guoyi; Ding, Liang; Li, Yueqiu; Lee, Seungho


    In this study, sedimentation field-flow fractionation (SdFFF) was, for the first time, applied for determination of size distribution of Hβ zeolite particles modified by citric acid (CA-Hβ). Effects of the particle dispersion and the carrier liquid composition (type of dispersing reagent (surfactant) and salt added in the carrier liquid, ionic strength, and pH) on SdFFF elution behavior of CA-Hβ zeolite particles were systematically investigated. Also the SdFFF separation efficiency of the particles was discussed in terms of the forces such as van der Waals, hydrophobic, and induced-dipole interactions. Results reveal that the type of salt and pH of the carrier liquid significantly affect the SdFFF separation efficiency of the zeolite particles. It was found that addition of a salt (NaN3) into the carrier liquid affects the characteristic of the SdFFF channel surface. It was found that the use of an acidic medium (pH 3.2) leads to a particle-channel interaction, while the use of a basic medium (pH 10.6) promotes an inter-particle hydrophobic interaction. Result from SdFFF was compared with those from scanning electron microscopy (SEM) and dynamic light scattering (DLS). It seems that, once the experimental conditions are optimized, SdFFF becomes a valuable tool for size characterization of the zeolite particles. Copyright © 2015 Elsevier B.V. All rights reserved.

  4. Isotopic Composition of Carbon Dioxide Released from Confidence Hills Sediment as Measured by the Sample Analysis at Mars (SAM) Quadrupole Mass Spectrometer (United States)

    Franz, H. B.; Mahaffy, P. R.; Stern, J.; Archer, P., Jr.; Conrad, P.; Eigenbrode, J.; Freissinet, C.; Glavin, D.; Grotzinger, J. P.; Jones, J.; hide


    In October 2014, the Mars Science Laboratory (MSL) "Curiosity" rover drilled into the sediment at the base of Mount Sharp in a location namsed Cionfidence Hills (CH). CH marked the fifth sample pocessed by the Sample Analysis at Mars (SAM) instrument suite since Curiosity arrived in Gale Crater, with previous analyses performed at Rocknest (RN), John Klein (JK), Cumberland (CB), and Windjana (WJ). Evolved gas analysis (EGA) of all samples has indicated H2O as well as O-, C- and S-bearing phases in the samples, often at abundances that would be below the detection limit of the CheMin instrument. By examining the temperatures at which gases are evolved from samples, SAM EGA data can help provide clues to the mineralogy of volatile-bearing phases when their identities are unclear to CheMin. SAM may also detect gases evolved from amorphous material in solid samples, which is not suitable for analysis by CheMin. Finally, the isotopic composition of these gases may suggest possible formation scenarios and relationships between phases. We will discuss C isotope ratios of CO2 evolved from the CH sample as measured with SAM's quadrupole mass spectrometer (QMS) and draw comparisons to samples previously analyzed by SAM.

  5. Characterization of the water chemistry, sediment (13)C and (18)O compositions of Kolleru Lake-a Ramsar wetland in Andhra Pradesh, India. (United States)

    Das Sharma, Subrata; Sujatha, D


    The chemistry of surface water sampled at different locations of the Kolleru Lake in Andhra Pradesh (India) show heterogeneous variability. The concentrations of dissolved sodium and chloride ions, total dissolved solids (TDS) together with high conductivity documented in water samples are indicative of mixing of saline seawater. This interpretation is further corroborated by enriched δ(18)O compositions of the carbonate fraction of the surface sediments collected at the same locations (as that of water) of the lake, and fairly good positive correlations of δ(18)O -Na(+) and δ(18)O-TDS. The saline water intrusion into the lake appears to be resulted due to its near stagnant to dry condition with reduced inflow and outflow. Such dry condition facilitated seawater intrusion into the lake due to several reasons: (i) proximity of lake to the sea (~35 km), (ii) overexploitation of fresh groundwater for agriculture as well as livestock farming, and (iii) incursion of tidal seawater (high sea waves) through Upputeru River, which is directly linked to the sea. We also document highly heterogeneous distribution of certain potentially toxic metal ions like chromium, copper, manganese, and zinc in the lake waters. Indiscriminate disposal of domestic and industrial effluents around the lake appears to be responsible for the presence of potentially toxic heavy metals. Based on these results, we finally suggest some measures for environmental rehabilitation of the lake and its surroundings.

  6. Growth of early continental crust controlled by melting of amphibolite in subduction zones. (United States)

    Foley, Stephen; Tiepolo, Massimo; Vannucci, Riccardo


    It is thought that the first continental crust formed by melting of either eclogite or amphibolite, either at subduction zones or on the underside of thick oceanic crust. However, the observed compositions of early crustal rocks and experimental studies have been unable to distinguish between these possibilities. Here we show a clear contrast in trace-element ratios of melts derived from amphibolites and those from eclogites. Partial melting of low-magnesium amphibolite can explain the low niobium/tantalum and high zirconium/samarium ratios in melts, as required for the early continental crust, whereas the melting of eclogite cannot. This indicates that the earliest continental crust formed by melting of amphibolites in subduction-zone environments and not by the melting of eclogite or magnesium-rich amphibolites in the lower part of thick oceanic crust. Moreover, the low niobium/tantalum ratio seen in subduction-zone igneous rocks of all ages is evidence that the melting of rutile-eclogite has never been a volumetrically important process.

  7. Tracing carbonate-silicate interaction during subduction using magnesium and oxygen isotopes. (United States)

    Wang, Shui-Jiong; Teng, Fang-Zhen; Li, Shu-Guang


    Subduction of carbonates and carbonated eclogites into the mantle plays an important role in transporting carbon into deep Earth. However, to what degree isotopic exchanges occur between carbonate and silicate during subduction remains unclear. Here we report Mg and O isotopic compositions for ultrahigh pressure metamorphic marbles and enclosed carbonated eclogites from China. These marbles include both calcite- and dolomite-rich examples and display similar O but distinct Mg isotopic signatures to their protoliths. Their δ(26)Mg values vary from -2.508 to -0.531‰, and negatively correlate with MgO/CaO ratios, unforeseen in sedimentary carbonates. Carbonated eclogites have extremely heavy δ(18)O (up to +21.1‰) and light δ(26)Mg values (down to -1.928‰ in garnet and -0.980‰ in pyroxene) compared with their protoliths. These unique Mg-O isotopic characteristics reflect differential isotopic exchange between eclogites and carbonates during subduction, making coupled Mg and O isotopic studies potential tools for tracing deep carbon recycling.

  8. Carbon and Sulfur Isotopic Composition of Yellowknife Bay Sediments: Measurements by the Sample Analysis at Mars (SAM) Quadrupole Mass Spectrometer (United States)

    Franz, H. B.; Mahaffy, P. R.; Stern, J. C.; Eigenbrode, J. L.; Steele, A.; Ming, D. W.; McAdam, A. C.; Freissinet, C.; Glavin, D. P.; Archer, P. D.; hide


    Since landing at Gale Crater in Au-gust 2012, the Sample Analysis at Mars (SAM) instru-ment suite on the Mars Science Laboratory (MSL) “Curiosity” rover has analyzed solid samples from the martian regolith in three locations, beginning with a scoop of aeolian deposits from the Rocknest (RN) sand shadow. Curiosity subsequently traveled to Yellowknife Bay, where SAM analyzed samples from two separate holes drilled into the Sheepbed Mudstone, designated John Klein (JK) and Cumberland (CB). Evolved gas analysis (EGA) of all samples revealed the presence of H2O as well as O-, C- and S-bearing phas-es, in most cases at abundances below the detection limit of the CheMin instrument. In the absence of definitive mineralogical identification by CheMin, SAM EGA data can help provide clues to the mineralogy of volatile-bearing phases through examination of tem-peratures at which gases are evolved from solid sam-ples. In addition, the isotopic composition of these gas-es may be used to identify possible formation scenarios and relationships between phases. Here we report C and S isotope ratios for CO2 and SO2 evolved from the JK and CB mudstone samples as measured with SAM’s quadrupole mass spectrometer (QMS) and draw com-parisons to RN.

  9. Cascadia subduction tremor muted by crustal faults (United States)

    Wells, Ray; Blakely, Richard J.; Wech, Aaron G.; McCrory, Patricia A.; Michael, Andrew


    Deep, episodic slow slip on the Cascadia subduction megathrust of western North America is accompanied by low-frequency tremor in a zone of high fluid pressure between 30 and 40 km depth. Tremor density (tremor epicenters per square kilometer) varies along strike, and lower tremor density statistically correlates with upper plate faults that accommodate northward motion and rotation of forearc blocks. Upper plate earthquakes occur to 35 km depth beneath the faults. We suggest that the faults extend to the overpressured megathrust, where they provide fracture pathways for fluid escape into the upper plate. This locally reduces megathrust fluid pressure and tremor occurrence beneath the faults. Damping of tremor and related slow slip caused by fluid escape could affect fault properties of the megathrust, possibly influencing the behavior of great earthquakes.

  10. The north-subducting Rheic Ocean during the Devonian: consequences for the Rhenohercynian ore sites (United States)

    von Raumer, Jürgen F.; Nesbor, Heinz-Dieter; Stampfli, Gérard M.


    Base metal mining in the Rhenohercynian Zone has a long history. Middle-Upper Devonian to Lower Carboniferous sediment-hosted massive sulfide deposits (SHMS), volcanic-hosted massive sulfide deposits (VHMS) and Lahn-Dill-type iron, and base metal ores occur at several sites in the Rhenohercynian Zone that stretches from the South Portuguese Zone, through the Lizard area, the Rhenish Massif and the Harz Mountain to the Moravo-Silesian Zone of SW Bohemia. During Devonian to Early Carboniferous times, the Rhenohercynian Zone is seen as an evolving rift system developed on subsiding shelf areas of the Old Red continent. A reappraisal of the geotectonic setting of these ore deposits is proposed. The Middle-Upper Devonian to Early Carboniferous time period was characterized by detrital sedimentation, continental intraplate and subduction-related volcanism. The large shelf of the Devonian Old Red continent was the place of thermal subsidence with contemporaneous mobilization of rising thermal fluids along activated Early Devonian growth faults. Hydrothermal brines equilibrated with the basement and overlying Middle-Upper Devonian detrital deposits forming the SHMS deposits in the southern part of the Pyrite Belt, in the Rhenish Massif and in the Harz areas. Volcanic-hosted massive sulfide deposits (VHMS) formed in the more eastern localities of the Rhenohercynian domain. In contrast, since the Tournaisian period of ore formation, dominant pull-apart triggered magmatic emplacement of acidic rocks, and their metasomatic replacement in the apical zones of felsic domes and sediments in the northern part of the Iberian Pyrite belt, thus changing the general conditions of ore precipitation. This two-step evolution is thought to be controlled by syn- to post-tectonic phases in the Variscan framework, specifically by the transition of geotectonic setting dominated by crustal extension to a one characterized by the subduction of the supposed northern slab of the Rheic Ocean


    African Journals Online (AJOL)

    An effective medium theory of ferroelectric ceramic-polymer composite materials which treats both components symmetrically has been investigated to demonstrate the role played by the microgeometry of inclusions on dielectric, mechanical and piezoelectric properties of 0-3 composites. The limits of the various theoretical ...

  12. Primary carbonatite melt from deeply subducted oceanic crust

    Energy Technology Data Exchange (ETDEWEB)

    Walter, M.J.; Bulanova, G.P.; Armstrong, L.S.; Keshav, S.; Blundy, J.D.; Gudfinnesson, G.; Lord, O.T.; Lennie, A.R.; Clark, S.M.; Smith, C.B.; Gobbo, L.


    Partial melting in the Earth's mantle plays an important part in generating the geochemical and isotopic diversity observed in volcanic rocks at the surface. Identifying the composition of these primary melts in the mantle is crucial for establishing links between mantle geochemical 'reservoirs' and fundamental geodynamic processes. Mineral inclusions in natural diamonds have provided a unique window into such deep mantle processes. Here they provide exper8imental and geochemical evidence that silicate mineral inclusions in diamonds from Juina, Brazil, crystallized from primary and evolved carbonatite melts in the mantle transition zone and deep upper mantle. The incompatible trace element abundances calculated for a melt coexisting with a calcium-titanium-silicate perovskite inclusion indicate deep melting of carbonated oceanic crust, probably at transition-zone depths. Further to perovskite, calcic-majorite garnet inclusions record crystallization in the deep upper mantle from an evolved melt that closely resembles estimates of primitive carbonatite on the basis of volcanic rocks. Small-degree melts of subducted crust can be viewed as agents of chemical mass-transfer in the upper mantle and transition zone, leaving a chemical imprint of ocean crust that can possibly endure for billions of years.

  13. Subduction initiation close to the continental margin? Implications from U-Pb zircon geochronology of the Pιnarbaşι metamorphic sole, central Turkey (United States)

    Peters, Kalijn; van Hinsbergen, Douwe J. J.; Corfu, Fernando; Gurer, Derya; Brouwer, Fraukje M.; van Roermund, Herman L. M.


    Metamorphic soles below ophiolites record high (up to 850°C) metamorphic temperatures at pressures up to 10-15 kbar uncommon in normal subduction zones. They are therefore interpreted to form during intra-oceanic subduction initiation at locations within ocean basins where high temperatures exist at relatively shallow depths, i.e. in the vicinity of mid-ocean ridges. The Pιnarbaşι metamorphic sole in Turkey is a particularly well-preserved example and consists of a sequence a few hundred meters thick of strongly foliated metabasites and pelagic sediments. The sole structurally overlies a serpentinite-hosted tectonic mélange, and underlies the mantle section of the supra-subduction zone Pιnarbaşι ophiolite. The sole rocks preserve an inverted metamorphic field gradient with garnet-clinopyroxene-amphibolites at the top and greenschists at the contact with the underlying tectonic mélange. The Pιnarbaşι sole thus fits well in the general tectonostratigraphy and metamorphic facies of soles worldwide, generally interpreted to represent the top of a nascent intra-oceanic subducting slab that accreted to the base of the hot overriding oceanic plate. This implies that the metamorphic sole could yield constraints on the initiation of subduction in an oceanic domain, something that is not yet well understood. One of the remaining questions is: did subduction start at, close to or further away from the mid oceanic ridge? The age of metamorphic soles has commonly been dated by 40Ar/39Ar chronology. Across Turkey, soles consistently provide Ar-Ar ages of 94-91 Ma, interpreted as cooling of the soles during exhumation and subduction zone maturation. In the top of the metamorphic sole of the Pιnarbaşι ophiolite we found zircon which indicate a preliminary U-Pb ID-TIMS age in the comparable range of 94 - 91 Ma, which we interpreted as the age of peak metamorphism in the garnet-clinopyroxene amphibolites. Surprisingly, the zircon grains also include inherited cores

  14. Smectite reactions and slip instabilities in subduction zones (United States)

    Gadenne, Leslie; Raimbourg, Hugues; Champallier, Remi; Yamamoto, Yuzuru


    instabilities in natural conditions, as (1) smectite is a major component of subducted sediments and (2) its transformation into illite may occur over a large depth range.

  15. The initiation of subduction: criticality by addition of water? (United States)

    Regenauer-Lieb, K; Yuen, D A; Branlund, J


    Subduction is a major process of plate tectonics; however, its initiation is not understood. We used high-resolution (less than 1 kilometer) finite-element models based on rheological data of the lithosphere to investigate the role played by water on initiating subduction. A solid-fluid thermomechanical instability is needed to drive a cold, stiff, and negatively buoyant lithosphere into the mantle. This instability can be triggered slowly by sedimentary loading over a time span of 100 million years. Our results indicate that subduction can proceed by a double feedback mechanism (thermoelastic and thermal-rheological) promoted by lubrication due to water.

  16. Deformation cycles of subduction earthquakes in a viscoelastic Earth. (United States)

    Wang, Kelin; Hu, Yan; He, Jiangheng


    Subduction zones produce the largest earthquakes. Over the past two decades, space geodesy has revolutionized our view of crustal deformation between consecutive earthquakes. The short time span of modern measurements necessitates comparative studies of subduction zones that are at different stages of the deformation cycle. Piecing together geodetic 'snapshots' from different subduction zones leads to a unifying picture in which the deformation is controlled by both the short-term (years) and long-term (decades and centuries) viscous behaviour of the mantle. Traditional views based on elastic models, such as coseismic deformation being a mirror image of interseismic deformation, are being thoroughly revised.

  17. Estimation of seismic velocity in the subducting crust of the Pacific slab beneath Hokkaido, northern Japan by using guided waves (United States)

    Shiina, T.; Nakajima, J.; Toyokuni, G.; Kita, S.; Matsuzawa, T.


    A subducting crust contains a large amount of water as a form of hydrous minerals (e.g., Hacker et al., 2003), and the crust plays important roles for water transportation and seismogenesis in subduction zones at intermediate depths (e.g., Kirby et al., 1996; Iwamori, 2007). Therefore, the investigation of seismic structure in the crust is important to understand ongoing physical processes with subduction of oceanic lithosphere. A guided wave which propagates in the subducting crust is recorded in seismograms at Hokkaido, northern Japan (Shiina et al., 2014). Here, we estimated P- and S-wave velocity in the crust with guided waves, and obtained P-wave velocity of 6.6-7.3 km/s and S-wave velocity of 3.6-4.2 km/s at depths of 50-90 km. Moreover, Vp/Vs ratio in the crust is calculated to be 1.80-1.85 in that depth range. The obtained P-wave velocity about 6.6km/s at depths of 50-70 km is consistent with those estimated in Tohoku, northeast Japan (Shiina et al., 2013), and this the P-wave velocity is lower than those expected from models of subducting crustal compositions, such as metamorphosed MORB model (Hacker et al., 2003). In contrast, at greater depths (>80 km), the P-wave velocity marks higher velocity than the case of NE Japan and the velocity is roughly comparable to those of the MORB model. The obtained S-wave velocity distribution also shows characteristics similar to P waves. This regional variation may be caused by a small variation in thermal regime of the Pacific slab beneath the two regions as a result of the normal subduction in Tohoku and oblique subduction in Hokkaido. In addition, the effect of seismic anisotropy in the subducting crust would not be ruled out because rays used in the analysis in Hokkaido propagate mostly in the trench-parallel direction, while those in Tohoku are sufficiently criss-crossed.

  18. A record of spontaneous subduction initiation in the Izu-Bonin-Mariana arc

    NARCIS (Netherlands)

    Arculus, Richard J.; Ishizuka, Osamu; Bogus, Kara A.; Gurnis, Michael; Hickey-Vargas, Rosemary; Aljahdali, Mohammed H.; Bandini-Maeder, Alexandre N.; Barth, Andrew P.; Brandl, Philipp A.; Drab, Laureen; Do Monte Guerra, Rodrigo; Hamada, Morihisa; Jiang, Fuqing; Kanayama, Kyoko; Kender, Sev; Kusano, Yuki; Li, He; Loudin, Lorne C.; Maffione, Marco; Marsaglia, Kathleen M.; McCarthy, Anders; Meffre, Sebastién; Morris, Antony; Neuhaus, Martin; Savov, Ivan P.; Sena, Clara; Tepley, Frank J.; Van Der Land, Cees; Yogodzinski, Gene M.; Zhang, Zhaohui


    The initiation of tectonic plate subduction into the mantle is poorly understood. If subduction is induced by the push of a distant mid-ocean ridge or subducted slab pull, we expect compression and uplift of the overriding plate. In contrast, spontaneous subduction initiation, driven by subsidence

  19. Three-dimensional dynamic laboratory models of subduction with an overriding plate and variable interplate rheology

    NARCIS (Netherlands)

    Duarte, João C.; Schellart, Wouter P.; Cruden, Alexander R.


    Subduction zones are complex 3-D features in which one tectonic plate sinks underneath another into the deep mantle. During subduction the overriding plate (OP) remains in physical contact with the subducting plate and stresses generated at the subduction zone interface and by mantle flowforce the

  20. Shift in the species composition of the diatom community in the eutrophic Mauritanian coastal upwelling: Results from a multi-year sediment trap experiment (2003-2010) (United States)

    Romero, Oscar E.; Fischer, Gerhard


    A multiannual, continuous sediment trap experiment was conducted at the mooring site CBeu (Cape Blanc eutrophic, ca. 20 °N, ca. 18 °W; trap depth = 1256-1296 m) in the high-productive Mauritanian coastal upwelling. Here we present fluxes and the species-specific composition of the diatom assemblage, and fluxes of biogenic silica (BSi, opal) and total organic carbon (TOC) for the time interval June 2003-Feb 2010. Flux ranges of studied parameters are (i) total diatoms = 1.2 ∗ 108-4.7 ∗ 104 valves m-2 d-1 (average = 5.9 × 106 valves ± 1.4 × 107); (ii) BSi = 296-0.5 mg m-2 d-1 (average = 41.1 ± 53.5 mg m-2 d-1), and (iii) TOC = 97-1 mg m-2 d-1 (average = 20.5 ± 17.8 mg m-2 d-1). Throughout the experiment, the overall good match of total diatom, BSi and TOC fluxes is reasonably consistent and reflects well the temporal occurrence of the main Mauritanian upwelling season. Spring and summer are the most favorable seasons for diatom production and sedimentation: out of the recorded 14 diatom maxima of different magnitude, six occurred in spring and four in summer. The diverse diatom community at site CBeu is composed of four main assemblages: benthic, coastal upwelling, coastal planktonic and open-ocean diatoms, reflecting different productivity conditions and water masses. A striking feature of the temporal variability of the diatom populations is the persistent pattern of seasonal groups' contribution: benthic and coastal upwelling taxa dominated during the main upwelling season in spring, while open-ocean diatoms were more abundant in fall and winter, when the upper water column becomes stratified, upwelling relaxes and productivity decreases. The relative abundance of benthic diatoms strongly increased after 2006, yet their spring-summer contribution remained high until the end of the trap experiment. The occurrence of large populations of benthic diatoms at the hemipelagic CBeu site is interpreted to indicate transport from shallow waters via nepheloid

  1. Methane-carbon flow into the benthic food web at cold seeps--a case study from the Costa Rica subduction zone. (United States)

    Niemann, Helge; Linke, Peter; Knittel, Katrin; MacPherson, Enrique; Boetius, Antje; Brückmann, Warner; Larvik, Gaute; Wallmann, Klaus; Schacht, Ulrike; Omoregie, Enoma; Hilton, David; Brown, Kevin; Rehder, Gregor


    Cold seep ecosystems can support enormous biomasses of free-living and symbiotic chemoautotrophic organisms that get their energy from the oxidation of methane or sulfide. Most of this biomass derives from animals that are associated with bacterial symbionts, which are able to metabolize the chemical resources provided by the seeping fluids. Often these systems also harbor dense accumulations of non-symbiotic megafauna, which can be relevant in exporting chemosynthetically fixed carbon from seeps to the surrounding deep sea. Here we investigated the carbon sources of lithodid crabs (Paralomis sp.) feeding on thiotrophic bacterial mats at an active mud volcano at the Costa Rica subduction zone. To evaluate the dietary carbon source of the crabs, we compared the microbial community in stomach contents with surface sediments covered by microbial mats. The stomach content analyses revealed a dominance of epsilonproteobacterial 16S rRNA gene sequences related to the free-living and epibiotic sulfur oxidiser Sulfurovum sp. We also found Sulfurovum sp. as well as members of the genera Arcobacter and Sulfurimonas in mat-covered surface sediments where Epsilonproteobacteria were highly abundant constituting 10% of total cells. Furthermore, we detected substantial amounts of bacterial fatty acids such as i-C15∶0 and C17∶1ω6c with stable carbon isotope compositions as low as -53‰ in the stomach and muscle tissue. These results indicate that the white microbial mats at Mound 12 are comprised of Epsilonproteobacteria and that microbial mat-derived carbon provides an important contribution to the crab's nutrition. In addition, our lipid analyses also suggest that the crabs feed on other (13)C-depleted organic matter sources, possibly symbiotic megafauna as well as on photosynthetic carbon sources such as sedimentary detritus.

  2. First results of high-resolution modeling of Cenozoic subduction orogeny in Andes (United States)

    Liu, S.; Sobolev, S. V.; Babeyko, A. Y.; Krueger, F.; Quinteros, J.; Popov, A.


    The Andean Orogeny is the result of the upper-plate crustal shortening during the Cenozoic Nazca plate subduction beneath South America plate. With up to 300 km shortening, the Earth's second highest Altiplano-Puna Plateau was formed with a pronounced N-S oriented deformation diversity. Furthermore, the tectonic shortening in the Southern Andes was much less intensive and started much later. The mechanism of the shortening and the nature of N-S variation of its magnitude remain controversial. The previous studies of the Central Andes suggested that they might be related to the N-S variation in the strength of the lithosphere, friction coupling at slab interface, and are probably influenced by the interaction of the climate and tectonic systems. However, the exact nature of the strength variation was not explored due to the lack of high numerical resolution and 3D numerical models at that time. Here we will employ large-scale subduction models with a high resolution to reveal and quantify the factors controlling the strength of lithospheric structures and their effect on the magnitude of tectonic shortening in the South America plate between 18°-35°S. These high-resolution models are performed by using the highly scalable parallel 3D code LaMEM (Lithosphere and Mantle Evolution Model). This code is based on finite difference staggered grid approach and employs massive linear and non-linear solvers within the PETSc library to complete high-performance MPI-based parallelization in geodynamic modeling. Currently, in addition to benchmark-models we are developing high-resolution (Paleozoic-Cenozoic sediments above the uppermost crust in the Subandean Ranges. Future work will be focused on the origin of different styles of deformation and topography evolution in Altiplano-Puna Plateau and Central-Southern Andes through 3D modeling of large-scale interaction of subducting and overriding plates.

  3. Subduction, back-arc spreading and global mantle flow (United States)

    Hager, B. H.; Oconnell, R. J.; Raefsky, A.


    It is pointed out that the subducted lithosphere associated with Benioff zones provides the only direct evidence about the flow in the earth's interior associated with plate motions. It is the primary objective of the present investigation to study the relation between the orientation of subducting lithosphere and the flow patterns (both local and global) near subduction zones. Most of the calculations conducted are based on simple flow models for radially symmetric, Newtonian viscous spheres. The investigation is concerned with the possibility that a simple model of global mantle flow could account for some features of subduction zones. It is found that such a model can account for the orientation of the seismic zones, and, in addition, also for features related to back-arc spreading and perhaps the maximum earthquake size.

  4. Potential for generation of natural gas in sediments of the convergent margin of the Aleutian Trench Area

    Energy Technology Data Exchange (ETDEWEB)

    Kvenvolden, K.A.; von Huene, R.


    Sediment being subducted in the eastern part of the convergent margin of the Aleutian Trench has a potential to generate large volumes of natural gas, perhaps as much as 2.8 x 10/sup 6/ m/sup 3/ of methane per km/sup 3/ of sediment, even though the content of organic carbon in the sediment is very low, averaging about 0.4%. This high potential for gas generation results primarily from the enormous volume of sediment undergoing subduction. Along the eastern Aleutian Arc-Trench system a 3-km thick sheet of sediment is being subducted at a rate of about 60 km per million years. We estimate, based on considerations of the stability requirements for gas hydrates observed as anomalous reflectors in some of our seismic records, and on one measurement in a deep well, that the geothermal gradient in this region is about 30/sup 0/C/km. Such a gradient suggests a temperature regime in which the maximum gas generation in the subducting sediment occurs beneath the upper slope. Thus the sediment of the upper slope, as opposed to that of the shelf and lower slope, could be the most prospective for gas accumulation if suitable reservoirs are present. 40 refs., 11 figs., 3 tabs.

  5. Reaction-induced rheological weakening enables oceanic plate subduction


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


    Earth is the only terrestrial planet in our solar system where an oceanic plate subducts beneath an overriding plate. Although the initiation of plate subduction requires extremely weak boundaries between strong plates, the way in which oceanic mantle rheologically weakens remains unknown. Here we show that shear-enhanced hydration reactions contribute to the generation and maintenance of weak mantle shear zones at mid-lithospheric depths. High-pressure friction experiments on peridotite goug...

  6. Ambient seafloor noise excited by earthquakes in the Nankai subduction zone. (United States)

    Tonegawa, Takashi; Fukao, Yoshio; Takahashi, Tsutomu; Obana, Koichiro; Kodaira, Shuichi; Kaneda, Yoshiyuki


    Excitations of seismic background noises are mostly related to fluid disturbances in the atmosphere, ocean and the solid Earth. Earthquakes have not been considered as a stationary excitation source because they occur intermittently. Here we report that acoustic-coupled Rayleigh waves (at 0.7-2.0 Hz) travelling in the ocean and marine sediments, retrieved by correlating ambient noise on a hydrophone array deployed through a shallow to deep seafloor (100-4,800 m) across the Nankai Trough, Japan, are incessantly excited by nearby small earthquakes. The observed cross-correlation functions and 2D numerical simulations for wave propagation through a laterally heterogeneous ocean-crust system show that, in a subduction zone, energetic wave sources are located primarily under the seafloor in directions consistent with nearby seismicity, and secondarily in the ocean. Short-period background noise in the ocean-crust system in the Nankai subduction zone is mainly attributed to ocean-acoustic Rayleigh waves of earthquake origin.

  7. Current levels and composition profiles of PBDEs and alternative flame retardants in surface sediments from the Pearl River Delta, southern China: Comparison with historical data

    Energy Technology Data Exchange (ETDEWEB)

    Chen, She-Jun [State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 (China); Feng, An-Hong; He, Ming-Jing; Chen, Man-Ying [State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 (China); Graduate University of Chinese Academy of Sciences, Beijing 100049 (China); Luo, Xiao-Jun [State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 (China); Mai, Bi-Xian, E-mail: [State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 (China)


    Polybrominated diphenyl ethers (PBDEs) and alternative flame retardants were measured in surface sediments collected during 2009–2010 from the Pearl River Delta, southern China (a large manufacturing base for electronics/electrical products), to evaluate the influence of China's RoHS directive (adopted in 2006) on their environmental occurrence. The concentrations in sediments from different water systems ranged from 3.67 to 2520 ng/g (average of 17.1–588 ng/g) for PBDEs and from 0.22 to 5270 ng/g (average of 11.3–454 ng/g) for the alternative retardants. Although the PBDE levels have decreased significantly compared with those in sediments collected in 2002 in this region, the levels of alternative decabromodiphenyl ethane (DBDPE) have exceeded those of BDE209 (two predominant halogenated flame retardants (HFRs) in China) in the majority of sediments. This finding suggests a different contaminant pattern of HFRs in current sediments due to the replacement of the deca-BDE mixture with DBDPE in this region. In addition, sediment concentrations of discontinued PBDEs in the rural area are clearly elevated due to e-waste dismantling. The congener profiles of PBDEs in the current sediments (with more abundant lower-brominated congeners) differed substantially from those in 2002 and from the technical products, suggesting that biological or photolytic debromination of PBDEs may have occurred in the environment. - Highlights: ► PBDE levels in sediments have decreased substantially since China's RoHS directive. ► Contamination of novel DBDPE has exceeded that of deca-BDE in the PRD sediments. ► The congener profiles of PBDEs in the sediments have changed significantly. ► Significant biological or photolytic degradation of PBDEs may occur in the environment.

  8. Reconstruction of the biogeochemistry and ecology of photoautotrophs based on the nitrogen and carbon isotopic compositions of vanadyl porphyrins from Miocene siliceous sediments

    Directory of Open Access Journals (Sweden)

    Y. Kashiyama


    Full Text Available We determined both the nitrogen and carbon isotopic compositions of various vanadyl alkylporphyrins isolated from siliceous marine sediments of the Onnagawa Formation (middle Miocene, northeastern Japan to investigate the biogeochemistry and ecology of photoautotrophs living in the paleo-ocean. The distinctive isotopic signals support the interpretations of previous works that the origin of 17-nor-deoxophylloerythroetioporphyrin (DPEP is chlorophylls-c1-3, whereas 8-nor-DPEP may have originated from chlorophylls-a2 or b2 or bacteriochlorophyll-a. Although DPEP and cycloheptanoDPEP are presumably derived from common precursory pigments, their isotopic compositions differed in the present study, suggesting that the latter represents a specific population within the photoautotrophic community. The average δ15N value for the entire photoautotrophic community is estimated to be –2 to +1‰ from the δ15N values of DPEP (–6.9 to –3.6‰; n=7, considering that the empirical isotopic relationships that the tetrapyrrole nuclei of chloropigments are depleted in 15N by ~4.8‰ and enriched in 13C by ~1.8‰ relative to the whole cells. This finding suggests that nitrogen utilized in the primary production was supplied mainly through N2-fixation by diazotrophic cyanobacteria. Based on the δ13C values of DPEP (–17.9 to –15.6‰; n=7, we estimated isotopic fractionation associated with photosynthetic carbon fixation to be 8–14‰. This range suggests the importance of β-carboxylation and/or active transport of the carbon substrate, indicating in turn the substantial contribution of diazotrophic cyanobacteria to primary production. Based on the δ15N values of 17-nor-DPEP (–7.4 to –2.4‰ n=7, the δ15N range of chlorophylls-c-producing algae was estimated to be –3

  9. Impact-driven subduction on the Hadean Earth (United States)

    O'Neill, C.; Marchi, S.; Zhang, S.; Bottke, W.


    Impact cratering was a dominant geologic process in the early Solar System that probably played an active role in the crustal evolution of the young terrestrial planets. The Earth's interior during the Hadean, 4.56 to 4 billion years ago, may have been too hot to sustain plate tectonics. However, whether large impacts could have triggered tectonism on the early Earth remains unclear. Here we conduct global-scale tectonic simulations of the evolution of the Earth through the Hadean eon under variable impact fluxes. Our simulations show that the thermal anomalies produced by large impacts induce mantle upwellings that are capable of driving transient subduction events. Furthermore, we find that moderate-sized impacts can act as subduction triggers by causing localized lithospheric thinning and mantle upwelling, and modulate tectonic activity. In contrast to contemporary subduction, the simulated localized subduction events are relatively short-lived (less than 10 Myr) with relatively thin, weak plates. We suggest that resurgence in subduction activity induced by an increased impact flux between 4.1 and 4.0 billion years ago may explain the coincident increase in palaeointensity of the magnetic field. We further suggest that transient impact-driven subduction reconciles evidence from Hadean zircons for tectonic activity with other lines of evidence consistent with an Earth that was largely tectonically stagnant from the Hadean into the Archaean.

  10. Sediment Transport

    DEFF Research Database (Denmark)

    Liu, Zhou

    Flow and sediment transport are important in relation to several engineering topics, e.g. erosion around structures, backfilling of dredged channels and nearshore morphological change. The purpose of the present book is to describe both the basic hydrodynamics and the basic sediment transport...... mechanics. Chapter 1 deals with fundamentals in fluid mechanics with emphasis on bed shear stress by currents, while chapter 3 discusses wave boundary layer theory. They are both written with a view to sediment transport. Sediment transport in rivers, cross-shore and longshore are dealt with in chapters 2...

  11. A Dynamical Context for Small-scale Heterogeneity Throughout the Mantle Beneath Subduction (United States)

    Frost, D. A.; Rost, S.; Garnero, E.


    Subduction zones are a source for mantle heterogeneity within the convection system and there is mounting evidence that seismic signatures can be used to track slabs down from the surface throughout the mantle. Seismic studies of the mantle beneath Central America demonstrate that subducted slab material reaches the Core-Mantle Boundary (CMB). The lowermost mantle beneath this convergent margin shows strong seismic evidence for heterogeneity. Tomographic models characterise subduction zones to be underlain by increased seismic velocities over 100s-1000s km laterally, in association with D'´ discontinuities 100-300 km above the CMB, consistent with phase transitions in the Bridgmanite system. Recent analyses have found evidence for isolated Ultra Low Velocity Zones in addition to prevalent fine-scale heterogeneity, on the order of 1-10 km, scattering high frequency waves. These techniques indicate thermal and/or chemical anomalies within the mantle on a range of scales. Numerical geodynamical simulations suggest small-scale mechanical mixing of initially coherent compositionally anomalous subducted material separating into entities of various sizes consistent with the range of heterogeneity sizes observed in the lower mantle.Investigating seismic scattering, the re-radiation of a wavefront due to interaction with a sharply contrasting volumetric anomaly, is an effective method for studying small-scale elastic heterogeneities in the Earth's mantle. Studies commonly record structure with scale lengths of about 10 km. Here we analyse scattered energy related to PKPPKP — PKP•PKP (the • indicates the scattering location along the raypath) — sampling a large volume of the mantle beneath Central America. We reveal the character of heterogeneity in various frequency bands within the whole mantle using both broadband and short-period data. These observations will be placed in context with other studies in this region illustrating the large-scale background structure

  12. Neoarchean Subduction Recorded in the Northern Margin of the Yangtze Craton, South China (United States)

    Zhang, S. B.; Zheng, Y. F.


    The Neoarchean is an important era during which plate tectonics began to operate widely on the earth and the continental crust compositions changed dramatically. However, reliable record of plate subduction has never been reported yet in the Yangtze Craton. Here we report geochemical studies on gneissic tonalite, trondhjemite and amphibolite in the Yudongzi Complex in the northern margin of the Yangtze Craton, which suggests that there is a plate subduction recorded in this area at about 2.7 Ga.The rocks in the Yudongzi Complex are gneissic granite, gneissic tonalite, amphibolite gneiss and magnetite quartzite. Most rocks are enriched in sodic. The gneissic granites show positive Eu anomalies, high (La/Yb)cn and Sr/Y ratios, low Ybcn and Y, resembling typical TTG. The amphibolite and tonalite gneiss show less fractionated REE patterns. SHRIMP zircon U-Pb dating on one gneissic trondhjemite, one amphibolite and one tonalite gave crystallization ages of 2667±21 Ma, 2701±10 Ma and 2697±9 Ma, respectively. They all recorded a metamorphic event at about 2.48 Ga. The SHRIMP zircon oxygen isotope analysis for a trondhjemite and an amphibolite gave δ18O values of 6.2±0.3‰ and 6.3±0.4‰, respectively. The oxygen isotope ratios higher than normal mantle values suggest a source experienced low temperature alteration. The laser fluoration analysis of bulk minerals gave δ18O values of 6.4-8.8‰ for zircon and 12.5-15.2‰ for quartz. The zircon Lu-Hf isotope analysis on the trondhjemite and amphibolite gave similar ɛHf(t) values of 0.08±0.48 and 0.07±0.63, respectively. Whole-rock ɛNd(t) values range from -1.5 to +1.0. These trondhjemite and tonalite can be interpreted as derivation from partial melting of subducted oceanic slab with a garnet-amphibolite residue.Considering the 2.67 Ga A-type granitic rocks at Huji in the interior of the craton, plate subduction took place in the northern edge of the Yangtze Craton. The Yudongzi trondhjemite and tonalite were

  13. Paleotethyan subduction process revealed from Triassic blueschists in the Lancang tectonic belt of Southwest China (United States)

    Fan, Weiming; Wang, Yuejun; Zhang, Yanhua; Zhang, Yuzhi; Jourdan, Fred; Zi, Jianwei; Liu, Huichuan


    The subduction of the Paleotethyan Ocean and subsequent continental collision along the Lancang tectonic belt of the southeastern Paleotethyan belt is a major tectonic event in Southwest China, but the event of the subduction preceding the final collision is still not well-constrained. The mafic blueschists exposed in the Lancang accretionary complex provide crucial records of the Paleotethyan subduction process. In this paper, we present a set of new petrologic, geochronological and geochemical data for the Suyi mafic blueschists in the Lancang metamorphic zone. The mineral assemblage of these blueschists consists of zoned sodic amphibole (25-30%), albite (15-20%), epidote (25-30%), phengite (5-10%), chlorite (~ 5-10%), and minor amounts of actinolite, apatite, sphene, zircon, ilmenite, quartz and secondary limonite. This suggests a prograde metamorphism from ~ 0.5 to ~ 0.9 GPa and retrograde metamorphic overprinting (back to ~ 0.6 GPa) within the temperature range of 300-450 °C. The Suyi blueschists give a zircon U-Pb age of 260 ± 4 Ma and glaucophane minerals formed during prograde metamorphism yield a 40Ar/39Ar plateau age of 242 ± 5 Ma (MSWD = 0.77; P = 0.54). The blueschists have geochemical compositions of subalkaline basalt and show typical OIB-type REE and multi-elemental patterns and εNd(t) values ranging from + 3.35 to + 4.85. Based on available data, it is inferred that the protolith formed at 260 Ma and originated from a basaltic seamount. The basaltic rocks subducted down to 30-35 km depths beneath the Lincang arc to form the epidote blueschists at ~ 242 Ma. The blueschists were subsequently transported to shallower crustal levels in response to the continuous underthrust of the subducted slab and the continent-continent collision in the middle-late Triassic. These results provide a systematic constraint on the tectonic evolution and temporal framework of the southeastern Paleotethyan belt in Southwest China.

  14. Multiscale Architecture of a Subduction Complex and Insight into Large-scale Material Movement in Subduction Systems (United States)

    Wakabayashi, J.


    The >1000 km by >100 km Franciscan complex of California records >100 Ma of subduction history that terminated with conversion to a transform margin. It affords an ideal natural laboratory to study the rock record of subduction-interface and related processes exhumed from 10-70 km. The Franciscan comprises coherent and block-in-matrix (mélange) units forming a nappe stack that youngs structurally downward in accretion age, indicating progressive subduction accretion. Gaps in accretion ages indicate periods of non-accretion or subduction erosion. The Franciscan comprises siliciclastic trench fill rocks, with lesser volcanic and pelagic rocks and serpentinite derived from the downgoing plate, as well as serpentinite and felsic-intermediate igneous blocks derived as detritus from the upper plate. The Franciscan records subduction, accretion, and metamorphism (including HP), spanning an extended period of subduction, rather than a single event superimposed on pre-formed stratigraphy. Melanges (serpentinite and siliciclastic matrix) with exotic blocks, that include high-grade metamorphic blocks, and felsic-intermediate igneous blocks from the upper plate, are mostly/entirely of sedimentary origin, whereas block-in-matrix rocks formed by tectonism lack exotic blocks and comprise disrupted ocean plate stratigraphy. Mélanges with exotic blocks are interbedded with coherent sandstones. Many blocks-in-melange record two HP burial events followed by surface exposure, and some record three. Paleomegathrust horizons, separating nappes accreted at different times, appear restricted to narrow fault zones of structures, are accommodated by discrete faults or narrow shear zones, rather than by significant penetrative strain. Exhumation of Franciscan HP units, both coherent and mélange, was accommodated by significant extension of the overlying plate, and possibly extension within the subduction complex, with cross-sectional extrusion, and like subduction burial, took place at

  15. Foreland sedimentary record of Andean mountain building during advancing and retreating subduction (United States)

    Horton, Brian K.


    As in many ocean-continent (Andean-type) convergent margins, the South American foreland has long-lived (>50-100 Myr) sedimentary records spanning not only protracted crustal shortening, but also periods of neutral to extensional stress conditions. A regional synthesis of Andean basin histories is complemented by new results from the Mesozoic Neuquén basin system and succeeding Cenozoic foreland system of west-central Argentina (34-36°S) showing (1) a Late Cretaceous shift from backarc extension to retroarc contraction and (2) an anomalous mid-Cenozoic (~40-20 Ma) phase of sustained nondeposition. New detrital zircon U-Pb geochronological results from Jurassic through Neogene clastic deposits constrain exhumation of the evolving Andean magmatic arc, retroarc thrust belt, foreland basement uplifts, and distal eastern craton. Abrupt changes in sediment provenance and distal-to-proximal depositional conditions can be reconciled with a complex Mesozoic-Cenozoic history of extension, post-extensional thermal subsidence, punctuated tectonic inversion involving thick- and thin-skinned shortening, alternating phases of erosion and rapid accumulation, and overlapping igneous activity. U-Pb age distributions define the depositional ages of several Cenozoic stratigraphic units and reveal a major late middle Eocene-earliest Miocene (~40-20 Ma) hiatus in the Malargüe foreland basin. This boundary marks an abrupt shift in depositional conditions and sediment sources, from Paleocene-middle Eocene distal fluviolacustrine deposition of sediments from far western volcanic sources (Andean magmatic arc) and subordinate eastern cratonic basement (Permian-Triassic Choiyoi igneous complex) to Miocene-Quaternary proximal fluvial and alluvial-fan deposition of sediments recycled from emerging western sources (Malargüe fold-thrust belt) of Mesozoic basin fill originally derived from basement and magmatic arc sources. Neogene eastward advance of the fold-thrust belt involved thick

  16. Rapid sedimentation and overpressure in shallow sediments of the Bering Trough, offshore southern Alaska (United States)

    Daigle, Hugh; Worthington, Lindsay L.; Gulick, Sean P. S.; Van Avendonk, Harm J. A.


    Pore pressures in sediments at convergent margins play an important role in driving chemical fluxes and controlling deformation styles and localization. In the Bering Trough offshore Southern Alaska, extreme sedimentation rates over the last 140 kyr as a result of glacial advance/retreats on the continental shelf have resulted in elevated pore fluid pressures in slope sediments overlying the Pamplona Zone fold and thrust belt, the accretionary wedge resulting from subduction of the Yakutat microplate beneath the North American Plate. Based on laboratory experiments and downhole logs acquired at Integrated Ocean Drilling Program Site U1421, we predict that the overpressure in the slope sediments may be as high as 92% of the lithostatic stress. Results of one-dimensional numerical modeling accounting for changes in sedimentation rate over the last 130 kyr predicted overpressures that are consistent with our estimates, suggesting that the overpressure is a direct result of the rapid sedimentation experienced on the Bering shelf and slope. Comparisons with other convergent margins indicate that such rapid sedimentation and high overpressure are anomalous in sediments overlying accretionary wedges. We hypothesize that the shallow overpressure on the Bering shelf/slope has fundamentally altered the deformation style within the Pamplona Zone by suppressing development of faults and may inhibit seismicity by focusing faulting elsewhere or causing deformation on existing faults to be aseismic. These consequences are probably long-lived as it may take several million years for the excess pressure to dissipate.

  17. IODP Expedition 334: An Investigation of the Sedimentary Record, Fluid Flow and State of Stress on Top of the Seismogenic Zone of an Erosive Subduction Margin

    Directory of Open Access Journals (Sweden)

    Paola Vannucchi


    Full Text Available The Costa Rica Seismogenesis Project (CRISP is an experiment to understand the processes that control nucleation and seismic rupture of large earthquakes at erosional subduction zones. Integrated Ocean Drililng Program (IODP Expedition 334 by R/V JOIDES Resolution is the first step toward deep drilling through the aseismic and seismicplate boundary at the Costa Rica subduction zone offshore the Osa Peninsula where the Cocos Ridge is subducting beneath the Caribbean plate. Drilling operations included logging while drilling (LWD at two slope sites (Sites U1378 and U1379 and coring at three slope sites (Sites U1378–1380and at one site on the Cocos plate (Site U1381. For the first time the lithology, stratigraphy, and age of the slope and incoming sediments as well as the petrology of the subducting Cocos Ridge have been characterized at this margin.The slope sites recorded a high sediment accumulation rate of 160–1035m m.y.-1 possibly caused by on-land uplift triggered by the subduction of the Cocos Ridge. The geochemical data as well as the in situ temperature data obtained at the slope sites suggest that fluids are transported from greater depths. The geochemical profiles at Site U1381 reflect diffusional communication of a fluid with seawater-likechemistry and the igneous basement of the Cocos plate (Solomon et al., 2011; Vannucchi et al., 2012a. The present-day in situ stress orientation determined by borehole breakouts at Site U1378 in the middle slope and Site U1379 in the upper slope shows a marked change in stress state within ~12 km along the CRISP transect; that maycorrespond to a change from compression (middle slope to extension (upper slope.

  18. Composition. (United States)

    Communication: Journalism Education Today, 2002


    Considers how photography is more than just pointing a camera in the right direction. Explains that good pictures use elements of composition such as the Rule of Thirds, leading lines, framing and repetition of shapes. Presents 16 photographs from college and secondary school publications, and describes the techniques that makes them effective.…

  19. Identification of source lithology at south segment of Kamchatka subduction zone (United States)

    Gavrilenko, M.; Herzberg, C. T.; Portnyagin, M.; Ozerov, A.


    Kamchatka peninsula (Russia) is an island-arc with a complex geological history and structure. It has three distinct volcanic fronts, the origin of which is still debated. Moreover, a junction with the Aleutian Arc (at ~56°N) complicates the understanding of geodynamics at the region. However, the south part (from ~53°N) of Kamchatka peninsula is thought to be a "textbook case" of subduction zone with relatively rapid (over 8 cm/yr) near-normal convergence and a steep (over 50°) angle of subduction. Kamchatka is unusual in the world because its volcanoes contain a significant amount of primitive high MgO lavas that are rich in olivine crystals. Furthermore, high precision contents of Ni, Ca, and Mn can help to constrain the source lithology. Straub et al. (2008) reported high Ni contents on olivines from a limited number of samples from the Mexican Volcanic Front, and concluded that pyroxenite melting was important. Portnyagin et al. (2009) reported high precision Ni, Ca, and Mn contents of olivines from a wide range of volcanoes from Kamchatka, and similarly concluded that pyroxenite melting is widespread. We have extended the work of Portnyagin et al. (2009) by analyzing olivine phenocrysts from volcanoes in the southernmost Kamchatka peninsula. Our work confirms that there are regional variations in olivine phenocryst composition that likely arises from variations in pyroxenite composition, the amount of peridotite melt that mixes with pyroxenite melts, and a variable role played by magnetite fractionation. We conclude that pyroxenite melting is likely to be important in subduction zones world-wide, but its significance has been underestimated because of the general rarity of olivine-bearing high MgO lavas.

  20. Three-dimensional magnetotelluric imaging of Cascadia subduction zone from an amphibious array (United States)

    Yang, B.; Egbert, G. D.; Key, K.; Bedrosian, P.; Livelybrooks, D.; Schultz, A.


    We present results from three-dimensional inversion of an amphibious magnetotelluric (MT) array consisting of 71 offshore and 75 onshore sites in the central part of Cascadia, to image down-dip and along strike variations of electrical conductivity, and constrain the 3D distribution of fluids and melt in the subduction zone. A larger scale array consisting of EarthScope transportable-array data and several 2D legacy profiles (e.g. EMSLAB, CAFE-MT, SWORMT) which covers WA, OR, northern CA and northern NV has been inverted separately, to provide a broader view of the subduction zone. Inverting these datasets including seafloor data, and involving strong coast effects presents many challenges, especially for the nominal TE mode impedances which have very anomalous phases in both land and seafloor sites. We find that including realistic bathymetry and conductive seafloor sediments significantly stabilizes the inversion, and that a two stage inversion strategy, first emphasizing fit to the more challenging TE data, improved overall data fits. We have also constrained the geometry of the (assumed resistive) subducting plates by extracting morphological parameters (e.g. upper boundary and thickness) from seismological models (McCrory et al 2012, Schmandt and Humphreys 2010). These constraints improve recovery and resolution of subduction related conductivity features. With the strategies mentioned above, we improved overall data fits, resulting in a model which reveals (for the first time) a conductive oceanic asthenosphere, extending under the North America plate. The most striking model features are conductive zones along the plate interface, including a continuous stripe of high conductivity just inboard of the coast, extending from the northern limits of our model in Washington state, to north-central Oregon. High conductivities also occur in patches near the tip of the mantle wedge, at depths appropriate for eclogitization, and at greater depth beneath the arc, in

  1. IODP Expedition 333: Return to Nankai Trough Subduction Inputs Sites and Coring of Mass Transport Deposits

    Directory of Open Access Journals (Sweden)

    Michael Strasser


    Full Text Available Integrated Ocean Drilling Program (IODP Expedition 333 returned to two sites drilled during IODP Expedition 322 on the ocean side of the Nankai Trough to pursue the characterization of the inputs to the Nankai subduction and seismogenic zone, as part of the Nankai Trough Seismogenic Experiment (NanTroSEIZE multi-expedition project. SiteC0011 is located at the seaward edge of the trench and Site C0012 on a basement high, Kashinozaki Knoll (Fig. 1. The main objectives of drilling again at these sites were to fill coring gaps in the upper part (<350 m of the sedimentary sequence, to measure heat flow, and to core the oceanic basement to a greater depth on the Knoll. New results include the observation of a diagenetic boundary within the Shikoku Basin sediments that may be compared to one documented further west by ODP Legs 131, 190 and 196 but occurs here at a lower temperature. Borehole heat flow measurements confirm spatial variations in the Shikoku Basin that were indicated by short probe surveys. Heat flow variations between topographic highs and lows may be related to fluid convection within the basement. This expedition also included the objectives of the Nankai Trough Submarine LandSLIDEhistory (NanTroSLIDE Ancillary Project Letter (APL and cored at Site C0018 a pile of mass transport deposits on the footwall of the megasplay fault, a major out of sequence thrust that presumably slips coseismically during large subduction earthquakes. This brought newinsight on the timing of these mass wasting events and on the deformation within the sliding slope sediments.

  2. Subduction initiation and Obduction: insights from analog models (United States)

    Agard, P.; Zuo, X.; Funiciello, F.; Bellahsen, N.; Faccenna, C.; Savva, D.


    Subduction initiation and obduction are two poorly constrained geodynamic processes which are interrelated in a number of natural settings. Subduction initiation can be viewed as the result of a regional-scale change in plate convergence partitioning between the set of existing subduction (and collision or obduction) zones worldwide. Intraoceanic subduction initiation may also ultimately lead to obduction of dense oceanic "ophiolites" atop light continental plates. A classic example is the short-lived Peri-Arabic obduction, which took place along thousands of km almost synchronously (within ~5-10 myr), from Turkey to Oman, while the subduction zone beneath Eurasia became temporarily jammed. We herein present analog models designed to study both processes and more specifically (1) subduction initiation through the partitioning of deformation between two convergent zones (a preexisting and a potential one) and, as a consequence, (2) the possible development of obduction, which has so far never been modeled. These models explore the mechanisms of subduction initiation and obduction and test various triggering hypotheses (i.e., plate acceleration, slab crossing the 660 km discontinuity, ridge subduction; Agard et al., 2007). The experimental setup comprises an upper mantle modelled as a low-viscosity transparent Newtonian glucose syrup filling a rigid Plexiglas tank and high-viscosity silicone plates. Convergence is simulated by pushing on a piston at one end of the model with plate tectonics like velocities (1-10 cm/yr) onto (i) a continental margin, (ii) a weakness zone with variable resistance and dip (W), (iii) an oceanic plate - with or without a spreading ridge, (iv) a subduction zone (S) dipping away from the piston and (v) an upper active continental margin, below which the oceanic plate is being subducted at the start of the experiment (as for the Oman case). Several configurations were tested over thirty-five parametric experiments. Special emphasis was

  3. Pore water composition of Permeable reef flat sediments on Checker Reef in Kaneohe Bay, Oahu, Hawaii from 07 October 1996 to 03 July 1997 (NODC Accession 0000271) (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Geochemical behaviour of the top 70 cm of permeable reef flat sediments on Checker Reef, Oahu, Hawaii was examined using spatial and temporal changes in pore water...

  4. The Geodynamics of Continental Lithosphere Entering a Subduction Zone (United States)

    Steedman, C. E.; Kaus, B. J.; Becker, T. W.; Okaya, D.; Wu, F. T.


    As deformation patterns resulting from subduction of a passive continental margin are insufficiently understood, here we perform 2-D numerical simulations to explore the effects of continental lithosphere entering a subduction zone. The model setup consists of a subduction zone in which the oceanic part of a passive continental margin initially subducts beneath an oceanic plate. A particle-based 2-D visco-elasto-plastic thermo-mechanical finite element code is employed to study the dynamics of the system. A novel new feature of the code is that the resolution of the model can be significantly increased in selected parts of the domain, which allows for self-consistent modelling of mantle-lithosphere interaction. In the present study this feature is employed to study how crustal scale deformation around the subduction zone is influenced by surface processes and by flow in the upper mantle. Using systematic 2-D numerical simulations, we explore the parameters that are dominant in controlling near- surface structures, both with regards to changes in topography over time, and subsurface features such as Moho undulations. The main parameters that have been varied are: the lithospheric density structure; the strength of the lower crust; the amounts of erosion; imposed pushing versus density-driven (slab-pull and ridge- push) convergence; the upper boundary condition (free surface versus free slip); rheology (non-Newtonian versus Newtonian, viscous, visco-elasto-plastic); and finally the effect of an imposed slab breakoff. In all cases we track surface uplift, subduction evolution and rock exhumation history. The results can be compared to evidence from areas such as Taiwan where continental subduction or convergence is thought to be happening. Preliminary results indicate that a low viscosity lower crust may contribute to crustal uplift.

  5. Subduction-driven recycling of continental margin lithosphere. (United States)

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


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

  6. Deep electrical resistivity structure of Costa Rican Subduction Zone (United States)

    Worzewski, T.; Jegen, M.; Brasse, H.; Taylor, W.


    The water content and its distribution play an important role in the subduction process. Water is released from the subducting slab in a series of metamorphic reactions and the hydration of the mantle wedge may trigger the onset of melting, weakening and changes in the dynamics and thermal structure of subduction zones. However, the amount of water carried into the subduction zone and its distribution are not well constrained by existing data and are subject of vigorous current research in SFB574 (Volatiles and Fluids in Subduction Zones: Climate Feedback and Trigger Mechanisms for Natural Disasters). We will show numerical modeling studies which are used to determine the resolution and sensitivity of the MT response to fluids in the crust and subducting slab under the special condition of a coastal setting. In 2007-2008 we conducted a long-period magnetotelluric investigations in northwestern Costa Rica on- and offshore, where the Cocos Plate subducts beneath the Carribean plate. Eleven marine magnetotelluric Stations newly developed and constructed by IFM-GEOMAR and University of Kiel were deployed on the 200 km long marine extension of the profile for several months. We will present the data and its processing, as well as our attempts to eliminate motion induced noise observed on some stations on the cliffy shelf due to tidal waves hitting the shelf and trench parallel- and perpendicular currents. The marine profile was extended landwards by the Free University of Berlin over length of 160 kilometers with further 18 stations. We present preliminary modeling results of land data, which revealed interesting features, inter alia a possible image of fluid release from the downgoing slab in the forearc, as well as ongoing modeling of the combined on- and offshore data sets.

  7. Seismicity, topography, and free-air gravity of the Aleutian-Alaska subduction zone (United States)

    Wells, R. E.; Blakely, R. J.; Scholl, D. W.; Ryan, H. F.


    The Aleutian-Alaska subduction zone, extending 3400 km from the Queen Charlotte Fault to Kamchatka, has been the source of six great megathrust earthquakes in the 20th Century. Four earthquakes have ruptured the 2000-km-long Aleutian segment, where the Cenozoic Aleutian arc overlies the subducting Pacific plate. These include the 1946 M 8.6 earthquake off Unimak Is., the 1957 M 8.6 and 1986 M 8.0 earthquakes off the Andreanoff Is., and the 1965 M 8.7 Rat Is. earthquake. The source regions of these earthquakes inferred from waveform inversions underlie the well-defined Aleutian deep-sea terrace. The deep-sea terrace is about 4 km deep and is underlain by Eocene arc framework rocks, which extend nearly to the trench. It is bounded on its seaward and landward margins by strong topographic and fee-air gravity gradients. The main asperities (areas of largest slip) for the great earthquakes and nearly all of the Aleutian thrust CMT solutions lie beneath the Aleutian terrace, between the maximum gradients. Similar deep-sea terraces are characteristic of non-accretionary convergent margins globally (75% of subduction zones), and, where sampled by drilling (e.g., Japan, Peru, Tonga, Central America), are undergoing sustained subsidence. Sustained subsidence requires removal of arc crust beneath the terrace by basal subduction erosion (BSE). BSE is in part linked to the seismic cycle, as it occurs in the same location as the megathrust earthquakes. Along the eastern 1400 km of the Alaskan subduction zone, the Pacific plate subducts beneath the North American continent. The boundary between the Aleutian segment and the continent is well defined in free-air gravity, and the distinctive deep-sea terrace observed along the Aleutian segment is absent. Instead, the Alaskan margin consists of exhumed, underplated accretionary complexes forming outer arc gravity highs. Superimposed on them are broad topographic highs and lows forming forearc basins (Shumagin, Stevenson) and islands

  8. Trace-Element Mobility in Eclogite-Facies Subducted Crust: Garnet, Zircon, and Rutile Petrochronology of As Sifah, Oman (United States)

    Garber, Joshua M.; Rioux, Matthew; Kylander-Clark, Andrew R.; Vervoort, Jeff D.; Wilford, Diane; Hacker, Bradley R.; Searle, Michael P.; Waters, David J.; Warren, Clare


    Trace element flux in subduction zones is strongly affected by the chemistry and availability of an accompanying fluid, in addition to mineral partitioning behavior. These factors may be exacerbated in certain lithologies, suggesting a role for lithology-specific rock permeability, fluid fugacity, and/or trace-element partitioning during subduction. To assess lithological controls on elemental transport in subducted mafic crust and sediment, we obtained dates (Sm-Nd, Lu-Hf, and U-Pb) and major- and trace-element concentrations for garnet, zircon, and rutile in end-member mafic and metapelitic rocks from the ultrahigh-pressure As Sifah unit of Oman. The three phases record similar isotopic dates among all lithologies, but trace-element records for each phase are distinct for each rock type. For example, i) mafic rocks show expected garnet/zircon rare-earth element (REE) partitioning, but metapelitic garnet and zircon do not, and ii) mafic rutiles record lower intergranular solubilities for high-field-strength elements (HFSEs) than pelitic rutiles. Together, these data suggest that REE and HFSE equilibrium length-scales varied significantly between adjacent lithologies, implicating crucial differences in fluid flux during subduction. Further, Lu-Hf isotopic data are scattered and non-isochronous for all rocks - even in metapelites that exhibit cm- to outcrop-scale HFSE equilibrium length-scales - suggesting that achievement of elemental equilibrium does not imply isotopic equilibrium, even at the same scale. Our approach illustrates the power of multi-phase petrochronology in determining the behavior of distinct trace-element groups during metamorphism.

  9. Did high Neo-Tethys subduction rates contribute to early Cenozoic warming? (United States)

    Hoareau, G.; Bomou, B.; van Hinsbergen, D. J. J.; Carry, N.; Marquer, D.; Donnadieu, Y.; Le Hir, G.; Vrielynck, B.; Walter-Simonnet, A.-V.


    The 58-51 Ma interval was characterized by a long-term increase of global temperatures (+4 to +6 °C) up to the Early Eocene Climate Optimum (EECO, 52.9-50.7 Ma), the warmest interval of the Cenozoic. It was recently suggested that sustained high atmospheric pCO2, controlling warm early Cenozoic climate, may have been released during Neo-Tethys closure through the subduction of large amounts of pelagic carbonates and their recycling as CO2 at arc volcanoes. To analyze the impact of Neo-Tethys closure on early Cenozoic warming, we have modeled the volume of subducted sediments and the amount of CO2 emitted along the northern Tethys margin. The impact of calculated CO2 fluxes on global temperature during the early Cenozoic have then been tested using a climate carbon cycle model (GEOCLIM). We show that CO2 production may have reached up to 1.55 × 1018 mol Ma-1 specifically during the EECO, ~ 4 to 37 % higher that the modern global volcanic CO2 output, owing to a dramatic India-Asia plate convergence increase. The subduction of thick Greater Indian continental margin carbonate sediments at ~ 55-50 Ma may also have led to additional CO2 production of 3.35 × 1018 mol Ma-1 during the EECO, making a total of 85 % of the global volcanic CO2 outgassed. However, climate modeling demonstrates that timing of maximum CO2 release only partially fits with the EECO, and that corresponding maximum pCO2 values (750 ppm) and surface warming (+2 °C) do not reach values inferred from geochemical proxies, a result consistent with conclusions arising from modeling based on other published CO2 fluxes. These results demonstrate that CO2 derived from decarbonation of Neo-Tethyan lithosphere may have possibly contributed to, but certainly cannot account alone for early Cenozoic warming. Other commonly cited sources of excess CO2 such as enhanced igneous province volcanism also appear to be up to 1 order of magnitude below fluxes required by the model to fit with proxy data of pCO2 and

  10. Dynamic Subsidence across the Late Cretaceous Western Interior Basin in Response to Farallon Slab Subduction (United States)

    Liu, S.; Nummedal, D.; Liu, L.


    The United States Cretaceous Western Interior Basin has long been considered a foreland basin, driven by the Sevier thrust and associated basin sediment loads. However, flexural studies demonstrate that this effect exists only within a narrow band in front of the thrust belt. Most of the basin appears to be due to mantle flow-induced dynamic subsidence associated with Farallon plate subduction. Here we show how the components of evolving long-wavelength dynamic subsidence and flexural subsidence created the accommodation space and controlled the stratigraphy across the western United Sates, based on the correlated stratigraphic sections across central Utah-Colorado and southern Wyoming.These backstripped subsidence data reveal a component of continuously evolving long-wavelength dynamic subsidence, in addition to subsidence driven by the Sevier thrust belt and associated sediment loads. The loci of maximum rates of this dynamic subsidence moved eastward from ~98 to 74 Ma in phase with the west-to-east passage of the Farallon slab, as reconstructed from tomography based on quantitative inverse models. These subsidence data allow testing of existing subduction models and confirm the dynamic-topography driven nature of the Western Interior Basin. The results seem to support that the depocenters track the trough of dynamic subsidence with ca.18 Myr cycles through time and space and the stratigraphic patterns of large-scale progradation, eastward migration of depocenter, and regional clinoform-like downlap are related with the dynamic subsidence. Interpretation of these data also provides more insights into the repeated, ca.2 to 6 Myr cycles of thrust-induced subsidence in front of the thrust belt, which control the local eastward progradation of the sand bodies from the thrust belt. The dynamic, flexural subsidence and eustatic sea level changes interacted and controlled the timing and distribution of unconformities. Our work shows how the stratigraphy precisely

  11. Sediment-associated aliphatic and aromatic hydrocarbons in coastal British Columbia, Canada: Concentrations, composition, and associated risks to protected sea otters

    Energy Technology Data Exchange (ETDEWEB)

    Harris, Kate A. [Fisheries and Oceans Canada, Institute of Ocean Sciences, P.O. Box 6000, Sidney BC V8L 4B2 (Canada); University of Victoria, School of Earth and Ocean Sciences, P.O. Box 1700 STN CSC, Victoria BC V8W 2Y2 (Canada); Yunker, Mark B. [7137 Wallace Dr., Brentwood Bay, BC V8M 1G9 (Canada); Dangerfield, Neil [Fisheries and Oceans Canada, Institute of Ocean Sciences, P.O. Box 6000, Sidney BC V8L 4B2 (Canada); Ross, Peter S., E-mail: [Fisheries and Oceans Canada, Institute of Ocean Sciences, P.O. Box 6000, Sidney BC V8L 4B2 (Canada)


    Sediment-associated hydrocarbons can pose a risk to wildlife that rely on benthic marine food webs. We measured hydrocarbons in sediments from the habitat of protected sea otters in coastal British Columbia, Canada. Alkane concentrations were dominated by higher odd-chain n-alkanes at all sites, indicating terrestrial plant inputs. While remote sites were dominated by petrogenic polycyclic aromatic hydrocarbons (PAHs), small harbour sites within sea otter habitat and sites from an urban reference area reflected weathered petroleum and biomass and fossil fuel combustion. The partitioning of hydrocarbons between sediments and adjacent food webs provides an important exposure route for sea otters, as they consume {approx}25% of their body weight per day in benthic invertebrates. Thus, exceedences of PAH sediment quality guidelines designed to protect aquatic biota at 20% of the sites in sea otter habitat suggest that sea otters are vulnerable to hydrocarbon contamination even in the absence of catastrophic oil spills. - Highlights: > Sediment hydrocarbon signatures differed between remote and impacted coastal sites. > A natural background comprised terrestrial plant alkanes and petrogenic PAHs. > Impacted sites reflected a history of petrogenic and pyrogenic hydrocarbon inputs. > Hydrocarbons at some sites exceeded guidelines for the protection of aquatic life. > Protected sea otters may thus be at risk as they rely primarily on benthic prey. - Anthropogenically-derived hydrocarbons in coastal sediments in British Columbia may pose a risk to protected sea otters.

  12. Subduction zone decoupling/retreat modeling explains south Tibet (Xigaze) and other supra-subduction zone ophiolites and their UHP mineral phases (United States)

    Butler, Jared P.; Beaumont, Christopher


    The plate tectonic setting in which proto-ophiolite 'oceanic' lithosphere is created remains controversial with a number of environments suggested. Recent opinions tend to coalesce around supra-subduction zone (SSZ) forearc extension, with a popular conceptual model in which the proto-ophiolite forms during foundering of oceanic lithosphere at the time of spontaneous or induced onset of subduction. This mechanism is favored in intra-oc